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Since the risk of catch fire using non-aqueous electrolyte solution, aqueous solution-based rechargeable lithium batteries (ARLB) have been highlighted. However, the conventional positive electrodes of lithium transition-metal oxide such as LiCoO2 (LCO) and LiNi1/3Mn1/3Co1/3O2 (NMC) have suffered from poor cyclability in aqueous medium. Representatively, the layered two-dimensional structure of LCO shows notably poor stability, possibly due to the surface degradation from water [1] and proton [2]. The understanding of interfacial reaction of LCO in the aqueous electrolyte solution is still superficial however. Here we present degradation phenomena of LCO electrode in aqueous medium using various X-ray measurement techniques, and suggest the solution to avoid such an irreversible electrochemical reaction. The aqueous solution was prepared with 0.5 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and pH was controlled to ~6.8 and 10. In both cases, there was no evidence for the formation of cathode-electrolyte interphase (CEI) on LCO in contrast to the one with non-aqueous electrolyte solution. The direct contact of aqueous electrolyte solution to LCO surface results in the short-range disorder of LCO structure such as the distortion of octahedral CoO6, and irreversible Li+ desertion during 10 cycles. To improve electrochemical reversibility and structural stability of LCO, we prepared the organic protection layer that opened the Li+ mass transport route while inhibiting H2O contact from hydrophobic surface. As a result, the capacity retention was improved to ~85% during 30 cycles at pH ~ 6.8. Furthermore, we developed the way to protect LCO surface by anion engineering and in the absence of protection layer, which give insight into the inner Helmholtz plane (IHP) structure and its effect for LCO degradation in aqueous medium.

Introduction Many attempts have been made to increase the energy density of Li-ion batteries using positive electrode materials such as LiMO2 (LiCoO2, LiNiO2, LiNi1/3Mn1/3Co1/3O2, etc.), which have high charging voltages (typically ≥4.4 V). Various studies to understand the associated degradation mechanism and improve the capacity reversibility during high-voltage charge/discharge have been reported. Generally, the inter-terminal voltage of Li-ion batteries can be practically controlled by changing the electric potential of the positive electrode. Thus, the positive electrodes used for high-voltage charge/discharge are exposed to a high electric potential as well as a large change in the electric potential. In this study, we examined the influence of the operating voltage range on the charge/discharge characteristics, and found that the discharge cutoff voltage greatly influences the capacity reversibility during high-voltage charge/discharge. Additionally, we discuss the mechanisms that determine the capacity reversibility based on the results of electrochemical impedance analysis and soft X-ray absorption spectroscopy (soft XAS). Experimental LiNi1/3Co1/3Mn1/3O2 powder, with a secondary particle diameter of 10 μm (Toda Kogyo Corp.), was used as the active material. Positive electrodes were fabricated from a mixture of 90 wt% LiNi1/3Co1/3Mn1/3O2, 5 wt% acetylene black, and 5 wt% polyvinylidene fluoride. The electrochemical characteristics of the samples were examined in coin cells with a Li-metal counter electrode. A 1.0 mol dm-3 solution of LiPF6 in ethylene carbonate + diethyl carbonate was used as the electrolyte. The cells were cycled at discharge-charge cutoff voltages of 2.5–4.6, 3.0–4.6, 3.8–4.6, and 4.2–4.6 V, at a current rate of 1 C. The Li-ion transfer characteristics were measured by alternating current impedance spectroscopy. The electronic structure of the LiNi1/3Co1/3Mn1/3O2was investigated using soft XAS at the beam line BL11 of Ritsumeikan University SR Center (Shiga, JAPAN). Results and Discussion Figures 1a and b show the discharge capacity and discharge capacity retention versus cycle number for LiNi1/3Co1/3Mn1/3O2 cycled with different voltage ranges. As the discharge cutoff voltage was increased, the initial discharge capacity decreased, accompanied by an improvement in the discharge capacity retention. The retentions at the 143rd cycle for LiNi1/3Co1/3Mn1/3O2cycled with 2.5–4.6, 3.0–4.6, 3.8–4.6, and 4.2–4.6 V, were 8, 37, 56, and 81%, respectively. Figure 2a shows the Nyquist plots for LiNi1/3Co1/3Mn1/3O2 cycled with different voltage ranges at an open circuit voltage of ~4.2 V after 3 cycles. The charge transfer resistances (R ct) calculated from the semicircles in the lower frequency region were almost equal (5–8 Ω) regardless of the discharge cutoff voltage. From the Nyquist plots after 143 cycles (Figure 2b), the R ct for LiNi1/3Co1/3Mn1/3O2 cycled with 2.5–4.6, 3.0–4.6, 3.8–4.6, and 4.2–4.6 V, were obtained as 3800, 300, 65, and 17 Ω, respectively. The increase of R ct with the number of cycles was significantly suppressed as the discharge cutoff voltage was increased, resulting in the higher capacity retention observed in Fig. 1b. These results suggest that a stable interface is retained between the electrode and electrolyte when the charge/discharge voltage is limited to the high-voltage region only. The interface structure and the capacity reversibility mechanism will be discussed along with the electronic state of LiNi1/3Co1/3Mn1/3O2analyzed by soft XAS. Acknowledgements This work is financially supported by the RISINGII project of the NEDO and METI, Japan. Figure 1

Li2FeSiO4 is one of interesting cathode material for lithium ion batteries. The two lithium composition per one iron atom and one poly-anion unit, in principle, exhibits a multi-electron charge transfer with Fe2+/Fe4+redox couple, which enables much high theoretical capacity of 331 mAhg–1. This value is approximately twice as high as the commercialized cathode materials, such as LiCoO2 and LiFePO4. However, the accessible charge-discharge capacity of Li2FeSiO4 was limited to one-electron reaction with Fe2+/Fe3+ redox couple in the early research 1 , 2 ). Recently, some research groups have reported more than one-electron reaction by using nanostructured materials3-6 ). Unfortunately, their high capacity is not stable during charge-discharge cycle and there is a large polarization at high voltage reaction. Therefore, the utilization of Fe2+/Fe3+ redox couple in this system is preferred for the stable battery operation. To maximize this Fe2+/Fe3+ redox reaction in lithium iron silicate system, we investigate composition dependency of Li x Fe2+ (4-x)/2SiO4 on charge-discharge capacity. Although the nonstoichiometric lithium iron silicate has been reported in the previous conference by the other group7 ), we cannot access enough data to discuss the possibility of the nonstoichiometric system. We synthesized various Li x Fe2+ (4-x)/2SiO4 samples and the charge-discharge measurements were performed. Their reaction mechanisms are discussed by using X-ray absorption spectroscopic data. Carbon-coated Li x Fe2+ (4-x)/2SiO4 samples were synthesized by the solid-state reaction. A given amounts of SiO2, FeC2O4・2H2O and Li2CO3 powders were weighed and 10 wt% of carbon (acetylene black) was added prior to mixing. These powders were mixed in a planetary ball mill at 400 rpm for 6 hours. The mixture was calcined at 700°C for 6 hours with a fixed Ar flux. The products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). For electrochemical measurements, Li x Fe2+ (4-x)/2SiO4 samples, carbon black, and polyvinylidene fluoride were mixed at a ratio of 80:10:10 with 1-methyl-2-pyrrolidone. The slurry was coated onto an aluminum foil current collector and dried in a vacuum oven at 80°C. For the charge-discharge measurements, the prepared electrode, lithium metal, and electrolyte-soaked separator (Celgard #2500) were constructed into a stainless steel flat cell. The electrolyte was a 1 mol dm–3 solution of LiPF6 in ethylene carbonate/ethyl methyl carbonate (3:7 volume ratio, Kishida). The cell construction process was performed in an Ar-atmosphere glove box. Galvanostatic charge-discharge measurements were performed at 55°C. For the prepared Li x Fe2+ (4-x)/2SiO4 samples, their crystal structures are almost similar from XRD measurements. Considering the Fe2+/Fe3+ redox reaction in Li x Fe2+ (4-x)/2SiO4 system, the maximum charge-discharge capacity is 203 mAh g-1 in Li1.33Fe1.335SiO4. However, the observed discharge capacity was smaller than the stoichiometric system. The diffusion path of lithium ion might be blocked by the occupation of iron ion in the lithium site. We will discuss the charge-discharge mechanism in this system by using X-ray absorption spectroscopy data. 1) A. Nyten, A. Abouimrane, M. Armand, T. Gustafsson, J.O. Thomas, Electrochem. Commun., 7, 156-160 (2005). 2) A. Nyten, S. Kamali, L. Haggstrom, T. Gustafsson, J.O. Thomas, J. Mater. Chem., 16, 2266-2272 (2006). 3) D. Rangappa, K.D. Murukanahally, T. Tomai, A. Unemoto, I. Honma, Nano Lett., 12, 1146-1151 (2012). 4) Z.X. Chen, S. Qiu, Y.L. Cao, J.F. Qian, X.P. Ai, K. Xie, X.B. Hong, H.X. Yang, J. Mater. Chem. A, 1, 4988-4992 (2013). 5) D.P. Lv, J.Y. Bai, P. Zhang, S.Q. Wu, Y.X. Li, W. Wen, Z. Jiang, J.X. Mi, Z.Z. Zhu, Y. Yang, Chem. Mat., 25, 2014-2020 (2013). 6) T. Masese, C. Tassel, Y. Orikasa, Y. Koyama, H. Arai, N. Hayashi, J. Kim, T. Mori, K. Yamamoto, Y. Kobayashi, H. Kageyama, Z. Ogumi, Y. Uchimoto, J. Phys. Chem. C, 119, 10206-10211 (2015). 7) K. Kam, A. Liivat, D. Ensling, T. Gustafsson, J. Thomas, ECS Meeting Abstracts, MA2009-02, 390 (2009).

Li2MnO3-based materials have been extensively studied as positive electrode materials in the past decade. The reaction mechanism of this material had been the controversial subject for a long time. Since the oxidation state of manganese ions is tetravalent, further oxidation of manganese ions is difficult in Li cells. Instead of manganese ions, negatively charged anions, oxide ions (O2-), donate electrons on charge. However, oxidation of oxide ions results in partial loss of oxygen as an irreversible process, i.e., decomposition reaction. The use of anion redox, especially oxide ions, is a crucial strategy to design and develop new electrode materials with high gravimetric/volumetric energy density for rechargeable lithium batteries. Reversible capacity of electrode materials is potentially further increased by the enrichment of lithium contents with less transition metals in the close-packed structure of oxide ions. Our group has reported that Li3Nb5+O4[1] and Li4Mo6+O5[2], which have higher lithium contents than those of Li2MnO3, are potentially utilized as host structures for a new series of high-capacity electrode materials. Among them, Mn3+-substituted Li3NbO4, Li1.3Nb0.3Mn0.4O2 (0.43Li3NbO4 – 0.57LiMnO2), delivers large reversible capacity (approximately 300 mAh g-1) with highly reversible solid-state redox reaction of oxide ions.[1] Recently, Li2Ti4+O3 is also proposed as the host structure for high-capacity electrode materials with redox reaction of oxide ions.[3] Mn3+-substituted sample, 0.5Li2TiO3 – 0.5LiMnO2 (Li1.2Ti0.4Mn0.4O2), also delivers large reversible capacity as shown in Figure 1a. A voltage profile of Li1.2-x Ti0.4Mn0.4O2 quite resembles that of Li1.3-x Nb0.3Mn0.4O2. Available energy density of Li1.2-x Ti0.4Mn0.4O2 exceeds 1,000 mWh g-1 as a positive electrode material. Moreover, charge compensation is realized by oxidation of oxide ions as evidenced by O K-edge X-ray absorption spectroscopy (Figure 1b) as a reversible process. In contrast to the Mn system, an iron counterpart, xLi2TiO3 – (1 – x) LiFeO2 binary system, shows large polarization on charge/discharge,[4] which is similar to that of Li3NbO4-LiFeO2 binary system.[1] For these Fe-containing materials, oxidation of oxide ions seems to trigger oxygen loss as an irreversible process. From these results, we will discuss the origin of stabilization and destabilization in solid-state redox reaction of oxide ions, and the possibility of high-capacity positive electrode materials, which effectively use the solid-state redox of oxide ions for the charge compensation, consisting of only 3d-transtion metals. Acknowledgements This research has been partly supported by Advanced Low Carbon Technology Research and Development Program of the Japan Science and Technology Agency (JST) Special Priority Research Area “Next-Generation Rechargeable Battery.” References [1] N. Yabuuchi, M. Takeuchi, M. Nakayama, H. Shiiba, M. Ogawa, K. Yamanaka, T. Ohta, D. Endo, T. Ozaki, T. Inamasu, K. Sato, and S. Komaba, Proceedings of the National Academy of Sciences, 112, 7650 (2015). [2] N. Yabuuchi, Y. Tahara, S. Komaba, S. Kitada, and Y. Kajiya, Chemistry of Materials, 28, 416 (2016). [3] N. Yabuuchi et al., submitted [4] S. L. Glazier, J. Li, J. Zhou, T. Bond, and J. R. Dahn, Chemistry of Materials, 27, 7751 (2015). Figure 1

High capacity cathode materials of lithium ion secondary battery are desirable to apply to the large-scaled energy devices such as electric vehicles or electricity storage systems. Recently, lithium-rich layered materials such as Li2MnO3 and Li2RuO3 are attended as interesting cathode materials because of their a few times larger theoretical capacity than that of LiCoO2 [1].The reaction mechanism of the lithium-rich cathodes has not been fully understood, especially at the high potential. In this study, Li2MnO3 and Li2RuO3 electrodes were prepared, and the electronic structure change of Li2MnO3 and Li2RuO3 were investigated by using operandosoft X-ray absorption spectroscopy under charge-discharge reaction of these electrodes. The cathode materials were synthesized by solid-state reaction method. Li2MnO3 was prepared from a stoichiometric amount of LiOH-H2O and MnO2. They were dispersed in acetone and ground by a ball milling machine for 3 hours at a speed of 400 rpm using 2 mm ZrO2 beads as grinding media. After drying, the mixture powder was pressed into pellets (10 mm diameter.) and heated at 450 °C for 24 hours in air and then calcined at 400 °C for 48 hours. Li2RuO3 was prepared from LiOH-H2O and RuO2in the same way, however, heated at 1000 °C for 15 hours in air and then ground for 3 hours before calcined at 900 °C for an hour. The cathode for operando X-ray absorption measurements was prepared from a paste by mixing 80 wt% of as-prepared cathode active materials, 10 wt% of acetylene black and 10 wt% of polyvinylidene difluoride binder in 1-methyl-2-pyrrolidone solvent. This paste was coated on the platinum-sputtered silicon nitride thin film. Li4Ti5O12 was used as the counter electrode material and 1 mol/L LiPF6 in an acetonitrile solvent was used as an electrolyte. The operando soft X-ray absorption spectroscopy measurement was carried out at BL27SU of SPring-8. The oxygen K-edge XANES spectra for Li2MnO3 and Li2RuO3 during first charge reaction were measured. For the charge reaction of Li2MnO3, the peaks located at 529.5 eV and 532.0 eV were progressively weaken and broadened (Figure 1a). It implies that the main reaction during the charge process is the oxygen evolution because of the small contribution of Mn 3d - O 2p orbital. For Li2RuO3 (Figure 1b), on the other hand, the peaks at 529.5 eV and 532.0 eV were shifted to the lower energy during the delithiated process from x=2.00 to x=1.00 in LixRuO3 and these peaks were sharpen from x=1.00 to x=0.48. In the Ru L3-egde XANES spectra, the peak was shifted to the higher energy from x=2.00 to x=1.00, however not changed from x=1.00 to x=0.48. These results suggest that the Li2RuO3 charge reaction includes two process, (1) the oxidized reaction of Ru4+→Ru5+, (2) O2 charge compensation owing to the hybridization state between Ru 4d and O 2porbital. This work revealed the contribution of the Ru-O hybrid orbital during the charge process directly and was a guide to design the high-capacity cathode materials in the future. Reference [1] M. Sathiya, K. Ramesha, G. Rousse, D. Foix, D. Gonbeau, A. S. Prakash, M. L. Doublet, K. Hemalatha, and J.-M. Tarascon, Chem. Mater. 25(2013), 1121−1131

Introduction Elemental sulfur is one of the promising cathode active materials for high-energy rechargeable lithium batteries because of its high theoretical capacity (ca. 1670 mAh-g-1) and relatively low cost [1]. However, sulfur cathode has some disadvantages, such as low electrical conductivity and dissolution as polysulfides into electrolyte during electrochemical cycling, resulting in shuttling in Li-S batteries. Several attempts have been performed to solve these problems, and the major improvements have been made by forming composites with carbon matrix, whereby sulfur was physically confined in some fine structures [2]. Despite the improved electrical transfer and the suppressed shuttling of polysulfides, these S-C composites cells still showed gradual capacity degradation. This is originated from the low binding energy between sulfur and carbon matrix [3]. Another type of S-C composites has been developed, based on the concept of embedding sulfur into a conductive polymer matrix, such as sulfurized poly(acrylonitrile) (S-PAN) [4-6]. In these organosulfur materials, sulfur is thought to be incorporated in cavity of molecular scale, which significantly prevents the dissolution as polysulfides, leading to the excellent cycle stability of the cells. Although many kinds of polymer framework have been investigated, there still remain challenges for exploring the organosulfur materials with higher sulfur contents, using inexpensive and non-toxic reagents [3]. In the present work, we have tried to prepare new type of organosulfur cathode materials using primary alcohol. The structure and the electrochemical properties of the obtained sulfurized alcohol composites (SAC) were examined. Experiments SAC was prepared by refluxing primary alcohol 1-C n H2n+1OH (n = 3 – 10) (1g) and elemental sulfur (5g) in a glass tube equipped in an electric furnace, which was heated at 400oC. After cooling, the resulting powder was ground and then heated again at 300oC under N2 flow in order to eliminate residual elemental sulfur to yield the SAC. We also prepared S-PAN after the method reported previously [7]. The obtained SAC was characterized by XRD, Raman spectroscopy, TEM observation, and elemental analysis, as well as S and C K-edge XAFS measurements (SR Center, Ritsumeikan University). Electrochemical lithium insertion / extraction reactions were carried out at 30oC using lithium coin-type cells with 1M LiPF6 / (EC + DMC) electrolyte at a current density of 30 mA-g-1 between 1.0 and 3.0 V initially with discharging. The electrochemical performances were also examined by assembling all-solid-state cells using the Li2S-P2S5 solid electrolyte and indium anode in a similar manner as described previously [8] at a current density of 30 mA-g-1 between 0.4 and 3.5 V. Results and Discussion The obtained SAC samples were black in color, and the XRD patterns showed no significant peaks, irrespective of the primary alcohol (n-value). High-resolution TEM observations showed no obvious crystalline domains, indicating an amorphous phase. The EDX mapping showed relatively homogeneous distribution of sulfur and carbon in the SAC samples. The elemental analyses indicated that the sulfur content was more than 60 wt%, which was higher than that reported previously for S-PAN (ca. 30 – 53 wt%) [4,5]. The Raman spectra showed some peaks at 480, 1250, 1440cm-1, suggesting the S-S, C-S, and C-C bonds, respectively. Analyses of the D- and G-bands indicated that the C-C bonds mainly consisted of sp3-type configuration, which makes a clear contrast to the S-PAN where the C-C bonds consisted of mainly sp2-configuration. The electrochemical tests for the SAC sample cells showed that the initial discharge capacity was ca. 800 - 1000 mAh-g-1, which was higher than that of S-PAN, due possibly to higher sulfur contents. Also, the all-solid-state cells with the SAC samples showed the discharge capacity of ca. 600 – 800 mAh-g-1. The charge/discharge mechanism was examined using S and C K-edge XAFS measurements, and the results will be presented in the conference. Acknowledgment This work was financially supported partly by “Next-generation storage battery material evaluation technology development” project of NEDO and METI, Japan. References [1] P. G. Bruce et al., Nat. Mater., 11, 19 (2012). [2] X. Ji et al., Nat. Mater., 8, 500 (2009). [3] H. Kim et al., Nat. Commun., 6, 7278 (2015). [4] J. Wang et al., Adv. Mater., 14, 963 (2002). [5] T. Miyuki et al., Sen’i Gakkaishi, 68, 179 (2012) [6] Y. Liang et al., Adv. Energy Mater., 2, 742 (2012). [7] J. E. Trevey et al., J. Electrochem. Soc., 159, A1019 (2012). [8] T. Takeuchi et al., J. Electrochem. Soc., 157, A1196 (2010).

Rechargeable lithium batteries have rapidly risen to prominence as fundamental devices for green and sustainable energy development. Lithium batteries are now used as power sources for electric vehicles. However, materials innovations are still needed to satisfy the growing demand for increasing energy density of lithium batteries. In the past decade, lithium enriched materials, Li2MeO3-type layered materials (Me = Mn4+, Ru4+ etc.), which are classified as one of cation-ordered rocksalt-type structures, have been extensively studied as potential high-capacity electrode materials, especially for the tetravalent manganese system (Li2MnO3). Li2MnO3 had been originally thought to be electrochemically inactive because oxidation of manganese ions beyond the tetravalent state in Li cells is difficult. However, the fact is that Li2MnO3 is electrochemically active, presumably because of the contribution of oxide ions for redox reaction. Although the oxidation of oxide ions in Li2MnO3 results in the partial oxygen loss with irreversible structural changes, it has been reported that the solid-state redox reaction of oxide ions is effectively stabilized in Li2Ru1-x Sn x O3 system. Nearly 1.6 moles of lithium ions are reversibly extracted/inserted from/into Li2Ru0.75Sn0.25O3 with excellent capacity retention, indicating that unfavorable phase transition is effectively suppressed in this system. The use of oxide ion redox is the important strategy to further increase the reversible capacity of positive electrode materials for LIBs because the lithium content is potentially further enriched with a lower amount of transition metals in the framework structure. Reversible capacity as electrode materials is not limited by the absence of oxidizable transition metals as a redox center. Negatively charged oxide ions can potentially donate electrons instead of transition metals. However, oxidation without transition metals inevitably result in the release of oxygen molecules, for instance, electrochemical decomposition of Li2O2. Based on these considerations, we have decided to investigate the rocksalt phase with pentavalent niobium ions, i.e., Li3NbO4. Increase in oxidation numbers of transition metals from “tetravalent to pentavalent” states (or even higher than pentavalent) allows us to enrich a lithium content in the close-packed framework structure of oxide ions with fewer transition metals. Similar to Li2MeO3, Li3NbO4 with pentavalent niobium ions is also classified as one of the cation-ordered rocksalt structures. Although Li3NbO4 crystallizes into the lithium-enriched rocksalt-type phase, it is electrochemically inactive because of its insulating character without electrons in a conduction band (4d0 configuration for Nb5+). Therefore, to induce electron conductivity in Li3NbO4, transition metals are partly substituted for Nb5+ and Li+. In this study, x Li3NbO4 – (1-x) LiMeO2 (Me = Mn3+, Fe3+, and V3+) system has been studied as a new series of electrode materials. Among these samples, the Mn3+-substituted sample can deliver large reversible capacities of 250 – 300 mAh g-1 at elevated temperatures (50 – 60 oC). Moreover, the large reversible capacity partly originates from the solid-state redox reaction of oxide ions, which has been evidenced by DFT calculation and soft X-ray absorption spectroscopy. Together with these results, electrode performance and reaction mechanisms are also compared with those of Fe3+- and V3+-substituted samples. From these results, we will discuss the possibility of the new series of positive electrode materials for rechargeable batteries, beyond the restriction of the solid-state redox reaction based on the transition metals used for past three decades.

Despite high theoretical capacity, a Li-O2 cell has suffered from huge oxidation potential polarization on carbon-based positive electrode for charge (>4.2 V vs. Li/Li+), due to sluggish decomposition of non-conductive discharge product, lithium peroxide (Li2O2 ↔ 2Li+ + O2 + 2e-) [1]. Such high potential triggers side reactions such as degradation of electrolyte and carbonaceous electrode, which results in poor cycle-ability [1]. To mitigate this problem during oxygen evolution reaction (OER), solid-state metal or metal oxide nanoparticles (indicated as promoters), which have been widely employed as catalysts in aqueous media, were introduced to the electrode [2]. However, the specific role of promoters in the Li-O2 battery is little known due to complication from accompanying parasitic side reactions [3]. In addition, reasonable comparison of promoters’ activities is not feasible under different performance conditions when various reports were referred [2]. Therefore, to gain a reasonable assessment of their activities in the Li-O2 cell and an understanding of the promoters’ role, it is necessary to examine Li-O2 cells with these promoters under the same condition and analyze their reaction processes in detail. Here I present diagnosis of the true role of promoters, representative of platinum (Pt), gold (Au), palladium (Pd) and cobalt oxide (Co3O4), for OER in Li-O2 cells. After preparation of comparable size and mass loading of promoters on carbon nanotube (CNT) electrode, the Li-O2 cells containing these promoter/CNT combinations were examined using galvanostatic mode under the same operating conditions. The promoter/CNT electrodes show reasonably lower charge potentials than the promoter-free electrode for the 1st charge. Through in situ gas analysis of online electrochemical mass spectroscopy (OEMS) and ex situ chemical analysis of X-ray near-edge fine structure (XANES) spectroscopy, the evolved gas amount and remaining product after charge could be correlated, which accounted for the true reaction occurring for each promoter. References [1] (a) G. Girishkumar, B. McCloskey, A. C. Luntz, S. Swanson and W. Wilcke, J. Phys. Chem. Lett., 2010, 1, 2193–2203; (b) P. G. Bruce, S. A. Freunberger, L. J. Hardwick and J.-M. Tarascon, Nature Mater., 2012, 11, 19–29. [2] (a) Y. –C. Lu, H. A. Gasteiger and Y. Shao-Horn, J. Am. Chem. Soc., 2011, 133, 19048-19051; (b) Z. Peng, S. A. Freunberger, Y. Chen and P. G. Bruce, Science, 2012, 337, 563-566; (c) F. Li, D. –M. Tang, Y. Chen, D. Golberg, H. Kitaura, T. Zhang, A. Yamada and H. Zhou, Nano Lett., 2013, 13, 4702-4707; (d) R. Black, J.-H. Lee, B. Adams, C. A. Mims and L. F. Nazar, Angew. Chem. Int. Ed., 2013, 52, 392–396; [3] B. D. McCloskey, R. Scheffler, A. Speidel, D. S. Bethune, R. M. Shelby and A. C. Luntz, J. Am. Chem. Soc., 2011, 133, 18038-18041. Figure 1

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