The dry electrode process is a next-generation electrode manufacturing method that eliminates the solvent-drying step entirely, cutting both capital equipment investment and energy costs, and it is an area where Tesla, LG Energy Solution, and Samsung SDI have each already been building up their own patent portfolios. SK On is no exception. In U.S. Patent US12199265B2 — filed starting from a May 2022 priority claim and granted in January 2025 — SK On pinned down a highly specific numerical range in its claims for the “compression ratio” of the gap between rolls.
The industry is trying to strike a balance between the expectation that dry electrodes will reduce capital investment and process time compared to wet processes, and the practical constraint that if the binder is not sufficiently fibrillated, cracks form in the sheet and hurt mass-production yield. Amid this tension, the patent SK On has secured is the result of answering, with numbers, the experimental question of “how much pressure is enough to avoid both cracking and tearing.”
This article seeks to answer two questions. First, how broad is this patent’s claim scope in practice? Second, where are the points at which a competitor could design around this patent?
① What’s the Story
This SK On patent (application number US18/321,222, Korean priority application 10-2022-0062784) was filed in the United States on May 22, 2023, and granted on January 14, 2025. The inventors are Jae Youn Kim, Yong Hee Kang, Young Jun Kim, and Dong Hoon Lee — four in total — and roughly one year and eight months elapsed from filing to grant. The expiration date is expected to be May 22, 2043, based on the filing date. The dry electrode process itself is already a competitive field that several cell makers have entered, but what makes this SK On patent interesting is that it quantifies the qualitative phenomenon of “degree of fibrillation” into an arithmetic formula based on roll gap, and turns that into claim language.
② Basic Principle
The wet electrode process mixes active material, binder, and conductive material into a slurry using a solvent (water or NMP), coats it onto the current collector, and then evaporates the solvent in a drying oven. The dry electrode process removes the solvent from this process altogether — rather than kneading a dough with water and drying it, it’s closer to pressing a powder dough directly with rollers to draw out noodles. Because the drying step disappears, equipment and energy costs are reduced, but in exchange, the binder must be “fibrillated” by roll pressure and heat alone to hold the particles together and maintain the sheet form.
Source: reconstructed by the editorial team from claim 1 of US12199265B2
SK On’s patent controls this fibrillation in two stages within a calender roll assembly made up of three or more rolls. The dry electrode composition is fed between two rolls set at a first gap (W1) to form a primary sheet, and this primary sheet is then fed between two rolls set at a second gap (W2) to form the final sheet. The difference between the two gaps is expressed as the “compression ratio,” defined by the following formula.
Compression ratio = (W1 − W2) / W1
The granted claims require this compression ratio to be between 0.10 and 0.27 inclusive (the published application US20230378422A1 claimed 0.10 to 0.65, a range that still appears in the granted patent’s abstract, and the specification gives 0.14 to 0.54 as an example range). If the compression ratio is too low, insufficient pressure leaves the binder inadequately fibrillated, weakening particle-to-particle bonding; if it is too high, excessive pressure causes cracking or tearing of the sheet.
③ Comparison: Sheet Properties by Compression Ratio (Specification Example Data)
| Category | Primary Gap W1 | Secondary Gap W2 | Compression Ratio | Tensile Strength | Surface Cracking |
|---|---|---|---|---|---|
| Example 1 | 300 µm | 260 µm | 0.14 | 0.71 N/mm² | None |
| Example 2 | 300 µm | 220 µm | 0.27 | 0.84 N/mm² | None |
| Comparative Example 1 | 300 µm | 280 µm | 0.07 | 0.31 N/mm² | Occurred |
| Comparative Example 2 | 300 µm | 140 µm | 0.54 | Not measurable (fracture) | Occurred |
Source: compiled by the editorial team from the example table in the specification of US12199265B2 (Google Patents)
What This Table Tells Us: At a compression ratio of 0.07 — below the claimed lower bound of 0.10 — tensile strength drops sharply to 0.31 N/mm² and cracking occurs, while at 0.54, the upper end of the specification’s example range (0.14 to 0.54), the sheet tore outright and could not be measured. The granted range of 0.10 to 0.27 includes the two crack-free examples (0.14 and 0.27) and excludes the torn comparative example (0.54), so the claim scope has been narrowed toward the experimentally confirmed “narrow window between cracking and tearing” (how it was narrowed from the published 0.10 to 0.65 requires a check of the prosecution history).
④ Patent Perspective
Claim Summary: Independent Claim 1 is a method claim comprising: (a) preparing a dry electrode composition containing an electrode active material and a binder; (b) feeding this composition directly into a calender roll assembly composed of three or more rolls; (c) feeding the composition between two adjacent rolls set at a first gap (W1) to obtain a primary electrode sheet; and (d) feeding the primary electrode sheet between two adjacent rolls set at a second gap (W2) to obtain the final dry electrode sheet, with the requirement that W1 and W2 satisfy a compression ratio of (W1−W2)/W1 = 0.10 to 0.27 and that the first, second and third rolls rotate at speeds V1<V2<V3 (V1:V2:V3 = 10:11–20:12–40).
The granted patent has 10 claims in total, and both independent claims (1 and 10) are method claims. The dependent claims further limit the calender roll temperature (40 to 200°C) and the type of binder (a fibrillatable binder such as PTFE). At the published-application stage (US20230378422A1), the 0.10-to-0.65 method claim sat alongside independent apparatus and electrode claims, and the speed condition was in a dependent claim.
Filing History: Korean priority filing date May 23, 2022 (10-2022-0062784) → U.S. filing date May 22, 2023 → publication November 23, 2023 (US20230378422A1) → grant January 14, 2025 (US12199265B2). SK On Co., Ltd. is the sole applicant and sole patentee.
Claim Scope Analysis: Claims that are limited by numerical ranges generally tend to be interpreted narrowly in terms of claim scope. Designing a compression ratio below 0.10 or above 0.27, departing from the three-roll speed condition, or simply not using the two-stage calendering structure at all, may avoid constituting literal infringement of this claim. That said, from the perspective of the doctrine of equivalents (the legal doctrine that treats a configuration as infringing if it has substantially the same function, way, and result even when it differs from the literal claim language), it should also be noted that if the compression ratio is extremely close to the claim boundary — such as 0.08 or 0.28 — the possibility of infringement cannot be entirely ruled out.
Design-Around Scenario (Counterargument): Two realistic paths for a competitor to design around this patent have been discussed. First, using a gradient rolling method that continuously varies the pressure within a single calender gap, rather than dividing the roll gap into two discrete stages (W1, W2), would lack the element of “calender rolls having two distinct gaps” altogether. Second, adopting an electrostatic dry coating method — in which powder is uniformly applied to the current collector using electrostatic force and then separately sintered and pressed, instead of roll calendering — would bypass the very process of “passing between calender rolls” that this claim presupposes. In fact, companies such as Dragonfly Energy have had this line of electrostatic dry coating patents separately recognized by the European Patent Office, which can be seen as circumstantial evidence that this design-around path is not merely theoretical.
⑤ Limitations and Outlook
An optimistic outlook is possible in which SK On stabilizes dry electrode yield early by transplanting this compression-ratio know-how into its pilot line. But there is also an opposing scenario. All of this patent’s granted claims are method claims, and verifying the actual roll gap and compression ratio inside a competitor’s line from the outside is realistically difficult. In other words, the claim scope a granted patent holds on paper and the ability to actually enforce it in the market are separate matters. If, even where infringement is suspected, there is no adequate way to prove the roll settings inside the other party’s factory, the practical deterrent effect of this patent may be lower than its scope on paper suggests.
Strategic Alternative: From SK On’s standpoint, rather than the numerical compression-ratio range itself, it may be more advantageous for securing enforceability to reinforce this with a follow-on application for an inline-sensor-based method that can measure and verify the ratio on an actual mass-production line (for example, a method that estimates the compression ratio by back-calculating it in real time from sheet thickness or density). This is because a measurable claim makes proving infringement correspondingly easier.
The practical action this article leaves for IP and planning personnel is as follows: first check, against your own company’s in-house process data, whether the number of calender roll stages and the gap-control logic on your dry electrode line correspond one-to-one with this patent’s elements — three or more rolls, discrete two-stage gaps (W1, W2), a compression ratio of 0.10 to 0.27, and the V1<V2<V3 speed condition.
※ The patent description in this article is a restatement based on direct review of the original US12199265B2 text as published on Google Patents (claims, specification, and example tables), and does not reproduce the full text of the patent claims or drawings verbatim. Final determinations regarding the validity of the patent’s registration or infringement/non-infringement require expert legal review of the specific case, and this article is intended for general informational purposes only.