Fundamental degradation mechanisms of layered oxide Li-ion battery cathode materials: Methodology, insights and novel approaches

Hausbrand, René; Cherkashinin, Gennady; Ehrenberg, Helmut; Gröting, Melanie; Albe, Karsten; Heß, Christian; Jaegermann, Wolfram

doi:10.1016/j.mseb.2014.11.014

Cited by 396 publications

(297 citation statements)

References 162 publications

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“…Bulk crystal structure changes leading to microstrain, 33 cracking, 34 and disconnection 35 have been implicated in cycling losses of layered oxide materials. Synchrotron based in operando XRD offers the opportunity to capture subtle structure changes while performing electrochemistry simultaneously.…”

Section: Resultsmentioning

confidence: 99%

Depth-Dependent Redox Behavior of LiNi_0.6Mn_0.2Co_0.2O₂

Tian

Nordlund

Xin

et al. 2018

J. Electrochem. Soc.

135

125

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Nickel-rich layered materials are emerging as cathodes of choice for next-generation high energy density lithium ion batteries intended for electric vehicles. This is because of their higher practical capacities compared to compositions with lower Ni content, as well as the potential for lower raw materials cost. The higher practical capacity of these materials comes at the expense of shorter cycle life, however, due to undesirable structure and chemical transformations, especially at particle surfaces. To understand these changes more fully, the charge compensation mechanism and bulk and surface structural changes of LiNi 0.6 Mn 0.2 Co 0.2 O 2 were probed using synchrotron techniques and electron energy loss spectroscopy in this study. In the bulk, both the crystal and electronic structure changes are reversible upon cycling to high voltages, whereas particle surfaces undergo significant reduction and structural reconstruction. While Ni is the major contributor to charge compensation, Co and O (through transition metal-oxygen hybridization) are also redox active. An important finding from depth-dependent transition metal L-edge and O K-edge X-ray spectroscopy is that oxygen redox activity exhibits depth-dependent characteristics. This likely drives the structural and chemical transformations observed at particle surfaces in Ni-rich materials. The need for lithium-ion batteries with higher energy density and lower cost than currently available, particularly for transport applications, has led to intensified interest in Ni-rich NMC (LiNi x Mn y Co z O 2 ; x+y+z≈1, where x>y) cathode materials.1-5 These materials deliver higher practical capacities in a typically used voltage range than NMCs with lower Ni content (e.g., LiNi 1/3 Mn 1/3 Co 1/3 O 2 or NMC-333), and most formulations contain less of the expensive Co component, reducing raw material costs. The increase in practical capacity roughly scales with the Ni content, but comes at the expense of cycle life and thermal stability at high states-of-charge (SOC). 6 To circumvent these problems, several different strategies have been utilized to improve cycling, particularly to higher potentials. These include partial substitution with Ti 7-9 or Zr, 10 engineering the micro-or nano-structure to reduce surface Ni content using metal segregation, 11 surface pillared structures, 12 and concentration gradients, 13 coating particle surfaces, 14 and development of electrolyte additives. 15,16 While all of these approaches have resulted in improvements, further understanding of the factors that lead to capacity fading is clearly needed in order to meet the stringent performance requirements of traction applications.The formation of a resistive cathode/electrolyte interphase (CEI), such as an electrolyte decomposition layer, has been observed during cycling of LiNi 0. 20 In the study of NMC-532, it was found that surface reconstruction to a rock salt phase dominates when high voltage (4.8 V) cutoffs are used due to oxygen loss under the highly oxidizing conditions, while ...

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Section: Resultsmentioning

confidence: 99%

Depth-Dependent Redox Behavior of LiNi_0.6Mn_0.2Co_0.2O₂

Tian

Nordlund

Xin

et al. 2018

J. Electrochem. Soc.

135

125

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“…These surface films also increase electrode impedance, which can shorten the time for the cell to reach cutoff voltages and affect rate capability of the cell. 3,4 Capacity loss can also originate due to physical mechanisms. For example, stress may accumulate in electrode materials during lithiation and delithiation owing to the large volumetric alterations induced by these processes.…”

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confidence: 99%

“…For example, stress may accumulate in electrode materials during lithiation and delithiation owing to the large volumetric alterations induced by these processes. 4,5 Volumetric expansion can be up to 10% in graphite and ∼1.6% in LiCoO 2 .6,7 Such expansion and the induced stress can, in turn, lead to fracturing of active particles, cracking and reforming of the SEI, and loss of contact among electrode components (i.e., active material, polymeric binder, and current collectors). 4 Taken together, these chemical and physical degradation mechanisms induce capacity fade with repeated cycling that curtail the lifetime of the battery.…”

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confidence: 99%

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Measuring Li⁺Inventory Losses in LiCoO₂/Graphite Cells Using Raman Microscopy

Snyder

Apblett

Grillet

et al. 2016

J. Electrochem. Soc.

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The contribution from loss of Li + inventory to capacity fade is described for slow rates (C/10) and long-term cycling (up to 80 cycles). It was found through electrochemical testing and ex-situ Raman analysis that at these slow rates, the entirety of capacity loss up to 80 cycles can be explained by loss of Li + inventory in the cell. The Raman spectrum of LiCoO 2 is sensitive to the state of lithiation and can therefore be leveraged to quantify the state of lithiation for individual particles. With these Raman derived estimates, the lithiation state of the cathode in the discharged state is compared to electrochemical data as a function of cycle number. High correlation is found between Raman quantifications of cycleable lithium and the capacity fade. Additionally, the linear relationship between discharge capacity and cell overpotential suggests that the loss of capacity stems from an impedance rise of the electrodes, which based on Li inventory losses, is caused by SEI formation and repair. Lithium ion batteries (LIB) provide the highest energy densities compared to other rechargeable battery types.1 For this reason, they are being pursued for usage in advanced applications such as electric vehicles and storage of intermittent renewable energies (solar, wind, etc.). Despite their promise, degradation caused by both chemical and physical mechanisms diminishes LIB performance. Chemically, formation of a solid electrolyte interphase (SEI) on the surface of both the graphite anode and the LiCoO 2 cathode accompanied by other side reactions between the electrolyte and the electrode surface 2 results in the loss of cycleable Li + and thus capacity. These surface films also increase electrode impedance, which can shorten the time for the cell to reach cutoff voltages and affect rate capability of the cell. 3,4 Capacity loss can also originate due to physical mechanisms. For example, stress may accumulate in electrode materials during lithiation and delithiation owing to the large volumetric alterations induced by these processes. 4,5 Volumetric expansion can be up to 10% in graphite and ∼1.6% in LiCoO 2 .6,7 Such expansion and the induced stress can, in turn, lead to fracturing of active particles, cracking and reforming of the SEI, and loss of contact among electrode components (i.e., active material, polymeric binder, and current collectors). 4 Taken together, these chemical and physical degradation mechanisms induce capacity fade with repeated cycling that curtail the lifetime of the battery.Beyond identification, it is necessary to assess the relative influence of individual mechanisms to the totality of capacity fade. 3,8,9 Specifically, comparisons between the relative impact of several mechanisms-primary active material loss (Li + inventory), secondary active material loss (LiCoO 2 and/or graphite), and increased internal cell resistance (caused by surface films)-remain the topic of continued investigation.3 Such effort is complicated by the dependence of these mechanisms to several parameters as it has been...

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“…either excessive external heat influx or heat generation surpassing the ability of dissipation, poses a serious threat to the integrity of the device [7,8]. Thermally induced degradation processes comprise the evolution of gas from evaporation and degradation of the electrolyte, melting of the separator leading to internal short circuits, changes of the electrodes' structure releasing oxygen and lithium respectively and other fast selfaccelerating exothermic reactions leading to thermal runaway [9][10][11][12][13][14]. Lithium ion cells not only offer a higher energy density but also more resistance towards aging than other types of electrochemical secondary cells like Pb-acid batteries and NiMH systems [15][16][17].…”

Section: Introductionmentioning

confidence: 99%