Precise Chemical Lithiation: A Pathway to Superior Li-Enriched Li1+xNCM523 Cathodes for Long Life Anode-Free Li Metal Batteries

Developing lithium-enriched cathodes, such as Li_1+xNCM523 (x ≥ 0), offers a promising approach to boost the cycling life of anode-free lithium metal batteries (AFLMBs). However, the traditional electrochemical prelithiation method is confined to laboratory studies, while conventional chemical prelithiation using highly reductive reagents like biphenyllithium (0.25 V vs Li⁺/Li) often causes severe surficial excessive-lithiation and structural degradation, compromising battery performance. Herein, we propose a precise chemical lithiation strategy using 9-fluorenone lithium (FL-2Li) as an optimal lithiation reagent to achieve controllable and uniform lithium insertion in Li_1+xNCM523 cathodes. The redox potential of FL-2Li reagent (1.32 V vs Li⁺/Li) is strategically matched─slightly below the lithiation potential of Li_1.7NCM523 (1.50 V) to allow tolerable overlithiation, yet above that of Li_2.0NCM523 (1.0 V) to avoid excessive-lithiation, and significantly higher than Li_4.0NCM523 (Li₂O/TM, 0.75 V) to prevent irreversible structural collapse. This design yields a superior Li_1.7NCM523 cathode with a homogeneous bulk-lithiated structure, thereby eliminating the core–shell effects typically observed with conventional reagents. Consequently, the chemically prelithiated Li_1.7NCM523 exhibits superior electrochemical performance, achieving 86.16% capacity retention after 100 cycles at 1C in Cu||Li_1.7NCM523 anode-free cells. Our findings established a versatile framework for the rational selection of lithiation reagents, providing critical theoretical insights and practical guidance for designing high-performance, scalable lithium-enriched cathodes, which may potentially advance battery technology for electric vehicles and energy storage systems.