Hansong Cheng

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.

Fabrication of a proton exchange membrane via blended sulfonimide functionalized polyamide

A novel linear non-fluorinated sulfonimide functionalized polyamide (SPA) polymer electrolyte was successfully synthesized via an aromatic sulfonimide monomer with superior thermal stability and superacidity. The aromatic sulfonimide remains stable below 220xa0°C. To fabricate membranes with strong mechanical strength and dimensional stability, the polymer was blended with various quantities of PVdF. The PVdF/SPA blend membranes exhibit an excellent capacity of water uptake and high dimensional stability. However, their proton conductivity was found to be substantially lower than that of Nafion 211. Analysis on the SEM images of the PVdF/SPA blend membranes reveals that the low proton conductivity is primarily caused by the large pore structures (>1xa0μm), which lead to breakdown of the continuous proton transport channels.

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.

Highly selective carbon dioxide adsorption on exposed magnesium metals in a cross-linked organo-magnesium complex

A cross-linked organo-magnesium complex (MTF–Mg) was synthesized and investigated for selective CO2 adsorption over N2 at 298 K. Remarkably high selectivity and reversibility were achieved with an isosteric heat of adsorption of 45.2 kJ mol−1 for CO2, consistent with the predicted DFT value of 37.3 kJ mol−1. The CO2 preferential adsorption arises from its strong interaction with the exposed magnesium atoms.

A robust pendant-type cross-linked anion exchange membrane (AEM) with high hydroxide conductivity at a moderate IEC value

A novel pendant-type cross-linked anion exchange membrane (pc-AEM) was successfully synthesized using a pre-synthesis approach to precisely control the IEC value and the degree of cross-linking. The physical properties of the pc-AEMs and the non-cross-linked pc-AEMs as well as Nafion 117 were determined, and the results were systematically compared. It was found that the synthesized pc-AEMs show much better dimensional retention capacity than the non-cross-linked pc-AEM and Nafion 117. In addition, the mechanical strength of the pc-AEMs was also remarkably enhanced. By increasing the IEC value of the pc-AEMs to the same level of Nafion 117, the highest ionic conductivity of 0.036xa0S/cm at 80xa0°C was reached. The remarkable enhancement of conductivity is chiefly attributed to the construction of highly efficient ionic transport channels resulting from the combined pendant-type and cross-linked architectures of the pc-AEMs.

Fabrication of a polymer electrolyte membrane with uneven side chains for enhancing proton conductivity

Construction of effective proton transport channels in proton exchange membranes is the key to the design of high performance proton conductive materials. Enhancement of proton conductivity of polymer electrolyte membranes was achieved by broadening the proton transfer channels via attaching acid groups to both long and short side chains of polymer electrolytes simultaneously. To demonstrate the effectiveness of the uneven side chains on the conductive properties of polymer membranes, three types of polyamide based electrolyte membranes with long side chains, short side chains and long/short side chains were prepared. It was found that among the three types of membranes with the same ion exchange capacity (IEC) value, the one with uneven side chains exhibits the highest proton conductivity. An increase of the IEC value in the uneven side chain membrane leads to a significant increase of proton conductivity. The study provides useful insight into the structural design of polymer electrolyte materials with high conductivity for fuel cell applications.