Fluorine Doping-Induced Intrinsic Defect Modulation in Rock-Salt-Type High-Entropy Oxide for Lithium Storage Performance Optimization

doi:10.6023/A25040107

Abstract

High-entropy oxides (HEOs) have emerged as one of the most promising anode materials for lithium-ion batteries due to their flexible compositional design and synergistic effects among multiple components. However, their practical application is severely hindered by inferior intrinsic electronic/ionic conductivity, which leads to poor rate capability and cycling stability in lithium storage systems. In this study, we developed a fluorine anion doping strategy to regulate intrinsic defects including lattice distortion and oxygen vacancies in rock-salt type (Co_0.2Cu_0.2Mg_0.2Ni_0.2Zn_0.2)O through solution combustion synthesis. This approach successfully fabricated single-phase F-doped (Co_0.2Cu_0.2Mg_0.2Ni_0.2Zn_0.2)O_1－_xF_x (x=0, 0.05, 0.1) HEO anode materials. Electrochemical evaluations demonstrate that the (Co_0.2Cu_0.2Mg_0.2Ni_0.2Zn_0.2)O_0.95F_0.05 anode exhibits exceptional rate performance and cycling stability, delivering a high specific capacity of 389.5 mAh•g^－1 after 150 cycles at 200 mA•g^－1. Even under high current density of 1000 mA•g^－1, it maintains 233.4 mAh•g^－1after 150 cycles with 93.1% capacity retention, representing a 56% improvement compared to undoped counterparts. The enhanced electrochemical performance originates from optimized material characteristics induced by appropriate F^－ doping: increased specific surface area, elevated surface Cu^＋ content, reduced lattice distortion, and controlled oxygen vacancies. These structural modifications not only provide additional active sites and ion transport pathways but also enhance surface pseudocapacitive behavior, thereby significantly improving both electronic and ionic transport kinetics.

Key words: lithium-ion battery anode material, rock salt-type high-entropy oxide, anion doping, lattice distortion, oxygen vacancy

Cite this article

Zhengbing Wei, Mengfan Bao, Shibiao Xu, Yi Cheng, Shijie Chen, Na Lin, Aiqin Mao. Fluorine Doping-Induced Intrinsic Defect Modulation in Rock-Salt-Type High-Entropy Oxide for Lithium Storage Performance Optimization[J]. Acta Chimica Sinica, 2025, 83(8): 868-877.

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Fig. & Tab. 9

Figure 1. XRD spectra and local magnification spectra of as-synthesized samples (a), and the Rietveld refined XRD patterns of HEO (b), HEO-F0.05 (c) and HEO-F0.1 (d)

Sample	a/nm	b/nm	c/nm	V/nm³	R_wp	R_p
HEO	0.42389	0.42389	0.42389	0.07617	5.35%	3.92%
HEO-F0.05	0.42369	0.42369	0.42369	0.07606	3.49%	2.46%
HEO-F0.1	0.42351	0.42351	0.42351	0.07596	3.67%	2.62%

Table 1. The lattice constants and refinement factors of as-synthesized three samples

Figure 2. SEM images (different magnifications) and EDS elemental maps of HEO (a1,b1,c1), HEO-F0.05 (a2,b2,c2), and HEO-F0.1 (a3,b3,c3). TEM images (with insets showing SAED patterns), HR-TEM images (with insets showing IFFT images), and line scan intensity distribution curves of lattice fringes for samples HEO (d1,e1,f1) and HEO-F0.05 (d2,e2,f2)

Sample	S_BET/(m²•g^－1)	V_BJH/(cm³•g^－1)	D_aver./nm	D_most/nm
HEO	7.564	0.022	11.474	3.278
HEO-F0.05	18.810	0.016	3.399	3.092
HEO-F0.1	9.200	0.018	11.740	3.290

Table 2. Textural characteristics of as-synthesized samples

Figure 3. The N2 adsorption-desorption isotherms and pore size distributions of as-synthesized HEO (a, d), HEO-F0.05 (b, e), and HEO-F0.1 (c, f) samples

Figure 4. The XPS survey spectrum of the sample (a), high-resolution XPS spectra of Co 2p (b), Cu 2p (c), Ni 2p (d), and O 1s (e), valence state distribution ratios of different elements (f), electrical conductivity (g), UV-Vis spectrum (h), and the plot of [F(R∞)•hν]1/n versus hν (i)

Figure 5. Cyclic voltammetry curves (a~c), charge-discharge curves (d~f) and cycling behaviour at different current densities and multiplication behaviour (g~i) of HEO, HEO-F0.05 and HEO-F0.1 electrodes at 0.1 mV•s－1

Figure 6. In-situ impedance during the first charge-discharge of three electrodes (a~f); in-situ impedance of HEO-F0.05 during 2nd (g) and 3rd (h) discharge and impedance spectra after cycling (i); electrochemical impedance spectra and equivalent circuit before cycling (j); galvanostatic intermittent titration technique (GITT) curves (k) and Li⁺ diffusion coefficients during charge-discharge (l) for three electrodes

Figure 7. CV curves of HEO, HEO-F0.05 and HEO-F0.1 electrodes at different sweeping rates (a~c); lg(ip) versus lg(v) (d~f); Percentage contribution of pseudocapacitance at 1.0 mV•s－1 (g~i); Contribution ratios of pseudocapacitance at different scan rates (j~l)

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