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Vanadium pentoxide thin films used as positive electrode in lithium microbatteries: An XPS study during cycling
Journal of Physics and Chemistry of Solids 67 (2006) 1320–1324 www.elsevier.com/locate/jpcs
Vanadium pentoxide thin films used as positive electrode in lithium microbatteries: An XPS study during cycling A. Benayad a, H. Martinez a,*, A. Gies b, B. Pecquenard b, A. Levasseur b, D. Gonbeau a a
LCTPCM (CNRS-UMR 5624—FR 2606), Helioparc Pau Pyre´ne´es, 2 Avenue du pre´sident Angot, 64053 Pau Cedex 9, France ICMCB/ENSCPB (CNRS-UPR 9048), Groupe Ionique du Solide, 87 Avenue du Dr Schweitzer, 33608 Pessac Cedex, France
b
Abstract Vanadium pentoxide thin films, usable as positive electrode in microbatteries, have been prepared by radio frequency magnetron sputtering in a pure argon or mixed argon/oxygen atmosphere using a V2O5 target. Depending on the oxygen partial pressure in the discharge gas, we have obtained either crystallized or amorphous thin films, with different morphologies. These two kinds of thin films having different electrochemical behavior, an extensive XPS study was carried out. The main redox processes and their reversibility occurring during the 1st, 10th, and 30th discharge–charge cycles were discussed in relation with the electrochemical properties. Our results have revealed a good reversibility of the redox process for amorphous thin films and degradation for crystallized ones, in agreement with the discharge capacity evolution. Furthermore, the growth of a surface layer between the cathode and the liquid electrolyte was evidenced upon the discharge as well as its partial dissolution upon the charge. q 2006 Elsevier Ltd. All rights reserved. Keywords: A. Thin films; B. Plasma deposition; C. Photoelectron spectroscopy; D. Electochemical properties; D. Surface properties
1. Introduction During the last decade, the increasing development of miniaturized electronic systems has caused a strong demand for new rechargeable electrochemical systems. Therefore, considerable effort has been invested in developing solidstate microbatteries as possible integrated component in microelectronic devices. Intense research efforts are currently undertaken in order to improve the performances of positive electrode materials [1–3] usable in these systems. Among the various transition metal oxides studied, and according to the interesting properties of bulk V2O5 [4–6], we have studied this material in the form of thin layers, usable as positive electrode for microbatteries. To address this issue, V2O5 thin films were deposited by radio-frequency magnetron sputtering in a pure argon or mixed argon/oxygen atmosphere using a V2O5 target. Depending on the experimental conditions (especially the oxygen partial pressure), two types of thin layers can be obtained, either crystallized or amorphous, which are characterized by different electrochemical properties. The * Corresponding author. Tel: C33 5 5940 7599; fax: C33 5 5940 7622. E-mail address: [email protected] (H. Martinez).
0022-3697/$ - see front matter q 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2006.01.089
objective of the present work is to better understand these results by systematic XPS analyses during cycling; indeed, this technique is well suited for the analysis of the redox processes occurring during discharge–charge cycles. 2. Results and discussion A detailed description of the experimental details was already reported [7]. 2.1. Structure, morphology and electrochemical properties The structure and morphology of the as-deposited thin films depend strongly on the oxygen partial pressure [7]. Under a total gas pressure equal to 1 Pa, the thin films prepared at oxygen partial pressure lower or equal than 10% are amorphous and exhibit a dense morphology with a smooth surface. For an oxygen partial pressure higher than 10%, the thin films are crystallized, with a porous morphology, constituted by numerous tangled rods (Fig. 1). Preliminary electrochemical characterizations have been achieved galvanostatically on V2O5 thin films deposited onto a stainless steel substrate. The first cycle of a crystallized thin film prepared at an oxygen partial pressure equal to 14% is depicted in Fig. 2a. The first discharge curve shows a stepwise
A. Benayad et al. / Journal of Physics and Chemistry of Solids 67 (2006) 1320–1324
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Fig. 1. (A) XRD diffraction patterns and (B) Scanning electron microscopy (SEM) images for vanadium pentoxide thin films deposited at 1 Pa total gas pressure and under two different oxygen partial pressures: (a) pO2Z14% and (b) pO2Z0%.
Fig. 2. The first galvanostatic cycle for (a) crystallized and (b) amorphous thin films (each point indicates the potential stop where XPS analyses were carried out). (c) Discharge capacity evolution as a function of the cycle number for (:) crystallized and (&) amorphous thin films deposited at 1 Pa total gas pressure. The applied current density is 15 mA/cm2 between 1.5 and 3.7 V/Li.
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discharge with four plateaus,, respectively, at 3.4, 3.2, 2.3 and 1.9 V as it was previously observed for bulk V2O5 material [8]. On the following charge and discharge curves, the observed plateaus are no more present and the charge–discharge profile is therefore approaching that of a typical amorphous V2O5 cycling curve. Fig. 2b shows the first cycle of a thin film deposited in absence of oxygen. The featureless shape of the discharge and charge curves is typical for an amorphous material. Concerning the discharge capacities, even if the crystallized thin films are characterized by a slightly better reversibility of lithium insertion/deinsertion for the first cycle, a continuous capacity fading is observed during cycling. For the amorphous thin film, a good cycling stability is reached after a few cycles (Fig. 2c). 2.2. XPS analyses of the redox processes occurring during cycling Three compounds (V2O5, VO2, V2O3) purchased from Aldrich were used as references for the XPS analysis. The redox processes were systematically achieved at different stages of the first, the 10th, and the 30th cycle. For the as-deposited crystallized thin films, the XPS V2p3/2 core peak spectra (Fig. 3a) (pO2Z14%) is located at 517.4 eV, associated to a C5 formal degree for vanadium ions. The V2p3/2 core peak for the amorphous thin film (Fig. 3b), prepared in absence of oxygen, presents two components,, respectively, located at 517.4 and 516.2 eV, related to two formal oxidation degrees C5 and C4. In order to explain this difference, we can argue that when the thin films are deposited in absence of oxygen, a slight reduction of the target surface under bombardment with argon ions occurs, and the vanadium species are not
re-oxidized in the sputtering chamber. For crystallized thin films, the introduction of oxygen in the plasma leads to the re-oxidation and therefore the vanadium ions are in the highest oxidation degree. For both thin films, the analysis of V2p core peaks achieved at the first discharge (Fig. 3b and c) is characterized by a partial reduction of V5C ions into V4C and further ‘V3C’ ions. Note that similar XPS analyses at different stages of the first cycle were also achieved on the bulk V2O5 (Fig. 3a) and exhibit similar reduction phenomena. Moreover, let us notice that except for vanadium pentoxide, it is not usual to observe at the same time the presence of three oxidation states for a transition metal oxide. This behavior could be explained by the presence of several possible nonsymmetrical crystallographic sites or environments. One can also consider a disproportionation of two V4C ions in ‘V3C’ and V5C, considering that the respective percentages of these two last species are close at the end of the discharge (29 and 31%). At the same potential stage (1.5 V/Li), for the amorphous thin film, the relative percentage of the peak corresponding to V5C ions is about 26%, those of the V4C and ‘V3C’ ions are, respectively, 45% and 29%. On the whole, rather similar reduction processes were identified for both thin films during the discharge, which may confirm the disproportionation phenomenon of V4C ions. Note that the evolution of the O1s XPS core peak for both compounds does not allow to conclude concerning the eventual role played by the oxygen ions in the redox mechanism. At the end of the first charge (Fig. 4a), we observe for the crystallized thin film a partial re-oxidation; the ‘V3C’ peak disappears, while the intensity of the V4C peak decreases to 20%. At the end of the 10th and 30th cycle, the intensity of the V4C peak increases and reaches 40% at the end of the 30th charge.
Fig. 3. XPS analyses of V2p core peaks performed after mechanical erosion onto (a) bulk V2O5, (b) crystallized thin film and (c) amorphous thin films at different stages of the first cycle: the as-deposited sample and upon discharge (DZ3.2, 2.3, 1.9, 1.5 V/Li).
A. Benayad et al. / Journal of Physics and Chemistry of Solids 67 (2006) 1320–1324
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Fig. 4. XPS analyses for the as-deposited, at the end of the 1st, 10th and 30th for (a) crystallized and (b) amorphous V2O5 thin films.
The same analysis achieved for the amorphous thin films (Fig. 4b) shows that the V2p3/2 core peak spectrum at the end of the first charge is similar to the one of the as deposited sample. The ratio between V4C and V5C ions remains stable at the end of the 10th and 30th charge. Therefore, we can conclude that the redox mechanism is not fully reversible in the case of the crystallized thin films at the end of the first charge, as the V2p3/2 core peak is not perfectly similar to the one of the as-deposited sample. Moreover, a progressive degradation is observed during cycling. A better redox process reversibility is observed in the case of the amorphous thin films; the percentage of the V4C(40%) ions remain stable between the 1st and 30th charge. This feature seems to demonstrate that the presence of V4C ions for the as-deposited vanadium pentoxide thin films enhances the reversibility. These results are in agreement with the continuous capacity fading evolution for the crystallized thin film and with the cycling stability observed for the amorphous layer (Fig. 2c). 2.3. XPS analyses of the thin film/electrolyte interface Beside the previous detailed XPS studies, thorough analyses were also systematically carried out before mechanical erosion to probe the cathode/electrolyte interface. This interface, commonly encountered for anode materials seems also to play a major role regarding the electrochemical performances in term of capacity loss during first cycles or cycling stability. The XPS semi-quantitative analyses performed onto crystallized and amorphous thin films display that the vanadium amount decreases upon the discharge and
˚ , these increases back upon the charge. As XPS probesz50 A results seem to indicate that an interface is growing upon the discharge and partially dissolves during the charge for both samples. An analysis of the O1s core peaks carried out at different stages of the first cycle confirms the previous results. For both compounds, at the beginning of the discharge, beside the peak characteristic of V 2O 5 (530.3 eV), we have observed a new component located at 531.6 eV. The intensity of this peak increases during the discharge, and decreases upon the charge compared with the peak characteristic of oxygen ions from V2O5. Hence, the use of two independent probes (V2p and O1s core peaks) evidences the formation and the dissolution of a layer at the interface between the V2O5 cathodic thin films and the liquid electrolyte. The main difference between crystallized and amorphous thin films concerns the thickness of this interface, which appears thinner when the morphology of the thin film is porous. This last result may explain the higher capacity loss for the first cycle for amorphous thin films compared with the crystallized one (Fig. 2). The thorough analysis of the C 1s core peak provides valuable information regarding the nature of this layer. At the first cycle, it is mainly composed for crystallized and amorphous thin films by Li2CO3 and Alkyl carbonate R–O–CO2Li; frequently observed at anode/electrolyte interface (resulting from the reduction of organic solvent from the electrolyte). At the end of the 10th and 30th discharge, for both thin films, the peak attributed to Li2CO3 still remains with the same atomic percentage as we have observed at the end of the first discharge. The dissolution process occurring at the end of the different charges seems to affect mainly R–O–CO2Li species.
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Note that only a very few atomic percentage (less than 2%) of fluorine and arsenic was revealed by the XPS analyses at the surface of the thin layers.
Furthermore, we have evidenced a layer formed at the cathode/electrolyte interface, mainly composed of Li2CO3 and of Alkyl carbonate R–O–CO2Li.
3. Conclusion References The structure and the morphology (porous or dense) of the V2O5 thin films is affected by rf sputtering conditions, implying different electrochemical properties. To explain these characteristics, further XPS analyses were achieved on the as deposited V2O5 thin films and at different stages of the electrochemical cycles. For the first cycle, rather similar reduction processes for crystallized and amorphous thin films were identified even if a better reversibility is observed for the latter. Moreover, XPS results at the end of the 1st, 10th and the 30th charges have revealed a good reversibility of the redox process for amorphous thin films and degradation for crystallized ones, in agreement with the discharge capacity evolution.
[1] J.B. Bates, N.J. Dudney, D.C. Lubben, G.R. Gruzalski, B.S. Kwak, Xiahua Yu, R.A. Zuhr, J. Power Sources 54 (1995) 58–62. [2] P. Birke, W.F. Chu, W. Weppner, Solid State Ionics 93 (1997) 1–15. [3] J.L. Souquet, M. Duclot, Solid State Ionics 148 (2002) 375–379. [4] S. Koike, T. Fujieda, T. Sakai, S. Higuchi, J. Power Sources 81–82 (1999) 581–584. [5] D.B. Le, S. Passerini, J. Guo, J. Ressler, B.B. Owens, W.H. Smyrl, J. Electrochem. Soc. 142 (6) (1995) 102–103. [6] J.B. Bates, N.J. Dudney, D.C. Lubben, G.R. Gruzalski, B.S. Kwak, Y. Xiaohua, R.A. Zuhr, J. Power Sources 54 (1995) 58–62. [7] A. Gies, B. Pecquenard, A. Benayad, H. Martinez, D. Gonbeau, H. Fuess, A. Levasseur, Solid State Ionics 176 (2005) 1627–1634. [8] C. Delmas, H. Cognac-Auradou, J.M. Cocciantelli, M. Menetrie, J.P. Doumerc, Solid State Ionics 69 (1994) 257–264.
Vanadium pentoxide thin films used as positive electrode in lithium microbatteries: An XPS study during cycling A. Benayad a, H. Martinez a,*, A. Gies b, B. Pecquenard b, A. Levasseur b, D. Gonbeau a a
LCTPCM (CNRS-UMR 5624—FR 2606), Helioparc Pau Pyre´ne´es, 2 Avenue du pre´sident Angot, 64053 Pau Cedex 9, France ICMCB/ENSCPB (CNRS-UPR 9048), Groupe Ionique du Solide, 87 Avenue du Dr Schweitzer, 33608 Pessac Cedex, France
b
Abstract Vanadium pentoxide thin films, usable as positive electrode in microbatteries, have been prepared by radio frequency magnetron sputtering in a pure argon or mixed argon/oxygen atmosphere using a V2O5 target. Depending on the oxygen partial pressure in the discharge gas, we have obtained either crystallized or amorphous thin films, with different morphologies. These two kinds of thin films having different electrochemical behavior, an extensive XPS study was carried out. The main redox processes and their reversibility occurring during the 1st, 10th, and 30th discharge–charge cycles were discussed in relation with the electrochemical properties. Our results have revealed a good reversibility of the redox process for amorphous thin films and degradation for crystallized ones, in agreement with the discharge capacity evolution. Furthermore, the growth of a surface layer between the cathode and the liquid electrolyte was evidenced upon the discharge as well as its partial dissolution upon the charge. q 2006 Elsevier Ltd. All rights reserved. Keywords: A. Thin films; B. Plasma deposition; C. Photoelectron spectroscopy; D. Electochemical properties; D. Surface properties
1. Introduction During the last decade, the increasing development of miniaturized electronic systems has caused a strong demand for new rechargeable electrochemical systems. Therefore, considerable effort has been invested in developing solidstate microbatteries as possible integrated component in microelectronic devices. Intense research efforts are currently undertaken in order to improve the performances of positive electrode materials [1–3] usable in these systems. Among the various transition metal oxides studied, and according to the interesting properties of bulk V2O5 [4–6], we have studied this material in the form of thin layers, usable as positive electrode for microbatteries. To address this issue, V2O5 thin films were deposited by radio-frequency magnetron sputtering in a pure argon or mixed argon/oxygen atmosphere using a V2O5 target. Depending on the experimental conditions (especially the oxygen partial pressure), two types of thin layers can be obtained, either crystallized or amorphous, which are characterized by different electrochemical properties. The * Corresponding author. Tel: C33 5 5940 7599; fax: C33 5 5940 7622. E-mail address: [email protected] (H. Martinez).
0022-3697/$ - see front matter q 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2006.01.089
objective of the present work is to better understand these results by systematic XPS analyses during cycling; indeed, this technique is well suited for the analysis of the redox processes occurring during discharge–charge cycles. 2. Results and discussion A detailed description of the experimental details was already reported [7]. 2.1. Structure, morphology and electrochemical properties The structure and morphology of the as-deposited thin films depend strongly on the oxygen partial pressure [7]. Under a total gas pressure equal to 1 Pa, the thin films prepared at oxygen partial pressure lower or equal than 10% are amorphous and exhibit a dense morphology with a smooth surface. For an oxygen partial pressure higher than 10%, the thin films are crystallized, with a porous morphology, constituted by numerous tangled rods (Fig. 1). Preliminary electrochemical characterizations have been achieved galvanostatically on V2O5 thin films deposited onto a stainless steel substrate. The first cycle of a crystallized thin film prepared at an oxygen partial pressure equal to 14% is depicted in Fig. 2a. The first discharge curve shows a stepwise
A. Benayad et al. / Journal of Physics and Chemistry of Solids 67 (2006) 1320–1324
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Fig. 1. (A) XRD diffraction patterns and (B) Scanning electron microscopy (SEM) images for vanadium pentoxide thin films deposited at 1 Pa total gas pressure and under two different oxygen partial pressures: (a) pO2Z14% and (b) pO2Z0%.
Fig. 2. The first galvanostatic cycle for (a) crystallized and (b) amorphous thin films (each point indicates the potential stop where XPS analyses were carried out). (c) Discharge capacity evolution as a function of the cycle number for (:) crystallized and (&) amorphous thin films deposited at 1 Pa total gas pressure. The applied current density is 15 mA/cm2 between 1.5 and 3.7 V/Li.
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discharge with four plateaus,, respectively, at 3.4, 3.2, 2.3 and 1.9 V as it was previously observed for bulk V2O5 material [8]. On the following charge and discharge curves, the observed plateaus are no more present and the charge–discharge profile is therefore approaching that of a typical amorphous V2O5 cycling curve. Fig. 2b shows the first cycle of a thin film deposited in absence of oxygen. The featureless shape of the discharge and charge curves is typical for an amorphous material. Concerning the discharge capacities, even if the crystallized thin films are characterized by a slightly better reversibility of lithium insertion/deinsertion for the first cycle, a continuous capacity fading is observed during cycling. For the amorphous thin film, a good cycling stability is reached after a few cycles (Fig. 2c). 2.2. XPS analyses of the redox processes occurring during cycling Three compounds (V2O5, VO2, V2O3) purchased from Aldrich were used as references for the XPS analysis. The redox processes were systematically achieved at different stages of the first, the 10th, and the 30th cycle. For the as-deposited crystallized thin films, the XPS V2p3/2 core peak spectra (Fig. 3a) (pO2Z14%) is located at 517.4 eV, associated to a C5 formal degree for vanadium ions. The V2p3/2 core peak for the amorphous thin film (Fig. 3b), prepared in absence of oxygen, presents two components,, respectively, located at 517.4 and 516.2 eV, related to two formal oxidation degrees C5 and C4. In order to explain this difference, we can argue that when the thin films are deposited in absence of oxygen, a slight reduction of the target surface under bombardment with argon ions occurs, and the vanadium species are not
re-oxidized in the sputtering chamber. For crystallized thin films, the introduction of oxygen in the plasma leads to the re-oxidation and therefore the vanadium ions are in the highest oxidation degree. For both thin films, the analysis of V2p core peaks achieved at the first discharge (Fig. 3b and c) is characterized by a partial reduction of V5C ions into V4C and further ‘V3C’ ions. Note that similar XPS analyses at different stages of the first cycle were also achieved on the bulk V2O5 (Fig. 3a) and exhibit similar reduction phenomena. Moreover, let us notice that except for vanadium pentoxide, it is not usual to observe at the same time the presence of three oxidation states for a transition metal oxide. This behavior could be explained by the presence of several possible nonsymmetrical crystallographic sites or environments. One can also consider a disproportionation of two V4C ions in ‘V3C’ and V5C, considering that the respective percentages of these two last species are close at the end of the discharge (29 and 31%). At the same potential stage (1.5 V/Li), for the amorphous thin film, the relative percentage of the peak corresponding to V5C ions is about 26%, those of the V4C and ‘V3C’ ions are, respectively, 45% and 29%. On the whole, rather similar reduction processes were identified for both thin films during the discharge, which may confirm the disproportionation phenomenon of V4C ions. Note that the evolution of the O1s XPS core peak for both compounds does not allow to conclude concerning the eventual role played by the oxygen ions in the redox mechanism. At the end of the first charge (Fig. 4a), we observe for the crystallized thin film a partial re-oxidation; the ‘V3C’ peak disappears, while the intensity of the V4C peak decreases to 20%. At the end of the 10th and 30th cycle, the intensity of the V4C peak increases and reaches 40% at the end of the 30th charge.
Fig. 3. XPS analyses of V2p core peaks performed after mechanical erosion onto (a) bulk V2O5, (b) crystallized thin film and (c) amorphous thin films at different stages of the first cycle: the as-deposited sample and upon discharge (DZ3.2, 2.3, 1.9, 1.5 V/Li).
A. Benayad et al. / Journal of Physics and Chemistry of Solids 67 (2006) 1320–1324
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Fig. 4. XPS analyses for the as-deposited, at the end of the 1st, 10th and 30th for (a) crystallized and (b) amorphous V2O5 thin films.
The same analysis achieved for the amorphous thin films (Fig. 4b) shows that the V2p3/2 core peak spectrum at the end of the first charge is similar to the one of the as deposited sample. The ratio between V4C and V5C ions remains stable at the end of the 10th and 30th charge. Therefore, we can conclude that the redox mechanism is not fully reversible in the case of the crystallized thin films at the end of the first charge, as the V2p3/2 core peak is not perfectly similar to the one of the as-deposited sample. Moreover, a progressive degradation is observed during cycling. A better redox process reversibility is observed in the case of the amorphous thin films; the percentage of the V4C(40%) ions remain stable between the 1st and 30th charge. This feature seems to demonstrate that the presence of V4C ions for the as-deposited vanadium pentoxide thin films enhances the reversibility. These results are in agreement with the continuous capacity fading evolution for the crystallized thin film and with the cycling stability observed for the amorphous layer (Fig. 2c). 2.3. XPS analyses of the thin film/electrolyte interface Beside the previous detailed XPS studies, thorough analyses were also systematically carried out before mechanical erosion to probe the cathode/electrolyte interface. This interface, commonly encountered for anode materials seems also to play a major role regarding the electrochemical performances in term of capacity loss during first cycles or cycling stability. The XPS semi-quantitative analyses performed onto crystallized and amorphous thin films display that the vanadium amount decreases upon the discharge and
˚ , these increases back upon the charge. As XPS probesz50 A results seem to indicate that an interface is growing upon the discharge and partially dissolves during the charge for both samples. An analysis of the O1s core peaks carried out at different stages of the first cycle confirms the previous results. For both compounds, at the beginning of the discharge, beside the peak characteristic of V 2O 5 (530.3 eV), we have observed a new component located at 531.6 eV. The intensity of this peak increases during the discharge, and decreases upon the charge compared with the peak characteristic of oxygen ions from V2O5. Hence, the use of two independent probes (V2p and O1s core peaks) evidences the formation and the dissolution of a layer at the interface between the V2O5 cathodic thin films and the liquid electrolyte. The main difference between crystallized and amorphous thin films concerns the thickness of this interface, which appears thinner when the morphology of the thin film is porous. This last result may explain the higher capacity loss for the first cycle for amorphous thin films compared with the crystallized one (Fig. 2). The thorough analysis of the C 1s core peak provides valuable information regarding the nature of this layer. At the first cycle, it is mainly composed for crystallized and amorphous thin films by Li2CO3 and Alkyl carbonate R–O–CO2Li; frequently observed at anode/electrolyte interface (resulting from the reduction of organic solvent from the electrolyte). At the end of the 10th and 30th discharge, for both thin films, the peak attributed to Li2CO3 still remains with the same atomic percentage as we have observed at the end of the first discharge. The dissolution process occurring at the end of the different charges seems to affect mainly R–O–CO2Li species.
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Note that only a very few atomic percentage (less than 2%) of fluorine and arsenic was revealed by the XPS analyses at the surface of the thin layers.
Furthermore, we have evidenced a layer formed at the cathode/electrolyte interface, mainly composed of Li2CO3 and of Alkyl carbonate R–O–CO2Li.
3. Conclusion References The structure and the morphology (porous or dense) of the V2O5 thin films is affected by rf sputtering conditions, implying different electrochemical properties. To explain these characteristics, further XPS analyses were achieved on the as deposited V2O5 thin films and at different stages of the electrochemical cycles. For the first cycle, rather similar reduction processes for crystallized and amorphous thin films were identified even if a better reversibility is observed for the latter. Moreover, XPS results at the end of the 1st, 10th and the 30th charges have revealed a good reversibility of the redox process for amorphous thin films and degradation for crystallized ones, in agreement with the discharge capacity evolution.
[1] J.B. Bates, N.J. Dudney, D.C. Lubben, G.R. Gruzalski, B.S. Kwak, Xiahua Yu, R.A. Zuhr, J. Power Sources 54 (1995) 58–62. [2] P. Birke, W.F. Chu, W. Weppner, Solid State Ionics 93 (1997) 1–15. [3] J.L. Souquet, M. Duclot, Solid State Ionics 148 (2002) 375–379. [4] S. Koike, T. Fujieda, T. Sakai, S. Higuchi, J. Power Sources 81–82 (1999) 581–584. [5] D.B. Le, S. Passerini, J. Guo, J. Ressler, B.B. Owens, W.H. Smyrl, J. Electrochem. Soc. 142 (6) (1995) 102–103. [6] J.B. Bates, N.J. Dudney, D.C. Lubben, G.R. Gruzalski, B.S. Kwak, Y. Xiaohua, R.A. Zuhr, J. Power Sources 54 (1995) 58–62. [7] A. Gies, B. Pecquenard, A. Benayad, H. Martinez, D. Gonbeau, H. Fuess, A. Levasseur, Solid State Ionics 176 (2005) 1627–1634. [8] C. Delmas, H. Cognac-Auradou, J.M. Cocciantelli, M. Menetrie, J.P. Doumerc, Solid State Ionics 69 (1994) 257–264.