Research Progress and Prospect on Electrolyte Additives for Interface Reconstruction of Long-Life Ni-Rich Lithium Batteries

Abstract: One of the crucial directions in the pursuit of high-energy-density lithium batteries involves pairing Ni-rich cathodes with lithium metal anodes (LMAs). However, battery systems with high energy density often suffer from issues such as poor phase structure stability and inadequate interface compatibility. These problems are exacerbated under the actual operating conditions with high cut-off voltages and wide temperature ranges. Interface degradation, in such cases, accelerates the destruction of phase structure, leading to rapid performance deterioration of electrode materials. Compared to methods like ion doping and surface coating, an approach centered around electrolyte-induced interface reconstruction modification through solvent-lithium salt optimization or functional additives shows promise. This approach allows for simultaneous electrochemical cyclic modification of both high-energy-density cathode and anode materials, and it can be easily integrated into large-scale industrial production. Ester-based electrolytes, while possessing greater voltage stability compared to ether-based electrolytes, still exhibit side reactions at the interface between high Ni-content cathodes and the electrolyte, as well as between Li metal anodes and the electrolyte. In the absence of effective cathode-electrolyte interface (CEI) and solid-electrolyte interface (SEI) protection, persistent side reactions occur, ultimately leading to electrode failure. To address these challenges and simultaneously enhance electrode/electrolyte interface compatibility while regulating electrolyte solvation structure, functional additives are employed to modify the electrochemical behavior of the high-energy-density battery interface. Traditional ether electrolytes often employ lithium hexafluorophosphate (LiPF6) as the primary salt. However, LiPF6 suffers from poor thermal stability. Its decomposition or hydrolysis generates hydrogen fluoride (HF), which corrodes the cathode. Moreover, LiPF6 decomposition releases phosphorus pentafluoride (PF5), triggering the ring-opening of ethylene carbonate (EC), leading to electrolyte failure. PF5 can also react with water to produce acidic compounds, further deteriorating battery performance. The extraction of Li+ ions in the cathode reduces oxygen binding energy, facilitating the release of lattice oxygen. This can lead to side reactions between reactive oxygen species and the electrolyte, increasing interface impedance. To tackle these issues, choosing electrolyte additives with diverse functions can expand the potential of electrolytes. By leveraging various functional electrolyte additives, it becomes possible to inhibit irreversible structural transformations in the cathode, prevent O2/CO2 precipitation, suppress interface side reactions, and facilitate the removal of acid-water impurities. This comprehensive study delves into the impact of different functional electrolyte additives on interface film reconstruction, interfacial adsorption stability, synergy on high-energy-density anode interface, and acid-water impurity removal in Ni-rich cathode and anode materials. The research opens up new avenues for the identification and design of specific functionalized additives, paving the way for achieving stable cycling in high-energy-density Ni-rich lithium batteries.