Journal
CHEMELECTROCHEM
Volume 3, Issue 11, Pages 1856-1867Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/celc.201600365
Keywords
carbon electrodes; electrochemistry; sodium; structure-activity relationships; surface chemistry
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Funding
- Japan Society for the Promotion of Science JSPS
- Ministry of Education, Culture, Sports, Science and Technology (MEXT) under the Elemental Strategy Initiative for Catalysis and Batteries (ESICB)
- Japan Science and Technology Agency (JST) through Adaptable and Technology Transfer Program (A-STEP)
- JSPS KAKENHI Grant [JP16K14103, JP16H04225]
- Grants-in-Aid for Scientific Research [16H04225] Funding Source: KAKEN
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Electrochemical sodium insertion for hard carbon is examined in a cyclic alkylene carbonate based solution containing a NaClO4 or NaPF6 salt with a fluoroethylene carbonate (FEC) additive to study electrolyte dependency for sodium-ion batteries. NaPF6-based electrolytes provide superior reversibility and cyclability of sodium insertion into hard carbon compared with NaClO4-based ones. The FEC-derived passivation film improves capacity retention because of better passivation with a thinner surface layer, as revealed by hard and soft X-ray photoelectron spectroscopy (PES). The use of both the NaPF6 salt and FEC additive results in a synergetic effect on passivation for the hard-carbon electrode, leading to enhanced cycle per-formance. Hard-carbon electrodes with polyvinylidene difluoride binder in propylene carbonate based electrolytes containing NaPF6 and FEC demonstrate excellent capacity retention with a reversible capacity of about 250 mAhg(-1). The difference in capacity retention for the electrolytes is expected to originate as a consequence of the difference in the surface interphase layer formed on the hard-carbon electrodes. Surface analyses with PES and time-of-flight secondary ion mass spectrometry reveal differences in surface and passivation chemistry which depend on the salts, solvents, and FEC additives used for the hard-carbon negative electrodes.
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