| With the development of social economy,science,and technology,the demand for lithiumion batteries with high capacity,high energy density,and long life is becoming more and more urgent.The specific capacity of graphite negative electrode of traditional energy storage battery has reached its theoretical limit of 372 m Ah/g,and its development potential in the future is close to the limit.Silicon is the cathode material with the highest theoretical specific capacity among the known cathode materials,which has become the research hotspot of lithium-ion batteries;However,the volume expansion in the process of silicon charge and discharge affects its energy storage efficiency,which limits its application.Therefore,the main research direction of silicon materials now focuses on the structural design and modification of silicon cathode materials.In this thesis,the effect of melt treatment on the microstructure of hypereutectic Al-20 Si binary alloy,such as the amount of modifier,modification time,and cooling rate,was systematically studied,to achieve the purpose of regulating the microstructure of the silicon phase in the alloy.Porous silicon materials were prepared by acid etching and dealloying with silicon phase structure controlled alloy as precursor alloy.The porous silicon was characterized by BET and SEM.In the preparation of porous silicon as the cathode,lithium pills as the electrode assembly into CR2016 button batteries,different melt treatment process preparation systems studied the electrochemical properties of porous silicon material,studies the influence of different kinds of electrolyte on the electrochemical properties,characterized the circulation of electrode surface morphology before and after the change.And draw the following conclusions:（1）The microstructure of Al-20 Si alloy is uniform and fine,and the primary silicon phase can be controlled between 10μm and 20μm.Based on laboratory conditions,the microstructure of Al-20 si alloy with 1.2wt.% Al-3P intermediate alloy is better after holding at 780℃ for20 min,and the primary silicon can be refined to 28μm.At the same time,the size of primary silicon can reach 17μm,which is reduced by 39.3% compared with that before the quenching process.The microstructure of Al-20 Si alloy with 0.8wt.% rare earth yttrium（Y）added after holding at 780℃ for 20 min has a good metamorphism effect,and the size of primary silicon is refined to 19μm.The size of primary silicon can reach 16μm when combined with water quenching and chilling process.0.8wt.% Y was added to the Al-20 Si alloy melt,and 1.2wt.% Al-3P was added after holding at 780℃ for 20 min.Combined with the water quenching process,the primary silicon size of the alloy sample was refined to 14μm.（2）After the process of "modification refinement + water quenching ",the Al-Si alloy can be dealloying to prepare porous silicon with three-dimensional dendrite.The samples prepared by the dealloying process were characterized by XRD,SEM,BET,and other instruments.The experimental results show that the prepared samples match well with the diffraction pattern of pure silicon standard card PDF#78-2500,and there are no other impurity components such as aluminum.The silicon powder product prepared by this experimental process is a new type of porous silicon with porous structure characteristics,and the specific surface area of the prepared porous silicon powder sample is 29.9243m~2/g.（3）The prepared porous silicon was used as anode material to assemble the lithium-ion buckle semi-battery,and the battery showed good charge-discharge cycle performance.Using1 MLi PF6/EC: DMC: EMC=1:1:1（V/V）: 5%FEC as electrolyte,the cyclic charge-discharge test was carried out at the current density of 100 m A/g.The results show that: Based on the addition of 1.2wt.% Al-3P modifier at 780℃,the first charge specific capacity of porous silicon prepared after 10 min of modification treatment + water quenching and cooling is the largest,the charge and discharge specific capacity of the first cycle is 1579.1m Ah/g and 3708.2m Ah/g,and the first coulombic efficiency is about 42.58%.After 10 cycles,the charge-discharge capacities are 108.8m Ah/g and 107.8m Ah/g,respectively.After 50 cycles,the specific capacities of charge and discharge are 69.1m Ah/g and 68.4m Ah/g,respectively,and the coulombic efficiency is101.02%.For the specific capacity of the first charge,under the condition of Y modification of0.8wt.% at 780℃ and water quenching,the porous silicon prepared by Y modification holding for 30 min has the largest specific capacity for the first charge,which is 1628.4m Ah/g and3284 m Ah/g,respectively.The coulombic efficiency of the first cycle is 49.59%,and the specific capacities of charge and discharge after 10 cycles are 144 m Ah/g and 145.8m Ah/g,respectively.After 50 cycles,the specific capacities of charge and discharge are 114.4m Ah/g and 116.8m Ah/g,respectively,and the coulombic efficiency is 97.95%.The first charge specific capacity of porous silicon prepared by "Y+P" composite modification holding for 20min+water quenching and cooling at 780℃ is the largest,the first charge specific capacity of 2044.5m Ah/g and3628.3m Ah/g,respectively,and the coulombic efficiency of the first cycle is 56.35%.After 10 cycles,the charge-discharge capacities are 419.8m Ah/g and 434.6m Ah/g,respectively.After 50 cycles,the specific capacities of charge and discharge are 159.4m Ah/g and 159.6m Ah/g,respectively,and the coulombic efficiency is 99.87%.By comparing the charge-discharge cycle curves of porous silicon under the three technological conditions and the specific charging capacity after 10 and 50 cycles,it can be seen that the porous silicon prepared by "Y+P" composite metamorphic holding for 20 min at 780℃ + water quenching and cooling has better charge-discharge cycle stability.（4）By comparing different electrolytes,it can be seen that based on the electrolyte containing 5%FEC,the half-cell assembled with prepared porous silicon has a better charge specific capacity retention rate in the 1st,2nd,50 th,and 90 th cycles than the half-cell assembled with no FEC electrolyte.Through the AC impedance characterization,it is found that the electrolyte additive FEC can reduce the electrochemical impedance before and after half cell cycle,to improve the performance of the battery;The formation potential of SEI film increased from 0.6V to 1.2V,indicating that the formation potential of SEI film on the electrode surface will be increased in the presence of FEC.FEC is preferentially reduced at 1.2V to form SEI film,which effectively inhibits the decomposition of electrolyte solvent at 0.6V. |
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