Research into next-generation batteries involves continuous experimentation with alternative materials that might unlock significant performance gains, and a new breakthrough offers a compelling example of what this could look like. Scientists at the University of Twente in the Netherlands have produced an experimental lithium-ion cell that features a novel electrode design with an "open and regular" crystal structure, which they say allows for charging at 10 times the speed of today's devices.
The lithium-ion batteries that power today's electric vehicles, smartphones and countless other devices feature two electrodes, the cathode and the anode, and this new study focuses on the latter. Currently these anodes are made out of graphite, which serves them well in many ways but are unable to accommodate ultra-fast charging rates without breaking down.
One place scientists are looking to for new and improved anodes is in materials featuring nano-scale porous structures. Anodes of this nature promise greater contact area with the liquid electrolyte that transports the lithium ions, while enabling the ions to diffuse more easily into the solid electrode material, ultimately making for a device that charges much, much faster.
But there are shortcomings with the materials proposed so far. The disorganized and random nature of the channels in the porous nanostructure can cause those structures to collapse during charging, while also reducing the battery's density and capacity, and can cause lithium to build up on the anode surface and degrade its performance with every cycle. Further, manufacture of these materials is complicated, involves harsh chemicals and produces significant chemical waste.
The University of Twente scientists believe they have found a suitable alternative in a material called nickel niobate. As opposed to the irregular nature of previous solutions, nickel niobate features an "open and regular" crystal structure with identical, repeating channels for ion transport.
The researchers integrated this nickel niobate anode into a full battery cell and tested its performance, finding that it offered ultra-fast charging rates 10 times faster than today's lithium-ion batteries. They also note that nickel niobate is more compact than graphite and therefore has a higher volumetric energy density, which could equate to commercial versions of the cell that are lighter and more compact.
The scientists also report the new anode material has a high capacity, of around 244 mAh g−1, and because the volume change within the nickel niobate is minimal during operation, 81 percent of its capacity was retained across 20,000 cycles. All of this takes place without damage to the anode material, while the manufacturing process for nickel niobate is also said to be far more straightforward than other nanostructured materials and doesn't require a cleanroom to put together.
According to the researchers, these results demonstrate the energy storage potential of nickel niobate anodes in practical battery devices. They see immediate potential in grid applications to power electric machinery in need of fast charging, or in heavy electric vehicle transport. To see them adapted for use in standard electric vehicles, however, they say some further research and problem-solving will be required.
The research was published in the journal Advanced Energy Materials.
Source: University of Twente
