Porous sodium titanate nanofibers for high energy quasi‐solid‐state sodium‐ion hybrid capacitors

Sodium‐ion hybrid capacitors (SICs) have considered as promising candidate for lithium‐ion counterpart in large‐scale energy storage due to their advantages of natural abundance, potential low cost, and high energy‐power output. However, the sluggish electrochemical kinetics in the bulk of battery‐type materials is an intractable obstacle for practical applications. In this work, we employ porous sodium titanate (Na 2 Ti 3 O 7 ) nanofibers (p‐NTO‐NFs) as a negative electrode material for sodium‐ion storage with high‐efficiency ion transport. The p‐NTO‐NFs electrode provides a high reversible capacity of about 200 mAh·g −1 at low current density of 100 mA·g −1 , impressive rate capability of over 100 mAh·g −1 at 5 A·g −1 . Given the favorable sodium‐ion storage characteristics, a quasi‐solid‐state sodium‐ion hybrid capacitor (QSS‐SIC) based on p‐NTO‐NFs negative electrode is successfully assembled with a sodium‐ion conducting gel polymer electrolyte. This QSS‐SIC delivers a glorious energy output of 105.7 Wh·kg −1 , great power character of 16,156 W·kg −1 , and outstanding working stability of 10,000 cycles, revealing the potential application in high energy‐power supplies and large‐scale energy storage field.