How to improve the infiltration effect of lithium-ion battery electrolyte?

The infiltration of the pole piece by the electrolyte involves the three-phase contact of solid, liquid and gas. When the electrolyte is injected into the battery case, the electrolyte must first exhaust the air in the case, and then the electrolyte will adhere to the surface of the active material of the positive and negative electrodes, and some electrolyte will enter the positive electrode-diaphragm-negative electrode through the diaphragm of the winding core. between. As time goes on, the electrolyte will infiltrate the pole pieces, and the electrolyte in the diaphragm will infiltrate the pole pieces in the reverse direction. When the standing time is long to a certain extent, the infiltration of the pole pieces will be achieved under the application of surface tension. A state of balance. In this process, a concept of contact angle (wetting angle) in physical chemistry is involved. The blue area represents the liquid, and the gray area represents the solid interface. Then the blue and gray contact area is the solid-liquid contact interface. The position where the tangent of the liquid crosses the solid interface forms an angle θ. The smaller the contact angle θ, the better the wettability of the electrolyte to the pole piece or diaphragm. . However, in the actual operation process, it is often impossible to grasp the infiltration effect of the electrolyte on the pole piece. According to the principle of electrolyte infiltration mentioned above, we can find ways to improve the infiltration effect of the electrolyte on the pole piece from the following points : (1) Improving the liquid injection process Improving the liquid injection process is the most conventional method, which can effectively improve the infiltration effect of the electrolyte from the aspects of liquid injection efficiency, liquid injection conditions, standing time, and liquid injection methods. Liquid injection under vacuum conditions not only facilitates the discharge of gas in the cell, but also reduces the resistance of the gas to the electrolyte injection and helps the electrolyte to infiltrate the pole pieces. The principle is that vacuum injection can reduce the existence of gas resistance at the solid-gas-liquid three-phase interface, allowing the electrolyte to directly contact the pole piece, reducing the infiltration time. By extending the time of standing under vacuum, it can ensure that the electrolyte is fully infiltrated into the pole piece. After liquid injection, as the standing time is prolonged, the wetting angle between the electrode solution and the pole piece gradually decreases, the wetting radius gradually increases, and finally a good wetting effect is achieved. In order to prevent the phenomenon of insufficient electrolyte infiltration of the diaphragm and pole pieces, the electrolyte can be injected in batches to facilitate the electrolyte to fully infiltrate the pole pieces. In principle, this operation method is to increase the probability of solid-liquid contact and expand the contact area. , In the case of the same amount of electrolyte, the infiltration time can be shortened. (2) Improving the electrolyte infiltration effect of the winding core process is not unrelated to the particle properties of the electrode material, the compaction density of the pole piece, and the tightness of the winding core. Different morphology and particle size of the positive and negative active materials, conductive agents, and the electrolyte have different infiltration effects on the pole pieces. The larger the particle size of the raw material, the closer to the spherical shape, the greater the electrolyte penetration rate and the longer the infiltration time. short. When the compaction density of the pole piece is too large, the porosity in the pole piece will decrease, which is not conducive to the electrolyte infiltration of the pole piece. The appropriate compaction density should be adjusted to meet the electrolyte infiltration under the condition of ensuring the low impedance of the battery. degree. Similarly, the tightness of the cell stacking or winding will also affect the infiltration of the electrolyte. When the winding is loose, the pores between the positive electrode-the separator-the negative electrode are larger, and the amount of accumulated electrolyte is larger, resulting in enrichment in some places and lack in some places, which undoubtedly has a great impact on the performance of the battery. When the winding is tight, it will affect the infiltration speed and efficiency of the electrolyte, which is also undesirable. (3) Adding electrolyte infiltration agent The electrolyte usually used is an organic solvent, and the pole piece is an inorganic material, so the ability to absorb the electrolyte is weak. Adding additives to the electrolyte can also improve the infiltration of the electrolyte. Liu Fangfang and others used a fluoroether material as an additive to the electrolyte. The test results show that adding a small amount of infiltrant to the electrolyte can effectively shorten the battery injection time and significantly improve the cycle performance of the battery, but it should be noted that it is used as an infiltrant. When the addition amount reaches 1%, it will have a negative impact on the cycle performance. The essence of the sizing agent is a surfactant. This type of sizing agent has the advantages of high surface activity, high heat stability, low flammability, and high chemical stability. The addition of the sizing agent to the electrolyte can reduce the surface tension of the liquid. Improve the wetting ability and penetration ability of the electrolyte to the pole piece, thereby improving the electrochemical performance of the battery. Disclaimer: Some pictures and content of the articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous article: Where is the advantage of battery energy storage system?