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Germanium (Ge) is a promising anode material for lithium-ion batteries due to its large theoretical specific capacity, good electrical conductivity, and fast lithium-ion diffusivity. However, Ge still suffers from huge volume expansion during the delithiation/lithiation process. Herein, using "Mg" as a soft template, a honeycomb-like porous Ge (hp-Ge) anode was successfully synthesized via a facile thermal nitridation of Mg2Ge in N2, followed by an acid-etching process. The obtained hp-Ge presents a typical void-containing micro-/nano-hierarchical porous architecture, which can effectively alleviate the volume expansion of the host Ge. The formation of uniformly distributed voids in hp-Ge is closely related to the etching of Mg3N2, which is the by-product of the reaction between Mg2Ge and N2. Benefiting from the fascinating micro-/nano-hierarchical porous structure, the resulting hp-Ge anode without employing any complex surface modification techniques demonstrated a high specific capacity of 1534.70 mAh g−1 at 0.2 A g−1 with a high initial Coulombic efficiency of 85.0%, and a high capacity of 483.9 mAh g−1 at 8 A g−1. The hp-Ge anode also possesses excellent cyclability and can deliver a satisfying reversible specific capacity of 1375.40 mA h g−1 at 0.5 A g−1 after 200 cycles with a high capacity retention of 96.8%. The proposed facile and scalable void-introducing strategy in this study also provides an alternative route for designing advanced micro-/nano-hierarchical porous materials, especially for anodes with large volume expansion during the lithiation process. [ABSTRACT FROM AUTHOR]

Silicon (Si) is considered an ideal candidate for the next generation of lithium-ion batteries owing to its high specific capacity, low lithiation/delithiation potential, and abundance. However, its extensive volume expansion engenders electrode structure deterioration and cycle life truncation, substantially hindering its practical utility. In this investigation, we fashioned porous silicon via the etching of micron-sized aluminium–silicon alloy, and subsequently, porous silicon@hard carbon (PSi@C) composites were meticulously crafted through a sequence involving high-temperature pyrolysis after methyl acrylate (MA) suspension polymerization coating and a Soxhlet extraction pore-forming procedure. Characterization through scanning electron microscopy (SEM) revealed the composite material's abundance of pores and the presence of a fish-scale-like carbon framework. This unique architecture adeptly mitigates the stresses stemming from silicon's volumetric expansion, thus rectifying the issues associated with silicon's poor electronic conductivity and carbon materials' limited capacity. Simultaneously, it utilizes silicon's high specific capacity and carbon's extended cycle stability. Remarkably, after 300 cycles at 0.5 A g−1, the PSi@C electrode exhibited a capacity retention rate as high as 74.4% (652 mA h g−1). Even under a high current of 2 A g−1, the rate test still revealed a reversible capacity of 465 mA h g−1. These findings indicate exemplary long-cycle and rate performance characteristics, underscoring significant potential for research and application in lithium battery energy storage. [ABSTRACT FROM AUTHOR]

The vast volume expansion of the Si anode during the charging process leads to rapid cycling performance fading and limits its applications in lithium-ion batteries. In this study, a unique core–double-shell structured porous Si@graphene@glycerin-Al2O3 (p-Si@G@g-Al2O3) composite is successfully prepared by using a porous Si (p-Si) microsphere as the core and graphene(G)/Al2O3 as the double shell layer via an electrostatic self-assembly strategy and a glycerin-involved sol–gel process. The addition of glycerin can reduce the nucleation growth rate of Al(OH)3 during the sol–gel process and enable more uniform deposition of an ultrathin Al2O3 layer on p-Si@G microspheres. Owing to the crucial role of the lithiated Al2O3 (LiAlO2)/G double shell layer in shielding the inner p-Si microsphere from the electrolyte and consolidating the mechanical structure of the p-Si microsphere, the synthesized p-Si@G@g-Al2O3 shows good cycling stability with a high reversible capacity of 1804.5 mA h g−1 at 0.2 A g−1 and excellent rate capacity with a capacity of 439 mA h g−1 at 8 A g−1, superior to those of p-Si@G and p-Si electrodes. Moreover, the electrochemical performance of p-Si@G@g-Al2O3 can also be further improved by ∼10% by only adding 5 wt% of carbon nanotubes (CNTs) in a slurry, due to the good capability of CNTs in building the interconnecting network between p-Si@G@g-Al2O3 microspheres. [ABSTRACT FROM AUTHOR]