ABSTRACT
Aqueous Zn-ion battery is expected to become a substitute for Li-ion battery due to its inherent safety, low cost, and environmental friendliness. Dendrite growth and side reaction problems during electroplating lead to its low Coulombic efficiency and unsatisfactory life, which greatly limits its practical application. Here, we propose a dual-salts hybrid electrolyte, which alleviates the above issues by mixing Zn(OTf)2 to ZnSO4 solution. Extensive tests and MD simulations have shown that the dual-salts hybrid electrolyte can regulate the solvation structure of Zn2+, facilitating uniform Zn deposition, and inhibiting side reactions and dendrite growth. Hence, the dual-salts hybrid electrolyte exhibits good reversibility in Zn//Zn batteries, which can provide a lifetime of more than 880 h at 1 mA cm-2 and 1 mAh cm-2. Moreover, the average Coulombic efficiency of Zn//Cu cells in hybrid system can reach 98.2% after 520 h, much better than that of 90.7% in pure ZnSO4 electrolyte and 92.0% in pure Zn(OTf)2 electrolyte. Benefiting from the fast ion exchange rate and high ion conductivity, Zn-ion hybrid capacitor in hybrid electrolyte also displays excellent stability and capacitive performance. This effective strategy for dual-salts hybrid electrolytes provides a promising direction for designing aqueous electrolytes for Zn-ion batteries.
ABSTRACT
Herein, ZIF-8 pre-grown on carbon cloth (CC) leads to preferential and homogenizing Zn deposition to accelerate Zn-ion diffusion. CC with uniform Zn deposits induced from ZIF-8 promotes rapid Zn plating, resulting in balanced kinetics between electrodes. The as-assembled ZICs show a high specific capacitance of 302 F g-1 at 0.5 A g-1, an outstanding rate performance of 188 F g-1 at 20 A g-1 and 100% capacitance retention after 10000 cycles.
ABSTRACT
Carbon-based electric double layer capacitors (EDLCs) hold tremendous potentials due to their high-power performance and excellent cycle stability. However, the practical use of EDLCs is limited by the low energy density in aqueous electrolyte and sluggish diffusion kinetics in organic or/and ionic liquids electrolyte. Herein, 3D carbon frameworks (3DCFs) constructed by interconnected nanocages (10-20 nm) with an ultrathin wall of ca. 2 nm have been fabricated, which possess high specific surface area, hierarchical porosity and good conductive network. After deoxidization, the deoxidized 3DCF (3DCF-DO) exhibits a record low IR drop of 0.064 V at 100 A g-1 and ultrafast charge/discharge rate up to 10 V s-1. The related device can be charged up to 77.4% of its maximum capacitance in 0.65 s at 100 A g-1 in 6 M KOH. It has been found that the 3DCF-DO has a great affinity to EMIMBF4, resulting in a high specific capacitance of 174 F g-1 at 1 A g-1, and a high energy density of 34 Wh kg-1 at an ultrahigh power density of 150 kW kg-1 at 4 V after a fast charge in 1.11 s. This work provides a facile fabrication of novel 3D carbon frameworks for supercapacitors with ultrafast charge/discharge rate and high energy-power density.
ABSTRACT
Reasonable structure design and component selection are crucial to electrochemical performance of supercapacitor electrode materials. Sodium alginate (SA), with a novel structure which can immobilize multivalent metal cations, was used to coordinate with Fe3+ to fabricate a carbon and Fe3O4 composite by an easy sol-gel method. Due to the chelation effect between SA and Fe3+, the carbon composite was constructed into a two-dimensional sheet-like structure, and the Fe3O4 particles were nanosize and homogenously distributed on the surface of the carbon nanosheet. As an electrode material for supercapacitors, the composite electrode showed a high specific capacitance of 550 F g-1 at 1 A g-1 in the potential range from -1.1 to 0 V, and excellent cycling stability of 89% retention after 2000 cycles. The enhanced electrochemical performance could be attributed to the abundant exposed active sites, producing high pseudocapacitance, to the two-dimensional nanosheet structure, facilitating electrolyte transport and to the strong attachment strength, improving cycle life. This environmentally-friendly design can provide an alternative to existing methods, resulting in the development of a two-dimensional carbon/metal oxide composite for energy storage devices.
