How to solve the safety issues of high-capacity lithium-ion batteries?
The safety issue of lithium-ion batteries is not a peripheral problem, but a fundamental issue based on materials technology. Breakthroughs in materials technology are crucial.
1. Choose safe cathode materials. Currently, there are two mass-produced cathode materials: lithium cobalt oxide and lithium manganese oxide. Lithium cobalt oxide is a mature system for small battery cells. Due to the characteristics of its molecular structure (LiCo), even after a full charge, a large number of lithium ions remain at the cathode. When overcharged, the remaining lithium ions will surge to the anode, forming dendrites on the anode. This is an inevitable result of overcharging batteries using lithium cobalt oxide. Even during normal charging and discharging, excess lithium ions may ionize and form dendrites at the anode. Therefore, frequent explosions of mobile phone batteries are partly due to the failure of protection circuits, but more importantly, the problem has not been fundamentally solved in terms of materials. Furthermore, lithium cobalt oxide has strong oxidizing properties and decomposes at 175 degrees Celsius. If the casing leaks and comes into contact with air, it can burn or explode.
2. The selection of lithium manganese oxide material ensures, in terms of molecular structure, that in a fully charged state, lithium ions at the positive electrode are completely embedded in the carbon pores of the negative electrode, fundamentally preventing dendrite formation. Simultaneously, the stable structure of lithium manganese oxide makes its oxidation performance far lower than that of lithium cobalt oxide, and its decomposition temperature exceeds that of lithium cobalt oxide by 100 degrees Celsius. Even in the event of internal short circuits (needle penetration), external short circuits, or overcharging, it completely prevents the danger of combustion and explosion caused by the precipitation of metallic lithium.
3. Choose a separator with good thermal shut-off performance. The purpose of the separator is to isolate the positive and negative electrodes of the battery while allowing lithium ions to pass through. When the temperature rises, the separator should shut off before it melts, thereby increasing the internal resistance to 2000 ohms and stopping the internal reaction.
4. Explosion-proof valve: When the internal pressure or temperature reaches the preset standard, the explosion-proof valve will open to start depressurization to prevent excessive internal gas accumulation, deformation, and ultimately shell rupture.
5. Protection Circuit: Protection circuits typically prevent overcharging, over-discharging, and excessive current. The key principle is to control the switching circuit to shut down the entire circuit by measuring the voltage and total current of each cell. The circuit design itself isn't particularly complex. However, the rationality and reliability of the protection circuit design test the manufacturer's capabilities. The protection circuit is a PCB circuit composed of approximately dozens of electronic components such as resistors, capacitors, and switching MOSFETs. Each component has the potential to fail. A failed protection circuit will exhibit either an open circuit or a conducting state. An open circuit will render the battery pack unusable, while a conducting state will test the cell's ability to withstand overcharging.
