Graphene coated lithium iron manganese phosphate -Lithium - Ion Battery Equipment
Lithium iron phosphate (LFP) is a common cathode material for lithium-ion batteries. Because of its good thermal stability and safety performance, it is favored by power battery manufacturers. Relevant safety tests show that, under the existing technical conditions, only lithium ion batteries made of lithium iron phosphate can pass all safety tests, and will not catch fire or explode in acupuncture and extrusion tests, which is of great significance to electric vehicles, electric buses and other fields that require high battery safety. However, lithium iron phosphate material also has this inherent disadvantage, mainly because of its low working voltage, only about 3.4V, and poor conductivity, which not only makes the energy density of the material much lower than that of lithium cobalate and other materials, but also affects the rapid charging and discharging performance of the battery. In order to improve the working voltage of lithium iron phosphate material, people try to replace Fe element in lithium iron phosphate material with Mn element. However, relevant experiments and calculations show that LiMnPO4 has very poor conductivity, and its electronic conductivity is far lower than LiFePO4, resulting in extremely poor multiplying performance of the material and almost no discharge. Therefore, people took the second place and studied LiMn1-xFexPO4, a solid solution material of lithium iron phosphate and lithium manganese phosphate. On the one hand, this material inherited the "relatively good" conductivity of LiFePO4, and also inherited the high working voltage of LiMnPO4.(Lithium - Ion Battery Equipment)
In order to improve the conductivity of lithium iron manganese phosphate material, people have tried many materials to coat it. The most successful and mature method is graphite coating. However, because graphite cannot form a continuous conductive network on the surface of material particles, the improvement of graphite on the performance of lithium iron manganese phosphate material is very limited. Graphene materials are composed of single layer or few layers of graphite atoms, and have good conductivity. They are the best known materials with the best conductivity. The emergence of graphene gives people a choice. The excellent conductivity of graphene can significantly improve the electronic conductivity of lithium iron phosphate materials and improve the magnification performance of materials. At present, there are two main methods for graphene coating lithium iron phosphate: backward method and forward method. The backward method is to form a graphene layer on the surface of the material particles by mechanical mixing and self-assembly on the surface of the prepared lithium iron phosphate material particles. The forward method is to form pyrolytic carbon by pyrolysis of Fe containing organic matter, and form a graphene layer on the surface of material particles through catalytic carbonization, or directly synthesize precursor FePO4 in graphene oxide solution to attach it to graphene oxide sheets, and then synthesize lithium iron phosphate material. As olivine material has only one dimensional Li+diffusion channel, we prefer to coat the surface of lithium iron phosphate primary particles with a layer of graphene of hundreds of nanometers, so as to improve the electronic conductivity and ionic conductivity of the material at the same time.
Recently, Wei Xiang of Sichuan University and others synthesized graphene coated lithium iron manganese phosphate material by forward method. They first synthesized graphene oxide coated nano Li3PO4 material in graphene oxide solution by coprecipitation method, then reacted the precursor with Mn2+and Fe2+in ethylene glycol solution by solvothermal method to obtain LiMn0.5Fe0.5PO4 material, and then graphene oxide was reduced to graphene. This material inherited the morphology of the precursor Li3PO3, whose particle diameter was only about 20nm, greatly shortening the diffusion distance of Li+, The graphene network structure endows the material with good conductivity. The electrochemical test found that the material had two voltage platforms, 3.4-3.6V and 4.0-4.1V, respectively, corresponding to two reactions of Fe2+/Fe3+and Mn2+/Mn3+. The capacity test shows that the capacity of the material can reach 166mAh/g after carbon coating again. Due to the good conductivity of the material, the material has obtained good magnification performance. At the magnification of 0.1C, 0.2C, 0.5C, 1C, 3C, 5C, 10C and 20C, the specific capacity of the material reaches 166156136126115107101, 90mAh/g respectively, and the energy density of the material also reaches 612Wh/kg, which is higher than that of lithium cobalate material, After 500 cycles at 1C rate, the capacity retention rate of the material reaches 92%, showing excellent cycling performance.
In order to improve the conductivity of lithium iron manganese phosphate material, people have tried many materials to coat it. The most successful and mature method is graphite coating. However, because graphite cannot form a continuous conductive network on the surface of material particles, the improvement of graphite on the performance of lithium iron manganese phosphate material is very limited. Graphene materials are composed of single layer or few layers of graphite atoms, and have good conductivity. They are the best known materials with the best conductivity. The emergence of graphene gives people a choice. The excellent conductivity of graphene can significantly improve the electronic conductivity of lithium iron phosphate materials and improve the magnification performance of materials. At present, there are two main methods for graphene coating lithium iron phosphate: backward method and forward method. The backward method is to form a graphene layer on the surface of the material particles by mechanical mixing and self-assembly on the surface of the prepared lithium iron phosphate material particles. The forward method is to form pyrolytic carbon by pyrolysis of Fe containing organic matter, and form a graphene layer on the surface of material particles through catalytic carbonization, or directly synthesize precursor FePO4 in graphene oxide solution to attach it to graphene oxide sheets, and then synthesize lithium iron phosphate material. As olivine material has only one dimensional Li+diffusion channel, we prefer to coat the surface of lithium iron phosphate primary particles with a layer of graphene of hundreds of nanometers, so as to improve the electronic conductivity and ionic conductivity of the material at the same time.
Recently, Wei Xiang of Sichuan University and others synthesized graphene coated lithium iron manganese phosphate material by forward method. They first synthesized graphene oxide coated nano Li3PO4 material in graphene oxide solution by coprecipitation method, then reacted the precursor with Mn2+and Fe2+in ethylene glycol solution by solvothermal method to obtain LiMn0.5Fe0.5PO4 material, and then graphene oxide was reduced to graphene. This material inherited the morphology of the precursor Li3PO3, whose particle diameter was only about 20nm, greatly shortening the diffusion distance of Li+, The graphene network structure endows the material with good conductivity. The electrochemical test found that the material had two voltage platforms, 3.4-3.6V and 4.0-4.1V, respectively, corresponding to two reactions of Fe2+/Fe3+and Mn2+/Mn3+. The capacity test shows that the capacity of the material can reach 166mAh/g after carbon coating again. Due to the good conductivity of the material, the material has obtained good magnification performance. At the magnification of 0.1C, 0.2C, 0.5C, 1C, 3C, 5C, 10C and 20C, the specific capacity of the material reaches 166156136126115107101, 90mAh/g respectively, and the energy density of the material also reaches 612Wh/kg, which is higher than that of lithium cobalate material, After 500 cycles at 1C rate, the capacity retention rate of the material reaches 92%, showing excellent cycling performance.
