Electrode Binders

Electrode Binders

Polymer adhesive binders are important components of modern lithium-ion electrodes. Small amounts of polymer binders along with electrode particles and conductive additive particles form a unique polymer composite electrode. The polymer binder ensures mechanical integrity and a stable microstructure of the electrode, and maintains ion and electron pathways within the composite.

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Electrode Binder Fundamentals

Electrode Binder Fundamentals

Proper electrode design is critical to meeting both the energy and power performance requirements for any battery application. Polymer binders used in Li-ion batteries, although not electrochemically active, are essential components in the electrodes, along with acetylene black (AB) conductive additives and the active materials (AM) that store lithium ions.

The bulk polymer differentiates into three physical states when in contact with a particle surface. Bound polymer and immobilized polymer layers on a particle surface are defined as the fixed polymer layer.
The bulk polymer differentiates into three physical states when in contact with a particle surface. Bound polymer and immobilized polymer layers on a particle surface are defined as the fixed polymer layer.
Schematic of the formation of fixed polymer layers ba and bc on AM and AB, respectively, and the polymer binder redistribution when combining AM particles with the AB/PVDF composite. (A) AM particle. (B) AB/PVDF matrix. (C) Mixed AM/AB/PVDF. (D) There is enough polymer binder to form fixed layers on both AM and AB.  (E) There is a deficiency of polymer binder to form the fixed layer on AM and AB.
Schematic of the formation of fixed polymer layers ba and bc on AM and AB, respectively, and the polymer binder redistribution when combining AM particles with the AB/PVDF composite. (A) AM particle. (B) AB/PVDF matrix. (C) Mixed AM/AB/PVDF. (D) There is enough polymer binder to form fixed layers on both AM and AB.  (E) There is a deficiency of polymer binder to form the fixed layer on AM and AB.  
The schematics and SEM images of binder distributions between AB and AM at different electrode compositions. AB:PVDF = 0.8:1 at high AM loading (A) and low AM loading (B); AB:PVDF = 0.2:1 at high AM loading (C) and low AM loading (D). This distribution of binders between AB and AM has major implications of electrode performance. Scale bar: 20 μm.
The schematics and SEM images of binder distributions between AB and AM at different electrode compositions. AB:PVDF = 0.8:1 at high AM loading (A) and low AM loading (B); AB:PVDF = 0.2:1 at high AM loading (C) and low AM loading (D). This distribution of binders between AB and AM has major implications of electrode performance. Scale bar: 20 μm.

 

 

 

Multifunctional Conductive Polymer Binders

Conductive Polymer Binders

A functional conductive polymer binder implements the conceptual idea of combining adhesion and conductive additive into one elastic polymer material, solving the volume change problem of high-volume change alloy anode electrodes. A functional conductive polymer binder maintains both electric conductivity and mechanical integrity of the electrode during battery operation. This conductive polymer matrix is also compatible with the lithium-ion slurry manufacturing process.

Figure 1. Conductive polymer with dual functionality, as a conductor and binder, could keep both electric and mechanical integrity of the electrode during the battery cycles.

Conductive polymer with dual functionality, as a conductor and binder

 

Advantages:

  • Use Si particles
     
  • Fully compatible with conventional lithium-ion technologies

R&D100 2013 award

Zhao, H.;  Zhou, X.;  Park, S. J.;  Shi, F. F.;  Fu, Y. B.;  Ling, M.;  Yuca, N.;  Battaglia, V.; Liu, G., A polymerized vinylene carbonate anode binder enhances performance of lithium-ion batteries. Journal of Power Sources 2014, 263, 288-295.

Schematics of chemistry behind binding and electric conductionSchematics of chemistry behind versatile synthesis

 

Multifunctional Binders

Multifunctional Binders

We investigated the use of  polymerized vinylene carbonate (polyVC) as a binder for graphite anodes in lithium-ion cells. PolyVC has been shown to be a major component of the solid-electrolyte-interphase (SEI) in VC-containing electrolytes. It functions not only as a traditional binder, but also plays an important role in surface stabilization of graphite in propylene carbonate (PC)-based electrolytes. In an electrolyte with PC content as high as 30 wt%, the polyVC binder enhanced battery performance, with a reversible capacity of ~170 mAh/g at a discharge rate of 1C ; whereas a comparable graphite cell fabricated with a PVDF binder failed to cycle.  

The plyvinlyene carbonate (polyVC) polymer binder made with vinylene carbonate.
The plyvinlyene carbonate (polyVC) polymer binder made with vinylene carbonate.
In an electrolyte with PC content as high as 30 wt%, the polyVC binder enhanced battery performance, with a reversible capacity of 170 mAh/g at a delithiation rate of 1 C, whereas a comparable graphite cell fabricated with a polyvinylidene fluoride (PVDF) binder failed to cycle.
In an electrolyte with PC content as high as 30 wt%, the polyVC binder enhanced battery performance, with a reversible capacity of 170 mAh/g at a delithiation rate of 1 C, whereas a comparable graphite cell fabricated with a polyvinylidene fluoride (PVDF) binder failed to cycle.

Zhao, H.;  Zhou, X.;  Park, S. J.;  Shi, F. F.;  Fu, Y. B.;  Ling, M.;  Yuca, N.;  Battaglia, V.; Liu, G., A polymerized vinylene carbonate anode binder enhances performance of lithium-ion batteries. Journal of Power Sources 2014, 263, 288-295.

 

Aqueous Functional Binders

Aqueous Functional Binders

Water-soluble poly(amic acid)-based binder can withstand high temperature for industrial pre-lithiation process and effectively hold active materials together during repeated charge and discharge cycles. This lithium substituted poly(amic acid) binder (denoted as Li-Pa) can serve as a drop-in replacement for environmentally friendly electrode fabrication in large scale by providing aqueous solubility, exceptional thermal stability and mechanical flexibility.

Schematic showing high temperature pre-lithiation

 

Zhu, T. Y.;  Tran, T. N.;  Fang, C.;  Liu, D. Y.;  Herle, S. P.;  Guan, J.;  Gopal, G.;  Joshi, A.;  Cushing, J.;  Minor, A. M.; Liu, G., Lithium substituted poly(amic acid) as a water-soluble anode binder for high-temperature pre-lithiation. Journal of Power Sources 2022, 521, 7.

Chen, H.;  Ling, M.;  Hencz, L.;  Ling, H. Y.;  Li, G. R.;  Lin, Z.;  Liu, G.; Zhang, S. Q., Exploring Chemical, Mechanical, and Electrical Functionalities of Binders for Advanced Energy-Storage Devices. Chem. Rev. 2018, 118 (18), 8936-8982.

 

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