Improved Capacity Retention of SiO2-Coated LiNi0.6Mn0.2Co0.2O2 Cathode Material for Lithium-Ion Batteries

Abstract

Surface degradation of Ni-enriched layered cathode material Li[Ni0.6Mn0.2Co0.2]O2 (NMC622) is the main reason that leads to large capacity decay during long-term cycling. In the frame of this research, an amorphous SiO2 coating was applied onto the surface of the commercially available NMC622 powder by a wet coating process, through the condensation reaction of tetraethyl orthosilicate. The chemical composition of the coating layer was analyzed by inductively-coupled plasma. The morphology was studied by scanning electron microscopy and transmission electron microscopy. Electrochemical properties, including cyclic voltammetry, galvanostatic cycling, and rate capability measurements in a half-cell configuration, were tested to compare the electrochemical behavior of the non-coated and coated NMC622 materials. It is shown that the rate performance of the NMC622 materials is not affected by the coating layer. After 700 cycles in the range of 3.0–4.3 V at 2 C discharge, the cells with SiO2-coated NMC622 materials retained 80% of their initial capacity, which is higher than the uncoated ones (74%). Physicochemical characterizations, e.g., XRD and SEM, were performed post-mortem to reveal the stabilizing mechanism of the SiO2-coated NMC622 electrodes after long-term cycling. Based on these results, this is due to the shielding effect of the coating between the NMC622 particle surface and the liquid electrolyte, along with its scavenging effect on HF. SiO2 coating is therefore a facile surface modification method that results in potentially significant enhancement of the cyclic stability of Ni-rich NMC materials.

Ultrathin Li–Si–O Coating Layer to Stabilize the Surface Structure and Prolong the Cycling Life of Single-Crystal LiNi0.6Co0.2Mn0.2O2 Cathode Materials at 4.5 V

“…The function of the Li–Si–O coating layer is exhibited in Figure i,j. First, the Li–Si–O coating layer can be a robust physical protection layer that can segregate the NCM material and electrolyte interface and resist the NCM from the electrolyte erosion. ,, Moreover, the HF acids that originated from the LiPF 6 product reacted with the trace water molecules at a high operating potential can attack the naked cathode materials and further cause the transition metal dissolution and lattice oxygen escaping . Hence, Li–Si–O can also be a sacrificial material to deplete HF acids to stabilize the surface lattice.…”

High Performance Nickel Based Electrodes in State-of-the-Art Lithium-Ion Batteries: Morphological Perspectives

“…The unwanted side reactions that occur during cell use can also be suppressed by coating the materials. However, adding a coating to a nickel-rich cathode is considered uneconomical because the coating process requires additional processing and production (Lu X. et al, 2019). Tailoring the particle morphology can also reduce the reactivity of Ni-rich cathodes.…”

Improving Electrochemical Performance of High-Voltage Spinel LiNi0.5Mn1.5O4 Cathodes by Silicon Oxide Surface Modification

“…SiO 2 also can optimize organic electrolyte performance, remove H 2 O and HF, etc. Therefore, SiO 2 has been successfully applied in the surface modification of various cathode materials. − Fan et al used nanogas phase SiO 2 to directly modify the surface of LNMO through the wet chemical method and moderate temperature treatment at 500 °C . Recently, Nisar et al have completed the surface modification of LNMO by mixing nano-SiO 2 in the process of preparing the LNMO materials .…”