Concurrent electrode–electrolyte interfaces engineering via nano-Si3N4 additive for high-rate, high-voltage lithium metal batteries†

Electrolyte engineering is emerging as a key strategy for enhancing the cycle life of lithium metal batteries (LMBs). Fluorinated electrolytes have dramatically extended cycle life; however, intractable challenges in terms of rate capability and fluorine overuse persist. Here, we introduce a lithiophilic, solvent-interactive, and fluorine-free nano-Si₃N₄ additive that facilitates the fine-tuning of weak Li⁺ solvation to form inorganic-rich solid–electrolyte interphase (SEI) layers. Additionally, the alloying and conversion reactions between nano-Si₃N₄ and Li generated a fast Li⁺-conductive SEI, overcoming the poor rate performance of weakly solvating electrolytes. Simultaneously, nano-Si₃N₄ interacts with ethylene carbonate (EC), minimizing hydrogen (H)-transfer reactions and scavenging HF, thus increasing the high-voltage tolerance. Consequently, nano-Si₃N₄ extends the cyclability of the commercial carbonate-based electrolyte in 360 W h kg⁻¹-level Li||LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) pouch-cells, resulting in 74% capacity retention after 100 cycles, whereas failure occurred without it. Our study provides an in-depth understanding of the working mechanisms of suspension electrolytes through comprehensive analysis.