- Email: [email protected]
Carbonation and phase transformations of LiMO2 (M = Fe, Co, Ni) under CO2 atmosphere
Materials Chemistry and Physics 199 (2017) 18e22
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Materials science communication
Carbonation and phase transformations of LiMO2 (M ¼ Fe, Co, Ni) under CO2 atmosphere Ikuo Yanase*, Jun Miura, Hidehiko Kobayashi Saitama University, Faculty of Engineering, Department of Applied Chemistry, 255 Shimoohkubo, Sakura-ku, Saitama-shi, Saitama, 338-8570, Japan
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
O3-LiFeO2 with a layered structure transformed to a-LiFeO2 under a CO2 gas. LiCoO2 and LiNiO2 with a layered structure are chemically stable under a CO2 gas. Na substitution stabilizes LiFeO2 phases under a CO2 gas.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 4 May 2017 Received in revised form 2 June 2017 Accepted 9 June 2017 Available online 10 June 2017
Under a CO2 gas flow, O3-LiFeO2, having a layered structure, transformed to a-LiFeO2, and then b0 -LiFeO2 with increasing temperature. All LiFeO2 phases decomposed to Fe2O3 and Li2CO3 under a CO2 gas flow. Conversely, carbonation and structural phase transformations of LiCoO2 and LiNiO2, also having layered structures, were not observed at low temperatures under a CO2 gas flow. In particular, LiCoO2 was chemically stable and its layered structure was maintained even at 600 C. The carbonation and structural phase transformations of a-LiFeO2, having a cubic structure, were suppressed compared with those of O3-LiFeO2. To investigate the effect of cation doping into LiFeO2 on carbonation and structural phase transformations, Na-substituted a-LiFeO2, NaxLi1-xFeO2 with x ¼ 0 to 0.15 was synthesized. X-ray diffraction measurements revealed that substitution of Na for Li in LiFeO2 suppressed the particle growth induced by carbonation of LiFeO2 under a CO2 gas flow. © 2017 Elsevier B.V. All rights reserved.
Keywords: Lithium ferrite Phase transformation Carbonation CO2
1. Introduction Lithium ferrites, LiFeO2, are a candidate material for cathodes in rechargeable lithium-ion secondary batteries (LIBs) [1,2]. A polymorph of LiFeO2, O3-LiFeO2 has a hexagonal layered a-NaFeO2 type structure with the space group R-3m. Recently, it has been reported that cathode materials containing lithium, such as LiFePO4 and
* Corresponding author. E-mail address: [email protected] (I. Yanase). http://dx.doi.org/10.1016/j.matchemphys.2017.06.024 0254-0584/© 2017 Elsevier B.V. All rights reserved.
Li7La3Zr2O12, undergo reactions with H2O and CO2, resulting in lower electrochemical performance of their LIBs [3,4]. Lithium ferrites, including a-LiFeO2, also react with CO2 [5,6], motivate investigations of the stability of LiFeO2 phases under CO2 atmospheres from the viewpoint of preserving the electrochemical properties of LIBs. In addition to O3-LiFeO2, LiFeO2 has several other polymorphs, such as a, b0 , g-type structures. The a-type polymorph (hereafter, aLiFeO2) has a cubic structure with the space group Fm3m, in which Liþ and Fe3þ are randomly distributed at octahedral sites. The b0 type polymorph (hereafter, b0 -LiFeO2) has an orthorhombic
I. Yanase et al. / Materials Chemistry and Physics 199 (2017) 18e22
19
LiFeO2 phase. The transformation of a-LiFeO2 can be suppressed by decreasing the amount of Li defects in LiFeO2 [22], suggesting that the chemical composition influences the carbonation rate. In this study, the chemical stability of cathode materials including LiFeO2, LiCoO2, and LiNiO2 under a CO2 atmosphere was investigated from the viewpoint of their carbonation reactivity and structure phase transformations. 2. Experimental
Fig. 1. XRD patterns of the LiCoO2 powders at room temperature (R.T.), and 400, 500, and 600 C for 5 h under a CO2 gas flow.
structure with the space group C2/c, in which Liþ and Fe3þ are partially ordered. The g-type polymorph (hereafter, g-LiFeO2) has a tetragonal structure with the space group I41/amd, in which Liþ and Fe3þ are fully ordered [7e9]. At high temperatures a-LiFeO2 is the thermodynamically stable form, while b0 -LiFeO2 is stable at moderate temperatures, and g-LiFeO2 is stable at low temperatures [7,10]. Hence, a-LiFeO2 is a metastable phase at low and moderate temperatures. Previous studies [5,6] have also reported that LiFeO2 reacts with CO2, according to the carbonation reaction, 2LiFeO2 þ CO2 / Fe2O3 þ Li2CO3. The temperature at which this reaction can occur is reported to be lower than those of other carbonation reactions with materials such as Li2ZrO3 [11], Li4SiO4 [12e16], Li4TiO4 [17] and CaO [18e21]. Thus, the LiFeO2 phase readily decomposes in the presence of CO2. It has also been reported that a-LiFeO2 transforms to b0 -LiFeO2 through its reaction with CO2 [22,23], suggesting that the chemical reaction of LiFeO2 with CO2 influences the stability of the
Fig. 2. XRD patterns of the LiNiO2 powders at room temperature (R.T.), and 400, 500, and 600 C for 5 h under a CO2 gas flow.
Commercially available g-Fe2O3, NiO, Co3O4 (>99% purity, Wako), and LiNO3 (>99% purity, Wako) powders were mixed in a 1.15: 1 M ratio of Li: M (M ¼ Fe, Ni, Co) in ethanol for 20 h by ballmilling with Al2O3 balls. After removing the ethanol by an evaporator, the mixture was dried and then heated at 600 C for 4 h in air to synthesize a-LiFeO2, LiNiO2, and LiCoO2 powders. Similarly, Nasubstituted a-LiFeO2, NaxLi1-xFeO2 with x ¼ 0e0.20, was synthesized with NaNO3 (>99% purity, Wako). O3-LiFeO2 powders were synthesized as follows; first, NaNO3 and g-Fe2O3 powders were mixed at a molar ratio of Na/Fe ¼ 1.15 in ethanol by ball-milling for 24 h. After removing the ethanol, the powder mixture was heated at 600 C for 5 h in air to synthesize a-NaFeO2 with a layered structure. The synthesized a-NaFeO2 powder was manually mixed with a large amount of LiNO3 powder and the powder mixture was heated in air at 300 C for 20 h in an alumina crucible. Finally, the heat-treated powder was washed with ethanol to remove residual NaNO3 and LiNO3 and layered O3-LiFeO2 powder was obtained. Carbonation and structural phase transformations were measured under a CO2 gas flow at a rate of 200 ml/min and a
Fig. 3. XRD patterns of the powders obtained by heating the synthesized O3-LiFeO2 powder at temperatures from 150 to 500 C for 5 h under a CO2 gas flow. C; O3LiFeO2, 〇; a-LiFeO2, :; g-Fe2O3, ,; Li2CO3, ▽; b0 -LiFeO2.
20
I. Yanase et al. / Materials Chemistry and Physics 199 (2017) 18e22
pressure of 0.1 MPa for the LiFeO2, LiCoO2, LiNiO2 and a-NaxLi1(x ¼ 0 to 0.20) synthesized directly from raw materials. The crystalline phases and morphologies of the synthesized powders were examined by X-ray diffractometry (XRD; CuKa, RINT2000, Rigaku) and field emission scanning spectroscopy (FESEM; S4100, Hitachi), respectively. The specific surface areas of the powders were investigated by Brunauer-Emmett-Teller (BET) N2 adsorption measurements (Sorptmatic1990, ThermoFisher Scientific). The lattice constants of the synthesized powders were refined by the least-squared method from the diffraction peaks of the (111), (200), (220), (311), and (222) planes, which were measured at a scan rate of 1 /min. xFeO2
3. Results and discussion Fig. 1 shows XRD patterns of the synthesized LiCoO2 with a layered structure (JCPDS 44-0145) at room temperature (R.T.), and 400, 500, and 600 C under a CO2 gas flow. The LiCoO2 sample contained a small amount of Li2CO3 and Co3O4. These compounds were produced when LiCoO2 was synthesized. The peak intensity of the Li2CO3 and Co3O4 phases did not increase from room temperature to 600 C, indicating that the LiCoO2 phase was stable under a CO2 gas flow. Fig. 2 shows XRD patterns of the synthesized LiNiO2 with a layered structure (JCPDS 09-0063) at room temperature, and 400, 500, and 600 C under a CO2 gas flow. A small amount of Li2CO3 was produced when the LiNiO2 was synthesized, similar to the case of LiCoO2. The peak intensity of the Li2CO3 and NiO phases clearly increased in the range 500e600 C under the CO2 gas flow. Fig. 3 shows XRD patterns for the powders obtained by heating
Fig. 4. XRD patterns of the powders obtained by heating the synthesized a-LiFeO2 powder at temperatures from 150 to 500 C for 5 h under a CO2 gas flow. C; O3LiFeO2, 〇; a-LiFeO2, :; g-Fe2O3, , Li2CO3, ▽ b0 -LiFeO2.
Fig. 5. Powder XRD patterns of NaxLi1-xFeO2 powders with x ¼ 0e0.20 at 600 C for 4 h in air.
the synthesized O3-LiFeO2 at temperatures in the range of 150e500 C for 5 h under a CO2 gas flow. The O3-LiFeO2 sample reacted with CO2 above 150 C. In detail, the O3-LiFeO2 peaks disappeared, and g-Fe2O3 (:) and a-LiFeO2(B) were produced at 325 C. Li2CO3 (,) and b0 -LiFeO2 (▽) were also recognized in the range 400e425 C, Li2CO3 was not recognized above 450 C. Furthermore, O3-LiFeO2 transformed to a-LiFeO2 at temperatures of 150e275 C and the peak intensity of a-LiFeO2 increased with increasing temperature in the range 300e325 C. The a-LiFeO2 sample partially transformed to b0 -LiFeO2 at temperatures in the range 350e425 C and b0 -LiFeO2 transformed to a-LiFeO2 above 450 C. From the above results, we found that the carbonation and structural phase transformations of O3-LiFeO2 were more promoted than those of LiCoO2 and LiNiO2. Fig. 4 shows the XRD patterns for the a-LiFeO2 sample, with a
Fig. 6. Relationship between x and lattice constant of NaxLi1-xFeO2 with x ¼ 0e0.15.
I. Yanase et al. / Materials Chemistry and Physics 199 (2017) 18e22
Fig. 7. Powder XRD patterns of (a) NaxLi1-xFeO2 with x ¼ 0e0.15 at 400 C for 5 h under a CO2 gas flow. 〇; a-LiFeO2, ▽; b0 - LiFeO2, :; g-Fe2O3, ,; Li2CO3.
cubic structure, at temperatures in the range 150e500 C for 5 h under a CO2 gas flow. Carbonation and structural phase transformations of a-LiFeO2 were not observed at 150 C, suggesting higher chemical stability of the a-LiFeO2 sample, with a cubic structure, than that of O3-LiFeO2 with a layered structure. It has been reported [10] that the formation enthalpy of O3-LiFeO2 is greater than that of LiCoO2 and a-LiFeO2. The trend in the
21
carbonation temperature of these compounds appeared to depend on their formation enthalpies. This is because a larger formation enthalpy means a lower thermal stability of compounds. The XRD patterns of the a-NaxLi1-xFeO2 powder in the range x ¼ 0e0.20 are shown in Fig. 5. The single phase a-NaxLi1-xFeO2 (JCPDS 82-1495; a-LiFeO2) with x ¼ 0e0.15 was synthesized, while LiFe5O8 with a spinel structure was observed for a-NaxLi1-xFeO2 with x ¼ 0.20. The relationship between x and the lattice constants of a-NaxLi1-xFeO2 is shown in Fig. 6. The lattice constant linearly increased with increasing x in the range 0e0.075, suggesting that a solid solution of a-NaxLi1-xFeO2 was produced for x < 0.075. This is because the ionic radius of Naþ is larger than that of Liþ, resulted in the linearly increased lattice constant according to Vegard's law [24,25]. Fig. 7 shows the XRD patterns of the NaxLi1-xFeO2 powder with x in the range 0e0.15 heated at 400 C under a CO2 gas flow. The products g-Fe2O3 and Li2CO3 derived from the carbonation of NaxLi1-xFeO2. A structural phase transformation of a to b0 -LiFeO2 (JCPDS 80-1159) is clearly suppressed for all Na-substituted samples and it is most pronounced for x ¼ 0.05 in NaxLi1-xFeO2. In aLiFeO2, Liþ and Fe3þ were disordered at octahedral sites and partially ordered at octahedral sites in b0 -LiFeO2 [5,6]. Thus, doping of larger positive ions, such as Naþ ions, into the octahedral sites effectively suppressed the structural phase transformation of a to b0 -LiFeO2. This effect may be attributed to the larger ions were thought to prevent positive ions from diffusions [4] at octahedral sites of LiFeO2. Fig. 8 shows SEM images of the synthesized powders of NaxLi1xFeO2 with x ¼ 0 and 0.05. For LiFeO2, the particle size increased
Fig. 8. SEM photographs of the as-synthesized (before) and carbonated (after) powders of NaxLi1-xFeO2 with x ¼ 0e0.05.
22
I. Yanase et al. / Materials Chemistry and Physics 199 (2017) 18e22
through absorption of CO2 and the specific surface area decreased from 8.3 to 4.2 m2/g. For Na0.05Li0.95FeO2, the particle size did not increase markedly through absorption of CO2 and the specific surface area decreased from 9.0 to 8.0 m2/g. Hence, the decrease of specific surface area after CO2 absorption was suppressed by the Na-substitution. This result suggests that Na-substitution for LiFeO2 may be a more effective approach for maintaining the electrochemical properties of LIB electrodes because on exposure to CO2 the specific surface area of LiFeO2 decreases and the phase decomposition reduces the performance as an electrode in LIBs. 4. Conclusion Carbonation and accompanying structural phase transformations of LiCoO2, LiNiO2, and LiFeO2 samples were investigated under a CO2 gas flow. LiCoO2 was chemically stable and its layered structure was maintained even at 600 C, while LiNiO2 reacted with CO2 above 500 C. The synthesized O3-LiFeO2 with a layered structure transformed to a-LiFeO2, and then b0 -LiFeO2 with increasing temperature under a CO2 gas flow. In addition to the structural transformation, carbonation of LiFeO2 occurred through the reaction of 2LiFeO2 þ CO2 / Li2CO3 þ Fe2O3. The Nasubstitution of LiFeO2 changed the behavior of the carbonation and the transformation under a CO2 gas flow. In the case of x ¼ 0.05, the transformation of NaxLi1-xFeO2 and the particle growth caused by carbonation was suppressed, suggesting that the Nasubstitution effectively enhanced the chemical stability of LiFeO2 under a CO2 gas flow.
[5]
[6]
[7] [8]
[9]
[10] [11] [12] [13]
[14]
[15]
[16]
[17] [18]
Acknowledgements This research was supported by a Challenging Exploratory Research No. 15K13753 for Science and Research from the Ministry of Education, Culture, Sports, Science, and Technology of Japan.
[19]
[20] [21]
References [22] [1] M.N. Obrobac, O. Mao, J.R. Dahn, Structure and electrochemistry of LiMO2 (M¼Ti, Mn, Fe, Co, Ni) prepared by mechanochemical synthesis, Solid State Ionics 112 (1998) 91e99. [2] B. Delobel, D. Larcher, J.-F. Blach, L. Croguennec, M. Menetrier, E. Simon, E. Baudrin, One-step precipitation of nanometric LiMO2 powders (M¼Co,Fe) in alcoholic media, Solid State Ionics 181 (2010) 623e630. [3] K. Zaghib, et al., Aging of LiFePO4 upon exposure to H2O, J. Power Sources 185 (2008) 698e710. [4] Y. Wang, W. Lai, Phase transformation in lithium garnet oxide ionic
[23] [24]
[25]
conductors Li7La3Zr2O12: the role of Ta substitution and H2O/CO2 exposure, J. Power Source 275 (2015) 612e620. M. Kato, K. Essaki, K. Nakagawa, Y. Suyama, K. Terasaki, Carbonation properties of lithium ferrite for application as a high-temperature CO2 absorbent, J. Ceram. Soc. Jpn. 113 (2005) 684e686. H. Eba, Enhancement of CO2 absorbance for lithium ferrite-combinatorial application of X-ray reaction fine structure imaging, Mater. Trans. 46 (2005) 665e668. M. Barre, M. Catti, Neutron diffraction study of the b0 and g phases of LiFeO2, J. Solid State Chem. 182 (2009) 2549e2554. M. Tabuchi, S. Tsutsui, C. Masquelier, R. Kanno, K. Ando, I. Matsubara, S. Nasu, H. Kageyama, Effect of cations arrangement on the magnetic properties of lithium ferrites (LiFeO2) prepared by hydrothermal reaction and postannealing method, J. Solid State Chem. 140 (1998) 159e167. Y.S. Lee, S. Sato, Y.K. Sun, K. Kobayakawa, Y. Sato, A new type of orthorhombic LiFeO2 with advanced battery performance and its structural change during cycling, J. Power Sources 110e121 (2003) 285e289. M. Wang, A. Navrotsky, LiMO2 (M¼Mn, Fe, and Co): energetics, polymorphism and phase transformation, J. Solid State Chem. 178 (2005) 1230e1240. J. Ida, R. Xiong, Y.S. Lin, Synthesis and CO2 sorption properties of pure and modified lithium zirconate, Sep. Purif. Technol. 36 (2004) 41e51. K. Essaki, M. Kato, K. Nakagawa, CO2 removal at high temperature using packed bed of lithium silicate pellets, J. Ceram. Soc. Jpn. 114 (2006) 739e742. T. Okumura, Y. Matsukura, K. Gotou, K. Ohishi, Particle size dependence of Carbonation rate of Li4SiO4 with different particle size, J. Ceram. Soc. Jpn. 116 (2008) 1283e1288. S. Shan, Q. Jia, L. Jiang, Q. Li, Y. Wang, J. Peng, Novel Li4SiO4-based sorbents from diatomite for high temperature CO2 capture, Ceram. Int. 39 (2013) 5437e5441. K. Wang, Z. Yin, P. Zhao, Synthesis of macroporous Li4SiO4 via a citric acidbased sol-gel route coupled with carbon coating and its CO2 chemisorption properties, Ceram. Int. 42 (2016) 2990e2999. M.E. Bretado, V.G. Velderra, D.L. Gutierrez, V.C. Martinez, A.L. Ortiz, A new synthesis route to Li4SiO4 as CO2 catalytic/sorbent, Catal. Today 107e108 (2005) 863e867. N. Togashi, T. Okumura, K. Ohishi, Synthesis and Carbonation property of Li4TiO4 as a novel CO2 absorbent, J. Ceram. Soc. Jpn. 115 (2007) 324e328. I. Yanase, Y. Yamakawa, H. Kobayashi, Carbonation of CaO coated on aluminosilicate foam, J. Ceram. Soc. Jpn. 116 (2008) 176e180. S. Ueno, D.D. Jayaseelan, J. She, N. Kondo, T. Ohji, S. Kanzaki, Carbon dioxide reaction mechanisms of sodium added to calcium oxide at high temperatures, Ceram. Int. 30 (2004) 1031e1034. T. Witoon, Characterization of calcium oxide derived from waste eggshell and its application as CO2 sorbent, Ceram. Int. 37 (2011) 3291e3298. D.T. Beruto, R. Botter, A. Lagazzo, E. Finocchio, Calcium oxides for CO2 capture obtained from the thermal decomposition of CaCO3 particles coprecipitated with Al3þ ions, J. Eur. Ceram. Soc. 32 (2012) 307e315. I. Yanase, A. Kameyama, H. Kobayashi, Carbonation and structural phase transformation of a-LiFeO2, J. Ceram. Soc. Jpn. 118 (2010) 48e51. I. Yanase, H. Otsuka, H. Kobayashi, Carbonation of CeO2-coated a-LiFeO2, J. Ceram. Soc. Jpn. 119 (2011) 933e938. M.J. Lambregts, S. Frank, Application of Vegard's law to mixed cation sodalites: a simple method for determining the stoichiometry, Talanta 62 (2004) 627e630. Y.-K. Kuo, B.-T. Liou, S.-H. Yen, H.-Y. Chu, Vegard's law deviation in lattice constant and band gap parameter of zincblende InxGa1-xN, Opt. Comm. 237 (2004) 363e369.
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Materials science communication
Carbonation and phase transformations of LiMO2 (M ¼ Fe, Co, Ni) under CO2 atmosphere Ikuo Yanase*, Jun Miura, Hidehiko Kobayashi Saitama University, Faculty of Engineering, Department of Applied Chemistry, 255 Shimoohkubo, Sakura-ku, Saitama-shi, Saitama, 338-8570, Japan
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
O3-LiFeO2 with a layered structure transformed to a-LiFeO2 under a CO2 gas. LiCoO2 and LiNiO2 with a layered structure are chemically stable under a CO2 gas. Na substitution stabilizes LiFeO2 phases under a CO2 gas.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 4 May 2017 Received in revised form 2 June 2017 Accepted 9 June 2017 Available online 10 June 2017
Under a CO2 gas flow, O3-LiFeO2, having a layered structure, transformed to a-LiFeO2, and then b0 -LiFeO2 with increasing temperature. All LiFeO2 phases decomposed to Fe2O3 and Li2CO3 under a CO2 gas flow. Conversely, carbonation and structural phase transformations of LiCoO2 and LiNiO2, also having layered structures, were not observed at low temperatures under a CO2 gas flow. In particular, LiCoO2 was chemically stable and its layered structure was maintained even at 600 C. The carbonation and structural phase transformations of a-LiFeO2, having a cubic structure, were suppressed compared with those of O3-LiFeO2. To investigate the effect of cation doping into LiFeO2 on carbonation and structural phase transformations, Na-substituted a-LiFeO2, NaxLi1-xFeO2 with x ¼ 0 to 0.15 was synthesized. X-ray diffraction measurements revealed that substitution of Na for Li in LiFeO2 suppressed the particle growth induced by carbonation of LiFeO2 under a CO2 gas flow. © 2017 Elsevier B.V. All rights reserved.
Keywords: Lithium ferrite Phase transformation Carbonation CO2
1. Introduction Lithium ferrites, LiFeO2, are a candidate material for cathodes in rechargeable lithium-ion secondary batteries (LIBs) [1,2]. A polymorph of LiFeO2, O3-LiFeO2 has a hexagonal layered a-NaFeO2 type structure with the space group R-3m. Recently, it has been reported that cathode materials containing lithium, such as LiFePO4 and
* Corresponding author. E-mail address: [email protected] (I. Yanase). http://dx.doi.org/10.1016/j.matchemphys.2017.06.024 0254-0584/© 2017 Elsevier B.V. All rights reserved.
Li7La3Zr2O12, undergo reactions with H2O and CO2, resulting in lower electrochemical performance of their LIBs [3,4]. Lithium ferrites, including a-LiFeO2, also react with CO2 [5,6], motivate investigations of the stability of LiFeO2 phases under CO2 atmospheres from the viewpoint of preserving the electrochemical properties of LIBs. In addition to O3-LiFeO2, LiFeO2 has several other polymorphs, such as a, b0 , g-type structures. The a-type polymorph (hereafter, aLiFeO2) has a cubic structure with the space group Fm3m, in which Liþ and Fe3þ are randomly distributed at octahedral sites. The b0 type polymorph (hereafter, b0 -LiFeO2) has an orthorhombic
I. Yanase et al. / Materials Chemistry and Physics 199 (2017) 18e22
19
LiFeO2 phase. The transformation of a-LiFeO2 can be suppressed by decreasing the amount of Li defects in LiFeO2 [22], suggesting that the chemical composition influences the carbonation rate. In this study, the chemical stability of cathode materials including LiFeO2, LiCoO2, and LiNiO2 under a CO2 atmosphere was investigated from the viewpoint of their carbonation reactivity and structure phase transformations. 2. Experimental
Fig. 1. XRD patterns of the LiCoO2 powders at room temperature (R.T.), and 400, 500, and 600 C for 5 h under a CO2 gas flow.
structure with the space group C2/c, in which Liþ and Fe3þ are partially ordered. The g-type polymorph (hereafter, g-LiFeO2) has a tetragonal structure with the space group I41/amd, in which Liþ and Fe3þ are fully ordered [7e9]. At high temperatures a-LiFeO2 is the thermodynamically stable form, while b0 -LiFeO2 is stable at moderate temperatures, and g-LiFeO2 is stable at low temperatures [7,10]. Hence, a-LiFeO2 is a metastable phase at low and moderate temperatures. Previous studies [5,6] have also reported that LiFeO2 reacts with CO2, according to the carbonation reaction, 2LiFeO2 þ CO2 / Fe2O3 þ Li2CO3. The temperature at which this reaction can occur is reported to be lower than those of other carbonation reactions with materials such as Li2ZrO3 [11], Li4SiO4 [12e16], Li4TiO4 [17] and CaO [18e21]. Thus, the LiFeO2 phase readily decomposes in the presence of CO2. It has also been reported that a-LiFeO2 transforms to b0 -LiFeO2 through its reaction with CO2 [22,23], suggesting that the chemical reaction of LiFeO2 with CO2 influences the stability of the
Fig. 2. XRD patterns of the LiNiO2 powders at room temperature (R.T.), and 400, 500, and 600 C for 5 h under a CO2 gas flow.
Commercially available g-Fe2O3, NiO, Co3O4 (>99% purity, Wako), and LiNO3 (>99% purity, Wako) powders were mixed in a 1.15: 1 M ratio of Li: M (M ¼ Fe, Ni, Co) in ethanol for 20 h by ballmilling with Al2O3 balls. After removing the ethanol by an evaporator, the mixture was dried and then heated at 600 C for 4 h in air to synthesize a-LiFeO2, LiNiO2, and LiCoO2 powders. Similarly, Nasubstituted a-LiFeO2, NaxLi1-xFeO2 with x ¼ 0e0.20, was synthesized with NaNO3 (>99% purity, Wako). O3-LiFeO2 powders were synthesized as follows; first, NaNO3 and g-Fe2O3 powders were mixed at a molar ratio of Na/Fe ¼ 1.15 in ethanol by ball-milling for 24 h. After removing the ethanol, the powder mixture was heated at 600 C for 5 h in air to synthesize a-NaFeO2 with a layered structure. The synthesized a-NaFeO2 powder was manually mixed with a large amount of LiNO3 powder and the powder mixture was heated in air at 300 C for 20 h in an alumina crucible. Finally, the heat-treated powder was washed with ethanol to remove residual NaNO3 and LiNO3 and layered O3-LiFeO2 powder was obtained. Carbonation and structural phase transformations were measured under a CO2 gas flow at a rate of 200 ml/min and a
Fig. 3. XRD patterns of the powders obtained by heating the synthesized O3-LiFeO2 powder at temperatures from 150 to 500 C for 5 h under a CO2 gas flow. C; O3LiFeO2, 〇; a-LiFeO2, :; g-Fe2O3, ,; Li2CO3, ▽; b0 -LiFeO2.
20
I. Yanase et al. / Materials Chemistry and Physics 199 (2017) 18e22
pressure of 0.1 MPa for the LiFeO2, LiCoO2, LiNiO2 and a-NaxLi1(x ¼ 0 to 0.20) synthesized directly from raw materials. The crystalline phases and morphologies of the synthesized powders were examined by X-ray diffractometry (XRD; CuKa, RINT2000, Rigaku) and field emission scanning spectroscopy (FESEM; S4100, Hitachi), respectively. The specific surface areas of the powders were investigated by Brunauer-Emmett-Teller (BET) N2 adsorption measurements (Sorptmatic1990, ThermoFisher Scientific). The lattice constants of the synthesized powders were refined by the least-squared method from the diffraction peaks of the (111), (200), (220), (311), and (222) planes, which were measured at a scan rate of 1 /min. xFeO2
3. Results and discussion Fig. 1 shows XRD patterns of the synthesized LiCoO2 with a layered structure (JCPDS 44-0145) at room temperature (R.T.), and 400, 500, and 600 C under a CO2 gas flow. The LiCoO2 sample contained a small amount of Li2CO3 and Co3O4. These compounds were produced when LiCoO2 was synthesized. The peak intensity of the Li2CO3 and Co3O4 phases did not increase from room temperature to 600 C, indicating that the LiCoO2 phase was stable under a CO2 gas flow. Fig. 2 shows XRD patterns of the synthesized LiNiO2 with a layered structure (JCPDS 09-0063) at room temperature, and 400, 500, and 600 C under a CO2 gas flow. A small amount of Li2CO3 was produced when the LiNiO2 was synthesized, similar to the case of LiCoO2. The peak intensity of the Li2CO3 and NiO phases clearly increased in the range 500e600 C under the CO2 gas flow. Fig. 3 shows XRD patterns for the powders obtained by heating
Fig. 4. XRD patterns of the powders obtained by heating the synthesized a-LiFeO2 powder at temperatures from 150 to 500 C for 5 h under a CO2 gas flow. C; O3LiFeO2, 〇; a-LiFeO2, :; g-Fe2O3, , Li2CO3, ▽ b0 -LiFeO2.
Fig. 5. Powder XRD patterns of NaxLi1-xFeO2 powders with x ¼ 0e0.20 at 600 C for 4 h in air.
the synthesized O3-LiFeO2 at temperatures in the range of 150e500 C for 5 h under a CO2 gas flow. The O3-LiFeO2 sample reacted with CO2 above 150 C. In detail, the O3-LiFeO2 peaks disappeared, and g-Fe2O3 (:) and a-LiFeO2(B) were produced at 325 C. Li2CO3 (,) and b0 -LiFeO2 (▽) were also recognized in the range 400e425 C, Li2CO3 was not recognized above 450 C. Furthermore, O3-LiFeO2 transformed to a-LiFeO2 at temperatures of 150e275 C and the peak intensity of a-LiFeO2 increased with increasing temperature in the range 300e325 C. The a-LiFeO2 sample partially transformed to b0 -LiFeO2 at temperatures in the range 350e425 C and b0 -LiFeO2 transformed to a-LiFeO2 above 450 C. From the above results, we found that the carbonation and structural phase transformations of O3-LiFeO2 were more promoted than those of LiCoO2 and LiNiO2. Fig. 4 shows the XRD patterns for the a-LiFeO2 sample, with a
Fig. 6. Relationship between x and lattice constant of NaxLi1-xFeO2 with x ¼ 0e0.15.
I. Yanase et al. / Materials Chemistry and Physics 199 (2017) 18e22
Fig. 7. Powder XRD patterns of (a) NaxLi1-xFeO2 with x ¼ 0e0.15 at 400 C for 5 h under a CO2 gas flow. 〇; a-LiFeO2, ▽; b0 - LiFeO2, :; g-Fe2O3, ,; Li2CO3.
cubic structure, at temperatures in the range 150e500 C for 5 h under a CO2 gas flow. Carbonation and structural phase transformations of a-LiFeO2 were not observed at 150 C, suggesting higher chemical stability of the a-LiFeO2 sample, with a cubic structure, than that of O3-LiFeO2 with a layered structure. It has been reported [10] that the formation enthalpy of O3-LiFeO2 is greater than that of LiCoO2 and a-LiFeO2. The trend in the
21
carbonation temperature of these compounds appeared to depend on their formation enthalpies. This is because a larger formation enthalpy means a lower thermal stability of compounds. The XRD patterns of the a-NaxLi1-xFeO2 powder in the range x ¼ 0e0.20 are shown in Fig. 5. The single phase a-NaxLi1-xFeO2 (JCPDS 82-1495; a-LiFeO2) with x ¼ 0e0.15 was synthesized, while LiFe5O8 with a spinel structure was observed for a-NaxLi1-xFeO2 with x ¼ 0.20. The relationship between x and the lattice constants of a-NaxLi1-xFeO2 is shown in Fig. 6. The lattice constant linearly increased with increasing x in the range 0e0.075, suggesting that a solid solution of a-NaxLi1-xFeO2 was produced for x < 0.075. This is because the ionic radius of Naþ is larger than that of Liþ, resulted in the linearly increased lattice constant according to Vegard's law [24,25]. Fig. 7 shows the XRD patterns of the NaxLi1-xFeO2 powder with x in the range 0e0.15 heated at 400 C under a CO2 gas flow. The products g-Fe2O3 and Li2CO3 derived from the carbonation of NaxLi1-xFeO2. A structural phase transformation of a to b0 -LiFeO2 (JCPDS 80-1159) is clearly suppressed for all Na-substituted samples and it is most pronounced for x ¼ 0.05 in NaxLi1-xFeO2. In aLiFeO2, Liþ and Fe3þ were disordered at octahedral sites and partially ordered at octahedral sites in b0 -LiFeO2 [5,6]. Thus, doping of larger positive ions, such as Naþ ions, into the octahedral sites effectively suppressed the structural phase transformation of a to b0 -LiFeO2. This effect may be attributed to the larger ions were thought to prevent positive ions from diffusions [4] at octahedral sites of LiFeO2. Fig. 8 shows SEM images of the synthesized powders of NaxLi1xFeO2 with x ¼ 0 and 0.05. For LiFeO2, the particle size increased
Fig. 8. SEM photographs of the as-synthesized (before) and carbonated (after) powders of NaxLi1-xFeO2 with x ¼ 0e0.05.
22
I. Yanase et al. / Materials Chemistry and Physics 199 (2017) 18e22
through absorption of CO2 and the specific surface area decreased from 8.3 to 4.2 m2/g. For Na0.05Li0.95FeO2, the particle size did not increase markedly through absorption of CO2 and the specific surface area decreased from 9.0 to 8.0 m2/g. Hence, the decrease of specific surface area after CO2 absorption was suppressed by the Na-substitution. This result suggests that Na-substitution for LiFeO2 may be a more effective approach for maintaining the electrochemical properties of LIB electrodes because on exposure to CO2 the specific surface area of LiFeO2 decreases and the phase decomposition reduces the performance as an electrode in LIBs. 4. Conclusion Carbonation and accompanying structural phase transformations of LiCoO2, LiNiO2, and LiFeO2 samples were investigated under a CO2 gas flow. LiCoO2 was chemically stable and its layered structure was maintained even at 600 C, while LiNiO2 reacted with CO2 above 500 C. The synthesized O3-LiFeO2 with a layered structure transformed to a-LiFeO2, and then b0 -LiFeO2 with increasing temperature under a CO2 gas flow. In addition to the structural transformation, carbonation of LiFeO2 occurred through the reaction of 2LiFeO2 þ CO2 / Li2CO3 þ Fe2O3. The Nasubstitution of LiFeO2 changed the behavior of the carbonation and the transformation under a CO2 gas flow. In the case of x ¼ 0.05, the transformation of NaxLi1-xFeO2 and the particle growth caused by carbonation was suppressed, suggesting that the Nasubstitution effectively enhanced the chemical stability of LiFeO2 under a CO2 gas flow.
[5]
[6]
[7] [8]
[9]
[10] [11] [12] [13]
[14]
[15]
[16]
[17] [18]
Acknowledgements This research was supported by a Challenging Exploratory Research No. 15K13753 for Science and Research from the Ministry of Education, Culture, Sports, Science, and Technology of Japan.
[19]
[20] [21]
References [22] [1] M.N. Obrobac, O. Mao, J.R. Dahn, Structure and electrochemistry of LiMO2 (M¼Ti, Mn, Fe, Co, Ni) prepared by mechanochemical synthesis, Solid State Ionics 112 (1998) 91e99. [2] B. Delobel, D. Larcher, J.-F. Blach, L. Croguennec, M. Menetrier, E. Simon, E. Baudrin, One-step precipitation of nanometric LiMO2 powders (M¼Co,Fe) in alcoholic media, Solid State Ionics 181 (2010) 623e630. [3] K. Zaghib, et al., Aging of LiFePO4 upon exposure to H2O, J. Power Sources 185 (2008) 698e710. [4] Y. Wang, W. Lai, Phase transformation in lithium garnet oxide ionic
[23] [24]
[25]
conductors Li7La3Zr2O12: the role of Ta substitution and H2O/CO2 exposure, J. Power Source 275 (2015) 612e620. M. Kato, K. Essaki, K. Nakagawa, Y. Suyama, K. Terasaki, Carbonation properties of lithium ferrite for application as a high-temperature CO2 absorbent, J. Ceram. Soc. Jpn. 113 (2005) 684e686. H. Eba, Enhancement of CO2 absorbance for lithium ferrite-combinatorial application of X-ray reaction fine structure imaging, Mater. Trans. 46 (2005) 665e668. M. Barre, M. Catti, Neutron diffraction study of the b0 and g phases of LiFeO2, J. Solid State Chem. 182 (2009) 2549e2554. M. Tabuchi, S. Tsutsui, C. Masquelier, R. Kanno, K. Ando, I. Matsubara, S. Nasu, H. Kageyama, Effect of cations arrangement on the magnetic properties of lithium ferrites (LiFeO2) prepared by hydrothermal reaction and postannealing method, J. Solid State Chem. 140 (1998) 159e167. Y.S. Lee, S. Sato, Y.K. Sun, K. Kobayakawa, Y. Sato, A new type of orthorhombic LiFeO2 with advanced battery performance and its structural change during cycling, J. Power Sources 110e121 (2003) 285e289. M. Wang, A. Navrotsky, LiMO2 (M¼Mn, Fe, and Co): energetics, polymorphism and phase transformation, J. Solid State Chem. 178 (2005) 1230e1240. J. Ida, R. Xiong, Y.S. Lin, Synthesis and CO2 sorption properties of pure and modified lithium zirconate, Sep. Purif. Technol. 36 (2004) 41e51. K. Essaki, M. Kato, K. Nakagawa, CO2 removal at high temperature using packed bed of lithium silicate pellets, J. Ceram. Soc. Jpn. 114 (2006) 739e742. T. Okumura, Y. Matsukura, K. Gotou, K. Ohishi, Particle size dependence of Carbonation rate of Li4SiO4 with different particle size, J. Ceram. Soc. Jpn. 116 (2008) 1283e1288. S. Shan, Q. Jia, L. Jiang, Q. Li, Y. Wang, J. Peng, Novel Li4SiO4-based sorbents from diatomite for high temperature CO2 capture, Ceram. Int. 39 (2013) 5437e5441. K. Wang, Z. Yin, P. Zhao, Synthesis of macroporous Li4SiO4 via a citric acidbased sol-gel route coupled with carbon coating and its CO2 chemisorption properties, Ceram. Int. 42 (2016) 2990e2999. M.E. Bretado, V.G. Velderra, D.L. Gutierrez, V.C. Martinez, A.L. Ortiz, A new synthesis route to Li4SiO4 as CO2 catalytic/sorbent, Catal. Today 107e108 (2005) 863e867. N. Togashi, T. Okumura, K. Ohishi, Synthesis and Carbonation property of Li4TiO4 as a novel CO2 absorbent, J. Ceram. Soc. Jpn. 115 (2007) 324e328. I. Yanase, Y. Yamakawa, H. Kobayashi, Carbonation of CaO coated on aluminosilicate foam, J. Ceram. Soc. Jpn. 116 (2008) 176e180. S. Ueno, D.D. Jayaseelan, J. She, N. Kondo, T. Ohji, S. Kanzaki, Carbon dioxide reaction mechanisms of sodium added to calcium oxide at high temperatures, Ceram. Int. 30 (2004) 1031e1034. T. Witoon, Characterization of calcium oxide derived from waste eggshell and its application as CO2 sorbent, Ceram. Int. 37 (2011) 3291e3298. D.T. Beruto, R. Botter, A. Lagazzo, E. Finocchio, Calcium oxides for CO2 capture obtained from the thermal decomposition of CaCO3 particles coprecipitated with Al3þ ions, J. Eur. Ceram. Soc. 32 (2012) 307e315. I. Yanase, A. Kameyama, H. Kobayashi, Carbonation and structural phase transformation of a-LiFeO2, J. Ceram. Soc. Jpn. 118 (2010) 48e51. I. Yanase, H. Otsuka, H. Kobayashi, Carbonation of CeO2-coated a-LiFeO2, J. Ceram. Soc. Jpn. 119 (2011) 933e938. M.J. Lambregts, S. Frank, Application of Vegard's law to mixed cation sodalites: a simple method for determining the stoichiometry, Talanta 62 (2004) 627e630. Y.-K. Kuo, B.-T. Liou, S.-H. Yen, H.-Y. Chu, Vegard's law deviation in lattice constant and band gap parameter of zincblende InxGa1-xN, Opt. Comm. 237 (2004) 363e369.