微波辅助溶剂热法制备LiMn1-xMgxPO4/C正极材料

doi:10.11949/0438-1157.20190027

摘要/Abstract

摘要：

采用微波辅助溶剂热法的合成途径，成功制备出镁掺杂的磷酸锰镁锂(LiMn_1-_xMg_xPO₄/C)电极材料。采用X-射线衍射、扫描电镜、恒电流充放电等测试方法对晶体结构，微观形态和电化学性能进行表征。结果表明微波辅助溶剂热样品LiMn₁_-xMg_xPO₄/C为具备较大比表面积和介孔结构的片层状形貌材料。该片层状纳米结构有利于锂离子脱嵌/镶嵌反应，Mg²⁺掺杂在片层状纳米晶体合成过程中发挥着重要作用，可以提高材料的电化学活性和电化学表现。其中LiMn_0.95Mg_0.05PO₄/C材料在0.1 C和5 C倍率下最高可逆放电容量分别为141.2和95.3 (mA·h)/g，具备较高的放电容量和倍率性能表现。与传统溶剂热法相比，微波辅助溶剂热法的反应时间显著降低且制备得到的材料具备优异的电化学性能表现，对于制备其他锂离子电池材料具有指导意义。

关键词: 微波合成, 磷酸锰锂, 纳米材料, 电化学, 再生能源, 锂离子电池

Abstract:

Magnesium-doped lithium manganese phosphate(LiMn₁_-xMg_xPO₄/C) electrode materials were successfully prepared by microwave-assisted solvothermal synthesis. X-Ray diffraction, scanning electron microscope, thermogravimetry and Brunaur-Emmett-Teller method were employed to characterize crystal structures and morphology, and the electrochemical characteristics of the as-prepared materials were evaluated by galvanostatic charge/discharge, cyclic voltammetry and AC impedance method. The results showed that the plate-like LiMn₁_-xMg_xPO₄/C samples, which were synthesized from the microwave-assisted solvothermal method, possessed large specific surface area and well-defined mesoporous structure. In particular, Mg²⁺ doping exerts a significant effect on synthesizing flake-like nanocrystal which favors lithium-ion extraction/insertion reactions, improving the electrochemical activity and electrochemical performance of LiMnPO₄/C material. As a result, the LiMn_0.95Mg_0.05PO₄/C nanoparticle exhibited a high reversible capacity of 141.2 and 95.3 (mA·h)/g at 0.1 C and 5 C, respectively, exhibited outstanding charge/discharge performance and rate capability. Compared to conventional solvothermal synthetic route, microwave-assisted solvothermal approach led to a significant decrease in the reaction time and the as-prepared material possessed excellent electrochemical performance. It is extraordinary and remarkable for the preparation of high-performance LiMnPO₄ cathode material, providing a new method for the preparation of electrode materials for Li-ion batteries.

Key words: microwave synthesis, lithium manganese phosphate, nanomaterials, electrochemistry, renewable energy, Li-ion battery

中图分类号:

TM 912

朱计划, 陈姚, 丘秀莲, 黄宇明, 郑成, 杨伟. 微波辅助溶剂热法制备LiMn₁_-xMg_xPO₄/C正极材料[J]. 化工学报, 2019, 70(7): 2775-2785.

Jihua ZHU, Yao CHEN, Xiulian QIU, Yuming HUANG, Cheng ZHENG, Wei YANG. Preparation of LiMn₁_-xMg_xPO₄/C cathode materials by microwave-assisted solvothermal method[J]. CIESC Journal, 2019, 70(7): 2775-2785.

图/表 10

图1 微波辅助溶剂热LiMn1-xMgxPO4/C样品和采用不同合成方法制备LiMn0.95Mg0.05PO4/C材料的XRD谱图

Fig.1 XRD patterns of microwave-assisted solvothermal samples of LiMn1-xMgxPO4/C (x = 0, 0.025, 0.05, 0.075 and 0.1) and LiMn0.95Mg0.05PO4/C synthesized through different routes

表1 微波辅助溶剂热LiMn1-xMgxPO4/C (x = 0, 0.025, 0.05, 0.075和0.1)样品的单元晶胞参数

Table 1 Refined unit-cell parameters for LiMn1-xMgxPO4/C (x = 0, 0.025, 0.05, 0.075, 0.1)

样品	a/?	b/?	c/?	v/?³	I₀₂₀/I₃₁₁
LiMnPO₄/C	10.445	6.107	4.751	302.36	1.08
LiMn_0.975Mg_0.025PO₄/C	10.438	6.102	4.758	301.85	1.16
LiMn_0.95Mg_0.05PO₄/C	10.429	6.094	4.744	301.22	1.25
LiMn_0.925Mg_0.075PO₄/C	10.421	6.085	4.742	300.71	1.18
LiMn_0.90Mg_0.10PO₄/C	10.417	6.077	4.738	299.93	1.07

图2 微波辅助水热法和传统水热法制备的LiMn1-xMgxPO4/C材料SEM图

Fig.2 SEM images of LiMn1-xMgxPO4/C synthesized by microwave-assisted solvothermal and traditional solvothermal route

图3 微波辅助溶剂热LiMn0.95Mg0.05PO4/C材料的TEM、HRTEM和SEAD图

Fig.3 TEM, HRTEM and SEAD images of microwave-assisted solvothermal LiMn0.95Mg0.05PO4/C sample

表2 LiMn1-xMgxPO4/材料的比表面积、电子电导率、锂离子扩散系数和碳含量

Table 2 Specific surface area, electronic conductivity，lithium-ion diffusion coefficients and carbon content of LiMn1-xMgxPO4/C

样品	比表面积/(m²/g)	电导率/(S/cm)	离子扩散系数/(cm²/s)	碳含量/%(mass)
LiMnPO₄/C	64.2	4.5×10^-4	9.72×10^-14	7.13
LiMn_0.975Mg_0.025PO₄/C	79.9	6.3×10^-4	1.56×10^-13	7.21
LiMn_0.95Mg_0.05PO₄/C	88.2	7.6×10^-4	4.32×10^-13	7.16
LiMn_0.925Mg_0.075PO₄/C	82.8	5.4×10^-4	1.95×10^-13	7.08
LiMn_0.90Mg_0.1PO₄/C	68.6	3.8×10^-4	8.71×10^-14	7.11

图4 微波辅助溶剂热前体LiMnPO4和LiMn0.9Mg0.1PO4的TG图

Fig. 4 TG of microwave-assisted solvothermal precursor samples LiMnPO4 and LiMn0.9Mg0.1PO4

图5 微波辅助溶剂热LiMnPO4/C样品(a)和LiMn0.95Mg0.05PO4/C样品(b)的氮气吸脱附曲线和孔径分布(插图)

Fig.5 Nitrogen ad/desorption isotherms and pore size distributions(inset) of LiMnPO4/C (a) and LiMn0.95Mg0.05PO4/C (b)

图6 微波辅助溶剂热LiMn1-xMgxPO4/C (x = 0, 0.025, 0.05, 0.075, 0.1)样品充放电容量(a)与倍率性能(b)，采用不同合成方法制备LiMn0.95Mg0.05PO4/C材料充放电容量(c)与倍率性能(d)

Fig.6 Charge/discharge diagrams (a) and rate capability(b) of microwave-assisted solvothermal samples of LiMn1-xMgxPO4/C (x = 0, 0.025, 0.05, 0.075, 0.1) and charge/discharge diagrams (c) and rate capability (d) of LiMn0.95Mg0.05PO4/C synthesized through different routes

图7 0.1 mV/s扫速下微波辅助溶剂热法合成LiMn1-xMgxPO4/C材料(a)和采用不同合成方法制备LiMn0.95Mg0.05PO4/C材料(b)的CV曲线，不同扫描速率下微波辅助溶剂热法合成LiMn0.95Mg0.05PO4/C材料的CV曲线(c)和正极峰值电流与扫描速率平方根之间的线性拟合图(d)

Fig.7 CV curves of microwave-assisted solvothermal samples of LiMn1-xMgxPO4/C (x = 0, 0.025, 0.05, 0.075, 0.1) (a) and LiMn0.95Mg0.05PO4/C synthesized through different routes(b) at a scan rate of 0.1 mV/s; LiMn0.95Mg0.05PO4/C synthesized through microwave-assisted solvothermal route at different scan rates (c), plots of cathodic peak current (Ip) as function of square root of scan rate (v1/2) (d)

图8 微波辅助溶剂热LiMn1-xMgxPO4/C样品(a)和采用不同合成方法制备LiMn0.95Mg0.05PO4/C材料(b)的EIS图

Fig.8 EIS plots of microwave-assisted solvothermal samples of LiMn1-xMgxPO4/C (x = 0, 0.025, 0.05, 0.075, 0.1) (a) and LiMn0.95Mg0.05PO4/C synthesized through different routes (b)

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微波辅助溶剂热法制备LiMn₁_-xMg_xPO₄/C正极材料

Preparation of LiMn₁_-xMg_xPO₄/C cathode materials by microwave-assisted solvothermal method

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