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Electronic and electrochemical properties of LixNi1−yCoyO2 cathode material
Solid State Ionics 157 (2003) 115 – 123 www.elsevier.com/locate/ssi
Electronic and electrochemical properties of LixNi1yCoyO2 cathode material J. Molenda*, P. Wilk, J. Marzec Faculty of Materials Science and Ceramics, Stanisl/ aw Staszic University of Mining and Metallurgy, Al. Mickiewicza 30, 30-059 Cracow, Poland Received 12 May 2001; received in revised form 30 September 2001; accepted 18 January 2002
Abstract This studies are devoted to structural, electrical and electrochemical investigations of LixNi1yCoyO2 system. A modification of electrical properties of the cathode material was observed upon deintercalation. A correlation between electronic properties and effectiveness of lithium deintercalation process was confirmed. D 2002 Elsevier Science B.V. All rights reserved. Keywords: LixNi1yCoyO2 system; Cathode; Deintercalation
1. Introduction The LiNiO2 and LiCoO2 oxides are possible cathode materials due to their high voltage (3.5 – 4 V) in reversible lithium cells. The structural disorder caused by cation mixing in LiNiO2 results in poor transport and electrochemical properties of this oxide [1 – 3]. The already commercialised cathode of LiCoO2 is expensive and toxic. Partial substitution of nickel with cobalt stabilizes the LixNi1yCoyO2 crystallographic structure, leading to a better reversibility of the Li+/LixNi1yCoyO2 cathode as compared to the Li + /Li x NiO 2 one. During lithium deintercalation from starting Li1Ni1yCoyO2 compound, the valency of the transition metal undergoes a continuous increase and, simultaneously, a decrease of lattice parameters a and c takes place [4,5], which *
Corresponding author. Fax: +48-12-617-2493. E-mail address: [email protected] (J. Molenda).
leads to a modification of the electronic structure of the cathode material. The objective of this work was to find the optimal chemical composition of Li1Ni1yCoyO2 to obtain the cathode material with best transport and electrochemical properties. For the series of LiNi1y CoyO2 ( y=0.25, 0.5, 0.85) compounds, with electrical properties determined at first, electrochemical studies were performed in a Li/Li+/LixNi1yCoyO2type cell, which allowed to point to a relation between the electronic structure and the effective˜ Li). Strucness of lithium deintercalation process (D tural characterization and transport properties measurements were performed on LixNi1yCoyO2 systems as a function of the lithium content. Modification of the electronic structure of the cathode material upon deintercalation enabled to continuously follow relations among structure, composition, transition metal valency and reactivity of the electrode material.
0167-2738/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 2 7 3 8 ( 0 2 ) 0 0 1 9 7 - 2
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J. Molenda et al. / Solid State Ionics 157 (2003) 115–123
2. Experimental
3. Results and discussion
The LiNi1yCoyO2 oxide was obtained by a hightemperature synthesis [6]. The obtained LiNi0.75 Co0.25O2, LiNi0.5Co0.5O2, LiNi0.15Co0.85O2 compositions were annealed at 1123 K in air for 24 h. XRD showed all samples to be single phase with hexagonal R-3m symmetry lattice. The observed linear decrease of both lattice parameters a and c with increasing cobalt content in LiNi1yCoyO2 points to a formation of solid solution within the transition metal sublattice, with Co3+ ions replacing the Ni3+ ones (Fig. 1). In order to determine transport properties, the electrical conductivity and thermoelectric power were measured in the 120 – 300 K temperature range. The four-probe ac current method was used for electrical conductivity measurements. A dynamic method was applied for the measurements of thermoelectric power, with a small, increasing up to 2 – 3j, temperature gradient, for which the corresponding thermoelectric voltage was registered. Electrochemical studies were performed in the Li/ Li+(1 M LiClO4 in PC)/LixNi1yCoyO2 cell. Measurements of lithium chemical diffusion coefficient was made by the galvanostatic intermittent titration technique (GITT) [7].
3.1. Electrical properties of LiNi1yCoyO2 In Figs. 2 and 3, the electrical conductivity and thermoelectric power of the LiNi1yCoyO2 oxides are shown as a function of temperature. As can be seen, the increase of cobalt content over y=0.25 results in an almost two-order decrease of electrical conductivity and enlarge absolute values of thermoelectric power (Fig. 3) in spite of the falling metal – metal distance within the transition metal sublattice (Fig. 1). The positive sign of the thermoelectric power indicates electron holes to be the effective charge carriers. To explain the unexpected decrease of electrical conductivity upon cobalt doping, a concentration of effective carriers was estimated. If a charge transport mechanism via localized states over cations is assumed, the Heikes [8] formula for the thermoelectric power can be used for the estimation of carrier concentration n: a ¼ Fk=e½lnðl n=nÞ þ A, where a is the thermoelectric power, k is Boltzman constant, e is the elementary charge and A is entropy
Fig. 1. The lattice constants a and c for Li1Ni1yCoyO2 as a function of cobalt content.
J. Molenda et al. / Solid State Ionics 157 (2003) 115–123
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Fig. 2. Temperature dependence of electrical conductivity of the Li1Ni1yCoyO2 series (0
factor, usually neglected in transition metal oxides [9]. In Fig. 4, such calculated values of carrier concentration are plotted against cobalt content in LiNi1yCoyO2. As follows from this figure, the highest value of carrier concentration is for the y=0.25
cobalt content, i.e. for the composition, for which the highest conductivity was observed (Fig. 2). For higher cobalt contents, the fall of the effective carrier concentration (Fig. 4) can explain the observed decline in electrical conductivity with cobalt content.
Fig. 3. Temperature dependence of thermoelectric power of the Li1Ni1yCoyO2 series (0
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J. Molenda et al. / Solid State Ionics 157 (2003) 115–123
Fig. 4. Effective carrier concentration in the Li1Ni1yCoyO2 as a function of cobalt content.
3.2. Electrochemical properties of LixN1yCoyO2 (0VyV0.85)
process from the LiNi1yCoyO oxide can be described by equation:
In Fig. 5, the electromotive force of Li/Li+/LixNi1y CoyO2 cells as a function of lithium content in the cathode material is given. The lithium deintercalation
LiNi1y Coy O2 X Lix Ni1y Coy O2 þ ð1 xÞLiþ þ ð1 xÞe
Fig. 5. Electromotive force of Li/Li+/LixNi1yCoyO2 cells (0
ð1Þ
J. Molenda et al. / Solid State Ionics 157 (2003) 115–123
The increase of cobalt content in the LixNi1y CoyO2 system shifts up the cell voltage, as the substitution of Ni3+ ions (3d7 configuration) with Co3+ (3d6) shifts down the Fermi level in the considered cathode material. In Fig. 6, the chemical diffusion coefficient of lithium in LixNi1yCoyO2 systems, a factor responsible for the effectiveness of intercalation, is shown in function of deintercalation degree. As can be seen, the lower lithium content the higher the diffusion coefficient. For a certain lithium concentration in LixNi1y CoyO2, the measured values of diffusion coefficient decrease with growing cobalt content, being in accordance with the observed worsening of electronic conductivity with this parameter. It is worth noting that the highest diffusion coefficient value (of the order of 107 cm2/s) was obtained for the cobalt content y=0.25, for which the best transport properties were observed (Figs. 2 and 3). In Fig. 7, the dependence of electrical conductivity on temperature is shown for electrochemically deintercalated LixNi0.75Co0.25O2, LixNi0.5Co0.5O2 and Lix Ni0.15Co0.85O2 oxides, each with decreasing lithium amount. One can notice (Fig. 7) that upon deintercalation, all these oxides change their properties from nonmetallic towards metallic, as the conductivity
119
activation energy falls from Ea=0.19 eV down to 0.04 eV; meanwhile, the entire electrical conductivity increases. In Fig. 8, the evolution of lattice parameters a and c upon deintercalation of LixNi1yCoyO2 oxides is shown. The parameter a, that is responsible for the metal – metal distance, is falling upon lithium extraction, suggesting that the along dropping activation energy of electrical conductivity is a mobility activation energy of carriers. The dependencies of thermoelectric power on temperature obtained for following compositions: Li0.6Ni0.75Co0.25O2, Li0.4Ni0.75Co0.25O2, Li0.5Ni0.5 Co0.5O2, Li0.3Ni0.5Co0.5O2, Li0.8Ni0.15Co0.85O2 and Li0.6Ni0.15Co0.85O2 (Fig. 9) enable to estimate the effective mass of carriers m*, basing on the relation for a metallic state: a ¼ 2=3ðp=3Þ2=3 ðm*k 2 T =e t2 Þn2=3
ð2Þ
where n is carrier concentration governed by x, the amount of lithium in LixNi1yCoyO2. The observed lowering of effective mass during deintercalation process (from starting 5 down to 0.8 me) is related with the progressing delocalisation of electronic states.
Fig. 6. Chemical diffusion coefficient of lithium in LixNi1yCoyO2 (0
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J. Molenda et al. / Solid State Ionics 157 (2003) 115–123
Fig. 8. The lattice constants a and c for the LixNi1yCoyO2 series: (a) y=0.25, (b) y=0.5, (c) y=0.85.
3.3. Correlation between electronic properties and effectiveness of deintercalation process in LixNi1y CoyO2
Fig. 7. Temperature dependences of electrical conductivity of the LixNi1yCoyO2 series: (a) y=0.25, (b) y=0.5, (c) y=0.85.
To prove a relation between electronic properties of the LixNi1yCoyO2 cathode material and its reactivity to lithium in Figs. 10 –12, electrical and structural parameters as a function of deintercalation degree are shown together with corresponding
J. Molenda et al. / Solid State Ionics 157 (2003) 115–123
Fig. 9. Temperature dependences of thermoelectric power of the LixNi1yCoyO2 series: (a) y=0.25, (b) y=0.5, (c) y=0.85.
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degree in the considered LixNi1yCoyO2 oxides. The metallic-type of thermoelectric power characteristics and the well-pronounced drop of carrier mobility activation energy indicate a delocalisation of electronic states caused by overlapping of 3d orbitals of neighbouring ions during deintercalation process. Occurring metallic properties lead to a better ionic– electronic transport, resulting in the increase of the lithium chemical diffusion coefficient—the decisive
Fig. 10. Correlation of dependencies: thermoelectric power at 300 K, activation energy of electrical conductivity, lattice parameter a and chemical diffusion coefficient of lithium for LixNi0.75Co0.25O2 as a function of lithium content.
˜ Li, a factor dependence of the diffusion coefficient D determining the effectiveness of the lithium insertion/ extraction process. Therefore, the series of Figs. 10 – 12 consist of dependencies of the Seebeck coefficient a at room temperature, the conductivity (mobility) activation energy Ea, the lattice parameter a (here, the M– M distance is equal a) and the chemical diffusion coefficient of lithium as a function of deintercalation
Fig. 11. Correlation of dependencies: thermoelectric power at 300 K, activation energy of electrical conductivity, lattice parameter a and chemical diffusion coefficient of lithium for LixNi0.5Co0.5O2 as a function of lithium content.
J. Molenda et al. / Solid State Ionics 157 (2003) 115–123
123
close correlation between electrical and electrochemical properties of the cathode material. Electrical conductivity and thermoelectric power characteristics of LixNi1yCoyO2 against deintercalation degree indicate that the observed high effectiveness of deintercalation process is due to progressing modification of the electronic structure of the cathode material towards metallic behaviour. This modification of electronic properties is related to the decreasing lattice constant and, therefore, the M– M distance through deintercalation. The delocalisation of electronic states improve the electronic – ionic transport, as seen in the growth of lithium chemical diffusion coefficient, leading to a high effectiveness of the intercalation and deintercalation processes.
Acknowledgements The work is supported by the Polish Committee for Scientific Research under grant no. 7T08A 049 18.
References
Fig. 12. Correlation of dependencies: thermoelectric power at 300 K, activation energy of electrical conductivity, lattice parameter a and chemical diffusion coefficient of lithium for LixNi0.15Co0.85O2 as a function of lithium content.
parameter defining current density achieved from a lithium battery.
4. Conclusions The performed studies on electrochemical properties of the Li/Li+/LixNi1yCoyO2-type cells indicate a
[1] J.R. Dahn, U. von Sacken, Solid State Ionics 44 (1990) 87. [2] R. Kanno, H. Kubo, Y. Kawamoto, T. Kamiyama, Y. Takeda, M. Takano, J. Solid State Chem. 110 (1994) 216. [3] A. Rougier, P. Gravereau, C. Delmas, J. Electrochem. Soc. 143 (1996) 1168. [4] W. Li, J.N. Reimers, J.R. Dahn, Solid State Ionics 67 (1993) 123. [5] J.P. Pereira-Ramos, S. Bach, J. Farny, V. Bianchi, D. Caurant, N. Baffier, P. Willmann, ITE Battery Lett. 1 (1999) 80. [6] P. Wilk, J. Marzec, J. Molenda, Mol. Phys. Rep. 27 (2000) 126. [7] W. Weppner, R.A. Huggins, J. Electrochem. Soc. 124 (1977) 1569. [8] R.H. Heikes, R.W. Ure, Thermoelectricity, Interscience, New York, 1961. [9] J.G. Austin, N.F. Mott, Adv. Phys. 18 (1969) 41.
Electronic and electrochemical properties of LixNi1yCoyO2 cathode material J. Molenda*, P. Wilk, J. Marzec Faculty of Materials Science and Ceramics, Stanisl/ aw Staszic University of Mining and Metallurgy, Al. Mickiewicza 30, 30-059 Cracow, Poland Received 12 May 2001; received in revised form 30 September 2001; accepted 18 January 2002
Abstract This studies are devoted to structural, electrical and electrochemical investigations of LixNi1yCoyO2 system. A modification of electrical properties of the cathode material was observed upon deintercalation. A correlation between electronic properties and effectiveness of lithium deintercalation process was confirmed. D 2002 Elsevier Science B.V. All rights reserved. Keywords: LixNi1yCoyO2 system; Cathode; Deintercalation
1. Introduction The LiNiO2 and LiCoO2 oxides are possible cathode materials due to their high voltage (3.5 – 4 V) in reversible lithium cells. The structural disorder caused by cation mixing in LiNiO2 results in poor transport and electrochemical properties of this oxide [1 – 3]. The already commercialised cathode of LiCoO2 is expensive and toxic. Partial substitution of nickel with cobalt stabilizes the LixNi1yCoyO2 crystallographic structure, leading to a better reversibility of the Li+/LixNi1yCoyO2 cathode as compared to the Li + /Li x NiO 2 one. During lithium deintercalation from starting Li1Ni1yCoyO2 compound, the valency of the transition metal undergoes a continuous increase and, simultaneously, a decrease of lattice parameters a and c takes place [4,5], which *
Corresponding author. Fax: +48-12-617-2493. E-mail address: [email protected] (J. Molenda).
leads to a modification of the electronic structure of the cathode material. The objective of this work was to find the optimal chemical composition of Li1Ni1yCoyO2 to obtain the cathode material with best transport and electrochemical properties. For the series of LiNi1y CoyO2 ( y=0.25, 0.5, 0.85) compounds, with electrical properties determined at first, electrochemical studies were performed in a Li/Li+/LixNi1yCoyO2type cell, which allowed to point to a relation between the electronic structure and the effective˜ Li). Strucness of lithium deintercalation process (D tural characterization and transport properties measurements were performed on LixNi1yCoyO2 systems as a function of the lithium content. Modification of the electronic structure of the cathode material upon deintercalation enabled to continuously follow relations among structure, composition, transition metal valency and reactivity of the electrode material.
0167-2738/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 2 7 3 8 ( 0 2 ) 0 0 1 9 7 - 2
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J. Molenda et al. / Solid State Ionics 157 (2003) 115–123
2. Experimental
3. Results and discussion
The LiNi1yCoyO2 oxide was obtained by a hightemperature synthesis [6]. The obtained LiNi0.75 Co0.25O2, LiNi0.5Co0.5O2, LiNi0.15Co0.85O2 compositions were annealed at 1123 K in air for 24 h. XRD showed all samples to be single phase with hexagonal R-3m symmetry lattice. The observed linear decrease of both lattice parameters a and c with increasing cobalt content in LiNi1yCoyO2 points to a formation of solid solution within the transition metal sublattice, with Co3+ ions replacing the Ni3+ ones (Fig. 1). In order to determine transport properties, the electrical conductivity and thermoelectric power were measured in the 120 – 300 K temperature range. The four-probe ac current method was used for electrical conductivity measurements. A dynamic method was applied for the measurements of thermoelectric power, with a small, increasing up to 2 – 3j, temperature gradient, for which the corresponding thermoelectric voltage was registered. Electrochemical studies were performed in the Li/ Li+(1 M LiClO4 in PC)/LixNi1yCoyO2 cell. Measurements of lithium chemical diffusion coefficient was made by the galvanostatic intermittent titration technique (GITT) [7].
3.1. Electrical properties of LiNi1yCoyO2 In Figs. 2 and 3, the electrical conductivity and thermoelectric power of the LiNi1yCoyO2 oxides are shown as a function of temperature. As can be seen, the increase of cobalt content over y=0.25 results in an almost two-order decrease of electrical conductivity and enlarge absolute values of thermoelectric power (Fig. 3) in spite of the falling metal – metal distance within the transition metal sublattice (Fig. 1). The positive sign of the thermoelectric power indicates electron holes to be the effective charge carriers. To explain the unexpected decrease of electrical conductivity upon cobalt doping, a concentration of effective carriers was estimated. If a charge transport mechanism via localized states over cations is assumed, the Heikes [8] formula for the thermoelectric power can be used for the estimation of carrier concentration n: a ¼ Fk=e½lnðl n=nÞ þ A, where a is the thermoelectric power, k is Boltzman constant, e is the elementary charge and A is entropy
Fig. 1. The lattice constants a and c for Li1Ni1yCoyO2 as a function of cobalt content.
J. Molenda et al. / Solid State Ionics 157 (2003) 115–123
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Fig. 2. Temperature dependence of electrical conductivity of the Li1Ni1yCoyO2 series (0
factor, usually neglected in transition metal oxides [9]. In Fig. 4, such calculated values of carrier concentration are plotted against cobalt content in LiNi1yCoyO2. As follows from this figure, the highest value of carrier concentration is for the y=0.25
cobalt content, i.e. for the composition, for which the highest conductivity was observed (Fig. 2). For higher cobalt contents, the fall of the effective carrier concentration (Fig. 4) can explain the observed decline in electrical conductivity with cobalt content.
Fig. 3. Temperature dependence of thermoelectric power of the Li1Ni1yCoyO2 series (0
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Fig. 4. Effective carrier concentration in the Li1Ni1yCoyO2 as a function of cobalt content.
3.2. Electrochemical properties of LixN1yCoyO2 (0VyV0.85)
process from the LiNi1yCoyO oxide can be described by equation:
In Fig. 5, the electromotive force of Li/Li+/LixNi1y CoyO2 cells as a function of lithium content in the cathode material is given. The lithium deintercalation
LiNi1y Coy O2 X Lix Ni1y Coy O2 þ ð1 xÞLiþ þ ð1 xÞe
Fig. 5. Electromotive force of Li/Li+/LixNi1yCoyO2 cells (0
ð1Þ
J. Molenda et al. / Solid State Ionics 157 (2003) 115–123
The increase of cobalt content in the LixNi1y CoyO2 system shifts up the cell voltage, as the substitution of Ni3+ ions (3d7 configuration) with Co3+ (3d6) shifts down the Fermi level in the considered cathode material. In Fig. 6, the chemical diffusion coefficient of lithium in LixNi1yCoyO2 systems, a factor responsible for the effectiveness of intercalation, is shown in function of deintercalation degree. As can be seen, the lower lithium content the higher the diffusion coefficient. For a certain lithium concentration in LixNi1y CoyO2, the measured values of diffusion coefficient decrease with growing cobalt content, being in accordance with the observed worsening of electronic conductivity with this parameter. It is worth noting that the highest diffusion coefficient value (of the order of 107 cm2/s) was obtained for the cobalt content y=0.25, for which the best transport properties were observed (Figs. 2 and 3). In Fig. 7, the dependence of electrical conductivity on temperature is shown for electrochemically deintercalated LixNi0.75Co0.25O2, LixNi0.5Co0.5O2 and Lix Ni0.15Co0.85O2 oxides, each with decreasing lithium amount. One can notice (Fig. 7) that upon deintercalation, all these oxides change their properties from nonmetallic towards metallic, as the conductivity
119
activation energy falls from Ea=0.19 eV down to 0.04 eV; meanwhile, the entire electrical conductivity increases. In Fig. 8, the evolution of lattice parameters a and c upon deintercalation of LixNi1yCoyO2 oxides is shown. The parameter a, that is responsible for the metal – metal distance, is falling upon lithium extraction, suggesting that the along dropping activation energy of electrical conductivity is a mobility activation energy of carriers. The dependencies of thermoelectric power on temperature obtained for following compositions: Li0.6Ni0.75Co0.25O2, Li0.4Ni0.75Co0.25O2, Li0.5Ni0.5 Co0.5O2, Li0.3Ni0.5Co0.5O2, Li0.8Ni0.15Co0.85O2 and Li0.6Ni0.15Co0.85O2 (Fig. 9) enable to estimate the effective mass of carriers m*, basing on the relation for a metallic state: a ¼ 2=3ðp=3Þ2=3 ðm*k 2 T =e t2 Þn2=3
ð2Þ
where n is carrier concentration governed by x, the amount of lithium in LixNi1yCoyO2. The observed lowering of effective mass during deintercalation process (from starting 5 down to 0.8 me) is related with the progressing delocalisation of electronic states.
Fig. 6. Chemical diffusion coefficient of lithium in LixNi1yCoyO2 (0
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J. Molenda et al. / Solid State Ionics 157 (2003) 115–123
Fig. 8. The lattice constants a and c for the LixNi1yCoyO2 series: (a) y=0.25, (b) y=0.5, (c) y=0.85.
3.3. Correlation between electronic properties and effectiveness of deintercalation process in LixNi1y CoyO2
Fig. 7. Temperature dependences of electrical conductivity of the LixNi1yCoyO2 series: (a) y=0.25, (b) y=0.5, (c) y=0.85.
To prove a relation between electronic properties of the LixNi1yCoyO2 cathode material and its reactivity to lithium in Figs. 10 –12, electrical and structural parameters as a function of deintercalation degree are shown together with corresponding
J. Molenda et al. / Solid State Ionics 157 (2003) 115–123
Fig. 9. Temperature dependences of thermoelectric power of the LixNi1yCoyO2 series: (a) y=0.25, (b) y=0.5, (c) y=0.85.
121
122
J. Molenda et al. / Solid State Ionics 157 (2003) 115–123
degree in the considered LixNi1yCoyO2 oxides. The metallic-type of thermoelectric power characteristics and the well-pronounced drop of carrier mobility activation energy indicate a delocalisation of electronic states caused by overlapping of 3d orbitals of neighbouring ions during deintercalation process. Occurring metallic properties lead to a better ionic– electronic transport, resulting in the increase of the lithium chemical diffusion coefficient—the decisive
Fig. 10. Correlation of dependencies: thermoelectric power at 300 K, activation energy of electrical conductivity, lattice parameter a and chemical diffusion coefficient of lithium for LixNi0.75Co0.25O2 as a function of lithium content.
˜ Li, a factor dependence of the diffusion coefficient D determining the effectiveness of the lithium insertion/ extraction process. Therefore, the series of Figs. 10 – 12 consist of dependencies of the Seebeck coefficient a at room temperature, the conductivity (mobility) activation energy Ea, the lattice parameter a (here, the M– M distance is equal a) and the chemical diffusion coefficient of lithium as a function of deintercalation
Fig. 11. Correlation of dependencies: thermoelectric power at 300 K, activation energy of electrical conductivity, lattice parameter a and chemical diffusion coefficient of lithium for LixNi0.5Co0.5O2 as a function of lithium content.
J. Molenda et al. / Solid State Ionics 157 (2003) 115–123
123
close correlation between electrical and electrochemical properties of the cathode material. Electrical conductivity and thermoelectric power characteristics of LixNi1yCoyO2 against deintercalation degree indicate that the observed high effectiveness of deintercalation process is due to progressing modification of the electronic structure of the cathode material towards metallic behaviour. This modification of electronic properties is related to the decreasing lattice constant and, therefore, the M– M distance through deintercalation. The delocalisation of electronic states improve the electronic – ionic transport, as seen in the growth of lithium chemical diffusion coefficient, leading to a high effectiveness of the intercalation and deintercalation processes.
Acknowledgements The work is supported by the Polish Committee for Scientific Research under grant no. 7T08A 049 18.
References
Fig. 12. Correlation of dependencies: thermoelectric power at 300 K, activation energy of electrical conductivity, lattice parameter a and chemical diffusion coefficient of lithium for LixNi0.15Co0.85O2 as a function of lithium content.
parameter defining current density achieved from a lithium battery.
4. Conclusions The performed studies on electrochemical properties of the Li/Li+/LixNi1yCoyO2-type cells indicate a
[1] J.R. Dahn, U. von Sacken, Solid State Ionics 44 (1990) 87. [2] R. Kanno, H. Kubo, Y. Kawamoto, T. Kamiyama, Y. Takeda, M. Takano, J. Solid State Chem. 110 (1994) 216. [3] A. Rougier, P. Gravereau, C. Delmas, J. Electrochem. Soc. 143 (1996) 1168. [4] W. Li, J.N. Reimers, J.R. Dahn, Solid State Ionics 67 (1993) 123. [5] J.P. Pereira-Ramos, S. Bach, J. Farny, V. Bianchi, D. Caurant, N. Baffier, P. Willmann, ITE Battery Lett. 1 (1999) 80. [6] P. Wilk, J. Marzec, J. Molenda, Mol. Phys. Rep. 27 (2000) 126. [7] W. Weppner, R.A. Huggins, J. Electrochem. Soc. 124 (1977) 1569. [8] R.H. Heikes, R.W. Ure, Thermoelectricity, Interscience, New York, 1961. [9] J.G. Austin, N.F. Mott, Adv. Phys. 18 (1969) 41.