Li₂Se@C composite for dual-function lithium supplementation and conductivity enhancement in high-energy-density lithium-ion batteries

The minimization of irreversible active lithium loss is a critical challenge in rechargeable lithium batteries, especially for grid-storage applications where high energy density and low life-cycle cost are essential. In this study, a Li₂Se@C composite was synthesized via a simple carbothermal reduction method as a lithium supplement for lithium-ion batteries. The carbon-coated Li₂Se exhibits enhanced air stability, retaining its structural integrity without degradation for 5 h in air with 50 % humidity. Electrochemical evaluations conducted in LiFePO₄||graphite full cells demonstrate that the Li₂Se@C composite effectively compensates for lithium loss during solid electrolyte interphase (SEI) formation, resulting in an increase of the initial capacity from 113 mAh g⁻¹ to 126 mAh g⁻¹. Moreover, it enhances cycling stability, with capacity retention improving from 84 % to 89 % after 500 cycles. Characterization shows that delithiation of Li₂Se generates amorphous selenium, which forms selenium-carbon bonds to improve cathode conductivity and stability. Electrochemical calculations further confirm that the Li₂Se-carbon heterojunction facilitates electron transfer, significantly boosting conductivity. These results highlight the potential of Li₂Se@C as a reliable lithium supplement, offering improved energy density and overall battery performance.