New Study Reveals Critical Design Factors for Reliable Battery Busbars in EVs
In the race to electrify transportation, automakers and battery developers alike are confronting a quiet but vital engineering challenge — how to keep high-current connections inside electric vehicle (EV) battery packs operating safely, efficiently, and reliably over a decade or more of real-world use. While much attention has been paid to cell chemistry, thermal runaway, and pack-level cooling, a new technical paper published this month in Energy Storage Science and Technology shifts focus to a deceptively simple component: the busbar.
Far from being just a metal strip, the busbar — a flat, conductive connector linking battery cells into modules and modules into full packs — is now emerging as a linchpin of system durability. Its design, material choice, and welding quality directly influence everything from peak power delivery to long-term degradation, especially under the punishing vibration, temperature swing, and electrical stress of daily driving.
Authored by a team of engineers from Tianjin Lishen New Energy Technology Co., Ltd., the study titled “Reliability analysis of the module busbars of power battery systems” offers one of the most comprehensive public reviews to date on how busbar performance can make or break battery safety and longevity. And while the paper is technical in nature, its implications ripple across the entire EV development chain — from design studios in Stuttgart and Detroit to battery gigafactories in Ningde and Texas.
So why the sudden spotlight on busbars? As industry experts well know, reliability in EV batteries isn’t just about preventing catastrophic failure. It’s about predictable performance — kilowatt after kilowatt, year after year — without sudden drops in range, power, or charging speed. And as vehicle platforms become more modular and power-dense, the tolerance for variability in internal connections is shrinking to almost zero.
Let’s take a step back. Imagine a battery pack as a city’s power grid. Individual cells are like power plants — they generate the energy. The battery management system (BMS) is the control center, monitoring flows and balancing loads. But the busbars? They’re the high-voltage transmission lines tying it all together. If those lines sag, corrode, loosen, or overheat under load, the whole network suffers. Efficiency dips. Hot spots form. Over time, resistance climbs. In the worst cases, poor busbar design or faulty welds may even trigger localized arcing — a scenario no automaker wants to explain to regulators or customers.
The Lishen team focused their work on a widely used format: square lithium-ion cells, arranged in a 1P12S (one parallel, twelve series) configuration — a common architecture in commercial electric buses, logistics vans, and even some passenger EVs. They chose 1060 aluminum (O-temper) for the busbars — an industry-preferred alloy for its balance of conductivity, lightweight properties, and cost — but didn’t stop at material selection. Instead, they built a full reliability roadmap spanning mechanical, thermal, and process domains.
One of the paper’s most actionable findings involves the shape of the busbar itself. Most designers now prefer an Ω-shaped cross-section — think of a shallow “U” with flared ends — and for good reason. As cells expand and contract during charge/discharge cycles, and as the pack heats and cools in varying climates, linear metal pieces can develop dangerous mechanical strain. The Ω shape, by contrast, acts like a tiny spring, absorbing differential movement without stressing weld joints or deforming permanently. It’s a small geometry change with profound durability gains.
Then there’s the weld — the literal point of contact between busbar and cell terminal. Here, the team deployed a 6-kW fiber laser system, chosen for its precision and minimal heat-affected zone. But rather than relying on “standard” settings, they conducted a full-factorial Design of Experiments (DoE). Varying laser power from 3,000 to 5,000 W and travel speed from 60 to 120 mm/s, they mapped how those inputs affected two critical outputs: nugget width (the melted seam diameter) and nugget depth (how far the weld penetrates into the terminal).
The results were revealing. Too much power or too slow a speed? You get excessive melting — risking terminal damage or even micro-cracks from residual stress. Too little power or too fast? You get “cold” welds: superficial bonds that look fine to the eye but fail under vibration or torque. Crucially, the team identified an optimal “sweet spot”: 3,850–4,200 W power and 75–110 mm/s travel speed, producing welds with 1.0–1.6 mm width and 0.5–1.5 mm depth — values that consistently delivered pull strengths over 300 newtons, well above typical design targets.
But weld geometry isn’t the only variable. Perhaps the most surprising discovery concerned gap clearance — the microscopic space between the flat underside of the busbar and the top of the cell terminal before welding. Intuitively, one might expect perfect contact to be ideal. And indeed, the data showed that when this gap exceeds 0.5 mm, weld strength drops precipitously. Yet even gaps as small as 0.2 mm measurably reduce bond integrity — not because of electrical performance (temperature rise during 1C cycling varied by less than half a degree regardless of gap), but because laser energy dissipates unevenly when air gaps are present, leading to inconsistent melt pools.
As a result, the team tightened internal process controls: no more than 0.3 mm gap is now allowed on the production line. To enforce this, they deployed an inline vision system — a 2D camera paired with laser triangulation — that scans every terminal before welding. If height or planarity deviates beyond spec, the module is flagged. Even the cleaning step got an upgrade: just before welding, a secondary laser pulse ablates oxides and contaminants from the terminal surface — a move that eliminates a major source of weld inconsistency in high-volume settings.
Once welded, the busbars still face the rigors of real-world use. Here, the researchers leaned on China’s national standard GB/T 31467.3-2015 — the closest equivalent to global benchmarks like UN ECE R100 or the forthcoming ISO 6469-2 revisions. Modules were subjected to 21 hours of random vibration per axis (x, y, z), simulating years of road input on everything from cobblestone alleys to highway expansion joints. Immediately after, they endured mechanical shock tests — short, high-G jolts mimicking pothole impacts or curb strikes.
Throughout, the busbars held firm. No cracks. No loosening. Insulation resistance remained above 100 Ω/V — a safety-critical threshold confirming no unintended current paths had formed. Thermal imaging during cycling showed maximum cell temperatures hovering around 32.8°C under 1C continuous charge/discharge — well within safe operating limits — and critically, the hottest spot wasn’t at the busbar joints, but in the center of the cell stack, confirming that the busbar’s thermal design wasn’t creating new bottlenecks.
That last point bears emphasis. Some prior studies assumed busbars were passive — just conductors. But this work proves they’re active thermal participants. Using coupled electro-thermal simulation, the team modeled resistive heating not only in the cells, but in the busbars themselves — especially at high-current input/output terminals. Under load, the aluminum strips did warm, but thanks to their large surface area and strategic placement near cooling channels, they dissipated heat efficiently, avoiding dangerous local hotspots.
Beyond pure physics, the paper also reflects a maturing industry mindset — one where manufacturability and process control are inseparable from design excellence. The team didn’t just specify ideal welds; they engineered a full production ecosystem: custom one-piece needle-plate fixtures to prevent weld spatter, closed-loop feedback from vision to laser control, real-time screen monitoring for operators, and even integrated dust extraction to keep the workcell clean. This isn’t lab-scale tinkering; it’s scalable, factory-ready engineering.
For EV developers, these insights arrive at a pivotal moment. As battery costs plateau and cell energy densities approach theoretical limits, the next efficiency leaps will come not from chemistry breakthroughs, but from system integration — squeezing every last watt-hour out of existing platforms through smarter packaging, lower-loss connections, and more robust mechanical design. In that context, the humble busbar transitions from commodity part to strategic differentiator.
Consider fast-charging. A 5C charge rate can push hundreds of amps through a busbar in seconds. If contact resistance is even slightly elevated — say, 0.02 mΩ instead of 0.011 mΩ — that’s tens of watts of wasted heat localized at a single joint. Multiply that across dozens of connections, and you’re not just losing efficiency; you’re forcing the cooling system to work harder, potentially throttling charge speed to protect hardware. Tight busbar control, then, isn’t just about safety — it’s about delivering on the promise of 10-minute charging.
The same logic applies to vehicle weight. Aluminum busbars are already lighter than copper, but optimizing their cross-section — no thicker than needed, shaped for strain relief, welded for maximum strength — can shave grams here and there. Over an entire pack, those savings add up to meaningful range gains. And in an era where every kilometer counts, that’s competitive gold.
Looking ahead, busbar innovation shows no signs of slowing. Several automakers are experimenting with integrated busbars — stamped or extruded components that combine electrical conduction, mechanical support, and even coolant channeling in a single part. Others are exploring copper-aluminum hybrid designs, using ultrasonic welding or explosive bonding to leverage copper’s superior conductivity at terminals and aluminum’s light weight in spans. Meanwhile, solid-state battery developers are confronting entirely new busbar challenges, as ceramic or sulfide electrolytes demand radically different interconnect strategies.
What makes the Lishen study especially valuable is its grounding in pragmatism. There’s no hype about futuristic materials or unproven processes — just meticulous, repeatable engineering applied to a problem that’s already on assembly lines today. It’s a reminder that, in EV development, brilliance often hides in plain sight — in the weld bead you overlook, the bend radius you accept without question, the tolerance band you assume is “good enough.”
For procurement teams, the takeaway is clear: busbar sourcing can’t be reduced to material grade and unit price. Design maturity, process capability (especially laser welding CpK), and validation rigor must weigh just as heavily in supplier selection. For systems engineers, it’s a call to co-develop busbars with cell and module designers — not bolt them on as an afterthought. And for safety assessors, it reinforces the need to treat busbar joints as high-risk interfaces in failure mode analyses, right alongside cell venting and BMS faults.
In closing, the rise of the busbar may seem like a minor subplot in the EV revolution — but history suggests otherwise. After all, the internal combustion engine’s reliability breakthrough didn’t come just from better fuels or combustion chambers; it came from precision-ground crankshafts, hardened valve seats, and consistent bearing clearances. In the same way, the long-term success of electric mobility may hinge not on the next energy-density record, but on the quiet, consistent reliability of a well-welded strip of aluminum.
ZHAO Xiaojun, WANG Yingchao, CHEN Meng, YANG Peng, AN Zhanwang, LIU Jianli, WU Di
Tianjin Lishen New Energy Technology Co., Ltd., Tianjin 300384, China
Energy Storage Science and Technology, 2024, 13(7): 2450–2458
DOI: 10.19799/j.cnki.2095-4239.2024.0026