High-voltage Lithium-ion Batteries Research Articles

Recycled micro-sized silicon anode for high-voltage lithium-ion batteries

Recycled micro-sized silicon anode for high-voltage lithium-ion batteries

Maleic Anhydride and (Ethoxy)pentafluorocyclotriphosphazene as Electrolyte Additives for High-Voltage LiCoO2/Si-Graphite Lithium-Ion Batteries.

Anhydride additives including maleic anhydride and succinic anhydride are initially selected as additives in the commercial electrolytes for high-voltage lithium-ion batteries with a Si-based anode. The introduction of (ethoxy)pentafluorocyclotriphosphazene as a flame retardant realizes the nonflammability of electrolytes, and the conductivity of electrolytes exceeds 10 mS cm-1 at 25 °C. Maleic anhydride and (ethoxy)pentafluorocyclotriphosphazene jointly contribute to the exceptional performances of 4.45 V LiCoO2/Si-graphite pouch cells at 25 °C. The capacity retention at 1C of 300 cycles reaches 78%, and the discharge capacity ratio of 6C/1C is approximately 83%. These results suggest that this nonflammable electrolyte has good application prospect. Scanning electron microscopy and X-ray photoelectron spectroscopy measurements are implemented to analyze the interface properties of electrodes.

Fluorinated Linkers Enable High-Voltage Pyrrolidinium-based Dicationic Ionic Liquid Electrolytes.

Novel fluorinated, pyrrolidinium-based dicationic ionic liquids (FDILs) as high-performance electrolytes in energy storage devices have been prepared, displaying unprecedented electrochemical stabilities (up to 7 V); thermal stability (up to 370 °C) and ion transport (up to 1.45 mS cm‑1). FDILs were designed with a fluorinated ether linker and paired with TFSI/FSI counterions. To comprehensively asess the impact of the fluorinated spacer on their electrochemical, thermal, and physico-chemical properties, a comparison with their non-fluorinated counterparts was conducted. With a specific focus on their application as electrolytes in next-generation high-voltage lithium-ion batteries, the impact of the Li-salt on the characteristics of dicationic ILs was systematically evaluated. The incorporation of a fluorinated linker demonstrates significantly superior properties compared to their non-fluorinated counterparts, presenting a promising alternative towards next-generation high-voltage energy storage systems.

Enhanced electrochemical performance of a cost-effective Sm2O3-coated spinel LiNi0.5Mn1.5O4 cathode for high-voltage lithium-ion batteries

Spinel LiNi0.5Mn1.5O4 (LNMO) has gained significant attention as a promising cathode material for lithium-ion batteries due to its high working voltage (>4.7 V) and energy density. However, challenges such as electrolyte decomposition-induced material interface erosion and transition metal dissolution under high operating voltage hinder its commercial use. In this study, a thin and uniform Sm2O3 layer has been successfully deposited on the surface of LNMO using a wet chemical method. A comprehensive investigation of surface morphology, crystal structure, and electrochemical performance of the modified LNMO is conducted. The results demonstrate that the Sm2O3 surface modification acts as a robust multifunctional protective layer, effectively shielding against hydrofluoric acid-induced chemical attack and enhancing the migration efficiency of lithium ions. Notably, the capacity retention rate of LNMO@Sm2O3 (3 wt%) remains up to 88 % after 280 cycles, significantly surpassing the uncoated counterpart. The coated material exhibits a capacity of 114 mAh g−1 even under 10 C rate conditions. Moreover, the AC impedance values and manganese dissolution of the modified material in the organic electrolyte are considerably lower than those of the uncoated counterpart. Theoretical calculations strongly support the experimental findings, revealing higher Mn vacancy formation energy and density of states at the Fermi energy level for the Sm2O3-modified electrodes. This research contributes to the field of surface modification and paves the way for further enhancements in the electrochemical performance of other high-voltage manganese-based lithium-ion batteries (LIBs).

Electronic structure and delithiation mechanism of vanadium and nickel doped Li2MnPO4F cathode material for lithium-ion batteries

This study calculates the energy band structure and density of states of Lithium manganese fluorophosphate (Li2MnPO4F, a lithium transition metal phosphate compounds) using the first-principles plane-wave pseudopotential approach within the density-functional theory. The model of Li2M0.5Mn0.5PO4F (M = V, Ni) with transition metal doped Mn sites is constructed by using the CASTEP module. The calculation findings indicate that the transition metal doping can regulate the energy band structure of the intrinsic system, and Li2MnPO4F makes the band gap decrease, and the volume increase with the Li ions of being deintercalated, and the electrons can be readily stimulated from the valence band to the conduction band. The findings indicate that Li2MnPO4F is a favorable cathode material for high-voltage lithium ion batteries (LIBs). The introduction of vanadium (V) and nickel (Ni) doping reduces the band gap, facilitating an easier excitation of electrons from the valence band to the conduction band. This study provides a theoretical study of new cathode materials for high performance LIBs.

Constructing stable electrode–electrolyte interfaces by sulfone-based additive to improve the high-voltage performance of LiCoO2

LiCoO2 battery can provide high reversible capacity at a high voltage of 4.6 V, however, maintaining its stability at high voltages remains a major challenge. To address this issue, ethyl methyl sulfone (EMS) is employed as an electrolyte additive to construct stable interfaces between the electrode and electrolyte under high-voltage condition. The characterization results indicate that the addition of EMS can inhibit the decomposition of the standard electrolyte (STD) and the dissolution of Co2+ from cathode, as well as the formation of lithium dendrites on the Li anode, thereby enhancing the stability of both cathode/electrolyte and anode/electrolyte interfaces. Consequently, the cycling performance of LiCoO2 battery using STD+3 %EMS is augmented by 16.9 % at 1 C under a cut-off voltage of 4.6 V over 100 cycles, delivering a specific capacity of 137 mA h g−1. This research provides novel insights into the design of electrolyte additives for high-voltage LiCoO2 batteries and contributes to the further development of high-voltage lithium-ion batteries.

A synergistic duo for enhanced cathode stability in high-voltage lithium-ion batteries

Lithium-ion batteries with high-nickel cathode materials are promising candidates for achieving significantly higher energy densities. However, when Ni-rich subjected to higher charging cutoff voltages accelerates both electrolyte decomposition and structural degradation, leading to compromised cycling stability and reduced lifespan. In this study, we have developed a dual-additive strategy using lithium difluoro bisoxalate phosphate (LiDFBOP), and 1,3-divinyl-1,1,3,3-tetramethyldisilazane (DTDS) to address these challenges and improve the battery's performance. Theoretical calculations and experimental results indicate that the LiDFBOP regulates Li⁺ solvation for robust CEI formation, while DTDS scavenges impurities and promotes the formation of an inorganic/organic interphase. The synergistic effect of these additives combination allows Li||NCM811 coin cell to retain a capacity retention 87.9 % at 4.6 V and Graphite||NCM811full cell achieved 90.5 % capacity retention at 4.5 V. Moreover, the 1Ah pouch full cells exhibit excellent cycling stability, with a capacity retention of 91.4 % after 610 cycles at a constant current of 500 mA and voltage of 4.5 V. This work offers guidance on designing multifunctional additives to achieve synergistic electrolyte engineering for high-energy lithium-ion batteries.

Enhancing Structural Rigidity of Ultrahigh-Ni Oxide Through Al and Nb Dual-Bulk-Doping for High-Voltage Lithium-Ion Batteries.

The pursuit of high energy densities propels the design of next-generation nickel-based layered oxide cathodes. The utilization of low-cobalt, ultrahigh-nickel layered oxide cathodes, and the extension of operating voltages promise enhanced energy density. However, stability and safety face challenges associated with nickel content, including structural degradation, lattice oxygen evolution, and thermal instability. In this study, a promising strategy of Al and Nb dual-bulk-doping is presented in high-Ni cathode materials of LiNi0.96Co0.04O2 (NC) to stabilize the bulk structure, suppress oxygen release, and attain superior electrochemical performance at high voltages. The introduction of Al and Nb effectively raises the migration energy of Ni2+ into Li sites and stabilizes lattice oxygen through strengthened Al─O and Nb─O bonds. Furthermore, the substitution of high-valence Nb ions reduces the charge depletion of lattice oxygen and induces an ordered microstructure. The Al and Nb dual-bulk-doping strategy mitigates strain and stress associated with the H2↔H3 phase transition, reducing the generation and propagation of microcracks. The resulting Li(Ni0.96Co0.04)0.985Al0.01Nb0.005O2 (NCAN) cathode exhibits superior cycling stability, with a capacity retention of 77.8% after 300 cycles, even when operating at a high-voltage of 4.4V, outperforming the NC (48.5%). This work provides a promising perspective for developing high-voltage and high-Ni cathode materials.

Effect of Fe and Zn co-doping on LiCoPO4 cathode materials for High-Voltage Lithium-Ion batteries

Lithium cobalt phosphate (LiCoPO4) has great potential to be developed as a cathode material for lithium-ion batteries (LIBs) due to its structural stability and higher voltage platform with a high theoretical energy density. However, the relatively low diffusion of lithium ions still needs to be improved. In this work, Fe and Zn co-doped LiCoPO4: LiCo0.9-xFe0.1ZnxPO4/C is utilized to enhance the battery performance of LiCoPO4. The electrochemical properties of LiCo0.85Fe0.1Zn0.05PO4/C demonstrated an initial capacity of 118 mAh/g, with 93.4 % capacity retention at 1C after 100 cycles, and a good capacity of 87 mAh/g remained under a high current density of 10C. In addition, the diffusion rate of Li ions was investigated, proving the improvement of the materials with doping. The impedance results also showed a smaller resistance of the doped materials. Furthermore, operando X-ray diffraction displayed a good reversibility of the structural transformation, corresponding to cycling stability. This work provided studies of both the electrochemical properties and structural transformation of Fe and Zn co-doped LiCoPO4, which showed that 10 % Fe and 5 % Zn co-doping enhanced the electrochemical performance of LiCoPO4 as a cathode material in LIBs.

Experimental and Model Analysis of the Thermal and Electrical Phenomenon of Arc Faults on the Electrode Pole of Lithium-Ion Batteries

Aiming at the electrical safety problem of a high-voltage lithium-ion battery system caused by an arc, and based on the establishment of a battery arc fault experimental platform, the evolution law of safety caused by an arc in the negative terminal of a battery system under different working conditions is discussed. On this basis, a battery arc evolution model based on magnetohydrodynamics is established to analyze the arc’s electro-thermal coupling characteristics to further obtain the distribution of the arc’s multi-physical field. The results show that the arc generated by the high-voltage grade battery pack will break down the cell’s shell and form a hole, resulting in electrolyte leakage. When the loop current is 10 A, the evolution law of arc voltage and current is basically the same under different supply voltages, charges, and discharges. The accuracy of the battery arc simulation model is verified by comparing the simulation with the experimental results. The research in this paper provides a theoretical basis for the electrical safety design of lithium-ion batteries caused by the arc, fills the gaps in the field of battery system arc simulation, and is of great significance for improving the safety performance of arc protection.

Research on the synergistic effect of fluoroethylene carbonate and lithium difluoro(oxalato)borate in electrolyte on LiNi0.5Mn1.5O4-based high-voltage lithium-ion batteries

Research on the synergistic effect of fluoroethylene carbonate and lithium difluoro(oxalato)borate in electrolyte on LiNi0.5Mn1.5O4-based high-voltage lithium-ion batteries

Electrolyte Regulation in Stabilizing the Interface of a Cobalt-Free Layered Cathode for 4.8 V High-Voltage Lithium-Ion Batteries.

The cobalt-free layered oxide cathode of LiNi0.65Mn0.35O2 is promising for high-energy-density lithium-ion batteries (LIBs). However, under high-voltage conditions, severe side reactions between the Co-free cathode and electrolyte, as well as grain boundary cracks and pulverization of particles, hinder its practical applications. Herein, an electrolyte regulation strategy is proposed by adding fluoroethylene carbonate (FEC) and LiPO2F2 as electrolyte additives in carbonate-based electrolytes to address the above issues. As a result, a homogeneous and dense organic-inorganic hybrid cathode electrolyte interface (CEI) film is formed on the cathode surface. The CEI film consists of C-F, LiF, Li2CO3, and LixPOyFz species, which is proven to be highly conductive and effective in suppressing structure damage and alleviating the interfacial reactions between the cathode and electrolyte. With such a CEI film, the interfacial stability of the Co-free cathode and the high-voltage cycling performance of Li||LiNi0.65Mn0.35O2 are greatly improved. A reversible capacity of 155.1 mAh g-1 and a capacity retention of 81.3% over 150 cycles are attained at a 4.8 V charge cutoff voltage with the tamed electrolyte, whereas the cell without the additives only retains 76.1% capacity retention. Therefore, our work demonstrates the synergistic effect of FEC and LiPO2F2 in stabilizing the interface of Co-free cathode materials and provides an alternative strategy for the electrolyte design of high-voltage LIBs.

Tannic acid mediated coating of Al-Ti-oxide nanolayer on LiCoO2 cathode for high-voltage lithium-ion batteries

High-voltage LiCoO2 (LCO) satisfies the demand of high-energy lithium-ion batteries, but suffers adverse factors including structural irreversibility, micro-crack formation, active material erosion and electrode/electrolyte side reactions, which limits its electrochemical performance beyond 4.2 V. Here, we employed a surface coating method based on tannic acid (TA) pretreatment to vary the properties of LCO surface. The TA-mediated Al-Ti oxide (ATO) coating on LCO resulted in the interface doping of Al3+ and Ti4+ as well as the spinel phase transition layer, which inhibited the surface degradation and the structural instability. As a result, the obtained PLCO@ATO0.5% maintained 112 mAh g−1 after 600 cycles with a high voltage of 4.5 V. It also exhibited capacity retention of 80% after 100 cycles at 45 °C and the rate performance of 155 mAh g−1 at 10 C.

One-step calcination synthesis of interface-coherent crystallized and surface-passivated LiNi0.5Mn1.5O4 for high-voltage lithium-ion battery

One-step calcination synthesis of interface-coherent crystallized and surface-passivated LiNi0.5Mn1.5O4 for high-voltage lithium-ion battery

Eutectic Mixtures As Highly Concentrated and Molten Electrolytes with Nearly Single-Ion Conducting Behavior

Today's state-of-the-art liquid electrolytes in lithium ion batteries (LIBs) have a high ionic conductivity and good performance regarding their cycle life. (1) However, they pose a safety risk due to their high vapor pressures and low thermal stability. (1) Furthermore, due to the limited electrochemical stability of the solvent, liquid electrolytes are not suitable for the application in high-voltage LIBs. (2) Molten salts, also called ionic liquids (IL), or highly concentrated electrolytes (HCE) have high lithium ion concentrations, where nearly every solvent molecule is coordinated. Due to this, there are strong ion interactions and the formation of ion clusters that lead to an increased lithium ion transference number of >0.5. (3) Therefore, they can represent an alternative in the field of liquid electrolytes. Additionally, HCE exhibit a higher thermal and electrochemical stability compared to dilute electrolytes and can improve the cycle performance in lithium metal batteries. (4, 5)McOwen et al. reported the coordination of lithium ions and crystalline structures in HCE of the binary mixtures of ethylene carbonate (EC) and lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) with molar ratio up to 1:1. (6) Based on the concept of melting point depression as known from thermodynamics, room-temperature molten, highly concentrated electrolytes of a carbonate-based solvent with lithium sulfonyl imides were investigated. Instead of EC, the solvent pinacol carbonate (PIC) without acidic α-hydrogen atoms, but four bulky methyl groups was synthesized and used for eutectic mixtures, as the melting point of PIC is with 187 °C far above room-temperature. The physicochemical properties of these electrolytes are studied with respect to the different influence of lithium bis(fluorosulfonyl)imide and LiTFSI despite their same basic molecule structure. The focus will be on the electrochemical analysis by the means of the ionic conductivity, transference number and the electrochemical stability.In comparison to dilute liquid electrolytes the molten electrolytes show extremely high transference numbers, especially for the PIC-LiTFSI mixtures nearly a single-ion conducting behavior (0.9) is observed. This behavior can be explained by the formation of a 2D polymeric network within the HCE electrolyte as determined by crystallographic measurements in the solid state. Combined with the high electrochemical stability, a stable long-term cycling and dendrite suppression in symmetric lithium cells could be shown. Cycling in full cells with high-voltage cathode materials such as LiNi0.6Mn0.2Co0.2O2 (NMC622) or LiMn4O2 (LMO) against lithium metal anodes is applicable. References K. Xu, Chemical Reviews, 104(10), 4303–4417 (2004).J. Li, C. Ma, M. Chi, C. Liang and N. J. Dudney, Advanced Energy Materials, 5(4) (2015).K. M. Diederichsen, E. J. McShane and B. D. McCloskey, ACS ENERGY LETTERS, 2(11), 2563–2575 (2017).G. Jiang, F. Li, H. Wang, M. Wu, S. Qi, X. Liu, S. Yang and J. Ma, Small Struct., 2(5), 2000122 (2021).V. Nilsson, A. Kotronia, M. Lacey, K. Edstrom and P. Johansson, ACS Applied Energy Materials, 3(1), 200–207 (2020).D. W. McOwen, D. M. Seo, O. Borodin, J. Vatamanu, P. D. Boyle and W. A. Henderson, Energy & Environmental science, 7(1), 416–426 (2014).

Anionic Additive-Integrated Electrolyte Therapy: Enhancing High-Voltage Stability and Performance in Lithium-Ion Batteries

Significant endeavours have been undertaken to advance the development of eco-friendly, abundant, cost-effective, and high-performance cathode materials for lithium-ion batteries. Among the various contenders for next-generation energy storage systems, spinel LiNi0.5Mn1.5O4 has emerged as a leading high-voltage cathode candidate, owing to its aforementioned benefits. Nonetheless, the widespread adoption of LNMO-based lithium-ion batteries is substantially impeded by the electrochemical instability of conventional carbonate electrolytes above 4.5 V. High-voltage cycling of such batteries results in rapid capacity degradation and metal-ion dissolution from the LNMO electrode into the electrolyte, particularly at elevated temperatures, further causing deposition of metal-ions on anode electrode. Therefore, stabilizing the electrode/electrolyte interface is crucial to achieve improved electrochemical performance of the Li-ion cell at high voltages. The utilization of sacrificial electrolyte additives is regarded as a straightforward and efficacious method to accomplish this objective. These additives form a protective layer on the cathode surface, mitigating electrolyte decomposition and transition metal-ion dissolution and deposition on anode’s surface. Various additives facilitating high-voltage cathode materials have been documented, encompassing fluorides and sulfonates. However, borate salt-containing additives are particularly promising within this context.In the present study, we endeavour to elucidate the surface modifications transpiring on the electrode’s surface when minute quantities of borate-based salt are employed as an additive in the conventional EC:EMC electrolyte for high-voltage operation. We explored the impact of the additive salt in a standard LiPF6-EC/EMC base electrolyte on the discharge capacity and rate performance of the LiNi0.5Mn1.5O4/Graphite based Li-ion cell. The electrochemical behaviour, morphological behaviour, and electrode-electrolyte interphase layer stability on the electrode were meticulously examined using high-resolution transmission electron microscopy (HR-TEM), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). These characterisations conformed the presence of an electrode-electrolyte interface forming a thin-layer via the sacrificial decomposition of the utilised additive. The introduction of this salt exhibits favourable effects on enhancing the electrochemical performance of the LiNi0.5Mn1.5O4/Graphite in high-voltage lithium-ion batteries. Notably, the utilised additive excels in mitigating irreversible capacity loss and reducing cycling fade, as it preferentially decomposes and forms a conductive, protective film that impedes subsequent electrolyte decomposition, thereby substantially enhancing cell performance.

Ionic Liquids, Synthesized and Utilized by Greener Methods, for the Application in High-Voltage Lithium-Ion Batteries

Due to their high energy density and reliability, lithium-ion batteries (LIBs) are a crucial energy storage system for portable electronic devices, which has dominated the market for more than 30 years. To increase their energy density even more, it is imperative to replace the commonly employed cathode materials (such LiCoO2) with cathode materials that can operate at higher potentials, like LiNi0.5Mn1.5O4 (LNMO) working at 4.7V vs Li+/Li. However, standard electrolytes, typically containing carbonate-based solvents (e.g., LP30), are unstable at such high potentials and suffer from oxidation decomposition. To mitigate this problem, ionic liquids (ILs) have recently been proposed as an additive to them. Despite this, their application in industrial-scale is hindered by the high-cost and environmentally unfriendliness of their synthesis [1]. In this study, ILs containing oxalatoborate anions—known to form the so-called cathode-electrolyte interphase (CEI), a protective layer on the cathode surface [2]—have been obtained by using mostly water as solvent, to minimize the impact of the synthesis on the environment. Four different ILs have been synthesized: N-ethoxyethyl-N-methylpiperidinium bis(oxalato)borate (PIP1,2O2BOB), N-ethoxyethyl-N-methylpiperidinium difluoro(oxalate)borate (PIP1,2O2DFOB), N-propyl-N-methylpiperidinium bis(oxalato)borate (PIP1,3BOB) and N-propyl-N-methylpiperidinium difluoro(oxalate)borate (PIP1,3DFOB). All of them have been characterized by IR spectroscopy and thermal analysis (DSC and TGA). The thermal analyses highlighted that all the ILs are thermally stable up to 280°C. Furthermore, PIP1,2O2DFOB and PIP1,2O2BOB did not show any crystallization behavior even at sub-zero temperatures, but only a glass-transition (at -70 °C and -30 °C, respectively). The improved liquid property is related to the presence of an ether oxygen in the cation structure.The four ILs have been then used as the additive for LP30 at a concentration of 0.3M and the resulting mixtures have been tested in Li|LP30+IL|LNMO coin-cells at 1C (147 mA g-1) for over 150 charge/discharge cycles. The results obtained showed that the addition of the ILs to the electrolyte has ensured more stable charge/discharge cycles, with higher coulombic efficiency and improved discharge capacity retention especially in the case of BOB-based ILs, while Li|LP30|LNMO cells prepared as a reference failed after about 100 cycles. On the promise that the ILs play an important role at the surface of cathode, another approach has been tested: 3 wt% of IL has been added directly to the slurry during the preparation of LNMO electrodes. These IL-added electrodes have been tested in Li|LP30|LNMO+IL coin-cells. Remarkable improvements in the stabilities of the cells have been observed also in this case. In IL-added electrodes, the total amount of IL in the system is almost 40 times smaller than that used in LP30+IL mixtures as the electrolytes. These results show that presence of ILs closer to the electrode is crucial to obtain an improvement of the stabilities of high-voltage cathodes. The combination of greener synthesis and utilization is expected to enhance the sustainability of LIBs.[1] E. Simonetti, M. De Francesco, M. Bellusci, G. Kim, F. Wu, S. Passerini, G. B. Appetecchi, ChemSusChem, 2019, 12, 4946– 4952[2] A. Tsurumaki, M. Branchi, A. Rigano, R. Poiana, S. Panero, M.A. Navarra, Electrochimica Acta, 2019, 315, 17-23 Figure 1

Understanding the Development and Properties of SEI in Concentrated Aqueous Electrolytes Via Scanning Electrochemical Microscopy

Solid-electrolyte interphases (SEI) are essential to the stability of high voltage lithium-ion batteries (LIBs) where they act as a protective barrier that prevents electrolyte decomposition during charge-discharge and during storage of the energy. Within emerging water-in-salt electrolytes (WISE), the SEI are thought to play a similar role in preventing electrolyte decomposition and expanding the potential window.(1, 2) The SEI reported in WISE are derived from the electrolyte ions, producing inorganic SEI (e.g. LiF) of similar thickness to non-aqueous batteries.(1) Others suggest the superconcentrated regimes promote anion reduction and shift its reduction potential at similar or more positive potentials to hydrogen evolution. However, our knowledge on the SEI found in concentrated aqueous electrolytes and their properties remains quite limited. Furthermore, WISE full cells can access >1000 cycles at high rates, but their capacities and retention are still heavily lacking compared with commercial LIBs.(2) Improving our understanding of the WISE-based SEI formation process, its stabilization, and prevention of gas evolution are key to achieving higher performing aqueous batteries.Herein, we explore the use of advanced scanning electrochemical microscopy (SECM) methods(3) to characterize an SEI within a highly concentrated K(FSA)0.6(OTf)0.4 electrolyte. Focusing on a 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) composite electrode, we use both ex situ, approach curves as well as in situ single spot measurements to analyze SEI formation (Figure 1a). The approach curves were collected before and after galvanostatic cycling by using a three-electrode cell that could easily be converted between closed (cycling) and open-cell (SECM) measurements. After cycling, we observed passivating SEI structures with electron transfer rates comparable to those found in LIBs (Figure 1b). At the same time, our results indicated the SEI deposition was discontinuous with some regions showing reactivity comparable to an uncycled electrode. We noted an increase in roughness with cycling, which could produce some of the more reactive regions exposed at the electrode surface. Thereafter, we conducted in situ measurements at a constant distance from the PTCDI surface.(4) During the first cycle, we observed a reversible/transient decrease in the feedback current at ~ -0.7 V vs. Ag/AgCl, far positive to H2 evolution (Figure 1c,d). In addition, more stable passivation was observed when the PTCDI electrode reached more negative potentials accessing the second redox process of PTCDI (Figure 1c,e). As the electrode reached potentials more negative to -1.3 V, we observed significant hydrogen evolution. Our results were further confirmed with operando electrochemical mass spectrometry (OEMS). OEMS showed similar potentials for evolving hydrogen as well as the evolution of other gases indicative of SEI formation. In all, our interfacial SECM analyses combined with traditional battery measurements and OEMS provides direct quantification of the passivating properties of the SEI as well as identification of local and bulk gas evolution that can be expanded for other emerging aqueous systems.References1 L. Suo, et al., Science, 2015, 350, 938-943.2 L. Droguet, et al., Adv. Energy Mater., 2020, 10, 2002440.3 Gossage, Z.T., et al., "Application to Batteries and Fuel Cells." Scanning Electrochemical Microscopy. CRC Press, 2022. 481-512.4 G. Zampardi, et al., RSC Advances, 2015, 5, 31166-31171. Figure 1

Liquid Structure and Anti-Corrosion Effect of Super-Concentrated Electrolyte Solution

For realizing sustainable world, Lithium-ion batteries are required to have higher energy density. Aluminum metal have been dominantly used as a current collector of positive electrode. A mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) containing 1 mol dm-3 Lithium hexafluorophosphate (LiPF6) has been used as an electrolyte solution. Aluminum forms thin passivation layer on its surface, preventing the corrosion. However, aluminum corrosion may occur due to this electrolyte solution under high voltage condition. Recently, super-concentrated electrolyte solution (SCES) [1], which consists of only two or three times as much solvent as lithium salt, has been attracting attention as a new electrolyte solution of high-voltage lithium-ion battery. Motsumoto et al. proposed that aluminum corrosion was remarkably suppressed in lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-based SCES [2]. To clarify the corrosion-inhibiting factor of SCES, we investigated aluminum corrosion in the several lithium salts based SCESs [3]. And we found that lithium perchlorate (LiClO4)-based SCES could suppress corrosion of Aluminum current collector. Liquid structure of the SCES may plays an important role in corrosion suppression. In the present work, we demonstrated Raman spectroscopy and Quantum chemical calculations to reveal the liquid structure of the LiClO4-based SCES.The LiClO4 based SCES was prepared by dissolving LiClO4 into DMC as the molar ratio of 1 : 2. For comparison, DMC solution containing 1 mol dm-3 LiClO4 and neat DMC was also prepared. Raman spectroscopic experiments were conducted using Laser Raman spectrophotometer (NRS-5100, JASCO) installed a laser at 532 nm. Quantum calculations were performed using the Gaussion 9 program suite (Gaussian, USA). Geometry optimization were conducted at the B3LYP/6-311+G(d,p) level. An intensive peak is observed at approximately 915 cm-1 for neat DMC. When a small amount of LiClO4 is added to DMC (corresponding to 1 mol dm-3 LiClO4 solution), new peak is observed at approximately 932 cm-1. This peak can be assigned to ClO4 - anion. A new peak appears at approximately 950 cm-1 with increasing LiClO4 (corresponding to the SCES). According to the Quantum calculations, the new peak is assigned to aggregate in which the ClO4 - cross-links Li+. In addition, HOMO energy of a contact ion pair (CIP), in which ClO4 - coordinates to Li+, is lower than that of free ClO4 - anion. The oxidative stability of ClO4 - increases by forming CIP and aggregate. The decomposition products of ClO4 - may affect the Aluminum corrosion. The high oxidative stability of LiClO4-based SCES may prevent the Aluminum corrosion.

Rationally designing electrolyte additives for highly improving cyclability of LiNi0.5Mn1.5O4/Graphite cells

High voltage is necessary for high energy lithium-ion batteries but difficult to achieve because of the highly deteriorated cyclability of the batteries. A novel strategy is developed to extend cyclability of a high voltage lithium-ion battery, LiNi0.5Mn1.5O4/Graphite (LNMO/Graphite) cell, which emphasizes a rational design of an electrolyte additive that can effectively construct protective interphases on anode and cathode and highly eliminate the effect of hydrogen fluoride (HF). 5-Trifluoromethylpyridine-trimethyl lithium borate (LTFMP-TMB), is synthesized, featuring with multi-functionalities. Its anion TFMP-TMB− tends to be enriched on cathode and can be preferentially oxidized yielding TMB and radical TFMP.. Both TMB and radical TFMP. can combine HF and thus eliminate the detrimental effect of HF on cathode, while the TMB dragged on cathode thus takes a preferential oxidation and constructs a protective cathode interphase. On the other hand, LTFMP-TMB is preferentially reduced on anode and constructs a protective anode interphase. Consequently, a small amount of LTFMP-TMB (0.2%) in 1.0 M LiPF6 in EC/DEC/EMC (3/2/5, wt%) results in a highly improved cyclability of LNMO/Graphite cell, with the capacity retention enhanced from 52% to 80% after 150 cycles at 0.5 C between 3.5 and 4.8 V. The as-developed strategy provides a model of designing electrolyte additives for improving cyclability of high voltage batteries.