- Email: [email protected]
Annealing effects of TiO2 coating on cycling performance of Ni-rich cathode material LiNi0.8Co0.1Mn0.1O2 for lithium-ion battery
Materials Letters 265 (2020) 127418
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Annealing effects of TiO2 coating on cycling performance of Ni-rich cathode material LiNi0.8Co0.1Mn0.1O2 for lithium-ion battery Shunyu Zhao a, Yutao Zhu a, Yucheng Qian b, Nengneng Wang a, Meng Zhao a, Jinlei Yao a,⇑, Yanhui Xu c,⇑ a Jiangsu Key Laboratory of Micro and Nano Heat Fluid Flow Technology and Energy Application, School of Mathematics and Physics, Suzhou University of Science and Technology, Suzhou 215009, China b School of Chemistry, Biology and Materials Engineering, Suzhou University of Science and Technology, Suzhou 215009, China c School of Iron and Steel, Soochow University, Suzhou 215006, China
a r t i c l e
i n f o
Article history: Received 23 December 2019 Received in revised form 23 January 2020 Accepted 23 January 2020 Available online 24 January 2020 Keywords: Li-ion batteries Cathodes Crystal structure Microstructure Energy storage and conversion
a b s t r a c t Ni-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode particles were coated with anatase TiO2 layer to improve its cycle stability. The TiO2 coating was synthesized by the hydrolyzation method and subsequent annealing treatment ranging from 500 ℃ to 600 ℃. The well-ordered layered a-NaFeO2-type structure survives in the TiO2 coating process. The nanothick anatase TiO2 layer coveres on the surface of NCM811. The annealing temperature of coating was controlled to improve the electrochemical performances. The TiO2-coated NCM811 cathode annealed at 600 ℃ demonstrates the optimal capacity retention of 104.9% after 100 cycles at the current rate of 0.1 C, in contrast to 64.1% of pristine NCM811 and 96.7% of the coated sample annealed at 500 ℃. Ó 2020 Published by Elsevier B.V.
1. Introduction Nickel-rich layered oxides, such as LiNixCoyMn1-x-yO2 and LiNixCoyAl1-x-yO2, are considered as a kind of promising cathode materials for Li-ion batteries due to their high specific capacity (~200 mAh g 1), low cost, good rate capability, and environment friendly in contrast to conventional LiCoO2 [1]. However, the Ni-containing cathodes easily react with electrolyte, leading to the structural degradation and rapid capacity fading [2]. In addition, the lithium residues, such as LiOH and Li2CO3 [3], generate gas CO2, deteriorating the cycle performance and causing potential safety problems [4]. One effective way to enhance the electrochemical performances and thermal stability of Ni-rich cathodes is to coat the cathodic particles with a stable layer, e.g., fluoride (LiF [5]), metallic oxide (Al2O3 [6]), phosphate (Ni3(PO4)2 [7]), and carbon [8]. The coatings can mitigate the reaction between electrolyte and active materials, so that the cycle performance will not fade dramatically. Especially, TiO2 was widely used as a coating material due to its low cost, environment friendly, and excellent structural stability. For instance, Liu et al. demonstrated that the high-temperature electrochemical performances of LiNi0.5Co0.2Mn0.3O2 were improved
⇑ Corresponding authors. E-mail addresses: [email protected] (J. Yao), [email protected] (Y. Xu). https://doi.org/10.1016/j.matlet.2020.127418 0167-577X/Ó 2020 Published by Elsevier B.V.
by TiO2 coating, e.g., the capacity retention of 92.1% for the TiO2-coated cathode vs. 48.2% for the bare one after 100 cycles at 0.5 C at 328 K [9]. These TiO2 coating layers were generally synthesized by wet chemical processes and subsequent annealing treatment. Many efforts were devoted to optimize the amount of TiO2 coating to yield superior electrochemical performances of Ni-rich cathodes [10]. As known, the crystal structures and microstructures of coating layers are also affected by the annealing treatment, which was rarely discussed in the previous studies. In this work, we have attempted to investigate the annealing effects of TiO2 coating on the cathodic behaviors of a typical Ni-rich material LiNi0.8Co0.1Mn0.1O2 (NCM811).
2. Experimental The bare NCM811 powder was prepared by mixing LiOHH2O and precursor Ni0.8Co0.1Mn0.1(OH)2 with a molar ratio of 1.02:1 and then calcining in air at 700 ℃ for 15 h as reported in Ref. [1]. The TiO2-coated NCM811 samples were synthesized using a hydrolyzation method. Firstly, deionized water was dripped into TiOSO4xH2SO4xH2O, and added ammonium hydroxide solution (25%, AR) to the solution and stirred, followed by adding the former precipitate to ethanol with NCM811, which was evaporated in a vacuum oven at 60 ℃ for 2 h. Finally, the dried mixture was divided into three parts and then calcined in air at 500 ℃, 550 ℃, and 600 ℃
2
S. Zhao et al. / Materials Letters 265 (2020) 127418
for 3 h, which were respectively denoted as Ti@500, Ti@550, and Ti@600 below. The CR2032-type coin cells were assembled using the same procedure in Ref. [9]. The electrolyte was made from 1 M LiPF6 dissolved in a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate with a volume ratio of 1:1:1. The phase and crystal structure of samples were characterized by X-ray diffraction (XRD) diffractometer (Bruker D8) with Cu-Ka radiation. The particle morphology and element analysis were observed through scanning electron microscope (SEM, Japan SU8010) and transmission electron microscope (TEM, JOEL JEM2100F) with an energy dispersive X-ray spectroscopy detector (EDS, Bruker XFlash 6T|60). The charge-discharge and Nyquist spectra on the coin cells were recorded by a CT2001A system and a CHI660C electrochemical workstation, respectively.
3. Results and discussion The powder XRD patterns in Fig. S1a shows that all the pristine and TiO2-coated NCM811 samples crystallize in the a-NaFeO2 structure with space group R-3m [11]. The clear splitting peaks of (0 0 6)/(0 1 2) and (0 1 8)/(1 1 0) confirm the well-ordered layered structure, suggesting that the crystal structure of NCM811 is not changed by the TiO2 coating processes. No peaks associated with TiO2 can be observed in the patterns, indicating the trace mount of coating phase below the XRD detection limit. To investigate the coating phase on NCM811, the considerable amount of white TiO2 powder without NCM811 was calcined. The XRD patterns in Fig. S1b reveal that the powder annealed at 600 ℃ can be assigned to the crystallized anatase TiO2 phase [12], whereas that at 500 ℃ is a mixture of the anatase and amorphous phases. It suggests the high annealing temperature benefits the crystallization of TiO2 phase. The TiO2-coated samples have the refined lattice volume close to the bare NCM811, i.e., 101.74(3) ~ 101.81(4) Å3 vs. 101.76(1) Å3, indicating the Ti atoms do not incorporate into the NCM811 lattice. The relatively low sintering temperatures (lower than 600 ℃ this work) favor forming the secondary oxides for the metal
precursors, while the high temperatures (higher than 700 ℃) drives the precursors to substitute the metal atoms of NCM811 to form solid solutions as observed in the ZrO2-coated and Zr-doped NCM811 [13]. The SEM images in Fig. S2 display that all the samples are composed of spheroidal particles around 11 lm in diameter, which are composed of the compacting secondary sedimentation particles around 0.5 lm. The TEM-EDS mapping of Ti@600 in Fig. 1 displays uniform distribution of the constituent elements Ti, Ni, Co, Mn, and O, implying the TiO2 coating disperses homogenously on the surface of NCM811 particles. The low resolution TEM image in Fig. 2a displays a clear layer around 6 nm in thickness covering the active material. Furthermore, the high resolution TEM image in Fig. 2b exhibits the interplanar distance of 0.476 nm corresponding to the plane (0 0 3) of NCM811 [1], while the d-spacing of 0.239 nm is the plane (0 0 4) of anatase TiO2 [14]. Fig. 3a shows the initial charge/discharge capacity of NCM811 is 219.1/181.8 mAh g 1, resulting in a Coulombic efficiency of 83.0%. Its irreversible capacity reaches 37.3 mAh g 1, due to the Li+/Ni2+ disorder [15]. For the TiO2-coated samples, they display the similar charge/discharge features to the bare NCM811, e.g., stable and smooth voltage plateau, suggesting that the intrinsic electrochemical properties of NCM811 survive in the coated cathodes [16]. In Fig. 3b, the discharge capacity of pristine NCM811 fades from 181.8 mAh g 1 at the first cycle to 116.5 mAh g 1 after 100 cycles, corresponding to the capacity retention of 64.1%. In contrast, the TiO2-coated cathodes remain 96.7%, 93.9%, and 104.9% for Ti@500, Ti@550, and Ti@600 after 100 cycles, respectively. Obviously, the TiO2 coating is an effective way to prevent capacity fading. Compared to Ti@500, the Ti@550 and Ti@600 cathodes exhibit the better cycling performance, probably related to the crystallinity degree of coating. The Nyquist plots were fitted by the equivalent circuit model in Fig. 3c. The fits yielded the charge transfer resistance Rct of 73.1 X, 111.7 X, 89.0 X, and 83.1 X for the NCM811, Ti@500, Ti@550, and Ti@600 samples, respectively. Anatase TiO2 is a wide bandgap semiconductor (Eg ~ 3.2 eV) and thus has low electrical conductivity [17]. Consequently, the TiO2-coated cathodes are expected to show a higher Rct than NCM811 as reported in TiO2-coated
Fig. 1. TEM-EDS mapping of Ti@600 particle.
S. Zhao et al. / Materials Letters 265 (2020) 127418
3
Fig. 2. (a) Low and (b) high resolution TEM image of Ti@600.
Fig. 3. (a) Initial cycle capacity, (b) cycle number dependence of discharge capacity at 0.1 C, and (c) Nyquist plots of pristine and TiO2-coated NCM811 after 10 cycles. The solid lines in (c) represent the best fit to the data using the equivalent circuit in the inset.
Li2MnO3 (see Table S1) [14]. In the coated cathodes, high annealing temperature favors the Ti-containing amorphous precursor to crystallize on the particle surface. Therefore, the crystallized Ti@600 cathode displays smaller Rct than Ti@500 and Ti@550. The reduced Rct inhabits side reactions between electrode and electrolyte and thus improves the cycling performance, which was also observed in many surface-modified cathodes, such as LiNi0.8Co0.15Al0.05O2@Ni3(PO4)2 [7], Li2MnO3@TiO2 [14], and sulfonate-coated NCM811 [18] (see Table S1). The aforementioned TEM and XRD results demonstrate that anatase TiO2 acts as a shell material covering the core NCM811 particles. The coating decreases the contact between active material and electrolyte, therefore, the electrolyte corrosion during the charging/discharging cycles can be significantly inhibited, leading to excellent cycling stability. Furthermore, the electrochemical properties are affected by the crystallinity degree of coating. Compared to Ti@500 containing the partial amorphous phase, the completely crystallized Ti@600 exhibits the optimum electrochemical performance. 4. Conclusion In summary, the Ni-rich NCM811 particles can be covered with the anatase TiO2 coating. The coating layer is believed to suppress the electrolyte corrosion on the active cathodes, improving their cycling stability. Simultaneously, the processing factors of coating, such as annealing temperature and atmosphere, are worth controlling to get the high-quality layer, leading to the improvement of electrochemical performances of surface-modified cathodes. CRediT authorship contribution statement Shunyu Zhao: Data curation, Investigation, Writing - original draft. Yutao Zhu: Formal analysis, Validation, Writing - original draft. Yucheng Qian: Data curation. Nengneng Wang:
Methodology. Meng Zhao: Formal analysis. Jinlei Yao: Writing original draft, Writing - review & editing, Funding acquisition. Yanhui Xu: Conceptualization, Supervision. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgement This work is supported by CNSF (Nos. 21771136 and 51301116), Jiangsu Undergraduate Training Program for Innovation and Entrepreneurship (No. 201810332029Z), USTS Graduate Research and Practice Innovation Project (No. SKCX18_Y15), Natural Science Foundation of Jiangsu Higher Education Institutions (Nos. 17KJA140001 and 18KJA470004), Jiangsu Key Disciplines of Thirteen Five-Year Plan (No. 20168765), and Jiangsu 333 Project. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.matlet.2020.127418. References [1] T. Li, X. Li, Z. Wang, H. Guo, J. Power Sources 342 (2017) 495–503. [2] C. Lu, W. Lee, J. Mater. Chem. 10 (2000) 1403–1407. [3] Q. Liu, K. Du, H. Guo, Z. Peng, Y. Cao, G. Hu, Electrochim. Acta 90 (2013) 350– 357. [4] D. Cho, C. Jo, W. Cho, Y. Kim, H. Yashiro, Y. Su, S. Myung, J. Electrochem. Soc. 161 (2014) A920–A926. [5] X. Xiong, Z. Wang, X. Yin, H. Guo, X. Li, Mater. Lett. 110 (2013) 4–9. [6] S. Sheng, G. Chen, B. Hu, R. Yang, Y. Xu, J. Electroanal. Chem. 795 (2017) 59–67. [7] D. Lee, B. Scrosati, Y. Sun, J. Power Sources 196 (2011) 7742–7746. [8] B. Cushing, J. Goodenough, Solid State Sci. 4 (2002) 1487–1493.
4
S. Zhao et al. / Materials Letters 265 (2020) 127418
[9] W. Liu, M. Wang, X. Gao, W. Zhang, J. Chen, H. Zhou, X. Zhang, J. Alloys. Compd. 543 (2012) 181–188. [10] T. Subburaj, Y. Jo, K. Prasanna, K. Kim, C. Lee, J. Ind. Eng. Chem. 51 (2017) 223– 228. [11] R. Stoyanova, E. Zhecheva, R. Alcantara, J. Tirado, G. Bromiley, F. Bromiley, T. Ballaran, Solid State Ionics 161 (2003) 197–204. [12] A. Ghicov, S. Albu, R. Hahn, D. Kim, T. Stergiopoulos, J. Kunze, C. Schiller, P. Falaras, P. Schmuki, Chem. Asian J. 4 (2009) 520–525. [13] F. Schipper, H. Bouzaglo, M. Dixit, E. Erickson, T. Weigel, M. Talianker, J. Grinblat, L. Burstein, M. Schmidt, J. Lampert, C. Erk, B. Markovsky, D. Major, D. Aurbach, Adv. Energy Mater. 8 (2018) 1701682.
[14] S. Kim, M. Kim, D. Kwak, D. Kim, G. Lee, H. Choe, K. Park, J. Power Sources 304 (2016) 119–127. [15] C. Delmas, M. Menetrier, L. Croguennec, I. Saadoune, A. Rougier, C. Pouillerie, G. Prado, M. Grune, L. Fournes, Electrochim. Acta 45 (1999) 243–253. [16] S. Kalluri, M. Yoon, M. Jo, H. Liu, S. Dou, J. Cho, Z. Guo, Adv. Mater. 29 (2017) 1605807. [17] C. Dette, M. Perez-Osorio, C. Kley, P. Punke, C. Patrick, P. Jacobson, F. Giustino, S. Jung, K. Kern, Nano. Lett. 14 (2014) 6533–6538. [18] B. Chae, T. Yim, J. Power Sources 360 (2017) 480–487.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Annealing effects of TiO2 coating on cycling performance of Ni-rich cathode material LiNi0.8Co0.1Mn0.1O2 for lithium-ion battery Shunyu Zhao a, Yutao Zhu a, Yucheng Qian b, Nengneng Wang a, Meng Zhao a, Jinlei Yao a,⇑, Yanhui Xu c,⇑ a Jiangsu Key Laboratory of Micro and Nano Heat Fluid Flow Technology and Energy Application, School of Mathematics and Physics, Suzhou University of Science and Technology, Suzhou 215009, China b School of Chemistry, Biology and Materials Engineering, Suzhou University of Science and Technology, Suzhou 215009, China c School of Iron and Steel, Soochow University, Suzhou 215006, China
a r t i c l e
i n f o
Article history: Received 23 December 2019 Received in revised form 23 January 2020 Accepted 23 January 2020 Available online 24 January 2020 Keywords: Li-ion batteries Cathodes Crystal structure Microstructure Energy storage and conversion
a b s t r a c t Ni-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode particles were coated with anatase TiO2 layer to improve its cycle stability. The TiO2 coating was synthesized by the hydrolyzation method and subsequent annealing treatment ranging from 500 ℃ to 600 ℃. The well-ordered layered a-NaFeO2-type structure survives in the TiO2 coating process. The nanothick anatase TiO2 layer coveres on the surface of NCM811. The annealing temperature of coating was controlled to improve the electrochemical performances. The TiO2-coated NCM811 cathode annealed at 600 ℃ demonstrates the optimal capacity retention of 104.9% after 100 cycles at the current rate of 0.1 C, in contrast to 64.1% of pristine NCM811 and 96.7% of the coated sample annealed at 500 ℃. Ó 2020 Published by Elsevier B.V.
1. Introduction Nickel-rich layered oxides, such as LiNixCoyMn1-x-yO2 and LiNixCoyAl1-x-yO2, are considered as a kind of promising cathode materials for Li-ion batteries due to their high specific capacity (~200 mAh g 1), low cost, good rate capability, and environment friendly in contrast to conventional LiCoO2 [1]. However, the Ni-containing cathodes easily react with electrolyte, leading to the structural degradation and rapid capacity fading [2]. In addition, the lithium residues, such as LiOH and Li2CO3 [3], generate gas CO2, deteriorating the cycle performance and causing potential safety problems [4]. One effective way to enhance the electrochemical performances and thermal stability of Ni-rich cathodes is to coat the cathodic particles with a stable layer, e.g., fluoride (LiF [5]), metallic oxide (Al2O3 [6]), phosphate (Ni3(PO4)2 [7]), and carbon [8]. The coatings can mitigate the reaction between electrolyte and active materials, so that the cycle performance will not fade dramatically. Especially, TiO2 was widely used as a coating material due to its low cost, environment friendly, and excellent structural stability. For instance, Liu et al. demonstrated that the high-temperature electrochemical performances of LiNi0.5Co0.2Mn0.3O2 were improved
⇑ Corresponding authors. E-mail addresses: [email protected] (J. Yao), [email protected] (Y. Xu). https://doi.org/10.1016/j.matlet.2020.127418 0167-577X/Ó 2020 Published by Elsevier B.V.
by TiO2 coating, e.g., the capacity retention of 92.1% for the TiO2-coated cathode vs. 48.2% for the bare one after 100 cycles at 0.5 C at 328 K [9]. These TiO2 coating layers were generally synthesized by wet chemical processes and subsequent annealing treatment. Many efforts were devoted to optimize the amount of TiO2 coating to yield superior electrochemical performances of Ni-rich cathodes [10]. As known, the crystal structures and microstructures of coating layers are also affected by the annealing treatment, which was rarely discussed in the previous studies. In this work, we have attempted to investigate the annealing effects of TiO2 coating on the cathodic behaviors of a typical Ni-rich material LiNi0.8Co0.1Mn0.1O2 (NCM811).
2. Experimental The bare NCM811 powder was prepared by mixing LiOHH2O and precursor Ni0.8Co0.1Mn0.1(OH)2 with a molar ratio of 1.02:1 and then calcining in air at 700 ℃ for 15 h as reported in Ref. [1]. The TiO2-coated NCM811 samples were synthesized using a hydrolyzation method. Firstly, deionized water was dripped into TiOSO4xH2SO4xH2O, and added ammonium hydroxide solution (25%, AR) to the solution and stirred, followed by adding the former precipitate to ethanol with NCM811, which was evaporated in a vacuum oven at 60 ℃ for 2 h. Finally, the dried mixture was divided into three parts and then calcined in air at 500 ℃, 550 ℃, and 600 ℃
2
S. Zhao et al. / Materials Letters 265 (2020) 127418
for 3 h, which were respectively denoted as Ti@500, Ti@550, and Ti@600 below. The CR2032-type coin cells were assembled using the same procedure in Ref. [9]. The electrolyte was made from 1 M LiPF6 dissolved in a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate with a volume ratio of 1:1:1. The phase and crystal structure of samples were characterized by X-ray diffraction (XRD) diffractometer (Bruker D8) with Cu-Ka radiation. The particle morphology and element analysis were observed through scanning electron microscope (SEM, Japan SU8010) and transmission electron microscope (TEM, JOEL JEM2100F) with an energy dispersive X-ray spectroscopy detector (EDS, Bruker XFlash 6T|60). The charge-discharge and Nyquist spectra on the coin cells were recorded by a CT2001A system and a CHI660C electrochemical workstation, respectively.
3. Results and discussion The powder XRD patterns in Fig. S1a shows that all the pristine and TiO2-coated NCM811 samples crystallize in the a-NaFeO2 structure with space group R-3m [11]. The clear splitting peaks of (0 0 6)/(0 1 2) and (0 1 8)/(1 1 0) confirm the well-ordered layered structure, suggesting that the crystal structure of NCM811 is not changed by the TiO2 coating processes. No peaks associated with TiO2 can be observed in the patterns, indicating the trace mount of coating phase below the XRD detection limit. To investigate the coating phase on NCM811, the considerable amount of white TiO2 powder without NCM811 was calcined. The XRD patterns in Fig. S1b reveal that the powder annealed at 600 ℃ can be assigned to the crystallized anatase TiO2 phase [12], whereas that at 500 ℃ is a mixture of the anatase and amorphous phases. It suggests the high annealing temperature benefits the crystallization of TiO2 phase. The TiO2-coated samples have the refined lattice volume close to the bare NCM811, i.e., 101.74(3) ~ 101.81(4) Å3 vs. 101.76(1) Å3, indicating the Ti atoms do not incorporate into the NCM811 lattice. The relatively low sintering temperatures (lower than 600 ℃ this work) favor forming the secondary oxides for the metal
precursors, while the high temperatures (higher than 700 ℃) drives the precursors to substitute the metal atoms of NCM811 to form solid solutions as observed in the ZrO2-coated and Zr-doped NCM811 [13]. The SEM images in Fig. S2 display that all the samples are composed of spheroidal particles around 11 lm in diameter, which are composed of the compacting secondary sedimentation particles around 0.5 lm. The TEM-EDS mapping of Ti@600 in Fig. 1 displays uniform distribution of the constituent elements Ti, Ni, Co, Mn, and O, implying the TiO2 coating disperses homogenously on the surface of NCM811 particles. The low resolution TEM image in Fig. 2a displays a clear layer around 6 nm in thickness covering the active material. Furthermore, the high resolution TEM image in Fig. 2b exhibits the interplanar distance of 0.476 nm corresponding to the plane (0 0 3) of NCM811 [1], while the d-spacing of 0.239 nm is the plane (0 0 4) of anatase TiO2 [14]. Fig. 3a shows the initial charge/discharge capacity of NCM811 is 219.1/181.8 mAh g 1, resulting in a Coulombic efficiency of 83.0%. Its irreversible capacity reaches 37.3 mAh g 1, due to the Li+/Ni2+ disorder [15]. For the TiO2-coated samples, they display the similar charge/discharge features to the bare NCM811, e.g., stable and smooth voltage plateau, suggesting that the intrinsic electrochemical properties of NCM811 survive in the coated cathodes [16]. In Fig. 3b, the discharge capacity of pristine NCM811 fades from 181.8 mAh g 1 at the first cycle to 116.5 mAh g 1 after 100 cycles, corresponding to the capacity retention of 64.1%. In contrast, the TiO2-coated cathodes remain 96.7%, 93.9%, and 104.9% for Ti@500, Ti@550, and Ti@600 after 100 cycles, respectively. Obviously, the TiO2 coating is an effective way to prevent capacity fading. Compared to Ti@500, the Ti@550 and Ti@600 cathodes exhibit the better cycling performance, probably related to the crystallinity degree of coating. The Nyquist plots were fitted by the equivalent circuit model in Fig. 3c. The fits yielded the charge transfer resistance Rct of 73.1 X, 111.7 X, 89.0 X, and 83.1 X for the NCM811, Ti@500, Ti@550, and Ti@600 samples, respectively. Anatase TiO2 is a wide bandgap semiconductor (Eg ~ 3.2 eV) and thus has low electrical conductivity [17]. Consequently, the TiO2-coated cathodes are expected to show a higher Rct than NCM811 as reported in TiO2-coated
Fig. 1. TEM-EDS mapping of Ti@600 particle.
S. Zhao et al. / Materials Letters 265 (2020) 127418
3
Fig. 2. (a) Low and (b) high resolution TEM image of Ti@600.
Fig. 3. (a) Initial cycle capacity, (b) cycle number dependence of discharge capacity at 0.1 C, and (c) Nyquist plots of pristine and TiO2-coated NCM811 after 10 cycles. The solid lines in (c) represent the best fit to the data using the equivalent circuit in the inset.
Li2MnO3 (see Table S1) [14]. In the coated cathodes, high annealing temperature favors the Ti-containing amorphous precursor to crystallize on the particle surface. Therefore, the crystallized Ti@600 cathode displays smaller Rct than Ti@500 and Ti@550. The reduced Rct inhabits side reactions between electrode and electrolyte and thus improves the cycling performance, which was also observed in many surface-modified cathodes, such as LiNi0.8Co0.15Al0.05O2@Ni3(PO4)2 [7], Li2MnO3@TiO2 [14], and sulfonate-coated NCM811 [18] (see Table S1). The aforementioned TEM and XRD results demonstrate that anatase TiO2 acts as a shell material covering the core NCM811 particles. The coating decreases the contact between active material and electrolyte, therefore, the electrolyte corrosion during the charging/discharging cycles can be significantly inhibited, leading to excellent cycling stability. Furthermore, the electrochemical properties are affected by the crystallinity degree of coating. Compared to Ti@500 containing the partial amorphous phase, the completely crystallized Ti@600 exhibits the optimum electrochemical performance. 4. Conclusion In summary, the Ni-rich NCM811 particles can be covered with the anatase TiO2 coating. The coating layer is believed to suppress the electrolyte corrosion on the active cathodes, improving their cycling stability. Simultaneously, the processing factors of coating, such as annealing temperature and atmosphere, are worth controlling to get the high-quality layer, leading to the improvement of electrochemical performances of surface-modified cathodes. CRediT authorship contribution statement Shunyu Zhao: Data curation, Investigation, Writing - original draft. Yutao Zhu: Formal analysis, Validation, Writing - original draft. Yucheng Qian: Data curation. Nengneng Wang:
Methodology. Meng Zhao: Formal analysis. Jinlei Yao: Writing original draft, Writing - review & editing, Funding acquisition. Yanhui Xu: Conceptualization, Supervision. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgement This work is supported by CNSF (Nos. 21771136 and 51301116), Jiangsu Undergraduate Training Program for Innovation and Entrepreneurship (No. 201810332029Z), USTS Graduate Research and Practice Innovation Project (No. SKCX18_Y15), Natural Science Foundation of Jiangsu Higher Education Institutions (Nos. 17KJA140001 and 18KJA470004), Jiangsu Key Disciplines of Thirteen Five-Year Plan (No. 20168765), and Jiangsu 333 Project. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.matlet.2020.127418. References [1] T. Li, X. Li, Z. Wang, H. Guo, J. Power Sources 342 (2017) 495–503. [2] C. Lu, W. Lee, J. Mater. Chem. 10 (2000) 1403–1407. [3] Q. Liu, K. Du, H. Guo, Z. Peng, Y. Cao, G. Hu, Electrochim. Acta 90 (2013) 350– 357. [4] D. Cho, C. Jo, W. Cho, Y. Kim, H. Yashiro, Y. Su, S. Myung, J. Electrochem. Soc. 161 (2014) A920–A926. [5] X. Xiong, Z. Wang, X. Yin, H. Guo, X. Li, Mater. Lett. 110 (2013) 4–9. [6] S. Sheng, G. Chen, B. Hu, R. Yang, Y. Xu, J. Electroanal. Chem. 795 (2017) 59–67. [7] D. Lee, B. Scrosati, Y. Sun, J. Power Sources 196 (2011) 7742–7746. [8] B. Cushing, J. Goodenough, Solid State Sci. 4 (2002) 1487–1493.
4
S. Zhao et al. / Materials Letters 265 (2020) 127418
[9] W. Liu, M. Wang, X. Gao, W. Zhang, J. Chen, H. Zhou, X. Zhang, J. Alloys. Compd. 543 (2012) 181–188. [10] T. Subburaj, Y. Jo, K. Prasanna, K. Kim, C. Lee, J. Ind. Eng. Chem. 51 (2017) 223– 228. [11] R. Stoyanova, E. Zhecheva, R. Alcantara, J. Tirado, G. Bromiley, F. Bromiley, T. Ballaran, Solid State Ionics 161 (2003) 197–204. [12] A. Ghicov, S. Albu, R. Hahn, D. Kim, T. Stergiopoulos, J. Kunze, C. Schiller, P. Falaras, P. Schmuki, Chem. Asian J. 4 (2009) 520–525. [13] F. Schipper, H. Bouzaglo, M. Dixit, E. Erickson, T. Weigel, M. Talianker, J. Grinblat, L. Burstein, M. Schmidt, J. Lampert, C. Erk, B. Markovsky, D. Major, D. Aurbach, Adv. Energy Mater. 8 (2018) 1701682.
[14] S. Kim, M. Kim, D. Kwak, D. Kim, G. Lee, H. Choe, K. Park, J. Power Sources 304 (2016) 119–127. [15] C. Delmas, M. Menetrier, L. Croguennec, I. Saadoune, A. Rougier, C. Pouillerie, G. Prado, M. Grune, L. Fournes, Electrochim. Acta 45 (1999) 243–253. [16] S. Kalluri, M. Yoon, M. Jo, H. Liu, S. Dou, J. Cho, Z. Guo, Adv. Mater. 29 (2017) 1605807. [17] C. Dette, M. Perez-Osorio, C. Kley, P. Punke, C. Patrick, P. Jacobson, F. Giustino, S. Jung, K. Kern, Nano. Lett. 14 (2014) 6533–6538. [18] B. Chae, T. Yim, J. Power Sources 360 (2017) 480–487.