Preparation Of Nickel/Tin-based Micro-Nanostructured Metal Oxide And Selenide Materials And Their Applications In Energy Storage

With the gradual consumption of the fossil fuels and the increasing demand for energy,the development of clean energy storage system is particularly important.Lithium ion batteries(LIBs),as efficient energy storage systems,have been successfully applied in portable electronic devices.However,it is difficult for LIBs to meet the requirements of large-scale devices that require large power/energy density.Therefore,exploring new type of electrode materials with high capacity is the key to solve the above problems.At present,commercial graphite anode material has low capacity,so it is particularly important to develop new anode material with high capacity.The limited reserves and uneven distribution of lithium in the earth is also an obstacle for large-scale applications of LIBs.Sodium ion batteries(SIBs)have large application potential due to the sodium has larger reserves and more environmentally friendly than lithium,and they have similar reaction mechanism with LIBs.However,some anode materials for LIBs are not appropriate for SIBs,thus,developing novel anode materials for SIBs with high performance are urgently needed.Among anode materials for LIBs,conversion-type materials have great potential for application due to their high specific capacities when compared with insertion-type materials,especially nickel-based and tin-based oxides,for example,the specific capacities of NiO and SnO2 are 718 and 784 mAh g-1,respectively.Nickel and tin are environmentally friendly and also have relatively high reserves in the earth.However,nickel-based and tin-based oxides possess poor conductivity and volume expansion problems in the reaction processes,such as the volume expansion rate of the tin-based material is as high as 358%during the alloy/de-alloying process,which resulting in poor cycle and rate performances.Among anode materials for SIBs,nickel-based selenide shows high theoretical specific capacity(494 mAh g-1),which has been considered as one of the promising anode materials,however,its initial coulombic efficiency is low and resulting in a high irreversible capacity,and it would react with the traditional carbonate-based electrolytes during charge-discharge processes,which resulting the capacity loss quickly.In addition,the cycle performances at high current density need to be further improved.This dissertation focuses on the above shortcomings of nickel/tin-based oxides and nickel-based selenides by fabricating unique micro-nanostructures to buffer the volume expansion and shorten the diffusion paths of Li+/Na+.In addition,wrapping graphene on the surface of electrode materials,which could improve the overall conductivity and buffer the volume expansion.Through the above modification,the electrochemical performances of the electrode materials have been improved to some extent.The main research works are listed as follows:(1)Controllable preparation of hexagonal ring-core NiCo2O4/NiO composites and their electrochemical performances for lithium ion batteries.Mesoporous hexagonal ring-core NiCo2O4/NiO nanoparticle composites have been synthesized by hydrothermal and subsequent calcination processes.The size of hexagonal ring-core NiCo2O4 was 200-300 nm,and the size of granular NiO was 15-30 nm.When the composite was used as anode for LIBs,its capacity could be maintained at 894 mA g-1 at 200 mA g'1 after 200 cycles.The composite with unique mesoporous hexagonal ring-core structure shows large specific surface area,which is in favor for the sufficient contact between material and the electrolyte.It also could shorten the diffusion path of Li+ and accelerate the reaction rate during the electrochemical reaction processes.In addition,the synergy effect between nano-sized NiO and hexagonal ring-core structured NiCo2O4 might improve the electrochemical performance of the composite.(2)Synthesis of mesoporous Mn-Sn bimetallic oxide nanocubes and their electrochemical performances for lithium ion batteries.Mesoporous Mn-Sn bimetallic oxide nanocube materials(15-30 nm)have been synthesized by simple hydrothermal reaction and calcination process under Ar atmosphere.When the material was applied as anode for LIBs,the capacity could was 857 mAh g-1 after 400 cycles at 0.5 A g-1.Mn-Sn bimetallic oxide nanocube//LiCoO2 lithium ion full cells have been successfully assembled,and the full cell shows initial capacity of 1153.7 mAh g-1,and the capacity was 369 mAh g-1 after 320 cycles at 500 mA g-1.The mesoporous structure is beneficial for sufficient contact between electrolyte and the electrode material.In addition,the mesoporous structure could also buffer the volume expansion during the cycling processes to some extent.Synergistic effect might exist between the manganese oxide and the tin oxide,and the electrochemical mechanism might be a mixed alloy/de-alloy and the conversion-type mechanism.(3)Mesoporous tin-based oxide nanospheres/rGO composites as advanced anodes for lithium ion half/full cells and sodium ion batteries.Firstly,the NiSn(OH)6 nanosphere precursors have been prepared by hydrothermal reaction and then microporous Ni-Sn bimetallic oxide and mesoporous NiO/SnO2 composite nanospheres have been synthesized through calcining the precursors at different temperatures.The mesoporous SnO2 nanospheres have been prepared by etching the NiO/SnO2 composite using HNO3,and finally wrapping rGO via a hydrothermal process.When they were applied as anodes for LIBs,the NiO/SnO2@rGO exhibits best electrochemical performances among these composites.At a current density of 500 mA g-1,the capacity was maintained at 1078.3 mAh g-1 after 350 cycles.In addition,the NiO/SnO2@rGO-LiCoO2 lithium ion full cells have been successfully assembled to prove the possibility for application,the full cell shows capacity of 468 mAh g-1 after 400 cycles at 500 mA g-1.The unique mesoporous nanosphere structure could increase the contact area between the material and the electrolyte,and buffer the volume expansion.The wrapping of high conductive rGO could improve the overall conductivity,and the synergy effect between NiO and SnO2 also in favor the improving electrochemical performance of the composite.(4)Controllable preparation and electrochemical performances of hierarchical structured NiSe2 and NixCo1-xSe2 micro-nanospheres.The NixCo1-xSe2(0<x<1)micro-nanospheres with hierarchical structure have been fabricated by two-step solvothermal processes.The hierarchical micro-nanospheres are in favor of keeping the stable structure during the reaction process and increasing the contact area with the electrolyte.A series of nickel-based selenides with different ratios of nickel and cobalt have been synthesized,and when they were used as anode material for SIBs,the Ni0.5Co0.5Se2 micro-nanospheres show the best performances.The capacity could be maintained at-300 mAh g-1 after 1100 cycles at 2 A g-1.The electrochemical performances of Ni0.5Co0.5Se2 micro-nanospheres in carbonate-based and ether-based electrolytes were investigated,and the results showed that the selenide materials would partly dissolved in carbonate-based electrolytes,leading to rapid capacity decline,however,the electrode material was stable in the ether-based electrolyte.In addition,the material also exhibited excellent rate performances,to explain the reasons for this phenomenon,the CV curves at different scan rates were performed and the results indicated that there was capacitive contribution during the electrochemical processes.