Search

'Anode-free' or, more fittingly, metal reservoir-free cells could drastically improve current solid-state battery technology by achieving higher energy density, improving safety and simplifying manufacturing. Various strategies have been reported so far to control the morphology of electrodeposited alkali metal films to be homogeneous and dense, but until now, the microstructure of electrodeposited alkali metal is unknown, and a suitable characterization route is yet to be identified. Here we establish a reproducible protocol for characterizing the size and orientation of metal grains in differently processed lithium and sodium samples by a combination of focused ion beam and electron backscatter diffraction. Electrodeposited films at Cu|Li 6.5 Ta 0.5 La 3 Zr 1.5 O 12 , steel|Li 6 PS 5 Cl and Al|Na 3.4 Zr 2 Si 2.4 P 0.6 O 12 interfaces were characterized. The analyses show large grain sizes (>100 µm) within these films and a preferential orientation of grain boundaries. Furthermore, metal growth and dissolution were investigated using in situ electron backscatter diffraction, showing a dynamic grain coarsening during electrodeposition and pore formation within grains during dissolution. Our methodology and results deepen the research field for the improvement of solid-state battery performance through a characterization of the alkali metal microstructure., Competing Interests: Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)

Developing solid-state batteries (SSB) with a lithium metal electrode (LME) using only one type of solid electrolyte (SE) is a significant challenge since no SE fits all the requirements imposed by both electrodes. A possible solution is using multilayer SSBs with an LME where the drawbacks of each SE are overcome by using layers of different SEs. However, research on inorganic SE 1 |SE 2 heteroionic interfaces is still quite preliminary, especially regarding oxide|sulfide heteroionic interfaces. This work reports the electrochemical investigation of the heteroionic interface between Li 6.25 Al 0.25 La 3 Zr 2 O 12 (Al-LLZO) and two representative materials for sulfide-based SEs: argyrodite-based Li 6 PS 5 Cl (LPSCl) and glass-like Li 7 P 3 S 11 (LPS711). Through in-depth temperature- and pressure-dependent impedance analyses of multilayer symmetric cells at equilibrium (i.e., no current load), the electrical properties of the heteroionic interfaces are assessed. The pressure-dependent kinetic of the Al-LLZO|LPSCl pair is interpreted with the concept of geometric constriction resistance and show that its resistance is lower than for the Al-LLZO|LPS711 pair. Furthermore, the effect of Al-LLZO surface treatment on the electrical properties of the Al-LLZO|LPSCl heteroionic interface is evaluated. Such investigation shows that the value of the interface activation energy decreases when the Al-LLZO surface is heat treated, revealing a significant influence of the carbonate/hydroxide passivation layer on the heteroionic interface. Additionally, by cycling the symmetric cell for 900 h at 1.0 mAh·cm -2 , it is revealed that the Al-LLZO|LPSCl interface has a lower impedance increase than the Al-LLZO|LPS711 interface, especially if the Al-LLZO is heat treated. With this work, we highlight that the oxide|argyrodite combination can be a promising candidate for multilayer SSBs with an LME. However, we show that an optimized LLZO surface treatment and chemical analysis of the interface are recommended for future research.

Understanding Li-ion transport is key for the rational design of superionic solid electrolytes with exceptional ionic conductivities. LiNbOCl 4 is reported to be one of the most highly conducting materials in the recently realized new class of soft oxyhalide solid electrolytes, exhibiting an ionic conductivity of ∼11 mS·cm -1 . Here, we apply X-ray/neutron diffraction and pair distribution function analysis─coupled with density functional theory/ab initio molecular dynamics (AIMD)─to determine a structural model that provides a rationale for the high conductivity that we observe experimentally in this nanocrystalline solid. We show that it arises from unusually high framework flexibility at room temperature. This is due to isolated 1-D [NbOCl 4 ] - anionic chains that exhibit energetically favorable orientational disorder that is─in turn─correlated to multiple, disordered, and equi-energetic Li + sites in the lattice. As the Li ions sample the 3-D energy landscape with a fast predicted diffusion coefficient of 5.1 × 10 -7 cm 2 /s at room temperature (σ i calc = 17.4 mS·cm -1 ), the inorganic polymer chains can reorient or vice versa. The activation energy barrier for Li migration through the frustrated energy landscape is especially reduced by the elastic nature of the NbO 2 Cl 4 octahedra evident from very widely dispersed Cl-Nb-Cl bond angles in AIMD simulations at 300 K. The phonon spectra are predominantly influenced by Cl vibrations in the low energy range, and there is a strong overlap between the framework (Cl, Nb) and Li partial density of states in the region between 1.2 and 4.0 THz. The framework flexibility is also reflected in a relatively low bulk modulus of 22.7 GPa. Our findings pave the way for the investigation of future "flex-ion" inorganic solids and open up a new direction for the design of high-conductivity, soft solid electrolytes for all-solid-state batteries.

Conventional Li-S batteries rely on liquid electrolytes based on LiNO 3 /DOL/DME mixtures that produce a quasistable interface with the lithium anode. Electron pair donor (EPD) solvents, also known as high donor number solvents, provide much higher polysulfide solubility and close-to-ideal sulfur utilization, making them solvents of choice for lean electrolyte Li-S cells. However, their instability to reduction requires incorporation of an ion-conductive membrane that is stable with Li-such as garnet LLZO and also stable with sulfur/polysulfides. We report that even trace amounts of LiOH on a LLTZO surface trigger a complex reaction with sulfur dissolved in typical EPD solvents (i.e., N , N -dimethylacetamide, DMA) to produce a highly resistive impedance layer that quickly grows with time from 1000 to 10,000 Ω cm 2 over a few hours, thus impeding Li + transport across the interface. Decorating the LLZO with protective phosphate groups to produce a modified surface provides a very low charge-transfer resistance of 40 Ω cm 2 that is maintained over time and inhibits the reaction of LiOH and dissolved sulfur. Hybrid liquid-solid electrolyte cells constructed on this concept result in a high sulfur utilization of 1400 mAh g -1 which is 85% of theoretical and remains constant over cycling even with conventional, unoptimized carbon/sulfur cathodes.

We report a new sodium fast-ion conductor, Na 3 B 5 S 9 , that exhibits a high Na ion total conductivity of 0.80 mS cm -1 (sintered pellet; cold-pressed pellet=0.21 mS cm -1 ). The structure consists of corner-sharing B 10 S 20 supertetrahedral clusters, which create a framework that supports 3D Na ion diffusion channels. The Na ions are well-distributed in the channels and form a disordered sublattice spanning five Na crystallographic sites. The combination of structural elucidation via single crystal X-ray diffraction and powder synchrotron X-ray diffraction at variable temperatures, solid-state nuclear magnetic resonance spectra and ab initio molecular dynamics simulations reveal high Na-ion mobility (predicted conductivity: 0.96 mS cm -1 ) and the nature of the 3D diffusion pathways. Notably, the Na ion sublattice orders at low temperatures, resulting in isolated Na polyhedra and thus much lower ionic conductivity. This highlights the importance of a disordered Na ion sublattice-and existence of well-connected Na ion migration pathways formed via face-sharing polyhedra-in dictating Na ion diffusion., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Two major challenges hinder the advance of aqueous zinc metal batteries for sustainable stationary storage: (1) achieving predominant Zn-ion (de)intercalation at the oxide cathode by suppressing adventitious proton co-intercalation and dissolution, and (2) simultaneously overcoming Zn dendrite growth at the anode that triggers parasitic electrolyte reactions. Here, we reveal the competition between Zn 2+ vs proton intercalation chemistry of a typical oxide cathode using ex-situ/operando techniques, and alleviate side reactions by developing a cost-effective and non-flammable hybrid eutectic electrolyte. A fully hydrated Zn 2+ solvation structure facilitates fast charge transfer at the solid/electrolyte interface, enabling dendrite-free Zn plating/stripping with a remarkably high average coulombic efficiency of 99.8% at commercially relevant areal capacities of 4 mAh cm -2 and function up to 1600 h at 8 mAh cm -2 . By concurrently stabilizing Zn redox at both electrodes, we achieve a new benchmark in Zn-ion battery performance of 4 mAh cm -2 anode-free cells that retain 85% capacity over 100 cycles at 25 °C. Using this eutectic-design electrolyte, Zn | |Iodine full cells are further realized with 86% capacity retention over 2500 cycles. The approach represents a new avenue for long-duration energy storage., (© 2023. The Author(s).)

Lithium argyrodite-type electrolytes are regarded as promising electrolytes due to their high ionic conductivity and good processability. Chemical modifications to increase ionic conductivity have already been demonstrated, but the influence of these modifications on interfacial stability remains so far unknown. In this work, we study Li 6 PS 5 Cl and Li 5.5 PS 4.5 Cl 1.5 to investigate the influence of halogenation on the electrochemical decomposition of the solid electrolyte and the chemical degradation mechanism at the cathode interface in depth. Electrochemical measurements, gas analysis and time-of-flight secondary ion mass spectrometry indicate that the Li 5.5 PS 4.5 Cl 1.5 shows pronounced electrochemical decomposition at lower potentials. The chemical reaction at higher voltages leads to more gaseous degradation products, but a lower fraction of solid oxygenated phosphorous and sulfur species. This in turn leads to a decreased interfacial resistance and thus a higher cell performance., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The search for new solid electrolyte materials and an understanding of fast-ion conductivity are crucial for the development of safe and high-power all-solid-state battery technology. Herein, we present the synthesis, structure, and properties of a crystalline lithium-ion conductor, Li 3.3 Al 0.15 P 0.85 S 4 (i.e., Li 9.9 Al 0.45 P 2.55 S 12 ), found in the compositional range Li 3+2 x P 1- x Al x S 4 ( x = 0.15, 0.20, and 0.33). 31 P magic-angle spinning nuclear magnetic resonance (MAS-NMR) aided in identifying the successful introduction of Al into the lattice. At high values of x (>0.15), crystalline Li 5 AlS 4 and a glassy amorphous component exsolve to yield a multiphase mixture. The crystal structure of Li 3.3 Al 0.15 P 0.85 S 4 was elucidated by single-crystal X-ray diffraction and powder neutron diffraction, demonstrating that it belongs to the thio-LISICON family with the Pnma space group, a = 12.9572(13) Å, b = 8.0861(8) Å, c = 6.1466(6) Å, and V = 644.00(11) Å 3 . The Li + -ion conductivity and diffusivity in this bulk material (which contains about 10 wt % of an amorphous phase, as prepared) were studied by electrochemical impedance spectroscopy and 7 Li pulsed-field gradient nuclear magnetic resonance spectroscopy (PFG-NMR). The total ionic conductivity of Li 3.3 Al 0.15 P 0.85 S 4 is 0.22(2) mS·cm -1 at room temperature with an activation energy of 0.30(1) eV. A two-component analysis method based on the Kärger equations was developed to analyze the diffusive exchange between the bulk and amorphous phases of Li 3.3 Al 0.15 P 0.85 S 4 detected via the PFG-NMR signal attenuation curves. This approach was employed to quantitatively compare different sample morphologies (glass powder, crystalline powder, and crystalline pellets of Li 3.3 Al 0.15 P 0.85 S 4 ) and assess the influence of the macroscopic state on microscopic ion transport, as supported by NMR relaxation measurements.

Although batteries fitted with a metal negative electrode are attractive for their higher energy density and lower complexity, the latter making them more easily recyclable, the threat of cell shorting by dendrites has stalled deployment of the technology 1,2 . Here we disclose a bidirectional, rapidly charging aluminium-chalcogen battery operating with a molten-salt electrolyte composed of NaCl-KCl-AlCl 3 . Formulated with high levels of AlCl 3 , these chloroaluminate melts contain catenated Al n Cl 3n+1 - species, for example, Al 2 Cl 7 - , Al 3 Cl 10 - and Al 4 Cl 13 - , which with their Al-Cl-Al linkages confer facile Al 3+ desolvation kinetics resulting in high faradaic exchange currents, to form the foundation for high-rate charging of the battery. This chemistry is distinguished from other aluminium batteries in the choice of a positive elemental-chalcogen electrode as opposed to various low-capacity compound formulations 3-6 , and in the choice of a molten-salt electrolyte as opposed to room-temperature ionic liquids that induce high polarization 7-12 . We show that the multi-step conversion pathway between aluminium and chalcogen allows rapid charging at up to 200C, and the battery endures hundreds of cycles at very high charging rates without aluminium dendrite formation. Importantly for scalability, the cell-level cost of the aluminium-sulfur battery is projected to be less than one-sixth that of current lithium-ion technologies. Composed of earth-abundant elements that can be ethically sourced and operated at moderately elevated temperatures just above the boiling point of water, this chemistry has all the requisites of a low-cost, rechargeable, fire-resistant, recyclable battery., (© 2022. The Author(s), under exclusive licence to Springer Nature Limited.)