Pure cellulose lithium-ion battery separator with tunable pore size and improved working stability by cellulose nanofibrils

Cellulose-based Conductive Materials for Bioelectronics

The growing demand for electronic devices has led to excessive stress on Earth's resources, necessitating effective waste management and the search for renewable materials with minimal environmental impact. Bioelectronics, designed to interface with the human body, have traditionally been made from inorganic materials, such as metals, which, while having suitable electrical conductivity, differ significantly in chemical and mechanical properties from biological tissues. This can cause issues such as unreliable signal collection and inflammatory responses. Recently, natural biopolymers such as cellulose, chitosan, and silk have been explored for flexible devices, given their chemical uniqueness, shape flexibility, ease of processing, mechanical strength, and biodegradability. Cellulose is the most abundant natural biopolymer, has been widely used across industries, and can be transformed into electronically conductive carbon materials. This review focuses on the advancements in cellulose-based conductive materials for bioelectronics, detailing their chemical properties, methods to enhance conductivity, and forms used in bioelectronic applications. It highlights the compatibility of cellulose with biological tissues, emphasizing its potential in developing wearable sensors, supercapacitors, and other healthcare-related devices. The review also addresses current challenges in this field and suggests future research directions to overcome these obstacles and fully realize the potential of cellulose-based bioelectronics.

Cellulose-Derived Battery Separators: A Minireview on Advances Towards Environmental Sustainability

Cellulose-derived battery separators have emerged as a viable sustainable alternative to conventional synthetic materials like polypropylene and polyethylene. Sourced from renewable and biodegradable materials, cellulose derivatives-such as nanofibers, nanocrystals, cellulose acetate, bacterial cellulose, and regenerated cellulose-exhibit a reduced environmental footprint while enhancing battery safety and performance. One of the key advantages of cellulose is its ability to act as a hybrid separator, using its unique properties to improve the performance and durability of battery systems. These separators can consist of cellulose particles combined with supporting polymers, or even a pure cellulose membrane enhanced by the incorporation of additives. Nevertheless, the manufacturing of cellulose separators encounters obstacles due to the constraints of existing production techniques, including electrospinning, vacuum filtration, and phase inversion. Although these methods are effective, they pose challenges for large-scale industrial application. This review examines the characteristics of cellulose and its derivatives, alongside various processing techniques for fabricating separators and assessing their efficacy in battery applications. Additionally, it will consider the environmental implications and the primary challenges and opportunities associated with the use of cellulose separators in energy storage systems. Ultimately, the review underscores the significance of cellulose-based battery separators as a promising approach that aligns with the increasing demand for sustainable technologies in the energy storage domain.

Functionalized Separators Boosting Electrochemical Performances for Lithium Batteries

The growing demands for energy storage systems, electric vehicles, and portable electronics have significantly pushed forward the need for safe and reliable lithium batteries. It is essential to design functional separators with improved mechanical and electrochemical characteristics. This review covers the improved mechanical and electrochemical performances as well as the advancements made in the design of separators utilizing a variety of techniques. In terms of electrolyte wettability and adhesion of the coating materials, we provide an overview of the current status of research on coated separators, in situ modified separators, and grafting modified separators, and elaborate additional performance parameters of interest. The characteristics of inorganics coated separators, organic framework coated separators and inorganic-organic coated separators from different fabrication methods are compared. Future directions regarding new modified materials, manufacturing process, quantitative analysis of adhesion and so on are proposed toward next-generation advanced lithium batteries.

Electrospun Poly(vinyl Alcohol)/Chitin Nanofiber Membrane as a Sustainable Lithium-Ion Battery Separator

Commercial battery separators are made of polyolefin polymers due to their desired mechanical strength and chemical stability. However, these materials are not biodegradable and are challenging to recycle. Considering the environmental issues from polyolefins, biodegradable polymers can be developed as separators to reduce the potential waste from polyolefin separators. In this work, we investigated the potential of poly(vinyl alcohol)/chitin nanofiber (PVA/CHNF) nanofiber as a sustainable lithium-ion battery separator, which was successfully fabricated via the electrospinning and cross-linking method. The PVA/CHNF separator is biodegradable and has an ionic conductivity (1.41 mS cm-1), desirable porosity (86%), good thermal stability (1.4% shrinkage upon heating at 90 °C for 1 h), as well as high electrolyte uptake (388%). The PVA/CHNF separator is also evaluated in the assembled Li//LiFePO4 cells, showing an improved performance compared to the cell with the commercial separator. It shows a discharge capacity of 142 mAh g-1, which is stable throughout 120 charge-discharge cycles. Hence, according to these resulting properties, the PVA/CHNF separator shows promise as a sustainable and environmentally friendly lithium-ion battery separator, offering a high-value use of waste chitin materials.

Tailoring poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) membrane microstructure for lithium-ion battery separator applications

Novel battery separators based on poly(vinylidene fluoride-co-trifluoroethylene-chlorofluoroethylene)- P(VDF-TrFE-CFE)- were produced by different processing techniques (non-solvent and thermally induced phase separation, salt leaching and electrospinning), in order to evaluate their effect on separator morphology, degree of porosity and pore size, electrochemical parameters and battery cycling behavior. It has been demonstrated that the different processing techniques have a significant influence on the morphology and mechanical properties of membranes. The degree of porosity varies between 23 % and 66 %, for membranes obtained by salt leaching and thermally induced phase separation, respectively. The membranes present a high ionic conductivity value ranging between 1.8 mS.cm-1 for the electrospun membrane and 0.20 mS.cm-1 for the membrane processed by thermally induced phase separator. The lithium transference number value for all membranes is above 0.20, the highest value of 0.55 being obtained for samples prepared by salt leaching and thermally induced phase separation. For all membranes, battery capacity values have been obtained at different C-rates with excellent reversibility. P(VDF-TrFE-CFE) samples present an excellent battery performance at 1C-rate after 100 cycles with 74 mAh.g-1 and excellent coulombic efficiency, for membrane processed by the salt leaching technique. This work demonstrates that P(VDF-TrFE-CFE) terpolymer can be used as a porous membrane in lithium-ion battery separator application, the membrane processing technique allowing to tailor its morphology and, consequently, battery performance.

Unveiling potential of cellulose gel electrolyte: Molecular engineering for enhanced electrostatic interactions with Mg adatoms in Mg-ion battery

The Mg-ion battery faces significant limitations due to its liquid electrolyte, which suffers from inherent issues such as leakage and the growth of Mg dendrites. In contrast, gel polymer electrolytes (GPEs) offer heightened safety, a wide voltage window, and excellent flexibility, making them a promising alternative with outstanding electrochemical performance. In this study, a cyano-modified cellulose (CEC) GPE was engineered to aim at enhancing ion transportation and promoting uniform ion-flux through interactions between N and Mg2+ ions. The resulting CEC-based GPE demonstrated a high ionic conductivity of 1.73 mS cm-1 at room temperature. Furthermore, it exhibited remarkable Mg plating/stripping performance (coulombic efficiency ∼96.7 %) and compatibility with electrodes. Importantly, when employed in a Mo6S8//Mg battery configuration, the CEC GPE displayed exceptional cycle stability, with virtually no degradation observed even after 650 cycles at 1C, thereby significantly advancing Mg-ion battery technology due to its excellent electrochemical properties. This study provides valuable insights into the molecular engineering of cellulose-based GPEs.

Long-Cycling Cellulose-Based Gel Polymer Electrolyte Utilizing Nanohydrotalcite as a Li+ Transport Redistributor

The hydroxyl groups on the surface of the cellulose-based gel polymer electrolyte lead to poor interfacial compatibility due to side reactions with lithium sheets. In this paper, a novel cellulose-based gel polymer electrolyte was prepared by uniformly coating the surface of a cellulose membrane with a nanohydrotalcite/PVDF-HFP composite using electrospinning technology. This cellulose-based gel polymer electrolyte exhibits good interfacial compatibility and excellent cycling stability (91.7% specific capacity retention after 500 cycles at 0.5C). Theory and experiments have shown that nanohydrotalcite on the surface of cellulose membrane can effectively prevent the contact of hydroxyl groups with lithium sheets to reduce the side reactions. In addition, nanohydrotalcite can also act as a Li+ transport redistributor to facilitate the uniform deposition of Li+ and reduce the formation of lithium dendrites to extend the cycle life.

Enhancing CA-based separators with thermo-responsive ionic liquids: A path to eco-friendly membrane production and multifaceted applications

We synthesized a temperature-responsive ionic liquid, [N4444][SS], and incorporated it into an environmentally friendly cellulose acetate (CA)-based battery separator. A pore was formed in the battery separator by [N4444][SS], which pierced a plasticized part due to water pressure. Varying drying temperatures during membrane fabrication revealed that the CA/[N4444][SS] membrane dried at 50 °C exhibited greater thickness and a smaller average pore size, resulting in an asymmetric internal structure. Despite the asymmetry, this membrane demonstrated significantly higher water flux and a lower Gurley value compared to the membrane dried at 25 °C, indicating minimal tortuosity and low resistance within the internal pores. Thermal behavior analysis through TGA and DSC, as well as FT-IR spectroscopy, confirmed that [N4444][SS] remains within the CA matrix, forming coordinative bonds. The findings suggest that the CA/[N4444][SS] membrane, when used as a Li-ion battery separator, could enhance Li-ion transport properties and conductivity. Moreover, the recyclability of the IL in the membrane fabrication process contributes to a more environmentally friendly approach.

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.

Redox-active NiS@bacterial cellulose nanofiber composite separators with superior rate capability for lithium-ion batteries

Separator is an essential component of lithium-ion batteries (LIBs), which is placed between the electrodes to impede their electrical contact and provide the transport channels for lithium ions. Traditionally, the separator contributes the overall mass of LIBs, thereby reducing the gravimetric capacity of the devices. Herein, a dual-layer redox-active cellulose separator is designed and fabricated to enhance the electrochemical performances of LIBs by introducing NiS. The presented separator is composed of an insulating bacterial cellulose (BC) nanofiber layer and a conductive, and redox-active NiS@BC/carbon nanotubes layer. By using the NiS@BC separator, the discharge capacity of the LiFePO4//Li half battery is enhanced to 117 mAh g-1 at a current of 2C owing to the redox-activity of NiS. Moreover, the functional separator-electrode interface can facilitate the homogenous Li stripping/plating and depress the polarization upon the repeated stripping/plating process. Consequently, the battery containing the redox-active separator exhibits outstanding cycle stability and rate capability. The present study contributes a novel strategy for the developments of functional separators to improve the electrochemical properties of LIBs.

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.

Influence of citric acid concentrations on the porosity and performance of cellulose acetate-based porous membranes: A comprehensive study

This study investigates the influence of citric acid concentration on the fabrication of porous cellulose acetate (CA) membranes using the Non-Solvent Induced Phase Separation (NIPS) method. A notable aspect is the precise control over membrane properties, particularly pore size and porosity, achieved solely through the adjustment of citric acid concentration, serving as the additive. Higher concentrations of citric acid increase pore size by rendering polymer chains more pliable, whereas lower concentrations lead to smaller, denser pores due to improved dispersion in the CA matrix and altered water interactions during phase separation. A decrease in porosity and Gurley values with reducing citric acid concentrations (from 5 × 10-2 to 1 × 10-3 M ratios) indicates less plasticization of CA chains. However, at very low concentrations (1 × 10-4 and 1 × 10-5), porosity increases, despite the presence of smaller pores, and Gurley values approach those of pure CA in terms of gas permeability. Fourier Transform Infrared (FT-IR) spectroscopy confirms the presence of citric acid and its interaction with carbonyl groups, consistent with the pore size observations from Scanning Electron Microscopy (SEM). Spectral data deconvolution reveals weakened carbonyl bonds due to the reduced presence of citric acid, correlating with the smaller pores observed in SEM. Thermal Gravimetric Analysis (TGA) demonstrates that composite membranes are more thermally stable than pure CA, attributed to the citric acid-induced crosslinking within the polymer chains. Stability increases with decreasing citric acid concentration, with some anomalies at the lowest levels. In conclusion, this study highlights the capability of adjusting citric acid concentration to tailor membrane properties, offering valuable insights for the creation of porous materials across diverse industrial applications.

H2O/HF Scavenging Mechanism in Cellulose-Based Separators for Lithium-Ion Batteries with Enhanced Cycle Life

Lithium-ion batteries (LIBs) are increasingly being integrated into the transportation industry due to their high energy density, durability, and low cost. With the growing demand for transportation and other emerging applications, there is a concurrent rise in concern over LIB material sourcing and recycling. This urges the development of LIBs with extended cycle lifespans. One mechanism of capacity fading in LIBs is the dissolution of transition metals into the electrolyte after the cathode is etched with hydrofluoric acid (HF). HF is readily generated by the hydrolysis of the LIB electrolyte salt, lithium hexafluorophosphate (LiPF6), which makes minimizing moisture in the electrolyte a priority in manufacturing. In this study, a nonwoven, cellulose-based separator (CBS) is introduced as an alternative separator for battery technologies to scavenge residual water and HF from the electrolyte. The CBS is shown to be capable of scavenging varying amounts of water from the electrolyte based on different drying processes of the CBS, and a mechanism for this water scavenging is identified based on the materials present in the CBS. In addition, the chemical and electrochemical performance of the CBS in real battery conditions is investigated. Results suggest an effective H2O/HF scavenging capability in the CBS that allows LIB coin cells to have over 17% higher capacity retention than those with conventional separators. Furthermore, studies of the industrially manufactured, commercially relevant cylindrical and pouch cells show remarkable 761 and 103% improvements in the 60% capacity lifetime, respectively. The environmental friendliness, low cost, and easy application empowered by the cycle life improvements shown in this work make this nonwoven CBS a promising candidate for improving industry-level LIB performance.

Exploitation of function groups in cellulose materials for lithium-ion batteries applications

Cellulose, an abundant and eco-friendly polymer, is a promising raw material to be used for preparing energy storage devices such as lithium-ion batteries (LIBs). Despite the significance of cellulose functional groups in LIBs components, their structure-properties-application relationship remains largely unexplored. This article thoroughly reviews the current research status on cellulose-based materials for LIBs components, with a specific focus on the impact of functional groups in cellulose-based separators. The emphasis is on how these functional groups can enhance the mechanical, thermal, and electrical properties of the separators, potentially replacing conventional non-renewal material-derived components. Through a meticulous investigation, the present review reveals that certain functional groups, such as hydroxyl groups (-OH), carboxyl groups (-COOH), carbonyl groups (-CHO), ester functions (R-COO-R'), play a crucial role in improving the mechanical strength and wetting ability of cellulose-based separators. Additionally, the inclusion of phosphoric group (-PO3H2), sulfonic group (-SO3H) in separators can contribute to the enhanced thermal stability. The significance of comprehending the influence of functional groups in cellulose-based materials on LIBs performance is highlighted by these findings. Ultimately, this review explores the challenges and perspectives of cellulose-based LIBs, offering specific recommendations and prospects for future research in this area.

Bioresource Polymer Composite for Energy Generation and Storage: Developments and Trends

The ever-growing demand of human society for clean and reliable energy sources spurred a substantial academic interest in exploring the potential of biological resources for developing energy generation and storage systems. As a result, alternative energy sources are needed in populous developing countries to compensate for energy deficits in an environmentally sustainable manner. This review aims to evaluate and summarize the recent progress in bio-based polymer composites (PCs) for energy generation and storage. The articulated review provides an overview of energy storage systems, e. g., supercapacitors and batteries, and discusses the future possibilities of various solar cells (SCs), using both past research progress and possible future developments as a basis for discussion. These studies examine systematic and sequential advances in different generations of SCs. Developing novel PCs that are efficient, stable, and cost-effective is of utmost importance. In addition, the current state of high-performance equipment for each of the technologies is evaluated in detail. We also discuss the prospects, future trends, and opportunities regarding using bioresources for energy generation and storage, as well as the development of low-cost and efficient PCs for SCs.

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.

Pure cellulose nanofiber separator with high ionic conductivity and cycling stability for lithium-ion batteries

Conventional polyolefin separators are constrained by poor electrolyte wettability, inferior thermal stability, and low ionic conductivity, which seriously restrict their application in high-performance lithium-ion batteries (LIBs). Herein, cellulose nanofiber (CNF) as the matrix and tert-butyl alcohol (TBA) as the dispersion medium were used to prepare the pure CNF separators for LIBs by a facile filtration method. The effects of the drying temperature on the pore structure, electrolyte wettability, mechanical properties, thermal stability, and ionic conductivity of the separators were comprehensively investigated. The results showed that the freeze-dried separator at -80 °C with TBA as the dispersion medium (TBA-FD) had the best overall performance, with the porosity and electrolyte uptake up to 70.8 % and 296 %, respectively, as well as the ionic conductivity up to 1.90 mS/cm. The CNF separators had no apparent thermal shrinkage at 160 °C, illustrating good thermal stability. Moreover, the LiFePO4/lithium metal battery assembled with the TBA-HD (tert-butyl alcohol as the dispersion medium for heat-drying at 80 °C) and TBA-FD separators displayed superior cycling stability (with a capacity retention rate up to 97.5 % and 96.4 %, respectively) and rate performance. The pure CNF separators with good performance prepared by the facile method are greatly promising for high-performance LIBs.

Green synthesis of sulfonated cellulose/polyether block amide/polyethylene glycol diacrylate (SC/PEBAX/PEGDA) composite membrane by gamma radiation and sulfonation techniques for battery application

Sulfonated cellulose (SC) was successfully prepared through a two-step process of gamma radiation and subsequently sulfonation with potassium metabisulfite of microcrystalline cellulose extracted from sugarcane bagasse. The effect of gamma radiation dose on cellulose showed an increment of oxidation degree, which was evidenced by the intensity ratio of I1718 (carbonyl)/ I2892 (aliphatic) from FTIR analysis. The obtained SC was introduced into polyether block amide/polyethylene glycol diacrylate (PEBAX/PEGDA) polymer matrix as a reinforcement and hydrophilic filler for improving electrolyte affinity and thermal stability of its composite membrane. The increase of SC in PEBAX/PEGDA composite membranes resulted in enhancement of hydrophilicity, electrolyte uptake, and thermal stability compared to pristine composite membranes. However, the excess SC content in the composite membrane exhibited the low physical properties, caused by negligible dispersion on the surface membrane. With the optimum 2.0 wt% SC in PEBAX/PEGDA, the porosity, contact angle and electrolyte uptake capacity was found to be 64.0 %, 12.8° and 37.5 %, respectively. 2.0 wt% SC/PEBAX/PEGDA showed the outstanding thermal stability with negligible shrinkage <10 % at 150 °C whereas pristine PEBAX/PEGDA showed the shrinkage of 29 %. The obtained SC/PEBAX/PEGDA composite membrane is considered as a potential candidate to replace the commercial polyolefin-based separator in lithium-ion batteries.

A Sodiophilic Amyloid Fibril Modified Separator for Dendrite-Free Sodium-Metal Batteries

Sodium (Na) batteries are being considered as prospective candidates for the next generation of secondary batteries in contrast to lithium-based batteries, due to their high raw-material abundance, low cost, and sustainability. However, the unfavorable growth of Na-metal deposition and severe interfacial reactions have prevented their large-scale applications. Here, a vacuum filtration strategy, through amyloid-fibril-modified glass-fiber separators, is proposed to address these issues. The modified symmetric cell can be cycled for 1800 h, surpassing the performance of previously reported Na-based electrodes under an ester-based electrolyte. Moreover, the Na/Na3 V2 (PO4 )3 full cell with a sodiophilic amyloid-fibril-modified separator exhibits a capacity retention of 87.13% even after 1000 cycles. Both the experimental and the theoretical results show that the sodiophilic amyloid fibril homogenizes the electric field and Na-ion concentration, fundamentally inhibiting dendrite formation. Simultaneously, the glutamine amino acids in the amyloid fibril have the highest adsorption energy for Na, resulting in the formation of a stable Na3 N- and NaNx Oy -rich solid-electrolyte-interface film on the anode during cycling. This work provides not only a possible pathway to solve the dendrite problem in metal batteries using environmentally friendly biomacromolecular materials, but also a new direction for expanding biomaterial applications.

Electrospun Sandwich-like Structure of PVDF-HFP/Cellulose/PVDF-HFP Membrane for Lithium-Ion Batteries

Cellulose membranes have eco-friendly, renewable, and cost-effective features, but they lack satisfactory cycle stability as a sustainable separator for batteries. In this study, a two-step method was employed to prepare a sandwich-like composite membrane of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)/cellulose/ PVDF-HFP (PCP). The method involved first dissolving and regenerating a cellulose membrane and then electrospinning PVDF-HFP on its surface. The resulting PCP composite membrane exhibits excellent properties such as high porosity (60.71%), good tensile strength (4.8 MPa), and thermal stability up to 160 °C. It also has exceptional electrolyte uptake properties (710.81 wt.%), low interfacial resistance (241.39 Ω), and high ionic conductivity (0.73 mS/cm) compared to commercial polypropylene (PP) separators (1121.4 Ω and 0.26 mS/cm). Additionally, the rate capability (163.2 mAh/g) and cycling performance (98.11% after 100 cycles at 0.5 C) of the PCP composite membrane are superior to those of PP separators. These results demonstrate that the PCP composite membrane has potential as a promising separator for high-powered, secure lithium-ion batteries.

Advanced Sustainable Trilayer Cellulosic "Paper Separator" Functionalized with Nano-BaTiO3 for Applications in Li-Ion Batteries and Supercapacitors

In the quest of developing a sustainable, low-cost and improved separator membrane for application in energy storage devices like lithium-ion batteries (LIBs) and supercapacitors (SCs), here we fabricated a trilayer cellulose-based paper separator engineered with nano-BaTiO₃ powder. A scalable fabrication process of the paper separator was designed step-by-step by sizing with poly(vinylidene fluoride) (PVDF), thereafter impregnating nano-BaTiO₃ in the interlayer using water-soluble styrene butadiene rubber (SBR) as the binder and finally laminating the ceramic layer with a low-concentration SBR solution. The fabricated separators showed excellent electrolyte wettability (216-270%), quicker electrolyte saturation, increased mechanical strength (43.96-50.15 MPa), and zero-dimensional shrinkage up to 200 °C. The electrochemical cell comprising graphite|paper separator|LiFePO₄ showed comparable electrochemical performances in terms of capacity retention at different current densities (0.05-0.8 mA/cm²) and long-term cycleability (300 cycles) with coulombic efficiency >96%. The in-cell chemical stability as tested for 8 weeks revealed a nominal change in bulk resistivity with no significant morphological changes. The vertical burning test as performed on a paper separator showed excellent flame-retardant property, a required safety feature for separator materials. To examine the multidevice compatibility, the paper separator was tested in supercapacitors, delivering a comparable performance to that of a commercial separator. The developed paper separator was also found to be compatible with most of the commercial cathode materials such as LiFePO₄, LiMn₂O₄, and NCM111.

Advances in Cellulose-Based Composites for Energy Applications

The various forms of cellulose-based materials possess high mechanical and thermal stabilities, as well as three-dimensional open network structures with high aspect ratios capable of incorporating other materials to produce composites for a wide range of applications. Being the most prevalent natural biopolymer on the Earth, cellulose has been used as a renewable replacement for many plastic and metal substrates, in order to diminish pollutant residues in the environment. As a result, the design and development of green technological applications of cellulose and its derivatives has become a key principle of ecological sustainability. Recently, cellulose-based mesoporous structures, flexible thin films, fibers, and three-dimensional networks have been developed for use as substrates in which conductive materials can be loaded for a wide range of energy conversion and energy conservation applications. The present article provides an overview of the recent advancements in the preparation of cellulose-based composites synthesized by combining metal/semiconductor nanoparticles, organic polymers, and metal-organic frameworks with cellulose. To begin, a brief review of cellulosic materials is given, with emphasis on their properties and processing methods. Further sections focus on the integration of cellulose-based flexible substrates or three-dimensional structures into energy conversion devices, such as photovoltaic solar cells, triboelectric generators, piezoelectric generators, thermoelectric generators, as well as sensors. The review also highlights the uses of cellulose-based composites in the separators, electrolytes, binders, and electrodes of energy conservation devices such as lithium-ion batteries. Moreover, the use of cellulose-based electrodes in water splitting for hydrogen generation is discussed. In the final section, we propose the underlying challenges and outlook for the field of cellulose-based composite materials.

Preparation of Porous Hydroxyethyl Cellulose Materials to Utilize Lactic Acid with Vacuum-Assisted Process

For the first time, we succeeded in manufacturing a 2-hydroxyethyl cellulose (HEC)-based composite membrane with improved thermal stability, for use as a battery separator, coating a HEC polymer solution to a polypropylene (PP) support and using a vacuum-assisted process. A HEC polymer solution was prepared by utilizing HEC and lactic acid (LA) as a plasticizer. A vacuum-assisted process was used to move ethanol, which a mobile phase to permeate a plasticized region in the HEC polymer side for pore formation. The pores formed with uniform nano sizes, and areas in which some large pores formed were observed. The thermal stability of the composites was measured using TGA. The thermal decomposition temperatures were measured at about 250 °C for the neat HEC, about 210 °C for the HEC/LA film, and about 335 °C for the HEC/LA/PP membrane before the process. After the vacuum-assisted process, the first and second thermal decomposition were observed at about 360 °C and 450 °C, respectively. The HEC/LA/PP membrane after the process showed greater thermal stability than before the process. This means that the adhesion between the HEC polymer and the PP support was created through the rearrangement of the HEC chain, as LA escaped after the process, and it was seen indirectly that the mechanical strength was enhanced. In particular, the surface of the membrane was observed by SEM to investigate whether the HEC penetrated into the PP to block its pores, and whether the HEC region collapsed. Furthermore, the interaction of the HEC chain with the additives and the rearrangement of the HEC was confirmed using FT-IR. As a result, we demonstrated that the mechanical strength and thermal stability of the manufactured HEC/LA/PP membrane were enhanced.

"Pore-Hopping" Ion Transport in Cellulose-Based Separator Towards High-Performance Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have great potential for large-scale energy storage. Cellulose is an attractive material for sustainable separators, but some key issues still exist affecting its application. Herein, a cellulose-based composite separator (CP@PPC) was prepared by immersion curing of cellulose-based separators (CP) with poly(propylene carbonate) (PPC). With the assistance of PPC, the CP@PPC separator is able to operate the cell stably at high voltages (up to 4.95 V). The "pore-hopping" ion transport mechanism in CP@PPC opens up extra Na⁺ migration paths, resulting in a high Na⁺ transference number (0.613). The separator can also tolerate folding, bending and extreme temperature under certain circumstances. Full cells with CP@PPC reveal one-up capacity retention (96.97 %) at 2C after 500 cycles compared to cells with CP. The mechanism highlights the merits of electrolyte analogs in separator modification, making a rational design for durable devices in advanced energy storage systems.

Study on cellulose nanofibers/aramid fibers lithium-ion battery separators by the heterogeneous preparation method

In this study, a heat-resistant and high-wettability lithium-ion batteries separator (PI-CPM-PI) composed of cellulose nanofibers (CNF) and aramid fibers (PMIA chopped fiber/PPTA pulp) with the reinforced concrete structure was fabricated via a traditional heterogeneous paper-making process. CNF played crucial roles in optimizing the pore structure and improving the wettability of PI-CPM-PI separator. The effects of composition on separator properties were investigated and the results indicated that the optimal compositions were 0.5 wt% CNF, 0.5 wt% PMIA chopped fiber/PPTA pulp (ratio of 5:5), 0.05 wt% diatomite and 1.5 wt% polyimide. Relevant tests demonstrated that the performance advantages of PI-CPM-PI separators were exhibited at the wettability and thermal stability compared to the commercial separator (PP). Additionally, batteries assembled with PI-CPM-PI separators showed excellent electrochemical and cycling performance (ionic conductivity of 1.041 mS.cm^-1, the first discharge capacity of 158.2 mAh.g^-1 at 0.2C and capacity retention ratio of 99.76 % after 100 cycles).

Cellulose: Characteristics and applications for rechargeable batteries

Cellulose, an abundant natural polymer, has promising potential to be used for energy storage systems because of its excellent mechanical, structural, and physical characteristics. This review discusses the structural features of cellulose and describes its potential application as an electrode, separator, and binder, in various types of high-performing batteries. Various surface and structural characteristics of cellulose (e.g., fiber size, surface functional groups, the hierarchy of pores, and porosity levels) that contribute to its electrochemical performance are discussed. Cellulose structure/property/processing/function relationships are further focused and elucidated in terms of the latest developments in the emerging field of sustainable materials in Li-Ion, Na-Ion, and LiS batteries.

Silk fibroin and sericin polymer blends for sustainable battery separators

Natural polymers are a promising alternative for reducing the environmental impact of batteries. For this reason, it is still necessary to study their behavior and implement its use in these devices, especially in separator membranes. This work reports on new separator membranes based on silk fibroin (SF) and silk sericin (SS) prepared by salt leaching method. The effect of the different SS relative content on the physiochemical properties of the membranes and on the electrochemical performance of the corresponding batteries with lithium iron phosphate (LFP) as cathodes has been reported. It is observed that the increasing of SS content leads to a decrease of the overall crystallinity of the membranes. All SF/SS membranes presented a well-defined porosity above 75% with a uniform distribution of interconnected micropores. The electrolyte uptake and the ionic conductivity are dependent on the relative SS content. The addition of 10 wt% of SS into SF membranes, induce a high ionic conductivity of 4.09 mS.cm^-1 and high lithium transference number (0.52), due to the improvement of the Li⁺ ions conduction paths within the blended structure. Charge/discharge tests performed in Lithium/C-LFP half-cells reveal a discharge capacity of 85 mAh.g^-1 at 2C after 100 cycles for batteries with a SF/SS separator, containing a 10 wt% of SS, which suggests a stabilizing effect of Sericin on discharge capacity. Further, a 50% and 35% of capacity of retention and capacity fade, respectively, is observed. The presented SF/SS membrane show high electrochemical stability, being suitable for implementation in a next generation of sustainable battery systems. This could allow the SS valorization considering that 150,000 tons of SS are abandoned each year, reducing the contamination of environmental effluents.

Two-dimensional materials towards separator functionalization in advanced Li-S batteries

Functional separators have played important roles in improving the electrochemical performance of lithium-sulfur (Li-S) batteries by addressing the key issues of both the sulfur cathode and lithium anode. Compared with other materials that are used for separator functionalization, two-dimensional (2D) materials with atomic layer thickness and infinite lateral dimensions feature several advantages of ultra-thin laminate structure, remarkable physical properties and tunable surface chemistry, which show potential applications in separator functionalization towards addressing the issues of both the shuttle effect and formation of Li dendrites in Li-S batteries. In this review, the unique advantages of 2D materials for separator functionalization in Li-S batteries and their common construction methods are introduced. Then, recent progress and advances in the construction of 2D materials functional separators are summarized in detail towards inhibiting the shuttle effect of polysulfides and suppressing Li dendrite growth in Li-S batteries. Finally, some opportunities and challenges of 2D materials for constructing high-performance functional separators are proposed. We anticipate that this review will provide new insights into separator functionalization for developing advanced Li-S batteries.

Copper-coordinated cellulose ion conductors for solid-state batteries

Although solid-state lithium (Li)-metal batteries promise both high energy density and safety, existing solid ion conductors fail to satisfy the rigorous requirements of battery operations. Inorganic ion conductors allow fast ion transport, but their rigid and brittle nature prevents good interfacial contact with electrodes. Conversely, polymer ion conductors that are Li-metal-stable usually provide better interfacial compatibility and mechanical tolerance, but typically suffer from inferior ionic conductivity owing to the coupling of the ion transport with the motion of the polymer chains^1-3. Here we report a general strategy for achieving high-performance solid polymer ion conductors by engineering of molecular channels. Through the coordination of copper ions (Cu²⁺) with one-dimensional cellulose nanofibrils, we show that the opening of molecular channels within the normally ion-insulating cellulose enables rapid transport of Li⁺ ions along the polymer chains. In addition to high Li⁺ conductivity (1.5 × 10^-3 siemens per centimetre at room temperature along the molecular chain direction), the Cu²⁺-coordinated cellulose ion conductor also exhibits a high transference number (0.78, compared with 0.2-0.5 in other polymers²) and a wide window of electrochemical stability (0-4.5 volts) that can accommodate both the Li-metal anode and high-voltage cathodes. This one-dimensional ion conductor also allows ion percolation in thick LiFePO₄ solid-state cathodes for application in batteries with a high energy density. Furthermore, we have verified the universality of this molecular-channel engineering approach with other polymers and cations, achieving similarly high conductivities, with implications that could go beyond safe, high-performance solid-state batteries.

Rational Design of Cellulose Nanofibrils Separator for Sodium-Ion Batteries

Cellulose nanofibrils (CNF) with high thermal stability and excellent electrolyte wettability attracted tremendous attention as a promising separator for the emerging sodium-ion batteries. The pore structure of the separator plays a vital role in electrochemical performance. CNF separators are assembled using the bottom-up approach in this study, and the pore structure is carefully controlled through film-forming techniques. The acid-treated separators prepared from the solvent exchange and freeze-drying demonstrated an optimal pore structure with a high electrolyte uptake rate (978.8%) and Na⁺ transference number (0.88). Consequently, the obtained separator showed a reversible specific capacity of 320 mAh/g and enhanced cycling performance at high rates compared to the commercial glass fiber separator (290 mAh/g). The results highlight that CNF separators with an optimized pore structure are advisable for sodium-ion batteries.

Facile and Powerful In Situ Polymerization Strategy for Sulfur-Based All-Solid Polymer Electrolytes in Lithium Batteries

All-solid-state polymer electrolytes can improve the safety of lithium batteries. However, the common Bellcore polymer electrolyte technology faces several issues such as wasting a mass of solvent, high manufacturing cost, and poor interfacial compatibility between polymer electrolytes and electrodes. Herein, we propose an in situ polymerization technique to synthesize all-solid-state polymer electrolytes by a thiol-Michael addition click reaction. The alternating copolymer is made from the Michael addition reaction of ethylene glycol dimethacrylate (EGDMA) and 1,2-ethane dithiol (EDT). At ambient temperature, the obtained composite polymer electrolyte displays an ionic conductivity of 3.02 × 10^-5 S/cm, an electrochemical window of 4.5 V, and a lithium-ion transference number of 0.45. In light of this unique polymerization process, the traditional fabrication method of liquid electrolyte-based lithium batteries can be adopted in the current study for the preparation of all-solid-state Li/LiFePO₄ batteries. It was found that the assembled all-solid-state Li/LiFePO₄ batteries exhibited superior charging/discharging performance and preferable safety. Thus, this facile and powerful in situ polymerization strategy may open up a new approach for the design and fabrication of all-solid-state batteries with desirable performances.

Recent Advances on Materials for Lithium-Ion Batteries

Environmental issues related to energy consumption are mainly associated with the strong dependence on fossil fuels. To solve these issues, renewable energy sources systems have been developed as well as advanced energy storage systems. Batteries are the main storage system related to mobility, and they are applied in devices such as laptops, cell phones, and electric vehicles. Lithium-ion batteries (LIBs) are the most used battery system based on their high specific capacity, long cycle life, and no memory effects. This rapidly evolving field urges for a systematic comparative compilation of the most recent developments on battery technology in order to keep up with the growing number of materials, strategies, and battery performance data, allowing the design of future developments in the field. Thus, this review focuses on the different materials recently developed for the different battery components—anode, cathode, and separator/electrolyte—in order to further improve LIB systems. Moreover, solid polymer electrolytes (SPE) for LIBs are also highlighted. Together with the study of new advanced materials, materials modification by doping or synthesis, the combination of different materials, fillers addition, size manipulation, or the use of high ionic conductor materials are also presented as effective methods to enhance the electrochemical properties of LIBs. Finally, it is also shown that the development of advanced materials is not only focused on improving efficiency but also on the application of more environmentally friendly materials.