Li+ Solvation Shell Speciation (2D)

Electrolyte Formulation

Salt concentration 1.0 mol/kg

Diluent fraction 0%

Temperature 25°C

Solvation Speciation

SSIP — solvent-separated pair

CIP — contact ion pair

AGG — aggregate (≥2 anions)

CIP fraction

AGG fraction

SSIP fraction

Est. ΔG desolv.

0 kJ/mol

How it works

Each Li⁺ ion moves in a 2D box under three competing forces: short-range excluded-volume repulsion from every neighbor, a Coulomb-like attraction toward FSI⁻ anions, and a dipole-like coordination pull toward solvent molecules. The diluent is a fluorinated, non-coordinating filler — it takes up area but does not bind Li⁺.

F_ion-pair ∝ (q_Li·q_an) / (ε_eff · r²)
ε_eff = ε₀ − f_dil·(ε₀ − ε_min)   (more diluent → lower ε_eff → stronger pairing)

Raising the diluent fraction does not dissolve more salt — it dilutes the pool of free solvent per Li⁺ and lowers the local dielectric screening (ε_eff), so anions are pulled into direct contact instead of staying solvent-separated. This is the real mechanism behind localized high-concentration electrolytes (LHCE): the same salt/solvent ratio as a normal electrolyte, "diluted" with an inert fluorinated co-solvent that raises the Li⁺–anion contact fraction.

Each Li⁺ is classified every frame by counting anions within its first contact shell (radius r_CIP):

SSIP — 0 anions in contact (ion pair separated by solvent)
CIP — exactly 1 anion in direct contact
AGG — 2 or more anions in direct contact

The desolvation barrier is estimated from the average number of solvent molecules still coordinating each Li⁺ (n̄): ΔG ≈ ΔG₀ + n̄·ε_coord. More CIP/AGG character means fewer solvent molecules have to be stripped before the ion can intercalate at the electrode — exactly why LHCE and other concentrated-anion electrolytes enable faster charge-transfer kinetics and thinner, anion-derived SEI films.

This 2D version runs the identical force law and classification logic as the 3D particle model, projected onto a plane — the same pairwise physics, fewer spatial dimensions to track, so speciation trends respond to the sliders exactly as they do in the 3D engine. Drag the canvas to pan and scroll to zoom; the strip below tracks the SSIP/CIP/AGG population split over time.

Li⁺ FSI⁻ anion solvent diluent

Drag to pan · Scroll to zoom

Speciation history