Physics

Electrode

Organic chemistry

Anode

Endocrinology

Adsorption

Engineering

Electrochemical cell

Intercalation (chemistry)

Physical chemistry

Power (physics)

Inorganic chemistry

Chemistry

Materials science

Lithium (medication)

Lithium-ion battery

Graphite

Battery (electricity)

Quantum mechanics

Electrolyte

Chemical engineering

Electrochemistry

Medicine

Gravimetric analysis

Quartz crystal microbalance

Nature Nanotechnology

The solid–electrolyte interphase (SEI) is probably the least understood component in Li-ion batteries. Considerable effort has been put into understanding its formation and electrochemistry under realistic battery conditions, but mechanistic insights have mostly been inferred indirectly. Here we show the formation of the SEI between a graphite anode and a carbonate electrolyte through combined atomic-scale microscopy and in situ and operando techniques. In particular, we weigh the graphitic anode during its initial lithiation process with an electrochemical quartz crystal microbalance, which unequivocally identifies lithium fluoride and lithium alkylcarbonates as the main chemical components at different potentials. In situ gas analysis confirms the preferential reduction of cyclic over acyclic carbonate molecules, making its reduction product the major component in the SEI. We find that SEI formation starts at graphite edge sites with dimerization of solvated Li+ intercalation between graphite layers. We also show that this lithium salt, at least in its nascent form, can be re-oxidized, despite the general belief that an SEI is electrochemically inert and its formation irreversible. A set of in situ and operando techniques, as well as gravimetric and microscopic investigations are used to characterize the formation of the solid–electrolyte interphase in a Li-ion battery.

In situ quantification of interphasial chemistry in Li-ion battery