Improved cathode material for electric vehicle batteries delivers up to 25% more power for longer driving

Improved cathode material for electric vehicle batteries delivers up to 25% more power for longer driving

Scanning electron microscopy images at different magnifications revealed the spherical morphology of the NMC622 powder particles, one of two materials synthesized by the Skoltech researchers in the study. Images are relatively sparsely arranged by particles for better visibility, but their spherical morphology means that in actual batteries they can be compressed to a greater extent than conventional octahedral particles. , so the material will provide more energy density per unit volume, shrinking the battery in which it is used. Credits: Ivan Moiseev et al./Energy Advances

Skoltech researchers have developed a new material for the lithium-ion batteries that power electric vehicles. With extremely high energy density, the new cathode material promises longer driving range on a single charge. Reported in Energy progress and patented with Rospatent, the material is a familiar nickel-rich layered transition metal oxide, but with a modified microstructure to hold more energy per unit volume.

Principal investigator Professor Artem Abakumov from Skoltech Energy commented: “Cathode materials are an important bottleneck regarding electric vehicle batteries. “The negative terminals in the power supply battery Electric Car tend to use multiple layers transition metal oxide, including those rich in nickel. We have improved two commonly used materials of this class, achieving an increase in energy density from 10% to 25%. This translates into a smaller cathode, a more compact battery and therefore a greater capacity to store energy for the same volume. As an added bonus, the material is slower to deteriorate. “

The layered oxide originally used in the cathode of a battery has the formula LiCoO2. In the materials used today, some cobalt atoms are replaced by nickel and manganese. These materials are known by technical names like NMC811, where the numbers reflect the ratios between the three elements in the chemical formula — for example, eight nickel atoms to one manganese atom and one atom. cobalt. Without their change Chemical compositionSkoltech researchers have improved NMC811 and its cousin NMC622 by refining the material’s microstructural organization.

Conventional NMC is a powdery polycrystalline material, which means that each secondary grain is made up of randomly oriented particles. The crystal structure inside any given particle is almost perfect, but since no two particles fit perfectly, some empty space is bound to appear at the grain boundary. Monocrystalline copies of polycrystalline NMC are just as the name suggests: Each powder grain is essentially a large bead with no voids in it. These single crystals are usually octahedral in shape.

“Our material is monocrystalline NMC with spherical particles, which combines the best of both worlds when it comes to density maximization. Unlike polycrystalline, powder particles have no lateral structure. in, so there’s no wasted space at the grain boundaries.But Alternatively, you can also pack more spherical monocrystals into the same limited volume than you can with octahedral crystals, because so you also get higher density on that account,” said Skoltech study co-author Aleksandra Savina.

Besides denser packing, the spherical shape of the crystal reduces the contact area with the electrolyte, minimizing unwanted interactions over time that cause cathode degradation due to crack formation. in the particles of ordinary NMC. This will prolong the operating life of the cathode and the battery in general.

To change the layered oxide morphology, the Skoltech researchers adapted the synthesis process, which is based on the so-called flux method.

Typically, you start with a uniformly distributed nickel, manganese, and cobalt precursor. You mix lithium hydroxide or some other source of lithium and incubate at high heat.

“What we do is, after we add a lithium-containing compound, we also mix in an inert salt that has a low melting point, and we melt that mixture and annealing it at a high temperature. Then we Rinse the salt and incubate again to remove the product of any unwanted reactions with the water.But it is important that depending on what inert salt is used and how much, the geometry of the particles will change. On the other hand, with conventional synthesis, you can’t really do much to affect the morphology,” explained study co-author and Alina Pavlova, a Skoltech Master’s student.

The team identified salt parameters that promote spherical particle formation. Tests confirm that the resulting material has the same energy storage capacity per unit mass as commercial analogues but has power densityallowing more power to be packed into the same confined space.

When asked about future plans, the researchers said they plan to experiment with particle size, combining smaller and larger spheres to create an even denser packaging. The team will also pursue layered transition metal oxides that can replace more cobalt and manganese atoms with nickel, further improving energy storage.

New cathode design solves major barrier to better lithium-ion batteries

More information:
Ivan A. Moiseev et al., Ni-rich monocrystalline NMC cathode material for lithium-ion batteries with high volumetric energy density, Energy progress (In 2022). DOI: 10.1039 / D2YA00211F

Quote: Improved cathode material for electric vehicle batteries providing up to 25% more power for longer drives (2022, October 18), retrieved October 18, 2022 from https://techxplore. com/news/2022-10-cathode-material-electrical-vehicle-bataries.html

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