Electrolyte design weakens lithium-ion solvation for a fast-charging and long-cycling Si anode.

Silicon (Si) is considered a promising anode material for next-generation lithium-ion batteries due to its high theoretical specific capacity and earth-abundancy. However, challenges such as significant volume expansion, unstable solid electrolyte interphase (SEI) formation in incompatible electrolytes, and slow lithium-ion transport lead to its poor cycling and rate performance. In this work, it is demonstrated that superior cyclability and rate capability of Si anodes can be achieved using ethyl fluoroacetate (EFA) and fluoroethylene carbonate (FEC) solvents with low binding energy with Li but with sufficiently high relative dielectric constants. By weakening the interaction between Li and the solvent, the energy barrier for the Li desolvation process is lowered, while ensuring the conductivity and diffusion of Li. As a result, the silicon-carbon anode with the optimized electrolyte exhibits excellent cycling and rate performance, and can work reversibly with a high capacity of 1709.1 mAh g that proceeds for over 250 cycles and retains 85.2% of its capacity at 0.2C. Furthermore, the Si/C‖LiFePO (LFP) full cell shows an extended service life of more than 500 cycles. This work offers valuable insights into the design of weakly solvating electrolytes for high-performance Si-based batteries.