Recent Advances in Poly(vinylidene fluoride) and Its Copolymers for Lithium-Ion Battery Separators

Recent Development in Separators for High-Temperature Lithium-Ion Batteries

Lithium-ion batteries (LIBs) are promising energy storage devices for integrating renewable resources and high power applications, owing to their high energy density, light weight, high flexibility, slow self-discharge rate, high rate charging capability, and long battery life. LIBs work efficiently at ambient temperatures, however, at high-temperatures, they cause serious issues due to the thermal fluctuation inside batteries during operation. The separator is a key component of batteries and is crucial for the sustainability of LIBs at high-temperatures. The high thermal stability with minimum thermal shrinkage and robust mechanical strength are the prime requirements along with high porosity, ionic conductivity, and electrolyte uptake for highly efficient high-temperature LIBs. This Review deals with the recent studies and developments in separator technologies for high-temperature LIBs with respect to their structural layered formation. The recent progress in monolayer and multilayer separators along with the developed preparation methodologies is discussed in detail. Future challenges and directions toward the advancement in separator technology are also discussed for achieving remarkable performance of separators in a high-temperature environment.

Solvent-Free and Scalable Procedure to Prepare PYR13TFSI/LiTFSI/PVDF⁻HFP Thermoplastic Electrolytes with Controlled Phase Separation and Enhanced Li Ion Diffusion

Solid electrolytes for Li transport have been prepared by melt-compounding in one single step. Electrolytes are composed of polyvinylidene fluoride–hexafluoropropylene (PVDF–HFP) with PYR13TFSI on its own or with varying concentration of LiTFSI. While the extrusion of PVDF–HFP with PYR13TFSI is possible up to relatively high liquid fractions, the compatibility of PVDF–HFP with LiTFSI/PYR13TFSI solutions is much lower. An organo-modified sepiolite with D-α-tocopherol polyethylene glycol 1000 succinate (TPGS-S) can be used to enhance the compatibility of these blends and allows to prepare homogeneous PYR13TFSI/LiTFSI/PVDF–HFP electrolytes with controlled microphase separations by melt-compounding. The structure and morphology of the electrolytes has been studied by FTIR, differential scanning calorimetry (DSC), SEM, and AFM. Their mechanical properties have been studied by classical strain–stress experiments. Finally, ionic conductivity has been studied in the −50 to 90 °C temperature range and in diffusivity at 25 °C by PFG-NMR. These electrolytes prove to have a microphase-separated morphology and ionic conductivity which depends mainly on their composition, and a mechanical behavior typical of common thermoplastic polymers, which makes them very easy to handle. Then, in this solvent-free and scalable fashion, it is possible to prepare electrolytes like those prepared by solvent casting, but in few minutes instead of several hours or days, without solvent evaporation steps, and with ionic conductivities, which are very similar for the same compositions, above 0.1 mS·cm⁻¹ at 25 °C. In addition, some of the electrolytes have been prepared with high concentration of Li ion, what has allowed the anion exchange Li transport mechanism to contribute significantly to the overall Li diffusivity, making D_Li become similar and even clearly greater than D_TFSI.

Cellulosic materials-enhanced sandwich structure-like separator via electrospinning towards safer lithium-ion battery

The latent security issue has become the foremost anxiety for lithium-ion batteries (LIBs) wide-ranging of commercialized applications. Hence, the performance of a separator such as chemical durability, electrical insulator, and thermal stability must be superior. Herein, we exhibit a sandwich-structured composite membrane with enhanced thermal resistance and electrolyte affinity, which was prepared by layer-by-layer electrospinning deposition. After 50 cycles, the battery with a 3 wt.% halloysite nanotube electrospinning separator retained 91.80% of its initial discharge capacity, that was a drastic improvement over the commercial polypropylene separator with the numeric of 79.98%. This predominant composite membrane was prepared via an eco-friendly technics and can be thought of an assuring, expectant separator towards high performance lithium-ion batteries.