Synthesis And Electrochemical Performance Of Spinel/Layered Composite Cathode Materials

Lithium-ion batteries are widely used in portable electronic devices,electric vehicles and aerospace,and their energy capacity density has been the focus of attention,while the key is the positive electrode materials.The lithium-rich layered cathode material has a high charge-discharge specific capacity of 250 mAh g-1 or more,but it still remains problems such as continuous capacity,voltage attenuation and poor rate performance.The problem can be effectively solved by spinel compounding,which is an important strategy to promote its industrialization and realize the next generation of high-performance cathode materials.Based on the research progress of spinel/rich lithium composite cathode materials,this work focused on the systhesis and electrochemical performance studies of spinel/rich lithium three-phase composite cathode materials and carbon source induced in situ derived spinel/lithium-rich composite cathode materials.The paper studies the spinel type,synthesis temperature,crystal phase composition,material structure and electrochemical properties of the spinel/layered composite cathode materials with three-dimensional interpenetrating structure and core-shell structure.Among them,the materials delivered the best electrochemical performance when the composite content of spinel phase was 5%,the heat treatment temperature was 750℃ and the sintering time was 3 h.The materials reachd the highest discharge specific capacity of 249.8 mAh g-1 and capacity retention with 94.6%,which was 19.9%higher than the pristine materials.LiNi0.5Mn1.5O4 was proved to be the most suitable composite crystal phase.The first coulombic efficiency of the modified material reached 73%,the first discharge capacity reached 253.3 mAh g-1,and the capacity retention rate of the material after 100 cycles of 1 C was as high as 97.9%.This research had obtained a composite cathode material with high capacity and stable cycling performance.The material reached 282.5 mAh g-1 at 0.1 C,which was 52.8%higher than that of the unmodified material,and the capacity of the material at 5 C increased from 62.8 to 138.3 mAh g-1.The capacity retention rate of the modified material at 1 C rate after 100 cycles increased from 74.3%to 82.4%.The carbon/spinel/lithium-rich triple-layer positive electrode material was prepared by in-situ derivatization using phenolic resin and glucose as carbon sources.The carbon coating layer serves as electron highway while the spinel phase constract fast lithium-ion transport channel.The special structure lowers the impedance of the electrode and improve the electrochemical performance.The initial capacity of the material reached 275 mAh g-1 at 0.2 C,and the overall capacity and rate performance was significantly improved.When the glucose was used as carbon source,the material reached 313.9 mAh g-1 at 0.2 C,and still delivered a high specific capacity of 186 mAh g-1 at 5 C.After 100 cycles of 1 C,the capacity remained at 205.2 mAh g-1 and the capacity retention rate was 102.5%.In contrast,the carbon layer formed by glucose had better coating uniformity,and the electrochemical performance of the material was more obvious,and the modification effect was better.The results of the thesis show that the structural stability of lithium-rich cathode materials have been improved and the electrochemical impedance is reduced so that the materials obtain great rate and cycle performance.Using carbon as an agent to generate spinel phase is helpful to improve the immigration of lithium ions on the interface between the electrode and electrolyte as well as in bulk of lithium-rich cathode materials,which give a great improvement on the materials’specific capacity and rate performance.