Morphology Controlling of the High-voltage Cathode Materials with Different Co-solvents

doi:10.15541/jim20180425

Abstract

Abstract:

Cathode material LiCoPO₄ was synthesized by solvothermal method with a variety of water/alcohol solvent mixtures, including ethanol (ET), ethylene glycol (EG), and diethylene glycol (DEG). Focus of this work was set on the effect of the different alcohol solvent on morphology and particle size of material. Composition, crystal structure, morphology and particle size of the as-prepared samples were characterized by X-ray-diffraction, scanning electron microscopy and specific surface area test. The results show that relationship of the average particle size of the LiCoPO₄ samples synthesized with different alcohols solvents is in agreement with solubility of solvent for the precursor, but is inconsistent with the viscosity of solvent. Furthermore, LiCoPO₄ sample synthesized with EG/H₂O possesses the smallest particle size, great crystallinity and excellent cycle performance. Its initial discharge specific capacities reaches to 130 mAh/g at 0.05C, and it shows a capacity retention of the initial value of 88% in 20th cycle. A variety of shapes are obtained from various co-solvents: hexagonal platelets for LiCoPO₄ obtained from EG, whereas, square platelets for LiCoPO₄ from ET/H₂O and DEG/H₂O.

Key words: lithium cobalt phosphate, solvothermal synthesis, solubility, high-voltage cathode, lithium-ion battery

CLC Number:

TB911

Jian-Huang KE, Kai XIE, Yu HAN, Wei-Wei SUN, Shi-Qiang LUO, Jin-Feng LIU. Morphology Controlling of the High-voltage Cathode Materials with Different Co-solvents[J]. Journal of Inorganic Materials, 2019, 34(6): 618-624.

Figures/Tables 9

Fig. 1 XRD patterns of the LCP obtained from solvents (a) LCP-Theor. (ICSD#87422), (b) LCP-ET, (c) LCP-EG and (d) LCP-DEG

Table 1 Variation of crystal parameters for LCP obtained from various solvents

Sample	LCP-ET	LCP-EG	LCP-DEG	LCP-Theor.
a/nm	1.0197	1.0203	1.0203	1.0200
b/nm	0.5916	0.5922	0.5920	0.5920
c/nm	0.4703	0.4698	0.4698	0.4690
α/°	90	90	90	90
β/°	90	90	90	90
γ/°	90	90	90	90
V/nm³	0.2837	0.2839	0.2838	0.2832
I₍₀₂₀₎/I₍₂₀₀₎	5.975	3.208	2.836	1.576

Fig. 2 SEM images of the LCP obtained from various solvents

Table 2 BET analysis of the three samples

Sample	LCP-ET	LCP-EG	LCP-DEG
BET/(m²·g^-1)	1.1446	1.5840	1.3558

Table 3 Physical parameters of four solvents

Solvent	H₂O	ET	EG	DEG
Viscosity/(mPa·S)	1.005	1.074	19.9	35.7
Boiling point/℃	100	78	197.3	245

Fig. 3 Relationship curves for the viscosity and solubility with the average particle size of LCP powders obtained from different solvents

Fig. 4 Schematic illustration for nucleation and crystal growth of LiCoPO4 under solvothermal conditions

Fig. 5 (a) Capacity retentions and (b) specific capacities vs. C rate obtained in each cycle for LiCoPO4 samples synthesized by solvothermal process using various co-solvents

Fig. 6 (a) Charge and discharge profiles of the samples obtained from various solvents; (b) Cyclic voltammetry characteristics of LCP-EG at a scanning rate of 0.05 mV/s

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