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- ItemIn-situ XRD study of a Chromium doped LiNi0.5Mn1.5O4 cathode for Li-ion battery(Elsevier, 2021-09-01) Chladil, Ladislav; Kunický, Daniel; Kazda, Tomáš; Vanýsek, Petr; Čech, Ondřej; Bača, PetrThis paper deals with structural (in-situ XRD) and electrochemical characterization of high-voltage lithium-ion cathode materials LiMn2O4 (LMO), LiNi0.5Mn1.5O4 (LNMO), and LiCr0.1Ni0.4Mn1.5O4 (LCNMO) prepared by solid-state synthesis. Structural in-situ X-ray diffraction spectra were measured by an affordable Rigaku diffractometer. Our synthesis route produced the samples with similar morphologies where the average particle sizes were 1.11 mu m and 1.46 mu m for LNMO and LCNMO respectively. Results of the Rietveld analysis brought detailed insight into two-phase structure transitions for LMO and three-phase transitions for LNMO and LCNMO. XRD study revealed differences in the structural behavior of LMO and LNMO prepared by solid-state synthesis compared to the results of other authors using the sol-gel synthesis route. In the case of chromium-doped LNMO, our results indicate ability of the chromium metal to effectively reduce Mn3+ content while the ordering of the structure increases. Chromium doping also promotes a larger lattice parameter in a fully delithiated state than in the case of undoped LNMO. Therefore, lowering of the volume changes was observed and faster phase II/III transition taking place, when Ni3+/Ni4+ redox pair was oxidized, was also identified. Cr doping of LNMO also promotes the reaching the lattice parameters of phases in both phase transitions and thus could reduce the internal stress of active material under high C-rate cycling. Results thus suggested that chromium doping can improve the stability of the inner structure and performance at higher charging C-rates even though the structure goes through a three-phase region during charging as undoped LNMO. The evaluation of diffusion coefficients of Cr-doped LNMO revealed increased diffusivity in a full discharge state and as the cathode underwent the cycling the differences in diffusivity seemed to be more pronounced.
- ItemStudy of Zinc Deposited in the Presence of Organic Additives for Zinc-based Secondary Batteries(Elsevier, 2018-12-03) Chladil, Ladislav; Čech, Ondřej; Smejkal, Jan; Vanýsek, PetrThis work is focused on the effect of selected organic additives on zinc deposit properties in relation to a possible utilizing the additives for a zinc based battery systems worked with alkaline electrolyte. The Zn layers were deposited on tin substrate from the KOH based electrolytes saturated by zinc oxide and with addition of different organic surfactants - CTAB, Slovasol 2520/2, Tween 20 and Lugalvan G 35 in concentration 500ppm. Depositions were held under low current densities 10mA/cm2 where the mossy porous deposit grows from pure KOH solutions. All additives were examined with emphasis on the study of zinc deposit morphology and their ability to create uniformly distributed porous structure which could exhibit fast electrode kinetic. All deposits were studied by X-ray crystallography and preferred structure orientations are reported. For the purpose of using additives directly in the battery systems we evaluated also the corrosion properties of the KOH solution with addition of the above mentioned surfactants. It has been found that the presence of CTAB and Slovasol 2520/2 lead to a pyramidal texture, Lugalvan G 35 produced micro-crystalline deposit with opened porous structure and finally presence of Tween 20 lead to nano-crystalline highly porous deposit almost without preferred orientation.
- ItemSimple and efficient AlN-based piezoelectric energy harvesters(MDPI, 2020-01-28) Gablech, Imrich; Klempa, Jaroslav; Pekárek, Jan; Vyroubal, Petr; Hrabina, Jan; Holá, Miroslava; Kunz, Jan; Brodský, Jan; Neužil, PavelIn this work, we demonstrate the simple fabrication process of AlN-based piezoelectric energy harvesters (PEH), which are made of cantilevers consisting of a multilayer ion beam-assisted deposition. The preferentially (001) orientated AlN thin films possess exceptionally high piezoelectric coefficients d33 of (7.33 ± 0.08) pCN1. The fabrication of PEH was completed using just three lithography steps, conventional silicon substrate with full control of the cantilever thickness, in addition to the thickness of the proof mass. As the AlN deposition was conducted at a temperature of 330 °C, the process can be implemented into standard complementary metal oxide semiconductor (CMOS) technology, as well as the CMOS wafer post-processing. The PEH cantilever deflection and efficiency were characterized using both laser interferometry, and a vibration shaker, respectively. This technology could become a core feature for future CMOS-based energy harvesters.
- ItemSynthesis and Characterization of Porous Sulfur/MWCNTs Composites with Improved Performance and Safety as Cathodes for Li-S Batterie(ESG, 2018-01-01) Straková Fedorková, Andrea; Kazda, Tomáš; Gavalierova, Katarina; Gómez-Romero, Pedro; Shambel, ElenaSulfur-carbon (S-C-MWCNTs) composites and sulfur-LiFePO4 (S-LFP-MWCNTs) composites were synthesised with MWCNTs additive by sulfur sublimation and solid state reaction. As prepared materials are characterized with scanning electron microscopy, thermogravimetry, FTIR, elemental analysis, XPS, cyclic voltammetry and galvanostatic charge/discharge tests. The composite S-LFP cathode with MWCNTs additive shows improved discharge capacity and performance. It shows an initial discharge capacity of 1167 mAh/g-sulfur, or 70% of theoretical capacity. The discharge capacity measured after 20 cycles for S-LFP-MWCNTs composite cathode was 80% of the initial capacity and remained stable. After 160 charge/discharge tests, the cathode displays a stable capacity of 561 mAh/g-sulfur at the C-rate of 0.2 C. Combination of sulfur, LiFePO4 and MWCNTs prevents aggregation and volume change of the cathode particles and improves the conductivity and electrochemical stability during the long-term cycling. 3-D FTIR spectroscopy measurements confirmed improved chemical stability and safety of sulfur composites also at higher temperatures.
- ItemThe importance of observation of structural changes of lead acid battery active mass in special applications in the mining industry(Faculty of Mining, Ecology, Process Control and Geotechnologies (FBERG), Technical University of Kosice, 2015-10-26) Zimáková, Jana; Vaculík, Sebastian; Fryda, Daniel; Bača, PetrAby bylo možné používat olověných akumulátorů v mimořádně obtížných podmínkách v těžebním průmyslu, je velmi důležité pochopit děje, ke kterým dochází při trakčním provozu těžebních vozíků nebo při používání pomocného osvětlení. Selhání olověných akumulátorů v prostředí s nebezpečím výbuchu, kde je žádoucí nevýbušné provedení, může mít fatální následky. Příspěvek popisuje možnost sledování změn aktivních materiálů na mikroskopické úrovni. Proces nabíjení a vybíjení olověného akumulátoru byl popsána v mnoha publikacích. Cílem tohoto článku je doplnit známé informace o sérii snímků a analýzy, které přesně ukazují progresivní změny ve struktuře na záporné elektrodě. Negativní elektrody jsou, v každém cyklu, nabíjeny a vybíjeny za stejných podmínek, skenovány pomocí rastrovacího elektronového mikroskopu a je provedena elementární analýza (EDS). Měří se také velikost jednotlivých krystalů síranu. Předchozí výsledky měření ukazují, že v průběhu nabíjení není konverze PbSO4 krystalů do nabité formy aktivní hmoty úplná a dochází k rychlému nárůstu velikosti síran olovnatý krystalů na záporné elektrodě. Tento článek porovnává změny ve složení povrchu elektrody po dvou cyklech. Je zde zřejmá ztráta vedení a viditelný růst krystalů síranu olovnatého. To naznačuje progresivní sulfataci povrchu.