1. How the internal short circuit is formed: The biggest hidden danger of lithium-ion batteries is that when lithium-ion batteries using lithium cobalt oxide are overcharged (even during normal charge and discharge), lithium ions accumulate on the negative electrode to form dendrites and puncture The diaphragm forms an internal short circuit.
2. Large current: external short circuit, internal short circuit will cause excessive current of several hundred amperes
i. When an external short circuit occurs, the battery will be discharged with a large current due to the low external load. A large amount of energy is consumed on the internal resistance, and huge heat appears.
ii. Internal short circuit. The important reason is that the diaphragm is penetrated and a large current is formed inside. The temperature rise causes the diaphragm to melt and the short-circuit area expands, thus forming a vicious circle
3. Where does the gas come from: Li-ion batteries must be decomposed in order to achieve a high working voltage of 3-4.2V for a single cell (the working voltage of nickel-hydrogen and nickel-metal batteries is 1.2V, and the working voltage of lead-acid batteries is 2V). The organic electrolyte with voltage greater than 2V, and the organic electrolyte will be electrolyzed under the conditions of high current and high temperature, and the electrolysis will produce gas, which will cause the internal pressure to rise and severely break the shell.
4. How does combustion occur: Heat comes from high current, and at the same time, under high voltage (more than 5V), the oxide of positive electrode lithium will also undergo oxidation reaction, and metallic lithium will be precipitated. In the case of gas causing shell rupture, Direct contact with air will cause combustion and at the same time ignite the electrolyte, a strong flame will occur, and the gas will expand rapidly and explode.
5. Is there a safety problem for polymer batteries: The difference between polymer batteries and lithium ion batteries is that the electrolyte is gelatinous and semi-solid, while the electrolyte of lithium ion batteries is liquid. Therefore, the polymer battery can be used in soft packaging, and when gas appears inside, it can break through the shell earlier to prevent excessive gas accumulation and intense cracking. However, the polymer battery does not fundamentally solve the safety problem. It also uses lithium cobalt oxide and organic electrolyte, and the electrolyte is colloidal, not easy to leak, and will burn more violently. Combustion is the safest of polymer batteries. The problem.
