It is needless to say that the cycle performance is important for lithium-ion batteries; the longer cycle life of the battery in use means less waste of resources. There are many factors that affect the cycle performance of lithium ion batteries. This article mainly explores from the following aspects.
Types of raw materials used: The choice of materials is the first factor that affects the performance of lithium-ion batteries. The quality of the material determines the cycle performance of the battery. If the performance of the material is very poor, the process is reasonable and the cycle of the battery core will inevitably be unable to guarantee; from the perspective of materials, the cycle performance of a battery is determined by the positive electrode and the Among the two, liquid matching, negative electrode and electrolyte matching, the worse one is determined. The cycle performance of the material is poor. On the one hand, the crystal structure may change too fast during the cycle to continue the lithium insertion and delithiation. On the one hand, the active material and the corresponding electrolyte cannot generate a dense and uniform SEI film. Premature side reactions with the electrolyte cause the electrolyte to be consumed too quickly and affect circulation. In the design of the cell, if one pole confirms the selection of materials with poor cycle performance, the other pole does not need to select materials with better cycle performance, which is wasteful.
Positive and negative electrode compaction: The positive and negative electrode compaction is too high, although it can improve the energy density of the battery core, but it will also reduce the cycling performance of the material to a certain extent. If the positive and negative electrode compactions are too large, it is not conducive to the insertion and extraction of lithium ions, which may reduce the capacity of the battery and also reduce the cycle performance and rate performance of the battery.
Moisture: Excessive moisture will cause side reactions with the positive and negative electrode active materials and the electrolyte, destroying its structure and affecting the circulation, causing the side reactions to react on the surface of the pole piece, affecting the insertion and extraction of lithium ions. At the same time, too much water is not conducive to the formation of SEI film. If there is too much water, the water will be electrolyzed inside the battery to produce gas, which will cause excessive air pressure inside the battery and cause battery leakage. In severe cases, the battery explosion-proof valve may be disconnected. However, while trace amounts of water are difficult to remove, trace amounts of water can also ensure the performance of the battery cell to a certain extent.
Coated surface density: For batteries of the same model, same capacity and same material, reducing the film density is equivalent to adding one or more layers of winding or lamination layers. The correspondingly increased separator can absorb more electrolyte to ensure cycle. Considering that the thinner film density can increase the rate performance of the cell, the baking and dewatering of the pole piece and the bare cell will also be easier, but at a lower areal density, it is difficult for the operator to control the areal density during the drawing process. It affects product quality and the large particles in the slurry may also cause more difficulties in coating and rolling, while reducing production efficiency and increasing the difficulty of staff operations. Therefore, for the improvement of coating surface density, the above factors should be considered comprehensively.
Negative electrode excess: During the cycle of the lithium battery, the negative electrode material continuously accepts the intercalated lithium ions. After a long period of cycle, the structure of the negative electrode material is seriously damaged. Therefore, in the design of lithium batteries, we need to properly overcharge the negative electrode material. If the excess of the negative electrode is insufficient, the battery may not release lithium before cycling, but the structure of the positive electrode changes little after hundreds of cycles but the structure of the negative electrode is seriously damaged and cannot fully receive the lithium ions provided by the positive electrode to precipitate lithium, resulting in excessive capacity. Early drop.
The amount of electrolyte: There are three main reasons for the insufficient electrolyte to affect the circulation. One is the insufficient liquid injection. When the liquid injection is insufficient, the battery is in the process of circulation. Lithium ions cannot conduct normally, which leads to the failure of lithium ions to conduct normally, which reduces the capacity of lithium-ion batteries. Second, although the liquid injection volume is sufficient, the aging time is insufficient or the positive and negative electrodes are not immersed due to excessive compaction Sufficient, if the battery is insufficiently wetted and there is no electrolyte on the surface of the pole piece, the corresponding pole piece cannot exert its corresponding gram capacity, resulting in a decrease in the capacity of the battery. The third is that as the electrolyte inside the circulating cell is consumed, the microscopic performance of the positive and negative electrodes, especially the compatibility of the negative electrode and the electrolyte, is the formation of dense and stable SEI, and the visible performance in the right eye is both during the cycling process. The rate of electrolyte consumption. The incomplete SEI film cannot effectively prevent the negative reaction between the negative electrode and the electrolyte and consume the electrolyte. On the one hand, the SEI film will be regenerated as the cycle progresses to consume the reversible lithium source and the electrolyte . Whether it is a battery cell that has been circulated hundreds or even thousands of times or a battery cell that has been diving for dozens of times, if the electrolyte is sufficient before the cycle and the electrolyte has been consumed after the cycle, increasing the amount of electrolyte is likely to be certain To a certain extent, improve its cycle performance.
Objective conditions of the test: charge and discharge rate during test, cut-off voltage, charge cut-off current, over-charge and over-discharge during test, test room temperature, sudden interruption during test, contact resistance between test point and cell, etc. Factors will more or less affect the cycle performance test results.
Post time: May-26-2020