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This work introduces the facile and scalable two-step synthesis of Ti 2 Nb 10 O 29 (TNO)/carbon hybrid material as a promising anode for lithium-ion batteries (LIBs). The first step uses a mechanically-induced self-sustaining reaction via ball-milling at room temperature to produce titanium niobium carbide with a stoichiometric ratio of Ti and Nb of 1 to 5. The second step involves the oxidation of as-synthesized titanium niobium carbide to produce TNO. Synthetic air yields fully oxidized TNO, while annealing in CO 2 results in TNO/carbon hybrids. The electrochemical performance for the hybrid and non-hybrid electrodes was surveyed for a narrow potential window (1.0-2.5 V vs. Li/Li + ) and a large potential window (0.05-2.5 V vs. Li/Li + ). The best hybrid material displayed a specific capacity of 350 mAh/g at a rate of 0.01 A/g (144 mAh/g at 1 A/g) in the large potential window regime. The electrochemical performance of hybrid materials is superior compared to non-hybrid materials for operation within the large potential window. Due to the advantage of carbon in hybrid material, the rate handling is faster than that of the non-hybrid one. The hybrid materials display robust cycling stability and maintain ca. 70% of their initial capacities after 500 cycles. In contrast, only ca. 26% of the initial capacity is maintained after the first 40 cycles for non-hybrid materials. We also applied our hybrid material as an anode in a full-cell lithium-ion battery by coupling it with commercial LiMn 2 O 4 .
A new approach to produce carbide-derived carbon nanospheres of 20-200 nm in diameter based on a novel soft-templating technique is presented. Platinum catalysis is used for the cross-linking of liquid (allylhydrido)polycarbosilane polymer chains with para-divinylbenzene within oil-in-water miniemulsions. Quantitative implementation of the pre-ceramic polymer can be achieved allowing precise control over the resulting materials. After pyrolysis and high-temperature chlorine treatment, resulting particles offer ideal spherical shape, very high specific surface area (up to 2347 m 2 /g), and large micro/mesopore volume (up to 1.67 cm 3 /g). The internal pore structure of the nanospheres is controllable by the composition of the oil phase within the miniemulsions. The materials are highly suitable for electrochemical double-layer capacitors with high specific capacitances in aqueous 1 M Na 2 SO 4 solution (110 F/g) and organic 1 M tetraethylammonium tetrafluoroborate in acetonitrile (130 F/g).
In this study, we explore carbon onions (diameter below 10 nm), for the first time, as a substrate material for lithium sulfur cathodes. We introduce several scalable synthesis routes to fabricate carbon onion-sulfur hybrids by adopting in situ and melt diffusion strategies with sulfur fractions up to 68 mass%. The conducting skeleton of agglomerated carbon onions proved to be responsible for keeping active sulfur always in close vicinity to the conducting matrix. Therefore, the hybrids are found to be efficient cathodes for Li-S batteries, yielding 97-98% Coulombic efficiency over 150 cycles with a slow fading of the specific capacity (ca. 660 mA h g-1 after 150 cycles) in long term cycle test and rate capability experiments.
Desalination by capacitive deionization (CDI) is an emerging technology for the energy- and cost-efficient removal of ions from water by electrosorption in charged porous carbon electrodes. A variety of carbon materials, including activated carbons, templated carbons, carbon aerogels, and carbon nanotubes, have been studied as electrode materials for CDI. Using carbide-derived carbons (CDCs) with precisely tailored pore size distributions (PSD) of micro- and mesopores, we studied experimentally and theoretically the effect of pore architecture on salt electrosorption capacity and salt removal rate. Of the reported CDC-materials, ordered mesoporous silicon carbide-derived carbon (OM SiC-CDC), with a bimodal distribution of pore sizes at 1 and 4 nm, shows the highest salt electrosorption capacity per unit mass, namely 15.0 mg of NaCl per 1 g of porous carbon in both electrodes at a cell voltage of 1.2 V (12.8 mg per 1 g of total electrode mass). We present a method to quantify the influence of each pore size increment on desalination performance in CDI by correlating the PSD with desalination performance. We obtain a high correlation when assuming the ion adsorption capacity to increase sharply for pore sizes below one nanometer, in line with previous observations for CDI and for electrical double layer capacitors, but in contrast to the commonly held view about CDI that mesopores are required to avoid electrical double layer overlap. To quantify the dynamics of CDI, we develop a two-dimensional porous electrode modified Donnan model. For two of the tested materials, both containing a fair degree of mesopores (while the total electrode porosity is [similar]95 vol%), the model describes data for the accumulation rate of charge (current) and salt accumulation very well, and also accurately reproduces the effect of an increase in electrode thickness. However, for TiC-CDC with hardly any mesopores, and with a lower total porosity, the current is underestimated. Calculation results show that a material with higher electrode porosity is not necessarily responding faster, as more porosity also implies longer transport pathways across the electrode. Our work highlights that a direct prediction of CDI performance both for equilibrium and dynamics can be achieved based on the PSD and knowledge of the geometrical structure of the electrodes.
Mechanochemistry-assisted synthesis of hierarchical porous carbons applied as supercapacitors
(2017)
A solvent-free synthesis of hierarchical porous carbons is conducted by a facile and fast mechanochemical reaction in a ball mill. By means of a mechanochemical ball-milling approach, we obtained titanium(IV) citrate-based polymers, which have been processed via high temperature chlorine treatment to hierarchical porous carbons with a high specific surface area of up to 1814 m2 g−1 and well-defined pore structures. The carbons are applied as electrode materials in electric double-layer capacitors showing high specific capacitances with 98 F g−1 in organic and 138 F g−1 in an ionic liquid electrolyte as well as good rate capabilities, maintaining 87% of the initial capacitance with 1 M TEA-BF4 in acetonitrile (ACN) and 81% at 10 A g−1 in EMIM-BF4.
