The safety issue of lithium-ion batteries is not a peripheral issue, but an essential issue based on material technology.
A breakthrough in material technology:
1. Choose safe cathode materials. The current cathode materials are two mass-produced materials, lithium cobalt oxide and lithium manganate. Lithium cobalt oxide is a very mature system in terms of small batteries. Due to the characteristics of lithium cobalt oxide (LiCo) in terms of molecular structure: after fully charged, there are still a large amount of lithium ions left in the positive electrode, and when overcharged, it remains in the positive electrode Lithium ions will rush to the negative electrode, and the formation of dendrites on the negative electrode is an inevitable result of overcharging of batteries using lithium cobalt oxide materials. Even during normal charging and discharging, excess lithium ions may be released to the negative electrode to form Dendrite. Therefore, the frequent explosions of mobile phone batteries are due to the failure of the protection circuit on the one hand, but more importantly, there is no fundamental solution to the problem in terms of materials. At the same time, lithium cobalt oxide has a strong oxidizing property, it will decompose at 175 degrees, the shell will leak, and it will burn and explode in contact with air.
2. The choice of lithium manganate material ensures that in the fully charged state, the lithium ions of the positive electrode have been completely embedded in the carbon pores of the negative electrode in terms of molecular structure, which fundamentally prevents the appearance of dendrites. At the same time, the stable structure of lithium manganese oxide makes its oxidation performance far lower than that of lithium cobalt oxide, and its decomposition temperature exceeds 100 degrees of lithium cobalt oxide. Even if an internal short circuit (needle puncture), external short circuit, or overcharge occurs due to external forces, it can Prevent the danger of burning and explosion caused by the precipitation of metallic lithium.
3. Choose a separator with good thermal shutdown performance. The purpose of the separator is to allow lithium ions to pass through while isolating the positive and negative electrodes of the battery. When the temperature rises, the diaphragm is closed before melting, so that the internal resistance rises to 2000 ohms and the internal reaction stops.
4. Explosion-proof valve: When the internal pressure or temperature reaches the preset standard, the explosion-proof valve will open and begin to relieve pressure to prevent excessive internal gas accumulation and deformation, which will eventually cause the shell to burst.
5. Protection circuit: Generally, the protection circuit needs to prevent overcharging, overdischarging, and super current. The important principle is to control the switching circuit to turn off the entire loop by measuring the voltage and total current of each cell. There is no high difficulty in circuit design. However, whether the design of the protection circuit is reasonable and whether the reliability is high enough is a test of the manufacturer's ability. The protection circuit is based on a PCB circuit composed of about dozens of resistors, capacitors, switching MOS tubes and other electronic components, and each component has the possibility of failure. A failed protection circuit will appear in either an open circuit or a conductive state. When the circuit is open, the user cannot use the battery pack, and the conductive state will test the battery's ability to resist overcharge.
