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Two-phase transformation reaction is ubiquitous in solid-state electrochemistry; however, it usually involves inferior structure rearrangement upon extraction and insertion of large-sized Na

Chemistry of materials 34(18), 8163 - 8177 (2022). doi:10.1021/acs.chemmater.2c00995, Postsynthesis thermal treatments at various temperatures in air have been applied to LiNiO$_2$, and the induced structural and electronic changes have been uncovered. Except for the familiar decomposition process at higher temperatures, a series of transformations also take place under mild conditions. To identify such subtle changes, ex situ and in situ synchrotron radiation diffraction, ex situ$^7$Li nuclear magnetic resonance spectroscopy, and ex situ measurements of magnetic properties have been performed. We show that the reaction between LiNiO$_2$ and CO$_2$ starts already at a temperature of 200 °C, forming Li$_{1–z}$Ni$_{1+z}$O$_2$ layers. If the thickness of this layer is well adjusted, the electrochemical performance of LiNO$_2$ can be improved. A cation off-stoichiometry of [Li$_{0.90}$Ni$_{0.10}$]NiO$_2$ is identified at 600 °C even before the decomposition occurs. We also investigate the interplay of the reaction between LiNiO$_2$ and CO$_2$ with the decomposition at 700 °C. The changes in the Ni oxidation state and local Li environments are also monitored during the whole process., Published by American Chemical Society, Washington, DC

Energy storage materials 50, 464 - 472 (2022). doi:10.1016/j.ensm.2022.05.048, A cathode/anode compatible aqueous zinc triflate electrolyte is proposed by reorganizing the solvation structure of the electrolyte using an acetonitrile co-solvent. Acetonitrile notably alters the hydrogen bonds of the electrolyte, reducing the activity of water. Using this electrolyte, a ZnǁV2O5 full-cell exhibits high Coulombic efficiency, long cycle life and high rate capability. The interactions between electrolyte, cathode and Zn anode are clarified based on comprehensive in operando and ex situ experiments and molecular dynamics simulations. The addition of acetonitrile does not change the bulk ion storage of V2O5, but the unique electrode-electrolyte interfacial films with specific compositions and spatial distribution protect the Zn and V2O5 electrodes and improve the interfacial kinetics of the electrodes, thus significantly promoting the cycling performance of the full cell. This cathode/anode compatible electrolyte can overcome the challenges of both the cathode and anode which would promote aqueous rechargeable zinc batteries into practical application., Published by Elsevier, Amsterdam

The Laves phase Mg2MnGa3 was synthesized from the elements by arc-melting and subsequent annealing in a silica ampoule at T = 670 K. The structure of Mg2MnGa3 was refined from single-crystal X-ray diffractometer data: URe2 type, Cmcm, a = 543.24(1), b = 869.59(3), c = 858.58(2) pm, wR2 = 0.0556, 273 F 2 values and 24 variables. The manganese and gallium atoms form a three-dimensional network of corner- and face-sharing MnGa3 tetrahedra that derive as a ternary ordering variant from the hexagonal Laves phase MgZn2. The structures of the distortion and coloring variants, i.e., MgZn2, URe2, Mg2Cu3Si and Mg2MnGa3 are discussed on the basis of a Bärnighausen tree. The electronic structure calculation data indicate that in addition to the metallic type of bonding an additional covalent interaction appears between the Ga–Ga and Mn–Ga atoms.

The new ternary gallide MgMn4Ga18 (magnesium tetramanganese octadecagallium) was synthesized and its crystal structure determined by means of single-crystal X-ray diffraction. The MgMn4Ga18 structure can be described as that of a three core–shell cluster compound. The Mg atoms are surrounded by 16 adjacent Ga atoms, [MgGa16], and the respective coordination polyhedron is an octadecahedron. This [MgGa16] octadecahedron is encapsulated inside a [Ga32] icohexahedron, which is in turn encapsulated inside a [Ga40] pentacontaoctahedron. As a result, a three core–shell cluster, [MgGa16@Ga32@Ga40], is identified. Electronic structure calculations were performed by means of the TB-LMTO-ASA program and additionally confirm the existence of the core–shell packing of the clusters.

Sodium-ion batteries (SIBs) with fast-charge capability and long lifespan could be applied in various sustainable energy storage systems, from personal devices to grid storage. Inspired by the disordered Rubik's cube, here, we report that the high-entropy (HE) concept can lead to a very substantial improvement in the sodium storage properties of hexacyanoferrate (HCF). An example of HE-HCF has been synthesized as a proof of concept, which has achieved impressive cycling stability over 50 000 cycles and an outstanding fast-charging capability up to 75 C. Remarkable air stability and all-climate performance are observed. Its quasi-zero-strain reaction mechanism and high sodium diffusion coefficient have been measured and analyzed by multiple in situ techniques and density functional theory calculations. This strategy provides new insights into the development of advanced electrodes and provides the opportunity to tune electrochemical performance by tailoring the atomic composition.

Ni-rich layered oxides are one of the most attractive cathode materials in high-energy-density lithium-ion batteries, their degradation mechanisms are still not completely elucidated. Herein, we report a strong dependence of degradation pathways on the long-range cationic disordering of Co-free Ni-rich Li1-m(Ni0.94Al0.06)1+mO2 (NA). Interestingly, a disordered layered phase with lattice mismatch can be easily formed in the near-surface region of NA particles with very low cation disorder (NA-LCD, m ≤ 0.06) over electrochemical cycling, while the layered structure is basically maintained in the core of particles forming a "core-shell" structure. Such surface reconstruction triggers a rapid capacity decay during the first 100 cycles between 2.7 and 4.3 V at 1 C or 3 C. On the contrary, the local lattice distortions are gradually accumulated throughout the whole NA particles with higher degrees of cation disorder (NA-HCD, 0.06 ≤ m ≤ 0.15) that lead to a slow capacity decay upon cycling.

As contemporary battery applications such as electric vehicles demand higher energy densities, layered LiNiO2 (LNO) could contribute as the end-member of the LiNi1-x-yCoxMnyO2 (NCM) family with the highest extractable specific...

ACS materials letters 4(2), 418 - 423 (2022). doi:10.1021/acsmaterialslett.1c00817, High-entropy ceramics are attracting large interest because of their unique materials properties. Nevertheless, the effect of entropy on the lithium transport remains largely elusive. Here, we report, for the first time, about medium- and high-entropy polyanionic lithium superionic conductors crystallizing in the F–43m space group and adopting the so-called argyrodite structure. The Li6PS5[Cl0.33Br0.33I0.33], Li6P[S2.5Se2.5][Cl0.33Br0.33I0.33], and Li6.5[Ge0.5P0.5][S2.5Se2.5][Cl0.33Br0.33I0.33] materials were structurally characterized using complementary synchrotron and neutron scattering techniques in combination with 31P magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. We show that, in contrast to other high-entropy ceramics, an unequal distribution of elements over the respective crystallographic sites occurs in these materials. Using electrochemical impedance spectroscopy (EIS) and 7Li pulsed field gradient (PFG) NMR spectroscopy, we demonstrate that introducing entropy (compositional disorder) marginally affects the room-temperature ionic conductivity (∼10–3 S cm–1) but instead lowers the activation energy for conduction to 0.22 eV. Our results emphasize the possibility of increasing entropy in polyanionic materials, thereby opening up compositional space for the search of Li-ion conductors with unprecedented properties., Published by ACS Publications, Washington, DC

Silicon carbide derived from rice hull ash reveals, on long-term cycling, capacity increases to >900 mA h g−1 without significant volume changes. Lithiation mechanisms and the extraordinary capacity increment origins were assessed in detail.

This work reports on the structural, electrical and electrochemical properties of Zn doped LiNi0.5-xZnxMn1.5O4 (x = 0.0, 0.05, 0.1 and 0.2) porous microspheres cathode materials obtained by a hydrothermal route followed by low-temperature annealing. Structural properties are investigated by X-ray diffraction (XRD), nuclear magnetic resonance (NMR) spectroscopy; scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman, and Fourier transform infrared (FTIR) spectroscopy. The XRD patterns and NMR studies further demonstrate the successful incorporation of Zn into the spinel structure. SEM reveals morphology with porous spheres with a size range of 0.2 μm – 1 μm. Temperature dependent electrical conductivity was measured by impedance spectroscopy. The activation energies of total conductivity are determined as 0.41, 0.41, 0.47, and 0.48 eV for x = 0, 0.05, 0.1, and 0.2, respectively. Influence of Zn doping on the grain, grain boundary and total conductivities of LiNi0.5-xZnxMn1.5O4 were analyzed through brick-layer model. The grain conductivity increases with Zn content, whereas the total conductivity increases till x = 0.1. Overall, electrical properties of LiNi0.5-xZnxMn1.5O4 are governed by grain boundary conduction. Increasing the Zn content up to x = 0.1 in LiNi0.5-xZnxMn1.5O4 leads to an increment in specific capacity at a 1C rate. Among them, the LiNi0.4Zn0.1Mn1.5O4 exhibits a high discharge capacity of 114 mAh g−1 at 1C with capacity retention of 91.5% after 50 cycles. We also investigated the effect of Zn doping on Li+ ion diffusivity and observed improved Li+ ion diffusion (7.4⋅10−13 cm2 s−1) for LiNi0.4Zn0.1Mn1.5O4. Based on these electrochemical studies it is proposed that this material can be utilized as a cathode in Li-ion batteries for high-power applications.

Electrochemical performance of the layered compound CrPS4 for the usage as anode material in sodium-ion batteries (SIBs) was examined and exceptional reversible long-term capacity and capacity rete...

Various nuclear magnetic resonance (NMR) methods are combined to study the structure and dynamics of Li1.5Al0.5Ti1.5(PO4)3 (LATP) samples, which were obtained from sintering at various temperatures between 650 and 900 °C. 6Li, 27Al, and 31P magic angle spinning (MAS) NMR spectra show that LATP crystallites are better defined for higher calcination temperatures. Analysis of 7Li spin-lattice relaxation and line-shape changes indicates the existence of two species of lithium ions with clearly distinguishable jump dynamics, which can be attributed to crystalline and amorphous sample regions, respectively. An increase of the sintering temperature leads to higher fractions of the fast lithium species with respect to the slow one, but hardly affects the jump dynamics in either of the phases. Specifically, the fast and slow lithium ions show jumps in the nanoseconds regime near 300 and 700 K, respectively. The activation energy of the hopping motion in the LATP crystallites amounts to ca. 0.26 eV. 7Li field-gradient diffusometry reveals that the long-range ion migration is limited by the sample regions featuring slow transport. The high spatial resolution available from the high static field gradients of our setup allows the observation of the lithium ion diffusion inside the small (D = 2 × 10−12 m2/s at room temperature.

Highly crystalline CuFeS2 containing earth-abundant and environmentally friendly elements prepared via a high-temperature synthesis exhibits an excellent electrochemical performance as an anode material in sodium-ion batteries. The initial specific capacity of 460 mAh g-1 increases to 512 mAh g-1 in the 150th cycle and then decreases to a still very high value of 444 mAh g-1 at 0.5 A g-1 in the remaining 550 cycles. Even for a large current density, a pronounced cycling stability is observed. Here, we demonstrate that combining the results of X-ray powder diffraction experiments, pair distribution function analysis, and 23Na NMR and Mossbauer spectroscopy investigations performed at different stages of discharging and charging processes allows elucidation of very complex reaction mechanisms. In the first step after uptake of 1 Na/CuFeS2, nanocrystalline NaCuFeS2 is formed as an intermediate phase, which surprisingly could be recovered during charging. On increasing the Na content, Cu+ is reduced to nanocrystalline Cu, while nanocrystalline Na2S and nanosized elemental Fe are formed in the discharged state. After charging, the main crystalline phase is NaCuFeS2. At the 150th cycle, the mechanisms clearly changed, and in the charged state, nanocrystalline CuxS phases are observed. At later stages of cycling, the mechanisms are altered again: NaF, Cu2S, and Cu7.2S4 appeared in the discharged state, while NaF and Cu5FeS4 are observed in the charged state. In contrast to a typical conversion reaction, nanocrystalline phases play the dominant role, which are responsible for the high reversible capacity and long-term stability.

The new ternary gallide MgMn

Lithium- and manganese-rich layered oxides (LMLOs, ≥ 250 mAh g

We report here extracting SiO2 as spirosiloxane [(CH3)2C(O)CH2CH(O)CH3]2Si from rice hull ash (RHA) to carefully control the SiO2 : C mole ratios, allowing direct carbothermal reduction to SiC, Si3N4, or Si2N2O without the need to add extra carbon and as a mechanism to preserve the original nanocomposite structure. We can adjust SiO2 : C ratios from 2 : 15 to 13 : 35 simply by reacting RHA with hexylene glycol (HG) with catalytic base to distillatively extract SiO2 to produce silica depleted RHA (SDRHA) with SiO2 contents of 40–65 wt% and corresponding carbon contents of 60–35 wt% with specific surface areas (SSAs) of >400 m2 g−1. On heating SDRHA40–65 at 1400–1500 °C in an Ar, N2, or N2–H2 atmosphere, XRD patterns reveal formation of SiC, Si3N4, or Si2N2O as the major phase with some residual hard carbon. SEM studies reveal mixtures of particles and whiskers in the products, which show BET specific surface areas >40 m2 g−1 after oxidative removal of excess carbon. Dilute acid and boiling water prewashing of RHA with milling eliminates typical product impurities compared to those found using conventional carbothermal reduction of agricultural wastes, which qualifies the resulting composites as components for electrochemical energy storage devices among other applications, to be reported elsewhere.

Defect perovskites, AxBO3 such as (Li3xLa2/3-x)TiO3, are attracting attention as high capacity electrodes in lithium-ion batteries. However, the mechanism enabling high lithium storage capacities has not been fully investigated. In this work, the reversible insertion and removal of lithium up to an average A-site cavity occupancy of 1.71 in the defect perovskite (Li0.18Sr0.66)(Ti0.5Nb0.5)O3 is investigated. It was shown that subtle lithium reorganization during lithiation has a significant impact on enabling high capacity. Contrary to previous studies, lithium was coordinated to triangular faces of Ti/Nb oxygen octahedra and offset from O4 windows between A-site cavities in the as-synthesised material. Upon electrochemical lithiation Li-Li repulsion redistributes of all the lithium towards the O4 window position resulting in a loss of lithium mobility. Surprisingly, the mobility is regained during over-lithiation and following multiple electrochemical cycles. It is suggested that lithium reorganisation into the center of the O4 window alleviates the Li-Li repulsion and modifies the diffusion behavior from site percolation to bond percolation. The results obtained provide valuable insight into the chemical drivers enabling higher capacities and enhanced diffusion in defect perovskites. More broadly the study delivers fundamental understanding on the non-equilibrium structural transformations occurring within electrode materials during repeated electrochemical cycles.

A combination of the solution combustion and mechanochemical syntheses (SC-MS) presents a facile, low-energy, and cost-effective method to prepare layered lithium-rich oxide (LLO) composites and co...