What happens when a metal foreign body is mixed into the anode material of a lithium-ion battery?

When iron (Fe), copper (Cu), chromium (Cr), nickel (Ni), zinc (Zn), silver (Ag) and other metal impurities are present in the positive electrode material, the voltage in the battery formation stage reaches the REDOX potential of these metal elements, and these metals will be oxidized in the positive electrode and then reduced to the negative electrode.When the metal elements at the negative electrode accumulate to a certain extent, the hard edges and corners of the deposited metal will Pierce through the diaphragm, causing self-discharge of the battery. Self-discharge has a fatal effect on lithium-ion batteries.Therefore, it is very important to prevent the introduction of metal foreign bodies from the source.

There are many production processes of positive electrode materials, and every link in the manufacturing process will have the risk of metal foreign body introduction, which puts forward higher requirements for the equipment automation degree and on-site quality management level of material suppliers. However, due to cost constraints, material suppliers often have low degree of automation of their equipment, many breakpoints in the manufacturing process and uncontrollable risks. Therefore, in order to guarantee the stability of battery performance, self-discharge, prevention must promote material supplier from man, machine, material, method, ring five aspects introduced to prevent metal foreign body.

Starting from personnel control, it is forbidden for employees to bring metal foreign bodies into the workshop. Jewelry is prohibited. Work clothes, shoes and gloves should be worn in the workshop. The supervision and inspection mechanism should be established to cultivate the quality consciousness of employees so that they can consciously abide by and maintain the workshop environment.

Production equipment is the main link of the introduction of foreign bodies, such as equipment parts and tools in contact with the material rust, inherent material wear and other phenomena; No direct contact with the material of equipment parts and tools, dust adhesion after from workshop air floating into the material. According to the degree of influence, different treatment methods can be adopted, such as painting, changing to non-metallic coating (plastic, ceramic), and wrapping bare metal parts. Managers should also formulate relevant rules and regulations, make clear provisions on how to manage metal foreign bodies, develop point inspection table to require employees to check regularly, so as to prevent future problems.

Raw material is the direct source of the metal foreign bodies in the anode material, deal with the provisions of the purchase of raw materials for metal foreign body content should be strict inspection, after the factory to ensure its content within the prescribed scope.If metal foreign body excessive levels of raw materials, the subsequent process is hard to remove it.

In order to remove the metal foreign bodies, electromagnetic iron process has become a production of the anode materials. Electromagnetic iron removal machine is widely used, However, the device has no effect on non-magnetic metallic substances such as copper and zinc. so the workshop should avoid the use of copper and zinc components. If it must be used, do not contact directly with the powder or exposed in the air. In addition, the electromagnetic iron removal machine installation location, installation number, parameter settings and so on have a certain impact on the iron removal effect.

In order to ensure the workshop environment and realize the positive pressure of the workshop, it is necessary to establish double doors and air shower doors to avoid dust from the outside flowing into the workshop contaminated materials. At the same time, workshop equipment and steel structure should avoid rust, and the ground should be painted and regularly demagnetized.

The page contains the contents of the machine translation.