Applications of Conductive Agents in Lithium-Ion Batteries

Overview

Modern life heavily relies on various electronic devices, most of which are powered by lithium-ion batteries. Compared to other types of batteries, lithium-ion batteries are low-cost, environmentally friendly, energy-efficient, memory-free, and lightweight, making them vital components in communication devices, entertainment gadgets, electric vehicles, and medical equipment.

Importance of Conductive Agents in Lithium-Ion Batteries

In lithium-ion batteries, the anode typically uses metal oxides like layered lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt oxide, and lithium iron phosphate as active materials. The cathode uses graphite, silicon-based materials, and other substances. However, the poor conductivity of these cathode materials increases the internal resistance of the electrode and lowers the utilization rate of the active materials, severely affecting battery performance. Materials like hard carbon and graphite have good conductivity, but during repeated charge and discharge cycles, conductive agents in lithium batteries may expand and contract, leading to poor contact between active materials. To enhance the utilization of active materials and improve battery performance, materials with good conductivity, structural stability, and chemical stability are added to the active materials. These materials are known as “conductive agents.”

Conductive agents in lithium-ion batteries play a crucial role in enhancing electronic conductivity. Although they make up a small portion of the battery, they significantly impact its performance, including cycle performance, capacity retention, and rate performance. Conductive agents help collect micro-currents between active materials and between active materials and current collectors, reducing contact resistance and increasing the mobility of electrons and lithium ions within the electrode materials, thereby improving the efficiency of charge and discharge processes.

Types of Conductive Agents

1. Conductive Carbon Black
   • Conductive carbon black consists of small carbon particles and products of manganese pyrolysis, forming spherical nanoscale particles in a gaseous state. It forms a multi-cluster and fibrous structure, with particle sizes about one-tenth that of conductive graphite. Depending on its conductivity, it can be classified into conductive carbon black, super conductive carbon black, and ultra-conductive carbon black.
2. Conductive Graphite
   • Conductive graphite is primarily artificial graphite, with smaller particle sizes (typically 3-6 micrometers) and more developed porosity and surface area than graphite used as cathode material. Conductive graphite enhances compressibility and dispersibility, increases volumetric energy density, and improves the processing characteristics of electrodes. It is often used in combination with carbon black.
3. Fibrous Conductive Agents
   • Fibrous conductive agents include carbon fibers and carbon nanotubes, which can be single-walled or multi-walled. Vapor-grown carbon fibers (VGCF) have a linear structure that easily forms a good conductive network on the electrode, reducing electrode polarization and internal resistance, thus improving battery performance. In batteries, the contact between active materials and conductive agents is linear compared to the point contact of carbon black and graphite, enhancing electrode conductivity and allowing for a reduced amount of conductive agent, thereby increasing battery capacity.

The morphology and types of conductive agents vary, and their microstructure is a critical factor influencing conductivity. From carbon black to carbon fibers and now to graphene, conductive agents for lithium-ion batteries have continuously evolved. However, practical application requires careful consideration of material types, uniformity, and the performance requirements of the battery to select the appropriate conductive agent and its quantity.

Conclusion

Conductive agents are essential for the efficient performance of lithium-ion batteries, playing a vital role in enhancing conductivity, reducing internal resistance, and improving overall battery efficiency. Their application is crucial in various fields where lithium-ion batteries are used, ensuring that electronic devices operate effectively and efficiently.