【作者】 张旭；

【导师】 陈野；

【作者基本信息】 哈尔滨工程大学 ， 材料科学与工程， 2019， 博士

【摘要】 超级电容器是一种具有充放电速率快、功率密度高、循环寿命长、绿色环保等特点的新型电化学能量存储装置,有着广阔的应用前景。但是与电池相比,基于电极表面反应所存储电荷的超级电容器,其能量密度远不及电池。通常可通过提升材料的比容量和拓宽器件的工作电压区间来解决超级电容器的能量密度较低的问题。本论文拟采用双电层电容材料石墨烯与具有优异电荷存储能力的赝电容材料(铁氰化钴(PB-Co)、NiFe2O4、聚吡咯(PPy)、MnNb206、CoNb2O6)来共筑具有三维多孔结构的自支撑独立电极,得益于以下三点来提升电极的比电容:(1)三维的石墨烯碳骨架提供了充足的附着位点以分散赝电容材料,有利于改善复合材料的循环性能;(2)在石墨烯片层之间引入赝电容材料,可有效缓解石墨烯在充放电过程中的二次堆积问题,以此来提升材料的倍率性能和循环性能;(3)无导电剂与粘结剂的电极设计大大缩短了离子传输路径,降低了电极与电解液之间的接触电阻。此外,还将通过在有机体系下组装非对称的离子电容器来进一步拓宽器件的工作电压窗口,从而实现其能量密度的提升。主要研究内容如下:通过一步水热法,并引入氧化石墨烯,合成了 PB-Co/rGOH复合凝胶。通过扫描电镜和透射电镜测试结果可知,PB-Co的平均粒径为40 nm,且均匀分布在石墨烯上。通过电化学测试可知,当PB-Co的含量为0.3 g时,PB-Co/rGOH表现出最佳的电荷存储性能(当电流密度为0.5 A g-1时,其比容量为220 F g-1),经过10000次充放电循环后,电极的比容量保持率为82.4%。以PVA/KNO3作为固态电解质,PB-Co/rGOH为电极组装的对称全固态超级电容器的工作电压可以达到2.0 V,其最大能量密度和功率密度可以达到57 Wh kg-1和10 kW kg-1,经过10000次充放电循环后,其比容量保持率为92.8%。通过水热反应和引入石墨烯,成功将中间产物Ni3[Fe(CN)6]2转化为NiFe2O4,得到NiFe2O4@rGOH复合凝胶。通过扫描电镜和透射电镜测试结果可知,NiFe2O4呈现出规整的的立方体结构,且均匀散布在石墨烯片层上,平均粒径为35 nm。通过电化学测试可知,当电流密度为1 Ag-1时,NiFe2O4@rGOH的比电容为488 F g-1,经过10000次充放电循环后,电极的比容量保持率为89.8%。以PVA/KNO3作为固态电解质,NiFe2O4@rGOH为电极所组装的对称全固态超级电容器在0-1.8 V的电压区间内,表现出的最大能量密度和功率密度分别为62.5 Wh kg-1和13.5 kW kg-1。经过6000次充放电循环之后,比电容保持率为93.2%。通过水热法和电聚合法合成了具有丰富的交联孔洞结构的PPy@rGOH复合凝胶。通过对电聚合时间的控制,以达到对PPy含量的调控。结合电镜和电化学测试结果可知,当电聚合时长为20 s时,所得到的复合凝胶能够较好的保留rGOH的交联结构而不团聚,且表现出最佳比电容(1 Ag-1时比电容高达340 F g-1)和倍率性能(15 A g-1时比电容为285 F g-1)。以PVA/KNO3作为固态电解质,rGOH作为负极,PPy@rGOH-20s为正极,所组装的非对称全固态超级电容器在0-1.6 V的电压区间内,所能达到的最大能量密度和功率密度分别为46.9 Wh kg-1和24 kW kg-1。经过10000次充放电循环后,比电容保持率为94.57%。在不同弯曲状态下连续进行充放电循环各2000次,比电容保持率为87.1%,表现出优异的循环稳定性和可弯曲稳定性。基于腐蚀微电池原理,利用石墨烯界面自组装制备了石墨烯薄膜。然后采用异相之间的界面聚合反应对石墨烯薄膜进一步修饰,得到了 PPy-rGO复合薄膜。通过对聚合时间的控制以达到调控PPy层厚度的目的。通过表征可知,当PPy聚合时间为18 h时,PPy层的厚度为5 μm,PPy-rGO薄膜的电荷存储能力最佳,在电流密度为1 mA cm-2时,其面积比电容高达1480 mF cm-2;经过10000次恒流充放后,比电容保持率为88.2%,表现出优异的循环稳定性。以PVA/KNO3作为固态电解质,PPy-rGO薄膜为电极所组装的对称全固态超级电容器,在0-1.2 V的电压范围内所能达到的最大体积能量密度和功率密度分别为31.95 Wh L-1和9000 W L-1;经过10000次充放电循环后,比电容保持率为 89.7%。采用两步水热法制备了金盏花状的MnNb2O6和CoNb2O6颗粒,平均粒径分别为600 nm和55 nm。通过与石墨烯复合进一步提升了材料整体的电化学性能。当电流密度为50 mA g-1 时,MnNb2O6@rGO 和 CoNb206@G 的可逆容量分别为 460 mAh g-1 和 508.5 mAh g-1,表现出优异的储锂能力。以它们作为负极,活性炭作为正极,组装混合型锂离子电容器,分别在0-4.0 V和0-3.5 V的电压区间内所能达到的最大能量密度为118 Wh kg-1和94.1 Wh kg-1,所能达到的最大功率密度为8000 W kg-1和8750 W kg-1;经过10000次充放电循环后,其容量保持率为88%和74.5%,表现出优异的循环稳定性。更多还原

【Abstract】 Supercapacitor,a new type of electrochemical energy storage device with fast charging/discharging rate,high power density,long cycle life,environmental protection and so on,has a broad application prospects.However,the energy density of supercapacitors based on storing charge via electrode surface reaction is much lower than that of batteries.Usually,the weakness of low energy density for supercapacitors can be solved by increasing the specific capacity of materials and/or optimizing the operating voltage range of devices.In this paper,we propose to construct self-supporting independent electrodes with three-dimensional porous structure by using double-layer capacitive graphene and pseudocapacitive materials with excellent charge storage capability(such as PB-Co,NiFe2O4,PPy,MnNb2O6 and CoNb2O6).The specific capacitance of electrodes can be enhanced by the following three points:(1)graphene carbon skeleton with the three-dimensional structure provides sufficient attachment sites for dispersing pseudocapacitive materials,which is conducive to improving the cyclic performance of composites;(2)the introduction of pseudocapacitive materials between graphene sheets can effectively alleviate the secondary accumulation of graphene during charging/discharging poccess,thereby improving rate capability and cyclic performance of composites;(3)the design of electrodes without conductive agents and binders greatly shortens the ion transport path and reduces the contact resistance between electrolyte and electrodes.In addition,the asymmetric ion capacitors are assembled in organic system to further broaden the operating voltage window of the device,so as to improve its energy density.The main research contents are as follows.PB-Co/rGOH was synthesized by one-step hydrothermal method and introducing graphene oxide.The results of scanning electron microscopy and transmission electron microscopy test show that the average particle size of PB-Co is 40 nm,and it is evenly distributed on graphene.The results of electrochemical tests show PB-Co/rGOH with PB-Co loading mass of 0.3 g exhibits the best charge storage capacity(specific capacitance of 220 F g-1 at a current density of 0.5 A g-1).After 10000 charging/discharging cycles,the specific capacitance retention of the electrode is 82.4%.The symmetrical all-solid-state supercapacitor assembled by using PVA/KNO3 as solid electrolyte and PB-Co(0.3)/rGOH as electrodes exhibits an ultra-high operating voltage range of 2.0 V,the maximum energy density of 57 Wh kg-1 and power densityof 10 kW kg-1.After 10000 charging/discharging cycles,the specific capacitance retention can be as high as 92.8%.Through the hydrothermal reaction and the introducing graphene oxide,Ni3[Fe(CN)6]2 was successfully converted into NiFe2O4,and the NiFe2O4@rGOH was obtained.The results of scanning electron microscopy and transmission electron microscopy test show that NiFe2O4 present a cube with a diameter of 35 nm,and are distributed uniformly on the graphene sheet.NiFe2O4@rGOH exhibits high specific capacitance of 488 F g-1 at a current density of 1 A g-1.After 10000 charging/discharging cycles,the specific capacitance retention is 89.8%.The symmetrical all-solid-state supercapacitor assembled by using PVA/KNO3 as solid electrolyte and NiFe2O4@rGOH as electrodes exhibits maximum energy density of 62.5 Wh kg-1 and power density of 13.5 kW kg-1 in the operating voltage range of 0-1.8 V.After 6000 charging/discharging cycles,the specific capacitance retention is up to 93.2%.PPy@rGOH with abundant cross-linked pore structure was obtained by hydrothermal method and electropolymerization method.The content of PPy in PPy@rGOH can be adjusted by controlling the time of electropolymerization.According to the results of electron microscopy tests and electrochemical measurements,the obtained composite gel with the electropolymerization time of 20 s can keep the cross-linking structure of rGOH well without agglomeration,and exhibits the best specific capacitance of 340 F g-1 at a current density of 1 A g-1 and the rate performance(specific capacitance of 285 F g-1 at a current density of 15 A g-1).The asymmetrical all-solid-state supercapacitor assembled by using rGOH as negative electrode,PPy@rGOH-20s as positive electrode and PVA/KNO3 as solid electrolyte shows the maximum energy density of 46.9 Wh kg-1 and power density of 24 kW kg-1 in the operating voltage range of 0-1.6 V.After 10000 charging/discharging cycles,the specific capacitance retention is up to 94.57%.After continuous 2000 charging/discharging cycles under different bending conditions,the specific capacitance retention is 87.1%,indicating excellent cycling stability and flexibility stability.Graphene film was formed on the surface of copper foil based on the corrosion battery composed of copper foil and GO in acidic conditions.Then the PPy layer with a foam-like structure was polymerized on the graphene film by interfacial reaction between organic/water phase.By controlling the polymerization time,the PPy-rGO composite films with different thickness of PPy were obtained.According to the SEM and mapping of N elements,when the polymerization time of PPy is 18 h,the thickness of PPy layer is 5 um,and the PPy-rGO composite films have the best charge storage capacity of 1480 mF cm’2 at a current density of 1 mA cm-2.After 10000 charging/discharging cycles,the specific capacitance retention is 88.2%,showing excellent cyclic stability.The symmetrical all-solid-state supercapacitor assembled by using PVA/KNO3 as solid electrolyte and PPy-rGO-18 h as electrodes displays maximum volumetric energy density of 31.95 Wh L-1 and power density of 9000 W L-1 in the operating voltage range of 0-1.2 V.After 10000 charging/discharging cycles,the capacitance retention can be as high as 89.7%.Calendula-like MnNb2O6 particles with an average particle size of 600 nm and CoNb2O6 particles with an average particle size of 55 nm were prepared by two-step hydrothermal method,respectively.Then the electrochemical properties of the material were further improved by compounding with graphene.The reversible capacity of MnNb2O6@rGO and-CoNb2O6@G is 460 mAh g-1 and 508.5 mAh g-1 at a current density of 50 mA g-1,showing excellent lithium storage performance.The hybrid lithium ion capacitor assembled by using them as anode and activated carbon(AC)as cathode shows maximum energy density of 118Wh kg-1 and 94.1 Wh kg-1,as well as maximum power density of 8000 W kg-1 and 8750.W kg-1 in the operating voltage range of 0-4.0 V and 0-3.5 V,respectively.After 10000 charging/discharging cycles,the capacity retention can remain 88%and 74.5%.更多还原