Transition metal based battery-type electrodes in hybrid supercapacitors: A review

Hybrid supercapacitors (HSCs) assembled with battery-type and capacitive-type electrodes show combined advantages from both batteries and electric double-layer capacitors, rendering them promising advanced energy storage devices for commercial applications. However, electrochemical performances of HSCs towards high-rate and long-life energy storage are restricted by battery-type materials because of sluggish ion/electron diffusion and inferior structural stability. Herein, current research progress of transition metal based battery-type materials in hybrid supercapacitors is reviewed. We firstly introduce the hybridization principles, development requirements and material classification of HSCs. The battery-type materials are then categorized into intercalation-type and conversion-type electrodes with detailed review of materials and strategies to tune their energy storage performances. Finally, conclusive remarks and opinions for future development of high performance HSCs are proposed with the intention to provide some clues for build-up of high rate and long life energy storage systems.