A Multifunctional Electrolyte Additive K ₃ P ₇ for Simultaneous Capacity Compensation and Interphase Regulation in Lithium‐Ion Batteries

ABSTRACT The initial irreversible capacity loss (ICL) during the first charge significantly reduces the energy and power densities of lithium‑ion batteries (LIBs). Conventional prelithiation additives suffer from limited theoretical specific capacities (300–1000 mAh g −1 ), poor air stability, and low conversion efficiency. Herein, K 3 P 7 , which possesses high solubility in ester‐based electrolytes, is introduced as an electrolyte additive to improve the reversible capacities of various commercial LIBs. It provides an exceptional capacity‑compensation effect through the oxidation of P 7 3− , equivalent to 3048 mAh g −1 . Additionally, K + ions intercalate into the graphite interlayer, expanding the interlayer spacing and thereby improving the high‑rate performance of the graphite anode. The additive also promotes the formation of a stable cathode electrolyte interphase (CEI) and a uniform solid electrolyte interface (SEI), contributing to improved cycle stability of both electrodes. Furthermore, K 3 P 7 effectively scavenges free radicals, alleviating gas generation and internal pressure build‑up. When applied in a LiNi 0.8 Co 0.1 Mn 0.1 O 2 ||graphite full cell, the initial reversible capacity is 8% higher than that of the control sample, and the cell retains 92.9% of its capacity after 200 cycles. This work reveals a facile multi‐functional electrolyte additive that enhances the overall performance of LIBs.