When there are iron (Fe), copper (Cu), chromium (Cr), nickel (Ni), zinc (Zn), silver (Ag) and other metal impurities in the cathode material, after the voltage in the battery formation stage reaches the oxidation and reduction potential of these metal elements, these metals will be oxidized at the anode first, and then reduced at the cathode. When the metal elements in the cathode accumulate to a certain extent, the hard corners of the deposited metal will pierce the diaphragm. Self discharge can have a fatal impact on lithium-ion batteries, so it is particularly important to prevent the entry of metal foreign objects from the source.

　　There are many production processes for lithium battery positive electrode materials, and there is a risk of introducing metal foreign objects at every step of the manufacturing process, which puts higher requirements on the equipment automation level and on-site quality management level of material suppliers. However, due to cost constraints, the automation level of material suppliers' equipment is low, and there are many interruptions in the manufacturing process, resulting in an increase in uncontrollable risks. Therefore, in order to ensure the stability of battery performance and prevent self discharge, battery manufacturers must promote material suppliers to prevent the introduction of metal foreign objects from five aspects: human, machine, material, law, and environment.

　　Firstly, starting from personnel control, employees are prohibited from bringing metal foreign objects into the workshop and wearing jewelry. When entering the workshop, work clothes, shoes, and gloves should be worn to avoid contact with metal foreign objects before coming into contact with powder. To establish a supervision and inspection mechanism, cultivate employees' quality awareness, and make them consciously abide by and maintain the workshop environment.

　　Production equipment is the main link for introducing foreign objects, such as rusting of equipment components and tools in contact with materials, inherent material wear, etc. Equipment parts and tools that do not come into direct contact with materials will float into the material due to the airflow in the workshop after dust adheres. Depending on the degree of impact, different treatment methods can be used, such as painting, replacing non-metallic coatings (plastic, ceramic), and wrapping exposed metal components. Managers should also establish corresponding rules and regulations, make clear regulations on how to manage metal foreign objects, establish inspection lists, and require employees to conduct regular inspections to prevent potential problems.

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