| During the "14th Five-Year Plan" period,under the background of carbon peaking and carbon neutrality,my country will vigorously adjust the energy structure and plan to build a new type of green power with new energy as the main body.My country’s new energy industry will usher in a period of rapid development.As an important part of the new energy industry,lithium-ion batteries(LIBs)have attracted the attention of many researchers due to their high energy density,high specific capacity,excellent cycle performance,and no memory effect.Currently,it has made great progress in applications in mobile electronic devices,hybrid electric vehicles(HEV),and pure electric vehicles(EV).In the structural system of lithium-ion batteries,the cathode material is the main contributor to the energy density.Nickel-rich ternary cathode materials(LiNi1-x-yCoxMnyO2)have attracted wide attention due to their high energy density,high specific capacity,and low cost,but they have disadvantages such as low initial charge-discharge efficiency,poor cycle performance,and poor thermal stability.Therefore,it is urgent to optimize the performance of nickel-rich ternary cathode materials to obtain lithium-ion batteries with a lower voltage decay rate and better thermoelectrochemical performance.It is one of the better methods to improve its electrochemical performance and thermal stability using coating and doping.In this paper,based on theoretical calculation,the simulation calculation of LiNi0.8Co0.1MnO.1O2(NCM811)doped with titanium and vanadium group elements is carried out.The basic law of doping modification is obtained.Based on this,the selection of Nb.NCM811 cathode material was doped and modified with Nb2O5 to explore its electrochemical properties,physicochemical properties,and thermal stability under high voltage.1.To save experimental time and improve work efficiency,this paper firstly uses Material Studio software to establish pure-phase cathode materials and LiNi0.8Co0.1Mn0.1-xMxO2(M=Ti,Zr,Hf,V,Nb,Ta)crystal model,and use first-principles to analyze the connection between the structure,performance and complex electrochemical mechanism of cathode materials.The results show that the lattice parameters and unit cell volume of the dopant after the structure optimization are larger than those of the pure phase material,but the structure of NCM811 does not change;the energy band structure and state of NCM811 before and after doping.The density were visualized,which showed that the doped NCM811 was still a semiconductor,and the optimal doping amount of the titanium group element and vanadium group element doped NCM811 is obtained by comparing the bandgap.In the same group of elements,the smaller the atomic number is,the smaller the bandgap is due to the doping modification;for the same element,when the doping amount increases from 0.5%to 3%,the bandgap first decreases and then increases,and the bandgap increases at 1%.The tape width is the smallest and the conductivity is the best.Considering the experimental cost and process flow,Nb is finally selected for experimental research.2.The Nb-doped NCM811 cathode material is successfully prepared by a one-step calcination process.The results show that the optimal content of Nb is 1 wt%,and Nb doping helps to increase the interlayer spacing,electron transport,and structural stability of the lithium layer and reduce the cation disorder,thereby significantly improving the conductivity of Li+ in the material.At a high voltage of 4.6 V,the initial discharge specific capacity of 1 wt%Nb-doped NCM811 cathode material is 222.3 mAh/g at 0.1 C,and the capacity retention rate after 100 cycles at 1 C 92.03%.The capacity retention rate of pure phase NCM811 under the same conditions is only 74.30%.Nb doping can improve the cycle performance and improve the safety performance of the material.It can be seen from the thermogravimetric analysis that the weight loss peak temperature of the modified cathode material is shifted backward,the mass change trend is gentler,and the thermal stability is better. |
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