Anion-Acceptor Electrolyte Additive Strategy for Optimizing Electrolyte Solvation Characteristics and Electrode Electrolyte Interphases for Li||NCM811 Battery

Abstract

Metallic lithium (Li) offers Li metal batteries (LMBs) with an opportunity to meet the high-energy demand in many fields. At present, the main cathode materials used for high-energy-density batteries are nickel-rich layered oxides, including nickel cobalt lithium manganese oxides (NCM) with intercalation chemistry. According to this plan, NMC811 demonstrates great merits in this aspect. However, there are still many problems with Li metal anode. The failure of Li anode is mainly caused by the high reactivity of Li metal, which can cause irreversible continuous reactions between Li and electrolyte to shorten cycling life. Due to multiple electroplating and stripping processes, Li anode undergoes significant volume and morphology change, increasing side reactions and the growth of Li dendrites caused by the first two factors. Electrolyte engineering, as a simple and effective modification method, can effectively solve the above problems. Among them, using electrolyte additives is a simple, efficient, and economical electrolyte engineering strategy. Herein, we proposed an anion acceptor electrolyte additive strategy for optimizing the component/structural characteristics of solid/cathode electrolyte interphases to inhibit the growth of Li dendrites and Li⁺ transition on cathode surface for enhancing cycling and rate performance of Li||NCM811 battery, which is also ascribed to the regulation of Li⁺ solvation structure by hexafluorobenzene (HFBen) to realizing the stability of PF₆⁻ and the conductivity enhancement of electrolyte. As expected, Li||Li cells with 1% (wt) HFBen-contained electrolyte could achieve a stable cycling above 400 h at 1 mA·cm⁻², and the capacity retention rate of Li||NCM811 battery could reach 75% after 100 cycles at 200 mA·g⁻¹. Finally, the cycling and rate performance of Li||NMC811 batteries were significantly enhanced at 4.5 V with the help of HFBen. This work demonstrates that HFBen as an additive can effectively improve the electrochemical performance of LMBs. Moreover, the interfacial reaction mechanism across the batterywas analyzed and studied. This study provides new insights for the interface reaction between electrolyte and Li anode.

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