Tesla Gained Another Battery Cell Patent: Cell With A Tabless Electrode

Photo by Christian Ruoff/Chargedevs.com

Tesla is actively engaged in the development of its own batteries, as they are the most important component of an electric car. The company seeks to create a battery that allows Tesla cars to travel long distances without recharging, which will have a long service life.

Tesla filed a patent 'Cell with a tabless electrode'

Filed Date: November 4, 2019
Publication Date: May 7, 2020

A cell of an energy storage device with at least one electrode that is tabless, and methods of forming thereof, are described. The cell includes a first substrate having a first coating disposed thereon, wherein a second portion of the first substrate at a proximal end along the width of the first substrate comprises a conductive material. An inner separator is disposed over the first substrate. A second substrate is disposed over the inner separator. The second substrate has a second coating disposed thereon. The first substrate, the inner separator, and the second substrate in a successive manner, the first substrate, the inner separator, and the second substrate are rolled about a central axis.

FIG. 1 illustrates a perspective view of a cell showing a first substrate, an inner separator, a second substrate, and an outer separator according to certain embodiments of the present disclosure.
Source: Tesla patent

The present disclosure relates to a cell for energy storage devices. More particularly, the present disclosure relates to a cell with at least one electrode that is tabless, and therefore may be used to form an energy storage device with reduced ohmic resistance and reduced cost. For example, within a jellyroll cell design, the negative electrode may include a conductive portion at one end that runs the length of the electrode, and connects to the bottom of a can to electrically connect the electrode to the can. In some embodiments, the can includes a cap with a particular design configured to increase the connection of the electrode to the cap. The cap may include ridges, bumps, cavities, or other features that provide for additional connectivity between the cap and the electrode.

FIG. 4 illustrates a first cap having a contact surface that can be used to electrically connect with a conductive portion of a first substrate, according to certain embodiments of the present disclosure.
Source: Tesla patent

The present disclosure offers numerous advantages compared to other advanced electrochemical cells, which utilize a tab contact to electrically connect the negative electrode substrate to the can wall in addition to the tab to connect the positive electrode to the cathode connection. Removing the tab connected to the negative electrode and reorienting the conductive connection to a conductive portion 118 (in the FIG.1 above) allows the negative electrode to run along the length of the negative electrode. This reduces ohmic resistance through the negative electrode to the can, reduces current deviation across the length of the electrode, improves cell lifetime, reduces joule heating, and increases heat dissipation capability.

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.

FIG. 7 illustrates a method for manufacturing a cell according to certain embodiments of the present disclosure.
Source: Tesla patent

An electrochemical cell of the presently disclosed embodiment may also experience significantly less current deviation, the phenomena where some electrode regions pass more or less current than other regions over its cycle lifetime. Current will preferentially travel along paths where resistance is lowest, which in the absence of other factors will typically be along paths closer to the tab where the ohmic resistance is smallest. Current deviation is extremely undesirable in electrochemical cells because it can lead to local electrode hotspots where large overpotentials are generated, leading to unwanted chemical reactions that reduce the cell's lifetime. An example of such a reaction is the plating of metallic lithium on the surface of the negative electrode in lithium-ion cells. The reduced ohmic resistance of the disclosed embodiment provides a cell environment more conducive to uniform current distribution and cell lifetime.

The presently disclosed embodiment also offers superior heat generation and transfer properties compared to conventional electrochemical cell designs.

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