Inner Mongolia Sanxin Technology Development Co., Ltd
Inner Mongolia Sanxin Technology Development Co., Ltd
With the development of technology and technology mature, lithium-ion battery applications more and more widely. Lithium-ion battery with a single high voltage, relatively light weight, environmentally friendly, etc., but after a number of cycles after the charge and discharge cycle will appear the performance of the battery capacity decline. The same conditions, the faster the battery capacity attenuation, the battery quality is relatively poor. Lithium-ion battery cycle performance is an important measure of its quality indicators, many of the lithium-ion battery standards have a cycle of life of this project.
Lithium-ion battery charge and discharge cycle process is a complex physical and chemical reaction process, the cycle life of the factors that are multifaceted. On the one hand with the characteristics of the battery itself, such as design, manufacturing process and material degradation, etc .; on the other hand with the use of the battery during the impact of the outside world, such as the use of the environment and charge and discharge system. The following factors affect the cycle of lithium-ion battery life factor analysis.
1 lithium ion battery structure and principle
Lithium-ion battery is mainly composed of positive and negative materials, electrolyte, diaphragm, current collector and battery shell, positive and negative materials from two different lithium ion embedded compounds. Charging, lithium ions from the cathode off the sub-through the electrolyte through the diaphragm embedded in the negative, the discharge is the opposite. In the lithium ion battery for the first charge and discharge process, the negative electrode and electrolyte interface to form a layer of passivation film. It is between the electrode and the electrolyte play a role in the diaphragm, the electronic insulator is a good conductor of lithium ions, lithium ions can pass through the passivation layer free to insert and release, with a solid electrolyte characteristics, so this layer of passivation film Known as the "solid electrolyte interface" (solid electrolyte interface), referred to as SEI film [1].
2 design and manufacturing process
In the battery design process, the choice of material is the most important factor. Different performance characteristics of different materials, the performance of the battery is also a gap. Positive and negative material matching cycle performance is good, the battery cycle life will be long. In the ingredients, we should pay attention to positive and negative material added. In general, the design of the assembly process generally requires that the negative capacity of the cathode is relatively excessive, if not excessive, during the charging process will precipitate lithium, the formation of lithium dendrite and thus affect the safety. The anode is too much relative to the positive too much, the positive electrode may be excessive lithium, resulting in structural collapse.
Electrolyte in the battery reversible capacity is also a very important factor. Electrode material off, the process of intercalation of lithium ions is always the process of interaction with the electrolyte, this interaction on the electrode material interface conditions and internal structure changes have an important impact [3]. In the process of interaction with the positive and negative materials, the electrolyte will be lost, and in the battery into the SEI film and pre-charge, it will consume part of the electrolyte, so the type of electrolyte and injection volume also affect the battery life.
Lithium-ion battery manufacturing process mainly includes: positive and negative ingredients, coating, production, winding, into the shell, injection, sealing, chemical and so on. In the battery production process, the process for each step are very strict. Any process that is not well controlled can affect battery cycle performance.
In the process of positive and negative ingredients, should pay attention to the amount of binder, stirring speed, slurry concentration, temperature and humidity, and to ensure that the material can be dispersed evenly.
In the coating process, in the premise of ensuring high battery specific energy, reasonable control of positive (negative) coating, the appropriate reduction in electrode thickness is conducive to reducing the battery decay rate [4]. After the coating of the pole piece but also with the roller press further compaction, the appropriate positive compaction density can increase the battery discharge capacity, reduce the resistance, reduce the polarization loss, extend the battery cycle life.
When winding, roll into the batteries should be close, not loose [5]. The diaphragm and the positive and negative pole volume is tight, the smaller the internal resistance, but the volume is too tight will cause the pole piece and diaphragm wet difficult, resulting in smaller discharge capacity; roll too loose will make the pole in the charge and discharge process over-expansion , Increased resistance, reduced capacity, shortened cycle life.
3 battery material aging recession
Lithium-ion battery charge and discharge cycle is the process of lithium ions through the electrolyte in the positive and negative material back and forth between the de-embedded, moving the process. In the lithium-ion battery cycle, in addition to positive and negative redox reaction occurs, there are a lot of side effects. If the side effects of lithium-ion batteries can be reduced to a low level, so that lithium ions through the electrolyte can always smoothly between the positive and negative materials, can make lithium-ion battery cycle life can be increased.
Lithium ions from the positive electrode to the negative must be covered in the carbon anode on the SEI film, SEI film directly affects the battery life cycle. Foreign scholars on the aging of the battery material research earlier, especially on the SEI film research more in-depth. The main research method is through the battery life test data combined with electrochemical characterization means to analyze the battery material stability and recession mechanism [6].
The stability of the SEI film has an important effect on the stability of the battery. SEI film is unstable and easy to precipitate lithium metal, will lead to rapid degradation of the anode active material to form a stable SEI membrane lithium battery can be stored under high temperature conditions for more than 4 years [7]. D. Aurbach et al [8] after the dismantling of the lithium cobalt oxide battery cycle, by SEM, XRD experiments on the positive and negative electrode analysis, the capacity decline is mainly attributed to the negative electrode SEI film continued consumption of Li + and LiCoO2 and HF formation Of the LiF interface film and other irreversible side effects. P.Ramadass et al. [9] established a capacity decay model by describing the process of lithium ion loss caused by the continuous growth of the negative electrode SEI film during the charge-discharge cycle. S. Sankarasubramanian et al. [10] established a capacity decay model that included the diffusion of solvent and the growth mechanism of the SEI membrane and concluded that the capacity decline was linear with the SEI film thickness and the cell aging time.
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