Study On The Combustion Synthesis And Electrochemical Performances Of Li-rich Layered Cathode Material Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂

With the rapid development of economy,fossil energydepletion,environmental pollution and global warming are getting worse,which leads to the fact that the traditional fossil fuels can not effectively meet the real needs of the world economic development.Base on this background,the application and development of lithium-ion batteries began to draw widespread attention.There are many advantages in the lithium-ion battery,such as high energy density,long cycle life,high charge and discharge capacity,good safety and so on.Since the cathode materials have a great influence on the performance oflithium-ion battery.Synthesis of high-performance cathode materialis is the key to develop new high-performance lithium-ion battery.Compared with other cathode materials,lithium-rich manganese-based cathode materials is generally regarded as one of the candidates for the next generation of lithium-ion battery cathode materials,with higher discharge specific capacity,up to 250mAh g-1.For the lithium-rich layered cathode materials,different synthetic methods will result in different electrochemical performance.For the same synthetic method,the process parameters can significantly affect the final material properties.Therefore,it is necessary to try a variety of methods to synthesize lithium-rich cathode materials and optimize the electrochemical performance.In this paper,the specific research object is lithium-rich manganese-based cathode material Li[Li0.2Mn0.54Ni0.13Co0.13]O2.We have made an in-depth study on the related problems of cathod material preparation to effectively improve the electrochemical performance of the lithium-rich layered cathode materials by adjusting the experimental parameters.Nanocrystalline Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode materials are successfully prepared by sol-gel combustion method with urea as both chelating agent and fuel.The effects of calcining temperature and solvent on the electrochemical performance are studied.The as prepared samples are characterized and tested by means of XRD?SEM and electrochemical methods.The electrochemical tests indicates that the materials synthesized at 800? with water solvent deliver a high initial discharge capacity of 255.8 mAh g-1 and a capacity retention of 76.8%after 50 cycles at a current density of 20 mA g-1 between 2.0 V and 4.8 V vs.Li/Li+.It also shows better rate capability compared with the materials calcined at 750?,850? as well as the materials using alcohol solvent calcined at 800?.The experimental results show that enhanced electrochemical performance of the materials calcined at 800? with water solvent is due to the uniformly distributed nanoparticles with a shorter diffusion path,perfect crystallinity,and ordered layered structure including less cations mixing.Li-rich layered oxide Li[Li0.2Mn0.54Ni0.13Co0.13]O2 is synthesized successfUlly by solution-combusting method.The influence of different soaking time on the physical properties and electrochemical performance is studied.Based on the above conditions,Li-rich layered oxide Li[Li0.2Mn0.51Ni0.13Co0.13]O2 is synthesized successfully by sol-gel combustion method as reference to investigate the influence of different method on the electrochemical performance.The results demonstrated that soaking time has a great influence on the physical properties and electrochemical performance of the material synthesized by solution-combusting method.The sample SC-10 shows the best performance,with conditions of 850? calcining temperature and 10h soaking time.The sample SC-10 showes a high charge-discharge capacity of 335.1 mAh g'1?266.7 mAh g-1 after 1 cycle with a current density of 20 mA g-1,while the capacity of SCG-10 synthesized by sol-gel combustion is 302.8 mAh g-1,229.3 mAh g-1 under the same condition.Additionally,sample SC-10 exhibites better rate capability with the reversible discharge capacity over 70 mAh g-1 under the condition of 1000 mA g-1.According to EIS results,it is easily found that the charge-transfer resistance of the sample SC-10 is smaller than that of the sample SCG-10.At last,Li-rich layered materials Li[Li0.2Mn0.54Ni0.13Co0.13]O2 is synthesized via sucrose combustion(ZC)and urea combustion(NC)methods.From the SEM images of the sample ZC and sample NC,it can be seena great difference between the two samples.The particles in thesample ZC are larger with serious aggregation,while in the sample NC,they are in homogeneous dispersion and uniform size.From the XRD patterns of the sample ZC and sample NC,showed that there are two impurity phasesin the sample ZC,demonstrating that different oxidizers will affect the purity of synthesizedmaterials.The sample NC deliveres high reversible dischargecapacities of255.2 mAh g-1,201.7 mAh g-1,172.9 mAh g-1,145.6 mAh g-1,123.9mAh g-1 and 77 mAh g-1 at the current density of 0.1C,0.2C,0.5C,1C,2Cand5C,respectively.However the reversible discharge capacities for the sample ZC was just 136.5mAh g-1,111.0 mAh g-1,86.7 mAh g-1,68.1 mAh g-1,49.4 mAh g-1and 20.7 mAh g-1,respectively,at the samecurrent density.The electrochemical performance of the sample ZC is not as good as the sample NC.It can be concluded that urea is conducive to synthesize Li-rich layered materials Li[Li0.2Mn0.54Ni0.13CO0.13]O2 by solution-combusting method.