Electrochemical Performance Study Of Li₄Ti₅O₁₂ And LiFePO₄

Spinel Li4Ti5O12 and olivine LiFePO4 are two kind of promising electrode Li-ion materials candidate which may be applied widely in the secondary Li ion battery area for their excellent cycle performance and rate capability. A series of electrochemical performance test and charge characterization was performed using LiFePO4 positive electrode and Li4Ti5O12 negative electrode by assembling lithium-ion batteries.Orthogonal experiment was used to optimize the liquid phase preparing method for the Li4Ti5O12 materials. The influence factors to the synthesis were discussed by the cyclic voltammograms and AC impedance test research. The experimental results indicated that the calcining temperature, calcining time, the input rate of Li/Ti was of vital importance during the preparation process. The best Li4Ti5O12 material preparation technology conditions after the optimization determined that calcing temperature was 700?, the calcing time was 6 h as well as the raw material rate of Li and Ti was 0.9. The Li4Ti5O12 as prepared showed the lowest electrochemical impedance, and the best symmetry and peak current during the electrochemical characterization. The materials show good reversibility and fast charge-discharge capacity. Graphene doped Li4Ti5O12 based on the above mentioned method was characterized by the electrochemical performance. The best calcining temperature was 600?, calcination time was 8 h and the best grapheme addition was 50 mg. The graphene doped materials displayed lower reversibility and charge-discharge ability, but the electrochemical impedance has improved significantly according to the comparison between the graphene doped samples and the pure Li4Ti5O12 samples.The single factor method was chose to optimize the carbon coated LiFePO4 composite materials synthesis process according to the cyclic voltammograms experiment and AC impedance experiment. Experimental results showed that LiFePO4 materials performed best in the electrochemical impedance, and kept excellent symmetry and peak current, good reversibility and fast charge-discharge capacity if the calcination temperature was 650?, the calcination time was 11 hours, the glucose content was 15%. The LiFePO4/(carbon+ grapheme) composites was obtained by coating the LiFePO4/C with graphene based on the mentioned method. Cyclic voltammograms experiment and AC impedance experiment was carried out to discuss the best rate of glucose to graphene was:12:3. Compared with LiFePO4/C composite material, LiFePO4/(carbon+grapheme) decreased greatly in the solution resistance and charge transfer resistance, and remained in the electric double layer capacitance change and owned lower Warburg impedance value.The Li ion battery was composed by LiFePO4/(carbon+grapheme) composites anode and Li4Ti5O12/graphene negative electrode. The electrochemical performance was carried out.