Exploration on the Application of Dry Capacitor Binders in Lithium-Ion Battery Dry Electrodes

In the continuous innovation of lithium-ion battery technology, the optimization of electrode manufacturing processes has always been a focus. Although the traditional wet electrode process is mature, it faces many drawbacks, such as involving multiple procedures like slurry preparation, coating, drying, and organic solvent recovery, which result in a lengthy process, high energy consumption, and high costs. Against this background, the dry electrode process has emerged. With its streamlined "powder-to-film" route, it demonstrates significant advantages such as low energy consumption, low cost, and environmental friendliness, becoming a research hotspot in the lithium-ion battery field. In the dry electrode process system, dry capacitor binders play an extremely critical role; their performance and application effects have a decisive impact on the overall performance of electrodes and even batteries.

Common Dry Capacitor Binders and Their Characteristics

Polytetrafluoroethylene (PTFE)

PTFE is one of the earliest and most widely used binders in the field of dry electrodes. Its prominent characteristic is that it can undergo linear deformation under high-speed shear force, thereby forming a unique three-dimensional network structure. This structure, like a fine "molecular net", can efficiently wrap electrode active materials and conductive agent microparticles, laying a foundation for constructing a stable electrode structure. For example, in the preparation of some supercapacitor electrodes, the network structure formed by PTFE fibrillation effectively enhances the binding force between components inside the electrode, ensuring structural stability during charge-discharge cycles.

However, PTFE is not perfect. Its adhesion to the current collector is poor, which increases contact resistance. During long-term charge-discharge cycles of the battery, it can easily cause capacity fading, and in severe cases, even lead to the detachment of active materials from the current collector surface, significantly affecting battery service life. Studies have shown that electrodes using PTFE alone as a binder have low adhesion values, and obvious electrode sheet detachment occurs after 100 cycles. In addition, PTFE may undergo side reactions in the battery system, consuming active lithium and reducing the first charge-discharge efficiency (initial efficiency) of the battery. Relevant experimental data indicate that compared with binder systems commonly used in wet electrodes (such as SBR + CMC), the initial efficiency of dry electrodes with PTFE as the binder is approximately 6% lower; as PTFE content increases, the initial efficiency further decreases, which is a non-negligible loss for the actual available capacity of the battery.

Polyvinylidene Fluoride (PVDF)

As an excellent polymer material, PVDF is widely used in the battery field and also occupies an important position in dry electrodes. PVDF has excellent electrochemical stability and an extremely wide electrochemical stability window, allowing it to remain stable in the complex electrochemical environment of lithium-ion batteries without participating in harmful electrochemical reactions, thus ensuring the long-term stability of battery performance.

However, PVDF has shortcomings in dry electrode applications: it cannot form a three-dimensional network structure that effectively wraps active materials like PTFE. Nevertheless, researchers cleverly use conductive agents to make up for this defect. For example, introducing conductive agents such as carbon nanotubes (CNT) and multi-walled carbon nanotubes (MWNT) to construct a three-dimensional conductive network of the electrode. Relevant experiments through folding tests and adhesion tests show that when MWNT is used as the conductive agent, the adhesion effect of electrode sheets, whether cold-pressed or hot-pressed, is significantly improved. It is worth noting that in some studies, due to the relatively high binder content (e.g., reaching 15%), a large amount of inactive binder occupies electrode space, diluting the proportion of active materials and reducing the energy density of the battery to a certain extent.

Multi-Dimensional Impact of Binders on Dry Electrode Performance

Impact on Electrode Structural Stability

The primary role of dry capacitor binders in electrodes is to provide structural stability. Taking fibrillated PTFE as an example, its three-dimensional network structure is like the "reinforced skeleton" of a building, tightly binding active materials and conductive agents together, resisting volume change stress caused by ion intercalation/deintercalation during charge-discharge, and preventing electrode structure collapse. Studies have found that in dry electrodes of lithium iron phosphate cathodes, when PTFE fibrillation is well-developed and uniformly distributed, the electrode can still maintain a complete sheet structure after multiple cycles; in contrast, electrodes with insufficient fibrillation or uneven distribution show obvious particle detachment and structural looseness.

Although PVDF cannot form a similar three-dimensional network, it can form physical adhesion between particles during mixing and pressing into films with active materials and conductive agents, relying on its strong intermolecular forces, maintaining the integrity of the overall electrode structure. Moreover, by optimizing formulations and processes and adjusting the synergistic effect between PVDF and other additives, its ability to stabilize the electrode structure can be further enhanced.

Impact on Electrode Electrochemical Performance

In terms of battery charge-discharge efficiency, binder performance is crucial. As mentioned earlier, side reactions of PTFE can reduce battery initial efficiency, consume active lithium resources, and prevent the electricity stored in the first charge from being fully released in subsequent discharges, resulting in energy waste. In contrast, due to its good electrochemical stability, PVDF does not negatively affect battery initial efficiency under normal use conditions, ensuring the efficiency of initial energy storage and release of the battery.

Binders also have a profound impact on battery cycle life. If the adhesion between the binder and active materials or current collectors is insufficient, the binding force between components inside the electrode gradually weakens with the increase in charge-discharge cycles, and active materials are prone to detachment, leading to a reduction in active sites participating in electrochemical reactions and gradual capacity fading of the battery. Conversely, if the binder has excellent performance and matches other materials well—such as PTFE with modified adhesion or optimized PVDF systems—it can effectively delay this process and extend battery cycle life. For example, some studies have physically modified PTFE to enhance its adhesion to the current collector, enabling the battery to complete 100 cycles without electrode sheet detachment, significantly improving cycle performance.

Impact on Electrode Processing Performance

In the dry electrode preparation process, the impact of binders on processing performance is reflected in multiple links. In the dry powder mixing stage, the particle characteristics and fluidity of the binder affect mixing uniformity. For example, if PTFE dry powder agglomerates, it is difficult to uniformly disperse among active materials and conductive agents during mixing, resulting in inconsistent performance across different parts of the final electrode. In contrast, binders with uniform particle size distribution and good fluidity after special treatment—such as some surface-modified PVDF powders—are easier to uniformly mix with other materials in mixing equipment.

In the calendering and film-forming stage, the fibrillation characteristics (e.g., PTFE) or film-forming properties (e.g., PVDF) of the binder directly determine whether high-quality electrode films can be formed smoothly. Insufficient PTFE fibrillation fails to form a continuous and stable network structure, resulting in insufficient film strength and toughness, which is prone to cracking in subsequent processing. For PVDF, if process parameters such as film-forming temperature and pressure are not properly controlled, the compactness and uniformity of the film will be affected, thereby influencing the electrochemical performance of the electrode.

Strategies and Methods to Improve Binder Performance

Physical Modification

Physical modification is a common method to address the insufficient adhesion of PTFE. For example, mechanical grinding can change the surface morphology of PTFE particles, increase surface roughness, thereby expanding the contact area and mechanical interlocking force between PTFE and the current collector/active materials, and improving adhesion. Surface coating technology can also be used to apply a layer of highly adhesive substances—such as certain functional polymer coatings—on the PTFE surface, significantly improving its bonding performance with other materials without altering the main chemical properties of PTFE.

Chemical Modification

Chemical modification optimizes binders from the perspective of molecular structure. Taking PTFE as an example, graft copolymerization can introduce groups with strong adhesion or other functionalities (e.g., polar groups) into PTFE molecular chains. These introduced groups can chemically react or form strong interactions with metal atoms on the current collector surface or functional groups on the active material surface, effectively enhancing PTFE adhesion. Meanwhile, chemical modification can improve the electrochemical stability of PTFE and inhibit side reactions. For example, specific chemical modification of PTFE can change the distribution of molecular electron clouds, making it less likely to participate in side reactions in the battery's electrochemical environment, thereby improving battery initial efficiency.

For PVDF, chemical modification can adjust its molecular chain structure and performance by modifying polymerization processes or introducing comonomers. For instance, introducing functional comonomers can enhance the interaction between PVDF and active materials while maintaining its original electrochemical stability, optimize its dispersibility and film-forming performance in electrodes, and further improve overall electrode performance.

Construction of Composite Binder Systems

Building composite binder systems is also an effective strategy to enhance the comprehensive performance of binders. This involves mixing different types of binders in a certain ratio, leveraging their complementary advantages to overcome the defects of single binders. For example, combining PTFE (with good fibrillation ability) and PVDF (with excellent electrochemical stability): the three-dimensional network structure formed by PTFE provides good structural support and wrapping, while PVDF ensures the electrochemical stability of the system. Their synergistic effect can both enhance electrode structural stability and ensure stable battery performance in complex electrochemical environments.

In addition, other functional additives can be introduced into composite binder systems—such as plasticizers to improve electrode sheet flexibility and conductive polymers to enhance conductivity. By precisely regulating the proportion and synergistic effect of each component in the composite system, high-performance binder systems tailored to different application scenarios can be developed.

Application Cases and Practical Effect Verification

Supercapacitor Field

In the preparation of dry electrodes for supercapacitors, Lirong New Energy has achieved remarkable results through its unique Activated Dry Electrode™ technology by optimizing binder formulations and processes. This technology further reduces binder dosage compared to general dry electrode technologies and ensures more uniform dispersion of binders on the active material surface. Taking its special PTFE-based binder system as an example, after special fibrillation treatment and surface modification, it forms a stable three-dimensional network structure while significantly enhancing adhesion to active materials and the current collector. Practical test data show that supercapacitor electrodes prepared with this binder system have significantly reduced internal resistance, a cycle life of up to 1 million times, and both high power density and high energy density—fully demonstrating the great potential of optimized binders in improving supercapacitor performance.

Lithium-Ion Battery Field

Tsingyane focuses on the R&D and industrialization of dry electrode technology and has made remarkable achievements in the application of dry electrode binders for lithium-ion batteries. Its developed binder system for lithium-ion battery dry electrodes effectively solves many problems of traditional binders in lithium-ion batteries through chemical modification and composite formulation design. For example, to address the low initial efficiency and poor cycle performance of traditional PTFE-based binders in anode applications, Tsingyane successfully inhibited active material expansion through PTFE coating, copolymer modification, and compounding with secondary binders, increasing anode initial efficiency by 6% to 92%. In actual production, lithium-ion battery dry electrodes prepared with this binder system exhibit good flexibility and safety, effectively improving comprehensive battery performance and providing a new technical path for the development of the lithium-ion battery industry.

Dry capacitor binders in lithium-ion battery dry electrodes are core factors affecting electrode and battery performance. From the characteristics of common binders, their multi-dimensional impact on electrode performance, to strategies for improving performance and practical application cases, each link is closely connected and full of exploration potential. With the deepening of research on binders by scientists and the continuous progress of materials science and process technology, it is expected that more excellent dry capacitor binder systems—adaptable to different application scenarios—will be developed in the future, injecting strong impetus into the leapfrog development of lithium-ion battery technology and promoting its wide application and innovation in key fields such as new energy vehicles and energy storage.