Effects of Molecular Weight on the Electrochemical Properties of Poly(vinylidene difluoride)-Based Polymer Electrolytes

Abstract

Polymer-based electrolytes have attracted ever-increasing attention for solid-state batteries due to their excellent flexibility and processability. Among them, poly­(vinylidene difluoride) (PVDF)-based electrolytes with high ionic conductivity, wide electrochemical stability window, and good mechanical properties show great potential and have been widely investigated by using different Li salts, solvents, and inorganic fillers. Here, we report the influence of the molecular weight of PVDF itself on the electrochemical properties of the electrolytes by using two kinds of common PVDF polymers, i.e., PVDF 761 and 5130. Our results demonstrate that the electrolyte with a larger molecular weight (PVDF 5130) has a denser structure and lower crystallinity, and thus much better electrochemical performance, than one with a smaller molecular weight (PVDF 761). With PVDF 5130, the LiFePO4-based solid-state cells present a steady cycling performance with a capacity retention of 85% after 1000 cycles at 1 C and 30 °C. The cycle life of the LiCoO2-based solid-state cells is also extended by using PVDF 5130.

An organic additive assisting with high ionic conduction and dendrite resistance of polymer electrolytes

“…30 The degree of crystallinity X c of PVDF can be quantified by using the equation, X c = Δ H m /Δ H 0 m , where Δ H 0 m is the fusion enthalpy of fully crystallized PVDF (104.7 J g −1 ) and Δ H m is the fusion enthalpy of the electrolyte obtained from the area of the peak at T m . 47 The calculated results show that the X c gradually decreases with the increase of the AMPS content (Fig. 2c).…”

Fluorescence Lifetime-Based Characterization for Supramolecular Polymer Molecular Weight

“…Scheme S1 presents the synthetic routes of M1, BODIPY-C12a, and BODIPY-C12b, and details can be referred to in the Supporting Information. 1 H NMR spectroscopy, 13 C NMR spectroscopy, and high-resolution mass spectrometry were applied to characterize M1, BODIPY-C12a, BODIPY-C12b, and their precursors (Figures S1−S14, Supporting Information). The presence of even a single UPy unit impurity can act as a supramolecular chain terminator, exerting a substantial influence on the degree of polymerization (DP).…”

“…Scheme S1 presents the synthetic routes of M1, BODIPY-C12a, and BODIPY-C12b, and details can be referred to in the Supporting Information 1. H NMR spectroscopy,13 C NMR spectroscopy, and high-resolution mass spectrometry were applied to characterize M1, BODIPY-C12a, BODIPY-C12b, and their precursors (Figures S1−S14, Supporting Information).…”

Challenges of polymer electrolyte with wide electrochemical window for high energy solid‐state lithium batteries

“…However, owing to its high symmetry, it easily forms a highly crystalline structure, which restricts segment movement and affects the migration of Li + . [72][73][74] Pure PVDF is nearly insulated, and must be combined with other electrolyte materials to transmit Li + . Therefore, these electrolytes are often used to prepare the GPEs.…”

“…Owing to the strong electronegativity of fluorine, a dipole moment perpendicular to the chain length is formed in the PVDF monomer unit, which is conducive to the dissociation of lithium salt. However, owing to its high symmetry, it easily forms a highly crystalline structure, which restricts segment movement and affects the migration of Li + 72–74 . Pure PVDF is nearly insulated, and must be combined with other electrolyte materials to transmit Li + .…”