Charge Plateau Research Articles

Investigation of Reaction Mechanism in All-Solid-State Li-Air and Li-O2 Batteries

Introduction The lithium-air batteries have attracted much more attentions because of its high theoretical energy density, which is over 3500 Wh kg-1. However the lithium-air batteries still have a lot of problems and the problem related with the decomposition of organic liquid electrolytes is the most serious and one of the main research topics in the present stage. Thus, we have developed all-solid-state lithium-air batteries using the inorganic solid electrolytes, which are more stable than the liquid electrolytes. The application of the solid electrolytes to the lithium-air batteries can solve not only the decomposition of electrolytes but also the safety problem and some other problems specific to the liquid such as leakage and volatilization. In this study, all-solid-state cells consisting of Li anode, Li1+xAlyGe2-y(PO4)3 (LAGP) solid electrolyte, and LAGP-carbon nanotube (CNT) composite cathode was operated in the air atmosphere (so-called Li-air cell) and pure oxygen atmosphere (so-called Li-O2 cell). Reaction mechanism during discharge-and charge was investigated. Experiments The Li / LAGP / LAGP-CNT cells were assembled by the following procedure. LAGP powders and pellets were prepared by the conventional solid-state method. CNT and LAGP powders were dispersed into the ethanol solution. A drop of the solution was put on the LAGP pellet and dried at room temperature. The air electrode deposited on the LAGP pellet was heated at 700 oC. After sintering, the air electrode combined with the solid electrolyte layer was obtained. On the other side of the LAGP pellet, a Li anode was contacted with the LAGP pellet by a thermal adhesion process and sealed with a plastic film. An Al mesh and a Cu mesh were used as a current collector for the cathode and the anode, respectively. The laminate-type cell was sandwiched by two plastic plates and held by a screw clamp. The Li-air cell was operated in the laboratory air atmosphere. The Li-O2 cell was put into the bottle connecting to the oxygen gas flow channel, and discharged and charged under a pure oxygen gas-flowing condition. Results and discussion The all-solid-state cells were discharged and charged by the constant current mode in the voltage range of 2.0 - 4.8 V. The Li-O2 cell showed a discharge plateau at 2.0 - 2.5 V and, the charge plateau gradually increased from 3.0 to 4.2 V. On the other hand, the Li-air cell showed a discharge plateau, which starts 3.0 V at a low current density, and the charge curve obviously showed two plateaus. In such cells, the air electrode after discharging and charging was analyzed by using XRD, XPS, Raman, IR, and TEM. From these measurements, it was suggested that Li2O2 was electrochemically produced after discharging in both air and oxygen atmosphere. Also Li2CO3 was produced by side-reactions. The reaction products in air atmosphere were the same as that in oxygen atmosphere. However, the elementary process seems to be different between air and oxygen. It was also found that the CNT was degraded during cycling, which would cause the capacity degradation.

Carbon electrode with NiO and RuO2 nanoparticles improves the cycling life of non-aqueous lithium-oxygen batteries

Abstract Carbon has been regarded as one of the most attractive cathode materials for non-aqueous lithium-oxygen batteries due to its excellent conductivity, high specific area, large porosity, and low cost. However, a key disadvantage of carbon electrodes lies in the fact that carbon may react with Li2O2 and electrolyte to form irreversible side products (e.g. Li2CO3) at the active surfaces, leading to a high charge voltage and a short cycling life. In this work, we address this issue by decorating NiO and RuO2 nanoparticles onto carbon surfaces. It is demonstrated that the NiO-RuO2 nanoparticle-decorated carbon electrode not only catalyzes both the oxygen reduction and evolution reactions, but also promotes the decomposition of side products. As a result, the battery fitted with the novel carbon cathode delivers a capacity of 3653 mAh g−1 at a current density of 400 mA g−1, with a charge plateau of 4.01 V. This performance is 440 mV lower than that of the battery fitted with a pristine carbon cathode. The present cathode is also able to operate for 50 cycles without capacity decay at a fixed capacity of 1000 mAh g−1, which is more than twice the cycle number of that of the pristine carbon cathode.

Enabling high energy density Li-ion batteries through Li2O activation

Lithium oxide (Li2O) is activated in the presence of a layered composite cathode material (HEM) significantly increasing the energy density of lithium-ion batteries. The degree of activation depends on the current rate, electrolyte salt, and anode type. In full-cell tests, the Li2O was used as a lithium source to counter the first-cycle irreversibility of high-capacity composite alloy anodes. When Li2O is mixed with HEM to serve as a cathode, the electrochemical performance was improved in a full cell having an SiO-SnCoC composite as an anode. The mechanism behind the Li2O activation could also explain the first charge plateau and the abnormal high capacity associated with these high energy cathode materials.

Electrochemistry Characteristics of NaNi0.5Mn1.5O4 As the Cathode Material for Sodium Ion Batteries

Introduction Lithium ion batteries have been widely used in portable electronic devices and deploying in electric vehicles and power grid energy storing. After the topic of the limited lithium source was mentioned, sodium ion batteries resurged in recent years. Many kinds of cathode materials for sodium ion batteries have been studied, but more research is needed to realize the commercial use of sodium ion batteries, especially competing with current lithium ion batteries. Because of large ion size, Na+ cannot stay in tetragon position in close-packed oxygen structure, so spinel structure of sodium oxide isn’t thermal stable phase, which can only synthesized at high pressure[1]. Naoaki Yabuuchi et al. [2] reported that product of electrochemical exchanged LiMn2O4 isn’t NaxMn2O4, but NaMnO2. The NaMnO2 prepared by electrochemical exchange show a very high capacity of 190 mAh/g and better capacity retention in the 2.3-4.3V range than the directly prepared NaMnO2. Here we report the structure change and electrochemical performance of NaNi0.5Mn1.5O4 prepared by electrochemical exchange method. Experimental Spinel LiNi0.5Mn1.5O4 was prepared by solid state method. Stoichiometry Li2CO3, Ni(OH)2 and Mn2O3 were ball-milled and then sintered at 800℃ for 24h in air. The obtained LiNi0.5Mn1.5O4 was chartered by XRD, SEM and charge-discharge testing. For preparation of NaNi0.5Mn1.5O4 via electrochemical exchange, LiNi0.5Mn1.5O4 was first charged to 4.9V in a cell with Li electrolyte and Li anode to de-insert all of the lithium ions. Then the cell was disassembled and the cathode electrode was took out and washed by DMC for three time followed by assembling it with Na electrolyte (NaClO4 in PC+FEC) and Na anode. Charge and discharge the sodium ion cell at 10 mA/g current between 2 and 4.5V. Results and discussion LiNi0.5Mn1.5O4 shows a long charge plateau at 4.7V in lithium cell, which represents de-intercalation of Li+ and oxidation of Ni2+. At the end of charge process, Ni0.5Mn1.5O4 with very few lithium ions was gotten whose character of Na+ intercalation and de-intercalation was investigated in following cycles in sodium cell. It could be found that a discharge plateau at about 3.6V corresponding about a capacity of 80 mAh/g (Fig.1a). The electrochemical behavior is similar as the NaMn2O4 whose initial discharge plateau locates at about 3.2V with a capacity of 80 mAh/g in sodium cell [2]. However, in NaNi0.5Mn1.5O4 system, the capacity between 2 and 3V is little, so the total capacity is only about 110mAh/g for the first discharge process and decrease quickly during the following cycles. The structure of cycled NaNi0.5Mn1.5O4 was investigated by XRD, shown in Fig.1b. The spinel structure is kept when lithium ion is replaced by sodium ion, though some should peaks appears, which caused by strain because of a size gap between Li+ and Na+. After cycling, though no peaks corresponding to layered NaMnO2 can be found, the capacity decreases obviously, so new capacity decrease mechanism should be considered. Reference [1] Xizheng Liu, Xi Wang, Akira Iyo, et al., J. Mater. Chem. A, 2014, 2, 14822-14826 [2] Naoaki Yabuuchi, Masaya Yano, Satoru Kuze, et al., Electrochim. Acta, 2012,82, 296–301 Figure 1

Characterization of Lithium Superoxide from Lithium-Oxygen Battery Discharge Products

Lithium superoxide (LiO2) has long been known to be fairly unstable in the literature. It has only been isolated below 10 K with matrix isolation technique and characterized with use of electron paramagnetic resonance (EPR) spectroscopy as isolated molecules. Recently theoretical calculations suggested that LiO2 may be stabilized over the surface layer of lithium peroxide (Li2O2). Since Li2O2 is a commonly recognized discharge product from a Li-O2 battery through a two-electron oxygen reduction reaction (ORR), we are motivated to study the Li-O2 battery discharge process in details. Initial characterization of commercial Li2O2 powders with EPR technique indicates that a weak signal appears at temperature below 100 K. At 4 K the signal becomes fairly strong and notable. Since Li2O2 contains no unpaired electron and will not give any EPR signal, we attribute the low temperature EPR signal to a LiO2-like species. (ChemSusChem 2013 6 1196) Following the finding, when activated carbon is used as the cathode for a Li-O2 battery with tetra(ethylene) glycol dimethyl ether–lithium triflate (TEGDME/LiCF3SO3) as the electrolyte, a two-plateaus voltage profile during charging cycle at ~3.3 V and 4.2 V vs Li/Li+ is observed. To identify the uncommon low charge plateau, Raman spectroscopy of the discharge product reveals that a not yet reported peak at 1125 cm-1. Comparing to well characterized Li-discharge product Li2O2 (790 cm-1) and neutral oxygen (O2, 1538 cm-1), the newly identified Raman peak fits nearly in the middle. (Phys. Chem. Chem. Phys., 2013, 15, 3764) In addition, when other reported superoxides such as NaO2, KO2, NBu4O2 (in CH3CN), and K(18-crown-6)O2 (in DMSO) are plotted together with the LiO2-like species, the O-O Raman peaks (O2 2-, O2 -, and O2) form a nearly straight line (Figure 1). The O-O vibration peak of the LiO2-like species is in good agreement with other reported superoxides. To better understand the nature of the two-plateaus charging voltage profile at 3.3 and 4.2 V (vs Li/Li+), we analyze the charging voltage curve with the following assumption. Assuming we can carry out an one-electron ORR reaction, we will then generate exclusively LiO2 as the only Li-O2 battery discharge product. We carry out four parallel Li-O2 cells that are discharged at a constant current to four different capacities which are equivalent to four different time. Based on the quantitative amount of the low voltage plateau that is equivalent to the amount of remaining LiO2 from Li-discharge, a linear correlation between the natural log value of the disproportionated LiO2 vs discharge capacity (time) is observed. We reach the conclusion that LiO2 undergoes disproportionation with first order kinetics to generate Li2O2 and O2 (2LiO2 → Li2O2 + O2). (J. Am. Chem. Soc. 2013, 135, 15364) With micro-Raman technique, we further demonstrate that LiO2 is indeed coated over an inner core of Li2O2. In addition to the Raman O-O peak of LiO2 at 1125 cm-1, we also identify another Raman peak at 1505 cm-1 due to the interaction of LiO2 with carbon substrate. Therefore, the characteristic 1125 and 1505 cm-1 pair serves as the signature of the presence of LiO2 over carbon cathode. (J. Phys. Chem. Lett. 2014, 5, 2705) Another strong evidence for the presence of LiO2 in the Li-O2 battery discharge product under ambient temperature is that selected area electron diffraction pattern of it is in good consistency with the calculated LiO2 crystal structure based on density function theory. (Nano Lett. 2015, 15, 1041) Very recently, with use of Ir catalyst over reduced graphene oxide as cathode, our new Li-O2 cell demonstrates low charge voltage plateau, characteristic LiO2 Raman signature, one electron ORR reaction based on differential electrochemical mass spectroscopy (DEMS), and a new EPR signal at low temperature. (Nature 2016 asap on-line letter) This presentation will focus on the characterization of LiO2 from the Li-O2battery discharge product(s). This work was supported by the US Department of Energy under contract DE-AC02-06CH11357 from the Vehicle Technologies Office, Department of Energy, Office of Energy Efficiency and Renewable Energy. Figure 1

Structural Understanding of Superior Battery Properties of Partially Ni-Doped Li2MnO3 as Cathode Material.

We examined the crystal structures of Li2(NixMn1-x)O3(-δ) (x = 0, 1/10, 1/6, and 1/4) to elucidate the relationship between the structure and electrochemical performance of the compounds using neutron and synchrotron X-ray powder diffraction analyses in combination. Our examination revealed that these crystals contain a large number of stacking faults and exhibit significant cation mixing in the transition-metal layers; the cation mixing becomes significant with an increase in the Ni concentration. Charge-discharge measurements showed that the replacement of Mn with Ni lowers the potential of the charge plateau and leads to higher charge-discharge capacities. From a topological point of view with regard to the atomic arrangement in the crystals, it is concluded that substituting Mn in Li2MnO3 with Ni promotes the formation of smooth Li percolation paths, thus increasing the number of active Li ions and improving the charge-discharge capacity.

Investigation of Anatase-TiO2 As an Efficient Electrode Material for Magnesium-Ion Batteries

The advent of lithium-ion electrochemical has ushered in a new era of high energy density rechargeable batteries, with applications ranging from portable electronics to electric vehicles.1 However, several challenges have stymied the implementation of lithium-ion batteries that approach the thermodynamic capacity and energy density limit. This is largely associated with the use of a lithium-metal anode, which under extensive cycling conditions and current densities promotes the formation of dendritic lithium deposits. Lithium dendrites result in the formation of electrochemically “dead” lithium, resulting in poor cycling efficiency.2 In addition, dendritic lithium has been implicated in the cell shorting and thermal runaway. To mitigate such problems, alternative energy storage systems have been heavily pursued recently, with efforts largely focused on the development of sodium-ion and magnesium-ion electrochemical cells.3 The implementation of a magnesium metal anode is highly advantageous to lithium, as the volumetric capacity is nearly double (3833 mAh/mL vs. 2062 mAh/mL, respectively) and the deposition morphology is described as non-dendritic.2 As such, considerable attention has been focused the development of magnesium electrochemical cells utilizing a magnesium metal anode, high capacity cathode, and suitable electrolyte. One of the leading cathode materials is the Chevrel-phase Mo6S8, introduced in 2000 with an experimentally determined specific capacity of 105 mAh/g.4 Recently, Sheha described an anatase TiO2/ reduced graphene oxide (rGO) composite cathode material was used in a magnesium-ion electrochemical cell utilizing a Mg metal anode and polyvinyl alcohol/ MgBr2/ tetraglyme/ H2O electrolyte. This cathode was shown to maintain cyclability to fifty cycles. Following this report and the plethora of publications concerning the insertion electrochemistry of anatase-phase titanium dioxide, we decided to investigate the feasibility of TiO2/ carbon black/ poly tetrafluoroethylene (PTFE) as an electrode for magnesium-ion batteries. Herein, we report a study concerning the electrochemistry of Mg/TiO2 cells as well as a full characterization using spectroscopic and microscopic techniques. Figure 1 shows the voltage profiles of the TiO2/Mg coin cell with the All Phenyl Complex (APC) electrolyte between 0.05 and 2.2 V at a current density of 5 μA/ mg. During the first discharge, TiO2exhibits a well-defined plateau at approximately 0.5 V. The first discharge capacity is ~80 mAh/g. The material experiences a large polarization where the charge plateau increases to 1.2 V. The corresponding irreversible capacity in the first cycle is 20 mAh/g, which may arise from the poor conductivity of the electrode as well as the electrolyte side reactions. The close capacity between the discharge and charge process from the second cycle manifests excellent reversibility of the electrode. Figure 1 shows discharge and charge capacities with respect to cycle number at the same current density over 50 cycles. The capacity of the electrode remains at a quite considerable value after 50 cycles, which demonstrates relatively promising cycling stability. Following electrochemical galvanostatic/ potentiostatic charge/ discharge experiments, TiO2 electrodes were carefully removed from electrochemical cells and examined for magnesium insertion mechanism. Following a careful transfer step to mitigate any exposure to oxygen, the TiO2 electrodes were examined using scanning electron microscopy (Phillips XL30) with an equipped energy dispersive X-ray detector (EDX), synchrotron X-ray diffraction, and ultraviolet-visible spectroscopy. Both the spectroscopic and microscopic characterization confirm that a Mg:Ti ratio of ~0.1:1 is able to reversibly shuttle between the working and counter electrodes in this battery system. Acknowledgement The authors acknowledge the support by the seed funding from Sustainable Power and Energy Center under the Frontier of Innovation Award by Vice Chancellor of Research at UC San Diego. References (1) Whittingham, M. S. Chem. Rev. 2004, 104, 4271 – 4301. (2) Muldoon, J.; Bucur, C. B.; Gregory, T. Chem. Rev. 2014, 114, 11683 – 11720. (3) Dahbi, M.; Yabuuchi, N.; Kubota, K.; Tokiwa, K.; Komaba, S. Phys. Chem. Chem. Phys. 2014, 16, 15007 – 15028. (4) Aurbach, D.; Weissman, I.; Goffer, Y.; Levi, E. Chem. Record 2003, 3, 61 – 73. Figure 1

Job-sharing cathode design for Li–O2batteries with high energy efficiency enabled by in situ ionic liquid bonding to cover carbon surface defects

In the job-sharing design of carbon-based cathode for Li–O2batteries, the IL layer is aimed to cover carbon surface defects and suppress side reactions, whereas Ru nanodots are responsible for modifying product microstructure and crystallinity. It enables a high energy efficiency characterized by a substantial charge plateau with extremely small overpotential.

A comparative study of Li8NaV3(P2O7)3(PO4)2 and Li9V3(P2O7)3(PO4)2: Synthesis, structure and electrochemical properties

The energy-density improvement for cathode materials by using the method of occupying the Li site with the lowest formation enthalpy was first presented, and successfully applied to Li9V3(P2O7)3(PO4)2. Herein, the synthesis, structure and electrochemical properties (including both Li extraction and intercalation) of mixed alkali-ion phosphate Li8NaV3(P2O7)3(PO4)2 were comprehensively studied, and compared with its isologue Li9V3(P2O7)3(PO4)2. Both Li8NaV3(P2O7)3(PO4)2 and Li9V3(P2O7)3(PO4)2 were synthesized via an original two-step method for the first time. The sintering temperature of Li8NaV3(P2O7)3(PO4)2 (650 °C) was much lower than that of Li9V3(P2O7)3(PO4)2 (750 °C). The Rietveld structure refinement indicated that Na ions occupied the Li1(2b) site of Li9V3(P2O7)3(PO4)2 as expected, and Li8NaV3(P2O7)3(PO4)2 showed a single charge plateau at 4.4 V vs. Li in the 1st cycle. However, the Na ions migrated from Li1(2b) site after the initial cycle, and the charge plateau at 3.7 V vs. Li reappeared. On the other hand, both Li9V3(P2O7)3(PO4)2 and Li8NaV3(P2O7)3(PO4)2 can deliver a high reversible capacity (∼200 mAh g−1), and reveal excellent cycle and rate performance in 3.0–0.05 V vs. Li. The gentle structure changes along with abundant Li intercalation into the bulks suggested that Li9V3(P2O7)3(PO4)2 and Li8NaV3(P2O7)3(PO4)2 were also promising anode materials for Li-ion batteries.

The Efficiency and Mechanism of 3D-Ordered Macroporous La0.6Sr0.4Co0.2Fe0.8O3 as an Electrocatalyst for Aprotic Li-O2 Batteries

Lithium-oxygen (Li-O2) batteries with high energy density have thought to be the most attractive alternatives to nowadays Li-ion batteries. However, some challenges are still to be resolved, among which is the high charge overpotential that could compromise the cycle stability and capacity performance. [1, 2] The high overpotential is ascribed to the insolated discharge products Li2O2, which could not decompose completely during the charge processes. With the increasing cycles of battery tests, the Li2O2 will crystallize and block the porous cathode materials. [3, 4] However, recent studies have demonstrated that the structure and morphology could influence the conductivity and thus affect the overpotential. It is crucial to find an electrocatalyst that could accelerate the decomposition of Li2O2 and influence the crystallization of Li2O2 to get small size or amorphous Li2O2 products. [5, 6] Perovskite oxides La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) have been proved efficient to lower overpotential in aqueous Li-air batteries [7] but not have been applied in Li-O2 batteries. Herein the 3D-ordered macroporous LSCF (3D-LSCF) with very high BET surface area have been prepared and employed as electrocatalyst in Li-O2 batteries with DMSO based electrolyte. The Li-O2 batteries with this catalyst show lower overpotential, better cycle stability and capacity performance. As shown in Figure 1, the charge plateau of Li-O2 batteries with 3D-LSCF catalyst are flat and the charge potential is below 3.8V after nine cycles. The primary reason of the lower overpotential may be ascribe to the high oxygen pathways in 3D-LSCF structure which could accelerate the decomposition of Li2O2 products. [8] In order to conform the better ability of oxygen transmit of 3D-LSCF, the batteries have been tested in different levels of oxygen environments. With the increase of oxygen content, the performance of batteries without catalyst has increased more obviously than with 3D-LSCF catalyst, which indicates that the 3D-LSCF catalyst could transmit relatively sufficient oxygen. The morphologies of pure KB electrode and KB/3D-LSCF electrode at different states have been observed and the 3D-ordered macroporous structure of LSCF is beneficial to form small size of Li2O2 with large contact area to the KB that could assist in the decomposition at lower charge potential. The details of results and specific analysis will be exhibited in the presentation. Fig. 1 The cycle performance of Li-O2 batteries with 3D-LSCF catalyst at the current densities of 100mAg-1. Acknowledgements: This program was supported by Innovative Research Team in University (PCSIRT No. IRT1014).

A Bifunctional Air Electrode Catalyzed By Nano-Crystal Lead Ruthenate for Li-Air Batteries

It has been recognized that the catalyst may have triple functions toward increasing the charge/discharge capacity, decreasing over-voltage and improving cyclability [1]. Many catalysts, such as various carbons, metal oxides, metal nitrides, metal carbides, and precious metals, have been extensively studied and applied to the air electrode and catalysis has become one of the hottest topics for Li-air batteries. The commonly used carbon materials are, basically, good for catalyzing the oxygen reduction reactions (ORRs), however, they are insufficient for the oxygen evolution reactions (OERs). To promote both ORRs and OERs numerous efforts have been made. In particular, transition metal oxides with a perovskite, spinel or pyrochlore structure have been investigated due to their low cost, good catalytic activity and natural abundance. In this study, we report a nano-crystal lead ruthenate as a bifunctional electrocatalyst for non-aqueous Li-O2 batteries. The performance of the pyrochlore was studied in terms of morphology, polarization and cyclability. The nano-crystal lead ruthenate was synthesized using ruthenium(III) nitrosyl nitrate and lead sub-acetate, which is similar to the method described by Nazar et al. [2]. The precursor solution was prepared by dissolving ruthenium(III) nitrosyl nitrate and lead sub-acetate in deionized water and then 2 M aqueous NaOH solution was added. The resultant solution was stirred for 3 h at 25 °C followed by the addition of sodium hypochlorite solution, and the mixture was stirred for an additional 24 h. The product was then filtered and dried in a vacuum oven at 100 °C to form nano-crystal lead ruthenate. The synthesized catalyst was characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area analysis and Scanning Electron Microscopy (SEM). Air electrodes were fabricated by applying a catalyst ink on Ni foam or carbon paper. The catalyst ink contains catalyst/Ketjen black (KB), polytetrafluoroethylene (PTFE), and solvent. The composition of the KB supported catalyst is 30% catalyst and 70% KB. For comparison, electrodes with KB only were also made. Cell tests were carried out using ECC-AIR cells (EL-Cell, Germany) with an active diameter of 18mm and conducted on a Solartron Analytical 1470E system. All cell performance was measured in tetraethyleneglycol dimethyl ether (TEGDME) containing 1M lithium triflate under pure O2. All the capacities are calculated based on the weight of catalyst plus carbon support. The XRD pattern of the synthesized material indicates that the characteristic diffraction peaks correspond to the literature data [2], which can be readily indexed to the pyrochlore Fd-3m space group with a cubic lattice. SEM images show that the synthesized material is composed of aggregated nanocrystallites. The performance of the lead ruthenate/KB air electrode on carbon paper was carried out at different current densities. To demonstrate its catalytic activity, the performance of KB on carbon paper was also conducted. At a current density of 0.2 mA cm-2, although the lead ruthenate/KB electrode does not exhibit higher discharge/charge capacities, it has a lower charge plateau and higher columbic efficiency. As the charge/discharge rate increases to 0.5 mA cm-2, catalytic effect of the lead ruthenate is apparent as opposed to the KB baseline. Compared to the KB baseline, the lead ruthenate/KB electrode also exhibits impressive cyclabilities with negligible capacity loss after 5 cycles of complete charge/discharge. Results of the prepared nano-crystal lead ruthenate air electrode on Ni foam also shows greatly improved recharge behavior and cyclability. In summary, preliminary results have demonstrated that the nano-crystal lead ruthenate has the potential to be used as an efficient bifunctional electrocatalyst for non-aqueous Li-O2 batteries. Further investigations are ongoing to optimize this catalyst. The comprehensive study will be presented at the conference. Acknowledgements This work is financially supported by the Natural Resources Canada’s ecoENERGY Innovation Initiative (project ETRI-006).

A Rechargeable Lithium-Oxygen Battery with Li2O2 Cathode in Closed Systems

Introduction Li-O2 batteries have one of the highest theoretical specific energy of 3,458 Wh/kg when the weight of the primary discharge product, i.e., Li2O2, is considered. Thus, this BIL (Beyond Lithium Ion) battery technology, if made practical, will find extensive usage especially in the successful electrification of vehicles. However, there are many challenges.1 Current Li-O2 batteries demonstrated in labs have been limited to “open systems”, i.e., batteries that have a porous carbon cathode that “breathes” pure oxygen. One limitation of these systems is the requirement of pure oxygen. In addition, the consensus among researchers on specific capacity (mAh/g) calculations based on active materials is lacking because extra oxygen is continuously supplied to cells upon cycling. One solution to these limitations is the use of closed systems, i.e., storage and reuse of O2 within the cell. The most reversible discharge product in Li-O2 batteries has been identified to be Li2O2.2 Herein, we report some preliminary results on a closed, but rechargeable system starting with a Li2O2 cathode that has shown high specific discharge capacity close to theoretical figures of Li2O2. A novel Li2O2-carbon composite cathode has been developed that can not only support the cathodic reaction of Li2O2 but also store O2 in the charge. Experimental The Li2O2 cathode was made of a composite of Li2O2 and carbon, as shown in Fig. 1. 1 M LiCF3SO3 in 1,2-dimethoxyethane was used as electrolyte. Coin cells without open windows were used in the battery testing. Cells were assembled in an Argon-filled glove box and tested outside of the glove box. The specific capacities and C rates were calculated based on the mass of Li2O2 in the cathode. Results and Discussion As shown in Fig. 1, the carbon acts as a current collector that can form an electron conduction pathway into Li2O2 powder during the charging process. It also acts as O2 absorption medium to hold the O2 gas evolved during charging until the discharge process begins. In addition, the nanoscaled composite can permit fast transfer of Li+ ions. The voltage profiles corresponding to different C-rates for the first cycle in the closed system cell is shown in Fig. 2. The cell was initially charged and shows principle charge plateau at 3.8-4.0 V. The cell is then discharged and shows a consistent discharge at ~2.75 V for both C/10 and C/5. The discharge occurs at 2.4-2.5V for C/2. These voltages are in good agreement to voltages at similar current densities in open system cells reported by other groups.3 The specific charge capacity at all three rates approach the theoretical capacity of 1,168 mAh/g for lithium peroxide, meaning almost all Li2O2 can be converted to gaseous O2 in the first charge. The specific discharge capacities are ~1,000 mAh/g at low rates thus giving a round trip Coulombic efficiency of 85%. At C/2 rate, the discharge capacity is slightly lower than those at higher rates. These results demonstrate the composite electrode can facilitate almost complete conversion of Li2O2 in the charge and hold gaseous O2, most of which can be reduced in the following discharge. The cycling capability is shown in Fig. 2. It can be seen that the first cycle shows 85% efficiency. The subsequent cycles have a lower charge voltage which could be due to smaller Li2O2 particles after first discharge. Later cycles show capacity fade. This can be attributed to the decomposition of electroyte and loss of O2 produced in the charge.4 When capacity limited charging (50% depth of charge) to a lower cutoff voltage is applied, exceptional rechargability can be obtained which is shown in Fig. 3. It is believed the improvement is due to delayed electrolyte decomposition. In summary, a closed and rechargeable lithium battery with Li2O2 cathode has been demonstrated for the first time. This platform is unique as it shows, for the first time in literature, capacites and rate capability based on mass of Li2O2. It allows other studies on the stability of electrolyte, electrode kinetics, and oxygen storage materials. This system can eleminate the issues of open systems such as impurities oxygen gas and evaporation of electrolyte. Unstable electrolytes are a major bottleneck in Li-O2 batteries. Such a system provides a suitable medium to optimize electrolytes and other cell components. References G. Girishkumar, B. McCloskey et al., J. Phys. Chem. Lett. 1, 2193 (2010).T. Ogasawara, A. Débart et al., J. Am. Chem. Soc. 128, 1390 (2006).H.-G. Jung, J. Hassoun et al., Nat. Chem. 4, 579 (2012).R.S. Assary, J. Lu et al., ChemSusChem. 6, 51 (2013). Figure 1

Uniform and continuous carbon coated sodium vanadium phosphate cathode materials for sodium-ion battery

Sodium vanadium phosphate Na3V2(PO4)3 coated with uniform and continuous carbon film is synthesized by heat treatment of the precursors under C2H2-pyrolysis reducing atmosphere, in which Na3V2(PO4)3 is formed synchronously with carbon coating. As a cathode material for Na-ion batteries, Na3V2(PO4)3/C shows a flat charge plateau at about 3.39 V in the potential window of 2.5–4.0 V versus Na+/Na. The charge capacity of 83.7 mAh g−1 and discharge capacity of 82.1 mAh g−1 can be obtained at a current rate of 1C after 300 cycles and the coulombic efficiency averages 98% throughout. The enhanced electrochemical performance can be contributed to the uniform and continuous carbon layer, which greatly improves the electric conductivity of Na3V2(PO4)3.

Investigation of the reversible sodiation of Sn foil by ex-situ X-ray diffractometry and Mössbauer effect spectroscopy

The reversible sodiation of Sn foil was investigated using ex-situ X-ray diffractometry (XRD) and Mössbauer effect spectroscopy. The measured voltage profile indicated that the sodiation process of Sn foil proceeded in three stages. Ex-situ XRD patterns demonstrated that Na4Sn4, Na5Sn2 and Na15Sn4 phases were formed at the end of each discharge plateau. Na5Sn2, Na4Sn4 and β-Sn were formed at the end of each charge plateau. Three single-phase alloys, Na4Sn4, Na9Sn4 and Na15Sn4, were prepared by annealing stoichiometric ratios of Na and Sn. The Mössbauer spectra of ex-situ samples at the end of each discharge plateau were collected and compared with the Mössbauer spectra of the three single phase alloys. The measured parameters for the Mössbauer effect spectra were consistent with an analysis of the crystal structures. The center shift became less positive with an increase of the sodium content in Na–Sn phases and this was shown to be a useful indicator of the degree of sodiation of Sn electrodes.

Ultrasound assisted polymerization for synthesis of ZnO/Polypyrrole composites for zinc/nickel rechargeable battery

ZnO/Polypyrrole (PPy) composites are synthesized by ultrasound assisted chemical polymerization of PPy in the presence of ZnO particles. With different initial content of pyrrole, granular and layered ZnO/PPy composite are formed. The fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are adopted to characterize the as-prepared samples. ZnO/PPy composites are used as anode material for Zn/Ni batteries. Galvanostatic charge/discharge experiments, cyclic voltammograms (CV) and electrochemical impedance spectroscopy (EIS) are conducted to evaluate the cycle performance of electrodes. ZnO/PPy composites show superior capacity stability, more stable charge plateau and higher discharge plateau compared to conventional ZnO electrode. Furthermore, rate performance is also improved by ZnO/PPy composites.

Electrochemical Performance of LiFePO<sub>4</sub>/C Prepared from Different Carbon Source

Cathode material LiFePO4/C was prepared via optimized solid state reaction and calcinations using different carbon source. The crystalline and morphology of the resultant powder was evaluated by X-Ray diffraction (XRD), scanning electronic microscope (SEM). The electrochemical performance was measured by galvanostatic charge-discharge test at 0.1C and 0.5C. The results demonstrated that the sample with layer-like stacking microstructure had the best capacity retention up to 96% after 50-cycle at 0.5C; the sample with good carbon coating using glucose as carbon source exhibited the lowest flat charge plateau and the highest flat discharge plateau, also the best storage performance at 60 oC temperature. Nevertheless, the sample with spherical-like shape and homogeneous particle size had the most capacity loss, maybe due to the increased internal resistance caused by the big interstices between the particle sizes.

The new electrochemical reaction mechanism of Na/FeS2 cell at ambient temperature

FeS2 synthesized by hydrothermal method was used for sodium batteries for the first time. A large initial discharge capacity of 771 mAh g−1 and a high reversible capacity of 521 mAh g−1 were obtained. The reaction mechanism of electrochemical de-sodiation (charge) was investigated after the initial discharge. Our results have demonstrated that the composition and structure of electrode after the charging to 3.0 V could not recover its original state of FeS2 and a new phase of NaFeS2 was revealed. This should be responsible to the large irreversible capacity in the first cycle and the high discharge and charge plateaus after the initial cycle.

Polythiophene Mesoporous Birnessite-MnO2/Pd Cathode Air Electrode for Rechargeable Li-Air Battery

Mesoporous birnessite-manganese oxide (b-MnO2) was studied for air electrode for Li-air rechargeable battery. In this study, mesoporous b-MnO2 with an average pore size of 3.52nm and BET surface area of 237m2g−1 was successfully prepared using inorganic/organic phase. Prepared mesoporous b-MnO2 was applied for air electrode for Li-air battery and discharge capacity of 345mAh g−1 was observed at a current of 0.13mAcm−2. With the dispersion of small amount of Pd to mesoporous b-MnO2, it was found that the Li-air cell showed a reasonably large discharge capacity of 487mAh g−1 at 0.13mAcm−2 at the initial cycle. The first discharge plateau around 2.71V vs. Li/Li+ and charge plateau at 3.58V vs. Li/Li+ with highly reversible capacity were observed. The energy efficiency for the charge and discharge was estimated to be ca. 76.4%. The ex-situ XRD result of the mesoporous b-MnO2/Pd/TAB-2 (85/5/10) air electrode suggested that the observed capacity mainly came from Li+ and O2 to form Li2O2 after discharge to 2.0V. Formation of Li2CO3 was hardly observed.

Improved electrochemical activity of nanostructured Li2FeSiO4/MWCNTs composite cathode

Electrochemical activity of nano Li2FeSiO4 material with the Pmn21 symmetry is reported against lithium. Small amount of carboxylic group impurity distributed heterogeneously over the Li2FeSiO4 surface is concluded with Fourier transformed infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis. The electrode material with Pmn21 symmetry is prepared by simple sol-gel technique and further modified with multi-walled carbon nanotubes (MWCNTs) to achieve better electron passage to the particle-particle boundaries. Our strategy helps to improve the electrochemical performance and storage capacity to a level compared to bare material. The Li2FeSiO4/MWCNT composite electrode delivered first discharge capacity of 240 mAh g−1 at 16.5mAg−1, when it is cycled between 1.5 V- 4.8V at 20°C. This indicates more than one lithium is extracted. The voltage plateau of second charge is different and lower than that of first charge plateau whereas first and second discharge plateaus are almost similar, structural rearrangement involving the lithium and iron exchange between their sites and pre-activation during first oxidation step are the possible reasons for this phenomenon. Since silicates are inexpensive compared to other electrode materials, we have undertaken this work to improve the electrochemical activity and power performance by nanosizing of particle and adding MWCNTs as conductive additives.

Study of sulfonated polyether ether ketone with pendant lithiated fluorinated sulfonic groups as ion conductive binder in lithium-ion batteries

In an attempt to reduce the Li+ concentration polarization and electrolyte depletion from the electrode porous space, sulfonated polyether ether ketone with pendant lithiated fluorinated sulfonic groups (SPEEK-FSA-Li) is prepared and attempted as ionic conductivity binder. Sulfonated aromatic poly(ether ether ketone) exhibits strong adhesion and chemical stability, and lithiated fluorinated sulfonic side chains help to enhance the ionic conductivity and Li+ ion diffusion due to the charge delocalization over the sulfonic chain. The performances are evaluated by cyclic voltammetry, electrochemical impedance spectroscopy, charge–discharge cycle testing, 180° peel testing, and compared with the cathode prepared with polyvinylidene fluoride binder. The electrode prepared with SPEEK-FSA-Li binder forms the relatively smaller resistances of both the SEI and the charge transfer of lithium ion transport. This is beneficial to lithium ion intercalation and de-intercalation of the cathode during discharging–charging, therefore the cell prepared with SPEEK-FSA-Li shows lower charge plateau potential and higher discharge plateau potential. Compared with PVDF, the electrode with ionic binder shows smaller decrease in capacity with the increasing of cycle rate. Meanwhile, adhesion strength of electrode prepared with SPEEK-FSA-Li is more than five times greater than that with PVDF.