Industry challenges
Lithium-ion batteries are moving towards higher energy density, fast charging and higher safety, which raises the bar for separators, electrodes and interface materials. Separators need better thermal stability, electrolyte wettability and coating stability while keeping a suitable pore structure and ion transport; electrode slurries must solve dispersion of conductive agents and active materials, settling, coating rheology, drying cracks and electrode adhesion.
With nanoscale size, rich surface groups and good water dispersibility and interfacial action, nanocellulose can serve separator functional coatings and water-based electrode slurries, but the two directions use different products and methods.
Direction 1: separator coatings
As separators gain functionality, nanomaterials are increasingly used to build thinner, more uniform functional coatings. The 2026 standard T/CI 1675-2026 (nanofibre-coated separators) reflects the trend towards standardisation.
In current practice, carboxylated cellulose nanocrystals (C-CNC) can be developed as the functional nanomaterial in separator coating systems, optimising coating uniformity, pore structure, thermal stability, electrolyte wettability, ion transport and coating adhesion.
Note that the standard's nanofibre-coated separator is a separator technology term and is not the same as the product category cellulose nanofibrils (CNF); choose the product by the actual coating formulation and performance requirements.
Recommended for separator coatings
Recommended: carboxylated cellulose nanocrystals (C-CNC).
Carboxylated CNC is already used in separator coating systems in the industry. Its nanoscale size, high crystallinity and good water dispersibility suit compounding with water-based binders, inorganic particles and other functional components.
Position C-CNC as a functional nano-component and coating-structure modifier rather than a conventional binder or filler. In selection, look at C-CNC particle size and dispersion → carboxyl content → solids → viscosity → compatibility with the existing coating system. If you already have a mature separator slurry, keep it unchanged and add C-CNC as a gradient comparison instead of redesigning the whole formulation.
Separator trial suggestions
For an existing coating formulation: original formulation → pre-disperse C-CNC → add slowly to the slurry → low-speed mixing → degas → coat → dry → test. Set an original-formulation blank plus low, medium and high C-CNC levels; with no prior experience start from a low dosage relative to total coating solids and widen the gradient step by step.
Do not chase high dosage in the first round: too much C-CNC changes slurry viscosity, over-densifies the coating or alters the pore structure. The goal is the dosage window that works without hurting porosity and ion transport.
Separator slurry troubleshooting
- Slurry thickens clearly: dosage too high or stronger interactions; lower the dosage or solids.
- Particles or white spots in the coating: local C-CNC agglomeration; pre-disperse, then add slowly.
- Uneven coating: unsuitable viscosity or wetting; adjust slurry rheology and coating parameters.
- Poor coating adhesion: weak bonding to the base film; adjust the binder system or base-film surface treatment.
- Air permeability changes too much: coating too thick or pores affected; reduce coat weight or the C-CNC ratio.
- Little improvement in thermal shrinkage: unsuitable C-CNC ratio or composite structure; adjust dosage and other heat-resistant components.
- Higher electrolyte uptake without electrical gains: pores and ion transport not balanced; evaluate porosity, impedance and electrochemistry together.
A separator coating is not just about whether it coats: evaluate the balance between coating structure, porosity, wettability, ion transport and thermal stability. Keep the un-doped original formulation as a blank, otherwise performance changes cannot be attributed to C-CNC rather than coating variation.
Direction 2: water-based electrode slurries
Nanocellulose is also studied in water-based electrode slurries, where carboxylated cellulose nanofibrils (C-CNF) are recommended instead. With a high aspect ratio and strong network-building ability, C-CNF helps slurry suspension stability, dispersion of conductive agents and active materials, rheology control, particle bridging, electrode structural stability and adhesion.
Nanocellulose itself is not a conductive agent: it improves slurry and electrode structure and cannot replace conductive carbon black, CNT or other conductive materials.
Electrode slurry trial suggestions
On total electrode solids, set 0%, 0.5%, 1.0% and 2.0% C-CNF. Route: pre-disperse C-CNF → pre-disperse the conductive agent separately → combine gradually → add active material → adjust solids and viscosity → degas → coat → dry → calender.
Do not dump carbon black powder into a concentrated C-CNF system at once; high local concentration causes CNF-carbon black clumping or flocculation. Watch slurry uniformity, settling, coating viscosity, electrode cracking or shedding, peel strength and electrode resistance. If 1% C-CNF already thickens the slurry noticeably, do not raise the dosage blindly.
Electrode slurry common issues
- Slurry too thick: lower the C-CNF dosage rather than adding lots of water, which changes solids and drying.
- C-CNF clumps with carbon black: pre-disperse separately, then combine gradually; check addition order, local concentration and charge interactions.
- Stronger electrode but higher resistance: structure and conductive network conflict; reduce the insulating cellulose share and re-optimise the conductive agent ratio.
- Stable slurry but poorer cycling: slurry state alone does not prove suitability; verify electrolyte compatibility, electrochemical stability and long-term cycling.
Product selection by application
| Application | First choice | Main role |
|---|---|---|
| Separator coating | carboxylated CNC | functional coating, interface and structure tuning |
| Water-based electrode slurry | carboxylated CNF | rheology, suspension, bridging, adhesion support |
| Less thickening from CNF needed | CNC | nano-interface and filling studies |
| Composite separator coating | C-CNC | compounding with inorganic particles or polymers |
| Flexible, self-supporting electrodes | CNF / BC | three-dimensional network and structural support |
CelluBio supplies CNC, CNF and surface-functionalised grades for separator coatings, electrode slurries and composites, and supports material selection and preliminary trials for the target system.
Note
For material selection and preliminary trials in batteries and new-energy materials only, not fixed formulations, final process parameters or battery safety conclusions. Results depend on particle or fibre size, surface groups, carboxyl content, purity, solids, viscosity, dispersion and dosing, and on the separator substrate, coating formulation, binder, active material, conductive agent, electrolyte and process.
For separators, pay special attention to metal impurities, residual ions, moisture, thermal and electrochemical stability and effects on pore structure and ion transport. T/CI 1675-2026 is an industry reference; whether a product meets it must be confirmed by the tests the standard specifies, not by the material name.
