The Study Of Binders For Silicon Anodes In Lithium Ion Battery

Nowadays,anode materials with high capacity,safety and low cost for lithium ion batteries have attracted tremendous research interest.Silicon is considered as one of the most promising anode materials due to its high theoretical capacity?4200 mA h/g?,about 11 times higher than commercial graphite?372 mA h/g?.However,the huge volume change?>300%?of silicon during cycling can destroy the electrode structure and ultimately lead to poor cycle stability of the batteries.Polymeric binders,as a part of electrode materials,are usually used to bind silicon particles and conductive additives with metal collectors.Excellent binders can effectively inhibit the volume expansion of silicon particles.In this study,we have developed two kinds of polymeric binders to improve the electrochemical performance of silicon-based lithium-ion batteries.The main work and conclusions are as follows:?1?Vinyltriethoxysilane crosslinked poly?acrylic acid sodium?as polymeric binder?PVTES-NaPAA?was designed and synthesized.The structure of PVTES-NaPAA was confirmed by FT-IR and ¹H NMR.The electrochemical performance of PVTES-NaPAA as the binder for silicon electrode materials was measured.At the current density of 0.2 C?1 C=4200 mA h/g?,the initial capacity of Si _PVTES-NaPAA is 2654 mA h/g.After 100cycles,the electrode material can still maintain 2077 mA h/g with a capacity retention rate of 78.2%.The improvement of electrochemical performance can be attributed to the formation of three-dimensional crosslinked network structure of PVTES-NaPAA binder,which increases the interaction with the surface of silicon particles.In addition,the average peeling force and Young's modulus of PVTES-NaPAA binder are 3.9 N and 5.0 GPa.It shows that PVTES-NaPAA binder has excellent mechanical properties and can resist the volume expansion of silicon particles,thus maintaining the stability of the electrode structure and improving the cycle performance of batteries.?2?Polydopamine-poly?acrylic acid sodium?as polymeric binder?PDA-NaPAA?was synthesized.The structure of PDA-NaPAA was confirmed by FT-IR.PDA-NaPAA was used as the binder to prepare silicon electrode materials(Si _PDA-NaPAA).The electrochemical performance of Si_PDA-NaPAA was studied.At the current density of 0.2 C,the initial capacity of Si_PDA-NaPAA electrode is 2021 mA h/g.After 100 cycles,the capacity of Si _PDA-NaPAA electrode is 1535 mA h/g and the capacity retention rate is 75.9%.Moreover,Si_PDA-NaPAA possess good rate performance with capacity of 800mA h/g at 0.8 C.The average peeling force of PDA-NaPAA binder is 5.0 N,which indicates that PDA-NaPAA binder possess excellent adhesion performance.PDA-NaPAA binder can effectively bond active materials with metal collectors and prevent silicon from falling off from metal collectors during cycling,thus improving the cycle performance of batteries.