Understanding the Role of Triple Phase Boundaries on Coating-Free Solid-State Cathodes

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Batteries

Background:

• Sulfide solid electrolytes offer high ionic conductivity for solid-state batteries.
• Cathode active materials often need protective coatings to prevent electrolyte decomposition, adding manufacturing complexity and cost.

Purpose of the Study:

• To investigate the role of double and triple phase boundaries in the oxidative decomposition of sulfide solid electrolytes.
• To evaluate the performance of thick, uncoated solid-state cathodes by understanding decomposition mechanisms.

Main Methods:

• Decoupling the effects of double and triple phase boundaries on electrolyte decomposition in thick, uncoated cathodes.
• Analyzing oxidative decomposition in the presence of cathode active materials, carbon, and solid electrolyte.

Main Results:

• More severe oxidative decomposition occurs at the triple phase boundary where cathode active materials, carbon, and solid electrolyte coexist.
• A thick, uncoated electrode achieved an initial areal capacity of ~4.6 mAh cm⁻² at 30 °C and 2 MPa stack pressure.
• The electrode demonstrated ~85% capacity retention over 500 cycles when electronic pathways at the triple phase boundary were regulated.

Conclusions:

• The triple phase boundary is critical in controlling oxidative decomposition in solid-state battery cathodes.
• Regulating electronic pathways at the triple phase boundary allows for high-performance, durable, and cost-effective uncoated cathodes.