Why Do Lithium Ion Batteries Degrade?

Why Do Lithium Ion Batteries Degrade?

While there are a variety of models to explain how LIBs degrade, most of these models ignore the interplay of different mechanisms. In this article, we will look at a model that links several of the mechanisms involved in the degrading process. Specifically, we will examine how the growth of the SEI layer affects the pore blocking of the cell and the rate of lithium plating.

Loss of active material

Degradation of lithium ion batteries occurs when the active material in the cell becomes insufficient. This can happen through multiple mechanisms. Among these mechanisms are electrochemical reactions, loss of lithium inventory, loss of active material, and stoichiometric drift. Moreover, loss of active material leads to loss of the electrolyte’s potential and its impedance increases.

Loss of active material in the negative electrode accelerates degradation. The negative electrode experiences higher degradation rates when the temperature decreases. The degradation mechanism is similar to the one affecting the positive electrode. However, a negative electrode is affected more than the positive electrode. The negative electrode has a lower critical stress than the positive electrode, so the degradation process is accelerated.

The loss of active material in lithium ion batteries is due to various factors, including particle cracking in the electrodes, lithium plating, and SEI on cracks. Loss of active material is also caused by different types of mechanical stress, including hydrostatic tensile stress and compressive stress.

The loss of active material in lithium ion batteries is accelerated when temperatures are low. Graphite electrodes expand during lithiation and contract during delithiation. The mechanical stress produced by this stress is sufficient to cause cracking. The larger the particle size, the greater the risk of cracking.

Loss of lithium inventory

One of the major causes of lithium ion battery degrading is loss of lithium inventory. This happens due to a process known as SEI film formation. This film forms at the interface between the solid and liquid phases of a lithium ion battery. Its formation is due to a reaction between the electrode material and electrolyte. The result is a layer that has the characteristics of a solid electrolyte and is insulated from electrons. This film is formed on both the anode and the cathode, but it has a lesser effect on the anode.

The rate of degradation varies depending on the time a battery spends resting and cycling. Higher C-rates and longer cycles may accelerate degradation. The sequencing of ageing tests can also affect degradation rate. Some researchers have proposed path dependence as a potential cause for lithium ion battery degradation.

Other factors that may affect LiB degradation include electrode corrosion, which reduces the number of Li-ions that can be accepted by an electrode and depletes its capacity. It is also common for LiBs to degrade when exposed to cold temperatures. This misconception is based on the observation that smartphones tend to ‘die’ faster in colder temperatures, which slow down the shuttling of Li-ions between the electrodes.

Understanding lithium ion battery degradation is an important issue for sustainable decarbonisation of energy grids and transport systems. Developing a better understanding of this complex issue will facilitate cost-effective decarbonisation.

Loss of TM

The redox process can lead to a loss of TM from lithium-ion batteries. Loss of TM from lithium-ion batteries results in a reduced capacity. The loss of TM can be controlled by modifying the composition of the material. For instance, you can control the amount of oxygen that reaches the material’s surface.

The amount of active lithium is directly related to the degree of Coulombic efficiency. It is therefore important to determine the amount of active lithium in each cell to be used. This measurement is critical because it helps in stating the mechanisms that lead to degradation. However, this measurement is not accurate enough to determine the exact rate of TM.

Another method of determining TM loss is through temperature measurements. In this method, the surface and the internal temperature of the lithium ion battery are measured. The internal temperature is higher than the surface temperature. The difference between these temperatures is about 8 degC. However, this difference is smaller than the difference between the internal and external surface temperature.

The loss of TM in lithium ion batteries is a primary cause of limited battery life. In order to extend the life of lithium ion batteries, it is necessary to improve the design and process of lithium ion batteries. Ultimately, this will lead to cost reductions and a reduced environmental footprint.