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ORIGINAL ARTICLE

SnO2 quantum dots modified N-doped carbon as high-performance anode for lithium ion batteries by enhanced pseudocapacitance Cui-Ping Wu, Kai-Xuan Xie, Jia-Peng He, Qing-Peng Wang* Jian-Min Ma* , Shun Yang, Qing-Hong Wang*

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Received: 5 March 2020 / Revised: 20 April 2020 / Accepted: 10 October 2020 Ó GRINM Bohan (Beijing) Publishing Co., Ltd 2020

Abstract SnO2 is considered to be a promising candidate as anode material for lithium ion batteries, due to its high theoretical specific capacity (1494 mAhg-1). Nevertheless, SnO2-based anodes suffer from poor electronic conductivity and serious volume variation (300%) during lithiation/delithiation process, leading to fast capacity fading. To solve these problems, SnO2 quantum dots modified N-doped carbon spheres (SnO2 QDs@N–C) are fabricated by facile hydrolysis process of SnCl2, accompanied with the polymerization of polypyrrole (PPy), followed by a calcination method. When used as anodes for lithium ion batteries, SnO2 QDs@N–C exhibits high discharge capacity, superior rate properties as well as good cyclability. The carbon matrix completely encapsulates the SnO2 quantum dots, preventing the aggregation and Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12598-020-01623-x) contains supplementary material, which is available to authorized users. C.-P. Wu, K.-X. Xie, J.-P. He, S. Yang, Q.-H. Wang* School of Chemistry and Materials Science, Jiangsu Normal University, Xuzhou 221116, China e-mail: [email protected] Q.-P. Wang* Institute of Biopharmaceutical Research, Liaocheng University, Liaocheng 252059, China e-mail: [email protected] J.-M. Ma* School of Physics and Electronics, Hunan University, Changsha 410082, China e-mail: [email protected] J.-M. Ma Key Laboratory of Materials Processing and Mold (Zhengzhou University), Ministry of Education, Zhengzhou University, Zhengzhou 450002, China

volume change during cycling. Furthermore, the high N content produces abundant defects in carbon matrix. It is worth noting that SnO2 QDs@N–C shows excellent capacitive contribution properties, which may be due to the ultra-small size of SnO2 and high conductivity of the carbon matrix. Keywords Tin dioxide; Quantum dots; Nitrogen-doped carbon; Lithium ion batteries

1 Introduction Excessive exhaustion of fossil resource has caused serious energy crisis and environmental damage. Therefore, exploiting/refining high-performance energy storage/conversion systems is of great importance [1]. Lithium ion batteries (LIBs) have become dominant among energy storage devices due to the advantages of high energy density and long cycle life [2–4]. However, the electrochemical performance of commercial LIBs is largely limited by the low specific capacity of graphite anode (theoretical capacity is 372 mAhg-1) and poor rate performance [5]. SnO2 is presumed extraordinarily promising electrode material due to its high theoretical specific capacity (1494 mAhg-1) and environmental friendliness. Nevertheless, SnO2-ba