Cr-Doped Li2ZnTi3O8 as a High Performance Anode Material for Lithium-Ion Batteries

Li₂ZnTi_2.9Cr_0.1O₈ and Li₂ZnTi₃O₈ were synthesized by the liquid phase method and then studied comparatively using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), galvanostatic charge–discharge testing, cyclic stability testing, rate performance testing, and electrochemical impedance spectroscopy (EIS). The results showed that Cr-doped Li₂ZnTi₃O₈ exhibited much improved cycle performance and rate performance compared with Li₂ZnTi₃O₈. Li₂ZnTi_2.9Cr_0.1O₈ exhibited a discharge ability of 156.7 and 107.5 mA h g⁻¹ at current densities of 2 and 5 A g⁻¹, respectively. In addition, even at a current density of 1 A g⁻¹, a reversible capacity of 162.2 mA h g⁻¹ was maintained after 200 cycles. The improved electrochemical properties of Li₂ZnTi_2.9Cr_0.1O₈ are due to its increased electrical conductivity.

Introduction

Lithium-ion batteries (LIBs) are a new type of rechargeable batteries that are characterized by high specific capacities and specific energies, small volumes, long life cycles, low cost, low energy consumption, low self-discharge efficiencies, small internal resistance, and high working voltages (Yoshio, 2001; Junmin et al., 2005; Dong-il and Han, 2006; Wang M. X. et al., 2019; Wang S. et al., 2019; Huang et al., 2020; Wang et al., 2020; Yi et al., 2020a), and they have wide applications, including in mobile phones, laptops, cameras, digital cameras, electric automobiles, energy storage, aerospace, and space exploration (Tarascon and Armand, 2001; Xiao et al., 2018, 2019; An et al., 2019; Hong et al., 2019). The selection of suitable anode materials for LIBs is extremely important for the performance of these batteries to have excellent life cycles and charge/discharge rate characteristics.

Recently, there have been numerous studies of anode materials, including LiTi₂O₄, Li₂Ti₃O₇, Li₂Ti₆O₁₃, Li₄Ti₅O₁₂, Na₂Li₂Ti₆O₁₄, TiNb₂O₇, and Li₂ZnTi₃O₈ (Tang et al., 2014a; Chen B. K. et al., 2015; Li G. H. et al., 2016; Liu et al., 2016; Li Z. F. et al., 2016; Yi et al., 2020b). Li₂ZnTi₃O₈ with the cubic spinel structure has been considered as a promising material because of its lack of toxicity, low cost, relatively high theoretical capacity of 227 mA h g⁻¹, and its low discharge voltage plateau of ~0.5 V (vs. Li/Li⁺) (Jović et al., 2009; Chen B. K. et al., 2015; Chen W. et al., 2015). However, compared with other anode materials, Li₂ZnTi₃O₈ suffers from low electronic conductivity and an even worse rate performance, which means that its performance in practice is lower than the theoretical value (Tang and Tang, 2014; Chen B. K. et al., 2015). Hence, by increasing its electronic conductivity, its use can be extended to a wider range of applications.

Until now, this problem has been solved by applying a synthesized coating containing conductive species, nano-sized particles, and doping ions (Shenouda and Murali, 2008; Qi et al., 2009; Tian et al., 2010; Lin et al., 2011, 2013; Yu et al., 2011; Zhang et al., 2011; Bai et al., 2012; Jhan and Duh, 2012; Wu et al., 2013; Xu et al., 2013; Mani et al., 2014; Tang et al., 2014a; Yi et al., 2020c). As is widely known, by using a synthesized coating with conductive species on Li₂ZnTi₃O₈, the transportation of electrons can be improved while decreasing the particle size, which further accelerates ionic transportation. Moreover, it has been shown that doping ions into the material can increase its internal electronic conductivity (Lee et al., 2010; Fang et al., 2013; Lin et al., 2014). According to previous studies, the introduction of Al (Tang et al., 2014b), Ag (Tang et al., 2014a), Mo (Wang M. X. et al., 2019), and Ti (III) (Chen et al., 2018) to Li₂ZnTi₃O₈ greatly improved the electrochemical properties of these materials. For example, Tang et al. (2014b) partially replaced Ti with Al, and the resulting Li₂ZnTi_2.9Al_0.1O₈ composite showed a given capacity of 223.1 mA h g⁻¹ at 0.1 A g⁻¹ (Tang et al., 2014b). Wang M. X. et al. (2019) improved the electronic conductivity of the Li₂ZnTi₃O₈ compound by introducing Mo, and Li₂Zn_0.93Mo_0.07Ti₃O₈@graphene showed a high cycle capacity at high current densities of 5 A g⁻¹, with a power rating of 153 mA h g⁻¹ still being delivered on the 200th cycle (Wang M. X. et al., 2019). Recently, researchers have paid close attention to the use of Cr doping, which, according to one study (Ruan et al., 2017), can further enhance the electronic conductivity. Pan et al. (2018) have successfully prepared Cr-doped γ-Fe₂O₃/rGO cathode material by microwave method. The as-obtained 4.0 at% Cr-doped γ-Fe₂O₃/rGO sample exhibits the capacity of 1,060 mAh g⁻¹ after 100 cycles at 100 mA g⁻¹. Liu et al. (2018) have prepared Fe_1.95Cr_0.05F₅·H₂O material, which retains a discharge capacity of 171 mAh g⁻¹ after 100 cycles at 0.1 C (1 C = 200 mAh g⁻¹). Feng et al. (2009) have successfully synthesis Cr-LiV₃O₈ cathode material, and it showed an excellent electrochemical performance, with the retention of 94.4% after 100 cycles. To the best of our knowledge, the introduction of Cr³⁺-doped ions into Li₂ZnTi₃O₈ has not yet been reported. In this paper, we describe the improvement in electrochemical performance of Li₂ZnTi₃O₈ anode material as a result of Cr doping.

Materials and Methods

Li₂ZnTi_2.9Cr_0.1O₈ was prepared by the liquid phase method. Stoichiometric amounts of TiO₂, (CH₃COO)Li, (CH₃COO)₂Zn, and Cr(NO₃)₃ were mixed with anhydrous ethanol as solvent. The mixture was dried at 80°C for 2 h and then roasted in a muffle furnace at 700°C for 10 h to obtain the final Li₂ZnTi_2.9Cr_0.1O₈ compound. For comparison, Li₂ZnTi₃O₈ was also synthesized without using Cr(NO₃)₃ as the raw material.

X-ray diffraction (XRD, Brook AXS's D2 PHASER) was used to examine the crystalline phase of both Li₂ZnTi₃O₈ and Li₂ZnTi_2.9Cr_0.1O₈, which was recorded within the range of 10–70° (2θ). Scanning electron microscopy (SEM, TESCAN VEGA3) was used to examine the morphology of the samples. X-ray photoelectron spectroscopy (XPS) with Cr-Kα radiation was used to monitor the surface electronic states of the elements that were the sources of X-rays.

To construct the working electrodes, the as-prepared material, Super-P and LA-132 were mixed in weight ratios of 80:10:10 with water as solvent, and the prepared slurry was then pasted onto copper foil and dried at 100°C for 10 h in a vacuum oven. The working electrode, lithium metal, Celegard 2400 separator, and 1 M LiPF₆ electrolyte solution containing a 1:1:1 mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethylmethyl carbonate (EMC) were used to prepare CR2032 coin cells in an Ar-filled glovebox. All electrochemical performances were tested in the voltage range of 0.05–3.0V at room temperature.

Results and Discussion

Figure 1 shows the XRD patterns of Li₂ZnTi₃O₈ and Li₂ZnTi_2.9Cr_0.1O₈. It is clear from the figure that the diffraction peaks of the samples conform to the standard diffraction peaks of cubic spinel Li₂ZnTi₃O₈, which demonstrates that the presence of Cr(NO₃)₃ does not obviously affect the structure of cubic spinel Li₂ZnTi₃O₈. The crystal lattice constants calculated from the recorded XRD data are listed in Table 1, and the lattice parameters of Li₂ZnTi₃O₈ and Li₂ZnTi_2.9Cr_0.1O₈ were estimated to be a = 8.4305 and 8.4340 Å, respectively. The lattice parameters increased following introduction of Cr³⁺ into the Li₂ZnTi₃O₈ crystal structure due to the larger radius of Cr³⁺ (0.062 nm) compared with that of Ti⁴⁺ (0.061 nm) (Novikova et al., 2018), which promotes the transportation of lithium ions and further enhances the electrochemical performance (Tai et al., 2020).

FIGURE 1

Figure 1. XRD patterns of Li₂ZnTi₃O₈ and Li₂ZnTi_2.9Cr_0.1O₈.

TABLE 1

Table 1. The crystal lattice constant for Li₂ZnTi₃O₈ and Li₂ZnTi_2.9Cr_0.1O₈.

Additional information about the surface electronic states of the elements was gained from XPS measurements. Figure 2A shows the XPS survey spectra of Li₂ZnTi_2.9Cr_0.1O₈. As can be seen from the figure, the peaks of Li 1s, C 1s, O 1s, Ti 2p, Zn 2p, and Cr 2p are clearly visible. Figure 2B reveals that two peaks centered at approximately 576.36 and 585.60 eV correspond well to the Cr 2p_3/2 and Cr 2p_1/2 peaks, demonstrating that Cr is present as Cr³⁺ ions in the as-synthesized Li₂ZnTi_2.9Cr_0.1O₈. The two peaks shown in Figure 2C centered at approximately 458.4 and 464.40 eV are detected for Li₂ZnTi₃O₈ and Li₂ZnTi_2.9Cr_0.1O₈, which can correspond to the peaks of Ti (IV) 2p_3/2 and Ti (IV) 2p_1/2.

FIGURE 2

Figure 2. XPS spectra of (A) XPS survey spectrum, (B) Cr 2p, (C) Ti 2p of Li₂ZnTi₃O₈ and Li₂ZnTi_2.9Cr_0.1O₈.

Figure 3 shows the SEM images of the Li₂ZnTi₃O₈ and Li₂ZnTi_2.9Cr_0.1O₈ samples. It can be clearly seen that both samples are well-crystallized, with a small grain size distribution. It should be noted that the morphology of the particles did not appreciably change following doping with minute amounts of Cr³⁺. While increasing the contact area between active particles and the electrolyte, a good dispersion can narrow the transmission distance between Li⁺ and the electrons and increase the high-rate performance of 5C.

FIGURE 3

Figure 3. SEM images of (A) Li₂ZnTi₃O₈, (B) Li₂ZnTi_2.9Cr_0.1O₈.

The initial charge/discharge curves of Li₂ZnTi₃O₈ and Li₂ZnTi_2.9Cr_0.1O₈ are shown in Figure 4, which shows that the charge/discharge curves of Li₂ZnTi_2.9Cr_0.1O₈ are similar to those of Li₂ZnTi₃O₈, suggesting that Cr³⁺ doping exerts an effect on the electrochemical reaction. The specific capacities of Li₂ZnTi₃O₈ and Li₂ZnTi_2.9Cr_0.1O₈ at rates of 1 A g⁻¹ after the first cycle were 130.5 and 166.8 mA h g⁻¹, respectively. As can clearly be seen, Li₂ZnTi_2.9Cr_0.1O₈ demonstrates a higher specific capacity than Li₂ZnTi₃O₈. This can be explained by the fact that Cr doping can enlarge the transport tunnel of lithium ions, which further increases lithium ion transportation and electron transfer, thus enhancing the electronic conductivity (Zhang et al., 2018). In addition, Li₂ZnTi_2.9Cr_0.1O₈ appears to have the least voltage platform difference, indicating that a lower electrode polarization was obtained following Cr³⁺ doping and Li⁺ transport was improved.

FIGURE 4

Figure 4. The 1st charge and discharge curves for Li₂ZnTi₃O₈ and Li₂ZnTi_2.9Cr_0.1O₈.

The rate performances of Li₂ZnTi₃O₈ and Li₂ZnTi_2.9Cr_0.1O₈ are compared in Figure 5. Li₂ZnTi_2.9Cr_0.1O₈ delivered maximum discharge capacities of 221.7, 210.3, 185.1, 166, 156.7, and 107.5 mA h g⁻¹ at 0.1, 0.2, 0.5, 1, 2, and 5 C, respectively, whereas Li₂ZnTi₃O₈ delivered 193.4, 170.2, 147.8, 131, 98.3, and 43.5 mA h g⁻¹ at the same rates, respectively. As can be seen, Li₂ZnTi_2.9Cr_0.1O₈ showed better rate performance compared with Li₂ZnTi₃O₈, which may be due to either or both of the following reasons: (1) Cr doping improves the electronic conductivity, which leads to Li₂ZnTi_2.9Cr_0.1O₈ demonstrating better electrochemical performance than Li₂ZnTi₃O₈; (2) the improved cell volume following Cr doping enhances lithium ion diffusion and electron transfer (Chen et al., 2009; Nie et al., 2020).

FIGURE 5

Figure 5. Rate performance at different current density of Li₂ZnTi₃O₈ and Li₂ZnTi_2.9Cr_0.1O₈.

The cycling performance of Li₂ZnTi₃O₈ and Li₂ZnTi_2.9Cr_0.1O₈ was examined at a rate of 1 A g⁻¹, and the results are shown in Figure 6. As seen, the coulombic efficiency of Li₂ZnTi₃O₈ and Li₂ZnTi_2.9Cr_0.1O₈ were 80.2 and 84.8% in the first cycle, indicating that the coulombic efficiency can be enhanced after Cr doped. After several cycles, the coulombic efficiency of two samples is close to 100%. After 200 cycles, the reserving ratios were 90.2 and 97.2% for Li₂ZnTi₃O₈ and Li₂ZnTi_2.9Cr_0.1O₈, respectively. Therefore, Li₂ZnTi_2.9Cr_0.1O₈ possesses the better cycling performance. These results indicate that Li₂ZnTi_2.9Cr_0.1O₈ shows better capacity retention than Li₂ZnTi₃O₈, which can probably be explained by assuming that moderate Cr doping can enlarge the transport tunnel of lithium ions, which further increases lithium ion transportation and electron transfer.

FIGURE 6

Figure 6. Cycling capacity of Li₂ZnTi₃O₈ and Li₂ZnTi_2.9Cr_0.1O₈ for 200 cycles.

Electrochemical impedance spectroscopy (EIS) measurements for Li₂ZnTi₃O₈ and Li₂ZnTi_2.9Cr_0.1O₈ were carried out to probe the kinetic properties of these anode materials, and the results are shown in Figure 7. Similar patterns are displayed by the impedance spectra of the two samples, which formed a semicircle in the high-frequency regions and a straight line in the low-frequency regions. The semicircle in the high-frequency regions is associated with charge transfer resistance on the electrode/electrolyte interface, while the straight line in the low-frequency regions is ascribed to the diffusion of Li⁺ into the Warburg resistance (Long et al., 2011; Tang et al., 2019), which constitutes the bulk of the electrode materials. It is clear that the charge transfer resistance of the Li₂ZnTi_2.9Cr_0.1O₈ electrode material is lower than that of Li₂ZnTi₃O₈, showing that a certain small amount of Cr³⁺ doping of Li₂ZnTi₃O₈ is useful for enhancing the electronic conductivity (Li Z. F. et al., 2016; Kou et al., 2020). In addition, the slope for the Li₂ZnTi_2.9Cr_0.1O₈ electrode material in the low-frequency regions is slightly higher than that for Li₂ZnTi₃O₈ because Cr doping can strengthen lithium ion migration through Li₂ZnTi₃O₈.

FIGURE 7

Figure 7. EIS of pure Li₂ZnTi₃O₈ and Li₂ZnTi_2.9Cr_0.1O₈.

Conclusions

This study successfully prepared Li₂ZnTi₃O₈ and Li₂ZnTi_2.9Cr_0.1O₈ samples with the cubic spinel structure by the sol-gel method. XRD revealed that the element Cr successfully doped into the Li₂ZnTi₃O₈ exerted no effect on the spinel structure of Li₂ZnTi₃O₈. SEM (Chen B. K. et al., 2015) results demonstrated that the morphology of the particles did not obviously change following Cr³⁺ doping. The measured electrochemical properties indicated that Li₂ZnTi_2.9Cr_0.1O₈ shows a better rate performance and excellent cyclic reversibility than Li₂ZnTi₃O₈. The electrochemical performance might be significantly enhanced as a result of the higher electronic conductivity following Cr³⁺ doping, demonstrating that Li₂ZnTi_2.9Cr_0.1O₈ is a promising anode material for high-rate LIBs.

Data Availability Statement

All datasets presented in this study are included in the article/supplementary material.

Author Contributions

XZ and JP contributed conception and design of the study. HZ and YG organized the database. JP and XH wrote the first draft of the manuscript. XZ revised the whole manuscript. All authors contributed to the article and approved the submitted version.

Funding

This work was financially supported by Key Projects of Zigong Science and Technology Bureau (2018CXJD07).

Conflict of Interest

HZ was employed by the company Langxingda Technology Co, Ltd.

The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

References

An, F. Q., Zhao, H. L., Cheng, Z., Qiu, J. Y. C., Zhou, W. N., and Li, P. (2019). Development status and research progress of power battery for pure electric vehicles. Chin. J. Eng. 1, 22–42. doi: 10.13374/j.issn2095-9389.2019.01.003

CrossRef Full Text | Google Scholar

Bai, Y. J., Gong, C., Qi, Y. X., Lun, N., and Feng, J. (2012). Excellent long-term cycling stability of La-doped Li₄Ti₅O₁₂ anode material at high current rate. J. Mater. Chem. 22, 19054–19060. doi: 10.1039/c2jm34523d

CrossRef Full Text | Google Scholar

Chen, B. K., Du, C. J., Zhang, Y. Z., Sun, R. X., Zhou, L., and Wang, L. J. (2015). A new strategy for synthesis of lithium zinc titanate as an anode material for lithium ion batteries. Electrochim. Acta 159, 102–110. doi: 10.1016/j.electacta.2015.01.206

CrossRef Full Text | Google Scholar

Chen, C., Ai, C. C., and Liu, X. Y. (2018). Ti(III) self-doped Li₂ZnTi₃O₈ as a superior anode material for Li-ion batteries. Electrochim. Acta 265, 448–454. doi: 10.1016/j.electacta.2018.01.159

CrossRef Full Text | Google Scholar

Chen, W., Zhou, Z. R., Wang, R. R., Wu, Z. T., Liang, H. F., Shao, L. Y., et al. (2015). High performance Na-doped lithium zinc titanate as anode material for Li-ion batteries. RSC Adv. 5, 49890–49898. doi: 10.1039/C5RA06365E

CrossRef Full Text | Google Scholar

Chen, Y. H., Zhao, Y. M., An, X. N., Liu, J. M., Dong, Y. Z., and Chen, L. (2009). Preparation and electrochemical performance studies on Cr-doped Li₃V₂(PO₄)₃ as cathode materials for lithium-ion batteries. Electrochim. Acta 54, 5844–5850. doi: 10.1016/j.electacta.2009.05.041

CrossRef Full Text | Google Scholar

Dong-il, R., and Han, K. S. (2006). Used lithium ion rechargeable battery recycling using Etoile-Rebatt technology. J. Power Sources 163, 284–288. doi: 10.1016/j.jpowsour.2006.05.040

CrossRef Full Text | Google Scholar

Fang, W., Cheng, X. Q., Zuo, P. J., Ma, Y. L., and Yin, G. P. (2013). A facile strategy to prepare nano-crystalline Li₄Ti₅O₁₂/C anode material via polyvinyl alcohol as carbon source for high-rate rechargeable Li-ion batteries. Electrochim. Acta 93, 173–178. doi: 10.1016/j.electacta.2013.01.112

CrossRef Full Text | Google Scholar

Feng, Y., Li, Y. L., and Hou, F. (2009). Preparation and electrochemical properties of Cr doped LiV₃O₈ cathode for lithium ion batteries. Mater. Lett. 63, 1338–1340. doi: 10.1016/j.matlet.2009.03.009

CrossRef Full Text | Google Scholar

Hong, X. D., Huang, X. B., Ren, Y. R., Wang, H. Y., Ding, X., and Jin, J. L. (2019). Superior Na-storage performance of Na₃V₂(PO₄)₃/C-Ag composites as cathode material for Na-ion battery. J. Alloys Compd. 822:153587. doi: 10.1016/j.jallcom.2019.153587

CrossRef Full Text | Google Scholar

Huang, X. B., Yin, X., Yang, Q., Guo, Z. H., Ren, Y. R., and Zeng, X. G. (2020). Outstanding electrochemical performance of N/S co-doped carbon/Na₃V₂(PO₄)₃ hybrid as the cathode of a sodium-ion battery. Ceramics Int. 46, 28084–28090. doi: 10.1016/j.ceramint.2020.07.303

CrossRef Full Text | Google Scholar

Jhan, Y. R., and Duh, J. G. (2012). Electrochemical performance and low discharge cut-off voltage behavior of ruthenium doped Li₄Ti₅O₁₂ with improved energy density. Electrochim. Acta 63, 9–15. doi: 10.1016/j.electacta.2011.12.014

CrossRef Full Text | Google Scholar

Jović, N., Vučinić-Vasić, M., Kremenović, A., Antić, B., Jovalekić, C., Vulić, P., et al. (2009). HEBM synthesis of nanocrystalline LiZn_0.5Ti_1.5O₄ spinel and thermally induced order-disorder phase transition. Mater. Chem. Phys. 116, 542–549. doi: 10.1016/j.matchemphys.2009.04.033

CrossRef Full Text | Google Scholar

Junmin, N., Han, D., and Zuo, X. (2005). Recovery of metal values from spent lithium-ion batteries with chemical deposition and solvent extraction. J. Power Sources 152, 278–284. doi: 10.1016/j.jpowsour.2005.03.134

CrossRef Full Text | Google Scholar

Kou, Z. Y., Miao, C., Mei, P., Zhang, Y., Yan, X. M., Jiang, Y., et al. (2020). Enhancing the cycling stability of all-solid-state lithium-ion batteries assembled with Li_1.3Al_0.3Ti_1.7(PO₄)₃ solid electrolytes prepared from precursor solutions with appropriate pH values. Ceramics Int. 46, 9629–9636. doi: 10.1016/j.ceramint.2019.12.229

CrossRef Full Text | Google Scholar

Lee, J. S., Wang, X. Q., Luo, H. M., and Dai, S. (2010). Fluidic carbon precursors for formation of functional carbon under ambient pressure based on ionic liquids. Adv. Mater. 22, 1004–1007. doi: 10.1002/adma.200903403

PubMed Abstract | CrossRef Full Text | Google Scholar

Li, G. H., Li, F. C., Yang, H., Cheng, F. Y., Xu, N., Shi, W., et al. (2016). Graphene oxides doped MIL-101(Cr) as anode materials for enhanced electrochemistry performance of lithium ion battery. Inorg. Chem. Commun. 64, 63–66. doi: 10.1016/j.inoche.2015.12.017

CrossRef Full Text | Google Scholar

Li, Z. F., Cui, Y. H., Wu, J. W., Du, C. Q., Zhang, X. H., and Tang, Z. Y. (2016). Synthesis and electrochemical properties of lithium zinc titanate as an anode material for lithium ion batteries via microwave method. RSC Adv. 45, 39209–39215. doi: 10.1039/C6RA05244D

CrossRef Full Text | Google Scholar

Lin, C. F., Lai, M. O., Zhou, H. H., and Lu, L. (2014). Mesoporous Li₄Ti₅O_12−x/C submicrospheres with comprehensively improved electrochemical performances for high-power lithium-ion batteries. Phys. Chem. Chem. Phys. 16, 24874–24883. doi: 10.1039/C4CP03826F

PubMed Abstract | CrossRef Full Text | Google Scholar

Lin, J. Y., Hsu, C. C., Ho, H. P., and Wu, S. H. (2013). Sol-gel synthesis of aluminum doped lithium titanate anode material for lithium ion batteries. Electrochim. Acta 87, 126–132. doi: 10.1016/j.electacta.2012.08.128

CrossRef Full Text | Google Scholar

Lin, Y., Jhan, Y. R., and Duh, J. G. (2011). Improved capacity and rate capability of Ru-doped and carbon-coated Li₄Ti₅O₁₂ anode material. J. Alloys Compd. 509, 6965–6968. doi: 10.1016/j.jallcom.2011.04.018

CrossRef Full Text | Google Scholar

Liu, M., Wang, X. Y., Wei, S. Y., Hu, H., Zhang, R., and Liu, L. (2018). Cr-doped Fe₂F₅·H₂O with open framework structure as a high performance cathode material of sodium-ion batteries. Electrochim. Acta 269, 479–489. doi: 10.1016/j.electacta.2018.02.159

CrossRef Full Text | Google Scholar

Liu, T., Tang, H. Q., Zan, L. X., and Tang, Z. Y. (2016). Comparative study of Li₂ZnTi₃O₈ anode material with good high rate capacities prepared by solid state, molten salt and sol-gel methods. J. Electroanal. Chem. 771, 10–16. doi: 10.1016/j.jelechem.2016.03.036

CrossRef Full Text | Google Scholar

Long, W. M., Wang, X. Y., Yang, S. Y., Shu, H. B., Wu, Q., Bai, Y. S., et al. (2011). Electrochemical properties of Li₄Ti_5−2xNi_xMn_xO₁₂ compounds synthesized by sol-gel process. Mater. Chem. Phys. 131, 431–435. doi: 10.1016/j.matchemphys.2011.09.071

CrossRef Full Text | Google Scholar

Mani, V., Nathiya, K., and Kalaiselvi, N. (2014). Role of carbon content in qualifying Li₃V₂(PO₄)₃/C as a high capacity anode for high rate lithium battery applications. RSC Adv. 4, 17091–17096. doi: 10.1039/C4RA00963K

CrossRef Full Text | Google Scholar

Nie, Y., Xiao, W., Miao, C., Fang, R., Kou, Z. Y., Wang, D., et al. (2020). Boosting the electrochemical performance of LiNi_0.8Co_0.15Al_0.05O₂ cathode materials in-situ modified with Li_1.3Al_0.3Ti_1.7(PO₄)₃ fast ion conductor for lithium-ion batteries. Electrochim. Acta 353:136477. doi: 10.1016/j.electacta.2020.136477

CrossRef Full Text | Google Scholar

Novikova, S. A., Larkovich, R. V., Chekannikov, A. A., Kulova, T. L., and Yaroslavtsev, A. B. (2018). Electrical conductivity and electrochemical characteristics of Na₃V₂(PO₄)₃-based NASICON-type materials. Inorg. Mater. 54, 794–804. doi: 10.1134/S0020168518080149

CrossRef Full Text | Google Scholar

Pan, X., Duan, X. C., Lin, X. P., Zong, F. Y., Tong, X. B., Li, Q. H., et al. (2018). Rapid synthesis of Cr-doped gamma-Fe₂O₃/reduced graphene oxide nanocomposites as high performance anode materials for lithium ion batteries. J. Alloys Compd. 732, 270–279. doi: 10.1016/j.jallcom.2017.10.222

CrossRef Full Text | Google Scholar

Qi, Y. L., Huang, Y. D., Jia, D. Z., Bao, S. J., and Guo, Z. P. (2009). Preparation and characterization of novel spinel Li₄Ti₅O_12−xBr_x anode materials. Electrochim. Acta 54, 4772–4776. doi: 10.1016/j.electacta.2009.04.010

CrossRef Full Text | Google Scholar

Ruan, Y. L., Wang, K., Song, S. D., Liu, J. J., and Han, X. (2017). Improved structural stability and electrochemical performance of Na₃V₂(PO₄)₃ cathode material by Cr doping. Ionics 23, 1097–1105. doi: 10.1007/s11581-016-1919-3

PubMed Abstract | CrossRef Full Text | Google Scholar

Shenouda, Y., and Murali, K. R. (2008). Electrochemical properties of doped lithium titanate compounds and their performance in lithium rechargeable batteries. J. Power Sources 176, 332–339. doi: 10.1016/j.jpowsour.2007.10.061

CrossRef Full Text | Google Scholar

Tai, Z. G., Zhu, W., Shi, M., Xin, Y. F., Guo, S. W., Wu, Y. F., et al. (2020). Improving electrochemical performances of Lithium-rich oxide by cooperatively doping Cr and coating Li₃PO₄ as cathode material for Lithium-ion batteries. J. Colloid Interface Sci. 576, 468–475. doi: 10.1016/j.jcis.2020.05.015

PubMed Abstract | CrossRef Full Text | Google Scholar

Tang, H. Q., and Tang, Z. Y. (2014). Effect of different carbon sources on electrochemical properties of Li₂ZnTi₃O₈/C anode material in lithium-ion batteries. J. Alloys Compd. 613, 267–274. doi: 10.1016/j.jallcom.2014.06.050

CrossRef Full Text | Google Scholar

Tang, H. Q., Tang, Z. Y., Du, C. Q., Qie, F. C., and Zhu, J. T. (2014a). Ag-doped Li₂ZnTi₃O₈ as a high rate anode material for rechargeable lithium-ion batteries. Electrochim. Acta 120, 187–192. doi: 10.1016/j.electacta.2013.12.090

CrossRef Full Text | Google Scholar

Tang, H. Q., Zhu, J. T., Tang, Z. Y., and Ma, C. X. (2014b). Al-doped Li₂ZnTi₃O₈ as an effective anode material for lithium-ion batteries with good rate capabilities. J. Electroanal. Chem. 731, 60–65. doi: 10.1016/j.jelechem.2014.08.011

CrossRef Full Text | Google Scholar

Tang, Y. Q., Liu, L., Huang, X. B., Ding, X., Zhou, S. B., and Chen, Y. D. (2019). Synthesis and electrochemical properties of Li2FeSiO4/C/Ag composite as a cathode material for Li-ion battery. J. Central South Univ. 26, 1443–1448. doi: 10.1007/s11771-019-4100-0

CrossRef Full Text | Google Scholar

Tarascon, J. M., and Armand, M. (2001). Issues and challenges facing rechargeable lithium batteries. Nature 414, 359–367. doi: 10.1038/35104644

PubMed Abstract | CrossRef Full Text | Google Scholar

Tian, B. B., Xiang, H. F., Zhang, L., Li, Z., and Wang, H. H. (2010). Niobium doped lithium titanate as a high rate anode material for Li-ion batteries. Electrochim. Acta 55, 5453–5458. doi: 10.1016/j.electacta.2010.04.068

CrossRef Full Text | Google Scholar

Wang, M. X., Huang, X. B., Wang, H. Y., Zhou, T., Xie, H. S., and Ren, Y. R. (2019). Synthesis and electrochemical performances of Na₃V₂(PO₄)₂F₃/C composites as cathode materials for sodium ion batteries. RSC Adv. 9, 30628–30636. doi: 10.1039/C9RA05089B

PubMed Abstract | CrossRef Full Text | Google Scholar

Wang, M. X., Wang, K., Huang, X. B., Zhou, T., Xie, H. S., and Ren, Y. R. (2020). Improved sodium storage properties of Zr-doped Na₃V₂(PO₄)₂F₃/C as cathode material for sodium ion batteries. Ceramics Int. 46, 28490–28498. doi: 10.1016/j.ceramint.2020.08.006

CrossRef Full Text | Google Scholar

Wang, S., Bi, Y. F., Wang, L. J., Meng, Z. H., and Luo, B. M. (2019). Mo-doped Li₂ZnTi₃O₈@graphene as a high performance anode material for lithium-ion batteries. Electrochim. Acta 301, 319–324. doi: 10.1016/j.electacta.2019.01.168

CrossRef Full Text | Google Scholar

Wu, H. B., Chang, S., Liu, X. L., Yu, L. Q., Wang, G. L., Cao, D. X., et al. (2013). Sr-doped Li₄Ti₅O₁₂ as the anode material for lithium-ion batteries. Solid State Ionics 232, 13–18. doi: 10.1016/j.ssi.2012.10.027

CrossRef Full Text | Google Scholar

Xiao, H., Huang, X. B., Ren, Y. R., Ding, X., Chen, Y. D., and Zhou, S. B. (2019). Improved electrochemical performance of Na₃V₂(PO₄)₃ modified by N-doped carbon coating and Zr doping. Solid State Ionics 333, 93–100. doi: 10.1016/j.ssi.2019.01.025

CrossRef Full Text | Google Scholar

Xiao, H., Huang, X. B., Ren, Y. R., Wang, H. Y., Ding, J. N., Zhou, S. B., et al. (2018). Enhanced sodium ion storage performance of Na₃V₂(PO₄)₃ with N-doped carbon by folic acid as carbon-nitrogen source. J. Alloys Compd. 732, 454–459. doi: 10.1016/j.jallcom.2017.10.195

CrossRef Full Text | Google Scholar

Xu, Y. X., Hong, Z. S., Xia, L. C., Yang, J., and Wei, M. D. (2013). One step sol-gel synthesis of Li₂ZnTi₃O₈/C nanocomposite with enhanced lithium-ion storage properties. Electrochim. Acta 88, 74–78. doi: 10.1016/j.electacta.2012.10.044

CrossRef Full Text | Google Scholar

Yi, T. F., Pan, J. J., Wei, T. T., Li, Y. W., and Cao, G. Z. (2020a). NiCo₂S₄-based nanocomposites for energy storage in supercapacitors and batteries. Nano Today 33:100894. doi: 10.1016/j.nantod.2020.100894

CrossRef Full Text | Google Scholar

Yi, T. F., Qiu, L. Y., Mei, J., Qi, S. Y., Cui, P., Luo, S. H., et al. (2020c). Porous spherical NiO@NiMoO₄@PPy nanoarchitectures as advanced electrochemical pseudocapacitor materials. Sci. Bull. 65, 546–556. doi: 10.1016/j.scib.2020.01.011

CrossRef Full Text | Google Scholar

Yi, T. F., Wei, T. T., Li, Y., He, Y. B., and Wang, Z. B. (2020b). Efforts on enhancing the Li-ion diffusion coefficient and electronic conductivity of titanate-based anode materials for advanced Li-ion batteries. Energy Stor. Mater. 26, 165–197. doi: 10.1016/j.ensm.2019.12.042

CrossRef Full Text | Google Scholar

Yoshio, N. (2001). Lithium ion secondary batteries; past 10 years and the future. J. Power Sources 100, 101–106. doi: 10.1016/S0378-7753(01)00887-4

CrossRef Full Text | Google Scholar

Yu, Z. J., Zhang, X. F., Yang, G. L., Liu, J., Wang, J. W., Wang, R. S., et al. (2011). High rate capability and long-term cyclability of Li₄Ti_4.9V_0.1O₁₂ as anode material in lithium ion battery. Electrochim. Acta 56, 8611–8617. doi: 10.1016/j.electacta.2011.07.051

CrossRef Full Text | Google Scholar

Zhang, B., Huang, Z. D., Oh, S. W., and Kim, J. K. (2011). Improved rate capability of carbon coated Li_3.9Sn_0.1Ti₅O₁₂ porous electrodes for Li-ion batteries. J. Power Sources 196, 10692–10697. doi: 10.1016/j.jpowsour.2011.08.114

CrossRef Full Text | Google Scholar

Zhang, P., Li, X. L., Hua, Y., Yu, J. J. S, and Ding, Y. (2018). Enhanced performance and anchoring polysulfide mechanism of carbon aerogel/sulfur material with Cr doping and pore tuning for Li-S batteries. Electrochim. Acta 282, 499–509. doi: 10.1016/j.electacta.2018.06.068

CrossRef Full Text | Google Scholar