Tailoring Anion-Enriched Solvation Structures in Phosphate-Based Electrolytes for Safety-Enhanced Lithium Metal Batteries

Abstract

Both phosphate-based high-concentration electrolytes and localized high-concentration electrolytes effectively address safety concerns and interfacial compatibility issues in Ni-rich lithium metal batteries (LMBs). However, their high cost and viscosity have hindered further practical applications. Here, an intrinsically nonflammable phosphate-based low-concentration electrolyte is delicately presented, employing 0.7 M lithium difluoro(oxalato)borate and the flame-retardant trimethyl phosphate solvent, to overcome the aforementioned challenges. The weak interactions between trimethyl phosphate and difluoro(oxalato)borate anions facilitate the formation of anions-induced solvation structures and the protective layers that are rich in boron oxides and LiF. The as-designed electrolyte has been employed to build LiNi_0.9Co_0.05Mn_0.05O₂/Li cell which demonstrates stable cycling for over 180 cycles. Additionally, the battery is also able to operate successfully over a wide temperature range, from -20 to 60 °C, and displays elevated thermal runaway temperatures, enhanced high-temperature charge retention capability, and reduced gas evolution. Moreover, a 20.0 Ah pouch cell achieves a high energy density of 533.8 Wh kg⁻¹, showcasing great potential for commercial applications. Furthermore, this electrolyte is compatible with both layered and spinel cathodes. The delicate molecular design strategy in this work provides a promising avenue for the development of high-safety electrolytes for high-energy-density Ni-rich LMBs.