Зависимость электрохимических параметров композитных SiO/C-анодов для литий-ионных аккумуляторов от состава и температуры синтеза

The results of a study of anodes obtained by carbonization of silicon monoxide by means of a reaction with solid-phase fluorocarbon CF0.8 are presented. Charge/discharge voltage profiles were studied at different currents depending on the composition and temperature of the synthesis of composites. The irreversible losses of the 1st cycle and the contribution to them of intrinsic losses due to the formation of lithium oxide and its silicates and losses associated with the formation of SEI are analyzed. A difference has been established in the behavior of anodes made of SiO carbonized by annealing with CF0.8 at T=800°C (SiO/C composite) and silicon monoxide annealed with CF0.8 at T>1000°C, at which disproportionation occurs simultaneously with the carbonization of SiO (d-SiO/C composite). The difference consisting in a higher discharge capacity, a higher Coulomb efficiency, and better rate capability of d-SiO/C is explained by a change in the composition of the SiOx matrix that occurs during the disproportionation process. The effect of the formation of d-SiO/C anodes by preliminary lithiation with a low current, after which the electrodes can be charged and discharged with much higher currents, has been discovered. The effect is explained by the amorphization of silicon crystallites and the increasing diffusion coefficient of lithium

Structurally Dependent Electrochemical Properties of Ultrafine Superparamagnetic ‘Core/Shell’ γ-Fe2O3/Defective α-Fe2O3 Composites in Hybrid Supercapacitors

The paper presents a method for obtaining electrochemically active ultrafine composites of iron oxides, superparamagnetic ‘core/shell’ γ-Fe2O3/defective α-Fe2O3, which involved modifying sol-gel citrate synthesis, hydrothermal treatment of the formed sol, and subsequent annealing of materials in the air. The synthesized materials’ phase composition, magnetic microstructure, and structural, morphological characteristics have been determined via X-ray analysis, Mossbauer spectroscopy, scanning electron microscopy (SEM), and adsorption porometry. The mechanisms of phase stability were analyzed, and the model was suggested as FeOOH ® γ-Fe2O3 ® α-Fe2O3. It was found that the presence of chelating agents in hydrothermal synthesis encapsulated the nucleus of the new phase in the reactor and interfered with the direct processes of recrystallization of the structure with the subsequent formation of the α- Fe2O3 crystalline phase. Additionally, the conductive properties of the synthesized materials were determined by impedance spectroscopy. The electrochemical activity of the synthesized materials was evaluated by the method of cyclic voltammetry using a three-electrode cell in a 3.5 M aqueous solution of KOH. For the ultrafine superparamagnetic ‘core/shell’ γ-Fe2O3/defective α-Fe2O composite with defective hematite structure and the presence of ultra-dispersed maghemite with particles in the superparamagnetic state was fixed increased electrochemical activity, and specific discharge capacity of the material is 177 F/g with a Coulomb efficiency of 85%. The prototypes of hybrid supercapacitor with work electrodes based on ultrafine composites superparamagnetic ‘core/shell’ γ-Fe2O3/defective α-Fe2O3 have a specific discharge capacity of 124 F/g with a Coulomb efficiency of 93% for current 10 mA.

Dissolution and Reprecipitation of Sulfur on Carbon Surface

Further understanding of the redox process of lithium polysulfides (PSs) on carbon surface is helpful to design Li/S batteries with better performance. “Shuttle mechanism” can explain the low coulomb efficiency and self-discharge of a Li/S battery, but it cannot explain the fact that battery performance is closely affected by electrolyte volume and sulfur load. This paper aims to reveal main redox process of PSs on surface of carbon by examining cathodic behavior with different electrolyte volume and sulfur load. SEM photos and Impedance Spectra of cathode before and after 1st discharge were compared, it was found that the discharge process is the continuous dissolution of sulfur composited with carbon into the electrolyte to form PSs, at the same time, PSs re-precipitates sulfur on the surface of cathode through disproportionation reaction to form a solid film. CV curves showed that the solid film passivates electrode, and the electrode is activated only when potential sweeps negatively and Li2S is generated. When lean electrolyte is used, there is fluctuation in CV curves, which proves that the dissolution-reprecipitation of sulfur is the main process of cathode. The discharge-charge curves of cathodes with different sulfur load were compared, it was found that there is wavy fluctuation in the discharge curve with high sulfur load, which proves again that the sulfur reaction dominates the electrode process.

Effect of lithium borate coating on the electrochemical properties of LiCoO2 electrode for lithium-ion batteries

The effect of a protective coating of fused lithium borate, Li3BO3, on the physicochemical and electrochemical characteristics of LiCoO2 has been studied. A cathode material produced by the SCS method using binary organic fuel, glycine and citric acid. The influence of the experiment conditions on the morphology, crystal structure and specific surface of lithium cobaltite was studied. Electrochemical testing of LiCoO2∙nLi3BO3 samples, n = 5 and 7 mass %, has been performed in the cathode Li|Li+-electrolyte|LiCoO2∙nLi3BO3 half-cell using 1M LiPF6 in EC/DMC mixture (1:1) as electrolyte in the 2.7-4.3 V range at normalized discharge current С/10, С/5, С/2. The maximal initial discharge capacity of 185 mAh/g was detected for the samples with 5 mass % Li3BO3. The coulomb efficiency of optimal materials in the 40th cycle was 99.1%.

Electricity Generation, Salt and Nitrogen Removal and Microbial Community in Aircathode Microbial Desalination Cell for Saline-Alkaline Soil-Washing Water Treatment

An aircathode microbial desalination cell (AMDC) was successfully started by inoculating anaerobic sludge into the anode of a microbial desalination cell and then used to study the effects of salinity on performance of AMDC and effect of treatment of coastal saline-alkaline soil-washing water. The results showed that the desalination cycle and rate gradually shorten, but salt removal gradually increased when the salinity was decreased, and the highest salt removal was 98.00 ± 0.12% at a salinity of 5 g/L. COD removal efficiency was increased with the extension of operation cycle and largest removal efficiency difference was not significant, but the average coulomb efficiency had significant differences under the condition of each salinity. This indicates that salinity conditions have significant influence on salt removal and coulomb efficiency under the combined action of osmotic pressure, electric field action, running time and microbial activity, etc. On the contrary, COD removal effect has no significant differences under the condition of inoculation of the same substrate in the anode chamber. The salt removal reached 99.13 ± 2.1% when the AMDC experiment ended under the condition of washing water of coastal saline-alkaline soil was inserted in the desalination chamber. Under the action of osmotic pressure, ion migration, nitrification and denitrification, NH4+-N and NO3−-N in the washing water of the desalination chamber were removed, and this indicates that the microbial desalination cell can be used to treatment the washing water of coastal saline-alkaline soil. The microbial community and function of the anode electrode biofilm and desalination chamber were analyzed through high-throughput sequencing, and the power generation characteristics, organics degradation and migration and transformation pathways of nitrogen of the aircathode microbial desalination cell were further explained.

Nanoarchitectonics of Acicular Nanocrystal Assembly and Nanosheet Assembly for Lithium-Ion Batteries

Nanoarchitectonics of metal oxide nanocrystal electrodes were developed for lithium-ion batteries. The electrodes included copper nanoparticles and doped fluorine. For the acicular nanocrystals, charge–discharge reactions progressed at 1.8 V over 100 cycles at 100 and 10 μA. A 15-mmdiameter battery containing acicular nanocrystals showed capacity, coulomb efficiency, and specific capacity, respectively of 20 μAh, 98%, and ~242 mAh/g at 100 μA and 40 μAh, 99%, and 484 mAh/g at 10 μA. The TiO2/SnO2 electrode consisted of a SnO2 sheet-assembled structure with surface layers of anatase TiO2. The TiO2/SnO2 battery operated at 1.3 (100 cycles) and 1.2 (50 cycles) V at 100 and 10 μA, respectively; its capacity, coulomb efficiency, and specific capacity, respectively were 50 μAh, 98%, and 161 mAh/g at 100 μA and 200 μAh, 97–98%, and 643 mAh/g at 10 μA. The characteristic microstructure, chemical composition, and crystal faces of both materials contributed to battery performance.