Aqueous Li-ion battery enabled by halogen conversion-intercalation chemistry in graphite.
basic_science · Level V
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- Record sourced from PubMed, PMID 31068723.
- Also identified by DOI 10.1038/s41586-019-1175-6.
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Abstract
The use of 'water-in-salt' electrolytes has considerably expanded the electrochemical window of aqueous lithium-ion batteries to 3 to 4 volts, making it possible to couple high-voltage cathodes with low-potential graphite anodes<sup>1-4</sup>. However, the limited lithium intercalation capacities (less than 200 milliampere-hours per gram) of typical transition-metal-oxide cathodes<sup>5,6</sup> preclude higher energy densities. Partial<sup>7,8</sup> or exclusive<sup>9</sup> anionic redox reactions may achieve higher capacity, but at the expense of reversibility. Here we report a halogen conversion-intercalation chemistry in graphite that produces composite electrodes with a capacity of 243 milliampere-hours per gram (for the total weight of the electrode) at an average potential of 4.2 volts versus Li/Li<sup>+</sup>. Experimental characterization and modelling attribute this high specific capacity to a densely packed stage-I graphite intercalation compound, C<sub>3.5</sub>[Br<sub>0.5</sub>Cl<sub>0.5</sub>], which can form reversibly in water-in-bisalt electrolyte. By coupling this cathode with a passivated graphite anode, we create a 4-volt-class aqueous Li-ion full cell with an energy density of 460 watt-hours per kilogram of total composite electrode and about 100 per cent Coulombic efficiency. This anion conversion-intercalation mechanism combines the high energy densities of the conversion reactions, the excellent reversibility of the intercalation mechanism and the improved safety of aqueous batteries.