Selection And Optimization Of Film-Foring Additives For Lithium-Ion Battery

Li-ion batteries have the high energy density, low self-discharge rate, less pollution to environment and other excellent properties, and now have been applied to industriesthe such as mobile terminal electronics, hybrid electric vehicles; Research in the field of new energy have become hot spots in recent years. As technology advancing, demands for the performances of lithium-ion batteries have also become more and more harsh. The vast number of lithium-ion battery researchers face severe challenges such as improve energy density, broadening using temperature range, improve safety performance and so on. Call for immediate solution of these key technologies make to the application of additives for lithium-ion battery has become inescapable. And selection and optimization of additives is important way to improve compatibility of the room temperature ionic liquid electrolyte and lithium-ion battery electrode materials, then solve these technical problems.Compared with the flammability of organic additives which can not been eliminated , ammonium and other salts with a high security, low price, easy to get raw materials, etc. If dissolving appropriate amount in the appropriate system, it would be possible to improve some macroscopic performances of the battery costneutrality and not change the production process. Since 1993, JO Besenhard [1] took N₂O as a inorganic film-forming additive of lithium-ion batteries, Research in this area has been very little.In our paper, the natural graphite anode in traditional electrolytes which were added several kinds of ammonium salts, lithium salts, sodium salts, potassium salts was researched on its electrochemical lithium insertion-deinsertion properties, through the selection and optimization, filtering out the additive system improving the performance of graphite anode , and further study compatibility of optimized electrolyte additives system and cathode materials. Experimental test methods are mainly electrochemical performance testing, SEM, FTIR, etc, the main contents and conclusions of the experiments are as follows:(1) Filtering out the additive. 0.02mol / L of LiF, KF, NaF, NaCl, Na₂CO₃, Na₂SO₃, NH₄F, NH₄Cl, (NH₄)₂SO₄, CH₃COONH₄were added in 1mol/LLiClO₄/EC + DMC(1:1 by v) and 1mol/LLiPF₆/EC+EMC (1:1 by v)electrolyte, filter out the relatively superior performance of three kinds of salt, Na₂SO₃, (NH₄)₂SO₄, CH₃COONH₄ through the electrochemical performance testing.(2)Optimization of the electrolyte system. 0.02mol/LNa₂SO₃,(NH₄)₂SO₄, CH₃COONH₄ were added in 1mol/LLiPF₆/EC + EMC(1:1 by v) electrolyte. Compare with 1mol/LLiClO₄/EC + DMC(1:1 by v) electrolyte, these were better.(3)Optimization of the concentration. 0.01mol / L and 0.04mol / L of Na₂SO₃, (NH₄)₂SO₄, CH₃COONH₄ were added in 1mol/LLiPF₆/EC + EMC(1:1 by v) electrolyte. Compare the results with the concentration of 0.02mol / L, the results when the concentration 0.02mol / L were better than the others .(4) Filtering out electrolyte system having a good compatibility with LiFePO₄ cathode material. When the electrolyte system were 1mol/LLiPF₆/EC + EMC(1:1 by v) added 0.02mol / L Na₂SO₃, (NH₄)₂SO₄, CH₃COONH₄, LiFePO₄ as the cathode, lithium film as the anode, this electrolyte system shows good performance . In terms of the three additives, the performance of olivine-type LiFePO₄ in the electrolyte containing CH₃COONH₄ is the best overall , followed by (NH₄)₂SO₄, Na₂SO₃.After a series of work,one thing was made certain: the three kinds of additives have some different characteristics, there were no absolute superiority. However, this also provides us with greater choice and development space, allowing more flexibility in the use of additives.