W-Doping of Dense NMC811 Hydroxide through Wet-Impregnation and Its Impact on Crystal Structure, Phase Transition Related Gas Evolution and Electrochemical Performance at Elevated Upper Cut-Off Voltage

Abstract

Doping of Ni-rich LNMC cathode materials with tungsten via a solid-state route has been shown to stabilize the materials against structural degradation at high voltages during electrochemical cycling. Here we use a wet-chemical doping method to homogeneously introduce 0.5 mol% tungsten into dense NMC811 (Li[(Ni0.8Mn0.1Co0.1)]O2), followed by a detailed structural and electrochemical characterization. A homogeneous distribution of W in the materials was evidenced by elemental mapping and TOF-SIMS. The increase in bond-dissociation energy to oxygen of the transition metal (TM) site led to compressed slab thickness (TMO6 octahedron width in c-direction), indicating shorter, and thus strengthened, TM-O bonds, as also confirmed by TGA-MS results. Importantly, statistical analysis of electron backscatter diffraction data revealed a W-induced radial alignment of a-b planes of the primary particles. The cycling stability of the doped material was more than 7% higher for the W-doped (92.4%) as compared to the undoped NMC811 (85.3%) material at a higher upper cut-off voltage of 4.5 V vs. Li/Li+. Furthermore, the voltage decay was lower (0.2 V vs. 0.29 V), leading to >2% lower energy loss (5.3% vs. 7.4%) for the W-doped material.

The Effect of Doping Process Route on LiNiO2 Cathode Material Properties

“…It has previously been reported that Zr 4+ doping is associated with reduced primary particle size, 47 as are other dopants, mostly of higher valence state. 20,49,50,59 The observed restriction of grain growth can be explained by a dopant-induced change in surface energy, including segregation of dopant along grain boundaries. 17,59 This is not limited to battery materials, but can be applied to the sintering of ceramics in general.…”

“…In various studies, it has been shown that a higher capacity retention of doped material correlates with a smaller particle or grain size relative to undoped material achieved by modification with high valence dopants. 20,49,50,59 In these cases, the smaller particle size resulted from dopant-induced grain growth suppression. In this work, a similar performance dependency on particle size is observed and especially clear in the comparison of impregnated and cocalcined LNO, while the surface impurities and their presence, respectively removal, may additionally affect the performance of coprecipitated LNO.…”

“…[26][27][28][29][30][31][32][33][34][35][36][37][38][39] The impregnation of pCAM with a dopant solution or a suspension of smaller dopant particles and subsequent solvent removal provides a third option, especially if cocalcination leads to insufficient mixing and/or phase separation. [40][41][42][43][44][45][46][47][48][49][50][51] Despite these and various other process routes being available, 13,15,[52][53][54][55][56] comparisons between doped samples obtained from different routes are quite rare, 57,58 as usually comparisons are made with an undoped reference sample. The influence of the dopant on the CAM particle morphology is sometimes discussed in comparisons of doped and undoped samples.…”

“…The influence of the dopant on the CAM particle morphology is sometimes discussed in comparisons of doped and undoped samples. [17][18][19]26,30,41,47,49,50,52,57 Recently, Park et al demonstrated that, in a series of co-precipitated LiNi 0.95 Co 0.04 X 0.01 O 2 (X = one of Al, Ti, Ta, Sb, Nb, W, Mo), the primary particle size strongly depends on the chosen dopant, decreasing with dopant valence state. Furthermore, a linear trend between primary particle size of each doped CAM and capacity fading after 100 cycles was observed.…”

Tantalum Oxide Coating of Ni-rich Cathode Active Material via Atomic Layer Deposition and its Influence on Gas Evolution and Electrochemical Performance in the Early and Advanced Stages of Degradation

“…Radial texture of the materials leads to reduced mechanical stress during charge and discharge, resulting in less intense microcracking and subsequent capacity fade. 14,17,22,23 To inhibit the surface degradation of the Nirich materials, coating of the particles has been reported to be an effective method. 11,19,21,24,25 Surface film coatings on cathode particles can serve as a physical barrier between the reactive cathode surface and the electrolyte.…”