Tesla hybrid battery technology doesn’t mean hybrid as in ‘fossil fuels are involved’ but describes a dual purpose battery that can change from a short range mode to a long range mode at the flick of a switch.
In other articles about batteries in Plugboats we’ve covered how higher energy density is what EV and electric boat battery companies are in search of – meaning ‘the weight or volume of the battery has the capacity to store more energy’. Higher energy density means the same power can be stored in a smaller/lighter battery or, put another way, more energy stored in the same size battery. However you put it, it means the battery can take your boat farther without needing recharge.
Different from sold state technology
Most of the work to increase density is centred on solid state batteries, in which the liquid or gel part of a battery is replaced with a solid. We’ll get to which part is replaced in a minute. But some of Tesla’s battery developers are taking a different approach (as in so many things Tesla does) and they’ve just published a research paper in Science Direct that shows their ‘hybrid’ battery technology holds a lot of promise (again, like so many things Tesla does.)
In a (simplistic) nutshell, the way a battery works is that electricity flows between two electrodes – an anode (–) and a cathode (+) – through a material called an electrolyte. In a lithium-ion (Li-ion) battery the anode is usually some kind of carbon-based material like graphite. The cathode is a lithium metal – lithium mixed with a concoction of metals like cobalt, nickel, manganese, aluminum, phosphate. The liquid part, the electrolyte, also contains lithium – lithium salts dissolved in a liquid or gel.
Tesla hybrid battery plates lithium anode
It is generally agreed that using lithium in the anode (instead of carbon/graphite) can greatly increase the energy density of a battery, but because lithium is an unstable metal, there are a lot of challenges that need to be addressed. A solid state battery – putting in a solid electrolyte – addresses some of the issues, but then causes some different ones.
So what the Tesla team came up with is what could be called a hybrid anode. This is how they explained it in the Science Digest paper:
To develop a high energy density cell with longer lifetime, we propose a hybrid lithium-ion/lithium metal cell that is achieved by purposefully plating lithium metal on graphite. A hybrid anode cell design involving lithium metal plating on top of graphite provides a 20% increase in energy density over conventional lithium-ion cells.
We also found that…operating the cell with this protocol shows minimal impact to the underlying graphite capacity. Therefore, these hybrid cells can operate well in “lithium-ion mode” with periodic high energy full cycles accessing the lithium metal capacity.
Switch from one power/density mode to another
To put that in practical terms, it means that when driving a car (or boat) within its ‘regular’ range, the regular lithium-ion part of the anode is used, but this can be switched to using the lithium-metal part of the hybrid anode when extra distance is needed. It’s kind of like having an extra gas tank you could flip to if you were driving a fossil fuel boat.
As an example, the researchers say that “...if an electric vehicle with a conventional lithium-ion battery can deliver a range of 400 km, then hybrid cells could enable a range of 480 km.”
Tesla has looked at hybrid battery technology before and applied for a patent in 2014 for a hybrid battery that used metal-air cells. As the Sunday Times reports, they “married ‘high power, medium density’ lithium-ion cells, which are ideally suited for heavy lifting (acceleration, high speed, hill climbing), to ‘high density, medium power’ metal-air cells that could be used for ‘baseline power delivery’.
In terms of a boat, this could be the kind of innovation that enables switching from one kind of battery cell for getting a boat on plane to another kind of battery cell for cruising at a maintained speed.
Hybrid Tesla battery and university research team
As always, we have to make the point that it can be a long road from publishing a research paper to having a commercially viable battery. But certainly being part of the Tesla network is an advantage in having access to the necessary resources.
The work for this technology was done by a team at Dalhousie University in Nova Scotia, Canada headed by lithium battery guru Jeff Dahn – the NSERC/Tesla Canada Industrial Research Centre, established by Tesla and the Government of Canada in 2016. Since then they have filed for numerous patents focused on increasing energy density, including the famous ‘million mile’ battery.
For this specific work on hybrid lithium-ion/lithium metal cell research, Dahn works with his students Matthew Genovese, A.J.Louli, Rochelle Weber, and Cameron Martin.