Research On Lithium Iron Phosphate Battery To Improve The High-Power Performance

Lithium ion batteries have been widely used in laptops, mobile phones, camera and other portable electronic devices after many years' development due to the long cycle life, high energy density, non-toxicity, and environmental friendliness.Cathode material is the core material of lithium ion battery, after several generations of development, currently used stabilizing materials are LiCoO2, LiMn2O4, Li(NiCo Mn) O2, NCA, LiFePO4 and so on. Lithium iron phosphate having an olivine structure, stable and reliable, long cycle life, becoming the first choice for new energy electric car power supply. However, lithium iron phosphate has low intrinsic conductivity and ion diffusion coefficient, so that poor low-temperature performance, high rate performance. In particular, high-power performance, the EV, HEV, smart grid "load shifting" and other applications, directly affects the large-scale application. This paper was prepared using a sophisticated battery manufacturing process of lithium iron phosphate batteries 18650, by positive, negative, improved fluid collection research and other key materials to improve high-rate performance of the battery.First, we study on the effect of lithium iron phosphate on the high rate of the battery, were investigated synthesis process, material particle size, carbon content and other factors. By SEM study, lithium iron phosphate prepared by different processes have completely different morphology. Using the same process of preparing 18650 battery, the internal resistance of the battery, large current discharge platform, discharge temperature rise data of gathering contrast, found that does not exist in the influence of synthesis process on the performance of the rate to follow the rules, there is no decisive influence on the performance of the final magnification.The materials which D50 is 0.667 um, 1.151 um, 1.998 um and 2.481 um are selected to compare. Found that the particle size of the material 0.667 um battery internal resistance is 9.7m?, and has a higher discharge platform, with better high-rate performance. Because the smaller the particle size can be reduced by lithium ion diffusion radius, enhance ion transmission rate directly improve performance ratio. It is worth noting that a smaller particle size, processing more difficult, in the actual production, you need to consider performance and ease of operation.Carbon content of lithium iron phosphate is an important technical indicators, the current mainstream method is to add carbon source in the synthesis stage. By TEM test, we found the material uniformly coated the carbon layers. Laboratory synthesis of four different carbon content of the material tested, found that the battery maximum carbon content of 2.0% of the material preparation has 9.2m? internal resistance, discharge platform magnification 2.91 V voltage, the discharge temperature of 25 degrees, All figures are best test cell data. Description higher the carbon content, the better the rate performance.Secondly, we study on the influence of other key materials for battery cell. Electrode resistor manufactured by homemade equipment. Found that lower resistance, the lower the battery internal resistance, the better high-power performance. Test different thicknesses in aluminum foil, the battery 20 um thick aluminum foil has the best rate performance.Conductive coating is the latest development of aluminum foil pretreatment, the substrate is coated with a conductive coating applied around 1um, improve the interface condition between the active material and aluminum foil. Confirmed by cyclic voltammetry in the 2.0V-4.2V voltage range, there is no side effects, it does not affect the entire electrochemical system. The use of conductive coating, can effectively improve the battery cycle stability, platform voltage loop 3000 remained at about 3.15 V, capacity retention rate of 90%; low-temperature discharge capacity retention rate of 76%; significantly improve the overall performance of the battery.By orthogonal experiments to identify best conductive agent addition ratio, experiments showed that: add 1% flake graphite, conductive carbon black 2%, ECP, VGCF, CNTs and other large surface area, high conductivity material 1-2%, the battery has the best overall performance. SEM photos show, the electrode is well-dispersed, active material uniformly distributed gap conductive material, and build a more complete conductive network.Finally, we study on the influence of negative processes on the battery performance. New process using an organic-based negative electrode, the electrode baking 16 h at 95±5? environment, the moisture content is substantially stable, maintained at about 180 ppm. Battery low-temperature discharge capacity retention rate 73.92%, 20 A discharge capacity retention rate 92.63%, platform voltage 2.82 V, significantly better than the water-based negative, indicating that the organic-based negative can significantly improve battery performance.