Surface-to-Bulk Redox Coupling through Thermally Driven Li Redistribution in Li- and Mn-Rich Layered Cathode...

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Lithium- and manganese-rich (LMR) layered cathode materials offer high capacity and energy density due to coupled redox activity of transition metals and oxygen anions.
• Electrochemical redox evolution in LMR cathodes is well-studied at ambient temperatures.
• Thermal effects on LMR cathode behavior, especially under non-electrochemical conditions, remain largely unexplored.

Purpose of the Study:

• To investigate the thermally driven redox coupling effects in charged Li_1.2Ni_0.15Co_0.1Mn_0.55O₂ (LMR) materials at mildly elevated temperatures (up to ~100 °C).
• To understand the surface-to-bulk redox interactions influenced by temperature perturbations in the absence of electrochemical driving force.

Main Methods:

• Systematic study of charged Li_1.2Ni_0.15Co_0.1Mn_0.55O₂ material.
• Application of mild thermal stress (up to ~100 °C) to induce surface-to-bulk redox coupling.
• Analysis of charge transfer mechanisms between oxygen anions and transition metal cations.

Main Results:

• First observation of charge transfer between bulk oxygen anions and surface transition metal cations in LMR materials at ~100 °C.
• Attribution of this charge transfer to thermally driven redistribution of lithium ions.
• Demonstration of a dynamic, non-equilibrium state in deeply delithiated LMR materials under mild thermal perturbation.

Conclusions:

• Mildly elevated temperatures can induce significant redox activity in LMR cathode materials, independent of electrochemical cycling.
• The findings highlight the importance of thermal stability considerations for LMR materials in practical applications.
• Understanding these thermally driven processes is crucial for optimizing the performance and safety of advanced battery technologies.