Make the vehicle body the battery to decrease weight (Wired)

Today, batteries account for a substantial portion of the size and weight of most electronics. A smartphone is mostly a lithium-ion cell with some processors stuffed around it. Drones are limited in size by the batteries they can carry. And about a third of the weight of an electric vehicle is its battery pack. One way to address this issue is by building conventional batteries into the structure of the car itself, as Tesla plans to do. Rather than using the floor of the car to support the battery pack, the battery pack becomes the floor.

But for Greenhalgh and his collaborators, the more promising approach is to scrap the battery pack and use the vehicle’s body for energy storage instead. Unlike a conventional battery pack embedded in the chassis, these structural batteries are invisible. The electrical storage happens in the thin layers of composite materials that make up the car’s frame. In a sense, they’re weightless because the car is the battery. “It’s making the material do two things simultaneously,” says Greenhalgh. This new way of thinking about EV design can provide huge performance gains and improve safety because there won’t be thousands of energy-dense, flammable cells packed into the car.

A lithium-ion battery inside a phone or EV battery pack has four main components: the cathode, anode, electrolyte, and the separator. When a battery is discharged, lithium-ions flow through the electrolyte from the negative anode to the positive cathode, which are partitioned by a permeable separator to prevent a short circuit. In a conventional battery, these elements are either stacked like a wedding cake or wound around each other like a jelly roll to pack as much energy as possible into a small volume. But in a structural battery, they have to be reconfigured so the cell can be molded into irregular shapes and withstand physical stress. A structural battery doesn’t look like a cube or a cylinder; it looks like an airplane wing, car body, or phone case.

The first structural batteries developed by the US military in the mid-2000s used carbon fiber for the cell’s electrodes. Carbon fibre is a lightweight, ultra strong material that is frequently used to form the bodies of aircraft and high-performance cars. It’s also great at storing lithium ions, which makes it a good substitute for other carbon-based materials like graphite that are used as anodes in typical Li-ion batteries. But in a structural battery, carbon fiber infused with reactive materials like iron phosphate is also used for the cathode because it needs to provide support. A thin sheet of woven glass separates the two electrodes, and these layers are suspended in an electrolyte like fruit in an electrochemical jello. The entire ensemble is only a few millionths of a meter thick and can be cut into any desired

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