Ultrathin CuF₂ -Rich Solid-Electrolyte Interphase Induced by Cation-Tailored Double Electrical Layer toward Durable...

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• The solid-electrolyte interphase (SEI) is critical for battery longevity, particularly in high-capacity anodes where electrolyte decomposition is prevalent.
• Particle fracture in anodes leads to excessive electrolyte decomposition, negatively impacting cycling life.
• Developing stable SEI layers is crucial for enhancing the performance of sodium-ion batteries.

Purpose of the Study:

• To engineer an ultrathin SEI layer for copper sulfide (CuS) anodes in sodium-ion batteries.
• To suppress electrolyte consumption and improve the cycling stability of CuS anodes.
• To investigate the formation mechanism of the SEI layer and its impact on interfacial properties.

Main Methods:

• Utilized a Cu+-tailored double electrical layer (EDL) strategy to induce an ultrathin SEI (3-4 nm).
• Employed in situ surface-enhanced Raman spectroscopy, Cryo-Transmission Electron Microscopy (Cryo-TEM), and theoretical calculations to characterize the EDL and SEI.
• Investigated the composition of the SEI, identifying CuF2 and other fluorine-containing compounds.

Main Results:

• Demonstrated the formation of a unique EDL with a SO3CF3-Cu complex on the CuS surface in a NaSO3CF3/diglyme electrolyte.
• Revealed that the SO3CF3-Cu complex reduces to a CuF2-rich SEI, providing good interfacial contact and minimizing electrolyte consumption.
• Achieved exceptional cycling stability with the modified CuS anode delivering 402.8 mAh/g after 7000 cycles without capacity decay.

Conclusions:

• An ultrathin, stable SEI formed via Cu+-tailored EDL significantly enhances the cycling performance of CuS anodes in sodium-ion batteries.
• The CuF2-rich SEI effectively reduces electrolyte consumption and lowers the activation energy for Na+ transport.
• This work provides valuable insights into SEI construction for developing high-stability electrodes for next-generation batteries.