A thermostability gel polymer electrolyte with electrospun nanofiber separator of organic F-doped poly-m-phenyleneisophthalamide for lithium-ion battery

Recent Progress of Advanced Functional Separators in Lithium Metal Batteries

As a representative in the post-lithium-ion batteries (LIBs) landscape, lithium metal batteries (LMBs) exhibit high-energy densities but suffer from low coulombic efficiencies and short cycling lifetimes due to dendrite formation and complex side reactions. Separator modification holds the most promise in overcoming these challenges because it utilizes the original elements of LMBs. In this review, separators designed to address critical issues in LMBs that are fatal to their destiny according to the target electrodes are focused on. On the lithium anode side, functional separators reduce dendrite propagation with a conductive lithiophilic layer and a uniform Li-ion channel or form a stable solid electrolyte interphase layer through the continuous release of active agents. The classification of functional separators solving the degradation stemming from the cathodes, which has often been overlooked, is summarized. Structural deterioration and the resulting leakage from cathode materials are suppressed by acidic impurity scavenging, transition metal ion capture, and polysulfide shuttle effect inhibition from functional separators. Furthermore, flame-retardant separators for preventing LMB safety issues and multifunctional separators are discussed. Further expansion of functional separators can be effectively utilized in other types of batteries, indicating that intensive and extensive research on functional separators is expected to continue in LIBs.

A non-Newtonian fluid quasi-solid electrolyte designed for long life and high safety Li-O2 batteries

The Li dendrite growth and the liquid electrolyte volatilization under semi-open architecture are intrinsic issues for Li-O₂ battery. In this work, we propose a non-Newtonian fluid quasi-solid electrolyte (NNFQSE) SiO₂-SO₃Li/PVDF-HFP, which has both shear-thinning and shear-thickening properties. The component interactions among the sulfonated silica nanoparticles, liquid electrolyte, and polymer network are beneficial for decent Li⁺ conductivity and high liquid electrolyte retention without volatilization. Furthermore, NNFQSE exhibits shear-thinning property to eliminate the stress of dendrite growth during repeated cycling. Meanwhile, when the force suddenly increases, such as a high current rate, the NNFQSE may dynamically turn shear-thickening to respond and mechanically stiffen to inhibit the lithium dendrite penetration. By coupling with the NNFQSE, the lithium symmetrical battery can run over 2000 h under 1 mA cm^-2 at room temperature, and the quasi-solid Li-O₂ battery actualizes long life above 5000 h at 100 mA g^-1.

Optimizing the structural properties of electrospun polyimide membranes by response surface method

Recently, there has been a rising tendency for the fabrication of membranes using the electrospinning method because it can control the properties of the fibrous mats by changing the parameters of the process. For this reason, in the current research, polyimide (PI) membranes were fabricated by the electrospinning method. The effect of electrospinning parameters on the content of porosity and tensile properties of the electrospun PI mats were investigated. Solution concentration, device voltage, and feed rate were considered the process parameters. Response surface methodology was adopted to design the electrospinning experiments. The results showed that the feed rate had the most contribution to the content of porosity of electrospun PI membranes which increased by decreasing the feed rate. On the other hand, the polymer concentration had a remarkable effect on the tensile strength. Indeed, the tensile strength improved as the solution concentration increased. The optimized electrospinning parameters to achieve both the highest porosity (97.66%) and the highest tensile strength (2.25 MPa) in the PI membrane were as follows: solution concentration 16.78%wt, device voltage 17 kV, and feed rate 1.4 mL h−1. The experimental results were in good agreement with the predicted values.

Functional Ionic Liquid Modified Core-Shell Structured Fibrous Gel Polymer Electrolyte for Safe and Efficient Fast Charging Lithium-Ion Batteries

Fast charging is of enormous concerns in the development of power batteries, while the low conductivity and lithium ion transference number in current electrolytes degraded the charge balance, limited the rate performance, and even cause safety issues for dendrite growth. Combine inorganic fillers and ionic liquid plasticizer, here in this paper we prepared a core-shell structured nanofibrous membrane, by incorporating with carbonate based electrolyte, a gel polymer electrolyte (GPE) with high conductivity, outstanding Li+ transference number was obtained. Notably, the Li/electrolyte/LiNi0.6Co0.2Mn0.2O2 (NCM622) half-cell with this composite electrolyte delivers a reversible capacity of 65 mAh/g at 20C, which is 13 times higher than that of with Celgard 2325 membrane. It also shows enhanced long-term cycle stability at both 3C and 5C for the suppression of lithium dendrite. This organic-inorganic co-modified GPE guarantees the fast charging ability and safety of LIBs, thus provides a promising method in high performance electrolyte design.

A Parallel Bicomponent TPU/PI Membrane with Mechanical Strength Enhanced Isotropic Interfaces Used as Polymer Electrolyte for Lithium-Ion Battery

In this work, a side-by-side bicomponent thermoplastic polyurethane/polyimide (TPU/PI) polymer electrolyte prepared with side-by-side electrospinning method is reported for the first time. Symmetrical TPU and PI co-occur on one fiber, and are connected by an interface transition layer formed by the interdiffusion of two solutions. This structure of the as-prepared TPU/PI polymer electrolyte can integrate the advantages of high thermal stable PI and good mechanical strength TPU, and mechanical strength is further increased by those isotropic interface transition layers. Moreover, benefiting from micro-nano pores and the high porosity of the structure, TPU/PI polymer electrolyte presents high electrolyte uptake (665%) and excellent ionic conductivity (5.06 mS·cm-1) at room temperature. Compared with PE separator, TPU/PI polymer electrolyte exhibited better electrochemical stability, and using it as the electrolyte and separator, the assembled Li/LiMn₂O₄ cell exhibits low inner resistance, stable cyclic and notably high rate performance. Our study indicates that the TPU/PI membrane is a promising polymer electrolyte for high safety lithium-ion batteries.

Electrospun sandwich polysulfonamide/polyacrylonitrile/polysulfonamide composite nanofibrous membranes for lithium-ion batteries

The demands for novel approaches that ensure stability in lithium-ion batteries are increasing and have led to the development of new materials and fabrication strategies. In this study, sandwich structure-like polysulfonamide (PSA)/polyacrylonitrile (PAN)/polysulfonamide (PSA) composite nanofibrous membranes were prepared via an electrospinning method and used as a separator in lithium-ion batteries. The spinning time of each polymer nanofiber layer of the composite membranes was respectively and precisely controlled to maximize the merits of each component. It was found that the PSA/PAN/PSA composite nanofibrous membranes exhibited superior thermal stability and excellent porosity, liquid electrolyte uptake and ionic conductivity, showing obvious enhancement as compared to those of the commercial microporous polyolefin separator (Celgard 2400), pure PSA and pure PAN membranes. In addition, they were evaluated in the assembled Li/LiFePO₄ cells with an electrolyte solution, and good cycling performance and C-rate capacity were obtained; especially for the case of the PP6P membrane, the first discharge capacity of the battery reached 152 mA h g⁻¹, and the discharge capacity retention ratio was 85.94% from 0.2C to 2C; moreover, the battery displayed highest capacity retention ratio after 70 cycles, which was found to be 96.2% of its initial discharge capacity. Therefore, the PSA/PAN/PSA composite nanofibrous membranes can be regarded as a promising candidate for application in lithium-ion batteries.

The demands for novel approaches that ensure stability in lithium-ion batteries are increasing and have led to the development of new materials and fabrication strategies.

AP, A. S. A, Kalarikkal N, Stephen AM, G. GV, Rouxel D, Thomas S. Highly lithium ion conductive, Al2O3 decorated electrospun P(VDF-TrFE) membranes for lithium ion battery separators

Electrospun battery separators have drawn considerable attention due to their high porosity, surface area, and electrochemical performance.

Flexible, High-Wettability and Fire-Resistant Separators Based on Hydroxyapatite Nanowires for Advanced Lithium-Ion Batteries

Separators play a pivotal role in the electrochemical performance and safety of lithium-ion batteries (LIBs). The commercial microporous polyolefin-based separators often suffer from inferior electrolyte wettability, low thermal stability, and severe safety concerns. Herein, a novel kind of highly flexible and porous separator based on hydroxyapatite nanowires (HAP NWs) with excellent thermal stability, fire resistance, and superior electrolyte wettability is reported. A hierarchical cross-linked network structure forms between HAP NWs and cellulose fibers (CFs) via hybridization, which endows the separator with high flexibility and robust mechanical strength. The high thermal stability of HAP NW networks enables the separator to preserve its structural integrity at temperatures as high as 700 °C, and the fire-resistant property of HAP NWs ensures high safety of the battery. In particular, benefiting from its unique composition and highly porous structure, the as-prepared HAP/CF separator exhibits near zero contact angle with the liquid electrolyte and high electrolyte uptake of 253%, indicating superior electrolyte wettability compared with the commercial polyolefin separator. The as-prepared HAP/CF separator has unique advantages of superior electrolyte wettability, mechanical robustness, high thermal stability, and fire resistance, thus, is promising as a new kind of separator for advanced LIBs with enhanced performance and high safety.

Gel electrolytes based on poly(vinylidenefluoride-co-hexafluoropropylene)/thermoplastic polyurethane/poly(methyl methacrylate) with in situ SiO2 for polymer lithium batteries

Gel polymer electrolyte films based on poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF–HFP), thermoplastic polyurethane (TPU) and poly(methyl methacrylate) (PMMA) with and without in situ SiO₂ fillers are prepared by electrospinning polymer solution at room temperature.