A few years back, there was a lot of talk about Tesla potentially using a metal-air/li-ion hybrid powertrain to enable a longer range and faster charging in future vehicles. There’s no doubt that the company worked on such a system since they applied for several patents related to the tech, but that was mainly back in 2010 when they were still very much in the heavy development work for the Model S.

At this point, it looks like Tesla is very committed to li-ion batteries and metal-air doesn’t seem to be on the map anymore, but the company was recently granted another patent related to emerging battery technology.

A metal-air battery uses a metal as an anode just like a li-ion battery, but oxygen drawn in from the environment is used as the cathode.

It enables a much lighter cell and therefore, it offers a potential to achieve a greater energy density. In EVs, it means a potentially greater range.

Tesla had previously filed patent applications for a hybrid system that could use both a li-ion battery pack and a metal-air battery pack, which would act as a zero-emission range extender.

Several companies are working on similar technologies, but it has never materialized in a commercially available electric vehicle yet.

On January 31, Tesla was granted another patent for the technology. This one is about charging a metal-air battery. Here’s the abstract from the patent application:

“A method for charging a metal-air battery pack at the maximum possible rate while maintaining an ambient oxygen concentration below a preset concentration is provided, thereby minimizing the risks associated with generating oxygen during the charging cycle.”

It was first filed in 2010 when Tesla first started applying for metal-air patents, but it was then modified in 2013 when Tesla started being granted patents for the technology. Now it was finally granted a few weeks ago:screen-shot-2017-02-12-at-3-23-31-pm

Tesla co-founder and CTO JB Straubel is listed as one of the inventors of the new patented technology.

Of course, Tesla has open-sourced all its patents back in 2013 and therefore, any company can use this one – like the others – as long as it is with the goal of making electric vehicles.

The company still files for patents – though not as often as it used to – but with the goal of protecting itself from being blocked by some other corporation trying to patent to same technologies.

Also, it’s noteworthy that the fact that it was granted a new patent on metal-air doesn’t mean that Tesla is any closer to incorporating the tech into its vehicle line-up.

There are problems with metal-air battery technology that need to be solved in order for it to be used in electric vehicles, especially life cycle and cost. In the patent (see in full below), Tesla asserts that the new charging method addresses some of the issues, like managing the supply of air during the charge cycle.

Maybe we will one day see a breakthrough and the patented tech will become useful or maybe the energy density of li-ion batteries is improving too quickly for metal-air to matter any longer.