Is the Solid Electrolyte Interphase an Extra-Charge ... - ACS Publications

Research Article www.acsami.org

Is the Solid Electrolyte Interphase an Extra-Charge Reservoir in Li-Ion Batteries? S. Javad Rezvani,*,† Roberto Gunnella,† Agnieszka Witkowska,‡ Franziska Mueller,§,∥,⊥ Marta Pasqualini,∇ Francesco Nobili,∇ Stefano Passerini,§ and Andrea Di Cicco† †

Physics Division, School of Science and Technology, University of Camerino, 62032 Camerino (MC), Italy Department of Solid State Physics, Gdańsk University of Technology, 80-309, Gdansk, Poland § Helmholtz Institute Ulm (HIU), Albert-Einstein-Allee 11, 89081 Ulm, Germany ∥ Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany ⊥ Institute of Physical Chemistry, University of Muenster, Corrensstrasse 28/30, 48149 Muenster, Germany ∇ Chemistry Division, School of Science and Technology, University of Camerino, 62032 Camerino (MC), Italy ‡

S Supporting Information *

ABSTRACT: Advanced metal oxide electrodes in Li-ion batteries usually show reversible capacities exceeding the theoretically expected ones. Despite many studies and tentative interpretations, the origin of this extra-capacity is not assessed yet. Lithium storage can be increased through different chemical processes developing in the electrodes during charging cycles. The solid electrolyte interface (SEI), formed already during the first lithium uptake, is usually considered to be a passivation layer preventing the oxidation of the electrodes while not participating in the lithium storage process. In this work, we combine high resolution soft X-ray absorption spectroscopy with tunable probing depth and photoemission spectroscopy to obtain profiles of the surface evolution of a well-known prototype conversion-alloying type mixed metal oxide (carbon coated ZnFe2O4) electrode. We show that a partially reversible layer of alkyl lithium carbonates is formed (∼5−7 nm) at the SEI surface when reaching higher Li storage levels. This layer acts as a Li reservoir and seems to give a significant contribution to the extra-capacity of the electrodes. This result further extends the role of the SEI layer in the functionality of Li-ion batteries. KEYWORDS: solid electrolyte interphase, X-ray absorption spectroscopy, Li-ion battery, X-ray photoemission spectroscopy, metal alloying oxide anodes, extra-capacity

1. INTRODUCTION Lithium ion batteries using different types of high energy density electrodes are extensively used in electronic devices and are still under vast investigations due to their capability of future applications.1−3 Mixed metal oxide electrodes exchange lithium through reversible conversion and subsequent alloying reactions reaching higher specific capacity compared to conventional lithium insertion electrodes.4−9 The lithiation process of metal oxide electrodes is mainly associated with the reduction of metal ions with Li-ion involvement, but the measured capacities are often found to exceed the expected ones. Presently, the origin of this additional reversible capacity is not fully understood, and its explanation may represent a step forward for developing even more performant Li-ion cells. Different phenomena have been indicated as possible sources for extra-capacity, for example, the reversible reaction of LiOH to form LiH,10 as well as the decomposition of LiF to form transition metal fluorides, on the basis of the suggestion that additional lithiation results from the formation of a so-called © 2017 American Chemical Society

space charge region at the interface of the metal with Li salt particles.11−13 Transmission electron microscopy of MxOy electrodes has also shown formation of a polymer-gel-like film at the grain boundaries of the nanoparticles at low potentials,14 possibly associated with such extra-lithiation capabilities. It is well-known that the anode often operates outside the voltage stability window of the electrolyte components, while cycling a Li-ion cell. The electrolyte decomposition leads to the formation of a protective layer called SEI (solid electrolyte interphase)15 at electrochemically active sites. The electron insulation caused by SEI layer prevents further oxidation of the anode in contact with the electrolyte salt and solvents while the ionic conductivity of this layer facilitates the battery performance.16−18 Decomposition of the electrolyte salt initiates almost Received: September 29, 2016 Accepted: January 13, 2017 Published: January 13, 2017 4570

DOI: 10.1021/acsami.6b12408 ACS Appl. Mater. Interfaces 2017, 9, 4570−4576

Research Article

ACS Applied Materials & Interfaces

Figure 1. ZFO-C samples used in present experiments belong to different lithiation regions (A−C) and are marked by the corresponding voltage (GITT diagram in panel a). Main chemical species identified by spectral features in the C, Li, and O K-edge X-ray absorption spectra are indicated by dashed lines (panels b, c, e, f). Absorption spectra were obtained by total electron yield (TEY) and total fluorescence yield (TFY) experiments (see panel d). Details: (a) Open-circuit potential (E) vs specific capacity (Q) of the ZFO-C electrodes obtained during first lithiation (L) and delithiation (D). (b) Carbon K-edge TEY spectra for ZFO-C electrodes corresponding to specified potentials. (c) Lithium K-edge TEY spectra for ZFO-C electrodes corresponding to specified potentials. The Pt spectral feature is due to the beamline optics. (d) Schematic of the TEY (drain current measurement) and TFY (fluorescence measurement) techniques with corresponding typical effective probing depths (EPD). (e, f) Oxygen K-edge TEY (e) and TFY (f) spectra for ZFO-C electrodes corresponding to specified potentials.

during the charging−discharging process and after several cycles. Here, zinc iron oxide ZnFe2O4 (ZFO-C) is taken as an exemplary material for metal oxide anodes showing larger capacities (exceeding 1200 mAh/g)8,25−27 than the expected ones (∼1000 mAh/g) on the basis of the conversion and alloying mechanism. XAS is known to be a powerful technique to investigate oxidation states and evolution of the short-range structure while being element specific. By using tunable synchrotron radiation at different absorption edges (Li, O, C), we have been able to target the evolution of selected chemical species in complex systems (see ref 26 and references therein). As a further advantage, XAS spectra are surface-sensitive, and two different detection techniques are used with different probing depths. In particular, total electron yield (TEY) and total fluorescence yield (TFY) show effective probing depths (EPD) of 2−10 and 50−100 nm, respectively, facilitating a depth dependent structural analysis during the ZFO-C conversion reaction. XPS is used to get quantitative information about the presence of chemical species in the uppermost SEI layers, using a typical maximum probing depth of ∼5 nm. The combination of XAS and XPS thus makes it possible to provide chemical-selective depth-profiling in a range covering the entire thickness of the SEI (10−40 nm).

instantly, and the SEI layer is believed to be formed within the first half cycle of the battery operation.16 The redox process of the electrolyte salts results in formation of LiF and LiPFx which can be present in the whole SEI layer while the decomposition of the electrolyte carbonate solvents can lead to formation of Li2CO3 that is considered to be one of the SEI main components formed during the lithiation−delithiation process.19−22 Generally speaking, complex chemical reactions leading to composition and concentration gradients at the interface between the electrodes and the electrolyte take place during the charging−discharging cycles (see, for example, ref 23). Improved performances (higher capacity) of the batteries can be expected if this complex set of chemical reactions could be rationalized and optimized. Hence, a detailed profile of the core electrode structure along with the passivation layer formed on the surface can improve the understanding of the role of different components in the functionality of the Li-ion battery electrodes. In this work we combine soft X-ray absorption (XAS) along with X-ray photoemission spectroscopy (XPS)24 in order to obtain a detailed profile of the surface structure of well-known mixed metal oxide (carbon coated ZnFe2O4) electrodes8,25 during the first lithiation−delithiation cycle, and after 20 lithiation−delithiation cycles. The specific aim is to identify formation and location of different compounds containing Li (and possible Li extra-storage components) within the SEI 4571


Research Article


2. RESULTS AND DISCUSSION The ZFO-C electrodes under consideration were prepared using carbon coated ZnFe2O4 particles, with the structural properties described in the Supporting Information, following the procedures described in previous works8,25−27 and briefly described in the Supporting Information. Electrodes at selected lithiation levels were prepared, stored under controlled conditions, and inserted into the sample chambers for X-ray measurements (see for example refs 26 and 28 for XAS and XPS, respectively). The electrochemical performance of the electrodes was measured by galvanostatic intermittent titration technique (GITT), as shown in Figure 1a, and the results are in line with previous findings.8,25−27 GITT measurements24 were performed, as a series of galvanostatic steps (10 min each) at a current rate C/20, corresponding to 50 mAg−1, followed by open-circuit relaxation periods of 60 min. Open-circuit potential OCV (E) versus equilibrium capacity (Q) profile upon lithiation, resulting from by GITT measurements (Figure 1a), can be subdivided into three main regions (A, B, and C of Figure 1a). In region A the potential decreases rapidly to 1.0 V and then to 0.9 V with a lower slope corresponding to the first lithium insertion into the vacant octahedral 16c site of the spinel structure of ZnFe2O4.8,29,30 The second region (B) with a plateau from 0.9 V followed by a sloping region to 0.5 V corresponds to the complete conversion of the ZnFe2O4 to Zn0, Fe0, and Li2O corresponding to 889 mAh g−1.8 The formation of an SEI layer and its saturation also occur in this potential region. In the final regime (C), a continuous voltage drop is measured approaching a cutoff potential of 0.015 V which corresponds to the LiZn alloy formation in the fully amorphous phases of highly dispersed Fe0 and LiO2.8,31,32 It is well-known that the SEI layer is formed within the first lithiation, and its thickness is practically stable after this first cycle. On the other hand, it has been shown that the capacity of ZFO electrodes approaches stabilization afterward, typically after 20 cycles.8 Hence, in order to study the chemical and structural evolutions of the SEI layer and determine its effect on the overall capacity of the battery, we performed soft X-ray absorption spectroscopy (XAS) measurements at Li K-edge, O K-edge, and C K-edge for the set of ZFO-C electrodes obtained during the first cycle and after 20 cycles as shown in Figure 1b− f. The cycled samples were kept at maximum delithiation (3 V) to identify the reversibility of the structural evolutions. XAS measurements were obtained in total electron yield (TEY) and total florescence yield (TFY) modes with effective probing depths of around 2−10 and 50−100 nm, respectively.26 These probing depths facilitate depth profiling throughout the whole SEI layer. In Figure 1b we report the XAS TEY spectra taken at the C K-edge, after proper background subtraction and normalization to the incident photon flux. Those spectra show two initial major peaks at 285 and 289 eV (see dashed lines), corresponding to single bond π states attributed to CC bonds of an amorphous carbon mixture of the encapsulated nanoparticle and −CH2 elements of the EC solvent and CMC binder.33−35 A sharp peak observable at 291 eV corresponds to single bond π state absorption of Li2CO3 followed by two peaks at 298.3 and 301.3 eV corresponding to the double C bond σ states of Li2CO3.36,37 Carbonates are thus formed up to 0.7 V during the lithiation half cycle. Proceeding with lithiation, i.e., at voltages below 0.7 V, continuous reduction processes involving the electrolyte dramatically modify the C 1s core level

absorption spectra. At 0.5 and 0.015 V charge states, corresponding to the two last reduction potentials in the first lithiation half cycle, the abrupt increase of a component at ∼289 eV is clearly observed (blue dashed line in Figure 1). This metastable component (attributed to ROCO2Li) is subsequently reduced in intensity during the delithiation process (D1.4 V−D3 V), and at the end of the first cycle the two components at 289 and 291 eV show similar intensities. The C 1s XAS spectrum of the cycled sample (20 cycles) also indicates a predominant carbonate peak. The Li XAS K-edge TEY spectra shown in Figure 1c are also particularly interesting and confirm lithiation of chemical species containing carbon. Presence of Li2CO3 is indicated by clear features at 62 eV and by a major resonance around 67 eV38,39 (see dashed lines in the figure). Again, at potentials below 0.7 V (region C) the XAS spectra show clear extrafeatures growing at 61 and 66.5 eV, compatible with the metastable component identified in the C K-edge XAS spectra (blue dashed line, ROCO2Li in Figure 1). Similarly to the C Kedge case, the 20 cycle sample shows an increase of the Li2CO3 feature at 62 eV and a reduction of the metastable ROCO2Li component at 61 eV. Another component at 59 eV is visible below D0.79 V which can be attributed to the Li−C phase. The Li−C is a result of the Li intercalation within the electrode amorphous carbon which will be discussed in detail later. Formation of Li2O at the anode surface is expected within the overall redox process taking place in ZFO-C electrodes as shown in eq 1. ZnFe2O4 + 9Li+ + 9e− ↔ LiZn + 2Fe 0 + 4Li 2O

(1)

Weak Li2O spectral features38,39 can be observed within the initial stages of the lithiation process (region A in Figure 1a), but those features are negligible for potentials below 0.79 V and in the 20 cycle sample. The disappearance of the Li2O signal indicates that this oxide is formed mostly in the vicinity of the electrode active nanoparticles (or in deep layers of the electrode), in regions that are almost instantly covered by the SEI layer. The typically short probing depth (2 nm) of Li Kedge XAS and the thickness of the SEI (up to 40 nm) justify this observation. The formation of a thick SEI also prevents the observation of the LiZn phase formation expected to occur at low potentials (region c in Figure 1a). Figure 1c also provides evidence of an interchange between LiF (62 and 69 eV)38,40 and Li2CO3, from the very first stages of the lithiation process. This is compatible with a dynamical rearrangement of the surface region alternating LiF and lithium carbonate as major species. The endurance of a LiF peak indicates that the SEI contains phases directly associated with the electrolyte decomposition in the whole layer thickness. In fact, the electrolyte salt undergoes a redox process (eq 2), which results in the formation of LiF phases present in the SEI layer. However, the increasing alkyl carbonate signal with respect to LiF and the constant LiF signal within the whole cycle further indicate the formation of a reversible alkyl carbonate on top of the SEI layer. This also rules out the possibility of the alkyle carbonate coverage by such phases. LiPF6 ↔ LiF ↓ + PF5 +

PF5 + 2x Li + 2x e− ↔ LixPF5 − x ↓ +x LiF↓

(2)

The O K-edge XAS spectra measured by TEY and TFY techniques are shown in panels e and f of Figure 1. Those two experiments are characterized by very different probing depths 4572


Research Article

ACS Applied Materials & Interfaces as shown in Figure 1d. Typical probing depths are ∼5 and ∼30 nm for O K-edge TEY and TFY spectra (photon energy ∼540 eV), respectively. The formation of lithium carbonate, represented by the three main features at 533.7, 539.4, and 544.5 eV is clearly observable from the very beginning in the TEY O K-edge spectra (Figure 1e).38,39 Upon further lithiation, the Li2CO3 features at 539.4 and 544.5 eV tend to decrease (below 0.7 V) and are recovered upon delithiation (above 1.4 V). An extra-feature around 533 eV, very near to the Li2CO3 peak at 533.7 eV, is clearly observable during lithiation below 0.79 V and delithiation up to about 2 V. This feature is compatible with the formation of a new metastable carbonate phase (blue dashed line, ROCO2Li) which may also affect other spectral regions with broadened features. The TEY O K-edge spectra also indicate that the SEI formation starts within the initial charging steps as previously found (see for example26) since the peak at 529.6 eV, corresponding to the Fe−O component of the electrode nanoparticles, and the peak at 531.5 eV, corresponding to the C−O−H bonds in the binder, disappear even at potentials as high as 1.02 V.35,41,42 The probing depth of TFY experiments is almost 1 order of magnitude larger than that of TEY allowing the study of the deeper layers of the SEI, i.e., in contact with the ZFO-C particles. In fact, O K-edge TFY spectra of the pristine sample clearly show peaks related to the Fe−O (ZFO-C) and C−O (ZFO-C and binder) bonds at 529.6 and 531.5 eV photon energy, respectively (see Figure 1f). Further lithiation introduces new components to the spectra at 533.7, 539.4, and 544.5 eV, which are signature peaks of lithium carbonate formed in the structure. The shoulder observed at 544.5 is assigned to Li2O, and its decrease upon lithiation (at 0.79 V) is associated with the SEI growth which attenuates the XAS signal. However, the XAS signal is superimposed with another Li2CO3 feature, and a quantitative evaluation of lithium oxide is not possible. The absence in O K-edge TFY spectra of detectable features (extra-peak or broadening at 533.7 eV) associated with the metastable formation of lithium alkyl carbonate indicate that this substance is formed only on the topmost SEI layer. The SEI formation reaches its saturation at around 0.79 V as also expected by previous GITT and XAS results.26,27 The Fe−O XAS contribution (529.6 eV) is completely quenched after 0.79 V, indicating that a thick SEI layer attenuates the electrode signal. Our XAS results clearly indicate formation of a secondary carbonaceous component occurring below 0.7 V (lithiation, region C), superimposed on that of lithium carbonate. Formation of lithium carbonate phases due to the reduction of the EC and CMC present in the electrode porosity is compatible with single- and double-electron reduction processes as reported in eqs 3 and 4, while nucleophilic attack on EC in the presence of DMC is related to another possible reaction path described by eq 5.

These reactions can explain the carbonate formation and the building up of a SEI layer in which different lithiated carbonates compete in building up the SEI, especially in the uppermost layer. The surface and chemical sensitivity of X-ray photoemission spectroscopy (XPS) was used to get a deeper insight on the evolution of the uppermost SEI layers, i.e., in direct contact with the electrolytic salt. The C 1s XPS spectra reported in Figure 2 have been collected using a laboratory source (Al Kα,

Figure 2. C 1s XPS spectra of ZFO-C electrodes (hν = 1486.6 eV; EPD ∼ 5 nm) collected at selected points during the charge−discharge cycles and for a multiply cycled sample (20 cycle). XPS spectra are compared with the results of a peak-fitting analysis including different carbon components. The interchange of the XPS peaks related to lithium carbonate (peak A) and alkyl lithium carbonate (peak B) is clearly visible during the charging cycle.

photon energy hν = 1486.6 eV) and an hemispherical analyzer (see for example ref 28 and references therein). The kinetic energy of the collected photoelectrons (Ekin ∼ 1200 eV) corresponds to a typical electron mean free path of ∼2 nm and to maximum EPDs of about 5 nm. Standard peak-fitting analysis has been carried out on the XPS spectra reported in Figure 2, in which specific peaks are associated with the various chemical components (highlighted with colors in the figure). The presence of C−C bonding (284.2 eV), associated with the carbon encapsulated ZFO-C particles and amorphous carbon, along with the presence of −CH2 (285.2 eV) and C−O (287.3 eV) components (EC and Na-CMC) are clearly visible in the pristine electrode.23 Within the initial lithiation stages, a new prominent component at 288.9 eV (peak A), assigned to the formation of carbonates, appears. Upon further lithiation (below 0.5 V), the carbonate component ratio is reduced, and an additional contribution is found to increase (286.5 eV, peak B). This component is assigned to the formation of lithium alkyl carbonate (e.g., CH2OCO2Li), as a result of a

2EC + 2e− + 2Li+ → CH 2CH 2 + 2(CH 2OCO2 Li) (single‐electron)

(3)

EC + 2e− + 2Li+ → Li 2CO3 + CH 2CH 2 (double‐electron) ROLi + EC → Li 2CO3 + (CH 2OCO2 Li)

(4) (5) 4573


Research Article


Figure 3. Top: Trend of Li storage in the superficial SEI layer (below 0.7 V) by alkyl lithium carbonates as monitored by the corresponding intensity of the ROCO2Li component at the XAS C K-edge (see marked points of different colors). The ROCO2Li thickness reaches its maximum at 0.015 V, corresponding to the maximum of Li+ content (right-hand panel). Bottom: Sketch of the SEI formation on the ZFO-C particles during the charging−discharging cycle (E potential vs Q capacity), distribution, and evolution at each stage of the lithiation−delithiation cycle obtained by the relevant experimental results. The arrows indicate increase or decrease of the specified component thickness.

reduction, similar to reaction 3.43 During the delithiation process (above 2 V), an increase of peak A (lithium carbonate) is again observed. These results indicate that a dynamic, reversible, redox process is occurring within the uppermost superficial layers of the SEI (within ∼5−7 nm) as shown by the substitution of the XPS peaks of stable carbonate with those of alkyl Li carbonates. The extension of this layer is calculated considering the probing depths of the containing elements within the specific phase. A Li−C component (peak C) was also observed at the maximum reduction potential (L0.015 V). Li−C formation was also observed previously by XAS26 and can be mainly assigned to Li intercalation in the carbon present in the electrode. The Li−C formation is also expected below 0.7 V while this intercalation occurs mostly in the deep layers; hence, it is observed only at the cutoff point with the maximum intercalation. The formation and evolution of distinct chemical components at the surface of the electrode during the charge− discharge cycle are summarized and depicted in the lower panel of Figure 3. Our combined XAS and XPS experimental results suggest that SEI formation starts within the initial steps of the lithiation process (see Figure 3) forming Li2CO3 and LiF in the whole SEI layer. The SEI develops its structure, and its thickness increases reaching the saturation around 0.7 V. Below 0.7 V, the lithium carbonate formed in the SEI layer is covered by a thin superficial layer of alkyl lithium carbonate (∼5−7 nm). The growth of the alkyl lithium carbonate component, showing a maximum at the lower potentials (0.015 V), can be appreciated looking at the upper panels of Figure 3. The C Kedge XAS peak assigned to ROCO2Li is seen to increase upon further lithiation and then decrease again upon delithiation. During delithiation, the alkyl Li carbonate component is depressed as compared with the Li carbonate component. Lithium in this stage also intercalates within carbon, and a thin Li x C layer is formed. This reversible process occurs continuously while slightly increasing (least-squares fitting of

the XPS peaks show an slight increase of the ROCO2Li in the cycled sample) upon cycling. Hence, while the capacity retention increases, the impact on the Coloumbic efficiency of the electrode remains limited. The extra-contribution of carbon to the capacity is experimentally evaluated to be about 265 mAh g−1. Capacity calculations for two different prototypes of alkyl carbonates, i.e, EtOCO2Li and MtOCO2Li, also result in theoretical capacities of 279.1 and 326.9 mAh g−1, respectively. These values suggest that the reversible alkyl carbonate formed on the superficial layers of the SEI can also contribute to the extra-capacity detected below 0.7 V in these samples (excess of ∼300 mAh g−1) alongside the Li intercalation. Presence and quantity of carbon in our electrode is known and can contribute for about 60% of the observed extra-capacity. We thus estimate that up to 40% of the observed extra-capacity could be associated with the thin layer of alkyl carbonates formed in the SEI of the electrodes under consideration.

3. CONCLUSIONS In summary, we presented a detailed study of the evolution of the different chemical components in the SEI layer formed on C-ZnFe2O4 electrodes. Soft X-ray XAS and XPS experiments with different effective probing depths were used in order to get the chemical profile of the SEI layer. The structural analysis of distinct components forming the SEI gave detailed information on the SEI evolution at different charge−discharge stages. The experimental results show that the electrode reduction process, resulting in the formation of the Li2O in the vicinity of the electrode active material and formation of the passivation layer on the electrode core, is accompanied by the formation of a partly reversible layer as the uppermost SEI layer (typical thickness ∼5−7 nm). This consists mostly of alkyl lithium carbonate (ROCO2Li), being partly replaced by Li2CO3 during delithiation. A separate capacity calculation demonstrates that the storage of Li in this reversible SEI layer can be one source 4574


Research Article


(11) Jamnik, J.; Maier, J. Nanocrystallinity Effects in Lithium Battery Materials Aspects of Nano-ionics. Part IV. Phys. Chem. Chem. Phys. 2003, 5, 5215−5220. (12) Zhukovskii, Y. F.; Balaya, P.; Dolle, M.; Kotomin, E. A.; Maier, J. Enhanced Lithium Storage and Chemical Diffusion in Metal-LiF Nanocomposites: Experimental and Theoretical Results. Phys. Rev. B: Condens. Matter Mater. Phys. 2007, 76, 235414. (13) Ponrouch, A.; Taberna, P. L.; Simon, P.; Palacin, M. R. On the Origin of the Extra Capacity at Low Potential in Materials for Li Batteries Reacting Through Conversion Reaction. Electrochim. Acta 2012, 61, 13−18. (14) Laruelle, S.; Grugeon, S.; Poizot, P.; Dollé, M.; Dupont, L.; Tarascon, J.-M. On the Origin of the Extra Electrochemical Capacity Displayed by MO/Li Cells at Low Potential. J. Electrochem. Soc. 2002, 149, A627. (15) Peled, E.; Golodnitsky, D.; Ardel, G. Advanced Model for Solid Electrolyte Interphase Electrodes in Liquid and Polymer Electrolytes. J. Electrochem. Soc. 1997, 144, L208−L210. (16) Peled, E. Lithium Batteries; Gabano, J. P, Eds.; Academic Press: London, 1983. (17) Verma, P.; Maire, P.; Novak, P. A Review of the Features and Analyses of the Solid Electrolyte Interphase in Li-Ion Batteries. Electrochim. Acta 2010, 55, 6332−6341. (18) Zhang, S.; Ding, M. S.; Xu, K.; Allen, J.; Jow, T. R. Understanding Solid Electrolyte Interface Film Formation on Graphite Electrodes. Electrochem. Solid-State Lett. 2001, 4, A206−A208. (19) Aurbach, D. Advances in Lithium Ion Batteries, the Role of Surface Films on Electrodes in Li-Ion Batteries; Kluwer Academic Publishers: New York, 2002; p 26. (20) Aurbach, D.; Zaban, A.; Ein-Eli, Y.; Weissman, I.; Chusid, O.; Markovsky, B.; Levi, M.; Levi, E.; Schechter, A.; Granot, E. Recent Studies on the Correlation Between Surface Chemistry, Morphology, Three-Dimensional Structures and Performance of Li and Li-C Intercalation Anodes in Several Important Electrolyte Systems. J. Power Sources 1997, 68, 91−98. (21) Aurbach, D.; Moshkovich, M.; Cohen, Y.; Schechter, A. On the Correlation Between Surface Chemistry and Performance of Graphite Negative Electrodes for Li Ion Batteries. Langmuir 1999, 15, 2947− 2960. (22) Peled, E.; Golodnitsky, D.; Menachem, C.; Bar-tow, D. Advanced Tool for the Selection of Electrolyte Components for Rechargeable Lithium Batteries. J. Electrochem. Soc. 1998, 145, 3482. (23) Malmgren, S.; Ciosek, K.; Hahlin, M.; Gustafsson, T.; Gorgoi, M.; Rensmo, H.; Edström, K. Comparing Anode and Cathode Electrode/Electrolyte Interface Composition and Morphology Using Soft and Hard X-ray Photoelectron Spectroscopy. Electrochim. Acta 2013, 97, 23−32. (24) See Supporting Information. (25) Mueller, F.; Bresser, D.; Paillard, E.; Winter, M.; Passerini, S. Influence of the Carbonaceous Conductive Network on the Electrochemical Performance of ZnFe2O4 Nanoparticles. J. Power Sources 2013, 236, 87−94. (26) Di Cicco, A.; Giglia, A.; Gunnella, R.; Koch, S. L.; Mueller, F.; Nobili, F.; Pasqualini, M.; Passerini, S.; Tossici, R.; Witkowska, A. SEI Growth and Depth Profiling on ZFO Electrodes by Soft X-Ray Absorption Spectroscopy. Adv. Energy Mater. 2015, 5, 1500642. (27) Rezvani, S. J.; Ciambezi, M.; Gunnella, R.; Minicucci, M.; Munoz, M. A.; Nobili, F.; Pasqualini, M.; Passerini, S.; Schreiner, C.; Trapananti, A.; Witkowska, A.; Di Cicco, A. Local Structure and Stability of SEI in Graphite and ZFO Electrodes Probed by As K-Edge Absorption Spectroscopy. J. Phys. Chem. C 2016, 120, 4287−4295. (28) Ali, M.; Witkowska, A.; Abbas, M.; Gunnella, R.; Di Cicco, A. Evolution of the nanostructure of Pt and Pt-Co polymer electrolyte membrane fuel cell electrocatalysts at successive degradation stages probed by X-ray photoemission. J. Power Sources 2014, 271, 548−555. (29) Chen, C. J.; Greenblatt, M.; Waszczak, J. V. Lithium insertion into spinel ferrites. Solid State Ionics 1986, 18−19, 838−846.

of extra-capacity observed in these electrodes. These results indicate the SEI layer as an important component of the Li-ion cells, involved also in lithium storage, and significantly improve our understanding of the battery charging processes indicating possible routes for improving their performances.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.6b12408. Experimental methods, scanning electron microscopy of the electrodes, and X-ray diffraction analysis of electrodes (PDF)

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

S. Javad Rezvani: 0000-0002-6771-170X Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The support of the European Commission under the Project “Stable Interfaces for Rechargeable Batteries” (SIRBATT) (FP7-ENERGY-2013, grant agreement 608502) is gratefully acknowledged. We acknowledge the Elettra Synchrotron Radiation Facility for provision of beamtime (BEAR), and we would like to thank A. Giglia for assistance in using beamline BEAR.

■

REFERENCES

(1) Tarascon, J.-M.; Armand, M. Issues and Challenges Facing Rechargeable Lithium Batteries. Nature 2001, 414, 359−367. (2) Nitta, N.; Wu, F.; Lee, J. T.; Yushin, G. Li-ion Battery Materials: Present and Future. Mater. Today 2015, 18, 252−264. (3) Pacala, S. Stabilization Wedges: Solving the Climate Problem for the Next 50 Years with Current Technologies. Science 2004, 305, 968− 972. (4) Tarascon, J.-M.; Poizot, P.; Laruelle, S.; Grugeon, S.; Dupont, L. Nano-sized Transition-Metal Oxides as Negative-Electrode Materials for Lithium-ion Batteries. Nature 2000, 407, 496−499. (5) Idota, Y. Tin-Based Amorphous Oxide: A High-Capacity Lithium-Ion-Storage Material. Science 1997, 276, 1395−1397. (6) Balaya, P.; Li, H.; Kienle, L.; Maier, J. Fully Reversible Homogeneous and Heterogeneous Li Storage in RuO 2 with High Capacity. Adv. Funct. Mater. 2003, 13, 621−625. (7) Badway, F.; Cosandey, F.; Pereira, N.; Amatucci, G. G. Carbon Metal Fluoride Nanocomposites - High-Capacity Reversible Metal Fluoride Conversion Materials as Rechargeable Positive Electrodes for Li Batteries. J. Electrochem. Soc. 2003, 150, A1318−A1327. (8) Bresser, D.; Paillard, E.; Kloepsch, R.; Krueger, S.; Fiedler, M.; Schmitz, R.; Baither, D.; Winter, M.; Passerini, S. Carbon Coated ZnFe2O4 Nanoparticles for Advanced Lithium-Ion Anodes. Adv. Energy Mater. 2013, 3, 513−523. (9) Li, H.; Balaya, P.; Maier, J. Li-Storage via Heterogeneous Reaction in Selected Binary Metal Fluorides and Oxides. J. Electrochem. Soc. 2004, 151, A1878. (10) Hu, Y.-Y.; Liu, Z.; Nam, K.-W.; Borkiewicz, O. J.; Cheng, J.; Hua, X.; Dunstan, M. T.; Yu, X.; Wiaderek, K. M.; Du, L.-S.; Chapman, K. W.; Chupas, P. J.; Yang, X.-Q.; Grey, C. P. Origin of Additional Capacities in Metal Oxide Lithium-ion Battery Electrodes. Nat. Mater. 2013, 12, 1130−6. 4575


Research Article

ACS Applied Materials & Interfaces (30) Thackeray, M. M.; David, W. I. F.; Bruce, P. G.; Goodenough, J. B. Lithium Insertion into Manganese Spinels. Mater. Res. Bull. 1983, 18, 461−472. (31) NuLi, Y.-N.; Chu, Y.-Q.; Qin, Q.-Z. Nanocrystalline ZnFe2O4 and Ag-Doped ZnFe2O4 Films Used as New Anode Materials for LiIon Batteries. J. Electrochem. Soc. 2004, 151, A1077. (32) Guo, X.; Lu, X.; Fang, X.; Mao, Y.; Wang, Z.; Chen, L.; Xu, X.; Yang, H.; Liu, Y. Lithium storage in hollow spherical ZnFe2O4 as anode materials for lithium ion batteries. Electrochem. Commun. 2010, 12, 847−850. (33) Sandì, G. Raman and NEXAFS Spectroscopy Characterization of Templated-Carbon Anodes. J. New Mater. Electrochem. Syst. 2003, 6, 181−189. (34) Lenardi, C.; Piseri, P.; Briois, V.; Bottani, C. E.; Bassi, A. L.; Milani, P. Near-Edge X-ray Absorption Fine Structure and Raman Characterization of Amorphous and Nanostructured Carbon Films. J. Appl. Phys. 1999, 85, 7159−7167. (35) Comelli, G.; Stöhr, J.; Robinson, C. J.; Jark, W. Structural Studies of Argon-Sputtered Amorphous Carbon Films by Means of Extended X-Ray-Absorption Fine Structure. Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 38, 7511−7519. (36) Chen, J. G.; De Vries, B. D.; Lewandowski, J. T.; Hall, R. B. Direct Differentiation of Surface and Bulk Compositions of Powder Catalysts: Application of Electron-Yield and Fluorescence-Yield NEXAFS to LixNi1−xO. Catal. Lett. 1994, 23, 25−35. (37) Madix, R. J.; Solomon, J. L.; Stohr, J. The Orientation of the Carbonate Anion on Ag(110). Surf. Sci. 1988, 197, 253−259. (38) Tsuji, J.; Nakamatsu, H.; Mukoyama, T.; Kojima, K.; Ikeda, S.; Taniguchi, K. Lithium K-edge XANES Spectra for Lithium Compounds. X-Ray Spectrom. 2002, 31, 319−326. (39) Qiao, R.; Chuang, Y. D.; Yan, S.; Yang, W. Soft X-Ray Irradiation Effects of Li2O2, Li2CO3 and Li2O Revealed by Absorption Spectroscopy. PLoS One 2012, 7, e49182. (40) Braun, A.; Wang, H.; Shim, J.; Lee, S. S.; Cairns, E. J. Lithium K(1s) synchrotron NEXAFS Spectra of Lithium-ion Battery Cathode, Anode and Electrolyte Materials. J. Power Sources 2007, 170, 173−178. (41) Wu, Z. Y.; Gota, S.; Jollet, F.; Pollak, M.; Gautier-Soyer, M.; Natoli, C. R. Characterization of iron oxides by x-ray absorption at the oxygen K edge using a full multiple-scattering approach. Phys. Rev. B: Condens. Matter Mater. Phys. 1997, 55, 2570−2577. (42) Fischer, D. A.; Wentzcovitch, R. M.; Carr, R. G.; Continenza, A.; Freeman, A. J. Graphitic Interlayer States: A carbon K Near-Edge XRay Absorption Fine Structure Study. Phys. Rev. B: Condens. Matter Mater. Phys. 1991, 44, 1427−1429. (43) Dedryvère, R.; Gireaud, L.; Grugeon, S.; Laruelle, S.; Tarascon, J. M.; Gonbeau, D. Characterization of Lithium Alkyl Carbonates by X-Ray Photoelectron Spectroscopy: Experimental and Theoretical Study. J. Phys. Chem. B 2005, 109, 15868−15875.

4576


Is the Solid Electrolyte Interphase an Extra-Charge ... - ACS Publications

Recommend Documents