Freestanding silicon microparticle and self-healing polymer composite design for effective lithiation stress relaxation

Abstract

Self-healing features that mimic the biological mechanisms for self-repair have recently been applied to high-capacity but extreme volume expansion electrode materials such as silicon anodes to overcome the short cycle-life caused by electrical contact loss and active material pulverization. In this study, we adopt a freestanding composite design for effective relaxation of lithiation induced stresses and enhancement of electrochemical reliability. Silicon microparticles are homogenously dispersed and embedded within a self-healing polymer matrix that enables free volume expansion and contraction during lithiation and delithiation. The freestanding electrode, which does not require a separate current collector, demonstrated 91.8% capacity retention after 100 cycles at C/10 rate with an average specific capacity and gravimetric capacity, including current collector mass, of ∼2100 mA h g⁻¹ and ∼1050 mA h g⁻¹ respectively, which is a significant improvement compared to the conventional design of simple self-healing polymer coatings on silicon particle embedded current collectors. The fabricated freestanding silicon microparticle and self-healing polymer composite electrode demonstrated stable electrochemical performance after being completely cut, reattached, and cycled and retained at most 95% of its initial capacity. Overall, the proposed freestanding silicon microparticle and self-healing polymer composite design demonstrated excellent gravimetric capacity, cycle life, and self-healing capability without employing expensive and complex nanostructures.