Fluorinated reduced graphene oxide as a protective layer on the metallic lithium for application in the high energy batteries

International audienceMetallic lithium is considered to be one of the most promising anode materials since it offers high volumetric and gravimetric energy densities when combined with high-voltage or high-capacity cathodes. However, the main impediment to the practical applications of metallic lithium is its unstable solid electrolyte interface (SEI), which results in constant lithium consumption for the formation of fresh SEI, together with lithium dendritic growth during electrochemical cycling. Here we present the electrochemical performance of a fluorinated reduced graphene oxide interlayer (FGI) on the metallic lithium surface, tested in lithium symmetrical cells and in combination with two different cathode materials. The FGI on the metallic lithium exhibit two roles, firstly it acts as a Li-ion conductive layer and electronic insulator and secondly, it effectively suppresses the formation of high surface area lithium (HSAL). An enhanced electrochemical performance of the full cell battery system with two different types of cathodes was shown in the carbonate or in the ether based electrolytes. The presented results indicate a potential application in future secondary Li-metal batteries

Modifikacija površine litija za akumulatorske aplikacije

Increasing global energy demand requires high energy density batteries for which the replacement of intercalation or conversion anodes with lithium metal is a crucial step towards batteries with improved energy density. State-of-the-art secondary lithium metal batteries still suffer from low Coulombic efficiency and low safety related to the thermodynamically unstable solid electrolyte interphase (SEI) between metallic lithium and the electrolyte in most of the liquid electrolytes, resulting in high surface area lithium (HSAL) growth. Various approaches can be used to suppress HSAL formation, including protective layer preparation on the lithium surface. Properties of the protective layer should be high Li-ion conductivity, electronic resistivity, small thickness, and high Young’s modulus to withstand the applied stress during lithium stripping and the deposition process within the cell. In this work, we investigated three different approaches employed as a protective layer on a lithium surface to suppress HSAL growth. The protective layers were examined with electrochemical measurements supported by scanning electron microscopy, X-ray photoelectron spectroscopy, and other techniques. We demonstrate that the functionalization of graphene modifies its electronic and ionic properties to make it suitable for use in protective layer applications. The impact of graphene oxide (GO), reduced graphene oxide (rGO), and fluorinated reduced graphene oxide (FG) as protective layers on a lithium surface on HSAL growth suppression was studied in Li symmetric cells. Additionally, the FG protective nature was evaluated in two full cell configurations (Li-ion and Li-sulfur) in carbonate and ether-based electrolyte. The physical characteristics and electrochemical measures had shown the dual role of the FG protective layer. First, it acts as a Li-ion conductive layer and electronic insulator on metallic lithium surfacesecond, it successfully suppresses dendritic growth. Enhanced electrochemical performance of the full cell battery system indicates potential applications in the secondary lithium metal batteries of the future. Metal fluorides (MgF2and AlF3) were studied as precursors of protective layerson a lithium surface. The use of MgF2-modified lithium resulted in denser lithium deposits, enhanced stability in symmetric cells and prolonged cycling in Li-sulfur batteries with fluorinated electrolyte. Finally, the in-situ anionic polymerization of trimethylolpropane ethoxylate triacrylate on a lithium surface resulted in completely hindered lithium ion transport through the layer and exposure of the edge effect. Correspondingly, we designed a new cell configuration that enables more accurate electrochemical evaluation of protective layerswith edge effect avoidance.Povečana svetovna poraba energije kliče po razvoju novih akumulatorjev z visoko energijsko gostoto. Zamenjava interkalacijskih oziroma konverzijskih anod s kovinskim litijem je zato ključni korak pri razvoju akumulatorjev z izboljšano energijsko gostoto. Najsodobnejši akumulatorji s kovinskim litijem so trenutno še v razvoju, predvsem zaradi težav z nizko Coulombsko učinkovitostjo in pomanjkljivo varnostjo, ki je posledica prisotnosti termodinamsko nestabilnega pasivnega sloja elektrolita na medfazni meji (SEI) kovinski litij/elektrolit. Nestabilen SEI se tvori v večini tekočih elektrolitov, kar vodi do tvorbe visoko površinskega litija (HSAL). Proti nastanku tvorbe HSAL lahko uporabimo različne pristope, vključno s pripravo zaščitnega sloja na litijevi površini. Zaščitni sloj mora biti visoko Li-ionsko prevoden, elektronsko neprevoden, hkrati pa mora biti čim tanjši in z visokim modulom elastičnosti, da lahko prenese stres, ki se pojavi med elektrokemijskim jedkanjem in odlaganjem litija znotraj celice. V doktorskem delu smo raziskali tri različne pristope, ki smo jih uporabili kot zaščitni sloj na litijevi površini, da bi preprečili rast HSAL. Zaščitne sloje smo okarkaterizirali z elektrokemijskimi meritvami, z uporabo vrstične elektronske mikroskopije in rentgenske foto-elektronske spektroskopije ter z drugimi tehnikami. Pokazali smo, da lahko s funkcionalizacijo grafena krojimo njegove elektronske in ionske lastnosti, kar posledično omogoča uporabo v aplikacijah zaščitnega sloja. V litijevi simetrični celici smo proučevali vpliv grafen oksida (GO), reduciranega grafen oksida (rGO) in fluoriranega reduciranega grafen oksida (FG) kot zaščitnega sloja na litijevi površini za preprečevanje rasti HSAL. Poleg tega smo delovanje FG zaščitnega sloja ovrednotili tudi v Li-ionskem in Li-žveplovem akumulatorju v karbonatnih in etrskih elektrolitih. Fizikalne lastnosti in elektrokemijske meritve so pokazale dvojno vlogo FG zaščitnega sloja. Prvič deluje kot Li-ionski prevodnik in hkrati elektronski izolator na površini kovinskega litija in drugič uspešno zavira rast HSAL. Izboljšana elektrokemijska zmogljivost akumulatorja z FG zaščitenim litijem kaže na potencialno uporabo v modernih akumulatorjih z visoko energijsko gostoto. Kovinska fluorida (MgF2in AlF3) smo preučevali kot prekurzorja za tvorbo zaščitnega sloja na litijevi površini. Uporaba litija z MgF2 modificirano površino je vodila do nastajanja gostejših litijevih depozitov, povečane stabilnosti v litij simetrični celici in podaljšano življenjsko dobo Li-žveplovega akumulatorja s fluoriranimi elektroliti. In-situ anionska polimerizacija trimetilolpropan etoksilat triakrilata na litijevi površini je povzročila popolnoma blokiran Li-ionski transport skozi zaščitni sloj, kar je posledično izpostavilo t.i. »robni efekt«. V ta namen smo oblikovali novo konfiguracijo celice, ki je omogočila natančnejše elektrokemijsko vrednotenje zaščitnega sloja brez vpliva »robnega efekta«

Role of Cu current collector on electrochemical mechanism of Mg–S battery

Development of magnesium sulfur battery is accompanied with all known difficulties present in Li–S batteries, however with even more limited choice of electrolytes. In the present work, the influence of current collector on electrochemical mechanism was investigated in light of different reports where improved behavior was ascribed to electrolyte. Notable differences in cycling behavior are reported when Al current collector is replaced by Cu current collector independent of electrolyte. The initial reduction of sulfur follows similar reaction path no mater of current collector, but formation of MgS can be in competition with formation of CuS in the presence of Cu cations. With the subsequent cycling cells prepared from cathodes deposited on Cu current collector show decrease in the voltage and formation of single plateau during cycling. The change corresponds to the involvement of Cu into the reaction and formation of redox couple Mg/CuS as determined by Cu K-edge XANES measurements. Corrosion of Cu foil is identified by SEM and serves as a source of Cu cations for the chemical reaction between Cu and polysulfides. Mg/CuS redox couple shows improved cycling stability, but theoretical energy density is severely reduced due to substitution of S with CuS as cathode active material

Role of Cu current collector on electrochemical mechanism of Mg–S battery

Development of magnesium sulfur battery is accompanied with all known difficulties present in Li–S batteries, however with even more limited choice of electrolytes. In the present work, the influence of current collector on electrochemical mechanism was investigated in light of different reports where improved behavior was ascribed to electrolyte. Notable differences in cycling behavior are reported when Al current collector is replaced by Cu current collector independent of electrolyte. The initial reduction of sulfur follows similar reaction path no mater of current collector, but formation of MgS can be in competition with formation of CuS in the presence of Cu cations. With the subsequent cycling cells prepared from cathodes deposited on Cu current collector show decrease in the voltage and formation of single plateau during cycling. The change corresponds to the involvement of Cu into the reaction and formation of redox couple Mg/CuS as determined by Cu K-edge XANES measurements. Corrosion of Cu foil is identified by SEM and serves as a source of Cu cations for the chemical reaction between Cu and polysulfides. Mg/CuS redox couple shows improved cycling stability, but theoretical energy density is severely reduced due to substitution of S with CuS as cathode active material

Lithium Metal Protection by a Cross-Linked Polymer Ionic Liquid and Its Application in Lithium Battery

Lithium (Li) metal has been considered as an important anode candidate to reach more powerful energy storage devices with higher gravimetric and volumetric capacities. Nevertheless, the growth of high surface area lithium (HSAL) and dendrites during the stripping/deposition of Li causes safety concerns and a low cycle life of Li metal batteries. Here, we report the obtained results for protection of metallic lithium surface by using a gel polymer ionic liquid cross-linked by activation with UV radiation (UV-PIL). The UV-PIL protects Li against the constant degradation caused by the formation of unstable lithium metal-electrolyte interphase and cell dry out due to continuous electrolyte consumption. We observed retarded growth of dendrites when lithium metal was protected with UV-PIL, and due to the lower ionic conductivity of UV-PIL, some differences of mass transport are present compared to carbonate-based liquid electrolyte. Nevertheless, the UV-PIL@Li negative electrode was successfully applied in a Li-ion battery with a lithium iron phosphate (LFP) positive electrode, showing similar behavior compared to the bare Li surface.Fil: Calderon, Cecilia Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Vizintin, Alen. National Institute of Chemistry; EsloveniaFil: Bobnar, Jernej. National Institute of Chemistry; EsloveniaFil: Barraco Diaz, Daniel Eugenio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Leiva, Ezequiel Pedro M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Visintin, Arnaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Fantini, Sébastien. Solvionic; FranciaFil: Fischer, Florent. SAFT Research & Technology; FranciaFil: Dominko, Robert. National Institute of Chemistry; Eslovenia. University of Ljubljana; Faculty of Chemistry and Chemical Technology; Eslovenia. ALISTORE - European Research Institute; Franci

Vesicle cholesterol controls exocytotic fusion pore

In some lysosomal storage diseases (LSD) cholesterol accumulates in vesicles. Whether increased vesicle cholesterol affects vesicle fusion with the plasmalemma, where the fusion pore, a channel between the vesicle lumen and the extracellular space, is formed, is unknown. Super-resolution microscopy revealed that after stimulation of exocytosis, pituitary lactotroph vesicles discharge cholesterol which transfers to the plasmalemma. Cholesterol depletion in lactotrophs and astrocytes, both exhibiting Ca2+-dependent exocytosis regulated by distinct Ca2+sources, evokes vesicle secretion. Although this treatment enhanced cytosolic levels of Ca2+ in lactotrophs but decreased it in astrocytes, this indicates that cholesterol may well directly define the fusion pore. In an attempt to explain this mechanism, a new model of cholesterol-dependent fusion pore regulation is proposed. High-resolution membrane capacitance measurements, used to monitor fusion pore conductance, a parameter related to fusion pore diameter, confirm that at resting conditions reducing cholesterol increases, while enrichment with cholesterol decreases the conductance of the fusion pore. In resting fibroblasts, lacking the Npc1 protein, a cellular model of LSD in which cholesterol accumulates in vesicles, the fusion pore conductance is smaller than in controls, showing that vesicle cholesterol controls fusion pore and is relevant for pathophysiology of LSD.</p