Effects of Cycling Ranges on Stress and Capacity Fade in Lithium-Ion Pouch Cells

Abstract

The coupling between mechanics and electrochemistry can be a useful tool in identifying battery aging. Here we investigate the relationship between stress and capacity fade in different types of commercial batteries under various cycling ranges. We identify individual contributions from stress-increasing mechanisms, such as film growth, and non-linear stress relaxation mechanisms. Different cycling ranges affect the average stress level inside the batteries, leading to varying levels of stress relaxation, which dominates the overall stress behavior initially, but gradually is overtaken by linear stress-increasing mechanisms at higher cycle number. The slopes of the linear film growth vary with cycling range and battery type, and we correlate these effects with both mechanical and electrochemical phenomena. Commercial batteries with different compositions exhibit qualitatively similar results on stress vs. state of health (SOH), but vary quantitatively due to differences in their mechanical properties, which can be identified through mechanical tests. Battery aging and degradation remain as important challenges faced in efforts to extend battery lifetimes. Aging not only causes capacity fade and a reduced cycle life, but also imposes threats to safety and can lead to catastrophic failure of the entire system. Therefore, from both operational and safety perspectives, it is essential to monitor battery aging so that the exact level of the decay can be measured. To quantify aging, state of health (SOH) is often used, which is a parameter defined as the ratio between the measured capacity and the initially rated capacity of a cell. For instance, a pristine cell has a SOH of 1, while a cell having a SOH of 0.8 is considered highly degraded. There are a number of studies on battery diagnosis with different approaches. [1][2][3][4][5][6][7] The most accurate method of determining SOH is to measure capacities through controlled discharge tests. A more practical method involves mathematical models which take measurable parameters, such as current, voltage, and temperature, as inputs. [8][9][10] However, the accuracy of such methods depends on the complexity of the underlying model and can be further complicated by battery aging. Therefore, a practical and accurate stand-alone method is needed. Cannarella 6 has proposed a mechanical method of determining the SOH of a pouch cell using measured external stress. By measuring the initial peak stress and peak stress at a later time, with the known stress-SOH relationship, SOH can be determined. This method is based on the mechanically active nature of batteries.11,12 Batteries undergo volume changes during operation, such as electrode swelling, polymer deformation, and film growth, where the volume changes caused by the latter two are irreversible. [13][14][15][16][17][18][19] Polymer deformation largely results from separators and binders. [20][21][22][23][24][25] As the softest component inside the cell, the polymer accommodates the expansion from electrode swelling and gradu...

Understanding Full-Cell Evolution and Non-chemical Electrode Crosstalk of Li-Ion Batteries

“…electrochemical resistances, [10][11][12][13][14][15][16] the size of the battery, [17][18][19][20][21][22] and the stresses within the battery. [23][24][25][26][27][28] While existing studies have provided useful information about the progression of battery properties during cycling, questions still remain as to the root cause of capacity variation as a function of operation. In addition, they often fail to address an important question associated with battery reliability: is it possible to detect early on when a battery will fail?…”

Challenges in data‐based degradation models for lithium‐ion batteries

“…Several DBM-AT models have been proposed for both calendar aging and cycling aging modes and different cell chemistries, mostly using the capacity fade as a health indicator [11][12][13][14][15][16][17] ; we will turn our attention first to calendar aging. Schmalstieg et al 18 performed calendar aging tests on 2.15-Ah lithium nickel manganese cobalt (NMC) oxide cells, and they fitted the data of capacity loss as a function of temperature, SOC, and time using a set of quadratic equations.…”

Non-Destructive Detection of Local Aging in Lithium-Ion Pouch Cells by Multi-Directional Laser Scanning

“…Although their relatively high density in power and energy make Li-ion batteries the technology of choice for many applications, its aging and degradation behavior likewise limits their use in applications that require extreme safety standards and cycle life. 2 In order to quantify the decay of batteries, the state of health (SOH) 3 is used which refers to the capacity fade by relating the current capacity of the cell to its initial capacity. This relation can be seen as an overall concept introducing a measurable quantity of aging effects occurring during battery lifetime.…”

“…Detecting the cell's SOH by measuring external stress and strain on the surface of the cell's housing 2,4 is a recent method based on the mechanical behavior of Li-ion batteries in form of volume change effects during charge and discharge processes. These are largely caused by electrode swelling, [5][6][7][8] polymer deformation 5,9 and film growth.…”

“…40 The parameter t irrev is determined by subtracting the initial thickness (k = 0) from the thickness at the end of check-up after cycle quantity k. Both thickness values are measured in the fully discharged state of the cell (SOC = 0). [2] In addition to the causes mentioned above for reversible and irreversible thickness changes, lithium plating at the graphite anode needs to be considered. 16,24 Lithium plating describes the precipitation of metallic lithium on the surface of the solid particles.…”