The Quest for a Million Mile Battery

Currently, the Million Mile Battery is one of the most sought after technologies in the EV world. Driving for 1 million miles without needing to replace a battery pack is currently unheard of. In fact, batteries are usually replaced once they have lost around 20-30% of their capacity, something that usually happens after around 500,000 miles.

Last year, a research team led by John Dahn that is partnered with Tesla produced a research paper in the Journal of the Electrochemical Society. The paper was titled ‘A Wide Range of Testing Results on an Excellent Lithium-Ion Cell Chemistry to be used as Benchmarks for New Battery Technologies’.

One of the statements from the introduction of this paper includes the following snippet:

“We conclude that cells of this type should be able to power an electric vehicle for over 1.6 million kilometers (1 million miles) and last at least two decades in grid energy storage.”

According to their research, this special type of lithium ion cell is capable of at least 5000 cycles before its capacity drops below 90% of its original capacity.

However, Tesla isn’t the only manufacturer looking for such a battery.

GMs executive Vice President Doug Parks said that an EV battery that will last one million miles is ‘almost there’. Though, it is worth noting that this battery would only be used on long range vehicles at first.

What Would a Million Mile Battery Mean and Why Is It So Sought After?

Just before we start discussing the million mile battery, there’s something important to know.

Million mile battery means a battery that a car can use for 1 million miles of driving without needing to be replaced or suffering a major drop in capacity.

Tesla Model S 85 kWh Battery
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However, when researching cells, researchers aren’t bothered about how many miles it can do, they’re more interested in how many cycles it can do. One cycle is a full charge followed by a full discharge.

Hence, a car with a larger battery that has more range would need to complete fewer full cycles in order to drive 1 million miles. This essentially makes the feat easier to pull off in a car with more range. A few examples how many cycles a battery needs to make before reaching 1 million miles are listed below.

  • 300 miles: 3333 cycles (similar to Tesla Model 3)
  • 400 miles: 2400 cycles (similar to Tesla Model S)
  • 500 miles: 2000 cycles (possible upcoming Tesla Model S Plaid)
  • 600 miles: 1667 cycles (upcoming Tesla Roadster)

Possibilities of a Million Mile Battery

‘Robo-taxi Network’

The idea around Tesla’s proposed Robotaxi plan is to turn your Tesla into a $100,000 asset.

Whilst you’re at work, or anytime you’re not using your car, it will autonomously ferry people around, just like a robot taxi. Essentially, instead of your car sitting around parked and losing money, it will gain you some passive income.

Tesla reckons that the cost of a Robotaxi will be $0.18 per mile to run, factoring in all necessary overhead. By contrast, they California based automaker claims that the average Uber of Lyft journey costs $2-3 per mile.

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So, how would a million mile battery aid this initiative?

If your car is driving around all day, it would rack up quite some miles. Suppose you had a battery pack like those currently found in modern EVs. Eventually, your battery pack would need to be replaced. Although the figures are changing all the time, it is estimated that a full battery pack replacement would cost upwards of $15,000, most likely more than $20,000.

That would seriously eat into your profits, and mean that your car would have to be away from you for some time whilst the battery was being replaced.

Suppose now you have a Tesla fitted with a million mile battery, or maybe even a 1.2 million mile battery for that matter. Essentially, it would never need to be replaced. In fact, some of the other components on the car would die before the battery needed to be replaced.

Consequently, the taxi would be cheaper to run, meaning fares for customers could be reduced. Furthermore, it would mean you would spend less time without your car.

Most importantly, though, it would be much cleaner for the environment. Current battery packs, and the battery packs that Tesla would likely be using for their million mile battery, contain many precious resources like Lithium. The more battery packs that are used, the more lithium that must be mined, damaging the environment more.

Tesla Semi

With Musk having recently sent out an internal memo to the Tesla team, stating that they would be rapidly ramping up the production of Semi, it’s clear that the future of trucking is going electric.

Tesla Semi in sunset
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Tesla Semi

However, large logistics and delivery companies would need to be able to rely on an electric truck to last a very long time, and be very reliable in the process. Several companies have already placed preorders of the Semi, including Walmart.

Current long haul Semi trucks in the US are already capable of 1 million miles without too much replacement. However, these trucks spend most of their time on the highway in the highest gear, meaning there’s very little strain on the truck.

With its 300 and 500 mile range variants, the Tesla Semi is more focused on shorter journeys, including those through cities. This is territory where current diesel Semi’s don’t even begin to compete with an electric truck in.

For the company operating the trucks, it comes down to one line of reasoning. A longer lasting truck means components will have to be replaced less, meaning the truck costs less to operate. For the truck company, this means higher profit margins. For the customer, this means cheaper deliveries. A no brainer for all parties.

Grid Storage

The other main area where batteries are likely to be used heavily in the future is large scale grid storage.

For instance, Tesla produced and installed a 129 MWh battery pack at the Hornsdale Power Reserve in South Australia. Just in the couple of years that it has been installed, the battery has been estimated to save Australian consumers tens of millions of dollars.

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Tesla Battery Pack

More batteries like this can be used to replace natural gas ‘peaker plants’ in the future. These are only activated when demand surges past production and more energy is needed. However, they run on fossil fuels, and natural gas can be extremely damaging to the environment if it leaks out of its container.

Batteries all seem well and good, except when you consider that they’re in use constantly. Although many current grid scale systems are designed for a 20 year lifespan, batteries may need to be replaced within that time.

Replacing Giggawatt hours of battery storage every decade or so would become extremely costly, hence the need for a more resilient battery.

According to the paper by Jeff Dahn’s team, the battery which they were testing would be capable of at least 20 years of grid storage. That’s a long time. By the end of that cycle, it’s likely that lots of the other infrastructure around the batteries would need replacing anyway.

Other Large Vehicles (e.g. Buses)

In a similar way to Semi trucks, other large vehicles like buses could benefit from longer lasting batteries.

There are talks of using a fleet of commercial vehicles connected to the grid to act as batteries, stabilising the electricity supply. The buses wouldn’t just be driving in the day, they’d become grid scale batteries at night.

For the consumer, longer lasting batteries would mean cheaper, more environmentally sustainable transport.

Why do Batteries Lose Capacity Over Time?

Over many cycles, lithium ion batteries can lose some of their capacity. For example, straight out of the factory, a lithium ion battery would be able to hold 100% of its original energy. However, after 500 cycles, this may be down to 90%, or even 85%.

“The energy storage of a battery can be divided into three sections known as the available energy that can instantly be retrieved, the empty zone that can be refilled, and the unusable part, or rock content, that has become inactive as part of use and ageing. Figure 1 illustrates these three sections.”

Battery University
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Diagram illustrating battery capacity. Source: batteryuniversity

The rate of degradation of lithium ion batteries is mainly down to the battery’s coulombic efficiency. This is a concept developed by Jeff Dahn and his team at Dalhousie University in Halifax, Canada. Dahn is a leading researcher in the field of electrochemistry and works with Tesla.

In principal, coulombic efficiency is a measure of the efficiency with which electrons are transferred in an electrochemical system. The higher the value, the better, with a maximum value of 1.

A battery pack is made up of cells. Each cell consists of an anode (negative electrode) and a cathode (positive electrode). These electrodes are submerged in a liquid electrolyte, which, in Tesla’s case, contains lithium.

Finally, there is a permeable separator between the anode and the cathode. It’s role is to allow lithium ions to flow between the electrodes, but prevent the electrodes touching each other. If the electrodes were allowed to touch, the battery would short circuit and become a fire hazard.

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As the battery is charging, lithium ions gravitate towards the anode (negative electrode), which is made of graphite. Once the lithium reaches the anode, a chemical reaction takes place which generates a flow of electricity.

When the battery is discharged, the reaction is reversed, sending the lithium back through the separator and onto the cathode (positive electrode). However, during this process, some undesirable chemical reactions take solace, causing a build up of crystals in the cracks and crevices of the anode.

Eventually, over hundreds or thousands of charge cycles, this can cause the chemical reactions to produce much less electricity. Given enough charge cycles, the battery will become useless.

Common logic would suggest that the less capacity a battery has, the less time it would take to charge. Over time, the battery should charge quicker.

This is the case with many types of batteries, but not lithium ion. they take longer to recharge.

According to the US department of energy, the bigger the battery and the faster it is charged, the fewer number of charge cycles it can tolerate before losing capacity.

What Technological Developments Must Take Place to Alleviate This?

Additives

One of the most used solutions currently is additives. These are chemicals that are added to the electrolyte to reduce resistance.

As a consequence, there is less corrosion and the build of of crystals on the anode happens slower. This increases the lifespan of the battery.

Another reason additives are used is to improve the performance of the battery. Usually, at extreme temperatures, the performance of lithium ion batteries degrades. For example, an electric car will have less range when the temperature outside is very cold, rather than when it is around 20˚ Celsius. Additives can make the battery perform better at these extreme temperatures.

Chemistry

Some battery chemistries have higher coulombic efficiencies than others. Remember, coulombic efficiency is what determines how long the battery will last, and is defined as a measure of the efficiency with which electrons are transferred in an electrochemical system.

Currently, one of the best known chemistries for achieving a high coulombic efficiency is Lithium Titanate (LTO). However, it comes with a downside; cost.

Not only is it very expensive, but it also has a relatively low energy density, rendering it unsuitable for use in electric cars.

The million mile battery cells that were being researched in the paper by Jeff Dahn and his team were Lithium Nickel Manganese Cobalt Oxide (NMC). These have a good, though not excellent, coulombic efficiency, whilst having a high capacity and tolerance to a high power output.

Their efficiency starts to drop off once temperatures reach the 60˚ mark, but Tesla’s battery management system should keep temperatures from reaching those levels.

The current batteries in the Tesla Model S are Lithium Nickel Cobalt Aluminium Oxide (NCA).

Manufacturing

Small changes in the way cells are manufactured can lead to vast improvements in the longevity and capacity of a battery.

For example, one of the researchers on Jeff Dahn’s team who designed the cathode carefully tweaked the nanostructure of the cathode during production.

The cathode in these NMC batteries relies on larger NMC crystals, rather than smaller ones that are usually used. This change reduced the probability of the cathode developing cracks.

If you remember, the crystals that form on the electrodes that cause the battery to lose capacity can only form due to cracks and crevices in the electrodes.

Hence, by making this small tweak to the cathode, crystal build up was reduced, meaning the cell could tolerate a larger number of cycles before losing more than 10% of its original capacity.

Experimental Battery Types

Lithium Air

Lithium air battery cells promise to store far more energy than current lithium ion batteries. Specifically, they have a theoretical energy density of 13 kWh/kg. That’s on par with petrol.

The typical anatomy consists of a catalytic air cathode that supplies oxygen, an aqueous electrolyte, and a lithium anode.

Lithium–air battery - YouTube
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As a matter of fact, the battery does not have to be lithium air as such. A more generic term would be ‘metal air’ as these batteries can be constructed using other metals like Zinc and Aluminium too.

Despite these exciting claims on energy density, it seems as though the peak power output that the cells can provide may be a problem. In fact, many researchers believe that a metal air battery may end up more like a fuel cell rather than an actual battery.

Researchers at the University of Illinois have claimed that they have produced lithium air cells that are capable of 750 charge cycles, something that has never been seen before. However, right now, it’s not clear whether this is a valid result, especially given that other tests in the past have resulted in around 50 cycles. Regardless, they’re certainly not a 1 million mile battery yet.

Solid-State Lithium

In the past, I’ve written about solid state batteries. They’ve always seemed like the ‘next big breakthrough’ which has never really come about.

There are a few key changes from todays lithium ion batteries like those found in electric cars, compared to the solid state lithium ion batteries.

Panasonic, Tesla's Battery Partner, May Have Upcoming EV ...
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Solid State batteries take up much less space than their Lithium Ion counterparts.

Firstly, the graphite anode is replaced with a pure lithium anode. Unfortunately, this means that dendrites (growths of lithium inside the battery) become a more severe problem. If grow enough to make contact with each other, they can cause the battery to short circuit and catch fire.

Secondly, the liquid electrolyte is swapped out with a more dense solid polymer electrolyte and ceramic separator. This change is what increases the energy density of the cell.

Despite the move to a ceramic separator, lithium dendrites are still able to meet and touch each other. Hence, one of the main problems that researchers are currently trying to solve is dendrite growth.

Current solid state batteries are reaching energy densities of around 460 Wh/kg. That’s around 2x that of current lithium ion batteries that are used in a Tesla Model S.

There are claims of solid state batteries being capable of up to 10,000 cycles, though these should be taken with a grain of salt. For example, many batteries like these do not have a high energy density, and have a tendency to lose efficiency at the higher currents that would be needed for an electric car.

Seawater Battery

Researchers at IBM claim to have produced a new type of battery that sources its elements from seawater. Yes, water taken straight form the ocean.

IBM's Lithium-Ion Battery Uses Seawater Materials Instead ...
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IBM Researchers

As a result, these batteries would be very environmentally friendly, with the lack of cobalt being the major breakthrough. Cobalt is toxic and significantly damages the environment when mined.

Other researchers from Imperial College London have experimented with similar seawater batteries that can be charged in just seconds. The batteries use thin films of specially designed plastics and simple salt water instead of harmful elements like lithium and cobalt.

However, and this ones a big however, these batteries have only been able to hold very small amounts of charge so far.

If their energy density could be increased, they’d be an environmentally friendly, easy, and cost effective way of making batteries. Unsurprisingly, IBM has teamed up with Mercedes Benz to try to produce these batteries for their electric cars in the future.

Conclusion:

So, what does the future of battery technology hold for us?

Shortly after Jeff Dahn’s research paper was published, Tesla released a joint patent with Dahn for a single crystal lithium ion battery. The detailed battery is very similar to the one used in the paper, except for one extra additive. Tesla suggests that this additive can ‘enhance performance and lifetime of Li-ion batteries, while reducing costs’. Sounds promising.

Either way, some electric car company somewhere is going to find themselves with an electric car and a 1 million mile battery within the next few years. For all we know, one may just be around the corner at Tesla’s battery day which is due to happen within the next few months.

Electric cars may soon be getting quite the upgrade. Alongside that, with a lifespan of over 20 years, we may see grid scale batteries take off in popularity very soon.

As I’ve said before, the internal combustion engine had over 100 years of innovation to make it what it is today. It’s gone from powered carts to 300mph Bugatti Chirons.

Just imagine what electric cars may be like in 50 or 100 years.

References and Citations

[1] Harlow, Jessie & Ma, Xiaowei & Li, Jing & Logan, Eric & Liu, Yulong & Zhang, Ning & Ma, Lin & Glazier, Stephen & Cormier, Marc & Genovese, Matthew & Buteau, Samuel & Cameron, Andrew & Stark, Jamie & Dahn, John (2019). A Wide Range of Testing Results on an Excellent Lithium-Ion Cell Chemistry to be used as Benchmarks for New Battery Technologies. Journal of The Electrochemical Society. 166. A3031-A3044. 10.1149/2.0981913jes.

https://batteryuniversity.com/index.php/learn/article/what_causes_lithium_ion_to_die

https://www.ibm.com/blogs/research/2019/12/heavy-metal-free-battery/

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