How can lithium-ion batteries become more intelligent?

With the popularity of lithium-ion batteries in the global market, billions of lithium-ion batteries are produced every year and enter the hands of consumers. Lithium-ion batteries bring great convenience to our lives, but also hide many problems such as safety concerns. In recent years, with the development of the intelligent wave, more and more devices are moving towards the development of intelligent direction, such as TVs, speakers, cars, etc., which can be continuously improved according to the environment, user habits, etc., evolve and improve the user experience.

For lithium-ion batteries, they may face different application environments during their application. Some application scenarios may pose a big challenge for lithium-ion batteries. We hope that lithium-ion batteries can be more intelligent, and can adjust the operation strategy of lithium-ion batteries according to the application environment. On the one hand, the safety of lithium-ion batteries can be ensured, and on the other hand, the performance and service life of lithium-ion batteries can be guaranteed.

1. Intelligent self-protection

The self-protection of lithium-ion batteries is the most basic function of lithium-ion batteries. Now the BMS system of lithium-ion battery packs can basically achieve functions such as temperature protection and current protection, but this is the protection at the system level. The intelligent planning of lithium-ion batteries can achieve self-protection at the lithium-ion battery level, such as adding additional sensing electrodes in the battery, adding temperature feedback smart materials, and adding lithium ions to the lithium-ion battery to achieve lithium ions intelligent battery planning.

1.1 anti-internal short circuit planning

An internal short circuit is a serious problem affecting the safety of lithium ion batteries. Short circuit in lithium ion batteries caused by lithium dendrites and excess materials often causes serious safety problems.

In order to solve the internal short circuit accident caused by the growth of lithium dendrites, various methods have been planned to monitor the growth of lithium dendrites inside the lithium ion battery. For example, Wu et al.'s multi-functional membrane, which incorporates a layer of metal in the middle of a conventional polymer membrane, acts as a lithium dendrite detector by monitoring the metal to the cathode. The voltage difference can realize the monitoring of lithium dendrites so that the diaphragm retains the function of the traditional diaphragm and also realizes the monitoring of lithium dendrites. The KaiLiu three-layer composite multi-functional diaphragm of Stanford University is characterized by the addition of SIO2 to the middle layer of the diaphragm. When the lithium dendrite grows to a certain extent, SIO2 reacts with metallic lithium when the membrane is punctured, consuming lithium dendrites to avoid further growth of lithium dendrites.

1.2 Intelligently prevent lithium ion battery from overheating

If the lithium ion battery is overheated (such as external heating, self-heating during short circuit), it will cause the diaphragm to shrink, causing short circuit between positive and negative poles, which will lead to thermal runaway. The conventional PP-PE-PP composite diaphragm can realize the automatic closed-cell function at a lower temperature, thereby cutting off the reaction of the positive and negative electrodes, and suppressing the overheating of the battery, but if the temperature is too high, the PP layer also shrinks. This three-layer composite diaphragm will also fail.

In order to solve the safety problem of lithium-ion batteries in the case of overheating, Yim et al. planned an electrolyte-adding material that can protect the lithium-ion battery from overheating. We all know that general electrolyte flame retardants can have a serious impact on the performance of lithium-ion batteries, so it is difficult to use in practice. The flame retardant such as Yim is packed into separate small capsules. The outer wall material of these capsules is very stable in the electrolyte, so it does not affect the performance of the lithium ion battery under normal conditions. When the temperature exceeds 70 degrees Celsius, under the action of the vapor pressure of the flame retardant DMTP, the outer casing is broken, and the flame retardant is released into the electrolyte, causing the electrolyte conductivity to drop sharply and prevent a further reaction in the battery.

2. Intelligent automatic repair

With the popularity of lithium-ion batteries, the opportunities for various types of damage to lithium-ion batteries are increasing. If lithium-ion batteries can perform automatic repair functions like living organisms, this will extend the life of lithium-ion batteries and reduce lithium. The safety risks of ion batteries are very important.

2.1 Automatic repair of external damage

The battery with automatic repair function is not a completely new concept. For example, Li-I battery, the diaphragm is actually the reaction product LiI of Li and I. Therefore, after the diaphragm breaks, Li and I come into contact and the reaction product LiI is realized. Repair of the diaphragm.

The modern meaning of the automatic repair function of lithium-ion batteries, more based on multi-functional materials, such as Wang et al. planned self-repairing supercapacitor, which is mainly composed of a network of supramolecular materials, a large number of materials Hydrogen bonding allows the material to be self-repairing in the face of mechanical damage. At 50 degrees Celsius, after the material is cut, it can heal itself within 5 minutes.

The above self-healing plan is mainly for water-based supercapacitors. The planning of self-healing lithium-ion batteries is still facing no small challenge. This is large because the organic electrolyte of lithium-ion batteries leaks in the air and will be serious. The impact of lithium-ion battery performance, so self-healing lithium-ion battery planning also needs to rely on continuous improvement of the electrolyte.

2.2 shape memory ability

With the popularity of wearable devices, the traditional hard-shell lithium-ion battery cannot meet the needs of actual use so it can restore the originally planned shape after being deformed by external forces (such as heat, electromagnetic force, pressure, etc.). It has become a need for special lithium-ion batteries. Yan et al. use shape memory alloy TiNi to plan a supercapacitor with shape memory capability. The phase transition temperature of TiNi alloy is 15 degrees Celsius, and the surface temperature of human skin is about 35 degrees Celsius. Therefore, the capacitor can be under the action of human body temperature. Reverts to the original shape and automatically wraps around the wrist.

If the shape memory alloy TiNi described above is made into a fiber shape, it is also possible to manufacture a battery having a shape memory function of various shapes. This function has good use of the future in thespecial field. Before launching, first, fold the battery as much as possible at a lower temperature. After entering the space, the temperature is restored, and the battery automatically returns to its original shape, and throughout the entire, the electrical performance of the battery is not affected in the process, which will greatly improve the efficiency of space launch.

The wave of intelligence is an irreversible trend. The intelligent development of lithium-ion batteries will be a very important direction. With the continuous advancement of materials and planning technology, we believe that we will be able to witness smarter and more humanized batteries born in the future.

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