Forced Disorder in the Solid Solution Li3P-Li2S: A New Class of Fully Reduced Solid Electrolytes for Lithium Metal Anodes

Stable Oxyhalide-Nitride Fast Ionic Conductors for All-Solid-State Li Metal Batteries

Rechargeable all-solid-state lithium metal batteries (ASSLMBs) utilizing inorganic solid-state electrolytes (SSEs) are promising for electric vehicles and large-scale grid energy storage. However, the Li dendrite growth in SSEs still constrains the practical utility of ASSLMBs. To achieve a high dendrite-suppression capability, SSEs must be chemically stable with Li, possess fast Li transfer kinetics, and exhibit high interface energy. Herein, a class of low-cost, eco-friendly, and sustainable oxyhalide-nitride solid electrolytes (ONSEs), denoted as LixNyIz-qLiOH (where x = 3y + z, 0 ≤ q ≤ 0.75), is designed to fulfill all the requirements. As-prepared ONSEs demonstrate chemically stable against Li and high interface energy (>43.08 meV Å-2), effectively restraining Li dendrite growth and the self-degradation at electrode interfaces. Furthermore, improved thermodynamic oxidation stability of ONSEs (>3 V vs Li+/Li, 0.45 V for pure Li3N), arising from the increased ionicity of Li─N bonds, contributes to the stability in ASSLMBs. As a proof-of-concept, the optimized ONSEs possess high ionic conductivity of 0.52 mS cm-1 and achieve long-term cycling of Li||Li symmetric cell for over 500 h. When coupled with the Li3InCl6 SSE for high-voltage cathodes, the bilayer oxyhalide-nitride/Li3InCl6 electrolyte imparts 90% capacity retention over 500 cycles for Li||1 mAh cm-2 LiCoO2 cells.

Polyoxometalate Li3 PW12 O40 and Li3 PMo12 O40 Electrolytes for High-energy All-solid-state Lithium Batteries

Solid-state lithium (Li) batteries promise both high energy density and safety while existing solid-state electrolytes (SSEs) fail to satisfy the rigorous requirements of battery operations. Herein, novel polyoxometalate SSEs, Li3 PW12 O40 and Li3 PMo12 O40 , are synthesized, which exhibit excellent interfacial compatibility with electrodes and chemical stability, overcoming the limitations of conventional SSEs. A high ionic conductivity of 0.89 mS cm-1 and a low activation energy of 0.23 eV are obtained due to the optimized three-dimensional Li+ migration network of Li3 PW12 O40 . Li3 PW12 O40 exhibits a wide window of electrochemical stability that can both accommodate the Li anode and high-voltage cathodes. As a result, all-solid-state Li metal batteries fabricated with Li/Li3 PW12 O40 /LiNi0.5 Co0.2 Mn0.3 O2 display a stable cycling up to 100 cycles with a cutoff voltage of 4.35 V and an areal capacity of more than 4 mAh cm-2 , as well as a cost-competitive SSEs price of $5.68 kg-1 . Moreover, Li3 PMo12 O40 homologous to Li3 PW12 O40 was obtained via isomorphous substitution, which formed a low-resistance interface with Li3 PW12 O40 . Applications of Li3 PW12 O40 and Li3 PMo12 O40 in Li-air batteries further demonstrate that long cycle life (650 cycles) can be achieved. This strategy provides a facile, low-cost strategy to construct efficient and scalable solid polyoxometalate electrolytes for high-energy solid-state Li metal batteries.

In Situ Formed Tribofilms as Efficient Organic/Inorganic Hybrid Interlayers for Stabilizing Lithium Metal Anodes

The practical application of Li metal anodes (LMAs) is limited by uncontrolled dendrite growth and side reactions. Herein, we propose a new friction-induced strategy to produce high-performance thin Li anode (Li@CFO). By virtue of the in situ friction reaction between fluoropolymer grease and Li strips during rolling, a robust organic/inorganic hybrid interlayer (lithiophilic LiF/LiC6 framework hybridized -CF2-O-CF2- chains) was formed atop Li metal. The derived interface contributes to reversible Li plating/stripping behaviors by mitigating side reactions and decreasing the solvation degree at the interface. The Li@CFO||Li@CFO symmetrical cell exhibits a remarkable lifespan for 5,600 h (1.0 mA cm-2 and 1.0 mAh cm-2) and 1,350 cycles even at a harsh condition (18.0 mA cm-2 and 3.0 mAh cm-2). When paired with high-loading LiFePO4 cathodes, the full cell lasts over 450 cycles at 1C with a high-capacity retention of 99.9%. This work provides a new friction-induced strategy for producing high-performance thin LMAs.

Interfacial friction enabling ≤ 20 μm thin free-standing lithium strips for lithium metal batteries

A practical high-specific-energy Li metal battery requires thin (≤20 μm) and free-standing Li metal anodes, but the low melting point and strong diffusion creep of lithium metal impede their scalable processing towards thin-thickness and free-standing architecture. In this paper, thin (5 to 50 μm) and free-standing lithium strips were achieved by mechanical rolling, which is determined by the in situ tribochemical reaction between lithium and zinc dialkyldithiophosphate (ZDDP). A friction-induced organic/inorganic hybrid interface (~450 nm) was formed on Li with an ultra-high hardness (0.84 GPa) and Young's modulus (25.90 GPa), which not only enables the scalable process mechanics of thin lithium strips but also facilitates dendrite-free lithium metal anodes by inhibiting dendrite growth. The rolled lithium anode exhibits a prolonged cycle lifespan and high-rate cycle stability (in excess of more than 1700 cycles even at 18.0 mA cm-2 and 1.5 mA cm-2 at 25 °C). Meanwhile, the LiFePO4 (with single-sided load 10 mg/cm2) ||Li@ZDDP full cell can last over 350 cycles with a high-capacity retention of 82% after the formation cycles at 5 C (1 C = 170 mA/g) and 25 °C. This work provides a scalable approach concerning tribology design for producing practical thin free-standing lithium metal anodes.

Unraveling Sodium-Ion Dynamics in Honeycomb-Layered Na2MgxZn2-xTeO6 Solid Electrolytes with Solid-State NMR

All-solid-state sodium-ion batteries (SIBs) have the potential to offer large-scale, safe, cost-effective, and sustainable energy storage solutions by supplementing the industry-leading lithium-ion batteries. However, for the enhanced bulk properties of SIB components (e.g., solid electrolytes), a comprehensive understanding of their atomic-scale structure and the dynamic behavior of sodium (Na) ions is essential. Here, we utilize a robust multinuclear (23Na, 125Te, 25Mg, and 67Zn) magnetic resonance approach to explore a novel Mg/Zn homogeneously mixed-cation honeycomb-layered oxide Na2MgxZn2-xTeO6 solid solution series. These new intermediate compounds exhibit tailorable bulk Na-ion conductivity (σ) with the highest σ = 0.14 × 10-4 S cm-1 for Na2MgZnTeO6 at room temperature suitable for SIB solid electrolyte applications as observed by powder electrochemical impedance spectroscopy (EIS). A combination of powder X-ray diffraction (XRD), energy-dispersive X-ray (EDX) spectroscopy, and field emission scanning electron microscopy (FESEM) reveals highly crystalline phase-pure compounds in the P6322 space group. We show that the Mg/Zn disorder is random within the honeycomb layers using 125Te nuclear magnetic resonance (NMR) and resolve multiple Na sites using two-dimensional (triple-quantum magic-angle spinning (3QMAS)) 23Na NMR. The medium-range disorder in the honeycomb layer is revealed through the combination of 25Mg and 67Zn NMR, complemented by electronic structure calculations using density functional theory (DFT). Furthermore, we expose very fast local Na-ion hopping processes (hopping rate, 1/τNMR = 0.83 × 109 Hz) by using a laser to achieve variable high-temperature (∼860 K) 23Na NMR, which are sensitive to different Mg/Zn ratios. The Na2MgZnTeO6 with maximum Mg/Zn disorder displays the highest short-range Na-ion dynamics among all of the solid solution members.

Effect of grain boundary resistance on the ionic conductivity of amorphous xLi2S-(100-x)LiI binary system

Solid-state electrolytes (SSEs) hold the key position in the progress of cutting-edge all-solid-state batteries (ASSBs). The ionic conductivity of solid-state electrolytes is linked to the presence of both amorphous and crystalline phases. This study employs the synthesis method of mechanochemical milling on binary xLi2S-(100-x)LiI system to investigate the effect of amorphization on its ionic conductivity. Powder X-ray diffraction (PXRD) shows that the stoichiometry of Li2S and LiI has a significant impact on the amorphization of xLi2S-(100-x)LiI system. Furthermore, the analysis of electrochemical impedance spectroscopy (EIS) indicates that the amorphization of xLi2S-(100-x)LiI system is strongly correlated with its ionic conductivity, which is primarily attributed to the effect of grain boundary resistance. These findings uncover the latent connections between amorphization, grain boundary resistance, and ionic conductivity, offering insight into the design of innovative amorphous SSEs.

Hidden chemical order in disordered Ba7Nb4MoO20 revealed by resonant X-ray diffraction and solid-state NMR

The chemical order and disorder of solids have a decisive influence on the material properties. There are numerous materials exhibiting chemical order/disorder of atoms with similar X-ray atomic scattering factors and similar neutron scattering lengths. It is difficult to investigate such order/disorder hidden in the data obtained from conventional diffraction methods. Herein, we quantitatively determined the Mo/Nb order in the high ion conductor Ba₇Nb₄MoO₂₀ by a technique combining resonant X-ray diffraction, solid-state nuclear magnetic resonance (NMR) and first-principle calculations. NMR provided direct evidence that Mo atoms occupy only the M2 site near the intrinsically oxygen-deficient ion-conducting layer. Resonant X-ray diffraction determined the occupancy factors of Mo atoms at the M2 and other sites to be 0.50 and 0.00, respectively. These findings provide a basis for the development of ion conductors. This combined technique would open a new avenue for in-depth investigation of the hidden chemical order/disorder in materials.

Lithium-ion Mobility in Li6 B18 (Li3 N) and Li Vacancy Tuning in the Solid Solution Li6 B18 (Li3 N)1-x (Li2 O)x

All-solid-state batteries are promising candidates for safe energy-storage systems due to non-flammable solid electrolytes and the possibility to use metallic lithium as an anode. Thus, there is a challenge to design new solid electrolytes and to understand the principles of ion conduction on an atomic scale. We report on a new concept for compounds with high lithium ion mobility based on a rigid open-framework boron structure. The host-guest structure Li₆ B₁₈ (Li₃ N) comprises large hexagonal pores filled with ∞ 1 [ ${{}_{{\rm { \infty }}}{}^{{\rm { 1}}}{\rm { [}}}$ Li₇ N] strands that represent a perfect cutout from the structure of α-Li₃ N. Variable-temperature ⁷ Li NMR spectroscopy reveals a very high Li mobility in the template phase with a remarkably low activation energy below 19 kJ mol^-1 and thus much lower than pristine Li₃ N. The formation of the solid solution of Li₆ B₁₈ (Li₃ N) and Li₆ B₁₈ (Li₂ O) over the complete compositional range allows the tuning of lithium defects in the template structure that is not possible for pristine Li₃ N and Li₂ O.