Preparation And Electrochemical Performance Of Anode Materials For Sodium-ion Batteries

The application of lithium-ion batteries in smart electric grid and renewable energy storage is impeded by the limited reserve（20 ppm）and uneven distribution of lithium.In contrast,sodium-ion batteries have captured ever-growing interest due to the similarities of physicochemical nature between lithium and sodium as well as working principle between lithium-ion batteries and sodium-ion batteries.Furthermore,sodium-ion batteries are regarded as one of the most promising large-scale energy storage devices,because of the abundant reserves（23600 ppm）,widespread distribution and low cost of sodium.Carbon materials are a suitable candidate because of low cost,natural abundance,thermal stability,controllable structure and high electrochemical activity.In this paper,carbon nanospheres with high capacity are prepared from resorcinol,formaldehyde and propylamine.The effects of carbonization conditions on material structure and electrochemical performance are investigated.Carbon nanosheets with ultrahigh rate capacity are prepared by pre-carbonized polymer-sheets at different temperatures followed by NaNH₂ treatment.Some conclusions are as follows:（1）carbon nanospheres were prepared at carbonization temperature of 1200℃,which have an appropriate graphite-like crystallization,interlayer spacing and specific surface area,realizing excellent specific capacity.CSP-35-1200 delivers the reversible capacity of 276 and115 mA h g^-1 at a current density of 0.02 and 5 A g^-1,respectively.The capacity retention was42%at 250 times’current density.（2）N-doped carbon nanosheets with rich defects,nanopores and large interlayer spacing are prepared by pre-carbonized polymer-sheets at different temperatures（optimized pre-carbonized temperature:800℃）followed by NaNH₂ treatment.The combination of fast diffusion and fast storage of sodium ions effectively realizes ultrafast rate performance from the points of morphology,microstructure and reaction mechanism.The Na⁺diffusion coefficient has a significant enhancement from 5.85·10^-12 to 2.11·10^-11 cm² S^-1.The kinetic analysis proves that the capacitive behavior without diffusion control nearly dominated the entire sodium storage process and corresponding capacitance contribution ratio reaches 79%.In ether electrolyte,the material delivers the reversible capacity of 111.1 mA h g^-1 at 20 A g^-1,retains 108.3 mA h g^-1 after 400 cycles at 5 A g^-1 and exhibits initial Coulombic efficiency of81.4%.In ester electrolyte,it delivers a capacity decay of 0.014%per cycle at 5 A g^-1.The electrochemical performance is at the forefront of the literature and the material has certain application potential.