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The composition space between MnO2, NaFeO2, and Na[Ni1/2Mn1/2]O2 has been explored with the goal of identifying Earth-abundant single-phase P2 cathode materials. This has led to the identification of two compounds, P2-Na2/3[Ni1/3−y/2Mn2/3−y/2Fey]O2 (y = 1/6, 1/3) which exhibit state of the art specific energies. These materials were further evaluated through galvanostatic cycling and X-ray absorption spectroscopy. [ABSTRACT FROM AUTHOR]

Organically synthesized porous carbon (OSPC) is a subclass of conjugated microporous polymer materials that have shown potential applications as anodes in ion batteries. However, a challenging, low-yielding, multistep synthetic route (the A method) has hindered further exploration of this exciting family. Here, OSPC-1 has been synthesized via an alternative, efficient one-pot method from commercially available reagents (the B method), hereafter referred to as OSPC-1b in contrast to OSPC-1a, where it is synthesized via the A method. Characterization revealed the same polymer structure and the highest surface area to date of an OSPC (or OSPC analogue) family member for OSPC-1b with 909 m 2 g -1 . OSPC-1b was tested as an anode for Li-ion batteries, demonstrating the same high capacity, fast charging, resistance to degradation, and inhibition of the formation of dangerous lithium dendrites as OSPC-1a. Furthermore, the electrochemical properties of OSPC-0 were evaluated for the first time, agreeing with previously predicted values, giving scope for the design and targeting of specific properties.

Halide solid electrolytes do not currently display ionic conductivities suitable for high-power all-solid-state batteries. We explore the model system A 2 ZrCl 6 (A = Li, Na, Cu, Ag) to understand the fundamental role that A-site chemistry plays on fast ion transport. Having synthesised the previously unknown Ag 2 ZrCl 6 we reveal high room temperature ionic conductivities in Cu 2 ZrCl 6 and Ag 2 ZrCl 6 of 1 × 10 -2 and 4 × 10 -3 S cm -1 , respectively. We introduce the concept that there are inherent limits to ionic conductivity in solids, where the energy and number of transition states play pivotal roles. Transport that involves multiple coordination changes along the pathway suffer from an intrinsic minimum activation energy. At certain lattice sizes, the energies of different coordinations can become equivalent, leading to lower barriers when a pathway involves a single coordination change. Our models provide a deeper understanding into the optimisation and design criteria for halide superionic conductors., (© 2024. The Author(s).)

An understanding of the structural properties that allow for optimal cathode performance, and their origin, is necessary for devising advanced cathode design strategies and accelerating the commercialization of next-generation cathodes. High-voltage, Fe- and Mg-substituted LiNi 0.5 Mn 1.5 O 4 cathodes offer a low-cost, cobalt-free, yet energy-dense alternative to commercial cathodes. In this work, the effect of substitution on several important structure properties is explored, including Ni/Mn ordering, charge distribution, and extrinsic defects. In the cation-disordered samples studied, a correlation is observed between increased Fe/Mg substitution, Li-site defects, and Li-rich impurity phase formation-the concentrations of which are greater for Mg-substituted samples. This is attributed to the lower formation energy of Mg Li defects when compared to Fe Li defects. Li-site defect-induced impurity phases consequently alter the charge distribution of the system, resulting in increased [Mn 3+ ] with Fe/Mg substitution. In addition to impurity phases, other charge compensators are also investigated to explain the origin of Mn 3+ (extrinsic defects, [Ni 3+ ], oxygen vacancies and intrinsic off-stoichiometry), although their effects are found to be negligible., (© 2024 The Authors. Advanced Materials published by Wiley‐VCH GmbH.)

Hard carbon is a promising negative electrode material for rechargeable sodium-ion batteries due to the ready availability of their precursors and high reversible charge storage. The reaction mechanisms that drive the sodiation properties in hard carbons and subsequent electrochemical performance are strictly linked to the characteristic slope and plateau regions observed in the voltage profile of these materials. This work shows that electron paramagnetic resonance (EPR) spectroscopy is a powerful and fast diagnostic tool to predict the extent of the charge stored in the slope and plateau regions during galvanostatic tests in hard carbon materials. EPR lineshape simulation and temperature-dependent measurements help to separate the nature of the spins in mechanochemically modified hard carbon materials synthesised at different temperatures. This proves relationships between structure modification and electrochemical signatures in the galvanostatic curves to obtain information on their sodium storage mechanism. Furthermore, through ex situ EPR studies we study the evolution of these EPR signals at different states of charge to further elucidate the storage mechanisms in these carbons. Finally, we discuss the interrelationship between EPR spectroscopy data of the hard carbon samples studied and their corresponding charging storage mechanism., (© 2024. The Author(s).)

Layered transition metal oxide cathode materials can exhibit high energy densities in Li-ion batteries, in particular, those with high Ni contents such as LiNiO 2 . However, the stability of these Ni-rich materials often decreases with increased nickel content, leading to capacity fade and a decrease in the resulting electrochemical performance. Thin alumina coatings have the potential to improve the longevity of LiNiO 2 cathodes by providing a protective interface to stabilize the cathode surface. The structures of alumina coatings and the chemistry of the coating-cathode interface are not fully understood and remain the subject of investigation. Greater structural understanding could help to minimize excess coating, maximize conductive pathways, and maintain high capacity and rate capability while improving capacity retention. Here, solid-state nuclear magnetic resonance (NMR) spectroscopy, paired with powder X-ray diffraction and electron microscopy, is used to provide insight into the structures of the Al 2 O 3 coatings on LiNiO 2 . To do this, we performed a systematic study as a function of coating thickness and used LiCoO 2 , a diamagnetic model, and the material of interest, LiNiO 2 . 27 Al magic-angle spinning (MAS) NMR spectra acquired for thick 10 wt % coatings on LiCoO 2 and LiNiO 2 suggest that in both cases, the coatings consist of disordered four- and six-coordinate Al-O environments. However, 27 Al MAS NMR spectra acquired for thinner 0.2 wt % coatings on LiCoO 2 identify additional phases believed to be LiCo 1- x Al x O 2 and LiAlO 2 at the coating-cathode interface. 6,7 Li MAS NMR and T 1 measurements suggest that similar mixing takes place near the interface for Al 2 O 3 on LiNiO 2 . Furthermore, reproducibility studies have been undertaken to investigate the effect of the coating method on the local structure, as well as the role of the substrate.

The solid electrolyte interphase in rechargeable Li-ion batteries, its dynamics and, significantly, its nanoscale structure and composition, hold clues to high-performing and safe energy storage. Unfortunately, knowledge of solid electrolyte interphase formation is limited due to the lack of in situ nano-characterization tools for probing solid-liquid interfaces. Here, we link electrochemical atomic force microscopy, three-dimensional nano-rheology microscopy and surface force-distance spectroscopy, to study, in situ and operando, the dynamic formation of the solid electrolyte interphase starting from a few 0.1 nm thick electrical double layer to the full three-dimensional nanostructured solid electrolyte interphase on the typical graphite basal and edge planes in a Li-ion battery negative electrode. By probing the arrangement of solvent molecules and ions within the electric double layer and quantifying the three-dimensional mechanical property distribution of organic and inorganic components in the as-formed solid electrolyte interphase layer, we reveal the nanoarchitecture factors and atomistic picture of initial solid electrolyte interphase formation on graphite-based negative electrodes in strongly and weakly solvating electrolytes., (© 2023. The Author(s).)

The development of high-power anode materials for Na-ion batteries is one of the primary obstacles due to the growing demands for their use in the smart grid. Despite the appealingly low cost and non-toxicity, Na 2 Ti 3 O 7 suffers from low electrical conductivity and poor structural stability, which restricts its use in high-power applications. Viable approaches for overcoming these drawbacks reported to date are aliovalent doping and hydrogenation/hydrothermal treatments, both of which are closely intertwined with native defects. There is still a lack of knowledge, however, of the intrinsic defect chemistry of Na 2 Ti 3 O 7 , which impairs the rational design of high-power titanate anodes. Here, we report hybrid density functional theory calculations of the native defect chemistry of Na 2 Ti 3 O 7 . The defect calculations show that the insulating properties of Na 2 Ti 3 O 7 arise from the Na and O Schottky disorder that act as major charge compensators. Under high-temperature hydrogenation treatment, these Schottky pairs of Na and O vacancies become dominant defects in Na 2 Ti 3 O 7 , triggering the spontaneous partial phase transition to Na 2 Ti 6 O 13 and improving the electrical conductivity of the composite anode. Our findings provide an explanation on the interplay between intrinsic defects, structural phase transitions, and electrical conductivity, which can aid understanding of the properties of composite materials obtained from phase transitions., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Aqueous rechargeable zinc-ion batteries (AZIBs) have drawn enormous attention in stationary applications due to their high safety and low cost. However, the search for new positive electrode materials with satisfactory electrochemical performance for practical applications remains a challenge. In this work, we report a comprehensive study on the use of the vanadium tellurate (NH 4 ) 4 {(VO 2 ) 2 [Te 2 O 8 (OH) 2 ]}·2H 2 O, which is tested for the first time as a cathode material in AZIBs., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

In this work, we apply an amine-assisted silica pillaring method to create the first example of a porous Mo 2 TiC 2 MXene with nanoengineered interlayer distances. The pillared Mo 2 TiC 2 has a surface area of 202 m 2 g -1 , which is among the highest reported for any MXene, and has a variable gallery height between 0.7 and 3 nm. The expanded interlayer distance leads to significantly enhanced cycling performance for Li-ion storage, with superior capacity, rate capably and cycling stability in comparison to the non-pillared analogue. The pillared Mo 2 TiC 2 achieved a capacity over 1.7 times greater than multilayered MXene at 20 mA g -1 (≈320 mA h g -1 ) and 2.5 times higher at 1 A g -1 (≈150 mA h g -1 ). The fast-charging properties of pillared Mo 2 TiC 2 are further demonstrated by outstanding stability even at 1 A g -1 (under 8 min charge time), retaining 80% of the initial capacity after 500 cycles. Furthermore, we use a combination of spectroscopic techniques ( i.e. XPS, NMR and Raman) to show unambiguously that the charge storage mechanism of this MXene occurs by a conversion reaction through the formation of Li 2 O. This reaction increases by 2-fold the capacity beyond intercalation, and therefore, its understanding is crucial for further development of this family of materials. In addition, we also investigate for the first time the sodium storage properties of the pillared and non-pillared Mo 2 TiC 2 ., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Na 2 Ti 3 O 7 (NTO) is considered a promising anode material for Na-ion batteries due to its layered structure with an open framework and low and safe average operating voltage of 0.3 V vs. Na + /Na. However, its poor electronic conductivity needs to be addressed to make this material attractive for practical applications among other anode choices. Here, we report a safe, controllable and affordable method using urea that significantly improves the rate performance of NTO by producing surface defects such as oxygen vacancies and hydroxyl groups, and the secondary phase Na 2 Ti 6 O 13 . The enhanced electrochemical performance agrees with the higher Na + ion diffusion coefficient, higher charge carrier density and reduced bandgap observed in these samples, without the need of nanosizing and/or complex synthetic strategies. A comprehensive study using a combination of diffraction, microscopic, spectroscopic and electrochemical techniques supported by computational studies based on DFT calculations, was carried out to understand the effects of this treatment on the surface, chemistry and electronic and charge storage properties of NTO. This study underscores the benefits of using urea as a strategy for enhancing the charge storage properties of NTO and thus, unfolding the potential of this material in practical energy storage applications., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

As the only stable binary compound formed between an alkali metal and nitrogen, lithium nitride possesses remarkable properties and is a model material for energy applications involving the transport of lithium ions. Following a materials design principle drawn from broad structural analogies to hexagonal graphene and boron nitride, we demonstrate that such low dimensional structures can also be formed from an s-block element and nitrogen. Both one- and two-dimensional nanostructures of lithium nitride, Li 3 N, can be grown despite the absence of an equivalent van der Waals gap. Lithium-ion diffusion is enhanced compared to the bulk compound, yielding materials with exceptional ionic mobility. Li 3 N demonstrates the conceptual assembly of ionic inorganic nanostructures from monolayers without the requirement of a van der Waals gap. Computational studies reveal an electronic structure mediated by the number of Li-N layers, with a transition from a bulk narrow-bandgap semiconductor to a metal at the nanoscale.

MXenes are a recently discovered class of two-dimensional materials that have shown great potential as electrodes in electrochemical energy storage devices. Despite their promise in this area, MXenes can still suffer limitations in the form of restricted ion accessibility between the closely spaced multistacked MXene layers causing low capacities and poor cycle life. Pillaring, where a secondary species is inserted between layers, has been used to increase interlayer spacings in clays with great success but has had limited application in MXenes. We report a new amine-assisted pillaring methodology that successfully intercalates silica-based pillars between Ti 3 C 2 layers. Using this technique, the interlayer spacing can be controlled with the choice of amine and calcination temperature, up to a maximum of 3.2 nm, the largest interlayer spacing reported for an MXene. Another effect of the pillaring is a dramatic increase in surface area, achieving BET surface areas of 235 m 2 g -1 , a sixty-fold increase over the unpillared material and the highest reported for MXenes using an intercalation-based method. The intercalation mechanism was revealed by different characterization techniques, allowing the surface chemistry to be optimized for the pillaring process. The porous MXene was tested for Na-ion battery applications and showed superior capacity, rate capability and remarkable stability compared with those of the nonpillared materials, retaining 98.5% capacity between the 50th and 100th cycles. These results demonstrate the applicability and promise of pillaring techniques applied to MXenes providing a new approach to optimizing their properties for a range of applications, including energy storage, conversion, catalysis, and gas separations.

The search for improved energy-storage materials has revealed Li- and Na-rich intercalation compounds as promising high-capacity cathodes. They exhibit capacities in excess of what would be expected from alkali-ion removal/reinsertion and charge compensation by transition-metal (TM) ions. The additional capacity is provided through charge compensation by oxygen redox chemistry and some oxygen loss. It has been reported previously that oxygen redox occurs in O 2p orbitals that interact with alkali ions in the TM and alkali-ion layers (that is, oxygen redox occurs in compounds containing Li + -O(2p)-Li + interactions). Na 2/3 [Mg 0.28 Mn 0.72 ]O 2 exhibits an excess capacity and here we show that this is caused by oxygen redox, even though Mg 2+ resides in the TM layers rather than alkali-metal (AM) ions, which demonstrates that excess AM ions are not required to activate oxygen redox. We also show that, unlike the alkali-rich compounds, Na 2/3 [Mg 0.28 Mn 0.72 ]O 2 does not lose oxygen. The extraction of alkali ions from the alkali and TM layers in the alkali-rich compounds results in severely underbonded oxygen, which promotes oxygen loss, whereas Mg 2+ remains in Na 2/3 [Mg 0.28 Mn 0.72 ]O 2 , which stabilizes oxygen.

Conventional intercalation cathodes for lithium batteries store charge in redox reactions associated with the transition metal cations, e.g., Mn(3+/4+) in LiMn2O4, and this limits the energy storage of Li-ion batteries. Compounds such as Li[Li0.2Ni0.2Mn0.6]O2 exhibit a capacity to store charge in excess of the transition metal redox reactions. The additional capacity occurs at and above 4.5 V versus Li(+)/Li. The capacity at 4.5 V is dominated by oxidation of the O(2-) anions accounting for ∼0.43 e(-)/formula unit, with an additional 0.06 e(-)/formula unit being associated with O loss from the lattice. In contrast, the capacity above 4.5 V is mainly O loss, ∼0.08 e(-)/formula. The O redox reaction involves the formation of localized hole states on O during charge, which are located on O coordinated by (Mn(4+)/Li(+)). The results have been obtained by combining operando electrochemical mass spec on (18)O labeled Li[Li0.2Ni0.2Mn0.6]O2 with XANES, soft X-ray spectroscopy, resonant inelastic X-ray spectroscopy, and Raman spectroscopy. Finally the general features of O redox are described with discussion about the role of comparatively ionic (less covalent) 3d metal-oxygen interaction on anion redox in lithium rich cathode materials.

Lithium nitride hydride, Li₄NH, was synthesised from lithium nitride and lithium hydride over minute timescales, using microwave synthesis methods in the solid state for the first time. The structure of the microwave-synthesised powders was confirmed by powder X-ray diffraction [tetragonal space group I 4₁ /a ; a = 4.8864(1) Å, c = 9.9183(2) Å] and the nitride hydride reacts with moist air under ambient conditions to produce lithium hydroxide and subsequently lithium carbonate. Li₄NH undergoes no dehydrogenation or decomposition [under Ar (g) ] below 773 K. A tetragonal-cubic phase transition, however, occurs for the compound at ca . 770 K. The new high temperature (HT) phase adopts an anti -fluorite structure (space group Fm 3̅ m ; a = 4.9462(3) Å) with N 3- and H - ions disordered on the 4 a sites. Thermal treatment of Li₄NH under nitrogen yields a stoichiometric mixture of lithium nitride and lithium imide (Li₃N and Li₂NH respectively).