Correlating cycling history with structural evolution in commercial 26650 batteries using in operando neutron powder diffraction

Correlating cycling history with structural evolution in commercial 26650 batteries using in operando neutron powder diffraction

Damian Goonetilleke

^a

, James C. Pramudita

^a,b

, Mackenzie Hagan

^a

, Othman K. Al Bahri

^a

, Wei Kong Pang

^b,c

, Vanessa K. Peterson

^b,c

, Jens Groot

^d

, Helena Berg

^e

, Neeraj Sharma

^a,*

aSchool of Chemistry, UNSW Australia, Sydney, NSW, 2052, Australia

bAustralian Centre for Neutron Scattering, Australian Nuclear Science and Technology Organization, Locked Bag 2001, Kirrawee DC, NSW, 2232, Australia

cInstitute for Superconducting and Electronic Materials, Faculty of Engineering, School of Mechanical, Materials, and Mechatronic Engineering, University of Wollongong, NSW, 2522, Australia

dVolvo Group Trucks Technology, ATR-BF40560, Sven Hultins Gata 9D, 412 88, G€oteborg, Sweden

eAB Libergreen, F€oreningsgatan 39, SE-41127, G€oteborg, Sweden

h i g h l i g h t s

Firstin operandoneutron powder diffraction study of a 26650 commercial battery.

Relationship between rate of structural change and applied current determined.

Link of the rate of structural change to battery history.

a r t i c l e i n f o

Article history:

Received 14 October 2016 Received in revised form 9 December 2016

Accepted 26 December 2016 Available online 26 January 2017

Keywords:

Graphitic anode LiFePO4cathodes Rates of reactions Degradation

a b s t r a c t

Ex situand time-resolvedin operandoneutron powder diffraction (NPD) has been used to study the structural evolution of the graphite negative electrode and LiFePO4 positive electrode within ANR26650M1A commercial batteries from A123 Systems, in what to our knowledge is thefirst reported NPD study investigating a 26650-type battery. Batteries with different and accurately-known electro- chemical and storage histories were studied, enabling the tell-tale signs of battery degradation to be elucidated using NPD. Theex-situNPD data revealed that the intensity of the graphite/lithiated graphite (LixC6or LiyC) reflections was affected by battery history, with lower lithiated graphite (LiC12) reflection intensities typically corresponding to more abused batteries. This indicates that the lithiation of graphite is less progressed in more abused batteries, and hence these batteries have lower capacities.In operando NPD allows the rate of structural evolution in the battery electrode materials to be correlated to the applied current. Interestingly, the electrodes exhibit different responses to the applied current that depend on the battery cycling history, with this particularly evident for the negative electrode. Therefore, this work illustrates how NPD can be used to correlate a battery history with electrode structure.

Crown Copyright©2016 Published by Elsevier B.V. All rights reserved.

1. Introduction

The advent of the Li-ion battery, in particular the graphite- LiCoO2 “rocking chair” system commercialised in the late 20th century, has made possible the widespread adoption of various light-weight, portable, and wireless electronic devices thanks to their dependable cycling characteristics and high energy-density

compared to other electrochemical energy storage solutions [1].

These favourable characteristics combined with many years of further development, have helped to alleviate a portion of the initial safety concerns associated with Li-ion batteries. As a result, there has been a steady increase in the demand for Li-ion batteries as smartphones and tablets begin to replace many of the uses of traditional desktop computing[2], and new applications for Li-ion batteries such as electric vehicles (EVs) and large-scale stationary energy storage are also starting to be developed and commercial- ised[3,4].

Despite their widespread adoption, Li-ion batteries still suffer

*Corresponding author.

E-mail address:neeraj.sharma@unsw.edu.au(N. Sharma).

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0378-7753/Crown Copyright©2016 Published by Elsevier B.V. All rights reserved.

from significant degradation in their performance over time [5].

The most obvious degradation in battery performance is capacity fadeewhere the capacity of the battery reduces after extended cycling. The cycling conditions, such as current rate used, number of cycles, and state-of-charge (SOC) as well as external factors such as temperature, can all cause capacity fade which reduces the useful life of batteries [6]. A variety of mechanisms have been suggested as contributors to this degradation including decompo- sition of the electrolyte or lithium plating on the negative electrode, breakdown of the electrode lattices due to mechanical stress caused by repeated expansion/contraction and phase transitions during cycling[7], and growth of the solid-electrolyte interphase (SEI) layer[8], among others. For newer applications such as EVs or stationary energy storage, batteries will be expected to have a much longer useful calendar lifetime than previous applications[9], and thus the development of newer electrode materials and more sta- ble electrolyte systems is necessary[10], while also gaining a better understanding of the degradation mechanisms.

Battery systems typically integrate components for prognosis [11]which help to provide an indication of a battery's“health”or warn of imminent failure during use. However, in order to better understand the mechanisms underlying battery performance degradation, specialised techniques are required which should ideally be able to probe the internal components of the battery while being non-destructive. Techniques such as impedance spec- troscopy have been used to probe the state-of-health of batteries [12,13] however these techniques only allow electrochemical characterisation and the information they provide can only be used to extrapolate the state of the battery's internal components.

Neutron powder diffraction (NPD) allows for structural character- isation and the information it provides is directly related to the phases present within the battery. NPD has proven to be a useful and non-destructive technique for understanding the processes which occur during cycling of Li-ion batteries[14]. This is because the neutron beam is able to penetrate the battery casing and all of the cell components, providing information on the bulk crystal structure of the components concealed within the battery. Neutron diffraction also offers a relatively-high sensitivity for Li in this system compared to other similar techniques such as X-ray diffraction (XRD) or electron diffraction[15].

While Li-ion cells have been designed specifically for in situ/

operandoNPD studies[16,17], using commercial batteries for these studies remains favourable as they accurately represent real-world battery performance[15]. A number of NPD studies on commercial batteries have been reported for both cylindrical [18e21] and pouch-type[22e24]commercial lithium-ion batteries, which have demonstrated that NPD allows structural changes, phase transi- tions, and crystallite size changes of the electrode materials within the batteries to be measured and correlated with cycling conditions such as the battery potential, applied current, and SOC. The most successful category of commercial electrode materials explored to date are the layered transition-metal oxide positive electrodes (LiMO₂;M¼Mn, Co, Ni) paired with graphite negative electrodes [25]. However, more recently LiFePO4 positive electrodes have begun to appear in commercial batteries. Since it wasfirst proposed as a positive electrode material by Pahdi et al.[26], LiFePO₄has been studied extensively, and compared to conventional positive electrode materials, it offers increased theoretical capacity, aflat operating voltage, better thermal stability, lower cost and can be disposed or recycled with a smaller environmental impact[27]. A number of mechanistic studies have been carried out on LiFePO4as a positive electrode material and a two-phase (lithiated LiFePO4to delithiated FePO₄) transition is generally adopted to describe lithium extraction/intercalation in the bulk material[28].

The graphite negative electrode has been widely adopted in a

variety of Li-ion battery systems due to its relatively high capacity, good electrical conductivity, and high Li diffusivity [29]. The accepted mechanism for lithium insertion/extraction in graphite is that Li ions intercalate between the graphene planes (via combi- nations of solid-solution and two-phase reactions), while also forming LiCx compounds at high lithium concentrations [19,30].

Unfortunately, graphite suffers from the possibility of lithium plating when high rate cycling is carried out[31].

The most common geometries of commercial batteries are cy- lindrical and pouch-type/prismatic cells[15]. Cylindrical cells (e.g.

18650-type, 26650-type etc.) are typically found in larger devices such as power tools or laptops. Pouch-type cells meanwhile are favoured in applications where there is a restriction on the size or shape of the battery, such as in smartphones.

The current literature regardingin situ/operandoNPD of cylin- drical cells has focused on only 18650-type cells[19,32,33]. Here we report thefirstin operandoandex situstudy of a number of com- mercial 26650-type Li-ion cells containing a LiFePO₄ positive electrode and graphite negative electrode which have been sub- jected to various ageing conditions. The ageing conditions have been chosen to represent typical usage scenarios for batteries in electric vehicles[34]. By focusing on particular reflections within thein operandoNPD data we were able to observe evidence for two-phase transitions between LiFePO₄/FePO₄ and LiC₁₂/LiC₆ as well as the expansion/contraction of the lithiated graphite lattice, which occurs in these electrode materials during charge/discharge.

Further, time-resolved NPD data enabled the relationship between the reaction rate of the active materials in the battery and the applied current to be obtained.

2. Experimental

A123 Systems' rechargeable Li-ion ANR26650M1A cells con- taining LiFePO₄ positive electrodes and graphite negative elec- trodes were studied. The batteries, listed inTable 1, are 26 mm in diameter and 65 mm in height and since the batteries are com- mercial, they have been formed prior to our experiments, and are sold at typically 50e60% SOC. The battery components include:

aluminium casing, aluminium and copper current collectors, graphite negative electrode, positive electrode mixture composed

Table 1

The pre-cycled and aged batteries used for NPD measurements.

ID Status Cycle Current capacity (Ah) Potential (V)

103 Cycle aged þ4C/1C 1.60 3.309

þ23.3C

107 Cycle aged þ4C/4C 1.68 3.308

þ29.2C

109 Cycle aged þ4C/4C 1.49 3.309

þ35.2C Pause

113 Cycle aged þ4C/1C 1.38 3.304

þ33.5C

115 Cycle aged þ1C/4C 1.56 3.307

þ34.1C

117 Cycle aged þ4C/4C 1.65 3.309

þ30.5C 0-20% SOC

121 Cycle aged þ4C/4C 1.82 3.309

þ29.5C, 80e100% SOC

126 Cycle aged þ2C/2C 1.52 3.307

þ34.4C

136 Calendar aged 50% SOC, 2.17 3.309

þ23C, 3 years

137 Calendar aged 50% SOC, 2.18 3.309

þ23C, 3 years

D. Goonetilleke et al. / Journal of Power Sources 343 (2017) 446e457 447

of polyvinyldifluoride (PVDF) with carbon black and LiFePO4, and electrolyte composed of LiPF₆dissolved in a mixture of ethylene carbonate and dimethyl carbonate.

In operandoandex situNPD data were collected on WOMBAT, the high-intensity neutron powder-diffractometer, at the OPAL reactor facility at ANSTO [35]. The batteries were placed in a neutron beam of wavelength (l⁾¼2.4122(2) Å, determined using the NIST Al₂O₃676 standard reference material, and data collected in the range 252q135or 2.85<d<1.71 Å over 1 min, for both ex situand continuously collected in time-resolved (in operando) experiments during charge/discharge. NPD data correction, reduction, and visualization were undertaken using the program LAMP[36]. During thein operandoNPD experiment the electro- chemical cell was cycled under different conditions including gal- vanostatic (constant current) mode with applied current ranging from±0.5e2.0 A, potentiostatic (constant voltage) mode, and cur- rent free mode using an Autolab potentiostat/galvanostat (PG302N).

Single peak fits were carried out using Gaussian peak shapes with a linear background in LAMP[37].

3. Results and discussion

3.1. Ex situ NPD studies of 26650 batteries

All previous work using in situ/operando NPD studies on lithium-ion batteries was undertaken on custom-made, commer- cial 18650, or commercial prismatic batteries[4,19,21,38e50]. This work is thefirst using NPD to examine larger 26650-type lithium- ion batteries, which are 26 mm in diameter, thicker than 18650 cells which have an 18 mm diameter. Importantly, 26650- type batteries have significantly higher capacities than the 18650 type (2.5 Ah for 26650 versus 1.1 Ah for 18650 A123 batteries). Both 18650 and 26650-type cylindrical batteries have a non- homogeneous arrangement of battery components (Fig. 1), which has implications for the collection of NPD data. Although neutrons are highly penetrating, some battery components absorb neutrons

(notably those containing lithium and iron, for example, the elec- trodes), while others contribute significantly to the background (notably those that contain hydrogen such as the electrolyte and separator). The battery construction and chemical composition combine such that placing the battery exactly at the centre of the NPD instrument does not necessarily result in ideal NPD data collection. The thickness of the battery therefore has further im- plications for the NPD data collection, where the neutron absorp- tion and scattering path-lengths through the sample are significantly different between the 18650 and 26650 battery types.

The neutron beam dimensions (approximately 40 20 mm including divergence) are also smaller than the 65 mm26 mm 26650 battery, and this further impacts thefinal alignment of the battery on the neutron powder diffractometer. One indicator for neutron absorption effects that negatively impact NPD data is a background which varies as a function of 2qrather than beingflat.

Fig. 2a shows the influence of displacing the battery with respect to the incident neutron beam and the neutron detector on the measured powder diffraction pattern, with the battery position on the instrument outlined in Fig. 2b. Some orientations also represent rotations of the battery at a specified displacement off the beam centre. The NPD patterns for different rotations, about the central axis of the 26650-type battery (45, 0, 45) at 0 mm displacement show very little change between them, although the background is notflat (Fig. 2a)i)). This can be attributed to the fact that the ratio of electrode material, separator, casing and current collectors which the neutron beam penetrates is very similar irre- spective of the rotation.

The displacement from the beam centre (Fig. 2a)ii) and iii)) causes a larger change in the NPD patterns than battery rotation alone (Fig. 2a)i)), as the separator-rich and hence H-rich central core is moved from the beam (especially as a function of 2q^{). Note} that orientation #7 results in a smaller amount of sample in the beam as the central axis of the battery is furthest from the beam centre and the battery is rotated by45such that the beam is interacting only with the edge of the battery.

Thefluctuations shown inFig. 2a have significant ramifications for any attempted comparisons ofex situNPD data with the bat- teries in different cycled states (i.e.,without extracting the elec- trode). A number of batteries were cycled and tested with a variety of offline conditions as shown inTable 1. They were all placed on WOMBAT in a similar orientatione displacement off centre and aligned with respect to the manufacturer's text on the outer casing.

Before describing the results of these comparisons it is important to note that the batteries may have been placed on WOMBAT with a slightly different rotation or displacement (within one mm) and the assumption is that the batteries are identical to each other with respect to internal composition. Due to the dimensions of the beam and the size of the battery, subtle changes in position and rotation should not significantly influence NPD patterns, as demonstrated in Fig. 2a.Fig. 3aed shows NPD patterns for each battery at the 5th orientation (seeFig. 2a and b) directly overlaid. The background, which can be seen inFig. 3d, also shows minor differences between the samples, a strong indicator that the NPD data can be directly compared.Fig. 3b shows that the intensity of the strongest negative electrode peak, the lithiated graphite 002 reflection[51]is highest in the batteries under 115, 121, 137 conditions, and then decreases in the following order of conditions: 136 > 109 > 107 > 117, 113>103>126. In this state of the battery, the negative electrode has a majority phase of LiC₁₂, seefirst patterns inFig. 4where the initial charge transforms the negative electrode from lower to higher lithiated material, e.g. from the LiC18to LiC12and then to LiC6

phases as observed for batteries testedin operando[51]. There is also a subtle shift in peak position in approximately the same sequence of battery conditions. It should be noted that all batteries Fig. 1.A simplified diagram of the 18650 and 26650-type battery construction,

showing a) a side profile of the battery, and b) a top-down view of the battery with the direction of the incident neutron beam also indicated. The cell consists of concentric alternating layers of the negative and positive electrode materials between which separator layers are situated. The cell is thenfilled with electrolyte to allow ion conduction.

were tested at the same potential so the changes in the lithiated graphite 002 reflection are likely to be a result of the battery

history. The batteries 137 and 136 show some of the highest lithi- ated graphite 002 reflection intensities and these are calendar aged Fig. 2.(a) As collectedex situNPD patterns of a 26650 battery at different positions with respect to the neutron beam centre and with rotations at selected positions. Figure a) i) shows the effect of rotating the battery about its central axis within the beam. Figure a) ii) shows the effect of displacing the battery transversely away from the detector. Figure a) iii) shows the effect of rotating and displacing the batteries: in orientation #5 the battery was rotated to45and displaced 13 mm off the central axis, orientation #6 represents the battery displaced by 13 mm but not rotated, and in #7 the battery was rotated toþ45at 13 mm off the central axis. (b) A schematic of the orientations.

D. Goonetilleke et al. / Journal of Power Sources 343 (2017) 446e457 449

at 3 years (uncycled). These batteries represent as-received batte- ries that have been stored for later use. Battery 115 also shows a high lithiated graphite 002 reflection intensity, which corresponds to slow charging followed by faster discharging. Similarly high lithiated graphite 002 reflection intensity is shown for battery 109, which underwent fast charge/fast discharge with a pause. Lower lithiated graphite 002 reflection intensities are noted for the moderate charge/discharge (±2C) of battery 126, the fast charge/

slow discharge of batteries 103 and 113 (where battery 113 is tested at 10C higher in temperature than 103), and fast charge/discharge of batteries 107 and 117 (where battery 117 is cycled in a lower state of charge range compared to 107). Therefore, the uncycled, slow charged (with fast discharge) and paused during fast cycling bat- teries show higher lithiated graphite (LiC12) 002 reflection in- tensities while continuous moderate and fast rate cycled, fast charged (with slow discharge) and fast rate cycled within a small state of charge (SOC) range batteries show lower lithiated graphite (LiC12) 002 reflection intensities. These results suggest that gentler conditions or at least gentler charge conditions result in higher lithiated graphite 002 reflection intensities or the presence of more LiC12, with faster or harsher conditions reducing reflection intensity or less LiC12produced. At the same state of charge this suggests that more of the electrode has transformed to LiC₁₂ under gentler conditions.

Battery 121 is anomalous to this general trend, where the lithiated graphite 002 reflection intensity is highest following fast

rate cycling. It should be noted that this battery was only cycled between 80 and 100% SOC, which may explain this result. Inter- estingly, the other battery which was cycled in a limited SOC range (battery 117, cycled between 0 and 20% SOC), the lithiated graphite 002 reflection exhibits a shoulder at 2q^{~ 41.7}, which is indicative of a lower Li-content graphite (e.g. a LiC₁₈-type phase)[51]. This suggests that cycling between 0 and 20% SOC leaves some lower lithium content graphite while cycling between 80 and 100% SOC leaves a higher lithium content graphite. Therefore, the lithiated graphite (or LiC₁₂) 002 reflection appears to exhibit noticeable changes with battery history that is correlated to the state of health of the battery and to the conditions of electrochemical cycling. In terms of the positive electrode, which features characteristic re- flections in the region depicted inFig. 3c, very little difference is observed between the samples.

3.2. In operando NPD data

To correlate battery history with structural evolution three batteries were chosen representative of three different ageing conditions: 107 (high charge and discharge rate), 113 (high charge rate, but slow discharge rate) and 137 (calendar aged). The collected in operandoNPD patterns are shown as a colour contour plot with their respective potential curves overlaid inFig. 4. A Le Bailfit using the structural models of the components, LiFePO4, FePO4, lithiated graphite, Cu and Al, with NPD data for the as received battery 137 is Fig. 3.Ex situNPD data of 26650 batteries aged under the conditions listed inTable 1. Different 2qregions are shown, with (a) and (b) highlighting the graphite-type reflections, (c) a region of positive electrode reflections and (d) the background for the entire 2qregion of the NPD data.

shown in theSupporting Information, Figure S1. The most promi- nent feature in all cases is the evolution of the graphitic electrode with the lithiated graphite LiC12 002 (labelled) reflection (or the LiC₆ 001 reflection) [33,52]. The arrows in Fig. 4b indicate re- flections associated with LiFePO4and FePO4and the data clearly reveal that these alternatingly appear and disappear during cycling.

3.2.1. The negative electrode

As the battery is charged lithium intercalates into the graphite negative electrode. This is well-known to affect thed-spacing of the graphite layers, as revealed by the c lattice parameter and the strongest reflection in our data, the lithiated graphite 002 reflec- tion, which shifts in position (and changes in intensity). The evo- lution of graphite as a negative electrode material has been described in detail previously, with a staged mechanism being a generally-accepted description of the intercalation processes [51,53]. In this mechanism there are a number of distinct phases (Li_xC₆or Li_yC) which form as the Li content in graphite is increased and the transitions between these phases have been previously characterised [20,54,55]. Relatively recent in operandowork has also shown that these transitions appear as an apparent solid- solution transition for most of charge at high current rates[56].

Essentially the intermediate phases appear as a gradual transition

that is very close to solid-solution type behaviour from graphite to LiC12[57]. Thus the graphite-type 002 reflection changes 2q^value with charge and discharge in an apparently gradual manner until LiC₁₂. Close to the charged state the high lithiated graphite LiC₁₂ phase converts to LiC6via a two-phase reaction.

Fig. 4aec shows that the negative electrode evolves as an apparent solid-solution reaction for most of charge and discharge.

Close to the charged state, the intensity of the lithiated graphite 002 reflection decreases concurrently with the increasing intensity of the LiC6 001 reflection. To capture the kinetics of the lithiation/

delithiation processes taking place at the electrodes, single-peak fitting of the lithiated graphite 002 reflection position and in- tensity and the LiC6001 reflection intensity was performed and the results are shown inFigs. 5e7.

3.2.2. The positive electrode

The evolution of LiFePO4to FePO4in these batteries appears to proceed via the conventional two-phase reaction mechanism[26]

(see arrows in Fig. 4b). LiFePO4 is widely regarded to act as a two-phase system when used as a positive electrode material in Li- ion batteries[27]. During charge/discharge the removal/insertion of Li ions from/to the positive electrode material results in conversion between the lithiated LiFePO4 phase and the delithiated FePO4 Fig. 4.In operandoNPD patterns collated in time and shown as a colour scale with the potential profile shown on the right for the three batteries examined (a) 107, (b) 137, and (c) 113. The lithiated graphite 002 reflection is labelled and the reflections from either LiFePO4to FePO4are indicated by arrows in (b), where the transition between these two phases is clearly observed. (For interpretation of the references to colour in thisfigure legend, the reader is referred to the web version of this article.)

D. Goonetilleke et al. / Journal of Power Sources 343 (2017) 446e457 451

phase [23]. The particle size and morphology of LiFePO₄ can be modified to cause a solid-solution reaction for some, most or all of the LiFePO4charge/discharge[58]. Evidence for the two-phase re- action in our data can be seen in the cyclic change in intensity of the LiFePO₄102 reflection (Figs. 5e7)[59]. During charge, the intensity of the LiFePO4102 reflection decreases while the intensity of the reflections from the FePO4 phase increase, and vice versa on discharge. The FePO₄ reflections are fairly weak within these datasets and so the LiFePO4reflections are used to characterize the evolution of the positive electrode.

3.2.3. Reaction rates

The major advantage of time-resolved data is the ability to extract rates of change. The evolution of peak area and peak posi- tions can be modelled byfitting functions to the data in order to characterize their relationship to the applied current.Table 2shows the rate of change of the LiFePO4102 peak area (PA) during the electrochemical steps used and the corresponding applied current.

As expected, the LiFePO₄102 peak area is found to increase during the discharge steps and decrease during the charge steps with lithium intercalation and deintercalation, respectively. Moreover, in Fig. 5.Single peakfitting parameters using NPD data for battery 107 with b) graphite-type 002 reflection position, c) LiC6001 reflection area, d) LiFePO4102 reflection area. Errors bars are similar in size to the points.

all three batteries it is found that the rate at which the peak area grows and diminishes is linearly proportional to the applied cur- rent, as shown inFig. 8a, as consistent with previous studies of the two phase reaction of LiFePO4[60]. An empirical relationship can be drawn from the increase/decrease of the PA per second and the applied current, where the slope of the plot of the rate of change of PA versus current is R [d(PA/s)/dI).

The relationship between rate of change of peak area and applied current is found to have the highest magnitude for battery 137 (R¼ 0.273(7)), followed by battery 107 (R¼ 0.237(7)) and least for battery 113 (R¼ 0.196(11), seeFig. 8a). In this graph it is evident that on discharge the rate of change of the PA is positive as LiFePO4forms and that it is negative for the charge process where LiFePO4delithiates, with the data passing expectedly through 0,0.

The difference in slope appears to be related to the cycling history

of the batteries, where battery 137, which was calendar aged, ex- hibits a greater response than batteries 107 and 113 which have been previously cycled. This supports theex situfindings where the calendar-aged battery 137 was found to show markedly different behaviour than cycle-aged batteries 107 and 113.

Peak fitting of the LiC₆ 001 reflection during charge and discharge reveals the peak area increases as the battery reaches its charged potential, seeTable 3andFig. 8b. There was some difficulty infitting the LiC₆001 reflection using the NPD data of the 107 and 113 batteries due to the superposition of this reflection with the adjacent reflection from the negative electrode, resulting in some data in Table 3 being absent. The rate at which the LiC₆ 001 reflection area grows/diminishes is again, as expected, linearly related to the applied current, being positive on charge and nega- tive on discharge, and passing through 0,0. The response of the LiC₆ Fig. 6.Single peakfitting parameters using NPD data for battery 113 with b) graphite-type 002 reflection position, c) LiC6001 reflection area, d) LiFePO4102 reflection area. Errors bars are similar in size to the points.

D. Goonetilleke et al. / Journal of Power Sources 343 (2017) 446e457 453

Fig. 7.Single peakfitting parameters using NPD data for battery 137 with b) graphite-type 002 reflection position, c) LiC6001 reflection area, d) LiFePO4102 reflection area. Errors bars are similar in size to the points.

Table 2

Change in LiFePO4120 peak area versus applied current. Rate of change of peak area is obtained by performing linearfits to the data shown inFigs. 5e7.

Final voltage (V) Applied current (A) Rate of change of peak area (area/s)

Battery 107 Battery 137 Battery 113

1^stDischarge 2 0.5 0.111(3) 0.134(4) 0.0821(71)

1^stCharge 4.2 0.5 0.122(4) 0.142(43) 0.105(6)

2^ndDischarge 2 0.5 0.121(6) 0.156(7) 0.0904(7)

2^ndCharge 4.2 2 0.611(39) 0.508(56)

3^rdDischarge 2 1 0.270(13) 0.274(14)

3^rdCharge 4.2 2 0.468(31) 0.518(29)

4^thDischarge 2 1 0.245(26) 0.281(13)

4^thCharge 4.2 2 0.486(36) 0.572(25)

5^thDischarge 2 2 0.421(29) 0.451(27)

5^thCharge 4.2 2 0.420(24) 0.471(26)

6^thDischarge 2 2 0.544(35) 0.572(36)

001 reflection exhibits a slightly different relationship to that of the LiFePO4120 reflection. The relationship that can be established for

the LiC₆001 reflection is R¼5.95 and R¼5.20 for batteries 137 and 113, respectively which is significantly lower than for battery 107 (high rate charge/discharge), where R¼7.83.

In all of the batteries, the position of the lithiated graphite 002 reflection shifts between 2q^{~ 40.5} (near the charged state) and 42.5(the discharged state). This shift corresponds to the expan- sion (and contraction) of the spacing between the graphitic layers of the negative electrode as Li is inserted and removed during cycling. Examining the rate of change of the peak position, rather than peak area, is therefore more pertinent to understanding the degree of graphite lithiation (an approximate solid-solution reac- tion), as opposed to the examination of peak area for the positive electrode (a two-phase reaction). Results of linearfits to the peak position with time are shown inTable 4andFig. 8c. In this case, doubling the current results in a doubling of the rate of the peak position shift, see 1^stdischarge for battery 107 and compare to the 3^rddischarge for battery 107 inTable 4.

The rate of structural changes within the electrode materials can be related to the applied current, a summary of the relationships observed is shown inTable 5. It appears that a history of high rate charge/discharge (battery 107) results in a relatively larger struc- tural response (or R) of the negative electrode phase. This is probably an indicator of better battery health for 113 and 137, which have not previously been subjected to high rate discharge and which exhibit similar negative electrode phase rates of struc- tural changes to each other, consistent with theex situresults. For the positive electrode, LiFePO₄102 peak area is lower in absolute magnitude for batteries 113 and 107.

4. Conclusions

In operando neutron powder diffraction, for thefirst time, is applied to examine electrodes within larger 26650-type commer- cial batteries. Thein operandoNPD data shows the expected phase evolution of both the LiFePO4positive electrode and the graphitic negative electrode phases. Importantly, the use of time resolved data enabled examination of the rate of electrode changes taking place. A linear relationship between the electrochemical reactions which occur during cycling and the applied current was found for all batteries tested, with the slope (R) of the rate of change of structural parameters versus current being different for each of the batteries tested. There is some evidence that the different re- lationships observed may be related to the cycling history of the batteries: the rate of structural evolution of the negative electrode was found to be significantly higher for the battery with a history of

high current charge/discharge. Further work, with a larger sample size of batteries examined byin operandoNPD will address in more Fig. 8.Rate of change of the (a) LiFePO4120 reflection intensity, (b) LiC6001 reflection

integrated area and (c) graphite-type LixC6or LiyC 002 reflection position versus applied current. Lines are the linearfits applied to the data. *Additional points for battery 137 are due to the battery being charged at the same current multiple times.

Table 3

Rate of change in LiC6001 reflection peak area versus applied current.

Final voltage (V) Applied current (A) Rate of change of peak area (area/s)

Battery 107 Battery 113 Battery 137

1^stDischarge 2 0.5 3.23(88) 2.20(16) 2.58(8)

1^stCharge 4.2 0.5 4.21(85) 2.72(15) 2.83(6)

2^ndDischarge 2 0.5 2.75(12) 2.57(5)

2^ndCharge 4.2 2 11.12(61)

3^rdDischarge 2 1 5.27(18)

3^rdCharge 4.2 2 17.34(117) 12.07(65)

4^thDischarge 2 1 7.16(15) 5.11(17)

4^thCharge 4.2 2 16.88(83) 13.23(74)

5^thDischarge 2 2 13.47(50) 10.37(34)

5^thCharge 4.2 2 16.89(44) 13.35(30)

6^thDischarge 2 2 14.80(23) 12.68(40)

D. Goonetilleke et al. / Journal of Power Sources 343 (2017) 446e457 455

detail the relationship between cycle history and electrode response and whether NPD can be used as a diagnostic tool for a batch of batteries.

Acknowledgments

Neeraj Sharma would like to thank AINSE for providing support through the research fellowship scheme and the Australian Research Council through the DECRA (DE DE160100237). James C.

Pramudita would like to thank AINSE Ltd for the PGRA and ANSTO for PhD scholarship funding.

Appendix A. Supplementary data

Supplementary data related to this article can be found athttp://

dx.doi.org/10.1016/j.jpowsour.2016.12.103.

References

[1] Y. Nishi, Chem. Rec. 1 (2001) 406e413.

[2] C. Pillot, Batteries 2012, Avicenne Energy, Nice, France, 2012.

[3] B. Dunn, H. Kamath, J.-M. Tarascon, Science 334 (2011) 928e935.

[4] M.M. Thackeray, C. Wolverton, E.D. Isaacs, Energy Environ. Sci. 5 (2012) 7854e7863.

[5] J.M. Tarascon, M. Armand, Nature 414 (2001) 359e367.

[6] I. Bloom, B. Cole, J. Sohn, S. Jones, E. Polzin, V. Battaglia, G. Henriksen, C. Motloch, R. Richardson, T. Unkelhaeuser, J. Power Sources 101 (2001) 238e247.

[7] P. Kubiak, M. Wolfahrt-Mehrens, K. Edstr€om, M. Morcrette, J. Power Sources 12 (2013) 03691.

[8] M. Winter, J.O. Besenhard, M.E. Spahr, P. Novak, Adv. Mater. 10 (1998) 725e763.

[9] J. Groot, M. Swierczynski, A.I. Stan, S.K. Kær, J. Power Sources 286 (2015) 475e487.

[10] M.S. Whittingham, MRS Bull. 33 (2008) 411e419,http://dx.doi.org/10.1557/

mrs2008.82.

[11] S.M. Rezvanizaniani, Z. Liu, Y. Chen, J. Lee, J. Power Sources 256 (2014) 110e124.

[12] A. Barai, G.H. Chouchelamane, Y. Guo, A. McGordon, P. Jennings, J. Power Sources 280 (2015) 74e80.

[13] M. Reichert, D. Andre, A. R€osmann, P. Janssen, H.G. Bremes, D.U. Sauer,

S. Passerini, M. Winter, J. Power Sources 239 (2013) 45e53.

[14] N. Sharma, V.K. Peterson, J. Solid State Electrochem. 16 (2011) 1849e1856.

[15] N. Sharma, W.K. Pang, Z. Guo, V.K. Peterson, ChemSusChem 8 (2015) 2826e2853.

[16] O. Bergst€€ om, A. Andersson, K. Edstr€om, T. Gustafsson, J. Appl. Crystallogr. 31 (1998) 823e825.

[17] H. Berg, H. Rundl€ov, J.O. Thomas, Solid State Ion. 144 (2001) 65e69.

[18] M. Alam, T. Hanley, W.K. Pang, V.K. Peterson, N. Sharma, Powder Diffr. 29 (2014) S35eS39.

[19] A. Senyshyn, M.J. Mühlbauer, K. Nikolowski, T. Pirling, H. Ehrenberg, J. Power Sources 203 (2012) 126e129.

[20] M.A. Rodriguez, M.H. Van Benthem, D. Ingersoll, S.C. Vogel, H.M. Reiche, Powder Diffr. 25 (2010) 143e148.

[21] O. Dolotko, A. Senyshyn, M.J. Muhlbauer, K. Nikolowski, F. Scheiba, H. Ehrenberg, J. Electrochem. Soc. 159 (2012) A2082eA2088.

[22] I.A. Bobrikov, A.M. Balagurov, C.-W. Hu, C.-H. Lee, T.-Y. Chen, S. Deleg, D.A. Balagurov, J. Power Sources 258 (2014) 356e364.

[23] C.-W. Hu, N. Sharma, C.-Y. Chiang, H.-C. Su, V.K. Peterson, H.-W. Hsieh, Y.- F. Lin, W.-C. Chou, B.-Y. Shew, C.-H. Lee, J. Power Sources 244 (2013) 158e163.

[24] N. Sharma, V.K. Peterson, M.M. Elcombe, M. Avdeev, A.J. Studer, N. Blagojevic, R. Yusoff, N. Kamarulzaman, J. Power Sources 195 (2010) 8258e8266.

[25] B.L. Ellis, K.T. Lee, L.F. Nazar, Chem. Mater. 22 (2010) 691e714.

[26] A.K. Padhi, K. Nanjundaswamy, J. Goodenough, J. Electrochem. Soc. 144 (1997) 1188e1194.

[27] Z. Li, D. Zhang, F. Yang, J. Mater. Sci. 44 (2009) 2435e2443.

[28] C. Delacourt, P. Poizot, J.-M. Tarascon, C. Masquelier, Nat. Mater. 4 (2005) 254e260.

[29] N. Nitta, F. Wu, J.T. Lee, G. Yushin, Mater. Today 18 (2015) 252e264.

[30] Z.X. Shu, R.S. McMillan, J.J. Murray, J. Electrochem. Soc. 140 (1993) 922e927.

[31] C. Uhlmann, J. Illig, M. Ender, R. Schuster, E. Ivers-Tiffee, J. Power Sources 279 (2015) 428e438.

[32] X.L. Wang, K. An, L. Cai, Z. Feng, S.E. Nagler, C. Daniel, K.J. Rhodes, A.D. Stoica, H.D. Skorpenske, C. Liang, W. Zhang, J. Kim, Y. Qi, S.J. Harris, Sci. Rep. 2 (2012) 747.

[33] O. Dolotko, A. Senyshyn, M.J. Mühlbauer, K. Nikolowski, H. Ehrenberg, J. Power Sources 255 (2014) 197e203.

[34] M. Klett, R. Eriksson, J. Groot, P. Svens, K. Ciosek H€ogstr€om, R.W. Lindstr€om, H. Berg, T. Gustafson, G. Lindbergh, K. Edstr€om, J. Power Sources 257 (2014) 126e137.

[35] A.J. Studer, M.E. Hagen, T.J. Noakes, Phys. B 385e386 (2006) 1013e1015.

[36] D. Richard, M. Ferrand, G.J. Kearley, J. Neutron Res. 4 (1996) 33e39.

[37] D. Richard, M. Ferrand, G. Kearley, J. Neutron Res. 4 (1996) 33e39.

[38] M. Wagemaker, D.P. Singh, W.J.H. Borghols, U. Lafont, L. Haverkate, V.K. Peterson, F.M. Mulder, J. Am. Chem. Soc. 133 (2011) 10222e10228.

[39] R.P. Rao, W. Gu, N. Sharma, V.K. Peterson, M. Avdeev, S. Adams, Chem. Mater.

27 (2015) 2903e2910.

[40] J. Qian, M. Zhou, Y. Cao, X. Ai, H. Yang, Adv. Energy Mater. 2 (2012) 410e414.

[41] R. Liu, J. Duay, S.B. Lee, Chem. Commun. 47 (2011) 1384e1404.

[42] C.-W. Hu, N. Sharma, C.-Y. Chiang, H.-C. Su, V.K. Peterson, H.-W. Hsieh, Y.- F. Lin, W.-C. Chou, B.-Y. Shew, C.-H. Lee, J. Power Sources 244 (2013) 158e163.

[43] N. Sharma, V.K. Peterson, J. Solid State Electrochem. 16 (2012) 1849e1856.

[44] N. Sharma, M.V. Reddy, G. Du, S. Adams, B.V.R. Chowdari, Z. Guo, V.K. Peterson, J. Phys. Chem. C 115 (2011) 21473e21480.

[45] N. Sharma, G. Du, A.J. Studer, Z. Guo, V.K. Peterson, Solid State Ion. 199e200 (2011) 37e43.

[46] G. Du, N. Sharma, J.A. Kimpton, D. Jia, V.K. Peterson, Z. Guo, Adv. Funct. Mater.

21 (2011) 3990e3997.

[47] A. Senyshyn, M.J. Muhlbauer, K. Nikolowski, T. Pirling, H. Ehrenberg, J. Power Sources 203 (2012) 126e129.

[48] J.-F. Colin, V. Godbole, P. Novak, Electrochem. Comm. 12 (2010) 804e807.

[49] H. Berg, H. Rundlov, J.O. Thomas, Solid State Ion. 144 (2001) 65e69.

[50] M.A. Rodriguez, D. Ingersoll, S.C. Vogel, D.J. Williams, Electrochem. Solid-State Lett. 7 (2004) A8eA10.

[51] J. Dahn, Phys. Rev. B 44 (1991) 9170.

Table 4

Rate of change of the graphite-like 002 reflection position with time (/s).

Final voltage (V) Applied current (A) Rate of change of peak position (/s)

Sample 107 Sample 113 Sample 137

1^stDischarge 2 0.5 0.000442(8) 0.000497(1) 0.000346(9)

1^stCharge 4.2 0.5 0.000439(9) 0.000470(1) 0.000293(6)

2^ndDischarge 2 0.5 0.000444(8) 0.000477(1) 0.00037(1)

2^ndCharge 4.2 2 0.00157(7) 0.00139(1) 0.00131(7)

3^rdDischarge 2 1 0.000901(2) 0.000733(3)

3^rdCharge 4.2 2 000157(7) 0.00124(6)

4^thDischarge 2 1 0.000964(2) 0.000673(4)

4^thCharge 4.2 2 0.000172(7) 0.00129(7)

5^thDischarge 2 2 0.00183(6) 0.00132(8)

5^thCharge 4.2 2 0.00156(6) 0.00122(6)

6^thDischarge 2 2 0.00131(9) 0.00138(1)

Table 5

Summary of kinetic parameters for the different batteries.

Battery

107 113 137

Battery History þ4C/4C þ4C/1C 50% SOC,

þ29.2C þ33.5C þ23C, 3 years

R R R

LiFePO4120 0.2365(65) 0.196(11) 0.2725(74)

LiC6001 7.83(14) 5.20(48) 5.95(17)

LixC6graphite-type 002

8.13(29)10⁴7.59(61)10⁴6.54(60)10⁴

[52] A. Senyshyn, M.J. Mühlbauer, O. Dolotko, H. Ehrenberg, J. Power Sources 282 (2015) 235e240.

[53] T. Ohzuku, Y. Iwakoshi, K. Sawai, J. Electrochem. Soc. 140 (1993) 2490e2498.

[54] A. Senyshyn, O. Dolotko, M.J. Muhlbauer, K. Nikolowski, H. Fuess, H. Ehrenberg, J. Electrochem. Soc. 160 (2013) A3198eA3205.

[55] L. Boulet-Roblin, P. Borel, D. Sheptyakov, C. Tessier, P. Novak, C. Villevieille, J. Phys. Chem. C 120 (2016) 17268e17273.

[56] N. Sharma, V.K. Peterson, Electrochim. Acta 101 (2013) 79e85.

[57] N.S. Nazer, V.A. Yartys, T. Azib, M. Latroche, F. Cuevas, S. Forseth, P.J.S. Vie,

R.V. Denys, M.H. Sørby, B.C. Hauback, L. Arnberg, P.F. Henry, J. Power Sources 326 (2016) 93e103.

[58] N. Sharma, X. Guo, G. Du, Z. Guo, J. Wang, Z. Wang, V.K. Peterson, J. Am. Chem.

Soc. 134 (2012) 7867e7873.

[59] G. Rousse, J. Rodriguez-Carvajal, S. Patoux, C. Masquelier, Chem. Mater. 15 (2003) 4082e4090.

[60] Y. Orikasa, T. Maeda, Y. Koyama, T. Minato, H. Murayama, K. Fukuda, H. Tanida, H. Arai, E. Matsubara, Y. Uchimoto, Z. Ogumi, J. Electrochem. Soc.

160 (2013) A3061eA3065.

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