Study On Synthesis And Performance Of The Novel LiCoBo₃ Cathode Material For Lithium-ion Batteries

The polyanion-type cathode materials for lithium ion batteries have attracted great attention due to the safety and the property that the operating voltage is flexible and controllable. Li MBO3 borate compounds(M=Fe, Mn, Co) have a high theoretical specific capacity(>210 m Ah/g), high energy density, and low volume change upon cycling, are promising cathode materials for lithium ion batteries.Li Co BO3 was prepared by molten-salt methods. The experimental temperature was determined by TG-DSC. The microstructure, morphology and particle size of the samples were investigated by X-ray diffraction(XRD) and scanning electron microscopy(SEM). And the electrochemical performances were evaluated by galvanostatic and galvanostatic-potentiostatic charge-discharge, AC impedance method.The synthesis parameters of the molten-salt method, in which Li Cl-KCl was used as molten salt, have been studied, and results showed that the the optimal molar ratio of Li Cl-KCl and Co2+ is 6:1, the sintering temperature is 450 °C, the duration time is10 h. The Li Co BO3 product delivers a first discharge capacity of 18 m Ah/g. The sample which prepared at 525 °C for 10 h using Li OH-Li2CO3 as molten salt, delivers an initial discharge specific capacity of 7.4 m Ah/g(C/20).In an attempt to improve eletrochemical properties of Li Co BO3, Mg2+ doped Li Co1-xMgxBO3, Mn2+ doped Li Co1-xMnxBO3, Li Co BO3/Li2O-2B2O3 composite and Li Co BO3/C composite were synthesized.(1)In the case of Li Co1-xMgxBO3, when x=0,0.1, 0.2, the initial discharge capacities are 15.0, 11.1, 23.3, 22.9 m A/g respectively.The sample of x=0.1 delivers a lower discharge capacity, but with a better cycle performance. The sample of x=0.2, 0.3 deliver a higher discharge capacity, but with a poor cycle performance.(2)In the case of Li Co1-xMnxBO3, when x=0, 0.3, 0.5, 1, the initial discharge capacities are 11.8, 8.8, 17.2, 62.3 m Ah/g respectively. The samples of x=0.3 and 0.5 have a good cycle performance.(3)When LBO content is 5wt%, the sample delivers the highest discharge capacity of 14.3 m Ah/g.(4)For Li Co BO3/C composite prepared by molten salt Li Cl-KCl and using ketjen black as carbon source with good conductivity and large specific surface area, the sample with a carbon content of 10wt% delivers an initial discharge specific capacity of 47.8 m Ah/g(C/20)after ballmilled with conductive carbon for 4 hours, and the cycling performance is also improved. When prepared by molten salt Li OH-Li2CO3, Li Co BO3/C compositeshave a higher discharge specific capacity and better cycling performance to some extent.