The development of poly(vinylidene fluoride)-based composite solid-state electrolytes is severely hindered by slow Li+ transport and unstable solid-state electrolyte interphases. This study addresses these challenges by proposing a supramolecular ligand intervention strategy using 18-crown-6 as an additive. Coordination between the large-pore crown ethers and Li+ promotes lithium bis(fluorosulfonyl)imide dissociation and increases the free Li+ concentration, thereby enhancing ion transport with a high ionic conductivity and an improved Li+ transference number. Moreover, this coordination homogenizes the Li+ flux, suppressing side reactions and dendrite formation. Consequently, the modified electrolyte significantly enhances the cycling stability of Li||Li cells up to 800 h with a reduced overpotential. Additionally, the Li||NCM811 cells delivered 84.2% capacity retention after 2500 cycles at 10C, and retained 72.5% capacity after 780 cycles even at a high cut-off voltage of 4.5 V at 5C. Structural and interfacial characterizations confirmed the formation of a dense LiF/Li3N-rich SEI layer, which enhances mechanical strength and ionic transport. This study provides a robust modification approach using supramolecular ligands to achieve high-performance solid-state lithium-metal batteries.
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Open Access
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Composite solid electrolytes (CSEs) are considered among the most promising candidates for solid-state batteries. However, their practical application is hindered by low ionic conductivity and a limited lithium-ion transference number, primarily owing to the insufficient mobility of Li+. In this work, we design a heterojunction nanoparticle composed of bimetallic zeolitic imidazolate frameworks (ZIFs) coupled with amorphous titanium oxide (TiO2@Zn/Co–ZIF) as a filler to fabricate a composite solid-state electrolyte (PVZT). The amorphous TiO2 coating facilitates salt dissociation through Lewis acid–base interactions with the anions of the lithium salt. Meanwhile, the Zn/Co–ZIF framework not only provides additional selective pathways for Li+ transport but also effectively restricts anion migration through its confined pore size. The synergistic effect results in a high room-temperature ionic conductivity (8.8 × 10−4 S·cm−1) and a lithium-ion transference number of 0.47 for PVZT. A symmetrical cell using PVZT demonstrates stable Li+ deposition/stripping for over 1100 h at a current density of 0.1 mA·cm−2. Additionally, a LiNi0.8Co0.1Mn0.1O2/Li full cell using PVZT retains 75.0% of its capacity after 1200 cycles at a 2 C rate. This work offers valuable insights into the design of functional fillers for CSEs with highly efficient ion transport.
The rapid expansion of lithium-ion batteries in consumer electronics, electric vehicles, and energy storage systems escalates a demand for batteries with higher energy density and enhanced safety. However, conventional lithium-ion batteries employing liquid electrolytes are increasingly constrained due to their limited electrochemical stability, susceptibility to leakage, and lithium dendrite formation, which pose risks of short circuits and thermal runaway. Solid-state batteries (SSBs) with solid electrolytes present a promising solution to these challenges, offering a potential for higher safety and energy density.
Recent advancements in SSBs include the development of solid electrolytes with a high ionic conductivity, solid–solid interface optimization, and composite electrode design. Nonetheless, some issues such as lithium-ion transport barriers across phases, interfacial impedance, and the performance limitations of thick electrodes continue to impede the commercial viability of SSBs. To address these multifaceted challenges, a concept of "lithium-ion transport throughput" is proposed as a comprehensive descriptor for evaluating SSB performance. This descriptor quantifies the quantity of lithium ions transported across the electrode/electrolyte interface per unit area over time, considering some factors such as areal capacity and charge/discharge rates.
This review systematically examines strategies to enhance lithium-ion transport throughput from three key perspectives, i.e., bulk ionic transport in solid electrolytes, electrode/electrolyte interface design, and synergistic ionic/electronic transport networks within electrodes. we aim to offer insights into improving the overall performance of SSBs to meet the demands for high safety and energy density in next-generation energy storage systems via integrating materials design with structural optimization. In addition, we also conduct quantitative calculations to analyze lithium-ion transport throughput in recently published high-performance SSBs, providing a detailed comparison of various systems. We illustrate how material advancements and interface designs affect overall performance via compiling representative data (i.e., areal capacity, charge/discharge rates, and resulting throughput values). These calculations highlight trends and identify strategies that can achieve significant throughput improvements, offering a robust foundation for future optimization efforts.
The introduction of lithium-ion transport throughput offers a novel and integrated approach to assess the charging and discharging capabilities of SSBs. Lithium-ion transport throughput provides a holistic understanding of the electrochemical processes within SSBs via considering both areal capacity and current density, bridging a gap between theoretical performance and practical application. Future studies should focus on refining this descriptor and employing it as a standard for evaluating SSB performance across various material systems.
The ionic conductivity of solid electrolytes remains a key property of SSB performance. Recent advancements, such as high-entropy doping, amorphous structures, and vacancy engineering, achieve significant improvements in ionic transport. For instance, high-entropy sulfide electrolytes exhibit ionic conductivities, compared to liquid electrolytes. The development of halide electrolytes shows their high voltage stability and ionic conductivities.
Interface impedance is a critical barrier in SSBs. Conventional solid–solid contacts restrict ionic transport efficiency. Innovations such as mixed-conductive interlayers, magnetron sputtering techniques, and porous or functionalized interface layers demonstrate effectiveness in reducing interface resistance and enhancing long-term stability. Future research should emphasize scalable techniques for interface engineering to ensure compatibility with large-scale production.
High-loading electrode designs are essential for improving energy density, but often face ionic and electronic transport challenges. Constructing electronic and ion dual-transport networks within electrodes has a potential to address these issues. Some strategies such as integrating conductive nanomaterials and designing vertically aligned structures can optimize the utilization of active materials and improve high-rate performance. The integration of lithium alloy layers in anodes also offers an approach to enhance lithium-ion transport and address volume change issues during cycling.
The development of solid-state batteries (SSBs) requires a multidisciplinary approach that combines materials science, interface engineering, and structural design. One key research priority is material innovation, which involves developing solid electrolytes with higher ionic conductivities and lower costs. Another priority is to achieve long-term stability and low impedance at solid-solid interfaces, which can be accomplished through techniques such as surface coating, interfacial buffer layers, and in-situ formation of interfacial layers. Structural optimization is also crucial, as it involves designing thick electrode architectures with optimized ionic and electronic transport pathways. Finally, system-level integration is essential, as it requires attention to thermal management, mechanical integrity, and scalability. Collaborative efforts between academia and industry are vital to accelerate the transition from laboratory-scale innovations to commercial products.
SSBs can overcome current limitations and be widely used in electric vehicles and grid-scale energy storage via addressing the challenges above. The ongoing development of SSB technology is crucial for promoting energy sustainability and reaching global carbon neutrality goals.
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Composite solid-state electrolytes have received significant attention due to their combined advantages as inorganic and polymer electrolytes. However, conventional ceramic fillers offer limited ion conductivity enhancement for composite solid-state electrolytes due to the space-charge layer between the polymer matrix and ceramic phase. In this study, we develop a ferroelectric ceramic ion conductor (LiTaO3) as a functional filler to simultaneously alleviate the space-charge layer and provide an extra Li+ transport pathway. The obtained composite solid-state electrolyte comprising LiTaO3 filler and poly (vinylidene difluoride) matrix (P-LTO15) achieves an ionic conductivity of 4.90 × 10−4 S cm−1 and a Li+ transference number of 0.45. The polarized ferroelectric LiTaO3 creates a uniform electric field and promotes homogenous Li plating/stripping, providing the Li symmetrical batteries with an ultrastable cycle life for 4000 h at 0.1 mA cm−2 and a low polarization overpotential (~50 mV). Furthermore, the solid-state NCM811/P-LTO15/Li full batteries achieve an ultralong cycling performance (1400 cycles) at 1 C and a high discharge capacity of 102.1 mAh g−1 at 5 C. This work sheds light on the design of functional ceramic fillers for composite solid-state electrolytes to effectively enhance ion conductivity and battery performance.
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The poor contact and side reactions between Li1.3Al0.3Ti1.7(PO4)3 (LATP) and lithium (Li) anode cause uneven Li plating and high interfacial impendence, which greatly hinder the practical application of LATP in high-energy density solid-state Li metal batteries. In this work, a multifunctional ferroelectric BaTiO3 (BTO)/poly(vinylidene fluoride-co-trifluoroethylene-co-chlorotrifluoroethylene) (P[VDF-TrFE-CTFE]) composite interlayer (B-TERB) is constructed between LATP and Li metal anode, which not only suppresses the Li dendrite growth, but also improves the interfacial stability and maintains the intimate interfacial contact to significantly decrease the interfacial resistance by two orders of magnitude. The B-TERB interlayer generates a uniform electric field to induce a uniform and lateral Li deposition, and therefore avoids the side reactions between Li metal and LATP achieving excellent interface stability. As a result, the Li/LATP@B-TERB/Li symmetrical batteries can stably cycle for 1800 h at 0.2 mA cm−2 and 1000 h at 0.5 mA cm−2. The solid-state LiFePO4/LATP@B-TERB/Li full batteries also exhibit excellent cycle performance for 250 cycles at 0.5 C and room temperature. This work proposes a novel strategy to design multifunctional ferroelectric interlayer between ceramic electrolytes and Li metal to enable stable room-temperature cycling performance.
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