Current collectors and auxiliary materials for battery research in the laboratory

In the field of laboratory battery research, although current collectors and auxiliary materials may seem insignificant, they play a crucial role in battery performance. They are like the "unsung heroes" of the battery, silently supporting the realization of various functions of the battery.

The current collector in a battery plays a crucial role in collecting and conducting electric current, and is a core component of the battery electrode system. Its performance directly affects key indicators such as the energy density, cycle life, and safety of the battery.

The selection of the current collector material requires comprehensive consideration of various factors. Firstly, it needs to match the positive and negative electrode potentials to ensure that no chemical reactions occur during the battery charging and discharging process, which would affect the battery performance. At the same time, good conductivity is a necessary condition, which helps to reduce the internal resistance of the battery and improve the charging and discharging efficiency. Additionally, the material should have good ductility to enable it to adapt to various processing techniques during battery manufacturing, and it should have the characteristics of low cost, easy processing, and stability in the air. Based on these requirements, in lithium-ion batteries, aluminum is widely used as the positive electrode current collector due to its relatively low density and good conductivity; while copper, with its high conductivity and good chemical stability, becomes the preferred choice for the negative electrode current collector. Moreover, there are specific requirements for the purity, thickness, and surface roughness of the current collector. For example, high-purity current collectors can reduce the impact of impurities on battery performance, appropriate thickness can ensure the mechanical strength of the current collector and reduce the overall weight of the battery, and the appropriate surface roughness helps to enhance the adhesion to the active material.

The manufacturing process of the positive electrode aluminum current collector is rather complex. It requires multiple rolling processes to achieve the desired thickness and surface quality of the Aluminum Foil. Subsequently, heat treatment is carried out to improve the internal structure of the material and enhance its performance. Finally, surface treatment such as anodization is also necessary to enhance the corrosion resistance of the aluminum foil and its bonding strength with the active material. The negative electrode copper current collector is mainly divided into drawn copper foil and electrolytic copper foil. The electrolytic copper foil is made by the electrolytic deposition method. First, the copper raw material is dissolved in the electrolyte, and then a copper foil is formed by deposition on the cathode. Subsequently, a series of surface treatment processes, such as roughening and anti-oxidation treatment, are also required to improve the performance of the copper foil.

With the continuous advancement of technology, the design of the next-generation lithium battery current collectors is innovating in multiple directions. To enhance energy density, researchers are dedicated to reducing the thickness of copper foil and exploring new materials, such as copper nanowires, foamed copper, and polymer-based composite materials. These new materials have unique structures and properties, and are expected to reduce the weight of the current collector while improving the overall performance of the battery. Regarding the reversibility issue of the metal lithium anode, by modifying the surface of the current collector, such as using liquid alloy coatings or lithium-adsorbing materials, to improve the deposition behavior of metal lithium on the anode and inhibit the growth of lithium dendrites, the safety and cycle life of the battery can be enhanced. In the case of aqueous batteries, solving the problem of the corrosion resistance of the current collector has become a research focus. Developing new corrosion-resistant materials or protective coatings to adapt to the special working environment of aqueous batteries.

Apart from the current collector, the auxiliary materials in battery research are also indispensable. They play their own unique roles within the battery.

Electrode conductive additives play a crucial role in batteries. The positive electrode active materials usually have poor conductivity, and the negative electrode graphite also experiences unstable conductivity during charging and discharging. At this point, conductive additives come into play. Their main function is to collect microcurrents between the active substances and between them and the current collector, reducing contact resistance, thereby improving the charging and discharging efficiency of the battery. Different types of conductive additives have different mechanisms of action and performance characteristics. Carbon black-based conductive additives tend to provide lithium ion conductivity, graphite-based ones focus on electron conductivity, and fiber-based and carbon tube-based additives have both. For example, the new conductive agent carbon nanotubes, although with a low addition amount, due to their unique one-dimensional structure, can form an efficient conductive network, significantly improving battery performance, but its overall cost is relatively higher than that of traditional carbon black. In addition, an ideal conductive additive should also have thermal stability, good wetting properties, processing properties, flame retardancy, chemical stability, and so on, and it is hoped that its dosage is small and the price is low.

The role of the adhesive in the battery is to firmly bond the active substances, conductive agents and current collectors in the electrodes together, ensuring the stability of the electrode structure. In the positive electrode, oil-soluble polyvinylidene fluoride (PVDF) is widely used; while in the negative electrode, water-based polytetrafluoroethylene (PTFE) emulsions, styrene-butadiene rubber (SBR) emulsions, etc. are more commonly used. The new negative electrode adhesives enhance the stability of the electrode structure by improving the mechanical interlocking effect and interfacial adhesion, thereby effectively improving the battery performance. For example, some adhesives containing special functional groups can form stronger chemical bonds with the surfaces of the active substances and current collectors, improving the reliability of the electrode during charging and discharging processes.