Facile Fabrication of Functionalized Separators for Lithium-Ion Batteries with Ionic Conduction Path Modifications via the γ-Ray Co-irradiation Grafting Process

Abstract

Separators play a vital role in electronic insulation and ionic conduction in lithium-ion batteries. The common improvement strategy of polyolefin separators is mostly based on modifications with a coating layer, which is simple and effective to some extent. However, the improvement is often accompanied by negative effects such as the increase of the thickness and the blockage of the porous structure, resulting in the decrease of energy density and power density. The porous structure of the separators serves as a conduction path for ions to travel back and forth between the anode and cathode, which has an important impact on the performance of lithium-ion batteries. If the porous structure of the separators can be modified, it will essentially affect the ionic transport behavior through the whole conduction path. Herein, we provide a simple and effective method to functionalize the porous polyolefin separator via the γ-ray co-irradiation grafting process, where high-energy γ-ray is used to generate active sites on the polymer chain to initiate the grafting polymerization of chosen monomers with selected functional groups. In this work, 4,4,5,5-tetramethyl-2-vinyl-1,3,2-dioxaborolane, a kind of borane molecule with an electron-deficient group, was chosen as the grafting monomer. After the γ-ray co-irradiation grafting process, both the surface and pores of the polyolefin separators were functionalized by electron-deficient groups in the borane molecule and the whole electrolyte conduction path within the separator was activated. Due to the electron-deficient effect of the B atom, the lithium-ion conduction is promoted and the lithium-ion transference number can be increased to 0.5. As a result, the half-cell assembled with the functionalized separator shows better cycle stability and better capacity retention under high current rate.

Capillary-induced self-crumpled and sulfur-deficient MoS2 nanosheets inhibit polysulfide cycling in lithium–sulfur batteries

“…The higher amount of loading can affect the porosity of the coated layer and electrolyte uptake which can lead to heightened resistance at the interface between the cathode and separator, potentially deteriorating the battery performance. 40 The performance of the MC separator prepared with a higher amount of c-MoS 2 (5 mg and 10 mg) has been studied in comparison to 2 mg dispersion. A tape adhesion test revealed that the c-MoS 2 was undetachable from the PP separator; in contrast, the commercial MoS 2 and ce-MoS 2 readily became stuck on the gummed side of the tape, confirming its poor adhesivity (Fig.…”

Direct Fabrication of PET-Based Thermotolerant Separators for Lithium-Ion Batteries with Ion Irradiation Technology

“…Since there are only Li + participating in the electrochemical reactions during the energy conversion process, the Li + transference number (t Li + ), which reflects the contribution of lithium ions to the overall ionic conduction, was calculated using eq 1 by the combination of chronoamperometry and AC impedance analysis. 31 The calculated t Li + of PP and ITE PET separators is 0.53 and 0.59, respectively, as displayed in Figure 4c,d. The higher t Li + value of the ITE PET separator also reveals that the vertical channels possess a relatively higher Li + ion conducting ability than that of the PP separator.…”

Electrode Protection and Electrolyte Optimization via Surface Modification Strategy for High‐Performance Lithium Batteries

“…For example, Lee et al [243] developed a polydopamine interlayer between two PE films as a selective layer, thus suppressing the diffusion of the decomposed production of electrolytes. According to this idea, Zhao group [244] fabricated grafted boronated monomer onto the surface of PE to enhance the Li + transference number (t Li + ). The boronated molecule on [241] Copyright 2020, Elsevier.…”