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The adoption of EVs is being pushed by governments to help reduce emissions and improve air quality while lessening our reliance on fossil fuels.
But, before the vehicles have even managed to embed themselves in our daily lives, some people are already talking about what battery technology will power them next: lithium-air, lithium-sulphur and solid-state systems are just some of the examples. As innovative as those systems could be, they are all still under development and their application lies far in the future. Now and for the foreseeable future we will rely on lithium-ion batteries.
We’ve been using Li-ion for 30 years in mobile phones, computers and power tools. But the car has been a bigger challenge for the technology.
Performance boosted
Electric vehicle range and recharge times have been an issue because we’ve grown so used to an abundance of petrol stations and the ability to drive hundreds of miles on each tank of fuel. But lithium-ion battery development is catching up.
“Lithium-ion batteries have seen a 6% energy density improvement on an annual basis over the last several years,” says Phillip Weicker, head of powertrain at California EV start-up Evelozcity.
Energy density has been key. The Nissan Leaf, arguably the first mass-market EV when it was launched in 2010, had a range of 100 miles from its 24kWh battery pack, according to the then official New European Driving Cycle (NEDC) test. The current Leaf manages 235 miles from its 30kWh pack. And newer vehicles will go even further.
“A lot has been done on power, density, recharge times, weight and size but more still needs to be done. In future generations of products, it’s hoped that we’ll be able to get great performance in more of these areas,” says Weicker.
Jaguar Land Rover first introduced Li-ion batteries to its vehicles with its hybrid Range Rover SUV in 2013. Today the company has its first battery-electric vehicle on the road, the Jaguar I-Pace. It uses a 90kWh battery pack to give a range of 292 miles (the change in the test cycle from NEDC to the Worldwide Harmonised Light Vehicle Test Procedure, WLTP, has reduced official range figures as the testing has become more stringent).
“Lithium-ion developments were mainly focused on increasing the cell energy density (Wh/kg) and power density (W/kg). These translate as increased range and performance capability respectively, and these were obtained predominantly by cell active material and technology development,” says Dr Valentina Gentili, batteries specialist at Jaguar Land Rover.
Batteries aren’t the perfect solution - there are issues around recycling, energy density and sourcing of materials. A lot of effort has been focused on the development of active material chemistries that increase energy density. These developments include increased nickel content in the positive electrode material, and the introduction of silicon oxide compounds to the negative electrode material.
And the work continues, because, as Weicker and Gentili agree, there is a lot more to come from Li-ion batteries.Gentili says: “There is still a lot of work dedicated to advancing Li-ion, not only in the material chemistry, but also in cell design and engineering aspects. The most obvious gains from material development are to the energy stored, the power delivered and the rate of charging. There are also key gains being made in advanced cell engineering to safety, power capability, and life.”
Still out front
It’s likely that Li-ion will remain dominant for the next decade. Weicker says: “We’ll still see a majority of battery-powered vehicles using liquid-electrolyte lithium-ion battery technologies, maybe 70 or 80%, a little bit of the tail end of nickel-metal hydride based hybrids, and emerging ‘beyond lithium-ion’ technologies starting to show up in 10 years’ time.” Li-ion batteries will remain key to weaning us off the combustion engine.
Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.