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Manganese-based cathodes are critical to the performance of zinc ion batteries, but structural changes during charging and discharging often limit their operating life. Computational investigations show that inserting zinc ions into a layered manganese dioxide cathode triggers a relocation of manganese atoms. Driven by electrostatic repulsion and ion movement, this process transforms the material into an irreversible spinel phase. Reversing this transformation requires substantially more energy than forming it, locking the material into the spinel state. This structural change sharply increases the energy barrier for zinc ion movement, reducing charging speeds. Over continuous cycles, the accumulation of this inactive spinel product degrades the battery's energy storage capacity.
Zinc ion batteries offer a promising alternative for clean energy storage, but their cathodes often degrade too quickly for practical use. Identifying the exact atomic mechanisms that trap manganese cathodes in unreactive states helps researchers understand why these batteries lose capacity, guiding future efforts to design more durable and faster-charging battery materials.
This research provides fundamental theoretical insights into cathode degradation mechanisms for developers of zinc ion battery systems. The work sits at an early computational stage, offering a molecular-level baseline that battery material manufacturers and chemical engineers could use to design strategies that suppress degradation, though no direct application pathway or practical device prototype is presented in the abstract.
AI-generated from the published abstract. Always read the original work before citing.
Phase transitions of Mn-based cathode materials associated with the charge and discharge process play a crucial role on the rate capability and cycle life of zinc ion batteries. Herein, a microscopic electrochemical failure mechanism of Zn-MnO<sub>2</sub> batteries during the phase transitions from δ-MnO<sub>2</sub> to λ-ZnMn<sub>2</sub>O<sub>4</sub> is presented via systematic first-principle investigation. The initial insertion of Zn<sup>2+</sup> intensifies the rearrangement of Mn. This is completed by the electrostatic repulsion and co-migration between guest and host ions, leading to the formation of λ-ZnMn<sub>2</sub>O<sub>4</sub>. The Mn relocation barrier for the λ-ZnMn<sub>2</sub>O<sub>4</sub> formation path with 1.09 eV is significantly lower than the δ-MnO<sub>2</sub> re-formation path with 2.14 eV, indicating the irreversibility of the layered-to-spinel transition. Together with the phase transition, the rearrangement of Mn elevates the Zn<sup>2+</sup> migration barrier from 0.31 to 2.28 eV, resulting in poor rate performance. With the increase of charge-discharge cycles, irreversible and inactive λ-ZnMn<sub>2</sub>O<sub>4</sub> products accumulate on the electrode, causing continuous capacity decay of the Zn-MnO<sub>2</sub> battery.
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DOI: 10.1002/smll.202401379
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