Citation: Xinrun Yu, Jun Ma, Chunbo Mou, Guanglei Cui. Percolation Structure Design of Organic-inorganic Composite Electrolyte with High Lithium-Ion Conductivity[J]. Acta Physico-Chimica Sinica, ;2022, 38(3): 191206. doi: 10.3866/PKU.WHXB201912061 shu

Percolation Structure Design of Organic-inorganic Composite Electrolyte with High Lithium-Ion Conductivity

  • Corresponding author: Jun Ma, majun@qibebt.ac.cn Guanglei Cui, cuigl@qibebt.ac.cn
  • Received Date: 25 December 2019
    Revised Date: 14 January 2020
    Accepted Date: 15 January 2020
    Available Online: 10 March 2020

    Fund Project: the National Natural Science Foundation of China 51625204

  • With the increasing demand for safe high energy density energy storage systems, solid-state lithium metal batteries have attracted extensive attention. The solid electrolyte, which is expected to replace the traditional liquid organic electrolyte core in solid-state lithium metal batteries because of its excellent mechanical properties and non-flammability. Lithium-ion solid-state electrolytes can be categorized into two broad types: inorganic electrolytes and polymer electrolytes. Inorganic solid electrolytes have the advantages of high room-temperature ionic conductivity, wide electrochemical window, and high mechanical strength. However, their high brittleness, high solid-solid interface contact resistance, complex preparation process, and high cost make future development and practical applications challenging. In contrast to inorganic electrolytes, polymer electrolytes are easy to process and exhibit better flexibility and easy formation of a good, stable interface with lithium metal. However, solid polymer electrolytes still exhibit insufficient ionic conductivity at room temperatures compared with polymer solid electrolytes. Therefore, neither the inorganic electrolytes nor the polymer electrolytes alone can meet the requirements of high-performance solid-state lithium metal batteries. Recently, dispersing ceramic fillers (especially fast lithium-ion conductors) in a polymer matrix to integrate with composite polymer electrolytes has been developed as an effective strategy for enhancing room-temperature ionic conductivity, mechanical properties, and thermal stability of solid polymer electrolytes. Inorganic fillers do not only reduce the polymer matrix crystallization but also improve the lithium-ion conductivity by promoting the dissociation of lithium salts. The Lewis acid-base groups and oxygen vacancy at the surface of inorganic fillers can increase the migration number of lithium ions. Nevertheless, the effect of the percolation structure of inorganic fillers on the conductivity of organic-inorganic composite electrolytes should be discussed. It is believed that the organic-inorganic interface is the main reason for the significantly enhanced lithium-ion conductivity of composite electrolytes based on the percolation theory. In this paper, from the perspective of percolation structure design, we summarize the progress on high lithium-ion conductive organic-inorganic composite electrolytes with different dimensional-structured inorganic fillers. From one-dimensional filler to three-dimensional filler, the ionic conductivity of a composite electrolyte can be significantly influenced by the rational design and optimization of the percolation structure and orientation of the inorganic filler. Vertically aligned inorganic fillers provide optimal ion transport pathways in the polymer matrix, significantly improving the lithium-ion conductivity of the composite electrolytes. Furthermore, the advantages and disadvantages of the different percolation structures are compared and discussed objectively. Finally, future development trends of organic-inorganic composite electrolytes are discussed.
  • 加载中
    1. [1]

      Cheng, F.; Liang, J.; Tao, Z.; Chen, J. Adv. Mater. 2011, 23, 1695. doi: 10.1002/adma.201003587  doi: 10.1002/adma.201003587

    2. [2]

      Tarascon, J. M.; Armand, M. Nature 2001, 414, 359. doi: 10.1038/35104644  doi: 10.1038/35104644

    3. [3]

      Lin, D.; Liu, Y.; Cui, Y. Nat. Nanotechnol. 2017, 12, 194. doi: 10.1038/nnano.2017.16  doi: 10.1038/nnano.2017.16

    4. [4]

      Liu, B.; Zhang, J. G.; Xu, W. Joule 2018, 2, 833. doi: 10.1016/j.joule.2018.03.008  doi: 10.1016/j.joule.2018.03.008

    5. [5]

      Fan, L.; Wei, S.; Li, S.; Li, Q.; Lu, Y. Adv. Energy Mater. 2018, 8, 1702657. doi: 10.1002/aenm.201702657  doi: 10.1002/aenm.201702657

    6. [6]

      Chen, S.; Wen, K.; Fan, J.; Bando, Y.; Golberg, D. J. Mater. Chem. A 2018, 6, 11631. doi: 10.1039/c8ta03358g  doi: 10.1039/c8ta03358g

    7. [7]

      Nowak, S.; Winter, M. J. Electrochem. Soc. 2015, 162 (14), A2500. doi: 10.1149/2.0121514jes  doi: 10.1149/2.0121514jes

    8. [8]

      Schroeder, D. J.; Hubaud, A. A.; Vaughey, J. T. Mater. Res. Bull. 2014, 49, 614. doi: 10.1016/j.materresbull.2013.10.006  doi: 10.1016/j.materresbull.2013.10.006

    9. [9]

      Cui, W. Y.; An, M. Z.; Yang, P. X. Acta Phys. -Chim. Sin. 2010, 26 (5), 1233.  doi: 10.3866/PKU.WHXB20100530

    10. [10]

      Chen, R.; Qu, W.; Guo, X.; Li, L.; Wu, F. Mater. Horiz. 2016, 3, 487. doi: 10.1039/c6mh00218h  doi: 10.1039/c6mh00218h

    11. [11]

      Hu, Y. S. Nat. Energy 2016, 1, 16042. doi: 10.1038/nenergy.2016.42  doi: 10.1038/nenergy.2016.42

    12. [12]

      Janek, J.; Zeier, W. G. Nat. Energy 2016, 1, 16141. doi: 10.1038/nenergy.2016.141  doi: 10.1038/nenergy.2016.141

    13. [13]

      Zhou, D.; Shanmukaraj, D.; Tkacheva, A.; Armand, M.; Wang, G. Chemistry 2019, 5, 2326. doi: 10.1016/j.chempr.2019.05.009  doi: 10.1016/j.chempr.2019.05.009

    14. [14]

      Cheng, X. B.; Zhao, C. Z.; Yao, Y. X.; Liu, H.; Zhang, Q. Chemistry 2019, 5, 74. doi: 10.1016/j.chempr.2018.12.002  doi: 10.1016/j.chempr.2018.12.002

    15. [15]

      Zhu, Y.; He, X.; Mo, Y. ACS Appl. Mater. Interfaces 2015, 7, 23685. doi: 10.1021/acsami.5b07517  doi: 10.1021/acsami.5b07517

    16. [16]

      Bachman, J. C.; Muy, S.; Grimaud, A.; Chang, H. H.; Pour, N.; Lux, S. F.; Paschos, O.; Maglia, F.; Lupart, S.; Lamp, P.; et al. Chem. Rev. 2016, 116, 140. doi: 10.1021/acs.chemrev.5b00563  doi: 10.1021/acs.chemrev.5b00563

    17. [17]

      Chinnam, P. R.; Wunder, S. L. ACS Energy Lett. 2016, 2, 134. doi: 10.1021/acsenergylett.6b00609  doi: 10.1021/acsenergylett.6b00609

    18. [18]

      Han, F.; Zhu, Y.; He, X.; Mo, Y.; Wang, C. Adv. Energy Mater. 2016, 6(8), 1501590. doi: 10.1002/aenm.201501590  doi: 10.1002/aenm.201501590

    19. [19]

      Yao, X.; Huang, B.; Yin, J.; Peng, G.; Huang, Z.; Gao, C.; Liu, D.; Xu, X. Chin. Phys. B 2016, 25, 018802. doi: 10.1088/1674-1056/25/1/018802  doi: 10.1088/1674-1056/25/1/018802

    20. [20]

      Hu, P.; Chai, J.; Duan, Y.; Liu, Z.; Cui, G.; Chen, L. J. Mater. Chem. A 2016, 4, 10070. doi: 10.1039/c6ta02907h  doi: 10.1039/c6ta02907h

    21. [21]

      Zhang, X.; Wang, S.; Xue, C.; Xin, C.; Lin, Y.; Shen, Y.; Li, L.; Nan, C. W. Adv. Mater. 2019, 31, e1806082. doi: 10.1002/adma.201806082  doi: 10.1002/adma.201806082

    22. [22]

      Zhang, W.; Nie, J.; Li, F.; Wang, Z. L.; Sun, C. Nano Energy 2018, 45, 413. doi: 10.1016/j.nanoen.2018.01.028  doi: 10.1016/j.nanoen.2018.01.028

    23. [23]

      Fei, H. F.; Liu, Y. P.; Wei, C. L.; Zhang, Y. C.; Feng, J. K.; Chen, C. Z.; Yu, H. J. Acta Phys. -Chim. Sin. 2020, 36 (5), 1905015.  doi: 10.3866/PKU.WHXB201905015

    24. [24]

      Quartarone, E.; Mustarelli, P. Chem. Soc. Rev. 2011, 40, 2525. doi: 10.1039/c0cs00081g  doi: 10.1039/c0cs00081g

    25. [25]

      Zhou, Q.; Ma, J.; Dong, S.; Li, X.; Cui, G. Adv. Mater. 2019, 31(50), 1902029. doi: 10.1002/adma.201902029  doi: 10.1002/adma.201902029

    26. [26]

      Hu, T. S.; Hong, P. K.; Saikia, D.; Kao, H. M.; Chen, M. C. Ionics 2014, 20, 1561. doi: 10.1007/s11581-014-1107-2  doi: 10.1007/s11581-014-1107-2

    27. [27]

      Masoud, E. M.; El-Bellihi, A. A.; Bayoumy, W. A.; Mousa, M. A. J. Alloy. Compd. 2013, 575, 223. doi: 10.1016/j.jallcom.2013.04.054  doi: 10.1016/j.jallcom.2013.04.054

    28. [28]

      Zhang, X.; Liu, T.; Zhang, S.; Huang, X.; Xu, B.; Lin, Y.; Xu, B.; Li, L.; Nan, C. W.; Shen, Y. J. Am. Chem. Soc. 2017, 139, 13779. doi: 10.1021/jacs.7b06364  doi: 10.1021/jacs.7b06364

    29. [29]

      Zheng, J.; Tang, M.; Hu, Y. Y. Angew. Chem. Int. Ed. 2016, 55, 12538. doi: 10.1002/anie.201607539  doi: 10.1002/anie.201607539

    30. [30]

      Zhao, Y.; Wu, C.; Peng, G.; Chen, X.; Yao, X.; Bai, Y.; Wu, F.; Chen, S.; Xu, X. J. Power Sources 2016, 301, 47. doi: 10.1016/j.jpowsour.2015.09.111  doi: 10.1016/j.jpowsour.2015.09.111

    31. [31]

      Dieterich, W.; Dürr, O.; Pendzig, P.; Bunde, A.; Nitzan, A. Phys. A 1999, 266, 229. doi: 10.1016/S0378-4371(98)00597-4  doi: 10.1016/S0378-4371(98)00597-4

    32. [32]

      Li, Z.; Huang, H.; Zhu, J.; Wu, J.; Yang, H.; Wei, L.; Guo, X. ACS Appl. Mater. Interfaces 2018, 11 (1), 784. doi: 10.1021/acsami.8b17279  doi: 10.1021/acsami.8b17279

    33. [33]

      Kitajima, S.; Kitaura, H.; Im, D.; Hwang, Y.; Ishida, M.; Zhou, H. Solid State Ionics 2018, 316, 29. doi: 10.1016/j.ssi.2017.12.018  doi: 10.1016/j.ssi.2017.12.018

    34. [34]

      Chen, L.; Li, Y.; Li, S. P.; Fan, L. Z.; Nan, C. W.; Goodenough, J. B. Nano Energy 2018, 46, 176. doi: 10.1016/j.nanoen.2017.12.037  doi: 10.1016/j.nanoen.2017.12.037

    35. [35]

      Liu, X.; Peng, S.; Gao, S.; Cao, Y.; You, Q.; Zhou, L.; Jin, Y.; Liu, Z.; Liu, J. ACS Appl. Mater. Interfaces 2018, 10, 15691. doi: 10.1021/acsami.8b01631  doi: 10.1021/acsami.8b01631

    36. [36]

      Zhai, H.; Xu, P.; Ning, M.; Cheng, Q.; Mandal, J.; Yang, Y. Nano Lett. 2017, 17, 3182. doi: 10.1021/acs.nanolett.7b00715  doi: 10.1021/acs.nanolett.7b00715

    37. [37]

      Liu, W.; Liu, N.; Sun, J.; Hsu, P. C.; Li, Y.; Lee, H. W.; Cui, Y. Nano Lett. 2015, 15, 2740. doi: 10.1021/acs.nanolett.5b00600  doi: 10.1021/acs.nanolett.5b00600

    38. [38]

      Zhu, P.; Yan, C.; Dirican, M.; Zhu, J.; Zang, J.; Selvan, R. K.; Chung, C. C.; Jia, H.; Li, Y.; Kiyak, Y.; et al. J. Mater. Chem. A 2018, 6, 4279. doi: 10.1039/c7ta10517g  doi: 10.1039/c7ta10517g

    39. [39]

      Liu, W.; Lee, S. W.; Lin, D.; Shi, F.; Wang, S.; Sendek, A. D.; Cui, Y. Nat. Energy 2017, 2, 17035. doi: 10.1038/nenergy.2017.35  doi: 10.1038/nenergy.2017.35

    40. [40]

      Tang, W.; Tang, S.; Zhang, C.; Ma, Q.; Xiang, Q.; Yang, Y. W.; Luo, J. Adv. Energy Mater. 2018, 8, 1800866. doi: 10.1002/aenm.201800866  doi: 10.1002/aenm.201800866

    41. [41]

      Tang, W.; Tang, S.; Guan, X.; Zhang, X.; Xiang, Q.; Luo, J. Adv. Funct. Mater. 2019, 29, 1900648. doi: 10.1002/adfm.201900648  doi: 10.1002/adfm.201900648

    42. [42]

      Jia, W.; Li, Z.; Wu, Z.; Wang, L.; Wu, B.; Wang, Y.; Cao, Y.; Li, J. Solid State Ionics 2018, 315, 7. doi: 10.1016/j.ssi.2017.11.026  doi: 10.1016/j.ssi.2017.11.026

    43. [43]

      Kammoun, M.; Berg, S.; Ardebili, H. Nanoscale 2015, 7, 17516. doi: 10.1039/c5nr04339e  doi: 10.1039/c5nr04339e

    44. [44]

      Cheng, S.; Smith, D. M.; Li, C. Y. Macromolecule 2015, 48, 4503. doi: 10.1021/acs.macromol.5b00972  doi: 10.1021/acs.macromol.5b00972

    45. [45]

      Yuan, M.; Erdman, J.; Tang, C.; Ardebili, H. RSC Adv. 2014, 4, 59637. doi: 10.1039/c4ra07919a  doi: 10.1039/c4ra07919a

    46. [46]

      Li, A.; Liao, X.; Zhang, H.; Shi, L.; Wang, P.; Cheng, Q.; Borovilas, J.; Li, Z.; Huang, W.; Fu, Z.; et al. Adv. Mater. 2019, 32, 1905517. doi: 10.1002/adma.201905517  doi: 10.1002/adma.201905517

    47. [47]

      Zekoll, S.; Marriner-Edwards, C.; Hekselman, A. K. O.; Kasemchainan, J.; Kuss, C.; Armstrong, D. E. J.; Cai, D.; Wallace, R. J.; Richter, F. H.; Thijssen, J. H. J.; et al. Energy Environ. Sci. 2018, 11, 185. doi: 10.1039/c7ee02723k  doi: 10.1039/c7ee02723k

    48. [48]

      Xie, H.; Yang, C.; Fu, K.; Yao, Y.; Jiang, F.; Hitz, E.; Liu, B.; Wang, S.; Hu, L. Adv. Energy Mater. 2018, 8, 1703474. doi: 10.1002/aenm.201703474  doi: 10.1002/aenm.201703474

    49. [49]

      Bae, J.; Li, Y.; Zhang, J.; Zhou, X.; Zhao, F.; Shi, Y.; Goodenough, J. B.; Yu, G. Angew. Chem. Int. Ed. 2018, 57, 2096. doi: 10.1002/anie.201710841  doi: 10.1002/anie.201710841

    50. [50]

      Zhou, Q.; Zhang, J.; Cui, G. Macromol. Mater. Eng. 2018, 303, 1800337. doi: 10.1002/mame.201800337  doi: 10.1002/mame.201800337

    51. [51]

      Duan, H.; Fan, M.; Chen, W. P.; Li, J. Y.; Wang, P. F.; Wang, W. P.; Shi, J. L.; Yin, Y. X.; Wan, L. J.; Guo, Y. G. Adv. Mater. 2019, 31, e1807789. doi: 10.1002/adma.201807789  doi: 10.1002/adma.201807789

    52. [52]

      Zhou, W.; Wang, Z.; Pu, Y.; Li, Y.; Xin, S.; Li, X.; Chen, J.; Goodenough, J. B. Adv. Mater. 2018, 31, 1805574. doi: 10.1002/adma.201805574  doi: 10.1002/adma.201805574

  • 加载中
    1. [1]

      Tao Jiang Yuting Wang Lüjin Gao Yi Zou Bowen Zhu Li Chen Xianzeng Li . Experimental Design for the Preparation of Composite Solid Electrolytes for Application in All-Solid-State Batteries: Exploration of Comprehensive Chemistry Laboratory Teaching. University Chemistry, 2024, 39(2): 371-378. doi: 10.3866/PKU.DXHX202308057

    2. [2]

      Qiangqiang SUNPengcheng ZHAORuoyu WUBaoyue CAO . Multistage microporous bifunctional catalyst constructed by P-doped nickel-based sulfide ultra-thin nanosheets for energy-efficient hydrogen production from water electrolysis. Chinese Journal of Inorganic Chemistry, 2024, 40(6): 1151-1161. doi: 10.11862/CJIC.20230454

    3. [3]

      Qi Li Pingan Li Zetong Liu Jiahui Zhang Hao Zhang Weilai Yu Xianluo Hu . Fabricating Micro/Nanostructured Separators and Electrode Materials by Coaxial Electrospinning for Lithium-Ion Batteries: From Fundamentals to Applications. Acta Physico-Chimica Sinica, 2024, 40(10): 2311030-. doi: 10.3866/PKU.WHXB202311030

    4. [4]

      Qingqing SHENXiangbowen DUKaicheng QIANZhikang JINZheng FANGTong WEIRenhong LI . Self-supporting Cu/α-FeOOH/foam nickel composite catalyst for efficient hydrogen production by coupling methanol oxidation and water electrolysis. Chinese Journal of Inorganic Chemistry, 2024, 40(10): 1953-1964. doi: 10.11862/CJIC.20240028

    5. [5]

      Feiya Cao Qixin Wang Pu Li Zhirong Xing Ziyu Song Heng Zhang Zhibin Zhou Wenfang Feng . Magnesium-Ion Conducting Electrolyte Based on Grignard Reaction: Synthesis and Properties. University Chemistry, 2024, 39(3): 359-368. doi: 10.3866/PKU.DXHX202308094

    6. [6]

      Bao Jia Yunzhe Ke Shiyue Sun Dongxue Yu Ying Liu Shuaishuai Ding . Innovative Experimental Teaching for the Preparation and Modification of Conductive Organic Polymer Thin Films in Undergraduate Courses. University Chemistry, 2024, 39(10): 271-282. doi: 10.12461/PKU.DXHX202404121

    7. [7]

      Yuanpei ZHANGJiahong WANGJinming HUANGZhi HU . Preparation of magnetic mesoporous carbon loaded nano zero-valent iron for removal of Cr(Ⅲ) organic complexes from high-salt wastewater. Chinese Journal of Inorganic Chemistry, 2024, 40(9): 1731-1742. doi: 10.11862/CJIC.20240077

    8. [8]

      Zian Lin Yingxue Jin . Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry (MALDI-MS) for Disease Marker Screening and Identification: A Comprehensive Experiment Teaching Reform in Instrumental Analysis. University Chemistry, 2024, 39(11): 327-334. doi: 10.12461/PKU.DXHX202403066

    9. [9]

      Junjie Zhang Yue Wang Qiuhan Wu Ruquan Shen Han Liu Xinhua Duan . Preparation and Selective Separation of Lightweight Magnetic Molecularly Imprinted Polymers for Trace Tetracycline Detection in Milk. University Chemistry, 2024, 39(5): 251-257. doi: 10.3866/PKU.DXHX202311084

    10. [10]

      Wenjun Zheng . Application in Inorganic Synthesis of Ionic Liquids. University Chemistry, 2024, 39(8): 163-168. doi: 10.3866/PKU.DXHX202401020

    11. [11]

      You Wu Chang Cheng Kezhen Qi Bei Cheng Jianjun Zhang Jiaguo Yu Liuyang Zhang . ZnO/D-A共轭聚合物S型异质结高效光催化产H2O2及其电荷转移动力学研究. Acta Physico-Chimica Sinica, 2024, 40(11): 2406027-. doi: 10.3866/PKU.WHXB202406027

    12. [12]

      Yifeng Xu Jiquan Liu Bin Cui Yan Li Gang Xie Ying Yang . “Xiao Li’s School Adventures: The Working Principles and Safety Risks of Lithium-ion Batteries”. University Chemistry, 2024, 39(9): 259-265. doi: 10.12461/PKU.DXHX202404009

    13. [13]

      Kai CHENFengshun WUShun XIAOJinbao ZHANGLihua ZHU . PtRu/nitrogen-doped carbon for electrocatalytic methanol oxidation and hydrogen evolution by water electrolysis. Chinese Journal of Inorganic Chemistry, 2024, 40(7): 1357-1367. doi: 10.11862/CJIC.20230350

    14. [14]

      Yongmei Liu Lisen Sun Zhen Huang Tao Tu . Curriculum-Based Ideological and Political Design for the Experiment of Methanol Oxidation to Formaldehyde Catalyzed by Electrolytic Silver. University Chemistry, 2024, 39(2): 67-71. doi: 10.3866/PKU.DXHX202308020

    15. [15]

      Zunxiang Zeng Yuling Hu Yufei Hu Hua Xiao . Analysis of Plant Essential Oils by Supercritical CO2Extraction with Gas Chromatography-Mass Spectrometry: An Instrumental Analysis Comprehensive Experiment Teaching Reform. University Chemistry, 2024, 39(3): 274-282. doi: 10.3866/PKU.DXHX202309069

    16. [16]

      Siyu Zhang Kunhong Gu Bing'an Lu Junwei Han Jiang Zhou . Hydrometallurgical Processes on Recycling of Spent Lithium-lon Battery Cathode: Advances and Applications in Sustainable Technologies. Acta Physico-Chimica Sinica, 2024, 40(10): 2309028-. doi: 10.3866/PKU.WHXB202309028

    17. [17]

      Shuang Yang Qun Wang Caiqin Miao Ziqi Geng Xinran Li Yang Li Xiaohong Wu . Ideological and Political Education Design for Research-Oriented Experimental Course of Highly Efficient Hydrogen Production from Water Electrolysis in Aerospace Perspective. University Chemistry, 2024, 39(11): 269-277. doi: 10.12461/PKU.DXHX202403044

    18. [18]

      Hong LIXiaoying DINGCihang LIUJinghan ZHANGYanying RAO . Detection of iron and copper ions based on gold nanorod etching colorimetry. Chinese Journal of Inorganic Chemistry, 2024, 40(5): 953-962. doi: 10.11862/CJIC.20230370

    19. [19]

      Zunyuan Xie Lijin Yang Zixiao Wan Xiaoyu Liu Yushan He . Exploration of the Preparation and Characterization of Nano Barium Titanate and Its Application in Inorganic Chemistry Laboratory Teaching. University Chemistry, 2024, 39(4): 62-69. doi: 10.3866/PKU.DXHX202310137

    20. [20]

      Zhenming Xu Mingbo Zheng Zhenhui Liu Duo Chen Qingsheng Liu . Experimental Design of Project-Driven Teaching in Computational Materials Science: First-Principles Calculations of the LiFePO4 Cathode Material for Lithium-Ion Batteries. University Chemistry, 2024, 39(4): 140-148. doi: 10.3866/PKU.DXHX202307022

Metrics
  • PDF Downloads(34)
  • Abstract views(698)
  • HTML views(147)

通讯作者: 陈斌, bchen63@163.com
  • 1. 

    沈阳化工大学材料科学与工程学院 沈阳 110142

  1. 本站搜索
  2. 百度学术搜索
  3. 万方数据库搜索
  4. CNKI搜索
Address:Zhongguancun North First Street 2,100190 Beijing, PR China Tel: +86-010-82449177-888
Powered By info@rhhz.net

/

DownLoad:  Full-Size Img  PowerPoint
Return