Regulated external lithium supply enables high-energy sulfurized polyacrylonitrile-graphite fiber batteries

Fiber batteries employing sulfurized polyacrylonitrile (SPAN) redox chemistry address the critical limitations of conventional layered oxide cathodes by offering high theoretical energy density, low cost, and environmental friendliness. However, the complete absence of lithium in the system, coupled with the significant safety concerns associated with lithium metal anodes, makes the development of lithium-SPAN fiber batteries (LSFBs) highly challenging. Herein, by exploiting the inherent twistability of fiber electrodes, we incorporate a lightweight, lithium-infiltrated aramid fiber containing a precisely controlled amount of lithium between the fiber electrodes. This strategy successfully introduces active lithium into the SPAN-graphite fiber system, enabling, for the first time, the efficient and safe operation of LSFBs. The multistrand fiber cell configuration, featuring three independent tabs, enables a sequential activation protocol (SAP) that lithiates the SPAN cathode and promotes the pre-formation of the solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) before normal full-cell operation. Consequently, the resulting LSFB full cell, with a low negative-to-positive capacity (N/P) ratio of 1.08, achieves a high initial coulombic efficiency (ICE) of 98.82% and a high specific capacity of 673.2 mAh g^-1, corresponding to an energy density of 132.2 Wh kg^-1. This study represents the first realization of a high-energy, dendrite-free SPAN-graphite fiber battery, paving the way for the development of safe, stable, and flexible energy storage systems.