Materials Today Energy
Volume 17, September 2020, 100465
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Aluminum electrolysis derivative spent cathodic carbon for dendrite-free Li metal anode

https://doi.org/10.1016/j.mtener.2020.100465Get rights and content

Highlights

  • Spent cathodic carbon of aluminum electrolysis is used to prepare FMC.

  • FMC contains two types of C–F bonds, C(sp2)-F and C(sp3)-F.

  • C(sp2)-F serves as lithiophilic site for Li nucleation with reduced barrier.

  • C(sp3)-F produces LiF during Li deposition, facilitating formation of stable SEI.

  • Symmetric cells demonstrate ultra-low voltage hysteresis of 14 mV.

Abstract

Li metal anode is one of the most promising anodes for next-generation high-energy-density batteries. However, some lethal challenges, such as Li dendrite, inferior coulombic efficiency, and infinite volume change during repeated Li plating/stripping restrict its practical application. Although carbon-based materials are ideal hosts for Li deposition, unsatisfied lithiophilic property and vulnerable solid electrolyte interphase (SEI) film still remain unsolved. Herein, we report the fluorinated mesoporous carbon (FMC) nanosheets derived from spent cathodic carbon of aluminum electrolysis as a versatile dendrite-free current collector. Two types of C–F bonds are discovered in FMC. One is C(sp2)-F, which serves as lithiophilic site for Li nucleation with reduced barrier. The other is C(sp3)-F, which breaks to produce extra LiF during Li deposition, facilitating the formation of stable LiF-rich SEI film. The synergistically designed Li@FMC|LiFePO4 full cells demonstrate improved cycling performance with high coulombic efficiency. This work provides possibility for direct utilization of waste electro-carbon in energy storage application.

Graphical abstract

A fluorinated mesoporous carbon (FMC) is developed to stabilize Li metal anode. The FMC contains two types of C–F bonds. One type is C(sp2)-F, which can induce lithiophilic Li nucleation with reduced barrier. The other type is C(sp3)-F bond with weakened C–F bond, facilitating the formation of stable LiF-rich SEI film. The lithiophilic Li nucleation with a stable SEI film realizes long-life Li metal anode.

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Introduction

Nowadays, high-rate and high-energy-density are two keys to energy storage system [1,2]. Lithium-ion batteries have been widely applied to portable devices and electric transportation [3,4]. However, limited energy density stands in the way of further development (graphite only owns 372 mAh g−1 and would fail in high-rate performance). Li metal anode possesses high specific capacity and the lowest negative electrochemical potential (3,860 mAh g−1 and −3.04 V versus standard hydrogen electrode, respectively) [5,6]. Therefore, reviving Li metal battery is promising for higher-energy-density system. Nevertheless, some notorious issues severely hinder the commercial application of Li anode, which are summarized in high reactivity of Li metal and Li dendrite induced infinite volume expansion.

Enormous efforts have been devoted to resolving these problems, such as constructing artificial solid electrolyte interphase (SEI) [7,8], modifying separator and electrolyte [[9], [10], [11]], designing lithiophilic Li deposition site [[12], [13], [14], [15]]. However, a single strategy cannot handle these challenges completely. For example, additive will be depleted during repeated Li plating/stripping. Then Li dendrite still grows underneath the artificial SEI, bringing about severe electrode pulverization. Besides, although lithiophilic substrates can guide Li nucleation, the lithiophilic sites may be unstable and vanish in long-term cycling. Recently, carbon-based nanomaterials (carbon nanotubes, carbon nanofibers, and graphene) have been widely applied for dendrite-free Li deposition due to the following advantages [16,17]. To begin with, carbon-based nanomaterials can serve as ideal hosts to relieve the volume change of Li anodes. Moreover, they can also decrease the local current density and restrain the growth of Li dendrite [18]. Unfortunately, carbon-based materials are lithiophobic, and the SEI film induced by them is still vulnerable [19]. As shown in Fig. 1a, even stable SEI film will be punctured under the condition of lithiophobic nucleation. Since the uneven Li+ flux in surface aggravates the local stress distribution, resulting in dendrite growth and rupture of SEI film at high polarization area [20,21]. From Fig. 1b, lithiophilic nucleation enables SEI film to endure smaller stress, whereas the unstable SEI film may be pierced because of thermodynamic inherent instability [22]. In a word, the challenges of Li metal anode are inherent and complicated. Some strategies should be combined to further stabilize Li anodes. The method shown in Fig. 1c, integrating uniform lithiophilic nucleation and stable SEI film, is able to contribute to a long-life Li metal anode.

Herein, we report the fluorinated mesoporous carbon (FMC) nanosheets, which are derived from the spent cathode of aluminum electrometallurgy in fluoride molten salt, and can stabilize Li deposition through regulating the Li nucleation and SEI component. The FMC is eroded by NaAlF6 (an additive used to reduce the melting point of alumina) at high temperature (about 800 °C) for a long time [23,24], facilitating the formation of F-doped carbon. On one hand, FMC owns abundant lithiophilic nucleation sites (C(sp2)-F), reducing the barrier for Li nucleation. On the other hand, FMC possesses weakened C–F bond (C(sp3)-F), which can induce stable LiF-rich SEI film. As a consequence, dendrite-free Li deposition is achieved onto FMC@Cu collector. The resulted Li@FMC|LiFePO4 (LFP) full cells are expected to demonstrate improved cycling performance and high coulombic efficiency (CE).

Section snippets

Treatment of spent cathodic carbon

The spent cathodic carbon was provided by China Guizhou aluminum industry co., Ltd, and was crushed in advance. Then, it was ball-milled (ND7-2L) for 10 h at a speed of 400 rpm to obtain uniform powder. Afterwards, the powder was washed by 1 mol L−1 NaOH for three times to remove water-soluble impurities and potential Al2O3 (2NaOH+Al2O32NaAlO2+H2O). After rinsed with deionized water for five times and dried at 60 °C for 24 h, the pure FMC was obtained.

Preparation of FMC@Cu 3D current collector

The FMC, carbon nanotube and PVDF were

Characterization of FMC materials

Fig. S1 shows TEM images of FMC nanosheets. The lattice fringes show a d-spacing of 0.34 nm, in according with the graphite phase detected in XRD (Fig. S2). In Fig. S3a, it can be seen that FMC contains abundant pores with a diameter of 2.5 nm (mesoporous), which can serve as extra rooms for Li deposition. What's more, the moderate specific surface area (28.4 m2 g−1, Fig. S3b) provides enough active sites for Li deposition and avoids excessive side reactions with electrolyte. Additionally,

Conclusions

In summary, the fluorinated mesoporous carbon (FMC) nanosheets derived from the spent cathode of aluminum electrometallurgy in fluoride molten salt, was used as a versatile current collector for dendrite-free Li deposition. With the synergy of C(sp2)-F and weakened C(sp3)-F, FMC stabilized Li metal anode via inducing the Li nucleation with reduced barrier [C(sp2)-F] and facilitating the formation of robust LiF-rich SEI [C(sp3)-F]. Based on the versatile properties, the Li@FMC anode realized

Data availability statement

Supplementary data to this article is available from the author.

Author contribution

Tiancheng Liu: Methodology, Experiment, Writing – original draft, Data curation. Zezhou Lin: Computation. Dong Wang: Methodology, Conceptualization, Writing – review and editing. Man Zhang: Experiment. Qiyang Hu: Project administration. Lei Tan: Formal analysis. Yingpeng Wu: Conceptualization. Xi Zhang: Computation. Haitao Huang: Supervision. Jiexi Wang: Conceptualization, Supervision, Validation, Writing – review and editing, Resources.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We thank the financial supporting from the National Natural Science Foundation of China (51874360, 51704332, 51804344), the Natural Science Foundation for Distinguished Young Scholars of Hunan Province (2020JJ2047), the Program of Huxiang Young Talents (2019RS2002), and the Innovation-Driven Project of Central South University (2020CX027).

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