Linkai Ren,Quanxing Ren,Ziqiang Yin,Tihao Cao,Xuxin Ping,Fangfang Ge,Zhengren Huang,Qing Huang,Yinsheng Li
In order to achieve low-temperature densification of SiC ceramic, β-SiC nanopowder was doped with Li 2 O together with Y 2 O 3 –Al 2 O 3 –MgO as sintering aids, and then spark plasma sintered at temperatures ranging from 1450 °C to 1600 °C for 30 min under 30 MPa pressure in argon. The densities, microstructures and mechanical properties of SiC ceramics were systematically investigated, in comparison to the counterparts sintered with Y 2 O 3 –Al 2 O 3 –MgO additives. Since Li 2 O has a low melting point, Li 2 O addition effectively decreased the formation temperature of liquid secondary phase, enabling SiC ceramics to obtain higher density and lower porosity after low-temperature sintering (T ≤ 1550 °C). Besides, Li 2 O addition was found to decrease the viscosity of liquid phase and enhance grain growth of SiC through dissolution-reprecipitation process. When sintered at 1550 °C, Li 2 O addition led to a remarkable increase of density from 3.03 g/cm 3 to 3.21 g/cm 3 for SiC ceramic. Meanwhile, the SiC ceramic with Li 2 O addition exhibited a high Vickers hardness of 22.75 ± 0.35 GPa and a good fracture toughness of 3.83 ± 0.27 MPa m 1/2 . The research results are expected to benefit the low-cost fabrication of SiC ceramics based on pressure-assisted sintering and alleviate the thermal damage of SiC fiber in hot-pressed SiC f /SiC composites.
High-entropy oxides (HEOs) have started to attract widespread interest as anode materials for lithium-ion batteries (LIBs), because of their high theoretical discharge capacities, fast ionic conductivity, and stable structure caused by the unique entropy stabilization effect and the “cocktail” effect. However, the lithiation mechanism of HEO anode is still conversional, which prevents its further development. Herein, we propose an Li2O-doping strategy for improving the lithium storage ability of HEO anodes. Li2O is successfully introduced into the spinel high-entropy oxide to obtain a (FeMgNiCrMnLi)3O4 anode (Li-SHEO) via a solution combustion synthesis and ball milling method. Experimental results show Li doping would induce the growth of oxygen vacancies and regulate the conversion reactions during the discharge process, leading to improved electrochemical performance. As a result, the lithiation process of an Li-SHEO anode includes an enhanced Li+ ion intercalation process and a typical conversion reaction. Compared with the (FeMgNiCrMnLi)3O4 (SHEO) anode, the Li-SHEO anode shows a high reversible discharge capacity of 850.7 mA h g−1 after 200 cycles under a large current density of 2.0 A g−1.
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