Pre-sodiated nickel cobaltite for high-performance sodium-ion capacitors

• Published in: Journal of power sources Vol. 362; pp. 358 - 365
• Main Authors: Yang, Dongfang, Sun, Xiaoming, Lim, Kyungmi, Ranganathan Gaddam, Rohit, Ashok Kumar, Nanjundan, Kang, Kisuk, Zhao, Xiu Song
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15-09-2017
• Subjects: Energy density; Nickel cobaltite; Pre-sodiation; Sodium-ion capacitors; Pre-sodiation; Sodium-ion capacitors; Energy density; Nickel cobaltite
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2017.07.053

Sodium-ion capacitors (NICs) are a hybrid energy storage system that store energy via both charge adsorption at the cathode/electrolyte interface and charge intercalation in the bulk of the anode, thereby possessing a higher energy density than supercapacitors and a higher power density than batteries. In this work, nickel cobaltite (NiCo2O4) hollow spheres with a chestnut shell morphology have been solvothermally synthesized and tested in a sodium half-cell. The NiCo2O4 material exhibits a reversible capacity of 313 mAh g−1 at 1 A g−1. Pre-sodiation of NiCo2O4 is found to significantly improve its energy density. A NIC fabricated with pre-sodiated NiCo2O4 as the anode and an activated carbon (AC) as the cathode delivers an energy density of 60 Wh kg−1 at the power density of 10,000 W kg−1. Ex-situ X-ray diffraction (XRD) and transmission electron microscopy (TEM) results reveal that NiCo2O4 is converted to metallic nickel and cobalt and Na2O phases during the pre-sodiation. The metallic nickel and cobalt phases are kinetically favourable for the electrolyte diffusion and electrochemical reactions, thus significantly improving the performance of the pre-sodiated NiCo2O4 electrode.
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•NICs are fabricated based on NiCo2O4 and activated carbon electrodes.•Pre-sodiation of NiCo2O4 is found to significantly improve its energy density.•The NIC shows an energy density of 60 Wh kg−1 at a power density of 10,000 W kg−1.