Controlled Presodiation of Sodium-Ion Cathode via Electron Cloud Engineering.

Chemical presodiation offers a promising pathway to compensate sodium deficiency in cathode and anode materials, thereby enhancing the usable energy density of sodium-ion batteries. This approach is particularly critical for P2- and tunnel-type cathodes, such as Na0.44MnO2, where the as-synthesized materials typically exhibit a 50%-60% sodium deficiency. However, conventional presodiation reagents possess excessively high reductive potential, often leading to oversodiation, structural degradation, and compromised electrode reversibility. Here, we report a rational electron-cloud engineering strategy to precisely control the sodium chemical potential of presodiation agents. Guided by Hückel's rule, we demonstrate that tailoring π-conjugation size and introducing electron-withdrawing groups enables the adjustment of sodium chemical potential via a balance of conjugative and inductive effects. We identify 1-indanone as an optimal presodiation reagent, capable of delivering sodium to Na0.44MnO2 cathodes without any oversodiation. The resulting electrodes exhibit fully restored sodium inventories, an unprecedented first-cycle Coulombic efficiency of ∼100%, and improved capacity retention over 350 cycles compared to untreated controls. Our findings establish a versatile framework for controlling sodium delivery in chemical presodiation, providing a new avenue for the design of next-generation sodium-ion batteries with enhanced stability and performance.