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Title: Probing the mechanism of sodium ion insertion into copper antimony Cu2Sb anodes

Cycling Cu2Sb films with fluoroethylene carbonate additive drastically improves the capacity retention of the electrode compared to cycling in pure PC with about 250 mAh g-1 retained capacity for about two hundred cycles. TEM photographs reveal that the pristine films are formed of nanoparticles of 5-20 nm diameters. XRD results highlight that during the first discharge the reaction leads to the formation of Na3Sb via an intermediate amorphous phase. During charge, Na3Sb crystallites convert into an amorphous phase, which eventually crystallizes into Cu2Sb at full charge, indicating a high degree of structural reversibility. The subsequent discharge is marked by a new plateau around 0.5 V at low Na/Sb content which does not correspond to the formation of a crystalline phase. XAS data show that the fully discharged electrode material has interatomic distances matching those expected for the coexistence of Cu and Na3Sb nanodomains. At 1 V charge, the structure somewhat differs from that of Cu2Sb whereas at 2 V charge, when all Na is removed, the structure is significantly closer to that of the starting material. 121Sb Mössbauer spectroscopy isomer shifts of Cu2Sb powder (-9.67 mm s-1) and thin films (-9.65 mm s-1) are reported for the first time, andmore » agree with the value predicted theoretically. At full discharge, an isomer shift (-8.10 mm s-1) rather close to that of a Na3Sb reference powder (-8.00 mm s-1) is measured, in agreement with the formation of Na3Sb domains evidenced by XRD and XAS data. As a result, the isomer shift at 1 V charge (-9.29 mm s-1) is close to that of the pristine material and the higher value is in agreement with the lack of full desodiation at 1 V.« less
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [1] ;  [1] ;  [3] ;  [4] ;  [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. Univ. of California, San Diego, La Jolla, CA (United States)
  3. Univ. of Tennessee Space Inst. (UTSI), Tullahoma, TN (United States)
  4. Univ. of California, San Diego, CA (United States)
Publication Date:
OSTI Identifier:
1159405
Grant/Contract Number:
AC05-00OR22725; DMR105717; AC02-98CH10886; FG02-05ER15688
Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 118; Journal Issue: 15; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY copper antimony (Cu₂Sb) thin films; sodium-ion anode; transmission electron microscopy (TEM); x-ray diffraction (XRD); Cu and Sb K-edge x-ray absorption spectroscopy (XAS); ¹²¹Sb Mössbauer spectroscopy