Potential-Resolved In Situ X-ray Absorption ... - ACS Publications

Subscriber access provided by GAZI UNIV

Article

Potential-Resolved In situ X-ray Absorption Spectroscopy Study of Sn and SnO Nanomaterial Anodes for Lithium-Ion Batteries 2

Christopher J Pelliccione, Elena V. Timofeeva, and Carlo U. Segre J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.5b12279 • Publication Date (Web): 17 Feb 2016 Downloaded from http://pubs.acs.org on February 25, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry C is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Potential-Resolved In Situ X-ray Absorption Spectroscopy Study of Sn and SnO2 Nanomaterial Anodes for Lithium-Ion Batteries Christopher J. Pelliccione,∗,† Elena V. Timofeeva,‡ and Carlo U. Segre∗,† †Department of Physics & CSRRI, Illinois Institute of Technology, 3101 S. Dearborn St., Chicago, IL ‡Energy Systems Division, Argonne National Laboratory, Argonne, IL E-mail: [email protected]; [email protected] Phone: 312-567-3498

1 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT This work provides detailed analysis of processes occurring in metallic Sn and SnO2 anode materials for lithium ion batteries during first lithiation, studied in situ with rapid continuous X-ray absorption spectroscopy (XAS). The X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra provide information on dynamic changes in the Sn atomic environment, including type and number of neighboring atoms and interatomic distances. A unique methodology was used to model insertion of Li atoms into the electrode material structure and to analyze the formation of SnLi phases within the electrodes. Additionally, analysis of fully lithiated and delithiated states of Sn and SnO2 electrodes in the first two cycles provides insight into the reasons for poor electrochemical performance and rapid capacity decline. Results indicate that use of SnO2 is more promising than metallic Sn as an anode material but more effort in nanoscale and atomic engineering of anodes is required for commercially feasible use of Sn-based materials.


Page 2 of 41

Page 3 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


INTRODUCTION Lithium-ion batteries (LIBs) are the standard power source for portable electronic devices such as cell phones, laptops, tablets, etc. Graphite is a common anode material in LIBs because of its long cycle life and adequate specific capacity (theoretical capacity 372 mAh/g). 1,2 However, for LIBs to progress and become an efficient and cost effective option for electric vehicles, significant improvements need to be made in the energy and power densities of current electrode materials. 3–5 Metallic tin is an attractive alternative to graphite because of it’s nearly three times higher theoretical capacity (994 mAh/g) enabled by the formation of Li-Sn alloys. However, due the large number of lithium atoms involved in the discharging process (4.4 Li for every Sn atom), the initial crystal structure of metallic tin undergoes significant alterations including a ca. 260% volumetric expansion that severely degrades the anode’s crystallinity, resulting in a rapidly declining capacity. 6 For tin to successfully supplant carbon-based anodes, these catastrophic volumetric changes must be controlled to achieve extended cycle life with enhanced specific capacities. Using oxidized tin phases has been shown to significantly improve the longevity of Snbased anodes through the conversion of SnO2 to metallic Sn and Li2 O during the first lithiation/delithiation cycle. Although SnO2 exhibits a lower theoretical capacity than metallic Sn (790 mAh/g and 994 mAh/g respectively), 7,8 the cycle life is significantly better, with the reversible capacity on the 20th cycle showing ca. 70% improvement over metallic Sn. 9,10 These structural changes during Li alloying with SnO2 result in a primarily amorphous environment in which the Li2 O network provides rigid structural support for metallic tin clusters embedded within, controlling the stress of the volumetric expansions during the lithiation process. 11–13 Common techniques to study battery materials such as X-ray diffraction (XRD) require long-range crystalline order to acquire representative spectra, thus are generally ineffective to study greatly amorphized systems. 14–16 A technique that can adequately account for both amorphous and crystalline contributions is needed to have a complete understanding



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

of the mechanism of lithium insertion/removal and the effect it has on the observed capacity. X-ray absorption spectroscopy (XAS) is an ideal technique to study the structural changes of battery electrodes because it is element specific so it can probe only elements of interest, but also sufficiently accounts for both the crystalline and amorphous phases present within the sample. 17–24 XAS, specifically X-ray absorption near-edge structure (XANES) spectroscopy and extended X-ray absorption fine structure (EXAFS) spectroscopy provide detailed information about the local electronic and atomic environment (< 6 ˚ A) around each absorbing atom. The XANES region is primarily responsive to changes in the electronic structure of the absorbing atom (i.e. changes in oxidation state) while the EXAFS region indicates the neighboring atomic structure. Theoretical models used to interpret the EXAFS region of the spectra help deduce the coordination numbers, interatomic distances, and element species surrounding the absorbing atom as the material is lithiated and delithiated. XAS has not been used to investigate lithiation of pure metallic Sn anodes, however EXAFS studies have been previously conducted on SnO2 -based anodes to gain insight on the specifics of the structural changes the electrode undergoes during initial discharge/charge cycles. Kim et al 25 were able to directly observe the evolution of SnO2 into a metallic tin phase during the first lithiation. Kisu et al 26 also conducted a similar EXAFS study on 2 – 4 nm SnO2 nanoparticles at various points of the first lithiation and delithiation processes with similar results – through changes observed around the Sn atoms, it is deduced that the oxygen is converted to Li2 O early in the charging process with the simultaneous evolution of a metallic tin phase. In the fully lithiated state, the metallic tin phase disappears from the spectra and then returns upon delithiation. These studies provide insight into the general changes occurring within SnO2 electrodes during the lithiation/delithiation process, however they do not report any theoretical modeling of the EXAFS nor do they discuss direct observation of lithium atoms in the lithiated electrode material. Pelliccione et al. have previously shown that detailed XAS modeling


Page 4 of 41

Page 5 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


results can be achieved including direct observation of neighboring lithium atoms in anode materials. 11,27 In this work we report a comparative study of capacity fading mechanisms in metallic Sn and SnO2 electrodes using in situ, continuous, rapid scanning XAS. This approach permits the collection of XAS spectra directly correlated to a specific electrode potential to investigate the structural changes as lithiation progresses. Theoretical models fitted to the resulting spectra allow the potential-specific determination of coordination number and interatomic distances. The direct observation of lithium insertion into the electrodes is also included in the theoretical modeling. Potential-resolved in situ EXAFS measurements were conducted on both Sn and SnO2 electrodes during the first lithium insertion, as well as in the fully discharged and charged states of the first two cycles. Our results provide comparative, quantitative details of the mechanism of lithium insertion and resulting structural changes in Sn and SnO2 nanoparticle electrodes which are consistent with previous qualitative studies 25,26

METHODS Electrode Preparation Electrodes of Sn (Aldrich, 576883; less than 150 nm) and SnO2 nanoparticles (MTI Corporation, NP-SnO2 ; 50 nm) for electrochemical characterization were casted onto 0.03 mm thick copper foil current collectors. The suspension used for electrode casting was prepared from a 80:10:10 wt. % mixture of active material (Sn or SnO2 ), poly(vinylidene fluoride) binder (Aldrich, 24937-79-9) and acetylene carbon black (STREM Chemicals, 138-86-4) respectively, dispersed in 3 mL of 1-methyl-2-pyrrolidinone (Aldrich, 872-50-4) per gram of solid. The suspension was sonicated and mixed for over 24 hours then applied to copper foil with a doctor blade film casting knife (MTI Corporation, EQ-Se-KTQ-50) to create a uniform deposition thickness. The resulting deposition was dried in an oven at 80◦ –100◦ C for three hours and then calendered to improve the electrode performance. The deposition 5 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

density of active material was determined through measuring the total change in mass after deposition and normalizing per surface area of deposition.

X-ray Absorption Spectroscopy XAS spectra were acquired at the Materials Research Collaborative Access Team (MRCAT) beamline, Sector 10–ID, of the Advanced Photon Source at Argonne National Laboratory. Both the Sn and SnO2 electrodes were placed in pouch-type electrochemical cells with Li metal as reference/counter electrode and measured in transmission mode at the Sn K–edge (29.2 keV) with a reference Sn foil measured simultaneously for proper alignment of multiple scans. For in situ tests, a custom sample chamber was used to ensure the pouch cell was under inert atmosphere by flowing He through a sealed chamber. 28 Pouch cell preparation and mounting within the sample chamber were conducted inside an Ar atmosphere glovebox (VAC). Since this study is based around Sn materials in a half-cell configuration with the more negative metallic Li as the counter electrode, designations of “discharge” for lithiation and “ charge” for delithiation will be used throughout the text. In the context of a full cell, where Sn-based materials would be used as anodes, the nomenclature would be reversed. During the in situ XAS experiment, both the Sn and SnO2 electrodes were lithiated/delithiated galvanostatically at a rate of 124 mA/g (C/8) between 0.01 – 1.50 V vs. Li/Li+ using an EzStat Pro potentiostat/galvanostat system (Nuvant Systems, Inc.). Before the first lithiation, the electrodes were held at open circuit voltage (OCV, ca. 3.0 V) to measure the spectra of the pristine electrodes. During the following lithiation and delithiation process XAS measurements were continuously acquired with each individual XAS scan lasting less than two minutes. Since each XAS scan was significantly shorter than the total duration of the discharge, a potential-resolved XAS analysis was conducted on the first lithiation for both Sn and SnO2 electrodes. The fully discharged and charged states of the first two cycles were also analyzed. In those tests, the potential was held at 0.01 V for the discharged states and 1.50 V for the charged states and multiple scans (3-4) were taken at


Page 6 of 41

Page 7 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


each discharged/charged state in order to reduce the noise in the XAS measurements. The EXAFS spectra were aligned, merged and normalized using Athena. 29,30 The built-in AUTOBK algorithm was used to minimize background below Rbkg = 1.0 ˚ A. Each spectrum was fit using Artemis with theoretical models of β-Sn metal, 31 SnO2 32 and a three Sn-Li path (“short”, “medium”, and “long”) model derived from several Li-Sn phases, including the fully lithiated Li22 Sn5 phase, previously developed by our group 11 to obtain quantitative details about the neighboring lithium atoms. 33–37 As the tin-based electrode is converted from metallic tin to the fully lithiated Li22 Sn5 , it goes through several Li-Sn phases such as LiSn, Li2 Sn5 , etc. When in these initial Li-Sn phases, the lithium atoms are exclusively observed at medium and long distances from the tin atoms. As the electrode gradually converts to the Li22 Sn5 phase when fully discharged, the short Sn-Li distances are also observed. Using this distinctive signature in the location of the lithium atoms for the initial and final states of the electrode, we are able to track the state of discharge by comparing the relative ratios of lithium atoms at short (ca. 2.76 ˚ A), medium (ca. 2.90 ˚ A) and long (ca. 3.30 ˚ A) distances away from the tin atoms. All the theoretical EXAFS models were constructed starting with the simplest interpretation, and adding complexity only if needed to achieve a reasonable fit to the experimental data. For both the Sn and SnO2 series of potential-resolved EXAFS modeling, all spectra were initially fit with the pristine crystal structure. When that model could no longer adequately describe the experimental data, the Sn-Li model was included. If there was a path that resulted in parameters with no physical significance (unusually high number of near neighbors, negative Debye-Waller factor, etc.) or large estimated standard deviation it was excluded from further fitting of that spectrum. All possible combinations of Sn-O, Sn-Sn and Sn-Li paths were explored to ensure the correct model was being used. All spectra were fit using k, k2 and k3 weightings simultaneously to confirm the fitting model was complete in a k-range of 2 – 10 ˚ A−1 . The R-space window was defined as 1.0 – 3.4 ˚ A to fully encompass the first and second atomic shells around the absorbing atom. If no oxygen was present, the



R-range was reduced to 1.7 – 3.4 ˚ A for analysis of the second shell.

RESULTS AND DISCUSSION Figure 1 shows the discharge/charge capacity curves of the first two cycles from both the Sn and SnO2 in situ electrodes. Both the Sn and SnO2 exceed their respective theoretical capacities on the first lithiation (discharge) most likely because of formation of the solid-electrolyte interface (SEI). On the second cycle, the metallic Sn electrode has a low Coulombic efficiency of ca. 36% while the SnO2 electrode has a Coulombic efficiency of ca. 80%. This discrepancy in reversible capacity is an indication of the state of the electrode – a highly reversible capacity indicates lithium atoms are inserted and removed with almost the same efficiency. A low Coulombic efficiency indicates the lithium atoms that are inserted during discharging are not removed during charge, suggesting the electrode has started to degrade.

1.0 0.9

+

Potential (V vs Li/Li )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

0.8 0.7 0.6 0.5

SnO2

0.4

Sn

0.3 0.2 0.1 0.0 0

300

600

900

1200

1500

1800

Capacity (mAh/g)

Figure 1: Discharge and charge capacity curves for the first (solid line) and second (dashed line) cycles for Sn (black) and SnO2 (red) electrodes, during in situ XAS measurements.

XAS Results of the First Lithiation of Metallic Sn Nanoparticles From the data collected during the first lithiation of the metallic Sn electrode, 20 EXAFS spectra corresponding to various states of lithiation (discharge) were analyzed and a selected 8 ACS Paragon Plus Environment

Page 8 of 41

Page 9 of 41

Sn-Sn Metal

.4 0

-3

+

Potential (V vs Li\Li )

1.0

| (Å

)

.6 0

) | (R

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.8

.2 0

0.6

0.4

0

0.2

1 2 3

R ( Å)

4

0.0

Figure 2: 3D representation of selected |χ(R)| plots for the metallic Sn electrode on the first lithiation cycle as a function of electrode potential. number of these are shown in Figure 2 as a 3D representation of |χ(R)| (Fourier transform of k2 χ(k)) as a function of the electrode potential. The initial state of the electrode clearly corresponds to the crystal structure of metallic Sn. As the electrode lithiation progresses, the amplitude of the metallic Sn-Sn peak at ca. 2.9 ˚ A is quickly reduced, indicating an amorphization of the crystal structure. When the electrode potential reaches ca. 0.40 V the original sharp metallic Sn-Sn peak broadens, and when the electrode is at 0.01 V, the peak transitions into two broad peaks spanning the range of 1.5 – 3.0 ˚ A. These peaks indicate large structural disorder in the electrode, and particularly the appearance of new neighboring atoms between ca. 2 – 3 ˚ A. The XANES region of the XAS spectra indicate a change in the average oxidation state of the Sn atoms (Figure 3). At 1.0 V, the electrode is in the initial metallic Sn state as the edge energy (defined as the maximum of the first derivative of xµ(E)) is exactly at 29,200 eV. As the material is being lithiated, the edge position gradually shifts to lower energy, reaching ca. 29,198 eV at 0.40 V and ca. 29,196 eV at 0.01 V. Since the edge position at 0.01 V is lower than metallic Sn, this indicates that Sn is now in a Sn− -type oxidation state 9 ACS Paragon Plus Environment


1.0

Normalized x (E) (arb. units)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 41

1.00 V 0.80 V 0.60 V

0.5

0.40 V 0.20 V 0.05 V

29190

29195

29200

29205

0.0 29175

29200

29225

29250

29275

29300

Energy (eV)

Figure 3: XANES of the metallic Sn electrode as a function of potential in 0.20 V steps. Inset depicts shifts in the edge position. (i.e. Li+ has alloyed with Sn). To quantitatively determine the the structural changes during first lithiation, the EXAFS spectra shown in Figure 2 were modeled using theoretically calculated contributions from Sn-O, Sn-Sn, and Sn-Li neighbors and the results are shown in Figure 4. In the initial OCV state for metallic Sn nanoparticles, there is a small contribution due to oxygen, which is assumed to be surface oxidation of the nanoparticles as no oxidized phases were present in the XRD patterns of the electrode starting materials (Supporting Information Figure S1). This Sn-O contribution is only present during first lithiation with very low number of near neighbors (0.5 ± 0.1 oxygen atoms) and is not observed in later cycles. The Sn-Sn contribution was modeled with the first two Sn-Sn paths (3.01, and 3.16 ˚ A) of the I41/amd metallic Sn crystal structure. 31 The pristine metallic Sn structure remains unchanged until 0.65 V, corresponding to the first plateau observed in the first discharge capacity curve (Fig. 1). Further discharging to 0.60 V results in a significant expansion in both the short and long Sn-Sn interatomic distances (from 3.01 ± 0.01 ˚ A to 3.05 ± 0.01 ˚ A in the shorter and from 3.16 ± 0.01 ˚ A to 3.20 ± 0.01 ˚ A in the longer Sn-Sn paths). Between 0.60 V and 0.40 V the Sn-Sn distances are stable at these expanded values, but


Page 11 of 41

Distance (Å)

3.3

3.2

Sn-Sn

3.1

3.0

2.9

Sn-O 2.1

14

Near Neighbor s

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


12

Sn-Li

10

8

6

4

2

0 1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

+


Figure 4: Number of near neighbors and corresponding interatomic distances for Sn-Sn (black), Sn-O (blue) and combined Sn-Li (red) contributions determined from EXAFS fits of the first lithiation of the metallic Sn electrode as a function of potential.



once the electrode reaches 0.40 V both Sn-Sn distances begin to contract from 3.05 ± 0.01 ˚ A to 2.91 ± 0.01 ˚ A and from 3.20 ± 0.01 ˚ A to 3.10 ± 0.01 ˚ A for short and long distances, respectively, at 0.01 V. The number of neighboring Sn atoms continously drops from 5.0 ± 0.4 atoms in the initial OCV state to 1.0 ± 0.3 at 0.01 V. 8

7

Sn-Li Short Sn-Li Medium

6

Near Neighbor s

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 41

Sn-Li Long

5

4

3

2

1

0

-1

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

+


Figure 5: Number of neighboring lithium atoms at the short, medium and long Sn-Li distances determined from EXAFS fits of the first lithiation of the metallic Sn electrode as a function of potential.

Sn-Li contributions begin to appear at 0.60 V with a total of 3.6 ± 2.3 neighboring lithium atoms from all the relevant Sn-Li paths. The emergence of lithium at 0.60 V is in agreement with previous in situ XRD studies that observe the evolution of a Li-Sn crystal phase at around the same point in the lithiation process. 16 The total number of lithium atoms increases until reaching a stable value of ca. 12 near neighbors at 0.40 V. In a fully lithiated (0.01 V) state, we observe 11.2 ± 1.7 lithium neighboring atoms. If the system was fully converted to Li22 Sn5 , a total of 14 lithium near neighbors would be expected. Figure 5 shows the number of near neighbor fitting results for each of the three Sn-Li paths used to fit all spectra. The distances for each path were determined by fitting the most lithiated (0.01 V) state, and setting those distances for all further modeling as 2.71 ± 0.03 ˚ A, 2.96 ± 0.03 ˚ A and 3.36 ± 0.02 ˚ A for the short, medium and long Sn-Li paths 12 ACS Paragon Plus Environment

Page 13 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


respectively. The number of near neighbors was allowed to vary freely for each individual Sn-Li path. In the potential range from 0.6 V to 0.45 V only medium and long Sn-Li paths could be included in the fits. Once the electrode potential reaches 0.45 V, Sn-Sn distances are stabilized in an expanded state and a contribution from the short Sn-Li path is first observed. As the electrode approaches 0.05 V, a transition is observed in the relative ratio of Sn-Li neighbors as a reduction in the number of lithium atoms located at the longer distance and an increase in the number of lithium atoms located at the shorter distance while the total number of Sn-Li neighbors remains the same. This is also consistent with the decrease in Sn-Sn near neighbors, as lithiation progresses packing more Li into the crystalline structure. Once fully discharged, the number of lithium atoms at each distance is 3.1 ± 0.4, 5.0 ± 0.5 and 3.0 ± 1.6 for the short, medium and long Sn-Li paths respectively. If all the tin had been fully converted to the Li22 Sn5 crystalline phase, those numbers should be 2, 6.5, and 5.5 respectively. Thus our experimental results indicate a significant degree of disorder within the LiSn alloy in the most lithiated state.

XAS Results of the First Lithiation of SnO2 Nanoparticles Analysis of the SnO2 electrode is carried out in much the same way as for the pure Sn described above. Selected |χ(R)| of the SnO2 electrode during the first lithiation are shown in the 3D plot in Figure 6. At 1.00 V, the initial SnO2 crystal structure with both an Sn-O peak at ca. 1.4 ˚ A and an Sn-Sn peak at ca. 3.8 ˚ A are intact. As the electrode potential is reduced to 0.80 V there is a significant reduction in the intensity of both these peaks. By 0.60 V, a new Sn-Sn peak, characteristic of metallic Sn, appears at ca. 2.8 ˚ A with low intensity. As lithiation continues, the Sn-O and metallic Sn-Sn peaks continue to lose intensity, and once in the fully discharged state there are only two broad peaks observed between 1.5 ˚ A and 3 ˚ A. These trends are in agreement with previous XAS studies on tin oxide anodes. 25,26 Figure 7 shows the XANES region of the spectra as a function of electrode potential for SnO2 . The Sn oxidation state changes correlate to changes observed in the |χ(R)|. At 1.00



Sn-O

Sn-Sn Sn-Sn Metal

1.0

1

0.8

0.6

0.4

0

1

+ Potential (V vs Li/Li )

)| | (R

-3 (Å )

2

0.2

2 R ( Å)

3

0.0

4

Figure 6: 3D representation of |χ(R)| plots of SnO2 nanoparticle electrode during the first lithiation.

1.5

Normalized x (E) (arb. units)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 41

1.0

1.00 V 0.80 V 0.60 V 0.40 V

0.5

0.20 V 0.01 V

29190

29195

29200

29205

0.0 29175

29200

29225

29250

29275

29300

29325

29350

Energy (eV)

Figure 7: XANES of SnO2 particles as a function of potential in 0.2 V steps. Inset depicts edge position shifts


Page 15 of 41

V, the edge is at 29,203 eV and by 0.70 V the edge has shifted to 29,200 eV corresponding to the metallic-like state. This is in agreement with the evolution of the Sn-Sn distances seen in Figure 6. When the electrode is in the most lithiated state (0.01 V), the edge moves to 29,198 eV similar to the results for the metallic Sn electrode, indicating the formation of a LiSn alloy. Figure 8 displays the EXAFS fitting results for near neighbors and distances of the SnO and Sn-Sn paths along with the total number of Sn-Li near neighbors. The number of neighboring oxygen atoms drops very quickly in the early stages of lithiation, dropping from 5.9 ± 0.5 oxygen atoms at 1.00 V to 2.8 ± 0.3 neighboring oxygen atoms at 0.80 V. The number of oxygens continues to decrease until 0.05 V where Sn-O paths are no longer observed. Throughout the first lithiation process, the distance between tin and oxygen is quite stable, beginning at 2.05 ± 0.01 ˚ A and decreasing to 2.02 ± 0.03 ˚ A at 0.05 V. 3.8

Distance (Å)

3.6 3.4

Sn-Sn

3.2 3.0

2.0

Near Neighbors

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Sn-O

8

Sn-O 6

Sn-Li

4

Sn-Sn

2

0 1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

+


Figure 8: EXAFS fitting results showing near neighbor and distances for Sn-O (blue squares), Sn-Sn (black circles) and Sn-Li (red triangles) paths on the first lithiation of the SnO2 electrode as a function of potential. 15 ACS Paragon Plus Environment


The Sn-Sn distances of pristine tetragonal SnO2 crystal structure 32 remain unchanged until 0.85 V, however the number of Sn-Sn neighbors continuously decreases from ca. 4 to ca. 1 in this segment. Below this potential, the long-range Sn-Sn neighbors (ca. 3.70 ˚ A ) are no longer observed in the system. For a short period of lithiation between 0.85 V and 0.75 V, no Sn-Sn neighboring atoms are observed within the fitting window of 3.5 ˚ A. Once the electrode approaches 0.70 V, Sn-Sn neighbors with distances characteristic of the metallic tin phase emerge. This metallic tin is in the form of very small clusters as deduced from the reduced number of neighboring atoms (1.0 ± 0.6 Sn atoms opposed to 6 for bulk metallic Sn) and a shifted interatomic distance (2.91 ± 0.02 ˚ A) compared to bulk metallic Sn (3.02 ˚ A). As the lithiation continues, the Sn-Sn distances and number of near neighbors are very stable with no appreciable variation. At the end of the first lithiation, beyond 0.05 V, there are no significant contributions either from Sn-Sn or Sn-O neighbors in the spectra. 4.0

Sn-Li Short 3.5

Sn-Li Medium Sn-Li Long

Near Neighbors

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 41

3.0

2.5

2.0

1.5

1.0

0.5

0.0 0.6

0.5

0.4

0.3

0.2

0.1

0.0

+


Figure 9: Fitting results for individual Sn-Li paths: short (black squares), medium (blue circles) and long (red triangles) for in situ SnO2 electrode as a function of electrode potential on the first lithiation.

Significant contributions from Sn-Li bonds are first observed in the SnO2 electrode at 0.40 V, much further along in the lithiation process compared to the first observation of Sn-Li contributions at 0.80 V in the metallic Sn electrode (Fig. 4). The number of Sn-Li neighbors 16 ACS Paragon Plus Environment

Page 17 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


linearly increases with lithiation from 0.35 V to 0.10 V and at 0.05 V, a significant jump in the total number of Sn-Li neighbors from 5.2 ± 0.9 to 8.0 ± 0.8 is observed, which also coincides with the disappearance of residual Sn-O and Sn-Sn contributions. When SnO2 is in the most lithiated state, 8.2 ± 0.9 lithium atoms are observed around the tin atoms. Figure 9 shows the number of neighboring lithium atoms at the short (2.71 ± 0.03 ˚ A), medium (2.93 ± 0.03 ˚ A) and long (3.43 ± 0.03 ˚ A) Sn-Li distances. In this SnO2 electrode, lithium first appears at short and medium distances, as opposed to the medium and long distances in the metallic Sn electrodes (Fig. 5). The long distance Sn-Li neighbors are observed starting from 0.10 V, when the electrode is close to the most lithiated state. This divergence in the process of lithiation is likely due to the smaller sizes of the metallic tin clusters that form in the SnO2 system and also formation of a Li2 O network surrounding the tin sites. XAS of Discharged and Charged States In addition to the potential-resolved study of the initial lithiation processes of both Sn and SnO2 electrodes, XAS spectra were acquired at each fully discharged and fully charged state of the first two discharge/charge cycles. The fits to the spectra for each electrode and state were conducted using the previously described procedure and presented together in Figures 10 and 11 for comparison. Figure 10 shows the fit results for coordination number and interatomic distances for the Sn-Sn neighbors. In the metallic Sn electrode the transition from OCV to the first lithiated (discharged) state is accompanied by a large reduction in both the number of neighboring tin atoms along with a contraction in the distance between them. The presence of neighboring Sn-Sn atoms in the fully discharged state of the metallic Sn electrode is not consistent with complete conversion to Li22 Sn5 phase indicating that some Sn atoms were not fully lithiated. This is likely due to the inhomogeneity and non-equilibrium nature of lithiation process, where during first lithiation large volumetric expansions of the outer shell of the Sn nanoparticle forms a Li22 Sn5 -like phase, with reduced electrical conductivity and slower



Li ion diffusion. In this situation the core of the nanoparticles (ca. 1 Sn-Sn near neighbor) could get insulated from the rest of the electrode and remain in the metallic Sn phase, while the nanoparticle shell is in a highly lithiated Li22 Sn5 -like phase. In the SnO2 electrode, however, the first most lithiated state exhibits no statistically significant contributions from Sn-Sn neighbors, indicating complete conversion of newly formed Sn clusters to LiSn alloy. In the first delithiated (charged) state, there is a small contribution from Sn-Sn with 0.9 ± 0.2 neighbors at the compressed distances of 2.92 ± 0.01 ˚ A and 3.08 ± 0.01 ˚ A , similar to the environment in the metallic Sn electrode.

Distance (Å)

3.8 3.7

Sn-Sn 3.0

2.9

Near Neighbors

Sn

5

SnO

2

4 3 2 1

C h a rg e 2 n d

D is c h a rg e 2 n d

C h a rg e 1 s t

1 s t

D is c h a rg e

0 O C V

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 41

Figure 10: Comparison of changes in the distance and number of neighboring Sn atoms for OCV, and fully discharged (lithiated) and charged (delithiated) states in the 1st and 2nd cycles for both metallic Sn and SnO2 electrodes. In the second discharged state, both Sn and SnO2 nanoparticles have neighboring metallic tin atoms, indicating incomplete lithiation of Sn atoms as supported by reduced capacity of both electrodes (Fig. 1). The metallic Sn electrode shows no appreciable change in the local tin atomic structure from the first discharged to charged state, indicating a limited amount of reversible lithiation. As the Sn electrode is cycled further, independent of discharged or charged state, the number of neighboring Sn atoms and the Sn-Sn distance increase toward 18 ACS Paragon Plus Environment

Page 19 of 41

values typical of metallic Sn (2.99 ± 0.02 ˚ A after the second charge compared to 3.01 ˚ A for Sn metal). This suggests that larger clusters of metallic Sn are forming, but not participating in the lithiation reaction, and most likely electrically insulated. The SnO2 electrode shows a slight decrease in the number of neighboring Sn atoms in the second discharged state (0.6 ± 0.2 Sn atoms in the second discharged opposed to 0.9 ± 0.2 in the first charge) with no statistically significant change in the distance between them. After the 2nd delithiation, the local Sn environment returns to what was observed in the first delithiated (charged) state. 14

Sn-Li

Near Neighbors

12

10

8

6

Sn SnO

2

C h a rg e 2 n d

2 n d

D is c h a rg e

C h a rg e 1 s t

1 s t

D is c h a rg e

4

O C V

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 11: Comparison of the total number of neighboring lithium atoms in the metallic Sn and SnO2 electrodes during 1st and 2nd cycles. Figure 11 displays the fitting results for the number of lithium near neighbors in the first two cycles for both Sn and SnO2 electrodes. In the first lithiated (discharged) state the metallic Sn electrode has 11.7 ± 1.7 neighboring lithium atoms while the SnO2 electrode has a total of 8.2 ± 0.9 lithium neighbors. The discrepancy between the number of Sn-Li neighbors in Sn and SnO2 electrodes is likely due to the difference in the nanoscale and atomic arrangements around the Sn atoms. The average size of nanoparticles in the metallic Sn electrode is ca. 100 nm, while the metallic tin clusters that form during the first lithiation of SnO2 electrodes are very small, likely on the order of a few atoms. When particles are 19 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

at this size the ratio of surface to bulk atoms is high and a reduction in the number of Sn-Sn neighbors is observed compared to a bulk Sn metal phase. Neither system reaches the expected 14 neighboring lithium atoms typical of the Li22 Sn5 crystal structure, indicating structural disorder and that the entire electrode does not fully convert to this phase. This conclusion is also supported by the low capacity observed past the first lithiation in both electrodes. In the first delithiated (charged) state, there is a small reduction in the number of lithium atoms in the metallic Sn electrode (from 11.7 ± 1.7 to 9.8 ± 1.7), while in the ideal case no SnLi neighbors would be observed in the charged state corresponding to complete delithiation. Upon continued cycling there is a monotomic reduction in the number of lithium neighbor atoms and a corresponding increase in the number of Sn-Sn neighbors, in both discharged and charged states, indicating very poor reversibility of lithium insertion, most likely due to a reduction of electrical conductivity within the active material. This lack of reversibility in lithium insertion and removal is also supported by the poor electrochemical performance of the metallic Sn electrode (Fig. 1). It may be suggested that Li diffusion within the electrode assists in the segregation of Sn atoms into larger clusters, which also become electrically insulated. For the SnO2 electrode, there is an appreciable reduction from 8.2 ± 0.9 Li atoms to 5.9 ± 1.2 Li during the first delithiation, and on the second lithiation the total number of lithium atoms returns close to the amount observed in the first lithiated state. Upon subsequent delithiation, the number of lithium atoms again approaches what was observed for the first delithiated state, indicating better reversibility of lithiation in SnO2 electrodes versus the metallic Sn material but still only partial removal of Li. Interestingly, the Sn clusters in the SnO2 electrode do not grow during subsequent discharge/charge cycles. These local structural changes in both Sn and SnO2 electrodes aligns well with the electrochemical performance displayed in Figure 1. The initial lithiation of both Sn and SnO2 materials is accompanied by a large contribution of irreversible capacity from SEI formation.


Page 20 of 41

Page 21 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


This process is not reflected in EXAFS data as only a minor fraction of Sn surface atoms are directly exposed to SEI. The latter makes it difficult to directly compare the local structural changes determined through EXAFS modeling to the electrochemical capacities on the first lithiation cycle, where majority of the SEI is formed. For that reason the EXAFS results from the first lithiation are correlated to the electrode/cell potentials, not to the experimental capacities. Once SEI is mostly stabilized, on the second lithiation, both Sn and SnO2 electrodes show similar capacities (ca. 600 mAh/g), which correspond well to the similarities in the local structures at this state (Figures 10 and 11). On second delithiatiation the SnO2 electrode exhibits ca. 80% Coulombic efficiency while Sn electrode only ca. 36%. These electrochemical results are supported by the EXAFS, where the SnO2 electrode shows a decrease in Li neighbors upon delithiation (Figure 11). In contrast the metallic Sn electrode has no significant change in the number of Li neighbors for subsequent lithiation cycles, suggesting limited process reversibility and thus, low Coulombic efficiency. Based on this comparison of the electrochemical cycling results and corresponding EXAFS data on the changes in the local atomic environment around tin atoms in both metallic Sn and SnO2 nanoparticle electrodes, the positive effect of using SnO2 as starting electrode material becomes clear. During the first lithiation, metallic Sn nanoparticles undergo large structural changes, evidenced by a continual decrease in the number of Sn-Sn near neighbors throughout the lithiation process, which is also accompanied by expansion and then contraction of the Sn-Sn distances. The loss of the Sn crystal structure during the first lithiation process and amorphization of the electrode results in poor electrical conductivity within the particles which is manifested by the presence of metallic Sn atoms in the most lithiated state and poor reversibility of lithium removal upon charge (Figs. 4 and 11), indicating that these structural changes irreversibly passivate the electrode material. The SnO2 nanoparticles undergo different structural changes during the first lithiation. In the initial stages (1.00 V to 0.40 V) there is clear conversion of SnO2 to metallic Sn and Li2 O. Further lithiation results in full conversion of metallic Sn to LiSn alloy with little



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

variation in the number of tin atoms and the interatomic distances (Fig. 8). It is suggested that Li2 O formed from SnO2 serves as a buffer for mitigating the segregation of metallic Sn into large Sn particles thereby providing structural stability and maintaining sufficient electrical conductivity within the active material as evidenced by the better reversibility of lithium insertion/removal in the first two cycles. It is also worth noting the onset of observable Sn-Li neighbors is quite different in the metallic Sn and SnO2 systems. Sn-Li paths are first observed at ca. 0.80 V in metallic Sn and at ca. 0.40 V in SnO2 . This drastic difference is likely due to the process of converting SnO2 to Sn clusters embedded in a Li2 O matrix before lithiation of tin may begin. Limited electrical conductivity and slow Li diffusion rates through the Li2 O matrix to the metallic Sn domains may also contribute to the limited capacity and reversibility of Li insertion in SnO2 particles. Both electrodes show dramatic capacity fading within the first few cycles. In the case of the metallic Sn electrode, the main issue is the mobility of Sn atoms within the solid phase that results in unsuppressed volumetric expansion to accommodate lithium atoms into the crystal structure. Removal of some Li atoms from expanded SnLi structures on the first delithiation results in the loss of electical conductivity of the electrode material with large fractions of Li remaining in the form of SnLi, regardless of the electrode potential. In the case of the SnO2 electrode, segregation of metallic Sn atomic clusters within the Li2 O matrix during the first lithiation limits the mobility of Sn atoms but also the amount of lithium that can efficiently diffuse to and from the Sn atomic clusters. To achieve better cycle life performance of these tin-based electrodes, careful and intricate atomic and nanoscale engineering of electrode material is required to mitigate the capacity fading mechanisms identified above. In particular, use of Sn compounds that would result in a better conducting network upon Sn reduction to metal, as well as nanoscale confinement of such materials is suggested.


Page 22 of 41

Page 23 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


CONCLUSIONS Comparison of the in situ EXAFS spectra of Sn and SnO2 nanoparticles acquired during the first lithiation, along with discharged and charged states of the first two cycles, provides unique insight into the dynamic picture of atomic changes within the electrodes, indicating the cause for rapid capacity decline. The metallic Sn nanoparticles perform poorly electrochemically, and this is due to the large structural alterations observed during the first lithiation including ca. 11 lithium atoms that get inserted within a 3.4 ˚ A distance from each tin atom when fully discharged. Further cycling is accompanied by minimal structural alterations, indicating that lithium is no longer being reversibly inserted or removed from the anode material, likely due to the loss of electrical conductivity. The SnO2 system creates metallic Sn atomic clusters within the amorphous Li2 O matrix that forms during the early stages of the first lithiation process. This material exhibits much more reversible behavior with ca. 2 lithium atoms per tin being removed and re-inserted on the first two discharge/charge cycles. From these results it is clear that Li2 O is essential to controlling the volumetric expansions experienced by Sn during Li insertion, however the electrically insulating nature of Li2 O and full encapsulation of formed metallic Sn clusters in the SnO2 system limits Li diffusion and the overall conductivity of the system. Next generation Sn-based anodes for LIBs must consist of a composite electrode using a material that promotes Li ion diffusion pathways along with electrical conductivity throughout but also restricts the size of the Sn clusters so that volume expansion does not result in the loss of electrical contact within the rest of the electrode.

Supporting Information Available Representative EXAFS fits in k2 χ(k), Re[χ(R)] and |χ(R)| along with a table of detailed



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 41

fitting results for both SnO2 and Sn EXAFS fits. XRD of starting Sn and SnO2 nanoparticles is also presented.

This material is available free of charge via the Internet at http:

//pubs.acs.org/.

ACKNOWLEDGEMENTS C.J.P was supported by a Department of Education GAANN Fellowship, award #P200A090137. The project is supported by US Department of Energy, Office of Basic Energy Science and the Advanced Research Project Agency–Energy (ARPA–E) under Award #AR–000387. MRCAT operations are supported by the Department of Energy and the MRCAT member institutions. Use of the Argonne National Laboratory Advanced Photon Source is supported by the U.S. Department of Energy, under Contract No. DE–AC02–06CH11357.


Page 25 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


References (1) Reynier, Y. F.; Yazami, R.; Fultz, B. Thermodynamics of Lithium Intercalation into Graphites and Disordered Carbons. J. Electrochem. Soc. 2004, 151, A422–A426. (2) Wang, C.; Li, D.; Too, C.; Wallace, G. Electrochemical Properties of Graphene Paper Electrodes Used in Lithium Batteries. Chem. Mater. 2009, 21, 2604–2606. (3) Armand, A.; Tarascon, J. M. Building Better Batteries. Nature 2008, 451, 652–657. (4) Lu, L.; Han, X.; Li, J.; Hua, J.; Ouyang, M. A Review on the Key Issues for Lithium-Ion Battery Management in Electric Vehicles. J. Power Sources 2013, 226, 272–288. (5) Terada, N.; Yanagi, T.; Arai, S.; Yoshikawa, M.; Ohta, K.; Nakajima, N.; Yanai, A.; Arai, N. Development of Lithium Batteries for Energy Storage and EV Applications. J. Power Sources 2001, 100, 80–92. (6) Beaulieu, L. Y.; Ebermand, K. W.; Turner, R. L.; Krause, L. J.; Dahn, J. R. Colossal Reversible Volume Changes in Lithium Alloys. Electrochem. Solid-State Lett. 2001, 9, A137–A140. (7) Courtney, I. A.; Dahn, J. R. Electrochemical and In Situ X-ray Diffraction Studies of the Reaction of Lithium with Tin Oxide Composites. J. Electrochem. Soc. 1997, 144, 2045–2052. (8) Ding, S.; Luan, D.; Boey, F. Y. C.; Chen, J. S.; Lou, X. W. SnO2 Nanosheets Grown on Graphene Sheets with Enchanced Lithium Storage Properties. Chem. Commun. 2011, 47, 7155–7157. (9) Yuan, L.; Guo, Z. P.; Konstantinov, K.; Liu, H. K.; Dou, S. X. Nano-Structured Spherical Porous SnO2 Anodes for Lithium-Ion Batteries. J. Power Sources 2006, 159, 345– 348.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(10) Kim, C.; Noh, M.; Choi, M.; Cho, J.; Park, B. Critical Size of Nano SnO2 Electrode for Li-Secondary Battery. Chem. Mater. 2005, 17, 3297–3301. (11) Pelliccione, C.; Timofeeva, E.; Segre, C. U. In Situ X-ray Absorption Spectroscopy Study of the Capacity Fading Mechanism in Hybrid Sn3 O2 (OH)2 /Graphite Battery Anode Nanomaterials. Chem. Mater. 2015, 85, 126108. (12) Brousse, T.; Retoux, R.; Herterich, U.; Schleich, D. M. Thin-Film Crystalline SnO2 Lithium Electrodes. J. Electrochem. Soc. 1998, 145, 1–4. (13) Wang, Y.; Sakamoto, J.; Kostov, S.; Mansour, A.; denBoer, M.; Greenbaum, S. G.; Huang, C.-K.; Surampudi, S. Structural Aspects of Electrochemically Lithiate SnO: Nuclear Magnetic Resonance and X-ray Absorption Studies. J. Power Sources 2000, 89, 232–236. (14) Chouvin, J.; Branci, C.; Sarradin, J.; Oliver-Fourcade, J.; Jumas, J. C.; Simon, B.; Biensan, P. Lithium Intercalation in Tin Oxide. J. Power Sources 1999, 81-82, 277– 281. (15) Poizot, P.; Laruelle, S.; Grugeon, S.; Dupont, L.; Tarascon, J.-M. Nano-Sized Transition-Metal Oxides as Negative-Electrode Materials for Lithium-Ion Batteries. Nature 2000, 407, 496–499. (16) Rhodes, K. J.; Meisner, R.; Kirkham, M.; Dudney, N.; Daniel, C. In Situ XRD of Thin Film Tin Electrodes for Lithium Ion Batteries. J. Electrochem. Soc. 2012, 159, A294–A299. (17) Chouvin, J.; Vicente, C. P.; Oliver-Fourcade, J.; Jumas, J.-C.; Simon, B.; Biensan, P. Deeper Insight on the Lithium Reaction Mechanism with Amorphous Tin Composite Oxides. Solid State Sci. 2004, 6, 39–46.


Page 26 of 41

Page 27 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(18) Connor, P.; Irvine, J. Combined X-ray Study of Lithium (Tin) Cobalt Oxide Matrix Negative Electrodes for Li-Ion Batteries. Electrochimica Acta 2002, 47, 2885–2895. (19) Mansour, A. N.; Mukerjee, S.; Yang, X. Q.; McBreen, J. In situ XAS of the Reaction Mechanism of Lithium with Tin-Based Composite Oxide. J. Synchrotron Radiat. 1999, 6, 596–598. (20) Zhang, W.; Duchesne, P.; Gong, Z. L.; Wu, S. Q.; Ma, L.; Jiang, Z.; Zhang, S.; Zhang, P.; Mi, J. X.; Yang, Y. In Situ Electrochemical XAFS Studies on an Iron Fluoride High-Capacity Cathode Material for Rechargeable Lithium Batteries. J. Phys. Chem. C 2013, 117, 11498–11505. (21) Chouvin, J.; Oliver-Fourcade, J.; Jumas, J. C.; Simon, B.; Biensan, P.; Madrigal, F. J. F.; Tirado, J. L.; Vicente, C. P. SnO Reduction in Lithium Cells: Study by Xray Absorption, 119 Sn Mossbauer Spectroscopy and X-ray Diffraction. J. Electroanal. Chem. 2000, 494, 136–146. (22) Jung, H. R.; Lee, W. J. Electrochemical Characterization of Electrospun SnOx Embedded Carbon Nanofibers Anode for Lithium Ion Battery with EXAFS Analysis. J. Electroanal. Chem. 2011, 662, 334–342. (23) Goward, G. R.; Leroux, F.; Power, W. P.; Ouvrard, G.; Dmowski, W.; Egami, T.; Nazar, L. F. On The Nature of Li Insertion in Tin Composite Oxide Glasses. Electrochem. Solid-State Lett. 1999, 2, 367–370. (24) Yoon, S.; Lee, J. M.; Kim, H.; Im, D.; Doo, S. G.; Sohn, H. J. An Sn-Fe/Carbon Nanocomposite as an Alternative Anode Material for Rechargeable Lithium Batteries. Electrochim. Acta 2009, 54, 2699–2705. (25) Kim, H.; Park, G.; Kim, Y.; Muhammad, S.; Yoo, J.; Balasubramanian, M.; Cho, Y.H.; Kim, M.-G.; Lee, B.; Kang, K.; et al. New Insight into the Reaction Mechanism



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

for Exceptional Capacity Ordered Mesoporous SnO2 Electrodes via Synchrotron-Based X-ray Analysis. Chem. Mater. 2014, 26, 6361–6370. (26) Kisu, K.; Iijima, M.; Iwama, E.; Saito, M.; Orikasa, Y.; Naoi, W.; Naoi, K. The Origin of Anomalous Large Reversible Capacity for SnO2 Conversion Reaction. J. Mater. Chem. A 2014, 2, 13058. (27) Pelliccione, C. J.; Ding, Y.; Timofeeva, E. V.; Segre, C. U. In Situ XAFS Study of the Capacity Fading Mechanisms in ZnO Anodes for Lithium-Ion Batteries. J. Electrochem. Soc. 2015, 162, A1935–A1939. (28) Pelliccione, C.; Timofeeva, E.; Katsoudas, J.; Segre, C. Note: Sample Chamber for In Situ X-ray Absorption Spectroscopy Studies of Battery Materials. Rev. Sci. Instrum. 2014, 84, 126108. (29) Ravel, B.; Newville, M. ATHENA, ARTEMIS, HEPHAESTUS: Data Analysis for X-ray Absorption Spectroscopy using IFEFFIT. J. Synchrotron Radiat. 2005, 12, 537–541. (30) Newville, M. IFEFFIT: Interactive EXAFS Analysis and FEFF Fitting. J. Synchrotron Radiat. 2001, 8, 322–324. (31) Swanson, H. E.; Tatge, E. Standard X-ray Diffraction Powder Patterns. National Bureau of Standards (U.S.) 1953, 539, 1–95. (32) Baur, W.; Khan, A. Rutile-type Compounds VI. SiO2 , GeO2 and a Comparison with other Rutile-Type Structures. Acta Crystallogr. B 1971, 27, 2133–2139. (33) Hansen, D.; Chang, L. Crystal Structure of Li2 Sn5 . Acta Crystallogr. B 1969, 25, 2392–2395. (34) Blase, W.; Cordier, G. Crystal Structure of beta-Lithium Stannide, beta-LiSn. Zeitschrift fuer Kristallographie 1990, 193, 317–318.


Page 28 of 41

Page 29 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(35) Frank, U.; Mueller, W.; Schaefer, H. Die Struktur der Phase Li5 Sn2 . Zeitschrift fuer Naturforschung 1975, 30, 1–5. (36) Frank, U.; Mueller, W.; Schaefer, H. Die Kristallstruktur der Phase Li7 Sn2 . Zeitschrift fuer Naturforschung 1975, 30, 6–9. (37) Gladyshevskii, E.; Oleksiv, G.; Kripyakevich, P. New Examples of the Structural Type Li22 Pb5 . Soviet Physics, Crystallography 1964, 9, 269–271.



TOC Entry Li+

SnO2

1st lithia+on

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Li+

LixSn + Li2O


Page 30 of 41

1 .0

Page 31 of 41

P o te n tia l ( V v s L i/L i+ )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39


0 .9 0 .8 0 .7 0 .6 0 .5

S n O

0 .4 0 .3

2

S n

0 .2 0 .1 0 .0 0

3 0 0

6 0 0

9 0 0

1 2 0 0

ACS Paragon Plus Environment

C a p a c ity ( m A h /g )

1 5 0 0

1 8 0 0


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

Page 32 of 41

S n -S n M e ta l

0 .6

1 . 0

0 . 8

2 0.

0 . 6

0

0 .4

0 .2

1 2

3


R

(Å )

4

0 .0

P o t e n t ia l ( V v s L i\ L i +)

-3 ) Å ( | χ( R ) |

4 0.

Page 33 of 41

N o r m a l i z e d x µ( E ) ( a r b . u n i t s )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38


1 .0

1 .0 0 .8 0 .6 0 .4 0 .2 0 .0

0 .5

2 9 1 9 0

2 9 1 9 5

2 9 2 0 0

0 V 0 V 0 V 0 V 0 V 5 V

2 9 2 0 5

0 .0 2 9 1 7 5

2 9 2 0 0

2 9 2 2 5

2 9 2 5 0


E n e rg y (e V )

2 9 2 7 5

2 9 3 0 0


3 .3

N e a r N e ig h b o r s

D is ta n c e ( Å )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52

Page 34 of 41

3 .2

S n -S n

3 .1 3 .0 2 .9

S n -O

2 .1 1 4 1 2

S n -L i

1 0 8 6 4 2 0 1 .0

0 .9

0 .8

0 .7

0 .6

0 .5

0 .4


0 .3 +

P o te n tia l ( V v s L i/L i )

0 .2

0 .1

0 .0

8

Page 35 of 41

7

S n -L i S h o rt S n - L i M e d iu m S n -L i L o n g 6 5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43


4 3 2 1 0 -1 1 .0

0 .9

0 .8

0 .7

0 .6

0 .5

0 .4


+

0 .3

P o te n tia l ( V v s L i/L i )

0 .2

0 .1

0 .0


S n -O

S n -S n S n -S n M e ta l

2

1 . 0

1

0 . 8

0 . 6

0

0 . 4

1

0 . 2

R

2 3


(Å )

4

0 .0

P o t e n t ia l ( V v s L i/ L i +)

-3 ) Å ( | ) | χ( R

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46

Page 36 of 41

1 .5

Page 37 of 41

N o r m a l i z e d x µ( E ) ( a r b . u n i t s )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47


1 .0

1 .0 0 .8 0 .6 0 .4 0 .2 0 .0

0 .5

2 9 1 9 0

2 9 1 9 5

2 9 2 0 0

0 V 0 V 0 V 0 V 0 V 1 V

2 9 2 0 5

0 .0 2 9 1 7 5

2 9 2 0 0

2 9 2 ACS 2 5 Paragon2 Plus 9 2 5 Environment 0 2 9 2 7 5

E n e rg y (e V )

2 9 3 0 0

2 9 3 2 5

2 9 3 5 0

3 .8

Page 38 of 41

3 .6


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53


3 .4

S n -S n

3 .2 3 .0

2 .0

S n -O


8

S n -O 6

S n -L i 4

S n -S n 2 0 1 .0

0 .9

0 .8

0 .7

0 .6

0 .5

0 .4


0 .3


0 .2

0 .1

0 .0

Page 39 of 41

4 .0


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


S n -L i S h o rt S n - L i M e d iu m S n -L i L o n g

3 .5 3 .0 2 .5 2 .0 1 .5 1 .0 0 .5 0 .0 0 .6

0 .5

0 .4

0 .3


0 .2


0 .1

0 .0

3 .8

Page 40 of 41

3 .7

S n -S n 3 .0

2 .9

S n

5


S n O

4 3 2 1

2n d

2n d

D


is

1s tC

1s tD

is

C

ha rg e

ch ar ge

ha rg e

C

V

ch ar ge

0 O


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


2

1 4

Page 41 of 41

S n -L i

1 2

1 0

8

6

S n S n O 2

D

ha rg e 2n d

is

C

ch ar ge

ha rg e ACS Paragon Plus Environment

2n d

is 1s tD

1s tC

C

V

ch ar ge

4

O


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


Potential-Resolved In Situ X-ray Absorption ... - ACS Publications

Recommend Documents