Three-dimensional hard carbon matrix for sodium-ion battery anode with superior-rate performance and ultralong cycle life

Taking advantage of sodium polyacrylate, composed of interlaced carbon chains and inorganic functional groups (-COONa) uniformly grafted onto the carbon chains, a three-dimensional hard carbon matrix (3DHCM) has been obtained. The resultant material is composed of three-dimensional macroporous interconnected networks of carbon nanosheets (thickness, 5-30 nm). The 3DHCM has been studied as an anode material for sodium-ion batteries. The unique three-dimensional porous structure results in a high initial charge capacity of 341 mA h g(-1), stable cycling capacity of 232.8 mA h g(-1) (after 100 cycles, 50 mA g(-1)), superior-rate performance (stable capacities of 210, 197, 128 and 112 mA h g(-1) at 200, 500, 5000, 8000 mA g(-1), respectively) and ultralong cycle life (116 mA h g(-1) at 4 A g(-1) after 3000 cycles). At the same time, an increase in the trend of the sloping capacity percentage at total discharge is observed. More obvious graphitic domains with larger interplanar spacing (-0.46 nm) were produced in the electrochemical cycles and detected using ex situ HRTEM, further confirming that the first highervoltage region (above 0.1 V) should be attributed to the sodium insertion between the parael graphene layers in the hard carbon. We aka find that the electrolyte (1 M NaClO4 in PC) severely decomposes at the electrode/electrolyte interface during deep electrochemical cycles (6000 cycles), resulting in the deterioration of the electrode and fast capacity fading. Furthermore, a room-temperature sodium-ion full cell was constructed using 3DHCM as an anode and Na3V2(PO4)(3)/C as a cathode, (-) 3DHCM parallel to 1 M NaClO4 in PC parallel to Na3V2(PO4)(3)/C (+), delivering a discharge capacity of 90 mA h g(-1) at a current density of 500 mA g(-1). We believe that our findings will be helpful in speeding up the development of roomtemperature high-rate, long life and low cost sodium-ion batteries for large-scale energy storage systems, and even as alternatives to lithium-ion batteries.