New design on Li-ion battery anode of ternary complex metal/metal oxide@CNT: A case study of hierarchical NiCo-NiCo2O4@CNTs

Urgent and heavy demand of high energy/power density lithium-ion batteries (LIBs) challenges the ultimate limit of commercial anodes. Herein, enlightened by the extra capacity on transition metal oxides (TMO) anodes derived from the transition metal (TM) catalytic effect on reversible solid-electrolyte interface (SEI) films, a ternary composite consisting of TM, TMO, and carbon matrix, namely TM/TMO/carbon, is proposed as a novel and high-efficiency anode prototype. In this electrode design, TMO not only serve as active material but also pulverizes the TM nanoparticles via the conversion reaction during cycling. Pulverized TM nanoparticles can activate and/or promote the reversible transformation of SEI films more efficiently. And carbon matrix ensures the electronic conductivity and integrity of the overall electrode during multiple electrochemical reactions. As a proof-of-concept demonstration, NiCo-NiCo2O4@carbon nanotubes (NC-NCO@CNTs) is synthesized by a bottom-up strategy via in-situ growth on a simplified chemical vapor deposition (CVD) process. As designed, the NC-NCO@CNTs keeps gaining extra capacity upon cycling, delivering an unceasingly increased capacity up to 1324 mAh g−1 (500 mA g−1), splendid rate performance (945 mAh g−1 at 1000 mA g−1, 696 mAh g−1 at 2000 mA g−1), and ultralong lifespan (2200 cycles). Detailed electrochemical investigation reveals a transformation of lithium storage mechanism from battery-type conversion reaction to pseudocapacitive electrochemical interfacial reaction arising from SEI films. It is believed that our work offers a novel and effective prototype for designing high energy/power density anodes for LIBs.