Home > Knowledge > Content
Lithium battery working principle, basic structure
- Jun 12, 2018 -

      Lithium-ion batteries are rechargeable batteries that rely primarily on lithium ions to move between the positive and negative electrodes. During charge and discharge, Li+ reciprocally inserts and extracts between two electrodes: when the battery is charged, Li+ is deintercalated from the positive electrode, and the negative electrode is in the lithium-rich state through the electrolyte; the opposite occurs when discharging. A battery containing a lithium-containing material as an electrode is generally representative of modern high-performance batteries.

      Compared to other electrochemical currents, lithium ion batteries have many advantages, such as light weight, large energy storage capacity, large power, no pollution, long life, small self-discharge coefficient, and wide temperature adaptation range. Lithium-ion batteries can be used in power quality, reliability control, backup power, peak load shifting, energy management, renewable energy storage, and more.

    5.1. Types of Lithium Batteries

    Lithium batteries, which we usually refer to, are lithium-ion batteries, which are generally classified into energy storage lithium batteries and power lithium batteries according to applications. Energy-storage lithium battery is used for photovoltaic or UPS, the internal resistance is relatively large, the charging and discharging speed is slow, generally 0.5-1C, the power battery is generally used in electric vehicles, the internal resistance is small, the charging and discharging speed is fast, generally can reach 3- 5C, the price is about 1.5 times more expensive than the energy storage battery. According to the materials, there are mainly lithium iron phosphate batteries and lithium triple lithium batteries (LiNiCoMn). Comparison of two types of batteries:

Comparison projectLithium iron phosphate LithiumThe ternary lithium
1Power density (mAh/g)130160-190
2Discharge platform V3.2-3.33.6-3.7
3Cycle performance 80%>2000>2000
4High and low temperature performance-20~+75-30~+65
5materialLithium ore, iron oxide phosphate reservesCobalt deficiency

       5.2, lithium battery pack management

       Lithium battery management system, BatteryManagement System, BMS is a device made up of microcomputer technology, detection technology, etc. Its function is not only to charge and discharge the battery, but also to accurately measure the remaining power of the battery, and the important functions of equalization and charging of the single battery.

(1) Secure the battery: In the charge and discharge process of the battery, the terminal voltage and temperature, charge and discharge current and total battery pack voltage of each battery in the battery pack of the electric vehicle are collected in real time to prevent overcharge or overdischarge of the battery. .

(2) Accurately estimate the remaining battery power of the battery pack, and predict how much energy remains in the hybrid vehicle's energy storage battery or the state of charge of the energy storage battery. There is a certain relationship between the battery power and the voltage, but it is not a linear relationship. It is not possible to rely on the voltage to convert the remaining power. It needs to be calculated by the BMS.

(3) Equilibrium between individual cells: That is, the single cells are evenly charged, so that each cell in the battery group reaches a state of equilibrium.

      5.3 Selection and Design of Lithium Batteries

      Lithium battery system includes battery core and BMS battery management system, which is provided by the manufacturer. There are several points to note when designing:

1) The energy storage lithium battery pack needs to communicate with the inverter or the bidirectional energy storage converter PCS. To select the equipment that has the lithium battery function and the corresponding communication interface function.

2) Compared with lead-acid batteries, lithium-ion batteries have a smaller charge-discharge current.

3) If the system requires multiple battery packs, one battery pack needs a BMS system.