Manganese-based flow batteries have attracted increasing interest due to their advantage of low cost and high energy density. However, the sediment (MnO2) from Mn3+ disproportionation reaction creates the risk to...

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At present, the traditional CF and GF product need to go through processes such as spinning, oxidation, carbonization, graphitization, surface treatment, and sizing. [7a,55] The process flow is various and complicated, and further performance Review

teries are also attempted. [5,6] However, the poor reversibility of the MnOOH/MnO 2 redox couple limits further development.Additionally, Mn 2+ /Mn 3+ redox coupled with high voltage and high activity was widely used in acid-aqueous manganesebased batteries. [7][8][9][10][11][12] However, the Mn 3+ ions spontaneously convert into Mn 2+ ions and uncontrolled MnO 2 particles (the disproportionation reaction of Mn 3+ ) in an aqueous electrolyte, which shortens the cycling life of the battery. Then, some strategies, for example, introducing inorganic additives (H 2 SO 4 , [7] VO 2+ , [8][9][10] TiO 2+[11,12] ) have been tried. The inorganic additives could alleviate the disproportionation reaction of Mn 3+ and increase the cycle performance of the battery to a certain extent. Unfortunately, the battery finally stops working due to the blockage of MnO 2 at high SOC. So, it is necessary to limit the SOC of the batteries simultaneously, which would lead to low electrolyte utilization and serious capacity loss. Compared with the single electron transfer reaction of MnOOH/MnO 2 or Mn 2+ /Mn 3+ mentioned above, the deposition-dissolution reaction of Mn 2+ /MnO 2 (s) with the two-electron transfer was applied successfully in the aqueous manganesebased battery. [13,14] The conversion of Mn 2+ directly to MnO 2 without Mn 3+ was achieved by the constant-voltage charging mode, [15] adding acetate-based additive, [16] or bromide-acetate coadditive. [17] However, the low voltage of the Mn 2+ /MnO 2 redox couple (+1.228 V vs SHE) limits the energy density of the battery.Given that, our group proposed an electrochemical-chemical coupling strategy, where Mn 2+ /Mn 3+ redox couple with the high voltage of 1.51 V (vs SHE) was used in the charging process and MnO 2 from the disproportionation reaction of Mn 3+ was converted into Mn 2+ in the discharging process. [18,19] Benefiting from the TiO 2+ additives, the particle size and crystal structure of MnO 2 from the disproportionation reaction were adjusted, and the polarization of the battery was also alleviated. Moreover, thanks to the specific battery structure of the titanium-manganese single flow battery (TMSFB) (Scheme 1), where the catholyte was sealed in the cathode without pump and lines, the risk of the particle blockage was avoided. [18] Therefore, both long life and high voltage of Mn 2+ /Mn 3+ were achieved in TMSFB for the electrolyte with 0.5 m MnSO 4 . However, the areal capacity of the TMSFB just reached 10 mAh cm −2 , [18] and then TMSFB faced capacity decay with unknown reasons for the higher concentration of MnSO 4 electrolyte. Aqueous manganese-based flow batteries (AMFBs) have attracted great attention due to the advantages of low cost and environmental friendliness. Extending the cycle life of AMFBs has long been a challenging theme. The titanium-manganese single-flow batteries (TMSFB) are promising due to their special structure and electrolyte composition. However, TMSFB with high areal capacity faces capacity decay for unknown reasons. In this work, the capaci...

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