Gradient Interphase Engineering Enabled by Anionic Redox for High-Voltage and Long-Life Li-Ion Batteries.

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Anionic redox reactions (ARR) in Li-rich cathodes offer high energy density for next-generation batteries.
• Instability of the cathode-electrolyte interphase (CEI) is a major challenge for Li-rich cathodes due to complex ARR mechanisms like nucleophilic attacks.
• Existing high-voltage cathodes face CEI stability issues, which are exacerbated in Li-rich systems.

Purpose of the Study:

• To engineer a stable and functional CEI on Li-rich cathodes by manipulating interfacial reactions.
• To leverage the nucleophilic attack, typically detrimental, for constructive CEI formation.
• To enhance the electrochemical performance and cycle life of Li-rich battery cathodes.

Main Methods:

• Introduction of an all-fluorinated electrolyte to interact with nucleophilic attacks.
• Construction of a gradient CEI with distinct fluorinated layers on the Li-rich cathode surface.
• Formation of a LiF-based outer shield and a fluorinated polymer inner sheath for robust interphase protection.

Main Results:

• Achieved a gradient CEI with enhanced interfacial stability on the Li-rich cathode.
• Transformed detrimental nucleophilic electrolyte decomposition into a beneficial CEI fabrication process.
• Significantly improved capacity retention of the Li-rich cathode from 43% to 71% after 800 cycles.
• Demonstrated superior cycling stability in anode-free full cells (98.8% retention over 220 cycles).

Conclusions:

• Gradient CEI engineering effectively stabilizes Li-rich cathodes by mitigating issues associated with anionic redox reactions.
• The developed interfacial strategy enhances battery cycle life and energy density, crucial for practical applications.
• This approach offers a promising pathway for developing advanced high-energy rechargeable batteries.