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A Better Lithium Ion Battery Anode Found
September 1, 2016 | Leave a Comment
The National Institute for Materials Science (NIMS) researchers have developed an anode material for lithium-ion rechargeable batteries by forming nanoparticles made of silicon metal composites on metal substrates. The resulting anode material has a high capacity – almost twice as high as conventional materials – and a long cycling life. The results could lead to the development of higher-capacity, longer-life silicon anode materials for lithium-ion rechargeable batteries.
Scanning electron microscope image of a nanostructured silicon-metal composite developed in this study as a new anode material for Li-ion rechargeable batteries. Image Credit: National Institute for Materials Science. Click image for the largest view.
Currently, carbon-based materials are used as anodes for lithium-ion rechargeable batteries, and their capacities are up to 370 mAh/g. In theory, their capacities can be increased by more than 10 times to 4,200 mAh/g, provided that pure silicon is used as an anode material. However, pure silicon is highly expandable, swelling three to four times by volume, during the process in which lithium-ions are incorporated into it. Due to this property, pure silicon anode materials are prone to crack as a large amount of stress is applied to them during repeated charge-discharge cycles, and therefore the use of bulk pure silicon as an anode material severely shortens battery cycle life. Consequently, pure silicon had not been used up until recently.
Led by Naoki Fukata, a leader of Nanostructured Semiconducting Materials Group at the International Center for Materials Nanoarchitectonics, NIMS, and a research group at the Georgia Institute of Technology working as a joint research group formed one-dimensional germanium nanowires on metal substrates and then created nanostructured silicon metal composites using the nanowires as a base material layer.
The formed nanostructured material is characterized by numerous cavities existing inside aggregated nanoparticles of about several tens of nanometers to a hundred nanometers. There also are larger cavities present between the silicon metal composites and the germanium nanostructures. Another characteristic is that the material consists of not only pure silicon but also metal atoms (mainly iron) that are spontaneously provided from the substrate via the underlying germanium nanostructures and incorporated into the growing silicon material, forming silicon-metal composites.
Based on the evaluations of charge-discharge properties of fabricated samples, the research groups confirmed that the capacity of the new anode material was about double the capacity of current anode materials, and its cycle life was also extended compared to conventional materials.
The new material is capable of increasing both the capacity and life of lithium-ion rechargeable battery anodes. The research groups attained these features by regulating the composition of silicon and metal elements in the silicon-based nanostructure.
This is very promising research, a doubling of capacity would go far to make even more devices portable and more practical. While not a breakthrough so to speak, a doubling is a major advance, cutting the 10 fold possible improvement down to 5.
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