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Abstract:
In this current work, the pristine LiNi0.5Mn1.5O4 (LNMO) and fluorine-doped LiNi0.5Mn1.5O4–xFx (x = 0.1; 0.2; 0.3) cathode materials were successfully synthesized through a facile spray-drying method. The performed morphological and structural characterizations revealed that the fluorine doping led to a partial conversion of Mn4+ to Mn3+ ions in LNMO structure and an increase of their average particle sizes. These characteristics made the LiNi0.5Mn1.5O3.9F0.1 cathode exhibited the best rate capability at high C-rates and cycling performance among all investigated LNMO-based electrodes. Its improved electrochemical properties resulted from excellent crystallinity, high Li+ diffusion coefficient, and low charge-transfer resistance. Moreover, the LiNi0.5Mn1.5O3.9F0.1 electrode was found to possess the excellent resistant against Mn dissolution at elevated temperature. According to its great thermal stability, an impressive capacity retention of 81.5% after 100-cycle at 0.2 C at elevated temperature was achieved. In terms of the facile synthesis approach, superior electrochemical performances, and great thermal stability, the LiNi0.5Mn1.5O3.9F0.1 electrode synthesized by the scalable spray-drying method can be regarded as a promising high-voltage cathode material for high-performance Li-ion batteries.

Keywords:
Cathode material, Fluorine doping, Spinel LiNi0.5Mn1.5O4, Spray-drying synthesis, Li-ion batteries

Abstract:
Li4Ti5O12 (LTO) is a promising anode material for lithium-ion batteries (LIBs) due to its stable reversibility, high-rate cyclability, and high operational potential. On the other hand, it suffers from poor electronic conductivity and low capacitance. To overcome these disadvantages, modification of the LTO surface is frequently undertaken. Considering this idea, the production of a biomass-derived carbon-coated LTO material (LTO/C) and its application as an anode in LIBs is described in this work. The carbon precursor was obtained from commercial carrot juice, which was degraded using microwaves. According to the UV studies, the carbon precursor revealed similar properties to carbon quantum dots. Then, it was deposited on LTO synthetized through a sol-gel method. The LTO/C electrode exhibited a high specific capacity of 211 mAhg−1 at 0.1 C. Capacity retention equal to 53% of the initial value was found for the charge–discharge rate increase from 0.1 C to 20 C. The excellent electrochemical performance of LTO/C was caused by the carbon coating, which provided (i) short diffusion pathways for the Li+ ions into the LTO structure and (ii) enhanced electronic conductivity. The obtained results indicated that biomass-derived carbon quantum dot-coated LTO can be considered as a promising anode for LIBs.

Keywords:
anode material, biomass-derived carbon, carbon coating, carbon quantum dot, lithium-ion battery

Abstract:
In this study, spinel LiNi0.5Mn1.5O4 (LNMO) was successfully decorated with Al2O3 thin film by using atomic layer deposition (ALD) approach and evaluated as a cathode material for high-temperature applications in lithium ion batteries (LIBs). To optimize the LNMO-Al2O3 electrodes operated at elevated temperature (55 °C), the effects of Al2O3 thicknesses adjusted by controlling the ALD deposition cycle were systemically investigated. According to the series of electrochemical results, the LNMO coated with the Al2O3 thin layer in the thickness of ca. 2 nm was achieved by using one-cycle ALD and the LNMO-Al2O3 electrode exhibited superior electrochemical stability (capacity retention up to 93.7% after consecutive 150 charge/discharge cycles at 0.5 C to the pristine LNMO electrode at elevated temperature. This can be attributed to two factors: (i) the decoration of Al2O3 thin layer could not contribute remarkably to extra resistance for charge transfer; (ii) Al2O3 thin film deposition could efficiently stabilize the growth of cathode electrolyte interface (CEI) and suppress the dissolution of transition metals. Therefore, these results verify that the LNMO-Al2O3 electrode could be regarded as a promising cathode material for high-voltage LIBs, especially at elevated temperature operation.

Keywords:
atomic layer deposition, Al2O3 coating, lithium nickel manganese oxide, lithium-ion battery, elevated temperature

Abstract:
This work describes comparative study on the application of Li4Ti5O12 (LTO) as anode materials for lithium-ion batteries which were successfully prepared by sol-gel synthesis with the use of two titanium sources. One of them was anatase-type titanium dioxide (TiO2), whereas the second was tetrabutyl titanate (TBT). Both obtained LTO materials were very similar in terms of their crystallinity and purity. In turn, the sample synthetized with TBT source revealed better particle dispersibility, and its particles were slightly lower in size. These particular features resulted in higher Li+ diffusion coefficient and better kinetic of Li+ ions during charge transfer reactions for the LTO synthetized with TBT source. This reflected in specific capacitance values for both electrodes which equalled 150 mAh g^−1, 120 mAh g^−1, and 63 mAh g^−1 for TBT-LTO and 120 mAh g^−1, 80 mAh g^−1, and 58 mAh g^−1 for TiO2-LTO at C-rates of 1, 5, and 10 C, respectively.

Keywords:
anodematerial, lithiumtitanate, lithium-ion batteries, sol-gel synthesis, tetrabutyl titanate, titaniumdioxide

Abstract:
This work describes a use of a composite nanomaterial which consists of multiwall carbon nanotubes covered by iron oxide nanoparticles as a hybrid electrode in aqueous supercapacitor. The investigated nanomaterial was manufactured in a two-step simple chemical synthesis in which the first step was a functionalization of carbon nanotubes whereas the second one was the deposition of iron oxide. According the morphological and structural characterization, the carbon nanotubes with diameters of 10–40 nm were successfully covered by randomly-dispersed magnetite nanoparticles with average diameter of 10 nm. Moreover, the thermogravimetric analysis results indicated that the mass ratio between carbon nanotubes and iron oxide nanoparticles was about 65–35%. The electrochemical performance of studied hybrid electrode was tested in 1M aqueous KCl electrolyte. The highest specific capacitance of 143 F g^‒1 was recorded at a discharge current density of 1 A g^‒1. The investigated nanomaterial also exhibited excellent cycling stability i.e. 81% retention of the initial capacitance after 3000 cycles.

Keywords:
hybrid electrode, magnetite, multiwall carbon nanotube, nanocomposite, supercapacitor