A Carnot battery stores electrical energy by converting it to heat — typically via a reversible heat pump or resistive heating — and holds that heat in a storage medium until it is needed. On discharge, a thermodynamic cycle such as a Brayton or steam cycle converts the stored heat back into electricity. Unlike electrochemical batteries, there is no chemical energy storage involved; the round-trip efficiency depends heavily on the temperature lift achieved during charging and the working fluid used in the discharge cycle. The patent record shows most designs building on established steam and gas-turbine hardware rather than proposing entirely new cycle types.

The assignee ranking for this field covers 32 companies and research organisations, and it is heavily front-loaded: the top-ranked assignee alone holds 156 of the 234 records in scope, and the top 5 combined account for 85.5% of the entire corpus. This is a genuinely concentrated field rather than one with many comparably sized competitors. Anyone assessing freedom to operate should start with that leading portfolio before broadening the search.

Filing activity in this dataset peaked at 74 records in 2017 and has trended down since, falling from 23 in 2021 to 14 in 2024 — a 39% drop over that span. This pattern is consistent with an early wave of foundational filing by a small number of players followed by a period of narrower, incremental patenting rather than broad new claims. The 2025 and 2026 figures should be read cautiously, since publication typically lags actual filing by around 18 months and those years are still filling in.