The factor of affecting lithium-ion cell's internal resistance

The factor of affecting lithium-ion cell includes, design of cell’s cathode piece and tab, raw material, manufacturing process, applications, etc. The article mainly expound that raw material’s effect on lithium-ion cell’s internal resistance of lithium battery.

Active material for positive and negative electrodes: the positive electrode of lithium cell stores the li-ion, it mainly determines the performance of the cell. Positive electrode material mainly improve the electronic conductivity between particles through coating and doping. Doping the Ni enhance the strength of P-O chemical bond, stabilize the structure of LiFePO4/C, optimize the volume of unit cell, effectively reduce the electron transfer resistance of the positive electrode material. Through the simulation analysis of the electrochemical thermal coupling model, it is known that under the condition of high-rate discharge, the activation polarization, especially the significant increase in the activation polarization of the negative electrode, is the main reason for the serious polarization. Reducing the particle size of the negative electrode can effectively reduce the active polarization of the negative electrode. When the solid phase particle size of the negative electrode is reduced by half, the active polarization can be reduced by 45%. Therefore, in terms of battery design, research and improvement of positive and negative materials are essential.

Conductive agent: Graphite and carbon black are widely used in the field of lithium batteries because of their good properties. Compared with graphite-based conductive agent, the positive electrode with carbon black-based conductive agent has better battery rate performance, because graphite-based conductive agent has a flaky particle morphology, which causes a large increase in pore tortuosity at a large rate, and Li liquid phase diffusion is easy to occur The phenomenon that the process limits the discharge capacity. The battery with added CNTs has lower internal resistance, because compared to the point contact between graphite/carbon black and the active material, the fibrous carbon nanotubes are in line contact with the active material, which can reduce the interface impedance of the battery.

Current collector: Reducing the interface resistance between the current collector and the active material and improving the bond strength between the two are important means to improve the performance of lithium batteries. Coating a conductive carbon coating on the surface of the aluminum foil and corona treatment on the aluminum foil can effectively reduce the interface impedance of the battery. Compared with ordinary aluminum foil, the use of carbon-coated aluminum foil can reduce the internal resistance of the battery by about 65%, and can reduce the increase in the internal resistance of the battery during use. The AC internal resistance of corona treated aluminum foil can be reduced by about 20%. In the commonly used 20%~90% SOC range, the overall DC internal resistance is relatively small and the increase is gradually smaller as the depth of discharge increases.

Diaphragm: The ion conduction inside the battery depends on the diffusion of Li ions in the electrolyte through the porous diaphragm. The liquid absorption and wetting ability of the diaphragm is the key to forming a good ion flow channel. When the diaphragm has a higher liquid absorption rate and porous structure, It can improve the conductivity, reduce the battery impedance, and improve the rate performance of the battery. Compared with ordinary base membranes, ceramic diaphragms and rubber-coated diaphragms can not only greatly improve the high temperature shrinkage resistance of the diaphragm, but also enhance the liquid absorption and wetting ability of the diaphragm. The addition of SiO2 ceramic coating on the PP diaphragm can make the diaphragm absorb liquid The volume increased by 17%. Coating 1μm PVDF-HFP on the PP/PE composite diaphragm, the liquid absorption rate of the diaphragm is increased from 70% to 82%, and the internal resistance of the cell is reduced by more than 20%.

PLB has deeply researched the mechanism of the influence of raw materials on the internal resistance of the cells, and optimized the design. The 26650 cells produced have the excellent characteristics of low internal resistance and high consistency.

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