Letter Cite This: ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX
www.acsaem.org
Self-Healing Liquid Metal and Si Composite as a High-Performance Anode for Lithium-Ion Batteries Yingpeng Wu,† Xingkang Huang,† Lu Huang, Xiaoru Guo, Ren Ren, Dan Liu, Deyang Qu, and Junhong Chen* Department of Mechanical Engineering, University of WisconsinMilwaukee, 3200 North Cramer Street, Milwaukee, Wisconsin 53211, United States S Supporting Information *
ABSTRACT: Si is among the highest theoretical capacity anodes for lithium-ion batteries, but it suffers from huge volume expansion during lithiation. Here we report a new approach to alleviating the volume change-induced degradation of Si anodes by mixing Si with a room-temperature liquid metal (LM), namely, Ga−Sn alloy. The Ga−Sn alloy is fluid with self-healing ability, acting as the liquid buffer for the Si upon lithiation and delithiation and healing the cracks caused by the volume expansion and contraction. The resulting Si/ LM composite exhibits a high capacity and excellent cyclicability. The composite anode delivers a reversible capacity of ∼670 mAh/g after 1000 cycles, with an outstanding rate capability. KEYWORDS: liquid metal, self-healing, liquid buffer, silicon, lithium-ion battery
D
Si and heal the cracks caused by the volume expansion/ contraction. With its large theoretical capacity, Si can be an outstanding contributor of the capacity. Combined with these two outstanding features, our new anode exhibits a high capacity (950 mAh/g at 100 mA/g) and excellent cyclic performance (no obvious decay over 1000 cycles). The SLC was fabricated by sonication and milling. Synthesis of the SLC is illustrated in Figure 1a and detailed in the Experimental Methods section in Supporting Information. The Si/LM ratio is 1:2 by weight. The one-dimensional and flexible carbon nanotubes (CNTs) acted as the conductive network and the bandage, while the graphene oxide (GO) was used as a thickener and stabilizer.15 A scanning electron microscopy (SEM) image shows a porous structure formed during the solvothermal process17,18 (Figure 2c). Benefiting from the high wetting ability of the Ga,19 the LM and Si nanoparticles were homogeneously dispersed in the whole material, as shown by the energy dispersive X-ray spectroscopy (EDS) results (Figure 2c−g). Figure 1b−f shows the SEM and EDS results for the SLC composite. The Si nanoparticles with sizes of ∼100 nm embedded in the carbon/LM skeleton formed a 3D structure. The EDS elemental mapping shows that the LM was homogeneously dispersed, and the Ga:Sn ratio was 88:12, the same as in the designed LM composition.
riven by growing global power supply requirements, industries and consumers are seeking lithium-ion batteries (LIBs) with longer cycle life and higher energy density,1,2 and great efforts have been made to improve the cycle life of the LIB.3−5 Si is one of the most widely studied anode materials due to its extremely large theoretical capacity;6,7 however, its high lithiation ratio causes a high volume change that will crack electrodes, detach active materials from current collectors, and break down the electronically conductive network within the electrode, thereby deactivating Li+ storage ability and leading to inferior cyclic performance.8,9 Recent studies have shown that self-healing materials, such as self-healing binders10−12 or self-healing Li-active metals,13−16 can improve the cycle life of batteries, which suffer from the mechanical fracture triggered by large volume change. Benefiting from fluidity and surface tension, material in a liquid form is one of the best candidates for self-healing applications.13 Previous studies on anodes reported using room-temperature liquid metal (LM), as it possesses selfhealing properties that can lead to an ultralong cycle life.15 Although such promising work offers a new path toward achieving a long cycle life for LIBs, a drawback is the limited capacity of LM. Thus, inspired by the self-healing ability of LM and the high energy density of Si, we fabricated a Si/LM composite (SLC) in this study to achieve a high capacity with excellent cyclic performance. With its fluidity and self-healing ability, LM can serve as a liquid buffer during the lithiation and delithiation of © XXXX American Chemical Society
Received: January 5, 2018 Accepted: March 20, 2018 Published: March 20, 2018 A
DOI: 10.1021/acsaem.8b00022 ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX
Letter
ACS Applied Energy Materials
Figure 1. (a) Schematic illustration of the synthesis of SLC, (b) SEM image, and (c−f) EDS elemental mapping of the SLC.
Figure 2. (a) Long-term cycling performance of the LIB based on the SLC anode, (b) cycling performance of the control material without the protection of LM, (c) SEM image, and (d−g) EDS mapping of the 3D SLC.
Benefiting from its liquid state and self-healing ability,15 the LM can be a good buffer for the volume change of Si. During the charging process, the Si expanded and pushed the surrounding LM away and occupied its space. The LM flowed away and was forced into the void spaces formed by the solvothermal process (Figure 2c). This process avoided the expansion/contraction-causing crack formation, thereby preventing the active materials from detaching from the current collector and maintaining the electronically conductive network. Such protection from the LM leads to an enhanced cycle life (Figure 2a).
In the past several years, many efforts have been made to buffer the volume change in Si anodes. In addition to using a self-healing polymer,10−12 another approach is to use material with elasticity and robustness such as graphene,20−22 carbon nanotubes,23,24 or other allotropes of carbon.5,25−27 Compared with these materials, there are several advantages to using the LM buffer: (1) the self-healing ability of LM offers a long-life buffer in the anode system; (2) the liquid state can easily change its shape to buffer the stress caused by the volume expansion/contraction of Si without breaking the main structure of the anode; (3) the metallicity of LM can offer better conductivity than self-healing polymers or carbon B
DOI: 10.1021/acsaem.8b00022 ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX
Letter
ACS Applied Energy Materials
Figure 3. (a) Rate capability of the SLC, (b) charge/discharge curves under different rates, and (c) CV curve of the SLC at 0.05 mV/s.
LM-free electrode dropped quickly to ∼370 mAh/g after 100 cycles. The high current rate tolerance of the SLC anode was achieved due to the geometric confinement effect and the high conductivity of the LM coated on the Si surface. Figure 3a shows the rate capability of the SLC: the capacities at 100, 200, 500, 1000, 2000, and 3000 mA/g are 950, 878, 807, 735, 618, and 546 mAh/g, respectively. After cycling at 3000 mA/g, the capacity at 1000 mA/g went back to 805 mAh/g, suggesting a total recovery. In addition, the dependence of electrode areal capacity on the mass loading was investigated and shown in Figure S2. The areal capacity was based on delithiation capacity at the 20th cycle at the 1 A/g rate. As the mass loading increased from 0.47 to 0.9 mg cm−2, the electrode areal capacity showed a good linearity from 0.36 to 0.66 mAh cm−2. This result indicated that high electrochemical activity was preserved due to our self-healing LM.28 To further characterize the electrochemical performance of the SLC, the cyclic voltammetry (CV) test was performed at the rate of 0.05 mV/s and in the voltage range 0.01−2.5 V (versus Li+ /Li). In the first cycle, there are irreversible peaks, which are associated with the SEI layer formation (∼1.2 V) and the reduction of oxygen groups.29 After the first few cycles, the redox reactions became stable at the fourth cycle. The cathodic lithium insertion mainly occurs at 0.41 V for the Sn, at 0.51 and 0.71 V for the Ga, and at 0.16 V for Si; the anodic lithium extraction occurs at 0.87 V for the Sn, at 0.77 and 0.95 V for the Ga, and at 0.36 and 0.53 V for Si. These results all agree well with previous reports.7,8,13,30,31 In the whole SLC anode, Si remedies the low-capacity shortcoming of the LM, while the LM buffers the problem of the huge volume change of the Si; therefore, the ratio of the Si/
materials; and (4) LM offers a relatively higher theoretical capacity than carbon materials. Figure 2a depicts the cyclic performance of the SLC anode, which was evaluated using galvanostatic discharge−charge measurements. The initial discharge (delithiation) capacity at 100 mA/g was ∼1400 mAh/g with an initial Coulombic efficiency (CE) ∼ 66%. The irreversible capacity loss was likely caused by the formation of the solid−electrolyte interphase (SEI) layer and the reduction of the remaining oxygencontaining functional groups on the RGO and CNTs.15 After activation for three cycles at 100 mA/g, the SLC anode was cycled at 1000 mA/g and then at 2000 mA/g for the cycling test. Benefiting from the high capacity of Si, the capacity of the SLC is much higher than that of the reported LM anode at the same current rates.15 At the same time, protected by the LM, the SLC electrode showed excellent cyclic performance. Figure 2a shows that the high reversible capacity remained at ∼670 mAh/g with a CE more than 99.3% after 1000 cycles. Although the LM was in the liquid state, no short-circuit occurred due to our precautions. We used a separator consisting of trilayer porous polymers (polypropylene/polyethylene/polypropylene), which helps block particles traveling to the counter electrode. Meanwhile, a poor wettability of the LM on the separator was observed with a contact angle of 144° (Figure S1a). More importantly, we used CNTs and graphene oxide as the skeleton to prevent the Si and LM from traveling and aggregating (Figure S1b). A control experiment without the LM was performed under the same conditions. Without the protection of the LM, the volume expansion/contraction during lithiation and delithiation reactions resulted in crack formation, thereby deactivating the Li+ storage ability and leading to inferior cycle performance.8,9 The capacity of the C
DOI: 10.1021/acsaem.8b00022 ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX
Letter
ACS Applied Energy Materials
Figure 4. (a) Cycling performance and (b) rate capability of SLC2v1, and (c) cycling performance and (d) rate capability of SLC1v1.
which the Si/LM ratio is between SLC2v1 and SLC. The gullies of the SLC1v1 after cycling are not as deep as those of the SLC2v1 (Figure S3d), and the conductivity network was not completely destroyed, leading to in-between battery performance between the SLC2v1 and SLC. All these results clearly suggest the role of LM and Si in the whole anode system. For the first time, LM was used as the self-healing liquid buffer, cooperating with the Si for the LIB anode. Si offers outstanding theoretical capacity while the LM works as the selfhealing buffer and contributes to the capacity as well. Due to these advantages, the SLC anode delivered a high capacity of 950 mAh/g at 100 mA/g, and no obvious decay is observed with a capacity of ∼670 mAh/g at 2000 mA/g over 1000 cycles. The anode also had an outstanding rate performance with capacities of 950, 878, 807, 735, 618, and 546 mAh/g at 100, 200, 500, 1000, 2000, and 3000 mA/g, respectively. This work provides a new route to overcome the capacity decay of the high-volume-change anode materials, and can be extended to other applications calling for buffering or healing ability to support the host materials, such as in catalysis, various electrodes, artificial muscle, and intelligent materials.
LM is important to the performance of the SLC anode. Further control experiments were carried out to understand the relationship. Figure 4 shows the cyclic performance and rate capability of the SLC with different Si/LM ratios. With the increasing Si/LM ratio (2:1, named SLC2v1), the initial capacity of the anode increased accordingly and can reach ∼2000 mAh/ g (Figure 4a, at a current density of 100 mA/g); however, the capacity quickly dropped to 584 mAh/g after 300 cycles at 2000 mA/g, which is even smaller than the capacity of Si/LM with a ratio of 1:2. The SLC2v1 also showed a poor C-rate performance: due to the high percentage of the Si, the capacity is quite high at the beginning, but it cannot fully recover, as the SLC2v1 retained only 87% capacity after a 24 cycle rate test (Figure 4b). The SLC1v1 anode (Si/LM with a ratio of 1:1), which has a Si/LM ratio in between the SLC2v1 and SLC, showed an inbetween performance (Figure 4c,d): the initial capacity was lower than that of SLC2v1 but higher than that of SLC; after 250 cycles, the capacity of SLC1v1 turned higher than that of SLC2v1 but lower than that of SLC. This trend clearly shows the role of the LM in the SLC: an optimum amount of LM occurs when it can fully cover the Si nanoparticle and leave enough buffer space for the volume change. The LM was in the liquid state whose shape could be easily changed when a force was applied and would not destroy the whole carbon skeleton. Combined with the self-healing ability of LM, such a buffer will not lose this outstanding ability during cycling and thus lead to longlasting cycle performance. However, with a lower LM ratio there is not enough regulated space for the Si, and thus the volume change can crash the carbon skeleton nearby, destroy the conductive network, and cause crack formation. Figure S3 shows the morphology of the anode before (Figure S3a−c) and after (Figure S3d−f) 100 cycles with different Si/LM ratios. There was no significant difference before cycling; after cycling, differentiation was caused by the Si/LM ratio. The anode with the higher Si ratio (SLC2v1) had big, deep gullies caused by the volume change of the Si (Figure S3d). The anode with an appropriate Si ratio (SLC) showed very little surface morphology change (Figure S3f); there was no gully, as seen in Figure S3d, and the conductivity network was well maintained. Figure S3e is from the SLC1v1 after cycling, of
■
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsaem.8b00022. Details on the experimental methods and extra information about the anode behavior (PDF)
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Xingkang Huang: 0000-0001-7965-1866 Deyang Qu: 0000-0003-3413-6574 Junhong Chen: 0000-0002-2615-1347 Author Contributions †
These authors contributed equally to this work.
D
DOI: 10.1021/acsaem.8b00022 ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX
Letter
ACS Applied Energy Materials Notes
Graphene Material with Super Compressive Elasticity and Near-Zero Poisson’s Ratio. Nat. Commun. 2015, 6, 6141−6146. (19) Chatain, D.; Wynblatt, P. Experimental Evidence for a Wetting Transition in Liquid Ga-Pb Alloys. Surf. Sci. 1996, 345, 85−90. (20) Chang, J.; Huang, X.; Zhou, G.; Cui, S.; Hallac, P. B.; Jiang, J.; Hurley, P. T.; Chen, J. Multilayered Si Nanoparticle/Reduced Graphene Oxide Hybrid as a High-Performance Lithium-Ion Battery Anode. Adv. Mater. 2014, 26, 758−764. (21) Du, Y.; Zhu, G.; Wang, K.; Wang, Y.; Wang, C.; Xia, Y. Si/ Graphene Composite Prepared by Magnesium Thermal Reduction of SiO2 as Anode Material for Lithium-Ion Batteries. Electrochem. Commun. 2013, 36, 107−110. (22) Wen, Y.; Zhu, Y.; Langrock, A.; Manivannan, A.; Ehrman, S. H.; Wang, C. Graphene-Bonded and-Encapsulated Si Nanoparticles for Lithium Ion Battery Anodes. Small 2013, 9, 2810−2816. (23) Epur, R.; Ramanathan, M.; Datta, M. K.; Hong, D. H.; Jampani, P. H.; Gattu, B.; Kumta, P. N. Scribable Multi-Walled Carbon Nanotube-Silicon Nanocomposites: A Viable Lithium-Ion Battery System. Nanoscale 2015, 7, 3504−3510. (24) Hieu, N. T.; Suk, J.; Kim, D. W.; Chung, O. H.; Park, J. S.; Kang, Y. Silicon Nanoparticle and Carbon Nanotube Loaded Carbon Nanofibers for Use in Lithium-Ion Battery Anodes. Synth. Met. 2014, 198, 36−40. (25) Li, X.; Meduri, P.; Chen, X.; Qi, W.; Engelhard, M. H.; Xu, W.; Ding, F.; Xiao, J.; Wang, W.; Wang, C. Others, Hollow Core−Shell Structured Porous Si−C Nanocomposites for Li-ion Battery Anodes. J. Mater. Chem. 2012, 22, 11014−11017. (26) Magasinski, A.; Dixon, P.; Hertzberg, B.; Kvit, A.; Ayala, J.; Yushin, G. High-Performance Lithium-Ion Anodes Using a Hierarchical Bottom-Up Approach. Nat. Mater. 2010, 9, 353−358. (27) Zhang, R.; Du, Y.; Li, D.; Shen, D.; Yang, J.; Guo, Z.; Liu, H. K.; Elzatahry, A. A.; Zhao, D. Highly Reversible and Large Lithium Storage in Mesoporous Si/C Nanocomposite Anodes with Silicon Nanoparticles Embedded in a Carbon Framework. Adv. Mater. 2014, 26, 6749−6755. (28) Chen, Z.; Wang, C.; Lopez, J.; Lu, Z.; Cui, Y.; Bao, Z. HighAreal-Capacity Silicon Electrodes with Low-Cost Silicon Particles Based on Spatial Control of Self-Healing Binder. Adv. Energy Mater. 2015, 5, 1401826. (29) Xu, J.; Zhang, L.; Wang, Y.; Chen, T.; Al-Shroofy, M.; Cheng, Y. Unveiling the Critical Role of Polymeric Binders for Silicon Negative Electrodes in Lithium-Ion Full Cells. ACS Appl. Mater. Interfaces 2017, 9, 3562−3569. (30) Huang, X.; Cui, S.; Chang, J.; Hallac, P. B.; Fell, C. R.; Luo, Y.; Metz, B.; Jiang, J.; Hurley, P. T.; Chen, J. A Hierarchical Tin/Carbon Composite as an Anode for Lithium-Ion Batteries with a Long Cycle Life. Angew. Chem., Int. Ed. 2015, 54, 1490−1493. (31) Winter, M.; Besenhard, J. O. Electrochemical Lithiation of Tin and Tin-based Intermetallics and Composites. Electrochim. Acta 1999, 45, 31−50.
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS Financial support for this work was provided by the University of Wisconsin System through an Applied Research Grant. The SEM imaging was conducted at the University of Wisconsin Milwaukee Bioscience Electron Microscope Facility. The authors thank Dr. H. A. Owen for the technical support with SEM.
■
REFERENCES
(1) Tarascon, J. M.; Armand, M. Issues and Challenges Facing Rechargeable Lithium Batteries. Nature 2001, 414, 359−367. (2) Yang, Z.; Zhang, J.; Kintner-Meyer, M. C. W.; Lu, X.; Choi, D.; Lemmon, J. P.; Liu, J. Electrochemical Energy Storage for Green Grid. Chem. Rev. 2011, 111, 3577−3613. (3) Goodenough, J. B.; Park, K. The Li-Ion Rechargeable Battery: A Perspective. J. Am. Chem. Soc. 2013, 135, 1167−1176. (4) Ji, L.; Lin, Z.; Alcoutlabi, M.; Zhang, X. Recent Developments in Nanostructured Anode Materials for Rechargeable Lithium-Ion Batteries. Energy Environ. Sci. 2011, 4, 2682−2699. (5) Liu, N.; Wu, H.; McDowell, M. T.; Yao, Y.; Wang, C.; Cui, Y. A Yolk-Shell Design for Stabilized and Scalable Li-Ion Battery Alloy Anodes. Nano Lett. 2012, 12, 3315−3321. (6) Wu, H.; Cui, Y. Designing Nanostructured Si Anodes for High Energy Lithium Ion Batteries. Nano Today 2012, 7, 414−429. (7) Wu, H.; Zheng, G.; Liu, N.; Carney, T. J.; Yang, Y.; Cui, Y. Engineering Empty Space Between Si Nanoparticles for Lithium-Ion Battery Anodes. Nano Lett. 2012, 12, 904−909. (8) Chan, C. K.; Peng, H.; Liu, G.; McIlwrath, K.; Zhang, X. F.; Huggins, R. A.; Cui, Y. High-performance Lithium Battery Anodes Using Silicon Nanowires. Nat. Nanotechnol. 2008, 3, 31−35. (9) Kovalenko, I.; Zdyrko, B.; Magasinski, A.; Hertzberg, B.; Milicev, Z.; Burtovyy, R.; Luzinov, I.; Yushin, G. A Major Constituent of Brown Algae for Use in High-Capacity Li-Ion Batteries. Science 2011, 334, 75−79. (10) Sun, Y.; Lopez, J.; Lee, H.; Liu, N.; Zheng, G.; Wu, C.; Sun, J.; Liu, W.; Chung, J. W.; Bao, Z.; Cui, Y. A Stretchable Graphitic Carbon/Si Anode Enabled by Conformal Coating of a Self-Healing Elastic Polymer. Adv. Mater. 2016, 28, 2455−2461. (11) Wang, C.; Wu, H.; Chen, Z.; McDowell, M. T.; Cui, Y.; Bao, Z. Self-Healing Chemistry Enables the Stable Operation of Silicon Microparticle Anodes for High-Energy Lithium-Ion Batteries. Nat. Chem. 2013, 5, 1042−1048. (12) Luo, C.; Fan, X.; Ma, Z.; Gao, T.; Wang, C. Self-Healing Chemistry between Organic Material and Binder for Stable SodiumIon Batteries. Chem. 2017, 3, 1050−1062. (13) Deshpande, R. D.; Li, J.; Cheng, Y.; Verbrugge, M. W. Liquid Metal Alloys as Self-Healing Negative Electrodes for Lithium Ion Batteries. J. Electrochem. Soc. 2011, 158, A845−A849. (14) Lee, K. T.; Jung, Y. S.; Kim, T.; Kim, C. H.; Kim, J. H.; Kwon, J. Y.; Oh, S. M. Liquid Gallium Electrode Confined in Porous Carbon Matrix as Anode for Lithium Secondary Batteries. Electrochem. SolidState Lett. 2008, 11, A21−A24. (15) Wu, Y.; Huang, L.; Huang, X.; Guo, X.; Liu, D.; Zheng, D.; Zhang, X.; Ren, R.; Qu, D.; Chen, J. A Room-Temperature Liquid Metal-Based Self-Healing Anode for Lithium-Ion Batteries with an Ultra-Long Cycle Life. Energy Environ. Sci. 2017, 10, 1854−1861. (16) Fan, X.; Mao, J.; Zhu, Y.; Luo, C.; Suo, L.; Gao, T.; Han, F.; Liou, S.; Wang, C. Superior Stable Self-Healing SnP3 Anode for Sodium-Ion Batteries. Adv. Energy Mater. 2015, 5, 1500174. (17) Chang, H.; Qin, J.; Xiao, P.; Yang, Y.; Zhang, T.; Ma, Y.; Huang, Y.; Chen, Y. Highly Reversible and Recyclable Absorption Under Both Hydrophobic and Hydrophilic Conditions Using a Reduced Bulk Graphene Oxide Material. Adv. Mater. 2016, 28, 3504. (18) Wu, Y.; Yi, N.; Huang, L.; Zhang, T.; Fang, S.; Chang, H.; Li, N.; Oh, J.; Lee, J. A.; Kozlov, M. Three-dimensionally Bonded Spongy E
DOI: 10.1021/acsaem.8b00022 ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX
