① What’s the Story
One problem that had long gone unsolved in the secondary-battery electrode-coating process was this: “Can two different slurries be coated simultaneously, at high speed, and layered on top of each other without a thickness variance?” As double-layer electrode structures — where active-material composition varies by position, as with silicon anode materials or nickel-rich cathode materials — have become more common, this coating-uniformity problem has turned into a bottleneck directly tied to yield. LG Energy Solution’s U.S. patent application US20250375790A1 (“Dual Slot-Die Coater and Electrode Active-Material Slurry Coating Method Using the Same”), published on December 11, 2025, takes direct aim at exactly this point.
The industry has often addressed double-layer electrode coating by placing two single slot dies in sequence, or by mixing in a comma-coating approach. But these methods have the drawback of a larger equipment footprint and more process steps. The question this patent sets out to answer is clear: “If only the shape of the two slots within a single die head is designed differently, can a uniform double layer be produced without sequential coating?”
② Basic Principle
Slot-die coating is an extrusion-coating method that pushes slurry at constant pressure through a narrow gap (slot) to form a thin film on the surface of the current collector. The core idea of this patent is to stack the die in three tiers — a lower plate, a middle plate, and an upper plate — creating two slots, a lower slot and an upper slot, between them, and to design the thickness of the “die lip” at the end of each plate differently from the others.
An analogy: it is similar to shaving the rim height of each tier of a three-tier cake mold by a slightly different amount, so that two kinds of cream can be piped out at the same time without mixing, forming clean, distinct layers top and bottom. Per the claim, the lower die lip is designed to be thicker than the middle and upper die lips, and this thickness difference serves to stabilize the flow so that the slurry does not back up or mix.
Source: reconstructed by the editorial team from the description in publication US20250375790A1
③ Comparison: Structure and Characteristics by Coating Method
| Category | Single Slot-Die Sequential Coating | Comma Coating | US20250375790A1 (Dual Slot-Die) |
|---|---|---|---|
| Layer-forming method | First coat, then dry, then apply the second coat in sequence | Thickness controlled by the gap between roll and blade | Simultaneous extrusion of a double-layer slurry from a single die |
| Equipment footprint | Large (requires two drying-oven passes) | Medium | Relatively small (single die head) |
| Thickness-uniformity control | Registration error between process steps possible | Shear-force dependent, favorable for low-viscosity slurry | Inter-layer mixing suppressed by the differentiated die-lip thickness design (claim element) |
| Publication/filing info | Industry-generic process | Industry-generic process | Published December 11, 2025; applicant LG Energy Solution Ltd; a continuing (divisional) application; priority claim KR10-2020-0119919 (filed September 17, 2020) |
Source: compiled by the editorial team from the bibliographic data and description of US20250375790A1 (Google Patents) and general industry process descriptions
What this table shows: this patent’s point of differentiation is not a new coating principle, but the fact that it fixes a specific structural parameter — the “die-lip thickness ratio” — as a claim element; this targets a middle ground that reduces equipment footprint compared to sequential coating or comma coating, while still suppressing inter-layer mixing.
④ Patent Perspective — Claim Element Mapping
Per the published patent application, independent Claim 1 is a method claim asserting “a method of forming an electrode active-material slurry layer while moving the current collector from the lower die lip toward the upper die lip, using a dual slot-die coater having a lower slot and an upper slot,” and it specifies as claim elements the lower-plate/middle-plate/upper-plate structure and the numerical relationship “lower die-lip thickness > upper die-lip thickness, lower die-lip thickness > middle die-lip thickness.” Dependent Claim 4 goes further, extending the scope of rights to a method of simultaneously extrusion-coating multiple electrode active-material slurries through the lower and upper slots.
| Claim Element | Comparison Target: Conventional Single Slot-Die Structure | Infringement-Exposure Assessment Point |
|---|---|---|
| Lower/middle/upper 3-tier plate structure | Typically an upper/lower 2-tier plate (single-slot) structure | Without the 3-tier structure itself, literal infringement is difficult to establish |
| Formation of two slots — a lower slot and an upper slot | A single slot | Equipment with only one slot can support a non-infringement argument on grounds of a missing claim element |
| Lower die-lip thickness > middle/upper die-lip thickness | A uniform die-lip thickness design is typical | If the thickness relationship is reversed or equal, a Doctrine-of-Equivalents review is needed; literal infringement is difficult |
| Simultaneous extrusion of multiple slurries (dependent Claim 4) | Sequential coating of a single slurry | Room for a design-around if the “simultaneous” requirement is not met |
Source: paraphrased by the editorial team from publication US20250375790A1 (claim-number mapping to be verified)
Design-around scenario (counter-argument): a structure that designs the lower, middle, and upper die-lip thicknesses all equal, or, conversely, makes the upper die lip the thickest, may avoid literal infringement, since it would not satisfy the claim-language element that “the lower die lip is the thickest.” That said, if the thickness difference functionally produces the same effect — preventing slurry backflow — a Doctrine-of-Equivalents determination could follow; a design-around effort would therefore do better to change not just the thickness relationship but the flow-control mechanism itself (for example, by inserting a separate partition wall, or a pressure-differential valve between slots).
⑤ Limitations and Outlook
This patent is a continuing (divisional) application published in December 2025, and its examination status is “Pending.” In other words, whether it will ultimately be granted, and the scope of its claims, remain subject to amendment during examination, and there is no guarantee it will be granted exactly as currently claimed. As a counter-scenario to the optimistic outlook, the die-lip thickness-relationship claim could be narrowed by amendment or rejected during examination on the basis of prior art — the multi-tier plate structure of a slot-die head is itself a concept that already exists in several prior patents (for example, prior-art documents related to slot-die coating such as KR102301210B1).
As a strategic alternative, a competitor could pursue a two-track strategy: continuously monitoring this patent family’s prosecution history (File Wrapper) while holding off on adopting a similar structure until grant is confirmed, or designing the die-lip thickness ratio to fall outside the claim’s threshold.
One practical action for planning and IP staff: obtain your own coating equipment’s die-lip thickness specification drawings, cross-check them 1:1 against the elements of Claims 1 and 4 of this patent, and if there is overlap, recommend prioritizing a formal FTO (freedom-to-operate) inquiry.
Note: This analysis restates content set out in the published patent application (US20250375790A1) and does not reproduce the original patent text or drawings verbatim. Assessments of examination outcome, likelihood of grant, and infringement are presented as possibilities, not confirmed facts, and any actual legal determination requires separate expert review.