Elucidating the Relationship between Quality Control of the Coating Layer and Suppression of Gas Evolution in Li-Ion Batteries

The difference in homogeneity and uniformity of the coating layer based on the melting point of the coating material using mechanofusion (MF) was investigated for the overall electrochemical performance improvement as well as structural stability and safety against hydrogen fluoride (HF) gas formation. Depending on the high temperature (650–1250 °C) generated by the mechanical energy of MF, a low-melting-point coating material (LMPM) forms a uniform and homogeneous coating layer, whereas a high-melting-point coating material (HMPM) forms an island-type coating. Representative candidates for the HMPM and LMPM are ZrO2 and Co3O4, which have melting points of 2715 and 896 °C, respectively. The capacity retention of the LMPM after 100 cycles in the coin cell increased by 20% over that of the pristine material. Structural stability and resistance changes due to the coating layer according to the melting point of the material and direct current internal resistance (DCIR) of the pouch cell were confirmed. Moreover, capacity retention of the LMPM at the pouch cell increased by more than 40% compared to that of the pristine material and showed a low resistance increase rate after cycling through the DCIR. Safety against HF was also confirmed through artificial H2O injection experiments and gas component analyses.