Method for improving high temperature operation performance of lithium ion battery
(1) Improvement of materials manufactured from lithium-ion batteries
In view of the poor cycle performance of lithium batteries at high temperatures, the positive electrode material can be modified to improve its high-temperature cycle performance. The main material modification of the product includes bulk doping, surface modification and so on.
Body phase doping includes cation doping, anion doping, composite doping and so on. Cation doping is mainly for lithium manganate materials. By incorporating low-valent cations, the Mn element is partially replaced in the crystal, which increases the average valence state and reduces the lattice constant, thereby reducing the dissolution of manganese; another On the one hand, the bond strength between the substituted cation and oxygen is higher than the bond strength between manganese ion and oxygen, which makes the structure more stable and inhibits the occurrence of the Jahn-Teller effect. Commonly used doping cationic elements are Al, Mg, Fe, Ni and so on. Anion doping mainly includes F, Cr, s2*, etc., and these electronegative anions are used to partially replace oxygen ions, thereby improving the stability of the material. Compound doping is doping with a variety of cations and anions [21-].
The bulk doping method can improve the cycle performance of the battery to a certain extent, but it will cause the decrease of the initial capacity of the lithium ion battery. At present, the most ideal doping method has not been found. The surface modification method can reduce the direct contact between the material and the electrolyte and reduce the specific surface area of u200bu200bthe material, thereby reducing the dissolution of metal ions. The more commonly used method is to coat materials with metal oxides, metal fluorides, and more stable cathode materials.
In addition to the modification of the positive electrode material, the surface of the graphite negative electrode is also coated to reduce the deposition of metal ions in the electrolyte on the surface of the negative electrode.
(2) Improvement from the electrolyte of lithium-ion batteries
The improvement of the electrolyte of lithium-ion batteries is mainly to improve its circulation by changing conductive salts and using electrolyte additives. performance.
An important reason for the dissolution of the battery cathode material is the presence of HF in the electrolyte, so reducing the production of HF can reduce the dissolution of the cathode material. The use of LiBOB lithium salt can avoid the generation of HF and reduce the dissolution of metallic iron, thereby improving the high-temperature cycle performance of the lithium iron phosphate battery. The use of LiC104 conductive salt and the mixed conductive salt of LiBF4 and LiBOB improves the high temperature cycle performance of lithium iron phosphate batteries. In addition, water-removing additives such as organic silicon such as silane can be used to reduce the generation of HF.
In addition to preventing the dissolution of positive metal ions, it is also necessary to reduce the deposition of metal ions in the electrolyte on the graphite surface. The most researched method is the use of additives. There are two ways for additives to inhibit the deposition of metal ions on the surface of graphite. One is to form a dense passivation film on the surface of the negative electrode, thereby preventing the contact between metal ions and the graphite electrode, thereby reducing To prevent the deposition of metal ions; the other is to restrain the deposition of metal ions by trapping the metal ions in the electrolyte.
(3) New binders
Binders are an important part of lithium battery pack pole pieces and have a significant impact on battery performance. The performance of using CMC binder pole piece, compared with PVDF binder, the lithium ion battery using CMC binder shows better cycle performance and rate performance.
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