單離子導電嵌段共聚物作為鋰離子電池之石墨和Si@G負極保護塗層之研究

Abstract

本研究從商業上可獲得的三嵌段共聚物SEBS磺化獲得磺酸鋰(SO3-Li)系鏈(苯乙烯-乙烯/丁烯-苯乙烯)嵌段共聚物(SSEBS)，作為鋰離子電池（LIB）中負極的活性石墨與活性Si@G(矽在石墨上)的保護塗層。保護塗層應防止液體電解質與石墨和Si@G直接接觸，從而避免液體電解質的負面影響，例如石墨剝落和不希望的SEI形成，因此改善了LIB的長期穩定性。 在SSEBS中，SO3-Li基團接枝到聚苯乙烯上使磺化聚苯乙烯區域具有鋰離子傳導能力的鋰離子，而聚(乙烯/丁基)區段提供塗層的延展性和柔韌性以適應 充放電循環過程中石墨和Si@G的體積變化； 此外，PS的芳環與石墨表面之間的π-π相互作用也提供SSEBS與石墨的強黏附力。 在研究中，我們系統地改變了石墨與Si@G上的SSEBS數量，以優化電池性能。結果表明，保護塗層可以有效地提高負極的電化學穩定性，而不會犧牲電池的性能。

This work employed lithium sulfonate (SO3-Li) tethered poly(styrene-block-(ethylene-ran-butylene)-block-styrene) (SSEBS), obtained from sulfonation of commercial available triblock copolymer SEBS, to serve as the protective coating on the active graphite and active Si@G (silicon on graphite) of the anode in a lithium ion battery (LIB). The protective coating should prevent direct contact of liquid electrolyte with the graphite and Si@G, thus to avoid the negative effects of the liquid electrolyte such as exfoliation of graphite and undesired SEI formation, and therefore improve the long term stability of the LIB. In SSEBS, the SO3-Li groups are grafting onto polystyrene to allow the sulfonated polystyrene domains having lithium ion conducting capability of lithium ion, while the poly(ethylene-ran-butylene) segment provide the ductility and flexibility of the coating layer to accommodate the volume change of graphite and Si@G during charging and discharging cycles. Moreover, the π-π interaction between the aromatic ring of PS and the graphite surface should provide strong adhesion of SSEBS to the graphite. In this work, we systematically varied the amount of SSEBS on the graphite/Si@G to optimize the battery performance. It is demonstrated that the protective coating could effectively improve the electrochemical stability of the anode without sacrificing the battery performance.