膨胀石墨/MnO<sub>2</sub>超级电容器电极材料中膨胀石墨的作用机制

桂阳; 曾靖宇; 范宝安; 张春桃

doi:10.13801/j.cnki.fhclxb.20210313.001

膨胀石墨/MnO₂超级电容器电极材料中膨胀石墨的作用机制

doi: 10.13801/j.cnki.fhclxb.20210313.001

桂阳^1,,
曾靖宇^1,,
范宝安^1, ,,
张春桃^2,

1.
武汉科技大学　化学与化工学院，武汉 430081
2.
湖北省煤转化与新型碳材料重点实验室，武汉 430081

基金项目: 国家自然科学基金 (21206129；21776225)

详细信息

通讯作者:
范宝安，博士，教授，硕士生导师，研究方向为燃料电池、超级电容器　E-mail：fanbaoan@wust.edu.cn

中图分类号: TM53; TB332
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- 被引次数: 0
出版历程
- 收稿日期: 2021-01-08
- 修回日期: 2021-02-12
- 录用日期: 2021-03-10
- 网络出版日期: 2021-03-15
- 刊出日期: 2022-01-15

Action mechanism of expanded graphite in the composite of expanded graphite/MnO₂ supercapacitor electrode materials

GUI Yang^1
,,
ZENG Jingyu^1
,,
FAN Baoan^{1
, ,},
ZHANG Chuntao^2
,

1.
School of Chemistry and Chemical Engineering, Wuhan University of Science and Technology, Wuhan 430081, China
2.
Key Laboratory of Hubei Province for Coal Conversion and New Carbon Materials, Wuhan 430081, China

摘要

摘要: 采用一种简便的方法制备出了单相α-MnO₂和膨胀石墨(EG)/MnO₂复合物。实验结果表明EG/MnO₂复合物有着比单相α-MnO₂更高的比电容和更加优异的倍率性能。随后采用XRD、TG、EIS、BET等手段对复合材料中EG的作用机制进行了研究，结果发现在EG/MnO₂复合物中出现了δ相MnO₂ (δ-MnO₂为层状结构，相较于α-MnO₂更加有利于离子的扩散和传输)，δ-MnO₂大约占复合物总质量的30wt%，EG占3.4wt%。EG/MnO₂复合物的电荷转移电阻显著低于单相α-MnO₂。EG/MnO₂的比表面积为38.7 m²·g⁻¹，而单相α-MnO₂的比表面积只有21.6 m²·g⁻¹，更大的比表面积使材料与电解液接触更为充分，从而降低了电荷转移电阻。综上，复合材料中EG的作用机制是通过自身的层状结构诱导了MnO₂在其上沉积形成了层状的δ-MnO₂，同时抑制了MnO₂颗粒的生长，增加了颗粒与电解液的接触面积，降低了电荷转移电阻，从而增大了比电容，也提高了其倍率性能。
- 超级电容器 /
- 二氧化锰 /
- 石墨 /
- 复合材料 /
- 机制
Abstract: The pure MnO₂ and the composite of expanded graphite (EG)/MnO₂ were prepared by a very facile method. The experimental results show that the composite presents higher specific capacitance and more stable rate capacity. The action mechanism of EG in the composite was investigated by the measurements of XRD, TG, EIS, BET, etc. It is found that the δ-MnO₂ appears in the composite, whose mass percentage is approximately 30% compared with 3.4% of EG in the composite. The δ-MnO₂ has a special layered structure compared with the channel structure of α-MnO₂, which makes the ions diffuse and transport easier. The charge exchange resistance of the EG/MnO₂ composite is significantly lower than that of pure α-MnO₂ which may be caused by more tiny particles size of composite because the specific surface area of the composite being 38.7 m²·g⁻¹, with the pure α-MnO₂of21.6 m²·g⁻¹. The larger specific surface area makes the contact between the material particles and the electrolyte solution more sufficient along with lower charge exchange resistance. In all, the action mechanism of EG in the composite can be summed as follow. The δ-MnO₂ with the layered structure is induced to grow on the surface of the EG which has the similar layered structure. At the same time, the grows-up of the MnO₂ particles is restrained by EG which makes the contact of particles with electrolyte solution more sufficient with the result of the reduce of charge exchange resistance. And, therefore, the specific capacitance is elevated accompanied with more stable rate capacity.
- supercapacitor /
- manganese dioxide /
- graphite /
- composite /
- mechanisms

HTML全文

图 1 单一MnO₂(a)和膨胀石墨(EG)/MnO₂ (b)复合材料的恒流充放电曲线

Figure 1. Constant current charge-discharge curve of single MnO₂(a) and expanded graphite (EG)/MnO₂ composite (b)

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图 2 MnO₂和EG/MnO₂的XRD图谱

Figure 2. XRD pattern of MnO₂ and EG/MnO₂

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图 3 MnO₂和EG/MnO₂的交流阻抗谱

Figure 3. Electrochemical impedance spectroscopy of MnO₂ and EG/MnO₂

R_ct—Charge transfer resistance; R_S—Ohmic resistance; Z_w—Warbury impedance; CPE—Constant phase angle impedance

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图 4 MnO₂和EG/MnO₂的等温吸附曲线(77.35 K)

Figure 4. Adsorption isotherm of MnO₂和EG/MnO₂ (77.35 K)

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图 5 MnO₂和EG/MnO₂的TG曲线

Figure 5. TG curve of MnO₂和EG/MnO₂

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图 6 MnO₂和EG/MnO₂的FESEM照片

Figure 6. FESEM images of MnO₂ and EG/MnO₂ ((a) Single MnO₂; (b) EG/MnO₂ composite)

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图 7 MnO₂和EG/MnO₂的循环稳定性(a)和充放电效率(b)

Figure 7. Cycle stability (a) and coulombic efficiency (b) of MnO₂ and EG/MnO₂

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表 1 MnO₂和EG/MnO₂在不同电流密度下的比电容C_m(F·g⁻¹)

Table 1. Specific capacitance C_m of single MnO₂ and EG/MnO₂ composite under different current density (F·g⁻¹)

Current density/(A·g⁻¹)	0.1	0.2	0.5	1.0	2.0
MnO₂	327	271	258	150	106
EG/MnO₂	476	435	428	422	410

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表 2 通过EIS拟合得到的MnO₂和EG/MnO₂的R_S和R_ct

Table 2. R_S and R_ct of MnO₂ and EG/MnO₂ fitted by EIS data

	R_s/(Ω·cm²)	R_ct/(Ω·cm²)
MnO₂	1.050	3.535
EG/MnO₂	1.247	2.519

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表 3 本研究中EG/MnO₂复合材料的储能性能与文献中类似研究结果的对比

Table 3. Comparison of energy-storing capability of EG/MnO₂ in this work with other work

Compounds	C_m/ (F·g⁻¹)	Measure rate	Electrolyte/ (Na₂SO₄ mol·L⁻¹)	Rate capability	Cycle stability	Literature
UN-MnO₂	810	1.0 A·g⁻¹	1	58.5% (1.0-20 A·g⁻¹)	88.45% (5000cyc@5.0 A·g⁻¹)	[2]
δ-MnO₂/Ni foam	325	1.0 A·g⁻¹	1	67.6% (1-5 A·g⁻¹)	86% (1000cyc@30 mV·s⁻¹)	[11]
MnO₂/CNFs	324.5	0.5 A·g⁻¹	1	55.4% (0.5-2 A·g⁻¹)	97.0 (1000cyc@3.5 A·g⁻¹)	[15]
δ-MnO₂/Corn-C	520	5 mV·s⁻¹	1	53.5% (5-100 mV·s⁻¹)	80.9% (5000cyc@5 A·g⁻¹)	[16]
Ni/δ-MnO₂	883	10 mV·s⁻¹	1	46.2% (0.01-0.2 V·s⁻¹)	73.8% (2000cyc@1 mA·cm⁻²)	[17]
δ-MnO₂ HMS	394	1.0 A·g⁻¹	1	71.3% (1-10 A·g⁻¹)	95.2% (5000cyc@5 A·g⁻¹)	[20]
C@δ-MnO₂	345	0.5 A·g⁻¹	1	55.9% (0.5-5 A·g⁻¹)	92.8% (5000cyc@ 5 A·g⁻¹)	[22]
α-MnO₂/CNTs	276	3.0 A·g⁻¹	0.5	65.4% (3–9.5 A·g⁻¹)	91.6% (5000cyc@3.0 A·g⁻¹)	[23]
EG/MnO₂	220	2 mV·s⁻¹	1	95% (0.1-0.5 A·g⁻¹)	100% (400cyc@5 mV·s⁻¹)	[24]
EG/MnO₂	161	0.1 A·g⁻¹	1	68.3% (0.1-5 A·g⁻¹)	100% (1000cyc@1 A·g⁻¹)	[25]
EG/MnO₂	428	0.5 A·g⁻¹	1	86% (0.1-2 A·g⁻¹)	100% (100cyc@0.5 A·g⁻¹)	This work
Notes: UN-MnO₂—Ultrasonic and NH⁴⁺ assisted MnO₂ deposited on Ni foam substrate; CNFs—Carbon nanofibers; HMS—Hollow microsphere; CNTs—Carbon nanotubes; C_m—Specific capacitance.

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