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

The Role of Cellulose Based Separator in Lithium Sulfur Batteries

International audienceIn this work, abundant and environmentally friendly nano-fibrillated (NFC) cellulose is used for fabrication of porous separator membranes according to the procedure adopted from papermaking industry. As-prepared NFC separators were characterized in terms of thickness, porosity, wettability, electrochemical stability and electrochemical performance in lithium-sulfur and Li-symmetrical pouch cells and compared to a commercial Celgard 2320 separator membrane. Results demonstrated that morphology and electrochemical performance of NFC separator outperforms the conventional polyolefin separator. Due to exceptional interplay between lithium metal and cellulose, this research provides a self-standing NFC separator that can be used besides the lithium-sulfur also in other lithium metal battery configurations

Anionic Redox Activity in a Newly Zn-Doped Sodium Layered Oxide P2-Na2/3 Mn1− y Zn y O2 (0 < y < 0.23)

The revival of the Na‐ion battery concept has prompted intense research activities toward new sustainable Na‐based insertion compounds and their implementation in full Na‐ion cells. Efforts are parted between Na‐based polyanionic and layered compounds. For the latter, there has been a specific focus on Na‐deficient layered phases that show cationic and anionic redox activity similar to a Na0.67Mn0.72Mg0.28O2 phase. Herein, a new alkali‐deficient P2‐Na2/3Mn7/9Zn2/9O2 phase using a more electronegative element (Zn) than Mg is reported. Like its Mg counterpart, this phase shows anionic redox activity and no O2 release despite evidence of cationic migration. Density functional theory (DFT) calculations show that it is the presence of an oxygen nonbonding state that triggers the anionic redox activity in this material. The phase delivers a reversible capacity of 200 mAh g−1 in Na‐half cells with such a value be reduced to 140 mAh g−1 in full Na‐ion cells which additionally shows capacity decay upon cycling. These findings establish Na‐deficient layered oxides as a promising platform to further explore the underlying science behind O2 release in insertion compounds based on anionic redox activity

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

Materials, Mechanisms and Performance

The electrochemical energy storage is a means to conserve electrical energy in chemical form. This form of storage benefits from the fact that these two energies share the same vector, the electron. This advantage allows us to limit the losses related to the conversion of energy from one form to another. The RS2E focuses its research on rechargeable electrochemical devices (or electrochemical storage) batteries and supercapacitors.The materials used in the electrodes are key components of lithium-ion batteries. Their nature depend battery performance in terms of mass and volume capacity, energy density, power, durability, safety, etc. This book deals with current and future positive and negative electrode materials covering aspects related to research new and better materials for future applications (related to renewable energy storage and transportation in particular), bringing light on the mechanisms of operation, aging and failure

Cascading degradations artificially improving the lifetime of Li-ion full cells using DMC-based highly concentrated electrolyte

The deployment of energy dense Ni-rich NMC (LiNixMnyCozO2 with x > 0.8) in Li-ion batteries is hampered by a poor interfacial stability above 4.2 V. Among the strategies to mitigate this instability, highly concentrated electrolytes (HCE) has shown a promising resilience at high potential. In this work, we demonstrate that although cells using HCE experience low capacity fading compared to conventional carbonate based-electrolyte, HCE does not prevent oxidation of dimethyl carbonate at high potential. Even worse, this phenomenon cannot be fully offset by lithium intercalation at the negative electrode and eventually leads to lithium plating that precipitates the cell end of life. To circumvent lithium plating, cycling at high temperature is shown to build a more passivating solid electrolyte interphase (SEI); while promising at first, the lithium losses associated with the SEI formation trigger a jump of graphite staging. Only replacing DMC by ethyl carbonate (EC) solvent reduces efficiently the parasitic oxidation and prevents capacity rollover. This work, by the use of adapted testing protocols and analysis workflows, provides the necessary understanding to open new routes for tackling parasitic reaction at high voltage in Li-ion batteries, which including mastering of SEI formation conditions and the use of appropriate solvent

Phase separation and amorphisation in lithium inserted Cu-In-Sn sulfospinels: Experimental and theoretical approach

cited By 3International audience119Sn Mössbauer spectroscopy, X-ray diffraction (XRD) and electrochemical experiments were carried out to characterise the reaction mechanism of lithium with spinel phases CuxInySnzS4. The electrochemical investigations have shown interesting reversible capacities for these materials, and their possible use as anode materials in lithium-ion cells. This analysis reveals a multi-phase mechanism linked to the reduction of the cations involving a spinel to rocksalt transformation followed by a structural breakdown. Density functional calculations by the linearised augmented plane wave (LAPW) method give a good interpretation of experimental results for crystalline phases. © 2001 Elsevier Science B.V

Direct Quantification of Anionic Redox over Long Cycling of Li-Rich NMC via Hard X-ray Photoemission Spectroscopy

International audienceCumulative anionic/cationic bulk redox processes lead to the outstanding specific energy (1000 Wh kg-1) of Li-rich Mn-based layered oxides as lithium-ion battery cathodes. Previous attempts to quantify redox processes in these materials were either limited to initial cycles or relied solely on the transition metals. It thus remains unclear to what extent does oxygen redox persist over cycling. This study provides an answer via synchrotron-based bulk-sensitive hard X-ray photoemission spectroscopy (HAXPES) by directly following the changes in the electronic state of lattice oxygen. We find that oxygen redox contribution stabilizes after initial cycles in Li1.2Ni0.13Mn0.54Co0.13O2 (Li-rich NMC), and even after 70 cycles, it accounts for more than one-third of the overall capacity. Consequently, we observe a gradual but limited growth of Mn3+/4+ redox, instead of a complete activation. Partial degradation of the Ni2+/3+/4+ redox is also detected. This fundamental study generates optimism for the concept of anionic redox in long-cycling batteries and also highlights the capability of HAXPES for understanding bulk versus surface effects in energy materials

Electrode/electrolyte interface reactivity in high-voltage spinel LiMn 1.6Ni0.4O4/Li4Ti5O 12 lithium-ion battery

cited By 129International audienceHigh-voltage spinel oxides combined with Li4Ti5O 12 result in 3 V lithium-ion batteries with a high power capability; however, the electrochemical performances are limited by electrode/electrolyte interfacial reactivity at high potential. We have investigated electrode/electrolyte interfaces in LiMn1.6Ni0.4O 4/Li4Ti5O12 cells by X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectrocopy (EIS). EIS has shown that both electroadsorption and film-formation mechanisms occur at the positive electrode. XPS has revealed that very low amounts of lithiated species are deposited at the surface of the positive electrode, despite the high potential, but that great amounts of organic species are deposited. Interesting results were obtained for the Li4Ti 5O12 electrode. Whereas Li4Ti5O 12 is usually considered as a passivation-free electrode material, large amounts of organic and inorganic species were deposited at the surface of this electrode. The question of a possible interaction between both electrodes in the formation mechanisms of surface films is discussed. © 2010 American Chemical Society