Cell-to-cell strip
Thin 1060 or 1050 strip, typically 0.3 – 3 mm, stamped with weld pads and sometimes a fuse neck or voltage-sense tab. Laser welded to prismatic terminals or ultrasonically welded to pouch tabs.
Battery interconnects
Battery Bus Bar Materials for EV Packs & Energy Storage
A battery bus bar carries current between cells, modules and the pack terminals, so its material decides weight, heat, joint reliability and cost. Aluminium busbars weigh about half as much as copper bars of the same resistance and weld directly to the aluminium terminals of most prismatic and pouch cells. Metline supplies electrical-grade aluminium strip, sheet, bar and composite conductor for battery busbars to pack builders worldwide.
- Main alloys
- 1050 · 1060 · 1350 · 6101
- Conductivity
- 55 – 62 % IACS
- Forms
- Strip, sheet, flat bar, laminated
- Joining
- Laser, ultrasonic, bolted
What a battery bus bar has to do
Inside a battery pack, hundreds or thousands of cells are tied together in series and parallel. Busbars make those connections, and every milliohm they add is turned into heat at full current. A good busbar therefore balances four things: low resistance, low mass, a joint that stays sound for the life of the pack, and a shape that can be produced by the thousand without variation.
Busbars in a pack fall into three groups. Cell-to-cell busbars are short, thin strips laser- or ultrasonically welded to cell terminals or tabs. Module-to-module busbars are thicker, often insulated, and usually bolted. Main power busbars run from the modules to the contactors, fuse and pack connectors, carrying the full pack current, sometimes several hundred amperes continuously.
Energy storage systems (ESS) use the same building blocks at larger scale: racks of LFP modules joined by flat or laminated busbars, then main bars into the power conversion system. Low-voltage 12 V and 48 V batteries for vehicles, telecom backup and mobility use smaller versions of the same parts.
Aluminium, copper and copper-clad aluminium compared
The table compares the conductor materials used for battery busbars. Conductivity is given as a percentage of the International Annealed Copper Standard (IACS); values are typical for the stated temper and vary slightly with processing.
| Material | Typical conductivity | Density | Strength | Typical battery use |
|---|---|---|---|---|
| 1350 / 1370 (EC grade) | 61 – 62 % IACS | 2.70 g/cm³ | Low (O to H14) | Main power bars and long flat runs where conductivity is the priority |
| 1060 / 1070 | 61 – 62 % IACS | 2.70 g/cm³ | Low | Cell-to-cell strips, laser-welded to prismatic terminals |
| 1050 | about 61 % IACS | 2.70 g/cm³ | Low | General cell connectors and flexible foil stacks |
| 3003 | about 40 – 50 % IACS | 2.73 g/cm³ | Medium | Connectors needing extra stiffness where current is modest |
| 6101 (T6, T61, T63, T64) | about 55 – 59 % IACS | 2.70 g/cm³ | High | Rigid extruded or machined bars, bolted module links |
| Copper C11000 (ETP) | ≥ 100 % IACS | 8.89 – 8.94 g/cm³ | Medium | Compact high-current paths, negative-side connections |
| Copper-clad aluminium (CCA) | between Al and Cu, depends on clad ratio | about 3.3 – 4.0 g/cm³ | Low–medium | Bars that need a copper surface for joining but aluminium weight |
For equal DC resistance an aluminium bar needs roughly 1.6 times the cross-section of a copper bar, yet weighs about half as much. Where space is tight, copper or CCA may win; where weight matters, aluminium usually does.
A worked sizing example: aluminium vs copper
Consider a 150 mm module link carrying 200 A continuously. Resistivity at 20 °C is about 0.0282 Ω·mm²/m for 1350 aluminium and 0.0172 Ω·mm²/m for annealed copper.
| Option | Section | Resistance | Loss at 200 A | Mass |
|---|---|---|---|---|
| Copper bar 2 × 20 mm | 40 mm² | about 65 µΩ | about 2.6 W | about 54 g |
| Aluminium bar 3 × 20 mm | 60 mm² | about 71 µΩ | about 2.8 W | about 24 g |
| Aluminium bar 3 × 25 mm | 75 mm² | about 56 µΩ | about 2.3 W | about 30 g |
The aluminium bar that is 1 mm thicker comes within about 10 % of the copper loss and saves more than half the weight; a slightly wider aluminium bar beats copper on both loss and weight. Multiply that across dozens of links in a pack and the saving reaches kilograms.
Final sizing is set by temperature rise, not by a fixed current density. Check the hottest steady-state point, short-circuit withstand (the bar must survive the fault current until the fuse opens), and the voltage drop allowed by the battery management system. Contact resistance at the joints often matters more than the bar itself, which is why joint design gets its own section below.
Common battery busbar configurations
Terminal and post busbar
Thicker bar with holes or studs for bolting to module posts. Often 6101 or half-hard 1350 for stiffness, with tin or nickel plating at the contact face.
Flat pack and bank busbar
Long flat bars connecting modules in battery banks and ESS racks. Usually 1350 or 6101 flat bar, insulated by heat-shrink, powder coating or film.
Flexible busbar
A stack of thin aluminium foils or strips pressure-welded at the ends, leaving a flexible centre that absorbs vibration, tolerance and thermal expansion between modules.
Laminated busbar
Positive and negative conductors separated by thin insulating film and bonded together. Low inductance and compact; used for main DC links and inverter connections.
Positive / negative distribution bar
Collects module outputs and feeds contactors, fuses and the pack connector. Sized for full pack current and short-circuit duty.
Joining, plating and the copper-aluminium interface
Aluminium forms a thin, hard oxide layer within seconds of exposure to air. It protects the metal but is a poor conductor, so every busbar joint needs a method that breaks through or prevents that layer.
| Method | How it works | Points to control |
|---|---|---|
| Laser welding | Fibre or disc laser fuses the busbar to the cell terminal; wobble scanning widens the seam | Clean surface, tight fit-up, avoiding brittle Al-Cu or Al-Fe intermetallics in dissimilar joints |
| Ultrasonic welding | High-frequency vibration under pressure creates a solid-state bond | Ideal for foil stacks and pouch tabs; limited total thickness |
| Wire or ribbon bonding | Aluminium wire bonded from cell to busbar, common with cylindrical cells | Bond wire can act as a cell-level fuse |
| Bolted joint | Bolt or stud clamps bar to post | Use plating or contact compound, conical spring washers to hold clamp force as aluminium relaxes, and set torque values |
| Friction or explosion welding | Creates bimetal Cu-Al transition pieces | Used where an aluminium bar must meet a copper terminal |
Many prismatic LFP and NMC cells now use an aluminium positive terminal and a copper-aluminium composite negative terminal, which lets the whole busbar be aluminium. Where a bar must join copper directly, use a bimetal transition, nickel or tin plating on both faces, or a CCA bar, so that the galvanic couple is not exposed to moisture.
Nickel plating (electroless or electrolytic) improves laser weldability and contact stability; tin plating is common for bolted contacts. Plating thickness is specified by the pack designer and checked on incoming inspection.
Design and fabrication checklist
- Temper: O or H111 strip for tight bends and flexible stacks; H14 or H24 for flat, stiff connectors; 6101-T6 or T61 where rigidity and holding torque matter
- Thermal expansion: aluminium expands about 23 µm/m·K against about 17 µm/m·K for copper; long bars need a flexible section or slotted holes
- Creep and relaxation: bolted aluminium joints lose clamp force over time; use spring washers, larger contact areas and re-torque procedures
- Insulation: epoxy powder coating, PET or PI film, heat-shrink sleeving or overmoulding; specify dielectric test voltage and creepage distances
- Flatness and burrs: weld pads must be flat and burr-free for consistent laser welds; specify flatness on the drawing
- Surface cleanliness: oil and oxide on weld zones cause porosity; specify degreasing and storage conditions
- Traceability: mill test certificates by lot so conductivity and chemistry can be tied to production batches
Relevant standards and approvals
| Standard | Scope |
|---|---|
| ASTM B317 / B317M | 6101 extruded bar, rod, tube and shapes for electrical conductors |
| EN 14121 | Aluminium strip, sheet and plate for electrotechnical applications |
| ASTM B209 / EN 485 | General aluminium sheet and plate tolerances and properties |
| IEC 61439-1 | Low-voltage switchgear assemblies, including busbar temperature-rise verification |
| ISO 6469-3 | Electrical safety of electrically propelled road vehicles |
| UL 2580 / UL 9540 | Batteries for electric vehicles / energy storage systems (system-level safety) |
Material standards cover the conductor itself; vehicle and ESS standards cover the finished pack. A busbar supplier provides material certification, while the pack builder qualifies the assembled design.
Where aluminium battery busbars are used
- Electric vehicles: cell-to-cell links in prismatic and pouch modules, module links, high-voltage junction boxes
- Energy storage systems: rack busbars for LFP modules in grid, commercial and residential storage
- 12 V and 48 V batteries: start-stop, mild-hybrid and auxiliary batteries
- Two- and three-wheelers: lightweight packs where every gram matters
- Telecom and data-centre backup: UPS battery strings and DC distribution
- Industrial and marine: forklift, AGV and boat propulsion batteries
A typical ESS rack, for example, uses laser-welded 1060 strips inside each module, 1350 or 6101 flat bars between modules, and a laminated pair for the main DC output to the inverter.
Supply forms and how to order
Supply range
- Strip and coil
- 1050, 1060, 1070, 1350, 3003; about 0.2 – 6 mm thick, slit to width
- Sheet and plate
- For laser- or waterjet-cut busbars, up to about 20 mm thick
- Flat bar
- 1350, 1060, 6101 rectangular bar, sharp or rounded edges
- Composite
- Copper-clad aluminium strip and bar, Cu-Al bimetal transitions
- Processing
- Cutting to length, punching, bending, plating and insulation on request
- Documents
- EN 10204 3.1 mill test certificate with chemistry and conductivity
- SpecifyAlloy, temper, thickness, width, length or drawing, plating and insulation, annual and first-order quantity.
- ConfirmWe confirm conductivity, tolerances, certification and terms (EXW, FOB, CIF or DAP).
- InspectDimensions, flatness, surface and conductivity are checked before packing.
- ShipCoils on eye-to-sky or eye-to-wall pallets, bars in wooden cases, protected from moisture.
References and standards
- ASTM B317/B317M – Aluminum-Alloy Extruded Bar, Rod, Pipe and Structural Shapes for Electrical Purposes (Bus Conductor)
- EN 14121 – Aluminium and aluminium alloys: strip, sheet and plate for electrotechnical applications
- IEC 61439-1 – Low-voltage switchgear and controlgear assemblies: general rules
- ISO 6469-3 – Electrically propelled road vehicles: safety specifications, electrical safety
- The Aluminum Association – Aluminum Electrical Conductor Handbook
Battery bus bars: frequently asked questions
Is aluminium or copper better for battery busbars?
Neither is better everywhere. Aluminium gives the same resistance at about half the weight and welds directly to aluminium cell terminals; copper is more compact and easier to bolt. Most modern EV and ESS packs use aluminium for cell-to-cell links and choose case by case for main power bars.
Which aluminium alloy is used for battery busbars?
1060 and 1050 are the usual choices for thin laser-welded cell connectors, 1350 for maximum conductivity in flat bars, and 6101 in T6 or T61 temper where a stiff, strong bar is needed. 3003 is used occasionally for stiffness where current is low.
How thick should an aluminium battery busbar be?
Cell connectors are commonly 0.3 – 3 mm thick and module or main bars 3 – 10 mm, but thickness follows from current, allowed temperature rise, short-circuit duty and joint design. Size by calculation and thermal testing rather than a fixed rule.
Can an aluminium busbar be connected to copper?
Yes, but not bare and exposed to moisture. Use a friction-welded bimetal piece, nickel or tin plating on the contact faces, copper-clad aluminium, or cells with a Cu-Al composite negative terminal.
Why are aluminium busbars nickel plated?
Nickel plating gives a stable, low-resistance surface for bolted contacts and makes laser welding to nickel-plated steel cans or copper more consistent by reducing brittle intermetallic formation.
Do you supply aluminium busbar material for battery makers outside India?
Yes. Metline supplies busbar strip, sheet, flat bar and composite conductor worldwide, with mill test certificates and export packing.
Building a battery pack or ESS?
Share your busbar drawing or material specification. Our team will propose the alloy, temper and form and quote a delivered price.
