Li-ion Conductivity Research Articles

Influence of atmospheric moisture on the gas evolution tolerance of halide solid electrolytes

Much attention has been paid on research and development on solid electrolytes for all-solid-state Li batteries. Although halide solid electrolytes such as Li3YCl6 and Li3InCl6 are promising due to fast Li ion conductivity and oxidation-resistant against positive electrode, a better understanding of their reactivity with atmospheric H2O is required for commercialization. In this study, the gas evolution tolerances of Li3YCl6 and Li3InCl6 were investigated. Temperature-programmed desorption mass spectrometry (TPD-MS) experiments at dew points below − 60 °C and gas detector tube experiments at dew points of − 30 °C both revealed significant differences in the H2O and HCl evolution behavior of Li3YCl6 and Li3InCl6. In TPD-MS, the onset temperature of HCl evolution for Li3YCl6 (~ 100 °C) was significantly lower than that for Li3InCl6 (~ 220 °C), indicating that Li3InCl6 solid electrolytes have superior gas evolution tolerance. This difference may be attributable to differences in the retention of H2O derived from the material synthesis stage and from contact with the atmosphere during the measurements. In particular, based on first-principles calculations, the low-temperature HCl evolution observed in Li3YCl6 was ascribed to the partial replacement of Cl− ions by OH− ions upon contamination with trace H2O. Because the heating and drying of solid electrolytes (including slurries) are inevitable processes during battery manufacturing, these findings can aid in the rational design of halide solid electrolytes for all-solid-state batteries.

Nitrogen‐Doped Anodic Li Oxide Films as Robust Li Metal Anodes and Solid‐State Electrolytes

AbstractThe performance of the lithium (Li) metal anode in rechargeable batteries has been hampered by the formation of unstable solid‐electrolyte interphase layers, which compromise cycle life and pose significant safety concerns. Herein, for the first time, the anodizing oxidation of pure Li in a liquid electrolyte is developed by using tetrahydrofuran with LiNO3. With this novel process, thickness‐controllable Li oxide films with in situ nitrogen doping during the anodizing process can be obtained. The resulting nitrogen‐doped Li oxide film (NLO) exhibits a uniform surface of the Li metal anode, effectively suppressing Li dendrite growth and simultaneously improving Li ionic conductivity. In addition, the Li metal full cells with Li/NLO anodes perform a long stable life of 1100 cycles at 5C. More importantly, this work demonstrates the great potential of NLO films as a solid‐state electrolyte in solid‐state Li metal batteries. The symmetric Li cells with NLO films perform excellent cycling stability for 300 h at 2 mA cm−2 current density and high Li+ ion conductivity of ≈3 ×10−4 S cm−1 at room temperature. This research not only provides a novel Li anodizing process and a stable Li metal anode but also opens up new possibilities for new solid‐state Li metal battery technologies.

A Functional Air-Stable Li9.8GeP1.7Sb0.3S11.8I0.2 Superionic Conductor for High-Performance All-Solid-State Lithium Batteries.

Solid-state electrolytes (SSEs) based on sulfides have become a subject of great interest due to their superior Li-ion conductivity, low grain boundary resistance, and adequate mechanical strength. However, they grapple with chemical instability toward moisture hypersensitivity, which decreases their ionic conductivity, leading to more processing requirements. Herein, a Li9.8GeP1.7Sb0.3S11.8I0.2 (LGPSSI) superionic conductor is designed with a Li+ conductivity of 6.6 mS cm-1 and superior air stability based on hard and soft acids and bases (HSAB) theory. The introduction of optimal antimony (Sb) and iodine (I) into the Li10GeP2S12 (LGPS) structure facilitates fast Li-ion migration with low activation energy (Ea) of 20.33 kJ mol-1. The higher air stability of LGPSSI is credited to the strategic substitution of soft acid Sb into (Ge/P)S4 tetrahedral sites, examined by Raman and X-ray photoelectron spectroscopy techniques. Relatively lower acidity of Sb compared to phosphorus (P) realizes a stronger Sb-S bond, minimizing the evolution of toxic H2S (0.1728 cm3 g-1), which is ∼3 times lower than pristine LGPS when LGPSSI is exposed to moist air for 120 min. The NCA//Li-In full cell with a LGPSSI superionic conductor delivered the first discharge capacity of 209.1 mAh g-1 with 86.94% Coulombic efficiency at 0.1 mA cm-2. Furthermore, operating at a current density of 0.3 mA cm-2, LiNbO3@NCA/LGPSSI/Li-In cell demonstrated an exceptional reversible capacity of 117.70 mAh g-1, retaining 92.64% of its original capacity over 100 cycles.

Revealing the effect of double bond-modified Li6.75La3Zr1.75Ta0.25O12 on the Li-ion conduction of composite solid electrolytes

Lithium metal batteries with polyethylene oxide (PEO) electrolytes have shown great potential to be one of the next-generation energy candidates. As the branch family of PEO electrolytes, poly(ethylene glycol) acrylates (PEGAs) attract more attention owing to their better electrochemical properties than that of PEO electrolytes. Introducing double bond-modified Li6.75La3Zr1.75Ta0.25O12 fillers (KH@LLZTO) has been a popular method to improve the electrochemical properties of PEGAs electrolytes due to the homogeneous dispersion of LLZTO. However, in this work, an inverse phenomenon is discovered. The electrochemical properties of PEGAs electrolytes get worse when introducing KH@LLZTO. By exploring the Li+ transport mechanism, the reason for the inverse phenomenon is revealed. More importantly, the design principle of PEGAs electrolytes with fast ionic conductor fillers is presented. Double bond-modified LLZTO can decrease the electrochemical properties of PEGAs electrolytes instead when there are low-molecular weight monomers that can participate in the PEGAs polymer network and interact with Li+, while the double bond-modified LLZTO can improve the electrochemical properties of PEGAs electrolytes when there are not aforementioned low-molecular weight monomers. This work provides a new understanding for componential design and optimization of PEGAs electrolytes with fast ionic conductors, hoping to promote the practical application of PEGAs electrolytes.

In Situ Construction of a Lithiophilic and Electronically Insulating Multifunctional Hybrid Layer Based on the Principle of Hydrolysis for a Stable Garnet/Li Interface

AbstractAdapting solid‐state Li‐metal batteries is an attractive way to pursue higher energy density and safety compared to liquid‐based ones. With high ionic conductivity and excellent stability with Li, Ta‐doped Li7La3Zr2O12 (LLZTO) is an effective option. However, the poor solid–solid interface contact induced by the lithiophobic Li2CO3 layer hinder its practical application. Herein, a versatile strategy is proposed based on the hydrolysis of sodium tetrafluoroborate (NaBF4), aiming to convert the Li2CO3 into multifunctional hybrid layer containing LiF, LiBO2, and NaF. Among them, LiF and LiBO2 serve as the primary Li ion conductors, the introduction of NaF with high surface energy not only enhances the interface wettability, but also further elevates the critical dendrite strength against Li dendrites. All three components serve as excellent electronic insulators, suppressing electron invasion at the interface and preventing Li dendrite growth in the solid electrolyte. As expected, the interfacial impedance of the NaBF4 treated symmetric cell is reduced to 6.0 Ω cm2, the critical current density (CCD) comes to 2.0 mA cm−2, and cycles over 3000 h at 0.3 mA cm−2 and 1500 h at 0.5 mA cm−2 respectively. Besides, the modified SSBs matched with LiFePO4 or LiNi0.6Co0.2Mn0.2O2 cathode show great long‐term cycling and rate performance.

A bifunctional strategy enabling 4.55 V LiCoO2 with improved electrochemical performance

LiCoO2 (LCO) has been functionally modified with electronic conductor of Al doped ZnO (AZO) and ionic conductor of Li3PO4 (LPO). The physicochemical characterization results demonstrated that the hexagonal structured AZO small crystal particles epitaxial growth formed island-like structures on the surface of LCO particles and LPO filled on the surface of remaining exposed LCO particles. Due to the unique composite coating layer with excellent electronic conductivity and Li ion conductivity, the AZO and LPO coated LCO exhibits outstanding rate capability and cycle stability in the voltage range of 2.75–4.55 V. The modified LCO delivered a specific capacity 206 mA h g−1 at 0.5C rate (100 mA g−1), and the capacity retention was 91.7 % after 50 cycles, which was a remarkable improvement comparing with uncoated LCO (34.8 %). Moreover, it exhibited an outstanding rate property, maintaining a discharge capacity of 161.4 mA h g−1 at 4C. This bifunctional strategy with AZO and Li3PO4 is an efficient approach to improve the electrochemical performance of LCO at high cut-off voltage (>4.5 V).

Exploring the Relationship between Composition and Li-Ion Conductivity in the Amorphous Li–La–Zr–O System

Exploring the Relationship between Composition and Li-Ion Conductivity in the Amorphous Li–La–Zr–O System

Influence of mixing technique on properties of Li1.3Al0.3Ti1.7(PO4)3 solid electrolyte prepared by the solid-state reaction - A comparison of dry 3D mixing technique with wet ball-milling

Li1.3Al0.3Ti1.7(PO4)3 (LATP) NASICON(Na Super Ion Conductive)-type solid electrolyte is prepared using conventional wet ball-milling and dry 3D mixing techniques to investigate the influence of mixing technique on properties of LATP. The mixing techniques influence impurity formation of calcined LATP powder. Thus, sintering behavior of the calcined powders is also affected by the mixing technique, i.e. LiTiPO5 formation is confirmed in the ball-milling samples and Li-ion conductive Li4P2O7 is main impurity in the 3D mixing samples. The influence is not limited to impurity formation. Uniform grains are observed in the 3D mixing pellet, contrarily, non-uniform sintering occurs in the ball-milling sample. As a result, the 3D mixing pellets demonstrate higher Li-ion conductivity than the ball-mill samples. The dry 3D mixing technique, which can omit drying process, is promising for LATP preparation owing to simplification of preparation process and a formation of high Li-ion conductive LATP pellets. Also, this study clearly shows that the mixing techniques affect ionic conductivity of the sintered LATP significantly, emphasizing importance of mixing procedure in the solid-state reaction.

Investigating the Effect of Co-doping on Structural and Electrical Properties of Li7La3Zr2O12 Solid Electrolyte

Garnet-type Li<sub>7</sub>La<sub>3</sub>Zr<sub>2</sub>O<sub>12</sub> (LLZO) has garnered significant attention for solid-state Li-ion batteries due to its commendable Li-ion conductivity, wide electrochemical window, and exceptional chemical and thermal stability. Nonetheless, challenges related to structural instability and air stability persist, impeding its market expansion. Herein, we explore the effects of co-doping (Ga with Sc/Y/In/Er) on the crystal structure and Li-ion conductivity of LLZO through x-ray diffraction (XRD), scanning electron microscope (SEM), and AC impedance measurements. XRD refinement confirms the formation of pure-phase samples with a cubic crystal structure. SEM analysis reveals a dense microstructure with grain sizes exceeding 200 μm and a relative density approaching∼94%. While Ga/Sc and Ga/Y doped LLZO exhibit relatively lower Li-ion conductivity, Ga/Er and Ga/In doped samples demonstrate high conductivity more than 1 mS/cm at room temperature (25°C). Thus, the judicious selection of dopants emerges as an effective strategy for enhancing conductivity in all-solid-state batteries.

Insight into the effect of strain on Li-ion diffusivity and conductivity in Li3OCl anti-perovskite solid-state electrolyte: A perspective from AIMD simulations

Utilizing first-principle calculations, this study elucidated the underlying mechanism of elastic strains affecting the Li-ion diffusivity and conductivity in Li3OCl anti-perovskite solid-state electrolyte. Strain was shown to modulate the Li-ion vibrational amplitude, attempt frequency and adjacent site jumps, as revealed by ab initio molecular dynamics (AIMD) simulation post-processing. Additionally, analysis of lattice dynamics and phonon behavior under various strain conditions demonstrated that tensile strains soften the lattice and lower the phonon band center frequency, thereby diminishing the energy barriers impeding ion transport. Further, we have systematically investigated strain-induced distortions of the coordination environment via continuous symmetry measures (CSM), assessing the variations at initial and saddle sites along the Li-ion migration routes. And the study of bonding variability under strain provided a deeper understanding of strain-induced conducting behavior. These results underscore insights into the fundamental mechanisms governing ionic transport in Li3OCl anti-perovskite under elastic strain, highlighting the potential of strain engineering as a promising avenue for optimizing the performance of solid-state electrolytes in energy storage applications.

Ce doped UiO-66(Hf) electrolyte for all-solid-state lithium metal batteries

Solid electrolytes have garnered significant attention as promising candidates for all-solid-state batteries due to their excellent safety, and cycling stability. However, the development of solid electrolytes faces challenges in achieving high ionic conductivity and low interfacial impedance. In this study, we prepared a Ce doped UiO-66(Hf)-base electrolyte using a solvothermal method. The resulting electrolyte exhibited remarkable properties, including high Li-ion conductivity (3.72 × 10−3 S cm−1), a high lithium ion transfer number (tLi+ = 0.66), and stability during stripping electroplating. These impressive results can be attributed to that the shorter length of the Ce-O bond in UiO-66(Hf) compared to the Hf-O bond, which enhances the transformation of Li+ ions. The incorporation of Ce as a dopant into UiO-66(Hf) in solid electrolytes holds great promise for future applications in solid-state batteries.

Enhancing bismuth-rich SEI on Li anode under high current density through the use of highly conductive additives

The forming of Li-Bi alloy can build a lithiophilic protective layer on the lithium anode, however, it is found that the lithium dendrites trend to grow on the surface of bismuth-rich solid electrolyte interphase (SEI) and there is an exfoliation of SEI from substrate caused by de-alloying process at a large current density. The failure cause of the bismuth-rich SEI is considered as the inadequate Li-ionic conductivity of the passivation layer, which cannot facilitate the lithium deposition on the substrate. Then the components with high Li-ionic conductivities such as Li3N, LiF and Li2S are introduced into the SEI to adjust the characteristic of the bismuth-rich layer by the addition of LiNO3, Bi2S3 and FEC. All of them enhance the SEI’s performances effectively and LiNO3 presents the best. With the addition of LiNO3, the SEI thickness is decreased and Li-ionic conductivity is enhanced while Li3N became one of the major components of the layer. Utilizing the improved bismuth-rich protective layer the Li/Li symmetric cell presents an overpotential at ∼10 mV in a long cycle over ∼1700 h at 4 mA cm−2, and the LiFePO4/Li cell with the cathode loading of ∼10 mg cm−2 exhibits a capacity retention rate 72.1% in 400 cycles. This work provides a new SEI design strategy for lithium metal anode operating at high current density and an inspiration for improving other functional interfacial layers in lithium batteries.

Control of Li-ion transport through a combination of conductive coating and charging protocol for a stable and extremely fast charging cathode

This study demonstrates the importance of controlling Li-ion transport through a combination of conductive coating and charging protocol to achieve a stable and extremely fast charging cathode. In this research, the LiFePO4 (LFP) material coated with carbon (C) and Li1.3Al0.3Ti1.7(PO4)3 (LATP) solid electrolyte exhibits superior performance to the conventional carbon-coated LFP (LFP@C), especially at high current rates, demonstrating the possibility of developing an extremely fast charging cathode for practical applications. Our systematic experimental results reveal that the LATP coating effectively regulates the surface reactions, prolongs the voltage plateaus, and contributes additional capacity to the olivine LFP cathode material. To take advantage of the coating, a charging protocol consisting of multi-step constant current (MCC) charging combined with constant voltage (CV) charging has been proposed. During MCC charging, the current gradually increases to initiate Li-ion transport on the particle surface before accelerating charging in a short time. Under the proposed charging protocol, the LFP@C_LATP can stably deliver an average charge capacity of 161.7 mAh g−1 within 10 min for 100 cycles. This research also demonstrates the advantage of incorporating a Li-ion conductor into the electrode for the development of an extremely fast charging electrode.

Influence of Zr aggregation on Li-ion conductivity of amorphous solid-state electrolyte Li-La-Zr-O.

In our study, we investigated the influence of the local structure of amorphous Li-La-Zr-O (a-LLZO) on Li-ion conductivity using abinitio molecular dynamics (AIMD). A-LLZO has shown promising properties in inhibiting the growth of lithium dendrites, making it a potential candidate for solid electrolytes in all-solid-state lithium batteries. The low Li-ion conductivity of a-LLZO is currently limiting its practical applications. Our findings revealed that the homogeneous distribution of Zr-O polyhedra within the pristine structure of a-LLZO contributes to enhanced Li-ion conductivity. By reducing the interconnections among Zr-O polyhedra, the AIMD-simulated a-LLZO sample achieved a Li-ion conductivity of 5.78 × 10-4 S/cm at room temperature, which is slightly lower than that of cubic LLZO (c-LLZO) with a Li-ion conductivity of 1.63 × 10-3 S/cm. Furthermore, we discovered that Li-ion conductivity can be influenced by adjusting the elemental ratios within a-LLZO. This suggests that fine-tuning the composition of a-LLZO can potentially further enhance its Li-ion conductivity and optimize its performance as a solid electrolyte in lithium batteries.

A solid-state lithium-ion battery with micron-sized silicon anode operating free from external pressure

Applying high stack pressure (often up to tens of megapascals) to solid-state Li-ion batteries is primarily done to address the issues of internal voids formation and subsequent Li-ion transport blockage within the solid electrode due to volume changes. Whereas, redundant pressurizing devices lower the energy density of batteries and raise the cost. Herein, a mechanical optimization strategy involving elastic electrolyte is proposed for SSBs operating without external pressurizing, but relying solely on the built-in pressure of cells. We combine soft-rigid dual monomer copolymer with deep eutectic mixture to design an elastic solid electrolyte, which exhibits not only high stretchability and deformation recovery capability but also high room-temperature Li-ion conductivity of 2×10−3 S cm−1 and nonflammability. The micron-sized Si anode without additional stack pressure, paired with the elastic electrolyte, exhibits exceptional stability for 300 cycles with 90.8% capacity retention. Furthermore, the solid Li/elastic electrolyte/LiFePO4 battery delivers 143.3 mAh g−1 after 400 cycles. Finally, the micron-sized Si/elastic electrolyte/LiFePO4 full cell operates stably for 100 cycles in the absence of any additional pressure, maintaining a capacity retention rate of 98.3%. This significantly advances the practical applications of solid-state batteries.

Effect of Ca doping on Li ion conductivity of Ge and Ta doped garnet LLZO

The series Li6.55+xGe0.05La3-xCaxZr1.75Ta0.25O12 (x = 0, 0.05, 0.10, 0.15, 0.20) was prepared by conventional solid state reaction method with the sintering temperature of 1050 °C for 7.30 h by substituting Ca at the La site to increase the Li ion conductivity. The synergistic effects of Ca incorporation on Li6.55Ge0.05La3Zr1.75Ta0.25O12 were studied using various structural and electrochemical analyses. X-ray diffraction, scanning electron microscopy, and Impedance analysis were used to determine the crystal structure, morphology, and AC conductivity of the prepared ceramic samples, respectively. The highest conductivity of 9.95 x 10−4 S/cm was obtained for a 0.05 Ca ceramic sample with minimum activation energy of 0.23 eV. The DC polarization measurements confirmed the dominance of ionic conduction in 0.05 Ca ceramic. The results obtained make the 0.05 Ca ceramic sample a promising candidate as solid electrolytes for all solid state Li-ion batteries (ASSLIBs).

Nanohoneycomb rGO foam as a promising anode material for unprecedented ultrahigh Li storage and excellent endurance at ampere current stability

Most rechargeable lithium-ion batteries (LIBs) exploit bulk carbon (e.g., graphite with low interlayer spacing of 0.335 nm) as an anode material despite its low theoretical capacity of 372 mAh/g because it has a high coulombic efficiency, good cycling performance, and low production costs. However, it is difficult to increase the specific capacity of graphite-based anodes without sacrificing these inherent advantages. In the present study, we developed reduced graphene oxide nanohoneycomb foam (H-rGO) as an anode material with higher surface area, porosity, and interlayer spacing for the rapid and efficient lithiation-delithiation of Li-ions. The combination of the hierarchical three-dimensional sponge-like mesoporous structure with highly efficient Li-ion conduction pathways and enlarge active surface area leads to a significantly improved specific capacity (1031 mAh/g at 0.1 A/g) and rapid charging with exceptional stability over 5,000 cycles. The H-rGO anode achieves an outstanding reversible capacity of ∼534 mAh/g over 2,500 cycles at 1.0 A/g, with a capacity retention of 87 and 84 % at high current densities of 10 and 20 A/g, respectively. Our approach is fully compatible with current LIBs technology and offer a simple and efficient strategy to significantly increase Li-storage capacity of under current graphite-based anode technology.

Mechanism of high Li-ion conductivity in poly(vinylene carbonate)-poly(ethylene oxide) cross-linked network based electrolyte revealed by solid-state NMR

Solid polymer electrolytes (SPEs) have become increasingly important in advanced lithium-ion batteries (LIBs) due to their improved safety and mechanical properties compared to organic liquid electrolytes. Cross-linked polymers have the potential to further improve the mechanical property without trading off Li-ion conductivity. In this study, focusing on a recently developed cross-linked SPE, i.e., the one based on poly(vinylene carbonate)-poly(ethylene oxide) cross-linked network (PVCN), we used solid-state nuclear magnetic resonance (NMR) techniques to investigate the fundamental interaction between the chain segments and Li ions, as well as the lithium-ion motion. By utilizing homonuclear/heteronuclear correlation, CP (cross-polarization) kinetics, and spin–lattice relaxation experiments, etc., we revealed the structural characteristics and their relations to lithium-ion mobilities. It is found that the network formation prevents poly(ethylene oxide) chains from crystallization, which could create sufficient space for segmental tumbling and Li-ion conduction. As such, the mechanical property is greatly improved with even higher Li-ion mobilities compared to the poly(vinylene carbonate) or poly(ethylene oxide) based SPE analogues.

Bi-Directional H-Bonding Modulated Soft/Hard Polyethylene Glycol-Polyaniline Coated Si-Anode for High-Performance Li-Ion Batteries.

Ultrahigh-capacity silicon (Si) anodes are essential for the escalating energy demands driven by the booming e-transportation and energy storage field. However, their practical applications are strictly hampered by their intrinsically low electroconductivity, sluggish Li-ion diffusion, and undesirably large volume change. Herein, a high-performance Si anode, comprised of a modulated soft/hard coating of polyethylene glycol (PEG) (as Li-ion conductor) and polyaniline (PANI) (as electron conductor) on the surface of Si nanoparticles (NPs) through H-bonding network, is introduced. In this design, the abundant ─OH groups of soft PEG allow it to uniformly cover Si NPs while the hard PANI binds to PEG through its ─N─H group, thus constructing a tight connectin between Si and PEG-PANI (PP). Consequently, the elastic PP allows Si@PP to accommodate the huge volume expansion while possessing fine electronic/ionic conductivity. Therefore, the Si@PP anode exhibits a high initial Coulombic efficiency of 90.5% and a stable capacity of 1871mAhg-1 after 100 cycles at 1Ag-1 with a retention of 85.7%. Additionally, the Si@PP anode also demonstrates a high areal capacity of 3.01mAhcm-2 after 100 cycles at 0.5Ag-1. This work reveals a scalable interface design of multi-layer multifunctional coatings for high-performance electrode materials in next-generation Li-ion batteries.

Polysulfide-mediated solvation shell reorganization for fast Li+ transfer probed by in-situ sum frequency generation spectroscopy

Understanding of interfacial Li+ solvation shell structures and dynamic evolution at the electrode/electrolyte interface is requisite for developing high-energy-density Li batteries. Herein, the reorganization of Li+ solvation shell at the sulfur/electrolyte interface along with the presence of a trace amount of lithium polysulfides is verified by in-situ sum frequency generation (SFG) spectroscopy together with density functional theory (DFT) calculations. Both the spectroelectrochemical and DFT calculation results reveal a strongly competitive anion adsorption of the polysulfide anion additive against the pristine electrolyte anion on the sulfur cathode surface, reorganizing the interfacial local solvation shell structure facilitating rapid Li ion transfer and conduction. Meanwhile, the evolution of the SFG signals along with the discharging/charging cycle exhibits improved reversibility, indicating the transformation of the inner Helmholtz plane layer into a stable molecular-layer polysulfide interphase rather than a dynamic diffusion layer. Consequently, applications in practical Li-S batteries reveal the capacity and cycling stability of the corresponding cells are significantly enhanced. Our work provides a methodology using in-situ SFG for probing solvation reorganization of charge carriers at electrochemical interfaces.