Boosting sodium storage performance of Na0.44MnO2 through surface modification with conductive polymer PPy utilizing sonication-assisted dispersion

Abstract

The search for suitable electrode materials for sodium storage in sodium-ion batteries (SIBs) poses significant challenges. Na_0.44MnO₂ (NMO) has emerged as a promising candidate among various cathode materials due to its distinct three-dimensional tunnel structure, which facilitates Na⁺ diffusion and governs structural stress fluctuations during Na⁺ intercalation/deintercalation. However, NMO faces obstacles such as limited electronic conductivity, lattice distortion induced by the Jahn–Teller effect of Mn³⁺ during cycling, and Mn³⁺ disproportionation leading to material dissolution, which affects cycling durability. To overcome these problems, Na_0.44MnO₂/polypyrrole (NMO/PPy) composites were fabricated through surface modification of the conductive PPy using an ultrasonically assisted dispersion method. Experimental results show that NMO/PPy with a 7 wt% PPy content exhibits superior sodium storage capabilities. Specifically, at a current density of 0.5C, the initial specific discharge capacity reaches 135.2 mA h g⁻¹, a 12.1% increase over pristine NMO, with a capacity retention of 94.5% after 100 cycles. Of particular note is a capacity retention of 82% after 500 cycles at 1C, attributed to the PPy coating, which suppresses Mn³⁺ side reactions, enhances the structural stability and electronic conductivity of NMO, and accelerates Na⁺ diffusion. These results suggest that the use of conductive polymer coatings represents a simple and effective strategy to improve the sodium storage capacity of NMO, paving the way for the further development of high-performance SIB cathodes.