基于不同共溶剂体系对于高电压正极材料LiCoPO4的形貌控制

doi:10.15541/jim20180425

摘要/Abstract

摘要：

水分别与乙醇、乙二醇、二乙二醇混合为共溶剂, 通过溶剂热法制备高电压锂离子电池正极材料LiCoPO₄, 研究不同醇类溶剂对于样品的微观形貌和颗粒尺寸的影响。借助X射线衍射、扫描电子显微镜和比表面积测试对样品的成分、晶型、微观形貌和颗粒尺寸进行分析。研究表明, 制备得到的LiCoPO₄颗粒平均尺寸大小与醇类溶剂对于前驱体的溶解度差异相一致, 而与溶剂粘度没有明显联系。通过乙二醇/水制备得到的LiCoPO₄颗粒呈六边形片状, 平均尺寸最小, 而通过乙醇/水和二乙二醇/水制备得到的LiCoPO₄颗粒呈菱形片状形态。此外, 前者结晶度较高且循环性能较好, 0.05C下首圈放电容量为130 mAh/g, 20圈后容量保留率为88%。

关键词: 磷酸钴锂, 溶剂热法, 溶解度, 高电压正极材料, 锂离子电池

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

中图分类号:

TB911

柯剑煌, 谢凯, 韩喻, 孙巍巍, 罗世强, 刘锦锋. 基于不同共溶剂体系对于高电压正极材料LiCoPO₄的形貌控制[J]. 无机材料学报, 2019, 34(6): 618-624.

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.

图/表 9

图1 不同溶剂下制得的LCP粉末的XRD图谱

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

表1 不同溶剂下制得的LCP晶格参数

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

图2 不同溶剂下制得的LCP粉末的扫描电镜照片 (a, d) LCP-ET; (b, e) LCP-EG; (c, f) LCP-DEG

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

表2 三个样品的比表面积测试结果

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

表3 四种溶剂的物理参数

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

图3 不同溶剂制得的LCP粉末的平均颗粒尺寸与溶剂粘度、溶解度的关系曲线(平均颗粒尺寸以平均颗粒厚度为指标)

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

图4 溶剂热条件下LiCoPO4的形核和晶体长大示意图

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

图5 在不同共溶剂下制得的(a) LCP循环性能及(b)倍率性能对比

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

图6 (a) 三个样品的首圈充放电曲线; (b) LCP-EG样品在0.05 mV/s速率下的循环伏安曲线

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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基于不同共溶剂体系对于高电压正极材料LiCoPO₄的形貌控制

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

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