Anode material allows for fast-charging Li-ion batteries
To overcome the slow charging times of conventional lithium-ion (Li-ion) batteries, scientists from the Japan Advanced Institute of Science and Technology (JAIST) have developed a new anode material that allows for ultrafast charging — one that retains most of its initial capacity over thousands of cycles. The team’s findings, published in the journal Chemical Communications, should pave the way to fast-charging and durable batteries for electric vehicles (EVs).
In order to make EVs a more attractive alternative for drivers, the charging time needs to be substantially reduced — from the current time of around 40 minutes to below 15 minutes. One way to shorten the charging time of Li-ion batteries is to increase the diffusion rate of lithium ions, which in turn can be done by increasing the interlayer distance in the carbon-based materials used in the battery’s anode. While this has been achieved with some success by introducing nitrogen impurities (‘nitrogen doping’), there is no method easily available to control interlayer distance or to concentrate the doping element.
Against this backdrop, JAIST scientists recently developed an approach for anode fabrication that could lead to extremely fast charging of Li-ion batteries. Their strategy constitutes a relatively simple, environmentally sound and highly efficient way to produce a carbon-based anode with very high nitrogen content. The precursor material for the anode is poly (benzimidazole), a bio-based polymer that can be synthesised from raw materials of biological origin. By calcinating this thermally stable material at 800°C, the team managed to prepare a carbon anode with a record-setting nitrogen content of 17% in weight. They verified the successful synthesis of this material, and studied its composition and structural properties using a variety of techniques.
To test the performance of their anode and compare it with the more common graphite, the researchers built half cells and full cells, and conducted charge–discharge experiments. The proposed anode material proved suitable for fast charging, thanks to its enhanced lithium-ion kinetics. Moreover, durability tests showed that the batteries with the proposed anode material retained about 90% of its initial capacity even after 3000 charge–discharge cycles at high rates, which is considerably more than the capacity retained by graphite-based cells.
“The extremely fast charging rate with the anode material we prepared could make it suitable for use in EVs,” said team leader Professor Noriyoshi Matsumi. “Much shorter charging times will hopefully attract consumers to choose EVs rather than gasoline-based vehicles, ultimately leading to cleaner environments in every major city across the world.”
Another notable advantage of the proposed anode material is the use of a bio-based polymer in its synthesis. As a low-carbon technology, the material naturally leads to a synergistic effect that reduces CO2 emissions further. Additionally, Professor Matsumi said, “The use of our approach will advance the study of structure–property relationships in anode materials with rapid charge–discharge capabilities.”
Modifications to the structure of the polymer precursor could lead to even better performance, which might be relevant to batteries in portable electronics as well as EVs. Finally, the development of highly durable batteries should decrease the global consumption of rare metals, which are non-renewable resources.
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