Beyond Conversion Chemistry: Unlocking a Cooperative Solid-Solution-Capacitive Sodium-Storage Mechanism in Nickel...

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Nickel phosphide (Ni₂P) is a potential anode material for sodium-ion batteries due to its high capacity and conductivity.
• The charge storage mechanism in Ni₂P is often oversimplified and not fully understood.

Purpose of the Study:

• To investigate the charge storage mechanism of Ni₂P anodes in sodium-ion batteries.
• To design and fabricate a high-performance Ni₂P-based electrode.
• To establish a new paradigm for designing advanced sodium-ion battery anodes.

Main Methods:

• Fabrication of a freestanding Ni₂P composite electrode with ultrasmall Ni₂P nanocrystals in a porous carbon matrix.
• In-situ and ex-situ analyses to elucidate the charge storage mechanism.
• Electrochemical testing including rate capability and long-term cycling.

Main Results:

• Demonstrated an interstitial solid-solution mechanism coupled with pseudocapacitance.
• Achieved a high reversible capacity of ≈560 mAh g⁻¹.
• Exhibited excellent rate capability (135 mAh g⁻¹ at 10 A g⁻¹) and long-term stability (263 mAh g⁻¹ after 2000 cycles).
• A full cell achieved an energy density of 245 Wh kg⁻¹.

Conclusions:

• The charge storage in Ni₂P anodes follows a synergistic solid-solution-capacitive dual-mode mechanism.
• This mechanism enables reversible lattice breathing without phase transformation.
• Solid-solution-capacitive coupling is a viable strategy for developing high-rate and durable sodium-ion battery anodes.