Rational Route for Increasing Intercalation Capacity of Hard Carbons as Sodium-Ion Battery Anodes

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Hard carbon (HC) is a leading anode material for sodium-ion batteries.
• Existing performance predictors like Raman intensity ratio, crystallite size (L_a), and interlayer distance (d₀₀₂) have limitations.
• These factors do not fully capture the bulk properties relevant to sodium ion (Na⁺) intercalation.

Purpose of the Study:

• To introduce and validate a new metric, crystallite interlayer area (A_i), for evaluating HC anode performance.
• To demonstrate that A_i, derived from L_a, d₀₀₂, and stacking height (L_c), governs Na⁺ intercalation behavior.
• To establish A_i as a more comprehensive and adaptable evaluation factor compared to conventional methods.

Main Methods:

• Calculation of crystallite interlayer area (A_i) using crystallite lateral size (L_a), interlayer distance (d₀₀₂), and stacking height (L_c).
• Analysis of Na⁺ intercalation capacity (C_i) in various wood-derived hard carbons.
• Correlation analysis between A_i and C_i, and validation against previous studies.

Main Results:

• Wood-derived hard carbons showed similar total capacities (~250 mAh g^-1).
• Sodium ion intercalation capacity (C_i) was found to be directly proportional to the crystallite interlayer area (A_i) (R² = 0.94).
• The A_i metric demonstrated strong correlation with C_i across various hard carbon materials, including those from previous reports.

Conclusions:

• Crystallite interlayer area (A_i) is a critical parameter governing Na⁺ intercalation in hard carbons.
• A_i provides a more accurate and broadly applicable method for predicting anode performance than traditional metrics.
• This finding facilitates the rational design and selection of advanced hard carbon materials for sodium-ion batteries.