Study On Electrochemical Properties Of Cathode Materials Of Lithium Ion Battery In Aqueous Solution

Aqueous lithium ion batteries have the advantages of non aqueous lithium ion battery and traditional seeondary batteries with aqueous electrolyte, which will eliminate burning, explosive crisis resulted from organic eleetrolyte. Compared with other low voltage batteries, it has competitive potential. LiFePO4 and LiMn2O4 cathode materials for lithium ion batteries with structural stability, high specific capacity, heat safety, low cost of raw materials, are considered the most research value of the material system, and will not be limited by aqueous electrochemical windows.The charge and discharge experiments of LiFePO4 with powder microelectrode in LiNO3 show that LiFePO4 has similar capacity in aqueous solution and organic electrolyte. The cyclic voltammetry studies show that:(1) lithium ion of LiFePO4 is reversible deintercalation in LiNO3 solution; (2) increasing the concentration of LiNO3 can accelerate lithium ion deintercalation rate. (3) the lithium ion diffusion coefficients in the solid phase increase significantly temperature increases.By potentiostatic intermittent titration measured lithium-ion diffusion coefficients of LiFePO4 in LiNO3 solution, the results show that:(1) the diffusion coefficients of six different particle-size samples are measured with the electrode powder morphology, values are all in 10-14 cm2s-1 magnitude; (2) the diffusion coefficients decrease with the increase of potentials; (3) at the platform of current charge-discharge potential, diffusion coefficient increase, we explain this phenomenon via the nucleation-growth mechanism of phase Change process; (4) apparent diffusion coefficient obtained in potential zone is not clear for the physical meaning. Phase transition occurs in the single-phase region before and after the actual value of the diffusion coefficient obtained in the range 10-14 cm2s-1; (5) By using potentiostatic intermittent titration to obtain diffusion coefficients with carbon fiber electrode contacting single particle of LiFePO4 in LiN03 is similar with that with the powder microelectrode, the diffusion coefficients from 10-15 to 10-14 cm2s-1 magnitude. The electrochemical behavior of LiMn2O4 particles (spherical and cubic) which are prepared in our group is tested by powder electrode and carbon fiber micro-electrode in LiNO3 solution. Results show that two redox peaks of Li-ion emerge can be clearly separated only at the slow scan rate; current peaks of spherical LiMn2O4 particles are larger and sharper than that of cubic particles, which indicates that spherical particles have better reversibility. By potentiostatic intermittent titration technique to research the diffusion coefficients of lithium ion in different particles, the results show that the diffusion coefficients of spherical particles are larger than that of cubic particles. These results are consistent with the material properties, which is the property of spherical particles is better than that of cubic particles.