Tag Lithium ion power battery

What is the second-order RC model of lithium-ion power battery? Next, the second-order RC model of lithium-ion power battery is introduced.

We have learned How does the lithium ion power battery work.The charge and discharge process of lithium-ion power batteries is a very complex electrochemical process, and its performance parameters are affected by many factors such as charge and discharge depth, current intensity, temperature, and vibration. It takes a lot of time and cost to detect the changes of various parameters of the battery through the method of battery charge and discharge test, and there are potential safety hazards such as fire and explosion. By establishing an accurate battery model to simulate the change state of various performance parameters of the battery during the charging and discharging process, not only can safety be improved, but also a lot of test time and cost can be saved. Therefore, this section studies the establishment of a lithium-ion power battery model..

The battery models commonly used at this stage mainly include equivalent circuit models, mechanism models, empirical models based on experimental data, electrochemical models, neural network models, and random models. Among them, the equivalent circuit model can express the relationship between the output characteristics of the battery and the internal parameters, and can be used to predict the state of charge SOC, the state of health SOH and other parameters of the battery. It can well reflect the working state of the battery. It has a simple structure, easy modeling, Convenient parameter identification and other advantages. Since the order of the second-order RC equivalent circuit model is appropriate, the engineering is easier to realize, and the steady-state and transient characteristics of the battery can be taken into account, so this article chooses the second-order RC model as the lithium-ion power battery model, as shown in Figure Shown.

Among them, V_OC represents the ideal voltage source, representing the open circuit voltage of the lithium-ion power battery; R₀ represents the ohmic internal resistance; two RC structures are used to represent the polarization reaction of the battery, where R_S, and R_L are the polarization internal resistance, C_S, and C_L is the polarization capacitance;
I(t) represents the current, and V_bat represents the measurable battery terminal voltage. Let τ1=Rs. Cs,τ2=R_L. C_L, τ1 and τ2 respectively represent the short time constant and long time constant in the dynamic response process of the lithium-ion power battery.

What are the characteristics of lithium ion power battery,You can also learn more about.

1. The working principle of lithium ion power battery

At present, lithium-ion power batteries have been widely used in electric vehicles, and the research on their performance has become a hot spot in the industry.

Lithium-ion power battery is a high-performance secondary battery composed of four parts: positive electrode, negative electrode, separator and electrolyte: the positive electrode undergoes a reduction reaction when the battery is discharged, and most transition metal oxides such as LCoO₂、Li_x2NiO₂、Li_xMn₂O₄ are used; there are many negative electrodes. Using carbon materials, oxidation reaction occurs during discharge; the diaphragm provides electronic isolation for the positive and negative electrodes; the electrolyte is generally an organic solution such as LiAsF₆, which is a transport medium for ion movement. When charging, Li⁺ is deintercalated from the positive electrode through the electrolyte and inserted into the negative electrode. At the same time, the electronic compensation charge is supplied from the external circuit to the carbon negative electrode to maintain the electric balance of the negative electrode. On the contrary, Li⁺ is deintercalated from the negative electrode and inserted into the positive electrode through the electrolyte. It can be seen that the lithium-ion power battery uses Li⁺ to reciprocally intercalate and de-intercalate between the positive and negative electrodes for charging and discharging. It is a lithium ion concentration difference battery. Its general working principle is shown in Figure 2-1. The electrode reaction expression is shown in the formula diagram (1-1), formula (1-2), and formula (1-3).

Figure 2-1 The working principle of lithium-ion power battery

Formula diagram

According to the different cathode materials, lithium-ion power batteries mainly include lithium manganese oxide batteries, lithium cobalt oxide batteries, lithium iron phosphate batteries, and ternary material lithium-ion batteries; according to different electrolyte materials, lithium-ion power batteries are divided into liquid lithium-ion There are two major categories of batteries and polymer lithium-ion batteries. Compared with power batteries of other structures, the main advantages of lithium-ion power batteries are:

(1) The working voltage is high. According to the different cathode materials, the operating voltage range of lithium-ion power batteries is 3.2~3.7V, which is about three times the operating voltage of other types of batteries such as nickel-cadmium batteries.

(2) Higher than energy. The theoretical specific energy of lithium-ion power batteries is as high as 200Wh/kg, and the actual specific energy is higher than 140Wh/kg, which is about twice that of nickel-hydrogen batteries.

(3) High capacity and energy conversion efficiency

(4) Long storage and cycle life. In a suitable environment, the lithium-ion power battery can be stored for more than 5 years, the number of deep-cycle charge and discharge can reach more than 1,000 times, and the cycle life is up to 10,000 times at low depth of discharge. The life characteristics are much better than other types of batteries.

(5) The self-discharge is small. When the ambient temperature is (20±5)℃, the monthly self-discharge rate of lithium-ion batteries is only 5%-9%, which greatly alleviates the problem of power loss caused by self-discharge when traditional secondary batteries are placed.

(6) No memory effect

(7) Wide operating temperature range. Lithium-ion power battery can work in the temperature range of -20~60℃. However, we should try our best to provide a suitable working temperature for the lithium-ion power battery, because the working environment of high temperature (≥40℃) and low temperature (≤0℃) will damage the electrical performance of the lithium-ion power battery and accelerate the lithium-ion power battery. The life of the decay.

(8) High environmental protection, lithium ion power battery does not contain cadmium, lead, mercury and other harmful substances, has low environmental pollution, and is a true green battery

The excellent electrical performance of lithium-ion power batteries lays the foundation for their application in electric vehicles and accelerates the research and development of new energy vehicles. However, it is not a perfect car power battery. Its main disadvantages are: large internal resistance, and large internal resistance causes the lithium-ion power battery to rapidly decrease its energy at high power output; due to the charging and discharging of the lithium-ion power battery It has a wide range and requires special protection circuits to prevent overcharge and overdischarge of the battery; poor compatibility with ordinary batteries, which is mainly due to the large difference in voltage between batteries; poor overcharge and overdischarge resistance.