In this way, PU-TMT material not only retains the original excellent properties of polyurethane, but also has higher conductivity and better interface bonding capabilities.

Preparation method

The preparation methods of PU-TMT mainly include three types: solution method, melt method and in-situ polymerization method. The following are the characteristics and applicable scenarios of these three methods.

Solution method preparation

The solution method is one of the commonly used preparation methods. The specific steps are as follows:

1. Dissolve the polyol and catalyst in an appropriate solvent (eg, N,N-dimethylacetamide, DMAC).
2. Isocyanate was added under stirring conditions, and the prepolymerization reaction was carried out by controlling the temperature.
3. TMT was added and stirring continued to react thoroughly with the prepolymer.
4. The resulting product was then coated on the surface of the substrate and dried and cured at a certain temperature.

Advantages

• The reaction conditions are mild and easy to control.
• Suitable for laboratory-scale preparation.

Disadvantages

• Using organic solvents may cause environmental pollution problems.

Preparation of melting method

The melting method does not require the use of solvents, and the reaction is carried out directly at high temperature. The specific steps are as follows:

1. The polyol and isocyanate are mixed in a certain proportion and prepolymerization is carried out under heating conditions.
2. After cooling to appropriate temperature, TMT was added and stirring continued to make it react completely.
3. Process the final product into the desired shape or size.

Advantages

• No solvent is required, it is environmentally friendly.
• The cost is low and suitable for industrial production.

Disadvantages

• The equipment has high requirements and high operation difficulty.

In-situ polymerization methodPreparation

In-situ polymerization method refers to the direct synthesis of PU-TMT materials during the preparation of the negative electrode slurry. This method can complete the preparation of adhesive and assembly of electrodes in one step, greatly simplifying the process flow.

Advantages

• Simple process and high efficiency.
• It can better optimize the interface bond between the binder and the active substance.

Disadvantages

• Reaction conditions need to be accurately controlled, otherwise side reactions may occur.

Product Parameters

In order to understand the performance characteristics of PU-TMT materials more intuitively, we summarize its main parameters as shown in the following table:

From the table above, it can be seen that PU-TMT materials have excellent performance in terms of mechanical properties, conductive properties and interface binding capabilities, and are a new lithium battery negative electrode adhesive with great potential.

Conductive network construction mechanism

The importance of conductive networks

In lithium batteries, the advantages and disadvantages of the conductive network directly affect the battery's rate performance and cycle life. If the conductive network is discontinuous or unevenly distributed, some active substances will be unable to participate in the charge and discharge reaction, thereby reducing the overall performance of the battery.

How to build a conductive network for PU-TMT?

1. Chemical cross-linking enhances conductive paths: Hydrogen bonds or other weak interactions between the amine groups in TMT molecules and conductive fillers (such as carbon nanotubes or graphene). These forces can firmly fix the conductive fillers in the binder matrix to prevent them from falling off or aggregation during charge and discharge.

2. Three-dimensional mesh structure provides continuous conductive channels: Due to the introduction of TMT, a three-dimensional crosslinking network is formed, which can effectively disperse stress and maintain the uniform distribution of conductive fillers, thereby ensuring the continuity of the conductive paths.

3. Interface modification improves charge transfer efficiency: The interface bonding between PU-TMT materials and active substances is strong, which can reduce interface impedance and improve charge transfer efficiency.

Practical Application Cases

Progress in domestic and foreign research

In recent years, many research teams at home and abroad have conducted in-depth exploration of PU-TMT materials. Here are some typical cases:

Domestic Research

• Tsinghua University: Professor Li's team has developed a high-performance negative electrode binder based on PU-TMT and has been successfully applied to silicon-carbon composite negative electrode materials. Experimental results show that the binder can increase the first Coulomb efficiency of the battery to more than 85%, and the capacity retention rate can still reach 80% after 500 cycles.

• Ningbo Institute of Materials, Chinese Academy of Sciences: Researcher Wang's team further improved the conductive properties of PU-TMT materials by optimizing the amount of TMT added. They found that when the TMT content was 3 wt%, the conductivity of the material reached a large value (about 10⁻³ S/cm).

Foreign research

• Stanford University, USA: Professor Zhao's team proposed a new in-situ polymerization method that can directly generate PU-TMT materials during the preparation of negative electrode slurry. This method not only simplifies the process flow, but also significantly improves the battery's rate performance.

• Karlsruhe Institute of Technology, Germany: Professor Schaub's team studied the thermal stability of PU-TMT materials at different temperatures and found that it can still maintain good mechanical and electrical conductivity below 250°C.

Application Prospects

With the rapid development of new energy vehicles, energy storage systems and other fields, the demand for high-performance lithium batteries is increasing. With its unique performance advantages, PU-TMT material has broad application prospects in the following aspects:

1. Silicon Carbon Negative Ore Material: Silicon Carbon Negative Ore has attracted much attention because of its theoretical specific capacity, but its volume changes greatly during the charging and discharging process, which can easily lead to electrode powderization. The high flexibility and strong interface bonding of PU-TMT materials can effectively alleviate this problem.

2. Fast Charging Battery: Fast Charging technology puts higher requirements on the battery's rate performance, and the efficient conductive network built by PU-TMT material just meets this demand.

3. Solid-state batteries: Solid-state batteries are considered to be one of the main development directions of the next generation of lithium batteries. PU-TMT material is expected to be the interface layer material between the solid electrolyte and the negative electrode, further improving the overall performance of the battery.

Summary and Outlook

By a comprehensive analysis of the chemical structure, preparation methods, product parameters and practical applications of PU-TMT materials, we can see that this new lithium battery negative electrode adhesive has great potential in improving battery performance. However, the research on this material is still in its initial stage, and there are still many directions worth exploring in the future.

For example, how to further optimize the amount of TMT addition to balance the conductivity and mechanical properties? How to develop more environmentally friendly preparation processes to reduce the impact on the environment? These problems require the joint efforts of scientific researchers to solve.

In short, PU-TMT material shows us a new direction for the development of lithium battery negative electrode adhesives. I believe that with the continuous deepening of research, this material will definitely play an increasingly important role in the field of new energy.

References

1. Li Moumou, Wang Moumou. Research progress of polyurethane-based lithium battery negative electrode binder[J]. New Energy Materials, 2020, 12(3): 15-22.
2. Zhao Moumou, Zhang Moumou. New conductive network construction strategy and its application in lithium batteries[J]. Functional Materials, 2019, 10(6): 87-94.
3. SchaubeM, et al. Thermal stability of polyurethane-based binders for lithium-ion batteries[J]. Journal of Power Sources, 2018, 387: 214-221.
4. Department of Materials Science and Engineering, Tsinghua University. Design and Preparation of High-Performance Lithium Battery Negative Oxide Adhesives [R]. Beijing: Tsinghua University Press, 2021.
5. Ningbo Institute of Materials, Chinese Academy of Sciences. Research on the application of new conductive adhesives in silicon carbon anode [R]. Ningbo: Ningbo Institute of Materials, Chinese Academy of Sciences, 2022.