An electrode design inspired by the structure of an egg - with a solid shell on top and a soft yolk-like substance inside - could protect li-ion batteries against degradation in repeated recharge cycles.
The innovation by a team from the Massachusetts Institute of Technology (MIT) and Tsinghua University in China could lead to "drastic" improvements in the battery life cycle and provide a dramatic boost in capacity and power, the researchers said.
Described in the latest issue of the Nature Communications journal, the technology uses a titanium oxide-based nanoparticle coating separating two soft aluminium-based electrodes.
The advantage of the aluminium is that it can expand and shrink without sustaining any damage.
In conventional li-ion batteries, electrodes degrade over time due to the repeated cycle of shrinking and expanding they have to go through with every recharge. During the process, the electrodes frequently double in volume, which leads to damage in the surface layer.
Current rechargeable batteries usually rely on graphite anodes that offer storage capacity of 0.35 ampere-hours per gram. The aluminium could offer up to 2 ampere-hours per gram, while being reasonably cheap at the same time. The problem is that in conventional designs, the aluminium expands and shrinks a lot, which can cause electrical contacts to disconnect.
Also, the liquid electrolyte in contact with aluminium will always decompose at the required charge/discharge voltages, forming a skin called the solid-electrolyte interphase (SEI) layer. This would be OK, if not for the repeated large volume expansion and shrinkage that cause SEI particles to shed. As a result, previous attempts to develop an aluminium electrode for lithium-ion batteries have failed.
“We made a titanium oxide shell that separates the aluminum from the liquid electrolyte,” said Professor Ju Li.
The shell does not expand or shrink much, Li says, so the SEI coating on the shell is very stable and does not fall off and the aluminium inside is protected from direct contact with the electrolyte.
In testing, the novel batteries demonstrated three times the capacity of those with graphite-based electrodes and their insides were free from any build-up, even after 500 recharge cycles. Moreover, the batteries were fully charged in just six minutes.
According to the researchers, all the materials used are inexpensive and the manufacturing method could be simple and easily scalable. They said the material would be particularly suitable for high-power and high-energy density applications.