Solid-state batteries are considered a key technology for the next generation of energy storage devices. They could offer higher energy densities, improved safety and a longer service life than conventional lithium-ion batteries – properties that are particularly important for electric vehicles and stationary energy storage devices. In practice, however, these advantages have not yet been fully exploited.
A recent publication in the renowned journal Chemical Reviews – one of the world's most cited scientific journals with an impact factor of 55.8 – analyses the key mechanisms that limit ion transport in solid-state batteries and describes strategies for improvement. It was written by Jianneng Liang and Alberto Varzi from the Helmholtz Institute Ulm (HIU) and Meisam Hasanpoor and Stefano Passerini from the AIT Austrian Institute of Technology.
Why solid-state batteries have not yet reached their full potential
The study shows that simple substitution – such as replacing liquid electrolytes with solid ones – does not automatically lead to more powerful batteries. In order to achieve the desired high energy density, the electrodes must contain as much active material as possible. At the same time, however, their properties are limited by several factors: Ions can only move relatively slowly in solid electrolytes, the contact surfaces between the electrolyte and the active material are often insufficient, and lithium-ion transport within the materials is also sluggish. Added to this are manufacturing challenges. It is therefore crucial to reduce the internal resistance and transport barriers for lithium ions in the active material. This is the only way to achieve higher effective current densities and reduce the disadvantages typical of solid-state batteries.
Various sophisticated imaging and measurement techniques are used to investigate the mechanisms, including high-resolution electron microscopy, synchrotron X-ray techniques, magnetic resonance imaging and neutron radiation-based analyses. These techniques make it possible to observe ion movements in real time, identify bottlenecks and reveal structural weaknesses in the electrodes.
Ways to achieve more powerful solid-state batteries
The paper also summarises strategies for improving ion transport in solid-state electrodes: targeted particle design by combining small electrolyte particles with larger active particles, optimised electrode architectures with layers, channels or material gradients, interface optimisation through coatings or doping, and new manufacturing processes, in particular solvent-free (‘dry’) processes. The latter are the focus of the AIT-led HyLiST project, which is developing more powerful and sustainable electrolytes for polymer batteries.
The publication also addresses the challenges of industrial manufacturing. Solid-state batteries are sensitive to moisture and process chemicals, and mechanical stresses occur that can lead to cracks and capacity loss during the charging and discharging cycle. The paper therefore provides clear guidance on how material selection, electrode structure and manufacturing processes interact to make solid-state batteries stable, powerful and industrially scalable in the long term.
This comprehensive review supports the scientific and industrial community in developing solid-state batteries with ultra-high energy density and shows ways in which the technology can be put into practice for electric vehicles and stationary energy storage.