Synthesis And Doping Modification Of Ternary Cathode Materials Based On The Lithium Salt Of Salt Lakes

Ni-Co-Mn ternary cathode material for lithium-ion battery as the next generation of battery cathode material candidates with high specific capacity,low price and other advantages.However,there are still some key problems that need to be solved urgently in the process of actualization,such as poor rate performance and severe attenuation of circulating capacity.Among many modification methods,doping modification is an effective method to solve this key problem.The content of impurity element such as Na,K,Mg,B,Cl^–,SO₄^2–in lithium salt of salt lakes is at high level.A variety of domestic and foreign researches show that the control of impurity elements within the appropriate range has a positive effect on the structure and performance of the cathode materials for lithium-ion battery.In this study,in view of the requirement of synthesis and modification of ternary materials and the impurity element content of lithium salt in salt lakes,Na,Mg single-element doping and Na and Mg mixed doping modification for 523-type LiNi_0.5Co_0.2Mn_0.3O₂,622-type LiNi_0.6Co_0.2Mn_0.2O₂ and 811-type LiNi_0.8Co_0.1Mn_0.1O₂ common ternary materials has been carried out.The synthesis of lithium-rich ternary materials and the modification of potassium doping were also studied.XRD,SEM,ICP,XPS,CV,EIS and constant current charge-discharge analysis methods were used to systematically study the crystal structure,physical morphology,electrochemical properties and the dynamics of electrode.The single element doping modification of Na and Mg elements for ternary cathode materials shows that when the doping amount of Mg element is within 3%,it is beneficial to stabilize the main structure but does not increase the specific capacity of the material.An appropriate amount of Na doping increases the distance between the lithium layers of the material and facilitates the transport of lithium ions,thereby increasing the specific capacity of the material and improving the cycle stability and the rate performance of the material.Research shows that the amount of single element doping should be maintained within 3%.The results show that the mixed element doping can exert the synergistic effect of all the elements.The electrochemical properties of the material can be improved when the doping content of the mixed elements is within 2%.Lithium rich ternary cathode material Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ was synthesized by co-precipitation method followed by high temperature solid-state process.The optimization of synthesis conditions and modification of potassium doping were studied.The carbonate precursor Ni_0.13Co_0.13Mn_0.54（CO₃）_0.8 was synthesized by carbonate co-precipitation method using ethylene glycol as solvent and triethanolamine as complexing agent,and the optimum synthesis conditions were discussed.Among them,the optimum synthesis temperature was 50-60°C,pH value was⁸.5,the concentration of the transition metal ions was 2 mol?L^-1,the precipitant concentration was 4 mol?L^–1 and the complexing agent concentration was 3 mol?L^–1.Combined with optimization of heat treatment process,Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ was synthesized and the effect of calcination temperature on the electrochemical performance of Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ was investigated.The results show that the Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ cathode material prepared under the calcination temperature of 900°C and calcination time of 12 h has an irregular square structure with a particle size of about 300 nm.They possess a smooth surface and the excellent dispersibility.The initial discharge specific capacity and coulombic efficiency were 263.8 mAh·g^–1and 73.3%,respectively.And the capacity retention after 200 cycles was above 94.2%with excellent cycle stability and rate performance.The lithium-rich ternary material also made a K⁺–doping modification.The structure and morphology characterization results show that the K⁺-doping does not change the lattice structure of the material.It is uniformly distributed with the particle size of about 300⁵00 nm.The electrochemical tests showed that Li_1.17K_0.03(Ni_0.13Co_0.13Mn_0.54)O₂ with 3%potassium-doped lithium-rich ternary material possessed the highest reversible specific capacity and coulombic efficiency of296.3 mAh·g^–1 and 76%,respectively.And also it had the excellent cycle stability and rate performance.The capacity retention is 98%after 200 cycles and the discharge capacity is about 185 mAh·g^–1 at 5C.Investigating the specific doping content of the element has the guiding significance for the purification of lithium salt for lake salt.This work not only has a certain theoretical value,but also the potential economic value.