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Understanding the interfacial dynamics of batteries is crucial to control degradation and increase electrochemical performance and cycling life. If the chemical potential of a negative electrode material lies outside of the stability window of an electrolyte (either solid or liquid), a decomposition layer (interphase) will form at the interface. To better understand and control degradation at interfaces in batteries, theoretical models describing the rate of formation of these interphases are required. This study focuses on the growth kinetics of the interphase forming between solid electrolytes and metallic negative electrodes in solid-state batteries. More specifically, we demonstrate that the rate of interphase formation and metal plating during charge can be accurately described by adapting the theory of coupled ion-electron transfer (CIET). The model is validated by fitting experimental data presented in the first part of this study. The data was collected operando as a Na metal layer was plated on top of a NaSICON solid electrolyte (Na3.4Zr2Si2.4P0.6O12 or NZSP) inside an XPS chamber. This study highlights the depth of information which can be extracted from this single operando experiment and is widely applicable to other solid-state electrolyte systems.

A series of higher-order Ruddlesden-Popper phase materials – La3PrNi3O10-d, La2Pr2Ni3O10-d and LaPr3Ni3O10-d – were synthesised and investigated by neutron powder diffraction to understand the oxygen defect structure and propose possible pathways for oxygen transport in these materials. Further complimentary DFT calculations of the materials were performed to support the experimental analysis. All of the phases were hypostoichiometric and it was observed that the majority of the oxygen vacancies were confined to the perovskite layers, with a preference for equatorial oxygen sites. A particular preference for vacancies in O(1) and O(5) sites at high temperatures was observed from neutron diffraction measurements which were further complimented by DFT calculations wherein the vacancy formation energy was found to be lowest at the O(1) site. Also, a preference for a curved oxygen transport pathway around the NiO6 octahedra was observed which agrees with the published literature for Ruddlesden-Popper phase materials. Lattice parameters for all three compositions showed a linear increase with increasing temperature, but the increase was greatest in the c parameter while the b parameter showed only a slight increase when compared to the a parameter. The thermal expansion coefficient was calculated for all compositions and was found to be in the range 13.0 - 13.4 × 10-6 /˚C, which is compatible with the commonly used electrolyte materials for solid oxide fuel cells.

To harness all of the benefits of solid-state battery (SSB) architectures in terms of energy density, their negative electrode should be an alkali metal. However, the high chemical potential of alkali metals makes them prone to reduce most solid electrolytes (SE), resulting in a decomposition layer called an interphase at the metal|SE interface. Quantitative information about the interphase chemical composition and rate of formation is challenging to obtain because the reaction occurs at a buried interface. In this study, a thin layer of Na metal (Na0) is plated on the surface of an SE of the NaSICON family (Na3.4Zr2Si2.4P0.6O12 or NZSP) inside a commercial X-ray photoelectron spectroscopy (XPS) system while continuously analyzing the composition of the interphase operando. We identify the existence of a solid electrolyte interphase at the Na0|NZSP interface, and more importantly, we demonstrate for the first time that this protocol can be used to study the kinetics of interphase formation. A second important outcome of this article is that the surface chemistry of NZSP samples can be tuned to improve their stability against Na0. It is demonstrated by XPS and time-resolved electrochemical impedance spectroscopy (EIS) that a native NaxPOy layer present on the surface of as-sintered NZSP samples protects their surface against decomposition.

To harness all the benefits of solid-state battery (SSB) architectures in terms of energy density, their negative electrode should be an alkali metal. However, the high chemical potential of alkali metals makes them prone to reduce most solid electrolytes (SE), resulting in a decomposition layer called an interphase at the metal|SE interface. Quantitative information about the interphase chemical composition and rate of formation are challenging to obtain because the reaction occurs at a buried interface. In this study, a thin layer of Na metal (Na0) is plated on the surface of a SE of the NaSICON family (Na3.4Zr2Si2.4P0.6O12 or NZSP) inside a commercial XPS system whilst continuously analysing the composition of the interphase operando. We identify the existence of an interphase at the Na0|NZSP interface, and more importantly, we demonstrate for the first time that this protocol can be used to study the kinetics of interphase formation. A second important outcome of this article is that the surface chemistry of NZSP samples can be tuned to improve their stability against Na0. It is demonstrated by XPS and time-resolved electrochemical impedance spectroscopy (EIS) that a native Na3PO4 layer present on the surface of as-sintered NZSP samples protects their surface against decomposition.

Understanding the interfacial dynamics of batteries is crucial to control degradation and increase electrochemical performance and cycling life. If the chemical potential of a negative electrode material lies outside of the stability window of an electrolyte (either solid or liquid), a decomposition layer (interphase) will form at the interface. To better understand and control degradation at interfaces in batteries, theoretical models describing the rate of formation of these interphases are required. This study focuses on the growth kinetics of the interphase forming between solid electrolytes and metallic negative electrodes in solid-state batteries. More specifically, we demonstrate that the rate of interphase formation and metal plating during charge can be accurately described by adapting the theory of coupled ion-electron transfer (CIET). The model is validated by fitting experimental data presented in the first part of this study. The data was collected operando as a Na metal layer was plated on top of a NaSICON solid electrolyte (Na3.4Zr2Si2.4P0.6O12 or NZSP) inside a XPS chamber. This study highlights the depth of information which can be extracted from this single operando experiment, and is widely applicable to other solid-state electrolyte systems.

P2-layered sodium-ion battery (NIB) cathodes are a promising class of Na-ion electrode materials with high Na+ mobility and relatively high capacities. In this work, we report the structural changes that take place in P2-Na0.67[Mg0.28Mn0.72]O2. Using ex situ X-ray diffraction, Mn K-edge extended X-ray absorption fine structure, and 23Na NMR spectroscopy, we identify the bulk phase changes along the first electrochemical charge-discharge cycle-including the formation of a high-voltage "Z phase", an intergrowth of the OP4 and O2 phases. Our ab initio transition state searches reveal that reversible Mg2+ migration in the Z phase is both kinetically and thermodynamically favorable at high voltages. We propose that Mg2+ migration is a significant contributor to the observed voltage hysteresis in Na0.67[Mg0.28Mn0.72]O2 and identify qualitative changes in the Na+ ion mobility.

Understanding the interfacial dynamics of batteries is crucial to control degradation and increase electrochemical performance and cycling life. If the chemical potential of a negative electrode material lies outside of the stability window of an electrolyte (either solid or liquid), a decomposition layer (interphase) will form at the interface. To better understand and control degradation at interfaces in batteries, theoretical models describing the rate of formation of these interphases are required. Yet, experimental data which could support these models are challenging to obtain considering that the decomposition reaction is dynamic in nature and occurs at a deeply buried interface making it inaccessible to quantitative non-destructive techniques such as X-ray photoelectron spectroscopy (XPS) which has a limited depth of analysis. In the first article of this two-parts study, an experiment was designed to study the formation of an interphase at the interface between a Na metal negative electrode and a NaSICON solid electrolyte (Na3.4Zr2Si2.4P0.6O12 or NZSP) using a recent XPS protocol. Data was collected operando as a Na metal layer was plated on top of the NZSP electrolyte inside the XPS chamber. It was demonstrated that an interphase forms at the Na0|NZSP interface but that a native Na3PO4 layer present on thermally activated NZSP samples can minimize the extent of decomposition. In this second article, it is demonstrated that the rate of plating and interphase formation at the Na0|NZSP interface can be accurately described by adapting the theory of coupled ion-electron transfer (CIET). Models are fitted using experimental data from the first part of this study (in particular, the peak positions and peak areas as a function of Na0 plating time). This second part of the study therefore highlights the depth of information which can be extracted from this single operando experiment.

To harness all the benefits of solid-state battery (SSB) architectures in terms of energy density, their negative electrode should be an alkali metal. However, the high chemical potential of alkali metals make them prone to reduce most solid electrolytes (SE), resulting in a decomposition layer called an interphase at the metal|SE interface. Quantitative information about the interphase chemical composition and rate of formation are challenging to obtain because the reaction occurs at a buried interface. In this study, a thin layer of Na metal (Na0) is plated on the surface of a SE of the NaSICON family (Na3.4Zr2Si2.4P0.6O12 or NZSP) inside a commercial XPS system whilst continuously analysing the composition of the interphase operando. We identify the existence of an interphase at the Na0|NZSP interface, and more importantly, we demonstrate for the first time that this protocol can be used to study the kinetics of interphase formation. A second important outcome of this article is that the surface chemistry of NZSP samples can be tuned to improve their stability against Na0. It is demonstrated by XPS and time-resolved electrochemical impedance spectroscopy (EIS) that a native Na3PO4 layer present on the surface of as-sintered NZSP samples protects their surface against decomposition.

Substituted Li-layered transition-metal oxide (LTMO) electrodes such as LixNiyMnzCo1-y-zO2 (NMC) and LixNiyCo1-y-zAlzO2 (NCA) show reduced first cycle Coulombic efficiency (90-87% under standard cycling conditions) in comparison with the archetypal LixCoO2 (LCO; ∼98% efficiency). Focusing on LixNi0.8Co0.15Al0.05O2 as a model compound, we use operando synchrotron X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) spectroscopy to demonstrate that the apparent first-cycle capacity loss is a kinetic effect linked to limited Li mobility at x > 0.88, with near full capacity recovered during a potentiostatic hold following the galvanostatic charge-discharge cycle. This kinetic capacity loss, unlike many capacity losses in LTMOs, is independent of the cutoff voltage during delithiation and it is a reversible process. The kinetic limitation manifests not only as the kinetic capacity loss during discharge but as a subtle bimodal compositional distribution early in charge and, also, a dramatic increase of the charge-discharge voltage hysteresis at x > 0.88. 7Li NMR measurements indicate that the kinetic limitation reflects limited Li transport at x > 0.86. Electrochemical measurements on a wider range of LTMOs including Lix(Ni,Fe)yCo1-yO2 suggest that 5% substitution is sufficient to induce the kinetic limitation and that the effect is not limited to Ni substitution. We outline how, in addition to a reduction in the number of Li vacancies and shrinkage of the Li-layer size, the intrinsic charge storage mechanism (two-phase vs solid-solution) and localization of charge give rise to additional kinetic barriers in NCA and nonmetallic LTMOs in general.

Three different structures of the composition Li2Ni2TeO6 have been synthesized and their electrochemical properties characterized: a disordered orthorhombic phase with tellurium ordering and strong Li/Ni cation mixing, a T#2-layered phase, and an O3-layered phase; each have a distinct cycling performance. The disordered orthorhombic structure is the most stable at room temperature and has the highest capacity with the lowest overpotential. The T#2 phase is the least stable and undergoes a phase transformation once lithium is extracted. Density functional theory calculations reconcile the relative structural stabilities and physical properties of each phase with their electrochemical performances. Calculations also confirmed experimental observations regarding the synthesis of each structure and indicated the mechanism for capacity fade of each Li2Ni2TeO6 cathode. Strong tellurium–oxygen covalent bonding increases the voltage of the Ni2+/3+ redox couple in each of these materials over what is normally obse...

Li-excess lithium-ion battery cathode materials and the role that reversible anionic redox may play in their high capacities have generated significant interest, motivating studies of the oxygen lo...

Solid-state batteries (SSBs) with alkali metal anodes hold great promise as energetically dense and safe alternatives to conventional Li-ion cells. Whilst, in principle, SSBs have the additional advantage of offering virtually unlimited plating current densities, fast charges have so far only been achieved through sophisticated interface engineering strategies. Here, we reveal that such interface engineering can be easily achieved by tuning the chemistry of NaSICON solid electrolytes (Na3.4Zr2Si2.4P0.6O12) and taking advantage of the thermodynamic stabilization of a Na3PO4 layer on their surface upon thermal activation. The optimized planar Na|NZSP interfaces are characterized by their exceptionally low interface resistances (down to 0.1 Ω cm2 at room temperature) and, more importantly, by their tolerance to large plating current densities (up to 10 mA cm-2) even for extended cycling periods of 30 minutes (corresponding to an areal capacity 5 mAh cm-2).

Sodium batteries have been regarded as promising candidates for large-scale energy storage application, provided cathode hosts with high energy density and long cycle life can be found. Herein, we report NASICON-structured Na3MnZr(PO4)3 as a cathode for sodium batteries that exhibits an electrochemical performance superior to those of other manganese phosphate cathodes reported in the literature. Both the Mn4+/Mn3+ and Mn3+/Mn2+ redox couples are reversibly accessed in Na3MnZr(PO4)3, providing high discharge voltage plateaus at 4.0 and 3.5 V, respectively. A high discharge capacity of 105 mAh g-1 was obtained from Na3MnZr(PO4)3 with a small variation of lattice parameters and a small volume change on extraction of two Na+ ions per formula unit. Moreover, Na3MnZr(PO4)3 exhibits an excellent cycling stability, retaining 91% of the initial capacity after 500 charge/discharge cycles at 0.5 C rate. On the basis of structural analysis and density functional theory calculations, we have proposed a detailed desodiation pathway from Na3MnZr(PO4)3 where Mn and Zr are disordered within the structure. We further show that the cooperative Jahn-Teller distortion of Mn3+ is suppressed in the cathode and that Na2MnZr(PO4)3 is a stable phase.

TiNb2O7 is a Wadsley-Roth phase with a crystallographic shear structure and is a promising candidate for high-rate lithium ion energy storage. The fundamental aspects of the lithium insertion mechanism and conduction in TiNb2O7, however, are not well-characterized. Herein, experimental and computational insights are combined to understand the inherent properties of bulk TiNb2O7. The results show an increase in electronic conductivity of seven orders of magnitude upon lithiation and indicate that electrons exhibit both localized and delocalized character, with a maximum Curie constant and Li NMR paramagnetic shift near a composition of Li0.60TiNb2O7. Square-planar or distorted-five-coordinate lithium sites are calculated to invert between thermodynamic minima or transition states. Lithium diffusion in the single-redox region (i.e., x ≤ 3 in LixTiNb2O7) is rapid with low activation barriers from NMR and DLi = 10-11 m2 s-1 at the temperature of the observed T1 minima of 525-650 K for x ≥ 0.75. DFT calculations predict that ionic diffusion, like electronic conduction, is anisotropic with activation barriers for lithium hopping of 100-200 meV down the tunnels but ca. 700-1000 meV across the blocks. Lithium mobility is hindered in the multiredox region (i.e., x > 3 in LixTiNb2O7), related to a transition from interstitial-mediated to vacancy-mediated diffusion. Overall, lithium insertion leads to effective n-type self-doping of TiNb2O7 and high-rate conduction, while ionic motion is eventually hindered at high lithiation. Transition-state searching with beyond Li chemistries (Na+, K+, Mg2+) in TiNb2O7 reveals high diffusion barriers of 1-3 eV, indicating that this structure is specifically suited to Li+ mobility.

We show the occurrence of local cation ordering in Li-ion battery material Li1.25Nb0.25Mn0.5O2, previously thought to be disordered. We deduce this ordering from X-ray diffraction, and test it against neutron diffraction & PDF, magnetic susceptibility and solid state NMR evidence. We identify the nature of the ordering as having a local structure related to that of gamma-LiFeO2, determine the correlation length of such ordering, and demonstrate its significant consequences for the material's electrochemistry.

β-NaMnO2 is a high-capacity Na-ion battery cathode, delivering ca. 190 mAh/g of reversible capacity when cycled at a rate of C/20. Yet, only 70% of the initial reversible capacity is retained after 100 cycles. We carry out a combined solid-state 23Na NMR and first-principles DFT study of the evolution of the structure of β-NaMnO2 upon electrochemical cycling. The as-synthesized structure contains planar defects identified as twin planes between nanodomains of the α and β forms of NaMnO2. GGA+U calculations reveal that the formation energies of the two polymorphs are within 5 meV per formula unit, and a phase mixture is likely in any NaMnO2 sample at room temperature. 23Na NMR indicates that 65.5% of Na is in β-NaMnO2 domains, 2.5% is in α-NaMnO2 domains, and 32% is close to a twin boundary in the as-synthesized material. A two-phase reaction at the beginning of charge and at the end of discharge is observed by NMR, consistent with the constant voltage plateau at 2.6–2.7 V in the electrochemical profile. G...

The doping of Al into layered Li transition metal (TM) oxide cathode materials, LiTMO2, is known to improve the structural and thermal stability, although the origin of the enhanced properties is not well understood. The effect of aluminum doping on layer stabilization has been investigated using a combination of techniques to measure the aluminum distribution in layered LiNi0.8Co0.15Al0.05O2 (NCA) over multiple length scales with 27Al and 7Li MAS NMR, local electrode atom probe (APT) tomography, X-ray and neutron diffraction, DFT, and SQUID magnetic susceptibility measurements. APT ion maps show a homogeneous distribution of Ni, Co, Al, and O2 throughout the structure at the single particle level in agreement with the high-temperature phase diagram. 7Li and 27Al NMR indicates that the Ni3+ ions undergo a dynamic Jahn–Teller (JT) distortion. 27Al NMR spectra indicate that the Al reduces the strain associated with the JT distortion, by preferential electronic ordering of the JT lengthened bonds directed to...

Layered LiMnO2 is a potential Li ion cathode material that is known to undergo a layered to spinel transformation upon delithiation, as a result of Mn migration. A common strategy to improve the structural stability of LiMnO2 has been to replace Mn with a range of metal dopants, although the mechanism by which each dopant stabilizes the structure is not well understood. In this work we characterize ion-migration barriers using hybrid eigenvector-following (EF) and density functional theory to study how trivalent dopants (Al3+, Cr3+, Fe3+, Ga3+, Sc3+, and In3+) affect Mn migration during the initial stage of the layered to spinel transformation in Li0.5MnO2. We demonstrate that dopants with small ionic radii, such as Al3+ and Cr3+, can increase the barrier for migration, but only when they are located in the first cation coordination sphere of Mn. We also demonstrate how the hybrid EF approach can be used to study the migration barriers of dopant species within the structure of Li0.5MnO2 efficiently. The transition state searching methodology described in this work will be useful for studying the effects of dopants on structural transformation mechanisms in a wide range of technologically interesting energy materials.

Experimental techniques that probe the local environment around O in paramagnetic Li-ion cathode materials are essential in order to understand the complex phase transformations and O redox processes that can occur during electrochemical delithiation. While Li NMR is a well-established technique for studying the local environment of Li ions in paramagnetic battery materials, the use of (17)O NMR in the same materials has not yet been reported. In this work, we present a combined (17)O NMR and hybrid density functional theory study of the local O environments in Li2MnO3, a model compound for layered Li-ion batteries. After a simple (17)O enrichment procedure, we observed five resonances with large (17)O shifts ascribed to the Fermi contact interaction with directly bonded Mn(4+) ions. The five peaks were separated into two groups with shifts at 1600 to 1950 ppm and 2100 to 2450 ppm, which, with the aid of first-principles calculations, were assigned to the (17)O shifts of environments similar to the 4i and 8j sites in pristine Li2MnO3, respectively. The multiple O environments in each region were ascribed to the presence of stacking faults within the Li2MnO3 structure. From the ratio of the intensities of the different (17)O environments, the percentage of stacking faults was found to be ca. 10%. The methodology for studying (17)O shifts in paramagnetic solids described in this work will be useful for studying the local environments of O in a range of technologically interesting transition metal oxides.

The migration mechanism associated with the initial layered-to-spinel transformation of partially delithiated layered LiMnO2 was studied using hybrid eigenvector-following coupled with density functional theory. The initial part of the transformation mechanism of Li0.5MnO2 involves the migration of Li into both octahedral and tetrahedral local minima within the layered structure. The next stage of the transformation process involves the migration of Mn and was found to occur through several local minima, including an intermediate square pyramidal MnO5 configuration and an independent Mn3+ to Mn2+ charge-transfer process. The migration pathways were found to be significantly affected by the size of the supercell used and the inclusion of a Hubbard U parameter in the DFT functional. The transition state searching methodology described should be useful for studying the structural rearrangements that can occur in electrode materials during battery cycling, and more generally, ionic and electronic transport ph...

Ultrasound can be used to oxidize aqueous pollutants; however, due to economic reasons, higher oxidation/destruction rates are needed. This study reports enhancements of reaction rates by the addition of sodium chloride salt. Using 20 kHz ultrasound, large salt-induced enhancements are observed6-fold for chlorobenzene, 7-fold for p-ethylphenol, and 3-fold for phenol oxidation. The reaction rate enhancements are proportional to the diethyl ether−water partitioning coefficient of the pollutants. It appears that the majority of oxidation reactions occur in the bubble−bulk interface region. The addition of salt increases the ionic strength of the aqueous phase which drives the organic pollutants toward the bubble−bulk interface. A first order reaction rate equation is proposed which can represent the observed enhancement with a good accuracy. A new sonochemical-waste-oxidation process is proposed utilizing the salt-induced enhancement.

Involves the determination of the acid dissociation constant of bromcresol green by a spectrophotometric method; using a graphing calculator, each student can perform the laboratory work and obtain his own data set.