A Korean research team from KIST and UNIST has developed a next-generation high-capacity cathode material for lithium-ion batteries by stabilizing the surface of over-lithiated layered oxides (OLO) using the DNA of salmon. Their paper appears in the journal Advanced Energy Materials.

Over-lithiated layered oxides (OLO) contain a large amount of lithium via the replacement of transition metal elements to lithium elements in the layered structure of material. Over-lithiated layered oxides (OLO) have a high reversible capacity of 250 mAh/g (compared to the reversible capacity of existing commercialized materials, which is only 160 mAh/g) and have long received attention as a next-generation cathode material, which can improve the energy storage capacity of batteries by more than 50%.

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.

—Kim et al.

The KIST research team used transmission electron microscopy to analyze changes in the crystallographic structure. The results of the analysis confirmed that the metal layers of the OLO begin to collapse at the surface after repeated charge/discharge cycling.

The joint research team used the DNA of a salmon, which has a strong affinity with lithium ions, to control the OLO’s surface structure, which was the cause of the material degradation. However, the salmon DNA showed a tendency to aggregate in aqueous solutions. To solve this problem, the research team synthesized the composite coating material that combined carbon nanotubes (CNT) and salmon DNA. The DNA/CNT mixture was uniformly arranged and attached to the surface of the OLO, resulting in the development of a new cathode material.

Schematic illustration depicting the stepwise chemical activation procedure of the DNA@MWCNT-treated OLO (i.e., D@C–OLO). Kim et al.

The research team at KIST performed integrated advanced analytical techniques (investigating a range of factors, from individual particles to electrodes) and found that the electrochemical characteristics of OLO and the mechanisms of its structural stability improved. The results of the in situ X-ray based analysis for the developed OLO was confirmed that the structural degradation was suppressed during charge/discharge cycling and the thermal stability was improved.

Hydrophobic aromatic bases of DNA have a good affinity for MWCNT via noncovalent π–π 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.

—Kim et al.

The work done at UNIST was supported by US Army Research Office (ARO), Basic Science Research Program, and Wearable Platform Materials Technology Center through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT, and future Planning. This work was also supported by the Korea Forest Research Institute and Batteries R&D of LG Chem.

The work done at KIST was supported by the Technology Development Program to Solve Climate Changes of the National Research Foundation (NRF) funded by the Ministry of Science & ICT and KIST Institutional Program.

Resources

• Kim, J.‐M., Park, J.‐H., Jo, E., Kim, H.‐S., Kim, S.‐H., Chang, W., Chung, K. Y., Lee, S.‐Y. (2020) “Ecofriendly Chemical Activation of Overlithiated Layered Oxides by DNA‐Wrapped Carbon Nanotubes.” Adv. Energy Mater. doi: 10.1002/aenm.201903658