Fast-charging lithium-ion battery protocols: LMFP pouch cells as a rate capability case study

The reduction of battery charge times is a key challenge in the wider adoption of electric vehicles (EVs), encompassing material, cell and system design aspects. Rate capability testing, the charging and discharging of a cell at various C-rates, is the most common technique used to assess the performance of Li-ion batteries, and particularly new electrode materials/cell designs, at high cycling rates. Data generated from this technique is however extremely sensitive to selected cell format and testing protocols, and thus lack of standardisation prevents both robust conclusions and comparison between studies. Furthermore, the figures of merit of such studies are often ill-defined and out of step with commercial requirements. Herein, we utilise LiMn0.6Fe0.4PO4\\Graphite (LMFP\\Gr) coin (half & full) and pouch cells to demonstrate these sensitivities. Cell format, electrode coat weight, and the inclusion of a constant voltage step during charge, are shown to dramatically alter the capacity observed at high C-rate in otherwise identical cells, reinforcing the advantages of testing in real-world conditions and the need for consistency between test samples/studies. To resolve this, we propose a commercially meaningful and industrially relevant protocol to evaluate fast-charging capabilities of Li-ion batteries.