Potassium-ion batteries (PIBs) have been considered as promising alternatives to lithium-ion batteries due to potassium's high natural abundance of 2.09 wt% ( vs. 0.0017 wt% for Li) and K/K + having ...a low redox potential of −2.93 V ( vs. −2.71 V for Na/Na + ). However, PIB electrodes still suffer huge challenges due to the large K-ion radius and slow reaction dynamics. Herein, we report a high-capacity Sb@CSN composite anode with Sb nanoparticles uniformly encapsulated by a carbon sphere network (CSN) for PIBs. First-principles computations and electrochemical characterization confirm a reversible sequential phase transformation of KSb 2 , KSb, K 5 Sb 4 , and K 3 Sb during the potassiation/depotassiation process. In a concentrated 4 M KTFSI/EC + DEC electrolyte, the Sb@CSN anode delivers a high reversible capacity of 551 mA h g −1 at 100 mA g −1 after 100 cycles with an extremely slow capacity decay of only 0.06% per cycle from the 10th to 100th cycle; when at a high current density of 200 mA g −1 , the Sb@CSN anode still maintains a capacity of 504 mA h g −1 after 220 cycles. The Sb@CSN anodes demonstrate one of the best electrochemical performances for all K-ion battery anodes reported to date. The exceptional performance of Sb@CSN should be attributed to the efficient encapsulation of small Sb nanoparticles in the conductive carbon network as well as the formation of a robust KF-rich SEI layer on the Sb@CSN anode in the concentrated 4 M KTFSI/EC + DEC electrolyte.
The controllable incorporation of multiple immiscible elements into a single nanoparticle merits untold scientific and technological potential, yet remains a challenge using conventional synthetic ...techniques. We present a general route for alloying up to eight dissimilar elements into single-phase solid-solution nanoparticles, referred to as high-entropy-alloy nanoparticles (HEA-NPs), by thermally shocking precursor metal salt mixtures loaded onto carbon supports temperature ~2000 kelvin (K), 55-millisecond duration, rate of ~10
K per second. We synthesized a wide range of multicomponent nanoparticles with a desired chemistry (composition), size, and phase (solid solution, phase-separated) by controlling the carbothermal shock (CTS) parameters (substrate, temperature, shock duration, and heating/cooling rate). To prove utility, we synthesized quinary HEA-NPs as ammonia oxidation catalysts with ~100% conversion and >99% nitrogen oxide selectivity over prolonged operations.
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BFBNIB, NMLJ, NUK, ODKLJ, PNG, SAZU, UL, UM, UPUK
Nano-Sn/C composites are ideal anode materials for high energy and power density Li-ion batteries. However, because of the low melting point of Sn and the tendency of grain growth, especially during ...high temperature carbonization, it has been a significant challenge to create well-dispersed ultrasmall Sn nanoparticles within a carbon matrix. In this paper, we demonstrate an aerosol spray pyrolysis technique, as a facile and scalable method, to synthesize a nano-Sn/C composite with uniformly dispersed 10 nm nano-Sn within a spherical carbon matrix. The discharge capacity of nano-Sn/C composite sphere anodes maintains the initial capacity of 710 mAh/g after 130 cycles at 0.25 C. The nano-Sn/C composite sphere anodes can provide ∼600 mAh/g even at a high rate of 20 C. To the best of our knowledge, such high rate performance for Sn anodes has not been reported previously. The exceptional performance of the nano-Sn/C composite is attributed to the unique nano-Sn/C structure: (1) carbon matrix offers mechanical support to accommodate the stress associated with the large volume change of nano-Sn, thus alleviating pulverization; (2) the carbon matrix prevents Sn nanoparticle agglomeration upon prolonged cycling; and (3) carbon network provides continuous path for Li ions and electrons inside the nano-Sn/C composite spheres.
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IJS, KILJ, NUK, PNG, UL, UM
It is axiomatic that the burning time dependence on particle size follows an integer power law dependence. However, a considerable body of experimental data show a power dependence less than unity. ...In this paper, we focus on what might be responsible for the fractional power dependence observed for the burning time for nanoparticles (e.g. Al and B). Specifically we employ reactive molecular dynamics simulations of oxide-coated aluminum nanoparticles (Al-NPs). Since most nanomaterials experimentally investigated are aggregates, we study the behavior of the simplest aggregate – a doublet of two spheres. The thermo-mechanical response of an oxide coated Al-NP is found to be very different than its solid alumina counterpart, and in particular we find that the penetration of the core aluminum cations into the shell significantly softens it, resulting in sintering well below the melting point of pure alumina. For such coated nanoparticles, we find a strong induced electric field exists at the core–shell interface. With heating, as the core melts, this electric field drives the core Al cations into the shell. The shell, now a sub-oxide of aluminum, melts at a temperature that is lower than the melting point of aluminum oxide. Following melting, the forces of surface tension drive two adjacent particles to fuse. The characteristic sintering time (heating time+fusion time) is seen to be comparable to the characteristic reaction time, and thus it is quite possible for nanoparticle aggregates to sinter into structures with larger length scales, before the bulk of the combustion can take place. This calls into question what the appropriate ‘effective size’ of nanoparticle aggregates is.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
An important proposed mechanism in nanothermites reactions - reactive sintering - plays a significant role on the combustion performance of nanothermites by rapidly melting and coalescing aggregated ...metal nanoparticles, which increases the initial size of the reacting composite powders before burning. Here, we demonstrate a high-speed microscopy/thermometry capability that enables ~ µs time and ~ µm spatial resolution as applied to highly exothermic reaction propagation to directly observe reactive sintering and the reaction front at high spatial and temporal resolution. Experiments on the Al+CuO nanocomposite system reveal a reaction front thickness of ~30 μm and temperatures in excess of 3000 K, resulting in a thermal gradient in excess of 10
K m
. The local microscopic reactive sintering velocity is found to be an order of magnitude higher than macroscale flame velocity. In this observed mechanism, propagation is very similar to the general concept of laminar gas reaction theory in which reaction front velocity ~ (thermal diffusivity x reaction rate)
.
In this study we investigate the role of gas phase oxygen on ignition of nanothermite reactions. By separately evaluating the temperature at which ten oxidizers release gas phase species, and the ...temperature of ignition in an aluminum based thermite, we found that ignition occurred prior to, after or simultaneous to the release of gas phase oxygen depending on the oxidizer. For some nanothermites formulations, we indeed saw a correlation of oxygen release and ignition temperatures. However, when combined with in situ high heating stage microscopy indicating reaction in the absence of O2, we conclude that the presence of free molecular oxygen cannot be a prerequisite to initiation for many other nanothermites. This implies that for some systems initiation likely results from direct interfacial contact between fuel and oxidizer, leading to condensed state mobility of reactive species. Initiation of these nanothermite reactions is postulated to occur via reactive sintering, where sintering of the particles can commence at the Tammann temperature which is half the melting temperature of the oxidizers. These results do not imply that gas phase oxygen is unimportant when full combustion commences.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The stability of single-atom catalysts is critical for their practical applications. Although a high temperature can promote the bond formation between metal atoms and the substrate with an enhanced ...stability, it often causes atom agglomeration and is incompatible with many temperature-sensitive substrates. Here, we report using controllable high-temperature shockwaves to synthesize and stabilize single atoms at very high temperatures (1,500-2,000 K), achieved by a periodic on-off heating that features a short on state (55 ms) and a ten-times longer off state. The high temperature provides the activation energy for atom dispersion by forming thermodynamically favourable metal-defect bonds and the off-state critically ensures the overall stability, especially for the substrate. The resultant high-temperature single atoms exhibit a superior thermal stability as durable catalysts. The reported shockwave method is facile, ultrafast and universal (for example, Pt, Ru and Co single atoms, and carbon, C
N
and TiO
substrates), which opens a general route for single-atom manufacturing that is conventionally challenging.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The aluminum–fluorine reaction is attracting growing interest due to its higher density over aluminum–oxygen. Fluorine rich polymers are particularly interesting for their applications as an ...energetic binder in advanced additive manufacturing of energetic materials. In this paper, three soluble polymers of PVDF (59 wt% F), Viton (66 wt% F) and THV (73 wt% F) are incorporated with aluminum nanoparticles (Al NPs) and prepared as free-standing films using solvent-based direct writing. The three composite films are compared for their mechanical properties as well as the ignition and combustion performance. Tensile stress was found to order as Al/PVDF > Al/THV > Al/Viton while the elasticity of Al/Viton is much higher than the other two. The burn rate of different composite films increases with Al content, while the flame temperature peaks slightly fuel-rich. The Al/PVDF had the highest burn rate, however, the flame temperature ordered as Al/THV (∼2500 K) > Al/Viton (∼2000 K) > Al/PVDF (∼1500 K), consistent with fluorine content. With higher fluorine and lower hydrogen content, THV releases more CFx gas than HF, which generates higher temperature. However, HF which is predominantly produced from PVDF has the lowest ignition by far and may be responsible for its high flame speed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Magnesium is a promising candidate as a solid fuel for energetic applications, however, the diffusion‐controlled oxidation mechanism impedes its reaction with an oxidizer, often resulting in ...diminished performance. In this study, non‐thermal plasma processing is implemented to modify the surface of magnesium nanoparticles with silicon in‐flight, in the gas‐phase to enhance the rate of interfacial reactions and tune the ignition pathways. Allowing the silicon coating to partially oxidize provides direct contact between the fuel and oxidizer, resulting in a nanostructured thermite system at the single particle level. The proximal distance between oxidizer and fuel directly impacts the ignition temperature and, therefore, the combustion kinetics. An intermetallic reaction occurs within the magnesium/silicon system to supplement the heating of the magnesium fuel to initiate its reaction with the oxidizer, resulting in highly reduced ignition thresholds. The ignition temperature is lowered significantly from ≈740 °C for magnesium particles with a native oxide layer to ≈520 °C for particles coated via the in‐flight plasma process.
The coating of magnesium nanoparticles with an oxidized silicon shell results in enhanced combustion kinetics. This is due to the highly exothermic reaction between the metal core and the oxidized shell. These nanothermites are realized by nucleating magnesium nanoparticles from the metal vapor, followed by their in‐flight coating in a silane‐containing low‐temperature plasma.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The realization of manganese oxide anode materials for lithium‐ion batteries is hindered by inferior cycle stability, rate capability, and high overpotential induced by the agglomeration of manganese ...metal grains, low conductivity of manganese oxide, and the high stress/strain in the crystalline manganese oxide structure during the repeated lithiation/delithiation process. To overcome these challenges, unique amorphous MnOx–C nanocomposite particles with interdispersed carbon are synthesized using aerosol spray pyrolysis. The carbon filled in the pores of amorphous MnOx blocks the penetration of liquid electrolyte to the inside of MnOx, thus reducing the formation of a solid electrolyte interphase and lowering the irreversible capacity. The high electronic and lithium‐ion conductivity of carbon also enhances the rate capability. Moreover, the interdispersed carbon functions as a barrier structure to prevent manganese grain agglomeration. The amorphous structure of MnOx brings additional benefits by reducing the stress/strain of the conversion reaction, thus lowering lithiation/delithiation overpotential. As the result, the amorphous MnOx‐C particles demonstrated the best performance as an anode material for lithium‐ion batteries to date.
Amorphous MnOx‐carbon nanoparticles as anode materials for lithium‐ion batteries are synthesized via aerosol spray pyrolysis. The resulting MnOx‐carbon anode shows high lithium storage capacity, superior cycling stability, rate capability, and lower overpotential owing to its amorphous nature and unique nanostructure of interdispersed MnOx and carbon.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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