Abstract:

The Li/CrO_x battery has gained attention in the construction of smart cities, aerospace, and national defense and military applications due to its high energy density and excellent rate performance. Developing a Li/CrO_x battery with high specific capacity, high energy density, excellent magnification performance, long storage life, and low cost is a primary goal. In this pursuit, the role of the electrolyte in battery performance for Li/CrO_x primary batteries cannot be underestimated. However, current research on Li/CrO_x primary batteries has primarily focused on electrode materials, with limited attention given to the electrolyte. Propylene carbonate (PC) solvent possesses a wide temperature range for melting and boiling points (−48.8 to 242 ℃) and a high dielectric constant of 64.92. As a result, it is frequently used as a key component in electrolytes that operate under extreme temperatures and high rates. Nevertheless, its use in Li/CrO_x batteries remains limited. Developing electrolyte systems based on PC with a wide temperature range and high dielectric constant is crucial for the advancement of high-power and environmentally robust lithium primary batteries. In this study, we investigated the discharge behavior of CrO_x in PC-based electrolytes and identified suitable electrolyte systems for high-current discharge, specifically a 1 mol∙L⁻¹ LiTFSI PC : DOL (1, 3-dioxolane) = 1 : 2 ratio. We also demonstrated that the coordination number of solvent molecules in the solvation sheath layer around Li⁺ ions and the solvated structure involved in coordination significantly influence the rate performance of Li/CrO_x battery systems in PC-based electrolytes. Reducing the coordination number of solvent molecules facilitates the desolvation behavior of solvated Li⁺, thereby enhancing the desolvation process on the material surface. Furthermore, lowering the coordination number of solvent molecules promotes the involvement of anions in the solvated sheath structure. When the coordination number of solvent molecules falls below 3, it tends to form a solvated coordination structure involving anions with a higher lowest unoccupied molecular orbital (LUMO) level. This enables anions to participate in forming a solid electrolyte interface (SEI), resulting in a thinner and denser SEI film that significantly improves battery performance. Ultimately, modifying the coordination number for PC-based electrolytes is a practical and effective approach to enhance the rate performance of solvated sheath structures. The coordination number and the solvated sheath structure of Li⁺ in PC-based electrolytes have a profound impact on the high-current-discharge performance of the Li/CrO_x battery system. A lower coordination number and the participation of anions in the solvated sheath structure effectively accommodate the high-rate discharge characteristics of the Li/CrO_x battery. Among several selected electrolyte solvents, an electrolyte with DOL (a cyclic ether) and PC reduces the solvent's coordination number to less than four, thereby enabling high-rate discharge. Understanding these principles is crucial for advancing the application of PC-based electrolytes in high-rate Li/CrO_x battery systems.

Key words: Chromium oxide, Electrolyte, Solvation structure, Propylene carbonate, Lithium primary battery