Synthesis Process Optimization And Doping Modification Of CuF2 As Cathode Material For Lithium Ion Batteries

CuF₂had been considered as one of the most promising candidates because of its high theoretical energy densities（gravimetric energy density of 1870 Wh/Kg and volumetric energy density of 7908 Wh/L）and theoretical potential（3.55 V）.In this paper,the co-precipitation method for the preparation of CuF₂materials was optimized,and the additive PVP was introduced.On this basis,Zn_xCu_1-xF₂and Zn_0.15-xNi_xCu_0.85F₂materials were prepared to improve the electrochemical performance of the original electrode.The specific research contents are as follows:（1）The CuF₂samples were synthesized by coprecipitation method.XRD results showed that the mixture of deionized water and anhydrous methanol at the volume ratio of 1:1 as NH₄F solvent effectively inhibited the formation of impurities.SEM and TEM images showed that the particle size was reduced,and the dispersion degree was improved significantly.The discharge capacity of this sample was 456.6 m Ah/g at 0.1 C.PVP additive was used to disperse copper fluoride particles.The results proved that the particle size of the sample with 0.5 g PVPK15 was smaller and more regular,and the number of secondary particles formed by agglomeration was greatly reduced.The first discharge capacity of this sample was 44.8 m Ah/g higher than pure one.（2）Zn_xCu_1-xF₂series samples were synthesized by improved coprecipitation method.XRD results confirmed that Zn²⁺did not affect the original phase structure of CuF₂.In the discharge-charge test,the initial discharge capacity of Zn_0.15Cu_0.85F₂at0.1 C was 528.6 m Ah/g,and the first coulombic efficiency was 57.0%.In rate performance,the discharge capacities of Zn_0.15Cu_0.85F₂at 0.2 C,0.5 C and 1 C reached 97.1%,95.2%and 92.5%of the capacity at 0.1 C,respectively.The capacity attenuation from 0.1 C to 1 C was 39.5 m Ah/g.In cycle test,the samples with Zn²⁺doping content exceeding 10%had higher reversibility from beginning to end.CV and EIS results proved that Zn_0.15Cu_0.85F₂electrode had better reversibility and dynamic characteristics in charge transfer process.（3）The Zn_0.15-xNi_xCu_0.85F₂samples were obtained after heat treatment at 275°C for 5 h.XRD results confirmed that the crystal structure of the samples was still distorted rutile structure.The results of the first discharge-charge tests at different rates showed that the doping of Zn²⁺and Ni²⁺significantly increased the discharge capacity of the bare electrode,up to 655.3 m Ah/g,and could increase the first coulombic efficiency by 13.2%,18.3%,16.9%and 22.4%at different current densities.In the cycle test,the capacity retention rate of Zn_0.1Ni_0.05Cu_0.85F₂was the highest at all rates,showing the best cycle performance.The results of CV and EIS indicated that the doping of Zn²⁺and Ni²⁺inhibited the growth of cathodic electrochemical polarization,and the voltage hysteresis was improved.