LiNi0.6Co0.2Mn0.2O2 Cathode-Solid Electrolyte Interfacial Behavior Characterization Using Novel Method Adopting Microcavity Electrode.

Due to the limitations of organic liquid electrolytes, current development is towards high performance all-solid-state lithium batteries (ASSLBs). For high performance ASSLBs, the most crucial is the high ion-conducting solid electrolyte (SE), with a focus on interface analysis between SE and active materials. In the current study, we successfully synthesized the high ion-conductive argyrodite-type (Li6PS5Cl) solid electrolyte, which has 4.8 mS cm-1 conductivity at room temperature. Additionally, the present study suggests the quantitative analysis of interfaces in ASSLBs. The measured initial discharge capacity of a single particle confined in a microcavity electrode was 1.05 nAh for LiNi0.6Co0.2Mn0.2O2 (NCM622)-Li6PS5Cl solid electrolyte materials. The initial cycle result shows the irreversible nature of active material due to the formation of the solid electrolyte interphase (SEI) layer on the surface of the active particle; further second and third cycles demonstrate high reversibility and good stability. Furthermore, the electrochemical kinetic parameters were calculated through the Tafel plot analysis. From the Tafel plot, it is seen that asymmetry increases gradually at high discharge currents and depths, which rise asymmetricity due to the increasing of the conduction barrier. However, the electrochemical parameters confirm the increasing conduction barrier with increased charge transfer resistance.

Toward Achieving a High Ionic Conducting Halide Solid Electrolyte through Low-Cost Metal (Zr and Fe) and F Substitution and Their Admirable Performance in All-Solid-State Batteries.

Recently, the halide solid electrolyte (SE) system has been widely used in lithium solid-state batteries due to their specific properties, such as the high electrochemical stability window that prevents any side reaction with the electrode/electrolyte interface. Conspicuously, the halide SE possesses very low ionic conductivity values in the range (0.2-0.5) mS cm-1. In this work, we enhance the ionic conductivity of Li3YCl6 SE by the substitution of low-cost Fe and Zr elements on the Y-site and F on the Cl site, in which the electrolyte is prepared through high-energy ball milling without a heat treatment process. The structural analysis reveals that the prepared halide SEs showed the pure phase of the Li3YCl6 tetragonal crystal structure and were free from impurity phases. In the prepared composition, the Li2.4Y0.4Zr0.6Cl6 and Li2.4Y0.4Zr0.6Cl5.85F0.15 electrolyte exhibited a higher ionic conductivity of 2.05 and 1.45 mS cm-1, respectively, than Li3YCl6 (0.26 mS cm-1). Interestingly, the Li2.4Y0.4Zr0.6Cl5.85F0.15 electrolyte possesses a better electrochemical stability window of 1.29-3.9 V than Li2.4Y0.4Zr0.6Cl6 (2.1-3.79 V). Moreover, the electrochemical results revealed that the assembled solid-state battery using Li2.4Y0.4Zr0.6Cl6 and Li2.4Y0.4Zr0.6Cl5.85F0.15 electrolyte demonstrated the higher initial Coulombic efficiency of 84.7 and 87%, respectively, than Li3YCl6 of 82.6%. We consider Li2.4Y0.4Zr0.6Cl5.85F0.15 to be an important electrolyte candidate in all-solid-state batteries.

Preparation of Metal-Oxide-Doped Li7P2S8Br0.25I0.75 Solid Electrolytes for All-Solid-State Lithium Batteries.

The all-solid-state lithium battery (ASSB) has received great attention due to its greater safety than the conventional lithium-ion battery (LIB). Sulfide-based inorganic solid electrolytes are an important component to fabricate the ASSB. But to attain a better performance, the ionic conductivity and electrochemical stability of the sulfide-based solid electrolytes need to be improved. In this work, we prepared the metal-oxide-doped/mixed Li7P2S8I0.75Br0.25 lithium superionic conductors by a dry ball-milling process. The high ionic conductivity was achieved by a low-temperature (200 °C) heat-treatment process. The metal-oxide-doped Li7P2S8I0.75Br0.25 solid electrolyte exhibited a higher ionic conductivity value of 7.3 mS cm-1 at room temperature than the bare Li7P2S8I0.75Br0.25 solid electrolyte. The structural characteristics of the prepared solid electrolytes were studied by solid NMR and laser Raman analysis. The electrochemical stability of the prepared solid electrolyte was studied by cyclic voltammetry and DC charge-discharge analysis. The addition of metal oxide increased the electrochemical stability and dry-air stability of the Li7P2S8I0.75Br0.25 solid electrolyte. The Ta2O5-doped Li7P2S8I0.75Br0.25 solid electrolyte was stable even after 300 charge-discharge DC cycles and also 100 h of dry-air exposure. Further, the Ta2O5-doped Li7P2S8I0.75Br0.25 solid electrolyte-based ASSB exhibited a high discharge capacity value of 184 mA h g-1 at 0.1 C rate with 66% initial cycle Coulombic efficiency.

Improving the electrochemical performance of cathode composites using different sized solid electrolytes for all solid-state lithium batteries.

We studied the efficiency of different particle-sized sulfide solid electrolyte-based cathode composites. First, we prepared the Li7P2S8I solid electrolytes with different particle sizes through a high energy ball milling process and solution method. The structural details of the prepared solid electrolytes were studied by powder X-ray diffraction. The surface morphologies and particle size of the electrolytes were studied by field emission electron microscopy. The ionic conductivity of the prepared solid electrolytes was studied by the electrochemical impedance spectroscopy technique. Finally, we have prepared a LiNi0.8Co0.1Mn0.1O2 (NCM 811) based cathode composite and studied the electrochemical performance of the fabricated all-solid-state lithium batteries. The mixed particle-sized solid electrolyte-based cathode composite exhibited higher specific capacitance (127.2 mA h g-1) than the uniform-sized solid electrolyte-based cathode composite (117.1 mA h g-1). The electrochemical analysis confirmed that the sulfide solid electrolytes with mixed particle size exhibited better electrochemical performance.

NiCo2S4 Bi-metal Sulfide Coating on LiNi0.6Co0.2Mn0.2O2 Cathode for High-Performance All-Solid-State Lithium Batteries.

NiCo2S4 nanoparticles (NPs) were dry coated on LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode using a resonant acoustic coating technique to produce all-solid-state lithium batteries. The NiCo2S4 coating improved the electrochemical properties of the NCM622 cathode. In addition, NiCo2S4 eliminated the space-charge layer and the cathode showed an excellent affinity with the interface with a sulfide-based solid electrolyte as an inert material. X-ray diffraction patterns of NCM622 coated with NiCo2S4 showed the same peak separations and lattice parameters as those of bare NCM622. Field-emission scanning electron microscopy and electron dispersive spectroscopy mapping analyses showed that 0.3 wt% NiCo2S4-coated NCM622 had an evenly modified surface with NiCo2S4 NPs. X-ray photoelectron spectroscopy (XPS) revealed that the surface of 0.3 wt% NiCo2S4-coated NCM622 had two different S 2p peaks, a Co-S peak, and Ni and Co peaks, compared to those of bare NCM622. Electrochemical studies with electrochemical impedance spectroscopy and galvanostatic charge-discharge cycle performances showed that NiCo2S4-coated NCM622 retained a higher specific capacity over multiple cycles than bare NCM622. Especially, 0.3 wt% NiCo2S4-coated NCM622 exhibited a capacity retention of 60.6% at a current density of 15 mA/g for 20 cycles, compared to only 37.3% for bare NCM622. Finally, interfacial XPS and transmission electron microscopy-electron energy loss spectroscopy analyses confirmed the stable state of 0.3 wt% NiCo2S4-coated NCM622 with minimal side reactions.

FeS-biochar and Zn(0)-biochar for remediation of redox-reactive contaminants.

To enhance the removal of redox-reactive contaminants, biochars including FeS and Zn(0) were developed via pyrolysis. These biochars significantly promoted the removal of 2,4-dichlorophenol (DCP) by means of sorption and reduction. Compared to direct reduction with FeS and Zn(0), the formation of reduction intermediates and product was enhanced from 21% and 22% of initial DCP concentration to 41% and 52%, respectively. 2,4-Dinitrotoluene (DNT), chromate (CrO4 2-) and selenate (SeO4 2-) were also reductively transformed to reduction products (e.g., 2,4-diaminotoluene [DAT], Cr3+, and selenite [SeO3 2-]) after they sorbed onto the biochars including FeS and Zn(0). Mass recovery as DAT, Cr3+ and selenite was 4-20%, 1-3%, and 10-30% under the given conditions. Electrochemical and X-ray analyses confirmed the reduction capability of the biochars including FeS and Zn(0). Fe and S in the FeS-biochar did not effectively promote the reductive transformation of the contaminants. Contrastingly, the stronger reducer Zn(0) yielded faster reductive transformation of contaminants over the Zn(0)-containing biochar, while not releasing high concentrations of Zn2+ into the aqueous phase. Our results suggest that biochars including Zn(0) may be suitable as dual sorbents/reductants to remediate redox-reactive contaminants in natural environments.