Electrochemical Characterization and Microstructure Evolution of Ni-Rich Layered Cathode Materials by Niobium Coating/Substitution

Abstract

The high nickel layered mixed metal oxides, such as LiNi z Co y Mn 1−z-y−q Al q O 2 , are the most utilized cathode materials in Li-ion batteries for electric vehicles due to their high energy density. However, as the nickel content increases, they suffer from poor capacity retention and from voltage fading due to interfacial/ structural instability. In this paper, a series of Nb-coated/substituted LiNi 0.9 Co 0.05 Mn 0.05 O 2 (NMC 9055) were synthesized by reacting the Nb precursors, Ni 0.9 Co 0.05 Mn 0.05 (OH) 2 , and LiOH. Nb is found in the NMC structure and also on the grain boundaries between the primary particles. These Nb-modified materials showed improved capacity retention and charge/discharge voltage profiles over the untreated material; the capacity retention was 86.4% (0.7 Nb-NMC 9055) vs 93.5% (1.4 Nb-NMC 9055) vs 99.7% (2.1 Nb-NMC 9055) vs 75.3% (NMC 9055) after 200 cycles and nearly no voltage fading (1.4 Nb-NMC 9055 and 2.1 Nb-NMC 9055) during cycling. High-angle annular dark-field (HAADF) scanning transition electron microscopy (STEM) images showed that the added niobium (Li−Nb−O phase) is located in the boundaries between the primary particles. This transferred obvious interparticles/intraparticles cracking into tiny intraparticles cracking, which benefits the release of strain/stress, maintains the mechanical integrity of secondary particles, and inhibits the structural transformation from the layer structure to rock-salt phase supported by large reduced charge transfer resistance, thus enhancing the electrochemical performance of NMC 9055.

Surface Stabilization of Cobalt-Free LiNiO2 with Niobium for Lithium-Ion Batteries

“…Expansion of the lattice parameters, indicated by a slight shift of corresponding diffraction peaks to lower 2θ values, is commonly observed upon the introduction of dopants into the bulk structure due to their different radii and charge compared to the host material: Nb 5+ has an ionic radius of 0.64 Å compared to Ni 3+ (0.56 Å) and Li + (0.76 Å). ,, Previous studies on Nb incorporation in other high-Ni compositions, such as LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC 811), LiNi 0.90 Mn 0.05 Co 0.05 O 2 (NMC 900505), and LiNi 0.85 Mn 0.10 Co 0.05 O 2 (NMC 851005), have frequently reported a distinct shift to lower 2θ values consistent with incorporation of Nb 5+ into the bulk lattice. − Here, a slight shift of the (003) peak is observed for Nb contents ≥2% (Figure c). This may result from an incorporation of Nb into the bulk lattice or from a slight chemical delithiation of LNO during calcination at these Nb contents, as discussed below.…”

“…Expansion of the lattice parameters, indicated by a slight shift of corresponding diffraction peaks to lower 2θ values, is commonly observed upon the introduction of dopants into the bulk structure due to their different radii and charge compared to the host material: Nb 5+ has an ionic radius of 0.64 Å compared to Ni 3+ (0.56 Å) and Li + (0.76 Å). 19,21,24 Previous studies on Nb incorporation in other high-Ni compositions, s u c h a s L i N i 0 . 8 M n 0 .…”

“…To this end, many different strategies have been proposed, among which elemental doping and surface coating are the most widely investigated. − While many different elements have been investigated, niobium appears to yield exceptionally remarkable performance enhancement. Nb incorporation has been investigated in a variety of high-nickel cathode materials, including NMC 532, NMC 811, NMC 85:10:05, NMC 88:02:10, NMC 90:05:05, and LNO, showing notable enhancements in cycle life, rate capability, and thermal stability. − Furthermore, computational screening of various elements suggests that Nb may be the optimal choice among transition-metal dopants . Lithium niobates, of the general formula Li x NbO y , have been widely investigated in the field of solid-state batteries, where they are used as coatings to improve the interfacial stability between the cathode and solid electrolyte. , Generally, they have been found to offer beneficial properties as thin coatings to passivate the surface of layered oxide particles due to their relatively high Li + conductivity, which may be improved further by inclusion of Ni 2+ to form Li + vacancies. , …”

“…In this work, we study the incorporation of Nb into LNO to form a niobium-based coating, which enhances the stability of the material. Ammonium niobium oxalate hydrate (ANO) is used as a niobium source due to its desirable characteristics of air stability and water solubility, in contrast to previously studied niobium sources such as niobium ethoxide and niobium oxide. − Furthermore, previous studies on Nb-LNO have demonstrated electrochemical testing only in half-cells, wherein a lithium-metal anode supplies excess lithium to the system. While this cell format can be useful for isolating the performance of a single electrode in a system, it is not an accurate predictor of the behavior of the full cells used in commercial applications, which generally utilize a graphite anode.…”

An artificially tailored functional layer on Li-rich layer cathodes enables a stable high-temperature interphase for Li-ion batteries

“…The phase transition and voltage attenuation can be sensitively detected from dQ/dV curves. 48,63 These characteristic oxidation and reduction peaks are associated with the complex phase transitions during the charge and discharge process. For the LRNCM sample, the higher voltage peak is associated with the anion redox and shows continuous shi and huge attenuation from the 1st to the 100th, suggesting that the LRNCM sample suffers severely from irreversible structural changes (Fig.…”