Synthesis And Modification Of Cathode Material LiFeBO₃/C For Lithium Ion Battery

Lithium iron borate (LiFeBO3) has been regarded as a promising lithium ion cathode material for its merits, which including higher specific capacity (220 mAh/g), higher energy density (660 Wh/Kg), environment friendly and low cost. However, moisture sensitivity and low conductivity hinder its further development and application. This paper summarized the development process of lithium ion battery cathode materials and successfully synthesized the LiFeBO3/C by ball-milling and spray-drying assisted high temperature solid state reaction.The modification of LiFeBO3/C by substituting Cr and adding graphene or carbon nanotubes conductive additives was studied, respectively.In this paper, LiOH H2O, FeC2O4·2H2O and H3BO3 as raw materials were mixed by nano ball milling. The relationship between ball milling parameters and the size distribution was investigated. The optimum process parameters of ball milling was as follows: the speed was 800 r/min, solid content was 30% and milling time was 240 min. Based on the optimized ball milling process, the effects of carbon content, calcination temperature and holding time on the physical and electrochemical properties of lithium iron borate (LiFeBO3) were investigated.Finally, the optimum content of carbon coating was 3wt%, the calcination temperature was 550? and the holding time was 7.5 h.Based on the optimized synthetic process of the LiFeBO3/C, the effect of graphene or carbon nanotubes conductive additives on the electrochemical performance of the LiFeB03/C electrode was studied. The results show that the LiFeBO3/C electrode with 3wt% graphene conductive additives (3%GN+SP) exhibited the best electrochemical performance, which had an initial discharge specific capacity of 189.6 mAh/g at 0.1 C. While the LiFeBO3/C electrode was prepared by 100% super-p as conductive additives (SP), the initial discharge specific capacity of which is 174.5 mAh/g at 0.1 C. Moreover, the charge-transfer resistance is reduced from 215 ?for 3%GN+SP to 64.1 ? for SP.Based on the optimized synthetic process of the LiFeBO3/C,the effects of the Cr substituting content on the structure, morphology and electrochemical properties of LiFe1-xCrxBO3 (x=0, 0.005, 0.008) were characterized. The results show that the trivial Cr substituting did not change the structure and the morphology of the LiFeBO3/C. The LiFe0.995Cr0.005BO3/C delivered the highest initial discharge specific capacity of 196.3 mAh/g at 0.1 C. Compared with LiFeBO3/C sample, the LiFe0.995Cr0.005BO3/C sample delivered the superior rate capability of 90 mAh/g at 5 C. The improvement of the performance is contributed to incensement of the electronic conductivity and the Li+ diffusion coefficient of the Cr substituting. The electronic conductivity and lithium ion diffusion coefficient of the LiFe0.995Cr0.0105BO3/C samples were 4.75×10-5 S/cm and 9.70×10-13 cm2 s-1, respectively, both one order of magnitude higher than that of the LiFeBO3/C sample.