In this paper, we review different types of polymer electrolytes, recent approaches and technological applications of polymer electrolytes. The report first discusses the characteristics, advantages and applications for three types of polymer electrolytes: gel polymer electrolytes, solid polymer electrolytes and composite polymer electrolytes. Next, we discuss the features and performance of different polymer hosts based on some important and recently published literature. Recent progress of some approaches used in improving the performance of the polymer electrolytes is highlighted. The last part of the review includes the technological applications of some electrical energy storing/converting devices: electrochemical capacitors, batteries, fuel cells and dye-sensitized solar cells. It is also stressed that the technological advancement in the polymer electrolytes plays a pivotal role in the development of energy storing/converting systems.

A review of polymer electrolytes: fundamental, approaches and applications

LiF modified stable flexible PVDF-garnet hybrid electrolyte for high performance all-solid-state Li–S batteries

A solid-state lithium-ion battery, in which all components (current collector, anode and cathode, electrolyte, and packaging) are stretchable, is introduced, giving rise to a battery design with mechanical properties that are compliant with flexible electronic devices and elastic wearable systems. By depositing Ag microflakes as a conductive layer on a stretchable carbon-polymer composite, a current collector with a low sheet resistance of ≈2.7 Ω □-1 at 100% strain is obtained. Stretchable electrodes are fabricated by integrating active materials with the elastic current collector. A polyacrylamide-"water-in-salt" electrolyte is developed, offering high ionic conductivity of 10-3 to 10-2 S cm-1 at room temperature and outstanding stretchability up to ≈300% of its original length. Finally, all these components are assembled into a solid-state lithium-ion full cell in thin-film configuration. Thanks to the deformable individual components, the full cell functions when stretched, bent, or even twisted. For example, after stretching the battery to 50%, a reversible capacity of 28 mAh g-1 and an average energy density of 20 Wh kg-1 can still be obtained after 50 cycles at 120 mA g-1 , confirming the functionality of the battery under extreme mechanical stress.

Fully Integrated Design of a Stretchable Solid-State Lithium-Ion Full Battery

Due to the large volume change of sulfur and the diffusion of dissolved polysulfides, the development of a high-performance binder with functionality beyond mechanical adhesion/support for sulfur cathodes is in high demand. This is especially true for the success of high-loading sulfur cathodes. Here, we report a soy-protein-based binder with high mechanical robustness and multiple functionality for high-energy lithium–sulfur batteries. The multi-functional binder (denoted as SP-PAA) is fabricated via facilely incorporating soy protein (SP) with poly(acrylic acid) (PAA) and it has been demonstrated to effectively buffer the large volume change of the sulfur cathode during cycling. More significantly, the abundant polar groups (e.g. amines, carboxyl groups, etc.) of soy protein empower the binder with a strong capability to adsorb polysulfides, as evidenced by density functional theory (DFT) calculations. Meanwhile, the good ion-conduction abilities of soy protein notably promote electrochemical reactions. With the use of this binder, the electrochemical performance (e.g. capacity, cycling stability and rate capability) of the sulfur cathode is substantially enhanced. In addition, owing to the excellent mechanical properties of SP-PAA and its effects on improving electrode microstructures, high-loading sulfur cathodes (>5 mg cm−2) with good and stable performance are achieved. The good performance is also attributed to the role that SP-PAA plays in adsorbing polysulfides, sustaining structural stability and promoting electrochemical reactions. This study brings about a cost-effective strategy for the fabrication of superior binders through exploiting natural materials and leads to the realization of high-loading sulfur cathodes for mass production.

A robust and ion-conductive protein-based binder enabling strong polysulfide anchoring for high-energy lithium–sulfur batteries

To achieve high ionic conductivity for solid electrolyte, an artificial Li-rich interface layer of about 60 nm thick has been constructed in polymer-based poly(ethylene oxide)-lithium bis(trifluoromethanesulfonyl)imide composite solid electrolyte (briefly noted as PEOm ) by adding Li-based alloys. As revealed by high-resolution transmission electron microscopy and electron energy loss spectroscopy, an artificial interface layer of amorphous feature is created around the Li-based alloy particles with the gradient distribution of Li across it. Electrochemical analysis and theoretical modeling demonstrate that the interface layer provides fast ion transport path and plays a key role in achieving high and stable ionic conductivity for PEOm -Li21 Si5 composite solid electrolyte. The PEOm -5%Li21 Si5 composite electrolyte exhibits an ionic conductivity of 3.9 × 10-5  S cm-1 at 30 °C and 5.6 × 10-4  S cm-1 at 45 °C. The LiFePO4 | PEOm -5%Li21 Si5 | Li all-solid-state batteries could maintain a stable capacity of 129.2 mA h g-1 at 0.2 C and 30 °C after 100 cycles, and 111.3 mA h g-1 after 200 cycles at 0.5 C and 45 °C, demonstrating excellent cycling stability and high-rate capability.

Constructing Li-Rich Artificial SEI Layer in Alloy-Polymer Composite Electrolyte to Achieve High Ionic Conductivity for All-Solid-State Lithium Metal Batteries.

In this work, we investigate the electrical, structural, and thermal properties of composite polymer electrolytes (CPEs). Different mass fractions of antimony trioxide filler, Sb2O3, are added into poly(acrylic acid) (PAA)-based polymer electrolytes with N-lithiotrifluoromethane sulphonamide [LiN(SO2CF3)2] (LiTFSI) as doping salt. Characteristics such as alternating current (AC)–impedance spectroscopy, attenuated total reflectance–Fourier transform infrared (ATR-FTIR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) are analyzed. The highest ionic conductivity of (2.15 ± 0.01) × 10−4 S cm−1 is achieved at room temperature with addition of 6 wt% of fillers. The ionic transportation is further proven in a transference number study under DC polarization, whereas ATR-FTIR is employed to explore the complexation between PAA, LiTFSI, and Sb2O3. TGA reveals the improved thermal stability of CPEs. The glass transition temperature (T
 g) is reduced upon addition of Sb2O3 as shown in DSC analysis.

W. Kam

Papers

Electrical, structural, and thermal studies of antimony trioxide-doped poly(acrylic acid)-based composite polymer electrolytes