Search

Poly(vinylidene fluoride-co-hexafluoropropylene) and Li7La3Zr2O12-poly(vinylidene fluoride-co-hexafluoropropylene) films were introduced to both Li and non-Li anodes. Via the recombination of poly(vinylidene fluoride-co-hexafluoropropylene)-Li7La3Zr2O12, the ionic conductivity of the anodes has been greatly improved, and the deposition/plating barrier has been decreased. On the one hand, the thin film introduced upon lithium metal ensures cyclic stability in both symmetrical cells and full cells. The Li metal with Li7La3Zr2O12-poly(vinylidene fluoride-co-hexafluoropropylene) films behaved stably over 500 h with little increase in polarization. On the other hand, the modification upon Cu foil provided a long cycle life over 300 cycles in Li–Cu cells. When the poly(vinylidene fluoride-co-hexafluoropropylene)-Li7La3Zr2O12@Cu foil (non-Li anode) failed, a type of self-protected mechanism was activated, ensuring better mechanical properties and safety.

To construct a suitable three-dimensional structure for ionic transport on the surface of the active materials for a supercapacitor, porous hollow nickel cobalt sulfides are successfully synthesized via a facile and efficient cation-exchange reaction in a hydrothermal process involving the Kirkendall effect with γ-MnS nanorods as a sacrificial template. The formation mechanism of the hollow nickel cobalt sulfides is carefully illustrated via the tuning reaction time and reaction temperature during the cation-exchange process. Due to the ingenious porous hollow structure that offers a high surface area for electrochemical reaction and suitable paths for ionic transport, porous hollow nickel cobalt sulfide electrodes exhibit high electrochemical performance. The Ni1.77Co1.23S4electrode delivers a high specific capacity of 224.5 mAh g–1at a current density of 0.25 A g–1and a high capacity retention of 87.0% at 10 A g–1. An all-solid-state asymmetric supercapacitor, assembled with a Ni1.77Co1.23S4electrode as the positive electrode and a homemade activated carbon electrode as the negative electrode (denoted as NCS//HMC), exhibits a high energy density of 42.7 Wh kg–1at a power density of 190.8 W kg–1and even 29.4 Wh kg–1at 3.6 kW kg–1. The fully charged as-prepared asymmetric supercapacitor can light up a light emitting diode (LED) indicator for more than 1 h, indicating promising practical applications of the hollow nickel cobalt sulfides and the NCS//HMC asymmetric supercapacitor.

The contact between Ni(OH)2and graphene oxide (GO) determines the specific capacitance, high-rate performance, and stability of Ni(OH)2-GO composites when they were used as capacitive materials with high/ultrahigh material loading. To improve this contact, the exfoliated GO from Hummers’ method is oxidized twice for anchoring Ni(OH)2nanoflakes. The X-ray photoelectron spectroscopy (XPS) results reveal that the further oxidation process increases the carbonyl (C–O) groups and oxygen content on the GO surface. The Ni(OH)2-GO composites were obtained through a simple hydrothermal process. Morphology and microstructure characterizations indicate that the further oxidation of GO improves the affinity of Ni(OH)2and GO via the increased surface groups on the GO. Due to the high conductivity and suitable structure, the Ni(OH)2anchored on the treated GO (Ni(OH)2/TGO) exhibits good capacitive performance and high areal specific capacitance. The Ni(OH)2/TGO exhibits high specific capacitance of 1236.4 F g–1at 1.0 mV s–1and 1374.8 F g–1at 0.1 A g–1, respectively, which is higher than that of Ni(OH)2on the untreated GO. The capacitance retention of Ni(OH)2/TGO is 52.2% even at 10 A g–1, which is higher than that of Ni(OH)2/GO (48.8%). For the high conductivity, the specific capacitance is still 996.2 F g–1at 1.0 A g–1even with ultrahigh material loading of 12.48 mg cm–2, which can be transferred to 12.06 F cm–2calculated by areal specific capacitance. Furthermore, low deterioration is observed in Ni(OH)2/TGO (8.8% loss) after 1000-cycle charge–discharge test at 1.0 A g–1, which is lower than that of Ni(OH)2/GO (19.5% loss). The asymmetric supercapacitor, using the Ni(OH)2/TGO and activated carbon as the positive material and negative material, respectively, exhibits high energy density of 22.5 Wh kg–1at 86.3 W kg–1and 17.8 Wh kg–1even at 4.05 kW kg–1.