Research On Transition Metal Chalcogenides Applied In Supercapacitors

As a new energy storage device,supercapacitors have the advantages of both traditional capacitors and batteries,and have attracted the attention of researchers worldwide.However,it is still very limited in practical applications due to the low energy density.According to the calculation formula(E=1/2 CV2)of the energy density of supercapacitors,it can be found that there are two main ways to increase energy density:one is to design and prepare a electrode material with high specific capacity(C),the other is to assemble an asymmetric supercapacitor to obtain a wide voltage window(V).According to the above analyses,the metal selenides((Ni,Co)Se2 microspheres,BiSe and Bi2Se3 nanosheets)and prussian blue and its analogues derived metal compounds(Co0.85Se nanocubes,Co9S8 hollow nanocubes and Fe2O3 nanoparticles)were design and prepare for electrode materials of supercapacitor.Moreover,a new asymmetric supercapacitor was constructed by using those electrode materials and appropriate electrolytes to further enhance the overall performance of the device.The main research contents and results are as follows:1.A facile one-step solvothermal method has been designed and employed to synthesize uniform Ni,Co bimetallic selenides(termed as(Ni,Co)Se2)microspheres and BiSe nanosheets.The(Ni,Co)Se2 demonstrate enhanced capacitive performances of 106 mAh g-1 at 1 A g-1,which are more than two times of pure NiSe2 and five times of pure CoSe2 at the same current densities.Similarly,the BiSe nanosheets also exhibits a high specific capacity of 104 mAh g-1 at 1 A g-1 and good rate capability.Interestingly,a novel asymmetric supercapacitor is fabricated by using(Ni,Co)Se2 nanospheres as the positive electrode and BiSe nanosheets as the negative electrode,which possesses extended operating voltage of 1.65 V,high energy density of 34.4 Wh kg-1 at a power density of 373 W kg-1,and an acceptable cycling stability of 85%capacity retention after 5000 cycles.2.The Co0.85Se nanocubes and Fe2O3 nanoparticles materials were designed and prepared by using corresponding prussian blue analogues(PBA)as precursors.The electrochemical test results show that the Co0.85Se has specific capacity of 40.8 mAh g-1 at 1 A g-1,which is higher than the corresponding Co-PBA precursor.Similarly,Fe2O3 nanoparticles also show a high specific capacity of 51.5 mAh g-1 at 1 A g-1 and a good rate capability.Based on their complementary potential window,a novel asymmetric supercapacitor is assembled by using Co0.85Se nanocubes and Fe2O3 nanoparticles as positive and negative electrodes,respectively.The results show that Co0.85Se//Fe2O3 ASC has a wide working voltage(1.6 V)and good long-term cycle durability.3.The uniform C09S8 hollow nanocubes and Bi2Se3 nanosheets were designed and prepared via one-step solvothermal method by employed prussian blue analogues(PBA)and bismuth metal-organic framework as precursors,respectively.The C09S8 hollow nanocubes exhibit high specific capacity of 108.6 mAh g-1 at 1 A g-1.Similarly,Bi2Se3 nanosheets also show a specific capacity of 49 mAh g-1 at 1 A g-1 and good rate capability.Based on their unique structure,high specific capacity and complementary working voltage,a novel asymmetric supercapacitor(ASC)is assembled based on C09S8 hollow nanocubes positive and Bi2Se3 nanosheets negative.The results show that the Co9S8//Bi2Se3 ASC has a wide working voltage(1.6 V)and excellent cycle performance(capacitance retention rate reaches 77%after 10,000 cycles).