A new Tesla patent shows a tabless design for a jelly roll lithium-ion battery cell, replacing tabs with conductive spikes built into the cap.
Removing tabs could save manufacturing time, resources, and costs.
Way more important than it sounds
— Elon Musk (@elonmusk) May 7, 2020
What’s a battery tab, and why does removing it make a big difference, according to Elon Musk? Let’s review the facts and then do some educated speculating.
First, a battery tab is kind of what it sounds like: a tab, connected to the battery cell, that makes a clean connection to whatever the battery is powering. “Battery tabs play an important role in lithium-ion cell manufacturing,” tab manufacturer Targray explains on its website:
“A typical large format lithium-ion cell uses copper foil as the anode current collector and aluminum as the cathode current collector. A ‘foil-to-tab’ weld is needed to gather all the current collector plates (foils) inside the cell and join them to a tab which exits the cell casing, allowing the cell’s energy to be transferred to an external source. There are two foil-to-tab welds in each cell, and hundreds of cells in a typical lithium-ion battery pack.”
Basically, one kind of lithium-ion battery, a prismatic type, is layered like a lasagna, and each layer links to the outside via a single energy-transferring tab. And as you can imagine, connecting that tab requires very specialized and careful welding during manufacturing. (Advanced readers can, indeed, try this at home.)
There’s nothing wrong with tab technology, but streamlining battery designs to remove them could save a lot of time, materials, and money. In a 2017 conference paper on tabless battery designs, the authors summed it up nicely: “The advantages of the tabless design are: More robust and reproducible; More easy to produce; Less scraps; More reliable.”
Tesla’s patent outlines a battery design where features like bumps and small spikes act to connect different layers rather than relying on a welded, unifying conductive tab. “In some embodiments, the can includes a cap with a particular design configured to increase the connection of the electrode to the cap,” the patent explains. “The cap may include ridges, bumps, cavities, or other features that provide for additional connectivity between the cap and the electrode.”
This is a really neat idea, and it hearkens back to effective vintage technology like the vampire tap—a piece of hardware with a sharp spike that literally bites into the thick trunk cable of a network in order to connect—or even the “poor man’s staple” fold. In both cases, the design acts as a de facto connector and can hold itself together without adhesive or welds.
Interesting Engineering describes the patent as “a novel way of building cells to avoid a jelly-roll design,” but that’s not true. The design is still a traditional jelly roll, the other trademark way of building rechargeable lithium ion batteries. And the idea of a tabless lithium-ion battery dates back to at least this 2006 patent, where a technology to make sealed, rechargeable batteries includes a diagram of deployment on a tabless battery.
“In the tabless structure, the current distribution becomes uniform both in positive electrode 3 and negative electrode 6, and the discharge characteristic of the battery improves,” the 2006 patent reads.
So what is Musk up to? Well, he plans to have “Battery Day” sometime in “mid May,” and that might involve the announcement of an advanced battery pack that uses an array of tabless jelly rolls instead of prismatic lasagnas. Other manufacturers are moving ahead with their own innovative batteries, like GM’s soft pack that “exceeds” Tesla (according to GM). It’s about time for one of Musk’s trademark counterpunches.
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