The Preparation Of High-nickel Ternary Cathode Material For Lithium Ion Battery

With the rapid development of digital electronic products such as mobile phones and notebook computers and the new energy source automobile industry,people have put forward higher requirements for high-performance lithium-ion batteries.At present,on the technical level,the capacity of the anode material is sufficient to meet people's needs,and the limitation of the development of the lithium ion battery is mainly the limitation of the capacity of the cathode material.The cathode materials currently commercialized on the market mainly include Li Co O₂?Li Mn2O4 and Li Fe PO4.The specific capacity of these cathode materials generally does not exceed the specific capacity of 160 m Ah/g.For the ternary cathode material,the content of nickel in the nickel-cobalt-manganese element in the ternary material can be reduced,and the cobalt element and the manganese element are reduced.Nickel is the main active material, which not only increases the specific capacity of the material,but also reduces the material.the cost of.The specific capacity of the NCM811 cathode material currently studied can reach a specific capacity of 190 m Ah/g or more,which can meet the current cruising range requirements for new energy vehicles.In this thesis,by further optimizing the synthesis conditions of high-nickel ternary materials,a more uniform and stable micro-scale spherical particle precursor is prepared,and the electrochemical properties of the material are further improved by structural modification and coating modification.In order to study the synthesis conditions of the precursors of the best high-nickel ternary materials,we selected two synthetic conditions,the co-precipitation reaction time and the complexing agent concentration,for comparison.Firstly,in order to obtain the optimal coprecipitation reaction time,we set the time of 4h,6h,8h,10h and 20h respectively,and explored the morphology and particle size of the material under different reaction time.When the reaction time is 8 h,the combined specific capacity and cycle performance of the obtained high nickel ternary positive electrode material are optimal.The current density of the charge and discharge test is 0.2C?40 m A/g?,and the working voltage range is 2.8?4.3V.Under the reaction condition,the first ring discharge specific capacity of the material is 186.2m Ah/g,and the capacity after 100cycles The retention rate was 78.7%.In order to obtain the optimum ammonia concentration of the complexing agent during the reaction,we set the concentration of three ammonia waters of 2mol/l,1mol/l and 0.5mol/l based on the reaction time of 8h.It is found that the prepared precursor has the best material morphology and electrochemical performance when the concentration of ammonia is 1mol/l.The first specific discharge capacity of the material is 194.0 m Ah/g and capacity retention rate is87.5%.The discharge specific capacity is 169.8 m Ah/g after 100 cycles of charge and discharge cycles.In order to improve the cycle performance and rate performance of Li[Ni_0.8Co_0.1Mn_0.1]O₂,the full concentration gradient structure of GM-1 and GM-2 was prepared by hydroxide co-precipitation method.Through the charge-discharge cycle and rate performance test,it is found that the GM-1 structure has the best cycle performance,while the GM-2 structure has the best rate performance.The analysis of this phenomenon is related to the element distribution inside the particle.In order to further improve the electrochemical performance of Li[Ni_0.8Co_0.1Mn_0.1]O₂ material,we carried out Li₃PO₄ coating experiments on the material,and the coated materials were characterized and electrochemically tested.Through the charge-discharge cycle test,it was found that the coated material first needs to be activated.After 10 cycles of charge-discharge cycle,the specific capacity reached a maximum of 191.1 m Ah/g.After 150 cycles of charge-discharge cycle,the discharge specific capacity was 173 m Ah/g.It is significantly higher than Li[Ni_0.8Co_0.1Mn_0.1]O₂material.Through the PITT test,it was found that the lithium ion diffusion coefficient of the material after coating modification was higher than that of the raw material.The main reason is that the coating modification increases the ionic conductivity of the material and prevents the electrolyte from continuously corroding the material.