This paper presents the mono-vacancy formation and migration energies of each element Ti, Ga, and C in the MAX phase Ti2GaC, which are obtained by first principles calculations. We also calculate the formation energie...This paper presents the mono-vacancy formation and migration energies of each element Ti, Ga, and C in the MAX phase Ti2GaC, which are obtained by first principles calculations. We also calculate the formation energies of oxygen substituting for Ti, Ga, and C and two formation energies of oxygen interstitial in different sites. The results show that the formation energy of oxygen substituting for Ti is the highest, and the formation energies of the O substitution for Ga atoms decrease as the oxygen concentration increases. The two different formation energies of one oxygen interstitial show that the stable site for the oxygen interstitial is at the center of the triangle composed by three Ga atoms. The effects of vacancy,oxygen substitution, and the interstitial on the electronic properties of Ti2GaC are also discussed in light of the density of states and the electron charge density.展开更多
Recently, MAX phases show great potential in lithium-ion uptake due to their excellent electrical conductivity and unique lamellar-structure accommodating lithium ions. However, the reports about MAX electrodes for li...Recently, MAX phases show great potential in lithium-ion uptake due to their excellent electrical conductivity and unique lamellar-structure accommodating lithium ions. However, the reports about MAX electrodes for lithium-ion battery up to now are relatively low. Herein we report the preparation of surface oxygen-deficient Ti2SC with abundant oxygen vacancies by a facile surface engineering method. When using as a lithium storage anode, this oxygen-deficient Ti2SC delivers a high capacity of 350 m Ah/g at a current density of 400 m A/g as well as excellent rate performance, doubling the capacity compared to that of Ti2SC without oxygen vacancies. Confirmed by electrochemical impedance spectroscopy(EIS)and kinetic mechanism analyses, after reducing surface oxides and generation of oxygen vacancies, the as-received Ti2SC exhibits higher electrical conductivity and faster lithium ion diffusion. Thus this work offers a facial and effective strategy of optimizing the surface structure of MAX phases, further to achieve an enhanced lithium-ion uptake for lithium-ion batteries or capacitors.展开更多
基金supported by the National Magnetic Confinement Fusion Science Program of China(Grant No.2014GB104002)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA03030100)the National Natural Science Foundation of China(Grant Nos.11275156 and11304324)
文摘This paper presents the mono-vacancy formation and migration energies of each element Ti, Ga, and C in the MAX phase Ti2GaC, which are obtained by first principles calculations. We also calculate the formation energies of oxygen substituting for Ti, Ga, and C and two formation energies of oxygen interstitial in different sites. The results show that the formation energy of oxygen substituting for Ti is the highest, and the formation energies of the O substitution for Ga atoms decrease as the oxygen concentration increases. The two different formation energies of one oxygen interstitial show that the stable site for the oxygen interstitial is at the center of the triangle composed by three Ga atoms. The effects of vacancy,oxygen substitution, and the interstitial on the electronic properties of Ti2GaC are also discussed in light of the density of states and the electron charge density.
基金supported by the National Natural Science Foundation of China (Nos. 21671167 and 51602277)Qinglan Project of Jiangsu Province。
文摘Recently, MAX phases show great potential in lithium-ion uptake due to their excellent electrical conductivity and unique lamellar-structure accommodating lithium ions. However, the reports about MAX electrodes for lithium-ion battery up to now are relatively low. Herein we report the preparation of surface oxygen-deficient Ti2SC with abundant oxygen vacancies by a facile surface engineering method. When using as a lithium storage anode, this oxygen-deficient Ti2SC delivers a high capacity of 350 m Ah/g at a current density of 400 m A/g as well as excellent rate performance, doubling the capacity compared to that of Ti2SC without oxygen vacancies. Confirmed by electrochemical impedance spectroscopy(EIS)and kinetic mechanism analyses, after reducing surface oxides and generation of oxygen vacancies, the as-received Ti2SC exhibits higher electrical conductivity and faster lithium ion diffusion. Thus this work offers a facial and effective strategy of optimizing the surface structure of MAX phases, further to achieve an enhanced lithium-ion uptake for lithium-ion batteries or capacitors.
