Synthesis,Characterization And Modification Of Cathode Materials For Alkali Metal-ion Batteries

Rechargeable alkali metal-ion（Li⁺/Na⁺/K⁺）batteries（AMIBs）have achieved rapid success since their inception.Lithium-ion batteries are widely used in current commercial energy storage devices due to their high energy density and abundant cathode materials.Sodium-ion batteries are considered potential candidates for lithium-ion batteries due to their abundant reserves and safety performance of aqueous sodium ion batteries.In this paper,we synthesized,characterized and modified the Prussian blue analogue Na2CoFe（CN）6 and the Ni-rich cathode material LiNi_0.8Co_0.1Mn_0.1O₂,The results show that the electrochemical performance of both materials in the batteries can be effectively improved by modification.The specific research contents and results of this paper are as follows:（1）The as-prepared Na2CoFe（CN）6（CoHCF）was synthesized by a reported facile co-precipitation method.By adjusting the ratio of raw materials,solution concentration,reaction temperature,reaction time,et al.We achieved controllable preparation of CoHCF particles with different morphologies and particle sizes.The results show that the synthesis conditions of sample No.6 is the best,that is,sodium ferrocyanide:cobalt chloride:sodium citrate=5:5:30（mmol）,temperature 25°C,reaction time 24 h,concentration 25 mmol L^-1（relative to cobalt chloride）.（2）By adding 1 wt.%Co₂SO₄ as electrolyte additive to electrolyte(1 mol L^-1 Na₂SO₄)of the aqueous sodium ion battery,the cycle performance of CoHCF was significantly improved.After circulating 100/2000/2000 cycles at 2 C,10 C,20 C(1 C=120 mA g^-1)current density,the capacity retention rate increased from 71.5%,20.8%,and 55.7%to 100%,respectively.69.2%,75.6%.The XRD,FT-IR and ICP results show that the CoHCF framework structure is more stable during charge and discharge after the addition of Co²⁺.（3）Ni-rich cathode material NCM811 doped with Nb was prepared by high temperature sintering.Compared with the undoped sample,the capacity retention rate was increased by³0%after cycling 200 cycles at 2 C(1 C=200 mA g^-1),and the rate performance was also better.XRD and TEM results show that the cationic disorder is effectively improved after doping.The in-situ XRD test of the battery shows that the structure of Nb-doped NCM811electrode maintains better stability.