Practical Challenges Associated with Catalyst Development for the Commercialization of Li-air Batteries

Myounggu Park; Ka Young Kim; Hyeryun Seo; Young Eun Cheon; Jae Hyun Koh; Heeyoung Sun; Tae Jin Kim

doi:10.5229/JECST.2014.5.1.1

J. Electrochem. Sci. Technol > Volume 5(1); 2014 > Article

Park, Kim, Seo, Cheon, Koh, Sun, and Kim: Practical Challenges Associated with Catalyst Development for the Commercialization of Li-air Batteries

Articles

Journal of Electrochemical Science and Technology 2014;5(1):1-18.

DOI: https://doi.org/10.5229/JECST.2014.5.1.1

Practical Challenges Associated with Catalyst Development for the Commercialization of Li-air Batteries

Myounggu Park^1,^*, Ka Young Kim², Hyeryun Seo², Young Eun Cheon², Jae Hyun Koh², Heeyoung Sun¹, Tae Jin Kim²

¹Advanced Battery Team, Battery R&D Center, SK innovation 325 Exporo, Wonchon-dong, Daejeon 305-712, South-Korea

²Catalyst Laboratory, Catalyst & Process R&D Center, SK innovation 325 Exporo, Wonchon-dong, Daejeon 305-712, South- Korea

^*Corresponding author. Tel.: +82-42-609-8756 E-mail address: myounggupark@sk.com

Received September 23, 2013 Accepted October 23, 2013

Abstract

Li-air cell is an exotic type of energy storage and conversion device considered to be half battery and half fuel cell. Its successful commercialization highly depends on the timely development of key components. Among these key components, the catalyst (i.e., the core portion of the air electrode) is of critical importance and of the upmost priority. Indeed, it is expected that these catalysts will have a direct and dramatic impact on the Li-air cell’s performance by reducing overpotentials, as well as by enhancing the overall capacity and cycle life of Li-air cells. Unfortunately, the technological advancement related to catalysts is sluggish at present. Based on the insights gained from this review, this sluggishness is due to challenges in both the commercialization of the catalyst, and the fundamental studies pertaining to its development. Challenges in the commercialization of the catalyst can be summarized as 1) the identification of superior materials for Li-air cell catalysts, 2) the development of fundamental, material-based assessments for potential catalyst materials, 3) the achievement of a reduction in both cost and time concerning the design of the Li-air cell catalysts. As for the challenges concerning the fundamental studies of Li-air cell catalysts, they are 1) the development of experimental techniques for determining both the nano and micro structure of catalysts, 2) the attainment of both repeatable and verifiable experimental characteristics of catalyst degradation, 3) the development of the predictive capability pertaining to the performance of the catalyst using fundamental material properties. Therefore, under the current circumstances, it is going to be an extremely daunting task to develop appropriate catalysts for the commercialization of Li-air batteries; at least within the foreseeable future. Regardless, nano materials are expected to play a crucial role in this field.

Keywords: Catalyst, Li-air cells, Commercialization

1. INTRODUCTION

In Fig. 1 ^1-9) a series of remarkable events pertaining to battery inventions (including fuel cells) is depicted in a chronological manner. The Li-air battery was first invented in 1996, utilizing polymer electrolyte (the non-aqueous Li-air cell), although the concept itself was formulated in 1976. However, until today this technology has not been commercialized due to the insurmountable barriers stemming from the lack of appropriate materials used in key components. As of today, Li-ion batteries have become an icon in the field of mainstream batteries. Ever since 1991, their prosperity has been the result of rigorous applications, ranging from electronic devices to electric cars (EVs). The technologies related to Li-ion batteries, such as the synthesis and manufacturing of active materials, separators, electrolytes, and cell assembly, have been rapidly developed over the years. However, focus on the Li-air battery and its recent revival should be noted.^10-12) Of course, there could be many reasons for this resurgence, but a rudimentary explanation can be found in the Ragonne plot (not shown here). The Ragonne Plot indicates the specific energy and power performance of a battery system. Specific energy density directly relates to how far an EV can travel. On the other hand, specific power density pertains to how much acceleration an EV can achieve. Currently, these two important performance descriptors demonstrate that the upper limits are going to be reached in the near future (around 2020) where Li-ion batteries are concerned. That is, a specific energy density of 250 Wh/ kg. Furthermore, it should be noted that the anticipated maximum performance of the advanced Li-ion battery still cannot meet the requirements of pure electric vehicles. Therefore, it is reasonable to conclude that the need for the next generation batteries is imminent and indispensible. Thus, it is not all that surprising to see so many researchers and scientists within the battery community paying close attention to Li-air batteries due to high theoretical energy density (gasoline:12,200 Wh/kg while Li-air batteries provide 13,000 Wh/kg, based on the weight of Li metal only, and 5,200 Wh/kg based on the weight of Li metal and oxygen).¹³⁾ In addition to this, there is a high safety factor to consider, i.e., only one part of the active material is contained in the battery system. Thus, thermal runaway (or short circuit) is unlikely¹³⁾ in spite of the conceivable shortcomings of the Li-air battery system due to its dependency on oxygen in order to function. Note that this battery system cannot be used in oxygen-free environments such as outer space, implanted heart pacemakers, and underwater conditions. ¹⁴⁾

Fig. 1.

Brief History of the Invention of Batteries and Fuel Cells.^1-9)

Previously, in an effort to better understand the overall status of Li-air battery research, the authors published a review article covering a rather broad scope of topics.¹⁰⁾ As a continuation of this effort, the authors undertook another round of review focusing on the catalysts and it is reported here. In this article, we mainly address the significance of catalysts (i.e., air cathodes), which is unfamiliar to the conventional battery developer. The authors established the following three goals:

1. Understanding catalysts (fundamental concepts and synthesis methods)
2. Understanding the role of catalysts in Li-air batteries
3. Obtaining perspectives for the commercialization of Li-air batteries

The methodologies utilized to fulfill the above goals are described in the next section, followed by the results. The perspectives gleaned by the authors are from a battery industry viewpoint, and thus may differ from perspectives held by other researchers facing different circumstances.

2. METHODS

Peer-reviewed journal articles are invaluable sources of information. Book chapters have also been consulted. The authors appreciate all of the pioneering research efforts exerted by both previous and contem-porary researchers. A web-based search engine has been mainly utilized.¹⁵⁾

3. RESULTS

3.1. Key Concepts Related to Catalysts

It has been shown that the catalyst in an air electrode is a crucially important component, as it can dictate the power and energy density, energy efficiency and cycle life of Li-air batteries.¹²⁸⁾ In this section fundamental concepts related to catalysts are addressed in a succinct manner.

General concept. A catalyst is normally defined as a material that can change the kinetic rate of a chemical reaction while the catalyst itself doesn’t change.¹⁶⁾ Changing the kinetic rate indicates the acceleration or deceleration of the rate induced by the function of a catalyst. For most cases, however, the catalysts are used to accelerate the reaction rates. The catalyst plays the role of reducing the activation energy of a specific reaction and enhancing the reaction rate. For non-catalytic reactions, products are made by the collisions between reactive molecules. On the other hand, catalytic reactions occur through the adsorption of reactant molecules and desorption of product molecules.

Constituents of catalyst system. A catalyst is normally comprised of an active material and a supporting material. The active material is deposited on, or chemically bounded with, a porous support that has a large surface area. An active material is directly related to a chemical reaction rate, and various materials are used such as metals, metal oxides, and metal sulfides. Sometimes “Promoters” (or additives) are added into a catalyst system. The promoters have no catalytic activity, but they can affect the activity of a catalyst, either chemically or electronically.

Major properties of catalysts. The important properties of a catalyst are: activity, selectivity, and lifetime. ^17-19) The activity refers to the ability of a catalyst to convert reactant molecules at a single active site. Selectivity is the fraction of a desired product among all the products. Selectivity is concerned when a reactant can be converted to several products, or when a desired product is in an intermediate stage and then might be converted into other materials. Lifetime is of great interest, especially from a cost reduction point of view. Catalysts lose their initial activity due to various reasons including coking, poisoning and sintering.

Types of catalyst reactions. Generally, there are two types of catalytic reactions: oxidation-reduction reactions (electronic) and acid-base reactions (ionic).²⁰⁾ Oxidation-reduction type reactions include oxidation, reduction, hydrogenation, dehydrogenation and hydrogenolysis (catalyzed by solids possessing free or easily excited electrons, i.e., metals), while acid-base type reactions include polymerization, isomerization, cracking, dehydration, alkylation, halogenations and dehalogenation (catalyzed by acidic or basic properties).

Surface reactions on catalysts. For heterogeneous catalysts, the surface reaction proceeds through: (1) diffusion of reactant molecules into the catalyst, (2) adsorption of the diffused reactants on the catalyst surface, (3) reaction between adsorbed molecules, (4) desorption of the product molecules from the catalyst surface, and (5) diffusion of the products into the bulk stream. Diffusion can be divided into “external diffusion” and “internal diffusion”. Adsorption, desorption, and reaction are affected by chemical properties, whereas diffusion is affected by physical properties, such as fluid velocity and pore structure (Fig. 2). Therefore, it is of great importance to understand the reactions at the internal and external surface of catalysts, along with the effects of pore structure, for the further development of Li-air cathode catalysts.

Fig. 2.

Surface Reaction on Heterogeneous Catalysts.

Surface area of catalysts. The total surface area of a catalyst is the sum of all the surface areas of pores with various sizes. For a given mass, the surface area of a catalyst is inversely related to the size of the pores. Thus, the surface area of a catalyst having a high percentage of small pores is larger than that of a catalyst having a high percentage of large pores. Also there are two kinds of pores depending on the formation process i.e., interstitial and internal pores. The interstitial pores are formed between the primary particles within the aggregated particles, and the internal pores are formed inside the primary particles. Therefore, external surfaces include all the outer surfaces of catalysts and aggregated catalysts, while the internal surface is composed of all the surfaces of the internal pores.²¹⁾

3.2. Synthesis Methods of Catalysts

External and internal morphologies of catalysts synthesized by various methods play a crucial role in the catalytic activities. When it comes to catalyst synthesis it can be broadly classified into two main methods− impregnation and colloidal, both of which are well documented for noble metal based catalysts (e.g., Pt, Pd, Ru). Meanwhile, sputtering and heat treatment methods^22-26) have been newly explored in transition metal based catalysts (e.g., Fe, Co, Mo) and metal-free carbon catalysts.^27,28) In this section two main synthesis methods are briefly summarized.

Impregnation method. Impregnation is the most widely utilized method, due to its simplicity, high dispersion on the support, and the easy scale-up for mass production. Features of impregnation method are summarized in Table 1.^29-34) This method is widely used for preparing ORR catalysts; e.g., the carbon supported Pt and Pd nanoparticles.^35,36) As for the general procedures, it is as follows: the calculated amount of active metal precursor (e.g., H₂PtC₁₆ _xH₂O, RuC₁₃, Na₆Pt(SO₃)₄, and Na₆Ru(SO₃)₄) is dissolved in a medium, such as alcohol and/or water. For a better dispersion of the metal precursor, a citric acid can be added as a stabilizer.³⁷⁾ The solution and carbon support are mixed with mild stirring. The carbon support loaded with the active metal precursor is then incubated in an oven at 100℃ overnight, and then treated with various reducing agents. Depending on the phase of the reducing agent, there are various methods including the hydrogen gas reduction method^31,32) and the liquid reduction method.^29,35,38-41) Recently carbide based catalysts (e.g., Pt-W₂C/C, Co₆Mo₆C₂/C) prepared by combining the impregnation and microwave heating methods have been intensively studied.^41-44)

Table 1.

Features of the Impregnation Method^29-34)

Colloidal method. The major disadvantages of the impregnation method are related to low activity, broad particle size distribution, and tendency to be easily aggregated. To overcome these drawbacks, the colloidal method has been developed, and is often used in the studies of Pt/C, Pd/C, and PtRu/C catalysts^45-47) (Fig. 3). A general description of the colloidal procedure^48-50) is as follows (Table 2^46,51,52)): 1) preparing a colloidal solution containing metal nanoparticles with stabilizers (e.g., tetraoctylammonium bromide (TOAB), Polyvinylpyrrolidone (PVP), and 1-propanol) and 2) depositing metal nanoparticles onto the surface of carbon supports.

Fig. 3.

General Process of the Impregnation Method.

Table 2.

Features of the Colloidal Method^51,46,52)

3.3. Roles of Catalysts in Li-air Cells

Based on the nature of the electrolytes and its reaction products, Li-air cells can be classified broadly into two types;⁵³⁾ i.e., non-aqueous and hybrid (also see Fig. 1 and 2 in ref.¹⁰⁾). The roles of catalysts are expected to differ for each type of Li-air cell (Table 3 ⁵⁴⁾).

Table 3.

Comparison of Li-air Cells: Non-aqueous vs. Aqueous Electrolytes⁵⁴⁾

Roles of catalysts in non-aqueous Li-air cells. The reaction mechanisms at the interfaces between the aircathode and the electrolyte are inevitably affected by Li₂O₂ formed inside the pores. Micro-pores and some of meso-pores are blocked by Li oxide during cycling and the surface area of those pores will not be accessed by either air or electrolyte, making them unavailable for the electrochemical reaction. Thus the manipulation of the carbon support’s pore structure are observed to be more central issues^55-58) although active catalyst materials themselves are researched a lot. Thus the selection of appropriate support materials is quite significant. To fulfill these unique requirements, carbon blacks (e.g., Acetylene Black, Vulcan XC-72, Ketjen Black) have been mainly adopted. The properties of a carbon support, such as the specific surface area, porosity, morphology, surface functional groups, electronic conductivity, and corr-osion resistance, must be down-selected in order to make an appropriate catalyst system. Currently Vulcan XC-72 with a surface area of approximately 250m²g⁻¹ has been widely utilized.^21,59) However, note that an accessible and sufficiently large surface area of carbon blacks for maximum catalyst dispersion has been argued to be a necessary, albeit insufficient condition, for obtaining optimized carbon sup-ported catalysts.^60-67) Overall, a salient observation is that the main roles of catalysts seem to control the morphology and accommodate Li₂O₂.⁶⁸⁾

Roles of Catalysts in Hybrid Li-air cells. In hybrid Liair cells, the role of catalysts can be clearly defined; it is to control the binding energy between oxygen species and metal surfaces. Because bound oxygen species are intermediates in the oxygen reduction reaction, the level of binding energy can have significant effects on catalytic activity.⁶⁹⁾ For metal surfaces that bind oxygen too weakly, the rate is limited by either the dissociation of O₂ or the transfer of electrons to adsorbed O₂, i.e., possible rate-limiting step can be dictated by different oxygen reduction mechanisms. Also, if Pt binds oxygen too strongly the catalytic activity is negatively affected. Therefore, in order to achieve better electrocatalystic activity, optimal binding energy should be acquired for each particular catalyst system. ⁷⁰⁾ A major advantage of the binding energy approach (utilizing the characteristics of electronic structure; i.e., HOMO and LUMO), is to provide a way to predict the electrocatalytic activity of a metal surface.

3.4. Survey of Catalyst Research in Li-air Cells

Catalysts vs. overpotential. Overpotential (and capacity) values of non-aqueous and hybrid Li-air cells utilizing various catalysts are summarized in Table 4^13,71-91) and Table 5^{53,92,133,154,164)} respectively. Also refer to Fig. 4¹³⁰⁾ for non-aqueous Li-air cells and Figs 5, 6, 7⁹³⁾ for hybrid Li-air cells regarding discharge/ charge plots and corresponding overpotentials. The results summarized in Table 4 imply that the dif-ferent overpotential values on discharge/charge of non-aqueous Li-air cells may be related to the different orientations and morphologies of the oxide precipitates. ^94-96) Catalysts can affect the choice of the specific reaction path and thus affect the appearance and structure of the specific <oxygen|metal> intermediates. ^97,98) Among various catalyst systems for nonaqueous Li-air cells, PtAu (bifunctional catalyst) on carbon support and nitrogen-doped carbon are reported to have the best performance in terms of overpotential reduction.⁹⁹⁾ Also, various carbon materials are demonstrated as active catalysts;^{12,85-88,100-102)} e.g., carbon nanotubes. Nonetheless, the consensus is that the effect of various catalyst systems examined so far is obscure and there is no dominant one yet to be found. Controversy over the effects of catalysts can be partly ascribed to undetermined ORR and OER mechanisms.^103,128) Most of all, the asymmetric discharge/charge curve (larger overpotential value for charge) is a distinctive feature indicating the significance and urgency of catalyst development for the charge process.

Table 4.

Catalysts Used for Non-aqueous Li-air Batteries^13,71-91)

1) Overvoltage and capacity values are based on the 1^st discharge/charge cycle as reported in the literature 2) ′ ⁄ C′ ′ MnO₂, ⁄ ′, ′ ⁄ RbRO′ and ′ ⁄ RGO′ indicate that the support material are carbon, manganese oxide, lead ruthenium, and reduced graphene oxide respectively 3) Except otherwise explicitly described as ‘bulk’ materials in the report, we classify them as nano-sized materials 4) A = Pb or Bi, B = Ru or Ir 5) The prefixes, such as α-, β-, γ-, λ-, represent polymorphs of MnO₂ 6) Except otherwise stated, all catalysts are monofunctional 7) PtAu is a bifunctional catalyst 8) Nano means nanostructured materials including nanoparticle, nanocrystals, nanowires, nanotubes, nanobelts and nanoflowers 9) ′Nano ⁄ nano′ indicates that nano-size substrate materials are decorated with nano-size catalysts

Table 5.

Catalysts Used for Hybrid Li-air Batteries^{53,92,133,154,164)}

1) Overvoltage and capacity values are based on 1^st discharge/charge cycle as reported in the literature 2) Generally, overvoltage and capacity are influenced by current density and catalyst loadings 3) FePc: Fe phthalocyanine 4) GNS: graphene nanosheet 5) AB: Acetylene Black 6) In this particular case, the hybrid Li-air cells were operating at 60℃

Fig. 4.

Cycling Performance of a non-aqueous Type Li-air Cell.¹³⁰⁾

Fig. 5.

Cycling Performance of a Hybrid Type Li-air Cell (Pt 0%).⁹³⁾

Fig. 6.

Cycling Performance of a Hybrid Type Li-air Cell (Pt 10%).⁹³⁾

Fig. 7.

Cycling Performance of a Hybrid Type Li-air Cell (Pt 40%).⁹³⁾

Different reaction paths of hybrid Li-air cells depending on catalyst materials and utilized electrolytes (alkaline or acidic) are summarized in Tables 6 and 7.^104,105) Noble metals (especially Pt) have been proved to be the best so far for ORR.¹⁰⁶⁾ However, Pt catalyst has been found to be not effective for oxygen evolution reaction (OER) due to the formation of a stable oxide layer. In the case of Ru catalyst, it is better than Pt for oxygen evolution. However, Ru catalyst is still problematic due to corrosion limiting its lifetime. As cost-effective alternatives to noble metals, investigation on noble metal oxides (e.g., RuO₂ or IrO₂) and transition metal oxides (e.g., NiCo₂O₄, spinel) have been on-going. Some transition metal oxides show good performance in oxygen evolution (particularly spinel) so far. Development of low-cost catalysts is going to be a key factor for the successful commercialization of Li-air battery.

Table 6.

Direct Four-Electron Pathways and Catalysts^104,105)

1) General formula of Perovskite type oxides: their properties are varied depending on the nature of A and B 2) General formula of Pyrochlore type oxides: their properties are varied depending on the nature of A and B

Table 7.

Two-electron Reduction Pathways and Catalysts^104,105)

In another example, concerning Co₃O₄/RGO catalyst, it has been observed that this catalyst does not act as a conventional one to lower the activation energy (or overpotential) via providing a higher-rate reaction path. Rather, it acts as a kind of ‘promoter’ to enhance surface transport (or mass transport) of Li_xO₂ species during cycling⁹⁰⁾ and the ultimate effects are the same (i.e., reduction of overpotential).

Nanostructured Catalysts. The nano-sized catalyst’s role in reducing discharge/charge overpotentials has been widely researched^107-111) (see also Table 4). It is based on very straightforward and intuitive reasoning that the specific catalyst activity increases as the surface area per gram of the catalyst increases, i.e., the smaller the size of the catalyst particle the greater the catalyst activity. For non-aqueous Li-air cells, the á- MnO₂ nanowire catalysts have been discussed as one of the excellent low-cost catalyst candidates. Various nanostructured MnO₂ materials (e.g., nanocrystals, nanotubes, nanofiber, and dendritic clusters) are mixed with nano-sized carbon-based materials (e.g., carbon black, carbon foam, and graphite). Recent calculations and experiments have suggested that nano-structured substrates decorated with nano-sized catalysts are also very promising.^84,112,113) For example, if Ptclusters are deposited onto a graphene support, the oxygen-reduction activity is observed to be much higher.¹²⁰⁾ Therefore, there are good grounds for the implementation of carbon-based nanomaterials; e.g., carbon nanotubes and graphene as support materials ^114-116) to accommodate a larger amount of Li oxide.^117,118) Regarding metal nanoparticles they are good candidates as well because their catalytic properties can be considerably higher than that of bulk metals. However, it has been suggested that when the sizes of catalyst particles are within the nanometer range, specific catalyst activity does not always follow the above rationale. Often the actual relation between specific catalyst activity and size is largely dependent on the particular type of catalyst;^114,119-123) e.g., Pt particles were found to show maximal mass catalyst activity¹²⁴⁾ when their size is ranging from 2 to 4 nm. Note that in the case of the Au catalyst, the particle size for maximum activity is smaller than that of Pt catalyst.^125-127)

4. DISCUSSION

In this section challenges related to non-aqueous and the hybrid Li-air cell are briefly discussed: These challenges are unique for each system for the development of catalyst.

4.1. Issues Regarding Organic Type Li-air Cells

As for non-aqueous Li-air cells, conceivable different chemical reactions are depicted in Fig. 8.^12,128-142) The reaction route producing Li₂O, compared to that of producing Li₂O₂, seems to be beneficial because a larger capacity is expected: However, it was found to increase irreversibility considerably. Other alternative reaction routes producing intermediate products are reported as well.^128,142-144) Most of all, organic electrolytes, Li salts (e.g., LiBOB), and binders (e.g., PVdF) are observed to react with superoxide (O₂ ⁻), and to decompose during discharge.¹⁴⁵⁾ During charge, the oxidation of decomposed electrolyte products is involved in CO₂ ¹⁴⁶⁾ and H₂O production instead of O₂. In addition to reactions induced by superoxide (O₂ ⁻), chemical reactions between Li₂O₂ (it is strongly nucleophilic like O₂ ⁻) and solvent are very problematic because they can produce carbonate which will ultimately limit the rechargeability of Li-air cells.¹⁴⁷⁾ In short, problems associated with the scantiness of stable electrolytes^138,149) toward reduced oxygen species and discharge product is the single biggest hurdle to overcome before the non-aqueous cells can be commercialized, ^{138,139,141,148-152)} not to mention the need for further catalyst study. Recent reports even argue that active catalyst material may not be a necessary component based on the kinetic overpoentials study.¹⁵³⁾ Overall, these complex issues are hampering the development of appropriate catalysts for the air cathode of non-aqueous Li-air cells.

Fig. 8.

Suggested Chemical Reactions During Discharge.12,128-142)

4.2. Issues Regarding Hybrid Type Li-air Cells

An outstanding difference between the hybrid and non-aqueous Li-ai r cel l s l ies in the cel l structures^{53,133,134,-156)} and, unlike non-aqueous Li-air cells, the hydrid Li-air cell’s oxygen reduction reactions (ORR) at air cathode is well established, particularly in the case of Pt¹⁵⁷⁾ and carbon surfaces in alkaline solution.^158,159) Chemical reactions at air cathode are critically dependent on the acid-base characteristics of aqueous electrolytes, i.e., acidic, neutral, or basic.¹⁶⁰⁾ From the cycling data of hybrid Li-air cells (Figs 5, 6, and 7), the effects of Pt catalysts are eminent. The role of catalysts has been observed to be critical in the reduction of overpotential. However, this does not indicate that there are no technical issues to be tackled. On the contrary, there are numerous technical obstacles including the limited lifetime of catalysts due to dissolution of Co catalysts^161-163), the corrosion of Pt catalysts in alkaline electrolytes,¹⁶²⁾ and the non-catalyst problems such as the instability of LiSICON in strong basic or alkaline electrolytes,^155,163) interfacial impedance increase due to insoluble phase formation,¹⁶⁴⁾ electrolyte degradation (e.g., CO₂ in ambient air can react with alkaline electrolytes (LiOH, NaOH, and KOH) producing insoluble carbonate,¹³⁴⁾ and Li dendrite formation^129,165) on the surface of Li metal. Finding a well matched pair of catalyst and aqueous electrolyte is still a hindrance in the development of hybrid Li-air cells, although it is not as deep a concern as is the case with non-aqueous Li-air cells. Most of all, the low-cost catalyst, which is alternating the expensive precious metal ones (e.g., Pt), is going to be one of the key factors in the commercialization of the Hybrid Li-air cell.

5. CONCLUDING REMARKS & PERSPECTIVES

The survey of previous research on catalysts clearly indicates that efforts have been primarily focused on the non-aqueous Li-air cell and its performance enhancement. The tendency toward more research of non-aqueous Li-air cells is based on the notion that these cells are expected to excel their hybrid counterparts in terms of gravimetric and volumetric energy density;¹³³⁾ i.e., less numbers of components are required for the final cell assembly. However, appropriate heterogeneous catalysts for non-aqueous Li-air cells have not yet appeared. Difficulties in developing suitable catalysts stem from considerable complexity in relation to the analysis of Li-air cell’s performance due to many involved parameters. These parameters, including pore structure of carbon support materials, ^80,166,167) the choice of electrolytes (the viscosity, oxygen solubility, and ionic conductivity),^82,168,169) wettability between electrolyte and electrode,^167,170) binder, and the thickness of the electrode,¹⁷¹⁾ if not properly sorted out, will obscure catalysts’ effects in the nano- and macro-scale. Thus, approaches for catalyst R&D should be multidisciplinary.^{19,120,123,172)} Regarding hybrid Li-air cells, there are also various parameters associated with cell performance, such as cathodic potential, oxygen purity, mass flow rate, cathode surface area, pH, and temperature.¹⁵⁹⁾ However, this is a wholly different kind of challenge compared to that of non-aqueous Li-air cells as pointed out in the discussion section: No suitable electrolyte for nonaqueous Li-air cells has yet been discovered, and it is still a matter of controversy concerning the effects of catalysts due to undetermined ORR and OER mechanisms. The unavailability of reliable platforms is pertinent to the sluggish pace of catalyst development for non-aqueous Li-air batteries. In the case of hybrid Liair cells, it is not uncommon to see that the current catalyst R&D is heavily resorted to the conventional catalysts developed (or being developed) for other metalair batteries (or fuel cells): The control of morphology and orientation of crystal plane and its defect sites.^{75,89,173-177)} Still, in many cases platinum (Pt) is considered and adopted as the best catalyst,¹⁷⁶⁾ although there are many reasons to devote research to developing cost-effective alternatives (e.g., perovskites, spinels, and pyrochlores²⁰⁾ from the commercialization standpoint.

One of the prominent features regarding catalysts based on previous research is that all the catalysts are fabricated in nano-scale and nano-structure. Peculiarities in the microstructure of catalysts such as vacancies and defects are found to play a critically important role in determining the performance of Li-air batteries. Thus, inevitably there will be challenges related to the mass production of nano-structured catalysts, particularly in terms of controlling its crystal structure as required by specifications, i.e., morphology, defects, vacancies.⁸⁹⁾ This perspective is based on the knowledge that nanomaterials are not always mass production friendly. However, despite these drawbacks, it is expected that nanomaterials will remain as a promising catalyst candidate for Li-air batteries, with the gradual maturity of related core technologies for upscale and mass production. In reality, for the commercialization success of Li-air batteries, simple and low cost catalyst production schemas should be devised.

ACKNOWLEDGEMENTS

This effort was supported by SK innovation. The authors deeply appreciate the support from our sponsor. We further acknowledge the helpful contributions of Mr. Brian Calanchie in regards to the preparation of this manuscript.

References

1. Farley Maggie Summit Decrees 6% Reduction in Main Global Warming Gases; Diplomacy: Delegates agree to cut six major pollutants below 1990 levels. Accord will change how nations produce and use power. Action on concessions requested by U.S. delayed, Los Angeles Times, Section Part: A, Start Page: 1. 1997.

2. Larminie James Lowry John Electric Vehicle Technology Explained. 2003.John Wiley & Sons.

3. Root Michael The TAB Battery Book. 2011.McGrow-Hill.

4. Buchmann Isidor Batteries in a Portable World. 2001.Cadex Electronics Inc.

5. Source. 0000.

6. Transform Your Drive. 0000.

7. Source. 0000.

8. Source. 0000.

9. Source. 0000.

10. Park Myounggu Sun Heeyoung Lee Hyungbok Lee Junesoo Cho. Jaephil Lithium-Air Batteries: Survey on the Current Status and Perspectives Towards Automotive Applications from a Battery Industry Standpoint. Advanced Energy Materials, 2012, 2, 780.

11. Black Robert Adams Brian Nazar. L.F. Non- Aqueous and Hybrid Li-O₂ Batteries. Advanced Energy Materials, 2012, 2, 801.

12. Hou Junbo Yang Min W. Ellis Michael B. Moore Robert Yi. Baolian Lithium oxides precipitation in nonaqueous Li-air batteries. Phys. Chem. Chem. Phys., 2012, 14, 13487.

13. Cheng H. Scott. K. Carbon-supported manganese oxide nanocatalysts for rechargeable lithium-air batteries. J. Power Sources, 2010, 195, 1370.

14. Mantell C. L. Batteries and Energy Systems. 2nd Edition. 1983.New York, McGraw-Hill.

15. . Source. 0000.

16. L. Robert Jr. Burwell Manual of Symbols and Terminology for Physicochemical Quantities and Units - Appendix II Heterogeneous Catalysis. Advances in Catalysis, 1977, 26, 351.

17. Louis Hegedus L. W. McCabe Robert Catalyst Poisoning. 1984.New York, Marcel Dekker.

18. Hughes R. Deactivation of Catalysts. 1984.New York, Academic Press.

19. . Ertl G. Knozinger H. Weitkamp J. Handbook of Heterogeneous Catalysis. 1997, 1–48.

20. Happel John Hnatow Miguel Bajars Laimonis Base Metal Oxide Catalysts. 1977.New York, Marcel Dekker.

21. S. Arico A. Srinivasan S. V. Antoucci. Fuel cells, 2001, 2, 133.

22. Wang. Bin Recent development of non-platinum catalysts for oxygen reduction reaction. Journal of Power Sources, 2005, 152, 1.

23. Zhang Lei Zhang Jiujun P. Wilkinson David Wang Haijiang Progress in preparation of non-noble electrocatalysts for PEM fuel cell reactions. Journal of Power Sources, 2006, 156, 171.

24. Bogdanoff P. Herrmann I. Hilgendorff M. Dorbandt I. Fiechter S. Tributsch. H. Probing Structural Effects of Pyrolysed CoTMPP-based Electrocatalysts for Oxygen Reduction via New Preparation Strategies. J. New Mater. Electrochem. Syst., 2004, 7, 85.

25. Herrmann I. Bruser V. Fiechter S. Kersten H. Bogdanoff. P. Electrocatalysts for Oxygen Reduction Prepared by Plasma Treatment of Carbon-Supported Cobalt Tetramethoxyphenylporphyrin. J. Electrochem. Soc., 2005, 152, A2179.

26. . Hampden-Smith M. Atanassova P. Kodas. T.T. Wielstich W. Gasteiger H.A. Lamm A. Fuel Cell Technology and Application;Handbook of Fuel Cells- Fundamentals, Technology and Applications, Vol. 3. 2003.

27. Qu L. Liu Y. Baek J.B. Dai. L. Nitrogen-Doped Graphene as Efficient Metal-Free Electrocatalyst for Oxygen Reduction in Fuel Cells. ACS Nano, 2010, 4, 1321.

28. Gong K. Du F. Xia Z. Durstock M. Dai. L. Nitrogen-doped carbon nanotube arrays with high electrocatalytic activity for oxygen reduction. Science, 2009, 323, 760.

29. William H. Valdecir A. Gonzalez. R. Electrochim. Acta, 2002, 47, 3715.

30. Deivaraj T.C. Lee. J.Y. J. Power Sources, 2005, 142, 43.

31. Yang B. Lu Q. Wang Y. Zhang L. Lu J. Liu. P. Chem. Mater., 2003, 15, 3552.

32. Friedrich K.A. Geyzers L.P. Dickinson A.J. Stimming. U. J. Electroanal. Chem., 2003, 524/525, 262.

33. Takasu Y. Fujiwara T. Murakami Y. Sasaki K. Oguri M. Asaki T. Sugimoto. W. J. Electrochem. Soc., 2000, 147, 4421.

34. Dickinson A.J. Carrette L.P.L. Collins J.A. Friedrich K.A. Stimming. U. Electrochim. Acta, 2002, 47, 3733.

35. Che Guangli Lakshmi Brinda B. Fisher Ellen R. Martin. Charles R. Carbon nanotubule membranes for electrochemical energy storage and production. Nature, 1998, 393, 346.

36. Cheng H. Scott. K. Selection of oxygen reduction catalysts for rechargeable lithium-airbatteries-Metal or oxide? Applied Catalysis B: Environmental, 2011, 108/109, 140.

37. Guo J.W. Zhao T.S. Prabhuram J. Chen R. Wong. C.W. Preparation and characterization of a PtRu/C nanocatalyst for direct methanol fuel cells. Electrochimica Acta, 2005, 51, 754.

38. . Tsurumi K. Nakamura T. Sato A. US Patent 4,956,331. 1990.

39. Antolini A. Cardellini. F. Formation of carbon supported PtRu alloys: an XRD analysis. Journal of Alloys and Compounds, 2001, 315, 118.

40. Lust E. Hark E. Nerut J. Vaarmets. K. Pt and Pt–Ru catalysts for polymer electrolyte fuel cells deposited onto carbide derived carbon supports. Electrochimica Acta, 2013, 101, 130.

41. Ma X. Meng H. Cai M. Shen. P.K. Bimetallic carbide nanocomposite enhanced Pt catalyst with high activity and stability for the oxygen reduction reaction. J. Am. Chem. Soc., 2012, 134, 1954.

42. Meng H. Shen. P.K. J. Phys. Chem. B, 2005, 109, 22705.

43. Savadogo O. Lee K. Oishi K. Mitsushima S. Kamiya N. Ota. K.-I. New palladium alloys catalyst for the oxygen reduction reaction in an acid medium. Electrochemistry Communications, 2004, 6, 105.

44. Deng C.Z. Dignam. M.J. Sputtered Cobalt-Carbon- Nitrogen Thin Films as Oxygen Reduction Electrocatalysts. J. Electrochem. Soc., 1998, 145, 3507.

45. Prabhuram J. Wang X. Hui C.L. Hsing. T. Synthesis and characterization of surfactant-stabilized Pt/C nanocatalysts for fuel cell applications. Journal of Physical Chemistry B, 2003, 107, 11057.

46. Kim T. Takahashi M. Nagai M. Kobayashi K. Electrochem. Acta, 2004, 50, 813.

47. Xue X. Lu T. Liu C. Xing. W. Chem. Commun., 2005, 12, 1601.

48. Narayanan R. El-Sayed. M.A. Carbon-supported spherical palladium nanoparticles as potential recyclable catalysts for the Suzuki reaction. Journal of Catalysis, 2005, 234, 348.

49. Wang C. Daimon H. Lee Y.M. Kim J.M. Sun. S. Synthesis of Monodisperse Pt Nanocubes and Their Enhanced Catalysis for Oxygen Reduction. J. Am. Chem. Soc., 2007, 129, 6974.

50. Okaya K. Yano H. Kakinuma K. Watanabe M. Uchida. H. Temperature Dependence of Oxygen Reduction Reaction Activity at Stabilized Pt Skin-PtCo Alloy/ Graphitized Carbon Black Catalysts Prepared by a Modified Nanocapsule Method. ACS Appl. Mater. Interfaces, 2012, 4, 6982.

51. Wang X. Hsing. I. Electrochem. Acta, 2002, 47, 2897.

52. Paulus U.A. Endruschat U. Feldmeyer G.J. Schmidt T.J. Bonnemann H. Behm. R.J. J. Catal., 2000, 195, 383.

53. He Hui Niu Wei Mahootcheian Asl Nina Salim Jason Chen Rongrong Kim. Youngsik Effects of aqueous electrolytes on the voltage behaviors of rechargeable Liair batteries. Electrochimica Acta, 2012, 67, 87.

54. Kraytsberg Alexander Ein-Eli. Yair Review on Li-air batteries-Opportunities limitations and perspective. Journal of Power Sources, 2011, 196, 886.

55. Lee Jang-Soo Kim Sun Tai Cao Ruiguo Choi Nam-Soon Liu Meilin Lee Kyu Tae Cho. Jaephil Metal- Air Batteries with High Energy Density: Li-Air versus Zn-Air. Advanced Energy Materials, 2011, 1, 34.

56. Ren X. Zhang S.S. Tran D.T. Read J. J. Mater. Chem, 2011, 21, 10118.

57. Capsoni Doretta Bini Marcella Ferrari Stefania Quartarone Eliana Mustarelli. Piercarlo Recent advances in the development of Li-air batteries. Journal of Power Sources, 2012, 220, 253.

58. Tran Chris Yang Xiao-Qing Qu. Deyang Investigation of the gas-diffusion-electrode used as lithium/air cathode in non-aqueous electrolyte and the importance of carbon material porosity. Journal of Power Sources, 2010, 195, 2057.

59. Takasu Y. Kawaguchi T. Sugimoto W. Murakami Y. Electrochim. Acta, 2003, 48, 3861.

60. Uchida M. Fukuoka Y. Sugawara Y. Ohara H. Ohta A. J. Electrochem. Soc, 1998, 145, 3708.

61. Anderson M. L. Stroud R. M. Rolison. D. R. Nano Lett., 2002, 2, 235.

62. Park G. Yang T. Yoon Y. Lee W. Kim C. Int. J. Hydrogen Energy, 2003, 28, 645.

63. Mastragostino M. Mossiroli A. Soavi. F. J. Electrochem. Soc., 2004, 151, 1919.

64. Rao V. Simonov P.A. Savinova E.R. Plaksin G.V. Cherepanova S. Kryukova G. Stimming. U. Journal of Power Sources, 2005, 145, 178.

65. Wang Z. Yin G. Shi. P. Carbon, 2005, 44, 133.

66. Chan K.Y. Ding J. Ren J. Cheng S. Tsang K.Y. J. Mater. Chem., 2004, 14, 505.

67. Liu Hansan Song Chaojie Zhang Lei Zhang Jiujun Wang Haijiang Wilkinson David P. A review of anode catalysis in the direct methanol fuel cell. Journal of Power Sources, 2006, 155, 95.

68. Tran Chris Yang Xiao-Qing Qu Deyang Investigation of the gas-diffusion-electrode used as lithium/air cathode in non-aqueous electrolyte and the importance of carbon material porosity. Journal of Power Sources, 2010, 195, 2057.

69. Lu Chun-Yaung Henkelman. Graeme Role of Geometric Relaxation in Oxygen Binding to Metal Nanoparticles. J.Phys.Chem.Lett, 2011, 2, 1237.

70. Stamenkovic Vojislav Mun Bongjin Simon Mayrhofer Karl J.J. Ross Philip N. Markovic Nenad M. Rossmeisl Jan Greeley Jeff Norskov Jens K. Changing the Activity of Electrocatalysts for Oxygen Reduction by Tuning the Surface Electronic Structure. Angew.Chem.Int.Ed., 2006, 45, 2897.

71. Debart Aurelie Bao Jianli Armstrong Graham Bruce Peter G. An O₂ cathode for rechargeable lithium batteries: The effect of a catalyst. Journal of Power Sources, 2007, 174, 1177.

72. Debart Aurelie Paterson Allan J. Bao Jianli Bruce. Peter G. α-MnO₂ Nanowires: A catalyst for the O₂ Electrode in Rechargeable Lithium Batteries. Angew. Chem., Int. Ed., 2008, 47, 4521.

73. Chung Ku-Bong Shin Ju-Kyung Jang Tae-Young Noh Dong-Kyun Tak Yongsug Baeck. Sung-Hyeon Preparation and analyses of MnO₂ carbon composites for rechargeable lithium-air battery. Rev. Adv. Mater. Sci., 2011, 28, 54.

74. Lu Yi-Chun Gasteiger Hubert A. Parent Michael C. Chiloyan Vazrik Yang Shao-Horn. The Influence of Catalysts on Discharge and Charge Voltages of Rechargeable Li-Oxygen Batteries. Electrochemical and Solid-State Letters, 2010, 13, A69.

75. Lu Yi-Chun Xu Zhichuan Gasteiger Hubert A. Chen Shuo Kimberly Hamad-Schifferli Yang Shao-Horn. Platinum-Gold Nanoparticles: A Highly Active Bifunctional Electrocatalyst for rechargeable Lithium-Air Batteries. Journal of the American Chemical Society, 2010, 132, 12170.

76. Oh Si Hyoung Nazar. Linda F. Oxide Catalysts for Rechargeable High-Capacity Li-O2 Batteries. Advanced Energy Materials, 2012, 2, 903.

77. Oh Si Hyoung Black Robert Pomerantseva Ekaterina Lee Jin-Hyon Nazar d Linda F. Synthesis of a metallic mesoporous pyrochlore as a catalyst for lithium-O₂ batteries. Nature chemistry, 2012, 4, 1004.

78. Thapa Arjun Kumar Saimen Kazuki Ishihara Tatsumi Pd/MnO₂ Air Electrode Catalyst for Recharegable Lithium/Air Battery. Electrochem. Solid- State Lett., 2010, 13, A165.

79. Thapa Arjun Kumar Ishihara Tatsumi Mesoporous α-MnO₂/Pd catalyst air electrode for rechargeable lithiumair battery. J. Power Sources, 2011, 196, 7016.

80. Thapa Arjun Kumar Hidaka Yuiko Hagiwara Hidehisa Ida Shintaro Ishihara Tatsumi Mesoporous α-MnO₂ Air Electrode Modified with Pd for Rechargeability for Lithium-Air Battery. J. Electrochem. Soc., 2011, 158, A1483.

81. Trahey L. Johnson C.S. Vaughey J.T. Kang S.-H. Hardwick L.J. Freunberger S.A. Bruce P.G. Thackeray. M.M. Activated Lithium-Metal-Oxides as Catalytic Electrodes for Li-O₂ Cells. Electrochem. Solid-State Lett., 2011, 14, A64.

82. Xiao Jie Xu Wu Wang Deyu Zhang Ji-Guang Hybrid Air-Electrode for Li/Air Batteries. J. Electrochem. Soc., 2010, 157, A294.

83. Ogasawara Takeshi Debart Aurelie Holzapfel Michael Novák Petr Bruce Peter G. Rechargeable Li₂O₂ Electrode for Lithium Batteries. J. Am. Chem. Soc., 2006, 128, 1390.

84. Li Jiaxin Wang Ning Zhao Yi Ding Yunhai Guan Lunhui MnO₂ Nanoflakes coated on multi-walled carbon nanotubes for rechargeable lithium-air batteries. Electrochem. Commun., 2011, 13, 698.

85. Li Yongliang Wang Jiajun Li Xifei Liu Jian Geng Dongsheng Yang Jinli Li Ruying Sun. Xueliang Nitrogen-doped carbon nanotubes as cathode for lithiumair batteries. Electrochem. Commun., 2011, 13, 668.

86. Kichambare Padmakar Kumar Jitendra Rodrigues Stanley Kumar Binod Electrochemical performance of highly mesoporous nitrogen doped carbon cathode in lithium-oxygen batteries. J. Power Sources, 2011, 196, 3310.

87. Sun Bing Wang Bei Su Dawei Xiao Linda Ahn Hyojun Wang Guoxiu Graphene nanosheets as cathode catalysts for lithium-air batteries with an enhanced electrochemical performance. Carbon, 2012, 50, 727.

88. Yang Yin Sun Qian Li Yue-Sheng Li Hong Fu Zheng- Wen Nanostructured Diamond Like Carbon Thin Film Electrodes for Lithium-Air Batteries. Journal of The Electrochemical Society, 2011, 158, B1211.

89. . Lee Jin-Hyon Black Robert Popov Guerman Pomerantseva Ekaterina Nan Feihong Botton Gianluigi A. Nazar Linda F. The role of vacancies and defects in Na_0.44MnO₂ nanowire catalysts for lithium-oxygen batteries. Energy & Environmental Science, 2012, .

90. Black Robert Lee Jin-Hyon Adams Brian Mims Charles A. Nazar Linda F. The Role of Catalysts and Peroxide Oxidation in Li-O₂ Batteries. Angew. Chem. Int. Ed., 2013, 52, 392.

91. . Su Dawei Kim Hyun-Soo Kim Woo-Seong Wang Guoxiu A study of PtxCoy alloy nanoparticles as cathode catalysts for lithium-air batteries with improved catalytic activity. Journal of Power Sources, 2012.

92. Wang Long Zhao Xin Lu Yuhao Xu Maowen Zhang Dawei Ruoff Rodney S. Stevenson Keith J. Goodenough John B. CoMn₂O₄ Spinel Nanoparticles Grown on Graphene as Bifunctional Catalysts for Lithium-Air Batteries. Journal of The Electrochemical Society, 2011, 158, A1379.

93. . Yoon Dockyoung Kim Kyongsik Park Myounggu Kim Sangjin Sun Heeyoung Lee Hyungbok Lee Junesoo An effort to Understand the Basic Characteristics of Hybrid Li-air Performance In: ECS Fall Meeting; Hawaii, US.

94. Harding Jonathan R. Lu Yi-Chun Tsukada Yasuhiro Yang Shao-Horn Evidence of catalyzed oxidation of Li₂O₂ for rechargeable Li-air battery applications. Physical Chemistry Chemical Physics, 2012, 14, 10540.

95. McCloskey Bryan D. Scheffler Rouven Speidel Angela Bethune Donald S. Shelby Robert M. Luntz A.C. On the Efficacy of Electrocatalysis in Nonaqueous Li-O₂ Batteries. Journal of the American Chemical Society, 2011, 133, 18038.

96. Zhang Sheng S. Foster Donald Read Jeffrey Discharge characteristics of a non-aqueous electrolyte Li/O₂ battery. J. Power Sources, 2010, 195, 1235.

97. Lu Yi-Chun Gasteiger Hubert A. Crumlin Ethan McGuire Robert Yang Sho-Horn. Electrocatalytic Activity Studies of Select Metal Surfaces and Implications in Li- Air Batteries. Journal of the Electrochemical Society, 2010, 157, A1016.

98. Chen Jingzhe Hummelshoj Jens S. Thygesen Kristian S. Myrdal Jon S.G. Norskov Jens K. Vegge Tejs The role of transition metal interfaces on the electronic transport in lithium-air batteries. Catalysis Today, 2011, 165, 2.

99. Lu Yi-Chun Gasteiger Hubert A. Yang Shao-Horn. Catalytic Activity Trends of Oxygen Reduction Reaction for Nonaqueous Li-Air Batteries. Journal of the American Chemical Society, 2011, 133, 19048.

100. Zhang G.Q. Zheng J.P. Liang R. Zhang C. Wang B. Hendrickson M. Plichta E.J. Lithium-Air Batteries Using SWNT/CNF Bucky-papers as Air Electrodes. Journal of the Electrochemical Society, 2010, 157, A953.

101. Kim Kinoshita Carbon. 1998.New York, John Wiley & Sons.

102. . Stiles Alvin B. Catalyst Supports and Supported Catalysts. 1987.Boston, Butterworths.

103. Cao Ruiguo Lee Jang-Soo Liu Meilin Cho Jaephil Recent Progress in Non-Precious Catalysts for Metal-Air Batteries. Advanced Energy Materials, 2012, 2, 816.

104. Jorissen Ludwig Bifunctional oxygen/air electrodes. Journal of Power Sources, 2006, 155, 23.

105. Bidault F. Brett D.J.L. Middleton P.H. Brandon N.P. Review of gas diffusion cathodes for alkaline fuel cells. Journal of Power Sources, 2009, 187, 39.

106. . Moore John W. Stanitski Conrad L. Jurs Peter C. Chemistry. Second Edition. 2005.Toronto Canada, Thomson.

107. Lu Y.-C. Gasteiger H. A. Crumlin E. McGuire R. Shao-Horn. Y. Electrocatalytic Activity Studies of Select Metal Surfaces and Implications in Li-air Batteries. J. Electrochem. Soc., 2010, 157, A1016.

108. Debart A. Bao J. Armstrong G. Bruce P.G. An O₂ Cathode for Rechargeable Lithium Batteries: The effect of a Catalyst. J. Power Sources, 2007, 174, 1177.

109. Debart A. Paterson A.J. Bao J. Bruce P.G. α-MnO₂ Nanowires: A catalyst for the O₂ Electrode in Rechargeable Lithium Batteries. Angew. Chem., Int. Ed., 2008, 47, 4521.

110. Lu Y.-C. Gasteiger H.A. Parent M. C. Chiloyan V. Shao-Horn. Y. The Influence of Catalysts on Discharge and Charge Voltages of Rechargeable Li-Oxygen Batteries. Electrochem. Solid-State Lett., 2010, 13, A69.

111. Lu Y.-C. Xu Z. Gasteiger H. A. Chen S. Hamad- Schifferli K. Shao-Horn. Y. Platinum-Gold nanoparticles: A Highly Active Bifunctional Electrocatalyst for Rechargeable Lithium-Air Batteries. J. Am. Chem. Soc., 2010, 132, 12170.

112. . Alexander Kraytsberg Yair Ein-Eli The impact of nanoscaled materials on advanced metal-air battery systems. Nanoenergy, 2013.

113. Thiele D. Colmenarejo E. Lopez-Camacho Grobety B. Zuttel. A. Synthesis of carbon nanotubes on La_0.6Sr_0.4CoO₃ as substrate. Diamond & Related Materials, 2009, 18, 34.

114. . Shao Yuyan Zhang Sheng Wang Chongmin Nie Zimin Liu Jun Wang Yong Lin Yuehe Highly durable graphene nanoplatelets supported Pt nanocatalysts for oxygen reduction. Journal of Power Sources, 2010, 195, 4600.

115. . Fampiou Ioanna Ramasubramaniam Ashwin Binding of Pt Nanoclusters to Point Defects in Graphene: Adsorption, Morphology, and Electronic Structure. Journal of Physical Chemistry C, 2012, 116, 6543–6555.

116. . Mitchell Robert R. Gallant Betar M. Thompson Carl V. Yang Shao-Horn. All-carbon-nanofiber electrodes for high-energy rechargeable Li-O₂ batteries. Energy & Environmental Science, 2011, 4, 2952–2958.

117. Benbow E. M. Kelly S. P. Zhao L. Reutenauer J. W. Suib. S. L. Oxygen Reduction Properties of Bifunctional a-Manganese Oxide Electrocatalysts in Aqueous and Organic Electrolytes. The Journal of Physical Chemistry C, 2011, 115, 22009.

118. Jin Lei Xu Linping Morein Christine Chen Chun-hu Lai Monique Dharmarathna Saminda Dobley Arthur Suib Steven L. Titanium Containing α-MnO₂(TM) Hollow Spheres: One-step Synthesis and Catalytic Activities in Li/Air Batteries and Oxidative Chemical Reactions. Advanced Functional Materials, 2010, 20, 3373.

119. Kou Rong Shao Yuyan Wang Donghai Engelhard Mark H. Kwak Ja Hun Wang Jun Viswanathan Vilayanur V. Wang Chongmin Lin Yuehe Wang Yong Aksay Ilhan A. Liu Jun Enhanced activity and stability of Pt catalysts on functionalized graphene sheets for electrocatalytic oxygen reduction. Electrochemical Communications, 2009, 11, 954.

120. Yumura Takashi Kimura Keisuke Kobayashi Hisayoshi Tanaka Ryo Okumura Norio Yamabe Tokio The use of nanometer-sized hydrographene species for support material for fuel cell electrode catalysts:a theoretical proposal. Physical Chemistry Chemical Physics, 2009, 11, 8275.

121. Gilliam Ryan J. Kirk Donald W. Thorpe Steven J. Influence of Structural Microstructural and Electrical Properties on Electrocatalytic Performance at the Nanoscale. Electrocatalysis, 2011, 2, 1.

122. Moshfegh A.Z. Nanoparticle catalysts. Journal of Physics D: Applied Physics, 2009, 42, 23301.

123. Tritsaris G.A. Greeley J. Rossmeisl J. Norskov J.K. Atomic-Scale Modeling of Particle Size Effects for the Oxygen Reduction Reaction on Pt. Catalysis Letters, 2011, 141, 909.

124. Gasteiger Hubert A. Kocha Shyam S. Sompalli Bhaskar Wagner Frederick T. Activity benchmarks and requirements for Pt Pt-alloy and non-Pt oxygen reduction catalysts for PEMFCs. Applied Catalysis B: Environmental, 2005, 56, 9.

125. Shao Minhua Shoemaker Krista Peles Amra Kaneko Keiichi Protsailo Lesia Pt Monolayer on Porous Pd-Cu Alloys as Oxygen Reduction Electrocatalysts. Journal of the American Chemical Society, 2010, 132, 9253.

126. Perez-Alonso Francisco J. McCarthy David N. Nierhoff Anders Hernandez-Fernandez Patricia Strebel Christian Stephens Ifan E.L. Nielsen Jane H. Chorkendorff Ib The Effect of Size on the Oxygen Electroreduction Activity of Mass-Selected Platinum Nanoparticles. Angewandte Chemie International Edition, 2012, 51, 4641.

127. Stephens Ifan E.L. Bondarenko Alexander S. Gronbjerg Ulrik Rossmeisl Jan Chorkendorff Ib Understanding the electrocatalysis of oxygen reduction on platinum and its alloys. Energy and Environmental Science, 2012, 5, 6744.

128. Shao Yuyan Park Sehkyu Xiao Jie Zhang Ji-Guang Wang Yong Liu Jun Electrocatalysts for Nonaqueous Lithium-Air Batteries: Status Challenges and perspective. ACS Catalysis, 2012, 2, 844.

129. Aurbach Doron Zinigrad Ella Cohen Yaron Teller Hanan A short review of failure of lithium metal and lithiated graphite anodes in liquid electrolyte solutions. Solid State Ionics, 2002, 148, 405.

130. . Nazar Linda F. Overcoming the Challenges in Li-O₂ Batteries. 2012.SK innovation.

131. Black Robert Oh Si Hyoung Lee Jin-Hyon Yim Taeeun Adams Brian Nazar Linda F. Screening for Superoxide Reactivity in Li-O₂ Batteries: Effect on Li₂O₂/LiOH Crystallization. Journal of the American Chemical Society, 2012, 134, 2902.

132. Laoire Cormac O. Mukerjee Sanjeev Abraham K.M. Elucidating the Mechanism of Oxygen Reduction for Lithium-Air Battery Applications. The Journal of Physical Chemistry C, 2009, 113, 20127.

133. . Yoo Eunjoo Zhou Haoshen Fe phthalocyanine supported by graphene nanosheet as catalyst in Li-air battery with the hybrid electrolyte. Journal of Power Sources, 2013.

134. Ghamouss Fouad Mallouki Mohamed Bertolotti Bruno Chikh Linda Vancaeyzeele Cedric Alfonsi Severine Fichet Odile Long lifetime in concentrated LiOH aqueous solution of air electrode protected with interpenetrating polymer network membrane. Journal of Power Sources, 2012, 197, 267.

135. Bryantsev Vyacheslav S. Giordani Vincent Walker Wesley Blanco Mario Zecevic Strahinja Sasaki Kenji Uddin Jasim Addison Dan Chase Gregory V. Predicting Solvent Stability in Aprotic Electrolyte Li–Air Batteries: Nucleophilic Substitution by the Superoxide Anion Radical (O₂ ^Π). Journal of Physical Chemistry A, 2011, 115, 12399.

136. Karan Naba K. Balasubramanian Mahalingam Fister Timothy T. Burrell Anthony K. Du Peng Bulk- Sensitive Characterization of the Discharged Products in Li-O₂ Batteries by Nonresonant Inelastic X-ray Scattering. Journal of Physical Chemistry C, 2012, 116, 18132.

137. Overbury S. H. Schwartz Viviane Mullins David R. Yan Wenfu Dai Sheng Evaluation of the Au size effect: CO oxidation catalyzed by Au/TiO₂. Journal of Catalysis, 2006, 241, 56.

138. Freunberger Stefan A. Chen Yuhui Peng Zhangquan Griffin John M. Hardwick Laurance J. Barde Fanny Novak Petr Bruce Peter G. Reactions in the Rechargeable Lithium-O₂ Battery with Alkyl Carbonate Electrolytes. Journal of the American Chemical Society, 2011, 133, 8040.

139. Chen Yuhui Freunberger Stefan A. Peng Zhangquan Barde Fanny Bruce Peter G. Li-O₂ Battery with a Dimethylformamide Electrolyte. Journal of the American Chemical Society, 2011, 134, 7952.

140. Oh Si Hyoung Yim Taeeun Pomerantseva Ekaterina Nazar Linda F. Decomposition Reaction of Lithium Bis(oxalate)borate in the Rechargeable Lithium-Oxygen Cell. Electrochemical and Solid-State Letters, 2011, 14, A185.

141. McCloskey B.D. Bethune D.S. Shelby R.M. Girishkumar G. Luntz A.C. Solvents' critical Role in Nonaqueous Lithium-Oxygen Battery Electrochemistry. The Journal of Physical Chemistry Letters, 2011, 2, 1161.

142. Peng Zhangquan Freunberger Stefan A. Hardwick Laurence J. Chen Yuhui Giordani Vincent Barde Fanny Novak Petr Graham Duncan Tarascon Jean-Marie Bruce Peter G. Oxygen Reactions in a Non-Aqueous Li⁺ Electrolyte. Angewandte Chemie, 2011, 50, 6351.

143. Hardwick Laurence J. Bruce Peter G. The pursuit of rechargeable non-aqueous lithium-oxygen battery cathodes. Current Opinion in Solid State and Materials Science, 2012, 16, 178.

144. Hassoun Jusef Croce Fausto Armand Michel Scrosati Bruno Investigation of the O₂ Electrochemistry in a polymer Electrolyte Solid-State Cell. Angewandte Chemie International Edition, 2011, 50, 2999.

145. Sawyer Donald T. Oxygen Chemistry. 1991.New York, Oxford University Press.

146. McCloskey B.D. Speidel A. Scheffler R. Miller D.C. Viswanathan V. Hummelshoj J.S. Norskov J.K. Luntz A.C. Twin Problems of Interfacial Carbonate Formation in Nonaqueous Li-O₂ Batteries. The Journal of Physical Chemistry Letters, 2012, 3, 997.

147. McCloskey B. D. Bethune D. S. Shelby R. M. Mori T. Scheffler R. Speidel A. Sherwood M. Luntz A. C. Limitations in Rechargeability of Li-O₂ Batteries and Possible Origins. The Journal of Physical Chemistry Letters, 2012, 3, 3043.

148. Freunberger Stefan A. Chen Yuhui Peng Zhangquan Griffin John M. Hardwick Laurence J. Barde Fanny Novak Petr Bruce Peter G. Reactions in the Rechargeable Lithium-O₂ Battery with Alkyl Carbonate Electrolytes. Journal of the America Chemical Society, 2011, 133, 8040.

149. Freunberger Stefan A. Chen Yuhui Drewett Nicholas E. Hardwick Laurence J. Barde Fanny Bruce Peter G. The Lithium-Oxygen Battery with Ether-Based Electrolytes. Angew. Chem., Int. Ed., 2011, 50, 8609.

150. Veith Gabriel M. Dudney Nancy J. Howe Jane Nanda Jagjit Spectroscopic Characterization of Solid Discharge Products in Li-Air Cells with Aprotic Carbonate Electrolytes. The Journal of Physical Chemistry C, 2011, 115, 14325.

151. Wang Hui Xie Kai Investigation of oxygen reduction chemistry in ether and carbonate based electrolytes for Li-O₂ batteries. Electrochimica Acta, 2012, 64, 29.

152. Assary Rajeev S. Curtiss Larry A. Redfern Paul C. Zhang Zhengcheng Amine Khalil Computational Studies of Polysiloxanes: Oxidation Potentials and Decomposition Reactions. The Journal of Physical Chemistry C, 2011, 115, 12216.

153. McCloskey Bryan D. Scheffler Rouven Speidel Angela Girishkumar Girish Luntz Alan C. On the Mechanism of Nonaqueous Li-O₂ Electrochemistry on C and Its Kinetic Overpotentials: Some Implications for Li- Air Batteries. The Journal of Physical Chemistry C, 2012, 116, 23897.

154. Li Yunfeng Huang Kan Xing Yangchuan A hybrid Liair battery with buckypaper air cathode and sulfuric acid electrolyte. Electrochimica Acta, 2012, 81, 20.

155. Shimonishi Y. Zhang T. Johnson P. Imanishi N. Hirano A. Takeda Y. Yamamoto O. Sammes N. A study on lithium/air secondary batteries-Stability of NASICONtype glass ceramics in acid solutions. Journal of Power Sources, 2010, 195, 6187.

156. Li Longjun Zhao Xinsheng Manthiram Arumugam A dual-electrolyte rechargeable Li-air battery with phosphate buffer catholyte. Electrochemistry Communications, 2012, 14, 78.

157. Markovic N.M. Ross P.N. Surface science studies of model fuel cell electrocatalysts. Surface Science Reports, 2002, 45, 117.

158. Yang Kyung Shik Mul Guido Moulijn Jacob A. Electrochemical generation of hydrogen peroxide using surface area-enhanced Ti-mesh electrodes. Electrochimica Acta, 2007, 52, 6304.

159. Qiang Zhimin Chang Jih-Hsing Huang Chin-Pao Electrochemical generation of hydrogen peroxide from dissolved oxygen in acidic solutions. Water Research, 2002, 36, 85.

160. He Ping Wang Yonggang Zhou Haoshen The effect of alkalinity and temperature on the performance of lithiumair fuel cell with hybrid electrolytes. Journal of Power Sources, 2011, 196, 5611.

161. Bagotzky V.S. Khrushcheva E.I. Tarasevich M.R. Shumilova N.A. Corrosion of platinum catalysts in alkaline solutions. Journal of Power Sources, 1982, 8, 301.

162. Kiros Y. Lindstrom O. Kaimakis T. Cobalt and cobaltbased macrocycle blacks as oxygen-reduction catalysts in alkaline fuel cells. Journal of Power Sources, 1993, 45, 219.

163. Hasegawa Satoshi Imanishi Nobuyuki Zhang Tao Xie Jian Hirano Atsushi Takeda Yasuo Yamamoto Osamu Study on lithium/air secondary batteries - Stability of NASICON-type lithium ion conducting glass - ceramics with water. Journal of power sources, 2009, 189, 371.

164. Zhang Tao Imanishi Nobuyuki Hasegawa Satoshi Hirano Atsushi Xie Jian Takeda Yasuo Yamamoto Osamu Sammes Nigel Li/Polymer Electrolyte/ Water Stable Lithium-Conducting Glass Cermaics Composite for Lithium-Air Secondary Batteries with an Aqueous Electrolyte. Journal of The Electrochemical Society, 2008, 155, A962.

165. Christensen Jake Albertus Paul Carrera Roel S. Sanchez- Lohmann Timm Kozinsky Boris Liedtke Ralf Ahmed Jasim Kojic Aleksandar A Critical Reivew of Li/Air Batteries. Journal of The Electrochemical Society, 2012, 159, R1.

166. Kuboki Takashi Okuyama Tetsuo Ohsaki Takahisa Takami Norio Lithium-air batteries using hydrophobic room temperature ionic liquid electrolyte. Journal of Power Sources, 2005, 146, 766.

167. Yang Xin-hui He Ping Xia Yong-yao Preparation of mesocellular carbon foam and its application for lithium/ oxygen battery. Electrochemistry Communications, 2009, 11, 1127.

168. Read J. Ether-Based Electrolytes for the Lithium/Oxygen Organic Electrolyte Battery. Journal of The Electrochemical Society, 2006, 153, A96.

169. Xu Wu Xiao Jie Zhang Jian Wang Deyu Zhang Ji-Guang Optimization of Nonaqueous Electrolytes for Primary Lithium/Air Batteries Operated in Ambient Environment. Journal of the Electrochemical Society, 2009, 156, A773.

170. Xu Wu Xiao Jie Wang Deyu Zhang Jian Zhang Ji-Guang Effects of Nonaqueous Electrolytes on the Performance of Lithium/Air Batteries. Journal of the Electrochemical Society, 2010, 157, A219.

171. Beattie S.D. Manolescu D.M. Blair S.L. High- Capacity Lithium-Air Cathodes. Journal of the Electrochemical Society, 2009, 156, A44.

172. James A Supported Metals in Catalysis;Adnerson and Marcos Fernandez Garcia. 2005.London, Imperial College Press.

173. Trahey L. Johnson C. S. Vaughey J. T. Kang S.-H. Hardwick L. J. Freunberger S. A. Bruce P. G. Thackeray M. M. Activated Lithium-Metal-Oxides as Catalytic Electrodes for Li-O₂ Cells. Electrochemical and Solid- State Letters, 2010, 14, A64.

174. Reddy Thomas B. Linden David Linden's Handbook of Batteries. 2011, 33.1–33.58.

175. Ohkuma Hirokazu Uechi Ichiro Imanish Nobuyuki Hiraro Atsushi Takeda Yasuo Yamamoto Osamu Carbon electrode with perovskite-oxide catalyst for aqueous electrolyte lithium-air secondary batteries. Journal of Power Sources, 2013, 223, 319.

176. Wang Xianyou Sebastian P.J. Smit Mascha A. Yang Hongping Gamboa S.A. Studies on the oxygen reduction catalysts for zinc-air battery electrode. Journal of Power Sources, 2003, 124, 278.

177. Li Neng Yan Xiaoming Zhang Wanjing Lin Bingxiong Electrocatalytic activity of spinel-type oxides LiMn₂−_xCo_xO₄ with large specific surface areas for metal-air battery. Journal of Power Sources, 1998, 74, 255.

Practical Challenges Associated with Catalyst Development for the Commercialization of Li-air Batteries

Abstract

1. INTRODUCTION

Fig. 1.

Brief History of the Invention of Batteries and Fuel Cells.1-9)

2. METHODS

3. RESULTS

3.1. Key Concepts Related to Catalysts

Fig. 2.

Surface Reaction on Heterogeneous Catalysts.

3.2. Synthesis Methods of Catalysts

Table 1.

Features of the Impregnation Method29-34)

Fig. 3.

General Process of the Impregnation Method.

Table 2.

Features of the Colloidal Method51,46,52)

3.3. Roles of Catalysts in Li-air Cells

Table 3.

Comparison of Li-air Cells: Non-aqueous vs. Aqueous Electrolytes54)

3.4. Survey of Catalyst Research in Li-air Cells

Table 4.

Catalysts Used for Non-aqueous Li-air Batteries13,71-91)

Table 5.

Catalysts Used for Hybrid Li-air Batteries53,92,133,154,164)

Fig. 4.

Cycling Performance of a non-aqueous Type Li-air Cell.130)

Fig. 5.

Cycling Performance of a Hybrid Type Li-air Cell (Pt 0%).93)

Fig. 6.

Cycling Performance of a Hybrid Type Li-air Cell (Pt 10%).93)

Fig. 7.

Cycling Performance of a Hybrid Type Li-air Cell (Pt 40%).93)

Table 6.

Direct Four-Electron Pathways and Catalysts104,105)

Table 7.

Two-electron Reduction Pathways and Catalysts104,105)

4. DISCUSSION

4.1. Issues Regarding Organic Type Li-air Cells

Fig. 8.

Suggested Chemical Reactions During Discharge.12,128-142)

4.2. Issues Regarding Hybrid Type Li-air Cells

5. CONCLUDING REMARKS & PERSPECTIVES

ACKNOWLEDGEMENTS

References

Brief History of the Invention of Batteries and Fuel Cells.^1-9)

Features of the Impregnation Method^29-34)

Features of the Colloidal Method^51,46,52)

Comparison of Li-air Cells: Non-aqueous vs. Aqueous Electrolytes⁵⁴⁾

Catalysts Used for Non-aqueous Li-air Batteries^13,71-91)

Catalysts Used for Hybrid Li-air Batteries^{53,92,133,154,164)}

Cycling Performance of a non-aqueous Type Li-air Cell.¹³⁰⁾

Cycling Performance of a Hybrid Type Li-air Cell (Pt 0%).⁹³⁾

Cycling Performance of a Hybrid Type Li-air Cell (Pt 10%).⁹³⁾

Cycling Performance of a Hybrid Type Li-air Cell (Pt 40%).⁹³⁾

Direct Four-Electron Pathways and Catalysts^104,105)

Two-electron Reduction Pathways and Catalysts^104,105)