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The composite lithium hydride superionic conductor 0.7Li(CB9H10)-0.3Li(CB11H12) was synthesized by (CB11H12)-partial replacement (CB9H10)-stabilized disordered high temperature phase Li(CB9H10), which has excellent stability to lithium metal. And conductivity at 25 ° C up to 6.7 × 10-3 S / cm;
At high current densities of 5016 mA/g, all-solid lithium-sulfur batteries exhibit high energy densities (>2500 Wh/kg).
[Introduction]
Since conventional lithium-ion batteries use flammable organic liquid electrolytes and low-capacity carbonaceous anodes, they are unable to meet the growing demand for safety and energy density. In recent years, all-solid-state batteries using lithium metal as a negative electrode have great potential, but there is a large lithium ion migration resistance between the solid electrolyte and lithium metal, which limits their use in actual batteries. Composite hydrides, the latest class of solid electrolytes, solve the problems associated with lithium metal anodes, primarily due to their high reductibility and good chemical/electrochemical stability. However, low ionic conductivity (~10-5 S/cm) requires stable electrochemical performance at higher temperatures (100 °C). Therefore, preparation of a composite hydride solid electrolyte exhibiting high ionic conductivity at room temperature is highly promising.
Recently, Prof. Sangryun Kim and Professor Shin-ichi Orimo from Tohoku University of Japan and colleagues have jointly reported that a composite lithium hydride was synthesized by using (CB11H12)-partially substituted (CB9H10)- to stabilize the disordered high temperature phase Li(CB9H10) at room temperature. Superionic conductor 0.7Li(CB9H10)-0.3Li(CB11H12), which has excellent stability to lithium metal and conductivity of up to 6.7×10-3 S/cm at 25 °C. At 0.2 mA/cm2, this composite hydride plating/de-lithium has negligible interfacial resistance (<1 Ω cm2), making the all-solid lithium-sulfur battery appear high at a high current density of 5016 mA/g. Energy density (>2500Wh/kg). This research has opened up an untapped research field in the field of solid electrolyte materials, contributing to the development of high energy density batteries. The related research results are published in the top international journal Nat. Commun. with the title "A complex hydride lithium superionic conductor for high-energy-density all-solid-state lithium metal batteries".
ã€core content】 
The disordered high temperature phase Li(CB9H10) has a low phase transition temperature (90 ° C) and a high lithium ion conductivity (10-1 S/cm), so it is selected as a host phase to synthesize a composite hydride lithium ion conductor solid electrolyte. Because of the similar geometry and size, and the same valence, (CB11H12) - can be partially replaced (CB9H10) - to achieve high temperature phase stabilization by using mechanical ball milling techniques. Select 0.3 mole fraction of (CB11H12)- as the composition amount, stabilize the high temperature phase (CB9H10)-(expressed as 0.7Li(CB9H10)-0.3Li(CB11H12)), and the low content (0.1 mole fraction) leads to incomplete stabilization. A high (0.5 mole fraction) leads to the formation of other impurity phases. It is also seen in Figure 1a that no new diffraction peaks appear in the synthesized material. By differential thermal analysis, Raman spectroscopy and SEM, it can be seen that a co-capacitance and deformable composite hydrogenated lithium ion conductor is prepared.
The impedance curve of Li(CB9H10) at 25 °C (= 298 K) shows a semicircle in the high frequency region and a peak in the low frequency region (Fig. 2a), the impedance measured by 0.7Li(CB9H10)-0.3Li(CB11H12). It is orders of magnitude lower than Li (CB9H10). At 25 ° C, the lithium ion conductivity (σ) of 0.7Li(CB9H10)-0.3Li(CB11H12) is 6.7×10-3 S/cm, which is three orders of magnitude higher than Li(CB9H10) (σ=3.6×10). -6 S/cm). As can be seen from Figure 2c, when the temperature is raised from 25 ° C to 90 ° C, Li (CB9H10) shows a sharp jump in ionic conductivity, which is due to the transition to the high temperature phase. The room temperature conductivity of 0.7Li(CB9H10)-0.3Li(CB11H12) (6.7 x 10-3 S/cm at 25 ° C) is the highest value of the complex hydride solid electrolyte reported so far.
The EIS measurement was further carried out using a symmetric battery Li/0.7Li(CB9H10)-0.3Li(CB11H12)/Li to study the interface resistance with the lithium metal negative electrode. The SEM image confirmed the close physical contact at the interface and the interface compatibility. Due to its high chemical stability and high physical deformability.
0.7Li(CB9H10)-0.3Li(CB11H12) is potentially used to implement various lithium metal based all solid state batteries. In lithium-sulfur solid-state batteries, the performance at different temperatures and different ratios is measured, with high energy density and excellent coulombic efficiency, reaching 2500Wh/kg, exceeding the previously reported Li-S, Li-LiCoO2, Li-LiNi0 .5Mn1.5O4 and Li-Li2FeMn3O8 all solid state batteries.
[Conclusion Outlook]
The room temperature conductivity of the composite lithium hydride superionic conductor 0.7Li(CB9H10)-0.3Li(CB11H12), 0.7Li(CB9H10)-0.3Li(CB11H12) was developed (6.7×10-3 S/cm at 25°C). ) is the highest value of the composite hydride solid electrolyte reported so far. It is worth noting that this study provides general guidelines for how to develop closed composite lithium hydride superionic conductors. The high ionic conductivity of 0.7Li(CB9H10)-0.3Li(CB11H12) combined with the stability of lithium metal allows the high energy density Li-S battery to have excellent performance over a wide temperature range. From the viewpoint of battery manufacturing, 0.7Li(CB9H10)-0.3Li(CB11H12) has excellent deformability, contributes to the preparation of a dense solid electrolyte and builds an electrode/electrolyte interface, thereby producing intimate contact throughout the battery. The unique properties of the developed complex hydride solid electrolyte not only stimulated the future efforts to find lithium ion conductors based on complex hydrides, but also opened up a new set of solid electrolytes for practical all-solid lithium metal batteries, in order to achieve high energy. The development of density electrochemical devices has laid a solid foundation.
[This article highlights] Figure 1. Stabilize the high temperature phase at room temperature. a) XRD pattern of Li(CB9H10) at 150 °C and 0.7Li(CB9H10)-0.3Li(CB11H12) at room temperature; b) Differential thermal analysis of Li(CB9H10) and 0.7Li(CB9H10)-0.3Li(CB11H12) (DTA) curve; c) Raman spectrum of Li(CB9H10), Li(CB11H12) and 0.7Li(CB9H10)-0.3Li(CB11H12); d) Field emission SEM of 0.7Li(CB9H10)-0.3Li(CB11H12) The image, the enlarged image (right) is the yellow mark area (left), the scale bar d, the left image is 20 μm, and the right image is 3 μm. Figure 2. Lithium ion conductivity of 0.7Li(CB9H10)-0.3Li(CB11H12). a) Nyquist plot of Li(CB9H10) and 0.7Li(CB9H10)-0.3Li(CB11H12) at 25 °C (left); Nyquist of 0.7Li(CB9H10)-0.3Li(CB11H12) in the high frequency region (right) Figure; b) Arrhenius lithium ion conductivity map of Li(CB9H10) and 0.7Li(CB9H10)-0.3Li(CB11H12); c) Arrhenius diffusion coefficient plot calculated from impedance and NMR measurements. Figure 3. Arrhenius conductivity of 0.7Li(CB9H10)-0.3Li(CB11H12) and other complex hydride lithium ion conductors, 0.7Li(CB9H10)-0.3Li(CB11H12) has 6.7× at 25°C High lithium ion conductivity of 10-3 S/cm, which is the highest value of complex hydride. Figure 4. Stability of 0.7Li(CB9H10)-0.3Li(CB11H12) and lithium metal matched cells. a) CV curve of Mo/0.7Li(CB9H10)-0.3Li(CB11H12)/Li battery under the condition of scanning rate of 0.5mV/s and scanning range of -0.1 to 5.0V (relative to Li+/Li); Nyquist diagram of Li/0.7Li(CB9H10)-0.3Li(CB11H12)/Li battery, the internal enlarged view shows its interface impedance; c) Field emission SEM of 0.7Li(CB9H10)-0.3Li(CB11H12)/ Li interface Image; d) 10th constant current cycle curve of Li/0.7Li(CB9H10)-0.3Li(CB11H12)/Li battery, the illustration is the enlarged contour; e) Constant current cycle curve, 1st to 100th cycles (on ), the 101st to 200th cycles (middle) and the 201st to 300th cycles (bottom). All electrochemical measurements were made at 25 °C. The scale bar is 30 μm. Figure 5. High energy density all solid state lithium metal battery. a) Schematic representation of the prepared all solid state battery. S, 0.7Li(CB9H10)-0.3Li(CB11H12) and lithium metal are used as a positive electrode, a solid electrolyte and a negative electrode, respectively; b) a voltage curve at a cycle of 0.03 C (50.2 mA/g) at 25 ° C; a charge-discharge curve after initial cycle at a rate of 0.03, 0.05, 0.1, 0.3, and 1 C at 25 ° C; d) a relationship between capacity retention and current density; e) a cycle of 1 C at 25 ° C Discharge capacity and coulombic efficiency; f) discharge capacity and coulombic efficiency at 3 °C at 50 °C. Figure 6. Stability of 0.7Li(CB9H10)-0.3Li(CB11H12) over long periods of time. a) Cyclic performance of discharge capacity and coulombic efficiency at 50 ° C, with a discharge of 5 C and a charge of 1 C; b) Field emission of 0.7Li (CB9H10)-0.3Li (CB11H12)/ Li interface after 100 cycles SEM image; c) XRD pattern of 0.7Li(CB9H10)-0.3Li(CB11H12) before and after 100 cycles; d) before and after 100 cycles, 0.7Li(CB9H10)-0.3Li(CB11H12) Raman pattern.