Relaxation of the Interface Resistance between Solid Electrolyte and 5 V-Class Positive Electrode

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Batteries

Background:

• Solid-state lithium batteries offer higher energy density using 5 V-class positive electrode materials.
• High interface resistance (Ri) between solid electrolytes and 5 V-class electrodes limits practical application.
• Understanding and mitigating this interface resistance is crucial for advancing battery technology.

Purpose of the Study:

• To investigate the relaxation behavior of interface resistance (Ri) between Li3PO4 (LPO) solid electrolyte and LiCo0.5Mn1.5O4 (LCMO) 5 V-class electrode.
• To determine the factors contributing to the increase and subsequent decrease of Ri at the LPO/LCMO interface.
• To explore the implications of interfacial layer formation on battery performance.

Main Methods:

• Electrochemical impedance spectroscopy (EIS) was used to measure interface resistance (Ri).
• Applied voltage cycling was performed on LPO/LCMO interfaces to study Ri changes.
• Analysis of Ri relaxation dynamics after high voltage exposure.

Main Results:

• Interface resistance (Ri) was low (11 Ω cm²) at 4.0 V vs Li/Li⁺ (Mn³⁺/⁴⁺ redox).
• Ri increased by over two orders of magnitude above 5.2 V vs Li/Li⁺ (Co³⁺/⁴⁺ redox).
• After reducing voltage to 4.0 V vs Li/Li⁺, Ri decayed to its original value within 3 hours, indicating reversible relaxation.

Conclusions:

• The rapid increase in Ri above 5 V vs Li/Li⁺ is attributed to the formation of an interfacial layer at the LPO/LCMO interface.
• The observed relaxation of Ri suggests this interfacial layer is reversible, potentially allowing for stable high-voltage operation.
• This finding is critical for developing practical high-energy-density solid-state batteries utilizing 5 V-class cathodes.