Researchers in South Korea have developed an electrode structure for rechargeable solid-state batteries that could increase the energy density significantly by eliminating the electrolyte.
The electrode structure of a conventional all-solid-state secondary cell consists of a solid electrolyte responsible for ionic conduction, a conductive additive that provides the means for electron conduction; active material responsible for storing energy; and a binder that holds these constituent parts physically and chemically.
A joint research team from Electronics and Telecommunications Research Institute (ETRI) and Daegu Gyeongbuk Institute of Science and Technology (DGIST) discovered that ions are transported even between graphite active material particles. So they proposed a new type of graphite diffusion electrode structure for a solid state secondary cell consisting of only the active material and the binder. The researchers confirmed the possibility that even without a solid electrolyte additive within the electrodes, the performance of an all-solid-state secondary cell could be superior.
The theoretical feasibility of the novel structure proposed by ETRI was verified at DGIST through electrochemical testing (using a supercomputer) of a virtual model. ETRI researchers succeeded in demonstrating this structure in an actual experiment. ETRI named this technology ‘diffusion-dependent all-solid-state electrode’ and submitted a paper to an international journal.
If ETRI’s technology is adopted, solid conduction additive material will become unnecessary in the electrode; instead, the more active material can be squeezed into the same volume. In other words, the amount of active material in the electrode can increase by up to 98wt% and as a result, the energy density can be made 1.5 times greater than the conventional graphite composite electrode.
The technology offers advantages in manufacturing process aspects as well. Sulfide-type solid electrolytes, which have high ion conductivity and moderate plasticity, are regarded as an excellent candidate for the fabrication of all-solid-state batteries. But due to its high chemical reactivity, these have limited options when it comes to solvents and binders. In contrast, with the new ETRI electrode, developers can freely select the type of solvent and binder to use in the battery because the electrode contains no solid electrolytes that are highly reactive. This also permits researchers to pursue new approaches for improving 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,” said researcher Dr. Young-Gi Lee.
Although ETRI conducted its research using graphite cathode active material, it intends to continue its research based on the same concept, using various other electrode materials. It is also planning to enhance the technology in order to increase efficiency. This can be accomplished by eliminating the interfacial issues between electrodes and thinning the volume of electrodes.
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