Introduction to Characteristics and Composition of Lithium Battery Module

Lithium battery module definition

The battery module can be understood as an intermediate product between the lithium-ion battery cells and packs, which are combined through series and parallel connections and equipped with single-cell monitoring and management devices. Its structure must play a supporting, fixing, and protective role for the battery cells. It can be summarized into three major aspects: mechanical strength, electrical performance, thermal performance, and fault handling capabilities. Whether it can fix the battery cell position intact and protect it from deformation that affects its performance, how to meet the current-carrying performance requirements, how to control the temperature of the battery cell, whether it can power off in case of serious anomalies, and whether it can avoid the spread of thermal runaway, etc. will be the criteria for evaluating the quality of the battery module. The thermal management solution for high-performance battery modules by  has turned to liquid cooling or phase-change materials. Click here for custom lithium ion battery manufacturers and get more information.

Characteristics of lithium battery module

• The lithium battery module requires the battery to have a high degree of consistency (capacity, impedance, voltage, discharge curve, and life).

• The cycle life of the lithium battery module is lower than that of a single battery.
  

• It should be used under specified conditions (including charging, discharging current, charging method, temperature, etc.).
  

• After the formation of the lithium battery module, the voltage and capacity of the battery have been greatly improved and must be protected by charging balance, temperature, voltage, and overcurrent monitoring.
  

• The lithium battery module must meet the design requirements of voltage and capacity.
  

Composition of lithium battery module

Series-parallel connection

The battery is composed of single cells connected in series and parallel. Parallel connection increases capacity with unchanged voltage, and series connection multiplies the voltage with constant capacity. For instance, a 3.6V/10Ah battery is composed of the 5 parallelly connected single cells. Connections should be made by first parallel and then series or first series and then parallel based on the overall battery capacity design accordingly. In parallel, the difference in resistance, uneven heat dissipation, and other factors will affect the cycle life of the battery after parallel connection. But a single cell failure will automatically exit without affecting the use of parallel connection except for reduced capacity. Parallel connection technology has strict requirements. If a unit cell is short-circuited in parallel, the resulting current is very high, and fuse protection techniques are usually used to avoid it. Serial connections are made based on the overall battery capacity, and cells with consistent types, models, capacity, impedance, and voltage, whose differences are not more than 2%, are arranged for series connections. Generally, after the battery cells are connected in series and in parallel, the capacity loss is 2% to 5%. As the number of cells increases, the capacity loss increases. Regardless of whether it is a soft-packed battery or a cylindrical battery, multiple series and parallel combinations are required. Poor consistency will affect the battery capacity, and the lowest battery capacity in a group determines the capacity of the entire battery. It requires good high-current discharge performance. The starting current of the motor is three times the normal operating current, and only high-current discharge can improve the motor's driving performance. It also requires good heat dissipation performance. With many battery cells, the temperature rise inside the battery box is not easy to dissipate, which causes uneven temperatures and discharge characteristics among the cells, leading to a long-term decline in battery performance. It also requires high production process level. The battery must withstand the vibration and shock of bumpy roads. Point welding technology, in particular, is required. After welding, testing should be carried out to prevent false welding and dislocation.

Battery cell requirements

Select the corresponding battery cells based on your design requirements. The requirements for the paralleled and series connected batteries are to have the same type, model, capacity, impedance, and voltage value differences no greater than 2%. Generally, after the battery cells are connected in series and in parallel, the capacity loss is 2% to 5%. As the number of cells increases, the capacity loss increases. Whether it is a soft-packed battery or a cylindrical battery, multiple series and parallel combinations are required. Poor consistency will affect the battery capacity, and the lowest battery capacity in a group determines the capacity of the entire battery. It requires good high-current discharge performance. The starting current of the motor is three times the normal operating current, and only high-current discharge can improve the motor's driving performance. It also requires good heat dissipation performance. With many battery cells, the temperature rise inside the battery box is not easy to dissipate, which causes uneven temperatures and discharge characteristics among the cells, leading to a long-term decline in battery performance. It also requires high production process level. The battery must withstand the vibration and shock of bumpy roads. Point welding technology, in particular, is required. After welding, testing should be carried out to prevent false welding and dislocation.

Lithium battery module process

The lithium battery module is realized through two methods: laser welding, ultrasonic welding, or pulse welding, which are reliable welding methods but are not easy to replace. The second method is through elastic metal sheet contact, which is easy to replace the battery but may result in poor contact.

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