Effect of Lithium Silicate Addition on the Microstructure and Crack Formation of LiNi0.8Co0.1Mn0.1O2 Cathode Particles.

The microstructure of LiNi0.8Co0.1Mn0.1O2 cathode materials was controlled by the addition of lithium silicate, and the influence on the cycle performance and the rate capability was investigated. Si was not included within the lattice, but localized at the grain boundaries of the primary particles and the pores inside the secondary particles. The addition of the lithium silicate greatly decreased the density of the pores between the primary particles and improved the density of the secondary particles. The capacity retention was successfully improved for lithium silicate-added LiNi0.8Co0.1Mn0.1O2. When lithium silicate-free LiNi0.8Co0.1Mn0.1O2 was charged to 4.3 V, many cracks were formed along the grain boundaries even in the first cycle, while crack formation was remarkably inhibited for lithium silicate-added LiNi0.8Co0.1Mn0.1O2. Moreover, lithium silicate-added LiNi0.8Co0.1Mn0.1O2 particles were almost free from visible microcracks even after 100 cycles at the discharged state. These results suggest that the lithium silicate reinforces the grain-adhesion at the grain boundaries, inhibiting crack formation and electrolyte decomposition inside the cracks.

Artificial lithium fluoride surface coating on silicon negative electrodes for the inhibition of electrolyte decomposition in lithium-ion batteries: visualization of a solid electrolyte interphase using in situ AFM.

The solid electrolyte interphase (SEI), which is a surface layer formed on the negative electrode, plays an important role in inhibiting the reductive decomposition of the electrolyte solution in a lithium-ion battery. However, it has not been understood well which components are important for the SEI to prevent the electrolyte decomposition. Lithium fluoride (LiF), as an artificial SEI, was formed on an amorphous-Si thin film by physical vapor deposition. Changes in the surface morphology of the Si electrode with potential sweeping were investigated using in situ atomic force microscopy (AFM). Although large amounts of non-uniform surface deposits that originate from electrolyte decomposition emerged on the bare Si-film electrode during the first lithiation process, few surface deposits were observed on the LiF-coated Si-film electrode even after two cycles in an ethylene carbonate-based electrolyte solution without additives. It is clear that LiF is a required SEI component that inhibits electrolyte decomposition on Si negative electrodes.

In situ Scanning Electron Microscopy of Silicon Anode Reactions in Lithium-Ion Batteries during Charge/Discharge Processes.

A comprehensive understanding of the charge/discharge behaviour of high-capacity anode active materials, e.g., Si and Li, is essential for the design and development of next-generation high-performance Li-based batteries. Here, we demonstrate the in situ scanning electron microscopy (in situ SEM) of Si anodes in a configuration analogous to actual lithium-ion batteries (LIBs) with an ionic liquid (IL) that is expected to be a functional LIB electrolyte in the future. We discovered that variations in the morphology of Si active materials during charge/discharge processes is strongly dependent on their size and shape. Even the diffusion of atomic Li into Si materials can be visualized using a back-scattering electron imaging technique. The electrode reactions were successfully recorded as video clips. This in situ SEM technique can simultaneously provide useful data on, for example, morphological variations and elemental distributions, as well as electrochemical data.

Negligible "negative space-charge layer effects" at oxide-electrolyte/electrode interfaces of thin-film batteries.

In this paper, we report the surprisingly low electrolyte/electrode interface resistance of 8.6 Ω cm(2) observed in thin-film batteries. This value is an order of magnitude smaller than that presented in previous reports on all-solid-state lithium batteries. The value is also smaller than that found in a liquid electrolyte-based batteries. The low interface resistance indicates that the negative space-charge layer effects at the Li3PO(4-x)N(x)/LiCoO2 interface are negligible and demonstrates that it is possible to fabricate all-solid state batteries with faster charging/discharging properties.