Enhancement of Structural, Electrochemical, and Thermal Properties of High-Energy Density Ni-Rich LiNi_0.85Co_0.1Mn_0.05O₂ Cathode Materials for Li-Ion Batteries by Niobium Doping

Abstract

Ni-rich layered oxide LiNi1 – x – y Co x Mn y O2 (1 – x – y > 0.5) materials are favorable cathode materials in advanced Li-ion batteries for electromobility applications because of their high initial discharge capacity. However, they suffer from poor cycling stability because of the formation of cracks in their particles during operation. Here, we present improved structural stability, electrochemical performance, and thermal durability of LiNi0.85Co0.1Mn0.05O2(NCM85). The Nb-doped cathode material, Li­(Ni0.85Co0.1Mn0.05)0.997Nb0.003O2, has enhanced cycling stability at different temperatures, outstanding capacity retention, improved performance at high discharge rates, and a better thermal stability compared to the undoped cathode material. The high electrochemical performance of the doped material is directly related to the structural stability of the cathode particles. We further propose that Nb-doping in NCM85 improves material stability because of partial reduction of the amount of Jahn–Teller active Ni3+ ions and formation of strong bonds between the dopant and the oxygen ions, based on density functional theory calculations. Structural studies of the cycled cathodes reveal that doping with niobium suppresses the formation of cracks during cycling, which are abundant in the undoped cycled material particles. The Nb-doped NCM85 cathode material also displayed superior thermal characteristics. The coherence between the improved electrochemical, structural, and thermal properties of the doped material is discussed and emphasized.

Enhancing Structural Stability and Electrochemical Properties of Co-Less Ni-Rich Layer Cathode Materials by Fluorine and Niobium Co Doping

“…With the doping of Nb, the initial discharge specific capacity of N-NCM (222.67 mAh g –1 ) is slightly higher than that of NCM. which may be due to the broadening of the Li-ion transfer channel by the doping of Nb ions . However, compared to the NCM, the FN-NCM exhibited a similar specific capacity of 219.53 mAh g –1 , which is attributed to the synergistic effect of F and Nb ions.…”

“…On the one hand, due to the stronger Nb–O bonds than TM–O bonds, the degradation of the structure and the release of oxygen are suppressed during the charging process . In addition, the doping of Nb 5+ can reduce the structural instability caused by the harmful H2 to H3 phase transition, which facilitates the reduction of microcracking as well as the improvement of electrochemical properties. , Moreover, with the introduction of F ions, the formation of strong TM–F bonds can prevent the migration of transition metal ions, thus alleviating the structural collapse of the cathode. On the other hand, both Nb ions with larger ionic radius and F ions with longer bond length (Ni–F) can broaden the layer distance of the layered cathode material, , which was verified by XRD and HRTEM.…”

“…Moreover, ionic substitution is divided into cationic substitution and anionic substitution. In NCM ternary cathode material, Al is the most widely used doping element, and other dopants include Zr, Mg, Fe, Ca, Ga, , Ti, B, Ce, Nb, Na, Mo, F, Pr, etc.…”

“…Particularly, Yehonatan Levartovsky et al recently found that dopant of Nb tends to replace transition metal ions and can reduce the amount of Jahn–Teller active Ni 3+ ions, forming a strong bond between niobium and oxygen, thus improving the stability of the material . Sung-Beom Kim et al have investigated that doping with appropriate amounts of F ions can effectively improve the transport properties of lithium ions and form stronger bonds between transition metals and F ions .…”

A uniform and high-voltage stable LiTMPO4 coating layer enabled high performance LiNi0.8Co0.15Mn0.05O2 towards boosting lithium storage

“…During high-temperature sintering, the Li salt is volatilized, and the Li/TM ratio should be in excess to compensate for the Li loss (the appropriate excess of Li salt). 30 As a result, a series of residual lithium carbon compounds of Li 2 O/Li 2 CO 3 are formed inevitably, which will produce harmful effects such as gelatinization of electrode slurry and aggravation of surface side reactions. 31 In this work, the introduced PO 4 3− can effectively avoid the formation of residual lithium carbon compounds on the surface of NMC through a consumption reaction.…”