Synthesis And Performance Of Concentration-gradient Cathode Materials For Lithium Ion Batteries

In recent years,lithium-ion batteries become the main sources of energy batteries,such as portable electronic devices and electric vehicles.Lithium-ion battery research and development is gradually turning to high-performance,low-cost,safety electrode materials.The layered oxide cathode of Ni-rich materials has high practical discharge capacity at a high voltage(4.4-4.6 V)and lower cost than LiCoO2.However,the intrinsic structure of Ni-rich materials leads to poor thermal stability and many side reactions.This is one of the challenges facing the commercialization of such high-energy cathode materials.In this paper,NiSO4·6H2O,COSO4·7H2O,and MnSO4·H2O were used as starting materials with the co-precipitation method to synthesize(Ni0.8Co0.1Mn0.1)(OH)2.The preparation conditions of the materials were discussed.The morphology,structure and particle size distribution of the samples were characterized,and the electrochemical properties of the materials were analyzed.The results showed that the precursor obtained under the conditions of pH=11.3 and ammonia concentration of 0.5 mol/L had the best morphology,mixed well with excess LiOH·H2O(molar ratio 1:1.05),and sintered at 750 ℃ for 10 h.Under this condition,LiNi0.8Co0.1Mn0.1O2 has the best performance.The initial discharge capacity is 214.5 mAh g-1 at 2.8-4.6V and the capacity retention is 70%after 100 cycles.There are many problems in the material itself,and it is necessary to further improve LiNi0.8Co0.1Mn0.1O2.In order to improve the performance of LiNi0.8Co0.1Mn0.1O2 materials,we redesigned their structure:LiNi0.8Co0.1Mn0.1O2 as the core to provide high capacity and Li[Ni1/3Co1/3Mn1/3]O2 as the shell with stable structure.The content of Ni,Co,and Mn is a function of the distance from the core to the surface of the microsphere.The relationship between the reaction conditions and morphology is discussed,and the reaction conditions are optimized.Full concentration-gradient material shows a high initial discharge capacity of 195.6 mAh g-1 in a voltage window of 2.8-4.6 V,and capacity retention more than 90%after 100 cycles.The improvement of electrochemical performance shows that full concentration-gradient material is a promising cathode material.This full concentration-gradient material material has a high reversible capacity and excellent cycle stability at high voltages.Based on this,the mechanism of precursor nuclei formation and growth is explored,which can qualitatively analyze the reasons for the stability of this material.In the experiment,it was found that the internal appearance of full concentration-gradient Li[Ni0.6Co0.2Mn0.2]O2 is different from that the homogeneous Li[Ni0.6Co0.2MnO2]O2.The results confirm that the precursors have different growth patterns.Homogeneous Li[Ni0.6Co0.2Mn0.2]O2 is polycrystalline aggregates to form a spherical shape.Concentration-gradient material is formed by cross-stack primary particles.It acts as a stable shell to protect the surface of the electrode.This inhibits the generation of intercrystalline cracks,increases the stability of the material and thus affects the electrochemical performance.The results show that high initial discharge specific capacity(185.2 mAh g-1)at a 1C rate in a voltage window of 2.8-4.4 V and the capacity retention is 81.1%after 300 cycles.