Solid-state batteries – a red herring?

Toyota's solid-state batteriesWhile ‘solid-state’ batteries have long been billed as the best way forward in terms of safety, energy density and speed of charging, electronics giant Toshiba has just announced a new battery that is at least as good as the solid-state one Toyota has been developing for a decade.

Before this shock announcement, major car manufacturers such as Porsche were planning to go solid-state. The race is on to develop a car battery system that will outcompete fossil fuel engines, and the time is coming fast when internal combustion engines may well be obsolete relics of the 20th Century. Let’s look at Toshiba’s and Toyota’s battery development programmes and show how quickly such technology is developing.

 

Porsche plans to go EV

Autocar reported on September 12, “Porsche is eyeing up solid-state batteries, which are lighter and more compact than lithium ion cells, as a possible future technology for an all-electric sports car, but production versions are several years away.” From Porsche’s perspective you need a smaller, lighter battery bank that has more range in order to compete with their existing fossil fuelled cars that have much higher power to weight ratios than EVs of today.

With existing technology for example, in order to make an EV 911 compete with its fossil fuel sister you might need to take out the back seats to reduce the weight. Porsche’s Head of R&D Michael Steiner told Autocar, “That’s a question we have asked ourselves: can it be a 911 with only two seats?”

If they can be made for cars, solid-state batteries should have a far greater energy density than existing lithium-ion batteries so you can fit more range into a smaller battery bank, and they may well be able to be charged much faster. We asked Porsche for an interview on the subject but they said that they had revealed all they can to Autocar. Instead, we spoke to Denis Pasero, Commercialisation Manager at Southampton based Ilika plc, who are helping Toyota to create solid state batteries for their EVs.

 

The problem of battery chemistry

In developing battery technology, scientists kept hitting the hurdles of how fast they can charge them, how much energy they can carry per kilogramme of weight, and safety issues when they try to cross these two hurdles.

Most of the EV car batteries we use today have electrodes that sit in a fluid, which carries the electrons as electricity between the two terminals. Over the years this has been refined by using different chemistries, and at the turn of the Century lithium-ion batteries were developed which deliver a far greater amount of energy per kilogramme than the older lead-acid batteries. Lithium-ion battery chemistry has been tweaked over the years but scientists kept hitting the problem of batteries either catching fire or exploding when they get too hot or are over-charged.

In 2014 for example, a number of Boeing Dreamliner jets had to make emergency landings after their batteries exploded or caught fire. Foreseeing the problem, and not wanting their EV car batteries to explode or catch fire, Toyota went to Ilika Technologies in 2008 to discuss developing solid state batteries.

One of the dangers of having a liquid electrolyte is that if they get too hot they can explode, and if too much current is put in while charging they can catch fire. Pasero told us, “Toyota were looking at moving away from batteries that had a liquid electrolyte to one with a solid electrolyte. They were worried that there would be an incident of some sort that would create a massive recall,” of the cars with (worst case scenario) exploding batteries. Pasero continued, “We worked with them to develop a solid electrolyte that would transfer the electrons between the cathode and anode.”

Over six years the two companies worked together, sharing intellectual property and Ilika itself is about to license the production of solid state micro-batteries for sensors on sports cars such as those made by McLaren.

 

Advantages of solid-state batteries

While safety is a very important factor in solid-state batteries they should in theory be far lighter for every kilowatt-hour of energy that they can carry. Pasero explained with regard liquid electrolyte batteries, the “size of the spacing between anode and cathode is determined by the polymer separator, this is a plastic-type film that makes a physical barrier between the 2 electrodes. You soak it with the liquid electrolyte. It’s a few 10’s of microns, whereas solid state batteries are a few microns, an order of magnitude difference.” A micron is 0.001 of a millimetre, so where in a liquid battery (up to now) you may get two electrodes in 0.03 of a mm, you might get 100 solid-state electrodes in the same space. This would create a far higher energy density than those in a liquid electrolyte battery.

Another advantage of solid state batteries is that they should be able to be charged far more quickly. Regarding the thin solid films, Pasero said, “the electricity can move much more quickly between the electrodes as it has a far smaller distance to travel. This means that you can charge the battery more quickly.”

With regard safety Pasero gave the example of an old AA battery you might have in your camera. After a few years it might leak corrosive liquid. In other cases, it could heat up and a gas will form in a process known as ‘gas evolution’ and the battery will explode. Solid-state batteries have no liquid inside and this cannot turn to gas and there is a far lower risk of explosion. Pasero also told us of another risk, “There is a problem of lithium atoms joining together and forming a spike that penetrates the membrane and connects to the other electrode”. ‘Lithium metal deposition’, as this is known is where the battery shorts itself and you could have a fire on your hands. He said that this can’t happen with a solid state-battery.

 

Toshiba takes the lead

Ilika have developed and are about to license the production of solid-state micro-batteries that can be given a full charge in minutes and never charged again for years. At that size, solid-state batteries are a proven concept and do work. At car battery level however, Pasero pointed out, “I haven’t seen a [solid-state] battery that works at a tens of kilowatt level yet.”

You read that right. For all the years in development and many millions of dollars spent, no-one has made a solid-state battery that can power a car yet. The week we interviewed Pasero, Toshiba made an announcement that in 2019 it will start production of a liquid electrolyte car battery that could be charged in six minutes and give a car a 200 mile range on each charge. If you drive 200 miles fairly regularly as I do, you’ll appreciate that that’s a good distance for a stop at a charging station if only for a pee and a cigarette. The press release stated, “its titanium niobium oxide anode is much less likely to experience lithium metal deposition during ultra-rapid recharging or recharging in cold conditions—a cause of battery degradation and internal short circuiting.” The battery is twice as energy dense as Toshiba’s current battery, meaning it is half the weight for every mile you can drive on a charge. The battery is capable of being charged far more quickly without exploding or catching fire.

I showed Pasero the announcement. With regard the lithium ion battery, he said the “only difference is that they swap the carbon in the anode for titanium niobium. This material seems to be able to insert more [lithium] (hence more energy and therefore range) than carbon and charge more rapidly. The claims are quite strong! 6 min ultra recharging and 320 km are above what I heard so far. This clearly is another marker for solid state batteries. How it compares: well, Toyota claims more than 300 miles range by 2020. I do not know how much faster [solid-state batteries] will be able to charge.”

Toshiba seems to have developed a liquid electrolyte battery that is far better than the much talked-of solid-state battery just by tweaking the chemistry of the electrodes in a normal lithium-ion battery. Could billions of battery research dollars have been wasted?

 

What’s holding solid-state batteries back?

Pasero explained that there are two essential problems with making solid-state batteries work. The first is that unlike liquid electrolyte batteries, they need to be relatively warm. Only a few years ago they needed to be 60 degrees C for electricity to pass through them but scientists have got that down to 20 degrees C today. That still might be a problem in New York City or in Chicago where temperatures in winter fall well below zero degrees C. Pasero said that in these cases, “they would work more slowly but would heat up in about one minute to optimum temperature.”

The other problem, and one that still stymies battery developers, is making these batteries in a factory. It is all very well making one in a lab but for Porsche or Toyota to make them you need production runs in the thousands or millions a year. Pasero went on, “With traditional batteries you take a foil and deposit an ink on it with the cathode, you do the same with the anode. You place them face to face to face with the liquid in between and you have your battery.” Through proven technologies it is quite easy to make a liquid electrolyte battery relatively cheaply. In making solid-state batteries, boffins need to develop a new manufacturing method.

Solid-state batteries are far more complicated. “You will have put one electrode on a foil as an ink and then dry it. The second layer is wet. This is going to start interfering with the dry one. They aren’t quite there yet with this,” Pasero said. This issue could significantly add to the cost of production of the batteries, meaning that if the problem can be resolved you will only see solid-state batteries in top end luxury cars such as the Porsche where they can afford very expensive components. You may not see them in Leafs or the Tesla Model 3 for a good while yet, though you never know about the Tesla Model S!

 

The race is on!

Billions of dollars are being poured into battery technology with the express intention of making EVs competitive kilo for kilo with fossil fuel engines – once EVs can be made lighter and of greater range can fossil fuel cars, no one will want a petrol or diesel car. The race is very much on to make this happen in the next few years.

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