Fe₂O₃ Catalysts Activating Size-Regulated Li₂C₂O₄ for Efficient Cathode Prelithiation in Li Ion Hybrid Capacitors

Prelithiation is a strategy to address the active lithium loss in Li ion hybrid capacitors (LICs) during initial charge-discharge process. Lithium oxalate (Li₂C₂O₄) emerges as a promising prelithiation additive due to its high lithium content and superior atmospheric stability. However, its practical application is hindered by sluggish reaction kinetics and a high decomposition potential. Herein, we develop a Li₂C₂O₄ recrystallization strategy combined with Fe₂O₃ catalysts (R-LCO@Fe₂O₃), enhancing the electrochemical activity of Li₂C₂O₄ and lowering its decomposition potential from approximately 4.76 to 4.28 V vs. Li⁺/Li. Also, the designed prelithiation additive facilitates the formation of a LiF-rich and compact solid electrolyte interphase, which is beneficial for extending the cycling lifespan of LICs. In activated carbon//graphite LICs, the R-LCO@Fe₂O₃ additive increases the initial charge capacity to 288.27 mAh g^-1, while the discharge capacity is significantly improved from 23.67 to 42.15 mAh g^-1. As a result, LICs incorporating R-LCO@Fe₂O₃ exhibit stable cycling performance over 2500 cycles, with a capacity retention of 75.93%. In contrast, the LICs without additives suffer a more rapid capacity fade, retaining 31.59% after 325 cycles. Overall, this work demonstrates a simple, cost-effective, and scalable strategy for preparing prelithiation materials in LIC applications.