Key points of electrical connection design for lithium battery packs

The electrical connection design of lithium battery packs directly determines the safety, efficiency and lifespan of the system. If the connection design is unreasonable, it may lead to risks such as increased contact resistance, local overheating, unbalanced voltage and even thermal runaway. The following analysis is conducted from three aspects: design principles, key elements, and typical application scenarios.

First, the core principles of design

Low resistance and high conductivity

The resistance at the connection points should be as low as possible to reduce energy loss and heat generation. For instance, due to insufficient cross-sectional area of the connecting wires in a certain energy storage power station, the system efficiency dropped by 3%, and after long-term operation, overheating at the connection points caused safety hazards.

Material selection should give priority to electrical conductivity (such as copper and aluminum) and corrosion resistance (such as tin plating and nickel plating treatment).

Anti-vibration and fatigue performance

In a vibrating environment (such as in electric vehicles and unmanned aerial vehicles), the connection parts must have fatigue resistance to avoid loosening or breaking due to long-term vibration. For instance, a certain drone battery pack had its wires not securely fixed. During flight, the wires broke due to vibration, causing a crash.

Thermal management and heat dissipation

Heat dissipation paths should be designed at the connection points to prevent overheating caused by excessive current or excessively high ambient temperatures. For instance, in high-power applications (such as power tools), thermal conductive adhesives or heat sinks should be used at the connection points to assist in heat dissipation.

Modularity and maintainability

The connection design should support quick disassembly and assembly to facilitate the replacement or maintenance of the battery pack. For instance, the adoption of plug-and-pull connectors can significantly shorten maintenance time and reduce operational difficulty.

Second, key design elements

Selection of connection mode

Welding: Suitable for high-reliability and low-resistance scenarios (such as the connection between battery tabs and busbars). Laser welding or ultrasonic welding can reduce the heat-affected zone and prevent damage to the battery cells.

Bolt connection: Suitable for high-current, detachable scenarios (such as parallel connection of battery modules). It is necessary to ensure that the bolt tightening torque conforms to the design value and use elastic gaskets to prevent loosening.

Crimping: Suitable for connecting wires to terminals. The crimping quality needs to be verified through pull-off force tests to ensure the stability of contact resistance.

Plug-in connector: Suitable for frequent plugging and unplugging scenarios (such as portable device batteries). Connectors with self-locking function and IP protection level should be selected to avoid poor contact.

Design of conductors and busbars

Cross-sectional area selection: The cross-sectional area of the wire should be calculated based on the current magnitude and length to avoid heat generation due to insufficient cross-sectional area. For instance, due to the overly small cross-sectional area of the wires in a certain electric vehicle battery pack, the insulation layer of the wires melted after long-term operation.

Busbar material and shape: The busbar should be made of highly conductive materials (such as copper or aluminum) and be designed to be flat to increase the heat dissipation area. For instance, a certain energy storage power station adopts special-shaped busbars, reducing the connection resistance by 20%.

Insulation treatment: The wires and busbars need to be insulated to avoid the risk of short circuits. For example, use heat shrink tubing or insulating tape to wrap the exposed parts to ensure that the thickness of the insulating layer meets the standard.

Voltage and current are balanced

Parallel connection: It is necessary to ensure that the voltage and internal resistance of the parallel battery packs are consistent to avoid local overheating caused by uneven current distribution. For instance, the battery pack of a certain unmanned aerial vehicle was damaged due to overcharging of a single battery caused by the large difference in internal resistance between the parallel batteries.

Series connection: It is necessary to monitor the voltage of each individual battery to prevent the overall performance from declining due to the unbalanced voltage of the series batteries. For instance, using a battery management system (BMS) to balance the voltage in real time can extend the lifespan of the battery pack.

Protection and Identification

Protection level: The connection parts must have waterproof and dustproof capabilities, especially in outdoor or humid environments. For instance, using connectors with an IP67 protection rating can prevent short circuits caused by water ingress.

Clear marking: The connection parts should be marked with polarity, voltage level and current capacity to avoid misoperation. For example, color coding (red positive and black negative) or laser marking can be used at the terminals of wires.

Third, typical application scenarios and design optimization

Electric vehicle battery pack

Design difficulty: It needs to withstand large currents, high vibrations and complex environments.

Optimization plan: Laser welding is adopted to connect the tabs and the busbar, bolts are used to fix the busbar and the module housing, high-temperature resistant silicone wires are selected for the wires, and the connectors have self-locking and waterproof functions.

Battery cabinet for energy storage power station

Design difficulty: It needs to be modularly assembled and easy to maintain.

Optimization plan: The battery module is connected to the cabinet body through plug-and-pull connectors. The busbar is designed to be detachable, and the wires adopt standardized cross-sectional areas for easy replacement and expansion.

Portable device battery pack

Design difficulty: It needs to be lightweight and vibration-resistant.

Optimization plan: The wires and terminals are connected by crimping. The wires are selected as flexible multi-strand wires. The connectors have the function of preventing misinsertion. The housing is designed as a shock-absorbing structure.

Fourth, design verification and testing

Contact resistance test

Use a micro-ohmmeter to measure the resistance at the connection points and ensure that the value is lower than the design threshold (such as <1mΩ). For instance, the resistance at the connection point of a certain battery pack exceeded the standard, resulting in a 5% decrease in system efficiency.

Vibration test

Simulate the vibration frequency and amplitude under actual working conditions to verify whether the connection parts have become loose or broken. For example, in the test of battery packs for electric vehicles, it is necessary to pass the GB/T 31467.3 vibration standard.

Temperature rise test

Under full-load operation, monitor the temperature changes at the connection points to ensure that the values are below the safety threshold (such as <80℃). For instance, a certain energy storage power station experienced accelerated aging of the insulation layer due to excessive temperature rise at the connection points.

Plug-and-pull life test

Conduct multiple plug-and-pull tests on the plug-in connector to verify whether the contact resistance and mechanical strength are stable. For example, the contact resistance of a certain connector increases by 30% after 500 insertions and removals, and it needs to be redesigned.