Tuning Electrochemical Performance through Non-stoichiometric Compositions in High-voltage Spinel Cathode Materials

doi:10.15541/jim20170579

Abstract

Abstract:

In this study, a simple method to prepare high-voltage spinel cathode materials though controlling stoichiometric ratio in their compositions was reported. Non-stoichiometric and stoichiometric high-voltage spinel LiNi_0.5Mn_1.5O₄ cathode materials were prepared by solid-state reaction between Li₂CO₃ and Ni_0.25Mn_0.75(OH)₂ prcursor. Their morphologies, structures and electrochemical performance were characterized by scanning electron microscopy, X-ray diffraction, neutron diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, as well as electrochemical curves. The second particles occupied the similar sizes ~8 μm, which were composed of nanoparticles. Compared to stoichiometric LiNi_0.5Mn_1.5O₄, Ni/Mn cations in non-stoichiometric LiNi_0.5Mn_1.5O₄ sample distributed randomly, resulting in structure disorder demonstrated by the analysis of X-ray diffraction, neutron diffration and Raman spectroscopy. Less Mn³⁺ content in stoichiometric LiNi_0.5Mn_1.5O₄ sample was detected though X-ray photoelectron spectroscopy. It is believed that more Mn³⁺ content and Ni/Mn cation disorder would benefit rate cpability and cycling performance. As a result, non-stoichiometric LiNi_0.5Mn_1.5O₄ sample delivers superior dicharge capacity at higher rates, even though it shows relatively minor discharge capacity at low rates. What’s more, higher capacity retention for the non-stoichiometric LiNi_0.5Mn_1.5O₄ sample was found, which was promoted to 91.2% at 1.0C rate after 400 cycles. At the same time, in situ X-ray diffraction measurements revealed that single-step phase transformation for non-stoichiometric LiNi_0.5Mn_1.5O₄ sample significantly enhanced structural stability during the electrochemical process. Spinel LiNi_0.5Mn_1.5O₄ with non-stoichiometric composition provides a promising solution for their potential application in high-energy-density lithium-ion batteries.

Key words: high voltage, spinel-structured, cathode materials, non-stoichiometric, cycling stability

CLC Number:

TQ174

LEE Sai-Xi, WANG Xue-Yin, GU Qing-Wen, XIA Yong-Gao, LIU Zhao-Ping, HE Jie. Tuning Electrochemical Performance through Non-stoichiometric Compositions in High-voltage Spinel Cathode Materials[J]. Journal of Inorganic Materials, 2018, 33(9): 993-1000.

Figures/Tables 10

Fig. 1 SEM images of (a) Non-stoichiometric-LNMO and (b) Stoichiometric-LNMO

Fig. 2 XRD patterns of (a) Non-stoichiometric-LNMO and (b) Stoichiometric-LNMO with refinement results

Fig. 3 Neutron diffraction patterns of (a) Non-stoichiometric- LNMO and (b) Stoichiometric-LNMO

Fig. 4 Raman spectra of Non-stoichiometric-LNMO and Stoichiometric LNMO

Fig. 5 XPS images of Mn 2P of (a) Non-stoichiometric- LNMO and (b) Stoichiometric-LNMO

Fig. 6 (a) Initial charge-discharge curves at 0.2C rate, and (b) cycling performance as well as coulombic efficiency at 1.0C rate for Non-stoichiometric-LNMO and Stoichiometric-LNMO samples

Table 1 Comparison with different methods to prepare high-voltage spinel cathode materials

Ref.	1^st discharge capacity?(mAh.g^-1)	Cycling performance??	Rate capabiity?(mAh.g^-1)
[15]	124 (0.1C)	90(250 cycles)	120 (0.2C charge, 5C discharge)
[19]	129 (0.1C)	83(300 cycles)	110 (1C charge, 2C discharge)
[20]	135 (0.1C)	88(80 cycles)	-
This work	132.8 (0.2C)	91.2(400 cycles)	122.4 (1C charge, 2C discharge)

Fig. 7 CV curves of (a) Non-stoichiometric-LNMO and (b) Stoichiometric-LNMO at the scan rate of 0.2 mV/s.

Fig. 8 Charge-discharge curves of (a) Non-stoichiometric- LNMO, (b) Stoichiometric-LNMO at different rates, and (c) Capacity retention at different rates

Fig. 9 In situ XRD results during lithium-ion intercalation or deintercalation of (a) Non-stoichiometric-LNMO and (b) Stoichiometric-LNMO samples

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