What are Battery Terminals?
Battery terminals are the conductive components that facilitate the transfer of electrical energy from the battery to external devices or circuits. They serve as the connection points where the positive and negative electrodes of the battery are accessible for electrical wiring. The primary functions of battery terminals are:
- Electrical Connectivity: Battery terminals provide a secure and efficient electrical connection between the battery’s internal electrochemical cells and external electrical systems or loads. They allow the flow of current from the battery during discharge and enable charging when connected to a power source.
- Polarity Identification: Battery terminals are typically labeled or designed to indicate polarity, with one terminal designated as positive (+) and the other as negative (-). This polarity identification ensures proper connection and prevents reverse polarity, which could damage the battery or connected devices.
How Do Battery Terminals Work?
Battery Terminal Structure and Components
A battery terminal is the conductive component that connects the battery to an external circuit or device. It typically consists of the following parts:
- The compression part that grips the outer circumference of the battery post
- The coupling part that compresses the battery post through fastening bolts
- The barrel part that extends from the compression part connects to a cable
- Pressurizing protrusion on the inner circumference to grip the battery post
Charging and Discharging Mechanisms
Battery terminals play a crucial role in the charging and discharging processes:
- During charging, the positive terminal connects to the positive electrode, and the negative terminal to the negative electrode
- Charging units detect the battery voltage level and control the charging current accordingly
- During discharging, the terminals provide the conductive path for the flow of electrons from the battery to the external circuit
Battery Terminal Designs
- Screw terminals: threaded conductive stems extending outside the battery casing. Nuts are tightened against a busbar to ensure an electrical connection. However, this design suffers from increased contact resistance and potential loosening due to vibrations.
- Tab terminals: conductive lamina with surface extensions, typically welded together directly or to a common busbar. Examples include crimping (mechanical deformation) and laser welding.
- Keyed terminals: Shaped to allow only specific battery types or polarities to connect, preventing incorrect installation.
- Integrated terminals: Terminals integrated with the battery housing, eliminating clearance and improving sealing.
Applications of Battery Terminals
Battery terminals serve as the primary interface for connecting batteries to external electrical circuits and devices. They facilitate the flow of current from the battery to power various applications:
- Automotive applications: Battery terminals connect the battery to the vehicle’s electrical system, powering components like the starter motor, lights, and electronics.
- Portable electronics: Terminals connect batteries to devices like laptops, smartphones, and power tools, enabling their operation.
- Energy storage systems: Large-scale battery packs use terminals to connect individual cells and transmit power for grid storage or electric vehicles.
Application Cases
| Product/Project | Technical Outcomes | Application Scenarios |
|---|---|---|
| Tesla Battery Terminal | Utilising advanced materials like nickel-plated copper, the terminals offer improved conductivity and corrosion resistance, enabling higher current flow and longer battery life. | Electric vehicles requiring efficient power transmission from high-capacity battery packs to motors and electrical systems. |
| Panasonic EverVolt Battery Terminal | Incorporating a multi-layered structure with tin-plated copper and stainless steel, these terminals provide superior vibration resistance and durability, reducing the risk of terminal loosening or breakage. | Automotive and industrial applications subjected to frequent vibrations and harsh environments. |
| Murata Lithium-Ion Battery Terminal | Employing a compact and lightweight design, these terminals minimise internal resistance and heat generation, allowing for higher power density and safer operation in confined spaces. | Portable electronics, drones, and other space-constrained applications requiring high energy density and thermal management. |
| Toshiba SCiB Battery Terminal | Featuring a unique design with a built-in safety mechanism, these terminals can disconnect the battery in case of overcurrent or short-circuit events, preventing potential thermal runaway and enhancing overall system safety. | Energy storage systems, electric vehicles, and applications where safety is a critical concern. |
| Saft Lithium-Ion Battery Terminal | Designed for high-temperature environments, these terminals utilise specialised materials and coatings to maintain conductivity and prevent degradation, ensuring reliable performance in extreme conditions. | Aerospace, military, and industrial applications operating in high-temperature environments. |
Latest Innovations in Battery Terminals
Terminal Design for Improved Performance
- Optimized tab configuration: Arranging positive and negative tabs in parallel with two negative tabs in the middle can minimize ohmic resistance, leading to superior capacity retention (around 86% at 7C discharge rate) compared to conventional designs (only 47% retention) . This optimized design suppresses electrolyte decomposition and lithium loss from cathodes, enabling excellent long-term cycling stability (≈91% capacity retention over 1000 cycles) .
- Integrated gasket and insulating member: Incorporating the gasket and lower insulating member prevents electrolyte leakage between components and terminals, avoiding short circuits and terminal erosion . This integrated design eliminates the need for special manufacturing processes required for separate components.
- Curved sealing protrusions: Terminals with curved sealing protrusions that make contact with the gasket can establish a barrier to prevent electrolyte leakage . The protrusions and gasket may be made of different materials for improved sealing performance.
Manufacturing Innovations
- Multi-stage metal forming: An alternative to casting, this process involves two metal forming operations followed by final piercing to induce the desired shape through plastic deformation. This approach can produce high-quality lead battery terminals with improved efficiency.
- Laser welding: Laser welding can electrically connect the terminal and bus bar without adding load on the block-shaped terminal, preventing damage to the insulating material. This method provides a robust electro-mechanical joint while allowing for serviceability.
Structural Advancements
- Replaceable terminals: Detachable terminals on the battery cover enable quick replacement, allowing the battery to be matched with various automobile and motorcycle models, improving applicability.
- Flexible bus bar connections: Increasing the diameter of the bus bar insertion hole larger than the terminal diameter can absorb displacement between adjacent batteries, reducing connection resistance.
- Terminal positioning: Arranging terminals on multiple surfaces surrounding the battery case, leaving at least one surface unexposed, can deactivate exposed terminals for improved safety .
Technical Challenges
| Optimised Tab Configuration for Battery Terminals | Arranging positive and negative tabs in parallel with two negative tabs in the middle to minimise ohmic resistance, leading to superior capacity retention and long-term cycling stability. |
| Integrated Gasket and Insulating Member | Incorporating the gasket and lower insulating member to prevent electrolyte leakage between components and terminals, avoiding short circuits and terminal erosion. |
| Curved Sealing Protrusions on Terminals | Terminals with curved sealing protrusions that make contact with the gasket to establish a barrier and prevent electrolyte leakage. |
| Multi-Stage Metal Forming for Terminal Manufacturing | An alternative to casting, involving two metal forming operations to induce the desired shape on the raw material through plastic deformation, followed by final piercing. |
| Improved Terminal Structure with Inspection Holes | A terminal structure with inspection holes that communicate the inner and outer surfaces of the case, enabling improved workability and inspection accuracy for contact resistance in bus bar fastening portions. |
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