Modeling and synthesis of carbon-coated LiMnPO4 cathode material: Experimental investigation and optimization using response surface methodology

Redouan El-Khalfaouy,Khadija Khallouk,Ahmed Lahsini,Alae Elabed,Ali Laajeb,Abdellah Addaou

doi:10.5599/jese.1191

Abstract

Nanostructured LiMnPO4 cathode materials for lithium-ion batteries (LIBs) have been successfully prepared by a modified solvothermal method under controlled conditions. Polyethylene glycol (PEG-10000) was used as a solvent to optimize the particle size/morphology and as a carbon conductive matrix. In order to investigate the effect of synthesis parameters such as concentration of PEG-10000, reaction time and reaction temperature on the LiMnPO4 phase purity, Response surface methodology was carried out to find variations in purity results across the composition. The purity of all materials was checked using HighScore software by comparing the matched lines score to ones of reference data. As a result, it has been found that the pure phospho-olivine material LiMnPO4 can be synthesized using the following optimum conditions: PEG concentration = 0.1 mol l-1, reaction time = 180 min, and reaction temperature = 250 °C. The as-prepared LiMnPO4 under optimum conditions delivered an initial discharge capacity of 128.8 mAh g-1 at 0.05 C‑rate. The present work provides insights and suggestions for optimizing synthesis conditions of this material, which has been considered the next promising cathode candidate for high-energy lithium-ion batteries.

Highlights

Rechargeable lithium-ion batteries (LIBs) with high-energy, high power density, durability, and lightweight have become the most requested energy source in order to meet future society's needs in many renewable energy storage systems, starting from laptops, cell phones to electric vehicles
The objective of this research was the optimization of solvothermal synthesis parameters using response surface methodology based on Box-Behnken design
Three independent variables were considered in this study, which are the concentration of solvent (PEG), reaction time and reaction temperature

Summary

Introduction

Rechargeable lithium-ion batteries (LIBs) with high-energy, high power density, durability, and lightweight have become the most requested energy source in order to meet future society's needs in many renewable energy storage systems, starting from laptops, cell phones to electric vehicles. Most commercial LIBs are currently based on LiCoO2 layered structure as a cathode material. One of the main challenges is to replace the commercialized layered structure cathode (which exhibits a theoretical specific capacity of 274 mAh g-1) with other promising and efficient cathode materials. LiMPO4 (M = Fe, Mn, Co, Ni) olivine-based high-performance cathodes are the recommended alternative cathode materials to replace traditional ones (LiCoO2) due to their low cost, non-toxicity, high thermal and cyclic stability, and environmental impact [1,2,3,4,5]. Compared to the first commercialized cathode, which is LiFePO4, LiMnPO4 is considered as the most promising cathode material in the generation of lithium-ion batteries due to the high theoretical energy density (701 Wh/kg), which is higher than that of LiFePO4 (586 Wh kg-1)[6,7]. The low voltage (4.1 V vs Li/Li+) of LiMnPO4, which is positioned within the stable window of the most commercialized electrolytes, makes it the best candidate material compared to LiCoPO4 and LiNiPO4, which have higher potentials, being respectively 4.8 and 5.1 V vs. Li/Li+ [8,9,10]

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Conclusion