Nondestructive detection, characterization, and quantification of lithium plating in commercial lithium-ion batteries

Li-ion cells are used in a variety of mobile and stationary applications. Their use must be safe under all conditions, even for aged cells in second-life applications. In the present study, different aging mechanisms are taken into account for accelerating rate calorimetry (ARC) tests. 18650-type cells are cycled at 0 • C (Li plating expected) and at 45 • C (SEI growth expected). After extensive evaluation of the electrochemical results (voltage curve analysis, capacity fade, energy fade, Coulombic efficiency), the cells are tested by PostMortem analysis (CT, GD-OES, SEM) to reveal the main aging mechanisms and by ARC to test the safety behavior. Besides typical ARC results such as onset-of-self-heating, onset-of-thermal runaway and maximum temperatures, as well as acoustic responses of thermal runaway are evaluated and a method is developed to compare fresh cells and cells aged until different SOHs. It turns out that the safety of aged cells is not simply a function of the SOH. However, safety is strongly affected by the main aging mechanism and to the history of operating parameters during the life-time of the cell. Driven by the demand for higher capacity, lower volume, and lower weight, Li-ion technology was developed in the 1980s.1,2 Nowadays, Li-ion technology is used for energy storage in a large variety of applications, e.g. smartphones, tablets, or drones. In particular, electric vehicles in combination with renewable energy sources are promising for reducing climate change and the corresponding glacier melting and sea level rise which is influenced by burning fossil fuels.3-6 For all applications, the safety behavior under all specified operating conditions is most important.7-9 The same is true for aged Li-ion cells used in second-life applications, for example cells which are utilized in stationary energy storage applications after their usage in electric cars.In the past, failure of Li-ion cells led to product recalls which are very expensive for the manufacturers and unsettle customers, even if such incidents happen only in very few cases (ppm range).10 At the moment, safety tests have to be performed with Li-ion prototypes cells before market release. In these tests, fresh cells are always used, however, aged cells are usually neglected. Even if fresh cells show an acceptable safety behavior, this can change for aged cells. 7,[11][12][13][14][15] While some authors observed decreases for certain safety properties, 7,11,12 others found improvements. 12,13,15 It is well known that aging mechanisms change the properties of the materials inside Li-ion cells. [16][17][18][19] Operating conditions and materials have a strong influence on these aging mechanisms. 12,[20][21][22][23] We recently reported on a change of the aging mechanism with temperature for cycling aging of commercial 18650-type cells with graphite anodes and NMC/LMO cathodes. 20 This mechanism change is expressed by a V-shape in Arrhenius plots of the capacity fade rates obtained from cycling at different ambient temperatures. 20 This c...

Section: Resultsmentioning

confidence: 60%

mentioning

confidence: 99%

Electrochemical, Post-Mortem, and ARC Analysis of Li-Ion Cell Safety in Second-Life Applications

Waldmann

Quinn

Richter

et al. 2017

“…The simulations show that during lithiation, the resistance overpotential due to the finite conductivity of the electrolyte (θ E ) in addition to the activation overpotential (η act ) can lead to regions of the electrode with potentials below 0 V vs. Li/Li + . This is the condition for lithium plating, which means decreased capacity and potential safety issues 47,48 and is reached earlier by an electrode showing higher inhomogeneity (Figure 3d). Assuming two electrodes have the same mean microstrutural parameters and the same material composition, the homogeneous electrode can thus be considered safer than the inhomogenous electrode having regions of better and worse transport.…”

Section: Resultsmentioning

confidence: 99%

Quantifying Inhomogeneity of Lithium Ion Battery Electrodes and Its Influence on Electrochemical Performance

Müller

Eller

Ebner

et al. 2018

110

This paper presents an approach to quantify microstructural inhomegeneity in lithium ion battery electrodes over multiple length scales and examines the impact of this microstructural inhomogeneity on electrochemical performance. Commerical graphite anodes are investigated because graphite remains the anode material of choice due to its low cost, mechanical robustness, and suitable electrochemical properties. At the same time, the graphite anode often plays a role in cell degradation and failure, as lithium plating can occur on the graphite anode during charge, when unfavorable microstructure in the graphite electrode leads to a large overpotential. Here, three-dimensional representations of four different commercial anodes obtained with X-ray tomographic microscopy are statistically analyzed to quantify the microstructural inhomogeneity that is commonly present in lithium ion battery electrodes. Electrochemical simulations on the digitalized microstructures are performed to isolate and understand the influence of different types of microstructural inhomogeneity on battery performance. By understanding how distributions in particle size and shape or slurry and electrode processing cause microstructural inhomogeneity and impact performance, it is possible to determine the extent to which homogeneity should be prioritized for specific applications and how homogeneity could be achieved through smart material selection and processing.

“…All of these increase cell polarization and drive the lithiated graphite to or below the potential of metallic Li. Therefore, the propensity toward unwanted Li plating in LIBs has a close relationship not only with the charging conditions such as low temperature, 8,9 high charging rates 10 and overcharging, 11,12 but also with the anode/cathode ratio, 13,14 carbonaceous materials selected 15,16 and the electrolyte used. 16,17 The effect of different electrolyte systems on unwanted lithium plating behavior has been reported in several works.…”

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confidence: 99%

Gas Evolution during Unwanted Lithium Plating in Li-Ion Cells with EC-Based or EC-Free Electrolytes

Liu

Xiong

Petibon

et al. 2016

Lithium plating can be induced in any Li-ion cell that has a graphite negative electrode by increasing the charge rate sufficiently at fixed temperature or by lowering the temperature at a fixed charge rate. Recently, ethylene carbonate (EC)-free electrolytes, such as 1 M LiPF 6 in 98% ethyl methyl carbonate (EMC): 2% vinylene carbonate (VC), have been shown to passivate lithiated graphite effectively and allow Li [Ni 0.42 Mn 0.42 Co 0.16 ]O 2 /graphite (NMC442/graphite) Li-ion cells to operate effectively for hundreds of charge discharge cycles. High charge rates and low temperatures were applied to Li[Ni 1/3 Mn 1/3 Co 1/3 ]O 2 /graphite (NMC111/graphite) pouch cells containing EC-free EMC-based electrolytes with additives to study unwanted lithium plating. In such electrolytes, the plated lithium metal is not well passivated and reacts to create gas while in the same cells with 1 M LiPF 6 EC:EMC (3:7) electrolyte no gas is observed when Li plating occurs because EC passivates metallic Li well. The volume of the pouch cells with EC-free electrolytes increased sharply when Li plating occurred as measured using in-situ methods. In cells having both EC-based and EC-free electrolytes, lithium plating was the cause of rapid capacity loss at high charge rates at both 10 • C and 22 • Unwanted lithium plating in lithium ion batteries with graphite negative electrodes can be a serious aging mechanism. Unwanted lithium plating is most likely at low temperatures and high charge rates.1-3 The deposited Li metal can react with electrolyte, consuming active lithium and electrolyte, thus resulting in fast capacity fade. Unwanted lithium plating can be caused by increased resistance of the solid electrolyte interphase (SEI), 4 sluggish charge transfer kinetics, 5 insufficient ionic transport to the back of the graphite electrode and limited solid state diffusion, 6,7 among others. All of these increase cell polarization and drive the lithiated graphite to or below the potential of metallic Li. Therefore, the propensity toward unwanted Li plating in LIBs has a close relationship not only with the charging conditions such as low temperature, 8,9 high charging rates 10 and overcharging, 11,12 but also with the anode/cathode ratio, 13,14 carbonaceous materials selected 15,16 and the electrolyte used. 16,17The effect of different electrolyte systems on unwanted lithium plating behavior has been reported in several works. Smart and Ratnakumar showed that cells with high EC-content and SEI-stabilizing additives (like VC) were relatively prone to unwanted lithium plating probably due to the high-resistance SEI formed by VC.17 Yariv et al. showed that fluoroethylene carbonate (FEC) as a co-solvent could improve the low-temperature behavior of the lithiated graphite electrode and reduce the propensity for lithium plating. 16During recent years, electrolyte systems that are suitable for higher-voltage operation have been widely studied in order to improve the energy density of lithium-ion batteries. High-voltage NMC/ graphite cells can...