Probing the Mysterious Behavior of Tungsten as a Dopant Inside Pristine Cobalt‐Free Nickel‐Rich Cathode Materials

Abstract

Nickel-rich cathode materials with small amounts of tungsten (W) dopants have attracted extensive attention in recent years. However, the chemical state, crystalline form, compound chemistry, and location of W in these layered cathodes are still not well-understood. In this study, these missing structural properties are determined through a combination of macro-, to atomic-sensitive characterization techniques and density functional theory (DFT). W-doped LiNiO 2 (LNO) particles, prepared with mechanofusion and coprecipitation methods, are used to probe changes in the structure and location of W-species. The results indicate that W is mainly distributed on the surfaces and inside grain boundaries of the secondary particles, regardless of the doping method. Electron energy loss spectroscopy (EELS) mapping confirms the simultaneous presence of W, O, with and without Ni in the grain boundaries as well as W-and O-rich regions on the very surface. The W-rich areas inside the grain boundaries are found to be in two forms, crystalline and amorphous. This paper suggests the presence of kinetically stabilized-Li 4+x Ni 1-x WO 6 (x = 0, 0.1) with the possibility of Li x W y O z phases in LNO which are consistent with the electron microscopy, X-ray absorption and diffraction data. The multiple roles of W in this complex microstructure are discussed considering the W distribution.

Single Crystal Li1+x[Ni0.6Mn0.4]1−xO2 Made by All-Dry Synthesis

“…W is known to primarily exist on the surface of layered-oxide positive electrode materials rather than as a bulk dopant. 17 As well, W inhibits the growth of primary crystallites, 15,16 which is supported by the comparison in Fig. 8.…”

“…Furthermore, the use of certain coatings on layered-oxide materials has been shown to improve cycle life. 3,[14][15][16][17] Specifically, tungsten (W) has gained interest for its ability to improve the cycle lifetime in Ni-rich positive electrode materials. 15,16 However, its application has thus far been focused on coating hydroxide polycrystalline precursors [15][16][17] as in the precursor-sintering process of Fig.…”

Benefits and Limitations of 226 Substitutions into Li-La-Ti-O Perovskites

“…Thus, the distribution of substituents can either be evenly distributed throughout the bulk of the material, phase-separated or concentrated at the surface. For example, in W-doped LiNiO 2 , W was found to be mainly concentrated at the surface of both primary and secondary particles . There were trade-offs between low potential stability limit and total conductivity; however, that could be overcome by tuning the sintering temperature and time.…”

“…For example, in W-doped LiNiO 2 , W was found to be mainly concentrated at the surface of both primary and secondary particles. 36 There were trade-offs between low potential stability limit and total conductivity; however, that could be overcome by tuning the sintering temperature and time. Finally, this study acts as an initial screen to find which substitutions in LLTO can improve the electrochemical stability window and the transport properties and discover trends.…”

Mg/Al Double-Pillared LiNiO2 as a Co-Free Ternary Cathode Material Ensuring Stable Cycling at 4.6 V

“…Cathode materials play a crucial role in the key components of LIBs. LiNiO 2 -based cathode materials, including LiNi x Co y Mn z O 2 and LiNi x Co y Al z O 2 ( x + y + z = 1), have garnered significant attention due to their high voltage platform and specific capacity. − The demand for low-cost and high-energy cathode materials has been increasing, driving the development of cobalt-free (Co-free) and nickel-rich (Ni-rich) LiNiO 2 -based alternatives. − However, increasing the nickel content presents a certain challenges. For example, the cathode is more susceptible to irreversible phase transition during the delithiation process.…”