The root cause of the lithium ion battery bulge

Source: 2020 - 03 - 24 when hits: time, the author analyzes the reasons of lithium ion battery bumps due to its high life and high capacity, lithium ion battery has been widely used, but with longer duration of use, its swelling, security function is not ideal, accelerate circulation attenuation problem is becoming more and more serious, leading to the depth of the lithium industry analysis and control research. According to experimental development experience, the author will be the cause of the lithium battery bulging is divided into two categories. 2 it is caused by differentiation of liquid oxygen in electrolyte gas production bulge. In different cell system, the battery is the dominant factor of different thickness changes. For example, in the lithium titanate cathode battery system, drum out of the gas drum is the main factor. In the graphite anode system, the thickness of the electrode and gas production role to play in promoting to the expansion of the battery. 1. Electricity in the process of the plate thickness changes in the use of lithium-ion batteries, change the thickness of the plate electrode, especially the graphite anode. According to the existing data, lithium batteries, after high temperature storage and circulation and blowout is simple, the thickness of the growth rate of about 6% ~ 20%, the positive rate is only 4%, the cathode inflation rate more than 20%. Lithium battery at the bottom of the sheet thickness increases, leading to the expansion of the reason was that the graphite material impact. The cathode LiCx forms after graphite combined with lithium ( LiC24, LiC12, LiC6, etc. ) 。 Lattice spacing changes lead to the formation of the micro internal stress, leading to the expansion of the cathode. Below is graphite anode plate structure change in the placement and charging and discharging process diagram. After the expansion of the graphite cathode mainly lithium ion implantation caused irreversible expansion. This part of the expansion is mainly related to the structure of the particle size, adhesive and electrode. The expansion of the cathode constitutes the core coil, the deformation of the electrode and the clearance form cavity, micro cracks negative particles, solid electrolyte interface ( SEI) Electrolyte membrane was broken and restructuring, consumption, make the loop function. There are many factors which can influence the cathode thickening. Graphite anode common adhesive is SBR. Different adhesives with different elastic modulus and mechanical strength, the influence of the electrode thickness is different. In battery applications, the rolling force of electrode coating can also influence the cathode coating thickness. Under the same stress, the greater the elastic modulus of adhesive, the smaller the physical frame of springback. When charging, due to the embedded lithium ion, graphite lattice expansion. Together, as a result of negative particles and SBR deformation, internal stress released in full, make the negative inflation rate has increased dramatically, SBR in the stage of plastic deformation. The swelling rate of the associated with the elastic modulus and fracture strength of SBR, and therefore the greater the elastic modulus and fracture strength of SBR, the smaller the irreversible swelling. Do not match the number of SBR, the plate roller pressure is different, the pressure is different, the residual stress of plate must be different, the greater the pressure, the greater the residual stress, lead to the physical expansion of early, full and empty state inflation rate increased; SBR content is less, the smaller the pressure on the roller, the application of physical expansion rate is smaller, the early stage of the charge and discharge status and the smaller the charge and discharge air state. Coil of core deformation due to the expansion of the cathode, the influence degree of the embedded in the lithium ions in the cathode and lithium ion diffusion rate, serious impact on the function of the cycle of the battery.