Lamination bonds the separator directly to both electrode faces using heat and pressure to soften a thin adhesive coating already on the separator before the electrode stack is built. Rather than leaving the separator as a free-floating layer held in place only by winding tension or external pack clamping.
Why Bond the Separator to the Electrode at All
The motivation is largely about the step that comes after lamination, not the bond itself. Alternating cathode/separator/anode stacking is inherently a slow, many-handling-step process, because each sheet has to be picked, placed and aligned without damaging brittle, ultra-thin material, and without letting cathode and anode material cross-contaminate each other’s handling path. Pre-bonding the separator to the electrodes turns two or three loose layers into one mechanically resilient unit that can be fed, cut and stacked (or Z-folded, see Stacking) as a single continuous roll-to-roll process, removing handling steps and the contamination risk that comes with them.[1]
LG Energy Solutions call the simple stacked unit a mono-cell:
The mono-cell is the basic unit cell of a battery, consisting of an electrode and two separators. It features a stacked structure in the form of “separator–central electrode–separator–outer electrode.
LG Energy Solutions
PVDF Adhesive Chemistry
The industry-standard lamination coating is a water-based polyvinylidene fluoride (PVDF) layer applied as spherical nanoparticles, typically quoted by coating suppliers in the 100–150 nm diameter range at a total coating thickness of 0.1–0.5 µm.[2] That spherical-particle structure is a deliberate departure from older organic-solvent PVDF coatings, which dissolve the polymer into a continuous, sponge-like film with an uneven pore structure. With water-based processing the particles stay discrete and simply pack against each other. So the gaps between spheres, rather than a solvent-cast pore network, become the ionic transport channels once the cell is filled. On heating, the PVDF particles soften enough to key into the electrode surface; once the dry cell is later filled with electrolyte, the same particles swell into a conductive gelled interface that reinforces the bond without materially blocking ion transport, provided the coating stays thin and porous rather than fusing into a continuous film (see the process window below).
The Process Window: Temperature, Pressure and Feed Rate
This is the part of lamination with genuinely solid published data behind it. Leithoff et al. ran a controlled study across three separator types using a heated-roller laminator, and the results make the trade-off concrete rather than abstract.[1]
Lamination temperature was varied from 60°C to 150°C and contact pressure from roughly 4 to 7 N/mm² (up to 30 N/mm² is achievable with rigid, non-elastomer rollers). How much headroom a separator has within that range depends heavily on its construction: a nonwoven, ceramic-impregnated separator in the study showed no measurable optical change anywhere across 60–150°C, while a PE/PP trilayer separator needed at least 80°C to bond at all, stayed stable up to about 120°C, and degraded sharply above 130°C. In other words, “the right lamination temperature” is separator-specific, not a single universal number.
More importantly, the study linked those process parameters directly to electrochemical outcome. Cells built with cathode–separator laminates produced at moderate settings (80–100°C, 10–20 N/mm²) showed discharge capacity statistically indistinguishable from an unlaminated reference after 300 cycles. In several parameter pairings laminated cells actually out-performed the unlaminated reference at higher C-rates, plausibly because the bonded interface improves ionic contact at the electrode-separator boundary. Push the parameters too far though, 120°C combined with 30 N/mm² was the worst case tested, and discharge capacity after 300 cycles dropped to roughly 60% of the reference, consistent with pore collapse in the separator raising ionic tortuosity. The practical takeaway: correctly-tuned lamination is not a compromise against an unlaminated stack, an incorrectly-tuned one is.
Inline Quality Control
Two inline-capable methods for checking laminate quality without destructive testing came out of the same study[1]:
- Grey-scale reflectance imaging. Thin separators are translucent enough that the darker electrode surface underneath shows through, and a monochrome camera system can quantify that as a grey value. Because thermal or pressure damage changes the separator’s optical transparency, the grey value tracks lamination quality in near-real time in the study, a trilayer separator’s grey value held steady around 120 across its usable 80–120°C window and fell toward 85 once lamination pushed past 130°C, giving a numeric, camera-readable proxy for “has this laminate been over-processed.”
- High-potential (hipot) testing. Before the laminate goes further downstream, a high DC voltage (400 V for one second, in the referenced methodology) is applied across the laminate stack. An intact separator holds that voltage with no discharge; a puncture, wrinkle or embedded particle shows up as a voltage collapse. This is worth distinguishing from the cell-level HiPot/isolation test already covered on the Cell Assembly page under Canning as that is a full-cell check at the very end of assembly, whereas this is an earlier, laminate-level gate that catches a bad separator before it’s built into a stack at all.
Alternative Bonding Approaches
Full-surface PVDF coating isn’t the only way to bond a separator, and coating the whole surface has a real downside: it blocks micropores across the entire laminate and slows electrolyte filling. Several alternatives address that directly:
- Patterned/discontinuous adhesive — rather than a continuous coating, adhesive is printed or sprayed as dots or striped patterns, leaving open channels that pull electrolyte in by capillary action while still providing a mechanically continuous bond.
- Crosslinked polymer interlayers — a thermosetting polymer is printed on the separator (rather than the thermoplastic PVDF above), heated to flow into the electrode’s pore structure, and then crosslinked in place. One example described in patent CA2306360A1 bonds the electrode-separator-electrode stack only at discontinuous points across the laminate surface using a crosslinked polymer, which the patent describes as giving strong adhesion even with separator materials that are otherwise difficult to bond, without leaving unwanted solvent residue, and allowing fast electrolyte impregnation even through a multi-layer laminate.
- Electrospun fibre bonding — used mainly with ceramic-coated (safety-reinforced) separators, where a sprayed or electrospun web of thermoplastic fibres provides adhesion without compromising the ceramic coating’s own thermal-shrinkage resistance.
References
- Leithoff, R.; Fröhlich, A.; Masuch, S.; Ventura Silva, G.; Dröder, K. Process-Product Interdependencies in Lamination of Electrodes and Separators for Lithium-Ion Batteries. Energies 2022, 15(7), 2670.
- Zheflon / Flurine PVDF: Lithium-ion battery requirements for separator materials (manufacturer coating specification, not independently verified).
- Daniele Versaci, Silvio Fugattini, Michele Serri, Andrea Moselli, Julia Amici, Silvia Bodoardo, The role of lamination conditions on the electrochemical behaviour of NMC811/graphite cells, Journal of Energy Storage, Volume 137, 2025
- How to Make a Battery STEP.2 – Cell Assembly: Pouch-Type Battery, LG Energy Solutions
- US20150033547A1, Electrode assembly manufacturing method including separator cutting process, LG Energy Solutions
See also: Winding, Stacking, Cell Assembly