Hierarchical Mn₃O₄/NiSe₂-MnSe₂: A Versatile Electrode Material for High-Performance All-Solid-State Hybrid...

As highly efficient electrochemical energy storage devices are in indispensable demand for numerous modern-day technologies, herein sluggish precipitation followed by an anion exchange procedure has been developed to synthesize an oxide-selenide mixed phase (Mn₃O₄/NiSe₂-MnSe₂) novel electrode material with high surface area and porosity for high-performance all-solid-state hybrid pseudocapacitors (ASSHPC). Mn₃O₄/NiSe₂-MnSe₂ shows a rich Tyndall effect (in H₂O) and possesses randomly arranged low-dimensional crystallites of nearly similar size and uniform shape. The electrochemical analyses of Mn₃O₄/NiSe₂-MnSe₂ corroborate good electrochemical reversibility during charge transfer, superior pseudocapacitive charge-storage efficiency, and very low charge transfer and series resistance, ion-diffusion resistance, and relaxation time, which endorse the quick pseudocapacitive response of the material. The Mn₃O₄/NiSe₂-MnSe₂||N-rGO ASSHPC device demonstrates excellent charge-storage physiognomies suggestive of rich electrochemical and electromicrostructural compatibility between the electrode materials in the fabricated assembly. The Mn₃O₄/NiSe₂-MnSe₂||N-rGO ASSHPC device delivers high mass and area specific capacitance/capacity, very low charge-transfer resistance (∼0.74 Ω), total series resistance (∼0.76 Ω), diffusion resistance, and a relaxation time constant, which endorse the quick pseudocapacitive response of the device. The device delivers higher energy and power density (∼34 W h kg^-1 at ∼2994 W kg^-1), rate efficiency (∼17 W h kg^-1 at ∼11,995 W kg^-1), and cyclic performance (∼97.2% specific capacity/capacitance retention after 9500 continuous GCD cycles). The superior Ragone and cyclic efficiencies of the ASSHPC device are ascribed to the multiple redox-active Ni and Mn ions which lead to the supplemented number of redox reactions; "electroactive-ion buffering pool"-like physiognomics of Mn₃O₄/NiSe₂-MnSe₂, which facilitate the electrolyte ion dissemination to the electroactive sites even at high rate redox condition; and ideal electro-microstructural compatibility between the electrode materials, which leads to assisted charge transfer and absolute ion dissemination during the charge-storage process.