What makes graphite battery grade, and how a new source gets qualified

How graphite stores lithium

Graphite is made of flat sheets of carbon atoms in a hexagonal pattern, stacked 0.335 nanometres apart. When a lithium-ion cell charges, lithium ions travel from the cathode, slip between those sheets and take up positions in the gaps. This is called intercalation. The layers move slightly apart, by about 10% at full charge, and lithium fills them in a series of ordered stages. At full lithiation every six carbon atoms hold one lithium atom, the compound LiC₆ (Asenbauer et al., 2020).

From that ratio follows the theoretical capacity: 372 milliampere-hours per gram of graphite. Commercial anode materials reach 350 to 365 mAh/g in practice, and many cell makers accept natural graphite only above 350 mAh/g (Evolution Energy Minerals). Because lithium sits in graphite at a potential only about 0.1 volts above lithium metal, the cell keeps a high voltage, which is why graphite has been the standard anode for three decades.

The first charge costs lithium

The electrolyte in a lithium-ion cell is not stable at the low potential of a charged graphite anode. On the very first charge, a thin layer of electrolyte decomposes on the graphite surface and forms a film, the solid electrolyte interphase or SEI (Peled, 1979). Once formed, this film lets lithium ions pass but blocks further electrolyte breakdown. It is what makes graphite usable at all: only after ethylene carbonate electrolytes were found to form a stable SEI in 1990 did graphite anodes become practical.

The price is lithium. The lithium built into the SEI never comes back, so the first discharge returns less than the first charge put in. The ratio between them is the first-cycle efficiency. Premium anode materials lose less than about 7% on the first cycle, so they reach about 93% or more (same source).

How much lithium is lost depends on the surface the electrolyte can reach. A classic study showed that the first-cycle loss grows with the graphite's BET surface area, and especially with the share of edge surfaces where the carbon layers end, because that is where most side reactions occur (Winter, Novák and Monnier, 1998). That is why battery graphite is rounded, sized and often coated with a thin layer of amorphous carbon: to keep the accessible surface small.

What buyers check

Purity. Anode graphite is usually specified at 99.95% carbon or higher, with trace metals listed in parts per million. Iron, copper, nickel and zinc are the main concern: they can dissolve, migrate and redeposit as metal inside the cell, which raises self-discharge and, in the worst case, causes internal short circuits.

Particle size distribution. Quoted as D10, D50 and D90, the sizes below which 10%, 50% and 90% of particles fall. A D50 between about 10 and 20 micrometres is common. Fine particles add surface area and therefore first-cycle loss; coarse particles slow down charging because lithium has further to travel.

Shape and packing. Natural graphite flakes are rounded into near-spherical particles so they pack densely and accept lithium from all sides. Buyers look at tap density and at electron microscope images.

Specific surface area. Measured by nitrogen adsorption (BET) in square metres per gram. Typical anode graphite sits at a few m²/g. As explained above, this number predicts much of the first-cycle loss.

Electrochemistry. Capacity and first-cycle efficiency in a half cell against lithium metal, then capacity retention, rate capability and swelling in full cells over hundreds or thousands of cycles.

What is different about recycled graphite

Graphite recovered from black mass has had a working life. Its particles may carry remains of the SEI, residues of binder and electrolyte salt, traces of cathode metals and copper, and some structural damage at the edges. A recovery process has to remove all of these and restore a clean, low-surface material, then prove it with the same data as any other supplier. Research shows that recovered graphite can reach capacities close to new material when purification is thorough (Chernyaev et al., 2024; Asenbauer et al., 2020).

How qualification works

No cell maker switches material on the strength of a data sheet. A new source moves through a series of stages, each needing more material and more consistency than the one before.

1. Data sheet. Powder properties and half-cell results are compared with the current specification.
2. Lab sample. Grams to kilograms. The buyer repeats the measurements and builds coin cells.
3. A-sample. Proof of concept in small pouch cells: cycle life, fast charging, storage at high temperature. Tens of kilograms.
4. B-sample. Cells in the final format on a pilot line, with batch-to-batch consistency. Hundreds of kilograms or more.
5. C-sample. Material from the final process on production-intent equipment, often with an audit of the supplier's plant, quality system and feedstock traceability.
6. Start of production. Supply contracts with quality agreements and capacity commitments.

Each stage involves months of cell testing, and the later stages depend on the supplier being able to make enough representative material. Moving from first sample to series production commonly takes two years or more. Suppliers outside China that began qualifying with major cell makers in 2024 and 2025 are aiming for series supply in 2027 (Charged EVs, 2026). Starting early, building capacity alongside testing, and offering a narrow, consistent specification all shorten the path (Volta Foundation).

Where Aeroborn fits

Aeroborn's recovered graphite is purified to 99.95% carbon and is under evaluation with three European battery makers. Its performance has been verified in testing at Bournemouth University. We share the full data sheet with buyers on request, so the numbers come with the context of how they were measured. Request the data sheet or read how the graphite is recovered in black mass and white mass.