Synthesis of LiMn 0.8 Fe 0.2 PO 4 Mesocrystals for High-Performance Li-Ion Cathode Materials

Optimum Morphology of Mixed-Olivine Mesocrystals for a Li-Ion Battery

“…Accordingly, the formation mechanisms of the flake-shaped LMFP mesocrystals can be divided into three steps. The first step is the nucleation of Mn/Fe-oxide nanoparticles as a precursor phase, which is confirmed in our previous work . In the second step, the formation of flake-like metal phosphate hydrate (M = Fe and Mn) proceeds soon after the introduction of H 3 PO 4 , LiOH·H 2 O, ascorbic acid, and HNO 3 (denoted as “before solvothermal”).…”

“…Since the H + concentration of the solution determines the type and surface concentration of the dominant functional group on the nanoparticle surfaces (which also determines the average surface charge of the nanoparticle surface), the pH value can control the adhesion and stabilizing behavior of the nanocrystals . Collisions and adhesions may have occurred among the primary particles unless net repulsive forces were applied to the equivalent surfaces between the stabilized nanoparticles. ,, Penn and co-workers postulate that when the crystal growth is restricted by electrostatic forces, selective attachment between two equivalent surfaces will be dominant when the pH range of the solution is similar to the isoelectric point of the surface. , From this point of view, it can be said that the time of the nanocrystal growth close to the isoelectric point of the crystals affects the degree of selective adhesion between equivalent surfaces. Although the exact isoelectric point of LiMnPO 4 has not been clearly examined or calculated before, it is reported to be within the range of pH 5–7. ,, As shown in Table S1, all of the mesocrystals are initially formed in the pH range between 3.3 and 6.7, and the pH values measured after synthesis are around 8.2–9.1.…”

“…47 Collisions and adhesions may have occurred among the primary particles unless net repulsive forces were applied to the equivalent surfaces between the stabilized nanoparticles. 20,47,48 Penn and co-workers postulate that when the crystal growth is restricted by electrostatic forces, selective attachment between two equivalent surfaces will be dominant when the pH range of the solution is similar to the isoelectric point of the surface. 49,50 From this point of view, it can be said that the time of the nanocrystal growth close to the isoelectric point of the crystals affects the degree of selective adhesion between equivalent surfaces.…”

“…The first step is the nucleation of Mn/Fe-oxide nanoparticles as a precursor phase, which is confirmed in our previous work. 20 In the second step, the formation of flake-like metal phosphate hydrate (M = Fe and Mn) proceeds soon after the introduction of H 3 PO 4 , LiOH•H 2 O, ascorbic acid, and HNO 3 (denoted as "before solvothermal"). In the third step, once the precursor-based solution is subsequently heated to 180 °C, the plate-like metal−phosphate hydrate particles completely dissolve in 5 min.…”

“…With the binary transition-metal phosphate LiMn 1– y Fe y PO 4 being a robust chemistry for realizing superior lithium-ion battery cathodes, various attempts have been made to fabricate the material with electrochemically favorable morphologies. − One typical approach is to reduce the particle size down to several tens of nanometers, since nano-sized particles have the benefit of improving the rate performance due to the enhanced conductance by reducing Li + -transport paths and increasing the interfacial area between the electrolyte and active materials. − Although the dramatic enhancement of battery performance is expected, nanosizing the material is not yet practical due to the tap density (density of powders after a tapping condensation process, 0.3–0.5 g cm –3 ) being lower than those in commercial cathode materials (>1.0 g cm –3 ), leading to a poor volumetric energy density. , …”