Hydrogenated borophene nanosheets based multifunctional quasi-solid-state electrolytes for lithium metal batteries

Structural characterization of cage clusters assembled borophene and implication for cathode electrocatalysts in Li-O2 batteries

The successful fabrication of quasi-freestanding bilayer borophene in experiments, combined with its superior metallic character, has propelled it to a rising star among two-dimensional materials, making it highly promising for applications in micro-electronic devices. Using first-principles calculations, we comprehensively explore and characterize cage cluster assembled borophenes through various methods for experimental references. The simulated scanning tunneling microscope (STM) images under diverse bias voltages exhibit distinct morphologies and closely associated with the partial densities of states (PDOS) of the surface boron atoms. High-resolution and large-scale simulated transmission electron microscope (TEM) images are investigated to detect the internal crystal structures, facilitating better identification of non-monolayer borophenes. The partial densities of states, electronic localization functions and Mulliken bond populations have been calculated to analyze the differences of morphology in STM and TEM images. Furthermore, simulated X-ray diffraction (XRD), Raman, and infrared (IR) spectra are characterized to further assist in distinguishing the phases of borophene. In light of ultrahigh stability and excellent metallic character, cluster assembled borophene of P3¯m1 symmetry act as cathode materials of Li-O2 battery with lower overpotential in oxygen evolution reaction (OER) than oxygen reduction reaction (ORR) processes. The overpotential is closely related to the adsorption strength of LiO2 and Li2O2 intermediates on surface of boron sheets. These theoretical results offer crucial guidance for the experimental identification of borophenes and suggest that the new type of cluster assembled systems might be suitable for the cathode materials of future Li-O2 batteries.

Polymeric Electrolytes for Solid-state Lithium Ion Batteries: Structure Design, Electrochemical Properties and Cell Performances

Solid-state electrolytes are key to achieving high energy density, safety, and stability for lithium-ion batteries. In this Review, core indicators of solid polymer electrolytes are discussed in detail including ionic conductivity, interface compatibility, mechanical integrity, and cycling stability. Besides, we also summarize how above properties can be improved by design strategies of functional monomers, groups, and assembly of batteries. Structures and properties of polymers are investigated here to provide a basis for all-solid-state electrolyte design strategies of multi-component polymers. In addition, adjustment strategies of quasi-solid-state polymer electrolytes such as adding functional additives and carrying out structural design are also investigated, aiming at solving problems caused by simply adding liquids or small molecular plasticizer. We hope that fresh and established researchers can achieve a general perspective of solid polymer electrolytes via this Review and spur more extensive interests for exploration of high-performance lithium-ion batteries.

Structurally integrated asymmetric polymer electrolyte with stable Janus interface properties for high-voltage lithium metal batteries

Solid-state polymer electrolytes are outstanding candidates for next-generation lithium metal batteries in the realm of high specific energy densities, high safeties and tight contact with electrodes. However, their applications are still hindered by the limitations that no single polymer is electrochemically stable with the oxidizing high-voltage cathode and the highly reductive Li anode, simultaneously. Herein, a bilayer asymmetric polymer electrolyte (SL-SPE) without accessional interface resistance that using poly (ethylene glycol) diacrylate (PEGDA) as a "bridge" to connect the sulfonyl (OS = O)-contained oxidation-tolerated layer and polyether-derived reduction-tolerated layer (SPE), is proposed and synthesized by sequential two-step UV polymerizations. SL-SPE can provide widened electrochemical stability window up to 5 V, while simultaneously deploying a stable Janus interface property. Eventually, the superior high-voltage (4.4 V) cycling durability can be displayed in LiNi_0.6Co_0.2Mn_0.2O₂|SL-SPE|Li batteries. This finding provides a bran-new idea for designing multifunctional polymer electrolytes in the application of solid-state batteries.

Three-dimensional polyimide nanofiber framework reinforced polymer electrolyte for all-solid-state lithium metal battery

The replacement of traditional liquid electrolytes with polyethylene oxide (PEO) based composite polymer electrolytes (CPEs) is an important strategy to address the current flammability and explosiveness of lithium batteries since PEO CPEs have high flexibility, excellent processability and moderate cost. However, the insufficient ionic conductivity and inferior mechanical strength of PEO CPEs do not suit the operating requirements of all-solid-state lithium metal batteries at room temperature. Herein, three-dimensional (3D) framework composed of interweaved high-modulus polyimide (PI) nanofibers along with functional succinonitrile (SN) plasticizers are employed to synergistically reinforce the ionic conductivity and mechanical strength of PEO CPEs. Impressively, benefitting from the synergistic effects of 3D PI framework and SN plasticizer, PI-PEO-SN CPEs exhibits high ionic conductivity of 1.03 × 10^-4 S cm^-1 at 30 °C, remarkable tensile strength of 4.52 MPa, and superior Li dendrites blocking ability (>400 h at 0.1 mA cm^-2). Such favorable features of PI-PEO-SN CPEs endow LiFePO₄/PI-PEO-SN/Li solid-state prototype cells with high specific capacity (151.2 mA h g^-1 at 0.2 C), long cycling lifespan (>150 cycles with 91.7 % capacity retention), and superior operating safety even under bending, folding and cutting harsh conditions. This work will pave the avenues to design and fabricate new high-performance PEO CPEs for the high energy density and safety all-solid-state batteries.

Scalable synthesis of hydroxyl-functionalized boron nanosheets for high ion-conductive solid-state electrolyte applications

A hydroxyl-functionalized boron nanosheet is developed as the filler material for the solid-state electrolyte (SSE) of lithium batteries. The nanosheet exhibits good oxidation resistance and thermal stability. Its composite SSE shows high ionic conductivity, and the resulting batteries present much enhanced capacities, rate capability and cycling performance, proving the electrochemical advances of the boron nanosheet.