Yuming Shang

Nanocomposite polymer membrane derived from nano TiO2-PMMA and glass fiber nonwoven: high thermal endurance and cycle stability in lithium ion battery applications

With the aim to overcome the high thermal shrinkage of conventional polyolefin separators and improve the electrochemical properties of lithium ion batteries, a nano-composite polymer electrolyte membrane (NCPE) is attempted by introducing highly dispersed nano-TiO2 hybrid doped poly(vinylidene fluoride–hexafluoro propylene) (PVDF–HFP) into a glass fiber nonwoven, which is easily available at low costs. The physical and electrochemical properties of the obtained NCPE are characterized using SEM, thermal shrinkage tests, AC impedance measurements, and charge–discharge and cycling tests. The results show that the NCPE possesses higher porosity and higher thermal dimensional stability temperature than a conventional PP separator. In addition, the electrochemical properties, such as liquid uptake, ionic conductivity and interface compatibility, of the polymer electrolyte membrane and the metallic Li electrode was improved significantly. In particular, the LiCoO2/Li coin cell with NCPE exhibits good C-rate performances of up to 85% at 10C-rate of the capacity at 1C-rate, and capacity retention ratios up to 80% after 1500 cycles at 1C/2C charge–discharge cycling. This study shows that the glass fiber nonwoven, which is easily available at low cost, can be a high performance separator for Li-ion battery applications.

Surface modification of polyolefin separators for lithium ion batteries to reduce thermal shrinkage without thickness increase

Surface chemical modification of polyolefin separators for lithium ion batteries is attempted to reduce the thermal shrinkage, which is important for the battery energy density. In this study, we grafted organic/inorganic hybrid crosslinked networks on the separators, simply by grafting polymerization and condensation reaction. The considerable silicon-oxygen crosslinked heat-resistance networks are responsible for the reduced thermal shrinkage. The strong chemical bonds between networks and separators promise enough mechanical support even at high temperature. The shrinkage at 150°C for 30 min in the mechanical direction was 38.6% and 4.6% for the pristine and present graft-modified separators, respectively. Meanwhile, the grafting organic-inorganic hybrid crosslink networks mainly occupied part of void in the internal pores of the separators, so the thicknesses of the graft-modified separators were similar with the pristine one. The half cells prepared with the modified separators exhibited almost identical electrochemical properties to those with the commercial separators, thus proving that, in order to enhance the thermal stability of lithium ion battery, this kind of grafting-modified separators may be a better alternative to conventional silica nanoparticle layers-coated polyolefin separators.

Composite electrospun membranes containing a monodispersed nano-sized TiO2@Li+ single ionic conductor for Li-ion batteries

In this work, we report novel composite electrospun membranes for Li-ion batteries. A monodispersed nano-sized TiO2@Li+ single ionic conductor containing a P(AALi-MMA) polymer layer grafted on a nano-sized TiO2 surface was prepared and used as functional fillers in composite membranes. The obtained results show that our material, based on the incorporation of a nano-sized TiO2@Li+ single ionic conductor into a composite electrospun membrane is a new generation battery separator for application in lithium-ion batteries.

Progress in synthesis of bismaleimide and its application in lithium-ion batteries

Bismaleimide (BMI) and its oligomer can be used as additives for improving the performance and safety of lithium-ion batteries. This review outlines the methods of BMI synthesis and some novel structure of BMI. Two different mechanisms, free radical polymerization and Michael addition polymerization, are proposed in terms of BMI polymerization. The recent progress of BMI additives applied in lithium-ion batteries is demonstrated.