What Is Busbars in Lithium Batteries?

Just thick pieces of copper or aluminum that collect current from thousands of cells and send it out to the two big terminals. Without them the pack can't work. With them done wrong the pack overheats, loses range, or catches fire.

Cells first get paralleled into modules using nickel strips or wire-bonded aluminum wires. Modules then get series-connected through real busbars. Three main flavors dominate today:

Laminated busbar

Several layers of 0.8–1.5 mm copper foil with thin PET or PI film in between, hot-pressed and shrink-wrapped. Almost every 800 V platform uses them because inductance drops below 20 nH. Porsche Taycan, Hyundai Ioniq 5/6, Kia EV6, most Chinese 800 V cars, all laminated.

Flexible busbar

A stack of 0.1–0.3 mm bare copper foils welded only at the ends, middle stays flexible. Tesla used them on early Model 3/Y packs, later switched to laminated. Still common where the pack has to twist with the chassis.

Rigid bar

Simple 10×50 mm or 10×100 mm milled copper bars you still see in BYD Blade packs, most energy-storage containers, and many LFP commercial-vehicle packs. Cheap and easy to machine, but they crack around bolt holes after a few thousand thermal cycles.

busbars

Copper in a battery pack (natural cooling, semi-enclosed): 2.0–2.2 A/mm² continuous is perfectly safe.
5 mm × 30 mm bar = 150 mm² → 300–330 A continuous, 600–700 A for 10–30 s bursts is routine.
People who quote 1.6 A/mm² are copying switchgear tables; inside a pack the airflow is actually better.

Laser welding: king. Copper-to-copper or copper-to-aluminum (with nickel transition shim) gives < 0.03 mΩ per joint.
Bolted: energy-storage guys love M10/M12 tin-plated bolts + Belleville washers, 20–25 Nm. Easy service.
Friction stir or magnetic pulse welding: CATL and a few others, not mainstream yet.

busbars

2021–2023 Model 3/Y (Panasonic 2170): 4-layer × 1 mm × 38 mm laminated ≈ 500 A continuous
2024 Model Y (LG 4680): 5-layer × 1.2 mm × 42 mm
Xiaomi SU7 800 V pack: 6-layer × 1 mm × 48 mm
BYD Seal / Qin Plus DM-i: 10 mm × 80 mm rigid bar, ~350 A
Megapack 2 XL: 12 mm × 120 mm tin-plated rigid bars, 1000 A continuous per phase

busbars

90 °C continuous on the copper surface, 110–120 °C short-term is acceptable, above 130 °C the insulation film starts to worry. Most packs stick NTCs directly on the busbar and the BMS watches it like a hawk.

ISO 6469-3 – electrical safety

ISO 12405 – pack test spec

IEC 62660-3 – cell and pack performance/safety

QC/T 1075 – Chinese EV pack spec (if selling in China)

UL 1973 or UL 2580 depending on the market

That's pretty much it. Any more detail and I'd just be repeating datasheets.