Cross-Linked Sodium Alginate-Sodium Borate Hybrid Binders for High-Capacity Silicon Anodes in Lithium-Ion Batteries

Silicon is considered one of the most promising next-generation anode materials for lithium-ion batteries. It has the advantages of high theoretical specific capacity (4200 mAh·g^-1), which is 10 times larger than that of a commercial graphite anode (372 mAh·g^-1). However, there are some problems such as the pulverization of the electrode and an unstable solid electrolyte interphase (SEI) layer aroused by the huge bulk effect (>300%) of Si during the repeated lithiation/delithiation process. A binder plays a vital role in the conventional lithium-ion batteries that can effectively relieve the bulk expansion stress of a silicon anode. In this work, the inorganic cross-linker sodium borate (SB) and the commonly used binder sodium alginate (SA) were condensed through an esterification reaction and the reaction product was marked as SA-SB. It is found that the mechanical robustness and the peel strength of SA-SB are improved after cross-linking, which is conducive to maintaining the structural stability of the silicon anode in long cycle life. In consequence, the capacity retention of the silicon anode using the SA-SB binder (64.1%) is higher than that of SA (50.6%) after 100 cycles at 0.2 A·g^-1.