What is the reason for the reduction in lithium battery capacity?

Lithium batteries are a common type of battery in people's lives. Nowadays, there are many applications in electric vehicles. However, consumers who have used it should know that the capacity of lithium batteries will be reduced after a period of use.

Lithium batteries are commonly used in people's lives. Nowadays, there are many applications in electric vehicles. However, consumers who have used them should know that lithium batteries will shrink after a period of use. This is a deficiency of lithium batteries. Because this is not enough, many consumers will hesitate to choose lithium batteries. I am afraid that problems will occur after using them for a period of time. Many car companies and related staff are trying their best to solve this problem. I’m going to introduce you today. The reason is that the capacity of lithium batteries is reduced.

Reasons for the reduction of lithium battery capacity: Structural changes of the cathode material

The positive electrode material is the main source of lithium ions. When lithium ions are removed from the positive electrode, in order to maintain the material's electrical neutral state, the metal element is inevitably oxidized to a high oxidation state, which is accompanied by a component transition. The conversion of the components is liable to cause changes in phase transfer and bulk structure. The phase transition of the electrode material can cause changes in lattice parameters and lattice mismatch. The induced stress caused by the induced grain breaks and causes the propagation of cracks, causing mechanical damage to the structure of the material, thereby causing electrochemical performance degradation.

KIM et al. studied the microstructure of layered LiNi0.6Co0.2Mn0.2O2 cathode material. Because Li+(0.76) and Ni2+(0.69) have similar ionic radii, nickel-rich materials are more prone to Ni2+. The migration to the Li+ hole leads to the disorder of the structure; the repeated changes in the volume cause the active material to generate cracks and pores. As the cycle progresses, the material structure gradually changes from the rhombohedral structure to the spinel phase, in the cycle. The drastic changes in the initial structure led to a rapid decline in capacity and voltage.

Reasons for the reduction of lithium battery capacity: negative electrode material structure

Commonly used anode materials for commercial lithium batteries are carbon materials, lithium titanate, etc., which are analyzed by typical negative graphite. The decay of the lithium battery capacity occurs for the first time in the formation phase, where SEI is formed on the surface of the negative electrode, consuming some of the lithium ions.

As lithium batteries are used, changes in the graphite structure can also cause a decrease in battery capacity. LIU [2] and so on studied the capacity decay mechanism of LiFePO4/C battery, which is also applicable to ternary lithium battery. It is found that the carbon material after circulation retains the morphology of graphite, but the half height of its (002) crystal plane When the width is large, the grain size in the c-axis direction becomes small, and the change of the crystal structure causes cracks in the carbon material, thereby destroying the SEI film on the surface of the negative electrode and promoting the repair of the SEI film. The excessive growth of the SEI film consumes active lithium, thus causing the irreversible capacity decay of the battery.

Reasons for the reduction of lithium battery capacity: oxidative decomposition and interfacial reaction of electrolyte

The properties of the electrolyte significantly affect the specific capacity, lifetime, rate charge and discharge performance, operating temperature range, and safety performance of the lithium ion battery. The electrolyte mainly includes three parts: solvent, electrolyte and additive. Decomposition of the solvent and decomposition of the electrolyte result in loss of battery capacity. The decomposition and side reactions of the electrolyte are the main factors for the capacity decay of the lithium battery. Regardless of the positive and negative materials used, and the process, the decomposition of the electrolyte and the interface with the positive and negative materials occur with the recycling of the lithium battery. The reaction will cause a decrease in capacity.

So that's why the small battery capacity reduction introduced, and that's largely because of the way lithium batteries work, but it's also because of the way it works. Although there are some problems in the use of this kind of battery, consumers should not ignore its advantages when they use it. Looking back, lithium battery brings great convenience to people's life.

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