Undesired electrode-electrolyte interactions prevent the use of many high-energy-density cathode materials in practical lithium-ion batteries. Efforts to address their limited service life have ...predominantly focused on the active electrode materials and electrolytes. Here an advanced three-dimensional chemical and imaging analysis on a model material, the nickel-rich layered lithium transition-metal oxide, reveals the dynamic behaviour of cathode interphases driven by conductive carbon additives (carbon black) in a common nonaqueous electrolyte. Region-of-interest sensitive secondary-ion mass spectrometry shows that a cathode-electrolyte interphase, initially formed on carbon black with no electrochemical bias applied, readily passivates the cathode particles through mutual exchange of surface species. By tuning the interphase thickness, we demonstrate its robustness in suppressing the deterioration of the electrode/electrolyte interface during high-voltage cell operation. Our results provide insights on the formation and evolution of cathode interphases, facilitating development of in situ surface protection on high-energy-density cathode materials in lithium-based batteries.
The mineral eldfellite, NaFe(SO
4
)
2
, is characterized as a potential cathode for a Na-ion battery that is fabricated in charged state; its 3 V discharge
versus
sodium for reversible Na
+
...intercalation is shown to have a better capacity, but lower insertion rate than Li
+
intercalation. The theoretical specific capacity for Na
+
insertion is 99 mA h g
−1
. After 80 cycles at 0.1C
versus
a Na anode, the specific capacity was 78 mA h g
−1
with a coulomb efficiency approaching 100%.
The mineral eldfellite, NaFe(SO
4
)
2
, is characterized as a potential cathode for a Na-ion battery that can be fabricated in charged-state.
To achieve practically high electrocatalytic performance for the oxygen evolution reaction (OER), the active surface area should be maximized without severely compromising electron and mass transport ...throughout the catalyst electrode. Though the importance of electron and mass transport has been studied using low surface area catalysts under low current densities (∼tens of mA/cm2), the transport properties of large surface area catalysts under high operating current densities (∼500 mA/cm2) for practical OER catalysis have rarely been explored. Herein, three-dimensional (3D) hierarchically porous anodized nickel foams (ANFs) with large and variable surface areas were synthesized via electrochemical anodization of 3D nickel foam and applied as OER electrocatalysts in Fe-free and unpurified KOH electrolytes. Using Fe-free and in situ Fe-doped ANF that were prepared in Fe-free and unpurified electrolytes, respectively, we investigated the interdependent effects of active surface area and transport properties on OER activity under practically high current densities. While activity increased linearly with active surface area for Fe-free ANF, the activity of Fe-doped ANF showed a nonlinear increase with active surface area due to lower electrocatalytic activity enhancement. Detailed investigations on the possible factors (Fe incorporation, mass transport, and electron transport) identified that electron transport limitations played the major role in restricting the activity enhancement with increasing active surface area for Fe-doped ANF, although Fe-doped ANF has electron transport properties better than those of Fe-free ANF. This study exemplifies the growing significance of electron transport properties in large surface area catalysts, especially those with superb intrinsic catalytic activity and high operating current density.
Synthesis and characterization of Cr2C MXenes Akinola, Otitoaleke; Chakraborty, Isha; Celio, Hugo ...
Journal of materials research,
05/2021, Letnik:
36, Številka:
10
Journal Article
Recenzirano
MXenes are a large class of materials that are chemically exfoliated from metal–aluminum–carbon (MAX) bulk crystals into low-dimensional sheets. While many MXenes have been theoretically predicted, ...the careful balance required in the exfoliation between breaking the inter-layer bonds without damaging the intra-layer bonds of the sheets has limited synthesis and experimental study. Here, we developed the synthesis of Cr
2
C from its parent Cr
2
AlC MAX phase and showed the etching is optimized using sodium fluoride and hydrogen chloride with a modified minimally intensive layer delamination (mMILD) method in a cold environment of 9 ℃. We further optimized the intercalation and delamination using sonication and washing methods. The resulting Cr
2
C crystal structure was characterized. These results open up Cr
2
C to experimental study, including of its predicted emergent magnetic properties, and develop guidelines for synthesizing new MXene materials.
Graphic abstract
Since the potential for alloying lithium with silicon is outside the window of stability of common commercial electrolytes, silicon surfaces form an amorphous solid electrolyte interphase (SEI) under ...applied potential, which hampers silicon's performance as a lithium-ion battery anode. We have investigated the composition, distribution, and ambient stability of the SEI formed on undoped silicon (001) wafers configured as model electrodes in three different electrochemical conditions using a reduced oxidation interface for transporting air-sensitive samples from a glovebox to an ultra-high-vacuum chamber for X-ray photoelectron spectroscopy (XPS) analysis. Variable potential cycling and step experiments included linear sweep voltammetry (LSV), cyclic voltammetry (CV), and chronoamperometry (CA). CV and LSV experiments on silicon electrodes scanned from open-circuit voltage to lithiation (3–0.01 V vs Li/Li+) showed a suppression of carbonate-containing species relative to CA experiments (potential step for 300 s at 0.01 V vs Li/Li+) in anoxic XPS measurements. When silicon electrodes were exposed to ambient air, SEI layers reacted through both fluorination and combustion processes to produce different SEI product distributions than those prepared under anoxic conditions.
The reaction of Fe(N(SiMe3)2)3 with PH3 in THF at 100 °C gives amorphous FeP2 in high yield. As an anode material in a Li ion battery, this material shows remarkable performance toward ...electrochemical lithiation/delithation, with gravimetric discharge and charge capacities of 1258 and 766 mA h g–1, respectively, translating to 61% reversibility on the first cycle and a discharge capacity of 906 mA h g–1 after 10 cycles. This translates to 66% retention of the theoretical full conversion capacity of FeP2 (1365 mA h g–1).
The poor kinetics of the oxygen evolution reaction (OER) are a considerable barrier to the development of water-derived hydrogen fuel. Previous work regarding theoretical calculations of the ...perovskite SrCoO3‑δ (SCO) predicts a surface binding energy ideal for OER catalysis but could not be matched to experimental results due to the material’s propensity to form the incorrect trigonal crystal structure. By doping with iron and scandium, X-ray diffraction confirms that we have been able to synthesize a series of SCO catalysts of various crystal structures, culminating in cubic SCO. In doing so, we show that there is a limited correlation between the crystal structure and OER performance in alkaline media. Instead, the use of iron as a dopant is found to decrease the OER overpotential of the SCO by 40 mV in 0.1 M KOH and yield catalysts capable of performing water oxidation at an overpotential of 410 mV at 10 mA/cm2. The doped, cubic SCO catalysts are found to be more stable than the undoped material when tested for extended periods, showing only an approximate 3 mV increase in overpotential over a 2 h period at 10 mA/cm2. Our results show that proper doping of the B-site cation in SCO allows for tuning the structure, performance, and stability of the oxide as an OER electrocatalyst.
A microwave-assisted heating method allows for the convenient and reproducible synthesis of defined Au-Rh core-shell metallic nanoparticles with tuneable shell thicknesses. Nanoparticles with shells ...as thin as two Rh monolayers can be prepared, which are effective in vapour-phase hydrogenation catalysis at room temperature without the need for pre-treatment. Particles with Rh shells consisting of two or four Rh overlayers show similar catalytic properties and are both significantly more highly active than pure Rh nanoparticles, per mol of Rh employed.
•Complex, electrically conductive structures with relatively high compressive strength.•Printable aqueous pastes made from graphite and cellulose nanocrystals.•Additively manufactured from ...sustainable and recyclable materials.•Structures made via direct ink writing (DIW) and dried at room temperature.•Minimal and controllable shrinkage of printed structures.
This study investigates the design and use of a printable, sustainable, aqueous paste for room-temperature low-energy material extrusion (ME) additive manufacturing (AM) of complex structures. To this end, pastes with controlled rheology and a total solid content of ∼42% are formulated. Constituents of the pastes are commercial graphite and cellulose nanocrystal (CNC) powder, as a dispersing additive, with 91:09 and 88:12 graphite:cellulose wt.% compositions. The AM structures are dried in air at three rates (slow, medium, and fast). The structure of printed parts is characterized using electron microscopy, X-ray diffraction, Infrared/X-ray photoelectron spectroscopy, X-ray micro-computed tomography, and thermogravimetric analysis. The compressive strength of AM graphite structures reached 5.8±0.6 MPa with almost no effect from drying rates. However, samples containing more cellulose were ∼30% stronger in compression. Carbonization of the AM parts increased their electrical conductivity by more than an order of magnitude to ∼2400 S.m−1. In addition, it enabled the fabrication of nearly pure graphite structures. The mechanical and electrical properties of samples fabricated in this study exceed the performance of previously reported AM graphite structures. Moreover, the recyclability of the printed parts was demonstrated by regenerating pastes via mixing printed parts in water and re-printing new parts with the paste. The AM graphite structures can be used in numerous applications, including but not limited to electrical discharge machining (EDM), electrochemical machining (ECM), high-temperature customized sealing, high-temperature composite tooling, and energy conversion and storage.
Adding 10 mM KPF6 to the 1 M LiPF6 in ethylene carbonate/dimethyl carbonate electrolyte of symmetrical Li | Li cells eliminated the growth of dendrites at 0.5 mA cm–2 current density and massively ...reduced, but did not eliminate, the growth of dendrites at 2.5 mA cm–2. The added KPF6 increased the fraction of inorganic salts in the solid electrolyte interface, making it thinner and more Li+ conductive. It overcame the growth of dendrites resulting from inadequate nucleation density but not dendrite growth into the depletion layer, which scales with the layer’s thickness, i.e., the current density.
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