Phosphonate-Pillared High-Entropy MXene Separator Enabling Ion-Sieving, Flame-Retardant, and Energy/Power-Dense...

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• High-energy-density batteries utilizing Ni-rich cathodes and lithium metal anodes face challenges from cation crosstalk, leading to anode interface destabilization, dendrite growth, and thermal runaway.
• Existing battery separators often fail to adequately address these coupled failure modes, limiting cycle life and safety.

Purpose of the Study:

• To develop an advanced ion-sieving, flame-retardant separator for high-energy-density batteries.
• To mitigate cation crosstalk and enhance the stability of the lithium metal anode interface.
• To improve the overall safety and performance of lithium-ion batteries.

Main Methods:

• Fabrication of a phosphonate-pillared high-entropy (HE) MXene (TiVNbMoC3/Tppm) functional layer via topological exfoliation.
• Utilizing tetraphosphonate (TppmH8) ligands as molecular pillars to expand MXene interlamellar spacing.
• Characterization of the separator's ion conductivity, mechanical strength, thermal stability, and metal ion sequestration capabilities.
• Performance evaluation in 1.0 Ah NCM811||Li pouch cells under lean-electrolyte conditions.

Main Results:

• Achieved few-layer (< 5 layers) HE MXene nanosheets with expanded interlamellar spacing (18.5 Å) and high yield (95%).
• Demonstrated rapid and homogeneous Li+ conduction (diffusion barrier 0.179 eV) and significant transition metal sequestration (82%).
• The composite separator exhibited high Li+ transference number (0.77), tensile strength (95.17 MPa), and thermal stability (180°C).
• Cells achieved 87.1% capacity retention after 200 cycles, high energy densities (411.8 Wh kg-1 / 838.2 Wh L-1), and power density (1127.0 W kg-1).
• Synergistic suppression of thermal propagation by phosphonate and MXene-derived components was confirmed during thermal testing.

Conclusions:

• The developed phosphonate-pillared HE MXene separator effectively addresses cation crosstalk and enhances lithium metal anode stability.
• The separator contributes to improved battery safety by suppressing thermal runaway and enabling stable operation under demanding conditions.
• This advanced separator technology holds significant promise for realizing next-generation high-energy-density batteries.