Micro-Nano Architecture with Carbonaceous Shell Enables Ultra-Long Cycling Life of Battery-Type Electrode Materials in Supercapacitors

In Faraday supercapacitors, battery-type materials despite their high theoretical capacity have not shown prospect yet in application primarily due to their especially low cycling stability (< 10,000 cycles), sharp contrast to the carbon materials in electrical double layer capacitors (>> 100,000 cycles). The so far materials structure-stabilizing strategies, established on the acknowledged structure-destabilizing mechanism under electrochemical stress, seem not significantly effective or practical. Actually, the misunderstanding on structure-destabilizing mechanism leads to the slow progress of battery-type materials in application. In this work, the intrinsic structure-destabilizing mechanism is revealed as the agglomeration of materials originating from their dissolution-recrystallization behavior instead of from electrochemical stress. Based on the as-proposed mechanism, a rod-like micro‑nano architecture with a thin carbonaceous shell is designed and built deliberately for Ni(OH)2 notorious in its especially low stability as a demonstration for stabilizing the structure of battery-type materials. The carbonaceous shell blocks the interflow of dissolved species between Ni(OH)2 rods, significantly reducing their agglomeration. This structure-stabilizing effect enables Ni(OH)2 ultra-long cycling life of > 100,000 cycles, thus verifying the as-proposed structure-destabilizing mechanism. The positive results in this work suggest that the significance of battery-type materials in supercapacitors should be revalued