Novel germanium-carbon anode for high-capacity lithium-ion batteries

Lithium-ion batteries (LIBs) are currently the most popular electrical energy storage devices worldwide, powering most electronic devices from smartphones to electric cars. Their success lies in their high storage capacity and fast rechargeability. While these properties have already established them as the dominant energy storage device in the market, there is still room for improvement.

A lithium-ion battery consists of a positive terminal, called a cathode, a negative terminal, called an anode, and an electrolyte between them to facilitate the transfer of charges. Improving the materials used in these components can further boost the performance of LIBs. Among these, one key area of improvement is improving anode materials. Current commercial LIBs use graphite-based carbon anodes due to their stable charging cycle performance and low cost. However, the lithium (Li)- storage capacity of graphite is limited. Alternatively, materials like silicon (Si) and germanium (Ge) offer much higher Li-storage capacities and can lead to more efficient LIBs. Unfortunately, Si and Ge form alloys with Li during charging, resulting in a 400% volume expansion that can rapidly degrade the storage capacity of LIBs.

To address this issue, a team of researchers from Japan, led by Dr. Giichiro Uchida from the Department of Electrical and Electronic Engineering at Meijo University, have now developed an innovative new multilayered nanostructured Ge/carbon(C) anode. “A promising method for addressing the expansion problem of Ge anodes is fabricating a Ge nanostructure on a copper current collector. This allows the Ge nanoparticles to freely expand while alloying with Li during charging, without any detrimental effects. Leveraging this method, we developed a binder-free nanostructured Ge-C multilayered anode demonstrating high capacity and high-capacity retention,” explains Dr. Uchida. Their findings were published in Volume 17, Issue 2 of Applied Physics Express on February 23, 2024.

This novel anode comprises multilayered C (top)/Ge (middle)/C (bottom) nanostructured anode film with grain sizes of 10–20 nanometers, fabricated on a Cu anode substrate using a special plasma co-sputtering method. Moreover, to study comparative performance, the researchers also fabricated a Ge monolayer anode and a Ge-C mixed film anode. They then tested the performance of the batteries with the different anodes, along with the traditional graphite anode battery, using a battery test apparatus at room temperature.

Tests revealed that the multilayer C/Ge/C anode showed much better performance than other anodes with a high discharge capacity of 910 mAh g^-1, significantly higher than the traditional graphite-based anode. Furthermore, the multilayered anode showed no reduction in capacity even after 90 charging cycles.

“These results suggest that a carbon stacking structure of Ge as an active material, is effective for realizing high capacity and high cycle in next-generation LIBs. Imagine using smartphones for a whole week before charging! Our study shows that by carefully controlling the materials and interfaces inside LIBs, we can dramatically improve battery capacities”, says Dr. Uchida, emphasizing the significance of the study.

In conclusion, this study marks a significant step towards realizing efficient LIBs with long lives, potentially reducing energy demand and promoting the adoption of electric vehicles. This, in turn, can lower carbon emissions and foster a more carbon-neutral and environment-friendly society.