Background
Maxell, Ltd. holds U.S. Patent No. 9,077,035, directed to a rechargeable lithium-ion battery. The patent’s claims specified a cathode material using a Markush group — a common patent drafting technique listing alternatives — that defined a transition metal element M1 as “selected from Co [cobalt], Ni [nickel] and Mn [manganese].” Under this formulation, cobalt was one option among three; a compound containing only nickel or only manganese would satisfy the claim.
A separate limitation within the same claim then required that “the content of Co in the transition metal M1 … is from 30% by mole to 100% by mole” — meaning the compound must contain cobalt in a specified amount. Amperex Technology Limited, a battery manufacturer accused of infringement, argued that these two limitations were irreconcilably contradictory: the first makes cobalt optional; the second makes cobalt mandatory. The district court agreed, held the claims indefinite under 35 U.S.C. § 112, and entered judgment for Amperex. Maxell appealed.
The Court’s Holding
The Federal Circuit reversed. The court applied the indefiniteness standard from Nautilus, Inc. v. Biosig Instruments, Inc., which asks whether the claims, read in light of the specification and prosecution history, inform a skilled artisan about the scope of the invention with reasonable certainty. The court held that two limitations are not contradictory — and therefore not indefinite — if both can be satisfied simultaneously by the same compound.
The court reasoned that a compound could satisfy both limitations at once: it could contain cobalt as one of its transition metal elements (satisfying the Markush group limitation, since cobalt is one of the listed options) while also containing cobalt in the required 30-100 mole percent range (satisfying the cobalt-content limitation). Rather than creating a contradiction, the cobalt-content limitation simply narrows the Markush group to only those variants that include cobalt — it eliminates the cobalt-free options from the broader claim. This type of narrowing is a common and well-understood patent drafting technique; it does not render a claim indefinite merely because it restricts a broader limitation to a subset of its alternatives.
Key Takeaways
- Two claim limitations are not contradictory — and do not render a claim indefinite — if both can be satisfied simultaneously by the same product or process.
- A narrowing limitation that restricts a Markush group (or other set of alternatives) to a specific subset does not create an irreconcilable contradiction; it simply defines the claim more narrowly.
- The indefiniteness inquiry asks whether a skilled artisan can determine the claim’s scope with reasonable certainty — mere analytical complexity or the need to reconcile two limitations does not meet the high bar for indefiniteness.
- Patent drafters should be aware that combining a broad Markush group with a narrowing limitation is generally permissible; courts will read the limitations together to identify the overlapping subset, not declare the claim invalid.
Why It Matters
Maxell v. Amperex Technology clarifies an important aspect of indefiniteness doctrine: courts should not use indefiniteness as a mechanism to invalidate claims simply because two limitations require some interpretive work to reconcile. The decision is particularly relevant for chemistry and materials patents, where Markush groups are ubiquitous. Patent claims covering alternative chemical compositions — alloys, polymers, pharmaceutical compounds — routinely use broad alternative groups in one limitation and narrowing constraints in another. This ruling confirms that such drafting is legally sound as long as the limitations are jointly satisfiable.
For battery, materials science, and chemical patent holders, the decision provides reassurance that claims using Markush groups combined with compositional range limitations will not automatically be deemed indefinite by accused infringers invoking apparent contradictions. The key question is always whether a skilled artisan can identify at least one scenario in which both limitations are satisfied simultaneously.