Faxing Wang

Stimulus-Responsive Micro-Supercapacitors with Ultrahigh Energy Density and Reversible Electrochromic Window

Stimulus-responsive micro-supercapacitors (SR-MSCs) with ultrahigh volumetric energy density and reversible electrochromic effect are successfully fabricated by employing a vanadium pentoxide and electrochemical exfoliated graphene-based hybrid nanopaper and viologen as electrode and stimulus-responsive material, respectively. The fabricated high-performance SR-MSCs offer new opportunities for intuitively observing the working state of energy devices without the aid of extra equipment and techniques.

Hollow TiO2–X porous microspheres composed of well-crystalline nanocrystals for high-performance lithium-ion batteries

Hollow TiO2–X porous microspheres consisted of numerous well-crystalline nanocrystals with superior structural integrity and robust hollow interior were synthesized by a facile sol-gel template-assisted approach and two-step carbonprotected calcination method, together with hydrogenation treatment. They exhibit a uniform diameter of ~470 nm with a thin porous wall shell of ~50 nm in thickness. The Brunauer-Emmett-Teller (BET) surface area and pore volume are ~19 m2/g and 0.07 cm3/g, respectively. These hollow TiO2–X porous microspheres demonstrated excellent lithium storage performance with stable capacity retention for over 300 cycles (a high capacity of 151 mAh/g can be obtained up to 300 cycles at 1 C, retaining 81.6% of the initial capacity of 185 mAh/g) and enhanced rate capability even up to 10 C (222, 192, 121, and 92.1 mAh/g at current rates of 0.5, 1, 5, and 10 C, respectively). The intrinsic increased conductivity of the hydrogenated TiO2 microspheres and their robust hollow structure beneficial for lithium ion-electron diffusion and mitigating the structural strain synergistically contribute to the remarkable improvements in their cycling stability and rate performance.

A Quasi-Solid-State Li-Ion Capacitor Based on Porous TiO2 Hollow Microspheres Wrapped with Graphene Nanosheets

The quasi-solid-state Li-ion capacitor is demonstrated with graphene nanosheets prepared by an electrochemical exfoliation as the positive electrode and the porous TiO2 hollow microspheres wrapped with the same graphene nanosheets as the negative electrode, using a Li-ion conducting gel polymer electrolyte. This device may be the key to bridging the gap between conventional lithium-ion batteries and supercapacitors, meanwhile meeting the safety demands of electronic devices.

Dual-Template Synthesis of 2D Mesoporous Polypyrrole Nanosheets with Controlled Pore Size.

The first synergistic dual-template self-assembly approach is presented for bottom-up construction of 2D mesoporous polypyrrole nanosheets based on different supramolecular assemblies, which feature a double-layered architecture, controlled pore sizes, ultrathin thickness, and large surface area. The unique structure rends them with superior reversible discharge capability, rate performance, and stable cyclability when serving as the cathode materials for Na-ion batteries.

A quasi-solid-state Li-ion capacitor with high energy density based on Li3VO4/carbon nanofibers and electrochemically-exfoliated graphene sheets

Electrochemical capacitors are playing increasing roles in our daily life but their low energy densities limit their wide applications. The appearance of Li-ion capacitors (LICs) is regarded as the beginning of a new era of increased energy densities in the field of electrochemical capacitors. However, it is a great challenge to find a suitable anode material with superior electrochemical performance. In addition, the intrinsic instability of the liquid electrolytes used in LICs can easily result in leakage of the electrolyte and causes a serious safety issue. Here, a quasi-solid-state LIC is fabricated by applying Li3VO4/carbon nanofibers as the anode and electrochemically-exfoliated graphene sheets as the cathode in a gel polymer electrolyte. It achieves an energy density of 110 W h kg−1 and a good cycling performance. Our results demonstrate that quasi-solid-state LICs provide a key system acting as a bridge between conventional Li-ion batteries and supercapacitors, while meeting the high safety demands of electronic devices.

Dual‐Graphene Rechargeable Sodium Battery

Sodium (Na) ion batteries are attracting increasing attention for use in various electrical applications. However, the electrochemical behaviors, particularly the working voltages, of Na ion batteries are substantially lower than those of lithium (Li) ion batteries. Worse, the state-of-the-art Na ion battery cannot meet the demand of miniaturized in modern electronics. Here, we demonstrate that electrochemically exfoliated graphene (EG) nanosheets can reversibly store (PF6- ) anions, yielding high charging and discharging voltages of 4.7 and 4.3 V vs. Na+ /Na, respectively. The dual-graphene rechargeable Na battery fabricated using EG as both the positive and negative electrodes provided the highest operating voltage among all Na ion full cells reported to date, together with a maximum energy density of 250 Wh kg-1 . Notably, the dual-graphene rechargeable Na microbattery exhibited an areal capacity of 35 μAh cm-2 with stable cycling behavior. This study offers an efficient option for the development of novel rechargeable microbatteries with ultra-high operating voltage and high energy density.

Soft-Template Construction of 3D Macroporous Polypyrrole Scaffolds

A bottom-up approach toward 3D hierarchical macroporous polypyrrole aerogels is demonstrated via soft template-directed synthesis and self-assembly of ultrathin polypyrrole nanosheets in solution, which present interconnected macropores, ultrathin walls, and large specific surface areas, thereby exhibiting a high capacity, satisfactory rate capability, and excellent cycling stability for Na-ion storage.

A Dual‐Stimuli‐Responsive Sodium‐Bromine Battery with Ultrahigh Energy Density

Stimuli-responsive energy storage devices have emerged for the fast-growing popularity of intelligent electronics. However, all previously reported stimuli-responsive energy storage devices have rather low energy densities (<250 Wh kg-1 ) and single stimuli-response, which seriously limit their application scopes in intelligent electronics. Herein, a dual-stimuli-responsive sodium-bromine (Na//Br2 ) battery featuring ultrahigh energy density, electrochromic effect, and fast thermal response is demonstrated. Remarkably, the fabricated Na//Br2 battery exhibits a large operating voltage of 3.3 V and an energy density up to 760 Wh kg-1 , which outperforms those for the state-of-the-art stimuli-responsive electrochemical energy storage devices. This work offers a promising approach for designing multi-stimuli-responsive and high-energy rechargeable batteries without sacrificing the electrochemical performance.

Thermoswitchable on-chip microsupercapacitors: one potential self-protection solution for electronic devices

Efficient thermal protection is of great significance for electronic devices. Herein, we demonstrate a novel thermoswitchable microsupercapacitor (TS-MSC) with the self-protection function utilizing the thermodynamic behavior of a smart electrolyte, a lithium salt–dissolved polymer sol, poly(N-isopropylacrylamide)-g-methylcellulose. Benefiting from the reversibility of ionic conductivity, the TS-MSC exhibited a broad temperature window (30–80 °C) and totally switch-off behavior at 80 °C, as well as excellent cycling stability upon heating/cooling cycles. In addition, the thermal protection of on-chip integrated MSCs in series or parallel was achieved by controlling a single TS-MSC connected with a computer CPU under different working conditions. Therefore, TS-MSCs are promising components in the thermal protection of practical on-chip electronic devices.

Exposed high-energy facets in ultradispersed sub-10 nm SnO 2 nanocrystals anchored on graphene for pseudocapacitive sodium storage and high-performance quasi-solid-state sodium-ion capacitors

The development of sodium (Na) ion capacitors marks the beginning of a new era in the field of electrochemical capacitors with high-energy densities and low costs. However, most reported negative electrode materials for Na+ storage are based on slow diffusion-controlled intercalation/conversion/alloying processes, which are not favorable for application in electrochemical capacitors. Currently, it remains a significant challenge to develop suitable negative electrode materials that exhibit pseudocapacitive Na+ storage for Na ion capacitors. Herein, surface-controlled redox reaction-based pseudocapacitance is demonstrated in ultradispersed sub-10 nm SnO2 nanocrystals anchored on graphene, and this material is further utilized as a fascinating negative electrode material in a quasi-solid-state Na ion capacitor. The SnO2 nanocrystals possess a small size of <10 nm with exposed highly reactive {221} facets and exhibit pseudocapacitive Na+ storage behavior. This work will enrich the methods for developing electrode materials with surface-dominated redox reactions (or pseudocapacitive Na+ storage).Capacitors: Tin dioxide nanosurfaces store sodium ionsGraphene studded with tin dioxide nanocrystals provides a novel electrode material for sodium-ion capacitors with fast storage and excellent cyclability (the number of times they can be effectively recharged). Lithium-ion batteries are the dominant choice in modern portable electronics. However, sodium-ion technology offers the advantage of sodium’s abundance and low-cost. Much research is required before the electrode materials suitable for sodium-ion batteries and capacitors match the performance of those used in lithium-ion devices. Yuping Wu from Nanjing Tech University, Panpan Zhang from Beijing University of Chemical Technology, China, and colleagues in China and Germany anchored tin dioxide nanocrystals to a sheet of graphene and demonstrated its application as a negative electrode in a sodium-ion capacitor. The team propose that the exposed surfaces of the highly reactive tin dioxide crystals give the electrode its sodium-ion storage behavior.The electrode based on ultradispersed sub-10 nm SnO2 nanocrystals anchored on graphene nanosheets can reversibly store Na ions through both a surface-controlled pseudocapacitive reaction and a diffusion-limited alloying reaction. The fabricated Na ion hybrid capacitor with ultradispersed sub-10 nm SnO2 nanocrystals anchored on graphene nanosheets as negative electrode exhibits superior electrochemical performance.