Abstract:                                                                                         Introduction          Lithium air secondary batteries exhibit higher theoretical energy density than lithium ion batteries and are expected to be used as the next generation of secondary batteries.   However, there remain technical challenges related to their poor cycle properties.          Since the first report by K. M. Abraham et al. [1], various oxygen reduction/evolution catalysts [1-4] and electrolyte [1, 5] materials have been intensively investigated for air batteries to improve their electrochemical properties, such as the their cyclability.  However, there have been a few studies on support materials for air electrodes, for example, nanoporous gold [6] .          We think that a decrease in the electrical contact of the air electrode during Li 2 O 2 deposition at discharge and oxygen generation at charge is one of the reasons for the poor cyclability.  The purpose of our research is to improve the cyclability by using a new air electrode structure.  We are focusing on a porous carbon monolith, which has a continuous interconnected network of carbon, as support material for air electrodes.  We have already fabricated porous-carbon-monolith supports to replace the current carbon-powder supports.  Here we report the preparation conditions for porous-carbon-monolith support materials and the performance of air batteries incorporating these supports.                                                                                          Experimantal          A porous polyacrylonitrile (PAN) monolith was prepared as the precursor of the porous-carbon-monolith support.  PAN was dispersed in dimethyl sulfoxide (DMSO).   After the solution with a concentration of 94 g/l was dissolved, water was sprayed on the solution.  The porous PAN monolith film was deposited from the solution due to water, which is poor solvent for PAN.  The monolith was washed with methanol and dried in vacuum at room temperature.  Then it was carbonized in Ar atmosphere at 1300 °C to obtain a porous carbon monolith.  In the next step, for activation treatment, the porous carbon monolith was heat treated in CO 2 atmosphere at 900 °C for 1 h [7].  The lithium air secondary battery consisted of the air electrode, a lithium metal sheet, and 1.0-mol/l lithium bis(trifluoromethanesulfonyl)amide (LiTFSA)/propylene carbonate (PC) as the positive electrode, negative electrode, and electrolyte solution, respectively.  The battery preparation is described in detail in our previous paper [4] .  Electrochemical measurements were carried out under a galvanostatic condition of 0.05 mA/cm 2 in an O 2 atmosphere.  The discharge and charge capacities were normalized by the weight of the air electrodes.                                                                                    Results and discussion          In the SEM image of the porous carbon monolith in Fig. 1, we see the continuous interconnected network of the carbon.  These particles build a 3-D disordered macroporous framework, with sizes in the range of 2-5 mm.  In XRD measurements of the porous carbon monolith, all of the peaks in the XRD patterns corresponded to the ICDD data for carbon (#01-077-7164).  These results indicate that our method can produce porous carbon monoliths.          Figure 2 shows the pore distributions of the porous carbon monolith measured using mercury intrusion porosimetry.  The porous carbon monolith has mesopores with size of ~10 nm, which correlated with first discharge capacities [8].          Figure 3 shows the first discharge/charge curves of the air batteries incorporating the as-synthesized and activation-treated porous carbon monolith.  The air batteries, showed higher discharge and charge capacities, with the activation-treated porous carbon monolith.   This is because activation-treated porous carbon monolith has many more active sites than the as-synthesized one.  In particular, the air batteries with the activation-treated porous carbon monolith show the capacity of 12 mAh/g and the average discharge voltage of 2.6 V.  This indicates that the porous carbon monolith can be used as support material for air electrodes.           However, compared with Ketjen Black EC600JD (KB) powder [9], the air batteries with the porous carbon monolith show lower discharge capacities.  It seems that KB-powder has many more active sites than the porous carbon monolith because its BET surface area of 1300 m 2 /g is larger than that of the porous carbon monolith, which is 4.3 m 2 /g.                                                                                            References [1] K. M. Abraham et al., J. Electrochem. Soc., 143 (1996) 1. [2] T. Ogasawara et al., J. Am. Chem. Soc., 128 (2006) 1390. [3] A. K. Thapa et al., Electrochem. Solid-State Lett., 13 (2010) A165. [4] H. Minowa et al., Electrochemistry, 78 (2010) 353. [5] N.-S. Choi et al., J. Power Sources, 225 (2013) 95. [6] Z. Peng et al., Science, 375 (2012) 563. [7] M. Nandi et al., Func. Mater. Lett., 4 (2011) 407. [8] M. Hayashi et al., Electrochemistry, 5 (2010) 325. [9] H. Lim et al., Chem. Commun., 48 (2012) 8374. Figure 1

Abstract: Introduction             Lithium air secondary batteries (LABs) have the highest theoretical energy density among secondary batteries reported so far. However, major problems are poor cycle characteristics and large discharge/charge overpotential. To improve these properties, various kinds of solid-phase catalysts loaded into air electrodes have been reported [1]. One of the significant problems is that the solid-phase catalysts become inactivated gradually because discharge product Li 2 O 2　 accumulats on the surface of the air electrode as a result of imperfect decomposition during the charging process after a large number of cycles [2]. Since a solution-phase catalyst dissolved in the electrolyte solution could work stably during the cycles, it would overcome these issues associated with the solid-phase catalyst. Recently, as solution-phase catalysts, transition metal complexes such as manganese phthalocyanine (MnPc) [3] , cobalt phthalocyanine (CoPc) [4] have been reported [3-5] . It is necessary to investigate the electrocatalytic activities for various kinds of solution-phase catalysts because the catalytic mechanism is unclear. We focused on manganese-containing salen-type complexes (MnSl) as a new solution-phase catalyst (Fig. 1). The electrochemical properties would be improved by involving oxygen adsorbed on the central Mn-ion site with the reaction over the air electrode [6].  Here, we report discharge/charge properties in LABs using MnSl as solution-phase catalyst.  Experimental             MnSl [(R,R)-(−)-N,N-Bis(3,5–di–tert-butylsalicylidene)-1,2-cyclohexanediaminomanganese(III)chloride] and MnPc [manganese(II) phthalocyanine] as a reference catalyst were purchased from Sigma-Aldrich Co. LLC. A 2.0 wt% of both catalysts vacuum-dried at 90 °C for 12 h was added to an electrolyte solution of 1.0 mol/l LiTFSA / TEGDME (tetraglyme). Ketjenblack EC-600JD (KB, 80 wt%) and polyvinylidene difluoride (PVdF, 20 wt%) coated on carbon paper (Toray, TGP-H-120) was used as the air electrode. A Li metal sheet was used as the negative electrode. The experimental LAB cell was assembled using a commercial cell (ECC-Air, EL-Cell GmbH). Electrochemical experiments were conducted under galvanostatic condition at 200 mA/g in dry air atmosphere. Current density and discharge/charge capacity were normalized by the mass of the reaction layer (KB + PVdF) in the air electrode.  Results and discussion             Figure 2 shows the first discharge/charge curves of LAB cells with MnSl, with MnPc catalyst, and whithout the solution-phase catalysts. The cells with MnSl catalyst and MnPc show higher average discharge voltages of 2.64 and 2.55 V and larger discharge capacities of 4903 and 3309 mAh/g, respectively, compared to the cell without the catalysts. In addition, the cell with MnSl catalyst shows lower average charge voltage of 3.93 V and larger charge capacity of 6390 mAh/g than the other cells. These results suggest that the solution-phase catalyst could have electrocatalytic activities. Moreover, the MnSl catalyst exhibits rather higher activity than the conventional catalyst, MnPc. However, with the MnSl catalyst, the first charge capacity was larger than the discharge capacity by about 2000 mAh/g. This behavior suggests that some side reactions might co-occur with the charge (oxygen evolution) reaction in the high-voltage region above 4.0 V.            Figure 3 shows SEM images of the air electrodes as prepared and after the first discharge without and with MnSl catalyst. Compared to the electrode surface as prepared shown in Fig. 3(a), the fine sub-micrometer discharge products with similar structures were deposited in a part of the electrode surface both without and with MnSl catalyst as shown in Fig. 3(b) and (c). In particular, there were spherical micrometer structures of the discharge products only with MnSl as shown in Fig. 3(c). MnSl catalyst three-dimensionally catalyzed deposition and decomposition of Li 2 O 2 　over the air electrode, which led to significant increase in the capacity.             According to the above results, the MnSl catalyst exhibited higher activities than MnPc. One of the reasons might be that the oxygen adsorption on the central metal Mn containing N-Mn-N bonds is stronger in MnSl than in MnPc. At the IMLB meeting, we will also discuss the cycle characteristics of LABs with the MnSl catalyst. References [1]A. Debart et al., J. Power Sources, 174 , 1177 (2007).  [2] Y. Shao et al., J. Adv. Funct. Mater. , 23,  987 (2013). [3]S. Heo, Master's thesis   “The study on the non aqueous electrolyte for lithium air battery.”   (2011). (URL: http://hdl.handle.net/10076/12935, accessed September 1, 2015). [4]S. Matsuda et al., Abstracts of the 55th Battery Symposium in Japan ， 1B25，p.130 (2014)． [5]D. Sun et al., J. Am. Chem. Soc, 136,  8941-8946 (2014). [6]N. S. Venkataramanan et al., Coord. Chem. Rev, 249 , 1249 (2005). Figure 1

Abstract: Introduction Lithium air secondary batteries (LABs) exhibit much higher theoretical energy density than lithium ion batteries and are anticipated as one of the most promising candidates for the next generation of batteries.  However, problems with LABs include their electrochemical properties, such as cyclability, overpotential, and round-trip efficiency need further improvement[1-2].  Various kinds of electrocatalysts have been studied to overcome these drawbacks [1-2] .  We have reported that a battery incorporationg Pt 33 Ru 67 electrocatalyst shows discharge capacities of more than 400 mAh/g for over 30 cycles in TEGDME-based electrolyte solution [2].  In this study, to further improve the cyclability, we prepared Pt 100- x Ru x /carbon electrocatalysts with wide composition range of 0 ≤ x ≤ 100 by the soft liquid process and examined the electrochemical properties of the cells loaded with the electrocatalysts into air electrodes. Experimental Pt 100- x Ru x /carbon was prepared by the formic acid reduction method [3].  KetjenBlack EC600JD (KB) was used as the carbon support material.  The KB powder was dispersed in formic acid solution by sonication, and H 2 PtCl 6 ¥6H 2 O and/or RuCl 3 solution was dropped into the solution, which was then stirred overnight.  The Ru content, x , in Pt 100- x Ru x was 0 (Pt alone) 30, 60, 75, 83, 90, or 100 (Ru alone).  Then, dried Pt 100- x Ru x /KB powder was obtained by heat-treating the mixture at 300°C for 12 h in Ar.  The air electrodes were prepared by coating the mixture of Pt-Ru/KB powder, and PVdF in N-methylpyrrolidone solvent, and drying it at 90°C.  The composition ratio of an air electrode with a diameter of 5 mm was KB/Pt 100- x Ru x /PVdF = 80: 10: 10.  The LAB cell (ECC-Air, EL-Cell) was assembled, incorporating the air electrode loaded with Pt 100- x Ru x /KB, an electrolyte solution (1 mol/l LiTFSA/TEGDME), a glass separator, and Li metal sheets.  Electrochemical measurements were carried out under a galvanostatic condition of 0.1 mA/cm 2 in a dry air atmosphere.  The discharge and charge capacities were normalized by the weight of Pt 100- x Ru x /KB powder and PVdF in the air electrodes. Results and discussion Figure 1 shows XRD patterns of samples with various composition ratios of Pt 100- x Ru x /KB.  The patterns of x = 0 and 30 corresponded to a single phase of Pt (PDF #00-004-0802), and the ones of x = 83, 90, 100 corresponded to a single phase of Ru (PDF#00-006-0663).  The sample with x = 60 and 75 was identified as a mixture of the Pt and Ru phase.  In addition, the XRD peaks became broad by increasing the content of Ru.  This suggests that the added Ru is effective in reducing the particle size of Pt 100- x Ru x alloy, and then it should enhance the electrocatalytic activities. Figure 2 shows the typical first discharge-charge curves of the cells incorporating the air electrodes loaded with Pt 100- x Ru x /KB catalysts.  First discharge capacities are 496, 671, 905, 1014, and 909 mAh/g in the cells with samples with x = 0, 30, 75, 90, and 100, respectively.  The discharge capacities clearly increased with increasing Ru content, indicating the maximum capacity in the x = 90 sample.  Moreover, the cell for the x = 90 shows the highest average voltage of 2.58 V, while the one for x = 0 shows rather low voltage of 2.43 V.  In the charging process, the average charge voltages decreased with increasing Ru content and, accordingly, the charge capacities increased as a result of the smaller charge overpotentals, indicating the maximum capacity of 867 mAh/g in the x = 90 sample. Figure 3 shows the cycle properties of cells incorporating the air electrodes loaded with Pt 100- x Ru x /KB catalysts.  The discharge capacities of all cells gradually decreased.  In particular, the cell for x = 0 shows very small capacity of less than 80 mAh/g at the 8th cycle. This result indicates the effectiveness of Ru addition for improving the cyclability.   Among the cells tested, the one with the x = 90 sample showed comparatively better cycle stability with discharge capacity of over 800 mAh/g at the 8th cycle.  These behaviors are very similar to the above discharge/charge properties.  As a result, the x = 90 sample was confirmed to be the optimized composition as the electrocatalyst for the air electrode. From the above results, it was found that the higher Ru content leads to a higher surface area and higher dispersion state of Pt 100- x Ru x electrocatalyst accompanied by inhibition of particle growth, which result in good electrochemical performance of cells incorporating Pt 10 Ru 90 /KB.   [1] A. Debart et al., Angew.Chem. , 120 , 4597 (2008). [2] M. Hayashi et al., The 56 th Battery Symposium in Japan , 3G02, (2015). [3] J. Prabhuram et al., J. Power Sources , 134 , 1 (2006). Figure 1

Abstract: Introduction Lithium air secondary batteries exhibit higher theoretical energy density than lithium ion batteries and are expected as next-generation secondary batteries. However, there remain technical challenges related to their poor cycle properties. Since the first report by K. M. Abraham et al. [1], various oxygen reduction/evolution catalyst [1-3] and electrolyte [1, 4] materials have been intensively investigated for air batteries to improve their electrochemical properties, such as their cyclability. However, there have only been a few studies on support materials for air electrodes, such as nanoporous gold [5] . We consider that one of the reasons for the poor cyclability is a decrease in the electrical contact of the air electrode during Li 2 O 2 deposition (discharge) and oxygen generation (charge), which results from large the volume change. The purpose of our work is to improve the cyclability by using a new air electrode structure and material. As an elastic support material for air electrodes, we focus on carbon fabricated from bacterial cellulose (BC), which has a continuous interconnected network of carbon. Such an elastic carbon support would prevent the large volume change of the air electrodes and improve the cycle performance. Here we report the preparation conditions for BC-derived carbon supports materials and the performance of lithium air secondary batteries incorporating them. Experimental A BC sheet (Fujicco Co., Ltd.) was frozen at -40 °C and then freeze-dried [6]. The freeze-dried BC sheet was carbonized in N 2 atmosphere at 600, 900, and 1200 °C to obtain BC-derived carbon. It was cut into a circle (diameter: 5 mm) to obtain the binder-free air electrode. The lithium air secondary battery consisted of the air electrode, a lithium metal sheet, and 1.0 mol/l lithium bis(trifluoromethanesulfonyl)amide (LiTFSA)/tetraethylen glycol dimethyl ether (TEGDME) as the positive electrode, negative electrode, and electrolyte solution, respectively. The battery was assembled with an ECC-Air Cell (EL-CELL GmbH). Electrochemical measurements were carried out under a galvanostatic condition of 0.1 mA/cm 2 in an O 2 atmosphere. The discharge and charge capacities were normalized by the weight of the BC-derived carbon (the air electrode). Results and discussion Figure 1 shows an SEM image of the BC-derived carbon prepared at 1200 °C. The continuous interconnected network of the carbon fibers with diameter of less than 10 nm can be seen in this image. These carbon fibers build a 3-D disordered macroporous framework. The BC-derived carbon prepared at 600 and 900 °C was confirmed to have morphologies similar to that at 1200 °C. Moreover, in a preliminary compression test, the BC-derived carbon showed a highly elastic compressibility and almost completely recovered its original volume after the compression was released. Figure 2 shows the first discharge/charge curves of the air batteries incorporating the BC-derived carbon prepared at 600, 900, and 1200 °C. The air batteries with the carbon prepared at 900 °C showed the largest discharge capacities of 8800 mAh/g and the average discharge voltage of 2.68 V. This is because it has the largest number of active sites among the carbons tested. The batteries incorporating BC-derived carbon prepared at 900 and 1200 °C showed almost the same charge capacities of about 8000 mAh/g. These charge properties have a tendency similar to the discharge properties even though the air electrodes have no catalysts. These results indicate that the BC-derived carbon can be used as support material for binder-free air electrodes. Figure 3 shows the correlation between the discharge capacities, D/G ratio, and carbonization temperature. In the Raman spectra of the carbon as shown in the inset, the peaks of D- and G-bands are derived from the edge-plane and basal-plane in the crystal structure of carbon, respectively. The D/G ratio was obtained from the results of wave analyses with the spectra in the inset. It correlates roughly with the discharge capacities as shown in Fig. 3. In particular, the battery incorporating the carbon prepared at 900 °C, which has the largest discharge capacity, has the highest D/G ratio. This indicates the importance of the number of carbon edge planes in relation to the discharge property, because the D/G ratio corresponds to a ratio of number of carbon edge planes to that of basal planes. These results indicate that the carbon edge planes would play an important role as active sites in the reaction mechanism with the air electrode. References [1] K. M. Abraham et al., J. Electrochem. Soc., 143 (1996) 1. [2] T. Ogasawara et al., J. Am. Chem. Soc., 128 (2006) 1390. [3] A. K. Thapa et al., Electrochem. Solid-State Lett., 13 (2010) A165. [4] N.-S. Choi et al., J. Power Sources, 225 (2013) 95. [5] Z. Peng et al., Science, 375 (2012) 563. [6] H. W. Liang et al., NPG Asia Materials, 4 (2012) e19. Figure 1

Abstract: Introduction Lithium air secondary batteries (LABs) have attracted attention due to their high theoretical energy density. One of the major problems is their poor cycle characteristics, which is caused by the decomposition of electrolytes, the strength degradation of air electrodes, and so on. These are related to the large resistivity of discharge products Li 2 O 2 deposited in the air electrodes. To solve these problems, the air electrodes of LABs have been developed by using various catalysts [1]. However, the catalysts become inactivated gradually after a large number of cycles because undecomposed Li 2 O 2 remains on the active catalytic sites in the air electrodes even after charging processes [2]. Since additives are dissolved in an electrolyte solution, they were predicted to promote the deposition and the decomposition of Li 2 O 2 without deactivation due to the undecomposed Li 2 O 2 . The additives are expected to overcome the problems associated with the catalyst for the air electrode. We are focusing on (R,R)-(-)-N,N-Bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminomanganese(III) chloride (MnSl) as an electrolyte additive. In our previous work, the LAB cells with 1 mol/l LiTFSA/TEGDME containing 2 wt% MnSl exhibited large first discharge capacity of 4903 mAh/g and good cycle retention of 61% at the 10th cycle [3]. However, the details of the reaction mechanisms were still unclear. In this study, we investigated the fundamental mechanisms by evaluating the electrochemical activities for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in an electrolyte containing 0.005 wt% MnSl additives. Experimental A 0.005 wt% of MnSl (Sigma-Aldrich) vacuum-dried at 90°C for 12 h was added to 1.0 mol/l LiTFSA/TEGDME. Ketjenblack EC-600JD (KB, 80 wt%) and polyvinylidene difluoride (PVdF, 20 wt%) coated on carbon paper (Toray, TGP-H-120) were used as an air electrode. A Li metal sheet was used as a counter electrode. These components were installed in a commercial two-electrode LAB cell (ECC-Air, EL-Cell GmbH). Electrochemical experiments were performed at a current density of 200 mA/g under dry air atmosphere with a dew point of less than -50°C. Cyclic voltammetry was performed at a scan rate of 100 mV/s under O 2 atmosphere using the three-electrode ECC-Air cell. Platinum disks were used as working and counter electrodes. A Li metal was used as a reference electrode. Results and discussion Figure 1 shows the first discharge /charge curves of LAB cells without and with MnSl. In the discharging process, the cell with MnSl shows a higher average voltage of 2.4 V and a larger capacity of 893 mAh/g than the other cell. In the charging process, the cell with MnSl shows a lower voltage during the early process and a larger capacity of 676 mAh/g than the other cell. These results indicate that MnSl promotes electrochemical activities for both ORR and OER. Electrochemical measurements were carried out to investigate how the MnSl additives work in the electrolyte solution during ORR/OER processes. Figure 2 shows cyclic voltammograms (CVs) of the three–electrode cells without and with MnSl under O 2 atmosphere. The cells without and with MnSl show a cathodic ORR peak at around 2.0 V and an anodic OER peak at around 4.4 V. The cell with MnSl shows higher current densities in the whole potential range than the cell without MnSl. In the cell with MnSl, the cathodic peak around 2.0 V for the ORR becomes larger, and the onset of that peak shifts significantly toward more positive potential. This might indicate that MnSl promoted the electrochemical activity for ORR. As a result, the average discharge voltage of the cell with MnSl becomes higher compared with the cell without MnSl, as shown in Fig. 1. In the cell with MnSl, the anodic peak for the OER also becomes larger compared with the cell without MnSl and exhibits a new peak at around 4.0 V. This peak was not observed in the CV result for the cell without MnSl. This might indicate that the MnSl interacted with Li 2 O 2 at around 4.0 V and such an interaction promoted the activities for OER at around 4.4 V The plateau voltage around 4.0 V shown in Fig. 1 might reflect the electrochemical behavior for the anodic process in the CV result of Fig. 2. Consequently, these results show a tendency similar to the charge and discharge properties shown in Fig. 1 indicating the effectiveness of MnSl as an electrolyte additive. References [1] A. K. Thapa et al., Electrochem. Solid. St. 13 , A165, (2010). [2] B. D. McClosky et al., J. Am. Chem. Soc. , 133, 18038 (2011). [3] S. Sakamoto et al., IMLB 2016 , 765, (2016). Figure 1