Tesla’s long run with Panasonic’s 18650 cells came to a halt recently with the launch of their new model 3, that packed the next generation 2170 cells (21mm width, 70mm height). According to experts, this new battery pack was no less than an engineering marvel, that contained 30 – 33% more energy when compared with previous generation 18650 cells.
In general, the company has always had contrasting ideas to the other big players in the industry, concerning the batteries used in their cars. Most companies when it comes to deciding the parameters for their car batteries, usually go in for hundreds of large format cells. Tesla on the other hand uses cells that are smaller in size, but comparatively more in number. The major advantage of this is reflected in its low price and high energy density of the battery. Also, a single cell malfunctioning would not cause much trouble, as it gets separated from the rest.
However, regardless of the size, the concern around battery safety, is something that is shared across the board. Tesla too has had some heating issues in its EVs, and recently came up with a solution to eliminate the issue.
The U.S. Patent & Trademark Office published a patent application from Tesla last week about “High Voltage Electrolysis of Coolant in a Battery Pack”. It was originally filed on May 3, 2018.
This battery coolant patent includes a coolant system that uses a mixture of two different liquids as a coolant solution. Apparently, the new liquid formed has different boiling points, as the predetermined ratio changes. This boiling point is about equal to the temperature sufficient to induce a thermal runaway condition for one or more battery modules. A sensor in the system monitors the battery module for a high voltage electrolysis and responds with a remediation system “ to decrease the risk associated with the possible high voltage electrolysis when operated”. What Tesla is trying to aim for here is to limit excessive thermal conditions of individual battery cells and modules. In their patent application they’ve mentioned: “Once the [runaway thermal condition ... chain] reaction starts, it can continue to spread throughout the battery pack or a portion thereof until overheating cells are sufficiently cooled or the entire battery pack or the portion is consumed. A typical battery pack has a high thermal mass, mostly due to the mass of the cells. A failure of an individual cell provides for a relatively low energy release. Also, surrounding battery cells must be heated to as much as 200 degree C or higher before they in turn release energy. These three factors mean that a full reaction that consumes all the cells of a battery pack may take anywhere from tens of minutes to many hours.”
https://www.forbes.com/sites/sebastianblanco/2018/09/10/tesla-battery-liquid-cooling-patent-application/#6b5d94f8127a
In addition to runway thermal condition, there is another risk factor which troubles the car maker. As a consequence of the chemical reaction of electrolysis, hydrogen gas is generated. Under some circumstances, this hydrogen gas can build up inside the battery pack and become a possible hazard. According to Tesla, a possible solution to this problem is to let the reaction run its course while the car is clear of any passengers or bystanders. Why this may be the best alternative for now is because stopping the thermal reaction itself, is practically very difficult.
As of today, Tesla has crossed the 300,000 mark of electric vehicles shipped worldwide, with its fleet reaching a total of 9 billion electric miles on road. These numbers sure tell that their product is loved around the globe. However, with $11 billion dollars in losses, it looks to me they have a lot more miles of their own to cover.