Application Of High-Performance Binders For Silicon Anode In Lithium-Ion Battery

Lithium-ion batteries have been widely used in different kinds of electronic devices for their advantages,such as high energy density,low self-discharge,long cycle life,and high cut-off voltage.Active anode materials like silicon have received increasing attention due to its high theoretical capacity.However,the high volumetric expansion of silicon anode,which often results in low rate capability and limited cycle life,has hindered the practical use of silicon anode.Binder is a crucial part of electrode fabrication.Therefore,it is expected to improve electrochemical performance by design,synthesis,and application of new binders.In this thesis,different binders such as elastic polymer,porous polymer,and organic/inorganic composite binders have been explored.The comprehensive structure characterization,property investigation,and fundamental mechanism studies are carried out.The main research results are as follows:?1?By introducing the DMS soft chain into PI,the elasticity of the prepared silicon electrode is improved.The mechanical stability is improved since the elastic binder is capable of accommodating the extreme volume change of silicon anode.The result demonstrates that the reversible capacity of PSI/Si is 1418 m Ah/g after 50cycles,with capacity retention of 88%.The capacity retention is still up to 73%after100 cycles,which is clearly superior to the properties of the PI/Si and SA/Si electrodes.?2?To enhance the processibility of the PSI binder,new binders of PEI-b-PDMS belong to the SILTEM family are used by replacing the hard PI chain with PEI.The elasticity and solubility of the binder is significantly improved compared to the PSI binder.After 50 cycles,the discharge capacities of the SILTEM/Si and SA/Si electrode are 2679 m Ah/g and 496 m Ah/g with capacity retention of 92%and 24%.After 100 cycles,the discharge capacities of the SILTEM/Si and SA/Si electrode are2312 m Ah/g and 319 m Ah/g and capacity retention of 81%and 15%.?3?A unique polymer of intrinsic microporosity with carboxylic acid functional groups?PIMCOOH?is designed,synthesized,and utilized as a binder for the silicon-based anode for lithium-ion battery.The mechanical test of the PIM-COOH/Si electrode suggests that the PIM-COOH binder has excellent adhesion to the components within the electrodes.The electrochemical test indicates that the discharge capacities PIM-COOH/Si and SA/Si electrode are 1561 m Ah/g and 1064m Ah/g and the corresponding capacity retention are 92%and 24%after 50 cycles.After 100 cycles,the discharge capacities of the PIM-COOH/Si and SA/Si electrodes are 872 m Ah/g and 319 m Ah/g.The SEM results indicate that the PIM-COOH binder is more capable of maintaining the electrode integrity.As to the rate performance,the average capacities of the PIM/Si electrode exceed those of the SA/Si electrode by 9%,46%,and 147%under the current densities of 0.2 A/g,0.5 A/g and 1 A/g.?4?An organic/inorganic composite binder of PAA/TEOS is used as binder which offers excellent adhesion strength due to abundant hydrogen bonding among components in the electrode.Excellent compatibility between the PAA chain segment and Si O₂ is demonstrated.After 50 cycles,the reversible capacity of the PAA/Si is327 m Ah/g with capacity retention of 41%,which are much lower than the PAA-TEOS/Si electrode?1418 m Ah/g and 74%?.After 100 cycles,the reversible capacity of the PAA-TEOS/Si electrode is still retained as 1178 m Ah/g with capacity retention of 50%,which are superior to those of the PAA/Si electrode?288 m Ah/g and 25%?.