Enabling stable MnO2 matrix for aqueous zinc-ion battery cathodes

Cost effective, safe and environmentally friendly energy storage devices as complement and alternative to Li-ion batteries are in urgent demand to sustain the implementation of smart grids and de-carbonification of the energy market. In this paper, TYC researchers have examined the performance of layered delta-MnO2 based materials as electrodes for aqueous Zn-ion batteries.

The performance of the parent MnO2 composition degrades quickly upon cycling, due to the competing formation of the tunnel alpha-MnO2 polymorph. Pre-intercalation of large ions, such as K, at sufficiently high concentration between the layers of delta-MnO2 prevents the phase transition and allows the material to retain promising performance upon cycling even at high rate. The paper combines synthesis and characterisation efforts, electrochemical tests and DFT calculations based on hybrid exchange functionals; the latter show that the threshold K content to prevent the delta-alpha MnO2 transition corresponds to K0.26MnO2. This rationalises the experimental measurements that show the material of composition K0.21MnO2 to have poor performance compared to K0.28MnO2, whose specific capacity of 300 mAh g-1 at high rate is competitive. Alternative doping and pre-intercalation strategies to prevent unwanted phase transitions can be investigated computationally as a rational materials design strategy.


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