title: Electrochemical activity and high ionic conductivity of lithium copper pyroborate Li6CuB4O10.
abstract: In the search for new cathode materials for Li-ion batteries, borate (BO3(3-)) based compounds have gained much interest during the last two decades due to the low molecular weight of the borate polyanions which leads to active materials with increased theoretical capacities. In this context we herein report the electrochemical activity versus lithium and the ionic conductivity of a diborate or pyroborate B2O5(4-) based compound, Li6CuB4O10. By combining various electrochemical techniques with in situ X-ray diffraction, we show that this material can reversibly insert/deinsert limited amounts of lithium (∼0.3 Li(+)) in a potential window ranging from 2.5 to 4.5 V vs. Li(+)/Li(0). We demonstrate, via electron paramagnetic resonance (EPR), that such an electrochemical activity centered near 4.25 V vs. Li(+)/Li(0) is associated with the Cu(3+)/Cu(2+) redox couple, confirmed by density functional theory (DFT) calculations. Another specificity of this compound lies in its different electrochemical behavior when cycled down to 1 V vs. Li(+)/Li(0) which leads to the extrusion of elemental copper via a conversion type reaction as deduced by transmission electron microscopy (TEM). Lastly, we probe the ionic conductivity by means of AC and DC impedance measurements as a function of temperature and show that Li6CuB4O10 undergoes a reversible structural transition around 350 °C, leading to a surprisingly high ionic conductivity of ∼1.4 mS cm(-1) at 500 °C.
authors.affiliation: National Institute of Chemistry, Hajdrihova 19, SI-1000 Ljubljana, Slovenia and University of Ljubljana, Faculty of Chemistry and Chemical Technology, Vecna Pot 113, 1000 Ljubljana, Slovenia and UMR 8260 "Chimie du Solide et Energie", Collège de France, 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, France. jean-marie.tarascon@college-de-france.fr and UPMC Univ Paris 06, Sorbonne Universités, 4 Place Jussieu, F-75005 Paris, France and ALISTORE - European Research Institute, 33 Rue Saint-Leu, Amiens 80039 Cedex, France.
authors.forename: Florian
authors.initials: F
authors.lastname: Strauss
authors.affiliation: UMR 8260 "Chimie du Solide et Energie", Collège de France, 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, France. jean-marie.tarascon@college-de-france.fr and UPMC Univ Paris 06, Sorbonne Universités, 4 Place Jussieu, F-75005 Paris, France and ALISTORE - European Research Institute, 33 Rue Saint-Leu, Amiens 80039 Cedex, France and Réseau sur le Stockage Electrochimique de l'Energie (RS2E), FR CNRS 3459, 80039 Amiens Cedex, France.
authors.forename: Gwenaëlle
authors.initials: G
authors.lastname: Rousse
authors.affiliation: UMR 8260 "Chimie du Solide et Energie", Collège de France, 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, France. jean-marie.tarascon@college-de-france.fr and Réseau sur le Stockage Electrochimique de l'Energie (RS2E), FR CNRS 3459, 80039 Amiens Cedex, France.
authors.forename: Daniel
authors.initials: D
authors.lastname: Alves Dalla Corte
authors.affiliation: Laboratoire SPMS, École Centrale Paris (ECP), Grande Voie des Vignes, 92295 Chatenay-Malabry Cedex, France.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Ben Hassine
authors.affiliation: ICGM Institut Charles Gerhardt, CNRS and Université Montpellier, Place Eugène Bataillon, 34095 Montpellier, France and Réseau sur le Stockage Electrochimique de l'Energie (RS2E), FR CNRS 3459, 80039 Amiens Cedex, France.
authors.forename: Matthieu
authors.initials: M
authors.lastname: Saubanère
authors.affiliation: CNRS, CEMHTI UPR3079, Université d'Orléans, 1D Avenue de la Recherche Scientifique, F-45071 Orléans Cedex 2, France and Réseau sur le Stockage Electrochimique de l'Energie (RS2E), FR CNRS 3459, 80039 Amiens Cedex, France.
authors.forename: Mingxue
authors.initials: M
authors.lastname: Tang
authors.affiliation: Université Lille Nord de France, CNRS UMR 8516-LASIR, Université Lille 1, F-59655 Villeneuve d'Ascq, France and Réseau sur le Stockage Electrochimique de l'Energie (RS2E), FR CNRS 3459, 80039 Amiens Cedex, France.
authors.forename: Hervé
authors.initials: H
authors.lastname: Vezin
authors.affiliation: Laboratoire de Réactivité et Chimie des Solides, Université de Picardie Jules Verne 33, Rue Saint Leu, 80039 Amiens, France and Réseau sur le Stockage Electrochimique de l'Energie (RS2E), FR CNRS 3459, 80039 Amiens Cedex, France.
authors.forename: Matthieu
authors.initials: M
authors.lastname: Courty
authors.affiliation: National Institute of Chemistry, Hajdrihova 19, SI-1000 Ljubljana, Slovenia and ALISTORE - European Research Institute, 33 Rue Saint-Leu, Amiens 80039 Cedex, France.
authors.forename: Robert
authors.initials: R
authors.lastname: Dominko
authors.affiliation: UMR 8260 "Chimie du Solide et Energie", Collège de France, 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, France. jean-marie.tarascon@college-de-france.fr and UPMC Univ Paris 06, Sorbonne Universités, 4 Place Jussieu, F-75005 Paris, France and ALISTORE - European Research Institute, 33 Rue Saint-Leu, Amiens 80039 Cedex, France and Réseau sur le Stockage Electrochimique de l'Energie (RS2E), FR CNRS 3459, 80039 Amiens Cedex, France.
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Tarascon