What limits the charging speed of lithium batteries？

In the battery industry, the charge-discharge rate is usually used to describe the relationship between the charging speed and the current. For example, the rate when the battery is fully charged in 1 hour is called 1C, and the rate that takes only 30 minutes is called 2C, and so on, if it exceeds 1C It can be called fast charge.

Generally speaking, the charging rate will follow a slow-fast-slow rhythm. When the SOC reaches more than 90%, the internal resistance of the battery will increase significantly, causing the charging rate to slow down. So if you are an electric vehicle user and want to save the charging time as much as possible, try not to use the battery below 10%. It does not have to be fully charged when charging, reaching more than 90%, or it can meet your next time. The mileage required for travel is sufficient.

In addition to the bottleneck of the battery itself, external charging equipment will also have an impact. In theory, the charging speed can be increased by increasing the current. However, if the current is too large, the diffusion speed of lithium ions inside the battery will not keep up with the electron diffusion speed, which will cause the electron-ion movement to be disconnected, which will affect the battery performance, and the achievable charging capacity will be correspondingly reduced. The battery life will be even more terrible. , There is even a danger of fire and explosion. So in general, we recommend using slow charging as much as possible when you are not in a hurry, which will help extend the life of the battery, and slow charging of lithium batteries is safer.

During charging, the diffusion rate of lithium ions inside a lithium battery is closely related to temperature, cathode material and structure.

The first is temperature. Generally speaking, the higher the temperature, the faster the diffusion rate, but if the temperature is too high, it will also cause problems such as reduced battery life and decreased charging safety. If the temperature is too low, the same will not work. If the temperature is too low, the lithium metal in the battery will deposit, which will cause a short circuit inside the battery.

Second is the material. The diffusion capacity of different materials is very different. For example, lithium cobalt oxide, lithium manganate, lithium iron phosphate, NCM, NCA, etc. are all positive electrode materials with very good performance. This is also an important reason why today's lithium batteries are named after cathode materials.