How to design intelligent and adaptive lithium-ion batteries in different environments?

With the popularity of lithium-ion batteries in the global market, billions of lithium-ion batteries are produced each year and enter the hands of consumers. Lithium-ion batteries bring great convenience to our lives, but also hide many safety problems. In recent years, with the development of the intelligence wave, more and more equipment have developed in the direction of intelligence, such as television, speakers, automobiles, etc.. They can constantly improve themselves and realize self-evolution according to the environment and user usage habits. Improve user experience.

For lithium-ion batteries, different use environments may be tested during use, and some use scenarios may pose greater challenges to lithium-ion batteries. We hope that lithium-ion batteries can be more intelligent and can adjust the use strategy of lithium-ion batteries in accordance with the operating environment. On the one hand, it guarantees the safety of lithium-ion batteries, and on the other hand, it can guarantee the performance and service life of lithium-ion batteries.

Smart Self Protection

The self-protection of lithium-ion cells is the most basic function of lithium-ion cells. At present, the BMS system of lithium-ion batteries can basically achieve functions such as temperature protection and current protection, but this is all protection at the system level. The intelligent design of lithium ion batteries can achieve self-protection of the lithium ion battery layer, such as adding additional induction electrodes to the battery, increasing temperature feedback smart materials, and adding some smart structures and materials to the lithium ion battery. So the intelligent design of lithium-ion battery can be realized.

1, anti-short-circuit design

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 lithium dendrite growth, various methods have been designed to monitor the growth of lithium dendrites inside the lithium ion battery. For example, Wu et al. designed a multi-functional membrane that incorporates a layer of metal in the middle of a conventional polymer membrane. This layer of metal acts as a lithium dendrite detector by monitoring the relationship between the metal and the negative electrode. 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, when the membrane is punctured, SiO2 reacts with metallic lithium to consume lithium dendrites. To avoid further growth of lithium dendrites.

2, smart to prevent lithium ion battery overheating

If the lithium ion battery is overheated(such as external heating, short-circuit self-release heat, etc.), it will cause the diaphragm to contract, causing a short circuit of the positive and negative poles, which will lead to thermal runaway. The traditional PP-PE-PP composite diaphragm can automatically close the hole at a lower temperature, thereby cutting off the positive and negative reactions and achieving the effect of inhibiting the overheating of the battery. However, if the temperature is too high, the PP layer also contracts. This three-layer composite diaphragm also failed.

In order to solve the safety problem of lithium ion batteries under overheating, Yim et al. designed an electrolytic additive material that can protect the safety of lithium ion batteries under overheating. We all know that the general electrolytic flame retardant will have a serious impact on the performance of lithium ion batteries, so it is difficult to apply in practice. The Yim et al. flame retardants are contained in independent small capsules. The outer wall materials of these capsules are very stable in the electrolyte, so under normal conditions there will be no effect on the performance of lithium ion batteries. When the temperature exceeds 70 degrees Celsius, under the action of the steam pressure of the flame retardant DMTP, the rupture of the shell causes the flame retardant to be released into the electrolyte, resulting in a sharp decrease in the conductivity of the electrolyte and preventing further reaction in the battery.

The protection of lithium-ion batteries in the above method is one-time, that is, once the protection mechanism is activated, the entire battery will fail. In order to solve the above problems, Yang et al. designed a protective measure that can be activated several times. The method is characterized by the use of an intelligent electrolyte that can reverse the sol-gel transformation under the influence of temperature. This electrolyte is mainly composed of PNIPAM/AM. When the temperature exceeds the transition temperature, PNIPAM will change from hydrophilic to hydrophobic, which will greatly inhibit the spread of ions in it. What is important is that the reaction is completely reversible when the temperature is reduced, so multiple protection of the battery can be achieved. This technology can be applied to the water Super capacitor to protect the safety of the capacitor.

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