Li-Ion battery--sei membrane

Lithium-ion battery in the first time from the discharge process, the electrode material and electrolyte in the solid-liquid phase of the interface reaction, forming a layer covering the electrode material surface passivation layer. This passivation layer is an interface layer, with the characteristics of solid electrolyte, is an electronic insulator is a good conductor of lithium ion, lithium ions can be freely embedded and out of the passivation layer, so this layer of passivation film is called "Solid electrolyte Interface membrane" (solids electrolyte interface), Referred to as Sei membrane.

performance impact of SEI membrane

1. The formation of SEI film consumes some lithium ions, which increases the irreversible capacity of the first charge and discharge, and reduces the charge-discharge efficiency of the electrode material.

2. Sei membrane has an organic solvent insoluble, in the organic electrolyte solution can be stable, and the solvent molecule can not pass the passivation film, so as to effectively prevent the co-embedding of solvent molecules, to avoid the solvent molecules are embedded in the electrode material damage caused, thus greatly improving the electrode cycle performance and service life.

difference between the generation of SEI membrane and the loss capacity of side reaction

1. After multiple charge and discharge, the surface of the graphite anode often forms a layer of SEI film, which prevents the interaction between the electrolyte and the graphite anode. However, when the temperature rises, the sei membrane will occur decomposition reaction, causing the electrolyte and cathode surface irreversible reaction, resulting in irreversible capacity formation and heat generation, so that the temperature further rise.

2. When the temperature rises, the solvent reacts with the electrolyte, releasing heat.

influence of ambient temperature on sei membrane

The use and storage temperature have a great effect on the SEI membrane, which affects the life of the battery. The stability of SEI film under high temperature is not only affected by temperature but also is related to Soc of charge state of battery. More than 45 degrees high temperature in the 100%SOC state will destroy the uniformity of the SEI membrane, resulting in an increase in electrode impedance and attenuation of cyclic performance. The negative surface of the SEI film disappears when the battery is stored at 70 degrees soc9%.

the effect of voltage on sei membrane

In the graphite anode system, the formation of the SEI film relies on the battery voltage. When the battery voltage 3.0V, the SEI film began to form, until 3.8V, this phase is mainly generated LI2CO3, but also a small amount of lif and Ch3oco2li generation, the final arrival of 4.2V is mainly the decomposition of electrolyte salts. Therefore, the most outer layer of the SEI membrane compound is mainly lif.

The impedance of SEI film is not the same under different state of charge. The impedance of the SEI film is higher than the discharge state when the cathode is full, which is caused by the change of the cathode volume during the process of lithium insertion and lithium removal.

When the battery is overcharge, the excess Li + does not have a negative material for embedding, that part of Li + will be reduced to the negative surface of metal lithium precipitation, resulting in the risk of short-circuit, and caused by the positive electrode active material structure irreversible changes and electrolyte decomposition, generating a large number of gases, releasing a large amount of heat, the battery temperature and internal There are dangers such as explosion, burning and so on. When the battery is over-discharged, the negative surface of the SEI film is fully removed, the sei membrane is destroyed. When the battery charge and discharge cycle, the re-formation of the SEI film stability and compactness may become worse, the need for a large number of Li +, resulting in discharge capacity and charge-discharge efficiency is reduced.