Synthesis of Tantalum Doped NMC811 and Its Impact on Crystal Structure and Electrochemical Performance at Higher Upper Cut-off Voltage

Abstract

Ni-rich, cathode active materials such as Li[Ni0.8Mn0.1Co0.1]O2 (NMC811) suffer from capacity fade, especially at higher upper cut-off voltages. There is an increasing interest on dopants such as Mo or Ta as a promising dopants for high-Ni materials. In this study four cathode active materials with Li[(Ni0.78Mn0.11Co0.11)1-xMx]O2 (NMC811, x=0, 0.005, 0.007, 0.013; M=Ta) were synthesized via a batch co-precipitation synthesis followed by calcination. To increase the probability of homogeneous distribution of the dopant, the highly porous hydroxide precursor was impregnated with Ta-ethoxide and afterwards calcined. The focus of this study is the effect of Ta on the crystal structure and its influence on stability at high-voltage operation. Using Rietveld method, trends for several unit cell parameters, such as c-parameter, crystallite size, microstrain, transition metal-oxygen bond lengths) were found. Doping NMC811 with 0.5 mol% Ta leads to <3% lower initial capacity (205 mAh g-1 at C/10), >5% higher capacity retention (>85%) and >7% higher accumulated energy output over 100 cycles at 1 C (66.3 kWh kg-1). This performance enhancement is attributed to the high transition metal – oxygen bond dissociation energy, which is thought to significantly suppress surface phase transformations, and hence, reduce the vulnerability towards material degradatio

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

“…[4][5][6][7] In order to further improve these materials and to reduce the intensity of bulk and surface degradation, doping and coating approaches are studied widely. [10][11][12][13][14][15][16][17][18][19][20][21] Recently, dopants with high oxidation states (e.g. Ta, Nb, W, Mo) were reported to be a promising solution, in that they reduce bulk degradation by adjustment of the primary-particle shape of the cathode.…”