What is the impact of electrolyte on battery performance

As an important part of the battery, the electrolyte, its composition, concentration, quantity, and the type and quantity of impurities will all have a vital influence on the performance of the battery. It directly affects the battery capacity, internal resistance, cycle life, internal pressure and other performance. Through comparison, it is found that the electrolyte generally uses a KOH solution of about 7mol/l (some NaOH is used instead of KOH). Of course, a small amount of other components such as LiOH are also added to the electrolyte, but for some impurities such as carbonate and chloride , Sulfides, etc. are all required to be higher. The positive and negative plates of the battery can only undergo electrochemical reactions in the electrolyte. For a sealed finished battery, the space in it is certain. If there is too much electrolyte, the space of the sealed air chamber will become smaller and the internal pressure of the battery will increase during the charging and discharging process; on the other hand, too much electrolyte will block the diaphragm pores and prevent the conduction of oxygen, which is not good for the rapid recombination of hydrogen. , It will also increase the internal pressure of the battery and may oxidize the pole pieces, causing the pole piece passivation capacity to decrease. The increase in internal pressure may cause battery leakage, creep alkali, and cause battery failure. However, if the electrolyte is too little, the pole pieces will not be completely immersed in the electrolyte, and the electrochemical reaction will be incomplete or some parts of the pole pieces will not undergo electrochemical reactions, making the battery capacity less than the design requirements, and the internal resistance will change. Larger, shorter cycle life. Attention should be paid to the concentration of electrolyte to reduce concentration resistance. Why does the internal resistance increase, the discharge capacity decrease, and the charging efficiency decrease during the storage and use of the battery (cycle)? There are many reasons: First, the additive Co will be transferred to the poles during storage and use. The Co content on the surface of the pole piece decreases, which increases the contact resistance on the surface of the pole piece (indicated by an increase in internal resistance), thereby reducing the charging efficiency and oxygen evolution overpotential, and ultimately resulting in a decrease in discharge capacity. Secondly, during the cycle, the pole pieces are corroded by the electrolyte, causing the pole piece powder to loosen, fall off, or have poor contact (between particles and particles, between particles and substrate), resulting in increased internal resistance, and excessive charging/discharging. The pole piece is damaged. Third, it may be due to the expansion of the pole pieces that squeezed and sucked out the electrolyte in the diaphragm. Since the electrochemical reaction always starts from the surface and then develops deeper, the electrochemical reaction is incomplete and the discharge capacity is reduced; And due to the lack of electrolyte, the internal resistance increases (concentration resistance and ion conduction resistance/migration resistance increase), the charging potential increases, and the discharge potential decreases. Fourth, it may be due to the fact that the water in the electrolyte exists in some unclear form after being recycled or stored for a period of time, such as crystal water, being bound by van der Waals forces, and being bound by forces such as hydrogen bonds. Participate in the electrochemical reaction (that is, increase the concentration of the electrolyte), causing difficulty in ion conduction during the electrochemical process, the internal resistance increases, the charging potential increases, and the discharge potential decreases, which ultimately leads to a decrease in discharge capacity. Finally, it may also be due to the fact that the electrolyte is redistributed, diffused and penetrated into the deep layer of the pole piece during the battery cycle or storage process, resulting in a decrease in the amount of electrolyte on the electrode surface, and the electrochemical reaction always starts from the surface Then it develops deeper, which leads to incomplete electrochemical reactions and a series of problems. Of course, the battery is overcharged/discharged during use, which causes the battery to pressurize, and the hydrogen/oxygen gas will take out the electrolyte at the same time, which will cause the electrolyte to dry up, which is also one of the important reasons. Dissecting the stored and used batteries, you will find that the plates and diaphragm paper inside the battery are dry (visually), which may be the result of one of the above-mentioned reasons or the combined use of several factors. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: Precautions for the first charge of polymer lithium ion battery