Reversible Silicon Oxychloride Redox for Energetic Zn Batteries With Near‐Zero Shuttle and Ultralow Self‐Discharge

Multi‐electron redox conversion cathode materials offer substantial promise for the development of high‐energy batteries. However, the pervasive challenges of soluble redox intermediates, usually causing severe shuttling and rapid self‐discharge, have long plagued almost all established conversion systems, including halogens, chalcogens, and pnictogens, across various electrolyte systems. Herein, for the first time, we unlock SiO as a high‐energy and sustainable conversion cathode with near‐zero shuttle and ultralow self‐discharge, via reversible two‐electron Si(II)/Si(IV) oxychloride conversion chemistry in nucleophilic ionic liquid (IL) electrolytes. When coupled with a Zn metal anode, the full cell delivers a specific capacity of 915 mAh g −1 SiO at 0.05 A g −1 (75.3% of theoretical limit: 1215 mAh g −1 SiO ), featuring a flat voltage plateau at 1.2 V and an ultrahigh energy density of ca. 1100 Wh kg −1 SiO . Remarkably, the system exhibits negligible shuttle behavior during 500 cycles, with a daily average self‐discharge rate of only 0.8% over 15 days, significantly surpassing conventional conversion cathodes (e.g., halogens, chalcogens, and pnictogens). After 920 cycles at 1 A g −1 , capacity retention remains at 92.7% with well‐kept voltage plateaus. This work decodes a new family of high‐energy conversion cathodes, which could be extended to other multivalent metal‐ion (e.g., Al 3+ ) batteries.