The diffusion property of the intercalated species in the graphite materials is at the heart of the rate performance of graphite-based metal-ion secondary battery.Here we study the diffusion process of a AlCl_(4) mole...The diffusion property of the intercalated species in the graphite materials is at the heart of the rate performance of graphite-based metal-ion secondary battery.Here we study the diffusion process of a AlCl_(4) molecule within graphite—a key component of a recently reported aluminum ion battery with excellent performance—via molecular dynamics(MD)simulations.Both ab-initio MD(AIMD)and semiempirical tight-binding MD simulations show that the diffusion process of the intercalated AlCl_(4) molecule becomes rather inhomogeneous,when the simulation time exceeds approximately 100 picoseconds.Specifically,during its migration in between graphene layers,the intercalated AlCl_(4) molecule may become stagnant occasionally,and then recovers its normal(fast)diffusion behavior after halting for a while.When this phenomenon occurs,the linear relationship of the mean squared displacement(MSD)versus the duration time is not fulfilled.We interpret this peculiar behavior as a manifestation of inadequate sampling of rare event(the stagnation of the molecule),which does not yet appear in short-time MD simulations.We further check the influence of strains present in graphite intercalated compounds(GIC)on the diffusion properties of AlCl_(4),and find that their presence in general slows down the diffusion of the intercalated molecule,and is detrimental to the rate performance of the GIC-based battery.展开更多
Controversial experimental reports on the crystal structure of T 1 precipitates in Al-Li-Cu alloys have ex-isted for a long time,and all of them can be classified into five models.To clarify its ground-state atomic st...Controversial experimental reports on the crystal structure of T 1 precipitates in Al-Li-Cu alloys have ex-isted for a long time,and all of them can be classified into five models.To clarify its ground-state atomic structure,herein,we have combined high-throughput first-principles calculations and CALPHAD,as well as aberration-corrected HAADF-STEM experiments.Employing the special quasi-random structure(SQS)and supercell approximation(SPA)methods to simulate the local disorder on Al-Cu sub-lattices,we find that none of the present models can satisfy the phase stability in Al-Li-Cu ternary system based on temperature-dependent convex hull analysis.Using the cluster expansion(CE)formulas,structural predic-tions derived from the five-frame models were performed.Subsequently,by introducing the vibrational contribution to the free energy at aging temperatures,we proposed a novel ground-state T 1 structure that maintains a coherent relationship with Al-matrix at the<112>Al orientation.The underlying phase transition between the variants of T 1 precipitates was further discussed.By means of ab initio molecular dynamics(AIMD)simulations,we resolved the controversy regarding the number of atomic layers con-stituting the T 1 phase and acknowledged the existence of Al-Li corrugated layers.The root cause of this structural distortion is triggered by atomic forces and bondings.Our work can have an positive impact on the novel fourth generation of Al-Cu-Li alloy designs by engineering the T 1 strengthening phase.展开更多
基金supported by the National Key Research and Development Program of China(Grant No.2016YFB0201202)the National Natural Science Foundation of China(Grant Nos.11874335 and 11774327)。
文摘The diffusion property of the intercalated species in the graphite materials is at the heart of the rate performance of graphite-based metal-ion secondary battery.Here we study the diffusion process of a AlCl_(4) molecule within graphite—a key component of a recently reported aluminum ion battery with excellent performance—via molecular dynamics(MD)simulations.Both ab-initio MD(AIMD)and semiempirical tight-binding MD simulations show that the diffusion process of the intercalated AlCl_(4) molecule becomes rather inhomogeneous,when the simulation time exceeds approximately 100 picoseconds.Specifically,during its migration in between graphene layers,the intercalated AlCl_(4) molecule may become stagnant occasionally,and then recovers its normal(fast)diffusion behavior after halting for a while.When this phenomenon occurs,the linear relationship of the mean squared displacement(MSD)versus the duration time is not fulfilled.We interpret this peculiar behavior as a manifestation of inadequate sampling of rare event(the stagnation of the molecule),which does not yet appear in short-time MD simulations.We further check the influence of strains present in graphite intercalated compounds(GIC)on the diffusion properties of AlCl_(4),and find that their presence in general slows down the diffusion of the intercalated molecule,and is detrimental to the rate performance of the GIC-based battery.
基金supported by the National Natural Science Foundation of China(52073030).
文摘Controversial experimental reports on the crystal structure of T 1 precipitates in Al-Li-Cu alloys have ex-isted for a long time,and all of them can be classified into five models.To clarify its ground-state atomic structure,herein,we have combined high-throughput first-principles calculations and CALPHAD,as well as aberration-corrected HAADF-STEM experiments.Employing the special quasi-random structure(SQS)and supercell approximation(SPA)methods to simulate the local disorder on Al-Cu sub-lattices,we find that none of the present models can satisfy the phase stability in Al-Li-Cu ternary system based on temperature-dependent convex hull analysis.Using the cluster expansion(CE)formulas,structural predic-tions derived from the five-frame models were performed.Subsequently,by introducing the vibrational contribution to the free energy at aging temperatures,we proposed a novel ground-state T 1 structure that maintains a coherent relationship with Al-matrix at the<112>Al orientation.The underlying phase transition between the variants of T 1 precipitates was further discussed.By means of ab initio molecular dynamics(AIMD)simulations,we resolved the controversy regarding the number of atomic layers con-stituting the T 1 phase and acknowledged the existence of Al-Li corrugated layers.The root cause of this structural distortion is triggered by atomic forces and bondings.Our work can have an positive impact on the novel fourth generation of Al-Cu-Li alloy designs by engineering the T 1 strengthening phase.
基金supported by the National Natural Science Foundation of China(21833004)Taishan Scholar Program of Shandong Provincethe Natural Science Foundation of Shandong Province(ZR2020QA055)。
