Structural Analysis of the LiCoPO₄ Electrode/NASICON-Type Li_1.3Al_0.3Ti_1.7(PO₄)_{3 Solid Electrolyte Interface}

The mixed composites of a high-voltage cathode materialin lithium-ionbatteries, LiCoPO4 (LCP), and an oxide-based solid electrolyte,Li1.3Al0.3Ti1.7(PO4)(3) (LATP), were sintered at a relatively high temperature, andthe structure of the bulk and interface was comprehensively analyzedby various techniques, including X-ray diffraction, X-ray absorptionfine structure (XAFS), and transmission electron microscopy, togetherwith selected-area electron diffraction, energy-dispersive X-ray spectroscopy,and electron energy loss spectroscopy (EELS). The crystal structureand electronic state of LCP and LATP remained unchanged throughoutthe temperature range, but amorphous reaction layers were formed attheir boundaries at temperatures over 700 & DEG;C. The reaction layerswere composed of Li, O, P, and Co, and P and Co were richer and poorerthan LCP, respectively. Linear combination fitting of XAFS data andmicroanalysis of EELS identified the major species of reaction layersto be Li3PO4 and divalent Co compounds suchas CoO. Li3PO4 presumably promoted the crystalgrowth of LATP and Li-ion transfer.