What is the impact of lithium-ion battery charge and discharge rate on battery performance?

The positive and negative electrodes and the electrolyte city affect the charging and discharging rate function of lithium-ion batteries. In this article, the author of Cuneng Electric will talk about the impact of lithium-ion battery charge and discharge rate on battery performance. We all know that with the increase in the number of charge and discharge of lithium-ion batteries, the capacity will become less and less, which directly means that the performance of lithium-ion batteries is getting worse and worse. What factors limit the charge-discharge rate function of lithium-ion batteries? The charge-discharge rate function of lithium-ion batteries is directly related to the migration ability of lithium ions at the positive and negative electrodes, electrolyte, and the interface between them. All factors that affect the migration speed of lithium ions (these influencing factors can also be equivalent to the battery The internal resistance), the city affects the charging and discharging rate function of lithium-ion batteries. In addition, the heat dissipation rate inside the battery is also an important factor affecting the rate function. If the heat dissipation rate is slow, the heat accumulated during high rate charging and discharging cannot be reported, which will seriously affect the safety and life of the lithium-ion battery. Therefore, to study and improve the charge-discharge rate function of lithium-ion batteries, it is important to start from two aspects: improving the lithium ion migration speed and the heat dissipation rate inside the battery. 1. The internal resistance of lithium-ion batteries generally adds a conductive agent inside the active material of the positive electrode to reduce the resistance between the active materials, the active material and the positive electrode matrix/current collector, and improve the conductivity of the positive electrode material (ionic and electronic conductivity) ), the promotion rate function. Different materials and different shapes of conductive agents affect the internal resistance of lithium-ion batteries, which in turn affect their rate performance. The current collectors (tabs) of the positive and negative electrodes are the carrier for the lithium-ion battery to communicate with the outside world. The resistance value of the current collector also has a great influence on the rate function of the battery. Therefore, by changing the material, size, extraction method, connection process, etc. of the current collector, the rate function and cycle life of the lithium-ion battery can be improved. In addition, the liquid absorption and porosity of the severing membrane also have a greater impact on the passability of lithium ions, and will inevitably affect the rate function of the lithium ion battery (relatively small). The level of infiltration between the electrolyte of the lithium ion battery and the positive and negative materials will affect the resistance at the interface between the electrolyte and the electrode, thereby affecting the rate function of the battery. The total amount of electrolyte, viscosity, impurity content, pores of the positive and negative materials, etc., changing the resistance between the electrolyte and the electrode in the city is an important research bias to improve the rate function. 2. The ionic conductivity of the electrolyte The ionic conductivity of the electrolyte communicates with the resistance of water, which has a great influence on the speed of lithium ion swimming. The ionic conductivity of the organic electrolyte recovered by the current lithium-ion battery, whether it is a liquid electrolyte or a solid electrolyte, is not very high. The resistance of the electrolyte has become an important component of the overall battery resistance, and its impact on the high-rate performance of lithium-ion batteries cannot be ignored. In addition to improving the ionic conductivity of the electrolyte, attention should also be paid to the chemical and thermal invariance of the electrolyte. When charging and discharging at a high rate, the electrochemical window of the battery changes in a wide range. If the chemical invariance of the electrolyte is not good, it is easy to oxidize and analyze the appearance of the positive electrode material, which affects the ionic conductivity of the electrolyte. 3. The diffusion capability of positive and negative lithium ion batteries. The rate at which lithium ion batteries are deintercalated and embedded in the positive/negative active material, that is, the speed at which lithium ions escape from the positive/negative active material, which may be from the positive/negative electrode How fast does the appearance enter the active material to find a place to settle down? This is an important factor that affects the charge and discharge rate. Factors affecting the high-rate charging and discharging performance of lithium-ion batteries: capacity and poor capacity retention are the biggest problems in the high-rate charging and discharging process of lithium-ion battery negative electrodes, which are important to the layout of electrode materials, particle size, electrode conductivity and electrode Factors such as the invariance of the appearance of the SEI film are related. The size of the material, the size of the negative material of the lithium-ion battery is directly related to the right and wrong of the diffusion path of lithium ions, and it has a great influence on the high-rate performance of the electrode. The surface resistance of the electrode. When lithium ions are inserted into the negative electrode, they must first diffuse to the interface between the solid electrolyte phase interface film (SEI film) and the negative electrode material. Therefore, the surface resistance of the electrode is equivalent to a threshold in the diffusion process of lithium ions. The insertion and extraction of lithium ions, especially during high-rate charging and discharging, becomes more and more obvious. What is the impact of over-discharge on battery performance? After the lithium-ion battery has discharged the internally stored power, after the voltage reaches a certain value, the continued discharge will cause over-discharge. Generally, the discharge cut-off voltage is determined according to the discharge current. 0.2C-2C discharge is generally set to 1.0V/piece, 3C or more, such as 5C or 10C discharge is set to 0.8V/piece, battery over-discharge may bring catastrophic effects to the battery, especially high current over-discharge, or Repeated over-discharge has a greater impact on the battery. Disclaimer: Some pictures and content of articles published on this site are from the Internet. 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