When charging lithium ion battery, Li + is de embedded from the positive electrode and embedded into the negative electrode; However, when some abnormalities occur, such as: insufficient lithium intercalation space in the negative electrode, too much resistance for Li + to be embedded in the negative electrode, too fast intercalation of Li + from the positive electrode but unable to be embedded in the negative electrode in the same amount, Li + that cannot be embedded in the negative electrode can only get electrons on the surface of the negative electrode, so as to form a silver white metallic lithium, which is often called lithium precipitation. Lithium precipitation not only reduces the performance of the battery and greatly shortens the cycle life, but also limits the fast charging capacity of the battery, and may cause disastrous consequences such as combustion and explosion.

In a series of articles we will discuss about the following problems from the macro scale of lithium-ion battery, working conditions, gradient existing in the battery, electrochemical test, safety test, etc.), micro scale (electrode, particle, microstructure, etc.) and atomic scale (atom, ion, molecule, activation energy barrier, etc.):

(1) What is the "fuse" of lithium evolution reaction?

(2) What are the experimental phenomena of lithium evolution reaction?

(3) What is the macro morphologies of metal lithium deposited on the negative electrode surface under different conditions? What is the direct experimental evidence of side effects?

(4) What is the relevant mechanism of battery aging caused by lithium evolution reaction? What is the capacity decay curve in this process (i.e. the change of capacity retention rate with the number of cycles)?

With the rapid development of lithium-ion battery related technologies and the continuous emergence of diversified energy storage needs, people put forward higher requirements for future lithium-ion batteries:

(1) Longer life (battery life of more than 10 years is required for electric vehicles);

(2) Excellent fast charging performance (charging to 80% SOC takes only 20 minutes);

(3) Excellent low temperature cycle performance and capacity recovery ability;

(4) Impeccable safety performance.

Interestingly, these four remarkable battery performances are closely related to the side reaction of lithium evolution. The battery aging process and the change of negative electrode reaction kinetics caused by the side reaction have a great impact on the above four performances.

When the lithium-ion battery is charged, Li + is de embedded from the positive electrode. These Li + diffuse to the negative electrode surface in the electrolyte and are embedded in the negative electrode material. Taking graphite negative electrode as an example, lithium intercalation occurs when the negative potential decreases to 200-65 MV vs. Li + / Li; As the charging continues, the negative electrode potential drops below 0 V vs. Li + / Li, and the lithium deposition side reaction occurs. At this time, the lithium deposition side reaction of the negative electrode and the lithium intercalation reaction are carried out at the same time. Considering the influence of polarization, lithium deposition side reaction occurs when the sum of equilibrium potential and over potential (from ohmic resistance, charge transfer and diffusion process) is negative relative to Li + / Li electric pair.

Conclusion:

To ensure the smooth operation of your application, EverExceed research and development engineers works day and night to research and design the state of art Lithium Iron phosphate batteries with the perfect charging and discharging parameters. So choose EverExceed as your brand for the complete reliability.