Boosting the anode performance of the porous Si coated with polydopamine and cross-linked with sodium alginate

Silicon-based materials are expected to be the next generation anode for lithium-ion batteries due to their high theoretical specific capacity (4200 mAh g-1) and abundant natural reserves. However, volume expansion (∼300%) and low conductivity issues hinder the further application of silicon-anode materials. Nano-sizing/confinement and the Si@C core-shell techniques are usually employed to depress volume expansion and enhance electrical conductivity of silicon anodes. However, the so-called "island effect" of nanoparticles and the loss of connection between the carbon shell and silicon core can lead to the degradation of electrochemical performance. In this work, nanoporous silicon (pSi) was prepared by means of magnesiothermic reduction of silicon aerogel as a precursor. The pSi is encapsulated by polydopamine (PDA) and then cross-linked by sodium alginate (SA) to form a three-dimensional network structure. It can effectively depress the drastic swelling-shrinking of silicon, avoid the "island effect" of silicon particles, and provide many effective conductive channels. The prepared Si@PDA-SA composite electrode delivers an initial discharge capacity of 3128 mAh g-1 and an initial coulombic efficiency (ICE) of 82.8%. At a current density of 2000 mA g-1, the reversible capacity of 820 mAh g-1 can be retained after 700 cycles. With enhanced mechanical properties and optimal link of the silicon particles, the gradual detachment of silicon particles from the adhesive can be effectively inhibited during long-term cycles. It offers the silicon anode superior cycling stability. Such a facile synthesis process and optimal electrochemical performance have laid a solid foundation for the large-scale application of silicon anode electrodes.