New research from the Lawrence Livermore National Laboratory has found that hydrogen can greatly improve both the capacity and conductivity of lithium-ion batteries. The research could also pave the way for better storage mediums for several energy options, including hydrogen itself.
The new developments center around treating the graphene nanofoam anodes of lithium-ion batteries with hydrogen.
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Graphene materials are prolific in commercial production for a variety of uses, including many types of energy storage devices like li-ion batteries. The most common is 3D graphene nanofoam, which is used in many types of electrical and chemical storage media including hydrogen tanks, supercapacitors, energy sorbents, and lithium batteries. They’re also used in filtration, insulation, and desalination systems. All of these could see improvement through this research, the scientists believe.
Atomic hydrogen is leftover in graphene production, but its role in electrical storage applications is not all that well understood. Hydrogen adsorbents are known to affect the structure of graphene and it’s also known that graphene that is without hydrogen contaminants is not conductive and actually works as an insulator, counter to the requirements of batteries. The goal at LLNL has been to figure out how hydrogen interacts with graphene during production and how it can be manipulated to improve the graphene’s qualities for storage media.
The team's experiments involved treating the graphene with hydrogen at low temperatures. This results in defects in the graphene being exploited by the hydrogen, causing small openings that allow easier lithium penetration. In a li-ion battery, this improves both transport of power out of the battery as well as power absorption characteristics. In addition, because the lithium can more easily bind near the edges of the graphene material, thanks to the hydrogen’s effects, overall capacity is improved.
Electrochemical characteristics of 3D GNFs. (a) Charge/discharge rate jump experiments show the improved rate performance after H2 treatment. (b) The percentage capacity enhancement at different charge/discharge rates before and after H2 treatment. The inset is the anodic differential capacity curves at various current densities at fifth cycle. (c) Coulombic efficiency of three representative GNF samples. Note that enhancement of Coulombic efficiency after H2 treatment. (d) Nyquist plots in impedance measurement imply easier charge transfer after H2 treatment. Ye et al
"We found a drastically improved rate capacity in graphene nanofoam electrodes after hydrogen treatment," said LLNL scientist Brandon Wood. "By combining the experimental results with detailed simulations, we were able to trace the improvements to subtle interactions between defects and dissociated hydrogen. This results in some small changes to the graphene chemistry and morphology that turn out to have a surprisingly huge effect on performance."
The authors point out that their experiments do not answer some key questions, such as how to optimize defect density and how best to incorporate hydrogen in graphene materials to achieve higher energy density in lithium-ion batteries specifically. Further studies are planned to continue the work.
The research paper was this month published in Nature Scientific Reports.