Atomic Horizons Interpretation on Enhancing Electrochemical Performance of Ni‐Rich NCM Cathode via W Doping: Dual Improvements in Electronic and Ionic Conductivities from DFT Calculations and Experimental Confirmation

Abstract

270 mAh g −1 , are candidates for the next generation of lithium-ion batteries (LIBs). [7,8] NCM cathodes with high nickel content have attracted increasing attention because of their higher capacities when more nickel cations provide a more electron transfer from Ni 2+ /Ni 3+ and Ni 3+ /Ni 4+ redox pairs. [9,10] Meanwhile, since the relative content of expensive cobalt will be reduced, the production cost will also be decreased. Therefore, it is a trend to increase the proportion of nickel in the ternary system of LiNi 1−x−y Co x Mn y O 2 . [11] However, when the nickel content exceeds 80%, [12,13] the battery suffers from serious capacity degradation during the cycle.The main role of elemental doping is to reduce the mixing of Li and Ni cations and stabilize the crystal structure. It is a feasible approach to slow the capacity decay. Presently, it has been found that W 6+ is a good choice as a doping element. W 6+ has a higher valence and stronger bond energy compared to other ions (such as Al 3+ , Mg 2+ , Ba 2+ , and Zn 2+ ), resulting in a dual functional enhancement of the electronic and cationic conductivities. In 2018, Kim [14] proposed that, after the doping with 1 mol% W into Ni-rich LiNi 0.9 Co 0.05 Mn 0.05 O 2 cathode, the salt rock phase with surface segregation could protect the cathode material from harmful reactions and improve the cycle stability. In 2019, Park [15] reported that 1 mol% W doping in LiNi 0.9 Co 0.05 Mn 0.05 O 2 cathode significantly improved the capacity retention from 60% to 89% after 500 cycles at a 4.3 V cutoff voltage. It was believed that the reason for the cathode performance improvement of the W-doped LiNi 0.9 Co 0.05 Mn 0.05 O 2 in the abovementioned reports was mainly due to the internal stress reduction to stabilize the bulk structure so that the formation of harmful microcracks was inhibited. Shang et al. [16] suggested that adding W stabilized the structure and slowed the diffusion of the rock salt phase from the surface to the interior. However, researchers have conflicting opinions on the effects of the formed rock salt structure after doping. For instance, concerning the abovementioned conflicting opinions, that is, Kim thinks the existence of rock salt phase is good, whereas Shang thinks it is bad. Furthermore, reports on the formation of the rock salt phase by non-W cation doping are controversial. Jianming Zheng et al. [17] believeThe rapid capacity degradation and poor rate capability hinder the application of Rich-Ni layered LiNi x Co y Mn z O 2 (NCM) as cathode materials for highenergy lithium-ion batteries. In this study, density functional theory (DFT) calculations, combined with conventional electrochemical measurements, reveal from the atomic view that the dual improvements in electronic and ionic conductivities are the main facts for the property enhancement. The bandgap of the cathode material is reduced to 1.1623 eV due to the increased number of electrons near the Fermi level after W intercalation. Such improved electronic conductivity subsequently lea...

Optimizing NCM811 nickel-rich cathode stability via suppressing asymmetric Li/Ni mixing by a “non-intrusive” strategy

“…The diffraction peaks related to the NaFeO 2 structure confirm the good crystallinity of both samples, displaying characteristic peaks corresponding to the hexagonal layered pattern α and falling within the R 3̄ m spatial group. 42 The primary objective of this analysis is to determine lattice parameters and evaluate Li/Ni mixing. Notably, the refinement process delivers satisfactory results, evident from the smaller R w and R p values (<10%).…”

Insight into the Role of Co and Mn Elements in Ni-Rich LiNi0.9CoxMn0.08–xAl0.02O2 Cathode Materials

“…When the current density is 5 C, the specific discharge capacity of the NCMA9712 sample is 144 mAh g –1 , while that of the NCMA9352 sample is only 128 mAh g –1 , with a difference of 16 mAh g –1 . It can be seen that the Co element is beneficial for enhancing the rate capability of Ni-rich quaternary cathode materials due to its large electronic conductivity. − …”

The role of niobium in layered oxide cathodes for conventional lithium-ion and solid-state batteries

“…21 These characteristics translate to an observed reduction in degradation and improvements to lithium diffusion kinetics when Nb 5+ is employed as a dopant. Other element dopants with comparable ionic radius and higher valence than the TMs in LTMOs, such as V 5+ , 22–24 Ta 5+ , 25–27 Mo 6+ , 28–30 and W 6+ , 31–33 have also been reported to exhibit similar improvements. Another work has outlined the impact of these and various other dopants and coating materials on Ni-rich CAMs.…”