Current collector materials play a critical role in battery performance, especially under high-temperature conditions. Elevated temperatures accelerate degradation mechanisms, making material selection crucial for maintaining conductivity, mechanical integrity, and electrochemical stability. Aluminum and copper foils dominate conventional battery designs, but advanced alternatives such as stainless steel and coated collectors offer improved performance in extreme environments. This article examines the properties of these materials, focusing on oxidation resistance, interfacial stability, and conductivity changes at high temperatures.

Aluminum foil is widely used as a current collector in lithium-ion batteries, particularly for the cathode due to its balance of conductivity, lightweight nature, and cost-effectiveness. At room temperature, aluminum forms a thin passive oxide layer that protects against further corrosion. However, at elevated temperatures above 60°C, this oxide layer thickens, increasing interfacial resistance and reducing charge transfer efficiency. Studies show that aluminum's bulk conductivity decreases by approximately 10-15% when exposed to temperatures exceeding 80°C. Additionally, prolonged high-temperature exposure can lead to pitting corrosion, especially in the presence of electrolyte decomposition products. Despite these drawbacks, aluminum remains a practical choice for moderate-temperature applications due to its established manufacturing compatibility.

Copper foil serves as the standard anode current collector in lithium-ion batteries because of its high electrical conductivity and ductility. Unlike aluminum, copper does not form a passivating oxide layer, making it more susceptible to oxidation at high temperatures. Above 70°C, copper undergoes accelerated oxidation, leading to the formation of resistive copper oxides that degrade cell performance. Furthermore, copper's thermal expansion coefficient can cause delamination from electrode coatings under repeated thermal cycling. While copper maintains higher bulk conductivity than aluminum even at elevated temperatures, its interfacial instability limits its suitability for prolonged high-temperature operation without protective measures.

Stainless steel emerges as a promising alternative for high-temperature applications due to its superior oxidation resistance and mechanical robustness. Grades such as 316L stainless steel exhibit excellent corrosion resistance even at temperatures exceeding 100°C. Unlike aluminum and copper, stainless steel forms a stable chromium oxide layer that self-repairs when damaged, preventing further degradation. However, stainless steel's higher density and lower intrinsic conductivity compared to aluminum or copper necessitate thinner foils or optimized designs to minimize weight and resistive losses. Research indicates that stainless steel current collectors can maintain stable interfacial resistance after hundreds of hours at 90°C, making them viable for demanding applications.

Coated current collectors provide another avenue for enhancing high-temperature performance. Aluminum or copper foils coated with conductive carbon layers or corrosion-resistant metals like nickel or gold demonstrate improved stability. Carbon coatings offer dual benefits: they act as a barrier against electrolyte reactions while maintaining low interfacial resistance. Nickel-coated aluminum, for instance, reduces oxidation while preserving the lightweight advantage of aluminum. Gold coatings, though costly, provide exceptional oxidation resistance and conductivity retention even above 100°C. These coatings add manufacturing complexity but can be justified in applications where extreme temperature resilience is critical.

The conductivity of current collector materials varies significantly with temperature. Pure metals like copper and aluminum experience decreased conductivity due to increased electron-phonon scattering at higher temperatures. Copper's conductivity drops by about 20% when heated from 25°C to 100°C, while aluminum sees a 25-30% reduction over the same range. Stainless steel, with its alloy composition, shows a less pronounced conductivity decrease but starts from a lower baseline. Coated collectors can mitigate these losses by providing alternative conduction pathways or protecting the underlying metal from oxidation-related degradation.

Interfacial stability between the current collector and active materials is equally critical at high temperatures. Poor adhesion or chemical reactions can lead to delamination or increased impedance. Aluminum's native oxide layer can react with certain cathode materials at elevated temperatures, forming resistive interphases. Copper may catalyze unwanted electrolyte decomposition reactions. Stainless steel generally exhibits better interfacial inertness, though its compatibility varies with specific electrode chemistries. Coatings can bridge these gaps by providing chemically stable interfaces that resist degradation even under thermal stress.

Mechanical properties also influence high-temperature performance. Thermal expansion mismatches between current collectors and electrode layers can cause warping or detachment during cycling. Aluminum and copper have higher coefficients of thermal expansion than stainless steel, making them more prone to dimensional instability. Stainless steel's rigidity helps maintain electrode integrity but may require careful handling during cell assembly due to reduced flexibility.

Material selection for high-temperature operation involves trade-offs between conductivity, weight, cost, and durability. Aluminum offers a balanced solution for moderate conditions but requires protection for extended high-temperature use. Copper provides superior conductivity but demands additional safeguards against oxidation. Stainless steel and coated collectors address many high-temperature challenges but introduce their own considerations regarding weight and manufacturability. The optimal choice depends on specific application requirements, including temperature range, lifetime expectations, and cost constraints.

Future developments may focus on hybrid approaches, such as nanostructured coatings or composite materials, to further enhance high-temperature performance. Advances in thin-film deposition techniques could make sophisticated coatings more economically viable for widespread battery use. Meanwhile, improved alloy formulations may push the boundaries of temperature stability for metallic collectors without compromising other essential properties.

In summary, current collector materials for high-temperature battery operation require careful evaluation of multiple factors. While traditional aluminum and copper foils serve well in standard conditions, advanced alternatives like stainless steel and coated collectors provide necessary enhancements for extreme environments. The ongoing evolution of these materials will support the development of batteries capable of reliable performance in increasingly demanding applications.