High-voltage Cathode Materials Research Articles

Improving electrochemical performance of spinel-type Ni/Mn-based high-voltage cathode material for lithium-ion batteries via La-F co-doping combined with in-situ integrated perovskite LaMnO3 coating layer

Spinel-type LiNi0.5Mn1.5O4 (LNMO) can provide high-voltage and high theoretical specific capacity as cathode material for lithium-ion batteries (LIBs), thereby LNMO is particularly suitable for electric/hybrid electric vehicles that require high power. Unfortunately, both serious structural deformation derived from the Jahn-Teller effect of Mn3+ and decomposition of electrolyte during repetitive charge/discharge processes at high operating potential result in fast capacity fade. In this work, lanthanum and fluorine co-doping LiNi0.5La0.01Mn1.49O3.97F0.03 (LF-LNMO) is proposed to eliminate its inherent defects. Fluorine can suppress Jahn-Teller effect of Mn3+ by reducing the generation of Mn3+; La3+ ions in LF-LNMO play a role in solidly riveting atoms together in the structure, and LaMnO3 coating layer acts as a physical protection barrier suppressing adverse side reactions that may damage battery performance. Thanks to the synergistic effect derived from structural modification of F−, the pinning effect of La3+ ions, and LaMnO3 surface coating interface reconstruction, the LF-LNMO cathode provides the best cycling performance and rate performance among all investigated electrode materials. Such as, LF-LNMO cathode can provide 64.02% capacity retention after the 1000th cycle at 500 mA g−1 and 30 °C, which is much higher than that (25.56%) of the undoped LiNi0.5Mn1.5O4 (P-LNMO). Besides, LF-LNMO electrode also behaves the excellent high-temperature cycling performance. This work provides a new strategy enhancing structural stability of spinel-type Ni/Mn-based oxide and would motivate us to further devise and prepare high power cathode materials for LIBs.

Unlocking the concentration polarization for Solid-State lithium metal batteries

Ceramic-polymer composite electrolytes for solid-state batteries are promising candidates due to the combination of safe reliability and mechanical flexibility. However, the sluggish lithium-ion transport and the inadequate electrochemical stability with high-voltage cathode materials limit the practical applications. Herein, we report a garnet-polymer solid electrolyte with high ionic conductivity and Li-ion transference number, favorable elasticity and good interface stability. A galvanostatic charge-relaxation process is designed to identify the inhibition effect of high Li-ionic transference number on concentration polarization and reveal its proportion to total polarization. By additionally adding lithium difluoro(oxalato)borate as stabilizer, the electrochemical window of the garnet-polymer composite electrolyte can extend to 5.3 V. The high cation conductivity and excellent antioxidant ability of composite electrolyte contribute to long cycling performance of LiNi0.8Mn0.1Co0.1O2 cathode at threshold voltage of 4.4 V. Furthermore, the pouch cell with high mass loading cathode and limited lithium anode was demonstrated successfully. Our findings provide an effective strategy on fabricating solid-state lithium-metal batteries towards practical applications.

A bimetal strategy for suppressing oxygen release of 4.6V high-voltage single-crystal high-nickel cathode

High-voltage cathode materials, such as single-crystal high-nickel layered oxide materials, are a necessary condition for achieving high energy density lithium-ion batteries, but they have to be accompanied by the structural instability and irreversible release of lattice oxygen during operation, posing serious safety hazards. Here, to solve the lattice oxygen release issue of single-crystal high-nickel cathode, we propose an improved strategy for overall cathode by synchronously addressing interface and lattice instability, ensuring stable operation at a high voltage up to 4.6 V. By Al-doping, in the bulk phase, we intensify the charge transfer between transition metals and oxygen, and the columnar effect caused by doped atoms effectively alleviates internal strain, thereby significantly limiting lattice shrinkage and then suppressing oxygen release. On the other hand, the protective layer of LiNbO3 as the fast ion conductor formed at the cathode interface suppresses parasitic reactions and hinders lattice oxygen loss caused by dissolution of transition metals. Therefore, after 200 cycles at a cut-off voltage of 4.6 V, our cathode material still maintains a capacity retention rate of 89.1%. Density functional theory (DFT) calculations predict the effective suppression of oxygen release for the modified cathode materials, which has been further confirmed by differential electrochemical mass spectrometry (DEMS) tests. This work provides a new perspective for solving the problem of oxygen release under high cut-off voltage conditions for single crystal high nickel cathode.

A High-Voltage Cathode Material with Ultralong Cycle Performance for Sodium-Ion Batteries.

Vanadium-based polyanionic materials are promising electrode materials for sodium-ion batteries (SIBs) due to their outstanding advantages such as high voltage, acceptable specific capacity, excellent structural reversibility, good thermal stability, etc. Polyanionic compounds, moreover, can exhibit excellent multiplicity performance as well as good cycling stability after well-designed carbon covering and bulk-phase doping and thus have attracted the attention of multiple researchers in recent years. In this paper, after the modification of carbon capping and bulk-phase nitrogen doping, compared to pristine Na3 V2 (PO4 )3 , the well optimized Na3 V(PO3 )3 N/C possesses improved electromagnetic induction strength and structural stability, therefore exhibits exceptional cycling capability of 96.11% after 500 cycles at 2C (1C=80mAg-1 ) with an elevated voltage platform of 4V (vs Na+ /Na). Meanwhile, the designed Na3 V(PO3 )3 N/C possesses an exceptionally low volume change of ≈0.12% during cycling, demonstrating its quasi-zero strain property, ensuring an impressive capacity retention of 70.26% after 10,000 cycles at 2C. This work provides a facial and cost-effective synthesis method to obtain stable vanadium-based phosphate materials and highlights the enhanced electrochemical properties through the strategy of carbon rapping and bulk-phase nitrogen doping.

A High‐Voltage Solid State Electrolyte Based on Spinel‐Like Chloride Made of Low‐Cost and Abundant Resources

AbstractRecently, halide solid state electrolytes (SSEs) have received great attention owing to their fast ionic conductivity, high oxidation potential, and good chemical and electrochemical compatibility with high voltage cathode materials. However, most of reported halide SSEs contain rather rare and expensive elements, which hinders their sustainable utilizations in practical batteries. Here in this work, under the guidance of systematic modelling based on the density functional theory (DFT), a low‐cost alternative is developed through optimizing the lattice chemistry in a recently identified spinel‐like chloride Li2CrCl4 into Li5/3Cr1/3Zr1/3Cl4 for remarkably enhanced ionic conductivity and stable electrochemical window with respect to the Li‐anode. This new phase has then been synthesized successfully, delivering an ionic conductivity over 1200 times of that of the pristine phase Li2CrCl4, in addition to a high oxidation potential (up to 4.1 V vs Li/Li+) to enable outstanding interfacial compatibility with high voltage cathodes. Such a high‐voltage and fast Li‐ion conducting solid‐state electrolyte is expected to provide a highly desirable basis toward developing high energy‐density all solid‐state batteries (ASSBs) using economical and Earth‐rich elements.

In Situ Construction of a Polymer Coating Layer on the LiNi0.8Co0.1Mn0.1O2 Cathode for High-Performance Lithium-Ion Batteries.

Lithium-ion batteries (LIBs) are known for their high energy density but exhibit poor cyclic stability and safety risks due to side reactions between the electrode and electrolyte. To address these issues, a novel approach involving construction of a polymer coating layer (PCL) via in situ self-polymerization using 2,2,3,4,4,4-hexafluorobutyl methacrylate (HFBM) as an electrolyte additive on the cathode is proposed. The PCL endows the electrolyte with a high onset oxidation potential (4.78 V) and lithium-ion transference number (0.52). The uniform and robust in situ constructed PCL can effectively inhibit the severe irreversible side reactions and suppress harmful reactions, thus providing a protective barrier against degradation. The resulting Li||LiNi0.8Co0.1Mn0.1O2 batteries exhibit an improved discharge capacity retention of 80% at 1C over 100 cycles. These results demonstrate that the in situ self-polymerization strategy holds promising potential for enhancing LIB performance and long-term stability, especially when high-voltage cathode materials are used.

9-Vinyl-9H-carbazole-3,6-dicarbonitrile

Carbazole polymers attract significant attention as promising luminophores, organic electronic and photovoltaic materials, photo/electrocatalysts, energy storage materials, redox mediators and catalysts. However, the oxidation potential of the commercially available poly(vinylcarbazole) is insufficient for some applications such as high-voltage Li-Ion batteries. We have proposed a monomer for the novel polycarbazole with an increased oxidation potential, which will be compatible with high-voltage cathode materials for Li-Ion. In addition, the proposed polymer is an interesting substrate for the further carbonization to obtain N-doped carbons with a high electrocatalytic activity level.

Protective Al2O3 Thin Film Coating by ALD to Enhance the Anodic Stability of Metallic Current Collectors in Ethereal Mg Electrolyte Solutions

Rechargeable magnesium batteries (RMBs) have the potential to contribute towards alternative energy storage due to their low cost, high abundance, dendrites free deposition of Mg and high volumetric energy density. Organometallic complex-based electrolytes in ethereal solutions have been extensively studied in the context of RMBs due to their ability to facilitate highly reversible magnesium deposition in rechargeable magnesium batteries, while demonstrating wide enough electrochemical stability windows. However, these solutions containing unique mixture of organo-halo aluminate complexes have detrimental effect on the anodic stability of metallic current collectors for cathodes, like Ni and Al foils. In this work, we were able to synthesize and isolate Mg2Cl3(THF)6Ph2AlCl2/THF electrolyte as the sole electroactive species using simple precursors: Ph2AlCl and MgCl2 in THF, via atom efficient mono-chloro abstraction Schlenk technique. We characterized the anodic stability of Ni, Ni@C, Al, and Al@C current collectors by monitoring their electrochemical behavior. In addition, we investigated the anodic stability enhancement of various current collectors by Al2O3 thin films coating using Atomic Layer Deposition (ALD). Linear sweep voltametric studies showed that coating current collectors enhanced the oxidative stability of Al and Ni foils by 0.1–0.3 V vs Mg/Mg2+ compared to the uncoated foils. In particular, Al2O3 coated Al@C showed an improved oxidative stability of 2.8 V vs Mg/Mg2+. Our findings show that current collectors protection by ALD coating can help in long-term stability and improving RMBs’ energy density by using high voltage cathode materials, a crucial step in developing practical rechargeable Mg batteries.

Low-strain layered Zn0.56VOPO4∙2H2O as a high-voltage and long-lifespan cathode material for Zn-ion batteries

Rechargeable aqueous zinc-ion batteries (ZIBs) have been regarded as a potential competitor in grid-scale energy storage scenarios due to the merits of high safety, easy manufacturing and cost-efficiency. However, the lack of suitable robust hosts to accommodate Zn2+ with high electrostatic repulsion remains the major obstacle to the development of ZIBs. The exploration of low-strain Zn-storage cathode materials is a critical strategy to address the challenges. In this work, we developed a layered phyllo-oxovanadophosphate Zn0.56VOPO4∙2H2O as a structurally stable cathode material for the first time. Benefiting from the "inductive effect" of strong P–O covalent bonds and the single-phase reaction mechanism with tiny lattice volume distortion of 1.9%, the Zn0.56VOPO4∙2H2O cathode manifests a high operating voltage of 1.46 V and ultralong cycle life (capacity retention of 70.5% after 8000 cycles). Importantly, the versatility and practicability of this layered cathode is verified in both "rocking-chair" ZIBs and anode-free ZIBs, all of which demonstrate outstanding cycling performance. The low-strain structural superiority and prominent electrochemical performance are expected to inspire more efforts in the research of Zn-storage polyanionic cathode materials and revitalize the development of rechargeable ZIBs towards energy storage applications.

Low-Dimensional Vanadium-Based High-Voltage Cathode Materials for Promising Rechargeable Alkali-Ion Batteries.

Owing to their rich structural chemistry and unique electrochemical properties, vanadium-based materials, especially the low-dimensional ones, are showing promising applications in energy storage and conversion. In this invited review, low-dimensional vanadium-based materials (including 0D, 1D, and 2D nanostructures of vanadium-containing oxides, polyanions, and mixed-polyanions) and their emerging applications in advanced alkali-metal-ion batteries (e.g., Li-ion, Na-ion, and K-ion batteries) are systematically summarized. Future development trends, challenges, solutions, and perspectives are discussed and proposed. Mechanisms and new insights are also given for the development of advanced vanadium-based materials in high-performance energy storage and conversion.

NASICON-Type Na3V1.5Cr0.4Fe0.1(PO4)3: High-Voltage and High-Rate Cathode Materials for Sodium-Ion Batteries.

Cationic alteration related to a sodium super ion conductor (NASICON)-structured Na3V2(PO4)3 (NVP) is an effective strategy for formulating high-energy and stable cathodes for sodium-ion batteries (SIBs). In this study, we altered the structure of NVP with dual cations, namely, Cr and Fe, to develop Na3V1.5Cr0.4Fe0.1(PO4)3 cathodes for SIBs with high-rate capability (∼71 mAh g-1 at 100 C) and an extreme cycle life output (∼75 mAh g-1 with 95% capacity retention for 10,000 cycles). These excellent electrochemical properties can be ascribed to the synergistic effects of Cr and Fe in the NVP structure, as verified experimentally and theoretically. Therefore, the proposed cosubstitution method can enhance the performance of SIBs by improving their structural stability, electronic conductivity, and phase-change behavior.

Understanding the role of TiO2 coating for stabilizing 4.6V high-voltage LiCoO2 cathode materials

TiO2 surface coating is considered to be an effective strategy for improving the cycling performance of commercially available high voltage LiCoO2 (HV-LCO) batteries. However, the mechanism underlying the TiO2 coating remains ambiguous due to the synergy of solid-state coating and annealing processes. In this work, the effects of TiO2 were systematically studied for 4.6 V HV-LCO batteries. The results showed that the coated TiO2 can be transformed into LiTiO2-rich layer, which can reduce surface residual lithium (SRL), lower the formation of Co3O4 and LiF-rich cathode electrolyte interphase (CEI) layer. Moreover, the annealed sample delivered improved surface texture, reduced specific surface area, and lower SRL, which was beneficial to improve the rate capability and cyclic performance. However, the LCO after annealing and coating exhibited weak static oxygen stability at high voltage due to the change in bulk Li/Co stoichiometry, leading to higher gas production. This work provides new insights into the effects of metal oxide coating and sheds light on the commercial process for HV-LCO.

Trilithium salt of tetrahydroxyanthraquinone: A high-voltage and stable organic cathode material for rechargeable lithium metal and lithium-ion batteries

Organic cathode materials (OCMs) have drawn considerable attention for lithium batteries but suffer from unfavorable dissolution problem and thus inferior cycling performance. Salification is a simple approach to restrain the dissolution but most reported lithium-salt-type OCMs are still unable to achieve good cycling stability due to poorly conjugated and/or asymmetric structure. Herein, we report a novel air-stable, largely conjugated, and symmetric organic lithium salt synthesized from 1,4,5,8-tetrahydroxyanthraquinone (THAQ), namely Li3THAQ. It possesses a layered crystalline structure with large interlayer spacings, which is relatively stable in the reversible conversion between Li4THAQ and Li2THAQ. Benefiting from this, Li3THAQ exhibits exceptional electrochemical performance within 2.0–3.6 V, including high reversible capacity (192 mAh g−1), high discharge potential (2.93 V vs. Li+/Li), high rate capability (75 % capacity retention at 5000 mAh g−1 vs. 50 mAh g−1), and high cycling stability (95 % capacity retention after 500 cycles). Additionally, it can be also matched with natural graphite anode to construct a Li-ion full-cell, which was rarely reported for OCMs. In brief, Li3THAQ shows great advantages in structure stability, electrochemical performance, and practicability compared to its counterparts, and the in-depth mechanism understanding provides important insights into the development of lithium-salt-type OCMs.

Electrochemical Reactivity and Passivation of Organic Electrolytes at spinel MgCrMnO4 Cathode Interfaces for Rechargeable High Voltage Magnesium-Ion Battery

Magnesium transition metal oxides such as MgCr2-xMnXO4 are the promising high-voltage and high-capacity cathode materials for rechargeable magnesium batteries (RMB). Understanding and improving the chemical and electrochemical stability of the...

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).

Chemical and Electrochemical Interaction of Halide and Sulfide-Based Electrolytes in Solid-State Batteries

Introduction Conventional lithium-ion batteries (LIBs) have found widespread small and large applications. However, safety issues and capacity degradation of the cells, in general, can occur due to the use of toxic and flammable liquid electrolytes [1]. As one of the next-generation LIBs, solid-state lithium batteries (SSBs) have the potential to replace liquid electrolyte LIBs due to their safety and potentially high energy density [2]. The key component of SSBs is the solid-state electrolyte (SSE). Sulfide and halide-based solid electrolytes are among the hot topics in solid electrolyte research for SSBs. Despite the advantages of solid electrolytes, such as good compatibility with high-voltage cathode materials and soft fabrication. However, the poor chemical and electrochemical stability of sulfide and halide-based solid electrolytes towards Li metal has a critical problem that causes the degradation of the lithium/solid electrolyte interface due to the formation of side reaction components that leads to inhibiting lithium kinetics [3]. Results and Discussion Here, we have shown that a combination of halide and argyrodite (Li6PS5Cl) solid electrolytes can lead to the prevention of the formation of unfavorable interactions between solid electrolytes and lithium metal anode. The combination of halide and argyrodite (Li6PS5Cl) in the Li/Li symmetric cell can stabilize cycle life and increase the high critical current density (CCD) from C/20 to C/2 in comparison with the pure halide and argyrodite electrolytes. Furthermore, compared to the original halide and argyrodite electrolytes, a high initial coulombic efficiency and cycle life can be maintained when combined with a full Li/NCM cell. This approach to improving halide-based SSBs can provide a fairly simple and efficient strategy. Acknowledgements This project has received funding from the European Union's Horizon Europe programme for research and innovation under grant agreement No. 101069681 (HELENA project).

Interface Modification of LATP-Based Solid-State Li Metal Batteries Using Composite Polymer Electrolyte and Li-in Alloy

NASICON-type Li1.3Al0.3Ti1.7(PO4)3 (LATP) solid electrolyte attracts attention because of its stability in the air and water and its chemical stability with high-voltage cathode materials. However, LATP solid electrolyte has interfacial problems, such as limited contact area. Additionally, Li/LATP interface is deteriorated by structural collapse due to its reduction products. Herein, we modified the electrode interface using PEO based protecting layer (PL) and Li-In alloy anode. PEO based protecting layer (PL) was applied to suppress the Li/LATP interface side reactions and minimize the LiFePO4 (LFP) /LATP interfacial resistance. We applied two kinds of PLs, solid polymer electrolyte (SPE) and composite polymer electrolyte (CPE). A CPE was prepared using a ceramic filler of LLZTO in order to improve the ionic conductivity and long-term cycling stability of PL. As an anode material Li foil and In1.5Li foil were utilized. The symmetric and full cells were prepared with a PL coated on both sides of the electrolyte. The symmetric cell consisted of Li/PL/LATP/PL/Li and the full cell consisted of Li (or In1.5Li) /PL/LATP/PL/LFP. The symmetric cell and full cell with CPE exhibited stable cycling performance, compared to that with SPE. The symmetric cell utilizing In1.5Li foil showed higher overpotential during the initial cycles, but it showed improved cycling stability, compared to that with Li metal foil. XRD and TOF-SIMS results indicate that there were no structural and chemical changes in the LATP coated with PL. Therefore, the modification strategies of CPE protecting layer and Li-In alloy anode are effective for enhancing cycling performance in all-solid-state batteries.

Towards Extreme Fast Charging of 4.6 V LiCoO2 Viamitigating High-Voltage Kinetic Hindrance

High-voltage LiCoO2 (LCO) is an attractive cathode for ultra-high energy density lithium-ion batteries (LIBs) in the 3 C markets. However, the sluggish lithium-ion diffusion at high voltage significantly hampers its rate capability. Herein, combining experiments with density functional theory (DFT) calculations, we demonstrate that the kinetic limitations can be mitigated by a facial Mg2++Gd3+ co-doping method. The as-prepared LCO shows significantly enhanced Li-ion diffusion mobility at high voltage, making more homogenous Li-ion de/intercalation at a high-rate charge/discharge process. The homogeneity enables the structural stability of LCO at a high-rate current density, inhibiting stress accumulation and irreversible phase transition. When used in combination with a Li metal anode, the doped LCO shows an extreme fast charging (XFC) capability, with a superior high capacity of 193.1 mAh g−1 even at the current density of 20 C and high-rate capacity retention of 91.3% after 100 cycles at 5 C. This work provides a new insight to prepare XFC high-voltage LCO cathode materials. Figure 1

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.

Trifluoroacetamide-Based Eutectic Electrolyte with High Oxidative Stability

Recently, the development of batteries with high energy densities is strongly expected due to the downsizing of electronic devices and the popularization of electric vehicles. The highly concentrated eutectic electrolyte has been recognized as a promising candidate of electrolyte for the next generation batteries. Various compounds such as ether, sulfolane, acetonitrile, and others have been studied as solvents for eutectic electrolytes. Some kinds of amide-based eutectic electrolytes have been also reported so far, whereas their oxidation stability is insufficient for application as electrolytes for the high-voltage cathode materials in lithium-ion batteries. In the present study, to improve the oxidation stability of amide-based eutectic electrolytes, we have prepared trifluoroacetamide-based eutectic electrolytes with lithium bis(fluorolsulfonyl)amide (LiFSA) and investigated their solution structure, physicochemical properties, and the potential for the electrolytes. Eutectic electrolyte composed of LiFSA and N-methyltrifluoroacetamide (MTFAA) at a molar ratio of 1:1.5 exhibited the reversible deposition and dissolution of lithium and very high electrochemical oxidation stability. We have also demonstrated the stable charge/discharge cycling of a high-voltage Li metal battery with a 5 V-class LiNi0.5Mn1.5O4 cathode using the electrolyte.