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.

The development of strategies to inhibit structural degradation and surface side reactions is the key to promoting the large-scale application of lithium-rich manganese-based cathode materials Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (LMNCO). Herein, LMNCO was triply modified from the inside to the outside, by bulk doping of Mo⁶⁺, fabricating oxygen vacancies (OVs) defects, and surface coating of S, N-doped carbon nanolayers (SNCN). The integration of Mo⁶⁺ doping and OVs defects widens and stabilizes the Li⁺ diffusion channel, and the surface coating of SNCN provides additional electrons for LMNCO in the conduction band region, achieving a simultaneous improvement in both ionic and electronic conductivity. Meanwhile, Mo⁶⁺ doping and OVs mitigate the irreversible phase transitions caused by oxygen loss and transition metal (TM) out-of-plane migration, while SNCN inhibits the corrosion of the electrolyte on the material surface and enhances the stability of the surface structure. Benefiting from the synergistic effect of these modifications, the structural evolution of the modified material is highly reversible, and the layered structure remains intact during repeated lithiation/delithiation processes, while the mechanical properties of material are also improved, effectively suppressing crack generation and TM dissolution. As a result, at room temperature (25 °C), the modified cathode demonstrates a high capacity retention of 94.6% after 200 cycles at 1 C, and a high rate capacity of 161.0 mAh·g⁻¹ at 5 C. Especially, under harsh conditions, the capacity retention is 76.3% after 150 cycles at 55 °C and 1 C. This work provides a new solution for developing advanced LMNCO cathode materials.