Mn 3 O 4 and (ZnFe)OOH Composites for Supercapacitors with High Active Mass
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I.
INTRODUCTION
MN3O4 is a promising ceramic cathode materials for supercapacitors due to its high capacitance and low cost.[1,2] However, the specific capacitance of Mn3O4 decreased significantly with increasing electrode mass due to poor electrolyte access to the active material and low electronic conductivity. It is challenging to achieve good electrode performance at practically important active mass above 10 mg cm 2. Therefore, research efforts were focused on the synthesis of nanoparticles with high surface area and design of advanced composites.[3,4] It is important to note that Mn3O4 is a member of a large group of advanced materials with a spinel crystalline structure. Therefore, the advantage of Mn3O4, compared to other pseudocapacitive ceramic materials, is the ability to form solid solutions with various spinel compounds. The rich chemistry of spinel offers possibilities[5] for the modification of composition, conductivity, and capacitive properties of Mn3O4. Many investigations focused on pure Mn3O4 films[6–10] and reported capacitances at low active mass loadings in the range of 0.16 to 1.2 mg cm 2
R. POON, W. LIANG, and I. ZHITOMIRSKY are with the Department of Materials Science and Engineering, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4L7, Canada. Contact e-mail: [email protected] Manuscript submitted August 15, 2019. R. Poon and W. Liang have contributed equally to this work.
METALLURGICAL AND MATERIALS TRANSACTIONS A
(Supplementary Material, Table S1). High specific capacitances of 568 F g 1[9] and 597 F g 1[10] were reported at mass loadings of 0.16 and 0.64 mg cm 2, respectively. Good electrochemical performance at higher mass loadings in the range of 2 to 9.5 mg cm 2 was achieved in composites, containing various conductive additives, such as graphite,[11] carbon black,[12] acetylene black,[13–15] and other materials.[16] High gravimetric capacitance of 222.4 F g 1 was achieved at a mass loading of 9.5 mg cm 2 and resulted[15] in areal capacitance of 2.11 F cm 2. Mn3O4 was combined with capacitive carbon materials such as graphene[17,18] and activated carbon[19] for the fabrication of composites. Of particular interest are Mn3O4-graphene oxide composites, which showed capacitances of 538 F g 1 (2.69 F cm 2)[20] and 258.6 F g 1 (2.33 F cm 2)[21] at mass loadings of 5 and 9 mg cm 2, respectively. Recent studies showed that good capacitive behavior can be achieved at higher mass loadings using advanced colloidal techniques.[22] Mn3O4-carbon nanotube electrodes showed areal capacitances of 2.8 F cm 2[22] and 4.2 F cm 2[23] at active mass loadings of 28.4 and 33 mg cm 2. Mn3O4 cathodes were combined with various anodes, such as graphene,[24] activated carbon,[25] lithium titanate,[26] and polypyrrole[27] for the fabrication of asymmetric devices with large voltage windows. However, the progress in the development of Mn3O4 cathodes introduces problems related to the use of various anodes, which have lower capacitances. Therefore, there is a need in the development of advanced ceram
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