Fraunhofer Institute for Mechanics of Materials IWM
Promising candidate for even more powerful lithium-ion batteries: solid-state electrolyte (here LiTi2(PO4)3, Li-green, Ti-blue, P-purple, O-red) with representation of the "migration paths" for lithium ions (yellow bands).
Electrochemical processes on an atomic and microstructural scale determine the energy density, charging speed, service life, and safety of batteries. With a sound understanding of mechanisms, multiscale simulation, and atomistic calculations, we aim to elucidate, model, and control these processes.
The material technology challenges we focus on are:
Increasing energy density through improved cathode and anode materials
- Voltage drops and unstable cycling are often observed in high-capacity cathodes such as Li-rich layered oxides (e.g., Li₁.₂Ni₀.₁₃Co₀.₁₃Mn₀.₅₄O₂).
- Mechanical and electrochemical instability due to expansion of high-capacity silicon anodes (~3500 mAh/g) by up to 300% during lithiation.
- Dendrite formation and reactivity of lithium metal anodes with maximum energy density.
Control of side reactions and degradation at increased charging speeds
- Loss of reversible capacity and safety risks (short circuit) due to lithium plating on the anode.
- Limited charging speed due to ion transport through the electrolytes and interfaces (SEI, CEI).
- Increase in polarization effects (overvoltage) during fast charging.
Reduction of capacity losses and increase in service life (cycle stability)
- Unstable interfaces due to growth of the SEI layer (solid electrolyte interface) on the anode as well as consumption of lithium and electrolyte.
- High-voltage materials undergo structural changes and release transition metal ions into the electrolytes (cathode degradation).
- Classic carbonate-based electrolytes decompose, especially in high-voltage cells (>4.3 V).
Increased safety
- Instability of electrolytes at high temperatures or voltages can lead to the formation of flammable gases.
- Lithium dendrites in metal anodes or during plating increase the risk of short circuits.
- Oxygen release from unstable cathode materials (e.g., NMC with a high nickel content) can cause exothermic reactions.