Researchers at the Japan Advanced Institute of Science and Technology have improved the performance of silicon anodes in LIBs using a self-healing composite polymer binder for the silicon particles. The new binder improves stability and maintains a thin SEI layer. The results of the study are published in ACS Applied Energy Materials.

The binder is a polymer composite consisting of an n-type conducting polymer poly(bisiminoacenaphthenequinone) (P-BIAN) and a carboxylate-containing polymer poly(acrylic acid) (PAA), each linked to the other via hydrogen bonds.

The composite polymer structure holds the silicon particles together like a net and prevents them from rupturing. The hydrogen bonds between the two polymers permit the structure to self-repair, as the polymers can reattach themselves if they break away at any point. Moreover, the n-doping ability of P-BIAN improves the conductivity of the anode and maintains a thin SEI by limiting the electrolytic decomposition of the electrolyte on the anode.

Gupta et al.

To test the binder, the researchers constructed an anodic half-cell consisting of silicon nanoparticles with graphite (Si/C), the binder (P-BIAN/PAA) and an acetylene black (AB) conductive additive. The Si/C/(P-BIAN/PAA)/AB anode was put through a repeated charge-discharge cycle.

The P-BIAN/PAA binder was observed to stabilize the silicon anode and maintain a specific discharge capacity of 2100 mAh g^-1 for more than 600 cycles. In contrast, the capacity of the bare silicon-carbon anode dropped to 600 mAh g^-1 within 90 cycles.

After the test, the researchers disassembled the anode and examined the material for any cracks that might have resulted from silicon rupture. A spectroscopic and microscopic examination after 400 cycles revealed a smooth structure with only a few microcracks indicating that the addition of the binder was able to improve the structural integrity of the electrode and maintain a uniform SEI.

The results demonstrate that the addition of the binder can improve the characteristics of the silicon anode and make it practically feasible.

As the demand for lithium-ion batteries increases, silicon, which is the eighth-most abundant material on earth, will be a promising environment-friendly alternative to graphite. The improvements to its structural stability and its conductivity with the use of binders will make it more suitable for use in future lithium-ion batteries.

This composite binder design principle will enable wider diffusion of EVs, creation of other battery driven vehicles, and drones, which requires a higher energy density for advanced performance.

—Prof. Noriyoshi Matsumi, corresponding author

Resources

• Agman Gupta, Rajashekar Badam, and Noriyoshi Matsumi (2022) “Heavy-Duty Performance from Silicon Anodes Using Poly(BIAN)/Poly(acrylic acid)-Based Self-Healing Composite Binder in Lithium-Ion Secondary Batteries” ACS Applied Energy Materials doi: 10.1021/acsaem.2c00278