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Since the announcement of a million-mile battery by Tesla, single-crystal processing of layered oxide cathode has received great attention recently. From single-crystal process, high Ni layered oxides with grain size in mm range tends to give better cycling performance due to better structural integrity against repeated charge/discharge cycles. However, during heating/calcination process of oxide/carbonates/nitrates powder compacts, it may involve decomposition, chemical reactions, diffusion, oxidation, sintering, grain-growth. For single-crystal process, the powder compacts need to be heated to higher temperatures (~950°C) for certain period of time. On the other hand, enough air/oxygen is need for Ni oxidation and better crystallization in Ni-rich layered structure. Therefore, it is important to investigate the processing of single-crystal Ni-rich layered oxide based on the sintering behavior, thermal gravimetric analysis, and phase transformation. Nevertheless, the lithiation/oxidation of Ni-containing oxides involves charge compensation resulted from defect reactions. As a result, the affected electrical, optical, structural, and electrochemical properties of layered oxides will be discussed based on defect chemistry consideration. The structural, microstructural and electrical properties of decomposed precursors and doped layered oxides will be examined using XRD, SEM and DC/AC impedance measurements. CV and charge/discharge tests from assembled coin cells will be used to evaluate electrochemical properties of single-crystal Ni-rich layered oxides.

Cathode materials with high energy density for Li ion batteries have received great attention due to the high demand in transportation applications. Although several crystal structures have been demonstrated and shown reversible capabilities during lithiation/delithiation processes in cathode of Li ion batteries; oxides with layered/spinel structure still remain the ones that provide higher energy densities. However, higher energy density means the creation of more ionic/electronic defects in both cation and/or anion sublattices of layered/spinel structures. Higher defect concentration in either cation or anion sublattices tend to destabilize its crystal structure. As a result, the phase change is frequently observed in repeatedly cycled cathode. Furthermore, the phase-changing cathode tends to show the capacity fading after cycling tests. Based on defect consideration, the stability of highly defective materials may be enhanced by using dopant and/or better processing routes. In this study, the electrical/electrochemical/structural properties of oxide cathodes will be investigated. First, the electrical measurement of spinel/layered oxides are conducted using sintered disc. Assembled cells using above-mentioned cathode and Li anode with desired liquid electrolyte will be tested and cycled. XPS, SEM and XRD analyses will be conducted on as-assembled as well as cycled cells. The analyzing results will be illustrated based on the processing parameters and defect chemistry of doping ions and the accompanying defects created.