Effects of CO2 in air on Li deintercalation from LiNi1−x−yCoxAlyO2

355

415

is one of the high-energy positive electrode (cathode) materials for next generation Li-ion batteries. However, compared to the structurally similar LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC111), it can suffer from a shorter lifetime due to its higher surface reactivity. This work studied and compared the formation of surface contaminations on NMC811 and NMC111 when stored under ambient conditions using electrochemical cycling, Raman spectroscopy, and X-ray photoelectron spectroscopy. NMC811 was found to develop a surface layer of up to ∼10 nm thickness that was mostly composed of nickel carbonate species mixed with minor quantities of hydroxide and water after ambient storage for 1 year, while no significant changes were observed on the NMC111 surface. The amount of carbonate species was quantified by gas chromatographic (GC) detection of carbon dioxide generated when the NMC particles were dispersed in hydrochloric acid. Surface impurity species formed on NMC811 upon ambient storage not only lead to a significant delithiation voltage peak in the first charge, but also markedly reduce the cycling stability of NMC811-graphite cells due to significantly growing polarization of the NMC811 electrode.

Section: Resultssupporting

confidence: 71%

Effect of Ambient Storage on the Degradation of Ni-Rich Positive Electrode Materials (NMC811) for Li-Ion Batteries

Jung

Morasch

Karayaylalı

et al. 2018

355

415

“…11 In their study of Li 2 CO 3 growth on Li 2 O, Mosqueda et al proposed that the formation of Li 2 CO 3 was limited at lower temperatures because of the inability for Li atoms to diffuse through the thin Li 2 CO 3 shell. When their samples were heated to 530…”

Section: Resultsmentioning

confidence: 99%

Editors' Choice—Growth of Ambient Induced Surface Impurity Species on Layered Positive Electrode Materials and Impact on Electrochemical Performance

Faenza

Bruce

Lebens-Higgins

et al. 2017

177

233

Surface impurity species, most notably Li 2 CO 3 , that develop on layered oxide positive electrode materials with atmospheric aging have been reported to be highly detrimental to the subsequent electrochemical performance. LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) was used as a model layered oxide compound to evaluate the growth and subsequent electrochemical impact of H 2 O, LiHCO 3 , LiOH and Li 2 CO 3 . Methodical high temperature annealing enabled the systematic removal of each impurity specie, thus permitting the determination of each specie's individual effect on the host material's electrochemical performance. Extensive cycling of exposed and annealed materials emphasized the cycle life degradation and capacity loss induced by each impurity, while rate capability measurements correlated the electrode impedance to the impurity species present. Based on these characterization results, this work attempts to clarify decades of ambiguity over the growth mechanisms and the electrochemical impact of the specific surface impurity species formed during powder storage in various environments.

“…In air and CO 2 , the formation of lithium (bi)carbonate and hydroxide coatings on z E-mail: abraham@anl.gov oxide surfaces has been reported. At advanced stages of weathering, this coating (that can grow to be > 10 nm thick) 14 can be observed using electron microscopy, X-ray powder diffraction (XRD) 16,17,[20][21][22] and infrared spectroscopy.14,15 As the material delithiates, repulsion between the oxygen layers increases and the lattice expands along the crystallographic c axis (that is orthogonal to the TM-O planes). [13][14][15][16][17][18]23 In some studies, in addition to the XRD pattern of the parent material, poorly resolved Bragg peaks from a cubic phase were observed, which was attributed either to LiNi 2 O 4 spinel 13,14 28 Most authors, however, suggest that such cation exchange plays a minor role if any at all, favoring instead a redox process that is fully analogous to the one occurring in electrochemical delithiation.…”

mentioning

confidence: 99%

Chemical Weathering of Layered Ni-Rich Oxide Electrode Materials: Evidence for Cation Exchange

Shkrob

Gilbert

Phillips

et al. 2017

153

160

Lithiated ternary oxides containing nickel, cobalt, and manganese are intercalation compounds that are used as positive electrodes in high-energy lithium-ion batteries. These oxides undergo changes, when they are stored in humid air or exposed to moisture, that adversely affect their electrochemical performance. There is a new urgency to better understanding of these "weathering" mechanisms as manufacturing moves toward a more environmentally benign aqueous processing of the positive electrode. Delithiation of the oxide and the formation of lithium salts (such as hydroxides and carbonates) coating the surface, are known to occur during moisture exposure. The redox reactions which follow this delithiation are believed to trigger all the other transformations. In this article we suggest another possibility: namely, the proton -lithium exchange. We argue that this hypothesis provides a simple, comprehensive rationale for our observations, which include contraction of the c-axis (unit cell) lattice parameter, rock salt phase formation in the subsurface regions, presence of amorphous surface films, and the partial recovery of oxide capacity during electrochemical relithiation. The detrimental effects of water exposure need to be mitigated before aqueous processing of the positive electrode can find widespread adoption during cell manufacturing. Improving the performance of lithium-ion batteries (LIBs) for electrically powered vehicles gives urgency to the development of high-capacity, high-voltage electrode materials, and layered Ni-rich oxides are presently among the most technological advanced materials that allow operation above +4.0 V vs Li + /Li. 1 Such materials (also known as NCMxyz materials) have the general composition of LiNi x/10 Co y/10 Mn z/10 O 2 , where x+y+z = 10. In these ternary oxides, the manganese stays in the Mn 4+ state during cell cycling, and the capacity mainly originates from the Ni 2+ /Ni 3+ and Ni 3+ /Ni 4+ redox couples. The monolayers of octahedra containing transition metal (TM) ions form a structural scaffold with the layers of mobile Li + ions placed in between. The crystalline material retains the structure of the progenitor material of the family, viz. α-LiCoO 2 , 2 with the unit cell belonging to the rhombohedral R(-3)m space group. During electrochemical cycling, the lithium ions intercalate into (and deintercalate from) the layered crystals as the redox state of (mainly the) nickel ions changes to provide the overall charge neutrality.In this study, we examine one such material, NCM523, which represents a particular trade-off between the cycling rate (that improves with Co content), safety (that improves with Mn content), and capacity (that increases with Ni content).1 The safety concerns mainly relate to the thermal and chemical stability, including oxidation of the organic electrolyte by catalytic centers at the oxide surface 3 and phase transitions in the delithiated material that occur when a significant fraction of nickel ions is reduced to Ni 2+ ions and molecular oxygen ...