Enhanced Interfacial Magnetization is Responsible for the Negative Capacity Fading of Cobalt Ditelluride Anodes for Lithium Storage.

ABSTRACT

In lithium-ion batteries (LIBs), the stabilized capacities of transition metal compound anodes usually exhibit higher values than their theoretical values due to the interfacial charge storage, the formation of reversible electrolyte-derived surface layer, or interfacial magnetization. But the effectively utilizing the mechanisms to achieve novel anodes is rarely explored. Herein, a novel nanosized cobalt ditelluride (CoTe2 ) anodes with ultra-high capacity and long term stability is reported. Electrochemical tests show that the lithium storage capacity of the best sample reaches 1194.7 mA h g-1 after 150 cycles at 0.12 A g-1 , which increases by 57.8% compared to that after 20 cycles. In addition, the sample offers capacities of 546.6 and 492.1 mA h g-1 at 0.6 and 1.8 A g-1 , respectively. During cycles, CoTe2 particles (average size 20 nm) are gradually pulverized into the smaller nanoparticles (<3 nm), making the magnetization more fully due to the larger contact area of Co/Li2 Te interface, yielding an increased capacity. The negative capacity fading is observed, and verified by ex situ structural characterizations and in situ electrochemical measurements. The proposed strategy can be further extended to obtain other high-performance ferromagnetic metal based electrodes for energy storage applications.