Yubao Sun

Influence of chemical microstructure of single-ion polymeric electrolyte membranes on performance of lithium-ion batteries.

A novel protocol to generate and control porosity in polymeric structures is presented for fabrication of single ion polymer electrolyte (SIPE) membranes for lithium ion batteries. A series of SIPEs with varying ratios of aliphatic and aromatic segments was successfully synthesized and subsequently blended with PVDF-HFP to fabricate membranes of various sizes of pores. The membranes were characterized using techniques including SEM, solvent uptake capacity measurement and ionic conductivity. We demonstrate that appropriate membrane porosity enhances ionic conductivity, reduces interfacial resistance between electrodes and electrolyte and ultimately boosts performance of Li-ion batteries. The implication of the structure-performance relationship for battery design is discussed.

A gel single ion polymer electrolyte membrane for lithium-ion batteries with wide-temperature range operability

We report excellent operability of a lithium-ion battery with a gel membrane of an sp3 boron-based single ion polymer, lithium poly(1,2,3,4-butanetetracarboxylic acid borate) (LiPBAB), as the electrolyte. The battery exhibits outstanding performance in a wide temperature range of 25–100 °C with high ionic conductivity of 2.9 × 10−4 S cm−1, high electrochemical stability of 4.3 V, a large cationic transference number t+ of 0.89 and an excellent mechanical strength of 33 MPa at room temperature. The remarkable cyclic stability of the battery at 100 °C demonstrates exceptional device safety enabled by the electrolyte membrane.

Design and synthesis of a single ion conducting block copolymer electrolyte with multifunctionality for lithium ion batteries

A novel single ion conducting block copolymer electrolyte (SI-co-PE) for applications in lithium-ion batteries is presented. The block copolymer is made of alternative ethylene oxide (EO) and aromatic segments to tune the glass transition temperature (Tg), the mechanical strength and the porosity of the material for achieving high electrochemical performance of lithium-ion batteries. Upon blending with a PVDF-HFP binder via a solution cast method, a gel SI-co-PE membrane with high ionic conductivity, a wide electrochemical window and a high lithium transference number was obtained. Excellent electrochemical stability and battery performance at both room temperature and 80 °C with various charge–discharge rates were demonstrated. The study underscores the fundamental importance of polymer electrolyte microstructures in battery performance enhancement and suggests ways to improve the design of new electrolyte materials for development of better battery devices with a long cycle life.

High rate lithium-sulfur battery enabled by sandwiched single ion conducting polymer electrolyte

Lithium-sulfur batteries are highly promising for electric energy storage with high energy density, abundant resources and low cost. However, the battery technologies have often suffered from a short cycle life and poor rate stability arising from the well-known “polysulfide shuttle” effect. Here, we report a novel cell design by sandwiching a sp3 boron based single ion conducting polymer electrolyte film between two carbon films to fabricate a composite separator for lithium-sulfur batteries. The dense negative charges uniformly distributed in the electrolyte membrane inherently prohibit transport of polysulfide anions formed in the cathode inside the polymer matrix and effectively blocks polysulfide shuttling. A battery assembled with the composite separator exhibits a remarkably long cycle life at high charge/discharge rates.

Single‐Ion Polymer Electrolyte Membranes Enable Lithium‐Ion Batteries with a Broad Operating Temperature Range

Conductive processes involving lithium ions are analyzed in detail from a mechanistic perspective, and demonstrate that single ion polymeric electrolyte (SIPE) membranes can be used in lithium-ion batteries with a wide operating temperature range (25-80 °C) through systematic optimization of electrodes and electrode/electrolyte interfaces, in sharp contrast to other batteries equipped with SIPE membranes that display appreciable operability only at elevated temperatures (>60 °C). The performance is comparable to that of batteries using liquid electrolyte of inorganic salt, and the batteries exhibit excellent cycle life and rate performance. This significant widening of battery operation temperatures coupled with the inherent flexibility and robustness of the SIPE membranes makes it possible to develop thin and flexible Li-ion batteries for a broad range of applications.

A lithium poly(pyromellitic acid borate) gel electrolyte membrane for lithium-ion batteries

Lithium poly(pyromellitic acid borate) (PPAB) was synthesized via polymerization of lithium tetramethanolatoborate and silylated pyromellitic acid. The synthesized material was characterized by Fourier transformation infrared spectroscopy, 11B nuclear magnetic resonance, scanning electron microscopy, and thermogravimetric analysis. And electrochemical characterizations were carried out on the blended PPAB/PVDF-HFP membrane. The PPAB-based composite membrane exhibits high lithium ionic conductivity, a broad electrochemical window and a high lithium-ion transference number. The battery cells assembled with the PPAB/PVDF-HFP/EC:PC composite membrane as the electrolyte perform reasonably well not only at elevated temperature but also at room temperature with good cyclability and discharge capacity, making the material suitable for applications in lithium-ion batteries.

Single ion conducting lithium sulfur polymer batteries with improved safety and stability

Li–S secondary batteries use lithium metal as the anode. The safety hazard arising from the Li dendrite formation on the metal surface presents a formidable challenge that has hindered the technology from practical applications for many years. It has been confirmed that tiny and random lithium deposition takes place at the ion depletion layer on the surface of lithium metal. The time required to reach the ion depletion layer can be quantified using Sands equation, in which the time is inversely proportional to the transference number of anions (t−). Therefore, restricting the mobility of anions enables avoidance of ion depletion. In this study, lithium 4-aminophenylsulfonyl(trifluoromethylsulfonyl)imide (LiATFSI) is grafted with poly(ethylene-alt-maleic anhydride) (PEMA, Mw = 100 000–500 000) using a cyclic imide to form a single ion conducting polymer electrolyte (PEMA-graft-LiATFSI). The polymer electrolyte membrane made of PEMA-graft-LiATFSI is capable of withstanding a high current density of ±50 mA cm−2 (normalized to the surface area of the lithium disk) in a lithium symmetric cell. More remarkably, the metallic luster of the lithium foil remains essentially intact even after a galvanostatic cycling test with a current density of ±10 mA cm−2 for over 1600 hours, suggesting that the membrane can effectively suppress Li dendrite formation and thus pave a way to use lithium metal directly as the anode material with sufficient energy capacity and good safety. The lithium–sulfur battery assembled with the membrane as the electrolyte as well as the separator delivered a stable capacity of 780.8 mA h g−1 after 1000 cycles at 1C. This work demonstrates the necessity and fundamental importance of single ion conducting electrolyte membranes for achieving safe and stable performance with high energy density lithium metal secondary batteries.