Aging Analysis of Graphite/LiNi 1/3 Mn 1/3 Co 1/3 O 2 Cells Using XRD, PGAA, and AC Impedance

Self Cite

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...

Section: Resultsmentioning

confidence: 91%

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

Teufl

Strehle

Müller³

et al. 2018

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157

“…9,11,13 While the error bars are hardly visibly for cutoff voltages ≤4.4 V and at low cycle numbers at a cutoff of 4.6 V, the error bars at higher cycle numbers significantly increase, which is due to the delayed onset of the so-called rollover-failure for the two cells. This failure mechanism was described previously by Dubarry et al and Burns et al and was shown to be due to growing kinetic resistances or more generally an impedance buildup.…”

Section: Resultsmentioning

confidence: 99%

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

Self Cite

1,016

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...

“…[66][67][68] Including those effects will be part of future investigations, as they are not crucial for the general improvement of the introduced SEI model representation by two conductivities.…”

Section: 62mentioning

confidence: 99%

A SEI Modeling Approach Distinguishing between Capacity and Power Fade

Kindermann

Keil

Frank

et al. 2017

In this paper we introduce a pseudo two-dimensional (P2D) model for a common lithium-nickel-cobalt-manganese-oxide versus graphite (NCM/graphite) cell with solid electrolyte interphase (SEI) growth as the dominating capacity fade mechanism on the anode and active material dissolution as the main aging mechanism on the cathode. The SEI implementation considers a growth due to non-ideal insulation properties during calendar as well as cyclic aging and a re-formation after cyclic cracking of the layer during graphite expansion. Additionally, our approach distinguishes between an electronic (σ SEI ) and an ionic (κ SEI ) conductivity of the SEI. This approach introduces the possibility to adapt the model to capacity as well as power fade. Simulation data show good agreement with an experimental aging study for NCM/graphite cells at different temperatures introduced in literature. © The Author Lithium-ion batteries are one of the most promising candidates for energy storage in future stationary storage systems and electric vehicles.1-3 Enormous research efforts have been conducted to get a thorough understanding of the system "lithium-ion cell" and to further develop it for higher energy and power density, higher safety standards as well as longer cycle life. 4 The aging behavior of lithium-ion batteries has been a focus issue of battery research since the introduction of lithium-ion cells by Sony in 1991. 5 Reviews by Agubra et al., 6,7 Arora et al., 8 Aurbach et al., 9,10 Birkl et al., 11 Broussely et al., 12 Verma et al. 13 and Vetter et al. 14 are just a few examples of the extensive literature regarding aging behavior. Commonly accepted and experimentally verified aging phenomena as mentioned in the previously cited literature are electrolyte decomposition leading to solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) growth, solvent co-intercalation, gas evolution with subsequent cracking of particles, a decrease of accessible surface area and porosity due to SEI growth, contact loss of active material particles due to volume changes during cycling, binder decomposition, current collector corrosion, metallic lithium plating and transition-metal dissolution from the cathode. The listed aging mechanisms can be assigned to three different categories that are a loss of lithium-ions (LLI), an impedance increase and a loss of active material (LAM). 12,[15][16][17][18] The LLI is synonymous to a decrease in the amount of cyclable lithium-ions as they are trapped in a passivating film on either of the electrodes or in plated metallic lithium. Due to the growth of the passivating layers and/or the formation of rock-salt in the cathode (residue of the cathode active material after transition-metal dissolution), kinetic transport of lithium-ions through those inactive areas is limited and results in an impedance rise. An LAM can be caused by the dissolution of transition-metal-ions from the cathode bulk material, changes in the electrode composition and/or changes in crystal structure of the a...