Battery charging speed is limited -Lithium - Ion Battery Equipment

Factors limiting the charging speed of the battery -Lithium - Ion Battery Equipment

When discussing charging speed, the endurance of the battery itself is definitely the most inescapable factor. No matter how powerful the peripheral charging equipment is, how powerful the power is, and how strong the charging capacity is, if the battery itself has shortcomings in the acceptable charging capacity, the charging speed will definitely not be faster. If the battery capacity is relatively large, the natural charging time will be longer.

If you have studied electrochemistry in high school, you will understand the process of battery charging and discharging. The essence is that a series of redox reactions are carried out inside the battery to realize the directional transfer of electrons between the positive electrode and the negative electrode. Taking the current mainstream lithium battery as an example, although there are various types, the general structure is nothing more than a positive electrode material, a negative electrode material, a diaphragm, an electrolyte, etc. The charging process is basically that lithium ions are extracted from the negative electrode, passing through the diaphragm and the battery. Electrolyte, the process of diffusion to the positive electrode - the diffusion speed naturally becomes the key to the charging speed.(Lithium - Ion Battery Equipment)

In theory, it is indeed possible to increase the charging speed by increasing the current. However, if the current is too large, the diffusion rate of lithium ions in the battery cannot keep up with the diffusion rate of electrons, which will lead to a disconnection of electron-ion transport, which will affect the performance of the battery, and the achievable charging capacity will be correspondingly reduced. , there is even a risk of fire and explosion.

Therefore, in general, we recommend using slow charging as much as possible when you are not in a hurry, which is beneficial to prolong the life of the battery.

The diffusion rate of lithium ions is closely related to temperature, material and structure of the cathode.

The first is temperature. Generally speaking, the higher the temperature, the faster the diffusion rate. However, if the temperature is too high, it will also lead to problems such as reduced battery life and reduced charging safety. If the temperature is too low, the same will not work. When the temperature is too low, the metal lithium in the battery will be deposited, resulting in an internal short circuit of the battery, especially the lithium iron phosphate battery. Generally, the capacity of the lithium iron phosphate battery is only about 60-70% at 0 °C, and only 20-40% is left at -20 °C. Therefore, in the cold northern winter, electric vehicles must have the function of heating the battery module, so the power consumption is naturally faster.

The second is the material. The diffusivity of different materials is very different. Lithium cobaltate, lithium manganate, lithium iron phosphate, NCM, NCA, etc. are all cathode materials with very good performance. The two materials are relatively high. This is also an important reason why today's lithium batteries are named after cathode materials.

In the field of 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 when it only takes 30 minutes is called 2C, and so on. 1C can be called fast charge. Nowadays, the charging rate of lithium-ion batteries can generally be 1C-3C, and the highest can go to 5C, but it is naturally far worse than the discharge rate of 10C when starting.

Typical Li-ion battery charging characteristic curve

In addition to the bottleneck of the maximum charging rate, the charging rate that the battery can withstand under different SOC (State of Charge, that is, the state of charge, that is, the remaining power) is also different. Generally speaking, the characteristics of the battery during the charging process are roughly similar to the above picture, and the charging rate will follow a slow-fast-slow rhythm. Generally, when the SOC reaches more than 90%, the internal resistance of the battery will increase significantly, which will slow down the charging rate. If you pay attention to most of the electric vehicles currently on sale, you will find that they will advertise that they can fully charge a large battery in a relatively short period of time, such as 1 hour or even 30 minutes in a certain fast charging state. The proportion of electricity is generally around 80%-90%, which is what it means.

So if you are an electric vehicle user and want to save as much time as possible for charging, try not to use the power less than 10% at every turn, and you don’t have to be fully charged when charging, reaching more than 90%, or it can meet your needs The mileage required for one trip is sufficient.




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