The High Performance Of Polyimide Binder For Li-ion Batteries Si-based Anode

Rechargeable Li-ion batteries(LIBs) have attracted widely attentions due to high working voltage, high specific energy and long cycle life. With development of new energy vehicles, the high capacity and high performance anode material has been one of the hot topics in Li-ion batteries. Silicon material has attracted considerable attention because it has an extremely high theoretical capacity of 4200 mAh g-1, high natural abundance and relatively low potential for alloying/de-alloying with Li ion. However, the volume expansion leads to fading capacity during the repeated insertion and extraction of lithium, which limit application of the high capacity anode material. The binder plays an essential role in Li-ion batteries. The commercial polyvinylidene fluoride(PVDF) binder is not sufficient to accommodate the significant volume changes(around 300%) in active silicon material. In this manuscript, we present polyimide(PI) with high mechanical strength and excellent thermal stability is firstly used as a polymeric binder of Si-based anode for lithium ion batteries. This thesis mainly includes the following aspects.1) Compared to mechanical strength and thermal stability of PI, PVDF and PAA-CMC, which showed PI with high mechanical strength and excellent thermal stability. The influence of content of binder was investigated on the electrochemical performance of silicon anode. When the slurry was prepared by mixing silicon particles as an active material(50 wt.%), cabon black(CB) and acetylene black(AB)(w:w=1:1) as an electronic conducting agent(25 wt.%) and PI(25 wt.%), the silicon electrode exhibited a first high reversible capacity of 963 mAh g-1. The annealed treatment can reconstructed the morphologies of silicon electrode, which further improved the electrochemical performance of silicon anode. The annealed silicon electrode exhibited a high reversible capacity of 843.3 mAh g-1 at a 0.1 C current density and charge capacity retention of 70.5% for 50 cycles.2) The core/shell structure silicon nanocomposites material for lithium ion batteries was synthesized by pyrolysis PAN as carbon source and PI as binder. The influence of the different carbonization temperature was investigated on the electrochemical performance of Si-based nanocomposites material. With increasing carbonization temperature, the electrochemical performance of nanocomposites material was improved. The carbon coating was formed on the surface of nano silicon, which is effective in improving conductivity and Li ion insertion of nanocomposites material. It revealed that the Si-based nanocomposites material exhibited first high reversible capacity of 2813.3 mAh g-1 and reversible capacity of 1663.5 mAh g-1 and charge capacity retention of 59.1% for 50 cycles.3) The mixed PI and cellulose acetate(CA) polymer was acted as a binder for lithium ion batteries Si-based anodes. The common function of PI with high mechanical strength and excellent thermal stability and CA with ester group mixed binder improved the cycle performance of Si anode. It revealed that the Si-based anode by 350 oC exhibited first high reversible capacity of 2132.8 mAh g-1 and a coulombic efficiency of 85.2% in the first cycle. After 50 cycles, the electrode still remains the stable reversible capacity of 1459.6 mAh g-1 and charge capacity retention of 68.4%.4) The mixed PI and polyphenyl derivative(PBP) polymer was acted as a binder for lithium ion batteries Si-based anodes. The common function of PI and PBP with conjugated system mixed binder improved the cycle performance of Si anode. It revealed that the Si-based anode by 400 oC exhibited first high reversible capacity of 1890.3 mAh g-1. After 50 cycles, the electrode still remained the stable reversible capacity of 1270.3 mAh g-1. The extraction capacity can achieved 1648.1 mAh g-1 even at high current density of 600 mA g-1, showing a good rate performance.