Rod-like NiCoCO·2HO in-situ formed on rGO by an interface induced engineering: Extraordinary rate and cycle performance as an anode in lithium-ion and sodium-ion half/full cells.

Transition metal oxalates have attracted wide attention due to the characteristics of the conversion reaction as anode materials in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), However, there are huge volume expansion and sluggish circulation dynamics during the reversible Li and Na insertion/extraction process, which would lead to unsatisfactory reversible capacity and stability. In order to solve these problems, a rod-like structure NiCoCO·2HO is in-situ formed on the reduced graphene oxide layer (NiCoCO·2HO/rGO) in a glycol-water mixture medium via an interface induced engineering strategy. Benefitting from the synergistic cooperation of nano-diameter rod-like structure and high conductive rGO networks, the experimental results show that the prepared NiCoCO·2HO/rGO electrode has predominant rate performance and ultra-long cycle stability. For the LIBs, it not only exhibits an ultrahigh reversible capacity (1179.9 mA h g at 0.5 A g after 300 cycles), but also presents outstanding rate and cycling performance (646.5 mA h g at 5 A g after 1200 cycles). Besides, the NiCoCO·2HO/rGO electrode displays remarkable sodium storage capacity of 221.6 mA h g after 100 cycles at 0.5 A g. Further, the extraordinary electrochemical capability of NiCoCO·2HO/rGO active material is also reflected in two full-cells, assembled using commercial LiCoO as cathode for LIBs and commercial NaV(PO) as cathode for SIBs, both of which can show wonderful specific capacity and cycling stability. It is found in in-situ Raman experiments that the reversible changes of oxalate peaks are monitored in a charge/discharge process, which is scientific evidence for the transform reaction mechanism of metal oxalates in LIBs. These findings not only provide important ideas for studying the charge/discharge storage mechanism but also give scientific basis for the design of high-performance electrode materials.