Design of Block-Copolymer Nanoporous Membranes for Robust and Safer Lithium-Ion Battery Separators

Robust and High-Wettability Cellulose Separators with Molecule-Reassembled Nano-Cracked Structures for High-Performance Supercapacitors

Separators in supercapacitors (SCs) frequently suffer from high resistance and the risk of short circuits due to inadequate electrolyte wettability, depressed mechanical properties, and insufficient thermal stability. Here, we develop a high-performance regenerated cellulose separator with nano-cracked structures for SCs via a binary solvent of superbase-derived ionic liquid and dimethylsulfoxide (DMSO). The unique nano-cracks with an average width of 7.45 nm arise from the acceleration of cellulose molecular reassembly by DMSO-regulated hydrogen bonding, which endows the separator with high porosity (70.2%) and excellent electrolyte retention (329%). The outstanding thermal stability (273 °C) and mechanical strength (70 MPa) enable the separator to maintain its structural integrity under high temperatures and external forces. With these benefits, the SC utilizing the cellulose separator enables a high specific capacitance of 93.6 F g-1 at 1.0 A g-1 and a remarkable capacitance retention of 99.5% after 10,000 cycles compared with the commercial NKK-MPF30AC and NKK-TF4030. The robust and high-wettability cellulose separator holds promise as a superior alternative to commercial separators for advanced SCs with enhanced performance and improved safety.

Making Accessible and Attractive Porosities in Block Copolymer Nanofibers for Highly Permeable and Durable Air Filtration

Submicron particulate matter (PM) can penetrate deeply into human tissue, posing a serious threat to human health. However, the electrostatic charge of commercial respirators is easily dissipated, making it difficult to maintain long-term filtration. Herein, a hierarchically porous filter based on nanofibers with accessible porosity and particulate-attractive surfaces, achieving significant filtration performance is developed through polarity-driven interactions. This is achieved by selective swelling of electrospun nanofibers of the block copolymer of polysulfone and poly(ethylene glycol) (PSF-b-PEG), in which the originally solid nanofibers are 3D perforated with the PEG chains lined along the pore walls. Thus-produces nanofiber filters exhibit a long-term continuous filtration with an efficiency of over 95% for PM0.3 and a low pressure drop of only 40 Pa. In particular, it maintains superior filtration performance even under high particle concentrations and high humidity conditions. Additionally, the filter exhibits high air permeability (10814 m3 m-2 h-1 kPa-1) and water vapor transmission rate (3707 g m-2 d-1). This work provides new strategies and understandings on the development of porous structures simultaneously exhibiting high gas permeability and efficient particulate rejection.

A high-safety lithium-ion battery electrospun separator with Si3N4-assisted sulfonated poly(ether ether ketone) for regulating lithium flux

The uncontrolled lithium (Li) dendrite growth significantly impacts the safety performance of polymer separators. To mitigate this growth, this study introduces Si3N4 into sulfonated poly(ether Ether Ketone) (SPEEK) and prepares Si3N4/SPEEK composite separators via electrospinning. At the interface between the Si3N4/SPEEK separator and the Li anode, the Si nanowires that form impede Li dendrite growth, thereby enhancing the electrochemical performance of lithium-ion batteries (LIBs). The Li deposition test of the 10 % Si3N4/SPEEK separator can operate for 1000 h without short-circuiting. Additionally, the LiFePO4||Li cell with the 10 % Si3N4/SPEEK separator shows improved initial discharge capacity (157.8 mAh g-1 at 1C) and superior rate performance (125 mAh g-1 at 10C). Moreover, the nano-scale Si3N4 endows the separator with robust thermal and mechanical properties. The FLIR observations reveal that the 10 % Si3N4/SPEEK separator maintains uniform thermal distribution and structural integrity even at 300 °C, ensuring safe battery operation at high temperatures. The additional load of the 10 % Si3N4/SPEEK separator can reach 10.2 mN, which enhances the puncture resistance of the separator. This work provides a solid approach for the application of SPEEK as a high-safety and high-rate LIB separator.

Effects of H2O on Improving the Performance of a Solid Composite Electrolyte Fabricated via an Air-Processable Technique

Inert atmosphere is normally necessary for fabrication of solid composite electrolytes (SCEs) as a crucial part of solid-state Li-metal batteries in order to avoid undesirable reactions induced by ambient moisture. Herein, we developed an air-processable technique to fabricate SCEs by employing LiCF3SO3 (LiOTf) as the Li salt, which was combined with Li6.4La3Zr1.4Ta0.6O12 (LLZTO) as the fast Li-conductor and polyvinylidene difluoroethylene/polyvinyl acetate (PVDF/PVAC) as the polymer matrix. With the assistance of trace H2O dissolved in electrolyte solution, the room-temperature Li+ conductivity of the obtained aSCE reached as high as 5.09 × 10-4 S cm-1, which was over 3 orders of magnitude higher than that of the one (iSCE, 1.93 × 10-7 S cm-1) cast by the electrolyte solution prepared in an inert atmosphere. The theoretical calculation results reveal that the oxygen atom of H2O exhibits a high propensity to interact with the Li atom in LiOTf (Li···O), thereby establishing a hydrogen bond with the oxygen atom (H···O) in N,N-dimethylformamide (solvent). Such interactions promoted the dissociation of LiOTf and led to the formation of uniform Li+ transportation channels. Simultaneously, the composition distribution was also altered, resulting in a smoother surface of aSCE and lowered crystallinity of PVDF. On this basis, the LiOTf/LLZTO/PVDF/PVAC solution at 60 °C was directly coated onto the surface of the LiFePO4 (LFP) cathode to fabricate the LFP-aSCE film after drying in an oven. The assembled LFP-aSCE/Li battery wetted by trace sulfolane exhibited an initial Coulombic efficiency of 94.7% and a capacity retention rate of up to 96% at 0.2 C (137 mAh g-1) after 180 cycles and a high capacity of 143.7 mAh g-1 at 0.5 C (150 cycles). Overall, this work could pave the way for the facile fabrication of solid electrolytes.

Scalable Preparation of Polyimide Sandwiched Separator for Durable High-Rate Lithium-Metal Battery

The ever-growing demands for efficient energy storage accelerate the development of high-rate lithium-metal battery (LMB) with desirable energy density, power density, and cycling stability. Nevertheless, the practical application of LMB is critically impeded by internal temperature rise and lithium dendrite growth, especially at high charge/discharge rates. It is highly desired but remains challenging to develop high-performance thermotolerant separators that can provide favorable channels to enable fast Li+ transport for high-rate operation and simultaneously homogenize the lithium deposition for dendrite inhibition. Polyimide-based separators with superior thermal properties are promising candidate alternatives to the commercial polyolefin-based separators, but previous strategies of designing either nanoporous or microporous channels in polyimide-based separators often meet a dilemma. Here, a facile and scalable approach is reported to develop a polyimide fiber/aerogel (denoted as PIFA) separator with the microporous polyimide fiber membrane sandwiched between two nanoporous polyimide aerogel layers, which can enable LMBs with remarkable capacity retention of 97.2% after 1500 cycles at 10 C. The experimental and theoretical studies unravel that the sandwiched structure of PIFA can appreciably enhance the electrolyte adsorption and ionic conductivity; while, the aerogel coating can effectively inhibit dendrite growth to realize durable high-rate LMBs.

Tough polycyclooctene nanoporous membranes from etchable block copolymers

Porous materials with pore dimensions of the nanometer length scale are useful as nanoporous membranes. ABA triblock copolymers are convenient precursors to such nanoporous materials if the end blocks are easily degradable (e.g., polylactide or PLA), leaving nanoporous polymeric membranes (NPMs) if in thin film form. The membrane properties are dependent on midblock monomer structure, triblock copolymer composition, overall molar mass, and polymer processing conditions. Polycyclooctene (PCOE) NPMs were prepared using this method, with tunable pore sizes on the order of tens of nanometers. Solvent casting was shown to eliminate film defects and allowed achievement of superior mechanical properties over melt processing techniques, and PCOE NPMs were found to be very tough, a major advance over previously reported NPMs. Oxygen plasma etching was used to remove the surface skin layer to obtain membranes with higher surface porosity, membrane hydrophilicity, and flux of both air and water. This is a straightforward method to reliably produce highly tough NPMs with high levels of porosity and hydrophilic surface properties.

Facile fabrication of PMIA composite separator with bi-functional sodium-alginate coating layer for synergistically increasing performance of lithium-ion batteries

Lack of safety and unenough electrochemical performance have been known as a fundamental obstacle limiting the extensive application of lithium-ion batteries (LIBs). It is really preferable but challenging to fabricate thermal-response separator with shutdown function for high-performance LIBs. Herein, a thermal-response sodium-alginate modified PMIA (Na-Alg/PMIA) composite separator with shutdown function was designed and prepared by non-solvent phase induced separation (NIPs). PMIA and Na-Alg are combined by hydrogen bonding. While Na-Alg increases polar groups and makes Li⁺ easy to be transported, a small amount of Na⁺ can provide Li⁺ active sites, accelerate Li⁺ deposition coating and effectively inhibit the formation of Li dendrites. The as-prepared Na-Alg/PMIA composite separators can close pores at 200 °C and maintain dimensional integrity without obvious thermal shrinkage. In addition, the Na-Alg/PMIA composite separators has excellent wettability and ionic conductivity, resulting in high specific capacity and retention during the charge-discharge cycles. After 50 cycles, the capacity retention of cells with the Na-Alg/PMIA-20 composite separator is 84.3 %. At 2 C, cells with the Na-Alg/PMIA-20 composite separators still held 101.1 mAh g^-1. This facile yet effective method improves the electrochemical performance while ensuring the safety of the LIBs, which provides ideas for the commercial application of PMIA separators.

Dewetting-Induced Hierarchical Self-Assembly of Block Copolymers Templated by Colloidal Crystals

Recent advances in high-performance flexible electronic devices have increased the demand for more diverse and complex nanofabrication methods; high-resolution, high-efficiency, and low-cost patterning strategies for next-generation devices are therefore required. In this study, we demonstrate the formation of dewetting-induced hierarchical patterns using two self-assembled materials: block copolymers (BCPs) and colloidal crystals. The combination of the two self-assembly methods successfully generates multiscale hierarchical patterns because the length scales of the periodic colloidal crystal structures are suitable for templating the BCP patterns. Various concentric ring patterns were observed on the templated BCP films, and a free energy model of the polymer chain was applied to explain the formation of these patterns relative to the template width. Frequently occurring spiral-defective features were also examined and found to be promoted by Y-junction defects.

Surfactant-Assisted Sulfonated Covalent Organic Nanosheets: Extrinsic Charge for Improved Ion Transport and Salinity-Gradient Energy Harvesting

Charge-governed ion transport is the vital property of nanofluidic channels for salinity-gradient energy harvesting and other electrochemical energy conversion technologies. 2D nanofluidic channels constructed by nanosheets exhibit great superiority in ion selectivity, but a high ion transport rate remains challenging due to the insufficiency of intrinsic surface charge density in nanoconfinement. Herein, extrinsic surface charge into nanofluidic channels composed of surfactant-assisted sulfonated covalent organic nanosheets (SCONs), which enable tunable ion transport behaviors, is demonstrated. The polar moiety of surfactant is embedded in SCONs to adjust in-plane surface charges, and the aggregation of nonpolar moiety results in the sol-to-gel transformation of SCON solution for membrane fabrication. The combination endows SCON/surfactant membranes with considerable water-resistance, and the designable extrinsic charges promise fast ion transport and high ion selectivity. Additionally, the SCON/surfactant membrane, serving as a power generator, exhibits huge potential in harvesting salinity-gradient energy where corresponding output power density can reach up to 9.08 W m^-2 under a 50-fold salinity gradient (0.5 m NaCl|0.01 m NaCl). The approach to extrinsic surface charge provides new and promising insight into regulating ion transport behaviors.

Well-Defined Nanostructures by Block Copolymers and Mass Transport Applications in Energy Conversion

With the speedy progress in the research of nanomaterials, self-assembly technology has captured the high-profile interest of researchers because of its simplicity and ease of spontaneous formation of a stable ordered aggregation system. The self-assembly of block copolymers can be precisely regulated at the nanoscale to overcome the physical limits of conventional processing techniques. This bottom-up assembly strategy is simple, easy to control, and associated with high density and high order, which is of great significance for mass transportation through membrane materials. In this review, to investigate the regulation of block copolymer self-assembly structures, we systematically explored the factors that affect the self-assembly nanostructure. After discussing the formation of nanostructures of diverse block copolymers, this review highlights block copolymer-based mass transport membranes, which play the role of “energy enhancers” in concentration cells, fuel cells, and rechargeable batteries. We firmly believe that the introduction of block copolymers can facilitate the novel energy conversion to an entirely new plateau, and the research can inform a new generation of block copolymers for more promotion and improvement in new energy applications.

A Multifunctional Gradient Solid Electrolyte Remarkably Improving Interface Compatibility and Ion Transport in Solid-State Lithium Battery

Solid electrolytes with both interface compatibility and efficient ion transport have been an urgent technical requirement for the practical application of solid-state lithium batteries. Herein, a multifuctional poly(1,3-dioxolane) (PDOL) electrolyte combining the gradient structure from the solid state to the gel state with the Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) interfacial modification layer was designed, in which the "solid-to-gel" gradient structure greatly improved the electrode/electrolyte interface compatibility and ion transport, while the solid PDOL and LLZTO layers effectively improved the interface stability of the electrolyte/lithium anode and the inhibition of the lithium dendrites via their high mechanical strength and forming a stable interfacial SEI composite film. This gradient PDOL/LLZTO composite electrolyte possesses a high ionic conductivity of 2.9 × 10^-4 S/cm with a wide electrochemical window up to 4.9 V vs Li/Li⁺. Compared with the pristine PDOL electrolyte and PDOL solid electrolyte membrane coated with a layer of LLZTO, the gradient PDOL/LLZTO composite electrolyte shows better electrode/electrolyte interfacial compatibility, lower interface impedance, and smaller polarization, resulting in enhanced rate and cycle performances. The NCM622/PDOL-LLZTO/Li battery can be stably cycled 200 times at 0.3C and 25 °C. This multifunctional gradient structure design will promote the development of high-performance solid electrolytes and is expected to be widely used in solid-state lithium batteries.

A Single-Layer Composite Separator with 3D-Reinforced Microstructure for Practical High-Temperature Lithium Ion Batteries

Incorporation of ceramic materials into separators has been frequently applied in both research and industry to improve the overall high-temperature performances of lithium ion batteries. However, inorganic ceramic particles tend to form aggregation in separators and even fall off in the separator matrix due to the inferior combination between ceramic particles and polymer matrix, giving rise to a decrease in separator porosity and thus the degradation of battery performances. Herein, a single-layer core-shell architecture is designed to reinforce the polymer matrix through encircling Al₂ O₃ particles by poly(vinylidene fluoride) with strong inter-molecular interaction. The 3D-reinforced microstructure effectively improves pore distribution and thermal stability to resist the dimensional deformation at high temperatures, thus giving rise to a high Coulombic efficiency of 99.16% and 87.5% capacity retention after 500 cycles at 80 °C for LiFePO₄ /Li batteries. In particular, the excellent performances of the proposed separator microstructure are confirmed with a thickness value of commercial separators. This work provides a promising strategy to fabricate a core-shell structural composite separator for stable lithium ion batteries at high temperatures.

Template synthesis of dual-functional porous MoS2 nanoparticles with photothermal conversion and catalytic properties

Advanced catalysis triggered by photothermal conversion effects has aroused increasing interest due to its huge potential in environmental purification. In this work, we developed a novel approach to the fast degradation of 4-nitrophenol (4-Nip) using porous MoS₂ nanoparticles as catalysts, which integrate the intrinsic catalytic property of MoS₂ with its photothermal conversion capability. Using assembled polystyrene-b-poly(2-vinylpyridine) block copolymers as soft templates, various MoS₂ particles were prepared, which exhibited tailored morphologies (e.g., pomegranate-like, hollow, and open porous structures). The photothermal conversion performance of these featured particles was compared under near-infrared (NIR) light irradiation. Intriguingly, when these porous MoS₂ particles were further employed as catalysts for the reduction of 4-Nip, the reaction rate constant was increased by a factor of 1.5 under NIR illumination. We attribute this catalytic enhancement to the open porous architecture and light-to-heat conversion performance of the MoS₂ particles. This contribution offers new opportunities for efficient photothermal-assisted catalysis.

3D Correlative Imaging of Lithium Ion Concentration in a Vertically Oriented Electrode Microstructure with a Density Gradient

The performance of Li+ ion batteries (LIBs) is hindered by steep Li+ ion concentration gradients in the electrodes. Although thick electrodes (≥300 µm) have the potential for reducing the proportion of inactive components inside LIBs and increasing battery energy density, the Li+ ion concentration gradient problem is exacerbated. Most understanding of Li+ ion diffusion in the electrodes is based on computational modeling because of the low atomic number (Z) of Li. There are few experimental methods to visualize Li+ ion concentration distribution of the electrode within a battery of typical configurations, for example, coin cells with stainless steel casing. Here, for the first time, an interrupted in situ correlative imaging technique is developed, combining novel, full-field X-ray Compton scattering imaging with X-ray computed tomography that allows 3D pixel-by-pixel mapping of both Li+ stoichiometry and electrode microstructure of a LiNi0.8 Mn0.1 Co0.1 O2 cathode to correlate the chemical and physical properties of the electrode inside a working coin cell battery. An electrode microstructure containing vertically oriented pore arrays and a density gradient is fabricated. It is shown how the designed electrode microstructure improves Li+ ion diffusivity, homogenizes Li+ ion concentration through the ultra-thick electrode (1 mm), and improves utilization of electrode active materials.