Hydrolysis-Engineered Robust Porous Micron Silicon Anode for High-Energy Lithium-Ion Batteries

Abstract

Micro-silicon (Si) anode that features high theoretical capacity and fine tap density is ideal for energy-dense lithium-ion batteries. However, the substantial localized mechanical strain caused by the large volume expansion often results in electrode disintegration and capacity loss. Herein, a microporous Si anode with the SiOx/C layer functionalized all-surface and high tap density (~0.65 g cm⁻3) is developed by the hydrolysis-driven strategy that avoids the common use of corrosive etchants and toxic siloxane reagents. The functionalized inner pore with superior structural stability can effectively alleviate the volume change and enhance the electrolyte contact. Simultaneously, the outer particle surface forms a continuous network that prevents electrolyte parasitic decomposition, disperses the interface stress of Si matrix and facilitates electron/ion transport. As a result, the micron-sized Si anode shows only ~9.94 GPa average stress at full lithiation state and delivers an impressive capacity of 901.1 mAh g⁻1 after 500 cycles at 1 A g⁻1. It also performs excellent rate performance of 1123.0 mAh g⁻1 at 5 A g⁻1 and 850.4 at 8 A g⁻1, far exceeding most of reported literatures. Furthermore, when paired with a commercial LiNi0.8Co0.1Mn0.1O2, the pouch cell demonstrates high capacity and desirable cyclic performance.

1. Introduction

Silicon (Si) stands out as a highly promising anode material for next-generation lithium-ion batteries (LIBs) [1–3], thanks to its exceptional gravimetric capacity (3579 mAh g⁻1) [4–6], favorable equilibrium potential (~0.4 V vs. Li+/Li) and natural abundance [7, 8]. However, the practical application of Si anode has long been impeded by the electrode disintegration from large volume change (>300%) during the (de)lithiation process, leading to sluggish reaction kinetics from the low intrinsic conductivity [9, 10], and the loss of Li+ inventory from the exacerbated solid electrolyte interphase (SEI) growth on the unstable interface [11–14]. To address above bottlenecks, porous nanostructured Si anodes have been widely explored to buffer the lithiation-induced mechanical stress for attenuating the material failure [15–18]. Nevertheless, nanostructures suffer from excessive specific surface area and low tap density (<0.3 g cm⁻3), leading to high electrolyte consumption, poor coulombic efficiency and reduced volumetric energy density [19–22]. Besides, the fragility of nanostructures limits their ability to withstand high mechanical pressure of up to 80 MPa during common electrode calendaring. Moreover, the hazardous pore pre-plantation technologies that commonly use corrosive etchants like HF or high-concentrated alkaline solution also face limitations in terms of scalability, cost and environmental impact [23–25].

In comparison, micron-sized Si with smaller specific surface area and higher tap density gains attention as a practical and scalable alternative to the nanostructured silicon to improve volumetric energy density [26–28], whereas micron-sized Si anode still undergoes >300% volume expansion, exacerbated SEI growth and poor electrical conductivity. Carbon layer coating has been commonly utilized to tackle the challenges associated with volume variation and electrical conductivity [29–32]. However, the absence of mechanical robustness of carbon layer fails to withstand repeated expansion and contraction of Si during lithiation/delithiation. The weak intermolecular forces of van der Waals and π–π stacking between carbon and Si matrix also fail to prevent the detachment of carbon network from Si particles and thus reduce electrode integrity [33–35]. Moreover, the concentrated strain always occurs at the edge of the Si surface, which accelerates the production of cracks for aggravating side reactions with the electrolyte and compromising structural stability [33, 36]. In addition, while a fully encapsulating carbon layer can improve interface stability [37], the carbon layer lacks enough Li+ conductivity to accelerate Li+ transport [36]. Therefore, as-designed carbon coating strategies often fall short of simultaneously addressing mechanical stability, interfacial integrity, and ionic transport.