Self-optimizing weak solvation effects achieving faster low-temperature charge transfer kinetics for high-voltage Na3V2(PO4)2F3 cathode

Various properties of sodium ion batteries deteriorate severely when dropping to subzero temperature. Herein, we reveal an accelerated charge-transfer mechanism for high-voltage Na3V2(PO4)2F3 cathode through constructing weakly-solvating architecture, which endows it with superior temperature adaptability (capacity retention of C−25∘C/C25∘C reaches 90.8%). The resulting weak solvation effects synergistically lower the activation energy barrier for charge-transfer reactions, thus accelerating the kinetics at low temperature and increasing the energy density by ∼75 Wh Kg−1. Ab initio molecular dynamics calculations show that a weakly-solvating structure forms spontaneously in a low-concentration electrolyte (merely 0.3 M) and thereby facilitates Na+ desolvation process. Besides, visual TOF-SIMS confirms the construction of a dense and uniform cathode/electrolyte interface layer, which optimizes the interface chemistry and improves the interfacial kinetics. In-situ and ex-situ XRD also evidence a smaller degree of structural evolution of the Na3V2(PO4)2F3 cathode, which contributes to long-term durability (attaining a high capacity retention of 93.4% after 1000 cycles at −25 °C). Furthermore, it is demonstrated that under such extreme conditions the Na3V2(PO4)2F3||hard-carbon full cell functions well for over 300 h. These findings elucidate the roles of weak solvation construction in realizing faster kinetics for high-voltage cathodes and provide a feasible pathway for achieving more practical sodium ion batteries.