Yunfeng Zhang

Fabrication of highly transparent and conductive indium-tin oxide thin films with a high figure of merit via solution processing.

Deposition technology of transparent conducting oxide (TCO) thin films is critical for high performance of optoelectronic devices. Solution-based fabrication methods can result in substantial cost reduction and enable broad applicability of the TCO thin films. Here we report a simple and highly effective solution process to fabricate indium-tin oxide (ITO) thin films with high uniformity, reproducibility, and scalability. The ITO films are highly transparent (90.2%) and conductive (ρ = 7.2 × 10(-4) Ω·cm) with the highest figure of merit (1.19 × 10(-2) Ω(-1)) among all the solution-processed ITO films reported to date. The high transparency and figure of merit, low sheet resistance (30 Ω/sq), and roughness (1.14 nm) are comparable with the benchmark properties of dc sputtering and can meet the requirements for most practical applications.

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 class of sp3 boron-based single-ion polymeric electrolytes for lithium ion batteries

A class of sp3 boron-based polymeric compounds with highly exposed lithium cations is both thermally and electrochemically stable for use in Li-ion batteries. Syntheses of a variety of the sp3 boron-based polymeric materials can be realized by taking advantage of the well-developed methods used for preparation of metal organic framework compounds.

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.

A high performance polysiloxane-based single ion conducting polymeric electrolyte membrane for application in lithium ion batteries

We report a polysiloxane based single-ion conducting polymer electrolyte (SIPE) synthesized via a hydrosilylation technique. Styrenesulfonyl(phenylsulfonyl)imide groups were grafted on highly flexible polysiloxane chains followed by lithiation. The highly delocalized anionic charges in the grafted moiety give rise to weak association with lithium ions in the polymer matrix, resulting in a lithium ion transference number close to unity (0.89) and remarkably high ionic conductivity (7.2 × 10−4 S cm−1) at room temperature. The high flexibility arising from polysiloxane enables the glass transition temperature (Tg) to be below room temperature. The electrolyte membrane displays high thermal stability and a strong mechanical strength. A coin cell assembled with the membrane comprised of the electrolyte and poly(vinylidene-fluoride-co-hexafluoropropene) (PVDF-HFP) performs remarkably well over a wide range of temperatures with high charge–discharge rates.

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.

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.

Melamine–terephthalaldehyde–lithium complex: a porous organic network based single ion electrolyte for lithium ion batteries

Cationic transference number and ionic conductivity of an electrolyte are among the key parameters that regulate battery performance. In the present work, we introduce a novel concept of using porous organic frameworks as a single ion-conducting electrolyte for lithium ion batteries. The synthesized lithium functionalized melamine–terephthalaldehyde framework (MTF–Li), a three dimensional porous organo–lithium complex, in a medium of organic solvent exhibits ionic conductivity comparable to the values of typical gel polymer electrolytes, and the battery cell assembled with the membrane of the material performs at both room temperature and at 80 °C. The rigid three-dimensional framework, functioning as the anionic part of the electrolyte, reduces the anionic transference number to a minimum. As a consequence, the cationic transference number increases to 0.88, close to unity. In addition, by virtue of its synthesis procedure, the electrolyte displays excellent sustainability at high temperatures, which is important for battery safety as well as for enhancing the performance and longevity of the battery.

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.

Remarkably durable platinum cluster supported on multi-walled carbon nanotubes with high performance in an anhydrous polymer electrolyte fuel cell

Reducing platinum (Pt) usage in the polymer electrolyte fuel cells (PEFCs) has become one of the main issues in the global commercialization of PEFCs. In this work, we describe a facile and scalable method to deposit Pt clusters (1.2 nm) on multi-walled carbon nanotubes (MWNTs) by the aid of NaOH in a reduction process. The electrocatalyst loses 50% of the initial electrochemical surface area (ECSA) after 200 000 potential cycles from 1.0 to 1.5 V vs. RHE, which is 20 times higher compared to commercial CB/Pt. The mass power density of the Pt cluster electrocatalyst measured under 120 °C without any humidification reaches 1320 mW mgPt−1, which is 6.7 times higher compared to that of commercial CB/Pt. To the best of our knowledge, the mass power density of our electrocatalyst is one of the highest values measured in high-temperature PEFCs.