Lithium iron phosphate (LFP) cathode active material

01

Check capacity, compaction density and particle size

Each LiFePO4 formula unit can release and take back only one lithium, which fixes the theoretical specific capacity at 170 mAh/g; adding excess lithium source does not raise it, because the surplus forms Li3PO4, which conducts lithium ions but stores no capacity. The 2023 review in Energy Storage Science and Technology reports that high-compaction LFP products in commercial cells give 155 mAh/g first-cycle activation capacity at 0.1C and room temperature, but only 130 mAh/g at 1C during cycling, and that the LFP half-cell works at 3.4 V. [1]

The same review names powder compaction density as the main route to higher energy: LFP electrodes in commercial cells are compacted to 2.4–2.5 g/cm³, the improvement target is 2.6–2.7 g/cm³, and the theoretical density of LiFePO4 is 3.60 g/cm³. It lists three routes to higher powder compaction: the raw-material route (the iron phosphate route has displaced ferrous oxalate, which gives fine, low-compaction powder), sintering above 700 °C so small particles bond and grow, and blending large and small particle grades; more carbon coating raises electronic conductivity but lowers compaction density. [1]

Two research-supply data sheets show how grades differ. MTI's LIB-LFPO lists D50 3.5 ± 1.0 µm, tap density 1.45 ± 0.2 g/cm³, packing density ≥ 2.1 g/cm³ (2.2–2.3 recommended), specific surface area 11.0 ± 2.0 m²/g, carbon 1.15 ± 0.25 wt%, and ≥ 150 mAh/g with ≥ 90% efficiency at 0.1C in the first cycle of a 20 Ah pouch cell; MTI states it does not manufacture the powder. [2] Ossila's batch M2408A2 lists 1.10% carbon, 24.5 Ω·cm resistivity, tap density 1.12 g/cm³, surface area 11.1 m²/g, D50 0.98 µm, pH 9.67, 98.4% first discharge efficiency and 158.7 mAh/g first capacity; its previous batch M2408A1 listed 1.85% carbon, 115 Ω·cm, 1.13 g/cm³, 12.2 m²/g, about 1.5 µm and 155.5 mAh/g. [3]

Editorial calculation: 155 ÷ 170 ≈ 91% and 130 ÷ 170 ≈ 76% of theoretical capacity at 0.1C and 1C; an electrode at 2.5 g/cm³ reaches 2.5 ÷ 3.60 ≈ 69% of LiFePO4's theoretical density. [1]

Give the supplier the cell format and application, the capacity required at your test rate and voltage window (with the test cell type), target electrode compaction density and the pressure at which powder compaction is to be measured, D50 and distribution limits, BET surface area and carbon content ranges, resistivity, slurry pH limit, impurity and magnetic-particle limits, moisture limit, packaging and lot size.

02

Control trace metals, magnetic particles and moisture

China's national standard GB/T 30835-2014, Lithium iron phosphate-carbon composite cathode materials for lithium ion battery, is a recommended standard issued on 2014-05-06 and in force from 2015-04-01; its 2016-12-31 review kept it valid, and a revision (plan 20264574-T-605) is being drafted. The public record gives the title and status; the limits themselves are in the purchased text. [5]

Raising sintering temperature to improve compaction also produces Fe2P, a hexagonal, strongly ferromagnetic by-product; the review shows it being pulled out of synthesized LFP powder by prolonged stirring with a strong magnetic bar, so magnetic-particle limits belong in the order. [1]

Iron, lithium and phosphorus are matrix elements, so an iron limit in an LFP specification means iron-bearing impurities, not total Fe. Thermo Fisher's ICP-OES application note dissolved a 0.2000 g customer LFP sample in perchloric acid and measured 23 impurity elements, finding up to 240 mg/kg Mn, with 97.98 mg/kg Zn, 167.64 mg/kg Na and 228.11 mg/kg Ti; Cd, Mo, Se and W were not detected, and the matrix averaged 34.55% Fe, 19.49% P and 4.41% Li. Cu is not among the elements reported, so request it by name. [4] MTI's sheet lists Fe 34.5 ± 1.0 wt%, P 19.5 ± 1.0 wt%, Li 4.40 ± 0.50 wt% and Na, Ca and Ni impurity ≤ 0.01 wt%. [2]

MTI lists moisture below 0.15% and advises keeping the powder in a vacuum box and baking it in a vacuum oven at 120–150 °C before making slurry. [2]

Editorial calculation: 97.98 mg/kg Zn is about 0.0098 wt%, and a 0.15% moisture limit equals 1,500 ppm, so state each impurity and moisture limit with its unit and test method. [4] [2]

03

Lot certificates and test cells to request from an LFP producer

When requesting quotations, ask each supplier for a certificate of analysis per lot covering capacity, density, particle size, surface area, carbon, trace metals, magnetic particles and moisture, with the test methods, plus a sample for your own coin-cell or pouch-cell test.

04

Trace what is in the powder

05

LFP powder values across the MTI and Ossila sheets and the ESST review

06

Send the cell design and test methods together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Cell: [format; application; voltage window]
Capacity: [mAh/g; rate; test cell]
Density: [tap; powder compaction at pressure; electrode target]
Particles: [D10/D50/D90; BET]
Carbon: [wt%; resistivity]
Purity: [trace metals; magnetic particles; moisture; pH]
Supply: [lot size; packaging; CoA per lot]

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