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Posted: Mar 28, 2017
Improving Li-ion batteries with nanostructured conductive polymer gels
(Nanowerk Spotlight) The electrode in lithium-ion (Li-ion) batteries is an integrated system in which both active materials and binder systems play critical roles in determining its final properties. In order to improve battery performance, a lot of research is focussing on the development of high-capacity active materials. However, without an efficient binder system, these novel materials can't fulfill their potentials.
A group of researchers now has contributed to this field from a slight different aspect, developing a high-performance and general binder system for batteries. This entirely new binder system with a nano-architecture promotes both electron and ion transport, which enhances the energy per unit mass and volume of the electrode.
This work by Guihua Yu group at University of Texas at Austin and Esther Takeuchi group at Stony Brook University, demonstrates a new generation of nanostructured conductive polymer gel based novel binder materials for fabrication of high-energy lithium-ion battery electrodes.
This gel framework could become a next-generation binder system for commercial Li-ion batteries.
"Compared to conventional binder system which typically consists of conductive additive and polymer binder, our novel binder plays dual functionalities simultaneously combining conductive and adhesive features, thus greatly improving the better utility of active electrode materials,"Professor Yu tells Nanowerk. "More importantly, owing to its unique 3D network structure, this gel binder promotes both electron and ion transport in electrode and improves the distribution of active particles, thus enhancing the rate performance and cycle life of battery electrodes."
He points out that this invention is important because it presents a new generation of powerful yet scalable binder materials for lithium ion batteries that show great potential in industrial manufacturing.
This novel gel binder can overcome the drawbacks of conventional binder systems, leading to next-generation lithium ion battery with high performance.
Schematic of synthetic and structural features of commercial lithium iron phosphate (C-LFP)/cross-linked polypyrrole (C-PPy) hybrid gel framework. The conductive polymer chains can be polymerized in situ with electrode materials and cross-linked by molecules with multiple functional groups, resulting in a polymeric network connecting all active particles. (Reprinted with permission by American Chemical Society) (click on image to enlarge)
"A traditional binder system in Li-ion battery electrodes is a binary hybrid with components acting separate functionalities," explains Yu. "In such system, polymer binders such as polyvinylidene fluoride (PVDF) adhere the active materials and other additives together to hold the mechanical integrity while a conductive additive (usually carbon particles) ensures the conductivity of the entire electrode."
In these electrodes, electrons transport through chains of particles while ions move through the liquid or solid electrolyte that fills the pores of the electrode. However, the conductive phases are randomly distributed, which may lead to bottlenecks and poor contacts that impede effective access to parts of the battery.
And both organic and inorganic components tend to aggregate, which also negatively impact electron and ion transport.
The team's novel conductive gel binder can overcome these drawbacks and thus improve the rate and cyclic performance of Li-ion batteries.
The conductive polymer gels potentially could also be used for responsive/smart electronics such as biosensors, artificial skins and soft robotics.
The scientific core of this work is that three-dimensional nanostructured conductive polymer gels can be built up by tunable molecule crosslinking and this unique conductive framework material can promote the electron/ion transport within battery electrodes.
"Firstly, our work provides a new method for synthesis of conductive polymer gel," elaborates Yu. "Traditionally, conductive polymer gels are synthesized by template-based method, which usually results in low conductivity and poor mechanical properties. The method we developed is to crosslink conductive polymer chains with functional molecules with multiple functional groups, enabling a network, interconnected structure promoting high electronic conductivity and electrochemical activity."
"Secondly, we demonstrated that this newly developed conductive polymer gel can be used as binder system and significantly improve conventional lithium-ion battery performance owing to their advantageous structural features," he continues. "The ease of processability and excellent chemical and physical properties of these nanostructured conductive gels enable a new class of binder materials for fabricating next-generation high-energy lithium-ion batteries."
Although the researchers' binder gel is mechanically strong, it lacks flexibility and stretchability. The plan is to further modify the mechanical properties by tailoring the molecular backbones of conductive polymers through the addition of side chains or other building block polymers.
The scientists further intend to demonstrate the versatility of their gel binders for other important electrode materials, such as some commercial electrode materials, as well as some next-generation ultrahigh-capacity materials, such as silicon, and sulfur.