The development of the new energy automobile industry also stimulates the market demand for power batteries. What are the factors that limit the charging speed of the power battery? What are the factors other than the bottleneck of the battery itself? The following is the content of the power battery that me bring about. I hope that everyone can gain something!
Taking the current mainstream lithium battery as an example, although the variety is varied, the general structure is nothing more than a positive electrode material, a negative electrode material, a separator, an electrolyte, etc. The charging process is basically that lithium ions are pulled out from the negative electrode, through the diaphragm and The electrolyte, the process of diffusion to the positive electrode – the diffusion rate naturally becomes the key to the charging speed.
When discussing the charging speed, the battery’s own capacity is definitely one of the most unavoidable factors. No matter how many peripheral charging devices, how much power, and how strong the charging capacity is, if the battery itself has a short board in terms of acceptable charging capability, the charging speed will definitely not be fast. In addition, if the battery capacity is relatively large, the natural charging time will be long.
If you have learned the knowledge of electrochemistry, you will understand the process of charging and discharging the battery. The essence is that the inside of the battery passes through a series of redox reactions to realize the directed transfer of electrons between the positive and negative electrodes. Taking the current mainstream lithium battery as an example, although the variety is varied, the general structure is nothing more than a positive electrode material, a negative electrode material, a separator, an electrolyte, etc. The charging process is basically that lithium ions are pulled out from the negative electrode, through the diaphragm and The electrolyte, the process of diffusion to the positive electrode – the diffusion rate naturally becomes the key to the charging speed.
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 inside the battery can not keep up with the electron diffusion speed, which will cause the electron-ion transport to be disconnected, affecting the battery performance, and the charge capacity that can be achieved is also reduced accordingly. The battery life is even more terrible. There is even a danger of fire and explosion.
Therefore, in general, we do not try to use slow charging when it is not in a hurry, which will help extend the life of the battery.
The diffusion rate of lithium ions is closely related to temperature, material and structure of the positive electrode.
The first is temperature. Generally speaking, the higher the temperature, the faster the diffusion rate. However, if the temperature is too high, the battery life will be reduced and the charging safety will be reduced.
If the temperature is too low, the same will not work. When the temperature is too low, the metal lithium in the battery will deposit, causing internal short circuit of the battery, especially the lithium iron phosphate battery.
Generally, the capacity of lithium iron phosphate battery at 0 ° C is only about 60 to 70%, and at -20 ° C, only 20 to 40% is left. Therefore, in the cold winter of the north, the electric vehicle must have the function of heating the battery module, and the power consumption is naturally faster.
Followed by materials, the diffusion potential of different materials is very large, such as lithium cobaltate, lithium manganate, lithium iron phosphate, NCM, NCA, etc. are very good performance of the cathode material, and the latter two are also the best performance, the application of the current Two materials with higher degrees. This is also an important reason why today’s lithium batteries are named after positive materials.
In the field of the battery industry, the charge-discharge ratio is usually used to describe the relationship between the charging speed and the current. For example, the rate at which the battery is fully charged for 1 hour is called 1C, and the rate at 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 the discharge rate of starting 10C is naturally far worse.
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) is also different.
In general, the characteristics of the battery during the charging process are roughly similar to the above picture, and the rate of charging will follow the slow-fast-slow rhythm. Generally, when the SOC reaches 90% or more, the internal resistance of the battery rises remarkably, causing the charging rate to slow down.
If you pay attention to most of the electric cars that are currently on sale, you will find that they will be able to promote themselves in a relatively fast charge state, in a relatively short period of time – for example, 1 hour or even 30 minutes, full of a big The proportion of electricity, generally between 80% and 90%, is what this means.
So if you are an electric car user and want to save the time and cost as much as possible, try not to use the power below 10%. When charging, you don’t have to be full, more than 90%, or you can meet your needs. The number of miles required for a trip is sufficient.
What is the charging speed of the charging device?
In addition to the bottleneck of the battery itself, peripheral charging devices have their own limitations. Simply put, the higher the output power of the charging post, the shorter the charging time. However, the charging pile is not able to increase the charging power indefinitely. Let’s first talk about what kind of process is the charging of electric vehicles.
When it comes to car charging, the first thing that people think of is the charging pile. Simply put, the higher the output power of the charging post, the smaller the battery capacity, and the shorter the charging time. This is the same as having to fill a pool with water. The larger the discharge pipe and the smaller the pool, the shorter the time is.
However, as an electric vehicle user, of course, I hope that my battery capacity is also large enough, so it is better to increase the charging pile power. Charging piles for vehicles are generally divided into AC charging piles and DC charging piles. We are divided into two situations.
Let’s talk about the AC charging pile with strong universality. It uses 220V AC charging with the same voltage as the household. The current is only 16A or 32A. The charging speed is relatively slow. In the case of battery capacity of 20kwh, it takes about 6-8 hours to fully charge.