Taking A Systems Approach To Electric Bus Battery Design

Why An Integrated Systems Approach To Lithium-Ion Battery Design Overcomes Safety, Reliability And Environmental Concerns About Fleet Electrification

By John Warner, Chief Customer Officer, American Battery Solutions / www.americanbatterysolutions.com

The electrification of buses and other commercial vehicles is ramping up, with more and more fleet managers looking to swap out the internal combustion (IC) engine for battery power. In tandem with decarbonization initiatives and tightening emissions regulations, this shift to all-electric fleets is only expected to accelerate over the next decade.

In addition to moving toward sustainable transport and reducing greenhouse gas emissions — which are some of the longer-term goals of electrification — transitioning to electric buses has compelling cost implications for fleet managers. The cost of lithium-ion battery technology has dropped by nearly 90 percent over the last 15 years, suddenly making electric fleets a feasible option in terms of total cost of ownership. Compared to traditional gasoline- or diesel-powered vehicles, electric buses eliminate fuel costs, oil changes and other recurring maintenance practices, lowering overall operating costs.

Electric buses bring many other benefits as well. They can operate hundreds of miles between charges while carrying the same payloads as their IC engine counterparts. Without all the extra noise and vibration from the engine, electric buses are also quieter, creating happier drivers and passengers.

For these reasons, it makes sense to transition to electric fleets sooner rather than later. As it stands, some applications are easier to electrify than others; airport shuttles and transit buses, which make frequent stops, don’t require a lot of mileage and sit in depots all night, representing some low-hanging fruit for electrification. So, why the holdup?

Debunking Common Battery Concerns With Holistic Battery Design

While the advantages of electrification are clear, many fleet managers remain hesitant to adopt battery technologies out of a concern for the safety, reliability and recyclability of lithium-ion chemistry. Some common worries we frequently hear include the following:

• Lithium-ion batteries are prone to dangerous thermal runaway, which is difficult to stop once it starts and can result in fires or explosions.
• Lithium-ion batteries are too unreliable and unpredictable. For example, they’re sensitive to high-power charging and mechanical abuse, both of which can erode their lifespan.
• These batteries are also sensitive to temperature: below freezing, and their performance will begin to decline. Too hot, and the electrolytes within the battery can react with the cathode material, leading to failure.
• End-of-life batteries are a source of waste, and any efforts to recycle them are too costly to effectively implement. Fleet and service managers don’t know what to do with the batteries once they reach end of life.

Fortunately, you can avoid all these issues by taking an integrated systems approach to battery design, which involves a holistic understanding of chemistry, thermal dynamics, mechanical and structural engineering, electrical design and software. This approach also means partnering with a battery supplier that takes a comprehensive, multi-tiered approach to safety. Doing so doesn’t just make a compelling case for the adoption of lithium-ion battery technology, it also begs the question: why haven’t you electrified your fleet sooner?

Tiered, Automotive-Grade Functional Safety Builds Confidence

We maintain that it’s not the cell that makes the system safe. Rather, it’s the system that makes the cell safe. This means taking a comprehensive, multi-layered approach to safe battery design at the levels of the cell, module, battery management system (BMS), control electronics and mechanical housing. Here’s what the approach looks like:

• Using high-quality lithium-ion cells with integrated current interrupt devices (CID) from world-class suppliers.
• Designing a module that eliminates propagation and includes multi-functional components like the current collector and mechanical structure with voltage and temperature sensors and vents — no loose wires.
• Integrating automotive-grade AEC-Q components into the BMS that meets ISO-26262 (ASIL-B) standards for functional safety. Other important features include the use of conformal coatings, precharge circuits and integrated field effect transistors (FET).
• At the software level, building in overcharge, over-discharge, overtemperature and overcurrent protections, as well as self-healing fault management and cell balancing with custom algorithms, SOH and SOL calculations.
• Combining these subsystems into a durable, laser-welded IP65-rated housing that can withstand harsh industrial and motive environments.

Beyond just the safety of the physical battery itself, the best battery suppliers meet the full gamut of manufacturing standards and prioritize inline, automated quality checks at every stage of the production process. Helpful standards to look for include UN38.3 for safe shipping, SAE J2464, SAE J2929, ISO16750, IEC62485, UL1642 for cell abuse, UL2580 and UL2271 for industrial safety.

Lithium-ion batteries achieve decade-long reliability. In the context of a properly engineered battery system, high-voltage lithium-ion batteries can last 10 to 12 years — a lifespan that exceeds typical fleet refurbishment times. Some battery suppliers even use custom software to create drive profiles for particular cities, enabling them to optimize the battery’s design, including form factor, geometry and chemistry, for the intended operating environment.

Closed-loop recycling processes are cost-effective and efficient. Emerging recycling methods are supporting circular economies for lithium-ion batteries, reducing costs and minimizing the environmental impact without resorting to conventional brute-force methods. Many battery suppliers also use highly recyclable materials in their designs. There are many emerging EV battery recycling companies emerging today.

Shift To Electric Today

As the world shifts to electrification, taking an integrated systems approach to battery design can optimize the safety and performance of your fleet, all while contributing to a greener future.