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, LixC6O6 (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 LixC6O6 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 LixC6O6 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.