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International audience; This paper describes an innovative way of using environmental scanning electron microscopy (ESEM) and the development of a suitable accessory to perform in situ observation of living seedlings in the ESEM. We provide details on fabrication of an accessory that proved to be essential for such experiments but inexpensive and easy to build in the laboratory, and present our in situ observations of the tissue and cell surfaces. Sample-specific configurations and optimized tuning of the ESEM were defined to maintain Arabidopsis and flax seedlings viable throughout repetitive exposure to the imaging conditions in the microscope chamber. This method permitted us to identify cells and tissues of the live plantlets and characterize their surface morphology during their early stage of growth and development. We could extend the application of this technique, to visualize the response of living cells and tissues to exogenous enzymatic treatments with polygalacturonase in Arabidopsis, and their interaction with hyphae of the wilt fungus Verticillium dahliae during artificial infection in flax plantlets. Our results provide an incentive to the use of the ESEM for in situ studies in plant science and a guide for researchers to optimize their electron microscopy observation in the relevant fields.

Flax (Linum usitatissimum L.) seed oil, which accumulates in the embryo, and mucilage, which is synthesized in the seed coat, are of great economic importance for food, pharmaceutical as well as chemical industries. Theories on the link between oil and mucilage production in seeds consist in the spatio-temporal competition of both compounds for photosynthates during the very early stages of seed development. In this study, we demonstrate a positive relationship between seed oil production and seed coat mucilage extrusion in the agronomic model, flax. Three recombinant inbred lines were selected for low, medium and high mucilage and seed oil contents. Metabolite and transcript profiling (1H NMR and DNA oligo-microarrays) was performed on the seeds during seed development. These analyses showed main changes in the seed coat transcriptome during the mid-phase of seed development (25 Days Post-Anthesis), once the mucilage biosynthesis and modification processes are thought to be finished. These transcriptome changes comprised genes that are putatively involved in mucilage chemical modification and oil synthesis, as well as gibberellic acid (GA) metabolism. The results of these integrative biology approach, suggest that transcriptional regulations of seed oil and fatty acid (FA) metabolism could occur in the seed coat during the mid-stage of seed development, once the seed coat carbon supplies have been used for mucilage biosynthesis and mechanochemical properties of the mucilage secretory cells.

Motivated by the request to build shape-conformable flexible, wearable and customizable batteries while maximizing the energy storage and electrochemical performances, additive manufacturing (AM) appears as a revolutionary discipline. Battery components such as electrodes, separator, electrolyte, current collectors and casing can be tailored with any shape, allowing the direct incorporation of batteries and all electronics within the final three-dimensional object. AM also paves the way toward the implementation of complex 3D electrode architectures that could enhance significantly the power battery performances. Transitioning from conventional 2D to complex 3D lithium-ion battery (LIB) architectures will increase the electrochemically active surface area, enhance the Li+ diffusion paths, thus leading to improved specific capacity and power performance [1]. Our recent modeling studies [2] involving the simulation of a classical Ragone plot illustrated that a gyroid 3D battery architecture has +158% performance at a high current density of 6C, in comparison to planar geometry. In this presentation, an overview of current trends in energy storage 3D printing will be discussed [3-11]. A summary of our recent works on lithium-ion battery 3D printing via Thermoplastic Material Extrusion / Fused Deposition Modeling will be presented [12-16]. The development of printable composite filaments (Graphite-, LiFePO4-, Li2TP-, PEO/LiTFSI-, SiO2-, Ag/Cu-based) corresponding to each part of a LIB (electrodes, electrolyte, separator, current collectors), and the importance of introducing a plasticizer (polyethylene glycol dimethyl ether average Mn 500 for polylactic acid) as an additive to enhance the printability will be addressed. Printing of the complete LIB in a single step using multi-material printing options, and the implementation of a solvent-free protocol [14] will also be discussed. Second part of this presentation will be dedicated to AM of batteries by means of Vat Photopolymerization (VPP) processes, including stereolithography, digital light processing and two-photon polymerization (offering a greater resolution down to 0.1μm), to print high resolution battery components [10]. Composite resins formulation approaches based on the introduction of solid battery particles or precursor salts will be introduced [17, 18]. Finally, an overview of our ongoing project dedicated to AM of sodium-ion batteries from resources available on the Moon and Mars will be presented. Due to its relative abundance in the Lunar regolith, the development of a composite photocurable resin loaded with TiO2 negative electrode material and conductive additives, to feed a VPP printer, will be discussed [18]. [1] Long et al., Three-dimensional battery architectures, Chemical Reviews 104(10) (2004) 4463-4492. [2] Maurel et al., Considering lithium-ion battery 3D-printing via thermoplastic material extrusion and polymer powder bed fusion, Additive Manufacturing (2020) 101651. [3] Maurel et al., Overview on Lithium-Ion Battery 3D-Printing By Means of Material Extrusion, ECS Transactions 98(13) (2020) 3-21. [4] Ragones et al., Towards smart free form-factor 3D printable batteries, Sustainable Energy & Fuels 2(7) (2018) 1542-1549. [5] Reyes et al., Three-Dimensional Printing of a Complete Lithium Ion Battery with Fused Filament Fabrication, ACS Applied Energy Materials 1(10) (2018) 5268-5279. [6] Yee et al., Hydrogel-Based Additive Manufacturing of Lithium Cobalt Oxide, Advanced Materials Technologies 6(2) (2021). [7] Saccone et al., Understanding and mitigating mechanical degradation in lithium–sulfur batteries: additive manufacturing of Li2S composites and nanomechanical particle compressions, Journal of Materials Research (2021). [8] Tagliaferri et al., Direct ink writing of energy materials, Materials Advances 2(2) (2021) 25. [9] Sun et al., 3D Printing of Interdigitated Li-Ion Microbattery Architectures, Advanced Materials 25(33) (2013) 4539-4543. [10] Maurel et al., Toward High Resolution 3D Printing of Shape-Conformable Batteries via Vat Photopolymerization: Review and Perspective, IEEE Access 9 (2021) 140654-140666. [11] Seol et al., All-Printed In-Plane Supercapacitors by Sequential Additive Manufacturing Process, Acs Applied Energy Materials 3(5) (2020) 4965-4973. [12] Maurel et al., Highly Loaded Graphite-Polylactic Acid Composite-Based Filaments for Lithium-Ion Battery Three-Dimensional Printing, Chemistry of Materials 30(21) (2018) 7484-7493. [13] Maurel et al., Three-Dimensional Printing of a LiFePO4/Graphite Battery Cell via Fused Deposition Modeling, Scientific Reports 9(1) (2019) 18031. [14] Maurel et al., Environmentally Friendly Lithium-Terephthalate/Polylactic Acid Composite Filament Formulation for Lithium-Ion Battery 3D-Printing via Fused Deposition Modeling, ECS Journal of Solid State Science and Technology 10(3) (2021) 037004. [15] Maurel et al., Poly(Ethylene Oxide)-LiTFSI Solid Polymer Electrolyte Filaments for Fused Deposition Modeling Three-Dimensional Printing, Journal of the Electrochemical Society 167(7) (2020). [16] Maurel et al., Ag-Coated Cu/Polylactic Acid Composite Filament for Lithium and Sodium-Ion Battery Current Collector Three-Dimensional Printing via Thermoplastic Material Extrusion, Frontiers in Energy Research 9(70) (2021). [17] Martinez et al., Additive Manufacturing of LiNi1/3Mn1/3Co1/3O2 battery electrode material via vat photopolymerization precursor approach, (submitted). [18] Maurel et al., Vat Photopolymerization Additive Manufacturing of Sodium-Ion Battery TiO2 Negative Electrodes from Lunar In-Situ Resources, (submitted).

In parallel with the considerable investigations on renewable energy sources, electrical energy storage systems used to store the energy produced now and to provide it when needed have received much attention lately.1 Amongst them, lithium-ion batteries (LIB) are today the most employed in a huge range of purposes including cellphones, laptops or even electric vehicles. Current LIB consists in a planar arrangement (2D) in which the different parts of the battery (positive and negative electrodes, separator, current collectors) are rolled or stacked. Unfortunately, in this type of 2D configuration, lithium ions diffuse only along one dimension. Additive manufacturing (AM) technologies, also called 3D-printing processes, could enable the production of much more complex 3D architectures thus allowing diffusion of the lithium cations towards two or three-dimensions. Advantage of those 3D designs is that the electrochemical active surface area is expected to increase as well as the battery specific capacity and power.2 On the other hand, AM could also allow the direct incorporation of LIB within the final object, thus enabling the possibility to maximize the energy storage capabilities while reducing the dead volume and weight. Amongst the various AM available technologies, we focused our work on the Fused Deposition Modeling (FDM) process using a thermoplastic filament as material source for the 3D-printer. In this presentation, the formulation of composite PLA-based filaments specially designed to print each parts of the LIB (with liquid electrolyte) will be described.3,4 The active material composition within the negative and positive electrodes (graphite and lithium iron phosphate (LiFePO4) respectively), was increased as high as possible in order to enhance the electrochemical performances. Furthermore, the addition of a plasticizer was required to maintain enough mechanical strength while, in the meantime, carbon black was added to confer adequate electrical properties. The impact of ceramic additives on ionic conductivity in the separator was also investigated. From the optimized filaments compositions, stepwise and then “one-shot” 3D-printing of complete LiFePO4/graphite battery cells of any shapes were carried out (Figure 1). In order to prevent short-circuits, classical 3D-printing parameters such as the infill patterns and infill density were investigated for the LIB separator improvement. Finally, this presentation will introduce our latest results5 regarding the printability of a polyethylene oxide/lithium bis(trifluoromethanesulfonyl)imide (PEO/LiTFSI) filament (2.18 × 10−3 S cm−1 at 90 °C) optimized to be used as solid polymer electrolyte in a lithium-ion battery. This presentation, by combining both battery and 3D-printing understandings, will tackle various electrochemical (thickness, electronic and ionic conductivity, liquid electrolyte uptake) and 3D-printing parameters (infill density, infill pattern, perimeters, over and under-extrusion, retraction), which clearly paves the way for enhanced 3D-printed LIB. References: [1] Tarascon, J. M. & Armand, M. Issues and challenges facing rechargeable lithium batteries. Nature 414, 359-367, doi:10.1038/35104644 (2001). [2] Long, J. W., Dunn, B., Rolison, D. R. & White, H. S. Three-dimensional battery architectures. Chemical Reviews 104, 4463-4492, doi:10.1021/cr020740l (2004). [3] Maurel, A. et al. Highly Loaded Graphite-Polylactic Acid Composite-Based Filaments for Lithium-Ion Battery Three-Dimensional Printing. Chemistry of Materials 30, 7484-7493, doi:10.1021/acs.chemmater.8b02062 (2018). [4] Maurel, A. et al. Three-Dimensional Printing of a LiFePO4/Graphite Battery Cell via Fused Deposition Modeling. Scientific Reports 9, 18031, doi:10.1038/s41598-019-54518-y (2019). [5] Maurel, A. et al. Poly(Ethylene Oxide)−LiTFSI Solid Polymer Electrolyte Filaments for Fused Deposition Modeling Three-Dimensional Printing. Journal of The Electrochemical Society 167, 070536, doi:10.1149/1945-7111/ab7c38 (2020). Figure 1

Actual parallel-plate architecture of lithium-ion batteries consists of lithium-ion diffusion in one dimension between the electrodes. To achieve higher performances in terms of specific capacity and power, configurations enabling lithium-ion diffusion in two or three dimensions is considered. With a view to build these complex three-dimensional (3D) battery architectures avoiding the electrodes interpenetration issues, this work is focused on fused deposition modeling (FDM). In this study, the formulation and characterization of a 3D-printable graphite/polylactic acid (PLA) filament, specially designed to be used as negative electrode in a lithium-ion battery and to feed a conventional commercially available FDM 3D printer, is reported. The graphite active material loading in the produced filament is increased as high as possible to enhance the electrochemical performance, while the addition of various amounts of plasticizers such as propylene carbonate, poly(ethylene glycol) dimethyl ether average Mn ∼ 2000, poly(ethylene glycol) dimethyl ether average Mn ∼ 500, and acetyl tributyl citrate is investigated to provide the necessary flexibility to the filament to be printed. Considering the optimized plasticizer composition, an in-depth study is carried out to identify the electrical and electrochemical impact of carbon black and carbon nanofibers as conductive additives. © 2018 American Chemical Society.

Among the 3D-printing technologies, fused deposition modeling (FDM) represents a promising route to enable direct incorporation of the battery within the final 3D object. Here, the preparation and characterization of lithium iron phosphate/polylactic acid (LFP/PLA) and SiO2/PLA 3D-printable filaments, specifically conceived respectively as positive electrode and separator in a lithium-ion battery is reported. By means of plasticizer addition, the active material loading within the positive electrode is raised as high as possible (up to 52 wt.%) while still providing enough flexibility to the filament to be printed. A thorough analysis is performed to determine the thermal, electrical and electrochemical effect of carbon black as conductive additive in the positive electrode and the electrolyte uptake impact of ceramic additives in the separator. Considering both optimized filaments composition and using our previously reported graphite/PLA filament for the negative electrode, assembled and “printed in one-shot” complete LFP/Graphite battery cells are 3D-printed and characterized. Taking advantage of the new design capabilities conferred by 3D-printing, separator patterns and infill density are discussed with a view to enhance the liquid electrolyte impregnation and avoid short-circuits.

International audience; The external seed coat cell layer of certain species is specialized in the production and extrusion of a polysaccharide matrix called mucilage. Variations in the content of the released mucilage have been mainly associated with genetically regulated physiological modifications. Understanding the mucilage extrusion process in crop species is of importance to gain deeper insight into the complex cell wall biosynthesis and dynamics. In this study, we took advantage of the varying polysaccharide composition and the size of the flax mucilage secretory cells (MSCs) to study mucilage composition and extrusion in this species of agricultural interest. We demonstrate herein that flax MSCs are structured in four superimposed layers and that rhamnogalacturonans I (RG I) are firstly synthesized, in the upper face, preceding arabinoxylan and glucan synthesis in MSC lower layers. Our results also reveal that the flax mucilage release originates from inside MSC, between the upper and deeper layers, the latter collaborating to trigger polysaccharide expansion, radial cell wall breaking and mucilage extrusion in a peeling fashion. Here, we provide evidence that the layer organization and polysaccharide composition of the MSCs regulate the mucilage release efficiency like a peeling mechanism. Finally, we propose that flax MSCs may represent an excellent model for further investigations of mucilage biosynthesis and its release.

In this paper, the development of an environmentally-friendly lithium-terephtalate/polylactic acid (Li2TP/PLA) composite filament, for its use, once 3D-printed via Fused Deposition Modeling (FDM), as negative electrode of a lithium-ion battery is reported. Solvent-free formulation of the 3D-printable filament is achieved through the direct introduction of synthesized Li2TP particles and PLA polymer powder within an extruder. Printability is improved through the incorporation of poly(ethylene glycol) dimethyl ether average Mn∼500 (PEGDME500) as plasticizer, while electrical performances are enhanced through the introduction of carbon black (CB). Thermal, electrical, morphological, electrochemical and printability characteristics are discussed thoroughly. By taking advantage of the 3D-printing slicer software capabilities, an innovative route is proposed to improve the liquid electrolyte impregnation within the 3D-printed electrodes.

In this paper, the ability to 3D print lithium-ion batteries through Pmnbspace thermoplastic material extrusion and polymer powder bed fusion is considered. Focused on the formulation of positive electrodes composed of polypropylene, LiFePO4 as active material, and conductive additives, advantages and drawbacks of both additive manufacturing technologies, are thoroughly discussed from the electrochemical, electrical, morphological and mechanical perspectives. Based on these preliminary results, strategies to further optimize the electrochemical performances are proposed. Through a comprehensive modeling study, the enhanced electrochemical suitability at high current densities of various complex three-dimensional lithium-ion battery architectures, in comparison with classical two-dimensional planar design, is highlighted. Finally, the direct printing capability of the complete lithium-ion battery by means of multi-materials printing options processes is examined.

Ferroelectric nanodomains give rise to diffuse X-ray scattering peaks in ultrathin films. Here we study a Pb(Zr0.2Ti0.8)O3/SrTiO3 superlattice, using X-ray diffraction and transmission electron microscopy, We show that both elastic relaxation and ferroelectric nanodomain pattern can contribute to distinct satellite peaks in the X-ray scattering pattern. We show that transmission electron microscopy is required to disentangle elastic relaxation and ferroelectric domain contributions to the in plane X-ray scattering profile.

Additive manufacturing technologies open the way to the direct-integration of electronics and solid-state battery within the final 3D object. Here, a 3D printable polyethylene oxide/lithium bis(trifluoromethanesulfonyl)imide (PEO/LiTFSI) filament (2.18 × 10−3 S cm−1 at 90 °C) optimized to be used as solid polymer electrolyte in a lithium-ion battery is produced to feed a fused deposition modeling (FDM) 3D-printer. Due to its relatively poor mechanical properties compared to classical polymer filament such as polylactic acid (PLA), deep modifications of the 3D-printer were implemented in order to facilitate its printability. The solid polymer electrolyte thermal, structural, morphological, mechanical and electrical characterization is reported. Interestingly, using three different electrochemical impedance spectroscopy sample holders (lateral, sandwich and interdigitated-comb), we demonstrate that conductivity values differs for a same sample, highlighting the PEO chains orientation effect on the conductivity measurements.

Artificial (BiFeO3)0.5Λ/(LaFeO3)0.5Λ superlattices have been grown by pulsed laser deposition. The periodicity Λ was varied from 150 A to 25 A and the relative ratio between BiFeO3 (BFO) and LaFeO3 (LFO) is kept constant in each period. X-ray diffraction, transmission electron microscopy, and Raman spectroscopy investigations indicate antiferroelectric-like structures for large periodicity (Λ ≥ 76 A), while Pnma LaFeO3-like structures are observed for small periodicity Λ ≤ 50 A. Room temperature magnetic measurements were obtained by vibrating sample magnetometry and suggest antiferromagnetic ordering with weak ferromagnetism. Temperature dependent x-ray diffraction studies show an important shift of paraelectric-antiferroelectric phase transition scaling with BFO thickness. Strain and size effects explain this behavior and discussion is also made on the possible role of the oxygen octahedral rotation/tilt degree of freedom.

This work describes the influence of a high annealing temperature of about 700C on the Si(substrate)/Si3N4/TiOx/Pt/LiCoO2 multilayer system for the fabrication of all-solid-state lithium ion thin film microbatteries. Such microbatteries typically utilize lithium cobalt oxide (LiCoO2) as cathode material with a platinum (Pt) current collector. Silicon nitride (Si3N4) is used to act as a barrier against Li diffusion into the substrate. For a good adherence between Si3N4 and Pt, commonly titanium (Ti) is used as intermediate layer. However, to achieve crystalline LiCoO2 the multilayer system has to be annealed at high temperature. This post-treatment initiates Ti diffusion into the Pt-collector and an oxidation to TiOx, leading to volume expansion and adhesion failures. To solve this adhesion problem, we introduce titanium oxide (TiOx) as an adhesion layer, avoiding the diffusion during the annealing process. LiCoO2, Pt and Si3N4 layers were deposited by magnetron sputtering and the TiOx layer by thermal oxidation of Ti layers deposited by e-beam technique. Asdeposited and annealed multilayer systems using various TiOx layer thicknesses were studied by scanning electron microscopy (SEM) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) and x-ray photoelectron spectroscopy (XPS). The results revealed that an annealing process at temperature of 700C leads to different interactions of Ti atoms between the layers, for various TiOx layer thicknesses (25–45 nm)., This work was financially supported by FEDER/ COMPETE and FCT funds with the Projects PTDC/ EEA-ELC/114713/2009, PEst-C/QUI/UI0686/2013 and UID/EEA/04436/2013, first author scholarship SFRH/BPD/95905/2013 and second author scholarship SFRH/BD/78217/2011. This work was carried out with the support of the Karlsruhe Nano Micro Facility (KNMF, www.kit.edu/knmf), a Helmholtz Research Infrastructure at Karlsruhe Institute of Technology (KIT, www.kit.edu).

This work reports the fabrication and characterization of lithium cobalt oxide films (LiCoO2) on flexible Kapton® substrate. LiCoO2 is commonly used as cathode of lithium microbatteries but needs an annealing of 700 °C, which is not compatible with most flexible substrates. LiCoO2 films were deposited by reactive RF sputtering followed by an annealing process at 400 °C for 1 h in vacuum and air atmospheres both in silicon and Kapton® substrates. Raman spectroscopy, X-ray diffraction patterns and scanning electron microscopy images were used to evaluate samples crystallinity and morphology. Films fabricated in Kapton® and silicon substrates were compared., This work was financial supported by FEDER/COMPETE and FCT funds with the Project PTDC/EEA-ELC/114713/2009, strategic Project PEst-C/FIS/UI607/2013, PEst-C/QUI/UI0686/2013 and UID/EEA/04436/2013, first author scholarship SFRH/BD/78217/2011 and third author scholarship SFRH/BPD/95905/2013.

(BiFeO3)(1−x)Λ/(LaFeO3)xΛ superlattices (SLs) have been grown using pulsed laser deposition and studied by X‐ray diffraction, transmission electron microscopy (TEM), and Raman spectroscopy. The composition is varied, 0.30 ≤ x ≤ 0.85, while the modulation period Λ is kept constant at about 10 nm. Unit cell doubling signatures typical of orthorhombic Pnma symmetry for x = 0.80 and 0.85 SLs and ¼{011} antiferroelectric PbZrO3‐like reflections in SLs with 0.30 ≤ x ≤ 0.7 are detected by TEM showing a complex structural mixture at the nanoscale level. The Raman spectra confirm these observations and show a change in the SLs from a Pnma LaFeO3‐like spectra for LaFeO3‐rich period to a PbZrO3‐like spectra for BiFeO3‐rich period. Electron–phonon interactions and resonant‐like excitations are also observed in the SLs. A temperature‐dependent X‐ray diffraction investigation shows a large shift of the paraelectric‐antiferroelectric phase transition scaling with the BiFeO3 thickness. This shift is correlated with the strain state and can be explained by a strong interplay between octahedral rotation/tilt and antipolar Bi displacement. Thickness–temperature phase diagram is constructed and differs from previous report showing the extreme sensitivity of the BiFeO3 phase stability to strain effects and rotation/tilt degrees of freedom.

International audience; Tavorite-type compositions offer rich crystal chemistry for positive electrodes in rechargeable batteries, among which LiVIIIPO4F has the highest theoretical energy density (i.e. 655 Wh kg−1). In this article, we report for the first time the synthesis of the related Na-based phase crystallizing in the Tavorite-like structure. Its in-depth structural and electronic characterization was conducted by a combination of several techniques, spanning electron and X-ray powder diffraction as well as infrared and X-ray absorption spectroscopy. The magnetic susceptibility measurement reveals an average oxidation state for vanadium slightly higher than V3+. This slight oxidation is supported by infrared and X-ray absorption spectroscopies which highlight the presence of V4+[double bond, length as m-dash]O vanadyl-type defects leading to an approximated NaVIII0.85(VIVO)0.15(PO4)F0.85 composition. In this material, the profile of the diffraction lines is governed by a strong strain anisotropic broadening arising from the competitive formation between the ionic V3+–F and the covalent V4+[double bond, length as m-dash]O bonds. This material shows a limited extraction of sodium, close to 15% of the theoretical capacity. Indeed, its electrochemical properties are strongly inhibited by the intrinsic low sodium mobility in the Tavorite framework.

International audience; All-solid-state Li/LiPONB/TiOS microbatteries were manufactured at the pilot scale on silicon substrate. In a first attempt, the characterization of the active materials constituting the microbattery was achieved in order to determine their accurate composition, structure and morphology. Finally, a thorough electrochemical characterization was carried out on all-solid-state cells. Excellent performances were noted in terms of cycle life (with more than 1000 cycles), efficiency and self-discharge (less than 5% per year). In addition, the positive electrode highlighted a high volumetric capacity close to 90 μAh cm−2 μm−1 when cycled at 100 μA cm−2 between 1 V and 3 V vs. Li+/Li.

Actual parallel-plate architecture of lithium-ion batteries consists in lithium ion diffusion in one dimension between the electrodes. To achieve higher performances in terms of specific capacity and power, configurations enabling lithium ion diffusion in two or three dimensions have been considered (1-5). With a view to build these complex 3D battery architectures avoiding the electrodes interpenetration issues, this work was focused on the Fused Deposition Modeling (FDM). In this presentation, the formulation and characterization of a 3D-printing graphite/polylactic-acid (PLA) filament, specially designed to be used as negative electrode in a lithium-ion battery, and to feed a conventional FDM 3D-printer will be described (6). Graphite loading into the produced filament was increased as high as possible (up to 62.5%wt) to enhance the electrochemical performances while maintaining sufficient mechanical strength to be printed. Formulation process is displayed in Fig. 1a. With such a high ratio of active material, the graphite/PLA filament was found to be very brittle. To overcome this problem, a plasticizer has been added to the PLA matrix to improve its ductility and decrease its stiffness. Influence of the amount of various plasticizers such as propylene carbonate (PC), poly(ethylene glycol) dimethyl ether average Mn~2000 (PEGDME2000), poly(ethylene glycol) dimethyl ether average Mn~500 (PEGDME500) and acetyl tributyl citrate (ATBC) was investigated by performing both differential scanning calorimetry and tensile mechanical tests. On the other hand, printability behavior of the extruded composite filaments was tested by using a commercially available 3D printer. From the optimized plasticizer composition, two-dimensional discs but also high resolution complex three-dimensional structures, such as a semi-cube lattice and a “3Dbenchy” boat, were successfully 3D-printed. Finally, considering this optimized composite, an in-depth study was carried out to identify the electronic percolation (Fig. 1b) and electrochemical impact of carbon black SuperP and carbon nanofibers as conductive additives; electrical conductivities were determined from impedance measurements performed at various stabilized temperatures ranging from 20ºC to 50°C and, in parallel, capacity retention was investigated in detail at different current densities after the different elaboration steps (film before extrusion and disc after printing). Significant progress has been achieved regarding the capacity retention as compared to Foster et al. (7) who was the first group to use FDM technology to 3D-print a negative electrode disc. They were aware that the low specific capacity values reported (15.8 mAh.g-1 at current density of 10 mA.g-1) were unfortunately caused by the use of a filament containing only 8%wt of graphene as active material and 92%wt of PLA. In this work, by increasing the graphite loading up to 62.5%wt, a reversible capacity of 201 mAh.g- 1 at current density of 4 mA.g-1 was achieved for the 3D-printed negative electrode disc by using the most printable filament (Fig. 1c). References: J. W. Long, B. Dunn, D. R. Rolison and H. S. White, Chemical Reviews, 104, 4463 (2004). S. Ferrari, M. Loveridge, S. D. Beattie, M. Jahn, R. J. Dashwood and R. Bhagat, Journal of Power Sources, 286, 25 (2015). H. S. Min, B. Y. Park, L. Taherabadi, C. L. Wang, Y. Yeh, R. Zaouk, M. J. Madou and B. Dunn, Journal of Power Sources, 178, 795 (2008). L. Taberna, S. Mitra, P. Poizot, P. Simon and J. M. Tarascon, Nature Materials, 5, 567 (2006). K. Sun, T. S. Wei, B. Y. Ahn, J. Y. Seo, S. J. Dillon and J. A. Lewis, Advanced Materials, 25, 4539 (2013). A. Maurel, M. Courty, B. Fleutot, H. Tortajada, K. Prashantha, M. Armand, S. Grugeon, S. Panier and L. Dupont, Advanced Energy Materials, (submitted April 2018). C. W. Foster, M. P. Down, Y. Zhang, X. B. Ji, S. J. Rowley-Neale, G. C. Smith, P. J. Kelly and C. E. Banks, Scientific Reports, 7 (2017). Figure 1

LiFePO4 thin films were grown on silicon (100) substrates by pulsed laser deposition using Traditional Geometry (TG) and Off-Axis Geometry (OAG) deposition chambers. We examined and compared the structure and composition of the so formed thin films. The nails observed on the OAG-film present an amorphous “body” and a crystallized “head”. The Fe/P ratio determined using energy dispersive spectrometry combined with high angle annular dark field images reveals a metallic iron heart surrounded by LiFePO4 shell. On the other hand, the protuberances on TG-film are pure iron. The focused ion beam prepared cross-section of the film suggests the presence of iron particles and iron dendritic like filaments inside the LiFePO4 layer.

Ceramic processes are currently used to prepare most of today’s electrode materials. For energy-saving reasons, there is a growing interest in electrode materials prepared via eco-efficient processes, which has led to the resurgence of low temperature hydro- and solvothermal processes. This review will highlight how some of these processes have been successfully used to prepare today’s most praised electrode material: LiFePO4. Particular attention is paid to the recently developed ionothermal synthesis process. This will be done in order to stress the versatility and richness of ionothermal synthesis, its control over particle size and shape, and the ability of ionic liquids to provide stabilization to new metastable phases. We outline the pertinent questions that should be clarified for continued advancement of the ionothermal process which opens the door to innovative inorganic synthesis and to materials which have remained hidden for a long time.

Li-ion batteries have contributed to the commercial success of portable electronics, and are now in a position to influence higher-volume applications such as plug-in hybrid electric vehicles. Most commercial Li-ion batteries use positive electrodes based on lithium cobalt oxides. Despite showing a lower voltage than cobalt-based systems (3.45 V versus 4 V) and a lower energy density, LiFePO(4) has emerged as a promising contender owing to the cost sensitivity of higher-volume markets. LiFePO(4) also shows intrinsically low ionic and electronic transport, necessitating nanosizing and/or carbon coating. Clearly, there is a need for inexpensive materials with higher energy densities. Although this could in principle be achieved by introducing fluorine and by replacing phosphate groups with more electron-withdrawing sulphate groups, this avenue has remained unexplored. Herein, we synthesize and show promising electrode performance for LiFeSO(4)F. This material shows a slightly higher voltage (3.6 V versus Li) than LiFePO(4) and suppresses the need for nanosizing or carbon coating while sharing the same cost advantage. This work not only provides a positive-electrode contender to rival LiFePO(4), but also suggests that broad classes of fluoro-oxyanion materials could be discovered.

The behavior of Li 3 PO 4 and Li 2 MSiO 4 ( M = Mn, Co) compounds under high pressure/high temperature is investigated. Pmn2 1 -Li 3 PO 4 remains stable up to the higher experimental limit of 80 kbar (900 °C). A sample of Li 2 MnSiO 4 consisting of a mixture of Pn2 1 and Pmnb polymorphs converts upon high pressure/high temperature treatment into the Pmn2 1 polymorph; the latter being stable at 80 kbar and 900 °C. A sample of Li 2 CoSiO 4 - P2 1 /n transforms to the denser Pmn2 1 polymorph at 40 kbar/900 °C, but decomposes at higher pressure (60 kbar/900 °C). No evidence on any novel Li 2 MSiO 4 polymorph is detected in any of the high-pressure products.

As opposed to ceramic methods, low-temperature solvothermal-hydrothermal methods using liquid media as reaction support are less energy demanding to design new electrode materials; therefore, they tend to replace ceramic routes. Here, we report the use of ionic liquids as both solvent and template to enable the growth of LiFePO4 (LFP) powders with controlled size and morphology at temperatures at least 200 °C lower than those required for conventional ceramic methods, while showing excellent electrochemical performances versus lithium. An inherent advantage to the use of ionic liquids lies in the feasibility of carrying out the reaction at atmospheric pressure. Besides, the recovery of the powders from the reacting medium is particularly easy, as are the effluents and ionic liquid recycling. Additionally, it is shown that ionic liquids can be used as a structural directing agent to orient crystal growth and obtain powders adopting a single morphology. Needless to say, such a new approach, which is not spe...

The present paper is in part a continuation of our recent work dealing with the fully reversible Li-driven Cu extrusion/injection of Cu in Cu2.33V4O11. The peculiar electrochemical property of such a compound was mainly ascribed to both structural considerations (presence of anchoring oxygen, giving flexibility to the [V4O11] layers) and electronic considerations, such as the existence of a delicate balance between the two Cu+/Cu2+ and V4+/V5+ redox centers. To support such suggestions, numerous compounds were revisited for their electrochemical–structural interplay. Network dimensionality, lattice flexibility, and cationic mobility parameters were addressed by exploring in depth the richness of the Cu–V–O system, while the importance of the donor/acceptor energy levels was checked via the choice of compounds having the right energy match between the two redox centers. As an extensive trial-and-error approach was not realistic, we relied on simple considerations based on the ionization energy of the various d-metals to narrow down metal pairs having redox levels occurring within the same range of energies. Bearing this in mind, it was logical to consider compounds still containing Cu ions but with Nb instead of V or compounds having V and Ag instead of Cu. Regardless of our effort, it turned out that the number of potential candidates worth considering for practical applications is still very limited, in spite of the elegance of this new Li reactivity mechanism.

The thermodynamic stability of Li2MnSiO4 polymorphs and their electrochemical properties as electrode for Li batteries are investigated combining experimental and computational methods. Three possible Li2MnSiO4 forms have been considered crystallizing in Pmnb, Pmn21 (β-Li3PO4 derivatives) and P21/n (γ-Li3PO4 derivative) space groups (S.G.). We have first demonstrated that the relative stability of β- and γ-Li3PO4 polymorphs is well-reproduced by density functional theory (DFT) methods (LDA, GGA). For Li2MnSiO4, the Pmnb form is predicted to be 2.4 meV/f.u. and 65 meV/f.u. more stable than the Pmn21 and P21/n forms, respectively (GGA + U results). Computational results indicate that the denser Pmn21 polymorph can be obtained by high pressure/high temperature treatment of the other polymorphs or their mixtures. A sample of Li2MnSiO4 prepared at 900 °C consists of a mixture of polymorphs, as detected by XRD and confirmed by means of SAED and 6Li MAS-NMR. As expected from DFT results, exposing the as-prepared...

Understanding and improving the behavior of interfaces is essential to the development of safer and high performance Li-based batteries regardless of their range of applications. Indirect methods such as impedance spectroscopy or direct methods such as the live in situ observation of batteries cycled within a scanning electron microscope (in situ SEM) are used to determine the interface microstructure/composition evolution upon cycling. These methods are used to establish a direct link between interface properties and batteries performance; they also enable us to spot local interface defects that are crucial to the development of 2D solid-state microbattery, for instance. Indeed, this technology is of interest in powering the new generation of microelectromechanical systems (MEMS). Here, we demonstrate the first ex situ TEM observation of “nanobatteries” obtained by cross-sectioning a microbattery using focus ion beam (FIB) in a dual beam SEM. Then, TEM analyses between pristine, cycled, and faulted all s...

Electrochemical lithium insertion into two isostructural titanium-based oxides, K 2 Ti 6 O 13 and Na 2 Ti 6 O 13 has been investigated. Although the two compounds differ mainly from their particle size and cell volume, pronounced differences in the insertion mechanism have been evidenced. They can accommodate about three Li per formula unit at relatively low potentials (1.5–0.9 V versus Li reference), which qualifies them as potential alternatives to Li 4 Ti 5 O 12 . The main limitations are their rate capabilities and capacity retention related to large particles and parasitic electrolyte decomposition, respectively.

Battery performance depends on many factors amongst which the selection of the appropriate electrode material and the control of the electrode/electrolyte interface upon cycling. In order to address these issues, electrochemists have to design new electrode materials, and 'enter the private life' of a battery. Transmission Electron Microscopy (TEM) is a powerful tool to help scientists to characterize each part of the device. Recent developments in TEM techniques have been proposed and developed, through the Alistore Electron Microscopy platform (AEMP), to allow the observation of Li-ion air sensitive electrode materials. Our team is now going one step further by using High Resolution Electron Energy Loss Spectroscopy (HREELS) and nanoprobe EDS as well as other TEM techniques exhibiting the advantage of high lateral resolution for chemical analysis and for structural determination (by means of electron diffraction and high-resolution imaging). The AEMP holds at the same time the equipment and the skills to run such experiments

Anatase type TiO 2 has been previously largely reported as a candidate negative electrode material for lithium-ion batteries. We report here for the first time the complete in situ Raman study of lithium insertion and de-insertion into three variously nano-sized TiO 2 anatase powders (Prolabo, ca. 80 nm, AK1, ca. 15 nm and MTi5 ca. 8 nm), of which AK1 and MTi5 show superior capacity and cyclability. From these measurements realized in a galvanostatic mode between 3 and 1 V versus Li/Li + , the phase transition from a tetragonal to an orthorhombic structure was clearly observed to take place at different quantities of x in Li x TiO 2 . These results confirm the extension of the solid solution domain as particle size is reduced. For the smaller TiO 2 nano-sized materials (AK1 and MTi5), a more pronounced decrease in band intensity when x > 0.3 for Li x TiO 2 , was observed and may be related to the decrease in the optical skin depth linked to the conductivity increase as lithiation proceeds.

Bi 2 O 4− x , a Bi mixed-valence phase was prepared at 95 °C, by a precipitation process, in a basic medium with a highly oxidizing K 2 S 2 O 8 /Na 2 S 2 O 8 . This phase has a low thermal stability as it decomposes below 400 °C in a multiple step process by some O 2 losses prior to finally transforming into γ-Bi 2 O 3 . The as-prepared powders are 50–60 nm in size with a narrow size distribution. Optical spectra of Bi 2 O 4− x exhibit a broad absorption band with a band gap of ∼1.4 eV as compared to 2.61 eV for Bi 2 O 3 . The composition of this non-stoichiometric phase, which crystallizes in cubic fluorite related structure with a cell parameter of 5.538(3) A, is Bi 2 O 3.65 ± 0.10 .

Rutile type TiO2 nanoparticles (10 nm × 200 nm in size) were prepared using a precipitation method in aqueous solution. Their lithium reactivities were followed using both classical galvanostatic insertion and in situ XRD measurements, and compared to that of a bulk and commercial nano-sized (50 nm) rutile TiO2 sample so as to stress the interlink between Li insertion electrochemical capacity and crystallite size. For the highly divided material, we obtained a reversible capacity of 0.5 Li ion per formula unit after a first reduction step during which, the material is irreversibly transformed. Such a reduction step is shown to enlist two solid solution domains followed by the formation of a rocksalt type phase LiTiO2. Such a specific reactivity of nano-sized rutile TiO2 is explained in terms of better lattice strains accommodation during the insertion of lithium. Keywords: Rutile TiO2, Nanotextured, Li batteries

Analytical high resolution transmission electron microscopy has been used to clearly evidence the electrochemical reactivity of Cr2O3 thin films versus lithium. We showed that during the reduction process, chromium sesquioxide (+III) transforms first into chromium monoxide (+II) and then into metallic chromium nanoparticles embedded into a Li2O matrix at 0 V. On the subsequent recharge up to 3 V, we did not convert back to Cr2O3, but only to a chromium monoxide implying a partial re-oxidation process, thus explaining the irreversibility measured during the first cycle. We extended this study to the comprehension of the electrochemical performances of Cr2O3-based electrodes obtained by thermal treatment, under different atmospheres, of chromium rich stainless steel disks. In addition to the characterization of the particles forming the so-obtained electro-active layers, we showed, using nano-probe EDS, that a mixed “Fe–Cr–O” oxide could react versus lithium, through a conversion reaction mechanism, leading to alloyed metallic nanoparticles upon reduction and nanograins of mixed oxide during the following oxidation.

Mg–Ni thin films were grown using Pulsed Laser Deposition. In situ optical changes from shiny metallic to transparent states were observed for films deposited in vacuum and under an Ar/H2 gas mixture (93/7%), respectively. Optical changes were also achieved by ex situ hydrogenation under hydrogen gas pressure of 15 bars at 200 °C. However, after ex situ hydrogenation, the optical transmittance of the Mg-based hydrogenated thin films did not exceed 25%. Such limitation was attributed to oxygen contamination, as deduced by High Resolution Transmission Electron Microscopy observations, showing the co-existence of both Mg-based and MgO phases for as-deposited films. A significant decrease in oxygen contamination was successfully achieved with the addition of carbon, leading to the preparation of (Mg-based)–Cx (x

The electrochemical reactivity of CuTi 2 S 4 and CuCr 2 S 4 spinel samples toward Li was studied over a wide range of voltages. Their electrochemical behavior can be decomposed into two steps. For less than two inserted lithium, we emphasized a Li-driven electrochemical displacement reaction that led to the extrusion of copper from lithium, leading to the rocksalt-type structure phases Li 2 Ti 2 S 4 and Li 2-x Cu 0.3 Cr 2 S 4 , whereas conversion reactions were observed beyond x = 2. These conversion reactions were shown to have a large rechargeable uptake and release of Li + ions (7 per formula unit) that rapidly fade on cycling. Regarding the Cu extrusion, we demonstrated that this process is reversible for the Ti-based spinel upon oxidation through a chemically assisted electrochemical process. For the Cr-based system, a new phase LiCu 0.7 Cr 2 S 4 was evidenced to form on oxidation. This difference is explained in terms of band structure considerations and d-sp redox chemistry. Chemical reinjection of Cu into Ti 2 S 4 forming the single phase Cu x Ti 2 S 4 (0 < x < 1) from the reaction of Ti 2 S 4 powders with an aqueous CuS O ·nH 2 O solution is also reported. It is shown that traces of H 2 S coming from the slight chemical instability of Ti 2 S 4 in water are necessary for initiating the chemical reinjection reaction to form Cu x Ti 2 S 4 .

Nanocrystalline Ce1-xTixO2 (0 ≤ x ≤ 0.4) and Ce1-x-yTixPtyO2-δ (x = 0.15, y = 0.01, 0.02) solid solutions crystallizing in fluorite structure have been prepared by a single step solution combustion method. Temperature programmed reduction and XPS study of Ce1-xTixO2 (x = 0.0−04) show complete reduction of Ti4+ to Ti3+ and reduction of ∼20% Ce4+ to Ce3+ state compared to 8% Ce4+ to Ce3+ in the case of pure CeO2 below 675 °C. The substitution of Ti ions in CeO2 enhances the reducibility of CeO2. Ce0.84Ti0.15Pt0.01O2-δ crystallizes in fluorite structure and Pt is ionically substituted with 2+ and 4+ oxidation states. The H/Pt atomic ratio at 30 °C over Ce0.84Ti0.15Pt0.01O2-δ is 5 and that over Ce0.99Pt0.01O2-δ is 4 against just 0.078 for 8 nm Pt metal particles. Carbon monoxide and hydrocarbon oxidation activity are much higher over Ce1-x-yTixPtyO2 (x = 0.15, y = 0.01, 0.02) compared to Ce1-xPtxO2 (x = 0.01, 0.02). Synergistic involvement of Pt2+/Pt° and Ti4+/Ti3+ redox couples in addition to Ce4+/Ce3+ due t...

International audience; We report the electrochemical study of cubic and monoclinic NiP2 polymorphs toward Li, as a candidate for anodic applications for Li-ion batteries. We found that the monoclinic form is the most attractive one performance-wise. Monoclinic NiP2 can reversibly uptake 5 lithium per formula unit, leading to reversible capacities of 1000 mAh/g at an average potential of 0.9 V vs Li+/Li°. From complementary X-ray diffraction (XRD) and HRTEM (high-resolution transmission electron microscopy) measurements, it was shown that, during the first discharge, the cubic phase undergoes a pure conversion process (NiP2 + 6 Li+ + 6e- f Ni° + 2Li3P) as opposed to a sequential insertion-conversion process for monoclinic NiP2. Such a different behavior rooted in subtle structural changes was explained through electronic structure calculations. Once the first discharged is achieved, both phases were shown to react with Li through a classical conversion process. More importantly, we report a novel way to design NiP2 electrodeswith enhanced capacity retention and rate capabilities. It consists in growing the monoclinic NiP2 phase,through a vapor-phase transport process, on a commercial Ni-foam commonly used in Ni-based alkaline batteries. These new self-supported electrodes, based on chemically made interfaces, offer new opportunities to fully exploit the capacity gains provided by conversion reactions

To benefit from the large electrochemical capacity advantages offered by Li-driven conversion reactions and to overcome poor kinetics, a new electrode configuration concept is reported. The originality of this electrode design is nested in metallurgical aspects of stainless steel, namely, the appearance of temperature-driven surface microstructures that enable the growth of a nanostructured, electrochemically active, chromium-rich oxide surface layer in close contact with a current collector. The thickness of the oxide layer can reach hundreds of nanometers and is shown to be rooted in the preferential migration of Cr toward the sample surface. We further show that chemical etching of the stainless steel surface, prior to high-temperature annealing, enables reversible capacities as high as 750 mAh/g of chromium-rich oxide for at least 800 cycles. On the basis of modeling, several scenarios involving stainless steel/chromium-based oxides current collectors of various porosities show how this new electrode ...

Mn1-xFexO2 samples, synthesized by a low-temperature process, were characterized for their structural, physical, and electrochemical properties. From X-ray data and EDX analysis in both SEM and HRTEM modes, combined with 57Fe Mossbauer spectroscopy, we gave direct evidence for the first time for a true Fe substitution for Mn up to x = 0.3. Beyond such value, the samples are multiphase. The presence of iron was found to affect the electrochemical behavior, with namely the appearance of a second plateau at −0.8 V (vs Hg/HgO) with increasing the iron content at the expense of the one occurring at −0.45 V in the pure MnO2 phase. We will present evidence, as deduced from both HREM and Mossbauer measurements on reduced samples, that the origin of the −0.8 V plateau could be nested in the electrochemical activity of the FeMn2O4 phase toward proton in aqueous media.

In our comprehensive understanding of reactivity of CoO towards Li, we studied the effect of CoO electrode weight and composition (carbon-free or not) on the cycling performances of CoO/Li half-cells. Capacity and lifetime were measured as a function of the cycling rate and temperature. The lightest electrodes (2 mg/cm 2 ) were shown to behave the best, with sustained capacities as high as 600 mAh/g up to about 250 cycles at 20 °C, and with capacities that peaked up to 1700 mAh/g when cycling was performed at 75 °C. Searching for the origin of this huge “extra capacity” over the normal conversion process (Co 2+ O→Co 0 , 715 mAh/g), we dissociated phenomena by testing carbon-loaded and carbon-free CoO-based electrodes in CoO/Li half cells. We unravelled a temperature-driven capacity rate increase similar for both cells, although the initial reversible capacity was quite different. The carbon-free CoO/Li half cell showed limited initial reversible capacity due to the poor efficiency of the conversion process for non-conducting electrodes. This increase appears to be nested in the reversible growth of a polymeric gel-like film resulting from kinetically activated electrolyte degradation. Polymeric layers were also shown to form from the Li electrochemical reduction of numerous binary phases, differentiating either by the nature of the 3d-metal (Cu, Ni, Fe instead of Co) or that of the anion (S, F, N instead of O). Finally, purely coincidental or not, from comparative studies of CoO, CoSb 3 , and CoSb 2 Li half-cells, we found that, to a certain extent, the capacity amplitude associated with the growth of the polymer film scales with the surface developed by Co nano-particles. This fact would imply a possible catalytic role of 3d metals in assisting the electrolyte decomposition.

Antimony–tin oxide (ATO) thin films were deposited using pulsed laser deposition. From a wide survey of deposition conditions (deposition atmosphere and substrate temperature), we deduced that the optimum experimental parameters to obtain electrochromic active films were a deposition temperature of 200 j Ca t a1 0 � 2 mbar oxygen pressure followed by an annealing at 550 jC, the latter being critical. Through potentiostatic tests, we showed that depending on the composition, which influences film morphology, the Sn–Sb–O films could present either a faradic or a capacitive-like behavior, associated to a color or a neutral switching over a wide range of potentials, respectively. In addition, a relationship between the film annealing temperature and its structure as well as its electrochromic properties was evidenced by means of complementary electrochemical, X-ray diffraction and electron microscopy techniques. Finally, the electrical and optical properties of the ATO films were discussed in terms of the energy band theory. D 2003 Elsevier Science B.V. All rights reserved.

a ´´ ´ Laboratoire d'Electrochimie et de Chimie Analytique (UMR 7575), Ecole Nationale Superieure de Chimie de Paris, b ´ Abstract A detailed investigation of the structural and opto-electrical properties of tin-doped indium-zinc oxide thin films prepared by pulsed laser deposition was carried out.The substitution of indium for tin in Zn In O compounds (ks2, 3 and 5 )( which k 2 kq3 structure is a mixture of homologous phases with different k, but mostly composed of the polytype having the target composition) led to a conductivity enhancement, caused by an increase in carrier concentration at low doping levels, whereas for higher doping levels a decrease in conductivity and carrier concentration together with an amorphisation of the films was noted.The best electrical properties (ss2500 Sycm) were obtained for the Zn In Sn O doped films having a layered Zn In O -type 21 . 9 0. 1 5 qd k 2 kq3 structure with essentially ks2.Independently of the composition an 85-90% average transmittance in the visible region was obtained.In contrast the band gap of the Sn-doped film slightly increased with tin ratio, in agreement with the Burstein-Moss theory. � 2002 Elsevier Science B.V. All rights reserved.

LiFeP2O7, LiFeAs2O7, and LiVP2O7 were prepared as pure microcrystalline powders via an aqueous solution route that allowed the formation of finely dispersed small particles. These three compounds, in which Fe or V is in the oxidation state +3, were evaluated as positive electrodes in lithium rechargeable batteries through galvanostatic, PITT, and GITT cycling modes and in situ X-ray diffraction. We show that the electrochemical activity of these materials is drastically enhanced by an intimate mixing of the pristine materials with conductive carbon, through ball-milling. This mandatory step resulted in producing amorphous Li−M−X−O domains at the surface of crystalline LiMX2O7 crystallites. A continuous voltage decrease is observed as lithium insertion proceeds into the amorphous part of the composite electrodes. Crystalline LiMX2O7 particles react with lithium through two-phase mechanisms, characterized by insertion plateaus located at 2.90 V for LiFeP2O7 (Fe3+/Fe2+ couple), 1.99 V for LiVP2O7 (V3+/V2+ co...