Fabrication of Bimetallic Oxides (MCo2O4: M=Cu, Mn) on Ordered Microchannel Electro-Conductive Plate for High-Performance Hybrid Supercapacitors

AB2O4-type binary-transition metal oxides (BTMOs) of CuCo2O4 and MnCo2O4 were successfully prepared on ordered macroporous electrode plates (OMEP) for supercapacitors. Under the current density of 5 mA cm−2, the CuCo2O4/OMEP electrode achieved a specific capacitance of 1199 F g−1. The asymmetric supercapacitor device prepared using CuCo2O4/OMEP as the positive electrode and carbon-based materials as the negative electrode (CuCo2O4/OMEP//AC) achieved the power density of 14.58 kW kg−1 under the energy density of 11.7 Wh kg−1. After 10,000 GCD cycles, the loss capacitance of CuCo2O4/OMEP//AC is only 7.5% (the retention is 92.5%). The MnCo2O4/OMEP electrode shows the specific and area capacitance of 843 F g−1 and 5.39 F cm−2 at 5 mA cm−2. The MnCo2O4/OMEP-based supercapacitor device (MnCo2O4/OMEP//AC) has a power density of 8.33 kW kg−1 under the energy density of 11.6 Wh kg−1 and the cycle stability was 90.2% after 10,000 cycles. The excellent power density and cycle stability prove that the prepared hybrid supercapacitor fabricated under silicon process has a good prospect as the power buffer device for solar cells.

Understanding the High-Performance Anode Material of CoC2 O4 ⋅2 H2 O Microrods Wrapped by Reduced Graphene Oxide for Lithium-Ion and Sodium-Ion Batteries

Metal oxalate has become a most promising candidate as an anode material for lithium-ion and sodium-ion batteries. However, capacity decrease owing to the volume expansion of the active material during cycling is a problem. Herein, a rod-like CoC₂ O₄ ⋅2 H₂ O/rGO hybrid is fabricated through a novel multistep solvo/hydrothermal strategy. The structural characteristics of the CoC₂ O₄ ⋅2 H₂ O microrod wrapped using rGO sheets not only inhibit the volume variation of the hybrid electrode during cycling, but also accelerate the transfer of electrons and ions in the 3 D graphene network, thereby improving the electrochemical properties of CoC₂ O₄ ⋅2 H₂ O. The CoC₂ O₄ ⋅2 H₂ O/rGO electrode delivers a specific capacity of 1011.5 mA h g^-1 at 0.2 A g^-1 after 200 cycles for lithium storage, and a high capacity of 221.1 mA h g^-1 at 0.2 A g^-1 after 100 cycles for sodium storage. Moreover, the full cell CoC₂ O₄ ⋅2 H₂ O/rGO//LiCoO₂ consisting of the CoC₂ O₄ ⋅2 H₂ O/rGO anode and LiCoO₂ cathode maintains 138.1 mA h g^-1 after 200 cycles at 0.2 A g^-1 and has superior long-cycle stability. In addition, in situ Raman spectroscopy and in situ and ex situ X-ray diffraction techniques provide a unique opportunity to understand fully the reaction mechanism of CoC₂ O₄ ⋅2 H₂ O/rGO. This work also gives a new perspective and solid research basis for the application of metal oxalate materials in high-performance lithium-ion and sodium-ion batteries.

Interfacial synthesis of micro-cuboid Ni0.55Co0.45C2O4 solid solution with enhanced electrochemical performance for hybrid supercapacitors

Efficient charge and energy storage relies essentially on the development of innovative electrode materials with enhanced electrochemical kinetics. Herein, Ni_0.55Co_0.45C₂O₄ solid solution was successfully synthesized by a liquid-liquid interfacial reaction. The observation of the morphologies of Ni_0.55Co_0.45C₂O₄ depicts a peculiar micro-cuboid structure composed of nanoparticles in the size range of 13 to 23 nm, benefiting the increase in the contribution of surface-controlled reactions to charge storage processes. The results from X-ray diffraction and thermogravimetric analysis demonstrate the similarity of the crystal structure and thermal decomposition behavior between Ni_0.55Co_0.45C₂O₄ and CoC₂O₄, and indicate that the CoC₂O₄ lattice plays a role as the fundamental framework in the solid solution instead of NiC₂O₄. The electrochemical measurements show that Ni_0.55Co_0.45C₂O₄ achieves a higher specific capacity of 562 C g^-1 at a current density of 1 A g^-1 than its counterpart NiC₂O₄/CoC₂O₄ hybrids, due to this the alternative arrangement of nickel and cobalt species in the solid solution expedites the diffusion process of active ions during the electrochemical reaction. Depending on the enhancement of the electrochemical stability in the solid solution, Ni_0.55Co_0.45C₂O₄ electrodes retain 87.4% of the initial capacity after 4000 cycles. The assembled Ni_0.55Co_0.45C₂O₄//AC hybrid supercapacitor attains an energy density of 38.5 W h kg^-1 at a power density of 799 W kg^-1 with a long cycling life (80% of the initial capacitance after 10 000 cycles). The excellent electrochemical performance suggests that Ni_0.55Co_0.45C₂O₄ is a promising candidate electrode material for supercapacitors.