Distribution and Transport of Lithium Ions at Interfaces between Graphite and Carboxymethyl Celluloses

Abstract

Carboxymethyl cellulose (CMC) is a water-processable binder widely used for graphite anodes. However, a microscopic understanding of why the identity of CMC counterions (Li⁺/Na⁺/K⁺) strongly affects electrode performance remains limited. Here, molecular dynamics (MD) simulations are used to track Li⁺ transport accessibility across electrolyte/CMC/graphite three-phase interfaces, comparing pure CMC-Li, CMC-Na, CMC-K, and mixed-counterion CMC binders. We find that CMC-Li sustains a continuous Li⁺ transport pathway from the electrolyte through the binder phase toward graphite. In contrast, in CMC-Na and CMC-K, Na⁺/K⁺ ions preferentially enrich at the graphite/binder interface, forming a cation-enriched interfacial layer which reduces Li⁺ accessibility to graphite. Partial replacement of Na⁺/K⁺ in CMC-Na and CMC-K with Li⁺ weakens this interfacial blocking effect and increases Li⁺ accessibility. Furthermore, a stage-resolved kinetic analysis visualizes the progressive suppression of Li⁺ crossing the binder phase upon the barrier layer formation. These results provide a microscopic rationale for the experimentally observed performance advantage of CMC-Li over CMC-Na and CMC-K binders.

Keywords

Carboxymethyl cellulose binder / Graphite anode / Binder counterions / Interfacial ion transport / Cation-enriched interfacial barrier

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