Today, lithium-ion batteries in an electric car need around half an hour to charge themselves to at least 80 percent at fast charging stations. This shouldn’t happen too often, as the high levels of heat generated during fast charging affect the performance and service life of the power storage system. Now researchers led by Clare Gray from Cambridge University in the UK were looking for a solution to both problems.
On the basis of many years of basic research, they found the anode material niobium tungsten oxide (NWO) to be a good alternative to the otherwise used graphite. The first prototypes of the lithium-ion batteries with NWO anode could actually be charged in less than five minutes to more than 90 percent of their charging capacity with reduced heat generation. This result was honored as a “breakthrough for next-generation batteries” at this year’s Falling Walls conference in Berlin last week.
It’s about the mobility of lithium ions
In their work, Gray and colleagues focused on the electrochemical reasons why lithium-ion batteries have not yet been able to be charged significantly faster. They discovered that the lack of mobility of the lithium ions plays an important role in this. “And if lithium-ions can’t move well, the battery gets warm too,” says Gray. This is absolutely critical, as the stability and longevity of the power storage system suffer at temperatures of more than 60 degrees Celsius. But niobium tungsten oxide now showed exactly the desired mobility: lithium ions could move and store in this metal oxide many times faster than in graphite. As a yardstick, Gray chose the diffusion length of the lithium ions, which was one micrometer for graphite and 33 micrometers for niobium tungsten oxide over a period of three minutes.
In prototypes that are already well developed, the researchers replaced graphite with niobium tungsten oxide. For the cathode they chose commercially used materials such as lithium iron phosphate (LFP) or lithium nickel manganese cobalt oxide (Li-NMC-622). The storage capacities showed values comparable to those in batteries with anodes made of graphite. But the loading times were drastically reduced to less than five minutes. At the same time, the batteries only heated up to a maximum of 40 degrees Celsius. Even after several hundred charging cycles, the prototypes retained a high storage capacity of around 90 percent. The researchers are now striving for a drastically longer service life of more than 10,000 charging cycles.
For the path to series production, Clare Gray and colleagues founded the Nyobolt company in Cambridge. After the first test runs of the fast-charging lithium-ion battery with vacuum cleaner robots and toy cars, practical use in Formula E racing cars could soon follow. Initial contacts have already been made. But Clare Gray has other goals in mind. She wants to increase the sustainability of electric cars by not being powered by ever larger, but consciously by smaller and therefore fast-charging batteries. “If you can rely on fast charging at many stations, then you will also accept smaller and more sustainable batteries,” says Gray.