Minchan Li

Highly durable organic electrode for sodium-ion batteries via a stabilized α-C radical intermediate.

It is a challenge to prepare organic electrodes for sodium-ion batteries with long cycle life and high capacity. The highly reactive radical intermediates generated during the sodiation/desodiation process could be a critical issue because of undesired side reactions. Here we present durable electrodes with a stabilized α-C radical intermediate. Through the resonance effect as well as steric effects, the excessive reactivity of the unpaired electron is successfully suppressed, thus developing an electrode with stable cycling for over 2,000 cycles with 96.8% capacity retention. In addition, the α-radical demonstrates reversible transformation between three states: C=C; α-C·radical; and α-C− anion. Such transformation provides additional Na+ storage equal to more than 0.83 Na+ insertion per α-C radical for the electrodes. The strategy of intermediate radical stabilization could be enlightening in the design of organic electrodes with enhanced cycling life and energy storage capability.

Facile electrodeposition of 3D concentration-gradient Ni-Co hydroxide nanostructures on nickel foam as high performance electrodes for asymmetric supercapacitors

Novel three-dimensional (3D) concentration-gradient Ni-Co hydroxide nanostructures (3DCGNC) have been directly grown on nickel foam by a facile stepwise electrochemical deposition method and intensively investigated as binder- and conductor-free electrode for supercapacitors. Based on a three-electrode electrochemical characterization technique, the obtained 3DCGNC electrodes demonstrated a high specific capacitance of 1,760 F·g−1 and a remarkable rate capability whereby more than 62.5% capacitance was retained when the current density was raised from 1 to 100 A·g−1. More importantly, asymmetric supercapacitors were assembled by using the obtained 3DCGNC as the cathode and Ketjenblack as a conventional activated carbon anode. The fabricated asymmetric supercapacitors exhibited very promising electrochemical performances with an excellent combination of high energy density of 103.0 Wh·kg−1 at a power density of 3.0 kW·kg−1, and excellent rate capability—energy densities of about 70.4 and 26.0 Wh·kg−1 were achieved when the average power densities were increased to 26.2 and 133.4 kW·kg−1, respectively. Moreover, an extremely stable cycling life with only 2.7% capacitance loss after 20,000 cycles at a current density of 5 A·g−1 was achieved, which compares very well with the traditional doublelayer supercapacitors.

Bimetallic organic frameworks derived CuNi/carbon nanocomposites as efficient electrocatalysts for oxygen reduction reaction

Catalysts of oxygen reduction reaction (ORR) play key roles in renewable energy technologies such as metal-air batteries and fuel cells. Despite tremendous efforts, highly active catalysts with low cost remain elusive. This work used metal-organic frameworks to synthesize non-precious bimetallic carbon nanocomposites as efficient ORR catalysts. Although carbon-based Cu and Ni are good candidates, the hybrid nanocomposites take advantage of both metals to improve catalytic activity. The resulting molar ratio of Cu/Ni in the nanocomposites can be finely controlled by tuning the recipe of the precursors. Nanocomposites with a series of molar ratios were produced, and they exhibited much better ORR catalytic performance than their monometallic counterparts in terms of limited current density, onset potential and half-wave potential. In addition, their extraordinary stability in alkaline is superior to that of commercially-available Pt-based materials, which adds to the appeal of the bimetallic carbon nanocomposites as ORR catalysts. Their improved performance can be attributed to the synergetic effects of Cu and Ni, and the enhancement of the carbon matrix.摘要氧还原催化剂在金属空气电池和燃料电池的可再生能源技术中起至关重要的作用. 尽管该方面研究已有很多, 高活性低成本的催化剂的开发仍然十分困难. 本文以金属有机骨架为前驱体, 成功合成出非贵金属铜镍双金属碳基纳米复合物并作为高效的氧还原催化剂. 单金属复合物Cu/C和Ni/C皆具有较好的氧还原催化作用, 铜镍双金属复合物进一步综合了二者优点从而提升了催化性能. 本文所合成的铜镍双金属复合物中的金属比例可通过调整前驱体中的原料配比来准确控制, 所得的一系列金属比例的铜镍双金属碳基纳米复合物在极限电流密度、起始电位和半波电位三个方面都超过了单金属复合物. 此外, 铜镍双金属碳基纳米复合物在碱性环境中具有良好的稳定性且超过了目前最好的氧还原催化材料铂, 大大加强了其作为氧还原催化剂的优势. 铜镍双金属碳基纳米复合物优越的电化学催化性能归功于金属铜和镍以及碳材料基底的协同作用.

Large-scale fabrication of porous carbon-decorated iron oxide microcuboids from Fe–MOF as high-performance anode materials for lithium-ion batteries

A facile, cost-effective and environmentally friendly route has been developed to synthesise porous carbon-decorated iron oxides on a large scale via annealing iron metal–organic framework (MOF) precursors. The as-prepared C–Fe3O4 particles exhibit microcuboid-like morphologies that are actually composed of ultrafine nanoparticles and show a greatly enhanced lithium storage performance with high specific capacity, excellent cycling stability and good rate capability. The C–Fe3O4 electrodes demonstrate a high reversible capacity of 975 mA h g−1 after 50 cycles at a current density of 100 mA g−1 and a remarkable rate performance, with capacities of 1124, 1042, 886 and 695 mA h g−1 at current densities of 100, 200, 500 and 1000 mA g−1, respectively. The satisfactory electrochemical performance was attributed to the hierarchical architecture, which benefitted from the synergistic effects of the high conductivity of the carbon matrix, the cuboid-like secondary particles on the microscale, and the ultrafine primary nanoparticles on the nanoscale. This low-cost and simple method provides the possibility to prepare anode materials on a large scale and hence may have great potential applications in energy storage and conversion.

Binder-free hydrogenated NiO–CoO hybrid electrodes for high performance supercapacitors

Binder-free NiO–CoO hybrid electrodes were directly grown on nickel foam by electrodeposition and subsequent annealing in 5% H2/95% N2 gas at 300 °C. Crystal structure, elemental analysis, surface morphology and chemical compositions of the composites were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) equipped with an energy dispersive X-ray analysis system. The hydrogenated NiO–CoO hybrid electrodes were evaluated as electrodes for supercapacitors which demonstrated promising electrochemical performance with high specific capacitance, excellent rate capability, and stable cycling.

Porous graphitic carbon prepared from the catalytic carbonization of Mo-containing resin for supercapacitors

A polystyrene-based ion exchange resin was utilized to recover Mo from wastewater, and the Mo was used as a catalyst and template to produce porous graphitic carbon possessing a large specific surface area and high electronic conductivity at moderate temperature. Further H2O2 oxidation leads to an increase in the pore volume due to the removal of molybdenum carbide and the partial oxidation of the porous carbon, resulting in a considerable enhancement of the specific capacitance.

MoC ultrafine nanoparticles confined in porous graphitic carbon as extremely stable anode materials for lithium- and sodium-ion batteries

Molybdenum carbide (MoC)/graphitic carbon nanocomposites are synthesized using a green and facile method. Well-crystallized MoC ultrafine nanoparticles (<5 nm diameter) are formed in situ inside the pores of a highly conductive graphitic carbon matrix. The resulting MoC/graphitic carbon nanocomposites exhibit very promising electrochemical performance when evaluated as anodes in LIBs and SIBs, because the synergistic effects of the small MoC nanoparticles provide fast and efficient transport and porous graphitic carbon can prevent continual rupturing as well as enhance conductivity. Meanwhile, this novel material has potential for broad application in rechargeable batteries, maintaining a reversible capacity of 742 mA h g−1 after 50 cycles at 200 mA g−1 for LIBs and a discharge capacity of 250 mA h g−1 after 50 cycles at 50 mA g−1 for SIBs. Furthermore, the required Mo can be recovered from wastewater, which gives this method an added environmental benefit and in return satisfy the current demand for sustainable development.

Facile synthesis of ultrathin MoS2/C nanosheets for use in sodium-ion batteries

We present a clean and simple method for the synthesis of MoS2/C hybrids. Commercial ion-exchange resins are used to absorb aqueous molybdate, followed by annealing with sulfur powder in an inert atmosphere. Even ultrathin MoS2 nanosheets with enlarged interlayers (0.63 nm) are homogeneously wrapped by mesoporous graphitic carbon. When evaluated as anodes for sodium-ion batteries, the MoS2/C nanocomposite exhibits good electrochemical performance. The first discharge/charge capacities at current density 50 mA g−1 are 784.3 and 590.0 mA h g−1, respectively, with initial coulombic efficiency of approximately 75%. It exhibits superior rate capabilities, with specific discharge capacities of 513.1, 467.3, 437.1, 399.2, 361.8, and 302.7 mA h g−1 at current densities of 50, 100, 200, 500, 1000, and 2000 mA g−1, respectively. This superior electrochemical performance is mainly due to the synergistic effect between the uniformly-distributed, ultrathin MoS2 nanosheets and the highly graphitized carbon. This not only mitigates mechanical stress during repeated cycling, but also provides good conductivity.

Low-Cost and Novel Si-Based Gel for Li-Ion Batteries

Si-based nanostructure composites have been intensively investigated as anode materials for next-generation lithium-ion batteries because of their ultra-high-energy storage capacity. However, it is still a great challenge to fabricate a perfect structure satisfying all the requirements of good electrical conductivity, robust matrix for buffering large volume expansion, and intact linkage of Si particles upon long-term cycling. Here, we report a novel design of Si-based multicomponent three-dimensional (3D) networks in which the Si core is capped with phytic acid shell layers through a facile high-energy ball-milling method. By mixing the functional Si with graphene oxide and functionalized carbon nanotube, we successfully obtained a homogeneous and conductive rigid silicon-based gel through complexation. Interestingly, this Si-based gel with a fancy 3D cross-linking structure could be writable and printable. In particular, this Si-based gel composite delivers a moderate specific capacity of 2711 mA h g-1 at a current density of 420 mA g-1 and retained a competitive discharge capacity of more than 800.00 mA h g-1 at the current density of 420 mA g-1 after 700 cycles. We provide a new method to fabricate durable Si-based anode material for next-generation high-performance lithium-ion batteries.

Encapsulated MnO in N-doping carbon nanofibers as efficient ORR electrocatalysts

Development of cheap, abundant and noble-metal-free materials as high efficient oxygen reduction electrocatalysts is crucial for future energy storage system. Here, one-dimensional (1D) MnO N-doped carbon nanofibers (MnO-NCNFs) were successfully developed by electrospinning combined with high temperature pyrolysis. The MnO-NCNFs exhibit promising electrochemical performance, methanol tolerance, and durability in alkaline medium. The outstanding electrocatalytic activity is mainly attributed to several issues. First of all, the uniform 1D fiber structure and the conductive network could facilitate the electron transport. Besides, the introduction of Mn into the precursor can catalyze the transformation of amorphous carbon to graphite carbon, while the improved graphitization means better conductivity, beneficial for the enhancement of catalytic activity for oxygen reduction reaction (ORR). Furthermore, the porous structure and high surface area can effectively decrease the mass transport resistance and increase the exposed ORR active sites, thus improve utilization efficiency and raise the quantity of exposed ORR active sites. The synergistic effect of MnO and NCNFs matrix, which enhances charge transfer, adsorbent transport, and delivers efficiency in the electrolyte solution, ensures the high ORR performance of MnO-NCNFs.摘要廉价、 储量丰富的非贵金属材料作为高效氧还原电催化剂是未来能量存储系统实际应用的关键. 基于此, 我们通过静电纺丝法并结合相应热处理制备了一维氮掺杂碳纳米纤维包覆一氧化锰(MnO-NCNFs). 该材料在碱性体系中表现出良好的电化学性能, 耐甲醇腐蚀性和稳定性. 其优异的电催化活性主要归结于以下几点: (1) 均一的一维纤维结构和导电网络能够促进反应过程中快速的电子转移; (2) 过渡金属锰的引入能够促进无定型碳向石墨碳的转变, 同时石墨化程度的提高意味着更好的导电性, 有利于氧还原活性的提高; (3) 多孔结构和高比表面积能够有效降低传质阻力并提高暴露的氧还原活性位点数量, 进而提高物质利用效率.