① What’s the Story
CATL has staked out another notable position on the all-solid-state battery patent map with an international patent aimed at mitigating the chronic weakness of sulfide solid electrolytes — “capacity fade at high temperature” — using only cathode surface treatment. This patent (publication number WO2026045270A1), published on March 5, 2026, was disclosed as an international application through the World Intellectual Property Organization (WIPO), with CATL (Contemporary Amperex Technology Co., Limited) as the applicant.
Looking at the industry situation, sulfide solid electrolytes are considered a strong candidate for all-solid-state batteries because of their high ionic conductivity, but they have continued to be held back by a problem: when in contact with the cathode active material, they undergo a decomposition reaction at high temperature that causes capacity to fall rapidly. This is where the tension arises — whether this problem is solved by “changing the electrolyte material itself” or by “treating only the cathode surface” completely changes the layer at which a patent’s claims sit, which in turn directly affects the room later entrants have for design-around strategies.
The question this article sets out to answer: exactly what does WO2026045270A1’s claims protect, and where, within this scope of claims, is the room for competitors and later entrants to maneuver in their designs?
② Basic Principle — The Idea of a “Coating Layer That Decomposes First”
The idea behind this patent, put as an analogy, is similar to inserting a sheet of “paper that melts first and becomes a thin protective film” between two materials (the cathode active material and the sulfide electrolyte) sitting on a hot frying pan (a high-temperature environment), to keep them from sticking together and burning. In CATL’s claim structure, the role of this “paper” is played by a fluorine-based electrolyte-salt coating layer. During charging, this coating layer decomposes before the sulfide electrolyte does, forming a stable film of lithium fluoride (LiF), and this film blocks direct side reactions between the cathode and the electrolyte.
Source: reconstructed by the editorial team from the claims of WO2026045270A1
One more feature is added on top of this. A “Co-rich (high-cobalt-content) interlayer,” with a higher cobalt content than the substrate, is first formed on the surface of the cathode active material substrate (a transition-metal oxide), which increases affinity and structural compatibility with the substrate and slows down the substrate’s own tendency to decompose the electrolyte. In other words, this patent is an approach that secures high-temperature stability through a dual-defense structure of “interlayer + coating layer.”
③ Comparison — Properties of the Coating Material Candidates Named in the Claims
| Candidate Coating Material | Chemical Formula/Name | Feature Stated in the Patent | Recommended Mass Fraction |
|---|---|---|---|
| Lithium difluorophosphate | Li2PO2F2 | Decomposes before the sulfide, forming LiF; favorable for securing ionic conductivity | 0.1-3 wt% |
| Lithium difluoro(oxalato)borate | LiDFOB | Low elastic modulus allows coating over a wide area | 0.1-3 wt% |
| Lithium difluoro bis(oxalato) phosphate | LiDFOP | Low elastic modulus, contributes to reducing side reactions | 0.1-3 wt% |
| Lithium tetrafluoro(oxalato)phosphate | LiTFOP | Low elastic modulus, stability at high temperature and high voltage | 0.1-3 wt% |
Source: paraphrased by the editorial team from WO2026045270A1 (Google Patents / WIPO Patentscope public records)
What This Table Tells Us: It stands out that, in the patent specification, all four candidate coating materials share the requirement of a “lower elastic modulus than the substrate” and a narrow mass-fraction range of “0.1-3 wt%.” In other words, there is room to interpret the patent’s substantive scope of protection as extending closer to the design principle itself of “thinly coating a low-elastic-modulus, fluorine-based electrolyte salt (at a mass fraction of 0.1-3%)” rather than protecting any single specific compound.
④ Patent Perspective — Claim Structure and Position Relative to Prior Art
Claim Summary (Claim 1 series): A cathode sheet comprising a cathode active material, on a cathode current collector, composed of (a) a transition-metal-oxide substrate, (b) a Co-rich (high-cobalt) interlayer on the substrate surface, and (c) an electrolyte-salt coating layer covering part of the interlayer surface, together with a sulfide solid electrolyte material. The dependent claims limit the coating material to a fluorine-based type (Claim 2 series), narrow it further to one or more of Li2PO2F2, LiDFOB, LiDFOP, and LiTFOP (Claim 3 series), and add numerical limitations on the coating-layer coverage (90-100% of the Co-rich layer’s surface) and the Co-rich layer’s thickness (0.5-50 nm).
Filing History: This international application (PCT/CN2025/086345) claims priority from a Chinese patent (CN202411215789.2) filed on August 30, 2024, was filed internationally on March 31, 2025, and was published as WO2026045270A1 on March 5, 2026. According to Google Patents, its current legal status is “Pending,” with national-phase entry and examination in individual countries currently underway.
Points to Note When Reviewing FTO (Freedom to Operate): This patent’s scope of claims is concentrated on the “surface structure design” of the cathode active material, which places it at a different claim layer from patents that claim the composition or crystal structure of the sulfide solid electrolyte material itself (for example, Toyota’s granted patent US10333170B2, priority date 2015-02-25, which claims the material itself — a Li-Si-P-S-based composition given a specific XRD crystalline phase).
A cross-check indicates the two patents do not appear to directly contest the same claim elements, but if an actual product simultaneously implements a “sulfide electrolyte of a specific crystalline phase + a Co-rich interlayer/fluorine-based coated cathode,” separate licensing review may be needed for both the cathode-side patent and the electrolyte-side patent. It should also be noted that this field has numerous other adjacent patents, such as EP4579845A4 (Sulfide-based solid electrolyte, priority date 2023-02-17), meaning the patent density itself in the sulfide-solid-electrolyte cathode/electrolyte interface area is fairly high.
Design-Around Scenario (Counterargument): If a later entrant wanted to avoid this patent’s scope of claims, a few directions could be considered. First, replacing the coating material with a family other than fluorine-based (for example, an oxide-based buffer layer) to fall outside the dependent claims’ material limitation. However, if the independent claim itself is broadly claimed at the higher-level concept of an “electrolyte-salt coating layer,” changing only the material may still leave a risk of infringing the independent claim.
Second, omitting the Co-rich interlayer and using only the coating layer, or conversely designing the interlayer’s cobalt-content gradient differently so as to omit one of the claim elements entirely — since patent claims generally require all elements to be met for infringement to be established (the all-elements rule), a design that intentionally excludes one element could potentially be a valid design-around strategy.
That said, this can only be confirmed by cross-checking against the exact wording of the finally granted claims together with prosecution history estoppel (the legal principle that a scope of claims narrowed during prosecution cannot later be asserted broadly again), and since examination is still ongoing, the claims themselves remain in flux for now.
⑤ Limitations and Outlook
The optimistic direction this patent suggests is that CATL is building a tight defensive line at the material level (stabilizing the cathode-electrolyte interface) with an eye toward moving beyond the 20 Ah sample stage to mass production of 60 Ah-class automotive cells. However, the opposing scenario must also be noted — this patent is aimed only at one specific failure mode, “improving the rate of capacity fade at high temperature,” and it is difficult to view it as solving the other challenges standing in the way of all-solid-state battery commercialization (high-pressure design for interface compaction, yield in large-area coating processes, cost). Even if the patent is granted, that does not guarantee the technology will actually be incorporated into mass-produced cells and translate into commercial success.
As a strategic alternative, until this patent’s scope of claims is finally settled, domestic material companies and cell makers may want to consider building their own patent portfolio in parallel around a different interface-stabilization approach that does not use the Co-rich interlayer method (for example, adjusting the electrolyte’s own composition without a separate buffer coating layer), so as to secure room to respond whether this patent is ultimately granted narrowly or broadly.
Action Item: Planning and IP staff are advised to track, on a quarterly basis via KIPRIS, USPTO Public PAIR, and Espacenet, whether WO2026045270A1 enters the national phase (Korea, the U.S., Europe, etc.) and how examination is progressing, and to check in advance whether their own cathode-coating R&D overlaps with this patent’s dependent-claim limitations (coating material type, mass fraction of 0.1-3%, coverage of 90-100%, Co-rich layer thickness of 0.5-50 nm).
This article was written after directly reviewing the original patent documents published on Google Patents and WIPO Patentscope, and it does not constitute a definitive conclusion regarding patent grant prospects or infringement. Specific determinations of infringement or design-around validity should always go through a claim-by-claim review by a qualified professional such as a patent attorney.