Solid-state batteries are the next big thing in batteries. However, the main challenge to be solved is the interface between the cathode and the electrolyte. An international team at the University of Bayreuth claims to have found a novel solution.
Safety of operation, longevity, and energy density: In these respects, solid-state batteries outperform conventional lithium-ion batteries with liquid electrolytes. A major problem preventing industrial applications – for example in electromobility – is the compatibility of the interface between the cathode and the electrolyte. An international team led by Prof. Dr Seema Agarwal, Professor of Macromolecular Chemistry at the University of Bayreuth, claims to have found a solution to this: a solid electrolyte that is only 7 µm thin and consists of a polymer-ceramic composite.
The solid electrolyte that the researchers have developed combines a polymer with ceramic nanofibres. This composite material is applied - similar to a coating - to the porous surface of the cathode. This fills the tiny cavities and forms a solid electrolyte that stably contacts the cathode.
In contrast to previous solid-state batteries, this new system features an electrolyte that encloses the cathode like a covering: Thus, the interface is significantly improved and offers the additional advantage of activating the ions in the cathode. Due to this modification of the interface, the new solid electrolyte increases the energy density as well as the energy storage capacity of the batteries.
Another major advantage of this ultra-thin solid electrolyte which interacts with the cathode is that it enormously increases the operational safety of the batteries. "Conventional lithium-ion batteries using liquid electrolytes always cause safety concerns," explains Prof. Dr Seema Agarwal. "The danger of leaking electrolyte is always looming, leading to short-circuiting and failure of the battery. Smartphones, laptops and electric vehicles have already caught fire because of this and caused serious accidents."
Agarwal continues: "An additional problem is the growth of dendrites, which can penetrate the electrolyte and lead to a short circuit or cause a fire. All these risks are eliminated or at least significantly reduced by our ultra-thin solid electrolyte, which is highly thermally stable."
The principal author of the study, Dr Sivaraj Pazhaniswamy, points out another advantage: "If a thermally stable solid electrolyte is used instead of a flammable liquid one, the advantages of lithium as an anode material can be fully exploited. Compared to other materials used in conventional liquid electrolyte batteries, lithium has very attractive properties, such as a high theoretical capacity and a low electrochemical potential."
Pazhaniswamy also provides an outlook: "Now that our new solid electrolyte has proven itself so excellently in its interactions with the cathode, we want to work towards optimising the contacts between electrolyte and anode with a similar system."
The Bayreuth team worked with research partners at the University of Chemistry and Technology in Prague and Jiangxi Normal University in Nanchang (China) to develop and test the new solid electrolyte.
S. Pazhaniswamy et al.: Hybrid Polymer Electrolyte Encased Cathode Particles Interface-Based Core–Shell Structure for High-Performance Room Temperature All-Solid-State Batteries. Advanced Energie Materials (2022), DOI: https://dx.doi.org/10.1002/aenm.202202981