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A hierarchical spheroidal MnO@C heterogeneous interface as a cathode material for AZIBs and synthesized through a MOF, which exhibits the excellent cycling stability. [Display omitted] Aqueous zinc-ion batteries (AZIBs) have shown great potential as energy storage devices owing to their high energy density, low cost, and low toxicity. Typically, high performance AZIBs incorporate manganese-based cathode materials. Despite their advantages, these cathodes are limited by significant capacity fading and poor rate performance due to the dissolution and disproportionation of manganese. Herein, hierarchical spheroidal MnO@C structures were synthesized from Mn-based metal–organic frameworks, which benefit from a protective carbon layer to prevent manganese dissolution. The spheroidal MnO@C structures were incorporated onto a heterogeneous interface to act as a cathode material for AZIBs, which exhibited excellent cycling stability (160 mAh g−1 after 1000 cycles at 3.0 A g−1), good rate capability (165.9 mAh g−1 at 3.0 A g−1), and appreciable specific capacity (412.4 mAh g−1 at 0.1 A g−1) for AZIBs. Moreover, the Zn2+ storage mechanism in MnO@C was comprehensively investigated using ex-situ XRD and XPS studies. These results demonstrate that hierarchical spheroidal MnO@C is a potential cathode material for high-performing AZIBs. [ABSTRACT FROM AUTHOR]

• A new strategy was raised for controlling Mn3+ of LNMO via MOFs. • An optimal LNMO electrode is demonstrated with a high discharge capacity of 145.3 mA h g−1. • The effects of MOFs on the structure and electrical properties of LNMO were investigated. Spinel LiNi 0.5 Mn 1.5 O 4 has drawn considerable attention due to its wide working voltage, high energy density, low cost, natural abundance, and environmental friendliness. However, as an electrode in lithium-ion batteries, its inferior ionic/electronic conductivity and high Mn3+ concentration at the surface lead to low specific capacitance and poor rate/cycling performance, which have impeded its applications. In this work, a series of LiNi 0.5 Mn 1.5 O 4 is synthesized via a hydrothermally assisted method coupled with a high-temperature calcination process based on metal-organic frameworks. In addition, this study systematically explores the effect of the organic ligand species on the electrochemical properties of synthesized LiNi 0.5 Mn 1.5 O 4. Furthermore, an optimal LiNi 0.5 Mn 1.5 O 4 electrode is demonstrated with a high discharge capacity of 145.3 mA h g−1 at a 1C rate. It provides a large capacity of 122.6 mA h g−1 even at a discharge rate as high as 20C. In particular, at an elevated temperature, 94.4% of the capacity is retained after 500 cycles at 1C and 40 °C. Thus, LiNi 0.5 Mn 1.5 O 4 will be a promising cathode for applications in next-generation lithium-ion batteries with high energy densities. [ABSTRACT FROM AUTHOR]

Spinel LiNi 0.5 Mn 1.5 O 4 (LNMO) cathode with high voltage plateau at around 4.7 V (vs. Li/Li+) and high energy density has attracted great attention. However, its application is limited because of the lack of matched electrolyte. Herein, we demonstrate that lithium difluorophosphate (LiPO 2 F 2 , LiDFP) as lithium difluoro(oxalate)borate (LiODFB) electrolyte additive significantly improves the electrochemical performance of high voltage LNMO/Li half cells and LNMO/G full cells at room temperature. Capacity retention of LNMO/Li half cell with 4% LiDFP achieves 89.69% after 200 cycles in comparison with 76.31% of that without LiDFP. Even discharging at 10C, the LNMO/Li half cell with 4% LiDFP still delivers a discharge capacity of 76.25 mAh g−1 and maintains at 75.94% capacity retention after 200 cycles. The electrochemical performance of LNMO/G full cells has a similar improvement. The enhanced electrochemical performance of LNMO can be ascribed to the steady and low-impedance cathode electrolyte interphase (CEI) film formed by priority decomposition of LiDFP. Besides, in order to further reveal the mechanism of film-forming additive, we studied on the changes of CEI film during initial cycles using transmission electron microscopies (TEM), X-ray photoelectron spectroscopy (XPS), Fourier Transform Infrared Spectrometer (FT-IR) and electrochemical impedance spectroscopy (EIS) measurements. The results indicate that the LiDFP preferential decomposition product can gradually prevent the contact between the electrolyte and the cathode with the growth of the CEI film, thereby reducing decomposition of the electrolyte. The finally grown CEI film is sufficiently dense to effectively isolate the electrolyte and the cathode, and CEI film formed by LiDFP-containing electrolyte is more conducive to the transmission of Li+,eventually leading to excellent electrochemical performance for the high-voltage LIBs. [ABSTRACT FROM AUTHOR]