The ternary materials

Common cathode materials for lithium batteries mainly include lithium cobalt acid (LCO), lithium manganese acid (LMO), lithium iron phosphate (LFP), ternary materials (NCM/NCA), etc.  

What are ternary materials?  

Ternary (LICoxMNyNi1-X-YO2), with a-NafEO2 layered structure (R-3M space group), has a theoretical capacity of about 275 mAh/g. In ternary materials, Mn always maintains +4 valence and has no electrochemical activity, but only acts as a material skeleton to stabilize the crystal structure, while Ni and Co are electrochemical activities with +2 valence and +3 valence, respectively. As the composition ratio of Ni, Co and Mn changes, the capacity, safety performance and many other properties of the material can be adjusted to a certain extent. People in the industry are used to naming the material according to the proportion, such as 111/442/532 (indicating the proportion of Ni, Mn and Co elements). Under the influence of Ni/Li interaction, the structure stability of the material is better when Ni/Mn/Co ratio is 1:1:1 and 4:4:2. However, in order to obtain more reversible capacity, the development of ternary materials tends to increase the nickel content, such as 532/622/721/811.  

The preparation method of ternary material

At present, there have been a variety of synthetic methods to prepare LiCoMnNiO2 ternary cathode materials, including coprecipitation, sol-gel, spray drying and solid phase reaction. Co-precipitation method is the most common method to prepare spherical ternary materials, including: hydroxide co-precipitation method, carbonate co-precipitation method.  

Modified  

Although ternary materials have good electrochemical performance, there are still many problems to be solved in practical application, such as mixing and discharging of lithium ions, improving the first efficiency, and increasing the diffusion coefficient and electronic conductivity of lithium ions. The main modification methods of LINI1/3Co1/3MN1/3O2 include ion doping and surface coating. The surface coating, proper doping ratio and uniform doping can make the structure of the material more stable and improve the cycling and thermal stability of the material.  

Iron doping  

The output power of lithium-ion battery is directly related to the electronic conductance and the ionic conductance of lithium ion in the material, so improving the electronic conductance and the ionic conductance by different means is the key to improve the material.  

Surface coating  

The surface of ternary material was modified with metal oxides (Al2O3, ZnO, ZrO2, etc.) to separate the material mechanically from the electrolyte, reduce the side reaction between the material and the electrolyte, inhibit the dissolution of metal ions, and optimize the cyclic properties of the material.  At the same time, the surface coating can also reduce the collapse of the material structure in the process of repeated charge and discharge, which is beneficial to the cyclic properties of the material.