Dongfeng Xue

Size-dependent oxygen storage ability of nano-sized ceria.

We thermodynamically studied the size-dependent oxygen storage ability of nano-sized ceria by tracing the surface Ce/O ratio of octahedral particles with different diameters, from the viewpoint of lattice Ce and O in a CeO2 crystallographic structure. The high surface Ce/O ratio with small scale particle size has more excess surface Ce(4+) ions, which allows ceria to have an increasing oxygen storage ability in a crystalline lattice. For the perfect octahedron growth shape of ceria, the nonstoichiometric surfaces can produce excess Ce(4+) ions, Ce(4+) ions can be stabilized by bonding with lattice oxygen, leading to an enhanced oxygen storage ability of ceria. With the increasing particle size, the surface Ce/O ratio approaches to 0.5 owing to the decreased contributions of atoms located at the edges and corners. When the octahedron diameter D = 0.55 nm, the surface Ce/O ratio can reach 0.75. When D = 7.58 nm, the surface Ce/O ratio decreases down to 0.51. If D≥ 14.61 nm, the surface Ce/O ratios are equal to 0.5. The present study deepens the insight of the size-dependent oxygen storage ability of nano-sized ceria, focusing on the size-dependent excess Ce(4+) on nonstoichiometric surfaces of ceria in thermodynamics.

Enhancing the Electrochemical Performance of the LiMn2O4 Hollow Microsphere Cathode with a LiNi0.5Mn1.5O4 Coated Layer

Spinel cathode materials consisting of LiMn2 O4 @LiNi0.5 Mn1.5 O4 hollow microspheres have been synthesized by a facile solution-phase coating and subsequent solid-phase lithiation route in an atmosphere of air. When used as the cathode of lithium-ion batteries, the double-shell LiMn2 O4 @LiNi0.5 Mn1.5 O4 hollow microspheres thus obtained show a high specific capacity of 120u2005mAu2009hu2009g(-1) at 1u2009C rate, and excellent rate capability (90u2005mAhg(-1) at 10u2009C) over the range of 3.5-5u2005V versus Li/Li(+) with a retention of 95u2009% over 500u2005cycles.

Facile Synthesis of Transition‐Metal Oxide Nanocrystals Embedded in Hollow Carbon Microspheres for High‐Rate Lithium‐Ion‐Battery Anodes

Charged up: A general soft-template route for the synthesis of uniform hollow carbon microspheres embedded with transition-metal oxide nanocrystals (OHCMs) has been developed (see figure). The obtained OHCMs possess a microsized spherical shape, embedded transition-metal oxide nanocrystals, and fully encapsulating conductive carbon shells, which endow the resulting anode materials with high specific capacities, rate capabilities, electrode densities, and cycle stabilities.

Polymorphic crystallization of Cu2O compound

Cu2O can crystallize into various polymorphs, such as cubes, rhombic dodecahedra, branching structures, and hopper cubes, instead of thermodynamically stable octahedra by designed kinetic-control routes instead of traditional thermodynamic control. The present results confirmed that Cu2O polymorphs have distinct physical and chemical properties, and morphology changes can occur due to polymorphic transitions in a kinetics-controllable reaction system. Both thermodynamic and kinetic factors on these polymorphism systems are believed to be significant for developing a polymorphism–property relationship, ultimately guiding the appropriate material selection for specific applications. Furthermore, we took Cu2O as an example to illustrate the development of “polymorphism” in modern materials science: polymorphism is an intrinsic physicochemical characteristic, and involves varying growth shapes, phase transformation and variation of physical properties. These findings can provide new insight to polymorphism–performance correlation and kinetic–thermodynamic control synthesis.

From chemistry to mechanics: bulk modulus evolution of Li–Si and Li–Sn alloys via the metallic electronegativity scale

Toward engineering high performance anode alloys for Li-ion batteries, we proposed a useful method to quantitatively estimate the bulk modulus of binary alloys in terms of metallic electronegativity (EN), alloy composition and formula volume. On the basis of our proposed potential viewpoint, EN as a fundamental chemistry concept can be extended to be an important physical parameter to characterize the mechanical performance of Li-Si and Li-Sn alloys as anode materials for Li-ion batteries. The bulk modulus of binary alloys is linearly proportional to the combination of average metallic EN and atomic density of alloys. We calculated the bulk moduli of Li-Si and Li-Sn alloys with different Li concentrations, which can agree well with the reported data. The bulk modulus of Li-Si and Li-Sn alloys decreases with increasing Li concentration, leading to the elastic softening of the alloys, which is essentially caused by the decreased strength of constituent chemical bonds in alloys from the viewpoint of EN. This work provides a deep understanding of mechanical failure of Si and Sn anodes for Li-ion batteries, and permits the prediction of the composition dependent bulk modulus of various lithiated alloys on the basis of chemical formula, metallic EN and cell volume (or alloy density), with no structural details required.