Exploring Electric Vehicle Battery Life, Degradation, and Developments

 In Vehicle Research

The battery pack of an electric vehicle (EV) is a crucial concern to consumers. What is the actual range of an EV? How long will it take me to charge? And will typical consumer behaviors have to change to adopt an EV? Below we focus on the anxieties surrounding battery life and degradation, but also a mention of the current developments in the market.

Automotive Research: Battery Life

A heated debate currently exists in the realm of battery life. EVs have not been in circulation long enough to gather comprehensive data on lifetime. However, a substantial indication may live in the warranties currently available from manufacturers. Tesla, for example, offers an 8-year warranty, the world’s best-selling Nissan Leaf with a 30kWh battery also provides an eight-year warranty period.

It is perhaps too early to estimate the actual life cycle of a lithium-ion battery, as the data just isn’t available. However, researchers at The Electrochemical Society found that partial discharge can increase battery life substantially.  For example, a 100% discharge cycle (most aggressive), batteries can typically last between 300-500 cycles. However, take the discharge rate consistently to 50% and the life expectancy can improve considerably to 3 to 4 times.

Significant for consumers, charging habits are likely to dictate the cost of your EV over its lifetime.

To extrapolate the battery life to the EV lifetime, a key consideration to take into account over its internal combustion engine (ICE) competitor is the number of moving parts. A Tesla powertrain has 18 moving parts, whereas an ICE vehicle has hundreds.

An implication of this is maintenance costs, while again studies are less than comprehensive, one can take a logical approach. The one substantial value of the EV is the replacement of a battery, essential to note the cost per kWh is declining all-the-time. According to a presentation delivered by the American Chemical Society, it is quite reasonable to estimate to the lifetime of a battery pack of an EV to be up to twenty years. And quote “That’s good news when you consider that some estimates put the average life expectancy of a new car at about eight years.” ICE vehicles have hundreds of ‘weak’ points. Timing belts are recommended to be replaced between 60 and 100k; other possible expenses include converter and transmission failures.

Degradation

Battery degradation in electric vehicles leads to capacity fade, thereby shortening the vehicle’s possible range.

The lack of battery degradation data for analysis sparked Maarten Steinbuch and Merijn Coumans to create a study in the field. So, what they achieved was the first of its kind. Maarten Steinbuch and Merijn Coumans, in cooperation with the Dutch-Belgium Tesla Forum, created a public spreadsheet entitled ‘MaxRange Tesla Battery Survey’ that allows Tesla drivers to post information about their remaining battery capacity. You can participate via the Google Document.

The project began in 2015, as of 29th November 2017, 396 users where participating.

Data in Focus

The first graph looks at the impact of kilometers driven and how it reduces battery capacity. We can see that the majority of Tesla drivers have achieved up to 100,000km and had a maximum loss of 10% battery capacity/range. A few outliers, however, have driven more than 200,000km and still have up to 90% battery capacity left.

Telsa Model S/X Mileage vs Remaining Battery Capacity

Source: Steinbuch, M. & Coumans, M. MaxRange Tesla Battery Survey.

The second graph looks at the impact of the age of the battery and how it reduces battery capacity. The majority of users have a 1-3-year-old battery with anything from 91% to 98% battery capacity/range remaining. We can again see a handful of users having up to a 5-year-old battery with around 95% capacity available.

Tesla Model S/X Battery Age vs Remaining Battery Capacity

Source: Steinbuch, M. & Coumans, M. MaxRange Tesla Battery Survey.

The data available here is far from full. However, patterns are beginning to emerge and provide valuable insight into EV battery capacity and lifetime.

Plug In America has a similar survey going on, and it has found roughly same results, despite the dataset being less comprehensive. Most drivers are retaining over 90% of original capacity. Outliers are getting even more impressive results – the shuttle service Tesloop reported in September that one of its Model S cars had passed the 200,000-mile mark, and had lost only 6% of its original range.

Developments

The average driver in the US travels 29 miles per day according to the Bureau of Transportation Statistics, however, range anxiety remains an obstacle for consumers.

Range anxiety

The 2012 Nissan Leaf had a range of 106 miles, equivalent to just over three times the average daily drive in the US. The 2018 edition of the Nissan Leaf is expected to have a range of up to 235 miles, a 220% increase on the 2012 model, and therefore range is constantly improving to address consumer concerns.

However, consumers may be more concerned with a shift in behavior. Charging an EV takes time, and unless you have fast in-home charging infrastructure or public charging infrastructure it will remain a barrier. Undoubtedly a point of address to boost EV adoption.

Are lithium-ion batteries the preferred choice?

Most of the EVs today run on lithium-ion batteries, the same technology that powers smartphones and laptops. Lithium-ion batteries have fallen in price by 80% in the last six years, according to McKinsey & Company. However, an EV battery pack are still relatively expensive, Chevy Bolt’s battery pack costs over $15,500 which makes up over 40% of the EV price.

Economies of scale will help drive the cost down further. Tesla’s claims, once the Gigafactory is at full capacity, it will reduce the battery costs a further 35% to $125kWh. Other Manufacturers are following suit with their battery factory, this ramp up in production will be the catalyst in bringing EVs into the market at competitive price points.

Fuel-cells are similar to batteries in that they produce electricity without combustion or emissions. However, like gasoline vehicles, they can run for over 300 miles on one tank, and refuel within minutes. At the Los Angeles Auto Show, Toyota announced they are building a renewable hydrogen generation station at the Port of Long Beach that will produce 1.2 tons of the fuel per day and 2.35 megawatts of electricity. While hydrogen fuel-cell is currently operating a fraction of market share, and lithium-ion batteries are the preferred choice, however, a desire exists to explore the opportunities in this technology.

It is not inconceivable to think that a few years down the line we are talking about a new battery compound, given the pace of technology.

There are challenges that EVs face before a material penetration can occur in the mass market. Developments in battery life, range, convenient charging, and competitive prices will be the catalyst in bringing EVs to the fore.

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