Hard carbon is a non-graphitizable, turbostratic carbon that stores lithium or sodium ions differently from ordered graphite, including a distinct plateau-capacity region at low voltage. Because its performance depends heavily on precursor chemistry and the resulting pore structure and interlayer spacing, patent claims in this space tend to center on processing parameters and measurable structural metrics rather than the base carbon chemistry itself. This is why IPC classification splits across H01M (battery construction) and C01B (the inorganic material itself) rather than sitting in one subclass.

The corpus shows a concentration among Chinese universities, a major battery cell maker, and a recycling group filing through multiple related entities. No single assignee dominates outright; the pattern is closer to a crowded upper tier than one clear leader, and recent-year filing momentum has turned negative for the most active filers tracked here. Anyone assessing freedom to operate should check both the cell-maker filings and the recycler's precursor claims, since they occupy different points in the value chain.

Filings climbed from 7 in 2017 to a peak of 132 in 2025 before falling to 22 in the partial 2026 count, but that drop is largely an artefact of publication lag: patent applications typically publish roughly 18 months after filing, so 2026 figures will keep rising as later filings become visible. The more meaningful signal is that growth already flattened once around the 2022 midpoint of 51 filings, and recent-year momentum by assignee is negative across every major filer tracked, which points to a filing wave that has already crested rather than a technology still in early growth.

Relative to the dense core claims on pore structure, precursor carbonization and coulombic efficiency, several adjacent IPC subclasses show thin filing activity: capacitor-grade hard carbon under H01G, nanostructured composites under B82Y, and precursor routes drawing from ceramics (C04B) or destructive distillation (C10B). These are not empty spaces — each has a handful of filings — but they are thin enough that a well-specified first claim tied to a novel precursor or measurable structural parameter in one of these branches would face far less crowded prior art than a general pore-structure claim.

Yes: 363 of the 463 families in this corpus were filed at China's receiving office, compared with 35 in the United States, 22 at the EPO, 17 in India and 16 via the WIPO PCT route. That concentration reflects both the scale of Chinese battery manufacturing and the presence of major domestic filers including universities and a large recycling group. A search strategy focused only on US or EPO filings would miss the majority of the documented prior art in this material class.