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

Boron-Based Functional Additives Enable Solid Electrolyte Interphase Engineering in Calcium Metal Battery

Calcium-metal batteries have received growing attention recently after several studies reporting successful metal plating and stripping with organic electrolytes. Given the low redox potential of metallic calcium, its surface is commonly covered by a passivation layer grown by the accumulation of electrolyte decomposition products. The presence of borate species in this layer has been shown to be a key parameter allowing for Ca2+ migration and favoring Ca electrodeposition. Here, boron-based additives are evaluated in order to tune the SEI composition, morphology, and properties. The decomposition of a BF3-based additive is studied at different potentiostatic steps and the resulting SEI layer was thoroughly characterized. SEI growth mechanism is proposed based on both experimental data and DFT calculations pointing at the formation of boron-crosslinked polymeric matrices. Several boron-based adducts are explored as SEI-forming additives for calcium-metal batteries paving the way to very rich chemistry leading to Ca2+ conducting SEI.Funding from the European Union's Horizon 2020 research and innovation program H2020 are acknowledged: European Research Council (ERC-2016-STG, CAMBAT, grant agreement no. 715087 and ERC-2020-STG, HiPeR−F, grant agreement no. 950625) and H2020-MSCA-COFUND-2016 (DOC-FAM, grant agreement no. 754397). A.P. is grateful to the Spanish Ministry for Economy, Industry and Competitiveness Severo Ochoa Programme for Centres of Excellence in R&D (CEX2019-000917-S). D.F., C.C. and R.D. thank the French National Research Agency (STORE-EX Labex Project ANR-10-LABX-76-01) for financial support. K.R. and M.L. gratefully acknowledge the research funding by the Slovenian Research Agency (P1-0045, N1-0189). Alistore-European Research Institute is gratefully acknowledged for financial support through the postdoc grant to C.B. The SR-FTIR experiments were performed at MIRAS beamline at ALBA Synchrotron with the collaboration of ALBA staff. All DFT calculations were carried out at the Wroclaw Centre for Networking and Supercomputing within grant no. 346.With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe

Crystal structure of CaSiF6·2H2O(mP2) and reevaluation of the SiIV–F bond-valence parameter R0

The structure of a second polymorph of CaSiF6·2H2O [calcium hexafluoridosilicate dihydrate; space group P2/c (No. 13), Pearson symbol mP2] was elucidated by single-crystal X-ray diffraction. It arose as an unexpected product when soda-lime glass was attacked by HF. Its crystal structure consists of infinite ∞2[Ca(H2O)2/1(SiF6)4/4] layers oriented parallel to the bc-crystallographic plane, a unique motif among structurally characterized hydrated hexafluoridosilicates. The crystal structure also exhibits inter- and intralayer hydrogen bonds, with the interlayer O—H...O hydrogen bonds involving a disordered hydrogen atom. The large deviation between the calculated bond-valence sum for Si and the expected value prompted a redetermination of the empirical SiIV–F bond-valence parameter R0. Based on a data set of 42 high-quality crystal structures containing 49 independent SiIV coordination environments, a revised value of 1.534 Å was derived for R0

Expanding the boron peroxide chemistry on BODIPY scaffold

Novel stable BODIPY boron mono- and diperoxides were prepared in good yields by TMSOTf activation of mono- and dialkoxy-BODIPY derivatives, followed by ligand exchange with organic hydroperoxides. The reactions of the methoxy derivative of BODIPY with hydroperoxides led to the formation of a novel group of peroxides with the structural element B(F)OOR. The reaction of the dimethoxy derivative of BODIPY with $^t$BuOOH provided the first organic boron diperoxide. Using gem-dihydroperoxide, a cyclic analogue with tetraoxaborinane ring was prepared. Both, mono- and diperoxo boron compounds are stable under ambient conditions, which allowed full characterization of compounds. A mechanistic study provided further insight into their formation and elucidated some of the possible intermediates, namely the borenium cations

Aqua-tri-fluorido-boron-1,3-dioxolan-2-one (1/2)

The crystal structure of the co-crystal of aqua-tri-fluorido-boron with two ethyl-ene carbonate (systematic name: 1,3-dioxolan-2-one) mol-ecules, BF3H2O·2OC(OCH2)2, was determined by low-temperature single-crystal X-ray diffraction. The co-crystal crystallizes in the ortho-rhom-bic space group P212121 with four formula units per unit cell. The asymmetric unit consists of an aqua-tri-fluorido-boron mol-ecule and two ethyl-ene carbonate mol-ecules, connected by O-H⋯O=C hydrogen bonds. This crystal structure is an inter-esting example of a superacidic BF3H2O species co-crystallized with an organic carbonate.Funding for this research was provided by: European Research Council (ERC) (StG HiPeR-F and StG CAMBAT) (grant agreement Nos. 950625 and 715087); Marie Skłodowska-Curie Actions (COFUND-2016 DOC-FAM) under the European Union’s Horizon 2020 research and innovation programme (grant No. 754397); Jozˇef Stefan Institute Director’s Fund; Slovenian Research Agency (grant No. N1-0189); Spanish Ministry for Economy, Industry and Competitiveness Severo Ochoa Programme for Centres of Excellence in R&D (contract No. CEX2019-000917-S).With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe

Hydrogen-bonding ability of Noyori–Ikariya catalysts enables stereoselective access to CF3_3-substituted syn-1,2-diols via dynamic kinetic resolution

Stereopure CF$_3$-substituted syn-1,2-diols were prepared via the reductive dynamic kinetic resolution of the corresponding racemic α-hydroxyketones in HCO$_2$H/Et$_3$N. (Het)aryl, benzyl, vinyl, and alkyl ketones are tolerated, delivering products with ≥95% ee and ≥87:13 syn/anti. This methodology offers rapid access to stereopure bioactive molecules. Furthermore, DFT calculations for three types of Noyori–Ikariya ruthenium catalysts were performed to show their general ability of directing stereoselectivity via the hydrogen bond acceptor SO$_2$ region and CH/π interactions

Homochiral β-CF3, -SCF3 and -OCF3 secondary alcohols: catalytic stereoconvergent synthesis, bioactivity and flexible crystals

An optimized catalytic protocol for enantio- and diastereoselective reduction of racemic α-CF3, α-SCF3 and α-OCF3 aryl ketones is described. The reaction involves a dynamic kinetic resolution (DKR) based on ruthenium catalyzed Noyori–Ikariya asymmetric transfer hydrogenation for simultaneous construction of two contiguous stereogenic centers. A range of previously inaccessible fluorinated secondary alcohols was prepared in excellent stereomeric purity (up to above 99.9% ee, up to above 99.9:0.1 dr) and in high isolated yield (up to 99%). The origin of DKR (exceptional stereoselectivity and racemization mechanism) is rationalized by density functional theory calculations. Pharmaceutically relevant further transformations of the products are demonstrated including incorporation into heat shock protein 90 inhibitor with in vitro anti-cancer activity. Moreover, needle-shaped crystals of representative stereopure products are mechanically responsive: either elastically or plastically flexible, opening the door to novel class of functional materials based on chiral molecular crystals