Hydroxyl-rich single-ion conductors enable solid hybrid polymer electrolytes with excellent compatibility for dendrite-free lithium metal batteries

Advances in poly(ethylene oxide)-based solid-state lithium-ion battery research

Solid-state lithium-ion batteries are increasingly recognized as a pivotal advancement for the next generation of energy storage technology, owing to their superior safety, high energy density, and extended cycle life. Among the various solid-state polymer materials for Li-ion batteries, poly(ethylene oxide) (PEO)-based solid-state electrolytes have garnered significant attention owing to their excellent interfacial affinity and high solubility for different lithium salts. However, PEO-based solid electrolytes continue to face obstacles, such as diminished ionic conductivity at ambient temperature, inadequate mechanical characteristics, and severe concentration polarization in practical applications. Researchers have proposed a series of modification strategies to enhance the room temperature ionic conductivity by exploring polymer copolymerization, blending, and hyperbranched methods. To optimize the mechanical properties, studies mainly focus on adding high-strength fillers, introducing cross-linking networks, and developing self-repairing materials. To mitigate the concentration polarization effect, a polyanionic configuration is introduced into the polymer backbone, accompanied by the addition of fillers having anionic receptor groups. In this review, the physicochemical properties and Li+ migration mechanisms of PEO-based solid polymer electrolytes are systematically described, focusing on the aforementioned modification strategies and their research progress. Additionally, it offers insights into future development trends.

A Fiber-Reinforced Poly(ionic liquid) Solid Electrolyte with Low Flammability and High Conductivity for High-Performance Lithium-Metal Batteries

Construction of polymer-based solid electrolytes with both low flammability and high ionic conductivity for lithium-metal batteries is still a great challenge but highly desirable. Herein, we report on a series of fiber-reinforced poly(ionic liquid) solid electrolytes prepared through an in situ copolymerization of ionic liquid monomers (IL) and poly(ethylene glycol) diacrylate (PEGDA) units with different ratios inside a polyacrylonitrile (PAN) fiber membrane. Such PAN/Poly-IL-PEGDA composite electrolytes demonstrate promising low flammability due to the excellent fire-resistant feature of the employed IL units. Moreover, it is remarkable to see that the optimized PAN/Poly-IL-PEGDA-1 electrolyte also exhibits highly dense structure with low thickness (31 μm), high ionic conductivity (0.32 mS cm-1 at 30 °C), and wide electrochemical window (up to 4.8 V). As a result, both LiFePO4//Li and NCM//Li full cells with such an electrolyte exhibit both excellent rate capability and cycling stability. This study provides a simple strategy for preparing composite polymer electrolytes with low flammability and high conductivity for high-performance lithium-metal batteries.

Diethylenetriaminepentaacetic Acid-based Conducting Solid Polymer Electrolytes Impede Lithium Dendrites and Impart Antioxidant Capacity in Lithium-Ion Batteries

In the development of lithium-ion batteries (LIBs), cheaper and safer solid polymer electrolytes are expected to replace combustible organic liquid electrolytes to meet the larger market demand. However, low ionic conductivity and inadequate cycling stability impede their commercial viability. Herein, a novel flexible conducting solid polymer electrolytes (CSPEs) based on polyvinyl alcohol (PVA) and ion-polarized diethylenetriaminepentaacetic acid (P-DETP) is developed for the first time and applied in LIBs. PVA and P-DETP form a compact polymer network through hydrogen bonding, enhancing the thermomechanical stability of CSPE while restricting the migration of larger anions. Furthermore, density functional theory calculations confirm that P-DETP can facilitate the dissociation of Li+-TFSI- via electrostatic attraction, resulting in increased mobility of lithium ions. Additionally, P-DETP contributes to the formation of a stable electrode-electrolyte interface layer, effectively suppressing the growth of lithium dendrites and improving antioxidant capacity. These synergistic effects enable CSPE to exhibit remarkable properties including high ionic conductivity (2.8 × 10-4 S cm-1), elevated electrochemical potential (5.1 V), and excellent lithium transference number (0.869). Notably, the P-DETP/LiTFSI CSPE demonstrates stable performance not only in LiFePO4 batteries but also adapts to high-nickel ternary LiNi0.88Co0.06Mn0.06O2 cathode, highlighting its immense potential for application in high energy density LIBs.

Enhanced Lithium-Ion Transport in Lithium Metal Batteries Using ZSM-5 Nanosheets Hybridized Solid Polymer Electrolytes

Solid polymer electrolytes (SPEs) are the key components of lithium metal batteries to overcome the obstacle of insecurity in conventional liquid electrolytes; however, the trade-off between their ionic conductivity and mechanical properties remains a significant challenge. In this work, two-dimensional ZSM-5 nanosheets as fillers are incorporated into a poly(ethylene oxide) (PEO) matrix and lithium salts to obtain composite polymer electrolytes (CPEs). The improved physicochemical and electrochemical properties of the CPE membranes are characterized in full detail. Stripping/plating measurements in symmetric Li/Li cells and cyclic charge/discharge tests are performed to investigate the cyclability and stability of the CPEs. All-solid-state LiFePO4/Li batteries deliver excellent cycling performance with an initial discharge capacity of 152.3 mAh g-1 and 91.4% capacity retention after 200 cycles at 0.2 C, with a discharge specific capacity of 118.8 mAh g-1 remaining after 350 cycles at 0.5 C. Therefore, CPEs containing ZSM-5 nanosheets are a promising option for all-solid-state lithium-ion batteries.

Imidazolium-Type Poly(ionic liquid) Endows the Composite Polymer Electrolyte Membrane with Excellent Interface Compatibility for All-Solid-State Lithium Metal Batteries

Developing a poly(ethylene oxide) (PEO)-based polymer electrolyte with high ionic conductivity and robust mechanical property is beneficial for real applications of all-solid-state lithium metal batteries (ASSLMBs). Herein, an excellent organic/inorganic interface compatibility of all-solid-state composite polymer electrolytes (CPEs) is achieved using a novel imidazolium-type poly(ionic liquid) with strong electrostatic interactions, providing insights into the achievement of highly stable CPEs. The key properties such as micromorphologies, thermal behavior, crystallinity, t_Li⁺, mechanical property, lithium anode surficial morphology, and electrochemical performance are systematically investigated. The combined experimental and density functional theory (DFT) simulation results exhibit that the strong electrostatic interaction and ion-dipole interaction cooperated to improve the compatibility of the CPE, with a high ionic conductivity of 1.46 × 10^-4 S cm^-1 at 40 °C and an incredible mechanical strain of 2000% for dendrite-free and highly stable all-solid-state LMBs. This work affords a promising strategy to accelerate the development of PEO-based polymer electrolytes for real applications in ASSLMBs.