Cellulosic Biomass-Reinforced Polyvinylidene Fluoride Separators with Enhanced Dielectric Properties and Thermal Tolerance

Eco-Friendly Lithium Separators: A Frontier Exploration of Cellulose-Based Materials

Lithium-ion batteries, as an excellent energy storage solution, require continuous innovation in component design to enhance safety and performance. In this review, we delve into the field of eco-friendly lithium-ion battery separators, focusing on the potential of cellulose-based materials as sustainable alternatives to traditional polyolefin separators. Our analysis shows that cellulose materials, with their inherent degradability and renewability, can provide exceptional thermal stability, electrolyte absorption capability, and economic feasibility. We systematically classify and analyze the latest advancements in cellulose-based battery separators, highlighting the critical role of their superior hydrophilicity and mechanical strength in improving ion transport efficiency and reducing internal short circuits. The novelty of this review lies in the comprehensive evaluation of synthesis methods and cost-effectiveness of cellulose-based separators, addressing significant knowledge gaps in the existing literature. We explore production processes and their scalability in detail, and propose innovative modification strategies such as chemical functionalization and nanocomposite integration to significantly enhance separator performance metrics. Our forward-looking discussion predicts the development trajectory of cellulose-based separators, identifying key areas for future research to overcome current challenges and accelerate the commercialization of these green technologies. Looking ahead, cellulose-based separators not only have the potential to meet but also to exceed the benchmarks set by traditional materials, providing compelling solutions for the next generation of lithium-ion batteries.

Dendrite-free lithium metal battery enabled by mesoporous silica host layer mediated cellulose/PVDF Janus separator

The commercialization of lithium metal batteries (LMBs) is encountering significant challenges due to the electrolyte incompatibility and poor mechanical properties of polyolefin separators, as well as the hazardous growth of lithium dendrites at the anode. Simultaneously, the development of safe and environmentally-friendly separators has become a central focus in rechargeable battery technology. In this study, we introduce a novel Janus separator (CP@SiO2), featuring a composite structure with cellulose paper (CP) as the base layer and electrospun polyvinylidene fluoride (PVDF) nanofibers as the top layer. The nanofibers are uniformly coated with mesoporous SiO2 nanoparticles through hydrogen bonding. The CP@SiO2 separator leverages its three-dimensional lithium-ion channels and rigid ceramic particles to enhance electrolyte retention and stabilize lithium metal anodes (LMA). Shielded by this separator, LMA exhibits an impressive cycling performance, enduring a current density of 2 mA cm-2 for 350 h without short-circuiting, effectively doubling the cycle life compared to conventional PP separators. Furthermore, the Li/LiFePO4 cell utilizing the CP@SiO2 separator demonstrates a high capacity of 101 mAh·g-1 at 5C, with 90 % capacity retention after 1000 cycles. This outstanding electrochemical performance is attributed to the compatible anode/separator interface and the effective inhibition of lithium dendrite growth. The research presented in this work capitalizes on a synergistic configuration design, offering a promising pathway towards the development of high-safety and advanced lithium-ion separators.

Chitosan nanofiber paper used as separator for high performance and sustainable lithium-ion batteries

Separators are indispensable components in lithium-ion batteries (LIBs), providing efficient pathways for lithium ions to travel and isolating the positive and negative electrodes to avoid short circuits. However, traditional polyolefin-based separators exhibit inferior electrolyte affinities, limited porosities, and low thermal stabilities. In this study, a novel method was developed to prepare chitosan micro/nanofiber membranes as LIB separators using natural materials. The pore sizes of the chitosan micro/nanofibers separators were modulated by changing the diameters of the chitosan fibers. The results demonstrated that the chitosan nanofiber separators (CSNFs) had superior electrolyte uptake (281 %), excellent thermal dimensional stability, and electrochemical performance in LiFePO4/Li half-cell, as indicated by the higher discharge capacity after 100 cycles, and higher rate capacity than commercial Celgard2325 separator. This study paves the way for the fabrication of eco-efficient and environment-friendly separators for high-performance LIBs.

Paper Supercapacitor Developed Using a Manganese Dioxide/Carbon Black Composite and a Water Hyacinth Cellulose Nanofiber-Based Bilayer Separator

Flexible and green energy storage devices have a wide range of applications in prospective electronics and connected devices. In this study, a new eco-friendly bilayer separator and primary and secondary paper supercapacitors based on manganese dioxide (MnO2)/carbon black (CB) are developed. The bilayer separator is prepared via a two-step fabrication process involving freeze-thawing and nonsolvent-induced phase separation. The prepared bilayer separator exhibits superior porosity of 46%, wettability of 46.5°, and electrolyte uptake of 194% when compared with a Celgard 2320 trilayer separator (39%, 55.58°, and 110%). Moreover, lower bulk resistance yields a higher ionic conductivity of 0.52 mS cm-1 in comparison to 0.22 mS cm-1 for the Celgard separator. Furthermore, the bilayer separator exhibits improved mean efficiency of 0.44% and higher specific discharge capacitance of 13.53%. The anodic and cathodic electrodes are coated on a paper substrate using MnO2/CB and zinc metal-loaded CB composites. The paper supercapacitor demonstrates a high specific capacitance of 34.1 mF cm-2 and energy and power density of 1.70 μWh cm-2 and 204.8 μW cm-2 at 500 μA, respectively. In summary, the concept of an eco-friendly bilayer cellulose separator with paper-based supercapacitors offers an environmentally friendly alternative to traditional energy storage devices.

Enabling high-capacity Li metal battery with PVDF sandwiched type polymer electrolyte

Polyvinylidene difluoride (PVDF) is one of the most attractive electrolyte materials for solid-state batteries due to its high ionic conductivity, however, the battery performance is limited by the high electrolyte-electrode interfacial resistance. Herein, PVDF polymer mixed with ceramic Li7La3Zr2O12 is coated on cellulose support membrane (PLCSM) through a simple slurry-casting method. The ionic transport of PLCSM is originated from dimethyl formamide (DMF)-Li+ solvation structure, which plays a critical role in conducting lithium ions. β-PVDF after dehydrofluorination offers a high dielectric constant and enhances the dissociation of lithium salt. As a result, PLCSM with a total thickness of 85 µm presents an oxidation voltage of 4.9 V. Li-Li symmetric cells by employing PLCSM reveal that the critical current density (CCD) is increased to 1 mA cm-2. A full cell of LiFePO4 |PLCSM |Li with high mass loading (1.2 mA h cm-2) shows a first-cycle discharge capacity of 160 mA h g-1. With LiNi0.6Mn0.2Co0.2O2 as the cathode, the initial discharge capacity is 153 mA h g-1, and the capacity retention after 80 cycles is 80 %. The sandwiched PLCSM provides an effective strategy to achieve high-performance dendrite-free Li metal batteries.

A Novel Lightweight Polyurethane Composite for Application on Ultra-High-Voltage Insulator Core Filler

This study aimed to prepare a new lightweight ultra-high-voltage insulator core filler composite, which can solve the problem of bulkiness. In this study, rigid polyurethane foam pellets with different densities are used as lightweight fillers and polyurethane resins to compound lightweight composite materials. On accounting for working conditions, the density, insulation, heat resistance, water absorption and mechanical properties are tested. The compressive properties of composites are determined by a foam skeleton and a process. Among three kinds of composites, in which the composites with the best comprehensive performance are materials filled with pellets to a density of 0.15g·cm⁻³. The density, surface resistance, volume resistance, leakage current, initial decomposition temperature, water absorption, force, rupture displacement and limiting oxygen index (LOI) of composites are 0.665 g·cm⁻³, 1.17 × 10¹⁴ Ω, 9.68 × 10¹⁴ Ω·cm, 0.079 mA, 208 °C, 0.047%, 2262 N, 2.54 mm, and 23.3%, respectively. The ultra-high-voltage insulator core filler in this study can reduce the weight of the solid core insulator crossarm for Ultra-High Voltage (UHV) by 50–75%.

Nanocomposites membranes from cellulose nanofibers, SiO2 and carboxymethyl cellulose with improved properties

The binary nanocomposites blended by carboxymethyl cellulose (CMC) and SiO₂ nanoparticles were constructed to prepare the films with superior thermal stability and flame retardant properties. The incorporation of cellulose nanofibers(CNFs) and SiO₂ nanoparticles were followed to prepare ternary nanocomposite films exhibiting excellent mechanical properties. The mechanism and chemical reaction of the thermal decomposition for the CMC/SiO₂ composite membrane were proposed, which showed that the mass residuals were Na₂CO₃, SiO₂ and Na₂SiO₃, Na₂CO₃ when the content of the SiO₂ nanoparticles was lowered and higher than 9.6 %, respectively. Compared with the pure CMC, micro combustion calorimeter (MCC) showed that the total heat release (THR) and the peak heat release rate (PHRR) both decreased from 6.4 kJ/g to 5.8 kJ/g, 134 w/g to 27 w/g, respectively. Moreover, mechanical properties of CMC/CNFs/SiO₂ membrane showed that the toughness and rigidity of the nanocomposites increased by 56.0 % and 63.0 % on the basis of CMC, respectively.

Electroactive γ-Phase, Enhanced Thermal and Mechanical Properties and High Ionic Conductivity Response of Poly (Vinylidene Fluoride)/Cellulose Nanocrystal Hybrid Nanocomposites

Cellulose nanocrystals (CNCs) were incorporated into poly (vinylidene fluoride) (PVDF) to tailor the mechanical and dielectric properties of this electroactive polymer. PVDF/CNC nanocomposites with concentrations up to 15 wt.% were prepared by solvent-casting followed by quick vacuum drying in order to ensure the formation of the electroactive γ-phase. The changes induced by the presence of CNCs on the morphology of PVDF and its crystalline structure, thermal properties, mechanical performance and dielectric behavior are explored. The results suggest a relevant role of the CNC surface -OH groups, which interact with PVDF fluorine atoms. The real dielectric constant ε' of nanocomposites at 200 Hz was found to increase by 3.6 times up to 47 for the 15 wt.% CNC nanocomposite due to an enhanced ionic conductivity provided by CNCs. The approach reported here in order to boost the formation of the γ-phase of PVDF upon the incorporation of CNCs serves to further develop cellulose-based multifunctional materials.

Cellulosic materials-enhanced sandwich structure-like separator via electrospinning towards safer lithium-ion battery

The latent security issue has become the foremost anxiety for lithium-ion batteries (LIBs) wide-ranging of commercialized applications. Hence, the performance of a separator such as chemical durability, electrical insulator, and thermal stability must be superior. Herein, we exhibit a sandwich-structured composite membrane with enhanced thermal resistance and electrolyte affinity, which was prepared by layer-by-layer electrospinning deposition. After 50 cycles, the battery with a 3 wt.% halloysite nanotube electrospinning separator retained 91.80% of its initial discharge capacity, that was a drastic improvement over the commercial polypropylene separator with the numeric of 79.98%. This predominant composite membrane was prepared via an eco-friendly technics and can be thought of an assuring, expectant separator towards high performance lithium-ion batteries.

Design Principles of Functional Polymer Separators for High-Energy, Metal-Based Batteries

Next-generation rechargeable batteries that offer high energy density, efficiency, and reversibility rely on cell configurations that enable synergistic operations of individual components. They must also address multiple emerging challenges,which include electrochemical stability, transport efficiency, safety, and active material loss. The perspective of this Review is that rational design of the polymeric separator, which is used widely in rechargeable batteries, provides a rich set of opportunities for new innovations that should enable batteries to meet many of these needs. This perspective is different from the conventional view of the polymer separator as an inert/passive unit in a battery, which has the sole function to prevent direct contact between electrically conductivecomponents that form the battery anode and cathode. Polymer separators, which serve as the core component in a battery, bridge the electrodes and the electrolyte with a large surface contact that can be utilized to apply desirable functions. This Review focuses specifically on recent advances in polymer separator systems, with a detailed analysis of several embedded functional agents that are incorporated to improve mechanical robustness, regulate ion and mass transport, and retard flammability. The discussion is also extended to new composite separator concepts that are designated traditionally as polymer/gel electrolytes.

Thermally Stable Cellulose Nanocrystals toward High-Performance 2D and 3D Nanostructures

Cellulose nanomaterials have attracted much attention in a broad range of fields such as flexible electronics, tissue engineering, and 3D printing for their excellent mechanical strength and intriguing optical properties. Economic, sustainable, and eco-friendly production of cellulose nanomaterials with high thermal stability, however, remains a tremendous challenge. Here versatile cellulose nanocrystals (DM-OA-CNCs) are prepared through fully recyclable oxalic acid (OA) hydrolysis along with disk-milling (DM) pretreatment of bleached kraft eucalyptus pulp. Compared with the commonly used cellulose nanocrystals from sulfuric acid hydrolysis, DM-OA-CNCs show several advantages including large aspect ratio, carboxylated surface, and excellent thermal stability along with high yield. We also successfully demonstrate the fabrication of high-performance films and 3D-printed patterns using DM-OA-CNCs. The high-performance films with high transparency, ultralow haze, and excellent thermal stability have the great potential for applications in flexible electronic devices. The 3D-printed patterns with porous structures can be potentially applied in the field of tissue engineering as scaffolds.