Lithium-ion batteries (LIBs) are widely used from small electronic devices to large-format electric vehicles and energy storage systems. However, as the energy density of LIBs increases, ensuring safety becomes more important to battery manufacturer. [1] As a result, battery engineers are reluctant to use bare polyethylene separators without the ceramic coating layer, which is generally fabricated from the slurry containing ceramic particles, binder, and solvent. Thus, the ceramic-coated separator (CCS) becomes a must-have item for state-of-the-art LIBs. However, since an additional ceramic layer not only reduces the energy density of LIBs, but also increases the cell resistance, there are previous works to reduce those resistive ceramic layers without compromising the thermal or mechanical properties of CCSs. [2] The key process they utilized was the deposition, which can coat the SiO₂, Al₂O₃, or TiO₂ ceramic layers of tens of nanometer on the surface of separators. [3,4,5,6] Thus, without ceramic coating layer of a few micrometers, they could show both improved electrolyte affinity and thermal stability comparable to the conventional slurry-based CCSs. However, except for oxide-based ceramics, other ceramics like nitride, which has a good thermal conductivity, have not been tried for this ultra-thin ceramic coating layers.

Thus, herein, we attempt to deposit nitride on polyethylene separators using RF sputtering method. After the CCS was prepared, its physical properties such as thickness, mass per area, permeability, and morphological change were evaluated with a control CCS with Al₂O₃ layer. Also, not only thermal stability but also thermal conductivity was compared between nitride- and oxide-based CCSs. Furthermore, their electrochemical properties such as cyclability and rate capability were also investigated with large-area pouch-type full cells. Through these comparative study, pros and cons of ultra-thin nitride layer would be reported for advanced LIBs.

[1] John B. Goodenough et al., J. Am. Chem. Soc. 2013, 135, 1167−1176.

[2] Karun Kumar Jana et al., ChemBioEng Reviews, 2018, 5, 346-371

[3] Taejoo Lee et al., Macromolecular Research, 2014, 22, 1190–1195

[4] Min Kim et al., Journal of Power Sources, 212, 2012, 22-27
[5] Yoon Seok Jung et al., Adv. Energy Mater. 2012, 2, 1022–1027

[6] Kun Peng et al., RSC Adv., 2015, 5, 81468