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Superior intracluster conductivity of metallic lithium-ion battery anode achieved by high-pressure torsion
Materials Letters 260 (2020) 126933
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Superior intracluster conductivity of metallic lithium-ion battery anode achieved by high-pressure torsion Chenhao Qian a,b,⇑,1, Ziyang He c,1, Chen Liang d, Yue Cha e, Weixi Ji a,b,⇑ a
Department of Mechanical Engineering, Jiangnan University, China Jiangsu Key Laboratory of Advanced Food Manufacturing Equipment and Technology, Jiangnan University, China c Department of Economics, Columbia University, United States d School of Engineering, University of Liverpool, United Kingdom e Department of Military Economic, Logistics University of People Armed Police Force, China b
a r t i c l e
i n f o
Article history: Received 14 October 2019 Received in revised form 30 October 2019 Accepted 1 November 2019 Available online 3 November 2019 Keywords: Metal forming and shaping Metallic composites High-pressure torsion Lithium-ion battery anode Germanium alloys
a b s t r a c t Researchers have always hoped to increase the capacity of lithium-ion battery electrodes. Given the unique plastic characteristic of alloy anodes, this paper puts forward the application of high-pressure torsion and subsequent high-energy ball milling to produce a secondary cluster metallic anode system. A common germanium cooper eutectic alloy nanosheet is used for typical illustration, and after highpressure torsion processing, the bulk nanocrystalline cluster with density of 14.7 g/cm3 was achieved, which is much higher than the original powder’s density (4.6 g/cm3). Meanwhile, it is also observed that the conductivity and the cycle performance of the processed samples are greatly improved, and the sample’s capacity retention after 2800 cycles is surprisingly remaining at 96%. Therefore, as a pure mechanical processing method, high-pressure torsion has a bright prospect in improving the tap density and the conductivity of existing functional nanomaterials. Ó 2019 Elsevier B.V. All rights reserved.
1. Introduction As a group of successful material used for the negative electrode of lithium-ion batteries, alloy anodes have various advantages. They have a high capacity [1], are easy to synthesize [2] and can be doped conveniently [3]. In general, the manufacturing of nanosized alloy electrodes uses hydrothermal synthesis of nanocrystals, high-energy ball milling to obtain nanoparticles, and nanoimprint to obtain nanostructures [4–6]. However, alloy anodes usually experience huge volumetric changes during charge and discharge. Such reciprocating changes can lead to the pulverization of alloy structures and the continuous formation of Solid Electrolyte Interface (SEI), thus making the anode material lose activity. To solve these problems, researchers have tried to manufacture various core-shell nanostructures [7] and used secondary reactions to consume electrolyte, aiming at eventually achieve a mechanical and chemical stable structure.
⇑ Corresponding authors at: Department of Mechanical Engineering, Jiangnan University, China. E-mail addresses: [email protected] (C. Qian), [email protected] (W. Ji). 1 These authors contribute equally. https://doi.org/10.1016/j.matlet.2019.126933 0167-577X/Ó 2019 Elsevier B.V. All rights reserved.
Although nanocrystallization can greatly improve cycle performance, over nanocrystallization can cause the large exposure of the specific surface, which will result in serious secondary reactions and thus reduce efficiency. Simultaneously, the large number of intracluster spaces will increase the resistance among particles, hampering the transmission of electrons between the current collector and the active electrodes [8]. High-pressure torsion (HPT) is a purely mechanical solution for processing plastic materials, which is often used for the top-down synthesis of bulk nanocrystalline materials. The technology is ideal for processing metal and alloy materials, due to the plasticity nature. In comparison, nanoparticles prepared by hydrothermal synthesis have relative lower space filling ability, in other words, lower tap density. Without compromising the advantages of nanostructure, the proposed solution establishes a highly efficient secondary network among original nanostructures, which could obtain superior cycling performance and high conductivity at the same time. 2. Experiment The experiment process, as shown in Fig. 1, illustrates a general strategy for synthesizing nano-size secondary structure. Firstly, high-pression torsion (HPT) was employed in Ge-Cu nanosheets
2
C. Qian et al. / Materials Letters 260 (2020) 126933
Fig. 1. Illustration diagram of high-pressure torsion and further mechanical treatment.
with an initial density of 4.6 g/cm3 to produce bulk nanocrystalline materials. Then, high-energy ball milling was adopted to further crush the bulk nanocrystalline materials into micrometer scale particles. Thus, a material with achieved density as high as 14.7 g/cm3 was obtained. Mechanical pressure and shearing force can produce a high tap density and ensure the stability of nanostructure. When it comes to plastic materials, then this solution can even further reduce the size of nanostructure cells by dislocation interconnection. Moreover, in order to test the effectiveness of the solution in reducing the resistance among original structures, Atomic Layer Deposition (ALD) is adopted to deposit a silver layer with a thickness of 1–2 nm on the original Ge-Cu nanostructures. At last, a comparison of the electrochemical performance of all secondary clusters is carried out.
3. Data analysis Based on the solution of using HPT to obtain secondary nanostructure with a high tap density, firstly the relationship between pressure applied and achieved density has been examined exhaustively. As shown in Fig. S1 (in the supplement information), there is an obvious increasing period in the low-pressure zone (200 MPa), then following with almost flat zone without increasing the achieved density. As the pressure increases to 1 GPa and higher, the flattened curve further increases sharply to a record density of 14.7 g/cm3. But in fact, this phenomenon is specific to eutectic germanium and cooper alloys, different alloy systems may have various results. To evaluate the size and microstructure of the secondary structure generated with this solution, Fig. 2(a) illustrates nanostructure in the original status, and Fig. 2(b) illustrates the microstructure of the bulk nanocrystalline material obtained through high-pressure torsion. After high-pressure torsion, although the nanosheets are compacted into a bulk nanocrystalline structure, the size of nanostructure cells remains stable and no larger cells are produced. Fig. 2 (c) illustrates the secondary structure obtained after high-energy ball milling. There are still thin nanosheets like those of the initial status on the surface, but the size of the particles is kept at are relatively uniform at micrometer scale.
To examine the electrochemical performance of the obtained secondary structure, a constant current circulation with voltage range of 1 V–0.01 V is set firstly. As shown in Fig. 3, it is found that with a large current of 2C (1C = 1.6 A g 1), materials with ALD coating silver layer and then high-pressure torsion treatment can work stably after as many as 2800 cycles and has a capacity retention rate of approximate 96%. In the contrary, it is found that the original samples with large intracluster space can only maintain around 800 cycles and has a capacity retention of less than 50%. Secondary structure which has only gone through pure mechanical processing can still work stably after over 2000 cycles. From the perspective of coulombic efficiency, it is found that compared with Ge-based alloy’s 80% of coulombic efficiency reported in previous investigation [9], coulombic efficiency is largely improved by the solution. The rise of coulombic efficiency can be closely related to the increased adhesion of the interconnected nanostructure and to the sharp decrease of intracluster resistance. For the unique plastic deformation of alloy materials, nano grain-size secondary structure generated through high-pressure torsion, to some degree, can offset the stress and strain resulted from the volumetric changes from charge and discharge, so it can greatly improve cycling stability. It is worth to notice that the raw secondary intracluster structure normally has a poor conductivity comparing original nanostructure, and ALD coating silver layer is adopted to avoid this disadvantage. It is also worth noting that high-energy ball milling and HPT can cause phase changes in certain situations, depending on the input stress and strain. For the Ge-Cu eutectic alloy of this experiment, XRD test after each processing step was performed (as shown in Fig. S2) and found that there was no obvious new phase formation. The specific mechanical alloying process of high-pressure torsion also provides a good combining point for physical doping. Therefore, high-pressure torsion can be said to be a positive solution for the aforementioned problem. To further measure the electric conductivity of anodes, after the first cycle of delithiation, as shown in Fig. 4, electrochemical impedance spectroscopy (EIS) is carried out. Compared with Nyquist semicircle in high-frequency areas, samples treated by highpressure torsion have an intracluster resistance is almost half of the original nanostructure, and samples with ALD coating Ag layer even have intracluster resistance that is relative one fourth of that
3
C. Qian et al. / Materials Letters 260 (2020) 126933
Fig. 2. Microstructure characterization for (a) original; (b) after high-pressure torsion and (c) after high energy ball-milling processing.
Fig. 3. Electrochemical cycling characterizations of HPT-treated and ALD + HPT treated electrodes at 320 mA g
1
and 3.2 A g
1
, respectively.
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. Acknowledgement This paper was funded by the National Natural Science Foundation of China (51905215). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.matlet.2019.126933. References
Fig. 4. Nyquist plots of HPT-treated and ALD + HPT treated electrodes.
of the original nanostructure. In low-frequency areas, the results are consistent to the previous pattern. 4. Conclusion From electrochemical experiment data and microstructure analysis, it can be proved that high-pressure torsion and the subsequent mechanical processing method can substantially reduce intracluster resistance, improve tap density and produce secondary structures of micrometer scale.
[1] Y. Zhao, A. Manthiram, High-capacity, high-rate Bi–Sb alloy anodes for lithiumion and sodium-ion batteries, Chem. Mater. 27 (2015) 3096–3101, https://doi. org/10.1021/acs.chemmater.5b00616. [2] T. Ramireddy, M.M. Rahman, T. Xing, Y. Chen, A.M. Glushenko, Stable anode performance of an Sb–carbon nanocomposite in lithium-ion batteries and the effect of ball milling mode in the course of its preparation, J. Mater. Chem. A 2 (2014) 4282–4291. https://pubs.rsc.org/en/content/articlehtml/2014/ta/ c3ta14643j. [3] S. Jenaa, A. Mitrab, A. Patrab, S. Senguptab, K. Dasb, S.B. Majumderc, S. Dasb, Sandwich architecture of Sn-SnSb alloy nanoparticles and N-doped reduced graphene oxide sheets as a high rate capability anode for lithium-ion batteries, J. Power Sources 401 (2018) 165–174. https://www.sciencedirect.com/science/ article/pii/S0378775318309170. [4] Z. Xie, Z. He, X. Feng, W. Xu, X. Cui, J. Zhang, C. Yan, M.A. Carreon, Z. Liu, Y. Wang, Hierarchical sandwich-like structure of ultrafine N-rich porous carbon nanospheres grown on graphene sheets as superior lithium-ion battery anodes, ACS Appl. Mater. Interfaces 8 (2016) 10324–10333, https://doi.org/ 10.1021/acsami.6b01430. [5] Y. Hwa, W. Kim, B. Yu, J. Kim, S. Hong, H. Sohn, Facile synthesis of Si nanoparticles using magnesium silicide reduction and its carbon composite as
4
C. Qian et al. / Materials Letters 260 (2020) 126933
a high-performance anode for Li ion batteries, J. Power Sources 252 (2014) 144–149. https://www.sciencedirect.com/science/article/pii/S1003632 617602905. [6] Z. Liu, G. Han, S. Sohn, N. Liu, J. Schroers, Nanomolding of crystalline metals: the smaller the easier, Phys. Rev. Lett. 122 (2019), https://doi.org/10.1103/ PhysRevLett.122.036101. [7] Q. Qu, Y. Zhu, X. Gao, Y. Wu, Core-Shell structure of polypyrrole grown on V2O5 nanoribbon as high performance anode material for supercapacitors,
Adv. Energy Mater. 8 (2012) 950–955, https://doi.org/10.1002/ aenm.201200088. [8] H. Umh, J. Park, J. Yeo, S. Jung, I. Nam, J. Yi, Lithium metal anode on a copper dendritic superstructure, Electrochem. Commun. 99 (2019) 27–31. https:// www.sciencedirect.com/science/article/pii/S1388248118303382. [9] M. Park, Y. Cho, K. Kim, J. Kim, M. Liu, J. Cho, Germanium nanotubes prepared by using the Kirkendall effect as anodes for high-rate lithium batteries, Angew. Chem. Int. Ed. 50 (2011) 9647–9650, https://doi.org/10.1002/anie.201103062.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Superior intracluster conductivity of metallic lithium-ion battery anode achieved by high-pressure torsion Chenhao Qian a,b,⇑,1, Ziyang He c,1, Chen Liang d, Yue Cha e, Weixi Ji a,b,⇑ a
Department of Mechanical Engineering, Jiangnan University, China Jiangsu Key Laboratory of Advanced Food Manufacturing Equipment and Technology, Jiangnan University, China c Department of Economics, Columbia University, United States d School of Engineering, University of Liverpool, United Kingdom e Department of Military Economic, Logistics University of People Armed Police Force, China b
a r t i c l e
i n f o
Article history: Received 14 October 2019 Received in revised form 30 October 2019 Accepted 1 November 2019 Available online 3 November 2019 Keywords: Metal forming and shaping Metallic composites High-pressure torsion Lithium-ion battery anode Germanium alloys
a b s t r a c t Researchers have always hoped to increase the capacity of lithium-ion battery electrodes. Given the unique plastic characteristic of alloy anodes, this paper puts forward the application of high-pressure torsion and subsequent high-energy ball milling to produce a secondary cluster metallic anode system. A common germanium cooper eutectic alloy nanosheet is used for typical illustration, and after highpressure torsion processing, the bulk nanocrystalline cluster with density of 14.7 g/cm3 was achieved, which is much higher than the original powder’s density (4.6 g/cm3). Meanwhile, it is also observed that the conductivity and the cycle performance of the processed samples are greatly improved, and the sample’s capacity retention after 2800 cycles is surprisingly remaining at 96%. Therefore, as a pure mechanical processing method, high-pressure torsion has a bright prospect in improving the tap density and the conductivity of existing functional nanomaterials. Ó 2019 Elsevier B.V. All rights reserved.
1. Introduction As a group of successful material used for the negative electrode of lithium-ion batteries, alloy anodes have various advantages. They have a high capacity [1], are easy to synthesize [2] and can be doped conveniently [3]. In general, the manufacturing of nanosized alloy electrodes uses hydrothermal synthesis of nanocrystals, high-energy ball milling to obtain nanoparticles, and nanoimprint to obtain nanostructures [4–6]. However, alloy anodes usually experience huge volumetric changes during charge and discharge. Such reciprocating changes can lead to the pulverization of alloy structures and the continuous formation of Solid Electrolyte Interface (SEI), thus making the anode material lose activity. To solve these problems, researchers have tried to manufacture various core-shell nanostructures [7] and used secondary reactions to consume electrolyte, aiming at eventually achieve a mechanical and chemical stable structure.
⇑ Corresponding authors at: Department of Mechanical Engineering, Jiangnan University, China. E-mail addresses: [email protected] (C. Qian), [email protected] (W. Ji). 1 These authors contribute equally. https://doi.org/10.1016/j.matlet.2019.126933 0167-577X/Ó 2019 Elsevier B.V. All rights reserved.
Although nanocrystallization can greatly improve cycle performance, over nanocrystallization can cause the large exposure of the specific surface, which will result in serious secondary reactions and thus reduce efficiency. Simultaneously, the large number of intracluster spaces will increase the resistance among particles, hampering the transmission of electrons between the current collector and the active electrodes [8]. High-pressure torsion (HPT) is a purely mechanical solution for processing plastic materials, which is often used for the top-down synthesis of bulk nanocrystalline materials. The technology is ideal for processing metal and alloy materials, due to the plasticity nature. In comparison, nanoparticles prepared by hydrothermal synthesis have relative lower space filling ability, in other words, lower tap density. Without compromising the advantages of nanostructure, the proposed solution establishes a highly efficient secondary network among original nanostructures, which could obtain superior cycling performance and high conductivity at the same time. 2. Experiment The experiment process, as shown in Fig. 1, illustrates a general strategy for synthesizing nano-size secondary structure. Firstly, high-pression torsion (HPT) was employed in Ge-Cu nanosheets
2
C. Qian et al. / Materials Letters 260 (2020) 126933
Fig. 1. Illustration diagram of high-pressure torsion and further mechanical treatment.
with an initial density of 4.6 g/cm3 to produce bulk nanocrystalline materials. Then, high-energy ball milling was adopted to further crush the bulk nanocrystalline materials into micrometer scale particles. Thus, a material with achieved density as high as 14.7 g/cm3 was obtained. Mechanical pressure and shearing force can produce a high tap density and ensure the stability of nanostructure. When it comes to plastic materials, then this solution can even further reduce the size of nanostructure cells by dislocation interconnection. Moreover, in order to test the effectiveness of the solution in reducing the resistance among original structures, Atomic Layer Deposition (ALD) is adopted to deposit a silver layer with a thickness of 1–2 nm on the original Ge-Cu nanostructures. At last, a comparison of the electrochemical performance of all secondary clusters is carried out.
3. Data analysis Based on the solution of using HPT to obtain secondary nanostructure with a high tap density, firstly the relationship between pressure applied and achieved density has been examined exhaustively. As shown in Fig. S1 (in the supplement information), there is an obvious increasing period in the low-pressure zone (200 MPa), then following with almost flat zone without increasing the achieved density. As the pressure increases to 1 GPa and higher, the flattened curve further increases sharply to a record density of 14.7 g/cm3. But in fact, this phenomenon is specific to eutectic germanium and cooper alloys, different alloy systems may have various results. To evaluate the size and microstructure of the secondary structure generated with this solution, Fig. 2(a) illustrates nanostructure in the original status, and Fig. 2(b) illustrates the microstructure of the bulk nanocrystalline material obtained through high-pressure torsion. After high-pressure torsion, although the nanosheets are compacted into a bulk nanocrystalline structure, the size of nanostructure cells remains stable and no larger cells are produced. Fig. 2 (c) illustrates the secondary structure obtained after high-energy ball milling. There are still thin nanosheets like those of the initial status on the surface, but the size of the particles is kept at are relatively uniform at micrometer scale.
To examine the electrochemical performance of the obtained secondary structure, a constant current circulation with voltage range of 1 V–0.01 V is set firstly. As shown in Fig. 3, it is found that with a large current of 2C (1C = 1.6 A g 1), materials with ALD coating silver layer and then high-pressure torsion treatment can work stably after as many as 2800 cycles and has a capacity retention rate of approximate 96%. In the contrary, it is found that the original samples with large intracluster space can only maintain around 800 cycles and has a capacity retention of less than 50%. Secondary structure which has only gone through pure mechanical processing can still work stably after over 2000 cycles. From the perspective of coulombic efficiency, it is found that compared with Ge-based alloy’s 80% of coulombic efficiency reported in previous investigation [9], coulombic efficiency is largely improved by the solution. The rise of coulombic efficiency can be closely related to the increased adhesion of the interconnected nanostructure and to the sharp decrease of intracluster resistance. For the unique plastic deformation of alloy materials, nano grain-size secondary structure generated through high-pressure torsion, to some degree, can offset the stress and strain resulted from the volumetric changes from charge and discharge, so it can greatly improve cycling stability. It is worth to notice that the raw secondary intracluster structure normally has a poor conductivity comparing original nanostructure, and ALD coating silver layer is adopted to avoid this disadvantage. It is also worth noting that high-energy ball milling and HPT can cause phase changes in certain situations, depending on the input stress and strain. For the Ge-Cu eutectic alloy of this experiment, XRD test after each processing step was performed (as shown in Fig. S2) and found that there was no obvious new phase formation. The specific mechanical alloying process of high-pressure torsion also provides a good combining point for physical doping. Therefore, high-pressure torsion can be said to be a positive solution for the aforementioned problem. To further measure the electric conductivity of anodes, after the first cycle of delithiation, as shown in Fig. 4, electrochemical impedance spectroscopy (EIS) is carried out. Compared with Nyquist semicircle in high-frequency areas, samples treated by highpressure torsion have an intracluster resistance is almost half of the original nanostructure, and samples with ALD coating Ag layer even have intracluster resistance that is relative one fourth of that
3
C. Qian et al. / Materials Letters 260 (2020) 126933
Fig. 2. Microstructure characterization for (a) original; (b) after high-pressure torsion and (c) after high energy ball-milling processing.
Fig. 3. Electrochemical cycling characterizations of HPT-treated and ALD + HPT treated electrodes at 320 mA g
1
and 3.2 A g
1
, respectively.
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. Acknowledgement This paper was funded by the National Natural Science Foundation of China (51905215). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.matlet.2019.126933. References
Fig. 4. Nyquist plots of HPT-treated and ALD + HPT treated electrodes.
of the original nanostructure. In low-frequency areas, the results are consistent to the previous pattern. 4. Conclusion From electrochemical experiment data and microstructure analysis, it can be proved that high-pressure torsion and the subsequent mechanical processing method can substantially reduce intracluster resistance, improve tap density and produce secondary structures of micrometer scale.
[1] Y. Zhao, A. Manthiram, High-capacity, high-rate Bi–Sb alloy anodes for lithiumion and sodium-ion batteries, Chem. Mater. 27 (2015) 3096–3101, https://doi. org/10.1021/acs.chemmater.5b00616. [2] T. Ramireddy, M.M. Rahman, T. Xing, Y. Chen, A.M. Glushenko, Stable anode performance of an Sb–carbon nanocomposite in lithium-ion batteries and the effect of ball milling mode in the course of its preparation, J. Mater. Chem. A 2 (2014) 4282–4291. https://pubs.rsc.org/en/content/articlehtml/2014/ta/ c3ta14643j. [3] S. Jenaa, A. Mitrab, A. Patrab, S. Senguptab, K. Dasb, S.B. Majumderc, S. Dasb, Sandwich architecture of Sn-SnSb alloy nanoparticles and N-doped reduced graphene oxide sheets as a high rate capability anode for lithium-ion batteries, J. Power Sources 401 (2018) 165–174. https://www.sciencedirect.com/science/ article/pii/S0378775318309170. [4] Z. Xie, Z. He, X. Feng, W. Xu, X. Cui, J. Zhang, C. Yan, M.A. Carreon, Z. Liu, Y. Wang, Hierarchical sandwich-like structure of ultrafine N-rich porous carbon nanospheres grown on graphene sheets as superior lithium-ion battery anodes, ACS Appl. Mater. Interfaces 8 (2016) 10324–10333, https://doi.org/ 10.1021/acsami.6b01430. [5] Y. Hwa, W. Kim, B. Yu, J. Kim, S. Hong, H. Sohn, Facile synthesis of Si nanoparticles using magnesium silicide reduction and its carbon composite as
4
C. Qian et al. / Materials Letters 260 (2020) 126933
a high-performance anode for Li ion batteries, J. Power Sources 252 (2014) 144–149. https://www.sciencedirect.com/science/article/pii/S1003632 617602905. [6] Z. Liu, G. Han, S. Sohn, N. Liu, J. Schroers, Nanomolding of crystalline metals: the smaller the easier, Phys. Rev. Lett. 122 (2019), https://doi.org/10.1103/ PhysRevLett.122.036101. [7] Q. Qu, Y. Zhu, X. Gao, Y. Wu, Core-Shell structure of polypyrrole grown on V2O5 nanoribbon as high performance anode material for supercapacitors,
Adv. Energy Mater. 8 (2012) 950–955, https://doi.org/10.1002/ aenm.201200088. [8] H. Umh, J. Park, J. Yeo, S. Jung, I. Nam, J. Yi, Lithium metal anode on a copper dendritic superstructure, Electrochem. Commun. 99 (2019) 27–31. https:// www.sciencedirect.com/science/article/pii/S1388248118303382. [9] M. Park, Y. Cho, K. Kim, J. Kim, M. Liu, J. Cho, Germanium nanotubes prepared by using the Kirkendall effect as anodes for high-rate lithium batteries, Angew. Chem. Int. Ed. 50 (2011) 9647–9650, https://doi.org/10.1002/anie.201103062.