Realizing an Energy-Dense\nPotassium Metal Battery\nat −40 °C via an Integrated Anode-Free and Dual-Ion Strategy

Potassium (K)-based batteries hold great promise for\ncryogenic\napplications owing to the small Stokes radius and weak Lewis acidity\nof K<sup>+</sup>. Nevertheless, energy-dense (>200 W h kg<sup>–1</sup><sub>cathode+anode</sub>) K batteries under subzero conditions have\nseldom been reported. Here, an over 400 W h kg<sup>–1</sup><sub>cathode+anode</sub> K battery is realized at −40 °C\nvia an anode-free and dual-ion strategy, surpassing these state-of-the-art\nK batteries and even most Li/Na batteries at low temperatures (LTs).\nBy introduction of a strongly associating salt as an additive to this\nanode-free K battery, an anion-derived solid electrolyte interphase\ncan be established for a highly reversible, zero-excess K plating/stripping\nbehavior on a bare current collector. Meanwhile, a binary solvent\nis rationally designed for lowering the cation desolvation energy\nbarrier, which ensures comparably facile cation and desolvation-free\nanion kinetics in this dual-ion structure even at LTs. Consequently,\nthe K||Al half-cell delivers a high Coulombic efficiency of 99.98%\nat −40 °C. By pairing with a high-energy cathode, a proof-of-concept\nanode-free K dual-ion battery (N/P = 0) is fabricated, delivering\na record-high energy density of 407 W h kg<sup>–1</sup><sub>cathode+anode</sub> with stable cycling of 183 cycles (80% capacity\nretention) at −40 °C. This work paves a way toward energy-dense\nbatteries at extreme scenarios.