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Na+-storage properties derived from a high pseudocapacitive behavior for nitrogen-doped porous carbon anode
Journal Pre-proofs Na+-storage properties derived from a high pseudocapacitive behavior for nitrogen-doped porous carbon anode Kaiqi Xu, Youpeng Li, Yanzhen Liu, Guobin Zhong, Chao Wang, Wei Su, Xin Li, Chenghao Yang PII: DOI: Reference:
S0167-577X(19)31696-9 https://doi.org/10.1016/j.matlet.2019.127064 MLBLUE 127064
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
15 September 2019 31 October 2019 20 November 2019
Please cite this article as: K. Xu, Y. Li, Y. Liu, G. Zhong, C. Wang, W. Su, X. Li, C. Yang, Na+-storage properties derived from a high pseudocapacitive behavior for nitrogen-doped porous carbon anode, Materials Letters (2019), doi: https://doi.org/10.1016/j.matlet.2019.127064
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 B.V.
Na+-storage properties derived from a high pseudocapacitive behavior for nitrogen-doped porous carbon anode Kaiqi Xua, Youpeng Lib, Yanzhen Liub, Guobin Zhonga, Chao Wanga, Wei Sua, Xin Lia, Chenghao Yangb, a Electric Power Research Institute of Guangdong Power Grid Co., Ltd., Guangzhou, Guangdong 510080, China b School of Environment and Energy, South China University of Technology, Guangzhou, Guangdong 510006, China Abstract High content N-doped porous carbon (NPC) has been fabricated and used as SIBs anode material. The NPC delivers a high capacity (230.1 mAh g-1 at 0.1 A g-1), excellent rate capability (195.8 mAh g-1 at 5 A g-1) and cycling stability (201.1 mAh g-1 at 1 A g-1 after 500 cycles). The excellent performances are ascribed to the unique porous structure and high content of N doped in NPC, they can also provide more active sites for Na+ ions accommodation and generate plenty of channels for the Na+ ions/electron transmission, which can greatly improve its pseudocapacitive effect and buffer the volume expansion during the cycling. The excellent Na+ ions storage capability makes the NPC a promising anode material for SIBs. Keywords: Carbon materials; Anode; Energy storage and conversion; Pseudocapacitive effect; Sodium ion battery 1. Introduction Sodium ion batteries (SIBs) have been one of the promising technologies for large-scale energy storage, duo to its similar electrochemical chemistry to lithium ion batteries (LIBs)
Corresponding author. Phone: +86-020-39381203; Email: [email protected] (C. Yang). 1
and the abundance nature of Na resource in the earth's crust [1, 2]. However, exploring g appropriate host materials to accommodate Na+ ions is still a challenge, as the diameter of Na+ (1.06 Å) is much bigger than Li+ (0.76 Å) [3, 4]. Carbonaceous materials have been regarded as one of the promising SIBs anode materials. Nevertheless, commercial graphite anode only display a limited specific capacity of ~35 mAh g-1 for Na+ storage [5]. Moreover, the (de)intercalation of Na+ ions in the carbonaceous materials suffer from sluggish Na+ diffusion kinetics and serious volume effect, which lead to a poor rate and cycling performance. Thus, developing suitable strategy to optimize the carbonaceous materials Na+ ions storage capability is highly desirable. Compared to traditional intercalation chemistry, Na+ ions storage by pseudocapacitive behavior has great advantages. First, the Na+ ions storage behavior only happens on the surface of host electrode, which can greatly enhance Na+ ions diffusion efficient [6]. Next, the large number of Na+ ions do not need to be inserted into crystal structure of electrode materials, volume swelling upon the Na+ ions insertion can be avoided [7]. Thus, boosting the pseudocapacitive contribution ratio is an effective solution to improve rate and cycling performance of SIBs carbonaceous anode. Generally, heteroatom-doping has been reported to be a great choice to enhance the pseudocapacitive behavior for Na+ storage of carbonaceous materials [8]. However, the carbonaceous materials only reported to display limited amount of N (lower than 5% in atom ratio) [9, 10], which greatly restricts its pseudocapacitive behavior and electrochemical performance. Nowadays, plenty of carbonaceous materials derived from metal-organic framework (MOF) has been widely applied in lithium, sodium and potassium storage for their biggish 2
surface area, ordered void structure and controllable structure [11-12]. These advantages could enlarge the contact area of electrode/electrolyte and accommodate the volume change during the charge-discharge process, which can effectively improve the electrochemical performance of these carbonaceous materials [13-15]. Herein, high content N (over 12.5% in atom ratio) doped porous carbon (NPC) has been fabricated and applied as SIB anode material. The fabricated process is described in Fig. 1A. Firstly, porous carbon (PC) was obtained by low temperature carbonization and etching process. Then, NPC was prepared by mixing PC and melamine (with a mass ratio of 1:2) and calcined at 700 °C. The unique porous structure and high content N-doping can effectively buffer the volume change, enhance the pseudocapacitive behavior and reaction kinetics, and eventually improve the rate and cycle performance of NPC. 2. Results and Discussion The MIL-88-Fe (Fig. S1) shows the smooth-faced clubbed structure with the diameter of 300 nm and length of 700 nm. After carbonization, morphology of precursor is well maintained (Fig. 1B, C). However, it is observed that surface of the nanorods becomes rough and many nanoparticles are distributed on the PC surface (Fig. 1B-D and Fig. S2). Meanwhile, these nanoparticles displayed the interplanar spacing of 0.251 nm, which is related to the (311) lattice plane of Fe3O4 (Fig. 1D), confirming the formation of Fe3O4 after the carbonization process. After the etching process, Fe3O4 nanoparticles are removed and graphitized PC is obtained (Fig. 1E, F), which is further confirmed by the results of HRTEM of PC (Fig. 1G). Finally, after the nitriding process, the clubbed structure is well maintained (Fig. 1H, I). However, it is found that the graphitized PC transformed into disordered NPC (Fig. 1J), 3
confirming the arising of defects and dangling bond from the N-doping feature [9, 16]. Raman spectra for PC and NPC are shown in Fig. S5B. The ID/IG value for PC is 0.94, which is lower than that of NPC (1.08), indicating N has been successfully doped into the PC. Meanwhile, the specific surface area and pore size distribution of PC and NPC displayed neglectable change before and after high nitrogen doping (detailed discuss has been provided in Fig S6), indicating the sufficient contact area between the electrode/electrolyte. Surface chemistry of N-doped NPC were analyzed by XPS. The XPS spectrum for NPC (Fig. S7) indicates the existence of N and C, and N occupies 12.5% atomic ratio in the total NPC. Specifically, the XPS curve of N 1s for NPC in Fig. S7B contains three peaks located at 402.1, 400.9 and 398.3 eV, corresponding to the different species of quaternary (N-Q), pyrrolic (N-5) and pyridinic (N-6), respectively. Among them, the pyridinic N is different from the quaternary N and pyrrolic N encircled by the C atoms, it is quietly active to capture electrons as locating at the edge side. Thus, the NPC contains more defects and active sites for Na+ ions storage. Moreover, the pyridinic N belongs to sp2 hybridized, which could be benefit to enhance the electronic conductivity of the NPC [17, 18]. The initial 4 cyclic cyclic voltammetry (CV) of NPC at the voltage range of 0.1-3.0 V is shown in Fig. 2A. In the first discharge process, two broad peaks at 1.12 V and 0.75 V and a strong peak at 0.5 V are observed, which are mainly related to the formation of solid electrolyte interface (SEI) films and the insertion process of Na+ ions into NPC, respectively. While, a peak at 0.2 V is noticed in the first charge step, which is mainly attributed to the deintercalation of Na+ ions. In following cycles, the CV curves are almost overlapped, demonstrating an excellent structure stability of NPC. Galvanostatic discharge/charge curves 4
of NPC and PC have also been investigated within 0.01-3.0 V at 100 mA g-1 (Fig. 2B and Fig. S8). The initial discharge and charge capacity of NPC are 423.1 and 230.1 mAh g-1, respectively. While, PC displays initial discharge and charge capacity of only 355.8 and 153.2 mAh g-1, respectively. Cycling performance for NPC and PC at 100 mA g-1 has also been investigated. As displayed in Fig. 2C, NPC exhibits a reversible specific capacity of 226.1 mAh g-1, after 100 cycles, with a capacity retention of 98.5%. While, PC displays a specific capacity of only 139.7 mAh g-1, with a capacity retention ratio of 76.2%. Rate property of NPC and PC have also been studied and the results are shown in Fig. 2D. NPC exhibits specific capacities of 245.1, 233.5, 225.9, 221.8, 217.6, 208.1 and 198.2 mAh g-1 at 200, 400, 600, 800, 1000, 2000 and 5000 mA g-1, respectively. When the current density is set back to 200 mA g-1, the specific capacity is 243.2 mAh g-1. However, PC only delivers specific capacities of 153.2, 135.4, 129.9, 127.4, 124.3, 120.6 and 116.8 mAh g-1 at 200, 400, 600, 800, 1000, 2000 and 5000 mA g-1, respectively. Moreover, the NPC can deliver stable specific capacity of 208.1 mAh g-1 at 1 A g-1 after 2000 loops, while PC only exhibits a specific capacity of 96.9 mAh g-1 at the same conditions (Fig. 2E). It indicates that NPC displays a much better rate and cycling performance than that of PC. CV of NPC and PC at different scan rate (0.2, 0.4, 0.6 and 0.8 mV s-1) within 0.1-3.0 V have been studied, as shown in Fig. 3A, B. Firstly, the relationship between peak current (i) and scan rate (v) can be related to the following equation (1) [19]: i = avb, b value can be calculated by the slope of Log(i)-Log(v) straight line. When the b value is close to 0.5, the Na+ ions storage behavior is determined by the diffusion process. When the b value is more 5
closed to 1, indicating Na+ ions storage process is mainly related to the surface-driven pseudocapacitive behavior. For NPC and PC, the b values were 0.95 and 0.73 (Fig. 3C), respectively. The pseudocapacitive contribution ratio of the samples can be quantitatively estimated by following equation (2) [20], i = k1v + k2v1/2, where k2 and k1 are constant, k2v1/2 and k1v represent the capacity contribution of Na+ ions diffusion and capacitive process. NPC displays much higher pseudocapacitive contribution ratio than that of PC (Fig. 3D-F). The improved electrochemical performance for NPC is ascribed to the following aspects: first, the defects and dangling bonds in NPC originated from the high content N-doping can provide extra active sites to capture more Na+ ions, which are attributed to responsible for its enhanced pseudocapacitive effect and rate performance. Moreover, the porous structure could also buffer the contraction/expansion of NPC during the charge/discharge process, resulting an excellent cycling performance. 3. Conclusions In summary, high content N-doped porous carbon has been fabricate and used as SIB anode materials. NPC delivers a high rate ability (198.2 mAh g-1 at 5 A g-1) and excellent cycling property (208.1 mAh g-1 at 1 A g-1 for 1000 loops). The greatly improved electrochemical performance of NPC is related to the unique porous structure and high content of N-doping, which can effectively suppress of volume expansion and enhance the pseudocapacitance effect as well as the rate and cycling performance. The excellent Na+ ions storage capability makes the NPC a promising anode material for SIBs. Acknowledgements We gratefully acknowledge the financial support from the Guangdong Power Grid Co., 6
Ltd (Grant No. GDKJXM20161890) References 1. H. Hou, C. Banks, M. Jing, Y. Zhang, X. Ji, Adv. Mater. 27 (2015) 7861-7866. 2. G. Wang, X. Xiong, P. Zou, X. Fu, Z. Lin, Y. Li, Y. Liu, C.Yang, M. Liu, Chem. Eng. J. 378 (2019) 122243.. 3. Y. R. Liang, C‐Z. Zhao, H. Yuan, Y. Chen, W. C. Zhang, J. Q. Huang, D. S. Yu, Y. L. Liu, M.‐M. Titirici, Y‐L. Chueh, H. J. Yu, Q. Zhang, InfoMat, 1 (2019) 6-32. 4. Z. H. Lin, Q. B. Xia, W. L. Wang, W. S. Li, S. L. Chou, InfoMat, 1 (2019) 376-389. 5. Z. Jian, W. Luo, X. Ji, J. Am. Chem. Soc. 137 (2015) 11566-11569. 6. Y. Shao, J. Xiao, W. Wang, M. Engelhard, X. Chen, Z. Nie, M. Gu, L. Saraf, G. Exarhos, J. Zhang, J. Liu, Nano Lett. 13 (2013) 3909-3914. 7. Z. Hong, Y. Zhen, Y. Ruan, M. Kang, K. Zhou, J. Zhang, Z. Huang, M. Wei, Adv. Mater. 30 (2018) 1802035. 8.
L. Kong, J. Zhu, W. Shuang, X. Bu, Adv. Energy Mater. 8 (2018) 1801515.
9.
K. Share, A. Cohn, R. Carter, B. Rogers, C. L. Pint, ACS Nano, 10 (2016) 9738-9744.
10. H. Zhang, J. Luan, X. Huang, Y. Tang, H. Wang, J. Mater. Chem. A 6 (2018) 23318. 11. W. Xia, A. Mahmood, R. Zou, Q. Xu, Energy Environ. Sci. 8 (2015) 1837. 12. Y. Li, W. Zhong, C. Yang, F. Zheng, Q. Pan, Y. Liu, G. Wang, X. Xiong, M. Liu, Chem. Eng. J. 358 (2019) 1147-1154. 13. H. Xu, C. Wu, X. Wei, S. Gao, J. Mater. Chem. A, 6 (2018) 15340. 14. S. Gao, M. Wang, Y. Chen, M. Tian, Y. Zhu, X. Wei, T. Jiang, Nano Energy 45 (2018) 21–27. 7
15 S. Gao, B. Fan, R. Feng, C. Ye, X. Wei, J. Liu, X. Bu, Nano Energy, 40 (2017) 462–470. 16. Y. Cho, H. Kim, H. Im, Y. Myung, G. Jung, C. Lee, J. Park, M. Park, J. Cho, H. Kang, J. Phys. Chem. C 115 (2011) 9451-9457. 17. D. Nan, Z. Huang, R. Lv, L. Yang, J. Wang, W. Shen, Y. Lin, X. Yu, L. Ye, H. Sun, F. Kang, J. Mater. Chem. A 2 (2014) 19678-19684. 18. H. Xiang, J. Chen, Z. Li, H. Wang, J. Power Sources, 196 (2011) 8651-8655. 19. Y. Li, C. Yang, F. Zheng, Q. Pan, Y. Liu, G. Wang, T. Liu, J. Hu, M. Liu, Nano Energy, 59 (2019) 582-590. 20. C. Yang, X. Liang, X. Ou, Q. Zhang, H-S. Zheng, F. Zheng, J-Han Wang, K. Huang, Meilin Liu, Adv. Funct. Mater. (2019) 1807971.
1. High N-doped porous carbon has been fabricated and used as SIBs anode material 2. NPC exhibits an excellent rate capability and cycling stability 3. The excellent performances is due to the improved the pseudocapacitance effect.
8
S0167-577X(19)31696-9 https://doi.org/10.1016/j.matlet.2019.127064 MLBLUE 127064
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
15 September 2019 31 October 2019 20 November 2019
Please cite this article as: K. Xu, Y. Li, Y. Liu, G. Zhong, C. Wang, W. Su, X. Li, C. Yang, Na+-storage properties derived from a high pseudocapacitive behavior for nitrogen-doped porous carbon anode, Materials Letters (2019), doi: https://doi.org/10.1016/j.matlet.2019.127064
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 B.V.
Na+-storage properties derived from a high pseudocapacitive behavior for nitrogen-doped porous carbon anode Kaiqi Xua, Youpeng Lib, Yanzhen Liub, Guobin Zhonga, Chao Wanga, Wei Sua, Xin Lia, Chenghao Yangb, a Electric Power Research Institute of Guangdong Power Grid Co., Ltd., Guangzhou, Guangdong 510080, China b School of Environment and Energy, South China University of Technology, Guangzhou, Guangdong 510006, China Abstract High content N-doped porous carbon (NPC) has been fabricated and used as SIBs anode material. The NPC delivers a high capacity (230.1 mAh g-1 at 0.1 A g-1), excellent rate capability (195.8 mAh g-1 at 5 A g-1) and cycling stability (201.1 mAh g-1 at 1 A g-1 after 500 cycles). The excellent performances are ascribed to the unique porous structure and high content of N doped in NPC, they can also provide more active sites for Na+ ions accommodation and generate plenty of channels for the Na+ ions/electron transmission, which can greatly improve its pseudocapacitive effect and buffer the volume expansion during the cycling. The excellent Na+ ions storage capability makes the NPC a promising anode material for SIBs. Keywords: Carbon materials; Anode; Energy storage and conversion; Pseudocapacitive effect; Sodium ion battery 1. Introduction Sodium ion batteries (SIBs) have been one of the promising technologies for large-scale energy storage, duo to its similar electrochemical chemistry to lithium ion batteries (LIBs)
Corresponding author. Phone: +86-020-39381203; Email: [email protected] (C. Yang). 1
and the abundance nature of Na resource in the earth's crust [1, 2]. However, exploring g appropriate host materials to accommodate Na+ ions is still a challenge, as the diameter of Na+ (1.06 Å) is much bigger than Li+ (0.76 Å) [3, 4]. Carbonaceous materials have been regarded as one of the promising SIBs anode materials. Nevertheless, commercial graphite anode only display a limited specific capacity of ~35 mAh g-1 for Na+ storage [5]. Moreover, the (de)intercalation of Na+ ions in the carbonaceous materials suffer from sluggish Na+ diffusion kinetics and serious volume effect, which lead to a poor rate and cycling performance. Thus, developing suitable strategy to optimize the carbonaceous materials Na+ ions storage capability is highly desirable. Compared to traditional intercalation chemistry, Na+ ions storage by pseudocapacitive behavior has great advantages. First, the Na+ ions storage behavior only happens on the surface of host electrode, which can greatly enhance Na+ ions diffusion efficient [6]. Next, the large number of Na+ ions do not need to be inserted into crystal structure of electrode materials, volume swelling upon the Na+ ions insertion can be avoided [7]. Thus, boosting the pseudocapacitive contribution ratio is an effective solution to improve rate and cycling performance of SIBs carbonaceous anode. Generally, heteroatom-doping has been reported to be a great choice to enhance the pseudocapacitive behavior for Na+ storage of carbonaceous materials [8]. However, the carbonaceous materials only reported to display limited amount of N (lower than 5% in atom ratio) [9, 10], which greatly restricts its pseudocapacitive behavior and electrochemical performance. Nowadays, plenty of carbonaceous materials derived from metal-organic framework (MOF) has been widely applied in lithium, sodium and potassium storage for their biggish 2
surface area, ordered void structure and controllable structure [11-12]. These advantages could enlarge the contact area of electrode/electrolyte and accommodate the volume change during the charge-discharge process, which can effectively improve the electrochemical performance of these carbonaceous materials [13-15]. Herein, high content N (over 12.5% in atom ratio) doped porous carbon (NPC) has been fabricated and applied as SIB anode material. The fabricated process is described in Fig. 1A. Firstly, porous carbon (PC) was obtained by low temperature carbonization and etching process. Then, NPC was prepared by mixing PC and melamine (with a mass ratio of 1:2) and calcined at 700 °C. The unique porous structure and high content N-doping can effectively buffer the volume change, enhance the pseudocapacitive behavior and reaction kinetics, and eventually improve the rate and cycle performance of NPC. 2. Results and Discussion The MIL-88-Fe (Fig. S1) shows the smooth-faced clubbed structure with the diameter of 300 nm and length of 700 nm. After carbonization, morphology of precursor is well maintained (Fig. 1B, C). However, it is observed that surface of the nanorods becomes rough and many nanoparticles are distributed on the PC surface (Fig. 1B-D and Fig. S2). Meanwhile, these nanoparticles displayed the interplanar spacing of 0.251 nm, which is related to the (311) lattice plane of Fe3O4 (Fig. 1D), confirming the formation of Fe3O4 after the carbonization process. After the etching process, Fe3O4 nanoparticles are removed and graphitized PC is obtained (Fig. 1E, F), which is further confirmed by the results of HRTEM of PC (Fig. 1G). Finally, after the nitriding process, the clubbed structure is well maintained (Fig. 1H, I). However, it is found that the graphitized PC transformed into disordered NPC (Fig. 1J), 3
confirming the arising of defects and dangling bond from the N-doping feature [9, 16]. Raman spectra for PC and NPC are shown in Fig. S5B. The ID/IG value for PC is 0.94, which is lower than that of NPC (1.08), indicating N has been successfully doped into the PC. Meanwhile, the specific surface area and pore size distribution of PC and NPC displayed neglectable change before and after high nitrogen doping (detailed discuss has been provided in Fig S6), indicating the sufficient contact area between the electrode/electrolyte. Surface chemistry of N-doped NPC were analyzed by XPS. The XPS spectrum for NPC (Fig. S7) indicates the existence of N and C, and N occupies 12.5% atomic ratio in the total NPC. Specifically, the XPS curve of N 1s for NPC in Fig. S7B contains three peaks located at 402.1, 400.9 and 398.3 eV, corresponding to the different species of quaternary (N-Q), pyrrolic (N-5) and pyridinic (N-6), respectively. Among them, the pyridinic N is different from the quaternary N and pyrrolic N encircled by the C atoms, it is quietly active to capture electrons as locating at the edge side. Thus, the NPC contains more defects and active sites for Na+ ions storage. Moreover, the pyridinic N belongs to sp2 hybridized, which could be benefit to enhance the electronic conductivity of the NPC [17, 18]. The initial 4 cyclic cyclic voltammetry (CV) of NPC at the voltage range of 0.1-3.0 V is shown in Fig. 2A. In the first discharge process, two broad peaks at 1.12 V and 0.75 V and a strong peak at 0.5 V are observed, which are mainly related to the formation of solid electrolyte interface (SEI) films and the insertion process of Na+ ions into NPC, respectively. While, a peak at 0.2 V is noticed in the first charge step, which is mainly attributed to the deintercalation of Na+ ions. In following cycles, the CV curves are almost overlapped, demonstrating an excellent structure stability of NPC. Galvanostatic discharge/charge curves 4
of NPC and PC have also been investigated within 0.01-3.0 V at 100 mA g-1 (Fig. 2B and Fig. S8). The initial discharge and charge capacity of NPC are 423.1 and 230.1 mAh g-1, respectively. While, PC displays initial discharge and charge capacity of only 355.8 and 153.2 mAh g-1, respectively. Cycling performance for NPC and PC at 100 mA g-1 has also been investigated. As displayed in Fig. 2C, NPC exhibits a reversible specific capacity of 226.1 mAh g-1, after 100 cycles, with a capacity retention of 98.5%. While, PC displays a specific capacity of only 139.7 mAh g-1, with a capacity retention ratio of 76.2%. Rate property of NPC and PC have also been studied and the results are shown in Fig. 2D. NPC exhibits specific capacities of 245.1, 233.5, 225.9, 221.8, 217.6, 208.1 and 198.2 mAh g-1 at 200, 400, 600, 800, 1000, 2000 and 5000 mA g-1, respectively. When the current density is set back to 200 mA g-1, the specific capacity is 243.2 mAh g-1. However, PC only delivers specific capacities of 153.2, 135.4, 129.9, 127.4, 124.3, 120.6 and 116.8 mAh g-1 at 200, 400, 600, 800, 1000, 2000 and 5000 mA g-1, respectively. Moreover, the NPC can deliver stable specific capacity of 208.1 mAh g-1 at 1 A g-1 after 2000 loops, while PC only exhibits a specific capacity of 96.9 mAh g-1 at the same conditions (Fig. 2E). It indicates that NPC displays a much better rate and cycling performance than that of PC. CV of NPC and PC at different scan rate (0.2, 0.4, 0.6 and 0.8 mV s-1) within 0.1-3.0 V have been studied, as shown in Fig. 3A, B. Firstly, the relationship between peak current (i) and scan rate (v) can be related to the following equation (1) [19]: i = avb, b value can be calculated by the slope of Log(i)-Log(v) straight line. When the b value is close to 0.5, the Na+ ions storage behavior is determined by the diffusion process. When the b value is more 5
closed to 1, indicating Na+ ions storage process is mainly related to the surface-driven pseudocapacitive behavior. For NPC and PC, the b values were 0.95 and 0.73 (Fig. 3C), respectively. The pseudocapacitive contribution ratio of the samples can be quantitatively estimated by following equation (2) [20], i = k1v + k2v1/2, where k2 and k1 are constant, k2v1/2 and k1v represent the capacity contribution of Na+ ions diffusion and capacitive process. NPC displays much higher pseudocapacitive contribution ratio than that of PC (Fig. 3D-F). The improved electrochemical performance for NPC is ascribed to the following aspects: first, the defects and dangling bonds in NPC originated from the high content N-doping can provide extra active sites to capture more Na+ ions, which are attributed to responsible for its enhanced pseudocapacitive effect and rate performance. Moreover, the porous structure could also buffer the contraction/expansion of NPC during the charge/discharge process, resulting an excellent cycling performance. 3. Conclusions In summary, high content N-doped porous carbon has been fabricate and used as SIB anode materials. NPC delivers a high rate ability (198.2 mAh g-1 at 5 A g-1) and excellent cycling property (208.1 mAh g-1 at 1 A g-1 for 1000 loops). The greatly improved electrochemical performance of NPC is related to the unique porous structure and high content of N-doping, which can effectively suppress of volume expansion and enhance the pseudocapacitance effect as well as the rate and cycling performance. The excellent Na+ ions storage capability makes the NPC a promising anode material for SIBs. Acknowledgements We gratefully acknowledge the financial support from the Guangdong Power Grid Co., 6
Ltd (Grant No. GDKJXM20161890) References 1. H. Hou, C. Banks, M. Jing, Y. Zhang, X. Ji, Adv. Mater. 27 (2015) 7861-7866. 2. G. Wang, X. Xiong, P. Zou, X. Fu, Z. Lin, Y. Li, Y. Liu, C.Yang, M. Liu, Chem. Eng. J. 378 (2019) 122243.. 3. Y. R. Liang, C‐Z. Zhao, H. Yuan, Y. Chen, W. C. Zhang, J. Q. Huang, D. S. Yu, Y. L. Liu, M.‐M. Titirici, Y‐L. Chueh, H. J. Yu, Q. Zhang, InfoMat, 1 (2019) 6-32. 4. Z. H. Lin, Q. B. Xia, W. L. Wang, W. S. Li, S. L. Chou, InfoMat, 1 (2019) 376-389. 5. Z. Jian, W. Luo, X. Ji, J. Am. Chem. Soc. 137 (2015) 11566-11569. 6. Y. Shao, J. Xiao, W. Wang, M. Engelhard, X. Chen, Z. Nie, M. Gu, L. Saraf, G. Exarhos, J. Zhang, J. Liu, Nano Lett. 13 (2013) 3909-3914. 7. Z. Hong, Y. Zhen, Y. Ruan, M. Kang, K. Zhou, J. Zhang, Z. Huang, M. Wei, Adv. Mater. 30 (2018) 1802035. 8.
L. Kong, J. Zhu, W. Shuang, X. Bu, Adv. Energy Mater. 8 (2018) 1801515.
9.
K. Share, A. Cohn, R. Carter, B. Rogers, C. L. Pint, ACS Nano, 10 (2016) 9738-9744.
10. H. Zhang, J. Luan, X. Huang, Y. Tang, H. Wang, J. Mater. Chem. A 6 (2018) 23318. 11. W. Xia, A. Mahmood, R. Zou, Q. Xu, Energy Environ. Sci. 8 (2015) 1837. 12. Y. Li, W. Zhong, C. Yang, F. Zheng, Q. Pan, Y. Liu, G. Wang, X. Xiong, M. Liu, Chem. Eng. J. 358 (2019) 1147-1154. 13. H. Xu, C. Wu, X. Wei, S. Gao, J. Mater. Chem. A, 6 (2018) 15340. 14. S. Gao, M. Wang, Y. Chen, M. Tian, Y. Zhu, X. Wei, T. Jiang, Nano Energy 45 (2018) 21–27. 7
15 S. Gao, B. Fan, R. Feng, C. Ye, X. Wei, J. Liu, X. Bu, Nano Energy, 40 (2017) 462–470. 16. Y. Cho, H. Kim, H. Im, Y. Myung, G. Jung, C. Lee, J. Park, M. Park, J. Cho, H. Kang, J. Phys. Chem. C 115 (2011) 9451-9457. 17. D. Nan, Z. Huang, R. Lv, L. Yang, J. Wang, W. Shen, Y. Lin, X. Yu, L. Ye, H. Sun, F. Kang, J. Mater. Chem. A 2 (2014) 19678-19684. 18. H. Xiang, J. Chen, Z. Li, H. Wang, J. Power Sources, 196 (2011) 8651-8655. 19. Y. Li, C. Yang, F. Zheng, Q. Pan, Y. Liu, G. Wang, T. Liu, J. Hu, M. Liu, Nano Energy, 59 (2019) 582-590. 20. C. Yang, X. Liang, X. Ou, Q. Zhang, H-S. Zheng, F. Zheng, J-Han Wang, K. Huang, Meilin Liu, Adv. Funct. Mater. (2019) 1807971.
1. High N-doped porous carbon has been fabricated and used as SIBs anode material 2. NPC exhibits an excellent rate capability and cycling stability 3. The excellent performances is due to the improved the pseudocapacitance effect.
8