High-Efficiency Separator Capacity-Compensation Strategy Applied to Sodium-Ion Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Sodium-ion batteries (SIBs) offer a sustainable alternative to lithium-ion batteries (LIBs) due to sodium's abundance.
• Initial capacity loss (ICL) in SIBs, caused by irreversible sodium ion trapping in the solid electrolyte interface (SEI) layer, hinders their practical application.

Purpose of the Study:

• To introduce and validate a separator capacity-compensation strategy for mitigating ICL in SIBs.
• To enhance the initial reversible specific capacity and overall energy density of SIBs.

Main Methods:

• A capacity compensator integrated into the separator oxidizes below the cathode's high cut-off voltage, releasing sodium ions.
• The strategy was tested in NaNi_1/3 Fe_1/3 Mn_1/3 O₂ (NMFO)||HC and Na₃ V₂ (PO₄ )₃ (NVP)||HC full cells.

Main Results:

• The strategy demonstrated adaptability to current production, preserved long-cycle life, and allowed controlled pre-sodiation.
• A compensated capacity ratio of 18.2% was achieved in the NMFO||HC cell.
• The initial reversible specific capacity in the NVP||HC cell increased from 61.0 mAh g^-1 to 83.1 mAh g^-1.

Conclusions:

• The separator capacity-compensation strategy effectively compensates for ICL in SIBs.
• This approach is universal and offers a promising new perspective for improving the energy density of sodium-ion batteries.