Zhi Chang

Hierarchical porous carbons with layer-by-layer motif architectures from confined soft-template self-assembly in layered materials

Although various two-dimensional (2D) nanomaterials have been explored as promising capacitive materials due to their unique layered structure, their natural restacking tendency impedes electrolyte transport and significantly restricts their practical applications. Herein, we synthesize all-carbon layer-by-layer motif architectures by introducing 2D ordered mesoporous carbons (OMC) within the interlayer space of 2D nanomaterials. As a proof of concept, MXenes are selected as 2D hosts to design 2D–2D heterostructures. Further removing the metal elements from MXenes leads to the formation of all-carbon 2D–2D heterostructures consisting of alternating layers of MXene-derived carbon (MDC) and OMC. The OMC layers intercalated with the MDC layers not only prevent restacking but also facilitate ion diffusion and electron transfer. The performance of the obtained hybrid carbons as supercapacitor electrodes demonstrates their potential for upcoming electronic devices. This method allows to overcome the restacking and blocking of 2D nanomaterials by constructing ion-accessible OMC within the 2D host material.

Co3O4 nanoneedle arrays as a multifunctional “super-reservoir” electrode for long cycle life Li–S batteries

Lithium–sulfur (Li–S) batteries are highly attractive as energy storage devices due to their low cost and high energy density. The undesired capacity degradation caused by the polysulfide shuttle, however, has hindered their commercialization. Herein, a Co3O4 nanoneedle array on carbon cloth (CC@Co3O4) nanocomposite has been prepared and demonstrated for the first time as a multifunctional “super-reservoir” electrode to prolong the cycle life of Li–S batteries. Owing to the polar surface of the Co3O4 nanoneedle array, soluble lithium polysulfides (Li2Sn, 4 < n < 8) can be effectively absorbed and then transformed to insoluble Li2S2/Li2S which evenly covers the surface of the Co3O4 nanoneedle during the discharge process. Further, during the charge process, the Co3O4 nanoneedle can catalyze the electrochemical transformation of Li2S2/Li2S into soluble polysulfides. A high initial capacity of 1231 mA h g−1 at 0.5C and a slow capacity decay of 0.049%/cycle at 2.0C over 500 cycles were achieved; excellent rate performance was also obtained.

Nanospace-confinement copolymerization strategy for encapsulating polymeric sulfur into porous carbon for lithium-sulfur batteries.

Given their high theoretical energy density, lithium-sulfur (Li-S) batteries have recently attracted ever-increasing research interest. However, the dissolution of polysulfides and uncontrolled deposition of insoluble discharge product significantly hinder the cycling stability. Herein, a nanospace-confinement copolymerization strategy for encapsulating polymeric sulfur into porous carbon matrix is presented. The morphologies and sulfur contents of carbon/polymeric sulfur (C/PS) composites could be readily tailored by controlling the copolymerization time. Confining polymeric sulfur in the porous carbon with abundant interparticle pores facilitates rapid electronic/ionic transport and mitigates dissolution of polysulfides intermediates. More importantly, the organic sulfur units dispersed in the insoluble/insulating Li2S2/Li2S phase could prevent its irreversible deposition. Such nanostructure with tailored chemistry property permits the C/PS electrodes to exhibit enhanced cycling stability and high rate capability. The nanospace-confinement copolymerization strategy features general and facial advantages, which may provide new opportunities for the future development of advanced sulfur cathodes.

PAA/PEDOT:PSS as a multifunctional, water-soluble binder to improve the capacity and stability of lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries as lithium secondary batteries have drawn tremendous interest due to their high theoretical specific capacity and energy density. However, the low practical specific capacity and poor cycling life keep them from large scale usage. Herein, a novel binder based on a mixture of polyacrylic acid (PAA) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is designed to significantly improve the specific capacity and cycling stability of Li–S batteries via the synergistic effect of the different functional groups. The conductive PEDOT:PSS successfully facilitates electron transfer and prevents polysulfide dissolution. PAA improves the solvent system for sulfur cathodes and promotes lithium-ion transfer. The sulfur cathode with PAA/PEDOT:PSS binder in a ratio of 2:3 exhibits an initial specific capacity of 1121 mA h g−1 and 830 mA h g−1 after 80 cycles at 0.5C. The electrochemical performance of the sulfur cathode with the composite binder is better than either of the single-component binders.

Nanospace-confined synthesis of oriented porous carbon nanosheets for high-performance electrical double layer capacitors

Two-dimensional (2D) carbon nanosheets have emerged as an attractive candidate for electrical double layer capacitors (EDLCs) due to their large specific surface area, good electrical conductivity and high charge mobility. However, the easy aggregation nature of nanosheets hinders rapid transport of electrolyte ions, reducing the ion-accessible area and restricting the ion transportation. Herein, we propose a template strategy for preparing three-dimensional (3D) porous carbon nanosheets (PCNs) with an oriented and interconnected nanostructure. Zinc layered hydroxide nitrate is used as a layered template and provides a nanospace to confine the carbonization process of the organic carbon precursor (gallic acid). The unique nanostructure and large surface area of chemically activated PCNs (aPCNs) significantly shorten the ion transport length in low dimensions and improve the electrolyte wettability and ion accessible surface area for charge storage. The aPCNs exhibit excellent performance as demonstrated by their large specific capacitance (327 F g−1 at a current density of 0.5 A g−1), superior rate capability (retaining 60.2% at 20 A g−1) and stable cyclability. In particular, the assembled symmetric device based on aPCNs delivers an energy density as high as 10.2 W h kg−1 at a power density of 301 W kg−1.

Confined Self‐Assembly in Two‐Dimensional Interlayer Space: Monolayered Mesoporous Carbon Nanosheets with In‐Plane Orderly Arranged Mesopores and a Highly Graphitized Framework

Although two-dimensional (2D) carbon materials are widely investigated, a well-defined 2D carbon nanosheet with an ordered mesostructure has rarely been realized. Monolayer-ordered mesoporous carbon nanosheets (OMCNS) were prepared through confinement assembly of resol and F127 in the interlayer of montmorillonite (MONT). The nanoscale distance of the interlayer space of MONT only allow the assembly of resol and F127 in the same plane, leading to ordered mesopores perpendicular to carbon nanosheets, and favor the formation of sp2 carbon, resulting in a high degree of graphitization. The mesopores on the carbon nanosheets provide efficient ion diffusion, and the high degree of graphitization provides a fast electron-transport route, enabling OMCNS as excellent electrode materials for electric double layer capacitors.

Interconnected core–shell pyrolyzed polyacrylonitrile@sulfur/carbon nanocomposites for rechargeable lithium–sulfur batteries

Elemental sulfur has attracted great interest for rechargeable batteries because of its high theoretical specific capacity and low cost. However, sulfur electrodes still suffer from rapid capacity fading, which is mainly caused by the undesirable dissolution of polysulfide intermediates and the irreversible deposition of discharge products. In this work, we describe an interconnected core–shell pyrolyzed polyacrylonitrile@carbon/sulfur (pPAN@C/S) nanostructure for high-performance lithium–sulfur batteries. Sulfur was firstly confined in a conductive porous carbon host as C/S to enhance the conductivity of sulfur, constrain polysulfide intermediates and alleviate volume expansion during cycling. Then a conductive pPAN shell was formed by annealing of PAN absorbed on the surface of C/S at 300 °C to further prevent polysulfide intermediates from dissolution by an additional physical and chemical barrier. Meanwhile, the conductive pPAN shell could prevent the irreversible deposition of insoluble discharge products, leading to improved cyclic stability. The interconnected core–shell pPAN@C/S electrodes exhibit a very high initial discharge capacity of 1269 mAh g−1 at 0.5 C and show excellent cycling stability and rate performance.

Facile Synthesis of Nitrogen-Containing Mesoporous Carbon for High-Performance Energy Storage Applications.

Porous carbon with high specific surface area (SSA), a reasonable pore size distribution, and modified surface chemistry is highly desirable for application in energy storage devices. Herein, we report the synthesis of nitrogen-containing mesoporous carbon with high SSA (1390 m(2) g(-1)), a suitable pore size distribution (1.5-8.1 nm), and a nitrogen content of 4.7 wt % through a facile one-step self-assembly process. Owing to its unique physical characteristics and nitrogen doping, this material demonstrates great promise for application in both supercapacitors and encapsulating sulfur as a superior cathode material for lithium-sulfur batteries. When deployed as a supercapacitor electrode, it exhibited a high specific capacitance of 238.4 F g(-1) at 1 A g(-1) and an excellent rate capability (180 F g(-1), 10 A g(-1)). Furthermore, when an NMC/S electrode was evaluated as the cathode material for lithium-sulfur batteries, it showed a high initial discharge capacity of 1143.6 mA h g(-1) at 837.5 mA g(-1) and an extraordinary cycling stability with 70.3% capacity retention after 100 cycles.

An in situ confinement strategy to porous poly(3,4-ethylenedioxythiophene)/sulfur composites for lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries are receiving intense interest because of their high theoretical energy density and low cost. However, the rapid capacity fading is a significant problem facing the application of Li–S batteries. Herein, we describe an in situ confinement strategy for preparing a porous poly(3,4-ethylenedioxythiophene)/sulfur (pPEDOT/S) composite for Li–S batteries. The as-prepared pPEDOT/S composite exhibits a monodispersed nanostructure with sizes in the range of 400–600 nm. The pPEDOT/S composite electrode exhibits excellent cycling stability and high specific capacity. At a current rate of 0.5C, the pPEDOT/S electrode exhibits a high specific capacity of 883 mA h g−1 and a capacity retention of 71% after 200 cycles. During the charge/discharge process, the porous nanostructure could facilitate rapid electrolyte diffusion and accommodate the volumetric expansion. The chemical interaction between the PEDOT and polysulfides and discharged products could efficiently avoid the dissolution of polysulfides and the irreversible deposition of discharged products. The unique nanostructure plus the excellent electrochemical performances of the composites described in the current study allow for new opportunities to design high-performance electrodes for Li–S batteries.

Heteroatom-Doped Porous Carbon Nanosheets: General Preparation and Enhanced Capacitive Properties.

High-performance electrical double-layer capacitors (EDLCs) require carbon electrode materials with high specific surface area, short ion-diffusion pathways, and outstanding electrical conductivity. Herein, a general approach combing the molten-salt method and chemical activation to prepare N-doped carbon nanosheets with high surface area (654 m2  g-1 ) and adjustable porous structure is presented. Owing to their structural features, the N-doped carbon nanosheets exhibited superior capacitive performance, demonstrated by a maximum capacitance of 243 F g-1 (area-normalized capacitance up to 37 μF cm-2 ) at a current density of 0.5 A g-1 in aqueous electrolyte, high rate capability (179 F g-1 at 20 A g-1 ), and excellent cycle stability. This method provides a new route to prepare porous and heteroatom-doped carbon nanosheets for high-performance EDLCs, which could also be extended to other polymer precursors and even waste biomass.