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Li 6 PS 5 Cl has attracted significant attention due to its high Li-ion conductivity and processability, facilitating large-scale solid-state battery applications. However, when paired with high-voltage cathodes, it experiences adverse side reactions. Li 3 InCl 6 (LIC), known for its higher stability at high voltages and moderate Li-ion conductivity, is considered a catholyte to address the limitations of Li 6 PS 5 Cl. To extend the stability of Li 6 PS 5 Cl toward LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA), we applied nanocrystalline LIC as a 180 nm-thick protective coating in a core-shell-like fashion (LIC@NCA) via mechanofusion. Solid-state batteries with LIC@NCA allow an initial discharge specific capacity of 148 mA h/g at 0.1C and 80% capacity retention for 200 cycles at 0.2C with a cutoff voltage of 4.2 V (vs Li/Li + ), while cells without LIC coating suffers from low initial discharge capacity and poor retention. Using a wide spectrum of advanced characterization techniques, such as operando XRD, XPS, FIB-SEM, and TOF-SIMS, we reveal that the superior performance of solid-state batteries employing LIC@NCA is related to the suppression of detrimental interfacial reactions of NCA with Li 6 PS 5 Cl, delamination, and particle cracking compared to uncoated NCA., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

NASICON-based solid electrolytes with exceptionally high Na-ion conductivities are considered to enable future all solid-state Na-ion battery technologies. Despite 40 years of research the interrelation between crystal structure and Na-ion conduction is still controversially discussed and far from being fully understood. In this study, microcontact impedance spectroscopy combined with single crystal X-ray diffraction, and differential scanning calorimetry is applied to tackle the question how bulk Na-ion conductivity σ bulk of sub-mm-sized flux grown Na 3 Sc 2 (PO 4 ) 3 (NSP) single crystals is influenced by supposed phase changes (α, β, and γ phase) discussed in literature. Although we found a smooth structural change at around 140 °C, which we assign to the β → γ phase transition, our conductivity data follow a single Arrhenius law from room temperature (RT) up to 220 °C. Obviously, the structural change, being mainly related to decreasing Na-ion ordering with increasing temperature, does not cause any jumps in Na-ion conductivity or any discontinuities in activation energies E a . Bulk ion dynamics in NSP have so far rarely been documented; here, under ambient conditions, σ bulk turned out to be as high as 3 × 10 -4 S cm -1  at RT ( E a, bulk = 0.39 eV) when directly measured with microcontacts for individual small single crystals., Competing Interests: The authors declare no competing financial interest.

Fast Li-ion-conducting Li oxide garnets receive a great deal of attention as they are suitable candidates for solid-state Li electrolytes. It was recently shown that Ga-stabilized Li 7 La 3 Zr 2 O 12 crystallizes in the acentric cubic space group I 4̅3 d . This structure can be derived by a symmetry reduction of the garnet-type Ia 3̅ d structure, which is the most commonly found space group of Li oxide garnets and garnets in general. In this study, single-crystal X-ray diffraction confirms the presence of space group I 4̅3 d also for Li 7-3 x Fe x La 3 Zr 2 O 12 . The crystal structure was characterized by X-ray powder diffraction, single-crystal X-ray diffraction, neutron powder diffraction, and Mößbauer spectroscopy. The crystal-chemical behavior of Fe 3+ in Li 7 La 3 Zr 2 O 12 is very similar to that of Ga 3+ . The symmetry reduction seems to be initiated by the ordering of Fe 3+ onto the tetrahedral Li1 (12 a ) site of space group I 4̅3 d . Electrochemical impedance spectroscopy measurements showed a Li-ion bulk conductivity of up to 1.38 × 10 -3 S cm -1 at room temperature, which is among the highest values reported for this group of materials.

Several "Beyond Li-Ion Battery" concepts such as all solid-state batteries and hybrid liquid/solid systems envision the use of a solid electrolyte to protect Li-metal anodes. These configurations are very attractive due to the possibility of exceptionally high energy densities and high (dis)charge rates, but they are far from being realized practically due to a number of issues including high interfacial resistance and difficulties associated with fabrication. One of the most promising solid electrolyte systems for these applications is Al or Ga stabilized Li 7 La 3 Zr 2 O 12 (LLZO) based on high ionic conductivities and apparent stability against reduction by Li metal. Nevertheless, the fabrication of dense LLZO membranes with high ionic conductivity and low interfacial resistances remains challenging; it definitely requires a better understanding of the structural and electrochemical properties. In this study, the phase transition from garnet ( Ia 3̅ d , No. 230) to "non-garnet" ( I 4̅3 d , No. 220) space group as a function of composition and the different sintering behavior of Ga and Al stabilized LLZO are identified as important factors in determining the electrochemical properties. The phase transition was located at an Al:Ga substitution ratio of 0.05:0.15 and is accompanied by a significant lowering of the activation energy for Li-ion transport to 0.26 eV. The phase transition combined with microstructural changes concomitant with an increase of the Ga/Al ratio continuously improves the Li-ion conductivity from 2.6 × 10 -4 S cm -1 to 1.2 × 10 -3 S cm -1 , which is close to the calculated maximum for garnet-type materials. The increase in Ga content is also associated with better densification and smaller grains and is accompanied by a change in the area specific resistance (ASR) from 78 to 24 Ω cm 2 , the lowest reported value for LLZO so far. These results illustrate that understanding the structure-properties relationships in this class of materials allows practical obstacles to its utilization to be readily overcome.

Li-oxide garnets such as Li 7 La 3 Zr 2 O 12 (LLZO) are among the most promising candidates for solid-state electrolytes to be used in next-generation Li-ion batteries. The garnet-structured cubic modification of LLZO, showing space group Ia -3 d , has to be stabilized with supervalent cations. LLZO stabilized with Ga 3+ shows superior properties compared to LLZO stabilized with similar cations; however, the reason for this behavior is still unknown. In this study, a comprehensive structural characterization of Ga-stabilized LLZO is performed by means of single-crystal X-ray diffraction. Coarse-grained samples with crystal sizes of several hundred micrometers are obtained by solid-state reaction. Single-crystal X-ray diffraction results show that Li 7-3 x Ga x La 3 Zr 2 O 12 with x > 0.07 crystallizes in the acentric cubic space group I -43 d . This is the first definite record of this cubic modification for LLZO materials and might explain the superior electrochemical performance of Ga-stabilized LLZO compared to its Al-stabilized counterpart. The phase transition seems to be caused by the site preference of Ga 3+ . 7 Li NMR spectroscopy indicates an additional Li-ion diffusion process for LLZO with space group I -43 d compared to space group Ia -3 d . Despite all efforts undertaken to reveal structure-property relationships for this class of materials, this study highlights the potential for new discoveries.

We investigate theoretically the site occupancy of Al 3+ in the fast-ion-conducting cubic-garnet Li 7-3 x Al 3+ x La 3 Zr 2 O 12 ( Ia -3 d) using density functional theory. By comparing calculated and measured 27 Al NMR chemical shifts an analysis shows that Al 3+ prefers the tetrahedrally coordinated 24 d site and a distorted 4-fold coordinated 96 h site. The site energies for Al 3+ ions, which are slightly displaced from the exact crystallographic sites (i.e., 24 d and 96 h ), are similar leading to a distribution of slightly different local oxygen coordination environments. Thus, broad 27 Al NMR resonances result reflecting the distribution of different isotropic chemical shifts and quadrupole coupling constants. From an energetic point of view, there is evidence that Al 3+ could also occupy the 48 g site with its almost regular octahedral coordination sphere. Although this has been reported by neutron powder diffraction, the NMR chemical shift calculated for such an Al 3+ site has not been observed experimentally.