Enhanced Structure/Interfacial Properties of Single-Crystal Ni-Rich LiNi_0.92Co_0.04Mn_0.04O₂ Cathodes Synthesized Via LiCl-NaCl Molten-Salt Method

Arising from the increasing demand for electric vehicles (EVs), Ni-rich LiNi_xCo_yMn_zO₂ (NCM, x + y + z = 1, x ≥ 0.8) cathode with greatly increased energy density are being researched and commercialized for lithium-ion batteries (LIBs). However, parasitic crack formation during the discharge–charge cycling process remains as a major degradation mechanism. Cracking leads to increase in the specific surface area, loss of electrical contact between the primary particles, and facilitates liquid electrolyte infiltration into the cathode active material, accelerating capacity fading and decrease in lifetime. In contrast, Ni-rich NCM when used as a single crystal exhibits superior cycling performances due to its rigid mechanical property that resists cracking during long charge–discharge process even under harsh conditions. In this paper, we present comparative investigation between single crystal Ni-rich LiNi_0.92Co_0.04Mn_0.04O₂ (SC) and polycrystalline Ni-rich LiNi_0.92Co_0.04Mn_0.04O₂ (PC). The relatively improved cycling performances of SC are attributed to smaller anisotropic volume change, higher reversibility of phase transition, and resistance to crack formation. The superior properties of SC are demonstrated by in situ characterization and battery tests. Consequently, it is inferred from the results obtained that optimization of preparation conditions can be regarded as a key approach to obtain well crystallized and superior electrochemical performances.