Lithium-ion batteries are everywhere–there’s probably one in the cell phone in your pocket, in the laptop on your desk, and in the wireless headphones in your ears. While they’ve become commonplace, lithium-ion batteries come with some inconvenient truths – particularly that they’re prone to fires and corrosive leaks. This is why we’re seeing patterns such as recalls for battery electric vehicles (BEVs), specific regulations for traveling with lithium-ion batteries on airplanes, and major fires breaking out in stationary applications and aboard shipping vessels transporting electric vehicles.
Why are fires still a threat? The answer can be traced to the materials inside lithium-ion batteries.
Why Do Lithium Batteries Catch Fire?
Like most types of batteries, a lithium-ion battery cell has four basic components: two electrodes – one positive (“cathode”) and one negative (“anode”), a separator, and a liquid electrolyte. Unlike technologies such as lead acid, lithium-ion chemistry allows a great deal of energy to be stored in a small weight and volume (referred to as “energy density”) and allows that stored energy to be extracted quickly (referred to as “power density”).
High energy and power density make lithium-ion batteries optimal for a range of applications because they can store high amounts of energy in tight spaces and deliver it quickly when needed. But there’s a catch: that high energy and power density doesn’t come risk-free. By nature, lithium-ion batteries are unstable and flammable. Inside each is a system of elements that must function harmoniously to prevent the battery from going into thermal runaway or short-circuiting. Even with perfect manufacturing and well-made components, some hazards are simply unavoidable.
During charging, lithium ions are sent up a chemical slope from the positive electrode to the negative one. When the battery is discharged, lithium ions are forced out of the anode and back to the side of the cathode, and simultaneously an electron is released to produce electricity. While batteries are almost 100% efficient, heat is produced as the battery discharges and electrons roll down the energy slope. The more electrical current that’s drawn, the more lithium ions are released, and the hotter the battery becomes.
Higher current can lead to a positive feedback loop of heat production. If left uninterrupted, it can lead to thermal runaway—a situation where batteries reach a point where internal cell temperature rises quickly and all of the energy stored inside is suddenly released. A failed cell can then pass on all of that heat to the next cell, causing a chain reaction that results in a fire.
Lithium Battery Fire Causes: Dendrite Growth
Aging and improper charging can lead to lithium dendrite growth. Lithium dendrites are metallic microstructures that form during the charging process when extra lithium ions accumulate on the anode surface and cannot be absorbed into the anode. If dendrites accumulate and grow long enough, they penetrate the internal separator and touch the opposite positive electrode, causing short circuits and leading to catastrophic failures, and even fires. Dendrite growth was the culprit behind the massive Samsung Galaxy Note 7 recall.
Lithium-ion batteries (including LFP / LiFePO4) are flammable by nature and can exacerbate fires that start in other ways. The recent fire aboard cargo ship Felicity Ace, which was hauling 4,000 luxury vehicles, may or may not have been started by lithium-ion batteries, but was certainly fueled by vehicles containing them.
Short circuits can also be caused other ways. Overcharging the battery will cause too many lithium ions to populate the negative electrode, resulting in expansion that can mechanically stress the battery and compromise the internal insulation. Even if there is no damage or dendrites, there’s also the looming possibility of metal contamination within the cells from the manufacturing phase.
Can Lithium Battery Fires Be Prevented?
High energy and power density don’t have to go hand-in-hand with fire risks. Alsym batteries use materials that are inherently non-flammable, reducing the associated risks to life and property, and cumulative liabilities. They contain no lithium or organic electrolytes and can be used in applications and environments where heat dissipation is an issue and thousands of cells per pack may be needed, such as in large-scale stationary storage.
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