Scientists in South Korea have recently designed a new kind of electrode structure specifically for all-solid-state secondary batteries.
Implementation of this latest technology may considerably boost the energy density of the batteries when compared to present-day technologies and thus contribute significantly to the advancement of high-performance secondary batteries.
After detecting the mechanism of facile diffusion of lithium ions between active materials, a collaborative research group had successfully developed a novel electrode structure for all-solid-state secondary batteries. The researchers were from the Electronics and Telecommunications Research Institute (ETRI) and Daegu Gyeongbuk Institute of Science and Technology (DGIST).
This breakthrough received global recognition when the results of the study were published by an international online academic journal, the ACS Energy Letters, which focuses on the energy sector and is operated by the American Chemical Society (ACS).
Secondary batteries are different from primary cells that can be used only once and can never be used again. These batteries can be recharged and used multiple times. With the latest developments in electronic devices, the significance of secondary battery technology to electric cars, robots, drones, and energy storage systems (ESS) is growing every year.
As a next-generation energy storage device, the all-solid-state secondary battery makes use of a solid electrolyte to transport ions inside battery electrodes. Besides this, solid electrolytes are safer when compared to liquid electrolytes, which tend to cause a fire. Solid electrolytes can also be used in a bipolar-type secondary cell to boost energy density through an easy battery configuration.
In the case of the traditional all-solid-state secondary cell, its electrode structure includes an active material that is responsible for preserving energy; a solid electrolyte that is responsible for conducting ions and is also a conductive additive that enables the conduction of electrons; and a binder that holds these two constituent parts chemically and physically.
But systematic experiments performed by the ETRI team revealed that ions are also transported between graphite active material particles. This made the team recommend a novel type of electrode structure for an all-solid-state secondary cell that contains only the binder and the active material.
The investigators confirmed the probability that the performance of an all-solid-state secondary cell would be superior even when the electrodes lack a solid electrolyte additive.
To verify the hypothetical feasibility of the new structure recommended by the ETRI team, a virtual model was subjected to electrochemical testing (using a supercomputer) at DGIST. The ETRI team successfully demonstrated the new structure in a real experiment.
ETRI dubbed this novel technology “diffusion-dependent all-solid-state electrode” and later submitted an article to an international journal.
In case the novel technology developed by ETRI is implemented, solid conduction additive material will no longer be required in the electrode; rather, the more active material can be integrated into the same volume.
To put this in simple terms, the amount of active material present in the electrode can increase as much as 98wt% and, consequently, the energy density can be increased by 1.5 times when compared to the traditional graphite composite electrode.
The new technology also provides benefits in manufacturing process aspects. Sulfide-type solid electrolytes, which are known to have moderate plasticity and high ion conductivity, are considered a superior candidate for developing all-solid-state batteries.
However, because of its high chemical reactivity, the sulfide-type solid electrolytes provide very minimal options to battery developers when it comes to binders and solvents.
On the other hand, with the latest electrode developed by the ETRI team, battery developers can easily choose the type of binder and solvent to utilize in the battery. This is because the electrode does not contain highly reactive solid electrolytes. This also allows investigators to look for new strategies to enhance the performance of all-solid-state secondary cells.
We have revealed for the first time that ions can be diffused just with active materials. We are no longer bound to the structure used in existing all-solid-state secondary cells. We plan to develop secondary cells with even high energy densities, using this technology. We will also secure our rights to the core technology and work on a version that could be commercialized.
Dr Young-Gi Lee, National Research Council of Science & Technology
Young-Gi had participated in the study.
While the ETRI team performed its study using graphite cathode active material, they are planning to continue the analysis based on the same idea, using numerous other electrode materials.
The researchers are also planning to improve the new technology to boost efficiency. This can be achieved by reducing the volume of electrodes and removing the interfacial problems between electrodes.
Kim, J. Y., et al. (2020) Diffusion-Dependent Graphite Electrode for All-Solid-State Batteries with Extremely High Energy Density. ACS Energy Letters. doi.org/10.1021/acsenergylett.0c01628.