Biodegradable Battery Separators From Cellulose Nanofibers

ISEF Category: Energy: Sustainable Materials and Design

Subcategory: Energy Storage  ·  Difficulty: Advanced  ·  Setup: University Lab  ·  Time: Full Year

The Hook

A battery can fail because of a layer you never see. That thin separator must block shorts, let ions move, and stay stable in the electrolyte. If you can tune a plant-based material to do all three, you are working on a real battery problem. You also get to connect green materials with energy storage.

What Is It?

A battery separator is the thin barrier between the positive and negative sides of a battery. Think of it like a spongey fence. It must keep the electrodes apart so they do not touch, but it also must let charged particles, called ions, pass through the liquid inside the battery.

This project looks at cellulose nanofiber made from blended toilet paper and acid hydrolysis. Cellulose is the main material in plant fibers. When you break it down into tiny fibers, the surface area grows and the material can soak up liquid more easily. That property is called wettability, which means how well a liquid spreads across and enters a surface. Better wettability can help ions move through the separator, but the material still has to stay strong enough to prevent shorts.

The core tradeoff is simple. A separator that absorbs electrolyte well may support higher ionic conductivity, which means ions move more easily. But if the structure becomes too loose or fragile, the battery may perform worse or fail safely. Your job is to test how changes in the cellulose material affect that balance.

Why This Is a Good Topic

This makes a strong science fair topic because you can test a real materials tradeoff with measurable data. You can compare absorbency, contact angle, thickness, porosity, and conductivity, then look for patterns instead of just one result. The topic connects to biodegradable batteries, safer energy storage, and low-waste materials. A student can learn sample prep, experimental controls, and basic data analysis, even if the first version of the project starts with simple comparisons.

Research Questions

• How does the degree of cellulose fibrillation affect wettability in a separator sheet?
• What is the effect of acid hydrolysis strength on ionic conductivity through a cellulose nanofiber film?
• Does blending ratio of toilet paper pulp to nanofiber change electrolyte uptake?
• To what extent does separator thickness influence ionic resistance in a simple electrochemical cell?
• Which cellulose processing method produces the best balance of wetting and mechanical stability?
• How does surface treatment of the cellulose film change liquid spread and electrolyte retention?

Basic Materials

• Blended toilet paper pulp or other cellulose pulp source.
• Acid hydrolysis setup with proper school or university supervision.
• Filter paper and vacuum filtration setup.
• Beakers, graduated cylinders, and glass stirring rods.
• Digital balance with 0.01 g or better resolution.
• Hot plate or drying oven.
• Micrometer or digital caliper.
• Simple electrolyte solution for wetting and conductivity tests.
• Conductivity meter or multimeter with appropriate probe setup.
• Safety goggles, acid-resistant gloves, and lab coat.

Advanced Materials

• Cellulose nanofiber processing setup with controlled acid hydrolysis.
• Vacuum filtration or membrane casting system.
• Electrochemical impedance spectroscopy instrument.
• Scanning electron microscope for fiber morphology.
• Contact angle goniometer for wettability measurements.
• Tensile tester for separator strength.
• Porosimetry equipment or equivalent pore analysis tools.
• Potentiostat with battery test fixture.
• Inert electrolyte and coin-cell assembly supplies.
• Thickness gauge and precision balance.

Software & Tools

• Google Sheets: Organizes measurements, calculates averages, and graphs separator performance trends.
• ImageJ: Measures pore size, fiber coverage, and wetting spread from photos.
• Python: Helps fit curves, compare groups, and run statistics on your results.
• JASP: Runs t tests, ANOVA, and effect size calculations without paid software.
• GeoGebra: Plots relationships between processing variables and conductivity or absorbency.

Experiment Steps

1. Define the separator property you care about most, then pick one processing variable to change first.
2. Set up a comparison plan that includes a plain cellulose control and at least one nanofiber version.
3. Choose measurements that capture both wetting behavior and ion transport, not just one of them.
4. Build a way to compare samples fairly by keeping thickness, area, and drying conditions consistent.
5. Plan a data table that links structure, absorbency, and conductivity so you can look for tradeoffs.
6. Decide how you will test whether better wettability really predicts better separator performance.

Common Pitfalls

• Using unevenly formed sheets, which makes thickness and porosity vary too much between trials.
• Comparing samples with different drying levels, which changes mass, wetting, and conductivity at the same time.
• Measuring absorbency without controlling sample area, which makes larger sheets look better for the wrong reason.
• Assuming higher liquid uptake always means better separator performance, which ignores shorting risk and mechanical weakness.
• Skipping structural imaging, which makes it hard to explain why two cellulose films behave differently.

What Makes This Competitive

A stronger project would connect structure to performance with more than one measurement. You could compare processing conditions, then test whether wettability, pore structure, and ionic resistance move together or split apart. Strong entries also include clean controls, repeated trials, and a clear statistical test for the tradeoff you claim. If you can explain why one cellulose design wins for battery use, not just show that it absorbs liquid, your project gets much stronger.

Project Variations

• Compare toilet paper derived cellulose nanofibers with lab-grade cellulose nanocrystals to see which separator wets faster.
• Test a salt, acid, or polymer surface treatment to see how surface chemistry changes electrolyte uptake.
• Swap the electrolyte type and compare how the same cellulose film performs in different ionic environments.

Learn More

• US Department of Energy Office of Science: Search for battery separator reviews and energy storage materials overviews.
• PubMed: Search review articles on cellulose nanofibers, wettability, and ionic transport.
• PubChem: Look up common acids, salts, and electrolyte additives used in materials tests.
• National Renewable Energy Laboratory: Find accessible background pages on batteries, separators, and energy storage materials.
• MIT OpenCourseWare: Search materials science and electrochemistry course notes for separator and transport fundamentals.
• ScienceDirect journals: Search recent peer-reviewed papers on cellulose-based separators and biodegradable battery materials.