Direct evidence of oxygen evolution from Li1+x (Ni1/3Mn1/3Co1/3)1−x O2 at high potentials

Structural investigation was performed on a range of NMC materials, Li 1þx (Ni 1/3 Mn 1/3 Co 1/3 ) 1-x O 2 (0 x 0.13), using in situ X-ray synchrotron diffraction while electrochemically cycling them between 2.5 and 5.0 V vs. Li/Li þ . From the analysis of the obtained data, an irreversible phase transformation of part of the starting O3 phase (R 3 m) to the O1 phase (P 3 m1) was observed for all the NMC samples, where the O1 phase was detected at more negative potentials with increasing overlithiation content. Moreover a second irreversible reaction was detected at positive potentials using ex situ X-ray synchrotron diffraction for overlithiated NMC (x ¼ 0.1) that involved loss of Li 2 MnO 3 ordering in the structure.

Section: Resultssupporting

confidence: 69%

Study of Overcharge Behavior of Li1+x(Ni1/3Mn1/3Co1/3)1-xO2 Using In Situ and Ex Situ X-ray Synchrotron Diffraction

Godbole

Colin

Novák

2011

“…For Li-rich NMC materials (Li 1+x (Ni,Mn,Co) 1-x O 2 ) the total amount of released lattice oxygen is comparably large in the first cycle. [32][33][34][35][36] For this material class Strehle et al 36 found a ratio of O 2 /CO 2 close to 1/1 in contrast to ∼1/20 for the NMC materials (s . Table II), which based on Eq.…”

Section: Discussionmentioning

confidence: 92%

Oxygen Release and Its Effect on the Cycling Stability of LiNi_xMn_yCo_zO₂(NMC) Cathode Materials for Li-Ion Batteries

Jung

Metzger

Maglia

et al. 2017

959

1,278

Layered LiNi x Mn y Co z O 2 (NMC) is a widely used class of cathode materials with LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC111) being the most common representative. However, Ni-rich NMCs are more and more in the focus of current research due to their higher specific capacity and energy. In this work we will compare LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC111), LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622), and LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) with respect to their cycling stability in NMC-graphite full-cells at different end-of-charge potentials. It will be shown that stable cycling is possible up to 4.4 V for NMC111 and NMC622 and only up to 4.0 V for NMC811. At higher potentials, significant capacity fading was observed, which was traced back to an increase in the polarization of the NMC electrode, contrary to the nearly constant polarization of the graphite electrode. Furthermore, we show that the increase in the polarization occurs when the NMC materials are cycled up to a high-voltage feature in the dq/dV plot, which occurs at ∼4.7 V vs. Li/Li + for NMC111 and NMC622 and at ∼4.3 V vs. Li/Li + for NMC811. For the latter material, this feature corresponds to the H2 → H3 phase transition. Contrary to the common understanding that the electrochemical oxidation of carbonate electrolytes causes the CO 2 and CO evolution at potentials above 4.7 V vs. Li/Li + , we believe that the observed CO 2 and CO are mainly due to the chemical reaction of reactive lattice oxygen with the electrolyte. This hypothesis is based on gas analysis using On-line Electrochemical Mass Spectrometry (OEMS), by which we prove that all three materials release oxygen from the particle surface and that the oxygen evolution coincides with the onset of CO 2 and CO evolution. Interestingly, the onsets of oxygen evolution for the different NMCs correlate well with the high-voltage redox feature at ∼4.7 V vs. Li/Li + for NMC111 and NMC622 as well as at ∼4.3 V vs. Li/Li + for NMC811. To support this hypothesis, we show that no CO 2 or CO is evolved for the LiNi 0.43 Mn 1.57 O 4 (LNMO) spinel up to 5 V vs. Li/Li + , consistent with the absence of oxygen release. Lastly, we demonstrate by the use of 13 C labeled conductive carbon that it is the electrolyte rather than the conductive carbon which is oxidized by the released lattice oxygen. Taking these findings into consideration, a mechanism is proposed for the reaction of released lattice oxygen with ethylene carbonate yielding CO 2 , CO, and Li-Ion batteries have recently been used as power supply for electric vehicles (EVs). In order to penetrate the mass market, a significant reduction in costs and further performance improvements have to be achieved to realize a longer driving range of EVs.1 The latter highly depends on the choice of the cathode active material, for which several potential materials exist, 2 of which layered lithium nickel manganese cobalt oxide (LiNi x Mn y Co z O 2 , NMC) is one of the most promising class of cathode materials.3 This is due to the high specific capacity and good stability of the lay...

“…19,20 At first sight, this seemed consistent with the mass spectrometrically detected O 2 and CO 2 evolution starting during the activation plateau, which was interpreted to indicate the release of Li 2 O from the bulk of the material during activation and accompanying structural changes within the bulk material. 15,17,18,23,24 However, the exact quantification of the released oxygen by Strehle et al and Luo et al revealed that the amount of released oxygen is an order of magnitude too low to be consistent with the assumed electrochemical oxygen release 25,26 and also that the O 2 evolution does not start until right after the activation plateau (only <10 μmol O2 /g AM during the plateau, but >100 μmol O2 /g AM following thereafter; shown by Strehle et al). 25 Both observations suggested that the observed oxygen release cannot be ascribed to a loss of oxygen from the bulk of the material, but that the oxygen is only being released from the near-surface Thus, more recent studies propose that bulk and surface of these overlithiated materials show distinctly different properties, rationalized by a bulk-shell model.…”

mentioning

confidence: 97%

“…Initially, it was thought that during the first cycle activation plateau at ≈4.5 V vs. Li + /Li an electrochemical activation of redox inactive Li 2 MnO 3 would take place, leading to a release of bulk lattice oxygen and to an electrochemically active LiMnO 2 phase which could charge compensate Li extraction to capacities >200 mAh/g. [15][16][17][18] This oxygen release was ascribed to cause strong structural changes within the bulk material, ultimately leading to a layered-to-spinel transformation of the particles. This transformation of the bulk material was believed to lead to the HE-NCM specific phenomena such as voltage fading and hysteresis.…”

mentioning

confidence: 99%

Oxygen Release and Surface Degradation of Li- and Mn-Rich Layered Oxides in Variation of the Li₂MnO₃Content

Teufl

Strehle

Müller³

et al. 2018

157

In this study, we will show how the oxygen release depends on the Li 2 MnO 3 content of the material and how it affects the actual voltage fading of the material. Thus, we compared overlithiated NCMs (x Li 2 MnO 3 • (1-x) LiMeO 2 ; Me = Ni, Co, Mn) with x = 0.33, 0.42 and 0.50, focusing on oxygen release and electrochemical performance. We could show that the oxygen release differs vastly for the materials, while voltage fading is similar, which leads to the conclusion that the oxygen release is a chemical material degradation, occurring at the surface, while voltage fading is a bulk issue of these materials. We could prove this hypothesis by HRTEM, showing a surface layer, which is dependent on the amount of oxygen released in the first cycles and leads to an increase of the charge-transfer resistance of these materials. Furthermore, we could quantitatively deconvolute capacity contributions from bulk and surface regions by dQ/dV analysis and correlate them to the oxygen loss. As a last step, we compared the gassing to the base NCM (LiMeO 2 , Me = Ni, Co, Mn), showing that surface degradation follows a similar reaction pathway and can be easily To face future issues, as global warming, air pollution, as well as the consumption of fossil fuels, an alternative is required to cover the future demand of energy and mobility in an environmentally friendly and sustainable way. In this context, lithium-ion batteries are viable options for large scale energy storage and for electric vehicles, as they have been used to power consumer electronics for many years. 1,2Since graphite is an excellent anode material at potentials of ≈0.1 V vs. Li + /Li with a roughly 2-fold higher specific capacity of about 360 mAh/g compared to currently used cathode active materials (CAMs), many efforts have been undertaken to increase the specific capacity and energy density of CAMs. As first practical cathode active material Lithium-Cobalt-Oxide (LCO) was investigated by Goodenough et al. in the 1980s, exhibiting a specific capacity of about 140 mAh/g and having a layered structure composed of lithium and transition metal layers.3 As these layered structures showed good structural stability during lithium extraction and insertion, and therefore good capacity retention, many attempts have been undertaken to further develop alternative layered structures which would offer higher capacity. One promising attempt that led to the currently used Lithium-NickelCobalt-Manganese-Oxides (NCMs) is to change the occupancy of the transition metal layer by not using exclusively cobalt, but also introducing nickel and manganese into the transition metal layer; hereby it was found that nickel shows a high redox activity, while manganese helps to stabilize the structure during lithium extraction.4-6 By using different transition metals and metal compositions, a playground has been created that allows to tune the properties of the material: while initially a Ni:Co:Mn ratio of 1:1:1 was used (also referred to as NCM-111), trends nowadays favor the so-called Ni...