MWCNTs composite anode for lithium-ion batteries

Journal Pre-proof Adding lithium fluoride to improve the electrochemical properties SnO2@C/MWCNTs composite anode for lithium-ion batteries

Liang Guodong, Sun Xiaogang, Lai Jiamei, Wei Chengcheng, Huang Yapan, Hu Hao PII:

S1572-6657(19)30669-1

DOI:

https://doi.org/10.1016/j.jelechem.2019.113401

Reference:

JEAC 113401

To appear in:

Journal of Electroanalytical Chemistry

Received date:

26 May 2019

Revised date:

25 July 2019

Accepted date:

23 August 2019

Please cite this article as: L. Guodong, S. Xiaogang, L. Jiamei, et al., Adding lithium fluoride to improve the electrochemical properties SnO2@C/MWCNTs composite anode for lithium-ion batteries, Journal of Electroanalytical Chemistry(2019), https://doi.org/ 10.1016/j.jelechem.2019.113401

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

© 2019 Published by Elsevier.

Journal Pre-proof

Adding Lithium Fluoride to improve the electrochemical properties SnO2@C/MWCNTs composite anode for lithium-ion batteries Liang Guodong1, Sun Xiaogang*12, Lai Jiamei1, Wei Chengcheng1, Huang Yapan1, Hu Hao1 (1. School of Mechantronics Engineering, Nanchang University, Nanchang 330031, China 2.NanoCarbon Co. Ltd, Nanchang 330052, China, e-mail: [email protected])

Introduction

lP

re

-p

ro

of

Abstract: In this paper, SnO2@C/MWCNTs-lithium fluoride (LiF) composite electrode was prepared. carbon-coated SnO2 (SnO2@C) was prepared by spray drying method with water-soluble asphalt as the carbon source and multiwalled carbon nanotubes (MWCNTs) as conductive agent. The electronic conductivity of the new type of anode was significantly enhanced and the volume expansion of SnO2 was refrained. LiF was utilized to enhance the stability of the SEI film and improve the coulombic efficiency and capacity retention rate of electrode. After 200 cycles, the SnO2@C/MWCNTs-LiF anode still maintain 70.1% capacity retention rate. And the specific capacity hold at 274 mAh/g at 2400 mA/g compared with 136 mAh/g of SnO2@C/MWCNTs anode. The results demonstrated that the addition of LiF can stabilize the SEI film and improve the electrochemical performance of the lithium-ion batteries (LIBs). Key words: SnO2@C; MWCNTs; lithium fluoride; lithium-ion batteries; capacity

Jo ur

na

As a new generation and widely used energy storage device, lithium ion battery (LIB) has the advantages of high energy density, long cycle life and little environmental pollution. However, the disadvantages of high production cost, low actual capacity and poor safety performance hinder the further development of LIBs and limit their application [1-5]. As is known to us, LIB is mainly composed of four parts, including anode material, separator, electrolyte and cathode material [6-9]. Anode materials usually play a vital role in LIBs. At present, the research on the anode material mainly includes tin-based, silicon-based, sulfhydryl-based alloys. These materials usually have higher specific capacities than commercial anode materials-graphite (372 mAh/g). Among these, SnO2 is considered as a promising new generation of anode material due to its low embedded lithium voltage, high lithium insertion capacity and environmental friendliness. However, SnO2 also facing its own problems such as large volume expansion and large irreversible capacity for the first time [10-12]. To alleviate its volume effect, researchers had done a lot of work to overcome this problem. The main methods focus on making different structures of SnO2 and compounding with carbon materials, such as carbon nanotube and graphene [13-16]. Carbon material not only relieves the volume effect to some extent, but also improves the conductivity of the electrode. In addition, lower initial coulomb efficiency (ICE) is also an urgent problem to be

Journal Pre-proof

lP

re

-p

ro

of

solved. The reason for low ICE is usually because of the consumption of a large portion of lithium ions during the formation of the solid electrolyte interface (SEI) film. The steady SEI film has a positive effect on the electrochemical performance of LIBs. SEI film contains a large amount of inorganic substances, especially lithium fluoride (LiF), which can stabilize the SEI layer and enhance transport [17-18]. Generally, pre-lithiation is a more common method to enhance the ICE. Cui et al. improved the performance of SnO2 electrode by introducing the Cu intermediate and LiF coating layers [19]. Yang et al. prepared pitch carbon and LiF co-modified Si-based anode material for LIBs [20]. Xiong et al. improved the electrochemical properties of a SiO@C/graphite composite anode by adding lithium fluoride [21]. However, as far as we know, the effect of LiF on SnO2-based anode materials has not been reported, so it is necessary to investigate the effect of LiF on SnO2. In this paper, SnO2@C/MWCNTs-LiF composite was prepared by spray drying method and a subsequent facile method. First, SnO2 was coated on the surface with a layer of amorphous carbon by spray drying. The amorphous carbon is formed by pyrolysis of water-soluble asphalt, which is inexpensive and readily available, and low crystallinity and easy to graphitize. The amorphous carbon layer can not only avoid the direct contact of SnO2 with the electrolyte, but also improve the conductivity of the active material. Then the MWCNTs was added as conductive agent and also used to inhibit the volume expansion of the active material. Finally, we added LiF, which was designed to maintain the stability of the SEI film and enhance electrochemical performance.

na

Fig.1 Synthesis process of SnO2@C/MWCNTs-LiF

Jo ur

2. Experiment 2.1 Preparation of SnO2@C The SnO2 nanoparticles were added to a 10wt% solution of water-soluble asphalt solution. After magnetic stirring and ultrasonic dispersion for 1 h, the homogeneous solution was obtained, then the solution was spray-dried with the spray dryer to obtain amorphous carbon-coated SnO2. 2.2 Preparation of SnO2@C/MWCNTs-LiF With continuous stirring, 0.075g LiF was dissolved in 200mL of deionized water and sonicated for 30 min to form a homogeneous cloudy solution. Afterwards, 1g MWCNTs which was ultrasonically dispersed for half an hour, was dropped into above solution. Then 1g obtained SnO2@C was added, after stirring for 4h on a magnetic stirrer, following centrifugation and drying at 60 °C, the final product was obtained. For comparison, SnO2@C/MWCNTs composite without LiF was also prepared in a similar way. The process of synthesis is presented in Fig. 1. 2.3 Materials characterizations The phase of the prepared composite material was measured by X-ray diffraction (XRD), the field emission scanning electron microscopy (SEM) was used to observe the microstructure of the composite. Energy dispersive spectroscopy (EDS) was also carried out to characterize the distribution of elements.

Journal Pre-proof

ro

of

2.4 Electrochemical tests The obtained SnO2@C/MWCNTs-LiF: Super-P carbon black (SP): polyvinylidene fluoride (PVDF) was dissolved in a solvent of 1-methyl-2-pyrrolidone (NMP) at a mass ratio of 8:1:1. Then the mixture was milled at 120 r/min for 3 hours to obtain uniformly dispersed slurry. The obtained slurry was uniformly coated on copper foil with the thickness of 100um, and placed in a vacuum drying oven at 60 °C to obtain the anode electrode. CR2025 coin cells were assembled in an argon-filled glove box, where the O2 and H2O contents were kept below 1ppm. Lithium metal pieces were used as a counter electrode, Celgard 2300 is used as a separator and a solution of 1 mol/L LiPF6 dissolved in EC: DMC: DEC (volume ratio 1:1:1) as electrolyte. The batteries tester was used to conduct galvanostatic charge-discharge. The voltage ranged from 0.01 to 3 V. Cyclic voltammetry (CV) was conducted on electrochemical workstation, and the scanning at a rate of 0.1 mV/s with a voltage variation ranging from 0.01 to 3V. Besides, electrochemical impedance (EIS) was also carried to evaluate the electrochemical performance.

na

lP

re

-p

Result and discussion Fig.2 shows the XRD patterns of SnO2@C, SnO2@C/MWCNTs and SnO2@C/MWCNTs-LiF. The XRD diffraction peak of the amorphous carbon-coated SnO2 is substantially identical to the peak of SnO2, corresponding to the card JCPDS card No. 41-1445 [22]. The peak appearing at 25.58° was the (002) crystal plane of MWCNTs. The additional peaks of SnO2@C/MWCNTs-LiF appeared at 38.6°, 44.9° and 65.5°, which corresponds to the characteristic peak of LiF (JCPDS card No.04-0857), indicating the presence of LiF. . Fig. 2 XRD of SnO2@C/MWCNTs-LiF, SnO2@C/MWCNTs and SnO2@C

Jo ur

Fig.3a shows the SEM image of SnO2@C/MWCNTs composite, and the SEM of SnO2@C/MWCNTs-LiF is shown in Fig3b, c. From the figures, we can clearly observe that MWCNTs was distributed among the composite, the exist of MWCNTs not only improve the conductivity but also buffer the expansion of the active material. And to characterize the presence of LiF, we performed the EDS test on SnO2@C/MWCNTs-LiF composite, the results are presented Fig.3d-h. Fig. 3g shows that there is a large amount of C element in the composite, which is mainly provided by the amorphous and MWCNTs, and the presence of C can effectively improve the electrical conductivity of the active material. The distribution of the F element in Fig. 3h indicates that the LiF powder is uniformly dispersed in the powder. As a main component of the SEI film, adding LiF can complement the Li+ ions which was consumed during the formation of the SEI film. which do good to maintain the stability of the SEI layer. Therefore, the electrochemical performance of SCG-LiF can be significantly improved.

Journal Pre-proof Fig. 3 (a)SEM of SnO2@C/MWCNTs and (b-c) SnO2@C/MWCNTs-LiF; (d) SEM images of SnO2@C/MWCNTs-LiF and corresponding of EDS elemental mappings of (e) Sn, (f) O, (g) C and (h) F

lP

re

-p

ro

of

Fig. 4a shows the initial discharge-charge curves of SnO2@C, SnO2@C/MWCNTs, SnO2@C/MWCNTs-LiF electrodes at 50 mA/g. During the discharge process, the platform appearing at around 0.9V related to the SEI film produced by the reaction between the electrolyte and lithium ions [23]. SnO2@C, SnO2@C/MWCNTs, SnO2@C/MWCNTs-LiF have initial reversible specific capacities of 1168, 1098 and 700 mAh/g, corresponding to initial coulombic efficiencies (ICE) of 64.9%, 65.3% and 64.7%, respectively. SnO2@C/MWCNTs-LiF composite exhibited similar ICE but lower specific capacity compared to SnO2@C/MWCNTs and SnO2@C composites, which mainly due to the presence of non-electroactive LiF. To activate the batteries, the cells were charged and discharged for three times at the current density of 50 mA/g. And the cycle performance of the three electrodes at 100 mA/g was presented in Fig. 4b. As shown in Fig.4b, SnO2@C decays faster than the other two types of cells. With the coating of amorphous carbon, its specific capacity decays to 352 mAh/g after 200 cycles, exhibits the capacity retention rate of 36.7%. Benefit from the adjustment of MWCNTs, the volume expansion of SnO2 is well buffered, SnO2@C/MWCNTs and SnO2@C/MWCNTs-LiF show better cycle performance. After 100 cycles, SnO2@C/MWCNTs-LiF specific capacity kept at 483 mAh/g, capacity retention rate is 70.1%, higher than that of SnO2@C/MWCNTs (58.5%). The main reason for the improvement in cycle performance is the exist of LiF can promote the recovery of capacity. .

na

Fig. 4 (a) First charge and discharge profile and (b) cycle performance of SnO2@C/MWCNTs-LiF, SnO2@C/MWCNTs and SnO2@C

Jo ur

After three cycles of pre-active of the electrodes at 50 mA/g, we further explored the rate performance, and the results are shown in Fig. 5. At the current density of 100 mA/g, the specific capacities of SnO2@C, SnO2@C/MWCNTs and SnO2@C/MWCNTs-LiF are 884, 642, 844 mAh/g, respectively. When the current density is gradually increased to 2400 mA/g, the specific capacities maintained at 136, 274, 69 mAh/g. The lower capacity of SnO2@C compared to another two electrodes indicated the buffering effect of MWCNTs on volume expansion. And SnO2@C/MWCNTs-LiF capacity stayed higher than SnO2@C/MWCNTs demonstrated that adding LiF benefit capacity retention at high rate current density. When the current density recovered to 100 mA/g, specific capacities returns to 812,621,738 mAh/g. The improvement of the electrochemical performance is because, during the formation of SEI layer, the addition of LiF can effectively compensate for the consumption of Li+ ions in the electrolyte, which is beneficial to maintain the stability of the SEI layer. Another reason for this significant improvement is because LiF is the major of SEI layer, adding LiF can directly enhance the stability of the SEI films [24-25].

Journal Pre-proof Fig. 5 Rate performance of SnO2@C/MWCNTs-LiF, SnO2@C/MWCNTs and SnO2@C

-p

ro

of

To better understand the lithiation/delithiation mechanism of SnO2@C/MWCNTs and SnO2@C/MWCNTs-LiF, we conducted CV tests on two electrodes, and the results are shown in Fig. 6. As we can see the CV curves of SnO2@C/MWCNTs from Fig.6a, during the first cathode scan, the peak appearing near 0.75V was contribute to the formation of the SEI films and the decomposed of SnO2 (eqn (1)), which disappeared in the subsequent cycles, indicating that the formation of the SEI film mainly occurred in the first cycle. And the process of decomposition of SnO2 into Sn, which usually results in a greatly irreversible specific capacity. The reduction peak appearing near 0V and the oxidation peak appearing near 0.6V correspond to the alloying and de-alloying process of lithium (eqn (2)). 1.25V and 1.7V involve a reversible process from Sn to SnO2 [26-28]. And as shown in Fig. 6b, SnO2@C/MWCNTs-LiF shows similar CV profile, in addition, we can clearly see that the SEI peak intensity is weaker than that of SnO2@C/MWCNTs. SnO2 + 4Li+ + 4e- → Sn + 2Li2O (1) + Sn + xLi + xe  LixSn (0≤x≤4.4) (2) Fig. 6 CV curves of (a) SnO2@C/MWCNTs and (b) SnO2@C/MWCNTs-LiF

Jo ur

na

lP

re

In addition, we performed EIS measurements on the cells after cycle test to clarify the effect of the addition of LiF on the electrochemical performance of the LIBs. The results are shown in Fig.7. In the Nyquist diagram, the intersection of the starting point and the axis of the high-frequency region is the resistance Rs in the solution, and the semicircle usually represents the charge transfer resistance Rct, and the oblique line composition of the low-frequency range represents the diffusion resistance Zw of the lithium ion in the solid-phase electrode material. The Rct of SnO2@C, SnO2@C/MWCNTs and SnO2@C/MWCNTs-LiF are 68Ω, 89Ω and 204Ω, the lower resistance of SnO2@C/MWCNTs and SnO2@C/MWCNTs-LiF is attributed to the connected and conductive structure built by MWCNTs. The addition of LiF stabilizes the structure of the SEI and contributes to the transport of lithium ions. Therefore, SnO2@C/MWCNTs-LiF exhibits lower resistance and better cycle performance. Fig. 7 EIS of SnO2@C/MWCNTs-LiF, SnO2@C/MWCNTs and SnO2@C

Fig.8 compares the SEM of electrodes after cycles. It is clear that the SnO2@C/MWCNTs-LiF electrode kept more complete structure, while SnO2@C/MWCNTs shows the obvious crack. The integrity electrode contributed to the adding of LiF, which supplemented the composite of SEI layer. Therefore, the SEI layer can maintain stability and protect the anode material from direct contact with the electrolyte, exhibited good electrochemical performance.

Journal Pre-proof

Fig.8 SEM of (a) SnO2@C/MWCNTs-LiF and (b) SnO2@C/MWCNTs electrode after cycles

re

-p

ro

of

Conclusion In summary, a new type of composite anode material of SnO2@C/MWCNTs-LiF was prepared. The electrochemical properties of SnO2@C/MWCNTs-LiF was investigated. Compared with SnO2@C/MWCNTs and SnO2@C anode. The presence of amorphous carbon and MWCNTs can effectively alleviate the stress caused by the volume expansion of SnO2 while improving its conductivity. The addition of LiF is beneficial to stabilize the SEI film. The test results shown that SnO2@C/MWCNTs-LiF anode obtained a good cycle and rate performance.

na

lP

Acknowledgements This study was supported by Jiangxi scientific fund (20142BBE50071) and Jiangxi education fund (KJLD13006).

Jo ur

Conflict of interest: We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted. Reference [1] PANWAR N L, KAUSHIK S C, KOTHARI S, Role of renewable energy sources in environmental protection: a review, Renewable Sustainable Energy Rev 15 (2011) 1513. [2] DINCER I. Renewable energy and sustainable development: a crucial review, Renewable Sustainable Energy Rev 4 (2000) 157. [3] WAKIHARA M. Recent developments in lithium ion batteries, Mater Sci Eng 33 (2001) 109. [4] HAN T H, LEE W J, LEE D H, Kim J E, Choi E Y, Kim S O, Peptide/graphene hybrid assembly into core/shell nanowires, Adv Mater, 22 (2010) 2060. [5] FANG Y, LV Y, CHE R, WU H, ZHANG X, Gu D, ZHENG G, ZHAO D, Two-dimensional mesoporous carbon nanosheets and their derived graphene nanosheets: synthesis and efficient lithium ion storage, J Am Chem Soc 135 (2013) 1524. [6] MURPHY D W, BTOADHEAD J, STEELE B C H, Materials for advanced batteries, NASA STI/Recon Tech Rep A 82 (1980) 18112.

Journal Pre-proof

Jo ur

na

lP

re

-p

ro

of

[7] ZHAO J, YANG W Z, ZHAO J M, Application and Development of Lithium-ion Battery, Chinese Battery Industry 5(2000) 31. [8] LANDI B J, GANTER M J, CRESS C D, DILEO R A, RAFFAELLE R P, Carbon nanotubes for lithium ion batteries, Energy Environ Sci 2 (2009) 638. [9] WU S H, YOU J K, LIU Z G, Study on carbon negative electrode for lithium ion batteries, Chinese Journal of Power Sources 22 (1998) 35. [10] Chen J S, Lou X W, SnO₂ -based nanomaterials: synthesis and application in lithium-ion batteries, Small 9(2013) 1877. [11] Zhou X, Wan L J, Guo Y G, Binding SnO2 nanocrystals in nitrogen-doped graphene sheets as anode materials for lithium-ion batteries, Advanced Materials, 25 (2013) 2152. [12] Deng Y, Fang C, Chen G, The developments of SnO2/graphene nanocomposites as anode materials for high performance lithium ion batteries: A review, Journal of Power Sources 304 (2016) 81. [13] Yin X M, Li C C, Zhang M, Hao Q Y, Liu S, Chen L B,Wang T H, One-Step Synthesis of Hierarchical SnO2 Hollow Nanostructures via Self-Assembly for High Power Lithium Ion Batteries, Journal of Physical Chemistry C 114 (2010) 8084. [14] Liang J, Yu X Y, Zhou H, Wu H B, Ding S, Lou X W D, Bowl-like SnO2 @carbon hollow particles as an advanced anode material for lithium-ion batteries, Angewandte Chemie 126 (2015) 13017. [15] Pan Z, Sun H, Pan J, Zhang J, Wang B, Peng H, The creation of hollow walls in carbon nanotubes for high-performance lithium ion batteries, Carbon 133 (2018) 384. [16] Lin J, Peng Z, Xiang C, Ruan G, Yan Z, Natelson D, Tour J M, Graphene nanoribbon and nanostructured SnO2 composite anodes for lithium ion batteries, Acs Nano 7 (2013) 6001. [17] Schroder K, Alvarado J, Yersak T A, Dudney N, Webb L J, Stevenson K J, The effect of fluoroethylene carbonate as an additive on the solid electrolyte interphase on silicon lithium-ion electrodes, Chem. Mater. 27 (2015) 5531. [18] Xu C, Lindgren F, Philippe B, Gorgoi M, Bjorefors F, Edstrom K, Gustafsson T, Improved Performance of Silicon Anode for Li-Ion Batteries: Understanding the Surface Modification Mechanism of Fluoroethylene Carbonate as an Effective Electrolyte Additive, Chemistry of Materials 27 (2015) 2591. [19] Cui Z, Huang Y, Guo X. Electrochemical properties of SnO2 thin-film anodes improved by introduction of Cu intermediate and LiF coating layers, Electrochimica Acta 60 (2012) 7. [20] Yang Y, Wang Z, Yan G, Guo H, Wang J, Li X, Pitch carbon and LiF co-modified Si-based anode material for lithium ion batteries, Ceram. Int. 43 (2017) 8590. [21] Xia M, Li Y, Wu Y, Zhang H, Yang J, Zhou N, Zhou Z, Xiong X, Improving the electrochemical properties of a SiO@C/graphite composite anode for high-energy lithium-ion batteries by adding lithium fluoride, Applied Surface Science 480 (2019) 410. [22] Lou X W, Chen J S, Chen P, Archer L A. One-Pot Synthesis of Carbon-Coated SnO2 Nanocolloids with Improved Reversible Lithium Storage Properties, Chemistry of Materials 13 (2009) 2868.

Journal Pre-proof

re

-p

ro

of

[23] Yun Q, Qin X, Lv W, He Y, Li B, Kang F, Yang Q H, "Concrete" inspired construction of a silicon/carbon hybrid electrode for high performance lithium ion battery, Carbon 93 (2015) 59. [24] Li, Nian-Wu, Yin, Ya-Xia, Yang, Chun-Peng, et al. An Artificial Solid Electrolyte Interphase Layer for Stable Lithium Metal Anodes, Advanced Materials 28 (2016) 1853. [25] Schroder K, Alvarado J, Yersak T A, et al. The Effect of Fluoroethylene Carbonate as an Additive on the Solid Electrolyte Interphase on Silicon Lithium-Ion Electrodes, Chemistry of Materials 27 (2015) 5531. [26] Shao Q, Tang J, Sun Y, Li J, Zhang K, Yuan J, Zhu D, Qin L C, Unique interconnected graphene/SnO2 nanoparticle spherical multilayers for lithium-ion battery applications, Nanoscale 9 (2017) 4439. [27] Huang M, Feng M, Li H, Huang P, Su Q, Zhang F, Du G, Rapid microwave-assisted synthesis of SnO2 quantum dots/reduced graphene oxide composite with its application in lithium-ion battery, Materials Letters 209 (2017) 260. [28] Sennu P, Aravindan V, Lee Y S, Marine algae inspired pre-treated SnO2 nanorods bundle as negative electrode for Li-ion capacitor and battery: An approach beyond intercalation, Chemical Engineering Journal 324 (2017) 26.

lP

highlights

na

1.SnO2@C/MWCNTs-LiF composite was prepared by spray drying method and a subsequent facile method

Jo ur

2.MWCNTs can improve the conductivity and inhibit the volume expansion 3.the capacity retention was significantly improved by adding LiF 4.the electrode exhibited good cycle and rate performance