Lithium ion batteries have been around for a long time, but it’s becoming clear that changes in their chemistry and a rethink of the way they’re incorporated into cars will yield major improvements.
Volvo’s first-generation battery uses dual layers of standardised modules. The nickel content of the cathode (the nickel-based positive electrode) has been raised and the reliance on cobalt reduced; and work is ongoing to improve the anode (the graphite-based negative electrode) by adding silicon to improve energy density. Volvo hopes these improvements will give its second-generation battery, due in 2024, an energy density significantly above 700Wh per litre.
The next step will bring more new materials into play up to pure-lithium anodes – the holy grail in terms of lithium ion battery development. That has so far proved impossible, due to the formation of tendril-like ‘dendrites’ on the anode, which will eventually short out the cell. Lithium-metal anodes would represent a huge leap in battery design, giving an energy density of around 1000Wh per litre, which Volvo says would “approach real solid-state batteries”.
The credit for that goes to the company’s new Swedish battery development partner, Northvolt, which acquired Silicon Valley start-up firm Cuberg early this year for its lithium-metal battery technology, which was originally aimed at powering aircraft.
Cuberg’s new electrolyte prevents issues with lithium-metal anodes, the use of which it says can increase battery capacity and range by 70% over conventional lithium ion technology. This invention should appear in Volvo EVs by the second half of this decade.
Volvo’s current standardised-module batteries will be replaced by types giving a flat floor and then, by a third generation, dispensing with what Volvo calls “putting a box in a box” and becoming a structural part of the floor. To do that, the prismatic cells will be housed in aluminium and then glued together to form a sealed-for-life unit.
Other improvements, such as a reduction in the internal resistance and improved thermal management of batteries in the third generation, plus an 800V architecture, should yield a 10-80% charging time of only around 15 minutes.
Volvo is confident that quality has reached a level at which the need to replace modules (already a rare occurrence) will be all but non-existent. Integration with the car’s structure is expected to reduce weight to the extent that the whole vehicle energy density will increase another 20%, further upping range to between 550 and 590 miles.
Batteries are already being produced at a Northvolt site with a 15GW annual capacity, which is enough for some 150,000 cars. The partners plan a new 50GWh factory making enough batteries for 500,000 cars per year.