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

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.

Overlooked Promising Green Features of Electrospun Cellulose-Based Fibers in Lithium-Ion Batteries

Lithium-ion batteries (LIBs) are accounted as promising power tools, applicable in a wide range of energy-based equipment, from portable devices to electric vehicles. Meanwhile, approaching a cost-effective, environmentally friendly, and safe LIB array has remained sluggish yet. In this regard, cellulose, as a nontoxic natural renewable polymer, has provided a stable and cohesive electrode structure with excellent mechanical stability and reduced electrode cracking or delamination during cycling. Additionally, the porous configuration of the cellulose allows for efficient and faster ion transport as a separator component. Miniaturizing cellulose and its derivatives have revealed more fabulous characteristics for the anode, cathode, and separator resulting from the increased surface-to-volume ratio and superior porosity, as well as their thin and lightweight architectures. The focal point of this review outlines the challenges relating to the extraction and electrospinning of cellulose-based nanofibers. Additionally, the efforts to employ these membranes as the LIBs' components are elucidated. Correspondingly, despite the great performance of cellulose-based LIB structures, a research gap is sensed in this era, possibly due to the difficulties in processing the electrospun cellulose fibers. Hence, this review can provide a source of recent advancements and innovations in cellulose-based electrospun LIBs for researchers who aim to develop versatile battery structures using green materials, worthwhile, and eco-friendly processing techniques.

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.

A Light-Thin Chitosan Nanofiber Separator for High-Performance Lithium-Ion Batteries

With the development of portable devices and wearable devices, there is a higher demand for high-energy density and light lithium-ion batteries (LIBs). The separator is a significant component directly affecting the performance of LIBs. In this paper, a thin and porous chitosan nanofiber separator was successfully fabricated using the simple ethanol displacement method. The thickness of the CME15 separator was about half that of mainstream commercial Celgard2325 separators. Owing to its inherent polarity and high porosity, the obtained CME15 separator achieved a small contact angle (18°) and excellent electrolyte wettability (324% uptake). The CME15 separator could maintain excellent thermal dimensional stability at 160 °C. Furthermore, the CME15 separator-based LIBs exhibited excellent cycling performance after 100 cycles (117 mAh g-1 at 1 C). The present work offers a perspective on applying a chitosan nanofiber separator in light and high-performance lithium-ion batteries (LIBs).

Recent Development in Novel Lithium-Sulfur Nanofiber Separators: A Review of the Latest Fabrication and Performance Optimizations

Lithium-Sulfur batteries (LSBs) are one of the most promising next-generation batteries to replace Li-ion batteries that power everything from small portable devices to large electric vehicles. LSBs boast a nearly five times higher theoretical capacity than Li-ion batteries due to sulfur's high theoretical capacity, and LSBs use abundant sulfur instead of rare metals as their cathodes. In order to make LSBs commercially viable, an LSB's separator must permit fast Li-ion diffusion while suppressing the migration of soluble lithium polysulfides (LiPSs). Polyolefin separators (commonly used in Li-ion batteries) fail to block LiPSs, have low thermal stability, poor mechanical strength, and weak electrolyte affinity. Novel nanofiber (NF) separators address the aforementioned shortcomings of polyolefin separators with intrinsically superior properties. Moreover, NF separators can easily be produced in large volumes, fine-tuned via facile electrospinning techniques, and modified with various additives. This review discusses the design principles and performance of LSBs with exemplary NF separators. The benefits of using various polymers and the effects of different polymer modifications are analyzed. We also discuss the conversion of polymer NFs into carbon NFs (CNFs) and their effects on rate capability and thermal stability. Finally, common and promising modifiers for NF separators, including carbon, metal oxide, and metal-organic framework (MOF), are examined. We highlight the underlying properties of the composite NF separators that enhance the capacity, cyclability, and resilience of LSBs.