Talk of EV fires still smolders
The latest figures from the National Fire Protection Association show that only about 20% of all vehicle fires arise from problems in the vehicle electrical system—most fires have something to do with the fuel system. Seeing as electric vehicles will do away with problematic petrol, you might wonder whether a fleet composed mainly of EVs will experience fewer vehicle fires, despite recent headlines about five Chevy Volts igniting without any external cause.
Of course, here’s the rub: Car fires documented by the NFPA started in electrical systems powered by one or two 12-V lead-acid batteries. In contrast, EVs carry behemoth 400 to 800-V battery packs spread out over the space beneath the passenger compartment. The issue is whether EV designers can balance safe operation with realities of charging, cost, and battery life.
You get a feeling for some of these tradeoffs from remarks made at the recent Battery Show in the Detroit area. There representatives from EV pickup maker Atlis Motor Vehicles, infrastructure engineering firm Black & Veatch, EV motorcycle maker Damon Motors, and battery maker Romeo Power sat on a panel that outlined a few of the obstacles to progress in battery technology.
Some of their comments pertained specifically to thermal runaway conditions in batteries which, obviously, can lead to outcomes involving fire departments. There is a lot of work underway in what’s called passive thermal propagation in battery packs. Basically, this refers to the heat generated during single-cell failures within high-energy batteries. The heat can force adjacent cells into thermal runaway, creating a cascading propagation through the whole battery.
One approach that can slow these potentially catastrophic effects is the use of passive mitigation strategies. Examples include putting 5-mm gaps between select rows and columns in the array of battery cells and inserting physical barriers such as ceramic fiber board into the gaps. Problem is, adding gaps and barriers makes the battery bigger and less energy dense. That’s definitely not the direction battery suppliers and automakers want to go, given the demand for ordinary EVs able to travel 600 miles before needing a recharge.
The tradeoff between energy density and thermal runaway problems also explains another trend: The steady growth in battery energy density seen over the past few years is starting to flatten out, panelists said. Thus EV batteries are still improving, but the improvements are taking longer to reach consumers.
Nevertheless, the companies making batteries and sophisticated EVs seem to believe that the problems presented by thermal issues and higher energy densities are solvable. Today, the cost of manufacturing EV battery cells is below $100/kWh. Panelists think within five years it will be less than $50/kWh.
But they also think the battery industry will have to change to get prices this low. For one thing, battery manufacturing processes are still too expensive. Panelists say gross profit margins for battery manufacturers–which tend to be in the 10–20% range today–will have to come down to perhaps 8%, the average margin enjoyed by a clothing retailer. Additionally, future batteries must move away from using conflict materials, natural resources extracted in conflict zones and sold to finance the fighting.
If it all comes true, you probably won’t have to worry about packing a fire extinguisher in the back seat of your EV.
LELAND TESCHLER • EXECUTIVE EDITOR
Filed Under: DIGITAL ISSUES • DESIGN WORLD, DIGITAL ISSUES • EE WORLD