Bosch is developing a solid state battery with twice the energy density of a lithium ion (Li-ion) cell, effectively doubling the range of electric vehicles with no increase in weight. A Tesla Model S equipped with an 85 kWh Li-ion battery pack has an estimated range of 426 km (265 miles). Swap out the Li-ion battery and replace it with a solid state battery and the car could go 852 km (530 miles) on a single charge. Even better, the new battery doesn’t use a flammable liquid electrolyte, so no more battery fires! And the icing on the cake: the solid state battery would come at a lower cost. Bosch claims that this next generation of batteries could be on the market in five years.
Li-ion batteries include a negative anode made of carbon (usually in the form of graphite), a positive cathode made of a composite material that includes lithium, and a porous separator through which the lithium ions travel during charge and discharge. A liquid electrolyte carries the lithium ions from anode to cathode and back.
Carbon is relatively heavy; in order to improve energy density, a lighter material is preferred. Since lithium is the 3rd lightest element on the periodic table, it would be desirable to make the anode from lithium, as shown below:
The problem is that lithium expands and contracts during the charge and discharge cycles, resulting in uneven cracks along the surface, like potholes on a road. Dendrites build up in the cracks, eventually short-circuiting the battery.
Bosch won’t say exactly how they’ve solved that problem, but in 2014 researchers at Stanford University made a breakthrough that could provide the answer. To protect the fragile lithium surface, Stanford engineers developed a thin layer of carbon domes that they call a nanosphere. It forms a honeycomb structure - just 20 nanometers thick - that’s flexible, uniform, and inert. The nanosphere blocks the chemical reactions that cause dendrite formation.
According to Stanford researchers, the nanotubes improve the coulombic efficiency - a measure of how well electrons are transferred during an electrochemical reaction - from 96% to 99%. Ideally, a coulombic efficiency of 99.9% or higher is needed to make a practical rechargeable battery. Engineers at Stanford believe that goal is achievable with new electrolytes and a little more engineering work, making Bosch’s five year estimate seem pretty reasonable.
In addition to its use in cars, a solid state lithium battery would give longer life to notebook computers, tablets, phones, and other consumer electronics. Just don't text while driving your electric vehicle, okay?
Images courtesy of Bosch
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