3D Copper Foam Foil — Solving the Challenge of Excessive Weight in Solid-State Batteries
According to a paper published in *Nature Energy* on February 28, 2024, by Professor Yi Cui of Stanford University, a porous current collector—proposed as a next-generation evolution of composite current collectors—can not only enhance energy density but also quadruple charging rates, enabling ultra-fast charging. Furthermore, this porous anode current collector is compatible with silicon-based anode Materials, effectively mitigating the issue of structural collapse in silicon; this opens up new possibilities for further increasing the energy density of lithium batteries, particularly solid-state batteries.
The advantages of copper Foam as an anode current collector material include:
① High safety: it does not produce sharp edges upon puncture, thereby preventing internal short circuits;
② High cost-effectiveness, light weight, and high energy density (copper usage is approximately one-seventh that of traditional copper foil);
③ Excellent ultra-fast charging performance (projected to reach 7–10C);
④Compatibility with lithium metal anodes, which promotes the adoption of lithium metal anodes and accelerates the industrialization of semi-solid and solid-state batteries. Various methods exist for producing 3D copper foil, such as laser or mechanical perforation and the growth of 3D structures on the foil surface via chemical reactions; common techniques include foaming and electroplating.
The principle behind producing copper foam via electroplating involves: first, depositing a thin metal film onto a mesh-structured organic substrate (typically polyurethane resin) via electroless plating to render the substrate conductive; next, depositing a metal layer onto the surface through electroplating; and finally, removing the organic substrate through sintering to yield the 3D mesh-structured metal foam. Copper foam is prepared using polyurethane foam as a substrate through a series of processes, including pretreatment, electroless copper plating, electroplating, and sintering/reduction. During preparation, scanning electron microscopy (SEM) is used to observe the foam's morphology, and key physical properties of the copper foam are tested.
- Pretreatment
(1) Degreasing: Removal of oily substances from the surface of the foam material to prevent interference with the electroless plating process.
(2) Roughening: Immersion of the degreased foam material in a roughening solution to open up blind pores in the foam matrix, generate hydrophilic groups on the surface, and increase surface roughness.
(3) Sensitization: Adsorption of a layer of reducing metal ions—specifically stannous ions (Sn²⁺)—onto the surface of the foam material. The sensitizing solution primarily consists of stannous chloride and hydrochloric acid. Sensitization conditions: 45°C for 5 minutes. Tin granules are added during the process; a milky white Sn(OH)Cl emulsion forms on the foam surface, creating a uniform adsorption layer on the substrate.
(4) Activation: Formation of a catalytic metal layer on the substrate surface. The palladium activation reaction is represented by the following equation [formation of palladium nuclei from (Pd-Cl₄)²⁻]: (PdCl₄)²⁻ + Sn²⁺ → Pd + Sn⁴⁺ + 4Cl⁻.
(5) Desizing: Cleaning the activated foam material with a 10% hydrochloric acid solution for 1 minute to remove the gel layer covering the palladium, thereby exposing the surface palladium atoms to enable catalytic activity.
- Electroless Copper Plating
A layer of metallic copper is deposited onto the catalytically active foam surface via a reduction reaction, imparting electrical conductivity and laying the foundation for the subsequent electroplating process.