Significantly enhanced lithium-ion conductivity of solid-state electrolytes via flower-like structured lamellar metal-organic frameworks with open metal sites.

Solid-state electrolytes (SSEs) are a frontier topic in battery technology with the potential to solve the safety problem of lithium ion batteries (LIBs). Metal organic frameworks (MOFs) are regarded as promising candidates for a new type of solid-state ion conductor, but the low ionic conductivity and unstable interface contact still seriously hinder the application of MOF based solid state electrolytes (SSEs). Herein, a HKUST-1 based solid-state electrolyte (SSE) was designed and prepared, which possess both a flower-like lamellar structure and sufficient accessible open metal sites (OMSs). These sites could capture anions and release free lithium ions (Li+), and the ultra-thin thickness shortened the Li+ transmission path. The lamellar HKUST-1 exhibits an ionic conductivity of 1.6 × 10-3 S cm-1 at 25 °C with an activation energy of 0.12 eV, Li-ion transference number of 0.73 and electrochemical stability window of 0-5.5 V. The MOF based electrolyte has been assessed with Li|MOFs|LiFePO4 cells at 25 °C, which showed a high capacity retention of 93% at 0.1C after 100 cycles and excellent rate capability. It also exhibited excellent cycle stability in Li symmetric cells. This Li+ conduction strategy of modulating the morphology and modifying pore walls provides a new research idea for designing advanced SSEs.

A Composite of Hierarchical Porous MOFs and Halloysite Nanotubes as Single-Ion-Conducting Electrolyte Toward High-Performance Solid-State Lithium-Ion Batteries.

Metal-organic frameworks (MOFs), as a promising rechargeable electrochemical energy storage material have emerged in the field of solid-state lithium batteries. However, low ionic conductivity and high interfacial impedance still severely hamper the application of MOF-based solid-state electrolytes (SSE). In this work, a novel hierarchical porous H-ZIF-8 solid-state electrolyte (SSE) material is harvested through the in situ growth of zinc nitrate hydroxide nanosheets, expressing excellent ion conductivity of 1.04 × 10-3  S cm-1 and Li+ -transference number of 0.71. Moreover, the morphology and structure of H-ZIF-8 is further optimized to obtain a composite H-ZIF-8/HNT by decorating halloysite nanotubes (HNT). Notably, functionalized H-ZIF-8/HNT as an electrolyte presents obvious enhancement on electrochemical properties: higher ionic conductivity of 7.74 × 10-3  S cm-1 , better single-ion transmittability ( t Li + ${t}_{{\mathrm{Li}}^{+}}$ = 0.84), good interfacial compatibility as well as excellent rate performance. More importantly, the Li/LiFePO4 battery equipped with H-ZIF-8/HNT SSE has efficient lithium-dendrite suppression and up to 84% capacity retention (104.16 mA h g-1 ) after 200 times galvanostatic charge/discharge cycles. This work enriches the solid-state lithium-ion composite electrolyte materials, opening an entirely new way for enhancing electrochemical performance.

Efficient improvement of the lithium ionic conductivity for a polymer electrolyte via introducing porous metal-organic frameworks.

The electrolyte membrane plays a vital role in the practical conduction application of lithium-ion batteries. In this study, a series of PVDF-HFP/MOF-5 composite electrolyte materials were harvested by incorporating MOF-5 into PVDF-HFP, presenting excellent electrochemical characteristics and mechanical properties. Importantly, the performances of the PVDF-HFP/MOF-5 composites depended greatly on the content of MOF-5 introduced and the channels change. The PVDF-HFP/MOF-5-II with a MOF-5 content of 2 wt% revealed optimal ionic conductivity of 1.20 × 10-3 S cm-1 and lithium ion transference number of 0.9 at room temperature, which shows potential application prospects in the field of electrolyte materials.

Significant improvement of the lithium-ion conductivity of solid-state electrolytes by fabricating large pore volume hollow ZIF-8.

Metal-organic frameworks (MOFs) emerging as a type of functional material have been widely used in electrochemical energy storage and conversion in recent years. Hollow MOFs with a large pore volume and surface area can increase the contact area between active materials and electrolytes, thus improving the ionic conductivity of the materials. Herein, we obtained a kind of hollow MOF (ZIF-8) using carboxylate-terminated polystyrene microspheres as exterior templates. Transmission electron microscopy and N2 adsorption/desorption analysis revealed that the average cavity diameter of hollow ZIF-8 is 1 µm. Moreover, hollow ZIF-8 exhibits excellent electrochemical quality with an ionic conductivity of 7.36 × 10-4 S cm-1, a lithium ion transference number of 0.83 and an activation energy of 0.15 eV in a wide stable electrochemical window of 2.0-6.5 V at room temperature. Compared with the traditional non-hollow ZIF-8, the electrochemical performance has been improved obviously. Consequently, our strategy of fabrication of large pore volume hollow MOFs provides a new perspective for the development of solid electrolytes with excellent lithium ionic conductivity.