Polymorphic Effects on Electrochemical Performance of Conversion‐Based MnO₂ Anode Materials for Next‐Generation Li Batteries

Abstract

In this study, four different MnO2 polymorphs are synthesized with a controlled morphology of hollow porous structures to systematically investigate the influences of polymorphs in conversion‐based material. As the structure of these materials transforms into nanosized metal and maintains an extremely low‐crystalline phase during cell operation, the effects of polymorphs are overlooked as compared to the case of insertion‐based materials. Thus, differences in the ion storage behaviors among various MnO2 polymorphs are not well identified. Herein, the structural changes, charge storage reaction, and electrochemical performance of the different MnO2 polymorphs are investigated in detail. The experimental results demonstrate that the charge storage reactions, as part of which spinel‐phased MnO2 formation is observed after lithiation and delithiation instead of recovery of the original phases, are similar for all the samples. However, the electrochemical performance varies depending on the initial crystal structure. Among the four polymorphs, the spinel‐type λ‐MnO2 delivers the highest reversible capacity of ≈1270 mAh g−1. The structural similarity between the cycled and pristine states of λ‐MnO2 induces faster kinetics, resulting in the better electrochemical performance. These findings suggest that polymorphs are another important factor to consider when designing high‐performance materials for next‐generation rechargeable batteries.

Core–Shell Structured C@SiO2 Hollow Spheres Decorated with Nickel Nanoparticles as Anode Materials for Lithium‐Ion Batteries

“…Lithium-ion batteries (LIBs) with high energy density have been regarded as one of the prominent devices to meet the demand of portable electronic devices and electric vehicles. [1][2][3][4][5][6][7] the tensile hoop stress arising from the volume variation. And carbon not only greatly enhances electron transport but also boosts mechanical robustness.…”

Challenges and Design Strategies for Conversion-Based Anode Materials for Lithium- and Sodium-Ion Batteries

“…During subsequent charging, the Na 2 Se peaks were gradually reduced, and NiSe 2 peaks were observed again after complete charging, indicating the reversibility of the conversion reaction [22]. Similarly, other researchers have proven the conversion reaction mechanism using XRD techniques by observing the metallic phase and LiX/NaX phases after full discharge [23][24][25][26][27][28]. However, although XRD is a powerful method for obtaining phase-sensitive information, it is not always the best choice for identifying conversion reactions because most conversion-based materials significantly lose their crystallinity during lithiation.…”

“…To explore the effects of polymorphs, H. Kim et al systematically investigated the charge storage behaviors of four different MnO 2 polymorphs possessing similar hollow porous morphology, as shown in Fig. 10(a) [24]. The voltage profiles of the four samples in Fig.…”

Atomistic Insights of Irreversible Li+ Intercalation in MnO2 Electrode

“…[1][2][3][4] In addition, owing to the different linking patterns of the [MnO 6 ] octahedral units, the MnO 2 structure exhibits a high degree of polymorphism featuring one-dimensional tunnel configurations in majority, [5] which greatly facilitate reversible charge transport and storage in MnO 2 and enables its use as electrode materials in rechargeable batteries. [6,7] Yet, the extensive application of MnO 2 for reversible energy storage is still in its infancy due to the existing drawbacks of MnO 2 materials, among which stands out the notorious fast capacity decay of MnO 2 electrode upon longterm cycling. [8,9] The rechargeability of tunnel-structured MnO 2 has been tested since two decades ago, led by Thackeray et al at Argonne National Laboratories, whose finding revealed a moderate first-cycle capacity ( % 180 mAh g À1 ) followed by quick capacity fading during the rest cycles.…”