Precision Coating And Electrochemical Study Of Ternary Cathode Materials For Lithium Ion Batteries

With the explosive growth of new energy vehicles,people put forward higher requirements for the continuation of new energy vehicles,and the development of high energy density lithium ion power battery has become a hot research field in the field of new energy vehicles.As a key component of determining the energy density of lithium ion batteries,cathode materials are the research and development focus of enterprises and research institutes.the high energy density characteristic lithium nickel cobalt manganese oxide ternary(Li Ni_1-x-yCo_xMn_yO₂,NCM)materials have great advantages,especially high nickel ternary materials(Li Ni_1-x-yCo_xMn_yO₂,1-x-y>0.6),but also stand out among many materials because of their high theoretical energy density,good stability and low cost advantages brought by cobalt content.However,the development of high nickel ternary positive electrode is limited because of its poor cycle stability,severe voltage attenuation and poor safety.Coating modification is the most effective way to improve high-nickel ternary cathode materials.The existing coating techniques:liquid phase,atomic layer deposition and chemical vapor deposition all have some defects and deficiencies.It is of great significance to develop low-cost,high-efficiency and accurate coating modification technology for high-nickel ternary cathode materials.This paper,based on the principle of fluidization,takes high nickel ternary(Li Ni_0.8Co_0.1Mn_0.1O₂,NCM811)as the research object,and uses the fluidized bed chemical vapor deposition（FB-CVD）technology to realize the accurate coating of the NCM811 surface protective layer to prepare the core-shell structure coated composite powder.The main work of this paper is to develop two coating media systems,namely TiO₂coating system and TiO₂/C composite coating system.The specific sections are as follows:（ⅰ）The feasibility of TiCl₄ vapor hydrolysis of titanium tetrachloride（TiCl₄）to form titanium dioxide（TiO₂）was verified by thermodynamic system analysis.The FB-CVD technology was used to accurately deposit on the NCM811 surface TiO₂coating state by regulating the reaction parameters.The material characterization of the coated samples verified that the deposited TiO₂ were uniformly coated on the surface of the NCM811 particles to form a core-shell-coated structure,in which the TiO₂ coating layer with nano-scale thickness was amorphous.The electrochemical test results showed that the NCM811 surface coating TiO₂ could significantly improve the cycling stability and the discharge capacity retention rate increased by nearly 7%after 50 cycles（89.08%and 95%,respectively）.The TiO₂ coating modification mechanism is that the TiO₂ coating layer can effectively insulate the direct contact between the active material of the electrode material and the electrolyte,slow down the interface corrosion,inhibit the mixing,improve the cycle stability of the battery,and increase its safety performance.（ⅱ）TiO₂ coating layer can improve the cycling stability of the material,but because the TiO₂ is not conductive,it limits the conductivity of the material and affects the charge-discharge performance at high rate.In order to improve the conductivity of the NCM811 powder,a composite coating strategy is proposed to improve the stability and electronic conductivity of the material by using TiO₂ and C,respectively.Proposed TiCl₄ mixed solution with toluene（C₇H₈）as sediment reaction precursor,designed one-step vapor deposition technology,used FB-CVD technology to deposit TiO₂/C composite cladding layer on the NCM811 surface;the material characterization results showed that TiO₂ and C were uniformly deposited on the surface of the particles to form a two-component composite coating state;the electrochemical test results show that NCM811 surface coating TiO₂ and C can significantly improve the cycling stability.The discharge specific capacity is 179.8 m Ah/g after 50 cycles,the first charge-discharge efficiency is increased from 79.66%to 86.52%,the capacity retention is increased by nearly 15%（67.63%and 82.8%,respectively）.The rate performance was tested at 2.7～4.5 V.The coated TC-NCM811 improved the comprehensive performance of the first discharge specific capacity ratio NCM811 3.7,23,25.6,31.8,11.7 m Ah/g at 1C,2C,4C,6C,1C。TiO₂/C composite coating can act as a direct contact between the active material and the electrolyte,reduce the mixing arrangement and improve the stability of the material.On the other hand,the carbon coating also improves the conductivity of the material.The composite coating plays a synergistic role and comprehensively improves the electrochemical performance of high nickel NCM811.