Tesla has published a new patent for battery storage and the contents are potentially very significant to Tesla’s mission to produce long-range, lower cost electric vehicle batteries that will last as long as its electric vehicle hosts.
The new patent – originally filed in November last year, but only published this month – describes a “tabless electrode” that does away with the tabs that connect the positive and negative terminals of a jelly-roll battery. The goal is to reduce resistance and manufacturing costs.
Tesla will soon host a Battery Day, currently slated for the third week in May, and when questioned regarding what will be revealed during this highly anticipated event at the company’s Q1 2020 earnings call, Musk foreshadowed news of some significance:
“We want to — leave the exciting news for that day, but there will be a lot of exciting news to tell. And I think it would be one of the most exciting days in Tesla’s history and we’re just trying to figure out the right timing for that.”
Now, Musk has responded on Twitter to news regarding the latest in a string of battery-related patents, advising that this latest patent filing is “way more important than it sounds.”
The patent description describes the significance of the technology as follows:
Many types of battery cells are currently used as energy sources in electric vehicles and energy-storage applications.
Current cells use a jelly-roll design in which the cathode, anode, and separators are rolled together and have a cathode tab and an anode tab to connect to the positive and negative terminals of the cell can. The path of the current necessarily travels through these tabs to connectors on the outside of the battery cell.
However, ohmic resistance is increased with distance when current must travel all the way along the cathode or anode to the tab and out of the cell. Furthermore, because the tabs are additional components, they increase costs and present manufacturing challenges.
The tab-less electrode technology negates the use of a tab to make the positive-negative connection by instead using two substrates, one of which has a conductive edge.
Between the main portion of the substrate and the conductive edge, an insulating layer ensures that there is no electrical contact between the first substrate, the substrate coating and the conductive edge.
By using a conductive edge, Tesla seeks to reduce the distance that the current needs to travel, thereby also reducing the ohmic resistance. As the patent describes it:
The electrical resistance of a given material is directly proportional to its length. In conventional electrochemical cell designs, the electrode tab contact is typically fixed at either the end or the middle of the wound electrode. In order to initiate an electrochemical reaction, current must thus travel length-wise down the electrode current collector to reach the active material where the charge-transfer reactions take place.
The distance the current will travel will vary from one half the length of the wound electrode if the tab is affixed at the electrode’s midpoint, to the entire length of the electrode if the tab is affixed at either end. Embodiments within the present disclosure may provide a more uniform electrical contact between the electrode current collector and the interior can surface.
The maximum distance current will travel is therefore the height of the electrode as opposed to its length. Depending on the cell form factor, the height of an electrode is typically 5% to 20% of its length. Therefore, the ohmic resistance in the negative electrode during electrochemical cycling can be reduced by 5 to 20 times via embodiments of the present disclosure.
You can view more diagrams and information about the patent here.
This new patent is just another piece of the puzzle in Tesla’s mission to continue pushing the boundaries of electric vehicle battery technology.
It follows Musk’s statement in April 2019’s Autonomy Day that Tesla has been working on a new battery pack that would be designed to last 1.6 million kilometres, and which has been earmarked in a paper published in the Journal of Electrochemistry in September 2019 by a team that includes by University of Dalhousie academic Jeff Dahn who also works on Tesla’s battery research team.
What other technological developments from Tesla may form key steps in reaching that goal have been the subject of great interest.
Another recent patent titled Method for “Synthesizing Nickel-Cobalt-Aluminum Electrodes” submitted by Tesla, to which Dahn has also put his name, describes a new lithiation process for battery electrodes.
Some media outlets have suggested that this new electrode patent will help achieve the 4,000+ cycles needed to reach the promised million mile battery lifespan.
However, a personal familiar with these technologies has confirmed to The Driven this patent shows a 10% capacity fade after only 100 cycles.
And on that note, we’ll repeat what we’ve said before: Bring on Battery Day!
Bridie Schmidt is lead reporter for The Driven, sister site of Renew Economy. She specialises in writing about new technology and has been writing about electric vehicles for two years. She has a keen interest in the role that zero emissions transport has to play in sustainability and is co-organiser of the Northern Rivers Electric Vehicle Forum.