Gel polymer electrolyte combined lignocellulose with sodium alginate in lithium-ion battery

The adoption of gel polymer electrolyte (GPE) is a solution to efficiently solve the serious security risk of lithium-ion batteries (LIBs). GPE based on lignocellulose (LC) and sodium alginate (SA) was prepared. When the proportion of SA reaches up to 20 wt.%, the obtained composite membrane has a liquid electrolyte uptake of 337 wt.% and a porosity of 58%, and its mechanical strength is over four times than that of pure LC-based membrane. In addition, the corresponding GPE with 20 wt.% SA (GLCSA-20) presents high lithium-ion transference number of 0.76, distinguished ion conductivity of 2.70 × 10[Formula: see text] S cm[Formula: see text], excellent discharge specific capacity (124 mAh cm[Formula: see text] at 1 C when 200th cycle of Li∥GLCSA-20∥LiFePO[Formula: see text] and outstanding cyclic stability. These virtues support that the GLCSA-20 has great potential for applications in safe LIBs.

Tissue Paper-based Composite Separator Using Nano-SiO2 Hybrid Crosslinked Polymer Electrolyte as Coating Layer For Lithium Ion Battery With Superior Security and Cycle Stability

With the development of energy-storage devices, separator is encountered by several challenges including adequate safety, higher current density and superior stability. Tissue paper, composed of packed cellulose fibers, possesses lower production cost, more easily accessibility, superior wettability and outstanding thermostability, thus being prospective as a substrate of high performance separator. To address structure collapse phenomenon occurred in conventional coating layer after long term electrolyte swelling, nano-SiO2 hybrid crosslinked network was constructed on tissue paper through chemical reactions between polymer poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and hyperbranched polyethyleneimine (PEI) in this work. The influences of crosslinking degree on physical properties and electrochemical performance were studied thoroughly. It can be found that when the crosslinking ratio of PVDF-HFP and PEI fixed at 10:1, the crosslinked composite separator displays excellent electrolyte uptake and wettability, superior ionic conductivity, better interfacial compatibility as well as higher Li+ transference number (0.56), thus offering battery with prominent rate capabilities. Besides, this crosslinked composite separator exhibits satisfying dimensional stability even treated at 250 oC, better flame retardancy, enhanced mechanical behavior, wider electrochemical window and outstanding cycle stability. Accordingly, tissue paper-based crosslinked composite separator can meet higher requirements put forward by high power lithium ion battery.

A Three-Dimensional Electrospun Li6.4La3Zr1.4Ta0.6O12–Poly (Vinylidene Fluoride-Hexafluoropropylene) Gel Polymer Electrolyte for Rechargeable Solid-State Lithium Ion Batteries

Developing high-quality solid-state electrolytes is important for producing next-generation safe and stable solid-state lithium-ion batteries. Herein, a three-dimensional highly porous polymer electrolyte based on poly (vinylidenefluoride-hexafluoropropylene) (PVDF-HFP) with Li6.4La3Zr1.4Ta0.6O12 (LLZTO) nanoparticle fillers (PVDF-HFP-LLZTO) is prepared using the electrospinning technique. The PVDF-HFP-LLZTO gel polymer electrolyte possesses a high ionic conductivity of 9.44 × 10–4 S cm−1 and a Li-ion transference number of 0.66, which can be ascribed that the 3D hierarchical nanostructure with abundant porosity promotes the liquid electrolyte uptake and wetting, and LLZTO nanoparticles fillers decrease the crystallinity of PVDF-HFP. Thus, the solid-state lithium battery with LiFePO4 cathode, PVDF-HFP-LLZTO electrolyte, and Li metal anode exhibits enhanced electrochemical performance with improved cycling stability.

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.

Aramid Nanofibers Reinforced Cellulose Paper-Based Lithium-Ion Battery Separator with Improved Safety and Cycling Stability

Commercial polyolefin separators with poor electrolyte wettability and inferior thermal stability have hampered the development of advanced lithium-ion batteries (LIBs) due to their unsatisfied electrochemical performance and severe safety hazards. Herein, a novel paper-based composite separator composed of electrolyte-affinitive cellulose fibers (CFs) and thermally stable aramid nanofibers (ANFs) was successfully fabricated through the traditional papermaking method. It was found that the incorporation of ANFs played crucial roles in improving the defects of pure CF separator such as large-sized pores, low mechanical strength and high flammability. Specifically, the CF/ANF composite separator with 20 wt.% ANFs (CF/ANF-20) possessed narrow micropores, satisfied tensile strength (33MPa), excellent thermal resistance (without dimensional shrinkage up to 200 °C) and flame retardancy, greatly enhancing the safe operation of battery. In addition, benefiting from the highly porous structure and exceptional electrolyte affinity of CF separator, the CF/ANF-20 composite separator exhibited appropriate porosity and superior electrolyte wettability, which brought about a high electrolyte uptake (157%), thus endowing it with better ionic conductivity (0.75 mS cm−1) and lower interfacial resistance than that of commercial polypropylene (PP) separator. Accordingly, the LiFePO4/Li half cells using CF/ANF-20 separator delivered outstanding rate capability and stable cycling performance. All results indicate that the CF/ANF-20 separator with great balance between the electrochemical performance and safety is an intriguing candidate for advanced LIBs.

The Effect of Different Ratios of Malonic Acid to Plyvinylalcohol on Electrochemical and Mechanical Properties of Polyacrylonitrile Electrospun Separators in Lithium-Ion Batteries

The present study aimed to investigate the mechanical, thermal, and electrochemical properties of Polyacrylonitrile (PAN) electrospun separators in the presence of Polyvinylalcohol (PVA) hydrophilic materials and Malonic Acid (MA) crosslinker inside the lithium-ion batteries. The results showed that the M3 modified separator with the MA to PVA+MA (wt./wt.) optimum ratio of 37.5 % had the best performance in all tests. This separator had a value of 3.16 mS/cm in the ion conductivity test. Additionally, it had an electrolyte uptake of 1172 % (2.39 times more than the neat PAN separator) and thermal shrinkage of 7.4 % at 180 °C, where this value was 14.5 % for neat PAN separator at the same experimental condition. Furthermore, the acceptable performance in the battery performance tests was compared with other separators.

Effect of additives on wettability, thermal stability and electrochemical properties of γ-Al2O3-coating separator for lithium-ion batteries

Physical properties of separator, as important parameters in affecting electrochemical performance and safety of lithium ion batteries, should be paid more attention. In this study, three kinds of surfactants and dispersants were adopted to investigate their effects on thermal stability, wettability and electrochemical properties of γ-Al2O3 coating polyethylene-based separator. The experimental results showed that with the synergistic helpfulness of PEG-2000 as surfactant and D-067 as dispersant, γ-Al2O3 coating polyethylene separator demonstrates superior thermal stability (no significant thermal shrinkage after heating at 120°C), electrolyte uptake ability and improved wettability (contact angle of 27.9°). Based on further testing results in Li//MCMB coin cells, the cell with γ-Al2O3 coating polyethylene separator exhibits higher capacity and superior cycling stability than other two bare counterparts separators at room temperature after 200 cycles. These results demonstrate that the as-prepared separator is highly promising for lithium ion battery application with the help of suitable surfactant and dispersant.

A Novel Electrospinning Polyacrylonitrile Separator with Dip-Coating of Zeolite and Phenoxy Resin for Li-ion Batteries

Commercial separators (polyolefin separators) for lithium-ion batteries still have defects such as low thermostability and inferior interface compatibility, which result in serious potential safety distress and poor electrochemical performance. Zeolite/Polyacrylonitrile (Z/PAN) composite separators have been fabricated by electrospinning a polyacrylonitrile (PAN) membrane and then dip-coating it with zeolite (ZSM-5). Different from commercial separators, the Z/PAN composite separators exhibit high electrolyte uptake, excellent ionic conductivity, and prominent thermal stability. Specifically, the Z/PAN-1.5 separator exhibits the best performance, with a high electrolyte uptake of 308.1% and an excellent ionic conductivity of 2.158 mS·cm−1. The Z/PAN-1.5 separator may mechanically shrink less than 10% when held at 180 °C for 30 min, proving good thermal stability. Compared with the pristine PAN separator, the Li/separator/LiFePO4 cells with the Z/PAN-1.5 composite separator have excellent high-rate discharge capacity (102.2 mAh·g−1 at 7 C) and favorable cycling performance (144.9 mAh·g−1 at 0.5 C after 100 cycles). Obviously, the Z/PAN-1.5 separator holds great promise in furthering the safety and performance of lithium-ion 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.