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Si nanowires on graphite for high-energy lithium batteries anode

Silicon is the most promising candidate for increasing energy density in the next generation of lithium-ion batteries. However, nanostructured Si-based materials are a technological challenge. Researchers in our laboratory with DEHT at CEA-LITEN have designed a composite that offers exceptional electrochemical performance. Using the microscopy tools of the MEM laboratory, our work is providing a better understanding of the promising engineering of these active composites at the nano- and microscales to design efficient Si-rich anodes.

Published on 22 September 2020
The lithium-ion batteries are prominent on most rechargeable electrical devices market today… and either as phone addicts, car drivers or wireless screwdriver users, we all ask for lighter batteries holding more cycles. This aim requires new materials with a higher capacity as lithium reservoir. The most promising material at the anode is silicon. It is used in the coming new generation of batteries, although at a low weight percentage (10%). At charge, silicon absorbs up to 3 times its volume of lithium, which ends up in inevitable movements in the electrode and thus a faster decay.

The article published in September 2020 in ACSNano by three teams of CEA-Grenoble from IRIG at the SYMMES and MEM laboratories and from LITEN at DEHT laboratory, deals with reducing this decay. It shows that part of these deleterious internal movements are reduced when silicon is grown as nanowires directly on graphite micropowder. Both graphite and silicon get lithiated at charge. Graphite absorbs part of the swelling due to silicon and maintains the electrode integrity. Electron microscopy of FIB cut electrodes show how the graphite flakes lying flat in the electrode layer orient the swelling movement vertically. This avoids electrode cracking at discharge. The composite anode material was optimized to fit present cathodes with a capacity of 1Ah/g. At 1/3 silicon in mass, it cycles up to full charge in 30 minutes for hundreds of cycles. Further work now deals with capacity loss in the first cycle.

Legend: Si nanowire anode on graphite: 87 % capacity retention after 250 cycles.

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