Hydrothermal and Solvothermal Process Towards Development of LiMPO₄ (M = Fe, Mn) Nanomaterials for Lithium‐Ion Batteries

Abstract

Positive electrodes such as LiFePO 4 and LiMnPO 4 nanomaterials with olivine structures are considered as most efficient cathode materials for application in lithium ion batteries. Recently, several methods have been proposed for the preparation of lithium metal phosphates as cathodes for lithium ion batteries and their electrochemical performances have been investigated. Over the last 20 years, several synthetic methods have been proposed for lithium metal phosphate nanomaterials. In this review, hydrothermal and solvothermal syntheses of LiFePO 4 and LiMnPO 4 nanomaterials at low and high temperatures are discussed, including microwave-hydrothermal and microwave-solvothermal methods. The effect of particle size and particle morphology on the electrochemical properties of LiFePO 4 and LiMnPO 4 cathode materials are also discussed. In addition, the recently emerged supercritical solvothermal and supercritical hydrothermal syntheses of LiFePO 4 and LiMnPO 4 nanomaterials and their electrochemical property also been addressed.in high-power systems such as hybrid electric vehicles (HEVs) and electric vehicles (EVs). In this context, olivine LiMPO 4 (M = Fe, Mn, Co, Ni) serves as an excellent candidate for cathode materials when compared with other cathodes such as LiCoO 2 , LiNiO 2 , and LiMn 2 O 4 , [1] because these materials are inexpensive and environmentally benign, and the covalently bonded PO 4 groups together with the chemically more stable Fe 2+/3+ couple offer excellent thermal stability and safety. [1,2] Moreover, with a theoretical capacity of 170 mAh g −1 , LiFePO 4 operates at a flat voltage of 3.45 V versus Li/Li + , which is compatible with the commercial electrolytes used now in lithium ion batteries. On the other hand, the other LiMPO 4 (M = Mn, Co, and Ni) cathodes with Mn 2+/3+ , Co 2+/3+ , and Ni 2+/3+ couples have been shown to operate at much higher voltages of 4.1, 4.8, and 5.

Olivine-Based Cathode Materials

“…The low conductivity is related to the small free volume and separation of MO 6 octahedra by oxygen atoms of the (PO 4 ) −3 anions 0.05C [71]. The solution-based synthetic routes such as spray pyrolysis [72,73], precipitation, sol-gel [74], hydrothermal method [75], solvothermal route [76,77] and polyol synthesis [78] provide nanostructured LMP powders with enhanced electrochemical properties, which is mostly attributed to the higher chemical homogeneity and narrow particle size distribution of the material. The best results were obtained for LiMnPO 4 prepared via sol-gel, hydrothermal and co-precipitation routes.…”

Effect of ethylene glycol on morphology, crystallinity, and electrochemical properties of LiFePO4/C in lithium-ion batteries

“…It seems that, adding the EG in the electrolyte of the preparation of LiFePO 4 by hydrothermal method can improve the electrochemical performance. However, the optimized amount of EG in previous reports was not determined [22,[30][31][32][33][34][35][36][37]. Therefore, in this work, LiFePO 4 /C has been synthesized using hydrothermal method with various volume ratios of EG to water, and the effects of EG on the morphology, crystallinity, and electrochemical properties of LiFePO 4 were investigated.…”

“…Hence, it can inhibit the crystal growth so that smaller particles are obtained [30][31][32][33][34][35]. In addition, EG is able to reduce the intrinsic defect concentration of the products [34,36].…”

Fast track to nanomaterials: microwave assisted synthesis in ionic liquid media

“…15,[31][32][33] Solvothermal syntheses are very well investigated and represent a versatile tool for the preparation of nanomaterials. [34][35][36] They bear the advantage to control size and shape by adjusting the reaction parameters. For convincing results solvents or even solvent mixtures must be varied.…”