With the use of lithium batteries, the performance of the battery continues to decay, mainly manifested in capacity attenuation, internal resistance increase, power decrease, etc., and the change of battery internal resistance is affected by various use conditions such as temperature and discharge depth. Therefore, this paper mainly expounds the factors affecting the internal resistance of batteries from the aspects of battery structure design, raw material performance, process technology and use conditions.

1. Structural design impact

In the battery structure design, in addition to the riveting and welding of the battery structural parts themselves, the number, size, and position of the battery tabs directly affect the internal resistance of the battery. To a certain extent, increasing the number of tabs can effectively reduce the internal resistance of the battery. The position of the lug can also affect the internal resistance of the battery, the internal resistance of the coiled battery at the head of the positive and negative electrodes is the largest, and compared with the winding battery, the laminated battery is equivalent to dozens of small batteries connected in parallel, and its internal resistance is smaller.

2. The impact of raw material performance

1. Positive and negative electrode active materials

The cathode material in lithium battery is the Li storage side, which determines the performance of lithium battery, and the cathode material mainly improves the electron conduction ability between particles through coating and doping. For example, Ni doping enhances the strength of P-O bonds, stabilizes the structure of LiFePO4/C, optimizes unit cell volume, and effectively reduces the charge transfer impedance of cathode materials.

Through the simulation analysis of the electrochemical thermal coupling model, it is found that the main reason for the serious polarization is the large increase of activation polarization, especially the negative electrode activation polarization, under the condition of high rate discharge. Reducing the particle size of the anode can effectively reduce the activation polarization of the anode, and when the solid particle size of the anode is reduced by half, the activation polarization can be reduced by 45%. Therefore, in terms of battery design, research on the improvement of the positive and negative electrode materials themselves is also essential.

2 Conductive agent

Graphite and carbon black are widely used in the field(s) of lithium batteries due to their good properties. Compared with graphite conductive agents, the battery rate performance of carbon black conductive agents added to the cathode is better, because graphite conductive agents have a flake particle morphology, which causes a large increase in the pore tortuosity coefficient at large magnification, and it is easy to limit the discharge capacity in the Li liquid phase diffusion process. The internal resistance of the battery with CNTs is smaller, because compared with the point contact between graphite/carbon black and the active material, the fibrous carbon nanotubes are in linear contact with the active material, which can reduce the interfacial impedance of the battery.

3 Current collectors

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. Applying conductive carbon coating to the surface of the aluminum foil and corona treatment of the aluminum foil can effectively reduce the interfacial 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 of internal resistance of the battery during use.

The AC internal resistance of aluminum foil treated with corona can be reduced by about 20%, and in the commonly used 20%~90% SOC range, the overall DC internal resistance is small and gradually decreases with the increase of discharge depth.

4 Diaphragm

The ion conduction inside the battery depends on the diffusion of Li ions in the electrolyte through the porous separator, and the liquid absorption and wetting ability of the separator is the key to the formation of a good ion flow channel. Compared with ordinary base films, ceramic separators and adhesive separators 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, and add SiO2 ceramic coating to the PP separator, which can increase the liquid absorption capacity of the diaphragm by 17%. When 1μm PVDF-HFP was coated on the PP/PE composite separator, the separator absorption rate increased from 70% to 82%, and the internal resistance of the cell decreased by more than 20%.