水熱合成鋰錳氧化物及其電容性能研究
發(fā)布時間：2019-05-31 18:35
【摘要】：超級電容器具有比傳統(tǒng)電容器更大的能量密度,可以在短時間內輸出較大的能量,還具有對環(huán)境綠色無污染、使用循環(huán)壽命長和較好的低溫工作特性等優(yōu)點,受到國內外研究者們的廣泛關注。超級電容器的研究主要集中在電極材料方面。鋰錳氧具有對環(huán)境無污染、資源豐富、價格低廉以及較好的倍率性等優(yōu)點,是一種具有廣闊發(fā)展前景的超級電容器電極材料。本文使用不同還原劑(CO(NH2)2、NaNO2、(NH4)2SO4、MnSO4)來還原KMnO4,通過水熱法制得不同形貌和晶型的MnO2前驅體;然后將這些MnO2前驅體與LiOH溶液水熱反應,合成了一系列LiMn2O4樣品,從而探討MnO2前驅體的形貌、晶型和粒徑對LiMn2O4電化學性能的影響。利用XRD和SEM對MnO2前驅體和LiMn2O4樣品的結構和形貌進行表征,利用循環(huán)伏安和恒流充放電測試探究其電化學性能。具體結果如下:(1)以KMnO4為錳源,尿素為還原劑,在不同水熱溫度(120℃,150℃,180℃)、反應8 h后制得不同形貌和晶型的MnO2。XRD和SEM測試結果表明,在120℃下制得花狀δ-MnO2納米球;當水熱溫度高至180℃時,得到線狀的α-MnO2。將制得的MnO2和活性炭(AC)分別作為正極和負極,組成非對稱超級電容器AC//MnO2。測試結果表明,在電流密度在200 mA·g-1,1 mol·L-1 Li2SO4中性電解液中,AC//δ-MnO2和AC//α-MnO2的初始比電容分別為31.2 F·g-1和25.4 F·g-1;經1000次循環(huán)后,比電容保持率分別為97.4%和94.6%。可見,在水熱溫度120℃制得的花狀δ-MnO2納米球電化學性能最好。保持水熱溫度為120℃,延長水熱時間,所合成的MnO2的晶型均為δ型,但形貌由花狀逐漸轉變?yōu)榫�狀,電化學性能也逐漸變差。因此,以尿素為還原劑,在水熱溫度120℃、反應時間8 h時得到的花狀δ-MnO2納米球具有最好的電化學性能,這方面工作尚未見報道。(2)本文以尿素輔助水熱合成的花狀δ-MnO2作為前驅體,和LiOH溶液在不同水熱溫度(140℃~200℃)、不同反應時間(6 h~36 h),生成一系列LiMn2O4樣品。測試結果表明,水熱溫度從140℃升高至180℃,LiMn2O4樣品的結晶度升高,晶型逐漸完整,電化學性能逐漸變好;當水熱溫度升高至200℃,LiMn2O4的晶體粒徑過大,導致電化學性能降低;因此在180℃下制備的LiMn2O4晶體電容性能最好。保持水熱溫度為180℃,反應時間從6 h延長至24 h,結果表明水熱24 h得到的LiMn2O4電化學性能最好;將水熱時間延長至36 h,產物的晶體結構易塌陷,導致電化學性能降低。因此,以花狀δ-MnO2作為前驅體,在水熱溫度180℃、24 h制得的LiMn2O4具有最好的電化學性能。將其與AC組成非對稱超級電容器AC//LiMn2O4,在200 mA·g-1電流密度下測得其初始比電容為45.4 F·g-1,經過1000次充放電循環(huán)后,其比電容保持率達到97.6%。此法與很多高溫固相法和水熱法合成的LiMn2O4相比具有更好的電化學性能。(3)以三種還原劑(NaNO2、(NH4)2SO4、MnSO4)輔助水熱制得三種不同晶型、形貌和粒徑的MnO2前驅體(分別為MO-1,MO-2和MO-3),首次探討了不同還原劑合成的Mn O2前驅體對LiMn2O4電化學性能的影響。結果表明,以NaNO2為還原劑制得納米級花狀δ-MnO2(MO-1)前驅體,由此制得純相LiMn2O4-1。以(NH4)2SO4為還原劑制得微米級花狀δ-MnO2(MO-2),由此得到含有雜質的LiMn2O4-2。以MnSO4為還原劑制得微米級刺球狀α-MnO2(MO-3),由此制得含有雜質的LiMn2O4-3。電化學性能測試表明,AC//LiMn2O4-1、AC//LiMn2O4-2、AC//LiMn2O4-3的初始比電容分別為41.98 F·g-1,37.12 F·g-1和35.07 F·g-1;經過1000次循環(huán)后,比電容保持率分別為98.9%,93.9%和84.5%�？梢�,LiMn2O4-1電容性能最好,而LiMn2O4-2和LiMn2O4-3電容性能較差。因此,利用NaNO2為還原劑制得納米級的花狀δ-MnO2,也適合用作水熱合成LiMn2O4的前驅體。綜上所述,以KMnO4為錳源,以CO(NH2)2和NaNO2為還原劑,采用水熱法在溫度120℃和時間8 h的條件下,均可制得納米級的花狀δ-MnO2;它們作為前驅體和LiOH在低溫水熱條件下可制備純相高結晶度的尖晶石Li Mn2O4,這兩種LiMn2O4樣品展現出良好的電化學性能,具有很好的實用潛力。
[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，
本文編號：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，
本文編號：2489934
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