The effects of vanadium substitution on one-dimensional tunnel structures of cryptomelane: Combined TEM and DFT study. (May 2020)

• Record Type: Journal Article
• Authors: Yang, Shi-Ze; Tallman, Killian R.; Liu, Ping; Lutz, Diana M.; Zhang, Bingjie; Kim, Sung Joo; Wu, Lijun; Marschilok, Amy C.; Takeuchi, Esther S.; Takeuchi, Kenneth J.; Zhu, Yimei
• Is Part Of: Nano energy. Volume 71(2020)
• Publication Date: 2020-05
• Subjects: Scanning transmission electron microscopy (STEM) -- In-situ TEM -- Battery -- Alpha-MnO2 -- DFT; Nanoscience -- Periodicals; Nanotechnology -- Periodicals; Nanostructured materials -- Periodicals; Power resources -- Technological innovations -- Periodicals; Nanoscience; Nanostructured materials; Nanotechnology; Power resources -- Technological innovations; Periodicals; 621.042
• DOI: 10.1016/j.nanoen.2020.104571
• Languages: English
• ISSNs: 2211-2855

Abstract

Abstract: Rational design of energy storage materials requires mechanistic understanding which relies on atomic scale characterization of structure and defects. Here we utilize vanadium (V)-substituted one-dimensional cryptomelane as a model material to study structural features critical to electrochemical reversibility of the cathode in lithium-ion batteries. We found the substitution of manganese (Mn) atoms in the tunnel wall with V enhances structural uniformity in the parent KMn8 O16 material by inhibiting formation of irregular (2 × 3 and 2 × 1) manganese oxide tunnel structures. Upon lithiation, both transmission electron microscopy (TEM) and density functional theory (DFT) reveal significant structural evolution, eventually resulting in phase separation and formation of highly reduced manganese oxide. During this process, Mn 4+ accepts electrons donated by intercalated Li, while the V 4+ substituent is not electrochemically reduced but acts to stabilize the tunnel framework structure. As a result, the V substituted material shows higher operating voltage and improved electrochemical reversibility. Our results highlight the benefits of V-substitution in cryptomelane, and the significance of integrating characterization with simulation for understanding and developing design principles for lithium ion battery materials. Graphical abstract: Image 1 Highlights: Vanadium dopant substituting Mn in the tunnel wall of cryptomelane enhances the crystallinity and decreases the tunnel length. The unique electronic structures of substituted VO6 octahedra enable the capacity enhancement of (2×2) tunnel upon lithiation. The stable V valence revealed during structural dynamics confirmed our theoretical explanation.