Hydrothermal Preparation And Electrochemical Properties Of High Nickel Ternary Cathode Materials

In recent years,a great deal of work has been done to develop lithium ion cathode materials with excellent cycling performance and large discharge capacity to meet the needs of increasing driving distance and reducing charging times of electric vehicles.Li Ni_0.8Co_0.1Mn_0.1O₂material has attracted much attention due to its high charging and discharging performance（200～220 m Ah/g）,environmental friendliness and low cost.However,it still has problems such as poor thermal stability,poor storage performance and short cycle life.To solve these problems,from the perspective of preparation to morphology control,in this paper,Li Ni_0.8Co_0.1Mn_0.1O₂material by hydrothermal method and analyzed its electrochemical performance.（1）By using ammonium bicarbonate（NH₄HCO₃）as precipitant and and chelating agent,using Ni SO₄·6H₂O,Co SO₄·7H₂O and Mn SO₄·7H₂O as raw materials,Li Ni_0.8Co_0.1Mn_0.1O₂materials were prepared by a hydrothermal method.The results shown that the addition of ethylene glycol（EG）and surfactant polyvinylpyrrolidone（PVP）can improve the dispersibility,reduce the particle size,and stabilize the structure,while the micro/nano structure is beneficial to promote the diffusion of Li⁺and protect the material from electrolyte corrosion.Through electrochemical tests,the capacity retention rate was 81.2%after cycling 100 cycles at a current density of 20 m A/g,and the capacity retention rate was 71.1%at a current density of 2000 m A/g（compared with discharge capacity at a current density of 20 m A/g）,which shown excellent cycle performance and rate performance.（2）Using urea as precipitant and chelating agent,using Ni（CH₃COO）₂·4H₂O,Co（CH₃COO）₂·4H₂O and Mn（CH₃COO）₂·4H₂O as raw materials,the Li Ni_0.8Co_0.1Mn_0.1O₂material with porous micro/nano structure was prepared by solvo/hydrothermal method.The results show that during the solvo/hydrothermal process,the addition of low dielectric constant ethylene glycol and glycerol will make the particle size smaller and the distribution more uniform.The porous micro/nano-layered structure can ensure structural stability in repeated Li⁺extraction/intercalation.After electrochemical tests,at a current density of 2000 m A/g,the capacity retention rate of the Li Ni_0.8Co_0.1Mn_0.1O₂material prepared by adding glycerol hydrothermally was 62.9%（compared to the discharge capacity at 20 m A/g）,which was higher than Li Ni_0.8Co_0.1Mn_0.1O₂material prepared by ethylene glycol-assisted hydrothermal progress（42.1%）.When the current density returned to 20m A/g,the discharge capacity of the Li Ni_0.8Co_0.1Mn_0.1O₂material recovered to 95.3%of the initial capacity after glycerol-assisted hydrothermal progress,which shown a excellent rate performance.（3）Innovative use of oxalic acid（H₂C₂O₄）,ammonium bicarbonate（NH₄HCO₃）and urea（CON₂H₄）as precipitant and chelating agent,different Ni,Co,Mn transition metal salts as raw materials,employing hydrothermal method to prepare novel rod-shaped morphology,spherical morphology and ellipsoid morphology of Li Ni_0.8Co_0.1Mn_0.1O₂cathode material and electrochemical testing of the material.The results show that rod-shaped materials,spherical morphology and ellipsoidal morphology all have excellent cycling performance,of which ellipsoidal materials have the best electrochemical performance（when the charge and discharge rate is 20 m A/g,the voltage range is 2.8 V～4.3 V,the first discharge capacity is 175.04 m Ah/g,the highest discharge capacity is 188.78 m Ah/g,the capacity retention rate is 88.7%,and the discharge capacity reaches 115.47 m Ah/g at a rate of 2000 m A/g）.The special ellipsoidal morphology and micro/nano layered structure,ellipsoidal materials can exhibit better electrochemical performance.Therefore,it has guiding significance for the performance of Li Ni_0.8Co_0.1Mn_0.1O₂cathode materials with different morphologies.