Short-circuit protection for lithium battery packs can take measures from aspects such as production and manufacturing, hardware circuit design, software management, and usage and maintenance. The following is a detailed introduction for you:

Production and manufacturing link

Optimize materials and processes

During the battery production process, a cleaner production environment is used to reduce dust and metal particles in the air and prevent them from entering the battery cells and causing micro-short circuits.

Improve the electrode sheet cutting process to reduce the generation of metal shavings and burrs on the electrode sheets, and prevent these foreign substances from being drawn into the battery cells during the lamination or winding process, which may cause a short circuit risk between the positive and negative electrodes and the separator.

Optimize the ultrasonic welding process to increase the welding area and strength, reduce the phenomenon of false welding, and prevent metal shavings at the current collector from splashing onto the ear rubber and the main body of the battery cell, causing a short circuit.

Control the quality of the diaphragm

Select diaphragms with sufficient mechanical strength and puncture resistance, especially during the cold and hot pressing process, to prevent the diaphragm from being torn by mechanical external forces.

Ensure that the physical insulation of the diaphragm is high, the breakdown voltage is within a reasonable range and as high as possible, and at the same time reduce the proportion of large pores in the pore size distribution of the diaphragm to prevent burrs from puncturing the diaphragm.

Coated separators can be adopted, which can enhance thermal stability while appropriately increasing mechanical strength and reducing the risk of battery short circuits.

Hardware circuit design

Design a short-circuit protection circuit

The short-circuit protection circuit is usually composed of a current detection circuit, a drive circuit and a MOSFET (Metal-Oxide-Semiconductor field-Effect Transistor). When the positive and negative terminals of the battery pack are short-circuited externally, a large short-circuit current will be generated. The short-circuit protection circuit needs to turn off the discharge MOSFET within tens to hundreds of microseconds to cut off the short-circuit current.

The short-circuit protection action process is divided into two parts: The first is the stage from the occurrence of a short circuit to the initial action of the MOSFET, that is, the delay time of short-circuit protection, which can be selected and adjusted through parameter configuration; The second stage is from when the MOSFET starts to operate until it is completely turned off, which is related to the hardware circuit design, including the driving capability of the driving circuit and the parasitic parameters of the MOSFET, etc.

Select and use MOSFETs reasonably

Considering the withstand voltage of the MOSFET, the general empirical value is twice the maximum steady-state voltage of the battery pack, that is, there is a 100% voltage margin.

Considering the current of the MOSFET, the current during a short circuit should not exceed the Avalanche current specified in its specification sheet. If the short-circuit current is very large, it is necessary to consider the parallel connection of multiple MOSFETs.

Taking into account the driving capacity of the driving circuit and the influence of the Cgs (gate-source capacitance) and Cgd (gate leakage capacitance) of the MOSFET comprehensively, the driving capacity, Cgs and Cgd of the driving circuit directly determine the turn-off time Tsw. If N MOSFETs are connected in parallel, the equivalent total Cgs and Cgd will also increase by N times.

In terms of software management

Set up early warning and control strategies

Through the BMS (Battery Management System), reasonable battery early warning and battery safety control strategies are set up to achieve real-time monitoring of the status of individual batteries, promptly detect the location of individual batteries with internal short circuits, and promptly eliminate potential safety hazards.

The battery self-discharge identification method is adopted. Through voltage comparison before and after static placement and benchmarking against constant voltage sources and other detection methods, it is detected whether the battery has an abnormal self-discharge process. If it exists, it is judged that the battery may have experienced an internal short circuit.

By using the consistency identification method of batteries and based on the assumption that there is consistency among individual battery cells, by monitoring parameters such as voltage, capacity, and remaining power of each individual battery cell in the same battery pack, if the parameters of a certain individual battery cell deviate significantly from the normal parameters of other cells, thereby disrupting the overall consistency of the battery, it can be determined that an internal short circuit may have occurred in that individual battery cell.

Implement the design of charging and discharging redundancy and balance

Carry out redundant design for battery cell charging and discharging to prevent the battery from being in a high-load state for a long time and reduce the risk of internal short circuits caused by high battery load.

By adopting a balanced design, the voltage, capacity and other parameters of each individual battery in the battery pack are kept consistent, preventing local overcharging and overdischarging caused by excessive performance differences among individual batteries, which may lead to short circuits.

Usage and maintenance link

Standardize installation and fixation

When installing lithium battery packs, make sure they are securely installed to prevent displacement or damage due to vibration or collision during use. The battery pack can be fixed on the equipment by using dedicated brackets and bolts. The strength and rigidity of the brackets must meet the requirements to withstand various forces during the operation of the equipment.

Install protective devices around the battery pack to prevent other objects from colliding with it. For instance, in electric vehicles, the battery pack is usually installed at the bottom of the vehicle. To prevent the battery pack from being damaged when the chassis is hit, protective plates can be installed around the battery pack.

Carry out regular inspections and maintenance

Regularly inspect the appearance of the battery pack to see if there are any abnormal conditions such as bulging, deformation or leakage. If any damage to the appearance of the battery pack is found, it should be repaired or replaced in a timely manner.

Check the electrical connection parts inside the battery pack, such as whether the connection between the battery terminals and the connection wires is firm, and whether there is any loosening, oxidation or other phenomena. Poor contact at the connection points can lead to an increase in resistance, generate heat, and accelerate the occurrence of thermal runaway.