Understanding the high performance anode material of CoC2O4·2H2O microrods wrapped by reduced graphene oxide for lithium‐ion and sodium‐ion batteries

Metal oxalate has become a most promising anode candidate material for lithium-ion and sodium-ion batteries. However, there exists the problem of capacity decrease due to the volume expansion of the active material during cycling. Herein, the rodlike CoC2O4·2H2O/rGO hybrid has been fabricated via a novel multi-step solvo/hydro-thermal strategy. The structure characteristic of microrod CoC2O4·2H2O wrapped using rGO sheet not only inhibits the volume variation of the hybrid electrode during the cycle, but also accelerates the transfer of electrons and ions amongst the 3D graphene network, thereby improving the electrochemical properties of CoC2O4·2H2O. The CoC2O4·2H2O/rGO electrode delivers specific capacity of 1011.5 mA h g-1 at 0.2 A g-1 after 200 cycles for lithium storage, and exhibits high capacity of 221.1 mA h g-1 at 0.2 A g-1 after 100 cycles for sodium storage. Moreover, the full cell CoC2O4·2H2O/rGO//LiCoO2 consisted of the CoC2O4·2H2O/rGO anode and LiCoO2 cathode maintains 138.1 mA h g-1 after 200 cycles at 0.2 A g-1 and has superior long-cycle stability. In addition, in-situ Raman, in-situ and ex-situ X-ray diffraction techniques have provided a unique opportunity to fully understand the reaction mechanism of CoC2O4·2H2O/rGO. This work also supplies a new perspective and certain research basis for the application of metal oxalate materials in high performance lithium-ion and sodium-ion batteries.