In July 2025, Tesla published international application WO2025015194A1, a patent covering the manufacturing process for lithium iron phosphate (LFP) cathode material. Running over 100 pages, it contains cathode-powder manufacturing know-how for the LFP version of the 4680 cell. LFP cost competitiveness has until now been the domain almost exclusively of Chinese battery makers such as CATL and BYD — Tesla has effectively jumped head-on into this territory.
What makes this patent interesting is that it addresses not cell design, but the seemingly mundane process question of ‘how to make the powder.’ Yet a significant share of LFP cost is decided precisely in this calcination process.
The Basic Mechanism — Working Around the Fine-Powder Problem with Recirculation
Making LFP involves mixing an iron source, a lithium source, a phosphorus source, and a carbon source into a slurry, granulating it via spray drying, and then calcining it in a high-temperature furnace to complete the crystal structure. The problem is that the initial particles formed right after spray drying are typically very fine, on the order of D50 1–5 micrometers. Such fine powder creates dusting problems and is difficult to handle in low-cost continuous furnaces (such as rotary kilns) that carry particles directly on a conveyor without a crucible. As a result, the industry has generally opted for batch furnaces that use crucibles, which have low throughput and high equipment costs.
Tesla’s solution is simple but effective. Instead of sending the initial particles straight to the calcination furnace, the process mixes them back with the raw material mixture inside the chamber and recirculates them, agglomerating them into larger subsequent particles (D50 in the range of hundreds of micrometers to several millimeters) before calcination. Once the particles are larger, the fine-dust problem disappears, and low-cost, crucible-free continuous furnaces (rotary kilns, roller hearth kilns, and the like) can be used as-is.
Source: editorial conceptual diagram reconstructed from the claim structure of WO2025015194A1 (not a reproduction of the original patent drawings or text).
Comparison — Conventional Wet Process vs. Tesla’s Recirculation Process
| Category | Conventional Spray-Drying + Batch Calcination | Tesla Recirculation Process (WO2025015194A1) |
|---|---|---|
| Initial particle size (D50) | 1–5μm (generates fine dust) | Forms the same way but absorbed via recirculation |
| Particle size fed to calcination | Fine powder as-is | D50 hundreds of μm to several mm (after recirculation) |
| Furnace required | Crucible-containing batch furnace (high cost) | No crucible needed, continuous kiln possible |
| Process safety | Dust-explosion/inhalation risk management required | Dust-free process |
| Fe incorporation in Li channel (Fe_Li%) | ~1.5–2% (comparative example) | ~0.8–0.9% (working example) |
Patent Perspective — The Core of the Claims
The independent claim of WO2025015194A1 is characterized by the following process: ① mixing an iron source, a lithium source, and a carbon source to form an initial mixture; ② forming initial particles within a chamber; ③ recirculating these back into the chamber ‘concurrently’ with the formation of the initial particles to form subsequent particles; and ④ calcining the subsequent particles to complete the LFP. A separate claim pins down, as part of the claim scope, the physical properties of the LFP particles produced by this process — a D50 range of 30μm to several millimeters, and an iron-incorporation rate in the lithium channel (Fe_Li%) below 2%. There is also a separate device claim covering the calcination furnace itself, protecting the equipment through language describing a furnace configured to process particles of D50 5μm or larger without a crucible.
Source: editorial reconstruction based on the gist of the WO2025015194A1 claims (not a verbatim reproduction of the original claim language).
What stands out is that the patent explicitly states this process applies equally to other cathode materials, not just LFP — including NMC and LMO. The working examples even include a case of compacting and recirculating NMC811 precursor with a roller compactor before sintering, showing that Tesla designed this recirculation process itself as a general-purpose cathode-material manufacturing platform.
Limits and Outlook
How much this patent will actually lower mass-production cost remains to be verified. A recirculation loop also means more process control is needed, so whether lab-scale success translates directly into Gigafactory-scale continuous production remains to be seen. That said, the fact that Tesla went to the trouble of protecting the calcination furnace itself with a separate device claim reads as a sign of the company’s intent to tightly fill out its own value chain, not just in cell design but down to the materials and equipment level. It’s a signal that the low-cost LFP competition arena may no longer be the exclusive domain of Chinese companies alone.