Increasing the yields of natural flake graphite spheronization with the NARA Hybridization System

• Natural flake graphite was successfully spheronized in 40 g batches via a rotary mill with short run times (>5 min). • Initial spheronization yields were 66 % of particles with a diameter of 4–30 µm with a D 50 particle size 16 µm. • Graphite particles (>30 µm) were refed to the mill increasing the yields to 71 %. • Fines (<4 µm diameter) were classified to a narrow PSD (D 90 /D 10 = 3) and a high tap density (0.9 g cm −3 ). Commercial natural flake graphite spheronization using mill trains, particularly for lithium-ion battery (LIB) materials, is known to produce low yields (30–50 %) post-processing. The NARA Hybridization System (NHS-0) is a rotary mill with the capability to spheronize natural flake graphite within the specifications required for LIB graphite materials. In this work, commercial natural flake graphite, with a D 50 particle size of ∼ 83 µm, was spheronized in a NHS-0 at various speeds and durations. Conditions were optimized to produce spheronized particles in the size range of 4 µm to 30 µm, ideal for LIB anodes for electric vehicle applications. The optimal conditions for 10 g batches were found to be 9000 RPM for 180 s, which produced the highest yield (52 %), in specification, with the least amount of fines (<4 µm). This product was sieved with coarser material (>25 µm) and re-fed into the NHS-0 in order to maximise the yields. The cumulative total yields from the re-spheronization were 65 %, 68 % and 71 % for the 1st, 2nd and 3rd re-spheronizations, respectively. Notably, the re-spheronization did not degrade the product as observed via X-ray diffraction, scanning electron microscopy and Raman spectroscopy. Coin cell testing showed a minor decrease in initial coulombic efficiency of 93.1 % to 90.1 % and capacity from the initial spheronization to the 3rd re-spheronized materials, respectively.