Elsevier

Journal of Power Sources

Volume 179, Issue 1, 15 April 2008, Pages 351-356
Journal of Power Sources

Short communication
Nonflammable electrolyte for 3-V lithium-ion battery with spinel materials LiNi0.5Mn1.5O4 and Li4Ti5O12

https://doi.org/10.1016/j.jpowsour.2007.12.089Get rights and content

Abstract

The compatibility between dimethyl methylphosphonate (DMMP)-based electrolyte of 1 M LiPF6/EC + DMC + DMMP (1:1:2 wt.) and spinel materials Li4Ti5O12 and LiNi0.5Mn1.5O4 was reviewed, respectively. The cell performance and impedance of 3-V LiNi0.5Mn1.5O4/Li4Ti5O12 lithium-ion cell with the DMMP-based nonflammable electrolyte was compared with the baseline electrolyte of 1 M LiPF6/EC + DMC (1:1 wt.). The nonflammable DMMP-based electrolyte exhibited good compatibility with spinel Li4Ti5O12 anode and high-voltage LiNi0.5Mn1.5O4 cathode, and acceptable cycling performance in the LiNi0.5Mn1.5O4/Li4Ti5O12 full-cell, except for the higher impedance than that in the baseline electrolyte. All of the results disclosed that the 3 V LiNi0.5Mn1.5O4/Li4Ti5O12 lithium-ion battery was a promising choice for the nonflammable DMMP-based electrolyte.

Introduction

Lithium-ion batteries are now widely used as energy storage devices for portable electronic devices such as laptop computers, cellular phones and digital cameras due to their high energy density. However, safety concern has become the main obstacle for the development of lithium-ion batteries for electric vehicles (EV) and hybrid electric vehicle (HEV) applications, which is greatly related to the high flammability of nonaqueous electrolyte [1], [2]. So, recent efforts have been focused on finding the nonflammable electrolytes [3], [4], [5], [6], [7], [8], [9]. In our previous work [10], [11], dimethyl methylphosphonate (DMMP) was considered as a promising flame-retardant additive or cosolvent, and also the DMMP-based electrolyte with a high concentration (exceeding 50 wt.%) has been validated to have the high safety characteristic. Unfortunately, the nonflammable DMMP-based electrolyte had a poor compatibility with the carbonaceous anodes, just as the trimethyl phosphate (TMP)-based nonflammable electrolyte, because both additives in the nonflammable electrolytes had similar stereo hindrances to propylene carbonate (PC) and would exert similar strains into the graphite structure and cause exfoliation [3], [8], [9]. Although the compatibility between the nonflammable electrolytes and the carbonaceous anodes could be improved by introducing film-formation additives, still the increased impedance from the thick solid electrolyte interface (SEI) would reduce the capacity and deteriorate the cycling performance [9], [11].

The spinel Li4Ti5O12 has been demonstrated as an alternative anode material because it has a very flat plateau at around 1.5 V versus Li+/Li and displays excellent reversibility and structural stability as a zero-strain insertion material in the charge–discharge process [12]. The stable spinel structure will seldom change in the PC-containing electrolyte [13], which is different from the graphite anode with the brittle layer structure that can be easily exfoliated for co-interaction of the solvent with lithium ion. Moreover, the 1.5 V voltage plateau also can avoid the carbonate solvent, especially PC, decomposing reductively to the gaseous products. Since the reduction of the flame retardant additive—DMMP occurs just at the potential below 1.2 V versus Li+/Li [11], it is logical that the DMMP-based electrolyte would be compatible with the Li4Ti5O12 anode.

To obtain an operating voltage of more than 3 V, the so-called 5 V spinel LiNi0.5Mn1.5O4 cathode will be used to couple with the spinel Li4Ti5O12 anode and fabricate the lithium-ion battery. LiNi0.5Mn1.5O4 is one of the most promising and attractive cathodes because of its acceptable stability, good cycling performance and high-dominant potential plateau at around 4.7 V [14], [15]. Compared with LiCoO2, LiNi0.5Mn1.5O4 also has the obvious advantage of low cost. By the partial substitution of Mn with Ni, the better cycling performance and higher energy density have been found for LiNi0.5Mn1.5O4 than plain LiMn2O4, even though the spinel LiNi0.5Mn1.5O4 has a limitation of requiring an electrolyte for the high-operating potential. Based on our previous work [10], [11], DMMP has excellent anodic stability, so it is expected that DMMP-based electrolyte would have such a wide electrochemical window that it could allow a stable electrochemical performance on the high-voltage LiNi0.5Mn1.5O4 electrode.

The objectives of this work are to examine whether or not the DMMP-based electrolyte with a high content of DMMP (50 wt.%), which could be considered as a nonflammable electrolyte with high safety characteristic, can be compatible with the spinel materials Li4Ti5O12 and LiNi0.5Mn1.5O4. Furthermore, the corresponding 3 V full-cell with the nonflammable electrolyte will also be investigated in detail, in order to find the new way to the high safety lithium-ion batteries.

Section snippets

Experimental

Li4Ti5O12 was prepared by solid-state reaction method [13]. The starting materials, TiO2-anatase and Li2CO3 in a Li:Ti molar ratio of 4.05:5.0 were mixed in cyclohexane and ball-milled for 48 h. Then the dried mixture was heated at 150 °C for 12 h and 800 °C for 24 h in air atmosphere to obtain white Li4Ti5O12 powder. LiNi0.5Mn1.5O4 was prepared by radiated polymer gel (RPG) method [16]. LiNO3, Ni(NO3)2radical dot6H2O, and Mn(CH3COO)2radical dot4H2O were dissolved in de-ionized water in the molar ratio of Li:Ni:Mn = 

Results and discussion

The Li4Ti5O12 and LiNi0.5Mn1.5O4 powders synthesized have been validated with a cubic spinel structure and no obvious impurity phase detected [13], [16]. In order to evaluate objectively the electrochemical performance of the two spinel materials, a baseline electrolyte, i.e. 1 M LiPF6/EC + DMC (1:1), is compared with the nonflammable DMMP-based electrolyte of 1 M LiPF6/EC + DMC + DMMP (2:1:1). Cyclic voltammetry results of the two electrolytes on the Li4Ti5O12 anode are shown in Fig. 1. In the

Conclusions

The DMMP-based electrolyte that has been validated as a nonflammable electrolyte in our previous work performs good compatibility with the spinel materials Li4Ti5O12 anode and LiNi0.5Mn1.5O4 cathode. The 3 V LiNi0.5Mn1.5O4/Li4Ti5O12 lithium-ion cells with the DMMP-based electrolyte have an acceptable capacity loss after 30 cycles. The higher impedance of the cells with the nonflammable electrolyte is one of the important reasons for its capacity loss. Therefore, the nonflammable DMMP-based

Acknowledgements

This study was supported by National Science Foundation of China (grant Nos. 50372064 and 20471057).

References (18)

  • S. Zhang et al.

    J. Power Source

    (2003)
  • Y.E. Hyung et al.

    J. Power Sources

    (2003)
  • X.L. Yao et al.

    J. Power Sources

    (2005)
  • H.F. Xiang et al.

    J. Power Sources

    (2007)
  • H.F. Xiang et al.

    J. Power Sources

    (2007)
  • X.L. Yao et al.

    Electrochim. Acta

    (2005)
  • T. Ohzuku et al.

    J. Power Sources

    (1999)
  • H.Y. Xu et al.

    Electrochim. Acta

    (2006)
  • H.Y. Xu et al.

    Electrochim. Acta

    (2006)
There are more references available in the full text version of this article.

Cited by (63)

View all citing articles on Scopus
View full text