NMR Investigations of Crystalline and Glassy Solid Electrolytes for Lithium Batteries: A Brief Review

Amorphous Materials for Lithium-Ion and Post-Lithium-Ion Batteries

Lithium-ion and post-lithium-ion batteries are important components for building sustainable energy systems. They usually consist of a cathode, an anode, an electrolyte, and a separator. Recently, the use of solid-state materials as electrolytes has received extensive attention. The solid-state electrolyte materials (as well as the electrode materials) have traditionally been overwhelmingly crystalline materials, but amorphous (disordered) materials are gradually emerging as important alternatives because they can increase the number of ion storage sites and diffusion channels, enhance solid-state ion diffusion, tolerate more severe volume changes, and improve reaction activity. To develop superior amorphous battery materials, researchers have conducted a variety of experiments and theoretical simulations. This review highlights the recent advances in using amorphous materials (AMs) for fabricating lithium-ion and post-lithium-ion batteries, focusing on the correlation between material structure and properties (e.g., electrochemical, mechanical, chemical, and thermal ones).  We  review both the conventional and the emerging characterization methods for analyzing AMs and present the roles of disorder in influencing the performances of various batteries such as those based on lithium, sodium, potassium, and zinc. Finally,  we  describe the challenges and perspectives for commercializing rechargeable AMs-based batteries.

Effects of LiPON Incorporation on the Structures and Properties of Mixed Oxy-Sulfide-Nitride Glassy Solid Electrolytes

Glassy solid electrolytes (GSEs) are promising solid electrolytes in the development of all solid-state batteries. Mixed oxy-sulfide nitride (MOSN) GSEs combine the high ionic conductivity of sulfide glasses, the excellent chemical stability of oxide glasses, and the electrochemical stability of nitride glasses. However, the reports on the synthesis and characterization of these novel nitrogen containing electrolytes are quite limited. Therefore, the systematic incorporation of LiPON during glass synthesis was used to explore the effects of nitrogen and oxygen additions on the atomic-level structures in the glass transition (T_g) and crystallization temperature (T_c) of MOSN GSEs. The MOSN GSE series 58.3Li₂S + 31.7SiS₂ + 10[(1 - x)Li_0.67PO_2.83 + x LiPO_2.53N_0.314], x = 0.0, 0.06, 0.12, 0.2, 0.27, 0.36, was prepared by melt-quench synthesis. Differential scanning calorimetry was used to determine the T_g and T_c values of these glasses. Fourier transformation-infrared, Raman, and magic angle spinning nuclear magnetic resonance spectroscopies were used to examine the short-range order structures of these materials. X-ray photoelectron spectroscopy was conducted on the glasses to further understand the bonding environments of the doped nitrogen. Finally, N and S elemental analyses were used to confirm the composition of these GSEs. These results are used to elucidate the structure of these glasses and to understand the thermal property impact oxygen and nitrogen doping in these GSEs.

Recent advances in the liquid-phase 6,7 Li nuclear magnetic resonance

The present review is focused on experimental methods and structural applications, including computational aspects, of classical lithium liquid-phase nuclear magnetic resonance (NMR). It consists of four parts covering accordingly a brief overview, early experimental reports (papers of up to about 2015) and more recent (papers appearing in the interim of about 2015 until 2022) results, together with very few but highly prospective computational results.

Toward Understanding of the Li-Ion Migration Pathways in the Lithium Aluminum Sulfides Li3AlS3 and Li4.3AlS3.3Cl0.7 via 6,7Li Solid-State Nuclear Magnetic Resonance Spectroscopy

Li-containing materials providing fast ion transport pathways are fundamental in Li solid electrolytes and the future of all-solid-state batteries. Understanding these pathways, which usually benefit from structural disorder and cation/anion substitution, is paramount for further developments in next-generation Li solid electrolytes. Here, we exploit a range of variable temperature ⁶Li and ⁷Li nuclear magnetic resonance approaches to determine Li-ion mobility pathways, quantify Li-ion jump rates, and subsequently identify the limiting factors for Li-ion diffusion in Li₃AlS₃ and chlorine-doped analogue Li_4.3AlS_3.3Cl_0.7. Static ⁷Li NMR line narrowing spectra of Li₃AlS₃ show the existence of both mobile and immobile Li ions, with the latter limiting long-range translational ion diffusion, while in Li_4.3AlS_3.3Cl_0.7, a single type of fast-moving ion is present and responsible for the higher conductivity of this phase. ⁶Li-⁶Li exchange spectroscopy spectra of Li₃AlS₃ reveal that the slower moving ions hop between non-equivalent Li positions in different structural layers. The absence of the immobile ions in Li_4.3AlS_3.3Cl_0.7, as revealed from ⁷Li line narrowing experiments, suggests an increased rate of ion exchange between the layers in this phase compared with Li₃AlS₃. Detailed analysis of spin-lattice relaxation data allows extraction of Li-ion jump rates that are significantly increased for the doped material and identify Li mobility pathways in both materials to be three-dimensional. The identification of factors limiting long-range translational Li diffusion and understanding the effects of structural modification (such as anion substitution) on Li-ion mobility provide a framework for the further development of more highly conductive Li solid electrolytes.

Ionic Liquid@Metal-Organic Framework as a Solid Electrolyte in a Lithium-Ion Battery: Current Performance and Perspective at Molecular Level

Searching for a suitable electrolyte in a lithium-ion battery is a challenging task. The electrolyte must not only be chemically and mechanically stable, but also be able to transport lithium ions efficiently. Ionic liquid incorporated into a metal-organic framework (IL@MOF) has currently emerged as an interesting class of hybrid material that could offer excellent electrochemical properties. However, the understanding of the mechanism and factors that govern its fast ionic conduction is crucial as well. In this review, the characteristics and potential use of IL@MOF as an electrolyte in a lithium-ion battery are highlighted. The importance of computational methods is emphasized as a comprehensive tool to investigate the atomistic behavior of IL@MOF and its interaction in electrochemical environments.

Thermal annealing of iridescent cellulose nanocrystal films

The properties of chiral nematic and iridescent cellulose nanocrystal films with different monovalent cations (CNC-X) obtained through evaporation-induced self-assembly (EISA) can be modified by a variety of external stimuli. Here, we study the transformations of their optical and structural properties when the films are thermally annealed at 200 °C and 240 °C for up to 2 days. The chiral nematic structure of the most thermally stable films is not destroyed even after extensive heating due to the thermochemical stability of the cellulose backbone and the presence of surface alkali counterions, which suppress catalysis of early stage degradation. Despite the resilience of the cholesteric structure and the overall integrity of heated CNC-X films, thermal annealing is often accompanied by reduction of iridescence, birefringence, and transparency, as well as formation of degradation products. The versatility, sustainability, and stability of CNC-X films highlight their potential as temperature indicators and photonic devices.

Use of Solid-State NMR Spectroscopy for the Characterization of Molecular Structure and Dynamics in Solid Polymer and Hybrid Electrolytes

Solid-state NMR spectroscopy is an established experimental technique which is used for the characterization of structural and dynamic properties of materials in their native state. Many types of solid-state NMR experiments have been used to characterize both lithium-based and sodium-based solid polymer and polymer-ceramic hybrid electrolyte materials. This review describes several solid-state NMR experiments that are commonly employed in the analysis of these systems: pulse field gradient NMR, electrophoretic NMR, variable temperature T1 relaxation, T2 relaxation and linewidth analysis, exchange spectroscopy, cross polarization, Rotational Echo Double Resonance, and isotope enrichment. In this review, each technique is introduced with a short description of the pulse sequence, and examples of experiments that have been performed in real solid-state polymer and/or hybrid electrolyte systems are provided. The results and conclusions of these experiments are discussed to inform readers of the strengths and weaknesses of each technique when applied to polymer and hybrid electrolyte systems. It is anticipated that this review may be used to aid in the selection of solid-state NMR experiments for the analysis of these systems.

Tracking Ions the Direct Way: Long-Range Li+ Dynamics in the Thio-LISICON Family Li4MCh4 (M = Sn, Ge; Ch = S, Se) as Probed by 7Li NMR Relaxometry and 7Li Spin-Alignment Echo NMR

Solid electrolytes are key elements for next-generation energy storage systems. To design powerful electrolytes with high ionic conductivity, we need to improve our understanding of the mechanisms that are at the heart of the rapid ion exchange processes in solids. Such an understanding also requires evaluation and testing of methods not routinely used to characterize ion conductors. Here, the ternary Li₄MCh₄ system (M = Ge, Sn; Ch = Se, S) provides model compounds to study the applicability of ⁷Li nuclear magnetic resonance (NMR) spin-alignment echo (SAE) spectroscopy to probe slow Li⁺ exchange processes. Whereas the exact interpretation of conventional spin-lattice relaxation data depends on models, SAE NMR offers a model-independent, direct access to motional correlation rates. Indeed, the jump rates and activation energies deduced from time-domain relaxometry data perfectly agree with results from ⁷Li SAE NMR. In particular, long-range Li⁺ diffusion in polycrystalline Li₄SnS₄ as seen by NMR in a dynamic range covering 6 orders of magnitude is determined by an activation energy of E _a = 0.55 eV and a pre-exponential factor of 3 × 10¹³ s^-1. The variation in E _a and 1/τ₀ is related to the LiCh₄ volume that changes within the four Li₄MCh₄ compounds studied. The corresponding volume of Li₄SnS₄ seems to be close to optimum for Li⁺ diffusivity.

Sulfide and Oxide Inorganic Solid Electrolytes for All-Solid-State Li Batteries: A Review

Energy storage materials are finding increasing applications in our daily lives, for devices such as mobile phones and electric vehicles. Current commercial batteries use flammable liquid electrolytes, which are unsafe, toxic, and environmentally unfriendly with low chemical stability. Recently, solid electrolytes have been extensively studied as alternative electrolytes to address these shortcomings. Herein, we report the early history, synthesis and characterization, mechanical properties, and Li+ ion transport mechanisms of inorganic sulfide and oxide electrolytes. Furthermore, we highlight the importance of the fabrication technology and experimental conditions, such as the effects of pressure and operating parameters, on the electrochemical performance of all-solid-state Li batteries. In particular, we emphasize promising electrolyte systems based on sulfides and argyrodites, such as LiPS5Cl and β-Li3PS4, oxide electrolytes, bare and doped Li7La3Zr2O12 garnet, NASICON-type structures, and perovskite electrolyte materials. Moreover, we discuss the present and future challenges that all-solid-state batteries face for large-scale industrial applications.