Air-Stable Li₂C₆O₆ and Li₄C₆O₆ as High-Efficiency Lithium Compensation Additives in Cathode

The continuous lithium consumption during cycling severely reduces the energy density of the lithium battery, and thus, lithium compensation is essential. Herein, Li_xC₆O₆ (x = 2, 4) was proposed as an air-stable high-efficiency sacrificial additive in the cathode to compensate for the lost lithium ions in solid-state lithium batteries. Below a delithiation (oxidation) potential as low as 3.8 V, Li₂C₆O₆ can release most of its Li⁺ ions (294.8 mAh g⁻¹ in theory). Similarly, Li₄C₆O₆ is also characteristic of low oxidation potential and high delithiation capacity (547.8 mAh g⁻¹ in theory). The feasibility of using Li_xC₆O₆ as the self-sacrificial additive in the cathode was verified with the marked increase of the initial charge capacity of the Li||LiFePO₄ (half) cells and the initial discharge capacity of Cu||LiFePO₄ (full) cells, and the improved electrolyte/cathode interface stability and interface contact, in the solid-state poly(ethylene oxide)-lithium bis(trifluoromethane)sulfonimide (PEO-LiTFSI) electrolyte. In addition, the structure and delithiation of Li_xC₆O₆ and the impacts of its decomposition product on the PEO-LiTFSI solid electrolyte were also evaluated on the basis of the comprehensive physical characterizations and the density functional theory (DFT) calculations. These findings open a new avenue for elevating the energy density and/or elongate the lifespan of the solid-state secondary batteries.