Redox Mediator as Highly Efficient Charge Storage Electrode Additive for All‐Solid‐State Lithium Metal Batteries

Abstract All‐solid‐state lithium metal batteries (ASSLBs) have the potential to provide a significant increase in energy density and safety. However, most ASSLBs are still suffering from low cathode loading, poor rate capability, and low attainable energy/power densities, which seriously limit their practical application. Besides developing solid electrolytes with high conductivity, constructing a highly loaded cathode with rapid reaction kinetics is also essential for achieving high‐performance ASSLBs. Herein, the methylamine hydroiodide (CH₆NI) is investigated as a functional electrode additive to enable rapid Li⁺ transport and charge transfer in LiFePO₄ (LFP) cathode, whereby the CH₆NI serves as a charge storage carrier that facilitates the reaction kinetics during the delithiation and lithiation process of LFP. As a result, the ASSLB assembled with LFP@CH₆NI cathode shows excellent cycling stability over 700 cycles at 2 C with a high capacity retention of 87.6%, while the cell with bare LFP cathode shows no capacity at high current rates (≥0.5 C). Moreover, the ASSLB pared with a high active loading cathode (5.6 mg cm⁻²) still exhibits a high specific capacity of 144.9 mAh g⁻¹ at 0.5 C. This work provides a facile strategy that opens new possibilities for designing high‐loading electrodes for high‐performance ASSLBs.