Jinping Wei

Preparation and electrochemical performances of doughnut-like Ni(OH)2–Co(OH)2 composites as pseudocapacitor materials

Doughnut-like nanostructured Ni(OH)(2)-Co(OH)(2) composites were prepared by combining hydrothermal and chemical deposition routes. The electrochemical performances of the composites were investigated as pseudocapacitor materials through galvanostatic charge-discharge and cyclic voltammetry tests. The Ni(OH)(2)-Co(OH)(2) composites delivered a specific capacitance of 2193 F g(-1) at 2 A g(-1) and 1398 F g(-1) at 20 A g(-1), much higher than those of pristine Ni(OH)(2). The enhancement of the overall electrochemical performances is ascribed to the synergetic contribution from nanostructured Ni(OH)(2) and electrically conductive CoOOH forming in the charge process.

Orderly Packed Anodes for High-Power Lithium-Ion Batteries with Super-Long Cycle Life: Rational Design of MnCO3/Large-Area Graphene Composites

MnCO3 particles uniformly distributed on large-area graphene form 2D composites whose large-area character enables them to self-assemble face-to-face into orderly packed electrodes. Such regular structures form continuous and efficient transport networks, leading to outstanding lithium storage with high capacity, ultralong cycle life, and excellent rate capability--all characteristics that are required for high-power lithium-ion batteries.

Rambutan-Like FeCO3 Hollow Microspheres: Facile Preparation and Superior Lithium Storage Performances

Rambutan-like FeCO3 hollow microspheres were prepared via a facile and economic one-step hydrothermal method. The structure and morphology evolution mechanism was disclosed through time-dependent experiments. After undergoing the symmetric inside-out Ostwald ripening, the resultants formed microporous/nanoporous constructions composed of numerous one-dimensional (1D) nanofiber building blocks. Tested as anode materials of Li-ion batteries, FeCO3 hollow microspheres presented attractive electrochemical performances. The capacities were over 1000 mAh g(-1) for initial charge, ~880 mAh g(-1) after 100 cycles at 50 mA g(-1), and ~710 mAh g(-1) after 200 cycles at 200 mA g(-1). The 1D nanofiber assembly and hollow interior endow this material efficient contact with electrolyte, short Li(+) diffusion paths, and sufficient void spaces to accommodate large volume variation. The cost-efficient FeCO3 with rationally designed nanostructures is a promising anode candidate for Li-ion batteries.

The First Introduction of Graphene to Rechargeable Li–CO2 Batteries

The utilization of the greenhouse gas CO2 in energy-storage systems is highly desirable. It is now shown that the introduction of graphene as a cathode material significantly improves the performance of Li-CO2 batteries. Such batteries display a superior discharge capacity and enhanced cycle stability. Therefore, graphene can act as an efficient cathode in Li-CO2 batteries, and it provides a novel approach for simultaneously capturing CO2 and storing energy.

Achieving battery-level energy density by constructing aqueous carbonaceous supercapacitors with hierarchical porous N-rich carbon materials

Pseudocapacitive materials hold great promise for achieving battery-level energy density integrated with power-related preponderance of electrostatic capacitors. However, it still remains a great challenge to find suitable capacitive material pairs to provide high operating voltage and high-level capacitance with good rate capability. Here, a three-dimensional hierarchical porous N-rich graphitic carbon (HNGC) material was prepared to construct novel symmetric aqueous carbonaceous supercapacitors (ACSCs). With ultrathin slice units, highly graphitic texture, and copious heteroatom functionalities, HNGC significantly promoted the faradic pseudo-capacitance, demonstrating an extremely high single-electrode capacitance of over 710 F g−1 in 1 M H2SO4 aqueous solution. First-principles computations revealed that copious N-induced defects tremendously boost the electrochemical performance of HNGC in acidic electrolytes by accommodating more protons, facilitating ion mobility and interfacial charge transport. Due to the co-existence of both electrical double-layer capacitance and pseudo-capacitance, the novel symmetric ACSCs with both structural and elemental advantages provide high operating voltage and a further high-level energy density of over 75 W h kg−1electrodes at a large power density of 1500 W kg−1, achieving battery-level energy density while retaining capacitor-level power delivery ability (30 kW kg−1) and cycling stability (ultra-long 8000 cycles). The proof-of-concept design of ACSCs outclasses the generally known high-voltage asymmetric counterparts under the same power and represents an advance towards battery-level energy density in supercapacitors.

Effect of lithium difluoro(oxalate)borate (LiDFOB) additive on the performance of high-voltage lithium-ion batteries

Lithium difluoro(oxalato)borate (LiDFOB) was investigated as an electrolyte additive for high-voltage lithium-ion batteries in order to decrease the decomposition of the electrolyte. As a typical high-voltage cathode material, LiCoPO4 was tested in the LiDFOB-containing electrolyte, exhibiting higher reversible charge/discharge capacity and better cyclic stability. The effect of LiDFOB on the formation of a stable interphase film was investigated through cyclic voltammetry and X-ray photoelectron spectroscopy. LiDFOB was helpful to form a stable interphase film and passivate the cathode surface; therefore, the decomposition of the electrolyte was inhibited accordingly.

Stable layered P3/P2 Na0.66Co0.5Mn0.5O2 cathode materials for sodium-ion batteries

Rechargeable sodium-ion batteries are promising next-generation energy storage devices due to the low cost and rich natural abundance of Na. However, it is still a great challenge to suppress phase changes of cathode materials in the high-voltage region. Unlike P-type single-phase composites, herein we present a facile strategy for preparing P3/P2-type biphasic layered Na0.66Co0.5Mn0.5O2, namely, integrating P2 into P3-layered materials. The crystalline structure of Na0.66Co0.5Mn0.5O2, which was investigated by ex situ X-ray diffraction, was well maintained over long cycling in a high-voltage range. Taking advantage of their structural stabilization, Na0.66Co0.5Mn0.5O2 cathode materials displayed remarkably steady discharge capacity at high rates. With outstanding structural flexibility and electrochemical performance, Na0.66Co0.5Mn0.5O2 would stimulate the development of sodium-ion batteries.

Preparation and electrochemical Li storage performance of MnO@C nanorods consisting of ultra small MnO nanocrystals

MnO, with low operation potential and cost, is very attractive among transition metal oxides as an anode material for Li ion batteries. In this work, hierarchical MnO@C nanorods, in which ultra-small MnO nanocrystals (generally <5 nm) were homogeneously dispersed in a carbon matrix and further coated with a well-proportioned carbon shell, were prepared through a two-step hydrothermal treatment and subsequent sintering at 600 °C, with a slow heating rate of 5 °C min−1. In contrast, when sintered at a higher temperature (800 °C) and a faster heating rate (10 °C min−1), the ultra-small MnO nanocrystals agglomerated into nanoparticles (30–80 nm) and partially lost the contact with the outer carbon shell. Profiting from the highly-dispersed ultra-small nanocrystals in the carbon matrix and the well-proportioned carbon shell, the carbon-coated MnO nanocrystals exhibited a reversible capacity of 481 mA h g−1 after 50 cycles at a current density of 200 mA g−1, which is higher than that of carbon-coated MnO nanoparticles. The results disclose the important roles of small particles and carbon shells in developing advanced anode materials for Li ion batteries.

Co2(OH)2CO3 Nanosheets and CoO Nanonets with Tailored Pore Sizes as Anodes for Lithium Ion Batteries

Co2(OH)2CO3 nanosheets were prepared and initially tested as anode materials for Li ion batteries. Benefiting from hydroxide and carbonate, the as-prepared sample delivered a high reversible capacity of 800 mAh g(-1) after 200 cycles at 200 mA g(-1) and long-cycling capability of 400 mAh g(-1) even at 1 A g(-1). Annealed in Ar, monoclinic Co2(OH)2CO3 nanosheets were transformed into cubic CoO nanonets with rich pores. The pore size had apparent influence on the high-rate performances of CoO. CoO with appropriate pore sizes exhibited greatly enhanced Li storage performances, stable capacity of 637 mAh g(-1) until 200 cycles at 1 A g(-1). More importantly, after many fast charge-discharge cycles, the highly porous nanonets were still maintained. Our results indicate that Co2(OH)2CO3 nanosheets and highly porous CoO nanonets are both promising candidate anode materials for high-performance Li ion batteries.

Ultrasmall MnO@N-rich carbon nanosheets for high-power asymmetric supercapacitors

Manganese monoxide (MnO) holds great potential for high-performance supercapacitors; however, it is highly desirable to establish a feasible structure to address common concerns of MnO materials. Herein, we have inserted ultrasmall MnO nanoparticles into N-rich carbon nanosheets (MnO@NCs) via a facile and scalable method. By integrating copious nitrogen species (over 13 wt%), flexible but robust carbon nanosheets offer powerful support for dispersing large amounts of MnO nanoparticles, creatively avoiding the inherent deficiencies of MnO such as poor electrical conductivity, low mechanical stability and severe electrochemical dissolution. Consequently, the MnO@NC electrode exhibited a striking capacitance of 570 F g−1 at 2 A g−1 within a wide operation voltage of 1 V, which spurs the low capacitance of MnO materials (generally 200–350 F g−1) to a higher level. Furthermore, initial attempts at fabricating asymmetric supercapacitors based on MnO@NCs demonstrated an energy density superior to its well-studied MnO2 counterpart. The introduction of N-rich species is of great significance for releasing restricted properties and fully exerting positive effects on the supercapacitors. Particularly, the impressive capacitance retention of ∼99% over 6000 cycles also propels a new direction for transition metal oxide/NC composites towards high-performance energy storage devices.