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An Asymmetric K/Li-ion Battery Based on Intercalation Selectivity Jiaxin Zheng, Wenjun Deng, Zongxiang Hu, Zengqing Zhuo, Fusheng Liu, Haibiao Chen, Yuan Lin, Wanli Yang, Khalil Amine, Rui Li, Jun Lu, and Feng Pan ACS Energy Lett., Just Accepted Manuscript • DOI: 10.1021/acsenergylett.7b01021 • Publication Date (Web): 27 Nov 2017 Downloaded from http://pubs.acs.org on November 27, 2017
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ACS Energy Letters
An Asymmetric K/Li-ion Battery Based on Intercalation Selectivity Jiaxin Zheng1, †, Wenjun Deng1, †, Zongxiang Hu1, †, Zengqing Zhuo1,2, Fusheng Liu2, Haibiao Chen1, Yuan Lin1, Wanli Yang3, Khalil Amine4, Rui Li1,*, Jun Lu4,* and Feng Pan1, * 1
School of Advanced Materials, Peking University, Shenzhen Graduate School, Shenzhen 518055, People’s Republic of China. 2
3
Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States.
College of Materials Science and Engineering, Shenzhen University and Shenzhen Key Laboratory of Special Functional Materials, Shenzhen 518060, People’s Republic of China
4
Electrochemical Technology Program, Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States. †
These authors contributed equally to this work.
*Corresponding author:
[email protected],
[email protected], and
[email protected] ABSTRACT: Using ab initio calculations combined with experimental confirmation, we design an asymmetric intercalation battery using K2NiFeII(CN)6 as the cathode, commercial graphite as the anode, and an organic electrolyte containing mixed lithium and potassium salts. It works by the reversible K-ion intercalation at the cathode side and the reversible Li-ions intercalation at the anode side simultaneously. The π-electron coordination environment in K2NiFeII(CN)6 ensures the preferred reversible intercalation of K-ion, and the small ionic radius ensures the preferred reversible intercalation of Li-ion in graphite. It also shows a high working voltage (~3.6 V) and an ultra-long cycling life with no capacity fading even after 5000 cycles.
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Due to the natural abundance and low cost compared with lithium, potassium-ion battery (PIB) shows great potential to be used in grid storage,1-5 where fast charge/discharge rate (CDR) and long cycling life are required. Recently, Prussian Blue and its analogues (PBAs) with the capability of reversible intercalation of K+ were demonstrated to be an attractive cathode candidate for PIBs,2, 4-10 featuring an excellent cycling performance. Other materials including FeSO4F11, KTiPO4O12, and AVPO4F13 were also demonstrated encouraging capacity and cycling life on the cathode side. Further development of such materials towards practical PIBs, however, remains big challenges, largely due to the limited choices of K+-intercalation anodes.1, 3, 14 Though graphite has been recently reported to be able to store K+ and deliver a high capacity of around 273 mAh/g through similar intercalation mechanism as Li+, its capacity retention and rate capability fall far short towards practical application.15 The relatively large volume change during the discharge and charge (about 60% expansion for K-ion intercalated in graphite,16 while only 12% expansion for Li-ion storage in graphitic17) is mainly responsible for such performance degradation. Metallic potassium, on the other hand, could be an ideal choice of anode for PIBs in terms of energy density. However, due to the much higher reactivity than lithium metal, it is more difficult to address the challenge facing potassium metal. Recent advances reported that graphitizable soft carbon18 and nongraphitizable hard carbon spheres (HCS)19 as anodes for PIBs show high specific capacities (273 mAh-1 for the soft carbon and 262 mAhg-1 for HCS) and improved cycling stability compared with graphite. Especially, HCS exhibited, to date, the best cycling 2
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ACS Energy Letters
stability among graphite, soft carbon, and hard carbon, where the electrode retained 83% of its initial capacity after 100 cycles at C/10.19 Exploring stable and reversible anodes beyond conventional category is of great interests to adjust the electrochemistry fitting well with a potassium cathode. However, the mission is very challenging due to the lack of qualified candidate with high potassium storage capability and extraordinary stability, as well as the sluggish kinetics of K+ intercalating into the electrode host material. Different from the traditional way, here we design an asymmetric cell to work by reversible intercalations of K+ at the cathode side and a different ion (e. g., Li+) at the anode side. This would not only extend the choice of anode materials but also be interesting from a fundamental perspective. To realize this concept, we need to choose appropriate electrode materials showing thermodynamic or kinetic priority for intercalation of targeted cation as well as excellent cycling stability. The thermodynamic priority mainly depends on the reaction energy and chemical potential for cation storage in the electrode materials at a certain temperature and pressure, which is correlated with the kind of redox couples for transition metals and the cation coordination environments.20 The kinetic priority mainly depends on the cation diffusion ability inside the bulk phase, as well as the nature and level of phase transition behavior of an electrode with a certain specific surface area. Strongly dependent on smaller ionic radius of Li-ion, various traditional intercalation electrode materials usually show a kinetic priority for Li+ intercalation. By introducing Li-ion into the PIB, the system would benefit synergistically by taking the electrochemical advantages of both Li+ and K+. The ultimate request for choosing the candidates of cathode for K+ and anode for Li+ should be both kinetically and thermodynamically favorable. By using ab initio calculations combined with experiments, we demonstrate that the π-electron coordination environment in PBAs can improve the potential for alkali cations storage with bigger size (VLi
