| Since the commercialization of lithium-ion batteries,the actual specific capacity of the traditional graphite anode is close to the theoretical value of 372 mAh g-1.The limited improvement space becomes the bottleneck to seriously restrict the further development of lithium ion battery.Therefore,the development of new anode material with the advantage of high energy density,high power density and high cycle stability to replace the traditional graphite anode,is particularly important.The silicon material is currently known to have the highest theoretical capacity about 4200 mAh g-1,and have a relatively low potential?<0.5V VS Li+/Li?,compared with other negative materials.Silicon anode can provide higher output voltage when matching with suitable cathode,and is regards as an important candidate for the anode material of lithium-ion batteries.However,the large volumes change of the Si material during the process of intercalation and disintercalation of lithium ions,?close to 400%?,causes the gradual pulverization of the material and the collapse of the structure,and results in the degradation of the cycle performance.In addition,the conductivity of silicon is relative low,about 6.7×10-4 S cm-1,which further damaged the cycle performance of battery.The nanostructures of Si help to reduce the volume change during the charge and discharge cycle,shorten the transport path of ions and electrons,and enhance the cycle performance.In this thesis,we designed silicon-CuO coaxial nanowire arrays structure,and enhanced the conductivity by suitable doing to improve the cycle performance of lithium-ion batteries based on Si-anode.The main content and results of this paper are as follow:1.The Cu?OH?2 nnaorod arrays were prepared by electrochemical anodic oxidation,and the CuO nanowires were obtained after thermal annealing.The effects of various annealing temperatures on the structure and morphology of CuO nanowires were investigated.The results showed that the phase transition and the separation of CuO nanowires could be realized by annealing at 200?.The CuO nanowire arrays maintain a good crystal structure and thus good transport properties,and are suitable for the base material of silicon anode.2.The silicon layer was perapared by plasma enhanced chemical vapor deposition.The effects of deposition time,carbon doping concentration,and C/B co-doping concentration on the structure and morphology of silicon nanostructure were investigated.SEM results showed the formation of silicon-Cu O coaxial nanowire arrays.Raman results found that the deposited silicon layer consisted of large amount of amorphous silicon,and small amount of nanocrystals.Suitable C-doping increased the deposition rate of silicon.Keeping the CH4 rate of flow at 2 sccm,the deposition rate of silicon increase with the increasing of B doping concnentration.The effect of B doping on the deposition rate of silicon is larger than that of C doping.3.The cycling performance of CuO-Si coaxial nanowire arrays as the anode electrode of the battery was studied,and the optimal C doping concentration and B doping concentration were explored.The results showed that although both Si and CuO contributed to the charge and discharge capacity of the battery,the main contribution was come from Si.The lower C doping concentration was favorable for the performance of the battery and the optimal rate of flow for C doping was 2 sccm,which related to a discharge capacity retention rate of 93.8%after rate charge/discharge 60 cycles,and a discharge capacity retention rate of 68.8%at a maximal current density of 0.36 mA cm-2.Keeping the rate of flow of CH4 at 2sccm,the optimal rate of flow for B doping was 3%,which related to a discharge capacity retention rate of95.3%after rate charge/discharge 60 cycles,and a discharge capacity retention rate of 73.8%at a maximal current density of 0.36 mA cm-2. |
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