Thermal Stability of NCM622 Cathode Material for Li-ion Batteries: A Real-time Synchrotron X-ray Scattering Study

Thermal Stability of NCM622 Cathode Material for Li-ion Batteries: A Real-time Synchrotron X-ray Scattering Study | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Thermal Stability of NCM622 Cathode Material for Li-ion Batteries: A Real-time Synchrotron X-ray Scattering Study Seung-Han Lee, Tae-Sik Cho This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7570733/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract We have studied the thermal stability of NCM622 oxide cathode material for Li-ion batteries using a real-time synchrotron x-ray scattering in air and in vacuum. The amount of crystal NCM622 phase in air and in vacuum showed almost constant values below 600°C. This indicates that the NCM622 cathode material with layered structure was thermally stable in air and in vacuum. Considering the amount of crystal phase and the change of crystal domain sizes, the NCM622 cathode material in air was more thermally stable than that in vacuum. These are due to the presence of 21% oxygen in the air, which is not in the vacuum. Our study revealed the detailed thermal stability of NCM622 cathode material during real-time annealing below 600°C in air and in vacuum. Li-ion batteries NCM622 cathode material Thermal stability Real-time synchrotron x-ray scattering Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 I. INTRODUCTION Li-ion batteries are attracting attention as a major material for the high-tech industry due to their excellent characteristics such as higher energy density and fast charging/discharging speed compared to conventional secondary batteries [ 1 , 2 ]. However, there are risks of explosion because the separator between cathode and anode is damaged by shocking or degraded by exposure to high temperatures [ 3 ]. LiNiCoMnO 2 (NCM) oxide cathode material is a cathode material in which Co and Mn are added to the conventional LiNiO2 to improve the stability of the battery [ 4 ]. Heat treatment of NCM cathode material induces a layered-to-rock salt structure phase transition near the high temperature of 700°C accompanied with the precipitation of Li 2 O, restricts the movement of Li-ions [ 5 ]. LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) cathode material has been used as batteries for electric vehicles requiring high energy density [ 6 ]. The thermal stability of NCM622 cathode material during real-time annealing below 700°C, however, has not been well characterized. In this article, we present a real-time synchrotron x-ray scattering study to examine the thermal stability of NCM622 cathode material during annealing below 600°C in air and in vacuum. Synchrotron x-ray scattering with very high flux and high resolution is one of the most effective ways to examine the detailed behaviors of advanced materials during annealing [ 7 , 8 ]. Our study revealed the detailed thermal stability of NCM622 cathode material during real-time annealing below 600°C in air and in vacuum. II. EXPERIMENTS DETAILS The NCM622 cathode powders were prepared by dry mixing NCM622 precursor powder (Ni 0.6 Co 0.2 Mn 0.2 (OH) 2 ) and Li 2 CO 3 powder (Sigma Aldrich, ≥ 99.0%) using ball milling, followed by sintering in the air with a high-temperature electric furnace [ 9 ]. The NCM precursor powders were synthesized by co-precipitation, in which metal sulfate was dissolved in NaOH and NH 4 OH in water and then precipitated [ 10 ]. The surface micrographs and chemical composition of the NCM622 cathode powders were investigated using scanning eletron microscope-energy dispersive spectroscopy (SEM-EDS). The NCM622 powders were post-annealed at several temperatures from room temperature (RT) to 600°C for 30 minutes. The chemical composition of the NCM622 powders indicated LiNi 0.62 Co 0.20 Mn 0.18 O 2 , sililar to the LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622). The mean particle size of the NCM622 powders was quantitatively measured using a particle size analyzer based on each SEM micrograph. In the meanwhile, the real-time synchrotron x-ray scattering experiments were performed at beamline 5D (GIST) at Pohang Light Source in Korea. The incident x-rays were vertically focused by a mirror, and monochromatized to a wavelength of 1.240 Å. The experiments were carried out by measuring the x-ray powder diffraction profiles during annealing in air and in vacuum. The NCM622 cathode powders were annealed using a heating stage, which was set on a four-circle x-ray diffractometer for the real-time x-ray measurements. The annealing temperature increased gradually and stayed constant during the x-ray measurements. III. RESULTS AND DISCUSSION Figure 1 shows the surface SEM micrographs of the NCM622 cathode powders at several post-annealed temperatures in air (a, b, and c) and in vacuum (d and e). At RT in Fig. 1 (a), the shape of the NCM622 powders was close to spherical, and the particle size distribution was very uniform. After post-annealed up to 600°C in air and in vacuum, the shape of the powders was equally close to spherical, and the particle size distribution was very uniform. In addition, the mean particle size of the NCM622 powders was quantitatively measured using a particle size analyzer based on each SEM micrograph. Figure 2 shows the mean particle sizes of NCM622 cathode powders at several post-annealed temperatures from RT to 600°C in air and in vacuum. At RT in air, the mean particle size of NCM622 powders was 9.7 µm. At all post-annealed temperatures, the mean particle sizes of the powders in air were smaller than those cathode in vacuum. In air, the mean particle size of the powders increased to 10.3 µm at 200°C, decreased to 9.4 µm at 250°C, and increased to 10.1 µm at 600°C. In vacuum, the mean particle size of the powders increased linearly to 10.6 µm at 200°C, decreased to 10.2 µm at 250°C, and slightly increased to 10.4 µm at 600°C. Meanwhile, the mean particle size of NCM622 powders with layered structure showed a tendency to increase at 200°C in air and in vacuum [ 5 ]. We believe that this is related to do with the existence of interlayer water in the NCM622 powders [ 11 ]. Real-time synchrotron x-ray scattering experiments with very high flux and high resolution were performed during annealing of the NCM622 cathode powders in air and in vacuum. Figure 3 shows the synchrotron x-ray diffraction profiles of NCM622 powders at various temperatures during annealing (a) in air and (b) in vacuum. Note that data were shifted in y-axis for clarity. Figure 3 (a) shows the synchrotron x-ray diffraction profiles of the NCM622 powders as a function of annealing temperature in air. At RT, the NCM(003), NCM(101), NCM(006), and NCM(012) Bragg reflections with a rhombohedral crystal structure were observed at q = 1.326, q = 2.568, q = 2.655, and q = 2.681 Å −1 , respectively (data not shown) [JCDPS 74–0917]. The real-time synchrotron x-ray scattering experiments were performed by increasing the annealing temperature at the NCM(003) reflection, which has the largest relative intensity. As the annealing temperature increases, the NCM(003) reflections were continuously shifted to the left due to thermal expansion. Figure 3 (b) also shows the synchrotron x-ray diffraction profiles of the NCM622 powders as a function of annealing temperature in vacuum. At RT, the NCM(003), NCM(101), NCM(006), and NCM(012) Bragg reflections were observed at q = 1.326, q = 2.568, q = 2.652, and q = 2.681 Å −1 , respectively (data not shown). As the annealing temperature increases, the NCM(003) reflections were also continuously shifted to the left due to thermal expansion. Figure 4 shows the thermal expansion coefficient of the (003) Bragg reflection of NCM622 cathode powders as a function of annealing temperature (a) in air and (b) in vacuum. The thermal expansion coefficient (dotted line) of NCM622 powders was previously known as 1.95x10 − 5 Å/(Å°C) [ 12 ]. Figure 4 (a) shows the thermal expansion coefficients obtained by measuring the position of the NCM(003) reflections during annealing in air. The mean thermal expansion coefficient (solid line) calculated from RT to 500°C in air was 1.62x10 − 5 Å/(Å°C), which was slightly smaller than the previously known thermal expansion coefficient, 1.95x10 − 5 Å/(Å°C) [ 12 ]. Figure 4 (b) also shows the thermal expansion coefficients obtained by measuring the position of the NCM(003) reflections during annealing in vacuum. The mean thermal expansion coefficient (solid line) calculated from RT to 500°C in the air was 1.49x10 − 5 Å/(Å°C), which was smaller than the previously known thermal expansion coefficient, 1.95x10 − 5 Å/(Å°C) [ 12 ]. The mean thermal expansion coefficient of NCM622 powders in air was also 1.62x10 − 5 Å/(Å°C), slightly larger than that in vacuum, 1.49x10 − 5 Å/(Å°C). In addition, the NCM(003) reflection after cooling to RT was observed at q = 1.326 Å −1 , and showed the same q value as before annealing at RT. Figure 5 shows the x-ray integrated intensities of NCM622 (003) Bragg reflections as a function of annealing temperature in air and in vacuum. The integrated intensity stands for the amount of crystal NCM622 phase quantitatively [ 7 , 8 ]. The amount of crystal NCM622 phase in air and in vacuum showed almost constant values regardless of annealing temperatures. Also, in all annealing temperatures, the amount of crystal NCM622 oxide phase in air showed a higher value than that in vacuum. This indicates that the crystal NCM622 phase during annealing in air is more thermally stable than that in vacuum. This is due to the presence of 21% oxygen in the air, which is not in the vacuum [ 13 ]. Figure 6 shows the crystal domain sizes of NCM622 phase inside a particle as a function of annealing temperature in air and in vacuum. The crystal domain size inside a particle was estimated from the full-width at half-maximum (FWHM) of the NCM(003) Bragg reflection using the Scherrer equation; CDS = 2π/FWHM [ 14 ]. At RT in air, the crystal domain size of the NCM622 phase inside a particle was 101.7 nm (0.1 µm), which is significantly smaller than the mean particle size of 9.7 µm. At most annealing temperatures, the crystal domain sizes of NCM622 phase in air showed larger values than those in vacuum. Also, the change of the crystal domain sizes in air showed fewer values than that in vacuum during annealing from RT to 500°C. These results indicate that the crystal NCM622 phase in air is more thermally stable than that in vacuum during annealing from RT to 500°C. This is also due to the presence of 21% oxygen in the air, which is not in the vacuum [ 13 ]. Recently, NCM811 and NCM9½½ cathode materials with increased Ni content for Li-ion batteries have been developed and used [ 15 , 16 ]. We will further study the thermal stabilities of NCM811 and NCM9½½ cathode materials using a real-time synchrotron x-ray scattering in air and in vacuum. Ⅳ. CONCLUSION The thermal stability of NCM622 cathode material for lithium-ion batteries was studied by using a real-time synchrotron x-ray scattering below 600°C in air and in vacuum. The amount of crystal NCM622 phase in air and in vacuum showed almost constant values. This indicates that the NCM622 cathode material with layered structure was thermally stable in air and in vacuum. The amount of crystal NCM622 phase in air showed a higher value than that in vacuum. The change of the crystal domain sizes in air showed fewer values than that in vacuum. These indicate that the NCM622 cathode material in air was more thermally stable than that in vacuum below 600°C. These are due to the presence of 21% oxygen in the air, which is not in the vacuum. Our study revealed the detailed thermal stability of NCM622 cathode material during real-time annealing below 600°C in air and in vacuum. Declarations ACKNOWLEDGMENT This research was supported by Kyungpook National University. This research was helped by Pohang Accelerator Laboratory in Korea. The authors also acknowledge Mr. K. J. Hwang for his contribution to SEM-EDS experiments in the Korean Basic Science Institute (Busan Center). References T. H. Kim, W. T. Song, D. Y. Son, L. K. Ono, Y. B. Qi, J. Mater. Chem. A 7 , 2942 (2019). https://doi.org/10.1039/C8TA10513H J. B. Goodenough, K. S. Park, J. Am. Chem. Soc. 135 , 1167 (2013). https://doi.org/10.1021/ja3091438 J. W. Wen, Y. Yu, C. H. Chen, Mater. Express 2 , 197 (2012). https://doi.org/10.1166/mex.2012.1075 D. D. MacNeil, Z. Lu, J. R. Dahn, J. Electrochem. Soc. 149 , 1332 (2002). https://doi.org/10.1149/1.1505633 Z. Y. Huang, M. H. Chu, R. Wang, W. M. Zhu, W. G. Zhao, C. Wang, Y. J. Zhang, L. H. He, J. Chen, S. H. Deng, L. W. 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Yoon, Advanced Science 7 , 1902413 (2020). https://doi.org/10.1002/advs.201902413 Y. B. Zhu, X. H. Tian, X. Zhou, P. F. Zhang, N. Angulakshmi, Y. K. Zhou, Electrochimica Acta 328 , 135116 (2019). https://doi.org/10.1016/j.electacta.2019.135116 B. E. Warren, X-ray Diffraction, 1st edn. (Dover Publications, New York , 1969). J. H. Kim, K. J. Park, S. J. Kim, C. S. Yoon, Y. K. Sun, J. Mater. Chem. A 7 , 2694 (2019). https://doi.org/10.1039/C8TA10438G J. H. Kim, H. H. Ryu, S. J. Kim, C. S. Yoon, Y. K. Sun, ACS Appl. Mater. Interfaces 11 , 30936 (2019). https://doi.org/10.1021/acsami.9b09754 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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11:34:10","extension":"html","order_by":16,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":47021,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7570733/v1/73081e3fbbe9f946657dd391.html"},{"id":92712254,"identity":"7de69704-2380-4caf-9312-3f7004c61edb","added_by":"auto","created_at":"2025-10-03 11:26:09","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":837213,"visible":true,"origin":"","legend":"\u003cp\u003eSEM micrographs of NCM622 cathode powders as a function of post-annealed temperature in air and in vacuum\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7570733/v1/0a8a9b2d889f4ccbf481bb02.png"},{"id":92712252,"identity":"13bec89c-e133-42fc-8f1a-bb89de61bb77","added_by":"auto","created_at":"2025-10-03 11:26:09","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":174061,"visible":true,"origin":"","legend":"\u003cp\u003eMean particle sizes of NCM622 cathode powders as a function of post-annealed temperature in air and in vacuum\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7570733/v1/6ee8fb979aa4f34e284fea44.png"},{"id":92712262,"identity":"c7ff71d5-3d62-4e7a-b246-d3431e4fe6e0","added_by":"auto","created_at":"2025-10-03 11:26:10","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":528385,"visible":true,"origin":"","legend":"\u003cp\u003eSynchrotron x-ray diffraction profiles of NCM622cathode powders at various temperatures during annealing (a) in air and (b) in vacuum\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-7570733/v1/95a5b9fc323c8fb0e51aae70.png"},{"id":92712457,"identity":"afa5ad65-f35a-43d0-8fee-26d47bda6877","added_by":"auto","created_at":"2025-10-03 11:34:09","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":30818,"visible":true,"origin":"","legend":"\u003cp\u003eThermal expansion coefficient of the (003) Bragg reflection of NCM622 cathode powders as a function of annealing temperature (a) in air and (b) in vacuum\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7570733/v1/f2aa52f89694218889aed106.png"},{"id":92712459,"identity":"f9e1cfb8-8eee-4129-8c6a-99d27f616a0e","added_by":"auto","created_at":"2025-10-03 11:34:09","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":30659,"visible":true,"origin":"","legend":"\u003cp\u003eIntegrated intensities of the (003) Bragg reflection of NCM622 cathode powders as a function of annealing temperature in air and in vacuum\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-7570733/v1/75b641fcf7b6cf840ede99f5.png"},{"id":92713440,"identity":"49703bb6-e277-45a6-9744-9db92b197469","added_by":"auto","created_at":"2025-10-03 11:42:10","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":29505,"visible":true,"origin":"","legend":"\u003cp\u003eCrystal domain sizes of the NCM622 phase\u003csub\u003e \u003c/sub\u003eas a function of annealing temperature in air and in vacuum\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-7570733/v1/e78e7e0fb7ffde177526c405.png"},{"id":93534124,"identity":"7fe0ce15-633b-49b7-9ccf-a187cece9a32","added_by":"auto","created_at":"2025-10-15 00:01:34","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1897531,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7570733/v1/73d9436e-3125-4dad-9708-7747dfa5f753.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Thermal Stability of NCM622 Cathode Material for Li-ion Batteries: A Real-time Synchrotron X-ray Scattering Study","fulltext":[{"header":"I. INTRODUCTION","content":"\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eLi-ion batteries are attracting attention as a major material for the high-tech industry due to their excellent characteristics such as higher energy density and fast charging/discharging speed compared to conventional secondary batteries [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. However, there are risks of explosion because the separator between cathode and anode is damaged by shocking or degraded by exposure to high temperatures [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. LiNiCoMnO\u003csub\u003e2\u003c/sub\u003e (NCM) oxide cathode material is a cathode material in which Co and Mn are added to the conventional LiNiO2 to improve the stability of the battery [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Heat treatment of NCM cathode material induces a layered-to-rock salt structure phase transition near the high temperature of 700\u0026deg;C accompanied with the precipitation of Li\u003csub\u003e2\u003c/sub\u003eO, restricts the movement of Li-ions [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. LiNi\u003csub\u003e0.6\u003c/sub\u003eCo\u003csub\u003e0.2\u003c/sub\u003eMn\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (NCM622) cathode material has been used as batteries for electric vehicles requiring high energy density [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. The thermal stability of NCM622 cathode material during real-time annealing below 700\u0026deg;C, however, has not been well characterized. In this article, we present a real-time synchrotron x-ray scattering study to examine the thermal stability of NCM622 cathode material during annealing below 600\u0026deg;C in air and in vacuum. Synchrotron x-ray scattering with very high flux and high resolution is one of the most effective ways to examine the detailed behaviors of advanced materials during annealing [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Our study revealed the detailed thermal stability of NCM622 cathode material during real-time annealing below 600\u0026deg;C in air and in vacuum.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e"},{"header":"II. EXPERIMENTS DETAILS","content":"\u003cp\u003eThe NCM622 cathode powders were prepared by dry mixing NCM622 precursor powder (Ni\u003csub\u003e0.6\u003c/sub\u003eCo\u003csub\u003e0.2\u003c/sub\u003eMn\u003csub\u003e0.2\u003c/sub\u003e(OH)\u003csub\u003e2\u003c/sub\u003e) and Li\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e powder (Sigma Aldrich, \u0026ge; 99.0%) using ball milling, followed by sintering in the air with a high-temperature electric furnace [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. The NCM precursor powders were synthesized by co-precipitation, in which metal sulfate was dissolved in NaOH and NH\u003csub\u003e4\u003c/sub\u003eOH in water and then precipitated [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe surface micrographs and chemical composition of the NCM622 cathode powders were investigated using scanning eletron microscope-energy dispersive spectroscopy (SEM-EDS). The NCM622 powders were post-annealed at several temperatures from room temperature (RT) to 600\u0026deg;C for 30 minutes. The chemical composition of the NCM622 powders indicated LiNi\u003csub\u003e0.62\u003c/sub\u003eCo\u003csub\u003e0.20\u003c/sub\u003eMn\u003csub\u003e0.18\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, sililar to the LiNi\u003csub\u003e0.6\u003c/sub\u003eCo\u003csub\u003e0.2\u003c/sub\u003eMn\u003csub\u003e0.2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (NCM622). The mean particle size of the NCM622 powders was quantitatively measured using a particle size analyzer based on each SEM micrograph.\u003c/p\u003e\u003cp\u003eIn the meanwhile, the real-time synchrotron x-ray scattering experiments were performed at beamline 5D (GIST) at Pohang Light Source in Korea. The incident x-rays were vertically focused by a mirror, and monochromatized to a wavelength of 1.240 \u0026Aring;. The experiments were carried out by measuring the x-ray powder diffraction profiles during annealing in air and in vacuum. The NCM622 cathode powders were annealed using a heating stage, which was set on a four-circle x-ray diffractometer for the real-time x-ray measurements. The annealing temperature increased gradually and stayed constant during the x-ray measurements.\u003c/p\u003e"},{"header":"III. RESULTS AND DISCUSSION","content":"\u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the surface SEM micrographs of the NCM622 cathode powders at several post-annealed temperatures in air (a, b, and c) and in vacuum (d and e). At RT in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(a), the shape of the NCM622 powders was close to spherical, and the particle size distribution was very uniform. After post-annealed up to 600\u0026deg;C in air and in vacuum, the shape of the powders was equally close to spherical, and the particle size distribution was very uniform. In addition, the mean particle size of the NCM622 powders was quantitatively measured using a particle size analyzer based on each SEM micrograph.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the mean particle sizes of NCM622 cathode powders at several post-annealed temperatures from RT to 600\u0026deg;C in air and in vacuum. At RT in air, the mean particle size of NCM622 powders was 9.7 \u0026micro;m. At all post-annealed temperatures, the mean particle sizes of the powders in air were smaller than those cathode in vacuum. In air, the mean particle size of the powders increased to 10.3 \u0026micro;m at 200\u0026deg;C, decreased to 9.4 \u0026micro;m at 250\u0026deg;C, and increased to 10.1 \u0026micro;m at 600\u0026deg;C. In vacuum, the mean particle size of the powders increased linearly to 10.6 \u0026micro;m at 200\u0026deg;C, decreased to 10.2 \u0026micro;m at 250\u0026deg;C, and slightly increased to 10.4 \u0026micro;m at 600\u0026deg;C. Meanwhile, the mean particle size of NCM622 powders with layered structure showed a tendency to increase at 200\u0026deg;C in air and in vacuum [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. We believe that this is related to do with the existence of interlayer water in the NCM622 powders [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eReal-time synchrotron x-ray scattering experiments with very high flux and high resolution were performed during annealing of the NCM622 cathode powders in air and in vacuum. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the synchrotron x-ray diffraction profiles of NCM622 powders at various temperatures during annealing (a) in air and (b) in vacuum. Note that data were shifted in y-axis for clarity. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a) shows the synchrotron x-ray diffraction profiles of the NCM622 powders as a function of annealing temperature in air. At RT, the NCM(003), NCM(101), NCM(006), and NCM(012) Bragg reflections with a rhombohedral crystal structure were observed at q\u0026thinsp;=\u0026thinsp;1.326, q\u0026thinsp;=\u0026thinsp;2.568, q\u0026thinsp;=\u0026thinsp;2.655, and q\u0026thinsp;=\u0026thinsp;2.681 \u0026Aring;\u003csup\u003e\u0026minus;1\u003c/sup\u003e, respectively (data not shown) [JCDPS 74\u0026ndash;0917]. The real-time synchrotron x-ray scattering experiments were performed by increasing the annealing temperature at the NCM(003) reflection, which has the largest relative intensity. As the annealing temperature increases, the NCM(003) reflections were continuously shifted to the left due to thermal expansion. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(b) also shows the synchrotron x-ray diffraction profiles of the NCM622 powders as a function of annealing temperature in vacuum. At RT, the NCM(003), NCM(101), NCM(006), and NCM(012) Bragg reflections were observed at q\u0026thinsp;=\u0026thinsp;1.326, q\u0026thinsp;=\u0026thinsp;2.568, q\u0026thinsp;=\u0026thinsp;2.652, and q\u0026thinsp;=\u0026thinsp;2.681 \u0026Aring;\u003csup\u003e\u0026minus;1\u003c/sup\u003e, respectively (data not shown). As the annealing temperature increases, the NCM(003) reflections were also continuously shifted to the left due to thermal expansion.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows the thermal expansion coefficient of the (003) Bragg reflection of NCM622 cathode powders as a function of annealing temperature (a) in air and (b) in vacuum. The thermal expansion coefficient (dotted line) of NCM622 powders was previously known as 1.95x10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e \u0026Aring;/(\u0026Aring;\u0026deg;C) [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(a) shows the thermal expansion coefficients obtained by measuring the position of the NCM(003) reflections during annealing in air. The mean thermal expansion coefficient (solid line) calculated from RT to 500\u0026deg;C in air was 1.62x10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e \u0026Aring;/(\u0026Aring;\u0026deg;C), which was slightly smaller than the previously known thermal expansion coefficient, 1.95x10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e \u0026Aring;/(\u0026Aring;\u0026deg;C) [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(b) also shows the thermal expansion coefficients obtained by measuring the position of the NCM(003) reflections during annealing in vacuum. The mean thermal expansion coefficient (solid line) calculated from RT to 500\u0026deg;C in the air was 1.49x10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e \u0026Aring;/(\u0026Aring;\u0026deg;C), which was smaller than the previously known thermal expansion coefficient, 1.95x10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e \u0026Aring;/(\u0026Aring;\u0026deg;C) [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. The mean thermal expansion coefficient of NCM622 powders in air was also 1.62x10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e \u0026Aring;/(\u0026Aring;\u0026deg;C), slightly larger than that in vacuum, 1.49x10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e \u0026Aring;/(\u0026Aring;\u0026deg;C). In addition, the NCM(003) reflection after cooling to RT was observed at q\u0026thinsp;=\u0026thinsp;1.326 \u0026Aring;\u003csup\u003e\u0026minus;1\u003c/sup\u003e, and showed the same q value as before annealing at RT.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e shows the x-ray integrated intensities of NCM622 (003) Bragg reflections as a function of annealing temperature in air and in vacuum. The integrated intensity stands for the amount of crystal NCM622 phase quantitatively [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. The amount of crystal NCM622 phase in air and in vacuum showed almost constant values regardless of annealing temperatures. Also, in all annealing temperatures, the amount of crystal NCM622 oxide phase in air showed a higher value than that in vacuum. This indicates that the crystal NCM622 phase during annealing in air is more thermally stable than that in vacuum. This is due to the presence of 21% oxygen in the air, which is not in the vacuum [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows the crystal domain sizes of NCM622 phase inside a particle as a function of annealing temperature in air and in vacuum. The crystal domain size inside a particle was estimated from the full-width at half-maximum (FWHM) of the NCM(003) Bragg reflection using the Scherrer equation; CDS\u0026thinsp;=\u0026thinsp;2π/FWHM [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. At RT in air, the crystal domain size of the NCM622 phase inside a particle was 101.7 nm (0.1 \u0026micro;m), which is significantly smaller than the mean particle size of 9.7 \u0026micro;m. At most annealing temperatures, the crystal domain sizes of NCM622 phase in air showed larger values than those in vacuum. Also, the change of the crystal domain sizes in air showed fewer values than that in vacuum during annealing from RT to 500\u0026deg;C. These results indicate that the crystal NCM622 phase in air is more thermally stable than that in vacuum during annealing from RT to 500\u0026deg;C. This is also due to the presence of 21% oxygen in \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003ethe\u003c/span\u003e air, which is not in the vacuum [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eRecently, NCM811 and NCM9\u0026frac12;\u0026frac12; cathode materials with increased Ni content for Li-ion batteries have been developed and used [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. We will further study the thermal stabilities of NCM811 and NCM9\u0026frac12;\u0026frac12; cathode materials using a real-time synchrotron x-ray scattering in air and in vacuum.\u003c/p\u003e"},{"header":"Ⅳ. CONCLUSION","content":"\u003cp\u003eThe thermal stability of NCM622 cathode material for lithium-ion batteries was studied by using a real-time synchrotron x-ray scattering below 600\u0026deg;C in air and in vacuum. The amount of crystal NCM622 phase in air and in vacuum showed almost constant values. This indicates that the NCM622 cathode material with layered structure was thermally stable in air and in vacuum. The amount of crystal NCM622 phase in air showed a higher value than that in vacuum. The change of the crystal domain sizes in air showed fewer values than that in vacuum. These indicate that the NCM622 cathode material in air was more thermally stable than that in vacuum below 600\u0026deg;C. These are due to the presence of 21% oxygen in the air, which is not in the vacuum. Our study revealed the detailed thermal stability of NCM622 cathode material during real-time annealing below 600\u0026deg;C in air and in vacuum.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eACKNOWLEDGMENT\u003c/p\u003e\n\u003cp\u003eThis research was supported by Kyungpook National University. This research was helped by Pohang Accelerator Laboratory in Korea. The authors also acknowledge Mr. K. J. Hwang for his contribution to SEM-EDS experiments in the Korean Basic Science Institute (Busan Center).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eT. H. Kim, W. T. Song, D. Y. Son, L. K. Ono, Y. B. Qi, J. Mater. Chem. A \u003cstrong\u003e7\u003c/strong\u003e, 2942 (2019). \u003cu\u003ehttps://doi.org/10.1039/C8TA10513H\u003c/u\u003e\u003c/li\u003e\n\u003cli\u003eJ. B. Goodenough, K. S. Park, J. Am. Chem. 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Interfaces \u003cstrong\u003e11\u003c/strong\u003e, 30936 (2019). https://doi.org/10.1021/acsami.9b09754\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Li-ion batteries, NCM622 cathode material, Thermal stability, Real-time synchrotron x-ray scattering","lastPublishedDoi":"10.21203/rs.3.rs-7570733/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7570733/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eWe have studied the thermal stability of NCM622 oxide cathode material for Li-ion batteries using a real-time synchrotron x-ray scattering in air and in vacuum. The amount of crystal NCM622 phase in air and in vacuum showed almost constant values below 600\u0026deg;C. This indicates that the NCM622 cathode material with layered structure was thermally stable in air and in vacuum. Considering the amount of crystal phase and the change of crystal domain sizes, the NCM622 cathode material in air was more thermally stable than that in vacuum. These are due to the presence of 21% oxygen in the air, which is not in the vacuum. Our study revealed the detailed thermal stability of NCM622 cathode material during real-time annealing below 600\u0026deg;C in air and in vacuum.\u003c/p\u003e","manuscriptTitle":"Thermal Stability of NCM622 Cathode Material for Li-ion Batteries: A Real-time Synchrotron X-ray Scattering Study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-03 11:26:05","doi":"10.21203/rs.3.rs-7570733/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"37d07e17-73dd-4de0-b01e-50341d44c2c0","owner":[],"postedDate":"October 3rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-10-14T23:53:27+00:00","versionOfRecord":[],"versionCreatedAt":"2025-10-03 11:26:05","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7570733","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7570733","identity":"rs-7570733","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}