Effect of Temperature on the Deterioration of Graphite-Based Negative Electrodes during the Prolonged Cycling of Li-ion Batteries

This paper mainly research the relationship between the lithium-ion battery management systems and charging policies and temperature.In the introduction of lithium-ion battery characteristics of the premise, the lithium-ion battery protection methods are described, based on a lithium-ion battery protection method in detail its charging policies and to study the effect of temperature on charging policies, compared with good interpretation of the lithium-ion rechargeable battery management system strategy selection and temperature control importance of the lithium-ion battery protection, providing a theoretical basis and ideas for research and specific battery management system.

Nickel–Cadmium Cells Cell Fabrication Methods Silver–Zinc Cells Performance Other Silver Positive Electrode Systems Nickel–Zinc Cells Nickel–Hydrogen Cells Other Cell Systems Electrolyte Safety and Disposal Keywords: sealed cells; secondary cells

Analysis of polarization and thermal characteristics in lithium-ion battery with various electrode thicknesses

Rechargeable batteries with aqueous electrolytes

Lithium-ion batteries (LIBs) are an important power source for both portable devices and electric vehicles. In order for electrical vehicles with LIBs to be embraced more fully, the specific energy of LIBs needs to be improved without sacrificing safety, material availability, and cost. Tin (Sn), as a negative electrode material with various morphologies or nanostructures, is one possible solution because tin not only provides high specific energy (994 mAhg-1) compared to graphite (~374 mAh g-1), but is also inexpensive and abundant [1]. Moreover, tin can be used for the negative electrode of a sodium ion battery, which have recently received much attention as an alternative of LiBs due to much lower cost due to the natural abundance of Na [2]. In spite of the aforementioned advantages of tin as negative electrode materials, tin based electrodes are still difficult to commercialize due to their severe capacity fading during battery cycling. The fade has been associated with the large volume expansion during lithiation, but the mechanism is not yet fully understood. In order to use tin materials in practical devices, the first step is to elucidate the cause of the degradation behavior, and next is to improve the cyclability of tin based electrodes through design of material, coating, and electrolyte additive, etc. Herein, we investigated the degradation behavior of the Sn-C composite negative electrodes, using electrochemical and micro-structural methods.The Sn material used in this study was synthesized by a chemical reducing method [3]. The Sn is spherical-shaped with diameter of 80 ~120 nm, as shown in Fig. a. To fabricate negative electrodes using the prepared nano-sized Sn particles, carbon black as conducting agent and PVdF binder were added and mixed well together in NMP solvent. The ink was applied to a copper foil, dried in a vacuum oven, and calendered. Fig. b shows the XRD pattern of the prepared Sn-C electrode, where Sn peak was mainly detected. Fig.c-d shows the lithiation and delithiation curves and capacity fade of the half cell employing the Sn-C negative electrode. The cell was lithiated and delithiated at 40 mAg-1 (20 mAg-1 for the 1st cycle) between 0.01 and 1.5 VLi/Li+. As shown in Fig. c, the first irreversible capacity loss (ICL) is large (~60%) presumably due to formation of a thick SEI layer, thus reducing the cyclable Li ions and active material during the 1st lithiation. During subsequent cycles (Fig.d), the capacity decreased gradually by about 1.2 % cycle-1 from 2nd to 50thcycles probably due to loss of conductivity and active materials. To reveal more clearly this degradation behavior, we analyze the initial cycle and subsequent cycles separately. Specific methods used in each cycle include: differential capacity (dC/dV) curve, electrochemical impedance spectroscopy (EIS), Focus Ion Beam (FIB)-Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), and X-ray Photoelectron Spectroscopy (XPS).

With the substantial increase in the demand for lithium-ion batteries (LIBs) for the adoption of electrification to reduce CO2 emission, safe and efficient recycling of spent LIBs is essential to utilize LIBs sustainably1. In hydrometallurgy-based or direct LIB recycling systems, which are expected to become mainstream in the future because of their low environmental impacts, deactivation is a crucial pretreatment step to safely handle LIBs during the processes2, 3. However, a common deactivation method, in which an external short circuit is induced using electronic loads or conductive liquid, cannot deactivate LIBs with disconnected electrical circuits or metallic Li plating on the negative electrode surface, despite their high safety risks.We propose the advanced deactivation method, injecting a redox mediator (RM) solution inside the LIBs. The RM delivers electrons from the negative electrode to the positive electrode by cycling the reduction and oxidation on the negative and positive electrodes, respectively (redox shuttle reaction), resulting in discharging LIBs. In other words, the RM causes a short circuit inside the LIB. Therefore, it is possible to discharge a LIB that cannot be discharged externally, for example, a LIB with disconnected electrical circuits due to a safety device operation. Furthermore, the RM can strip Li metal plated on the negative electrode even though it is “dead lithium.” This unique characteristic contributes to the improvement in the safety and the Li collection rate in the recycling processes. Additionally, in this presentation, the deactivation mechanism of LIBs and its relationship with the electrochemical properties of the RMs will be discussed. The present findings will be beneficial and helpful for designing RMs for deactivation of more and more diversified spent LIBs. References J. Neumann, et al.: "Recycling of Lithium‐Ion Batteries—Current State of the Art, Circular Economy, and Next Generation Recycling" Adv. Energy Mater. 12, (2022). A. Kwade, et al.: "Recycling of lithium-ion batteries" The LithoRec Way, Switzerland: Springler International Publishing AG (2018). H. Rouhi, et al.: "Voltage behavior in lithium-ion batteries after electrochemical discharge and its implications on the safety of recycling processes" Journal of Energy Storage 35, (2021).

Lithium ion batteries (LIBs) are considered as key technology for stationary energy storage systems and especially as power supply for electric vehicles (EVs). Even though LIBs are already used in EVs, there is a need of further improvements of the LIBs to achieve driving ranges of more than 500 km, what is considered to be a value for greater consumer acceptance of EVs. To reach this goal, the specific energy and energy density of LIBs need to be increased to approximately 350 Wh kg-1 and 750 Wh L-1 at cell level, respectively. The use of alternative anode materials to replace the state-of-the-art graphite anode, is considered as an efficient strategy to increase the energy density of LIBs. Silicon (Si) turns out to be the most promising material for advanced anodes in LIBs, as it offers a nearly 10 times higher specific capacity compared to graphite. However, the implementation of electrode materials containing contents of more than 5-10% Si in commercial LIBs is still hampered by huge volume changes leading to a continuous solid electrolyte interphase (SEI) re-formation, loss of active lithium and, therefore, to a poor capacity retention.[1] The application of nano-sized Si materials like nanoparticles, nanowires or thin films is reported to significantly improve the performance of Si based anodes, due to better accommodation of the huge volume changes upon lithiation/de-lithiation. Additionally, Si thin film electrodes exhibit improved specific capacities in comparison to typical composite-based electrodes, because of the absence of inactive components like binder and conductive additives.[2] An additional approach to improve the performance of Si based electrodes is the addition of additives to the electrolyte. Electrolyte additives like fluoroethylene carbonate (FEC) and vinylene carbonate (VC) are commonly known to enhance the capacity retention of Si electrodes by forming a more stable SEI, thus, preventing ongoing electrolyte decomposition and continuous active lithium loss.[3] Isocyanate compounds are able to undergo reductive polymerization and, therefore, may be considered as effective electrolyte additives for Si anodes. Actually, several isocyanates were reported to function as effective film-forming additives for graphite-based negative electrodes.[4] Within this work, magnetron sputtering was utilized for the preparation of thin film Si anodes, which contain neither a binder nor a conductive agent. Therefore, the effect of the electrolyte additive can be directly related to the Si active material. Since it was recently reported, that lithium consumption related to SEI reformation is the main failure mechanism of lithium ion full cells containing a Si anode[5], the electrochemical performance of these Si thin film electrodes was investigated in Si/NMC-111 full cells using different electrolyte formulations. DFT calculations (HOMO/LUMO energies) were performed prior to electrochemical investigations for reductive and oxidative stability predictions of the electrolyte solvent and additive molecules. The addition of the pentafluorophenyl isocyanate electrolyte additive leads to an increased Coulombic efficiency and a significantly enhanced capacity retention of the LIB full cells during prolonged cycling, in comparison to the baseline electrolyte. Post-mortem investigations of the negative Si electrodes by means of scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were performed to study the SEI layer, formed in the different electrolyte formulations. The enhanced cycling performance of the full cells can be correlated to an improved SEI formation. Reference s : [1] D. Andre, H. Hain, P. Lamp, F. Maglia, B. Stiaszny, Future high-energy density anode materials from an automotive application perspective, Journal of Materials Chemistry A, 5 (2017) 17174-17198. [2] M.N. Obrovac, V.L. Chevrier, Alloy Negative Electrodes for Li-Ion Batteries, Chemical Reviews, 114 (2014) 11444-11502. [3] S. Dalavi, P. Guduru, B.L. Lucht, Performance Enhancing Electrolyte Additives for Lithium Ion Batteries with Silicon Anodes, Journal of The Electrochemical Society, 159 (2012) A642-A646. [4] C. Korepp, W. Kern, E.A. Lanzer, P.R. Raimann, J.O. Besenhard, M.H. Yang, K.C. Möller, D.T. Shieh, M. Winter, Isocyanate compounds as electrolyte additives for lithium-ion batteries, Journal of Power Sources, 174 (2007) 387-393. [5] M. Klett, J.A. Gilbert, S.E. Trask, B.J. Polzin, A.N. Jansen, D.W. Dees, D.P. Abraham, Electrode Behavior RE-Visited: Monitoring Potential Windows, Capacity Loss, and Impedance Changes in Li1.03(Ni0.5Co0.2Mn0.3)0.97O2/Silicon-Graphite Full Cells, Journal of The Electrochemical Society, 163 (2016) A875-A887.

The vanadium redox flow battery (VRFB) is one of the strong candidates for massive electrical energy storage [1]. For the further implementation of the VRFBs, improvement of cell performance is important to achieving cost reduction. Recently, cell performance has been drastically improved by using thin carbon paper electrodes instead of conventional thick carbon felt electrodes [2-4]. Heat and acid treatments to carbon electrode materials has been also demonstrated to show better reaction kinetics in VRFBs [2-4]. To develop carbon electrodes with higher catalytic activity for VRFB application, clarifying reaction kinetics [5], as well as performance limiting electrode under cell operation are strongly needed. To identify performance-limiting electrode, asymmetric cell configuration was used in a VRFB [3] and showed the negative electrode limit the cell performance in VRFBs. A dynamic hydrogen electrode was applied to an operating VRFB and larger kinetic polarization was found at the negative electrode compared to the positive electrode [6]. In these literature, cell polarization at low current density operation where the reaction kinetics determine overall cell performance was intensively examined. It is also noteworthy that the reaction distribution in the carbon electrode has not been fully explored yet. In this study, we performed polarization experiments by using the symmetric cell geometry in a VRFB. The VRFB in which an interdigitated flow field was embedded [7] was used to achieve high current density operation. To examine the performance limiting electrode, we used heat-treated and raw (as-received) carbon porous materials as the better- and poor- kinetics electrode as reported [3]. Furthermore, we applied two sheets of electrode material to each the negative and positive electrode in order to investigate reaction distribution in the electrodes. In the experiments, one of the two sheets of the heat-treated electrodes was replaced by the raw electrode to determine the performance-limiting side of the electrode. Accordingly, we performed polarization experiments in the following five cases: Base case: (−) HT|HT|PEM|HT|HT (+) Case 1: (−) Raw|HT|PEM|HT|HT (+) Case 2: (−) HT|Raw|PEM|HT|HT (+) Case 3: (−) HT|HT|PEM|HT|Raw (+) Case 4: (−) HT|HT|PEM|Raw|HT (+) Figure 1 shows polarization curves obtained in case 1 and 2 where the negative electrode was partially replaced by the raw electrode. Both polarization curves corresponding to case 1 and 2 shows larger overpotentials than the base case in entire operational condition. This indicates that both the current collector side and the membrane side of the negative electrode contributed to the V(II)/V(III) reaction. However, polarization curves at low current density condition (<0.5A/cm2) indicate that cell performance was more deteriorated in case 2. Case 2 corresponds to the raw carbon material placed in the membrane side of the negative electrode. This suggests that V(II)/V(III) reaction was slightly concentrated in the membrane side of the negative electrode during the discharging process of the VRFB at low current density condition. On the other hand, case 1 showed less cell performance at high current density condition (>0.5A/cm2), indicating more reaction in the current collector side of the negative electrode at high current density condition. These observations can be attributed to the transport of proton (H+) and V(II) ion in the negative electrode. At low current density condition (<0.5A/cm2), sufficient amount of V(II) ion was supplied to the electrode and thus proton transport resistance in the electrode can affect the cell performance, resulting in the more reaction in the membrane side of the electrode. However, at high current density condition (>0.5A/cm2), reaction distribution was spatially shifted to the collector side possibly due to an insufficient supply of V(II) ion to the negative electrode. This further causes the concentration overpotential in the negative electrode at high current density operation. Acknowledgements This research was supported by Japan Science and Technology Agency (JST), Precursory Research for Embryonic Science and Technology (PRESTO). The authors acknowledge Prof. Mench for his fruitful communication on high performance VFRBs. The authors appreciate Dr. Kumbur for his useful suggestion on VFRB experiments. Prof. Nguyen is greatly acknowledged for his valuable comments on improving cell performance.

Supercapacitors can provide high rate capability and long-term cycleability, profited by their simple mechanism based on the adsorption and desorption of ions on the surface of electrodes. It is possible to charge or discharge supercapacitor cells in a minute for 10,000 cycles without notable degradation. Based on the high power characteristics, supercapacitors can augment the batteries or fuel cells for electric vehicles or heavy equipment. So far, most of supercapacitors have symmetric configuration with activated carbon electrodes as the positive and negative electrodes (Fig. 1a). And they follow Daniell-type mechanism, where the electrolyte is depleted of and replenished with ions upon charging and discharging, respectively (Fig. 1b). In this mechanism, electrolyte serves as an ionic reservoir, from which cations and anions are separated to negative and positive electrodes, respectively. As a result, sufficient volume of electrolyte is indispensable for the operation of supercapacitors. This leads to a limitation in energy density and an increase in the internal resistance as the starvation of the concentration of salts in the electrolyte decreases during operation. Herein, we introduce a hybrid supercapacitor that follows ‘rocking-chair’-type mechanism for the first time. This hybrid supercapacitor is composed of magnesium metal and activated carbon as the negative and positive electrodes, respectively (Fig. 1c). Mg2+ ions are replenished at the negative electrode while they are adsorbed into the pores of the positive electrode upon the discharging of the cell (Fig. 1d). On the other hand, Mg2+ ions are released from the positive electrode while Mg metal is deposited on the negative electrode upon the charging of the cell. As a result, only a minimum amount of electrolyte is needed to operate the cell since the electrolyte serves as a medium of Mg2+ ions. The use of Mg metal electrode can increase the energy density of the cell significantly by virtue of the large volumetric capacity of 3832 mAh/cc and the low redox potential of -2.2 V vs activated carbon’s open circuit potential. Therefore, the ‘rocking-chair’-type magnesium hybrid supercapacitor can double the energy density of a supercapacitor, and the internal resistance can be kept constant during the operation of the cell. The electrochemical results show highly reversible reactions at the positive and negative electrodes thanks to newly-developed Mg2+ electrolytes. Charge-discharge cycles at rates up to 5 mA/cm2 were possible, whereas cycling tests showed 64% retention of the capacity after 400 cycles. Detailed studies of the mechanisms of degradation and evidence of the ‘rocking-chair’-type mechanism will be presented. Figure 1

Supercapacitors can provide high rate capability and long-term cycleability, thanks to their simple mechanism based on the adsorption and desorption of ions on the surface of electrodes. It is possible to charge or discharge supercapacitor cells in a minute for 10,000 cycles without notable degradation. Based on the high power characteristics, supercapacitors can augment the batteries or fuel cells for electric vehicles or heavy equipment. So far, most of supercapacitors have symmetric configuration with activated carbon electrodes as the positive and negative electrodes (Fig. 1a). And they follow a Daniell-type mechanism, where the electrolyte is depleted of and replenished with ions upon charging and discharging, respectively (Fig. 1b). In this mechanism, electrolyte serves as an ionic reservoir, from which cations and anions are separated to negative and positive electrodes, respectively. As a result, sufficient volume of electrolyte is indispensable for the operation of supercapacitors. This leads to a limitation in energy density and an increase in the internal resistance as the starvation of the concentration of salts in the electrolyte decreases during operation. Herein, we introduce a hybrid supercapacitor that follows a ‘rocking-chair’ mechanism for the first time. This hybrid supercapacitor is composed of metal anodes and activated carbon as the negative and positive electrodes, respectively (Fig. 1c). Metal (M, e.g. Mg or Zn) ions are replenished at the negative electrode while they are adsorbed into the pores of the positive electrode upon the discharging of the cell (Fig. 1d). On the other hand, metal ions are released from the positive electrode while metal is deposited on the negative electrode upon the charging of the cell. As a result, only a minimum amount of electrolyte is needed to operate the cell since the electrolyte serves exclusively as a medium of metal ion transport. The use of metal electrodes can increase the energy density of the cell significantly by virtue of the large volumetric capacity. Therefore, ‘rocking-chair’ metal hybrid supercapacitors can double the energy density of a supercapacitor, and the internal resistance can be kept constant during the operation of the cell. The electrochemical results show highly reversible reactions at the positive and negative electrodes thanks to newly-developed Mg-ion and Zn-ion electrolytes. Charge-discharge cycles at rates up to 5 mA/cm2 were possible, whereas cycling tests showed 64% retention of the capacity after 400 cycles. Detailed studies of the mechanisms of degradation and evidences of the ‘rocking-chair’-type mechanism will be presented. Figure 1

【Background】 The need for Lithium-ion batteries (LIBs) with longer life is growing with the popularization of their applications, but LIBs lose capacity with use. These reduction in capacity of LIBs is mainly due to three factors: namely, the reduction of a positive electrode capacity, the reduction of a negative electrode capacity, and the mutual “capacity slippage” between the capacity of a positive and a negative electrodes [1]. The reduction of a positive and a negative electrode capacity is caused by deactivation of active materials due to decrease in the conducting paths of electrons and Li+. The capacity slippage is not only caused by the decreases in the capacity of a positive and a negative electrodes but also by deactivation of Li+. This Li+ deactivation is attributed to the formation of solid electrolyte interfaces and the immobilization of Li+ due to their trapping within a negative electrode [2, 3]. In this study, a method for recovering capacity by repeating short-term over-discharge was investigated, and the effect of this method on a LIB was evaluated. 【Experimental】 Laminated-type cells were fabricated by alternately stacking negative electrodes and positive electrodes. The positive and negative active materials were LiNi1/3Co1/3Mn1/3O2 and graphite, respectively. In the charge/discharge cycle test, the cells were charged and discharged at a constant current of 1 C between 3.0 V to 4.2 V at 50 oC. The rest time was 30 minutes. The capacity recovery treatment consisted of two steps at 25 oC. First, the cells were discharged at a constant current of 1 C until the cell voltage reached 2.5 V or 72 seconds had elapsed, followed by a rest period of 30 minutes, and the cycle was repeated until the behavior of the discharge curve did not change. Second, the cycle of discharging at a constant current of 10 C until the cell voltage reached 0.5 V or 1 second had elapsed and resting for 60/n minutes was repeated n times, where n is an integer from 3 to 6. 【Results & Discussion】 Figure 1a shows discharge capacity retention in the charge/discharge cycle tests with capacity recovery, and Figure 1b shows discharge curves at the specific cycles. Capacity recovery was performed after the 400th and specific cycles. As shown in Fig. 1a, the number of cycles at which the capacity retention fell bellow the value at the 400th cycle was extended by repeating the capacity recovery. As shown in Fig. 1b, because of performing capacity recovery after 400 cycles, the discharge capacity was recovered by 17.0 mAh, and the discharge curve at the 401st cycle is equivalent to that at the 100th cycle. To verify the origin of this capacity recovery, the discharge curve analysis [4] was carried out for these discharge curves. The results of discharge curve analysis are shown in Figures 2a and 2b. The horizontal axis shows discharge capacity, and the negative region is the surplus charge capacity. The vertical axis is the cell voltage and the potential of the positive and negative electrodes relative to lithium metal. The plots represent actual values during discharge, and the solid lines represent the potential curves of the positive and negative electrodes and the voltage curve of the cell plotted from the difference between them. According to the results of the analysis, the discharge endpoints of the negative electrode curves are located on the lower capacity side than the discharge endpoints of the positive electrodes. This result is due to capacity slippage and means the discharge endpoints of the negative electrode curves determine those of the cell curves. Focusing on the discharge endpoints of the negative electrode curves reveals that the position was shifted toward the higher capacity side by 17.6 mAh (from 201.6 to 219.2 mAh) owing to the capacity recovery. This value agrees well with 17.0 mAh which is the amount of recovery capacity obtained from the charge/discharge cycle tests shown in Fig. 1b. This agreement strongly suggests that the origin of the capacity recovery is the recovery of capacity slippage. On the day of the presentation, the mechanism by which capacity slippage is recovered will be discussed while the results of the disassembly analysis will be also introduced. [1] P. Ramadass et al., J. Power Sources, 112, 614 (2002).[2] H. J. Ploehn et al., J. Electrochem. Soc., 151, A456 (2004).[3] T. Yoshida et al., J. Electrochem. Soc., 153, A576 (2006).[4] K. Honkura et al., J. Power Sources, 264, 140 (2014). Figure 1

Our contribution deals with the study of surface processes and chemical composition on the surface of the negative electrode of a lead-acid battery during cycling at different speeds. Thin electrodes were created for the measurements. The negative electrode was analyzed at six SOC states (100 %, 80 %, 60 %, 40 %, 20 % and 0 % SOC). The proportion of individual elements on the surface of the negative electrode during cycling at 0.2 C, 0.3 C and 0.5 C was evaluated. Chemical changes occurring on the surface of the negative electrode during cycling of the lead-acid battery were measured using an X-ray diffractometer, and the presence of individual chemical elements on the surface of the electrode was evaluated using the Rietveld method. At higher cycling speeds, an increase in the material was observed, which did not convert during cycling, and higher cycling speeds caused a more significant material conversion near the negative electrode collector.

The expansion of lithium-ion battery (LIB) usage from small applications such as portable electronic devices to large applications such as electric vehicles and stationary power supply1 necessitates the improvement of high-rate LIB performance especially at the low-temperature region, due to the growing frequency of outside use.2 , 3 The major reason of LIB performance degradation during low-temperature operation is considered to be non-uniform reaction occurrence, which is due to a decrease in Li ion transport for charge compensation inside porous electrode during charge/discharge. In order to quantitatively determine this Li ion transport at the LiNiO2-based positive electrodes with various loading weight, porosity, and conductive carbon ratio, electrochemical impedance spectroscopy using symmetric cells (EIS-SC)4-9 was performed. In this presentation, the feasibility of the obtained ion transport was investigated in terms of parameters of predicting high-rate and low-temperature battery performance.10 The high-rate and low-temperature cycle performance of LIB was performed using a cylindrical battery composed of LiNiO2-based positive/graphite negative electrodes with LiPF6-based electrolyte at a rate of 5C corresponding 0.2 h charging/discharging and a temperature of 0 °C. The capacity retention was calculated from the capacity after 200 cycles relative to the initial capacity at a temperature of 25 °C. The electrochemical cell for impedance measurement consists of two uncharged LiNiO2-based positive electrodes via a separator containing the same Li-based electrolyte. The Nyquist plots obtained are straight line with a slop of 45° and vertical straight lines with respect to the real axis in the high and low-frequency regions, respectively, indicative of typical blocking behavior in porous electrode. Using the Nyquist plots and transmission line mode theory to investigate electrochemical processes in porous electrodes,11 the ionic resistances inside the porous positive electrodes (R ion) were quantitatively determined as ion transport parameter. The reciprocal of ionic resistance (R ion −1) for all electrodes of various configurations exhibits nicely positively correlation with capacity retention of low-temperature (0 °C) battery cycling; that is, the capacity retention of the low-temperature cycle test increases as R ion −1 increases. This result suggested that for a porous electrode, high ionic resistance (which corresponds to low ion transport) results in reaction non-uniformity, which causes the deterioration of high-rate and low-temperature cycling lifetime.Regarding the conventional cycle-test procedure for practical LIBs, there are problems of material and time consumption since it requires long testing after producing many large batteries. In this work, we subject symmetrical cells with small-sized and real-life electrodes to impedance analysis, and electrochemically quantify ion transport in practical porous electrodes employing a simple protocol that can be used to estimate high-rate and low-temperature LIB performance in a short time without finally producing many large batteries. Therefore, this criterion allows us the possibility of simple prediction for such high-rate and low-temperature LIB performance, and therefore contributes to the realization of an energy storage system that meets the demands for high-rate and low-temperature performances such as fast-charging in the future.References S. Chu and A. Majumdar, Nature, 488, 294-303 (2012). M.-T. F. Rodrigues, G. Babu, H. Gullapalli, K. Kalaga, F. N. Sayed, K. Kato, J. Joyner and P. M. Ajayan, Nat. Energy, 2, 17108 (2017). R. Schmuch, R. Wagner, G. Hörpel, T. Placke and M. Winter, Nat. Energy, 3, 267-278 (2018). N. Ogihara, Y. Itou, S. Kawauchi, C. Okuda, Y. Takeuchi and Y. Ukyo, Meeting s, MA2012-02, 723 (2012). N. Ogihara, S. Kawauchi, C. Okuda, Y. Itou, Y. Takeuchi and Y. Ukyo, J. Electrochem. Soc., 159, A1034-A1039 (2012). N. Ogiahra, Y. Itou, S. Kawauchi, T. Kobayashi and Y. Takeuchi, Meeting s, MA2013-02, 947 (2013). Y. Itou, N. Ogihara, C. Okuda, T. Sasaki, H. Nakano, T. Kobayashi and Y. Takeuchi, Meeting s, MA2014-04, 611 (2014). N. Ogihara, Y. Itou, T. Sasaki and Y. Takeuchi, J. Phys. Chem. C, 119, 4612-4619 (2015). Y. Itou, N. Ogihara and S. Kawauchi, J. Phys. Chem. C, 124, 5559-5564 (2020). N. Ogihara, Y. Itou and S. Kawauchi, J. Phys. Chem. Lett., 10, 5013-5018 (2019). R. de Levie, Electrochim. Acta, 9, 1231-1245 (1964).

The development of an all-solid-state lithium-ion battery (ASSB) as a next-generation storage battery is being promoted from the viewpoints of higher energy density and safety, but higher power density is an issue. One of the factors is that the interface resistance is high. At present, research is being actively conducted to reduce interface resistance by applying external stress. However, it is not clear how the volume change accompanying the lithium desorption and insertion of the active material particles affects the interface resistance. Therefore, in this research, we constructed an analysis model incorporating these effects and examined the effects on battery performance.The electrode layer is a three-phase uniform porous media including an active material (AM), a solid electrolyte (SE), and void space. There was no temperature distribution inside the battery, and the concentration distribution of lithium ions in the electrolyte was uniformly constant. In this research, based on the porous electrode theory [1], the effects of expansion and contraction of the active material were incorporated. The change in the thickness of the electrode layer was calculated from the balance between the local strain and the force of the entire cell. Assuming that the active material is a rigid body and the solid electrolyte is an elastic body, the reaction interface area was calculated by incorporating a geometric model that changes depending on the lithium concentration of the active material into the Random capillary model [2]. The change in tortuosity was calculated assuming that the change was a function of the volume fraction of each phase. The external stress dependence of the contact interface is given by equation of Tian et al [3]. The positive electrode active material is LiCoO2 (LCO), the negative electrode active material is graphite, and the high expansion negative electrode assumed to be 3 times the capacity of Si (virtual Si whose expansion volume at full charge is 3 times the volume before charging). As the solid electrolyte, Li10GeP2S12 was used. The volume fraction of the active material was set to 0.4, the porosity was set to 0.3, and the solid electrolyte ratio was set to 0.3. In the case of a Si negative electrode, a rise in surface pressure from the inside of the cell to the outside due to expansion of the Si active material upon charging has been reported [4]. In this study, this internal pressure is assumed to be proportional to the lithium intercalation rate of the negative electrode active material in the local area of the electrode layer. And it is treated as the force applied to the electrode-solid electrolyte interface together with the cell fastening pressure. The initial stress was 1 to 100 MPa, and the thickness of the positive electrode, negative electrode, and SE layer was 60 µm, 60 µm, and 20 µm. The Li ion conductivity of the solid electrolyte was set to 1.2 × 10-2 S/cm [5]. Figure 1 shows the charging curves of negative electrode graphite (a) and Si (b) at an external stress of 1 to 100 MPa. Comparing the two charging curves with the same external stress, it can be confirmed that the charging voltage of Si is lower than that of graphite and the charging rate (SOC) is higher. This is because the increase in internal pressure due to lithium insertion is large due to a large expansion rate, and the effective contact interface is increased due to an increase in stress applied to the interface. This reduced the reaction overpotential and led to an increase in the active material used. Figure 2 shows the SOC distribution at the external stress of 50 MPa. In the case of graphite having a low expansion rate, an effective contact interface is insufficient, and distribution occurs in the thickness direction. In general, expansion should be reduced to improve battery performance, but this research suggests that in order to form an effective solid-solid contact interface, expansion may be effective depending on the design of the expandable battery and fastening conditions.AcknowledgmentThis research was supported by Grants-in-Aid for Scientific Research on Innovative Areas, “Science on Interfacial Ion Dynamics for Solid State Ionics Devices” MEXT, Japan FY2019-2023.

With the growing need to increase the energy density of lithium batteries (LIBs), numerous studies have focused on developing high-capacity electrodes capable for operation at a wide potential range. Yet, extending the potential range often compromises the cycling stability because of accelerated mechanochemical ageing of the electrode active materials. Here, various coatings are applied via ALD or MLD on lithium battery electrodes to mitigate premature capacity fade. Focus is on investigating their attributes and effect of the coatings on the performance of a high voltage positive electrode material particularly LiNi0.8Mn0.1Co0.1O2 (NMC811), and lithium negative electrode. Additionally, some light is shed on the synthesis of the coatings.Motivated by high capacity when cycling to high potentials, coating of high-voltage Ni-rich layered metal oxide NMC811 is addressed. Coatings are anticipated to improve the cycle life of this material as it tends to suffer from various ageing processes, which in the state-of-the-art lithium batteries are mitigated via formation of a cathode electrolyte interface during battery cycling. Such coatings as lithium titanate, titanium terephthalate and lithium fluoride are investigated to understand attributes of coatings, or artificial cathode electrolyte interfaces, with different chemical and physicochemical features. In general, the electrodes with coated NMC811 report a higher capacity retention compared with the uncoated NMC811 electrodes when paired with graphite anode in full cells. Herein, correlation between the structural and interfacial evolution to the electrochemical performance of uncoated and coated NMC811 are discussed. Due to the complex interplay of the degradation mechanisms at the crystal structure, particle, and electrode levels, operando XRD and dilatometry are combined with ex-situ characterization techniques to have an in-depth understanding of the mechanism of enhancement by these coatings. The multiscale analyses show that at the room temperature electrodes with coated NMC811 experience suppressed volume changes during the cycling compared with uncoated NMC811. More reversible crystal lattice variations are also reported for the coated materials. Consequently, lesser particle cracking is produced. Based on the electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS), the coatings mitigate the parasitic side reactions. At the initial cycling the A-CEIs cause additional barrier for Li+ transfer across the electrode-electrolyte interface, but after prolonged cycling the coatings facilitate the ease of Li+ movement. While protecting the NMC811 structure, the A-CEIs also contribute to preserving the graphite negative electrode properties. As for the negative electrodes, highly reactive metallic lithium offering high capacity and most negative lithium redox potential is considered. Operando dilatometry, optical measurements reveal that optimized Al2O3 and TiOx coatings thickness requires a tradeoff between mechanical and chemical durability.