Li-salt mediated Mg-rhodizonate batteries based on ultra-large cathode grains enabled by K-ion pillaring

Abstract

Abstract Mg-based batteries modulated by Li-salt additive can bypass the sluggish Mg solid diffusion at cathode side by kinetically better Li intercalation. However for this dual-salt system the highly electroactive cathodes endowed with high intrinsic conductivity and multi-electron transfer are still lacking, especially under large-sized grains and their high loading. Here a rhodizonate organic salt pre-pillared by K-ions (K2C6O6) is proposed as high-rate cathode for Li-salt mediated Mg batteries. Under a high loading of 70\u202fwt%, well-crystallized K2C6O6 composed of ultra-large micro-sized grains (up to 30\u202fμm) shows a reversible capacity more than 300\u202fmA\u202fh/g at 0.1\u202fC (based on three electron transfer), and up to 200, 130 and 60\u202fmA\u202fh/g at 2\u202fC, 5\u202fC and 10\u202fC respectively. The high bulk electron/ion conductivity and low solubility are responsible for such a superior performance based on fast Li-K electrochemical exchange and highly reversible Li intercalation without the assistance of nano-sizing, as a consequence of optimization and stabilization of desired electron structure and open framework by K-ion pre-supporting (instead of Li/Na-pillaring) and Mg-ion trapping between C6O62- layers. These large monoliths of K2C6O6 do not undergo serious grain fracture after long-term cycling, and at that time the Mg anode still remains compact and dendrite-free.