Recently, Prof. Hui Xia’s research group from the Herbert Gleiter Institute of Nanoscience (Nanjing University of Science and Technology) reported important research progress on Mn-based cathode material for lithium-ion batteries with the title of “LiMnO2 cathode stabilized by interfacial orbital ordering for sustainable lithium-ion batteries” in “Nature Sustainability”. Prof. Hui Xia (Nanjing University of Science and Technology), Prof. Lin Gu (Institute of Physics, Chinese Academy of Sciences) and Prof. Qi Liu (City University of Hong Kong) are corresponding authors for this paper. Dr. Xiaohui Zhu (School of Materials Science and Engineering, Nanjing University of Science and Technology), Dr. Fanqi Meng and Prof. Qinghua Zhang (Institute of Physics, Chinese Academy of Sciences) are the co-first authors. (Link to the paper: https://www.nature.com/articles/s41893-020-00660-9)
As the rapid growth of global consumer electronics and new energy vehicles, the demand for lithium-ion batteries has grown rapidly, so the sustainability of lithium-ion batteries (LIBs) has become very important. At present, commercial lithium-ion batteries depend heavily on high-cobalt and high-nickel content cathode materials. However, the cobalt or/and nickel abundance is relatively low and the cost is high, and the cathode preparation process is accompanied by high pollution and other social problems. Therefore, it is urgent to replace them by other transition metals, which should be highly abundant, low-cost and environmentally friendly. The manganese-based cathode materials were initially suggested as a promising alternative cathode material because of its low cost, incorporation of highly abundant Mn, and large theoretical capacityassociated with the Mn3+/Mn4+ redox couple. The commercial use of LiMnO2 cathodes in LIBs, however, has been impeded by the cooperative Jahn-Teller distortion associated with high-spin Mn3+, which causes severe structural instability and rapid capacity fading.
The single-electron occupancy in the doubly degenerate eg level leads to a local Jahn-Teller distortion with Mn-O bonds elongated along one of the octahedral axes. The orbital ordering in LiMnO2 leads to collinear Jahn-Teller ordering, resulting in a strong cooperative Jahn-Teller effect and a large volume change. Prof. Xia and co-workers believe that it is necessary to destroy the long-range order of Jahn-Teller distortion from the interior of the material particles to effectively suppress the cooperative Jahn-Teller effect. In this work, the researchers used spinel-Mn3O4 as the original electrode, and transformed it into the spinel-layered heterostructure via in situ electrochemical conversion. The cooperative Jahn-Teller distortion of Mn3+ is largely suppressed by the interfacial orbital ordering in the current spinel-layered heterostructure, which breaks the collinear orbital ordering in the individual spinel and layered materials. Therefore, the spinel-layeredheterostructure substantially reduces the Jahn-Teller distortion and Mn dissolution, and enhances the structural stability of LiMnO2. This spinel-layered LiMnO2 cathode delivers a reversible specific capacity as high as 254.3 mAh g-1, excellent high-rate performance, and excellent cycle performance for 2000 cycles (Figure 1).
Prof. Arumugam Manthiram and his co-workers from the University of Texas at Austin believe that this work provides a new strategy to suppress Jahn-Teller distortion in manganese-based cathode materials, making it possible to develop highly stable manganese-based cathode materials and promoting the use of manganese-based materials for sustainable and large-scale energy storage devices. At the same time, this work also raises a series of important scientific questions. For example, the lattice distortion mechanism and precise synthetic chemistry in interface engineering. Furthermore, it can be expected that the cost reduction of energy storage technology will effectively promote energy framework in a more sustainable direction. Related link: https://www.nature.com/articles/s41893-020-00664-5.
This work was supported by the National Natural Science Foundation of China, the National Key R&D Program of China, and the Fundamental Research Funds for the Central Universities. In addition, this research work has also received strong support from Prof. Si Lan (School of Materials Science and Engineering, Nanjing University of Science and Technology), Prof. Xia Lu (Sun Yat-Sen University), and Prof. Yang Ren (Argonne National Laboratory).
Fig. 1 Spinel-layered heterostructured LiMnO2 with nearly orthogonal interfacial orbital ordering and ultra-long cycle life.