Xingxing Gu

A porous nitrogen and phosphorous dual doped graphene blocking layer for high performance Li–S batteries

Conductive confinement of sulfur and polysulfides via carbonaceous blocking layers can simultaneously address the issues of low conductivity, volume expansion of sulfur during the charge/discharge process and the polysulfide shuttling effect in lithium–sulfur (Li–S) batteries. Herein, a conductive and porous nitrogen and phosphorus dual doped graphene (p-NP-G) blocking layer is prepared via a thermal annealing and subsequent hydrothermal reaction route. The doping levels of N and P in p-NP-G as measured by X-ray photoelectron spectroscopy are ca. 4.38% and ca. 1.93%, respectively. The dual doped blocking layer exhibits higher conductivity than N or P single doped blocking layers. More importantly, density functional theory (DFT) calculations demonstrate that P atoms and –P–O groups in the p-NP-G layer offer stronger adsorption of polysulfides than the N species. The electrochemical evaluation results illustrate that the p-NP-G blocking layer can deliver superior initial capacity (1158.3 mA h g−1 at a current density of 1C), excellent rate capability (633.7 mA h g−1 at 2C), and satisfactory cycling stability (ca. 0.09% capacity decay per cycle), which are better than those of the N or P single doped graphene. This work suggests that this synergetic combination of conductive and adsorptive confinement strategies induced by the multi-heteroatom doping scheme is a promising approach for developing high performance Li–S batteries.

A conductive interwoven bamboo carbon fiber membrane for Li–S batteries

Natural bamboo, as a sustainable precursor, is used to prepare porous bamboo carbon fibers (BCFs) that are subsequently interwoven into a BCF membrane (BCFM) as a captor interlayer for the lithium polysulfide intermediates between the sulfur cathode and the separator in Li–S batteries. On one hand, the interwoven BCFs offer efficient conductive networks. On the other hand, the pores of the BCFM facilitate fast mass transport of the electrolyte and Li ions and accommodate severe volume changes of the sulfur cathode during charge/discharge processes. Furthermore abundant macro/microporous structures of BCFs provide substantial adsorption capability to remarkably suppress the formation of the Li2S2/Li2S layer on the cathode and extend the lifetime of the electrode by successfully confining sulfur within the carbon networks. Consequently, Li–S batteries with the BCFM deliver excellent electrochemical performances with a high coulombic efficiency (ca. 98%), low capacity fade at only 0.11% per cycle, and long-term cyclability over 300 cycles at a high charge/discharge rate of 1 C. This green, low cost BCFM can provide an attractive alternative for large-scale commercialization of Li–S batteries.

Multifunctional Nitrogen-Doped Loofah Sponge Carbon Blocking Layer for High-Performance Rechargeable Lithium Batteries

Low-cost, long-life, and high-performance lithium batteries not only provide an economically viable power source to electric vehicles and smart electricity grids but also address the issues of the energy shortage and environmental sustainability. Herein, low-cost, hierarchically porous, and nitrogen-doped loofah sponge carbon (N-LSC) derived from the loofah sponge has been synthesized via a simple calcining process and then applied as a multifunctional blocking layer for Li-S, Li-Se, and Li-I2 batteries. As a result of the ultrahigh specific area (2551.06 m(2) g(-1)), high porosity (1.75 cm(3) g(-1)), high conductivity (1170 S m(-1)), and heteroatoms doping of N-LSC, the resultant Li-S, Li-Se, and Li-I2 batteries with the N-LSC-900 membrane deliver outstanding electrochemical performance stability in all cases, i.e., high reversible capacities of 623.6 mA h g(-1) at 1675 mA g(-1) after 500 cycles, 350 mA h g(-1) at 1356 mA g(-1) after 1000 cycles, and 150 mA h g(-1) at 10550 mA g(-1) after 5000 cycles, respectively. The successful application to Li-S, Li-Se, and Li-I2 batteries suggests that loofa sponge carbon could play a vital role in modern rechargeable battery industries as a universal, cost-effective, environmentally friendly, and high-performance blocking layer.

Role of anions on structure and pseudocapacitive performance of metal double hydroxides decorated with nitrogen-doped graphene

Electrochemical capacitors (EC) bear faster charge-discharge; however, their real applications are still on a long away due to lower capacitance and energy densities which mainly arise from simple surface charge accumulation or/and reaction. Here, a novel synthesis strategy was designed to obtain the purposeful hybrids of nickel cobalt double hydroxide (NiCoDH) with genetic morphology to improve their electrochemical performance as electrode of EC. Nanostructures of metal hydroxides were grown on the nitrogen-doped graphene (NG) sheets by utilizing defects as nucleation sites and their composition was optimized both by tuning the ratio of Ni: Co as well as the counter halogen and carbonate anions to improve the porosity, stabilize the structure and mediate the redox reaction. The growth of the hybrids was guided by the Co ions through topochemical transformation supported by hoping charge transfer process and olation growth. NG overcoating successfully protects the nanostructure of NiCoDH during electrochemical test and enhances overall conductivity of the electrode, improving the mass and ionic transportations. As a result, the hybrid exhibits excellent capacitance of 2925 F g−1 at 1 A g−1, as well as long cyclic stability of 10,000 cycles with good capacity retention of 90% at 16 A g−1. Furthermore, the hybrid shows excellent energy and power densities of 52 W h kg−1 and 3191 W kg−1, respectively at discharge rate of 16 A g−1. It is expected that this strategy can be readily extended to other metal hydroxides, oxides and sulphides to improve their electrochemical performances.摘要超级电容器因为具有充放电时间短的特点引起了人们的广泛关注. 然而, 由于电极表面的电荷积聚和化学反应, 电容器的比电容及能量密度大大降低, 限制了超级电容器的实际应用. 本文提出了一种新颖的合成方法用以制备基于镍钴双氢氧化物的复合材料, 该复合材料作为超级电容器的电极具有优异的电化学性能. 利用氮掺杂石墨烯的缺陷, 金属氢氧化物纳米结构在氮掺杂石墨烯表面生长, 形成复合结构. 通过调节并优化镍钴的元素比以及卤素离子、 碳酸根离子的含量, 能够改善材料的孔隙度、 提高材料结构的稳定性以及促进电化学反应. 金属氢氧化物的形成由钴离子的氧化反应引导, 并通过定向生长方式形成一维结构. 氮掺杂石墨烯有效保护镍钴双氢氧化物的纳米结构, 使其在电化学测试中不被破坏, 同时, 氮掺杂石墨烯还能够提高电极的导电性, 利于物质及离子传输. 电化学测试表明, 该复合材料在电流密度为1 A g−1时, 比电容高达2925 F g−1, 并且在高电流密度下(16 A g−1)展现出了优异的循环稳定性, 在10,000次循环后比电容仍然保持在90%. 在16 A g−1的电流密度下, 材料的能量密度和功率密度分别达到了52 Wh kg−1和3191 W kg−1. 该合成方法为制备基于金属氢氧化物、 氧化物、 硫化物等高性能超级电容器电极提供了新的途径.

Ultrathin Fe2O3 nanoflakes using smart chemical stripping for high performance lithium storage

Two-dimensional (2D) nanomaterials are extraordinarily attractive for use in energy storage devices because of their unique electronic and mechanical properties. However, the synthesis of ultrathin 2D nanomaterials is still a great challenge. In this paper, a top-down strategy using a high-pressure hydrogen surface treatment and controlled etching to reduce the thickness of iron(III) oxide (Fe2O3) nanoplates is proposed. As a result, the ultrathin Fe2O3 hexagonal nanoflakes with a thickness of approximately 4 nm are successfully synthesized. When employed as an anode material in rechargeable lithium-ion batteries, it delivers a super-high reversible capacity of approximately 1043 mA h g−1 after 100 cycles at a current density of 0.1 A g−1 and approximately 578 mA h g−1 after 500 cycles at a current density of 5.0 A g−1. It is also the best performing Fe2O3 electrode among the reported Fe2O3 anodes in the literature. Such excellent cycling performances can be attributed to the ultrathin structure which is able to enhance the mass transport of the lithium ion, short electron transport length as well as tolerance of large volume changes. This work provides a guidance to the synthesis of ultra-thin 2D oxide nanomaterials for energy storage.