Chemical presodiation of alloy anodes with improved initial coulombic efficiencies for the advanced sodium-ion batteries

The alloy-type anodes such as P and Sn with high specific capacities are the rising stars for developing advanced sodium-ion batteries (SIBS). However, the low initial coulombic efficiency (ICE) due to the solid electrolyte interphase (SEI) formation and the large volume variation during sodiation/desodiation cycling still limit their practical application. This study reports a facile chemical presodiation method for P and Sn anodes using the sodium biphenyl/tetrahydrofuran (Na-Bp/THF) solution as the presodiation reagent. With a low redox potential of 0.095 V vs. Na/Na+, the Na-Bp/THF reagent is capable of preinserting Na+ into these anodes and compensating for the initial capacity loss. Through adjusting the treatment duration, the degree of presodiation could be feasibly controlled, and the initial CE of a P/C electrode could be significantly increased from 64 to 94%. Surface morphology characterization reveals a more robust NaF-rich SEI layer formed on the presodiated P/C electrode after cycling, which helps to preserve the integrity of the P/C electrode and enables a better cycling performance. [GRAPHICS] .