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Functional Nanostructured Materials (including low-D carbon)
Amorphous Carbon Derived Nanosheets-bricked Porous Graphite as High Performance Cathode for Aluminum-Ion Batteries Chunyan Zhang, Rui He, Jichen Zhang, Yang Hu, Zhiyong Wang, and Xianbo Jin ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b07590 • Publication Date (Web): 19 Jul 2018 Downloaded from http://pubs.acs.org on July 20, 2018
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ACS Applied Materials & Interfaces
Amorphous Carbon Derived Nanosheets-bricked Porous Graphite as High Performance Cathode for Aluminum-ion Batteries Chunyan Zhang, Rui He, Jichen Zhang, Yang Hu, Zhiyong Wang, Xianbo Jin*
Hubei Key Laboratory of Electrochemical Power Sources, College of Chemistry and Molecular Sciences, Hubei International Scientific and Technological Cooperation Base of Sustainable Resource and Energy, Wuhan University, Wuhan, 430072, P.R. China. *
Email address:
[email protected].
Abstract: Graphite is an attractive cathode material for energy storage because it allows reversible intercalation/deintercalation of many compound anions at high potentials. However, because the sizes of the compound anions are greatly larger than the lamellar spacing of graphite, common graphite for cathode uses may suffer from slow kinetics and large volume expansion. Here, it demonstrates that graphite with a high crystallinity and nanosheets-bricked porous structure can be an excellent cathode for the aluminum-ion batteries. This porous graphite is derived from carbon black via a simple electrochemical graphitization in molten CaCl2, and the high crystallinity and thin layer characters facilitate the high-capacity and high-rate storage of aluminum tetrachloride ions. Moreover, the bricked porous structure endows the fabricated cathode with a providential porosity to perfectly match the huge volume expansion of graphite (650% against a charging capacity of 100 mAh g-1), which thus exhibits integrated high gravimetric and volumetric capacities, as well as high structural stability during cycling. Keywords: graphite cathodes; rechargeable aluminum batteries; porous graphite; volumetric capacity; amorphous carbon; graphitization 1 ACS Paragon Plus Environment
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Introduction Graphite, a traditional anode for lithium ion batteries (LIBs), is emerging as a promising cathode for energy storage because it is cheap and allows reversible intercalation/deintercalation of various kinds of compound anions at high potentials.1-10 It can be used to assemble various kinds of batteries against metals or graphite anodes. In particular, Al/graphite batteries, also called as “aluminum-ion batteries” (AIBs), have attracted increasing interest for the safety, high earth abundance and specific capacity (2980 A h kg−1 and 8046 A h L−1) of Al and the ultralong cycling life of the graphite cathode.7, 11-17 It should be pointed out that although Al/graphite AIBs are rechargeable, there are not rocking chair batteries like LIBs. As well-known during discharging, in a LIB Li+ ions leave the anode, transfer through the electrolyte and integrate into the cathode, but the Al/graphite cell discharges of Al2Cl7- and/or AlCl4- ions at both electrodes.7 Recently it was confirmed that V2O5 allows intercalation of direct Al3+ ions,18 thus the Al/V2O5 battery may work similar to traditional LIBs. The intersection of Al/graphite AIBs and present commercial LIBs is the use of graphite electrode, but as cathode for AlCl4- intercalation and anode for Li+ intercalation, respectively. However, conventional graphite that works well in LIBs have proved to suffer from low specific capacity and poor rate performance when use as cathodes. It was reported that the cathode performance could be significantly improved after exfoliating the graphite into few-layer graphene, but it is essential to retain sufficiently large crystallite domains. Common graphene in an amorphous structure is unsuitable for the cathode use unless post recrystallization is carried out at temperatures higher than 2500 oC.19-24 The difficulty of graphite for cathode uses may arise from the fact that the lamellar spacing of graphite (0.335 nm) is too narrow in comparison with the sizes of compound anions.10, 25 AlCl4ion has a size of 0.609 nm, so its intercalation into graphite may encounter a great pressure stress.
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ACS Applied Materials & Interfaces
Using few-layer graphene may help to alleviate this stress, and a relative high gravimetric capacity can be achieved.19-24 On the other hand, the intercalation of large compound anions into graphite may lead to a huge volume expansion,7 which has been recognized as a main issue to address for the practice uses. It should be pointed out that there is still no experimental data of volume expansion determined for the graphite cathode. It is important for the graphite material to have a proper nanoporous structure to alleviate the intercalation stress and maintain a moderate porosity in the cathode. Ideally, the porosity should be high enough to buffer the volume change, so to avoid the cell failure as a result of volume expansion; but too high a porosity will lead to not only a low volumetric capacity, but also a low gravimetric capacity because the electrode would take in large amounts of superfluous electrolyte.26,27 Here we report that a nanosheets-bricked porous graphite (NSPG) derived from carbon black through a simple electrochemical graphitization can be a high performance cathode material for AIBs in an [Emim]Cl/AlCl3 (1-ethyl-3-methylimidazolium chloride/aluminum chloride) electrolyte. The NSPG has many advantageous features for the intercalation of large anions. The high crystallinity and thin layer nanosheet characters endow the NSPG with a large gravimetric capacity and high rate performance. The nanosheets-bricked porous structure helps to maintain the cathode an appropriate porosity (~87%), which guarantees a high volumetric capacity while well matches the about 650% volume expansion of graphite upon intercalation about 100 mAh g-1 of AlCl4- ions as we demonstrated. Experimental Section Preparation of nanosheets-bricked porous graphite (NSPG)
Typically, 0.5 g Carbon black (Vulcan XC-72, Cabot, USA ) was die-pressed into a cylindrical pellet and then packed with porous nickel foam to form the cathode, which was polarized in molten CaCl2 (1093 K) against a graphite anode by applying a cell voltage of 2.6 V for 30 min, 3 ACS Paragon Plus Environment
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60 min or 120 min. Then, the cathode was taken out, cooled to room temperature, washed and dried for use.28 Preparation of electrolyte for AIBs
The ionic liquid electrolyte is prepared by mixing [EMIm]Cl (97%, Acros Chemicals) and anhydrous aluminum chloride (AlCl3) (99.999%, Sigma Aldrich) (molar ratio of 1.3:1) in an argon-atmosphere glove box ([O2] < 0.1 ppm, [H2O] < 0.1 ppm). Before the mixing, the as received [EMIm]Cl was baked at 100°C under vacuum for 36 h to remove residual water. The resulting light yellow and transparent electrolyte was allowed to stand for at least 12 h before used. Electrochemical tests of AIBs
Swagelok-type cells were assembled and tested in the glove box, and a comparison between NSPG and commercial nanosheet graphite (CNG, graphite nanosheet, D50
