Abstract
Due to their exceptional high energy density, lithium-ion batteries are of central importance in many modern electrical devices. A serious limitation, however, is the slow charging rate used to obtain the full capacity. Thus far, there have been no ways to increase the charging rate without losses in energy density and electrochemical performance. Here we show that the charging rate of a cathode can be dramatically increased via interaction with white light. We find that a direct exposure of light to an operating LiMn2O4 cathode during charging leads to a remarkable lowering of the battery charging time by a factor of two or more. This enhancement is enabled by the induction of a microsecond long-lived charge separated state, consisting of Mn4+ (hole) plus electron. This results in more oxidized metal centers and ejected lithium ions are created under light and with voltage bias. We anticipate that this discovery could pave the way to the development of new fast recharging battery technologies.
Highlights
Due to their exceptional high energy density, lithium-ion batteries are of central importance in many modern electrical devices
For charging, LMO is bulk oxidized, lithium leaves the material, and lithium cations are reduced with lithium metal deposition at the opposite anode; the electrons travel in the external circuit with high average potential ~ 4.1 V vs. Li+/o
Galvanostatic cycling measurements confirm the operation of the ‘open’ cell (Fig. 1c), which is consistent with a conventional cell (Supplementary Fig. 2)
Summary
Due to their exceptional high energy density, lithium-ion batteries are of central importance in many modern electrical devices. We find that a direct exposure of light to an operating LiMn2O4 cathode during charging leads to a remarkable lowering of the battery charging time by a factor of two or more This enhancement is enabled by the induction of a microsecond long-lived charge separated state, consisting of Mn4+ (hole) plus electron. This results in more oxidized metal centers and ejected lithium ions are created under light and with voltage bias. Depending on the physicochemical properties of the composite electrodes, fast DC charging is in principle feasible when engineered active particle physical morphologies[1,2], or low electrode loadings of nanostructured materials are used[3,4] These approaches result in limited volumetric energy densities (or the amount of stored energy per volume of material) within the battery pack. The discovery that exposure of LMO to light lowers charge transport resistance can lead to new fast recharging battery technologies for consumer applications and battery-only electric vehicles
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