On the origin of the extra capacity at low potential in materials for Li batteries reacting through conversion reaction

The possibility of interfacial storage at low potential for electrode materials reacting through conversion reactions was evaluated. The amount of charge that could be stored through the proposed interfacial mechanism was estimated for a range of different materials and found to be much lower than those observed experimentally. Moreover, the slope of the potential decay and the influence of the current in the extent of stored capacity for experiments carried out in composite electrodes containing Co3O4 are not consistent with a capacitive-like mechanism. In summary, no evidence for capacitive storage could be found, our results being in agreement with the process taking place at low potential being solely related to electrolyte decomposition

Electrodeposition of arrays of Ru, Pt, and PtRu Alloy 1D metallic nanostructures

Arrays of Ru, Pt, and PtRu one dimensional 1D nanowires NWs and nanotubes NTs were prepared by electrodeposition through the porous structure of an anodic aluminum oxide AAO membrane. In each case, micrometer-long NW and NT were formed with an outer diameter of ca. 200 nm, close to the interior diameter of the porous AAO membrane. Arrays of NW and NT can be formed by varying the metallic salt concentration, the applied potential, and the conductivity of the electrolyte. The Ru and Pt deposition rates were measured in the various deposition conditions, using an electrochemical quartz crystal microbalance. The mechanisms responsible for the formation of Ru and Pt NW and NT are discussed based on the observed deposition rates and models found in the literature. Finally, it is shown that arrays of PtRu alloy NT and NW can be readily prepared and their compositions can be varied over the whole compositional range by changing the metallic salt concentration of the electrodeposition bath

Towards a calcium-based rechargeable battery

The development of a rechargeable battery technology using light electropositive metal anodes would result in a breakthrough in energy density1. For multivalent charge carriers (Mn+), the number of ions that must react to achieve a certain electrochemical capacity is diminished by two (n = 2) or three (n = 3) when compared with Li+ (ref. 2). Whereas proof of concept has been achieved for magnesium3, 4, 5, the electrodeposition of calcium has so far been thought to be impossible6 and research has been restricted to non-rechargeable systems7, 8, 9, 10. Here we demonstrate the feasibility of calcium plating at moderate temperatures using conventional organic electrolytes, such as those used for the Li-ion technology. The reversibility of the process on cycling has been ascertained and thus the results presented here constitute the first step towards the development of a new rechargeable battery technology using calcium anodes.Authors are grateful to F. Fauth for his assistance during data collection at the ALBA Synchrotron. The authors thank the Toyota Battery Research division at Higashi Fuji (M6) for their financial support.Peer reviewe

Towards standard electrolytes for sodium-ion batteries: physical properties, ion solvation and ion-pairing in alkyl carbonate solvents.

The currently emerging sodium-ion battery technology is in need of an optimized standard organic solvent electrolyte based on solid and directly comparable data. With this aim we have made a systematic study of "simple" electrolyte systems consisting of two sodium salts (NaTFSI and NaPF6) dissolved in three different alkyl carbonate solvents (EC, PC, DMC) within a wide range of salt concentrations and investigated: (i) their more macroscopic physico-chemical properties such as ionic conductivity, viscosity, thermal stability, and (ii) the molecular level properties such as ion-pairing and solvation. From this all electrolytes were found to have useful thermal operational windows and electrochemical stability windows, allowing for large scale energy storage technologies focused on load levelling or (to a less extent) electric vehicles, and ionic conductivities on par with analogous lithium-ion battery electrolytes, giving promise to also be power performant. Furthermore, at the molecular level the NaPF6-based electrolytes are more dissociated than the NaTFSI-based ones because of the higher ionic association strength of TFSI compared to PF6- while two different conformers of DMC participate in the Na+ first solvation shells - a Na+ affected conformational equilibrium and induced polarity of DMC. The non-negligible presence of DMC in the Na+ first solvation shells increases as a function of salt concentration. Overall, these results should both have a general impact on the design of more performant Na-conducting electrolytes and provide useful insight on the very details of the importance of DMC conformers in any cation solvation studies

On the strange case of divalent ions intercalation in V2O5

International audienceVanadium pentoxide has been investigated for multivalent ion battery technologies but the structural characterization of inserted phases is poor, and conflicting reports exist in the literature. This study presents a critical overview of controversial aspects related to Mg and Ca insertion in α-V2O5 under diverse conditions by combined electrochemical and ex-situ XRD experiments. Galvanostatic tests are carried out in dry and wet alkyl carbonate-based electrolytes at RT and 100 °C. The formation of protonated phases with negligible divalent ion content if any is evidenced by Rietveld refinements of the XRD data, unambiguously dismissing the presence of AV2O5 (A: Mg, Ca) as electrochemical reduction products. Furthermore, thermal instability of V2O5 at 100 °C in alkyl carbonate solvents is demonstrated by XRD and TEM analysis and the formation of an orthorhombic phase with increased a parameter, most likely due to degradation favored by both water and temperature, is observed for both Mg and Ca. In order to assess the feasibility of the reverse reaction, fully intercalated AV2O5 (A = Ca, Mg) phases were also prepared by solid state reaction and oxidation attempted both electrochemically and chemically without evidence of any significant amount of Mg2+ or Ca2+ extraction, further corroborating the sluggish diffusion kinetics of divalent cations in α-V2O5

Multivalent Batteries—Prospects for High Energy Density: Ca Batteries

Batteries based on Ca hold the promise to leapfrog ahead regarding increases in energy densities and are especially attractive as Ca is the 5th most abundant element in the Earth's crust. The viability of Ca metal anodes has recently been shown by approaches that either use wide potential window electrolytes at moderately elevated temperatures or THF-based electrolytes at room temperature. This paper provides realistic estimates of the practical energy densities for Ca-based rechargeable batteries at the cell level, calculated using open source models for several concepts. The results from the Ca metal anode batteries indicate that doubled or even tripled energy density as compared to the state-of-the-art Li-ion batteries is viable if a practical proof-of-concept can be achieved

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

Polyimides as Promising Cathodes for Metal-Organic Batteries: A Comparison between Divalent (Ca2+, Mg2+) and Monovalent (Li+, Na+) Cations

Ca- and Mg-based batteries represent a more sustainable alternative to Li-ion batteries. However, multivalent cation technologies suffer from poor cation mass transport. In addition, the development of positive electrodes enabling reversible charge storage currently represents one of the major challenges. Organic positive electrodes, in addition to being the most sustainable and potentially low-cost candidates, compared with their inorganic counterparts, currently present the best electrochemical performances in Ca and Mg cells. Unfortunately, organic positive electrodes suffer from relatively low capacity retention upon cycling, the origin of which is not yet fully understood. Here, 1,4,5,8-naphthalenetetracarboxylic dianhydride-derived polyimide was tested in Li, Na, Mg, and Ca cells for the sake of comparison in terms of redox potential, gravimetric capacities, capacity retention, and rate capability. The redox mechanisms were also investigated by means of operando IR experiments, and a parameter affecting most figures of merit has been identified: the presence of contact ion-pairs in the electrolyte.Funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 715087) is gratefully acknowledged. ICMAB-CSIC members are grateful for funding through PTI+ TRANSENER+: “Alta Tecnología clave en la transición en el ciclo energético”, part of the CSIC program for the Spanish Recovery, Transformation and Resilience Plan funded by the Recovery and Resilience Facility of the European Union, established by the Regulation (EU) 2020/2094 and thank the Spanish Agencia Estatal de Investigación Severo Ochoa Programme for Centres of Excellence in R&D (CEX2019-000917-S).With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe

2021 roadmap for sodium-ion batteries

Abstract: Increasing concerns regarding the sustainability of lithium sources, due to their limited availability and consequent expected price increase, have raised awareness of the importance of developing alternative energy-storage candidates that can sustain the ever-growing energy demand. Furthermore, limitations on the availability of the transition metals used in the manufacturing of cathode materials, together with questionable mining practices, are driving development towards more sustainable elements. Given the uniformly high abundance and cost-effectiveness of sodium, as well as its very suitable redox potential (close to that of lithium), sodium-ion battery technology offers tremendous potential to be a counterpart to lithium-ion batteries (LIBs) in different application scenarios, such as stationary energy storage and low-cost vehicles. This potential is reflected by the major investments that are being made by industry in a wide variety of markets and in diverse material combinations. Despite the associated advantages of being a drop-in replacement for LIBs, there are remarkable differences in the physicochemical properties between sodium and lithium that give rise to different behaviours, for example, different coordination preferences in compounds, desolvation energies, or solubility of the solid–electrolyte interphase inorganic salt components. This demands a more detailed study of the underlying physical and chemical processes occurring in sodium-ion batteries and allows great scope for groundbreaking advances in the field, from lab-scale to scale-up. This roadmap provides an extensive review by experts in academia and industry of the current state of the art in 2021 and the different research directions and strategies currently underway to improve the performance of sodium-ion batteries. The aim is to provide an opinion with respect to the current challenges and opportunities, from the fundamental properties to the practical applications of this technology

Ionic Liquid-Based Electrolytes for Calcium-Based Energy Storage Systems

In this work, aprotic and protic ionic liquid (IL)-based electrolytes designed for calcium-based energy storage systems are investigated. We have shown that these electrolytes display good transport properties and electrochemical stabilities comparable with those of IL-based electrolytes proposed for lithium and sodium-based systems. The use of these electrolytes in electrochemical double layer capacitors (EDLCs) leads to the realization of devices displaying good capacitances paired with a high reversibility and stability. Their use in combination with TiS2 cathode appears more problematic as the cation of the ILs is inserting in the layered structure of this material during the charge process. In this latter case a careful design of the cation appears necessary to guarantee selective insertion of Ca2+ and reversible charge-discharge process.AB and TS wish to thank the Friedrich Schiller University of Jena for the financial support. Funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (ERC-2016-STG, CAMBAT grant agreement No 715087) is acknowledged. RD acknowledges support of the Beatriu de Pinós postdoctoral programme of the Government of Catalonia's Secretariat for Universities and Research of the Ministry of Economy and Knowledge (2017 BP 00187). A. Ponrouch is grateful to the Spanish Ministry for Economy, Industry and Competitiveness Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2015-0496). We thank Dr. R. Verrelli for providing us with TiS2 electrodes and for helpful discussion.Peer reviewe