Application Of Low-temperature Combustion Method In Cathode Materials Of Lithium Ion Batteries

Lithium-ion batteries have been maturely used in 3C products and small power lithium battery markets such as electric tools and electric bicycles.They are also good choices for power and energy storage batteries in emerging fields such as new energy electric vehicles,energy storage,and communications.Currently,the synthesis methods of lithium ion battery cathode materials mainly are sol-gel method,hydrothermal method solvothermal synthesis method,microwave synthesis method,and co-precipitation method.Although the above various synthesis methods can produce more suitable cathode materials,the synthesis process is complicated.The low-temperature combustion method can prepare ultra-fine powders and it's easy to be pulverized.The powders can be mixed uniformly in the molecular scale and the components in product are uniform.The synthesis process has the advantages of high efficiency.However,this method is not yet mature,and it has not been industrially popularized.This paper explores the specific preparation process and its influencing factors of the low temperature combustion method,and further explores the effect of rare earth doping on the material properties and the physical and chemical properties of NCM ternary materials with different nickel contents.The main experimental conclusions are as follows:In terms of preparation technology,the particle size distribution and electrochemical performance of the samples obtained by tableting,high-temperature sintering,and crushing after the preparation of the secondary precursor are stronger than those of uncompressed and high-temperature sintering materials.The NCM333 material has a 72.81%higher specific discharge capacity than the uncompressed material after 100 cycle at a discharge rate of 1 C.All materials with different lithiation ratios have better layered structure and no heterogeneous phases.When the amount of lithium is 1.05(molar ratio),the cycle performance,first discharge specific capacity,and electrochemical performance of the NCM333 are the best.Therefore,it is most reasonable to use 1.05 lithium in the low-temperature combustion method.The results of the samples sintered for 10 h,the chemical AC impedance test and the cyclic voltammetry curve,are slightly better than the samples sintered for 12 h,but the specific discharge capacity during the cyclic process is lower than the samples sintered for 12 h.After determining the preparation process,take Ce as an example fristly,by preparing NCM333 materials doped with different Ce contents and comparing their physical and chemical properties.It is shown that the performance is best when the rare earth element doping amount is 0.01(molar ratio);Therefore,the doping amount of rare earth is 0.01(molar ratio)as the optimal doping amount for the preparation and doping of La,Pr,and Eu elements.By XRD test,they all have a better layered structure,a smaller degree of Li+/Ni2+mixing and a more complete crystal structure.And the doped rare earth elements are evenly distributed inside the material;The NCM333 materials doped with La,Pr,and Eu elements have higher discharge specific capacity and rate performance.The CV curve and the AC impedance show that the rare earth elements doping can reduce the potential difference ?U of the redox peak of the NCM333 material,reduce the electrode polarization,and improve the reversibility of the positive electrode material.The prepared NCM333,NCM523,NCM312,and NCM811 materials have relatively complete crystal structures.The degree of Li+/Ni2+mixing of the two materials,NCM333 and NCM523,are not serious,but the two materials,NCM312 and NCM811,are relatively low.It means that with the increase of nickel content,the surface of the material is more active in air to generate by-products,which reduces the cycle performance.It can be seen that high nickel materials will have an additional reduction peak at about 4.2V.At this voltage,a transition from H2 to H3 phase occurs.This phenomenon caused the capacity decay.As the nickel content increases,the first discharge specific capacity decreases from 143.35mAh/g of NCM333 to 63.31mAh/g of NCM811 material.After 100 discharge rate cycles are 78.06%,51.93%,48.28%,and 54.35%,respectively at 1C.It can be seen that with the increase of nickel content,the cycle performance of the battery decreases significantly.