Ecofriendly Chemical Activation of Overlithiated Layered Oxides by DNA-Wrapped Carbon Nanotubes

Abstract

Despite their exceptionally high capacity, overlithiated layered oxides (OLO) have not yet been practically used in lithium-ion battery cathodes due to necessary toxic/complex chemical activation processes and unsatisfactory electrochemical reliability. Here, a new class of ecofriendly chemical activation strategy based on amphiphilic deoxyribose nucleic acid (DNA)-wrapped multiwalled carbon nanotubes (MWCNT) is demonstrated. Hydrophobic aromatic bases of DNA have a good affinity for MWCNT via noncovalent pi-pi stacking interactions, resulting in core (MWCNT)-shell (DNA) hybrids (i.e., DNA@MWCNT) featuring the predominant presence of hydrophilic phosphate groups (coupled with Na+) in their outmost layers. Such spatially rearranged Na+-phosphate complexes of the DNA@MWCNT efficiently extract Li+ from monoclinic Li2MnO3 of the OLO through cation exchange reaction of Na+-Li+, thereby forming Li4Mn5O12-type spinel nanolayers on the OLO surface. The newly formed spinel nanolayers play a crucial role in improving the structural stability of the OLO and suppressing interfacial side reactions with liquid electrolytes, eventually providing significant improvements in the charge/discharge kinetics, cyclability, and thermal stability. This beneficial effect of the DNA@MWCNT-mediated chemical activation is comprehensively elucidated by an in-depth structural/electrochemical characterization.