The mechanism governing the pseudocapacitive lithium storage behavior is one of the most critical unsolved issues in conversion-type anodes for lithium-ion batteries. In this work, we, for the first time, demonstrate that the pseudocapacitive capability of iron oxide-based anodes is closely associated with the electronic structures of iron ions. As proof of concept, the introduction of amorphization, nitrogen doping, and oxygen vacancies reduces the coordination of iron ions and contributes significantly to the pseudocapacitive lithium storage capability of iron oxide, reaching up to 96% of the specific capacity at 1 mV·s⁻¹. Due to the significantly modulated coordination environment, the 3d electrons of Fe(II) are delocalized with increased spin state and the energy band gap is narrowed, accompanied by an upshift of Fermi energy. The redox activity and carrier mobility of iron oxides are substantially increased, which substantially enhance the exchange current density and thereby improve the pseudocapacitive capability of iron oxide.

Lithium metal has been considered one of the most promising anodes for next-generation rechargeable batteries, but its practical application is largely hindered by the uncontrollable dendrite growth and infinite volume change. Here, inspired by superior catalytic effects of single-atom catalysts, carbonsupported single atomic Co with asymmetric N, O-coordination (Co-N/O) is developed for Li metal battery. Experimental results and theoretical calculations indicate that single atomic Co atoms with asymmetric N, O-coordination present enhanced binding ability toward Li in comparison with N-coordinated atomic Co site and isolated O site, enabling uniform Li plating/stripping. Moreover, the asymmetric N, O-coordination around Co atoms induces co-activation effects, lowering the energy barriers toward Li⁺ to Li⁰ conversion and largely promoting the deposition kinetics. When used as a Li deposition host, the Co-N/O achieves a high average coulombic efficiency of 98.6% at a current density of 1 mA cm⁻² and a capacity of 2 mAh cm⁻², long cycling life of 2000 h in symmetrical cells, and excellent rate performance (voltage hysteresis of 23 mV at 8 mA cm⁻²). This work provides a comprehensive understanding of single atomic metals with asymmetric heteroatom coordination in the design of Li metal anode.