| There is no doubt that lithium ion battery is one kind of the most widely used energy conversion devices.With the upgrading of technology and the emergence of a large number of portable electronic devices and electric vehicles,the performance requirements for lithium ion batteries including safety,energy density and cycling life has improved.However,lithium ion battery using liquid electrolyte is prone to thermal runaway at high temperature,and has the potential safety hazards such as flammability of organic components.Much research has focused on the safer solid-state polymer battery（the polymer cathode+solid polymer electrolyte,lithium metal anode）.Among all of the investigated polymer,polyethylene oxide（PEO）is the most widely studied.However,the low ionic conductivity at room temperature of PEO can’t satisfy the requirements for application.On the other hand,more and more researches are directed to improve the energy density of lithium ion batteries.Two of the most important factors affecting energy density of lithium-ion batteries are the voltage of the cathode material or lithium storage capacity of the electrode materials.The choices of cathode materials are relatively few and their development is limited.Silicon shows a lot of advantages,such as low cost,very high lithium storage capacity.Theoretical capacity of silicon is 4200 mAh/g,which is 12 times more than graphite anode.So developing and modifying the anode have become the direction of many researches.But the application of silicon still exists a lot of problems,such as big irreversible capacity and serious volume change,bad cycle stability,and etc.Lithium aluminate（LiAlO2,abbreviated as LAO）is a fast lithium ion conductor with high ionic conductivity at low temperatures.Our work will proceed based on the property and the requirements of lithium ion battery materials.In the first part of this thesis,the main content is to improve the electrochemical properties of PEO by doping LAO doping,which reduced the crystallinity of PEO polymer electrolyte,improve the solubility of lithium salt and its ionic conductivity.In the second part of this thesis,we study the influence LAO coating on silicon particles on the irreversible capacity.The results are as follows:（1）Using a simple hydrothermal method,3-5μm rod-like lithium aluminate（LAO）was synthesized using cetyl trimethyl ammonium bromide（CTAB）as a surfactant.The rod-like lithium aluminate and SN were introduced into PEO/lithium salt system.And the film was also made by the traditional solution casting method.When the mass fraction of the lithium aluminate is 10%,SN is 15%,the conductivity at room temperature reaches the highest,which is 1.36×10-5 S/cm.When the test temperature is 80℃,the conductivity is up to 1.25×10-3 S/cm.The cell was tested under 60℃and 0.1 C rate.The first discharge capacity is 141.3 mAh/g.And the capacity retention rate was 84.9%after 25 cycles.Combined with the other characterization analysis of the composite electrolyte material,the co-addition of SN and lithium aluminate greatly improved the electrochemical properties of PEO as solid electrolyte in lithium ion batteries.（2）The silicon material coated with lithium aluminate was fabricated by hydrothermal reaction and co-stirring.A very thin coating layer was eventually formed.The irreversible capacity loss of silicon with lithium aluminate coating was greatly reduced.At a rate of 200mA/g,the discharge specific capacity of the first cycle was 2547 mAh/g,the discharge specific capacity of the second cycle was2398.7mAh/g.And the capacity retention rate was 94.2%,which was much higher than that of pristine silicon nano-material electrode（84.7%）.The pretreatment of aluminum aluminate on the surface of the silicon particles can effectively reduce the reaction of SEI film formation and reduce the irreversible capacity. |
