X-ray Diffraction Rietveld Refinement and Its Application in Cathode Materials for Lithium-ion Batteries

doi:10.15541/jim20220331

Abstract

Abstract:

2022 marks the 110th anniversary of X-ray diffraction (XRD), which is a powerful technique used to find out the nature of materials. Rietveld refinement method, as an important means of extracting material structure information, plays a significant role in establishing the relationship between structure and performance of materials. Cathode materials are a vital part of lithium-ion batteries (LIBs). In-depth understanding of their crystal structure and atomic distribution is extremely helpful to promote the development of cathode materials for LIBs. Cathode materials for LIBs are generally the hosts of lithium. Studies on lithium occupation and transfer are inseparable from a deep understanding of its structural characteristics. This review summarizes XRD Rietveld structure refinement and its application in cathode materials for LIBs. XRD Rietveld structure refinement in synthesis, degradation, and structural modification of cathode materials are analyzed by using several types of typical cathode materials as examples. XRD Rietveld method could provide useful structural information of the cathode materials, including phase ratio in composite and crystallographic parameters (e.g., cell parameters, key atomic occupation, and atomic coordinates). Therefore, exploring structure of cathode materials assisted with XRD Rietveld refinement method is of great significance for the development of high-performance cathode materials for LIBs. Finally, the opportunities and challenges in the field of X-ray diffraction technology in detecting structure of cathode materials for LIBs are prospected.

Key words: X-ray diffraction, Rietveld refinement, lithium-ion battery, cathode material, review

CLC Number:

TQ174

YANG Zhuo, LU Yong, ZHAO Qing, CHEN Jun. X-ray Diffraction Rietveld Refinement and Its Application in Cathode Materials for Lithium-ion Batteries[J]. Journal of Inorganic Materials, 2023, 38(6): 589-605.

Figures/Tables 18

Fig. 1 Influencing factors of X-ray diffraction patterns

Table 1 Structures and properties of common cathode materials for lithium-ion batteries[24⇓⇓⇓-28]

Cathode material	Crystal structure	Space group	Cell parameter	Atom site		Theoretical specific capacity/(mAh·g^-1)	Working voltage/ V (vs. Li⁺/Li)
LiFePO₄	Olivine	Pnma	a≠b≠c	Li	4a	170	3.4
				Fe	4c
				O	4c/8d
LiMn₂O₄	Spinel	Fd-3m	a=b=c	Li	8a	148	4
				Mn	16d
				O	32e
LiCoO₂	Layer	R-3m	a=b≠c	Li	3a	274	3.9
				Co	3b
				O	6c
LiNi_xCo_y(Mn/Al)_1-_x_-_yO₂	Layer	R-3m	a=b≠c	Li	3a	273-285	3.8
				Ni/Co/Mn/Al	3b
				O	6c
xLi₂MnO₃·(1-x)LiMO₂ (0<x<1, M=Ni, Co, Mn)	Layer	R-3m+ C2/m	a=b≠c	Li	2b/2c/4h	273-350	3.8
				Mn	4g
				O	4i/4j

Fig. 3 Schematic diagram of the crystal structures of cathode materials[25⇓⇓-28] (a) LiMPO4 (M=Fe, Mn)(© 2021, IOP Publishing)[25]; (b) LiMn2O4 (© 2022, MDPI)[26]; (c) LiMO2 (M=Ni, Co, Mn, Al) (© 2021, Elsevier Ltd.)[27]; (d) xLi2MnO3·(1-x)LiMO2 (M=Ni, Co, Mn) (© 2022, Springer Nature)[28] Colorful figures are available on website

Fig. 4 Application of XRD Rietveld refinement in cathode materials for lithium-ion batteries

Fig. 5 Structural evolution during high temperature synthesis of LiNi0.8Co0.2O2 (© 2017, Wiley-VCH)[41] (a) Concentration of the phases Ni(Co)O, Li2CO3, and LiNi0.8Co0.2O2 at different temperatures; (b) Ratio unit cell parameters (c/a), (c) content of Li+ occupying the 3a sites (Li sites), and (d) Ni-O and Li-O bond lengths as a function of temperature; (e) Schematic diagram of the structural evolution and variation of the interlayer distances of the Li and Ni(Co) slabs during the synthesis of LiNi0.8Co0.2O2. 1 Å=0.1 nm. Colorful figures are available on website

Fig. 6 Temperature-resolved XRD characterization of synthesis process of cathode material LiNi0.6Co0.2Mn0.2O2 (© 2021, Wiley-VCH)[43] (a) In situ XRD patterns of the mixture of Ni0.6Co0.2Mn0.2(OH)2 and LiOH·H2O during heating and (c) corresponding weight fractions of different phases as a function of temperature; (b) 3D profiles of in situ XRD patterns, corresponding (d) evolution of phase fraction and (f) lattice parameters of the samples as a function of heating temperature starting from mixture of the Ni0.6Co0.2Mn0.2CO3 and LiOH·H2O; (e) Schematic illustration of structural evolution during synthesis of LiNi0.6Co0.2Mn0.2O2; In (a, b), the subscripts T1, T2 and R represent Ni0.6Co0.2Mn0.2(OH)2 (P-3m1, T1 phase), LiNi0.6Co0.2Mn0.2O2 (R-3m, T2 phase) and the rock-salt-type, respectively. 1 Å=0.1 nm Colorful figures are available on website

Fig. 7 In-situ XRD characterization of microwave (MW) hydrothermal synthesis of NCM111(© 2020, AAAS) [44] (a) Schematic illustration of the experimental setup specialized for fast synchrotron X-ray probing of the microwave hydrothermal synthesis; (b) Time resolved synchrotron XRD patterns during MW hydrothermal synthesis of NCM111; (c) Lattice parameter c of the Ni1/3Co1/3Mn1/3(OH)2 precursor (green) as a function of temperature during solid-state synthesis (black), hydrothermal synthesis (blue), and MW hydrothermal synthesis (red). 1 Å=0.1 nm. Colorful figures are available on website

Fig. 8 In situ XRD characterization of Ni-rich cathode LiNi0.8Co0.1Mn0.1O2(NCM811) during charge-discharge (© 2015, ECS)[49] (a) In-situ XRD patterns of NCM811 cycled between 3.0-4.4 V at a rate of C/100 for two cycles; (b) Cell parameters c and a as functions of specific capacity and cell potential; (c) XRD refinement patterns, corresponding cell parameters and Li/Ni occupation information of fresh NCM811 electrode and the recovered electrodes that cycled 200 times to 4.1, 4.2, 4.3 and 4.4 V, respectively. 1 Å=0.1 nm; Ch: Charged; DisCh: Discharged. Colorful figures are available on website

Fig. 9 In-situ XRD characterization of Li1.2Ni0.13Co0.13Mn0.54O2 during charge-discharge process (© 2021, Springer Nature)[54] (a) Charge-discharge curve and corresponding contour plot of XRD pattern during the 201st cycle with the colour red to blue representing the decreasing peak intensity; (b, c) Lattice parameters (c and V) as functions of potential during the 1st and 201st cycles after the electrode activated at a rate of 0.1C. 1 Å=0.1 nm. Colorful figures are available on website

Fig. 10 In-situ XRD Rietveld refinement results of LiNi0.8Co0.1Mn0.1O2 cathode materials during charge and discharge process (© 2022, ECS)[57] (a, d) Lattice parameters a; (b, e) Lattice parameters c; (c, f) Unit cell volumes. 1 Å=0.1 nm. Colorful figures are available on website

Sample	Doped atomic radius/nm	Displace ion radius/nm	Lattice constant/nm	Lattice volume/nm³	Interatomic distance/nm	Reliability factor
LFP	r_Fe = 0.172	r_Fe2+ = 0.074	a=1.031634 b=0.600129 c=0.469139	0.29045	Li-O₁:0.21664 Li-O₂:0.20901 Li-O₃:0.21651 Li-O:0.214050	R_wp= 7.72% R_p=5.63% χ²= 2.794
LFMgP	r_Mg = 0.172	r_Mg2+ = 0.065	a=1.031583 b=0.600035 c=0.469090	0.29036	Li-O₁:0.21712 Li-O₂:0.21041 Li-O₃:0.21665 Li-O:0.214720	R_wp= 9.32% R_p= 6.79% χ²= 2.878
LFAlP	r_Al = 0.182	r_Al3+ = 0.050	a=1.032204 b=0.600358 c=0.469072	0.29068	Li-O₁:0.21670 Li-O₂:0.21001 Li-O₃:0.21747 Li-O:0.214730	R_wp= 9.14% R_p= 6.60% χ²= 2.989
LFNiP	r_Ni = 0.162	r_Ni2+ = 0.072	a=1.031083 b=0.599820 c=0.468923	0.29001	Li-O₁:0.21734 Li-O₂:0.20863 Li-O₃:0.21586 Li-O:0.213950	R_wp= 8.26% R_p= 6.12% χ²= 2.929
LFVP	r_V = 0.192	r_V3+ = 0.074	a=1.032223 b=0.600494 c=0.469485	0.291	Li-O₁:0.21864 Li-O₂:0.21074 Li-O₃:0.21794 Li-O:0.215770	R_wp= 9.86% R_p= 7.15% χ²= 2.426

Fig. 11 XRD Rietveld refinement results of LiFePO4 before and after modification (© 2021, RSC)[63] (a, b) XRD Rietveld refinement patterns of (a) LFP/C and (b) LFP/C-YF-2; (c, d) Schematic diagrams of change in Li-O bond length of (c) LFP/C and (d) LFP/C-YF-2. 1 Å=0.1 nm. Colorful figures are available on website

Sample	a/nm	b/nm	c/nm	V/nm³
LFP/C	1.03229	0.60061	0.46941	0.29104
LFP/C-YF-1	1.03054	0.59985	0.46903	0.28994
LFP/C-YF-2	1.03082	0.59977	0.46874	0.28980
LFP/C-YF-3	1.03069	0.59989	0.46892	0.28994

Atom	Site	z	Occupancy	U_iso
Li^a	3a	0	1.000	0.014(6)
Co^a	3b	0.50000	1.000	0.023(8)
O^a	6c	0.2300(6)	1.000	0.049(1)
Li^b	3a	0	0.98(1)	0.020(1)
Mg^b	3a	0	0.01(9)	0.020(1)
Co^b	3b	0.50000	0.99(7)	0.001(2)
Al^b	3b	0.50000	0.002(0)	0.001(2)
Ti^b	3b	0.50000	0.001(0)	0.001(2)
O^b	6c	0.2476(3)	1.000	0.068(5)

Fig. 12 XRD Rietveld refinement results of Li(Li0.2Ni0.2Mn0.6)O2 cathode materials (© 2022, Wiley-VCH)[66] (a, b) Experimental XRD patterns and Rietveld refinement results of (a) LLNMO-PC and (b) LLNMO-SC; (c, d) Changes of lattice parameters (a, b, c, and V) for (c) LLNMO-PC and (d) LLNMO-SC electrodes during charge and discharge 1 Å=0.1 nm. Colorful figures are available on website

Formula	Calculated				Experimental
Formula	a/nm	b/nm	c/nm	V/nm³	a/nm	V/nm³
Li₈Mn₁₆O₃₂	0.886205	0.886205	0.886205	0.695990	-	-
Li₈Mn₁₅AlO₃₂	0.826725	0.826725	0.826725	0.567617	0.82507	0.561658
Li₈Mn₁₄Al₂O₃₂	0.831493	0.831493	0.799071	0.552416	0.82466	0.560821
Li₈Mn₁₃Al₃O₃₂	0.814375	0.826337	0.820583	0.551780	0.82110	0.553590

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