Manufacturing method for use of lithium molecular sieve

For lithium ion secondary batteries, when there is too much moisture in the non-aqueous electrolyte, it will produce electrolyte deterioration, high internal pressure, high internal resistance, high self-discharge, low capacity, low cycle life, and battery leakage. Therefore, the removal of water from the non-aqueous electrolyte in the lithium ion secondary battery is very critical. When there is too much hydrogen fluoride in the non-aqueous electrolyte, it will react with lithium. On the one hand, it consumes the limited lithium ions in the battery, thereby increasing the irreversible capacity of the battery. On the other hand, a large amount of lithium fluoride appears in the reaction product. It is unfavorable to improve the electrochemical performance of the electrode. At the same time, the gas products produced in the aforementioned reaction will increase the pressure in the battery. Therefore, the removal of hydrogen fluoride in the lithium ion battery is also very important.

Researchers have proposed many methods for removing water from non-aqueous electrolytes. They are simply divided into two categories in terms of technical principles: one is to remove water from non-aqueous electrolytes by drying methods such as distillation, and the other is to use molecular sieves. Dewatering treatment for non-aqueous electrolyte. The former is difficult to achieve a very low moisture content, and the water removal requirements of lithium-ion batteries are relatively strict, so molecular sieves are usually used to remove water. It is worth noting that while the molecular sieve removes water, hydrogen fluoride can also be removed.

Due to the presence of exchangeable cations in the molecular sieve, the ion exchange process between the lithium ions in the solution and the cations in the molecular sieve will occur during the removal of water from the lithium ion battery. Therefore, when the water is removed, the cations in the molecular sieve will also be Exchange into the non-aqueous electrolyte, causing secondary pollution to the solution. For the non-aqueous electrolyte dewatering treatment of lithium ion batteries, if conventional molecular sieves are used, the sodium ions therein will be ion exchanged with lithium ions in the non-aqueous electrolyte, and the exchanged sodium ions will affect the positive and negative electrodes. The process of lithium insertion and the transportation of lithium ions make the lithium ion battery unable to charge and discharge normally.

In order to solve this problem, the researchers tried to exchange the exchangeable cations of the molecular sieve into lithium ions through ion exchange in advance. The exchanged lithium ions will not pollute the non-aqueous electrolyte of the lithium ion battery. The exchange ratio should be as high as possible to effectively avoid the adverse effects of sodium ions on lithium-ion batteries. However, to achieve this, if a conventional molecular sieve is immersed in a high-concentration lithium ion solution for lithium ion exchange, 5 ion exchanges are required, and each exchange needs to use an excess of more than 6 times the amount of lithium ion solution. The exchange time is too long, resulting in extremely low utilization of lithium ions and a long production cycle, resulting in a very high cost of lithium molecular sieves with a high exchange ratio. Due to the large proportion of lithium ions in the lithium molecular sieve, when it is applied to the process of removing water and acid from the non-aqueous electrolyte, the sodium ions that may remain in the non-aqueous electrolyte will be exchanged by the lithium ions in the molecular sieve. Sodium removal treatment of non-aqueous electrolyte.