What effect does the amount of electrolyte have on battery performance?

Choosing an appropriate electrolyte system for different positive and negative materials does not guarantee the battery has good electrochemical performance, and the appropriate amount of electrolyte must be determined according to the requirements of different positive and negative materials.

1. Judgment criteria for electrolyte volume demand

Electrolyte is used as a medium for lithium ion migration and charge transfer. In order to ensure that the active material is fully used, the gaps in the core of the battery are required to be filled with electrolyte. The compaction density of each cathode material is different, and the requirements for the amount of electrolyte are different. The general situation is that the demand for the electrolyte of the lithium cobalt oxide cathode material with high compaction density is small, and the demand for the electrolyte of the ternary and lithium manganate cathode system battery with low compaction density is the largest.

2. The influence of electrolyte volume on battery performance

(1) The influence of electrolyte volume on battery capacity

It can be seen from Figure 1 that the charging and discharging curve of the electrolyte with a small amount of dripping is abnormal, the charging capacity is much larger than other values, and the discharge capacity is much smaller than other values. The capacity increases as the amount of electrolyte increases. The battery with the best capacity has the diaphragm just wetted. It can be seen that the amount of electrolyte is insufficient, the positive electrode sheet is not sufficiently wetted, and the diaphragm is not wetted, resulting in a large internal resistance and a low capacity. The increase in the amount of electrolyte helps to make full use of the capacity of the active material. This shows that the battery capacity has a greater relationship with the amount of electrolyte, and the battery capacity increases with the increase in the amount of electrolyte, but finally tends to be basically constant.

(2) The influence of electrolyte volume on battery cycle performance

It can be seen from Figure 1 that with the increase of the rate, the capacity difference becomes more obvious, and the cycle performance of the battery becomes worse. The amount of electrolyte is small, the conductivity decreases, and the internal resistance increases rapidly after cycling, which accelerates the decomposition or volatilization of the partial electrolyte of the battery, and the deterioration of the battery cycle performance is gradually accelerated. Too much electrolyte causes the side reaction of the battery cell to increase relatively, and the gas production is large, which causes the cycle performance of the battery cell to decrease. Furthermore, excessive electrolyte is also wasted. It can be seen that the amount of electrolyte has a very obvious impact on the cycle performance of the battery. Too little or too much electrolyte is not conducive to the cycle performance of the battery.

(3) The influence of electrolyte volume on battery safety performance

The good safety performance of the battery is mainly due to the absence of bulging and explosion during use. One of the reasons for the explosion of the battery is that the injection volume cannot meet the technological requirements. When the amount of electrolyte is too small, the internal resistance of the battery is large, and the heat is high. The increase in temperature causes the electrolyte to rapidly decompose to produce gas, and the diaphragm melts, causing the battery to expand and short-circuit and explode. When the used electrolyte and the positive and negative materials produce excessive gas production by side reactions, an appropriate amount of electrolyte infiltrant can be added to reduce the amount of electrolyte added, thereby reducing the problem of excessive gas production and improving battery safety. When the amount of electrolyte is too much, the amount of gas generated during charging and discharging is large, the internal pressure of the battery is high, and the shell ruptures, causing electrolyte leakage. When the electrolyte temperature is high, it will catch fire when it encounters air.

Electrolyte is an indispensable part of lithium-ion batteries, and is a necessary condition for lithium-ion batteries to obtain the advantages of high voltage, high energy density, and high cycle performance. The amount of electrolyte has an important impact on the electrochemical performance and safety performance of the battery. Too much or too little is inappropriate. Experiments are needed to determine the amount of electrolyte that is compatible with the positive and negative materials and the diaphragm.