Li₂CO₃-rich interphase construction via alternating pulse current-driven CO₂ reduction for high performance LiFePO₄/graphite full-cell

Featuring of low Li⁺ diffusion barrier and high Li⁺ conductivity, a Li₂CO₃-rich solid electrolyte interphase (SEI) is critical for improving the energy density and cycle life of lithium-ion batteries. As a gaseous additive, CO₂ can be added into the electrolyte to in situ generating Li₂CO₃-contained SEI. However, CO₂-derived SEI formation is kinetics limitation. Here, we identify the adsorption of CO intermediate products impeding the full conversion of CO₂, and furtherly apply an alternating pulse current (APC) discharge to desorb CO and promote the CO₂ decomposition, ultimately in-situ forming a uniform, smooth, and Li₂CO₃-rich SEI in the first cycle. Owing to the excellent Li⁺ transport capability and structural stability, this APC-formed SEI enables lithium/graphite (Li/Gr) half-cells achieving a high rate performance (5 C, 180 mAh g^-1, and 80.1% after 170 cycles), exceeding currently advanced cells with Li₂CO₃-contained SEI. Furthermore, we directly employ the Gr anode with the APC pre‑formed Li₂CO₃-rich SEI to assemble LiFePO₄ (LFP)/Gr full-cell. Advantaged by the high Li⁺ diffusivity and stability, this pre‑formed SEI not only compensates for the active lithium loss, dramatically enhancing the initial coulombic efficiency from 69.2% to 91.7%, but also substantially increases the discharge capacity and long‑term cycling stability (131.8 mAh g^-1 after 100 cycles at 0.5 C). This straightforward strategy simultaneously enhances gas additive utilization efficiency and constructs a robust electrolyte/electrode interphase, demonstrating a dual-optimization approach through electrolyte design and interface engineering for high-performance batteries.