Mechanochemically Reduced SiO2 by Ti Incorporation as Lithium Storage Materials

Enabling high electrochemical activity of a hollow SiO2 anode by decorating it with ultrafine cobalt nanoparticles and a carbon matrix for long-lifespan lithium ion batteries

Silica is a very promising anode material for lithium-ion batteries, due to its advantages of being resource-rich and having high theoretical specific capacity. However, poor electrochemical activity severely limits its practical application. To solve this issue, a nanosheet-assembled silica hierarchical hollow sphere decorated with ultrafine cobalt nanoparticles and carbon (SiO2/Co/C) is successfully synthesized. The hollow structure can effectively alleviate the volume expansion, shorten the migration distance of lithium ions, and increase the binding site. Furthermore, the carbon matrix and highly active ultrafine cobalt nanoparticles enhance not only the electronic conductivity but also the electrochemical activity (catalyzing the breaking of Si-O and Li-O bonds) of SiO2. The resulting SiO2/Co/C composite has a high reversible capacity of 1160 mA h g-1 at 0.2 A g-1 and still has a specific capacity of 548 mA h g-1 after 1000 cycles at a high current density of 1.0 A g-1. Moreover, the SiO2/Co/C composite also exhibits good electrochemical performance in a full cell.

Anisotropic Compositional Expansion and Chemical Potential of Lithiated SiO2 Electrodes: Multiscale Mechanical Analysis

The use of high-capacity electrode materials (i.e., Si) in Li-ion batteries is hindered by their mechanical degradation. Thus, oxides (i.e., SiO₂) are commonly used to obtain high expected capacities and long-term cycle performances. Despite extensive studies of the electrochemical-mechanical behaviors of high-capacity energy storage materials, the mechanical behaviors of amorphous SiO₂ during electrochemical reaction remain largely unknown. Here, we systematically investigate the stress evolution, electronic structure, and mechanical deformation of lithiated SiO₂ through first-principles computation and the finite element method. The structural and thermodynamic role of O in the amorphous Li-O-Si system is reported and compared with that in Si. Strong Si-O bonds in SiO₂ show high mechanical strength and brittle behavior, but as Li is inserted, the Li-rich SiO₂ phases become mechanically softened. The relaxation kinetics of SiO₂, inducing deviatoric inelastic strains under mechanical constraints, is also compared with that of Si. The finite element model including the kinetic model for anisotropic expansion demonstrates that the long-term cycling stability of core-shell Si-SiO₂ nanoparticles mainly arises from the reaction kinetics and high mechanical strength of SiO₂. These results provide fundamental insights into the chemomechanical behavior of SiO₂ for practical use.

Effect of Li concentration-dependent material properties on diffusion induced stresses of a Sn anode

Sn is one of the promising Li ion battery anode materials with high theoretical capacity and mechanical properties that allow for effective relaxation of Li diffusion-induced stresses. Sn is a low melting point metal with a low modulus and strength and has the ability to relax stresses via plasticity and creep deformations. In this study, concentration-dependent material properties are used in numerical simulations to model the Li diffusion-induced stress evolution in Sn micropillars. Simulation results using concentration-dependent material properties resulted in a completely different failure mode in comparison to that of concentration-independent simulation results. Tensile hoop stress needed for crack propagation was analyzed to be at the core for concentration-independent material properties, and switched to being at the surface for concentration-dependent simulation results. In addition, by incorporating these maximum tensile DIS results, the critical size for the failure of Sn micropillars was determined to be 5.3 μm at C/10 charging rate. This was then correlated with experimental observations, where fracture occurred in Sn micropillars with sizes larger than 6 μm, while 4.4 μm sized Sn micropillars survived the lithiation cycle.