Wonderful Lithium-Ion Batteries
A few weeks ago, John Goodenough, Akira Yoshino and Stanley Whittingham won the 2019 Chemistry Nobel Prize for their work on Lithium-ion batteries (Li-ion).
Lithium-ion batteries have made our portable, cable-free, mobile world. From our mobile phones to cordless tools and electric vehicles, they are everywhere. They have a high energy density, can be charged quickly and thousands of times, and made in every conceivable shape and size.
But Li-ion batteries are not perfect. They are prone to catching fire if punctured or overcharged. In 2013 fires caused by faulty batteries grounded the entire Boeing 787 Dreamliner fleet.
They use relatively expensive materials and must be stored with at least 30% charge to avoid damage, so you can’t get the maximum theoretical power out of them.
At the Cenex Low Carbon Vehicles show held at Millbrook in September, batteries were a major topic. Everybody wants the same thing:
- Bigger capacity to give more range
- Improved safety
- Using cheaper and more sustainable materials.
The search for better batteries for electric vehicles
Lots of innovation was on show; particularly in the Faraday Battery Challenge. This £248m UK Government programme covers everything from new battery chemistries, through improved integration of battery systems, to scaling up manufacturing.
This programme has some ambitious performance targets:
- Reducing cost from $280/kWh to $100/kWh
- Increasing power density from 250Wh/kg to 500Wh/kg
- Improving charging rate from 3kW/kg to 12kW/kg
- Increasing battery life from 8 to 15 years
- Improving recyclability from the current 10% – 50% up to 95%
- Eliminate the possibility of thermal runaway and give batteries a wider operating range of temperature
Delivering this by the 2035 target date would give us batteries that are one third the cost, double the capacity, double the life, capable of being charged four times faster, safe and recyclable. That is a game-changer for the electric vehicle market.
Innovators are exploring many different ideas. One is to get rid of the fire-prone liquid electrolyte by making fully solid-state batteries. This will dramatically improve safety and will increase capacity by allowing cells to be thinner.
Another is to use different electrode materials inside the battery where the chemical reaction that generates the electricity happens. Current electrodes use expensive and environmentally damaging materials like cobalt. Nano-structuring readily available electrode materials could give better performance. Some projects are targeting doubling the energy density of batteries over the next few years.
It’s a matter of chemistry
You can also improve performance by changing the chemistry. So as NiCd changed to Li-ion we can expect to see new battery names entering the market.
One type being actively developed is Lithium-Sulphur batteries. These are light and hold a lot of energy. Airbus have used them in solar powered unmanned planes that are being tested as alternatives to satellites as a platform for earth observation and communications. They have already flown for 25 days continuously; day and night. The lifetime is not good enough for electric vehicles yet, so that is the research focus.
Another interesting chemistry is Sodium-ion (Na-ion) batteries. Na-ion batteries have some important advantages. The materials used are cheaper and more abundant. Na-ion batteries are much safer; they don’t go into thermal runaway on charging and don’t burst into flames if damaged. Unlike Li-ion, they can be completely discharged without becoming unusable. That means they are much easier and safer to transport, and you get more power out of the same weight of battery. At the moment, the energy density is not as good as Li-ion, but companies like Faradion and LiNa Energy are working hard to produce batteries that can compete in the electric vehicle market.
Electric vehicle batteries are hot!
The final big theme I spotted was heat management. Fast charging and discharging a powerful battery means pushing large currents into the battery and pulling large currents to drive the motors. Large currents mean the batteries get hot. Push too hard and the battery overheats and stops working properly. With Li-ion there is the risk of thermal runaway and fires. Na-ion batteries can operate at higher temperatures and don’t suffer from thermal runaway, but they can still be killed if they get too hot.
To overcome the problem a lot of work is going into battery monitoring and management systems that can control the charging and discharging of each cell in the battery; getting the best performance without risking the battery. Together with cooling systems to carry waste heat away from the cells, this gives the best balance between energy delivery and battery degradation.
I don’t know which combination of the innovations in the pipeline will successfully commercialise, but we can look forward to big improvements in battery capacity, safety and sustainability in the coming years.