Design of Alloying-Type Anodes for Advanced Lithium Batteries

Abstract

With the escalating demands of portable electronics, electric vehicles, and grid-scale energy storage systems, the development of next-generation rechargeable batteries, which boast high energy density, cost-effectiveness, and environmental sustainability, becomes imperative. Accelerating the advancements could substantially mitigate detrimental carbon emissions. The pursuit of main objectives has kindled interest in alloying elements (especially for silicon) as high-capacity electroactive materials, capable of further enhancing the gravimetric and volumetric energy densities compared to traditional graphite counterparts. Despite such promising attributes, silicon materials face significant hurdles, primarily due to their drastic volumetric changes during the lithiation/delithiation processes. Volume changes give rise to severe side effects such as fracturing, pulverization, and delamination, triggering rapid capacity decay. Therefore, mitigating silicon particle fracture stands as a primary challenge. Importantly, nanoscale silicon (below 150 nm in size) has shown resilience to stresses induced by repeated volume changes, thereby highlighting their potential as anode-active materials. However, the volume expansion stress not only affects the internal structure of the particle but also disrupts the solid−electrolyte interphase (SEI) layer, formed spontaneously on the outer surface of silicon, causing adverse side reactions. Therefore, despite silicon nanoparticles offering new opportunities, overcoming the associated issues is of paramount importance. Thus, this paper aims to spotlight the significant strides made in the development of pure silicon anodes, starting from Chapter II. From the emergence of nanoscale silicon, the following nanotechnology had a crucial role in growing the particle through nano-/microstructuring. Similarly, bulk silicon microparticles gradually surfaced with the post-engineering methods owing to their practical advantages. We briefly discuss the special characteristics of representative examples from bulk silicon engineering and nano-/microstructuring, all aimed at overcoming intrinsic challenges. Importantly, these advancements require superior material design and the incorporation of exceptional battery components to ensure compatibility and yield synergistic effects. In Chapter III, we introduce a heteroatom-bridged silicon microstructure via metallothermic reduction with auxiliary aluminum chloride salt, viable for practical production and fast-charging batteries. From waste borosilicate glass as a silicon precursor, we embed amorphous heteroatoms (boron, oxygen) on the inside/outside of crystalline silicon islands, along with an engineered SEI layer, to enhance structural stability and fast-charging capabilities. This approach proves the potential of recycling the waste into high-quality silicon, presenting a sustainable and mass-producible pathway for affording advanced battery materials. In Chapter IV, we explore a synergistic strategy to simultaneously address the issues of volume expansion and low electrical conductivity in silicon-based anodes. In addition to assigning printable and free-standing properties, MXene conductive binder improves conductivity at both the particle and electrode levels without the need for additional conductive agents. This innovative approach in fabricating hollow spherical silicon suboxide/carbon composite, combined with MXene binders, not only successfully resolves fundamental challenges associated with alloying-type anodes but also produces stable but complex-shaped, printable lithium-ion batteries. In Chapter V, we investigate a practical way for realizing the employment of silicon microparticle anodes through chemical integration with gel polymer electrolytes, facilitated by electron beam-induced covalent linkages. Silicon microparticle anodes offer exceptional commercial advantages due to the best cost-effectiveness and potential to maximize energy density compared to any other type of silicon, despite problems arising from the worst structural instabilities. Establishing direct covalent bonds between silicon microparticles and high-ion-conductivity, elastic gel polymer electrolytes reduce mechanical stresses associated with volume changes, thus extending battery lifespan and enhancing structural integrity. This tactic raises battery energy density by over 40%, thus proving the commercial feasibility of pure silicon microparticle anodes in terms of price, manufacturability, and performance. Finally, we present the design of alloying-type anodes, specifically silicon anodes, for advanced lithium batteries. We assess the advantages and drawbacks of various approaches, including surface coating, heteroatom doping, nano-/microstructuring, and microparticle engineering. Moreover, this study not only focuses on the material design itself but also highlights practical refinements through the synergistic effects of additional components such as binders and electrolytes. While primarily addressing silicon anodes within lithium-ion batteries, our findings provide insights that could usher the application of alloy-type materials in other battery systems, including lithium metal and all-solid-state batteries.