Issue 7, 2024

Ammonia-free synthesis of lithium manganese iron phosphate cathodes via a co-precipitation reaction

Abstract

LiMnxFe1−xPO4 (LMFP) has emerged as a promising cathode material for Li-ion batteries due to its lower cost, better sustainability, and improved thermal and cycling stabilities compared to layered oxide cathodes. The incorporation of Mn in LMFP increases the operating voltage, and therefore the theoretical energy density, compared to LiFePO4. However, with high Mn content, it is difficult to fully utilize the Mn2+/3+ redox due to sluggish kinetics, resulting in a lower practical capacity. Atomic-scale mixing of Mn and Fe is crucial for the optimal electrochemical performance of LMFP, yet the practical scalability and the ease of synthesizing precursor compositions with different Mn contents through co-precipitation reaction remains underexplored. We present here for LMFP manufacturing a novel, scalable precursor (Mn, Fe)5(PO4)2(HPO4)2·4H2O, which is air-stable and is synthesized without the use of ammonia, for the first time. The role of the reactants, pH, and temperature in controlling the phase purity and morphology of the precursor are explored. Particularly, it is found that phase purity is highly sensitive to the Mn : Fe ratio and temperature during co-precipitation. The LMFP cathodes synthesized with the precursor exhibit excellent cycling stability, retaining over 95% capacity after 150 cycles at a C/3 rate. However, while higher Mn content (>60%) increases the average voltage, the specific capacity decreases due to sluggish kinetics, limiting the benefit to energy density. This work presents an industrially scalable method to synthesize mixed precursors for LMFP cathodes with a wide range of Mn contents providing a pathway to fine-tune the Mn content and particle morphology for optimal electrochemical performance.

Graphical abstract: Ammonia-free synthesis of lithium manganese iron phosphate cathodes via a co-precipitation reaction

Supplementary files

Article information

Article type
Paper
Submitted
14 Mar 2024
Accepted
08 Jun 2024
First published
13 Jun 2024
This article is Open Access
Creative Commons BY-NC license

RSC Sustain., 2024,2, 1969-1978

Ammonia-free synthesis of lithium manganese iron phosphate cathodes via a co-precipitation reaction

P. Vanaphuti, K. Scanlan and A. Manthiram, RSC Sustain., 2024, 2, 1969 DOI: 10.1039/D4SU00125G

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