Particle size-controllable microwave-assisted solvothermal synthesis of the high-voltage cathode material LiCoPO4 using water/ethylene glycol solvent blends

Abstract

Particle size-tuned platelets of the high-voltage cathode material LiCoPO 4 for Li-ion batteries have been synthesized by a simple one-step microwave-assisted solvothermal process using an array of water/ethylene glycol (EG) solvent mixtures. Particle size control was achieved by altering the concentration of the EG co-solvent in the mixture between 0 and 100 vol%, with amounts of 0-80 vol% EG producing single phase, olivine-type LiCoPO 4. The particle sizes of the olivine materials were significantly reduced from about 1.2 μm × 1.2 μm × 500 nm to 200 nm × 100 nm × 50 nm with increasing EG content, while specific surface areas increased from 2 to 13 m 2 g −1. The size reduction could mainly be attributed to the modified viscosities of the solvent blends. Owing to the soft template effect of EG, the crystals exhibited the smallest dimensions along the [010] direction of the Li diffusion pathways in the olivine crystal structure, resulting in enhanced lithium diffusion properties. The relationship between the synthesis, crystal properties and electrochemical performance was further elucidated, indicating that the electrochemical performances of the asprepared materials mainly depend on the solvent composition and the respective particle size range. LiCoPO 4 products obtained from reaction media with low and high EG contents exhibited good electrochemical performances (initial discharge capacities of 87-124 mAh g −1 at 0.1 C), whereas materials made from medium EG concentrations (40-60 vol% EG) showed the highest capacities and gravimetric energy densities (up to 137 mAh g −1 and 658 Wh kg −1 at 0.1 C), excellent rate capabilities, and cycle life.

Optimization of dielectric heating parameters in the production of high‐voltage LiNiPO4‐core and carbon‐shell ceramics

“…13,16,26 As can be seen from Figure 7A, the 132 mAhÁg À1 portion of the total specific capacity exhibited by the LNP@C (180-30) electrode is provided from the 5.05 V fixed plateau region. 20 The discharge profiles of the LNP@C (180-30) electrode at 0.1 C to 5 C in the voltage range of 2.8-5.6 V at ambient temperature, are presented in Figure 7B. This remarkable electrochemical performance can be attributed to the stable diffusion of microwave energy during the synthesis through the use of 2-propanol as the reaction medium, leading to the formation of high quality crystals.…”

“…In this case, under more efficient conditions in terms of microwave efficiency and solvothermal synthesis temperatures, it is expected that the [010] oriented channels of the crystal structure of LiNiPO 4 will be more perfect, which is considered to allow the diffusion of lithium ions. 20 The discharge profiles of the LNP@C (180-30) electrode at 0.1 C to 5 C in the voltage range of 2.8-5.6 V at ambient temperature, are presented in Figure 7B. The electrode exhibits an impressive rate capability for the first cycle, with discharge capacities of 157, 149 and 125 mAhÁg À1 at 0.1, 0.5 and 1 C, respectively.…”

“…Solvents have also been found to play a dominant role in controlling the morphology and particle size of cathode-active materials, as well as their crystal structure. Ludwig et al 20 clearly demonstrated the effect of the solvent species on particle size and on electrochemical properties in the synthesis of high-voltage LiCoPO 4 cathode material by microwave and solvothermal methods. In Ludwig et al's study, the LiCoPO 4 products obtained from using solvent with a high ethylene glycol (C 2 H 4 (OH) 2 ) percentage as the reaction medium, exhibited the highest capacity and gravimetric energy density and demonstrated an excellent cycle performance.…”

Insights into the Enhanced Catalytic Activity of Fe-Doped LiCoPO4for the Oxygen Evolution Reaction

“…The morphology of all samples was examined by scanning electron microscopy (SEM). As shown in Figure S3, LCP and LCFPn samples exhibit a similar feature of slightly squashed nanospheres, 31 with a particle size of 100−300 nm. Besides, the amount of Fe-doping has little effect on the particle morphology, suggesting that all samples have a similar particle size and surface.…”

Synthesis of LiCopo<sub>4</sub> Powders as a High-Voltage Cathode Material via Solvothermal Method

“…Recently, there were many kinds of approach to synthesizing LCP powders, containing CAM sol-gel [8], hydrothermal method [9], solvothermal method [10] [11], polyol process [12], solid-phase method [13], microwave method [14] and so on. Among these, the mainstream method were hydrothermal method that synthetic crystals at relatively low reaction temperature and uniformity of product composition, phase and microstructure.…”