Increasing deployment of large scale electric storage applications would benefit from the development of inexpensive batteries. Na-ion batteries (NIBs) are of great interest since their cathodes can be made from inexpensive and abundant materials such as sodium, iron, and manganese. However, existing iron and manganese oxide cathodes lack the electrochemical performance, including capacity retention, required for these NIB applications and significant improvement is needed.

Prior work on lithium ion battery cathodes demonstrates that meso-structured materials can improve electrochemical performance for batteries. Incorporating spherical meso-structured materials in lithium ion battery cathodes was shown to improve capacity retention. To emulate this approach in NIB cathode materials, a synthesis method for producing pure phase spherical meso-structured sodium iron manganese oxide is first needed. No literature has been found that describes a method for this synthesis. Key synthesis parameters to be controlled include the choice of method, material precursors, pH of reaction, calcination time, and cooling rate.

In this work we demonstrate a modified co-precipitation method to synthesize spherical meso-structure pure phase P2-Na_0.67Fe_1/4Mn_3/4O₂ (see Figure 1) and we report initial characterization of the electrochemical performance of this material. The key parameter found to control the formation of a spherical meso-structure is the cooling rate applied during synthesis. The slow cooled material forms spherical meso-structures while the quenched material has no ordered meso-structure. Additionally, the spherical meso-structured material shows increased capacity, improved cyclability, and reduced polarization. The electrochemical performance enhancement is attributed to higher surface area, reduced surface concentration of sodium carbonate, and lower internal resistance during cycling. Further exploring the synthesis and mechanisms of meso-structured materials offers a path for improving Na-ion battery cathodes.