To address the significant challenges associated with large volume change of micrometer-sized Si particles as high-capacity anode materials for lithium-ion batteries, we demonstrated a simple but effective strategy: using Si nanoparticles as a structural and conductive additive, with micrometer-sized Si as the main lithium-ion storage material. The Si nanoparticles connected into the network structure in situ during the charge process, to provide electronic connectivity and structure stability for the electrode. The resulting electrode showed a high specific capacity of 2500 mAh/g after 30 cycles with high initial Coulombic efficiency (73%) and good rate performance during electrochemical lithiation and delithiation: between 0.01 and 1 V vs Li/Li(+).

Inverse opals are most widely used as photonic crystals for ultraviolet, optical, and infrared applications. [1] These highly interconnected porous structures are also attractive for applications such as sensors, fuel cells, filters, and catalysts. [2] At the same time, engineers are aiming for lightweight structures with optimized mechanical strength, often inspired by nature's cellular materials with foam-like structures such as sponges, [3] trabecular bone, [4] or plant parenchyma. [5] The resultant optimized strut-based structures have shown high stiffness-and compressive strength-to-weight ratios, [6][7][8][9] but can suffer from strut buckling and a lack of mass production techniques. Here, we show that mechanical metamaterials based on ceramic inverse opaline structures with densities in the range of 330-910 kg m À3 are not only suitable as photonic crystals but also show better stiffness-and compressive strength-to-weight ratios compared to microfabricated optimized strut-based structures, [6][7][8][9] but lower than carbon nanoframes fabricated by interference lithography. [10] Pure silica inverse opal structures and silica inverse opals whose pores have been internally coated by a thin TiO 2 layer have been fabricated and their structural and mechanical behavior was investigated. Our experimental results, supported by numerical simulations, show that these arch-shaped porous structures outperform both strut-based and honeycomb structures due to their nearly isotropic mechanical response.The silica inverse opal films presented here are fabricated by vertical co-assembly based on the procedure described by Hatton et al. [11] Monodisperse colloidal polystyrene (PS) spheres were mixed in a water-based suspension containing tetraethylorthosilicate (TEOS) solution and vertically assembled on soda-lime silica glass. The resulting FCC opaline structure was calcined at 500°C for 30 min to burn out the PS template leaving an inverse-FCC opaline structure of nanoporous amorphous silica in which the adjacent pores are interconnected by %170 nm diameter holes (Figure 1a). Some samples were subsequently coated with an amorphous layer of TiO 2 by atomic layer deposition (ALD). After full crystallization to anatase, the layer thickness was %28 nm (Figure 1b). The specular reflection in Figure 1c shows the characteristic reflection peaks, which can be tuned by both the pore diameter and/or the TiO 2 coating.The effective density of the silica inverse opals was estimated by four independent methods: gravimetric, pycnometric, and two opticals. All four methods yield a comparable density of 330 kg m À3 AE 10%. The effective density of the TiO 2 ALD-coated silica inverse opals was estimated gravimetrically and optically to be 910 kg m À3 AE 10%. Detailed information can be found in the Supporting Information.Some examples of mechanical properties of opaline structures can be found in the literature. These works investigated polymer, [12,13] metal, [14] and ceramic-based [14][15][16] opals. Toivola et al. [15] investigated s...

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