Oxygen Vacancy Modulation of Bimetallic Oxynitride Anodes toward Advanced Li‐Ion Capacitors

Abstract

Binary metal oxides (such as NiCo2O4) are regarded as attractive electrode materials for advanced energy storage devices since they offer more electrochemical activity and higher capacity than monometal oxide. However, the volume expansion and low electronic conductivity are the main bottleneck seriously hindering their application. To overcome these barriers, a novel strategy that introduces a bimetallic oxynitride layer (NiCoON) with oxygen vacancy to the surface of NiCo2O4 nanowires as an anode for Li‐ion capacitors (LICs) is proposed. The oxygen vacancy on the surface and the modulation of multiple valence states are investigated by the electron paramagnetic resonance, X‐ray photoelectron spectroscopy characterization, and first‐principles calculation. Benefiting from the merits of substantially improved electrical conductivity and increased concentration of active sites, the optimized NiCoON electrode delivers remarkable capacity (1855 mAh g−1 at 0.2 A g−1) and rate performance. The LIC device assembled by NiCoON anodes and N‐doped carbon nanowire cathodes delivers excellent rate capability, high energy density (148.5 Wh kg−1), and outstanding power density (30 kW kg−1). This study provides a new pathway for developing bimetallic oxides with an improved performance in electrochemical energy storage, conversion fields, and beyond.

Insight into Nickel‐Cobalt Oxysulfide Nanowires as Advanced Anode for Sodium‐Ion Capacitors

“…Some voids can also be found among these dispersed nanoparticles, which are formed along with the release of some gases (e.g., CO 2 and H 2 O) generated during the sulfidation treatment of Ni–Co precursor at the high temperature. [ 5 ] These voids should be advantageous for accommodating the volume expansion during the sodiation/desodiation processes. [ 24 ] The transmission electron microscopy (TEM) image (Figure 1e) again reveals the core‐shell‐like structure of NCOS.…”

“…20–0781). [ 5 ] The peak at 65.25° in both NCS and NCOS can be assigned to the (440) plane of NiCo 2 S 4 (JCPD card No. 20–0782), [ 26,27 ] again suggesting the successful partial substitution of oxygen atoms with sulfur atoms in NCOS.…”

“…As shown in Figure 2c, all samples show a special EPR signal with a certain g ‐value of about 2.002, indicating electrons trapped by surface oxygen vacancies. [ 5 ] The highest electron spin resonance intensity of NCOS indicates the presence of massive oxygen vacancies on the surface, and thus an improved electrochemical performance shall be expected. [ 31 ] Figure S6a, Supporting Information presents the survey spectra of the samples which prove the existence of C, O, Co, and Ni elements in NCO and an additional S peak in NCOS and NCS.…”

“…[ 3,4 ] Although strides have been made in the device design and construction of SICs, the development of high‐performance SICs still faces some challenges and drawbacks that have to be overcome, especially with respect to the anode. [ 5,6 ] Since the anode in SICs and its corresponding sodium storage mechanism are exactly the same as that in SIBs, SICs are also suffering from similar challenging issues arising from the anode as currently faced with SIBs, for example, the large volume expansion of the anode and the sluggish sodium diffusion kinetics in the anode. [ 7 ] Particularly due to the sluggish sodium diffusion kinetics, the diffusion rate of sodium ions in the battery‐type anode is much lower than the adsorption/desorption and/or redox reaction rate of anions in the capacitor‐type cathode at a high current density.…”

Defect Induced Polarization Loss in Multi‐Shelled Spinel Hollow Spheres for Electromagnetic Wave Absorption Application

“…In general, resonate peaks in ESR curve can be discerned due to the electrons trapped on oxygen vacancies. [ 60–62 ] However, the peaks were absence in curves but an interesting phenomenon was discovered instead. It should be noted that ESR is not only known to be a very sensitive method to probe paramagnetic centers but also to microwave absorption.…”