6 research outputs found
Designing Cathodes and Cathode Active Materials for Solid‐State Batteries
Solid-state batteries (SSBs) currently attract great attention as a potentially safe electrochemical high-energy storage concept. However, several issues still prevent SSBs from outperforming today\u27s lithium-ion batteries based on liquid electrolytes. One major challenge is related to the design of cathode active materials (CAMs) that are compatible with the superionic solid electrolytes (SEs) of interest. This perspective, gives a brief overview of the required properties and possible challenges for inorganic CAMs employed in SSBs, and describes state-of-the art solutions. In particular, the issue of tailoring CAMs is structured into challenges arising on the cathode-, particle-, and interface-level, related to microstructural, (chemo-)mechanical, and (electro-)chemical interplay of CAMs with SEs, and finally guidelines for future CAM development for SSBs are proposed
Fast Charging of Lithium‐Ion Batteries: A Review of Materials Aspects
Fast charging is considered to be a key requirement for widespread economic success of electric vehicles. Current lithium-ion batteries (LIBs) offer high energy density enabling sufficient driving range, but take considerably longer to recharge than traditional vehicles. Multiple properties of the applied anode, cathode, and electrolyte materials influence the fast-charging ability of a battery cell. In this review, the physicochemical basics of different material combinations are considered in detail, identifying the transport of lithium inside the electrodes as the crucial rate-limiting steps for fast-charging. Lithium diffusion within the active materials inherently slows down the charging process and causes high overpotentials. In addition, concentration polarization by slow lithium-ion transport within the electrolyte phase in the porous electrodes also limits the charging rate. Both kinetic effects are responsible for lithium plating observed on graphite anodes. Conclusions drawn from potential and concentration profiles within LIB cells are complemented by extensive literature surveys on anode, cathode, and electrolyte materials—including solid-state batteries. The advantages and disadvantages of typical LIB materials are analyzed, resulting in suggestions for optimum properties on the material and electrode level for fast-charging applications. Finally, limitations on the cell level are discussed briefly as well
Influence of Microstructure on the Material Properties of LLZO Ceramics Derived by Impedance Spectroscopy and Brick Layer Model Analysis
Variants of garnet-type Li7La3Zr2O12 are being intensively studied as separator
materials
in solid-state battery research. The material-specific transport properties,
such as bulk and grain boundary conductivity, are of prime interest
and are mostly investigated by impedance spectroscopy. Data evaluation
is usually based on the one-dimensional (1D) brick layer model, which
assumes a homogeneous microstructure of identical grains. Real samples
show microstructural inhomogeneities in grain size and porosity due
to the complex behavior of grain growth in garnets that is very sensitive
to the sintering protocol. However, the true microstructure is often
omitted in impedance data analysis, hindering the interlaboratory
reproducibility and comparability of results reported in the literature.
Here, we use a combinatorial approach of structural analysis and three-dimensional
(3D) transport modeling to explore the effects of microstructure
on the derived material-specific properties of garnet-type ceramics.
For this purpose, Al-doped Li7La3Zr2O12 pellets with different microstructures are fabricated
and electrochemically characterized. A machine learning-assisted image
segmentation approach is used for statistical analysis and quantification
of the microstructural changes during sintering. A detailed analysis
of transport through statistically modeled twin microstructures demonstrates
that the transport parameters derived from a 1D brick layer model
approach show uncertainties up to 150%, only due to variations in
grain size. These uncertainties can be even larger in the presence
of porosity. This study helps to better understand the role of the
microstructure of polycrystalline electroceramics and its influence
on experimental results