Flexible, high-wettability and thermostable separator based on fluorinated polyimide for lithium-ion battery

Effect of Carbon Nanomaterials Incorporated Polymeric Membrane Separators for Energy Storage Devices

The rapid expansion of the global population and technological advancements have heightened the need for efficient energy conversion and electrochemical energy storage. Electrochemical energy systems like batteries and supercapacitors have seen notable developments to meet this demand. However, conventional polymeric membrane separators in these systems face challenges due to limited porosity and poor mechanical and thermal properties, reducing overall electrochemical performance. Researchers have incorporated nanoparticles into the polymer matrix to address these limitations and enhance separator properties. Carbon-based nanomaterials, in particular, have gained prominence due to their unique features, such as surface-dependent characteristics, size, porosity, morphology, and electrical conductivity. These properties make carbon-based nanomaterials advantageous in improving energy storage compared to conventional materials. Advanced carbon-doped polymeric membrane separators have emerged as a potential solution to the issues faced by conventional separators. Adding carbon nanoparticles, such as graphene-based materials and carbon nanotubes to the polymeric separators of batteries and supercapacitors has helped researchers solve problems and improve electrochemical performance. This review article provides a state-of-the-art overview of carbon-doped polymeric membrane separators, their properties, fabrication processes, and performance in lithium batteries, as well as supercapacitors. It emphasizes advantages of these novel separator materials and suggests future research directions in this field.

Development of AlN-loaded PET separators from waste water bottle plastics with superior thermal characteristics for next-generation lithium-ion batteries

Preventing short circuit hazard due to lithium (Li) dendrite formation across a separator from the anode of a lithium-ion battery (LIB) throughout operation is important; however, conventional separator materials cannot fulfil the increasing safety standards of next-generation LIBs. Thus, developing separator materials with high Li dendrite suppression ability in order to prevent short circuit is of paramount importance for realising next-generation LIBs. In this study, aluminum nitride-loaded polyethylene terephthalate (PET/AlN) composites with micro-/nanoarchitecture were synthesized using PET that was recycled from commercial waste bottles via an electrospinning strategy. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) suggested that AlN nanoparticles were encapsulated in PET micro-/nanoarchitecture fibres. Thermogravimetric analysis indicated that the AlN content in the composite materials was about 4-5 wt%. X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR) spectroscopy confirmed the PET polymer structure of PET/AlN composites. The PET/AlN 4 wt% separator exhibited a porosity of 69.23%, according to the n-butanol uptake test, and a high electrolyte uptake of 521.69%. Most importantly, electrochemical results revealed that when evaluated at a current density of 0.5C, PET/AlN 4 wt% composites could deliver a reversible specific capacity of 238.2 mA h g-1 after 100 cycles. When C-rate capability tests were conducted at high charge-discharge densities of 0.2, 0.5, 1, 2, and 4C, the PET/AlN 4 wt% composite manifested average specific capacities of about 225.3, 218.4, 191.0, 127.5, and 28.1 mA h g-1, respectively. The excellent electrochemical performance of the PET/AlN 4 wt% composite could probably be attributed to the combined benefits of AlN nanoparticles and the micro-/nanoarchitecture. These unique features of PET/AlN were advantageous for effective Li ion transport in repeated charge-discharge cycles and strong hydrothermal stability, thereby resulting in safety, high capacity and excellent C-rate performance. Overall, this study demonstrated the excellent electrochemical performance of PET/AlN composites as stable separator materials for advanced LIBs.

Polyimide/cellulose composite membrane with excellent heat-resistance and fast lithium-ion transport for lithium-ion batteries

Polyimide membranes have long been of great interest in the battery industries due to their outstanding thermal stability and flame retardancy. However, the preparation of polyimide membranes with ideal pore structure and excellent lithium-ion transference remains a challenge. In this study, we reported for the first time, that a nano-porous fluorinated and partially carboxylated polyimide/cellulose composite membrane was successfully synthesized by selected monomers and prepared by thermal imidization, phase separation, and alkaline hydrolysis method. Particularly, an appropriate addition of cellulose acetate (CA) during the synthesis process can optimize the pore structure of the membrane. Besides, CA was converted to cellulose after alkaline hydrolysis, further enhancing the electrolyte affinity and lithium-ion transference of the membrane. Hence, this composite membrane exhibited distinct heat-resistance, high porosity (78 %), electrolyte absorption (344 %), and lithium-ion transfer number (0.84). Most importantly, thanks to the above characteristics of the membrane, the assembled LiFePO4/Li cells demonstrated excellent cycling stability compared with the cell with PP membrane, showing a capacity retention rate of as high as 93 % after 500 cycles at 1C. We anticipate that this composite membrane with superior physical and electrochemical properties would shed light on the development of next-generation membranes for high-power and high-safety batteries.

Review of Progress in the Application of Polytetrafluoroethylene-Based Battery Separators

Batteries have broad application prospects in the aerospace, military, automotive, and medical fields. The performance of the battery separator, a key component of rechargeable batteries, is inextricably linked to the quality of the batteries. The polytetrafluoroethylene (PTFE)-based membrane, in addition to PTFE's intrinsic properties of corrosion resistance and high temperature resistance, also possesses characteristics such as high porosity and high strength, making it an ideal substrate for the separator in current high-performance batteries, such as fuel cells (FC), all-vanadium redox liquid current batteries (VRBs), solid-state batteries (SSBs), and lithium-ion batteries (LIBs). This paper introduces the PTFE membrane's main preparation methods and application fields and outlines its advantages as a battery separator. It then comprehensively describes the status of PTFE-based battery separator applications, sums up the advantages and development prospects of PTFE-based battery separators, and looks forward to the important role and challenges PTFE-based battery separators will play in the future of rechargeable batteries and even in new energy equipment with even more harsh and complex electrolytes. In the future, PTFE-based battery separators will be used in rechargeable batteries and even in new energy devices with more severe and complex electrolytes, which will play an important role and challenge in providing a reference for the research on PTFE-based battery separators.

A novel high-performance electrospun of polyimide/lignin nanofibers with unique electrochemical properties and its application as lithium-ion batteries separators

Polypropylene is currently one of the most widely used separators in lithium batteries because of its low cost and chemical stability. However, it also has some intrinsic flaws that hamper the battery performance, such as poor wettability, low ionic conductivity, and some safety issues. This work introduces a novel electrospun nanofibrous consisting of polyimide (PI) blended with lignin (L) to serve as a new class of bio-based separators for lithium-ion batteries. The morphology and properties of the prepared membranes were studied in detail and compared with those of a commercial polypropylene separator. Interestingly, the polar groups in lignin promoted the affinity to the electrolytes and improved the liquid absorption properties of the PI-L membrane. Besides, the PI-L separator showed a higher ionic conductivity (1.78 × 10-3 S/cm) and Li+ transference number (0.787). Furthermore, the battery's cycle and rate performance improved due to adding of lignin. The capacity retention of the assembled LiFePO4 | PI-L | Li Battery was 95.1 % after 100 cycles at 1C current density, which was higher than that of the PP (90 %). Based on the results, PI-L, a bio-based battery separator, can potentially replace the current PP separators in lithium metal batteries.

Preparation of porous fluorinated polyimide separator for lithium-ion batteries by non-solvent induced phase separation process

A series of novel porous fluorinated polyimide (FPI) separators containing trifluoromethyl group (–CF3) were prepared by the non-solvent induced phase separation (NIPS) strategy. The prepared FPI separator with 60% molar content (fluorinated dianhydride: non-fluorinated dianhydride: diamine = 60: 40: 100) of fluorinated groups (FPI-60%) could stably exist in the electrolyte as a LIBs separator. The resultant FPI-60% separator possesses high thermal stability with the Tg of 289.4°C and exhibits no shrinkage even at 200°C. The morphologies of the FPI-60% separators were adjusted by introducing small molecular non-solvent additives-ethanol, and the FPI-60% separators present the spongy-like and interconnected structure with different porosity as the amount of ethanol changed from 1 wt% to 10 wt%. The FPI-60% separators display excellent electrolyte uptake with 170%–200% and the ionic conductive could reach 1.17 mS/cm which is four times approximately than that of the PP separator. The lithium-ion batteries (LIBs) using FPI-60% separators with 10 wt% ethanol added show better rate capacities (102.8 mAh/g, 70.8 mAh/g of PI-10 and PP separator at 2 C, respectively) and the capacity retention rate is 93.2% after 50 cycles. The results prove that the porous FPI separator is a promising candidate for high-performance LIBs.

Preparation and application of a high-temperature–resistant EVOH-SO3Li/PI fiber membrane with self-closing pores

A lithium ethylene-vinyl alcohol copolymer sulfate (EVOH-SO3Li)/polyimide (PI) composite fiber membrane prepared via high-voltage electrospinning and impregnation was used as a lithium-ion battery separator for research purposes. The polyamic acid spinning solution was synthesized from 3,3′′,4,4′′-benzophenone tetracarboxylic dianhydride and 4,4-diaminodiphenyl ether. The PI fiber membrane was prepared via high-voltage electrospinning and thermal imidization, and EVOH-SO3Li was then coated on the surface of the PI fiber to prepare an EVOH-SO3Li/PI composite fiber membrane material (t-EVOH-SO3Li/PI). Overall, the EVOH-SO3Li/PI membrane exhibits excellent basic physical properties, given the clear three-dimensional network microstructure. When compared with EVOH-SO3Li/PI composite fiber membrane prepared via the cospinning method (s-EVOH-SO3Li/PI), its electrolyte uptake and tensile strength can increase to 739% and 17.56 MPa, respectively. Additionally, the EVOH-SO3Li/PI composite fiber membrane prepared via high-voltage electrospinning and impregnation exhibits better heat shrinkage stability, electrochemical performance, and high-temperature self-closing pores function. The electrochemical stability window, electrochemical impedance, and ionic conductivity correspond to 5.8 V, 310 Ω, and 3.753 × 10−3 S cm−1, respectively. Specifically, at 200°C, the internal pores can close effectively, and this is extremely important for the safety of lithium-ion batteries.

Multilayer Nanofiber Composite Separator for Lithium-Ion Batteries with High Safety

An original Von Koch curve-shaped tipped electrospinneret was used to prepare a polyimide (PI)-based nanofiber membrane. A multilayer Al2O3@polyimide/polyethylene/Al2O3@polyimide (APEAP) composite membrane was tactfully designed with an Al2O3@ polyimide (AP) membrane as outer shell, imparting high temperature to the thermal run-away separator performance and a core polyethylene (PE) layer imparts the separator with a thermal shut-down property at low temperature (123 °C). An AP electrospun nanofiber was obtained by doping Al2O3 nanoparticles in PI solution. The core polyethylene layer was prepared using polyethylene powder and polyterafluoroethylene (PTFE) miniemulsion through a coating process. The addition of PTFE not only bonds PE power, but also increases the adhesion force between the PE and AP membranes. As a result, the multilayer composite separator has high safety, outstanding electrochemical properties, and better cycling performance as a lithium-ion battery separator.