Preparation And Energy Storage Research On Electrode Materials Of Lithium Ions Supercapacitors

Lithium-ion supercapacitors, one of the hybrid supercapacitors, are developed as a new type of energy storage device between lithium-ion storage batteries and electric double layer supercapacitors in recent years. Lithium-ion supercapacitors have different charge and discharge principle between cathode and anode electrode materials. Lithium-ion supercapacitors are designed using the same principles as electrode materials of electric double layer supercapacitors. Lithium-ion supercapacitors are constructed using electrode materials of being able to achieve lithium-ion deintercalation in lithium-ion batteries and electrode materials of electric double layer supercapacitors. Lithium-ion supercapacitors exhibit higher energy density than that of electric double layer supercapacitors. The higher energy density of lithium-ion supercapacitors is mainly related to its electrode materials and composition compared with electric double layer supercapacitors. The electrode materials of lithium-ion supercapacitors are able to achieve lithium-ion intercalation/deintercalation thin that of electric double layer supercapacitors during the charge and discharge process. Hence, lithium-ion supercapacitors exhibit higher energy density than that of electric double layer supercapacitors. Lithium-ion supercapacitors exhibit better power density than that of lithium-ion batteries. The better power density of lithium-ion supercapacitors is mainly related to its faster charge and discharge rates compared with lithium-ion batteries. Lithium-ion supercapacitors can achieve faster charge and discharge rate compared to lithium-ion batteries. Lithium-ion supercapacitors have broad development prospects. They are expected to be widely used in the field of new energy resources. The electrode materials of lithium-ion supercapacitors are one of the important factors, which affect the electrochemical properties of lithium-ion supercapacitors. The core issue of preparing electrode material of lithium-ion supercapacitor is how to achieve fast lithium-ion intercalation and deintercalation problem.Several electrode materials of lithium-ion supercapacitors are prepared and studied based on manganese and molybdenum compounds in this text. MnO₂/TiN NTA electrode material is prepared because that lithium-ion exchange capacity in manganese dioxide is strong in 1 M LiOH alkaline electrolyte. MnO₂/TiN NTA can intercalate and deintercalate lithium-ion. Li_0.7MnO₂/TiN NTA is prepared by pre-inserting lithium-ion into MnO₂ to solve the limited amount of lithium ion in manganese dioxide in near neutral solution. The Li_0.7MnO₂/TiN NTA can insert lithium-ion in 1 M Li₂SO₄ electrolyte. Conductivity of molybdenum oxide and molybdenum nitride is very similar to that of metal. The conductivity of them is greater than that of manganese dioxide, which is a semiconductor electrode material. Therefore, electrode materials based on molybdenum are also studied in this context. MoO_x/TiN NTA electrode material is prepared in ammonium molybdate electrolyte by electrochemical deposition method. A large number of MoO_x can fall off TiN NTA with increasing deposition time. Carbon-coating process is used to alleviate the phenomenen that electroactive material of MoO_x falls off TiN NTA with increasing deposition time effectively. MoNx/TiN NTA electrode material with high stability performance is prepared by nitriding process. To improve the electrical tramission capacity and specific capacitance of MoNx/TiN NTA, molybdenum nitride-graphene nitride/titanium nitride nanotube arrays （MoNx-GNN/TiN NTA） is fabricated by using nitride graphene. The main contents are as follows.（1） Preparation and energy storage research on electrode materials of lithium-ion supercapacitors based on manganese-containing compound/titanium nitride nanotube arrays.Manganese dioxide/titanium nitride nanotube arrays （MnO₂/TiN NTA） is prepared according to different exchange capacity of alkali metal ions in MnO₂ in 1 M LiOH electrolyte. MnO₂ is able to intercalate lithium-ion in alkaline electrolyte. TiN NTA with high conductivity improve the electron transport capacity of MnO₂. In order to further certify the exchange capacity of lithium-ion, the electrochemical performance of MnO₂/TiN NTA is researched in 1 M KOH electrolyte. The electrochemical mechanism of MnO₂/TiN NTA in both electrolytes is analyzed theoretically. Scanning electron microscope and X-ray diffraction are used to analysis and study the structure and morphology of MnO₂/TiN NTA. Scanning electron microscope, X-ray diffraction, and Raman spectrometer etc. are used to analysis and study the structure and morphology of prepared electrode materials. Electrochemical performances are studied using cyclic voltammetry curves, galvanostatic charge-discharge curves, and electrochemical impedance spectroscopy etc..MnO₂ can not able to intercalate a large number of lithium-ion because its lithium-ion exchange capacity is very weak in neutral electrolyte. So lithium manganese dioxide intercalation compound Li_0.7MnO₂ is synthesized by electrochemical deposition method to pre-insert lithium-ion into MnO₂. The Li_0.7MnO₂ can sufficiently intercalate lithium-ion in 1 M Li₂SO₄ electrolyte, which solves the limited amount of lithium ion in manganese dioxide in near neutral solution. Two different electrochemical reaction mechanisms on Li_0.7MnO₂ and MnO₂ are explained in 1 M Li₂SO₄ electrolyte. The morphology, microstructure, capacitance performance, cycle stability, and electrochemical impedance spectroscopy performance of Lio.7Mn02/TiN NTA and MnO₂/TiN NTA are studied and compared.（2） Preparation and energy storage research on electrode materials of lithium-ion supercapacitors based on molybdenum oxide/titanium nitride nanotube arrays.Molybdenum oxide/titanium nitride nanotube arrays （MoO_x/TiN NTA） is fabricated through electrochemical deposition method. MoO_x is able to intercalate and deintercalate lithium-ion in 1 M LiOH electrolyte. The pseudocapacitance storage mechanism of MoO_x is explained in 1 M LiOH electrolyte. Scanning electron microscope and X-ray diffraction are used to analysis the structure and morphology of MoO_x/TiN NTA. Energy dispersive X-ray detector is used to analyse and identify element composition of MoO_x/TiN NTA.Carbon-coating process is used in order to alleviate the phenomenen that electroactive material of MoO_x falls off TiN NTA with increasing deposition timey. It alleviates the exfoliate phenomenon of MoO_x effectively. Cycle stability of MoO_x/C-TiN NTA is better than that of MoO_x/TiN NTA after carbon coating. The reason that electroactive material of MoO₂ （or MoO3） falls off TiN NTA with increasing deposition time is explained. MoO_x/C-TiN NTA has stronger electron transport capability than that of MoO_x/TiN NTA.（3） Preparation and energy storage research on electrode materials of lithium-ion supercapacitors based on molybdenum nitride/titanium nitride nanotube arrays.Molybdenum nitride/titanium nitride nanotube arrays （MoNx/TiN NTA） is fabricated by the electrodeposition of molybdenum oxide onto titanium dioxide nanotube arrays （TiO₂ NTA） and subsequent nitridization in ammonia at high temperature. MoNx is able to intercalate and deintercalate lithium-ion during electrochemical charge and discharge process. Cycle stability of MoNx/TiN NTA is much better than that of MoO_x/TiN NTA. Scanning electron microscope and X-ray diffraction are used to analysis the structure and morphology of MoNx/TiN NTA. Energy dispersive X-ray detector is used to analyse and identify element composition of MoN/TiN NTA.Molybdenum nitrig-graphene nitride/titanium nitride nanotube arrays （MoNx-GNN/TiN NTA） is fabricated by putting MoO/TiO₂ NTA into graphene oxide aqueous for adsorption and subsequent nitridization in ammonia at high temperature. Scanning electron microscope and X-ray diffraction are used to analysis and study the structure and morphology of MoNx-GNN/TiN NTA. Energy dispersive X-ray detector is used to analyse and identify element composition of MoNx-GNN/TiN NTA. The electron transmission capacity of MoNx-GNN/TiN NTA is enhanced after introducing GNN into MoNx/TiN NTA. Specific capacitance of MoNx-GNN/TiN NTA is bigger than that of MoNx/TiN NTA.