Beam Effects in Synchrotron Radiation Operando Characterization of Battery Materials: X-Ray Diffraction and Absorption Study of LiNi0.33Mn0.33Co0.33O2 and LiFePO4 Electrodes.

Operando synchrotron radiation-based techniques are a precious tool in battery research, as they enable the detection of metastable intermediates and ensure characterization under realistic cycling conditions. However, they do not come exempt of risks. The interaction between synchrotron radiation and samples, particularly within an active electrochemical cell, can induce relevant effects at the irradiated spot, potentially jeopardizing the experiment's reliability and biasing data interpretation. With the aim of contributing to this ongoing debate, a systematic investigation into these phenomena was carried out by conducting a root cause analysis of beam-induced effects during the operando characterization of two of the most commonly employed positive electrode materials in commercial Li-ion batteries: LiNi0.33Mn0.33Co0.33O2 and LiFePO4. The study spans across diverse experimental conditions involving different cell types and absorption and scattering techniques and seeks to correlate beam effects with factors such as radiation energy, photon flux, exposure time, and other parameters associated with radiation dosage. Finally, it provides a comprehensive set of guidelines and recommendations for assessing and mitigating beam-induced effects that may affect the outcome of battery operando experiments.

Prussian Blue Analogues as Positive Electrodes for Mg Batteries: Insights into Mg2+ Intercalation.

Potassium manganese hexacianoferrate has been prepared by co-precipitation from manganese (II) chloride and potassium citrate, with chemical analysis yielding the formula K1.72 Mn[Fe(CN)6 ]0.92 □0.08 ⋅ 1.1H2 O (KMnHCF). Its X-ray diffraction pattern is consistent with a monoclinic structure (space group P 21 /n, no. 14) with cell parameters a=10.1202(6)Å, b=7.2890(5)Å, c=7.0193(4)Å, and ß=89.90(1)°. Its redox behavior has been studied in magnesium containing electrolytes. Both K+ ions deintercalated from the structure upon oxidation and contamination with Na+ ions coming from the separator were found to interfere in the electrochemical response. In the absence of alkaline ions, pre-oxidized manganese hexacianoferrate showed reversible magnesium intercalation, and the process has been studied by operando synchrotron X-ray diffraction. The location of Mg2+ ions in the crystal structure was not possible with the available experimental data. Still, density functional theory simulations indicated that the most favorable position for Mg2+ intercalation is at 32f sites (considering a pseudo cubic F m-3m phase), which are located between 8c and Mn sites.

Synchrotron radiation based operando characterization of battery materials.

Synchrotron radiation based techniques are powerful tools for battery research and allow probing a wide range of length scales, with different depth sensitivities and spatial/temporal resolutions. Operando experiments enable characterization during functioning of the cell and are thus a precious tool to elucidate the reaction mechanisms taking place. In this perspective, the current state of the art for the most relevant techniques (scattering, spectroscopy, and imaging) is discussed together with the bottlenecks to address, either specific for application in the battery field or more generic. The former includes the improvement of cell designs, multi-modal characterization and development of protocols for automated or at least semi-automated data analysis to quickly process the huge amount of data resulting from operando experiments. Given the recent evolution in these areas, accelerated progress is expected in the years to come, which should in turn foster battery performance improvements.

ß-V2O5 as Magnesium Intercalation Cathode.

Magnesium batteries have attracted great attention as an alternative to Li-ion batteries but still suffer from limited choice of positive electrode materials. V2O5 exhibits high theoretical capacities, but previous studies have been mostly limited to α-V2O5. Herein, we report on the ß-V2O5 polymorph as a Mg intercalation electrode. The structural changes associated with the Mg2+ (de-) intercalation were analyzed by a combination of several characterization techniques: in situ high resolution X-ray diffraction, scanning transmission electron microscopy, electron energy-loss spectroscopy, and X-ray absorption spectroscopy. The reversible capacity reached 361 mAh g-1, the highest value found at room temperature for V2O5 polymorphs.

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.

Appraisal of calcium ferrites as cathodes for calcium rechargeable batteries: DFT, synthesis, characterization and electrochemistry of Ca4Fe9O17.

Sustainability combined with high energy density prospects makes Fe-based oxides attractive as cathodes for calcium rechargeable batteries. This work presents a DFT evaluation of the CaFe2+nO4+n (0 < n < 3) family, for which both the average intercalation voltage and the theoretical specific capacity decrease with the increasing n value. The term n = 1/4, Ca4Fe9O17, meets the most appealing characteristics: a calculated average voltage of 4.16 V, a theoretical specific capacity of 230 mA h g-1 and the lowest energy barrier for Ca migration so far predicted for an existing oxide (0.72 eV). To overcome the previously reported synthesis difficulties, we employed a novel synthesis procedure in sealed quartz tubes followed by quenching in water. The XRD and SAED patterns of the prepared Ca4Fe9O17 powder reveal a certain degree of stacking defects along the c axis. Attempts to deinsert Ca ions from Ca4Fe9O17 by chemical means (NO2BF4 in ACN) and in electrochemical Ca cells were unsuccessful, although some hints of oxidation are observed in Li cells with the LP30 electrolyte. The suitability of Ca4Fe9O17 as a Ca cathode is pending further studies utilizing Ca-electrolytes with high anodic stability.

Achievements, Challenges, and Prospects of Calcium Batteries.

This Review flows from past attempts to develop a (rechargeable) battery technology based on Ca via crucial breakthroughs to arrive at a comprehensive discussion of the current challenges at hand. The realization of a rechargeable Ca battery technology primarily requires identification and development of suitable electrodes and electrolytes, which is why we here cover the progress starting from the fundamental electrode/electrolyte requirements, concepts, materials, and compositions employed and finally a critical analysis of the state-of-the-art, allowing us to conclude with the particular roadblocks still existing. As for crucial breakthroughs, reversible plating and stripping of calcium at the metal-anode interface was achieved only recently and for very specific electrolyte formulations. Therefore, while much of the current research aims at finding suitable cathodes to achieve proof-of-concept for a full Ca battery, the spectrum of electrolytes researched is also expanded. Compatibility of cell components is essential, and to ensure this, proper characterization is needed, which requires design of a multitude of reliable experimental setups and sometimes methodology development beyond that of other next generation battery technologies. Finally, we conclude with recommendations for future strategies to make best use of the current advances in materials science combined with computational design, electrochemistry, and battery engineering, all to propel the Ca battery technology to reality and ultimately reach its full potential for energy storage.

On the Study of Ca and Mg Deintercalation from Ternary Tantalum Nitrides.

Layered CaTaN2 and MgTa2N3 and cubic Mg2Ta2N4 were prepared by direct solid state reaction from the binary nitrides Ta3N5 and A3N2 (A: Mg, Ca). CaTaN2 showed a slight Ca deficiency (0.11 moles per formula), and a monoclinic distortion from previously reported R3̅m symmetry, with space group C2/m and cell parameters a = 5.4011(2), b = 3.1434(1), c = 5.9464(2) Å and ß = 107.91(3)°. Ca2+ and Mg2+ deintercalation was investigated in the three compounds both chemically and electrochemically. No significant Mg2+ extraction could be inferred for MgTa2N3 and Mg2Ta2N4, neither after reaction with NO2BF4 nor after electrochemical oxidation at 100 °C in alkyl carbonate electrolytes. Rietveld refinement of the X-ray powder diffraction pattern of chemically oxidized Ca0.89TaN2 indicates a decrease of the Ca content to 0.34 concomitant to the disappearance of the monoclinic distortion and expansion of the interlayer space from 5.658 to 5.762 Å, space group R3̅m and cell parameters a = 3.1103(1) and c = 17.287(1) Å. Deintercalation in this compound was also achieved electrochemically at 100 °C. Results of density functional theory calculations seem to indicate that reaction mechanisms for CaTaN2 oxidation additional and/or alternative to deintercalation are taking place, which is likely related to the loss of crystallinity observed upon oxidation and the irreversibility of the process.

Post-Li batteries: promises and challenges.

Current societal challenges in terms of energy storage have prompted an intensification in the research aiming at unravelling new high energy density battery technologies. These would have the potential of having disruptive effects in the world transition towards a less carbon-dependent energy economy through transport, both by electrification and renewable energy integration. Aside from controversial debates on lithium supply, the development of new sustainable battery chemistries based on abundant elements is appealing, especially for large-scale stationary applications. Interesting alternatives are to use sodium, magnesium or calcium instead of lithium. While for the Na-ion case, fast progresses are expected as a result of chemical similarities with lithium and the cumulated Li-ion battery know-how over the years, for Ca and Mg the situation is radically different. On the one hand, the possibility to use Ca or Mg metal anodes would bring a breakthrough in terms of energy density; on the other, development of suitable electrolytes and cathodes with efficient multivalent ion migration are bottlenecks to overcome. This article is part of a discussion meeting issue 'Energy materials for a low carbon future'.

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.

Electrochemical calcium extraction from 1D-Ca3Co2O6.

The electrochemical oxidation of a transition metal oxide through calcium extraction is achieved for the first time. The 1D framework of Ca3Co2O6 is maintained upon oxidation and the new phase formed exhibits a modulated structure. The process occurs at high potential and is partially reversible, which opens prospects for a calcium battery proof-of-concept.

Understanding ageing in Li-ion batteries: a chemical issue.

Performance degradation over Li-ion battery lifetime is unavoidable and ultimately rooted in chemical processes. Their extent is mostly determined by battery material components and operation conditions (charge/discharge rates, voltage operation limits and temperature) and can also be influenced by battery design. The two major factors contributing to loss of negative electrode performance are the instability of the passivation layer formed at the electrode/electrolyte interface (enhanced at higher temperatures) and lithium metal plating (intensified at low temperatures). In contrast, capacity fading at the positive electrode mostly results from partial dissolution of the active material during cycling/storage or electrolyte solvent oxidation, which is promoted by temperature and high potential. While it would be most useful to be able to monitor degradation at all levels while the cell is being cycled, the feasibility of this approach remains limited, and most approaches involve accelerated testing with ante/post mortem characterization. Yet, the use of suitable protocols for battery opening and disassembling is crucial to avoid biased interpretation. Finally, the relevance of degradation diagnosis coupled to modelling is also worth mentioning.

Recent achievements on inorganic electrode materials for lithium-ion batteries.

The lithium-ion battery technology is rooted in the studies of intercalation of guest ions into inorganic host materials developed ca. 40 years ago. It further turned into a commercial product, which will soon blow its 25th candle. Intense research efforts during this time have resulted in the development of a large spectrum of electrode materials together with deep understanding of the underlying structure-property relationships that govern their performance. This has enabled an ever increasing electrochemical yield together with the diversification of the technology into several subfamilies, tailoring materials to application requirements. The present paper aims at providing a global and critical perspective on inorganic electrode materials for lithium-ion batteries categorized by their reaction mechanism and structural dimensionality. Specific emphasis is put on recent research in the field, which beyond the chemistry and microstructure of the materials themselves also involves considering interfacial chemistry concepts alongside progress in characterization techniques. Finally a short personal perspective is provided on some plausible development of the field.

Synthesis and characterization of a novel sodium transition metal oxyfluoride: NaMnMoO3F3·H2O.

NaMnMoO3F3·H2O was precipitated at low temperature from aqueous dissolutions of Na2MoO4·2H2O in aqueous HF (or NaHF2) using either Mn(CH3COO)2·4H2O or MnF2 as manganese precursors. Chemical analysis, IR spectra, and effective paramagnetic moment are in agreement with the proposed formula. Electron microscopy studies indicate that the sample is constituted of very thin plate-like microcrystals. The average crystal structure (a = 3.5947(1), b = 21.246(1), and c = 7.3893(2) Å and Cmcm (No. 63) SG) has been elucidated through powder diffraction methods (synchrotron and neutron). Tiny superstructure peaks are observed that can be indexed with the space group Pbca and cell parameters a = 7.1894(2), b = 21.246(1), and c = 7.3893(2) Å. Electron diffraction confirms the doubling of a parameter. Ordering of O and F is proposed in agreement with Pauling's second crystal rule and bond strength sums for each anionic position. The structure that is formed has a layered stacking arrangement along the b-axis of the MnO4F2 octahedra layers that share corners along a- and c-directions. The large interlayer space contains MoO4F2 octahedra (connected to the layer) together with sodium ions and water molecules, tentatively forming hydrogen bonding with fluorine anions. The origin of the superstructure could not be fully elucidated, but it is presumably related to slight distortions within the MnO4F2 octahedra.

Beyond intercalation-based Li-ion batteries: the state of the art and challenges of electrode materials reacting through conversion reactions.

Despite the imminent commercial introduction of Li-ion batteries in electric drive vehicles and their proposed use as enablers of smart grids based on renewable energy technologies, an intensive quest for new electrode materials that bring about improvements in energy density, cycle life, cost, and safety is still underway. This Progress Report highlights the recent developments and the future prospects of the use of phases that react through conversion reactions as both positive and negative electrode materials in Li-ion batteries. By moving beyond classical intercalation reactions, a variety of low cost compounds with gravimetric specific capacities that are two-to-five times larger than those attained with currently used materials, such as graphite and LiCoO(2), can be achieved. Nonetheless, several factors currently handicap the applicability of electrode materials entailing conversion reactions. These factors, together with the scientific breakthroughs that are necessary to fully assess the practicality of this concept, are reviewed in this report.

Recent advances in rechargeable battery materials: a chemist's perspective.

The constant increase in global energy demand, together with the awareness of the finite supply of fossil fuels, has brought about an imperious need to take advantage of renewable energy sources. At the same time, concern over CO(2) emissions and future rises in the cost of gasoline has boosted technological efforts to make hybrid and electric vehicles available to the general public. Energy storage is a vital issue to be addressed within this scenario, and batteries are certainly a key player. In this tutorial review, the most recent and significant scientific advances in the field of rechargeable batteries, whose performance is dependent on their underlying chemistry, are covered. In view of its utmost current significance and future prospects, special emphasis is given to progress in lithium-based technologies.

Synthesis, short-range structure, and electrochemical properties of new phases in the Li-Mn-N-O system.

A crystal-chemical exploration of part of the Li-Mn-N-O system was carried out. Several samples were synthesized using Li(3)N, Mn(x)N and Li(2)O and characterized with chemical analysis, XRD, XAS, and NMR. An increase in the starting proportion of Li(2)O increases the amounts of lithium and oxygen in the compounds, but, according to the XANES Mn K-edge spectra, all the oxynitrides still contain Mn(5+) ions preferentially coordinated by N(3-), forming [MnN(4)] tetrahedra. The analysis of the position of these samples in the compositional Li(3)N-Li(2)O-MnN(x) ternary phase diagram and the plot of their cell parameters against the oxygen molar fraction indicates that all the oxynitrides belong to the same tie-line, which also includes Li(2)O but not Li(7)MnN(4). Although the XRD patterns suggest that these samples crystallize in a disordered antifluorite-type structure, the analysis of the (6)Li NMR data indicates that short-range ordering does exist. The performance as electrode materials in lithium batteries of the synthesized samples was also evaluated. Li(7.9)MnN(3.2)O(1.6) was shown to be the most attractive candidate because of its higher capacity values and improved retention upon cycling with respect to the other members of the series.

Antifluorite-type lithium chromium oxide nitrides: synthesis, structure, order, and electrochemical properties.

Antifluorite-type lithium chromium oxide nitrides were prepared by solid-state reaction of Li(3)N, Li(2)O, and Cr(2)N. Depending on the reaction time and starting Li/Cr and O/Cr ratios, either an ordered or a disordered phase (or mixtures of both) is obtained. The formation of the former is favored by short reaction times and low Cr/O ratios whereas the formation of the latter is favored by higher Cr/O ratios and longer reaction times. The two phases were characterized, and the first one was confirmed to be the already reported Li(14)Cr(2)N(8)O phase, whereas the stoichiometry of the second is Li(10)CrN(4)O(2). Interestingly, even if both contain cationic vacancies in the structure, electrochemical lithium intercalation could only be achieved for Li(10)CrN(4)O(2). This phase exhibits a reversible capacity of 160 mAh/g very stable upon cycling. Bond valence and first-principles DFT calculations were carried out to understand the absence of lithium insertion in Li(14)Cr(2)N(8)O. Li-Li repulsion and destabilization of the tetrahedral CrN(4) units induced by occupation of the potential sites, as well as the absence of energetically favorable pathways for transport of the ions to these sites, are suggested to be the reasons.

Chemical Transport Synthesis, Electrochemical Behavior, and Electronic Structure of Superconducting Zirconium and Hafnium Nitride Halides.

The layered nitrides beta-MNX (M = Zr, Hf; X = Cl, Br) crystallize in the space group R&thremacr;m with a hexagonal cell of dimensions a = 3.6031(6) Å, c = 27.672(2) Å for beta-ZrNCl, a = 3.5744(3) Å, c = 27.7075(9) Å for beta-HfNCl, and a = 3.6379(5) Å, c = 29.263(2) Å for beta-ZrNBr. Lithium intercalation using n-buthyllithium in hexane solutions leads to solvent free superconductors of formula Li(0.20)ZrNCl, Li(0.42)HfNCl, Li(0.67)HfNCl, and Li(0.17)ZrNBr showing critical temperatures of 12, 18, 24, and 13.5 K, respectively. Whereas several samples of beta-ZrNBr and beta-ZrNCl showed reproducibility in the lithium uptake and in the corresponding critical temperatures, different samples of beta-HfNCl subjected to the same treatment in n-buthyllithium showed lithium uptakes ranging from 0.07 to 0.67, and corresponding critical temperatures between 0 and 24 K. A linear dependence of T(c) versus the lithium content is observed when all the superconducting samples are considered. The results obtained from electrochemical lithiation are consistent with those obtained with chemical methods, as samples with larger capacity on discharge are also those found to have larger lithium contents after chemical lithiation. Most samples present a reduction step around 1.8 V vs Li(0)-Li(+) whose origin is still unclear. The electrochemical capacity on discharge for beta-HfNCl and beta-ZrNBr depends on the milling time spent in the preparation of the electrodes, with long milling times resulting in lower intercalation degree. Possible causes for this effect are either the creation of structural defects (e.g., stacking faults) or some sample decomposition induced by local heating. The same phenomena are proposed to account for the different behavior of beta-HfNCl samples, although additional aspects such as the presence of hydrogen, oxygen, or extra hafnium atoms in the structure have to be considered. Tight-binding band structure calculations for beta-MNX (M = Zr, X = Cl, Br; M = Hf, X = Cl), ZrCl, and Y(2)C(2)Br(2) are reported. The density of states and Fermi surfaces of the beta-MNX phases as well as the relationship between the electronic structure of the beta-ZrNCl and ZrCl are discussed. Despite the structural relationships, the electronic structures near the Fermi level of the beta-MNX and Y(2)Br(2)C(2) phases are found to be very different.