Sodium-ion anodes: when the current collector changes from copper to aluminium

One change in the current collector

In lithium-ion cells the anode must use copper foil, because lithium alloys with aluminium at low potential. Sodium does not, so sodium-ion anodes can use lighter, cheaper aluminium foil. As CATL and others bring sodium-ion batteries to passenger cars and energy storage, that difference is moving from the lab to the production line.

For the binder, the substrate changes: aluminium foil differs from copper in surface state, oxide layer and roughness, so adhesion data validated on lithium-ion anodes cannot simply be reused.

Hard carbon is not graphite under another name

Hard carbon dominates sodium-ion anodes. It is a disordered carbon with many micropores and surface functional groups: the pores govern sodium storage but also absorb binders and dispersants, and the surface chemistry affects CMC uptake, slurry rheology, storage stability and first-cycle efficiency. An SBR + CMC ratio that works on graphite usually has to be re-established on hard carbon.

On the cathode side, layered oxides dislike water

Sodium-ion cathodes follow three main routes: layered oxides, polyanionic compounds and Prussian-blue analogues. Layered oxides are sensitive to moisture and air and readily form alkaline surface species such as sodium carbonate and hydroxide, which makes aqueous processing as challenging as for nickel-rich NMC; polyanionic materials are comparatively stable; Prussian-blue analogues bring lattice water to manage. Binder and processing routes must be judged chemistry by chemistry.

Redefine the evaluation

Sodium-ion electrodes cannot simply borrow lithium-ion pass criteria. Peel and wet adhesion on aluminium, the rheology window of hard-carbon slurries, first-cycle efficiency and low-temperature rate all need new baselines within the sodium system.

How CASU approaches it

We manage sodium-ion projects as a chemistry of their own. On the anode side we start from aluminium adhesion and hard-carbon slurry stability; on the cathode side we design processing conditions separately for layered oxides and polyanionic materials. All references are built within the sodium system rather than borrowed from lithium-ion data.