The role of the physicochemical properties of the water-soluble polyacrylic acid (PAA) binder in the electrochemical performance of highly loaded silicon/graphite 50/50 wt % negative electrodes has ...been examined as a function of the neutralization degree x in PAAH1–x Li x at the initial cycle in an electrolyte not containing ethylene carbonate. Electrode processing in the acidic PAAH binder at pH 2.5 leads to a deep copper corrosion, resulting in a significant electrode cohesion and adhesion to the current collector surface, but the strong binder rigidity may explain the big cracks occurring on the electrode surface at the first cycle. The nonuniform binder coating on the material surface leads to an important degradation of the electrolyte, explaining the lowest initial Coulombic efficiency and the lowest reversible capacity among the studied electrodes. When processed in neutral pH, the PAAH0.22Li0.78 binder forms a conformal artificial solid electrolyte interphase layer on the material surface, which minimizes the electrolyte reduction at the first cycle and then maximizes the initial Coulombic efficiency. However, the low mechanical resistance of the electrode and its strong cracking explain its low reversible capacity. Electrodes prepared at intermediate pH 4 combine the positive assets of electrodes prepared at acidic and neutral pH. They lead to the best initial performance with a notable areal capacity of 7.2 mA h cm–2 and the highest initial Coulombic efficiency of around 90%, a value much larger than the usual range reported for silicon/graphite anodes. All data obtained with complementary characterization techniques were discussed as a function of the PAA polymeric chain molecular conformation, microstructure, and surface adsorption or grafting, emphasizing the tremendous role of the binder in the electrode initial performance.
The electrocatalytic activity of a Cu electrode for the electroreduction of nitrate in alkaline medium was investigated by linear sweep voltammetry at stationary and rotating disc electrodes. ...Nitrate-reduction products generated upon prolonged electrolyses at different potentials were quantified. In addition, adsorption phenomena associated with the nitrate electroreduction process were characterized by electrochemical quartz crystal microbalance (EQCM) experiments. This data revealed that nitrate electroreduction process strongly depends on the applied potential. Firstly, at
ca. −0.9
V vs. Hg/HgO, the electroreduction of adsorbed nitrate anions to nitrite anions was identified as the rate-determining step of the nitrate electroreduction process. Between −0.9 and −1.1
V, nitrite is reduced to hydroxylamine. However, during long-term electrolyses, hydroxylamine is not detected and presumably because it is rapidly reduced to ammonia. At potential more negative than −1.1
V, nitrite is reduced to ammonia. At
ca. −1.45
V,
i.e. just before the hydrogen evolution reaction, the abrupt decrease of the cathodic current is due to the electrode poisoning by adsorbed hydrogen. In addition, during the first minutes of nitrate electrolysis, a decrease of the copper electrode activity was observed at the three investigated potentials (−0.9, −1.1 and −1.4
V). From polarization and EQCM measurements, this deactivation was attributed to the adsorption of nitrate-reduction products, blocking the electrode surface and slowing down the nitrate electroreduction rate. However, it was demonstrated that the Cu electrode can be reactivated by the periodic application of a square wave potential pulse at −0.5
V, which causes the desorption of poisoning species.
Silicon is considered as a promising negative electrode active material for Li-ion batteries, but its practical use is hampered by its very limited electrochemical cyclability arising from its major ...volume change upon cycling, which deteriorates the electrode architecture and the solid–electrolyte interphase. In this Perspective, we aim at critically discussing the opportunities offered by coordination chemistry to tackle these challenges. More precisely, we will show how the characteristics of the coordination bonds, notably their tunability, medium strength, and dynamic character, can be exploited to offer alternative paths for binding, templating, and coating Si particles in order to ultimately improve the cycle life of Si electrodes in Li-ion batteries.
Electrochemical dilatometry is used to investigate Li plating/stripping on Cu foil and porous carbon paper substrates. Experiments are performed in standard electrolyte for Li–S batteries at a ...current density of 1 mA cm
−2
with a Li plating charge fixed at 1 mAh cm
−2
. A fully dense Li film (4.8 μm thick) is initially electrodeposited on the Cu electrode. However, from the 2nd Li plating/stripping cycle, Li deposit becomes porous to reach a thickness of 9.6 µm at the 27th cycle, corresponding to a film porosity of 50%, favoring its collapse during the subsequent cycles. When a carbon paper with a low surface area (0.02 m
2
g
−1
) is used as a substrate, Li deposition occurs preferentially in the pores of the carbon paper during the first few cycles. However, this does not prevent the formation of Li dendrites, which progressively extend on the top of the substrate, resulting in the degradation of the electrode cyclability after about 40 cycles. The use of a carbon paper with a higher surface area (4.2 m
2
g
−1
) favors Li deposition inside the electrode, with no apparent loss of cyclability after 50 cycles. However, this does not prevent the formation of dead Li, as suggested by the continuous and irreversible expansion of the electrode over cycling at a mean rate of 1.3 μm per cycle. Additionally, a large and irreversible expansion of 38 μm is observed during the first cycle, which is attributed to the lithium-solvent co-intercalation in the graphitic part of the carbon paper substrate.
Graphic abstract
In this study, nitrate removal in alkaline media by a paired electrolysis with copper cathode and Ti/IrO2 anode enabled the conversion of nitrate to nitrogen. Optimum conditions for carrying out ...reduction of nitrate to ammonia and subsequent oxidation of the produced ammonia to nitrogen were found. At the copper cathode, electroreduction of nitrate to ammonia was optimal near -1.4V vs Hg/HgO. At the Ti/IrO2 anode, a pH value of 12, the presence of chloride and a potential fixed around 2.3V vs Hg/HgO permitted the production of hypochlorite, leading to the oxidation of ammonia to nitrogen with a N2 selectivity of 100%. Controlling the cathode/anode surface area ratio, and thus the current density, appeared to be a very efficient way of shifting electrode potentials to optimal values, consequently favoring the conversion of nitrate to nitrogen during a paired galvanostatic electrolysis. A cathode/anode surface area ratio of 2.25 was shown to be the most efficient to convert nitrate to nitrogen.
Titanium diboride (TiB2) is considered as a promising cathode material for Al production. However, the manufacture of TiB2 cathodes is facing numerous challenges. In this study, electrodeposition of ...TiB2 on graphite was performed in molten fluoride (FLiNaK) electrolyte at 600°C by using a periodically interrupted current technique for various electrodeposition times (from 10 to 75 minutes) and at two different current densities (−0.12 and −0.5 A/cm2). It is shown that the TiB2 coating morphology/microstructure strongly depends on the applied current density. Denser coatings were obtained at jon = −0.12 A/cm2 with a growth rate of ca. 0.7 µm/min. The thicker films display a preferential crystallographic orientation along the 110 plan. At jon = −0.5 A/cm2, TiB2 coatings are deposited at a growth rate of ca. 6 µm/min with no crystallographic texture. They present a porous and stratified morphology with numerous transversal macrocracks. All TiB2 coatings show excellent wettability for molten Al as confirmed by sessile drop experiments. However, significant molten Al infiltration occurs in the TiB2 coatings, which accumulates at the coating/graphite interface, inducing the coating delamination.
A crucial step in the production of battery grade natural graphite for lithium-ion batteries is the spheroidization process. However, the spheroidization yield is typically only about 50%. The ...by-product consists of graphite fines that are not suitable for use in lithium-ion batteries due to their small particle size (<10 μm), therefore, graphite fines are discarded or sold at a loss. In this work, we report a method for graphite fines re-agglomeration and petroleum pitch coating that allows for revalorization and recycling of waste graphite from the spheroidization process. Re-agglomeration of graphite fines was achieved by spray drying technique using carboxymethyl cellulose as binder and citric acid as cross-linking agent to improve the mechanical strength of the agglomerate. The as-obtained particles were subjected to heat treatment in presence of petroleum pitch for simultaneous binder and pitch decomposition to obtain pitch-coated particles. Resulting agglomerate particles showed a median size comparable to a commercial battery grade natural graphite reference and proved structurally sound to withstand the electrode calendering process. Pitch-coated agglomerate particles exhibited lower surface area and improved stability in comparison with non-coated graphite agglomerate. The electrochemical performance of the coated material was comparable to a commercial graphite reference, particularly in terms of cumulative irreversible capacity. Analysis by X-ray nano-computed tomography provided further insight into morphological properties and dimensional changes after calendering and upon galvanostatic cycling. Overall, the material obtained through this method shows great potential for re-introduction in the production chain of battery grade natural graphite for lithium-ion batteries.
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•Graphite fines are revalorized via re-agglomeration by spray drying.•Binder carbonization and pitch coating are performed simultaneously.•The re-agglomerated product can be used as anode in lithium-ion batteries.•Performance of pitch-coated agglomerate is comparable to a commercial reference.
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► In this study, Cu
70Ni
30 has been identified as the most efficient cathode for nitrate reduction, with a selectivity of 100% toward ammonia. ► Also, Cu
70Ni
30 electrodes have a ...much better corrosion resistance than Cu and Cu
90Ni
10 in the presence of chloride, nitrate and ammonia. ► Paired electrolysis using Cu
70Ni
30 cathodes and Ti/IrO
2 anodes allowed the conversion of nitrate to nitrogen from 620
ppm NO
3
− to less than 50
ppm NO
3
− with a power consumption as low as 20
kWh/kg NO
3
−, performances which are unequalled to date.
Ni, Cu, Cu
90Ni
10 and Cu
70Ni
30 were evaluated as cathode materials for the conversion of nitrate to nitrogen by a paired electrolysis process using an undivided flow-through electrolyzer. Firstly, corrosion measurements revealed that Ni and Cu
70Ni
30 electrodes have a much better corrosion resistance than Cu and Cu
90Ni
10 in the presence of chloride, nitrate and ammonia. Secondly, nitrate electroreduction experiments showed that the cupro-nickel electrodes are the most efficient for reducing nitrate to ammonia with a selectivity of 100%. Finally, paired electrolysis experiments confirmed the efficiency of Cu
70Ni
30 and Cu
90Ni
10 cathodes for the conversion of nitrate to nitrogen. During a typical electrolysis, the concentration of nitrate varied from 620
ppm to less than 50
ppm NO
3
− with an N
2 selectivity of 100% and a mean energy consumption of 20
kWh/kg NO
3
− (compared to ∼35 and ∼220
kWh/kg NO
3
− with Cu and Ni cathodes, respectively).
In the present work, an alternative to the standard ex-situ and destructive focused ion beam scanning electron microscopy (FIB/SEM) analysis procedure is demonstrated for monitoring the morphological ...degradation of a single Si/graphite (1/1 mass ratio) blended electrode for Li-ion batteries. For this purpose, a FIB milled microcavity is created in the pristine electrode, which is observed in FIB- polished cross section by SEM at different cycling periods (pristine, 1st, 9th and 50th cycles). This allows studying the same cycled electrode as for an in-situ method. Its cycling-induced morphological change is characterized at the electrode and particle scales by monitoring the evolution of the electrode thickness, mass and porosity, the Si particle morphology, Si interparticle distance, surface fraction and twisting of the graphite flakes. This is correlated to the evolution of the electrode discharge capacity and impedance. As a result, a more comprehensive view of the degradation phenomena of the Si/graphite blended electrode is established.
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•An investigation technique based on sequential FIB/SEM analysis is demonstrated.•Cycling-induced morphological change of a single Si/Gr electrode is studied.•Morphological changes are correlated with EIS measurements.•The methodology can be extended to other battery systems.
In this study, nanocrystalline copper−palladium films were synthesized over a wide range of compositions by coelectrodeposition of Pd and Cu in a 1 M NaCl solution containing both CuCl2 and PdCl2 in ...various proportions. The deposition potential was fixed at −0.5 V versus a saturated calomel electrode (SCE). These coatings were characterized by scanning electron microscopy coupled to energy dispersive X-ray analysis (SEM−EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). These analyses revealed a fine and homogeneous distribution of Pd and Cu within and over the whole surface of the film. Depending upon the Cu(II)/Pd(II) ratio in solution, monophased Pd-rich films (Pd95Cu5 or Pd88Cu12 alloys) or biphased films (containing Pd80Cu20 and Cu phases in different proportions) were obtained. Theses materials were tested as electrocatalysts for nitrate reduction in alkaline media. Electrochemical measurements showed that biphasic (Pd80Cu20 + Cu) materials displayed the best electrocatalytic activity toward nitrate reduction. Results of prolonged electrolysis also proved that the selectivity of the modified electrodes clearly depends not only on the applied potential but also on their structure and chemical composition. At −1.3 V versus Hg/HgO, all the electrodes (except pure palladium, which is inactive for nitrate reduction) mainly produced ammonia. However, at −0.93 V versus Hg/HgO, biphasic Cu−Pd electrode composed of 77% Pd80Cu20 + 23% Cu successfully reduced nitrate to nitrogen with a current efficiency approaching 76%.
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