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A conceptually new approach has been developed for the fabrication of magnetite (Fe 3 O 4 )-decorated carbon nanotubes (M-CNTs) for negative electrodes of electrochemical supercapacitors. M-CNTs were prepared by an ultrasonic-assisted chemical synthesis method, which involved dispersion of functionalized CNTs in water, Fe 3 O 4 formation on the CNTs surface, and particle extraction through liquid-liquid interface (PELLI). Palmitic acid was found to be an efficient new extractor for PELLI. The slurries produced after drying and redispersing M-CNTs and slurries obtained using PELLI were used for electrode fabrication. The electrodes prepared using PELLI showed superior performance due to reduced particle agglomeration. Testing results provided an insight into the influence of Fe 3 O 4 /CNTs mass ratio on the capacitance and capacitance retention at high charge-discharge rates. A capacitance of 5.82 F cm −2 (145.4 F g −1 ) was achieved in Na 2 SO 4 electrolyte using electrodes with high active mass of 40 mg cm −2 and ratio of active mass to current collector mass of 0.6. Good electrochemical performance was achieved at low impedance.The capacitance of the negative M-CNTs electrodes was comparable with capacitance of advanced positive MnO 2 -CNTs electrodes, which was beneficial for the fabrication of asymmetric devices. The asymmetric device has been fabricated, which showed promising performance in a voltage window of 1.6 V. K E Y W O R D Sasymmetric device, capacitance, carbon nanotube, composite, magnetite, supercapacitor

Herein, a metamaterial is introduced that achieves tunable stiffness properties according to uploaded instructions, which control the phase of low‐melting‐temperature metals embedded in elastomeric spherical shells at selected locations within the lattice's microarchitecture. A macroscale cubic lattice of gallium‐filled silicone rubber spheres is fabricated as a proof of concept. Nickel–chromium (nichrome) wires are threaded through the spheres within each row in the lattice so that current can be applied to specific rows to melt their gallium cores, thereby achieving a drop in the lattice's stiffness. Using this approach, the lattice can achieve a 3.7× increase in stiffness at 7% strain when the gallium cores are all solid compared with when they are all liquid. Larger increases in stiffness are possible for larger compression strains and with thinner silicone shells. Lattices with solid gallium cores experience buckling when compressed, but lattices with liquid gallium cores do not. Simulations demonstrate that cores can be liquified and resolidified much faster as they are scaled down in size, thus enabling rapid metamaterial stiffness control. Shape reconfiguration is also possible by liquifying select gallium cores at desired locations within the lattice, deforming it, and then resolidifying the cores to passively retain the lattice's shape.

MnO2-carbon nanotube electrodes with high active mass loadings for supercapacitors have been fabricated with the goal of achieving a high area normalized capacitance, low impedance and enhanced capacitance retention at high charge-discharge rates. Interface synthesis and liquid-liquid extraction of MnO2 particles produced non-agglomerated MnO2 particles which allowed the fabrication of electrodes with good dispersion of carbon nanotubes in the MnO2 matrix. This strategy was used to fabricate electrodes with active mass loadings in the range of 21–50 mg cm−2 and mass ratios of active material to the nickel foam current collector of 0.33–0.78. The comparison of the experimental data for different extractor molecules provided an insight into the influence of the molecular structure, adsorption mechanism and interface phenomena on particle size and electrode performance. The analysis of capacitance data at different charge-discharge rates and different mass loadings was utilized to optimize electrode performance. The highest capacitance of 7.52 F cm−2 was achieved at a scan rate of 2 mV s−1 and active mass loading of 47 mg cm−2. Electrodes with mass loading of 35 mg cm−2 showed improved capacitance retention at high scan rates and the highest capacitance of 2.63 F cm−2 at a scan rate of 100 mV s−1.

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