Two of the most awkward waste problems of modern life may have found an unexpected shared answer. Researchers in China have turned shredded lithium-ion battery cathodes and discarded plastic packaging into a thin, flexible material that soaks up microwave radiation with remarkable efficiency. It is not a promise that your old phone battery will soon become a phone case. It is a laboratory demonstration with a clear and attractive idea at its heart: take two waste streams that are usually handled separately, heat them together in the right proportions, and let one waste supply what the other one lacks.
The study, published in October 2026 in the journal Advanced Composites and Hybrid Materials, is titled "Carbon-Supply-Programmed CNT Growth for Ultrathin Microwave Absorbers from Waste Batteries and Plastics." The team was led by Han-Ming Zhang of Hebei University of Science and Technology, with Ting Shi and Ningning Cao as corresponding authors. Their starting materials were familiar: nickel cobalt manganese oxide, known as NCM, from spent battery cathodes, and low-density polyethylene, or LDPE, the soft plastic used in bags and packaging film. Their product was far less familiar: sea urchin-like carbon nanotube structures that can absorb more than 99.9999 percent of incoming microwave energy at a thickness of just 1.63 millimetres.
Two waste problems, one process
To understand why this matters, it helps to look at each waste stream on its own. Spent lithium-ion batteries are piling up as electric vehicles, laptops and grid storage systems reach the end of their working lives. Their cathodes contain nickel, cobalt and manganese. Those metals are valuable, but they are also environmentally troublesome if batteries are dumped or handled badly. Recovering them is not always straightforward either. Conventional recycling often means melting material at high temperature or dissolving it in strong chemicals, and for some cathode types the cost and side effects can outweigh the value recovered.
Plastic packaging presents a different but equally stubborn problem. LDPE is produced in huge quantities, it is light and flexible, and it is often contaminated with food or mixed with other materials. That makes it one of the least effectively recycled plastics, even though the raw material itself is a rich source of carbon. Most recycling systems treat batteries and plastics as separate problems, with separate plants, separate chemistry and separate economics.
The Chinese team asked a simpler question: what happens if you process them together? In their one-step pyrolysis process, shredded cathode material and plastic are heated together under controlled conditions. The battery material supplies tiny metal particles that act as catalysts. The plastic breaks down at high temperature and supplies carbon atoms. Those carbon atoms feed into growing carbon nanotubes, which spread outwards from the catalyst particles like spines from a sea urchin. The result is an interconnected network of tubes, full of defects and interfaces, that is very good at trapping microwaves.
The surprising role of the carbon supply
The most interesting scientific finding is not just that the process works, but that it can be tuned. In conventional carbon nanotube growth, metal nanoparticles act as catalysts while a carbon source feeds atoms into the growing tube. The researchers found that the ratio of cathode material to plastic does much more than decide how much carbon is available. It controls the local flow of carbon at each catalyst particle, and therefore how fast and in what way the nanotubes grow.
By adjusting the NCM-to-LDPE mass ratio, they could continuously tune the length of the nanotubes and, crucially, the density of defects in their walls. At first, as the carbon supply increased, the tubes became more crystalline and better ordered. Beyond a certain point, however, the flood of carbon began to create defects instead of healing them. The team tracked this change with Raman spectroscopy, watching the ratio of the defect-related D band to the graphitic G band. Rather than rising or falling steadily, that ratio traced a volcano-shaped curve as the feed ratio changed, climbing, peaking and then falling again.
That volcano shape is the key to the whole design. It reveals a tug-of-war between graphitization, which makes the tubes more ordered and conductive, and defect generation, which breaks up that order. The best microwave absorption sits at the sweet spot between them, not at either extreme. The researchers call this a carbon-supply-driven kinetic regulation strategy, and they argue that it offers a general way to program nanostructure by controlling a process parameter.
This is a good example of why structure matters so much at the nanoscale. A material's behaviour is often decided not by what it is made of in bulk, but by how its smallest parts are arranged. Readers who enjoy that theme may also like our guide to nanotechnology and sustainability, which explains how tiny tools are being used for very large environmental challenges. The same lesson appears in biology: the recent SPRIZ discovery of the molecular pillars that shape your cells' powerhouses shows how small structural supports can decide how a whole system works. In the new absorber, the spiky nanotube architecture is doing a similar job, creating the network and the interfaces that microwaves cannot easily escape.
Why the absorber works so well
A good microwave absorber has to do two things at once, and they pull in opposite directions. First, it must let waves in rather than bouncing them off its surface. If a material is too conductive, waves reflect away, and the absorber fails before it has even started. Second, once the waves are inside, it must turn their energy into heat. That happens through two main routes: conduction loss, where induced currents travel through a conductive network and fade away as resistance, and polarization loss, where defects and interfaces trap charge and reorient under the oscillating electric field, converting electromagnetic energy into heat.
Too much conductivity causes reflection. Too many defects destroy the conductive pathways. The best absorbers sit in the delicate middle ground, and the optimized material in this study, designated NCC-6.7, appears to hit that balance with unusual precision. Its sea urchin-like architecture creates an interconnected conductive network for conduction loss, while preserving abundant defects and heterogeneous interfaces for dipolar polarization. In testing, it achieved a minimum reflection loss of minus 63.45 decibels at a thickness of only 1.63 millimetres. In plain terms, that corresponds to reflecting roughly one part in two million of the incident power. At an even thinner 1.46 millimetres, it maintained an effective absorption bandwidth of 4.25 gigahertz, meaning it suppresses reflections across a wide stretch of the microwave spectrum used by modern communications.
Thickness matters enormously in practice. Traditional absorbers often need millimetres to centimetres of material to reach comparable attenuation, adding weight and bulk to aircraft, vehicles, base stations and wearable electronics. An absorber that works at under two millimetres can be laminated into enclosures, woven into fabrics or applied as a coating without a meaningful weight penalty. The team went one step further and processed their optimized powder into a textile, showing that the material keeps its absorbing function in a flexible, fabric-like form. That textile also showed enhanced corrosion resistance and reduced electromagnetic scattering compared with reference materials, properties the authors highlight as important for marine use, where salt spray and humidity quickly degrade many coatings.
What this does not mean yet
It would be easy to overstate a result like this, so it is worth being clear about its limits. This is a laboratory-scale demonstration, not an industrial process. The authors frame the work as establishing a kinetics, structure and property paradigm that could be extended to other mixed-waste systems. They do not claim that factories are ready to convert battery scrap and plastic bags into shielding textiles tomorrow.
Scaling up will raise questions that a small laboratory study cannot fully answer. Real waste is messy: battery cathodes vary in chemistry, age and condition, and plastic packaging varies in thickness, additives and contamination. Maintaining precise control over feed ratios and pyrolysis conditions at industrial throughput is a much harder task than running a controlled experiment. The study's promise will therefore depend on pilot-scale tests, cost analysis and lifecycle assessment.
There is also a broader point about waves. They do not always behave the way intuition suggests. Astronomers recently found a similar surprise when they studied how light escapes young galaxies, as described in our report on how Hubble found supernova winds blocked, not aided, the light that reionized the universe. In both cases, the lesson is the same: to control waves, whether light or microwaves, you need to understand the material they travel through and the barriers in their path. The new absorber is interesting precisely because its internal structure, rather than its bulk thickness, does most of the work.
Why waste-to-material ideas are gaining ground
That logic is attractive for batteries and plastics alike. Battery cathodes already contain structured metal oxides. Plastics already contain long carbon chains. If those structures can be redirected, rather than destroyed and rebuilt, some of the energy and effort already invested in making them can be preserved. The co-pyrolysis approach does exactly that: the battery supplies catalytic metal centres and part of the inorganic framework, while the plastic supplies the carbon feedstock. Each waste stream compensates for the other's shortcomings in the reaction. A process that produces a functional absorber, textile or coating can also potentially earn more per tonne of waste than one that produces only commodity metals, which makes collecting and sorting that waste more worthwhile.
What to watch next
Three questions will decide whether this discovery moves beyond the laboratory. The first is consistency: can the same volcano-shaped tuning be reproduced with real, mixed waste, not just carefully prepared cathode and plastic samples? The second is durability: how does the textile perform after repeated bending, washing, heating and exposure to salt water over months or years? The third is scale: can the one-step process be run continuously, safely and affordably, without losing the precise control that makes the material work?
For now, the study stands as a vivid demonstration that the line between waste and advanced material can be surprisingly thin. A shredded battery cathode and a discarded plastic bag, heated together under the right conditions, can grow into spiny carbon structures that outperform many purpose-built absorbers. As wireless networks get denser and battery waste continues to mount, the idea that one form of technological pollution might be eased by material made from the leftovers of another is likely to resonate far beyond materials science. It is a reminder that discovery does not always mean finding something entirely new. Sometimes it means looking again at what we were about to throw away, and noticing that it still has work to do.