The self-protection of li-ion batteries is the most basic function of these batteries. Currently, BMS systems for li-ion battery packs can generally achieve temperature and current protection, but this is only at the system level. With intelligent design at the battery level, additional sensing electrodes and temperature feedback intelligent materials can be added to the battery to achieve intelligent self-protection. By adding intelligent structures and materials to the li-ion battery, the battery can be designed for intelligent use.
Anti-internal short circuit design
Internal short circuits are a serious safety issue for li-ion batteries as they can cause serious safety issues due to lithium dendrites and extraneous matter in the battery. To solve this problem, people have designed various methods to monitor the growth of lithium dendrites inside li-ion batteries. One such method is the multi-functional separator, which adds a layer of metal to the traditional polymer separator. This metal layer acts as a lithium dendrite detector and monitors the dendrites by detecting the voltage difference between the metal layer and the negative electrode. The three-layer composite multi-functional separator adds SiO2 to the middle layer of the separator. When the lithium dendrites grow to a certain extent, the SiO2 reacts with the lithium metal, consuming the dendrites and avoiding their further growth.
Intelligent overheat prevention for li-ion batteries
If a li-ion battery overheats, it can cause the separator to shrink, leading to a positive and negative pole short circuit and a thermal runaway event. Traditional PP-PE-PP composite separators can automatically close at low temperatures to cut off the reaction between the positive and negative electrodes and suppress battery overheating. However, this three-layer composite separator is ineffective when the temperature is too high and the PP layer also shrinks.
To solve the safety issue of li-ion batteries overheating, an electrolyte additive material was developed to protect them. Traditional flame retardants would have a severe impact on the performance of li-ion batteries, making them impractical for use. By encapsulating the flame retardant DMTP in independent small capsules, the outer wall of these capsules is stable in the electrolyte, so they have no negative impact under normal conditions. When the temperature exceeds 70 degrees Celsius, the pressure of DMTP vapor causes the shell to break and releases the flame retardant into the electrolyte, resulting in a sharp drop in the electrolyte's electrical conductivity and preventing further reactions inside the battery.
As the use of li-ion batteries has become more widespread, so have the number of potential harms they face. If they can function like living organisms with self-repair capabilities, this would be very significant for prolonging their lifespan and reducing safety risks.
Self-repair for external damage
Batteries with self-repair capabilities are not a new concept. For example, in Li-I batteries, the separator is actually a reaction product of Li and I - LiI - so after the separator is damaged, it comes into contact with Li and I, it will repair itself. In modern li-ion batteries, self-repair is achieved mainly through the use of multi-functional materials. Super-capacitors with self-repairing functionality are mainly composed of a network formed by supramolecular materials. Numerous hydrogen bonds within the material make it have self-repairing properties when subjected to mechanical damage. At 50 degrees Celsius, the material can self-heal within 5 minutes of being cut.
Shape memory capability
With the popularity of wearable devices, traditional hard-shell li-ion batteries are no longer suitable for practical use. Therefore, the ability to recover to their original designed shape after deformation caused by external forces (such as heat, electromagnetic force, pressure, etc.) has become a requirement for special li-ion batteries. Super-capacitors with shape memory alloys TiNi have been designed. The phase transition temperature of TiNi alloy is 15 degrees Celsius, while the surface temperature of human skin is around 35 degrees Celsius, so this capacitor can automatically wrap around a wrist when exposed to this temperature. If TiNi shape memory alloys were made into fiber, they could also be used to create batteries with shape memory functionality of various shapes. This function has great potential in the aerospace field. Before launch, the battery can be folded to the smallest possible volume at low temperatures. Once in space, the battery can automatically resume its original shape at the recovery temperature, without affecting its electrical performance throughout the process.
The trend towards intelligentization is irreversible, and the intelligent development of li-ion batteries will be a very important direction. With the continuous progress of materials and design technology, we believe that we will witness the birth of more intelligent and more humane batteries in the future.