Sample Rheology Diagnostic Report
A shortened version of a Rheology Diagnostic Report, built on a fictional cathode-slurry case so you can see the structure, depth and tone before you order.
Coating weight varies by about ±6% between batches of the same NMC cathode slurry, although the recipe is unchanged. Why does it vary, and what should be tested first?
| Item | Details (fictional) |
|---|---|
| Formulation | Solids 94 / 3 / 3 wt% (NMC / carbon black / PVDF), 70 wt% solids in NMP |
| Rheology | Flow curves 0.1–1000 1/s, four batches (A–D), protocol without a defined pre-shear |
| Process | Planetary mixing, 20–60 min; slot-die coating; coating weight per batch |
| Already tried | Adjusting coating gap; changing NMP lot |
The formulation-based model predicts the viscosity expected from solids loading, particle size and binder content. The difference between predicted and measured curves — the residual — is where the diagnosis starts.
| What the data shows | What it does not show |
|---|---|
| The excess over prediction grows as shear rate falls (1.06× → 2.0× for batch A). | The structure behind the excess — the flow curve alone cannot distinguish particle networks from binder gelation. |
| Longer mixing reduces the low-shear excess (batch D: 1.25× at 0.1 1/s). | Whether mixing time or mixing temperature is the active variable; both rose together in the logs. |
| High-shear viscosity agrees with prediction for all batches. | Any information about the measurement history of each sample, because no pre-shear was applied. |
| # | Hypothesis | Evidence for | Evidence against / gaps | Confidence |
|---|---|---|---|---|
| H1 | Incomplete dispersion of conductive carbon forms a weak network | Low-shear excess; decreases with mixing time; high shear unaffected | Not yet confirmed by oscillatory data | Moderate |
| H2 | Partial PVDF gelation from moisture | Also raises low-shear viscosity | No rise during storage; no moisture data | Low |
| H3 | Measurement artefact (no pre-shear, wall slip) | Protocol not standardised | Batch ordering is consistent across shear rates | Low |
| Priority | Test | Separates | Decision it supports |
|---|---|---|---|
| 1 | Re-measure retained samples with a fixed pre-shear and rest step | H3 vs. H1/H2 | Whether the variation is real or a protocol effect |
| 2 | Three-level mixing-energy series with amplitude sweep (storage-modulus plateau) and coating weight | H1 | Whether a minimum mixing energy should be specified |
| 3 | Moisture check of NMP and PVDF lots | H2 | Whether raw-material handling needs a moisture limit |
Decision rule: if the low-shear excess and the storage-modulus plateau both fall with mixing energy while coating-weight spread narrows, set a minimum mixing-energy specification and monitor low-shear viscosity as a release check.
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