Fast microwave-assisted synthesis of Li-stuffed garnets and insights into Li diffusion from muon spin spectroscopy

Lithium-stuffed garnets attract huge attention due to their outstanding potential as solid-state electrolytes for lithium batteries. However, there exists a persistent challenge in the reliable synthesis of these complex functional oxides together with a lack of complete understanding of the lithium-ion diffusion mechanisms in these important materials. Addressing these issues is critical to realizing the application of garnet materials as electrolytes in all solid-state lithium-ion batteries. In this work, a cubic phase garnet of nominal composition Li6.5Al0.25La2.92Zr2O12 is synthesized through a microwave-assisted solid-state route for the first time, reducing considerably the reaction times and heating temperatures. Lithium-ion diffusion behavior is investigated by electrochemical impedance spectroscopy (EIS) and state-of-art muon spin relaxation (μSR) spectroscopy, displaying activation energies of 0.55 ± 0.03 eV and 0.19 ± 0.01 eV respectively. This difference arises from the high inter-grain resistance, which contributes to the total resistance in EIS measurements. In contrast, μSR acts as a local probe providing insights on the order of the lattice, giving an estimated value of 4.62 × 10−11 cm2 s−1 for the lithium diffusion coefficient. These results demonstrate the potential of this lithium-stuffed garnet as a solid-state electrolyte for all-solid state lithium-ion batteries, an area of growing interest in the energy storage community

The Role of the Reducible Dopant in Solid Electrolyte-Lithium Metal Interfaces

Garnet solid electrolytes, of the form Li7La3Zr2O12 (LLZO), remain an enticing prospect for solid-state batteries owing to their chemical and electrochemical stability in contact with metallic lithium. Dopants, often employed to stabilize the fast ion conducting cubic garnet phase, typically have no effect on the chemical stability of LLZO in contact with Li metal but have been found recently to impact the properties of the Li/garnet interface. For dopants more “reducible” than Zr (e.g., Nb and Ti), contradictory reports of either raised or reduced Li/garnet interfacial resistances have been attributed to the dopant. Here, we investigate the Li/LLZO interface in W-doped Li7La3Zr2O12 (LLZWO) to determine the influence of a “reducible” dopant on the electrochemical properties of the Li/garnet interface. Single-phase LLZWO is synthesized by a new sol–gel approach and densified by spark plasma sintering. Interrogating the resulting Li/LLZWO interface/interphase by impedance, muon spin relaxation and X-ray absorption spectroscopies uncover the significant impact of surface lithiation on electrochemical performance. Upon initial contact, an interfacial reaction occurs between LLZWO and Li metal, leading to the reduction of surface W6+ centers and an initial reduction of the Li/garnet interfacial resistance. Propagation of this surface reaction, driven by the high mobility of Li+ ions through the grain surfaces, thickens the resistive interphases throughout the material and impedes Li+ ion transport between the grains. The resulting high resistance accumulating in the system impedes cycling at high current densities. These insights shed light on the nature of lithiated interfaces in garnet solid electrolytes containing a reducible dopant where high Li+ ion mobility and the reducible nature of the dopant can significantly affect electrochemical performance

Synthesis of H_xLi_1-xLaTiO₄ from quantitative solid-state reactions at room temperature

The layered perovskite HLaTiO4 reacts stoichiometrically with LiOH·H2O at room temperature to give targeted compositions in the series HxLi1-xLaTiO4. Remarkably, the Li+ and H+ ions are quantitatively exchanged in the solid state and this allows stoichiometric control of ion exchange for the first time in this important series of compounds

A family of nitrogen enriched metal organic frameworks with CCS potential

Materials with enhanced carbon capture capacities are required to advance post-combustive amelioration methods; these are necessary to reduce atmospheric carbon dioxide emissions and the associated rate of global temperature increase. Current technologies tend to be very energy intensive processes with high levels of waste produced; this work presents three new metal organic framework materials with embedded Lewis base functionalities, imparted by the nitrogen-rich ligand, demonstrating an affinity for carbon dioxide. Thus , we report the synthesis and characterization of a series of metal organic framework materials using a range of metal centers (Co, Ni, and Zn) with the 1,4-bis(pyridin-4-yl)-1,2,4,5-tetrazine organic linker, in the presence of ammonium hexafluorosilicate. Three distinct crystal structures are reported for Zn-pytz(hydro) 1D chains, and Ni-pytz and Co-pytz isostructural 1D Ladders. Co-pytz shows an uptake of 47.53mg CO2/g of sorbent, which equates to 15 wt % based on available nitrogen sites within the structure, demonstrating potential for carbon capture applications

Motherhood, Moral Authority and the Charismatic Matriarch in the Aftermath of Lethal Violence

Images of maternal suffering are an evocative and powerful means of communication in a world where the private grief of victims has increasingly become subject to commodification and public consumption. This article looks at the influence of bereaved mothers as symbols of respect, peace and dignity in the aftermath of violence, and as a result their persuasive presence in family activism. Drawing upon two case studies, this article explores the importance of victims’ stories in public life and, in particular, the presence of the charismatic matriarch in creating communities of solidarity, raising awareness of harms that have previously gone unheard and prompting policy change. It considers the ‘canonical’ story of the mother in public life and concludes by arguing that more attention should be paid to victims’ stories and their influence on policy-making, politics and eventually in becoming public grievances

Unexpected selective gas adsorption on a 'non-porous' metal organic framework

A metal organic framework Cu(tpt)BF 4· 3 4 H 2O was synthesized as a potential carbon capture material, with the aim being to exploit the Lewis base interaction of the incorporated ligand functionalities with acidic gas. The material displays high thermal stability but an exceptionally low surface area; however, this contrasts starkly with its ability to capture carbon dioxide, demonstrating significant activated diffusion within the framework. The full characterization of the material shows a robust structure, where the CO 2 sorption is 120% greater than current industrial methods using liquid amine solutions; the thermal energy required for sorbent regeneration is reduced by 65%, indicating the true industrial potential of the synthesized material

The role of the reducible dopant in solid electrolyte–lithium metal interfaces

Garnet solid electrolytes, of the form Li7La3Zr2O12 (LLZO), remain an enticing prospect for solid-state batteries owing to their chemical and electrochemical stability in contact with metallic lithium. Dopants, often employed to stabilize the fast ion conducting cubic garnet phase, typically have no effect on the chemical stability of LLZO in contact with Li metal but have been found recently to impact the properties of the Li/garnet interface. For dopants more "reducible"than Zr (e.g., Nb and Ti), contradictory reports of either raised or reduced Li/garnet interfacial resistances have been attributed to the dopant. Here, we investigate the Li/LLZO interface in W-doped Li7La3Zr2O12 (LLZWO) to determine the influence of a "reducible"dopant on the electrochemical properties of the Li/garnet interface. Single-phase LLZWO is synthesized by a new sol-gel approach and densified by spark plasma sintering. Interrogating the resulting Li/LLZWO interface/interphase by impedance, muon spin relaxation and X-ray absorption spectroscopies uncover the significant impact of surface lithiation on electrochemical performance. Upon initial contact, an interfacial reaction occurs between LLZWO and Li metal, leading to the reduction of surface W6+ centers and an initial reduction of the Li/garnet interfacial resistance. Propagation of this surface reaction, driven by the high mobility of Li+ ions through the grain surfaces, thickens the resistive interphases throughout the material and impedes Li+ ion transport between the grains. The resulting high resistance accumulating in the system impedes cycling at high current densities. These insights shed light on the nature of lithiated interfaces in garnet solid electrolytes containing a reducible dopant where high Li+ ion mobility and the reducible nature of the dopant can significantly affect electrochemical performance

Complex magnetic ordering behavior in the frustrated perovskite Ba2MnMoO6

New and exotic ground states of magnetic materials are highly sought after and are extensively studied for the insights they provide into the thermodynamics of disorder and fundamental magnetic interactions. By controlling the crystal structure of an appropriate magnetic lattice, it is possible to cause the strong magnetic exchange interactions to sum to zero and so be frustrated. Due to the presence of this frustration, the lowest energy configuration that results may be crucially dependent on the tiniest of energy differences between a multitude of states that have (almost) the same energy. The keen interest in these materials arises from the fact that these finely balanced systems offer a way of probing classical or quantum mechanical interactions that are of fundamental importance but are too weak to be observed in non-frustrated systems. Here, we combine local and crystallographic probes of the cation-ordered double perovskite Ba2MnMoO6 that contains a face-centered cubic lattice of S = 5/2 Mn2+ cations. Neutron diffraction measurements below 9.27(7) K indicate that a fourfold degenerate non-collinear antiferromagnetic state exists with almost complete ordering of the Mn2+ spins. Muon spin relaxation measurements provide a local probe of the magnetic fields inside this material over the t1/2 = 2.2 µs lifetime of a muon, indicating a slightly lower Néel transition temperature of 7.9(1) K. The dc susceptibility data do not show the loss of magnetization that should accompany the onset of the antiferromagnetic order; they indicate that a strongly antiferromagnetically coupled paramagnetic state [θ = −73(3) K] persists down to 4 K, at which temperature a weak transition occurs. The behavior of this material differs considerably from the closely related compositions Ba2MnMO6 (M = W, Te), which show collinear ordering arrangements and well defined antiferromagnetic transitions in the bulk susceptibility. This suggests that the Mo6+ cation leads to a fine balance between the nearest and next-nearest neighbor superexchange in these frustrated double perovskite structures

Phase behaviour in the LiBH4-LiBr system and structure of the anion-stabilised fast ionic, high temperature phase

The fast ionic, high temperature (HT) phase of LiBH4 can be stabilised by Br¯ substitution. Lithium borohydride bromide compounds, Li(BH4)1-xBrx have been synthesized mechanochemically, with and without thermal treatment and the resulting phase behaviour determined as a function of composition. Single phase materials exist for 0.29 ≤ x ≤ 0.50 with conductivity two orders of magnitude higher than LiBH4 at 313 K. Powder neutron diffraction has been used to resolve the details of the crystal structure of one such compound. These demonstrate that 7Li(11BD4)2/3Br1/3 retains the HT structure (hexagonal space group P63mc, a ≈ 4.2 Å, c ≈ 6.7 Å) from 293-573 K. The borohydride bromide exhibits considerable static and dynamic disorder, the latter invoking complex rotational motion of the (BH4)¯ anions

In situ fracture behavior of single crystal LiNi0.8Mn0.1Co0.1O2 (NMC811)

Single crystal particle morphologies have become highly desirable for next generation cathode materials, removing grain boundary fracture and thereby reducing the surface area exposed to electrolyte. The intrinsic mechanical behavior of single crystal layered oxides, however, is poorly understood. Here, faceted single crystal LiNi0.8Mn0.1Co0.1O2 (NMC811) particles are compressed in situ in a scanning electron microscope (SEM), to determine mechanical deformation mechanisms as a function of crystallographic orientation. In situ, the dynamical deformation sequence observed is initial cracking at the compression zone, followed by accelerated transparticle crack propagation and concurrent (0001) slip band formation. The greatest loads and contact pressure at fracture, non-basal cracking, and activation of multiple basal slip systems in larger (>3 μm) particles, occur for compression normal to the (0001) layered structure. Loading on {012} preferentially activates basal fracture and slip at lower loads. Regardless of particle orientation, non-basal slip systems are not observed, and non-basal cracking and particle rotation occur during compression to compensate for this inability to activate dislocations in 3-dimensions. Crystallographic dependent mechanical behaviour of single crystal NMC811 means that particle texture in cathodes should be monitored, and sources of localised surface stress in cathodes, e. g. particle-to-particle asperity contacts during electrode manufacture, should be minimised