Advanced Binders for Advancing Li-ion Batteries

Andrew Corselli

Li-ion batteries are widely used in various applications but need improved binders to enhance their performance to meet evolving demands. This is because silicon oxide (SiO), a promising anode material due to its high capacity and low cost, faces several challenges. These include poor conductivity, which leads to slower charging rates, and significant expansion during charging. Effective binders are thus essential to address these issues and ensure enhanced performance and prolonged durability for Li-ion battery systems.

In a recent study published in the journal ACS Applied Energy Materials, Professor Noriyoshi Matsumi from the Japan Advanced Institute of Science and Technology (JAIST) along with his team have utilized poly(vinylphosphonic acid) (PVPA) as a binder for micro-SiO electrodes, achieving superior performance compared to conventional cells.

"The PVPA binder should prove to be very useful in extending the life of high-performing Li-ion secondary batteries,” Matsumi said. “Particularly in the application of electric vehicles, there has been intense interest in enabling long life for Li-ion secondary batteries. The use of PVPA will offer improved alternatives to commercially available binders, such as poly(acrylic acid) (PAA) and poly(vinylidene fluoride) (PVDF), etc."

The study involved fabricating electrodes containing PVPA, PAA, and PVDF as binders, and their performance was assessed through electrochemical experiments and density functional theory. PVPA demonstrated notably stronger adhesion (3.44 N/m) to a copper support compared to conventional PAA (2.03 N/m), leading to significantly enhanced durability in Li-ion batteries.

The PVPA-based cell also delivered almost twice the discharging capacity compared to the PAA-based cell after 200 cycles, with the PVPA-based half-cell achieving 1,300 mAhg^-1 for the SiO after the same cycle count. Even after 200 cycles of charge-discharge, exfoliation from the current collector was not observed with scanning electron microscopy, unlike with PVDF or PAA binders. Furthermore, the stronger adhesion of PVPA helps stabilize the SiO-based anode, preventing its exfoliation even with significant volume expansion.

Additionally, Maruzen Petrochemical Company Ltd., whose researchers were part of the study, has established an industrial production process for PVPA. Continuous collaboration between JAIST and Maruzen Petrochemical Company Ltd., along with the inclusion of additional battery production expertise from the company, may further accelerate the process toward real-life applications. Patents for this technology have been submitted both domestically (Japan) and internationally as a joint application by JAIST and Maruzen Petrochemical Company Ltd.

"An industrially feasible, high-performing binder like this will aid in the development of technology for highly durable and high-energy-density batteries,” said Matsumi. “This will result in the wider adoption of EVs worldwide without concerns about performance degradation over a longer period. These materials can also be applicable to a variety of electric vehicles such as trains, ships, aircraft, etc., in the future."

Below is an exclusive Tech Briefs interview — edited for length and clarity — with Matsumi.

Tech Briefs: What was the biggest technical challenge you faced while developing this binder?

Matsumi: In this work, we tried to develop a suitable application for an already-existing polymer developed by Maruzen Petrochemical Co. Ltd. Poly(vinylphosphonic acid) has P-O functional groups that should show strong adhesion to current collectors in batteries.

We started with applying it to the most common battery setup of graphite anode-based battery cells. To our surprise, it was found to work even for SiO active materials, which have much higher theoretical capacity.

In the fundamental stage, our results are quite satisfactory, but we might face challenges in the following stage of industrialization in maintaining its high performance when scaling-up battery cells.

Tech Briefs: Can you explain in simple terms how it works?

Matsumi: Through strong adhesion of poly(vinylphosphonic acid), this polymer can hold active materials stably and can attach to a current collector tightly without significant exfoliation even during volumetric changes of SiO particles. Further, this polymer has a low-lying LUMO level. Usually, at the anodic side, due to its reductive environment, excessive decomposition of electrolytes takes place, leading to the formation of a thick passivation layer, which increases internal resistance. This polymer can be partially reduced at the anodic side prior to the reductive decomposition of the electrolyte, which prevents thick passivation layer formation.

Tech Briefs: You’re quoted in the article as saying, "An industrially feasible, high-performing binder like this will aid in the development of technology for highly durable and high-energy-density batteries. This will result in the wider adoption of EVs worldwide without concerns about performance degradation over a longer period. These materials can also be applicable to a variety of electric vehicles such as trains, ships, aircraft, etc., in the future." My question is: Do you have any plans for further research/work/etc.?

Matsumi: Through industrial collaboration, we hope larger-scale battery studies will bring us to a scenario of early industrial applications. From initial industrialization, we hope to move forward step by step to enable even larger scale applications in the future.

Tech Briefs: Do you have any advice for engineers/researchers aiming to bring their ideas to fruition?

Matsumi: As Maruzen petrochemical had already developed a synthetic method for poly(vinylphosphonic acid) on a large scale, the feasibility of such materials can accelerate the development of a scenario once the advantage of our material is more widely recognized. We hope many researchers will check the high-performing nature of poly(vinylphosphonic acid)-based cells.

Tech Briefs: Anything else you’d like to add?

Matsumi: Though PAA (polyacrylic acid) has been widely employed as a very common binder material, poly(vinylphosphonic acid) will be a more high-performing, attractive alternative, which will be able to replace PAA in various systems.

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