Strong
It holds its shape.
A tough fiber network that resists tearing and puncture, the separator's first job in a cell.
Why the name ARACHNE?
A weaver, a spider, a web.
In Greek myth, Arachne was a weaver so skilled she challenged the goddess Athena, and was turned into the first spider.
Spiders spin fine fibers into webs that are light, open and remarkably tough. Spider silk is often compared with Kevlar. ARACHNE starts from Kevlar's own chemistry, splits it into nanofibers and weaves them into a web that guards the inside of a battery.
- Silk fibers→Aramid nanofibers
- An open web→A porous separator mesh
- Lets air through, stops prey→Lets ions through, keeps electrodes apart
Six reasons it's called a web
Hover or tap an axis. Each strand of the web is one capability. Touch the strands and they vibrate.
Fig. 2 · ARACHNE capability web. Qualitative and illustrative, not measured data.
From membrane to cell
The separator you just touched, inside the cell.
The heart of your energy sits between the electrodes. ARACHNE aramid nanofiber separators are developed for cells like this 4EVR × Valerion pouch cell.
Move your cursor over the cell to turn it in the light and look inside through the lens.Tilt your phone to turn the cell in the light, and drag across it to look inside through the lens. Tap a marker to see what each part does.
Look inside
Hover or drag across the cell to see the stacked layers, or tap a marker.
Mock-upFig. 3 · Illustrative render, not a production cell. Cut-away layers are schematic.
Why aramid?
The fiber behind body armor, split down to the nanoscale.
Aramids are the polymer family behind protective fibers such as Kevlar. Split into nanofibers, the same chemistry becomes a thin, porous mesh that sits between a battery's electrodes.
Heat-resistant
It doesn't melt.
Aramids char at very high temperature instead of melting, so the separator stays in place when a cell runs hot.
Continuous
It's a mesh, not a film.
Nanofibers knit into an open, connected pore network that electrolyte fills and ions pass through.
OriginBuilt on aramid nanofiber research from Prof. Nicholas Kotov's lab at the University of Michigan, carried from lab to pilot line in Istanbul.
Thin without compromise
Thin enough for power. Tough enough for safety.
The separator stores no energy. It is overhead that ions must cross. Thinner is better for energy and power, but every film loses mechanical protection as it gets thinner, and a polyolefin film melts at the same temperature however thin it is. Here is how each effect scales.
1 · Energy density
Ev ∝ 1 / Lstack
A cell is a stack of repeating units: cathode, separator, anode, separator. Every micrometer of separator adds height but no capacity, so a thinner separator packs more electrode into the same volume.
2 · Power density
Rsep = N · L / σ0
Ions cross the separator through electrolyte-filled pores. Its area resistance grows with thickness L and with the MacMullin number N, which captures how tortuous and porous the pores are. Halve L and you halve this resistance and the voltage it costs at high current.
3 · Safety
Fpuncture ∝ L · strength
Resistance to puncture by particles, burrs or dendrites scales roughly with thickness times the material's strength. Melting does not depend on thickness at all: polyethylene melts near 130 °C whether it is thick or thin.
One repeating unit, drawn to scale. Dashed line: the same unit with a 20 µm separator.
Separator share of the stack–
Stack energy density vs a 20 µm separator–
Separator ionic resistance–
Voltage lost in the separator at 5 mA/cm²–
Puncture resistance of a polyolefin film, vs the same film at 20 µm
–
Polyolefin at this thickness
–
ARACHNE at this thickness
–
Fig. 3b · Textbook model, not product data. Stack: 60 µm cathode coatings on 12 µm Al, 70 µm anode coatings on 8 µm Cu, two separators per unit, volume only. Resistance: N = 8, typical of commercial separators; electrolyte σ0 = 10 mS/cm. ARACHNE's own properties are not modelled here.
How ARACHNE breaks the trade-off
Nanoscale strength
Strength from the material, not the bulk.
Stiff aramid chains, hydrogen-bonded into nanofibers and tangled into a continuous web, spread a load across countless fiber contacts. A stronger material can be made thinner and still resist puncture.
Thermal stability
No melting point, at any thickness.
Aramid does not melt and the web barely shrinks when hot. A thin layer keeps covering the electrodes right to the edges in temperature ranges where polyolefin films melt and pull back.
Engineered porosity
Short, even paths for ions.
Small, interconnected pores that wet readily with electrolyte keep the MacMullin number low, so thinness turns into lower resistance. Evenly spread ion flow also helps lithium plate smoothly instead of growing dendrites.
ARACHNE platform
Innovation in every layer.
4EVR Energy Tech pioneers advanced nanocomposite engineering for next-generation energy storage. ARACHNE is our breakthrough platform, built for high safety, strong performance and scalable reliability.
Our proprietary ARACHNE separator technologies enhance energy density, thermal stability and safety across EV and defense applications, bridging materials science with scalable manufacturing.
Chemistry-agnostic · our focus
Li–SLithium–sulfur
NMCNickel manganese cobalt
LFPLithium iron phosphate
From lab-scale nanomaterials to pilot-scale production, built to scale with the cell makers we work with.
ARACHNE separator
Drag to rotate · tap a layer
Fig. 4 · Exploded cell, schematic. Layer thicknesses exaggerated.
Structure
A mesh, not a slit.
Conventional polyolefin separators are stretched films with elongated, slit-shaped pores. ARACHNE is a continuous network of aramid nanofibers. Drag across the figure to compare.
Polyolefin film
ARACHNE mesh
Fig. 5a · Polyolefin, slit pores, schematic
Fig. 5b · ARACHNE, nanofiber network, schematic
The real thing
This is what the web looks like under an electron microscope.
A scanning electron micrograph of an aramid nanofiber network. A single aramid nanofiber is only a few to a few tens of nanometers thick, so the bright strands here are mostly bundles of them; the dark spaces between are the pores that fill with electrolyte. Move the loupe across it to look closer.
Fig. 5c · SEM micrograph, aramid nanofiber network. Image: 4EVR Energy.
Same molecule, new scale
Kevlar® fiber vs. aramid nanofiber.
Both are made of the same aramid polymer, poly(para-phenylene terephthalamide). The chains are stiff, lie side by side and are tied together by hydrogen bonds, which is where the strength and heat resistance come from. The difference is scale and shape. A Kevlar fiber is a thick, solid thread. Aramid nanofibers are what you get when that thread is gently split apart into strands about a thousand times thinner. Those strands can then be cast into a thin, continuous, porous web.
Drag the slider to split the fiber.
Fig. 5d · From fiber to nanofiber network, schematic, not to scale
Kevlar® fiber
- Scale
- Solid threads several micrometers across, finer than a human hair.
- Made by
- Spinning a liquid-crystalline solution of the polymer into continuous fibers.
- Forms
- Yarns, ropes and woven fabric.
- Known for
- Body armor, cut-resistant gloves, cables and tire reinforcement.
- As a separator
- Too thick, and the gaps in a woven fabric are far too large to keep electrodes apart or stop dendrites.
Aramid nanofiber · ARACHNE
- Scale
- A few to a few tens of nanometers across, yet still long and flexible.
- Made by
- Stirring aramid fibers in a strongly basic solvent. The base pulls hydrogen off the amide groups, which weakens the hydrogen bonds between chains and leaves the strands negatively charged. They repel one another, so the fiber peels apart into nanofibers that stay dispersed.
- Forms
- A stable dispersion. When the charge is neutralized, the nanofibers knit back together through hydrogen bonds into a gel that becomes a thin, continuous film.
- Keeps
- Aramid's strength and heat resistance. It does not melt the way polyolefins do.
- As a separator
- A tangled web with small, interconnected pores that wets with electrolyte and spreads ion flow evenly.
Kevlar® is a registered trademark of DuPont. It is named here only to describe the material class.
Battery safety
Why safety is the whole game.
A battery packs a lot of energy into a small space, right next to a flammable liquid. If the electrodes ever touch inside a cell, the energy can release as heat instead of electricity.
That heat can trigger a self-feeding chain called thermal runaway, and in a pack it can spread from one cell to the next. In electric vehicles, homes, aircraft and grid storage, preventing that chain is not optional. Safety has to be built into every layer, and the separator is the last physical barrier between the electrodes.
More energy
Higher stakes.
High-nickel cathodes and lithium-metal anodes store more energy, so there is more to release if something goes wrong.
Faster charging
More stress.
Fast charging creates heat and can plate lithium on the anode, the seed of dendrites.
Bigger packs
Wider reach.
Large EV and grid packs hold hundreds or thousands of cells, so one failure must not spread.
Thermal runaway ladder
Drag the temperature up and watch what happens inside a typical lithium-ion cell.
25 °C
- ~60 °C Above the normal operating range. Ageing reactions speed up.
- ~80–120 °C The protective SEI layer on the anode starts to break down and release heat.
- ~130 °C Polyethylene separators melt and shrink; electrodes can touch at the edges.
- ~150–250 °C Charged cathodes can release oxygen and the electrolyte decomposes; high-nickel cathodes react earlier.
- ~165 °C Polypropylene separators melt.
- Runaway Heat feeds more reactions. The cell vents gas and can catch fire.
- ~450 °C and up Para-aramid fibers begin to decompose, without ever melting.
Polyolefin separator
IntactARACHNE aramid separator
IntactTemperatures are approximate and depend on chemistry, state of charge and cell design. A separator cannot stop every reaction, but one that stays in place keeps the electrodes apart for longer and removes a key trigger.
See dendrites in the Lab →Separator under heat
What happens when a cell runs hot?
Polyolefin separators soften and shrink as they approach their melting point, which can let the electrodes touch at the edges. Aramid has no melting point, so the separator keeps the electrodes apart. Drag the slider to heat both cells.
Polyolefin separator
Intact. Electrodes are kept apart.
ARACHNE separator
Intact. Electrodes are kept apart.
Fig. 6 · Thermal behavior, schematic, not to scale
Electrochem Lab
Play with the electrochemistry.
Eight small tools for students, engineers and the curious. Numbers are textbook approximations for learning, not 4EVR product data.
Pick a cathode and an anode.
Cell voltage is the gap between the two electrode potentials. Theoretical energy combines that voltage with how much charge each material can store per gram.
CHEMISTRY
CATHODE
ANODE
–Cell voltage
–Couple capacity
–Theoretical energy, active materials
Average potentials vs Li/Li⁺ and theoretical capacities. Real cells reach a fraction of these values once inactive parts are added.
How much lithium moves when you charge?
Every electron through the outside circuit is matched by one Li⁺ ion through the separator. Faraday's constant turns battery capacity into a count of atoms.
PICK A DEVICE
Q = capacity (Ah) × 3600 · n = Q / F · mLi = n × 6.94 g/mol · F = 96,485 C/mol
Device presets are cell-level capacity at about 3.7 V (e.g. 75 kWh ÷ 3.7 V ≈ 20,270 Ah).
–Charge (coulombs)
–Electrons
–Moles of Li⁺
–Lithium shuttled per full charge
Bend the voltage of a Daniell cell.
Zn | Zn²⁺ ‖ Cu²⁺ | Cu has a standard voltage of 1.10 V. Change the ion concentrations and temperature and the Nernst equation moves it.
E = E° − (RT / nF) · ln([Zn²⁺] / [Cu²⁺]) · n = 2 · E° held at 1.10 V; activities taken as concentrations
Read a cell's impedance spectrum.
Electrochemical impedance spectroscopy (EIS) applies a small AC signal from high to low frequency. This Randles circuit, Rs + (Cdl ∥ [Rct + W]), is the classic starting model. Move the sliders and watch the Nyquist plot.
Z = Rs + 1 / ( jωCdl + 1 / (Rct + ZW) ) · ZW = σW(1 − j)/√ω · 100 kHz → 10 mHz
–High-frequency intercept (Rs)
–Semicircle ends (Rs + Rct)
–Characteristic frequency, 1/(2πRctCdl)
Separator mode · blocking-electrode cell
Sandwich a soaked separator between two steel discs and Rs becomes its bulk resistance Rb. Then σ = L / (Rb · A).
–Ionic conductivity, soaked separator
–MacMullin number (vs 10 mS/cm electrolyte)
Electrode area fixed at 2.01 cm² (16 mm disc). Lower MacMullin number means the separator obstructs ions less.
Ionic conductivity calculator.
Measure the bulk resistance Rb of a soaked separator (or a solid electrolyte pellet) between two blocking electrodes, usually the high-frequency intercept in EIS. Geometry turns it into conductivity.
σ = L / (Rb · A) · A = π(d/2)² · NM = σ₀ / σ · τ = NM · ε (tortuosity factor)
–Ionic conductivity σ
–Electrode area A
–MacMullin number NM
–Tortuosity factor τ
TEMPERATURE · ARRHENIUS
–σ at this temperature (measured at 25 °C)
–Relative to 25 °C
Design a lithium-metal cell.
Swap graphite for lithium metal and the anode almost disappears, so every other layer starts to matter. Tune the stack, try a solid-state build, and watch stack-level energy respond.
CATHODE
ELECTROLYTE
SEPARATOR
–Stack energy, Wh/kg
–Stack energy, Wh/L
–Lithium foil per side
YOUR STACK, TO SCALE (THICKNESS)
WHERE THE MASS GOES
Stack-level estimate for one repeating unit (cathode, separator, lithium, half of each current collector, electrolyte). Pouch, tabs and packaging excluded; electrolyte beyond the pore volume adds thickness. Assumptions: NMC811 200 mAh/g at 3.8 V; LFP 160 mAh/g at 3.4 V; sulfur 1,000 mAh/g at 2.1 V; 12 µm Al and 8 µm Cu foils; separator porosity 45%. Solid-state: dense Li₆PS₅Cl layer (1.64 g/cm³); composite cathodes hold ~25–30 wt% solid electrolyte.
Watch dendrites grow, side by side.
Charging plates lithium onto the anode. Where ions arrive unevenly, lithium piles up into needle-like dendrites that reach for the other electrode. If one gets through, the cell shorts.
Ready.
Ready.
Schematic model, not a quantitative simulation. Ions plate where they arrive. Large, uneven pores focus the ion flux into hot spots that grow needles; a fine, uniform and stiff nanofiber mesh spreads the flux and physically resists penetration. Higher charge rates make dendrites more likely in any cell.
Where it goes
Built for cells that ask more of a separator.
Electric vehicles
Separators that help packs carry more energy without giving up thermal stability.
Defense and safety-critical packs
Aramid chemistry for cells where a thermal event is not an option.
Li–S, NMC and LFP
Chemistry-agnostic by design, with a focus on lithium–sulfur, NMC and LFP cells, and ready for lithium-metal chemistries that push separators harder.
Solid-state and polymer electrolytes
ANF nanocomposites as a scaffold that reinforces solid and polymer electrolytes.
Fast charging
An open, continuous pore network that keeps ion pathways clear.
Structural batteries
Stiff aramid layers for energy storage that also carries mechanical load.
Our team
Deep science, scalable engineering.
Advisors
Forever safer.
Forever stronger.
We are shaping a higher standard for energy materials, combining deep science with engineering, built on discipline, sophistication and uncompromising intent.
Request a sample · get in touch
Boğaziçi University Technopark, Kandilli, Üsküdar, Istanbul
info@4evr.energy
4EVR Energy is part of Valerion.
Valerion is backed by LG Technology Ventures, Research Bridge Partners, Michigan Rise and HEST Group.