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

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 cationenriched 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.