Federal Circuit Affirms USPTO Ruling Against Multilayer Porous Separator Film Patent

Introduction

The U.S. Court of Appeals for the Federal Circuit has affirmed a USPTO ruling invalidating a patent application for multilayer porous separator film technology, closing a significant chapter in a dispute that pits an independent inventor against the nation’s top intellectual property authority. In In re: Kwangjin Song (Case No. 25-1705), the Federal Circuit upheld the USPTO Director’s position that the subject invention failed to meet patentability requirements — a decision with meaningful implications for battery technology innovators, materials scientists, and patent practitioners navigating the increasingly competitive energy storage patent landscape.

Filed on April 29, 2025, and resolved on February 18, 2026, this appeal underscores the formidable challenges independent inventors face when contesting USPTO rejections at the appellate level. For IP professionals tracking multilayer porous separator film patent litigation and energy storage technology patent trends, this case offers critical procedural and strategic lessons worth careful examination.

Case Overview

The Parties

The Patent at Issue

This appeal involved a patent application covering fundamental battery separator film technology:

• • Application No. US18/199940 (Publication No. US20240047826A1) — Multilayer Porous Separator Film

Multilayer porous separator films serve as critical safety and performance components in battery cells, preventing electrode short-circuits while enabling ionic transport. Patent claims in this space typically involve specific layer compositions, porosity characteristics, and manufacturing methods — each of which represents a potential point of patentability challenge under §102 (novelty) or §103 (obviousness) of the Patent Act.

Legal Representation

Song appeared pro se as his own agent, while Liso Plastics LLC served as the plaintiff law firm of record. The USPTO fielded a robust legal team, including Dr. Mary L. Kelly, whose scientific credentials likely proved valuable in analyzing the technical merits of the separator film claims.

Litigation Timeline & Procedural History

The appeal was filed in the District of Columbia circuit jurisdiction and adjudicated by the Court of Appeals for the Federal Circuit — the exclusive appellate forum for USPTO patent matters under 28 U.S.C. § 1295. The 295-day resolution timeline falls within the Federal Circuit’s typical processing range for ex parte patent appeals, suggesting no unusual procedural complications or en banc considerations arose.

The case’s appellate posture indicates that Song had already exhausted administrative remedies before the Patent Trial and Appeal Board (PTAB) prior to seeking Federal Circuit review — a prerequisite path that filters appeals to only those inventors most committed to defending their claimed inventions. The absence of any noted district court trial-level proceedings confirms this was a pure patent prosecution appeal rather than an infringement dispute.

The Verdict & Legal Analysis

Outcome

The Federal Circuit issued a clear and unambiguous disposition: **AFFIRMED**. The court upheld the USPTO’s underlying patentability determination against Kwangjin Song’s application for the multilayer porous separator film invention. No damages were applicable in this context, as this was a patent prosecution appeal rather than an infringement action. No injunctive relief was at issue.

Verdict Cause Analysis

The verdict cause is classified as **Patentability / Invalidity-Cancellation Action**, indicating the USPTO’s rejection was grounded in substantive patentability deficiencies — most commonly §102 anticipation, §103 obviousness, or §112 written description/enablement failures in patent prosecution contexts.

When the Federal Circuit affirms a USPTO patentability rejection, it signals one of several findings:

• • **Obviousness under §103:** The claimed invention, though perhaps novel in its specific configuration, would have been obvious to a person of ordinary skill in the art (POSITA) given the prior art landscape — a particularly rigorous bar in competitive materials science fields like battery separators.
• • **Anticipation under §102:** One or more prior art references disclose each limitation of the claimed invention, destroying novelty.
• • **Claim Indefiniteness or Enablement Failures under §112:** The specification may have failed to adequately enable the full scope of claimed separator film configurations or describe the invention with sufficient particularity.

The USPTO’s deployment of Dr. Mary L. Kelly Ph.D. as a representative is notable — her scientific credentials suggest the agency mounted a technically sophisticated defense of its rejection, likely anchored in detailed prior art analysis of existing separator film technology.

Legal Significance

Federal Circuit affirmances of USPTO rejections in materials science and battery technology carry meaningful precedential weight. As global investment in solid-state batteries, EV power systems, and energy storage accelerates, the patent landscape for separator films is increasingly crowded with overlapping claims from major manufacturers including CATL, Panasonic, Celgard, and academic institutions.

This affirmance reinforces the principle that the Federal Circuit will defer to USPTO technical expertise when the agency’s patentability analysis is well-reasoned and grounded in the prior art record. For independent inventors and small entities like Liso Plastics LLC, it highlights the steep evidentiary burden required to overcome an examiner’s rejection at the appellate level.

Strategic Takeaways

For Patent Attorneys & Prosecutors:

• Build prosecution records with robust technical differentiation from prior art at the examination stage — reversing rejections on appeal is statistically challenging.
• Consider claim amendment strategies before PTAB appeal rather than pursuing Federal Circuit review, which historically affirms USPTO determinations in a majority of ex parte cases.
• Engage technical experts early when prosecuting materials science claims in highly competitive fields.

For IP Professionals & In-House Counsel:

• Monitor Federal Circuit ex parte appeal outcomes in the battery and materials technology sectors as competitive intelligence.
• Evaluate whether continuation applications or divisional strategies could preserve patent rights where primary claims face rejection.

For R&D Teams:

• Rejected applications still publish as prior art (US20240047826A1 is publicly available), providing competitive technical intelligence into Song’s multilayer porous separator film design approach.
• Freedom-to-operate (FTO) analyses should account for published-but-rejected applications, as continuation filings may resurrect similar claims with narrowed scope.

Industry & Competitive Implications

The multilayer porous separator film market is a critical upstream segment of the global lithium-ion battery supply chain, with applications spanning consumer electronics, electric vehicles, and grid-scale energy storage. The separator film segment alone represents billions in annual market value, making patent protection a high-stakes strategic objective.

This Federal Circuit affirmance signals that the USPTO is maintaining rigorous examination standards in this space — a pattern consistent with the agency’s effort to avoid issuing low-quality patents in emerging technology areas where prior art is expanding rapidly. For established separator film manufacturers and battery OEMs, this reinforces the importance of proactive prior art generation and publication as a defensive IP strategy.

For independent inventors and small companies like Liso Plastics LLC operating in technically complex, capital-intensive fields, this case illustrates the resource disparity inherent in challenging USPTO determinations against a well-staffed government legal team. Strategic partnerships with specialized patent counsel or academic institutions may help level this playing field in future prosecution efforts.

Licensing activity in the separator film space is expected to continue growing as battery technology patents become core assets in M&A due diligence and cross-licensing negotiations among major energy storage players.

Frequently Asked Questions

What patent was involved in In re: Kwangjin Song, Case No. 25-1705?

The case involved U.S. Patent Application No. US18/199940 (Publication No. US20240047826A1), directed to multilayer porous separator film technology.

What was the basis for the Federal Circuit’s affirmance?

The Federal Circuit affirmed the USPTO’s patentability determination, upholding a finding of invalidity or unpatentability under applicable sections of the Patent Act. Specific grounds were consistent with an Invalidity/Cancellation Action classification.

How might this ruling affect multilayer porous separator film patenting?

The decision reinforces USPTO examination authority in battery materials technology and signals that inventors must establish strong technical differentiation from prior art at the prosecution stage to successfully defend claims on appeal.