Nonlinear aging characteristics of lithium-ion cells under different operational conditions

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This paper presents a lithium-ion battery aging study in which pouch cells comprising a LiCoO 2 /LiNi 0.8 Co 0.15 Al 0.05 O 2 blended cathode and a graphite anode are examined. The study focuses on the impact of temperature and discharge rate on the cycle life of the tested cells. Compared to the aging behavior of other lithium-ion cells in the literature, the cells tested here are less sensitive to the discharge rate but more vulnerable to low temperature cycling. The vulnerability to low temperature mainly comes from cathode degradation, especially of the LiCoO 2 component. This is identified by electrochemical impedance spectroscopy, differential voltage analysis and incremental capacity analysis. The cells are able to achieve 3000-5000 cycles before reaching a capacity fade of 20%, also at higher discharge rates up to 5C. All in all, the high discharge rate capability could be a general advantage of pouch cells due to less mechanical and thermal stress in their geometry. Furthermore, more attention should be paid to the cathode health in low temperature applications of lithium-ion cells containing layered oxides. This paper focuses mainly on non-invasive aging detection methods for lithium-ion cells. Post-mortem results will be published in a following paper.

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Impact of Temperature and Discharge Rate on the Aging of a LiCoO₂/LiNi_0.8Co_0.15Al_0.05O₂Lithium-Ion Pouch Cell

Keil

Schuster

et al. 2017

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“…In literature, typical limits for cell end of life (EOL) are a remaining capacity of 80% to the nominal value, corresponding to 20% of capacity loss, 9,20 or an increase in cell impedance of +50% to +100%.…”

Section: Methodsmentioning

confidence: 99%

Comprehensive Modeling of Temperature-Dependent Degradation Mechanisms in Lithium Iron Phosphate Batteries

Schimpe

Kuepach

Naumann

et al. 2018

142

For reliable lifetime predictions of lithium-ion batteries, models for cell degradation are required. A comprehensive semi-empirical model based on a reduced set of internal cell parameters and physically justified degradation functions for the capacity loss is developed and presented for a commercial lithium iron phosphate/graphite cell. One calendar and several cycle aging effects are modeled separately. Emphasis is placed on the varying degradation at different temperatures. Degradation mechanisms for cycle aging at high and low temperatures as well as the increased cycling degradation at high state of charge are calculated separately. For parameterization, a lifetime test study is conducted including storage and cycle tests. Additionally, the model is validated through a dynamic current profile based on real-world application in a stationary energy storage system revealing the accuracy. Tests for validation are continued for up to 114 days after the longest parametrization tests. The model error for the cell capacity loss in the application-based tests is at the end of testing below 1% of the original cell capacity and the maximum relative model error is below 21%. Today, stationary energy storage systems utilizing lithium-ion batteries account for the majority of new storage capacity installed. 1In order to meet technical and economic requirements, the specified system lifetime has to be ensured.For reliable lifetime predictions, cell degradation models are necessary. Physicochemical models that include aging mechanisms are based on a detailed set of parameters which are often not readily available, computationally costly and require experimental parameterization of degradation rates.2-4 Instead, purely empirical models can be parameterized without knowledge of internal cell setup through extensive testing. Several purely empirical studies capture calendar aging 5,6 or cycle aging 7,8 without evaluating interdependencies. Through superposition, some empirical model approaches combine calendar and cycle aging 9-12 but tend to neglect the temperature dependence of the cycle aging mechanisms and are prone to extrapolation errors due to the utilized mathematical functions.Due to the limited knowledge about degradation mechanisms, empirically based models conventionally lump multiple degradation effects into single functions. This leads to the aforementioned prediction errors when deviating from the parameterization test conditions. E.g. for cycle aging, Waldmann et al. reported a transition of dominating aging mechanisms at 25• C. 13 The aging for temperatures above 25• C was attributed to the solid-electrolyte interface (SEI) growth and cathode degradation, while below 25• C the aging was attributed to lithium plating. In fact, for an improved understanding of cell internal degradation, model development should aim for a separation of the degradation mechanisms wherever possible. The respective mechanisms can then be modeled through functions that are suitable for the degradation driving factors.In this work, ...

“…53,55,59,61,63 In these models, this non-linear aging behavior can be emulated by a high power fade, though, which shortens charging and discharging due to high overpotentials that decrease the usable capacity. 43,61 Measurements in literature ascribe this non-linear aging behavior to lithium plating 64,65 as well as to degradation mechanisms on the cathode. 5,48,50 For the here introduced model we chose to implement a cathode dissolution reaction as the responsible mechanism for the non-linear aging behavior.…”

Section: Model Developmentmentioning

confidence: 99%

A SEI Modeling Approach Distinguishing between Capacity and Power Fade

Kindermann

Keil

Frank

et al. 2017

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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...