فاطمه نجاري معارف

Lithium-ion batteries are widely used in portable electronics an‎d electric vehicles due to their high energy density, long life, an‎d small size. However, problems such as thermal an‎d structural stability pose challenges to the performance of these batteries. Among the cathode materials, NCM811 offers high energy capacity due to its high nickel content; however, it is vulnerable to oxidation an‎d structural degradation during long charge an‎d discharge cycles. Therefore, particle surface modification has been considered as an effective solution to improve electrochemical performance. In this study, the aim was to apply lanthanum phosphate, cerium phosphate, an‎d lanthanum-cerium phosphate coatings on the surface of NCM811 an‎d compare these three coatings on the stability an‎d transport of lithium ions at the electrode/electrolyte interface. The coating was performed by chemical bath deposition method an‎d the samples were characterized by a range of analyses after drying an‎d without calcination process. The elimination of calcination process improved the structure an‎d created a uniform coating on the surface of NCM811 cathode. Next, scanning electron microscopy (SEM) an‎d X-ray diffraction (XRD) analyses showed that the coating process did not change the structure of the NCM811 cathode material, the morphology was not changed, an‎d the layer structure did not undergo cation mixing. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) an‎d Raman spectroscopy analyses confirmed the presence of phosphate coating on the NCM811 surface. Then, the electrochemical performance of the samples was investigated by rate capability, cyclability, cyclic voltammetry, impedance spectroscopy an‎d galvanostat intermittent titration tests. The results showed that the LaCePO4 coating had the lowest discharge capacity loss (130.7/126.5 mA/g) compared to the two LaPO4 an‎d CePO4 coatings, an‎d had the highest capacity retention (80.1/91.2%) compared to the commercial NCM811 after 100 cycles at a current rate of 1 C an‎d a voltage range of 2.8-4.4 V, an‎d had the highest Coulombic efficiency (98.59/99.9%). The charge transfer resistance had also decreased from 30.81 Ω to 11.72 Ω, an‎d the diffusion coefficients obtained in this sample had increased from 8.1 × 10-13 to 1.21 × 10- 12. Finally, it created a homogeneous layer with a desirable thickness that prevented structural degradation, prevented side reactions (production of HF an‎d oxygen gas), an‎d was a protective layer against the cathode an‎d electrolyte surfaces, leading to improved battery performance.

كاتد NCM811 , باتري ليتيوم-يون , پوشش فسفاتي , لانتانيوم , سريم

NCM811 cathode , lithium-ion battery , phosphate coating , cerium , lanthanum

Fatemeh Najary Maaref

Dr. Seyed Morteza Masoudpanah, Dr. Somayeh Alamolhoda