A Chemical-Potential-Driven Self-Mitigation Mechanism during Calendar Aging.

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Sulfide-based all-solid-state batteries (ASSBs) face significant performance decay during storage, termed calendar aging, due to inherent thermodynamic instability.
• Understanding the mechanisms of capacity fade during open-circuit storage is crucial for improving ASSB longevity.

Purpose of the Study:

• To systematically investigate the impact of varying states-of-charge (SOC) on the calendar aging behavior of ASSBs.
• To elucidate the underlying mechanisms of capacity decay and identify strategies for mitigating performance loss during storage.

Main Methods:

• Investigated calendar aging effects across different SOC levels in Li6PS5Cl-based ASSBs.
• Analyzed the electrochemical behavior and structural integrity of cathode active materials (CAMs) after storage at various SOCs.

Main Results:

• A lower equilibrium voltage of the Li6PS5Cl electrolyte (2.06 V) compared to the cathode active material (LiNi0.94Co0.04Al0.02O2 >2.96 V) drives Li+ migration from electrolyte to CAMs, acting as a self-mitigation mechanism.
• High SOC aging (>50%) leads to lattice oxygen release and particle cracking in CAMs.
• Storage at 25% SOC maintains the well-ordered structure of CAMs, resulting in a significantly higher capacity (179.5 mAh/g) compared to 100% SOC (77 mAh/g).

Conclusions:

• Optimizing storage SOC is critical for mitigating calendar aging in ASSBs.
• Storing ASSBs at lower SOCs (e.g., 25%) effectively preserves structural integrity and electrochemical performance, offering a viable strategy for practical storage management.