Effect of hard carbon kinetic properties on low-temperature performance of Na-ion batteries
Pouch-type Na-ion batteries were fabricated using a Na4Fe3(PO4)2P2O7 cathode and hard carbon(HC)anodes obtained from different sources:biomass-derived(HC-A),resin-derived(HC-B),and biomass-derived(HC-C).The effect of the HC anode on the cycling durability and low-temperature performance was investigated.The charge transfer impedance,solid electrolyte interphase impedance,and diffusion coefficient values were determined for the three HC anodes by electrochemical impedance spectroscopy,distribution of relaxation times,and galvanostatic intermittent titration technique.The kinetic properties,which directly affect the battery performance,showed the following trend:HC-A>HC-C>HC-B.The best cycling durability was obtained with HC-A,which was stable at room temperature with 5C fast charging and-10℃ with 0.2C charging.In addition,a capacity ratio of 87.5％was achieved with a 0.5C discharge at-30℃.The HC-B anode led to the lowest kinetic performance;it failed when cycling at 15℃ with 0.5C charging,and the capacity ratio was only 83.7％with a 0.5C discharge at-30℃.The low-temperature performance of the battery using HC-B was significantly improved by increasing the N/P ratio of the battery.After 100 cycles at-10℃ with 0.1C charging,the capacity retention remained stable at about 104％.This work represents an important foundation to improve the design of Na-ion batteries.
Na-ion batteryhard carbonlow temperature performancekinetic propertyN/P ratio
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