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Aqueous Processing of Na0.44MnO2 Cathode Material for the Development of Greener Na-Ion Batteries Valentina Dall'Asta, Daniel Buchholz, Luciana Gomes Chagas, Xinwei Dou, Chiara Ferrara, Eliana Quartarone, Cristina Tealdi, and Stefano Passerini ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b09464 • Publication Date (Web): 15 Sep 2017 Downloaded from http://pubs.acs.org on September 16, 2017
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ACS Applied Materials & Interfaces
Aqueous Processing of Na0.44MnO2 Cathode Material for the Development of Greener Na-Ion Batteries Valentina Dall’Asta†, ‡, §, Daniel Buchholz‡, §, *, Luciana Gomes Chagas‡, §, Xinwei Dou‡, §, Chiara Ferrara†, Eliana Quartarone†, Cristina Tealdi†, Stefano Passerini†, ‡, §, * †
University of Pavia, Dept. of Chemistry and INSTM, Via Taramelli 12, 27100 Pavia, Italy Helmholtz Institute Ulm (HIU), Helmholtzstraße 11, 89081 Ulm, Germany § Karlsruhe Institute of Technology (KIT), P.O. Box 3640, 76021 Karlsruhe, Germany ‡
KEYWORDS: carboxymethylcellulose, cathode, green, electrode, binder, sodium-ion battery ABSTRACT: The implementation of aqueous electrode processing of cathode materials is a key for the development of greener Na-ion batteries. Herein, the development and optimization of the aqueous electrode processing for the ecofriendly Na0.44MnO2 (NMO) cathode material, employing CarboxyMethylCellulose (CMC) as binder, is reported for the first time. The characterization of such electrode reveals as the performances are strongly affected by the employed electrolyte solution, especially, the sodium salt and the use of electrolyte’s additives. In particular, the best results are obtained using the 1M solution of NaPF6 in EC:DEC 3:7 (v/v) + 2 wt% FEC. With this electrolyte, the outstanding capacity of 99.7 mA h g-1 is delivered by the CMC-NMO cathode after 800 cycles at 1C charge/discharge rate. Based on this excellent long-term performance, a full sodium cell, composed of CMC-based NMO cathode and hard carbon from bio-waste (corn cob), has been assembled and tested. The cell delivers excellent performances in terms of specific capacity, capacity retention and long-term cycling stability. After 75 cycles at C/5 rate the capacity of the NMO in the full cell approaches 109 mA h g-1 with a coulombic efficiency of 99.9%.
INTRODUCTION The Na-ion technology is attracting wide attention1–3 thanks to the high abundance and low cost of raw materials (sodium and manganese) further boosted by the possibility of using aluminum as current collector for both, the anode and the cathode.4 Various anode and cathode materials have been investigated in recent years.5–9 Prominent cathode materials for NIBs are ranging from layered transition metal oxides10–13 to polyanionic compounds14–16. A green and cheap material is the tunnel oxide with formula Na0.44MnO2 (hereafter called NMO). It has a theoretical capacity of 121 mA h g-1 and its orthorhombic structure is characterized by the presence of large S-shaped tunnels along which the sodium ions may diffuse.8,17 Three sodium sites exist in the structure: Na1, accommodated in smaller tunnels and Na2 and Na3 lying within the large S-shaped tunnels. Sauvage et al. found that sodium cations on Na2 and Na3 sites can be cycled very reversible while those on the Na1 site cannot or only hardly be accessed.17 Accordingly, the number of Na+ equivalents that can be reversibly inserted/extracted from the structure cannot exceed the range 0.22
