Factors affecting lithium-ion battery performance
1. Moisture
Excessive moisture can cause side reactions with the positive and negative electrode active materials, damage their structure, and thus affect the cycle. At the same time, excessive moisture is also not conducive to the formation of the SEI film. However, while trace amounts of moisture are difficult to remove, they can also ensure the performance of the battery cell to a certain extent.
2. Compaction of positive and negative electrodes
While excessive compaction of the positive and negative electrodes can increase the energy density of the battery cell, it can also reduce the cycle performance of the material to some extent. Theoretically speaking, the greater the compaction, the greater the damage to the material structure, which is the basis for ensuring that lithium-ion batteries can be cycled. In addition, battery cells with high positive and negative electrode compaction are difficult to guarantee a high liquid retention, which is the basis for the battery cell to complete normal cycles or more cycles.
3. Objective conditions of the test
External factors such as charge/discharge rate, cutoff voltage, charging cutoff current, overcharge/over-discharge during testing, test chamber temperature, sudden interruption during testing, and contact resistance between the test point and the cell can all affect the cycle performance test results to varying degrees. In addition, different materials have different sensitivities to the above objective factors. A unified testing standard and an understanding of the commonalities and characteristics of important materials should be sufficient for daily work.
4. Excessive negative electrode
In addition to considering the impact of the initial irreversible capacity and the deviation in coating density, the effect of excessive negative electrode on cycle performance is also a factor to consider. For lithium cobalt oxide plus graphite system, it is common for the negative electrode graphite to become the weak link in the cycle process. If the negative electrode is not sufficiently excessive, the lithium cell may not have lithium deposition before cycling, but after hundreds of cycles, the positive electrode structure changes very little, but the negative electrode structure is severely damaged and cannot fully receive the lithium ions supplied by the positive electrode, thus causing lithium deposition and premature capacity decline.
5. Coating film density
Thinner film density may make it more difficult to control the coating error, and large particles in the active material may also have a negative impact on coating and rolling. More layers mean more foil and separator, which in turn means higher cost and lower energy density. Therefore, a balanced approach should be taken into consideration during the evaluation.
6. Types of materials
Material selection is the primary factor affecting lithium-ion battery performance. Choosing materials with poor cycle performance means that even with the most efficient manufacturing process and the most refined fabrication, the cell's cycle life will inevitably suffer. Conversely, choosing better materials means that even with some manufacturing issues, the cycle performance may not be drastically worse. In cell design, if one electrode is confirmed to use a material with poor cycle performance, then there's no need to choose a material with better cycle performance for the other electrode, resulting in waste.
7. Electrolyte volume
There are three main reasons why insufficient electrolyte volume affects the cycle: first, insufficient electrolyte injection; second, although the electrolyte injection volume is sufficient, the aging time is not enough or the positive and negative electrodes are not fully immersed due to excessive compaction; and third, the electrolyte inside the battery cell is consumed as the cycle progresses.
Factors affecting lithium-ion battery life
The charge-discharge cycle of a lithium-ion battery is a complex physicochemical reaction process, and its cycle life is affected by many factors. On the one hand, it is related to the characteristics of the lithium-ion battery itself, such as design, manufacturing process, and material performance degradation; on the other hand, it is related to the external influences on the battery during use, such as the usage environment and charge-discharge regime.
●Impact of design and manufacturing processes
In the design of lithium-ion batteries, material selection is the most crucial factor. Different materials have different performance characteristics, resulting in variations in battery performance. Good cycle performance from a well-matched positive and negative electrode material ratio leads to a longer battery cycle life. In terms of formulation, careful attention must be paid to the amounts of positive and negative materials added.
● The impact of battery usage environment
The operating environment of lithium-ion batteries has a significant impact on their cycle life. Ambient temperature is a particularly important factor; both excessively low and high temperatures can negatively affect the cycle life of lithium-ion batteries.
