Fluorine doping of cathode materials for rechargeable batteries

In the continuing search for alternative cathode materials for rechargeable batteries with improved electrochemical performances, there is a need for a versatile approach that will address concerns regarding low reversible capacity, poor capacity retention, low operating voltage and structural instability. So far, a lot of investigation was focused on cation doping. On the other hand, there is much less investigation on anion doping of cathode materials. Taking olivine-type LiFePO4 and layered NaxCoO2 as example materials for lithium- and sodium- ion batteries, respectively, the influence of fluorine doping on both the structure and the electrochemical performances was examined. The crystal structure refinement revealed that fluorine incorporation preserves the parent structure. Furthermore, small oxygen replacement by fluorine ions changes electronic structure and consequently modifies electrical properties

A review of recent developments in the synthesis procedures of lithium iron phosphate powders

Olivine structure LiFePO4 attracted much attention as a promising cathode material for lithium-ion batteries. The overwhelming advantage of iron-based compounds is that, in addition to being inexpensive and naturally abundant, they are less toxic than Co, Ni, and Mn. Its commercial use has already started and there are several companies that base their business on lithium phosphate technology. Still, there is a need for a manufacturing process that produces electrochemically active LiFePO4 at a low cost. Therefore the interest in developing new approaches to the synthesis of LiFePO4 did not fade. Here is presented a review of the synthesis procedures used for the production of LiFePO4 powders along with the highlights of doped and coated derivatives. Apart from already established conventional routes of preparation, numerous alternative procedures are mentioned.This is the peer reviewed version of the following article: Jugović, D., Uskoković, D., 2009. A review of recent developments in the synthesis procedures of lithium iron phosphate powders. Journal of Power Sources 190, 538–544. https://doi.org/10.1016/j.jpowsour.2009.01.07

Synthesis and structural characterization of some cathode materials for lithium-ion batteries

Lithium-ion batteries are under intense scrutiny as alternative energy/power sources. Their electrochemistry is based on intercalation/deintercalation reactions of lithium ions within a crystal structure of an electrode material. Therefore, the structure itself determines both the electrode operating voltage and the transport pathways for lithium ions. Some oxide- and polyanion-based materials are synthesized and studied as positive electrodes. Several synthetic routes were investigated. The crystal structure refinement of an X-ray powder diffraction data was based on the Rietveld full profile method. All relevant structural and microstructural crystal parameters that could be significant for electrochemical intercalation/deintercalation processes were determined. Structural analysis revealed different dimensionality of lithium ion motion. It was also shown that the structural and microstructural properties are significantly dependent on the synthesis condition

Synthesis and Characterization of Oxide Cathode Materials for Lithium Power Sources

U okviru ove doktorske disertacije su izloženi različiti načini sinteze najnovijih oksidnih katodnih materijala za litijumske izvore struje LiFePO4 i LiCr0.175Mn1.825O4 kao i osobine ovih materijala koje su važne sa stanovišta hemijskih izvora struje. Prikazana su tri načina sinteze prahova: sinteza pomoću reakcije u čvrstoj fazi, ultrazvučna sprej piroliza i sinteza pomoću sonohemijske reakcije. Svaka sinteza praćena je metodom rendgenske difrakcije na polikristalnim uzorcima. Podaci dobijeni rendgenskom difrakcijom su iskorišćeni za rendgenostrukturnu analizu prahova, dok je morfologija prahova ispitana skenirajućom i transmisionom elektronskom mikroskopijom. Magnetna merenja su rađena pomoću magnetometra SQUID. Elektrohemijske osobine prahova kao katode u litijum-jonskoj ćeliji su ispitivane galvanostatskim punjenjem i pražnjenjem. Dobijeno je da različiti načini sinteze rezultuju u prahovima različitih strukturnih, mikrostrukturnih i elektrohemijskih osobina. Za dobijanje fazno čistih uzoraka litijum gvožđe fosfata neophodna je kontrola temperature i atmosfere, a kompoziti sa ugljenikom se mogu dobiti dodatkom organske komponente u prekursorski rastvor. Utačnjavanjem strukture je bilo omogućeno određivanje praktično svih relevantnih parametara kristalne strukture i kristalne građe. Najbolje elektrohemijske osobine je pokazao kompozit LiFePO4/C dobijen sintezom pomoću sonohemijske reakcije, koji je prilikom cikliranja C/10 strujom pokazao kapacitet pražnjenja od 125 mAh/g. Ultrazvučna sprej piroliza se pokazala pogodnom za dobijanje Cr-supstituisanog praha litijum manganata. Detaljna analiza magnetnih merenja je pokazala da može biti izuzetno važna i moćna tehnika u proučavanju strukture i kristalne građe čistih materijala i njihovih primesa koji sadrže 3d jone. Uporedna analiza dobijenih rezultata je pokazala jaku korelaciju transportnih osobina prahova i njihovih strukturnih i mikrostrukturnih parametaraThis PhD. thesis describes different ways of syntheses of the most recent oxide cathode materials for lithium power sources, LiFePO4 and LiCr0.175Mn1.825O4, as well as their properties that are significant in the light of chemical power sources. Three synthesis procedures were shown: solid state reaction, ultrasonic spray pyrolysis, and sonochemical reaction. Each synthesis was followed by X-ray powder diffraction (XRPD). XRPD data were used for the structural analysis of the synthesized powders, while the particle morphology was revealed by both scanning and transmission electron microscopies. Magnetic measurements were carried out with SQUID-based magnetometer. In order to examine the electrochemical properties of synthesized powders as cathode materials for lithium-ion battery galvanostatic charge/discharge tests were performed. It was demonstrated that various synthesis procedures result in powders with different structural, microstructural, and electrochemical properties. Optimization of both temperature and atmosphere is necessary for obtaining monophased lithium iron phosphate samples, while composites with carbon can be easily attained by the addition of an organic component in a precursor solution. Crystal structure refinement was used for the determination of all relevant structural and microstructural parameters. Sonochemically derived LiFePO4/C composite showed the best electrochemical performances, reaching discharge capacity of 125 mAh/g while cycling with current density of C/10. Ultrasonic spray pyrolysis has been proven to be a proper method for obtaining Cr-substituted lithium manganate powder. It has been shown that magnetic measurements are very efficient in crystal structure study of pure materials as well as their impurities that contain 3d ions. Parallel analysis of the obtained results showed a strong correlation between transport properties of powders and their structural and microstructural parameters

Characterization of LiMn 2-xMxO4 (M=Mn, Cr, Zn) cathode materials obtained through ultrasonic spray pyrolysis

Metodom ultrazvučne sprej pirolize sintetisani su prahovi LiMn2O4, LiCr0.175Mn1.825O4 i LiZn0,082Mn1,918O4. Prahovi su dobijeni raspršivanjem vodenog rastvora nitrata odgovarajućih metala, ultrazvučnim raspšivačem frekvencije 1,7 MHz, u horizontalnu električnu peć sa maksimumom temperature od 1073 K u centru peći. Noseći gas je bio vazduh protoka 0,5 dm3/min. Prahovi LiMn2O4, fluksa 0,0015 g/min, su sakupljani na izlazu iz reakcione cevi na dva načina sa različitim režimom hlađenja: u vodenoj ispiralici gde je došlo do naglog hlađenja praha ili sa zidova kvarcne cevi na kojima su čestice praha sporo hlađene do sobne temperature. Prahovi LiCr0.175Mn1.825O4 i LiZn0,082Mn1,918O4 su sakupljani sa zidova kvarcne cevi, na kojoj su se deponovali brzinom od 0,0017g/min i 0,0018 g/min, respektivno. \ud Na sintetisanim uzorcima su, na sobnoj temperaturi, urađena rendgenodifrakciona merenja na prahu. Dobijeni difraktogrami su poslužili da se uradi rendgenostrukturna analiza prahova. Dobijeno je da promena režima hlađenja prahova dovodi do promene u strukturi. Za sporo hlađen LiMn2O4 je dobijeno da je iskristalisao u prostornoj grupi Fd3m (Oh 7) u dobro poznatom strukturnom tipu spinela, dok je uzorak dobijen brzim hlađenjem, BH-LiMn2O4, iskristalisao u tetragonalnoj prostornoj grupi I4l/amd (D4h 19). Kod BH-LiMn2O4 je došlo do tetragonalne distorzije spinelne faze, a veličina ove tetragonalne distorzije iznosi c/a = 1.16. Dopiranje hromom i cinkom je dalo monofazne prahove koji su takođe dobro iskristalisali u prostornoj grupi Fd3m (Oh 7) u strukturnom tipu spinela. Pokazano je da kod LiCr0.175Mn1.825O4 i LiZn0,082Mn1,918O4 hrom i cink izomorfno zamenjuju mangan. Utačnjavanje struktura je pokazalo da hromovi joni preferiraju oktaedarske pozicije (16d), kao i mangan u čistom spinelu, ali da se izvesna količina hroma može naći i na tetraedarskim pozicijama (0.047(8)). Nasuprot njima, cinkovi joni zaposedaju tetraedarske pozicije (8a), koje su inače zaposednute litijumovim jonima. Kao posledica toga izvesna količina litijumovih jona se mora naći na oktaedarskim kristalografskim položajima. Poređenjem parametra kristalne rešetke može se zaključiti da dopiranje LiMn2O4 hromom i cinkom dovodi do smanjenja jedinične ćelije: a(LiMn2O4) = 8,2410(1) Å, a(LiCr0.175Mn1.825O4) = 8,2154(4) Å, a(LiZn0,082Mn1,918O4) = 8,2324(3) Å. Supstitucija manganovog jona jonom prelaznog metala je dovela i do smanjenja mikronaprezanja, koje je u slučaju hroma izraženije. Takođe je smanjena i veličina tetragonalne distorzije i uzima najmanju vrednost kod LiZn0,082Mn1,918O4, a najveću kod LiCr0.175Mn1.825O4. Sve navedeno upućuje da izomorfna zamena Mn3+ jona Cr3+ ili Zn2+ jonima dovodi do stabilisanja spinelne strukture. \ud Rezultati skenirajuće elektronske mikroskopije su pokazali razliku u morfologiji čestica sintetisanih prahova. Čestice svih prahova LiMn2-xMxO4 (M = Mn, Cr, Zn) pokazuju sfernu morfologiju i neaglomerisane su. Međutim, iako su ovi prahovi dobijeni na isti način, pod istim uslovima sinteze, variranjem metala M javlja se razlika u morfologiji čestica. U slučaju M = Cr površina čestice je izuzetno glatka, dok je u slučaju kada je M = Zn izrazito porozne strukture. Kod LiMn2O4 uočavaju se individualne čestice, hrapave površine, nalik pomorandžinoj kori, veličine 0,5-1,2 μm. Na jednoj od SEM fotografija LiCr0.175Mn1.825O4 je urađena stereološka analiza. Veličine čestica leže u opsegu od 0.37 μm do 1.45 μm, a najveći broj njih je veličine 0.78 μm. Ove vrednosti su dobijene za prah sintetisan iz rastvora koncentracije 0,94 mol/dm3 i deponovan fluksom 0,0017g/min. Na istom uzorku je urađena i transmisiona elektronska mikroskopija koja je pokazala da se radi o punim sferama, pri čemu se jedna čestica sastoji od velikog broja primarnih čestica, veličine 21.6 ± 8.1 nm. \ud Jedna od premisa da struktura određuje elektrohemijske osobine je potvrđena galvanostatskim cikliranjem u dvoelektrodnoj ćeliji pod argonom sa elektrolitom 1M rastvor LiClO4 u PC/EC smeši. Brzo hlađen LiMn2O4 koji je iskristalisao u tetragonalnoj fazi, koja predstavlja tetragonalno izduženu spinelnu fazu, je pokazao izuzetno slabe elektrohemijske osobine, sa početnim kapacitetom pražnjenja od samo 26 mAh/g dobijen cikliranjem strujom od 10.4 mA/g. Nasuprot njemu, pri cikliranju strujom od 18.7 mA/g sporo hlađeni LiMn2O4 je dao početni kapacitet od 115 mAh/g. Dopiranje hromom dalo je materijal manjeg početnog kapaciteta od 80 mAh/g, pri konstantnoj struji od 25.16 mA/g, što je i očekivano s obzirom na smanjenu količinu Mn3+ jona. S druge strane, posle desetog ciklusa dolazi do stabilizacije kapaciteta na vrednost od oko 70 mAh/g. Ove vrednosti kapaciteta su nešto niže od vrednosti kapaciteta koje se pominju u literaturi za ovaj materijal. Stabilizacija kapaciteta se dešava kao posledica smanjenja M - O veze (M = Mn, Cr)

Influence of platinization of mechanically activated nuclear grade graphite powders on the hydrogen adsorption process

Non-activated powder of nuclear grade graphite and powders of nuclear grade graphite that were milled for 10, 20 and 30 minutes are doped with 0.03% of platinum. XRD analysis of injtial and activated graphite powders was used for structural characterization. Hydrogen adsorption perfonned in isothermal conditions showed that platinization of powder samples of nuclear grade graphite decreases time needed for reaching adsorbent saturation during hydration. Simultaneously it was shown that platinization, due to the hydrogen spillower effect, increases adsorption capacity in a function of mechanical activation duration

Electrochemical properties of LiFePO4/C composites obtained by ultrasound assisted synthesis at different calcination temperatures

Olivine structure LiFePO4/C composite powders were prepared by combining sonochemical precipitation and calcination at three different temperatures. A polyvinyl alcohol solution was used as the source of an in situ formed carbon. The crystal structures of the powders were revealed by X-ray powder diffraction. Electrochemical properties of the powders calcined at different temperatures were discussed. It was shown that optimal electrochemical performance may be attained by using both slightly reductive atmosphere and moderate temperature of 600 °C.Physical chemistry 2008 : 9th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 24-28 September 200

Synthesis and structural characterization of some cathode materials for lithium-ion batteries

Lithium-ion batteries are under intense scrutiny as alternative energy/power sources. Their electrochemistry is based on intercalation/deintercalation reactions of lithium ions within a crystal structure of an electrode material. Therefore, the structure itself determines both the electrode operating voltage and the transport pathways for lithium ions. Some oxide- and polyanion-based materials are synthesized and studied as positive electrodes. Several synthetic routes were investigated. The crystal structure refinement of an X-ray powder diffraction data was based on the Rietveld full profile method. All relevant structural and microstructural crystal parameters that could be significant for electrochemical intercalation/deintercalation processes were determined. Structural analysis revealed different dimensionality of lithium ion motion. It was also shown that the structural and microstructural properties are significantly dependent on the synthesis condition

Heavily vanadium-doped LiFePO4 olivine as electrode material for Li-ion aqueous rechargeable batteries

Since LiFePO4 batteries play a major role in the transition to safe, more affordable and sustainable energy production, numerous strategies have been applied to modify LFP cathode, with the aim of improving its electrochemistry. In this contribution, a highly vanadium-doped LiFe0.9V0.1PO4/C composite (LFP/C-10V) is synthesized using the glycine combustion method and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Thermogravimetry Differential Thermal Analysis (TGDTA) and Cyclic Voltammetry (CV). It is shown that 10wt.% of vanadium can substitute Fe positions, thus decreasing unit cell volume, which is followed by generation of Li3V2PO4 traces, as detected by CV. High vanadium doping does not change the carbon content in the composite (≈ 13 wt.%) but improves its electronic conductivity and electrochemical performance in both aqueous and organic electrolytes. The reversibility and current response are increasing following the trend: LFP/C, LFP/C -3mol%V, LFP/C - 5mol % and LFP/C-10 mol %. The best specific capacity is obtained for the most highly doped olivine, which exhibits a reversible process at 1 mV s-1 in an aqueous electrolyte, thus showing a peak-to-peak distance of 56 mV. The high capacity of LFPC-10V is measured in both LiNO3 and NaNO3 electrolytes amounting to around 100 mAh g-1 at 20 mV s-1. Still, the material is only stable in LiNO3 electrolyte, making it more suitable for Li than Na-ion aqueous rechargeable batteries

Hydrothermal Synthesis of Cathode Materials for Lithium-ion Batteries

Poster presented at the 9th Conference of the Yugoslav Materials Research Society - YUCOMAT 2007, Herceg Novi, Montenegro, September 10-14, 2007