Understanding Of Working Mechanism Of Lithium Difluoro Oxalato Borate In Li Ncm85 Battery With Enhanced Cyclic Stability

Understanding of working mechanism of lithium difluoro(oxalato) borate in Li||NCM85 battery with enhanced cyclic stability

Despite the significant advances achieved in recent years, the development of efficient electrolyte additives to mitigate the performance degradation during long-term cycling of high-energy density lithium||nickel-rich (Li||Ni-rich) batteries remains a significant challenge. To achieve a rational design of electrolytes and avoid unnecessary waste of resources due to trial and error, it is crucial to have a comprehensive understanding of the underlying mechanism of key electrolyte components, including salts, solvents, and additives. Herein, we present the utilization of lithium difluoro(oxalate) borate (B) (LiDFOB), a B-containing lithium salt, as a functional additive for Li||LiNi0.85Co0.1Mn0.05O2 (NCM85) batteries, and comprehensively investigate its mechanism of action towards enhancing the stability of both anode and cathode interfaces. The preferential reduction and oxidation decomposition of DFOB- leads to the formation of a robust and highly electronically insulating boron-rich interfacial film on the surface of both the Li anode and NCM85 cathode. This film effectively suppresses the consumption of active lithium and the severe decomposition of the electrolyte. Furthermore, the presence of B elements in the cathode-electrolyte interfacial film, such as BF3, BF2OH, and BF2OBF2 compounds, can coordinate with the lattice oxygen of the cathode, forming strong coordination bonds. This can significantly alleviate lattice oxygen loss and mitigate detrimental structural degradation of the Ni-rich cathode. Consequently, the Li||NCM85 battery cycled in LiDFOB-containing electrolyte displays superior capacity retention of 74% after 300 cycles, even at a high charge cut-off voltage of 4.6 V. The comprehensive analysis of the working mechanisms of LiDFOB offers valuable insights for the rational design of electrolytes featuring multifunctional lithium salts or additives for high energy density lithium metal batteries.

Increased Cycling Performance of Li-ion Batteries by Phosphoric Acid Modified LiNi0.5Mn1.5O4 Cathodes in the Presence of Lithium Bis(oxalato)borate

Mechanisms of Discharge Product Evolution and Solvent Stability in Lithium-oxygen Batteries

Lithium-oxygen batteries offer the possibility of achieving twice the gravimetric energy density of lithium-ion batteries. However, several challenges remain to achieve commercially-available lithium-oxygen batteries. Capacity must be optimized by maximizing the formation of Li2O2 discharge product. Side reactions with the solvent and electrode must be suppressed. This study seeks to improve understanding of the mechanisms of Li2O2 evolution and Li-O2 decomposition reactions in order to design strategies to optimize capacity and stability. Decomposition reactions in the solvent dimethyl sulfoxide were studied due to conflicting reports about its stability. Discharged electrodes in dimethyl sulfoxide were aged for varying amounts of time then characterized. Li2O2 reacted with dimethyl sulfoxide to form LiOH and dimethyl sulfone. This demonstrated that dimethyl sulfoxide is unsuitable for commercial application. The study also illustrated the importance of performing aging studies in the discharged condition to determine the stability of Li-O2 battery components. Adding small amounts of water to Li-O2 solvents has been demonstrated to enhance capacity but the effect on stability was not well understood. Discharges were performed in dimethoxyethane and acetonitrile with and without added water. Water caused an unwanted side reaction to form LiOH in acetonitrile but not in dimethoxyethane, due to a higher favorability of deprotonation in acetonitrile. Interactions between capacity enhancing additives and solvent molecules must be carefully studied to avoid side reactions. A model of the two competing mechanistic pathways of Li-O2 discharge was developed to understand how these pathways depend on discharge conditions and solvent properties. The model was fitted to experimental results from rotating ring-disk electrode discharges in order to check that model assumptions were physical. The model demonstrates that Li2O2 film evolution is heavily dependent on solvent properties and that promotion of toroidal Li2O2 primarily depends on slower surface passivation rather than faster solvation of lithium superoxide.