Anion-induced electrolyte chemistry enables high energy density primary battery for ultralow-temperature conditions

Lithium/fluorinated-carbon (Li/CF_x) primary batteries are widely used in defense and military fields due to their stable discharge plateau, low self-discharge rate, and adaptability across a wide temperature range. However, enhancing their overall energy density and discharge capacity at low temperatures remains a critical challenge. Herein, we report a strategically designed LiBF₄-based sulfite/carboxylate electrolyte, where the anion-involved solvation structure significantly enhances electrochemical kinetics by reducing the desolvation barrier. Simultaneously, it introduces a radical reaction mechanism that contributes to additional capacity. As a result, the Li/CF_x primary batteries with this formulated electrolyte deliver a specific capacity of 2,257.15 mAh g⁻¹ at 25 °C. More importantly, when operating at −40 °C, the batteries exhibit an exceptionally high discharge capacity of 1,549.4 mAh g⁻¹ and an energy density of 2,868.6 Wh kg⁻¹. Even at −60 °C, the Li/CF_x cells achieve a specific capacity of 444.3 mAh g⁻¹ and an energy density of 821.8 Wh kg⁻¹ at 0.1 C, significantly outperforming previously reported organic-based liquid electrolytes. This work offers a viable strategy for enhancing the specific capacity and energy density of primary batteries in extreme environments, providing valuable insights for future developments.