The porous and biomimetic cobalt silicate@diatomite (Co2SiO4@diatomite) was successfully synthesized by a two-step method, including the hydrothermal method and calcination to improve the electromagnetic wave absorption property. Different hydrothermal times were well-tuned for Co2SiO4@diatomite composites with different loadings of Co2SiO4. Interestingly, the Co2SiO4@diatomite composites (6 h, 25 wt%) had a smaller minimum reflection loss. Moreover, the minimum reflection loss (RLmin) could reach −12.03 dB at 16.64 GHz and the matched absorber thickness was 10 mm, while the effective absorption bandwidth (EAB, RL ≤ −10 dB) could be 1.92 GHz. In principle, such findings indicate that Co2SiO4@diatomite nanocomposites could be a promising candidate for high-efficiency microwave absorption capability.Keywords:diatomite;Co2SiO4;electromagnetic wave absorption;nanomaterial
Tetravalent Si materials (SiO 2 and transition metal silicates) are receiving tremendous attentions for lithium storage, whereas a troublesome problem is how to improve the content of active Si. This work reports a novel method to boost their lithium storage capabilities by using highly-dispersed Co element in the form of nanofilm-like Co 2 SiO 4 /SiO 2 powder on the surface of reduced graphene oxide (RGO) that promotes the electronic diffusion and accommodates the volume changes. As a result, the Co 2 SiO 4 /SiO 2 /RGO exhibits over 20 times higher reversible capacity and better rate performance than the SiO 2 /RGO counterpart. In comparison, the Co 2 SiO 4 /SiO 2 /RGO shows the highest reversible capacity (1382 mAh g −1 at 500 mA g −1 ) and longest life span (500 cycles) in all known silicates-based materials and higher power/energy density than both of commercial graphite and Li 4 Ti 5 O 12 materials. Ex-situ X-ray photoelectron spectra and electrochemical tests at different voltage windows are conducted to illustrate the reason for the significantly improved performances. It demonstrates that tetravalent Si is gradually activated to lower-valence form by highly-dispersed Co generated with cycling. This observation provides new evidence for the electrochemical catalytic mechanism in transition metal silicates for lithium storage.
Liwei Su,Shihao Guo,Junjie Wang,Hao Wang,Shixiong Wu,Hao Wu,Lianbang Wang
Silicon-based materials are considered promising next-generation anode candidates for lithium-ion batteries due to their high theoretical capacity and natural abundance. However, severe volume expansion (∼300 %) during cycling and intrinsically low electrical conductivity significantly hinder their practical applications. Surface coating modification has been recognized as an effective strategy for silicon-based materials. However, common coating materials, such as C and metal oxides, are limited by weak interfacial bonding, insufficient stress buffering, and cracking of the coating layer, making it challenging to construct uniform, durable, and multifunctional shells. This work constructs a double core-shell structured nanocomposite, Si@Co 2 SiO 4 @C. The composite leverages the buffering and conductive properties of the double shells, as well as the catalytic effect of newly generated Co 0 , to facilitate reversible lithiation of the Li-Si-O compounds, thereby achieving high capacity and long-term cycling stability. As a result, the composite delivers a reversible capacity of 1296 mA h g −1 after 200 cycles at a current density of 300 mA g −1 . The role of the double-shell structure is investigated through electrochemical measurements and structure characterization. This double core-shell structure, utilizing a transition metal silicate intermediate layer, provides a novel approach to developing high-performance Si-based anodes with distinct advantages for balancing high capacity and structural stability.
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