The exploration towards cost-effective filler metal for ceramics joining has always been the key issues for ceramics joining. Herein, we reveal that the Al metal prefers to spread on the ZrO₂ based ceramic under the air heating condition, due to the geometric limit effects by in-situ formed dense Al₂O₃ surface. Inspired by this, the joining of ZrO₂ based ceramics was realized in air with Al metal as filler, through the diffusion of Al towards ceramic side. The Al element can induce obvious interfacial bonding effect on Al₂O₃ layer and ZrO₂ ceramic, where the hybridization among the Al-p, Zr-d and O-p orbitals plays a key role. The in-situ formed Al₂O₃ layer on Al filler surface is vital for forming the fine interface (shear strength of ~36 MPa), which results in the relief of lattice mismatch and peak stress at ceramic-filler metal transition interface.

Here, by using atomically resolved scanning transmission electron microscopy and electron energy loss spectroscopy, we investigate the structural and chemical evolution of Li₃V₂(PO₄)₃ (LVP) upon the high-voltage window (3.0–4.8 V). We find that the valence of vanadium gradually increases towards the core corresponding to the formation of electrochemically inactive Li_3-xV₂(PO₄)₃ (L_3-xVP) phases. These Li-deficient phases exhibit structure distortion with superstructure stripes, likely caused by the migration of the vanadium, which can slow down the lithium ion diffusion or even block the diffusion channels. Such kinetic limitations lead to the formation of Li-deficient phase along with capacity loss. Thus, the LVP continuously losses of electrochemical activity and Li-deficient phases gradually grow from the particle core towards the surface during cycling. After 500 cycles, the thickness of active LVP layer decreases to be ~ 5–20 nm. Moreover, the micromorphology and chemical composition of solid electrolyte interphase (SEI) have been investigated, indicating the thick SEI film also contributes to the capacity loss. The present work reveals the structural and chemical evolution in the cycled electrode materials at an atomic scale, which is essential to understand the voltage fading and capacity decaying of LVP cathode.