水热合成锂锰氧化物及其电容性能研究
发布时间：2019-05-31 18:35
【摘要】：超级电容器具有比传统电容器更大的能量密度,可以在短时间内输出较大的能量,还具有对环境绿色无污染、使用循环寿命长和较好的低温工作特性等优点,受到国内外研究者们的广泛关注。超级电容器的研究主要集中在电极材料方面。锂锰氧具有对环境无污染、资源丰富、价格低廉以及较好的倍率性等优点,是一种具有广阔发展前景的超级电容器电极材料。本文使用不同还原剂(CO(NH2)2、NaNO2、(NH4)2SO4、MnSO4)来还原KMnO4,通过水热法制得不同形貌和晶型的MnO2前驱体;然后将这些MnO2前驱体与LiOH溶液水热反应,合成了一系列LiMn2O4样品,从而探讨MnO2前驱体的形貌、晶型和粒径对LiMn2O4电化学性能的影响。利用XRD和SEM对MnO2前驱体和LiMn2O4样品的结构和形貌进行表征,利用循环伏安和恒流充放电测试探究其电化学性能。具体结果如下:(1)以KMnO4为锰源,尿素为还原剂,在不同水热温度(120℃,150℃,180℃)、反应8 h后制得不同形貌和晶型的MnO2。XRD和SEM测试结果表明,在120℃下制得花状δ-MnO2纳米球;当水热温度高至180℃时,得到线状的α-MnO2。将制得的MnO2和活性炭(AC)分别作为正极和负极,组成非对称超级电容器AC//MnO2。测试结果表明,在电流密度在200 mA·g-1,1 mol·L-1 Li2SO4中性电解液中,AC//δ-MnO2和AC//α-MnO2的初始比电容分别为31.2 F·g-1和25.4 F·g-1;经1000次循环后,比电容保持率分别为97.4%和94.6%。可见,在水热温度120℃制得的花状δ-MnO2纳米球电化学性能最好。保持水热温度为120℃,延长水热时间,所合成的MnO2的晶型均为δ型,但形貌由花状逐渐转变为线状,电化学性能也逐渐变差。因此,以尿素为还原剂,在水热温度120℃、反应时间8 h时得到的花状δ-MnO2纳米球具有最好的电化学性能,这方面工作尚未见报道。(2)本文以尿素辅助水热合成的花状δ-MnO2作为前驱体,和LiOH溶液在不同水热温度(140℃~200℃)、不同反应时间(6 h~36 h),生成一系列LiMn2O4样品。测试结果表明,水热温度从140℃升高至180℃,LiMn2O4样品的结晶度升高,晶型逐渐完整,电化学性能逐渐变好;当水热温度升高至200℃,LiMn2O4的晶体粒径过大,导致电化学性能降低;因此在180℃下制备的LiMn2O4晶体电容性能最好。保持水热温度为180℃,反应时间从6 h延长至24 h,结果表明水热24 h得到的LiMn2O4电化学性能最好;将水热时间延长至36 h,产物的晶体结构易塌陷,导致电化学性能降低。因此,以花状δ-MnO2作为前驱体,在水热温度180℃、24 h制得的LiMn2O4具有最好的电化学性能。将其与AC组成非对称超级电容器AC//LiMn2O4,在200 mA·g-1电流密度下测得其初始比电容为45.4 F·g-1,经过1000次充放电循环后,其比电容保持率达到97.6%。此法与很多高温固相法和水热法合成的LiMn2O4相比具有更好的电化学性能。(3)以三种还原剂(NaNO2、(NH4)2SO4、MnSO4)辅助水热制得三种不同晶型、形貌和粒径的MnO2前驱体(分别为MO-1,MO-2和MO-3),首次探讨了不同还原剂合成的Mn O2前驱体对LiMn2O4电化学性能的影响。结果表明,以NaNO2为还原剂制得纳米级花状δ-MnO2(MO-1)前驱体,由此制得纯相LiMn2O4-1。以(NH4)2SO4为还原剂制得微米级花状δ-MnO2(MO-2),由此得到含有杂质的LiMn2O4-2。以MnSO4为还原剂制得微米级刺球状α-MnO2(MO-3),由此制得含有杂质的LiMn2O4-3。电化学性能测试表明,AC//LiMn2O4-1、AC//LiMn2O4-2、AC//LiMn2O4-3的初始比电容分别为41.98 F·g-1,37.12 F·g-1和35.07 F·g-1;经过1000次循环后,比电容保持率分别为98.9%,93.9%和84.5%。可见,LiMn2O4-1电容性能最好,而LiMn2O4-2和LiMn2O4-3电容性能较差。因此,利用NaNO2为还原剂制得纳米级的花状δ-MnO2,也适合用作水热合成LiMn2O4的前驱体。综上所述,以KMnO4为锰源,以CO(NH2)2和NaNO2为还原剂,采用水热法在温度120℃和时间8 h的条件下,均可制得纳米级的花状δ-MnO2;它们作为前驱体和LiOH在低温水热条件下可制备纯相高结晶度的尖晶石Li Mn2O4,这两种LiMn2O4样品展现出良好的电化学性能,具有很好的实用潜力。
[Abstract]:The super capacitor has a larger energy density than that of a conventional capacitor, can output large energy in a short time, and has the advantages of no pollution to the environment, long service life and good low-temperature working characteristic, and the like, and is widely concerned by the researchers at home and abroad. The research of the super capacitor is mainly focused on the electrode material. The lithium manganese oxide has the advantages of no pollution to the environment, rich resources, low price and good multiplying power, and is a super capacitor electrode material with wide development prospect. In this paper, different reducing agents (CO (NH2)2, NaNO2, (NH4) 2SO4, and MnSO4) are used to reduce KMnO4, and the MnO2 precursor of different morphology and crystal form is obtained by hydrothermal method; then the MnO2 precursor and LiOH solution are hydrothermal reaction, and a series of LiMn2O4 samples are synthesized, thus the morphology of the MnO2 precursor is discussed, The effect of crystal form and particle size on the electrochemical performance of LiMn2O4. The structure and morphology of the precursor of MnO2 and LiMn2O4 were characterized by XRD and SEM. The electrochemical performance was investigated by cyclic voltammetry and constant current charge-discharge test. The specific results are as follows: (1) MnO2 with different morphology and crystal form is prepared by taking KMnO4 as a manganese source and urea as a reducing agent and reacting for 8 hours at different hydrothermal temperatures (120 DEG C,150 DEG C and 180 DEG C); and the XRD and SEM test results show that the flower-shaped dendritic-MnO2 nano ball is prepared at the temperature of 120 DEG C; and when the hydrothermal temperature is high to 180 DEG C, And the wire-like carbon dioxide-MnO2 is obtained. The prepared MnO2 and active carbon (AC) are used as positive and negative electrodes respectively to form an asymmetric super capacitor AC// MnO2. The results show that the initial specific capacitance of AC// HCO3-MnO2 and AC//-MnO2 is 31.2 F 路 g-1 and 25.4 F 路 g-1 in the neutral electrolyte of 200 mA 路 g-1 and 1 mol 路 L-1 Li2SO4, respectively. After 1000 cycles, the specific capacitance retention rate is 97.4% and 94.6%, respectively. It can be seen that the electrochemical performance of the flower-like carbon-MnO2 nanosphere prepared at the hydrothermal temperature of 120 DEG C is the best. The hydrothermal temperature was maintained at 120 鈩，
本文编号：2489934
[Abstract]:The super capacitor has a larger energy density than that of a conventional capacitor, can output large energy in a short time, and has the advantages of no pollution to the environment, long service life and good low-temperature working characteristic, and the like, and is widely concerned by the researchers at home and abroad. The research of the super capacitor is mainly focused on the electrode material. The lithium manganese oxide has the advantages of no pollution to the environment, rich resources, low price and good multiplying power, and is a super capacitor electrode material with wide development prospect. In this paper, different reducing agents (CO (NH2)2, NaNO2, (NH4) 2SO4, and MnSO4) are used to reduce KMnO4, and the MnO2 precursor of different morphology and crystal form is obtained by hydrothermal method; then the MnO2 precursor and LiOH solution are hydrothermal reaction, and a series of LiMn2O4 samples are synthesized, thus the morphology of the MnO2 precursor is discussed, The effect of crystal form and particle size on the electrochemical performance of LiMn2O4. The structure and morphology of the precursor of MnO2 and LiMn2O4 were characterized by XRD and SEM. The electrochemical performance was investigated by cyclic voltammetry and constant current charge-discharge test. The specific results are as follows: (1) MnO2 with different morphology and crystal form is prepared by taking KMnO4 as a manganese source and urea as a reducing agent and reacting for 8 hours at different hydrothermal temperatures (120 DEG C,150 DEG C and 180 DEG C); and the XRD and SEM test results show that the flower-shaped dendritic-MnO2 nano ball is prepared at the temperature of 120 DEG C; and when the hydrothermal temperature is high to 180 DEG C, And the wire-like carbon dioxide-MnO2 is obtained. The prepared MnO2 and active carbon (AC) are used as positive and negative electrodes respectively to form an asymmetric super capacitor AC// MnO2. The results show that the initial specific capacitance of AC// HCO3-MnO2 and AC//-MnO2 is 31.2 F 路 g-1 and 25.4 F 路 g-1 in the neutral electrolyte of 200 mA 路 g-1 and 1 mol 路 L-1 Li2SO4, respectively. After 1000 cycles, the specific capacitance retention rate is 97.4% and 94.6%, respectively. It can be seen that the electrochemical performance of the flower-like carbon-MnO2 nanosphere prepared at the hydrothermal temperature of 120 DEG C is the best. The hydrothermal temperature was maintained at 120 鈩，
本文编号：2489934
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