Elsevier

Journal of Power Sources

Volume 416, 15 March 2019, Pages 29-36
Journal of Power Sources

Functional additives assisted ester-carbonate electrolyte enables wide temperature operation of a high-voltage (5 V-Class) Li-ion battery

https://doi.org/10.1016/j.jpowsour.2019.01.085Get rights and content

Highlights

  • Wide temperature range (−60–50 °C) LiNi0.5Mn1.5O4/MCMB full cell is developed.

  • Methyl acetate (MA) is used to obtain a high-conductivity LiPF6-based electrolyte.

  • High reactivity between MA co-solvent and MCMB anode is innovatively proposed.

  • Functional additives can efficiently suppress high reactivity between MA and MCMB.

  • Both high Li+ conductivity and favorable graphite anode SEI layer are crucial.

Abstract

Nowadays, wide temperature range and high-energy Li-ion batteries are increasingly required. However, it is difficult to get a compromise between subzero temperature performance and high temperature performance. Herein, methyl acetate co-solvent with a freezing point of −98.1 °C (50% by volume) is blended with carbonates to obtain a high-conductivity LiPF6-based electrolyte, which contains tris(trimethylsilyl) phosphite and 1,3-propanediolcyclic sulfate binary functional additives to significantly enhance cycling performance of a challenging high-voltage (5 V-class) battery system using a LiNi0.5Mn1.5O4 cathode and a graphitic mesocarbon microbead anode, unprecedentedly ranging from −60 °C to 50 °C. High reactivity between methyl acetate co-solvent and graphitic mesocarbon microbead anode is innovatively proposed to be associated with graphitic mesocarbon microbead anode catalytic formation of methoxy free radical. More importantly, high reactivity between methyl acetate co-solvent and graphitic mesocarbon microbead anode can be greatly suppressed by species derived from functional additives. This paper highlights the crucial rule of both high Li+ conductivity and favorable graphite anode interface layer for achieving high performance wide temperature range Li-ion batteries.

Introduction

Although rechargeable Li-ion batteries (LIBs) are one of the most successful power sources for consumer electronics, electric transportation tools as well as stationary energy-storage systems, their operation has long been restricted to room temperature (adjusted by air-conditioning system if needed) [[1], [2], [3], [4], [5], [6], [7], [8]]. At both subzero and high temperatures, electrochemical performance and safety of LIBs are seriously affected. Moreover, it is a challenging work to get a compromise between subzero temperature performance and high temperature performance of LIBs. Whereas, wide temperature range LIBs are urgently required for applications such as those in electric vehicles (EVs), space and military missions.

Energy and power density decrease rapidly and safety risk gets rising at subzero temperatures, which are mainly ascribed to the following limiting factors: (i) increased viscosity and reduced Li+ conductivity in electrolyte; (ii) sluggish Li+ migration through solid-electrolyte interphase (SEI) passivating layers of both electrodes, especially graphite anode; (iii) poor Li+ diffusion in active material particles, especially graphite anode; (iv) significant increase of charge transfer resistances at electrolyte-electrode interfaces of both electrodes, especially graphite anode; (v) easy growth of dangerous metal Li dendrites at surface of graphite anode [2,3,7,[9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22]]. Therefore, dominate strategy of improving subzero temperature performance of LIBs has been focused on optimizing electrolyte formulations by perspectives of increasing Li+ conductivity (developing co-solvents with low viscosity and low freezing point [4,6,8,14,17,[23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33]]) and forming favorable SEI layer at graphite anode (adopting novel main lithium salts [6,8,32,[34], [35], [36], [37], [38], [39], [40]] and functional additives [7,16,17,19,[41], [42], [43], [44], [45], [46], [47], [48], [49], [50]]). A series of low freezing point aliphatic esters co-solvents (such as methyl formate (MF), methyl acetate (MA), etc.) are commonly used to enhance the subzero temperature discharging capability [14,17,[26], [27], [28], [29], [30]]. However, these aliphatic esters have high reactivity with graphite anode and lead to the formation of unstable SEI layers and battery swelling, deteriorating cycling performance of LIBs, especially at room and high temperatures [7,14,17,28,30]. It is reported that some SEI layer stabilizing functional additives can significantly improve cyclability of LIBs using ester-containing electrolyte [17,30,[51], [52], [53], [54]]. Nowadays, it is gradually accepted that functional additives can help to form low impedance SEI layers on both electrodes and alleviate lithium plating at graphite anode, at subzero temperatures [7,15,19,[46], [47], [48]]. Furthermore, at elevated temperatures, functional additives play a key role in suppressing thermal decompositions of LiPF6 salt, forming temperature-insensitive SEI layers on both electrodes, blocking gas evolution and transition metal dissolution [1,3,17,30,32,35,36,38]. Thus, screening compatible novel solvents and functional additives are important for improving the cycling performance of wide temperature range LIBs.

On the other side, the development of next generation high-energy LIBs adopting cathode materials with higher specific capacity or higher working voltage has attracted great interests [55,56]. Wherein, high-voltage (5 V-class) cathode material of LiNi0.5Mn1.5O4 has been widely focused. However, LiNi0.5Mn1.5O4/graphite full cell always exhibits unsatisfying cycling performance due to the severe active lithium consuming [38,[56], [57], [58], [59], [60], [61], [62], [63], [64]]. Recently, we has reported that the addition of tris(trimethylsilyl) phosphite (TMSP) and 1,3-propanediolcyclic sulfate (PCS) binary functional additives into carbonates electrolyte can significantly enhance cycling performance of a high-voltage LiNi0.5Mn1.5O4/MCMB (graphitic mesocarbon microbeads) battery system, at both room temperature and elevated temperatures [59]. In this paper, aliphatic ester MA (Tm = −98.1 °C) co-solvent (50% by volume) is blended with carbonates to obtain a high-conductivity LiPF6-based electrolyte, which contains TMSP and PCS to significantly enhance cycling performance of this challenging high-voltage LiNi0.5Mn1.5O4/MCMB battery system, unprecedentedly ranging from −60 °C to 50 °C. High reactivity between MA co-solvent and MCMB anode is innovatively proposed to be associated with the MCMB anode catalytic formation of radical CH3O•. More importantly, high reactivity between MA co-solvent and MCMB anode can be greatly suppressed by species derived from binary functional additives. This paper highlights the crucial rule of both high Li+ conductivity and favorable electrode interface for achieving high performance wide temperature range LIBs.

Section snippets

Electrolytes preparation

The baseline electrolyte (BE) consisted of a mixed solvent of EC/DEC/EMC (1:1:1 by volume ratio) with a LiPF6 concentration of 1 mol L−1 (bought from Suzhou Qianmin Chemistry Co., Ltd. (China)). The electrolyte functional additives, TMSP (>99%) and PCS (>98%) was purchased from Alfa Aesar and Sigma Aldrich, respectively. The co-solvent, MA (>99%) was purchased from Aladin. Battery-grade LiPF6 (>99.9%) was provided by Sigma Aldrich. All chemicals were used without further purification. The

Electrochemical performances of LiNi0.5Mn1.5O4/MCMB full cell over a wide temperature range (−60 °C–50 °C)

At −5 °C and a charge/discharge rate of 0.3 C, LiNi0.5Mn1.5O4/MCMB full cell using BE + MA + TMSP + PCS exhibits best capacity retention (99.7%, 101.7 mAh g−1/102 mAh g−1), lowest voltage polarization, and most stable voltage plateaus after 200 cycles (Fig. 1a-c). The specific capacity increase phenomenon for early cycles is ascribed to micro/nano-scale insufficient wettability of electrodes with additives-containing electrolyte [7]. In comparison, full cell using BE and BE + MA demonstrates

Conclusion

In summary, we blend MA co-solvent (50% by volume) with carbonates to obtain a high-conductivity LiPF6-based electrolyte, which contains TMSP and PCS functional additives to significantly enhance cycling performance of a challenging high-voltage (5 V-class) LiNi0.5Mn1.5O4/MCMB battery system, unprecedentedly ranging from −60 °C to 50 °C. This is the first attempt to develop wide temperature range LiNi0.5Mn1.5O4/MCMB battery system, using conventional LiPF6-based electrolyte. High reactivity

Acknowledgments

This original research was supported by the Think-Tank Mutual Fund of Qingdao Energy Storage Industry Scientific Research, the National Natural Science Foundation for Distinguished Young Scholars of China (No. 51625204), National Natural Science Foundation of China (No. 51502319), the National Key R&D Program of China (Grant No. 2018YFB0104300), the Key Scientific and Technological Innovation Project of Shandong (Grant No. 2017CXZC0505), Youth Innovation Promotion Association CAS (No. 2017253),

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    Gaojie Xu and Suqi Huang contributed equally to this work.

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