Understanding the phenomenon of capacity increasing along cycles: In the case of an ultralong-life and high-rate SnSe-Mo-C anode for lithium storage

A good cycling stability is a prerequisite for the application of metal-based materials in lithium-ion batteries(LIBs). However, an abnormal increase in capacity is often observed, which has rarely been focused on in many studies. In our SnSe-Mo-C composite anode, a high reversible capacity of 737.4 mAh g^(-1)remained after 5000 cycles at 5 A g^(-1)between 0.01 and 3.0 V versus Li/Li+. However, a continuous capacity increase occurred in the initial cycles, with 1086.9 mAh g^(-1)after 1000 cycles and 1216.9 mAh g^(-1)after 1500 cycles, respectively. Further studies revealed that the electrolyte decomposed at high potentials(2.5–3.0 V) and provided additional capacities. The cut-off voltage and electrolyte filling were controlled, which eliminated the impact of electrolyte decomposition, prevented rapid capacity decay, and provided a stable cycling performance for SnSe-Mo-C anodes in LIBs. This work shows that the composite anode is promising for lithium storage and the findings provide new insights into understanding and controlling the phenomenon of capacity increase with cycling in metal-based anode materials.