Insulating ceramics are applied to modern manufacturing industries for their improved material properties.But they are the difficult-to-machine materials because of their high rigidity,high brittleness and non-electri...Insulating ceramics are applied to modern manufacturing industries for their improved material properties.But they are the difficult-to-machine materials because of their high rigidity,high brittleness and non-electrical conductivity.A new method which employs a high energy capacitor for electric discharge machining of insulating ceramics efficiently is presented in this paper,and the single discharge experiments have been carried out.The process uses the high voltage,large capacitor and high discharge energy,it is able to effectively machine insulating ceramics,and the single discharge crater volume of insulating ceramics can reach 17.63 mm3.The effects of polarity,peak voltage,capacitance,current-limiting resistance,tool electrode feed,tool electrode section area and assisting electrode thickness on the process performance such as the single discharge crater volume,the tool wear ratio and the assisting electrode wear ratio have been investigated.The microstructure of the discharge crater is examined with a scanning electron microscope(SEM).The results show that the discharge craters have sputtering appearance,the insulating ceramic materials are mostly removed by spalling,in the center region of the discharge some materials are removed by melting and vaporization,and the material removal is enhanced with the machining parameters increasing.展开更多
The low energy efficiency and poor cycle stability arising from the high aggressivity of discharge products toward organic electrolytes limit the practical applications of Li-O_(2)batteries(LOBs).Compared with the typ...The low energy efficiency and poor cycle stability arising from the high aggressivity of discharge products toward organic electrolytes limit the practical applications of Li-O_(2)batteries(LOBs).Compared with the typical discharge product Li_(2)O_(2),LiOH shows better chemical and electrochemical stability.In this study,a free-standing cathode composed of hydrangea-likeδ-MnO_(2)with Ag nanoparticles(NPs)embedded in carbon paper(CP)(Ag/δ-MnO_(2)@CP)is fabricated and used as the catalyst for the reversible formation and decomposition of LiOH.The possible discharge mechanism is investigated by in situ Raman measurement and density functional theory calculation.Results confirm thatδ-MnO_(2)dominantly catalyzes the conversion reaction of discharge intermediate LiO_(2)*to LiOH and that Ag particles promote its catalytic ability.In the presence of Ag/δ-MnO_(2)@CP cathode,the LOB exhibits enhanced specific capacity and a high discharge voltage plateau under humid O_(2)atmosphere.At a current density of 200 mA g^(−1),the LOB with the Ag/δ-MnO_(2)@CP cathode presents an overpotential of 0.5 V and an ultra-long cycle life of 867 cycles with a limited specific capacity of 500 mA h g^(−1).This work provides a fresh view on the role of solid catalysts in LOBs and promotes the development of LOBs based on LiOH discharge product for practical applications.展开更多
基金supported by the National Natural Science Foundation of China (Grant No 50675225)the Ministry of Science and Technology of China (Grant No 2009GJC60047)
文摘Insulating ceramics are applied to modern manufacturing industries for their improved material properties.But they are the difficult-to-machine materials because of their high rigidity,high brittleness and non-electrical conductivity.A new method which employs a high energy capacitor for electric discharge machining of insulating ceramics efficiently is presented in this paper,and the single discharge experiments have been carried out.The process uses the high voltage,large capacitor and high discharge energy,it is able to effectively machine insulating ceramics,and the single discharge crater volume of insulating ceramics can reach 17.63 mm3.The effects of polarity,peak voltage,capacitance,current-limiting resistance,tool electrode feed,tool electrode section area and assisting electrode thickness on the process performance such as the single discharge crater volume,the tool wear ratio and the assisting electrode wear ratio have been investigated.The microstructure of the discharge crater is examined with a scanning electron microscope(SEM).The results show that the discharge craters have sputtering appearance,the insulating ceramic materials are mostly removed by spalling,in the center region of the discharge some materials are removed by melting and vaporization,and the material removal is enhanced with the machining parameters increasing.
基金financially supported by the High-level Talents’Discipline Construction Fund of Shandong University(31370089963078)the School Research Startup Expenses of Harbin Institute of Technology(Shenzhen)(20190037 and 20210028)+3 种基金China Postdoctoral Science Foundation(2019M661276 and 2021T140150)Guangdong Basic and Applied Basic Research Foundation(2019A1515110756)the National Natural Science Foundation of China(52002094)the Open Fund of Guangdong Provincial Key laboratory of Advanced Energy Storage Materials(AESM202107)。
文摘The low energy efficiency and poor cycle stability arising from the high aggressivity of discharge products toward organic electrolytes limit the practical applications of Li-O_(2)batteries(LOBs).Compared with the typical discharge product Li_(2)O_(2),LiOH shows better chemical and electrochemical stability.In this study,a free-standing cathode composed of hydrangea-likeδ-MnO_(2)with Ag nanoparticles(NPs)embedded in carbon paper(CP)(Ag/δ-MnO_(2)@CP)is fabricated and used as the catalyst for the reversible formation and decomposition of LiOH.The possible discharge mechanism is investigated by in situ Raman measurement and density functional theory calculation.Results confirm thatδ-MnO_(2)dominantly catalyzes the conversion reaction of discharge intermediate LiO_(2)*to LiOH and that Ag particles promote its catalytic ability.In the presence of Ag/δ-MnO_(2)@CP cathode,the LOB exhibits enhanced specific capacity and a high discharge voltage plateau under humid O_(2)atmosphere.At a current density of 200 mA g^(−1),the LOB with the Ag/δ-MnO_(2)@CP cathode presents an overpotential of 0.5 V and an ultra-long cycle life of 867 cycles with a limited specific capacity of 500 mA h g^(−1).This work provides a fresh view on the role of solid catalysts in LOBs and promotes the development of LOBs based on LiOH discharge product for practical applications.
