Correlating Li/O2 cell capacity and product morphology with discharge current.
ACS Appl Mater Interfaces
; 7(14): 7670-8, 2015 Apr 15.
Article
de En
| MEDLINE
| ID: mdl-25775079
ABSTRACT
The discharge rate is critical to the performance of lithium/oxygen batteries it impacts both cell capacity and discharge-phase morphology, and in so doing may also affect the efficiency of the oxygen-evolution reaction during recharging. First-discharge data from tens of Li/O2 cells discharged across four rates are analyzed statistically to inform these connections. In the practically significant superficial current-density range of 0.1 to 1 mA cm(-2), capacity is found to fall as a power law, with a Peukert's-law exponent of 1.6 ± 0.1. X-ray diffractometry confirms the dominant presence of crystalline Li2O2 in the discharged electrodes. A completely air-free sample-transfer technique was developed to implement scanning electron microscopy (SEM) of the discharge product. SEM imaging of electrodes with near-average capacities provides statistically significant measures of the shape and size variation of electrodeposited Li2O2 particles with respect to discharge current. At lower rates, typical "toroidal" particles are observed that are well approximated as cylindrical structures, whose average radii remain relatively constant as discharge rate increases, whereas their average heights decrease. At the highest rate studied, air-free SEM shows that particles take needle-like shapes rather than forming the nanosheets or compact films described elsewhere. Average particle volumes decrease with current while particle surface-to-volume ratios increase dramatically, supporting the notion that Li2O2 grows by a locally mass-transfer-limited nucleation and growth mechanism.
Texte intégral:
1
Collection:
01-internacional
Base de données:
MEDLINE
Langue:
En
Journal:
ACS Appl Mater Interfaces
Sujet du journal:
BIOTECNOLOGIA
/
ENGENHARIA BIOMEDICA
Année:
2015
Type de document:
Article
Pays d'affiliation:
États-Unis d'Amérique