Manipulated Fluoro-Ether Derived Nucleophilic Decomposition Products for Mitigating Polarization-Induced Capacity Loss in Li-Rich Layered Cathode.

Electrolyte engineering is a fascinating choice to improve the performance of Li-rich layered oxide cathodes (LRLO) for high-energy lithium-ion batteries. However, many existing electrolyte designs and adjustment principles tend to overlook the unique challenges posed by LRLO, particularly the nucleophilic attack. Here, we introduce an electrolyte modification by locally replacing carbonate solvents in traditional electrolytes with a fluoro-ether. By benefit of the decomposition of fluoro-ether under nucleophilic O-related attacks, which delivers an excellent passivation layer with LiF and polymers, possessing rigidity and flexibility on the LRLO surface. More importantly, the fluoro-ether acts as "sutures", ensuring the integrity and stability of both interfacial and bulk structures, which contributed to suppressing severe polarization and enhancing the cycling capacity retention from 39 % to 78 % after 300 cycles for the 4.8 V-class LRLO. This key electrolyte strategy with comprehensive analysis, provides new insights into addressing nucleophilic challenge for high-energy anionic redox related cathode systems.

Functional Localized High-Concentration Ether-Based Electrolyte for Stabilizing High-Voltage Lithium-Metal Battery.

Localized high-concentration electrolytes have attracted much attention of researchers due to their low viscosity, low cost, and relatively higher electrochemical performance than their low-concentration counterparts. In our work, 1.5 M (mol L-1) locally concentrated ether-based electrolyte has been obtained by adding 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE) into a 4 M LiFSI concentrated dimethoxyethane (DME)-based electrolyte. The optimal ratio is determined by density functional theory (DFT) calculation and experimental combination, and finally, DH(3/5)-1.5M-LiFSI (DME/HFE = 3:5 by volume) is obtained. The electrolyte not only has relatively good physical properties such as low viscosity and high conductivity but also shows decent electrochemical performance. Li∥Cu half-cells can maintain a coulombic efficiency of no less than 99% after circulating for 250 cycles under the condition of 1 mA cm-2 current density and 1 mAh cm-2 lithium deposition for each cycle, and the stable battery polarization voltage was about 50 mV. Furthermore, 0.15 M lithium trifluoromethyl acetate (LiCO2CF3) has been added as an additive to enhance the oxidation stability. The new electrolyte DH(3/5)-1.65M-LiFC (LiFC/LiFSI + LiCO2CF3) makes Li||NCM523 batteries maintain about 83% capacity after cycling for 250 times with a 0.5 C charge current density and a 1 C discharge current density of 160 mAh g-1 when charged to 4.3 V. Furthermore, this new additive has a little negative effect on the Li||Cu half-cell performance under the same condition as before, indicating this new type of localized high-concentration DME-based electrolyte benefits both high-voltage cathode and lithium-metal anode.