From the improvement of lithium ion battery
manufacturing materials, aiming at the phenomenon that lithium battery has poor cycle performance at high temperature, the high temperature cycle performance can be improved by modifying the positive electrode material, at present, the modification of positive electrode materials mainly includes bulk doping, surface modification, etc.
Bulk doping includes cation doping, anion doping, composite doping, etc.
Cation doping is mainly aimed at lithium manganese oxide materials. After doping with low-priced cations, Mn element is partially replaced in the crystal, which increases its average valence state and reduces its lattice constant, thus reducing manganese dissolution;
On the other hand, the bond strength between substituted cations and oxygen is higher than that between manganese ions and oxygen, thus making its structure more stable and inhibiting Jahn-The occurrence of Teller effect.
Commonly used doped cation elements include Al, Mg, Fe, Ni, etc.
Anion doping mainly includes F, Cr and s2 *, etc. These negative anions are used to replace oxygen ions, thus improving the stability of the material.
Composite doping is doping 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 reduce 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 the material, thus reducing the dissolution of metal ions.
The commonly used method is to coat the materials with metal oxides, metal fluorides and relatively stable anode materials.
In addition to the modification of the positive electrode material, the deposition of metal ions in the electrolyte on the negative electrode surface is also reduced by coating the surface of the graphite negative electrode. (2)
From the improvement of electrolyte for lithium ion batteries, the improvement of electrolyte for lithium ion batteries is mainly to improve its cycle performance by changing conductive salts and using electrolyte additives.
The important reason for the dissolution of the positive electrode material of the battery is due to the existence of HF in the electrolyte, so reducing the generation of HF can reduce the dissolution of the positive electrode material.
LiBOB lithium salt can be used to avoid the generation of HF and reduce the dissolution of metallic iron, thus improving the high temperature cycle performance of lithium iron phosphate battery.
LiC104 conductive salt and LiBF4 and LiBOB mixed conductive salt were used to improve the high temperature cycle performance of lithium iron phosphate battery.
In addition, organic silicon such as silane and other water removal additives can be used to reduce HF generation.
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 research is more about using additives, and 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, so as to hinder the contact between metal ions and graphite electrodes, and further reduce the deposition of metal ions;
The other is to inhibit the deposition of metal ions by binding metal ions in the electrolyte. (3)
The new binder is an important component of lithium ion battery pole piece, which has a significant impact on the performance of the battery.
The performance of pole sheets using CMC Binder shows better cycle performance and rate performance compared with PVDF binder.
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