Jahn–Teller Distortion Induced Mn²⁺‐Rich Cathode Enables Optimal Flexible Aqueous High‐Voltage Zn‐Mn Batteries

Abstract

Although one of the most promising aqueous batteries, all Zn‐Mn systems suffer from Zn dendrites and the low‐capacity Mn4+/Mn3+ process (readily leading to the occurrence of Jahn–Teller distortion, which in turn causes structural collapse and voltage/capacity fading). Here, the Mn3+ reconstruction and disproportionation are exploited to prepare the stable, Mn2+‐rich manganese oxides on carbon‐cloth (CMOs) in a discharged state through an inverted design, which promotes reversible Mn2+/Mn4+ kinetics and mitigates oxygen‐related redox activity. Such a 1.65 V Mn2+‐rich cathode enable constructing a 2.2 V Zn‐Mn battery, providing a high area capacity of 4.16 mA h cm–2 (25 mA h cm–2 for 10 mL electrolyte) and superior 4000‐cycle stability. Moreover, a flexible hybrid 2.7 V Zn‐Mn battery is constructed using 2‐pH hydrogel electrolytes to demonstrate excellent practicality and stability. A further insight has been gained to the commercial application of aqueous energy storage devices toward low‐cost, high safety, and excellent energy density.

The origin of capacity fluctuation and rescue of dead Mn-based Zn–ion batteries: a Mn-based competitive capacity evolution protocol

“…It should be pointed out that the deposition reaction of Mn 2+ in the charging process differs at different charging voltages or electrolyte environments; therefore, the deposition product might be MnO 2 in some other reported Mn-based Zn-battery systems instead of ZnMn 2 O 4 due to the promoted MnO 2 deposition kinetics. 9,50 In fact, these Mn-precipitation reactions could render extra discharge capacity no matter in which form, for the fact that Mn 2+ contribution is actually from the electrolyte. Moreover, the deposited tunnel MnO 2 tends to turn into a ZnMn 2 O 4 spinel upon cycling, especially when the pH value increases in the later period.…”

Synthesis of Nitrogen‐Doped KMn8O16 with Oxygen Vacancy for Stable Zinc‐Ion Batteries

“…[28] However, most reported 𝛼-MnO 2 suffer from poor electric conductivity (≈10 −5 to 10 −6 S cm −1 ), structural damage, and dissolution caused by unstable crystal structure and the Jahn-Teller distortion of Mn 3+ ions, eventually resulting in inferior rate performance and rapid capacity attenuation during cycling. [27,[29][30][31] To address these issues, strategies including compositing conductive materials (e.g., carbon materials and conductive polymers), [32] structural design, and defect engineering (e.g., oxygen vacancy, pre-intercalation of metal cations, or non-metal ions doping) have been extensively studied with some promising progress. [33][34][35][36] It is well known that oxygen vacancy can not only increase the electrical conductivity of metal oxides, but also regulate the electrochemical activity and promote ion diffusion.…”

“…[ 24 , 25 , 26 ] Among them, MnO 2 characterized by high theoretical capacity (308 mAh g −1 , contributed capacity of single electron transfer), cost‐effectiveness, high natural abundance, and environmental friendliness has attracted extensive scientific attention. [ 27 ] Moreover, because of the favorable 2 × 2 tunnels with size of 4.6 Å, α ‐MnO 2 is considered as a compelling cathode material for AZIBs. [ 28 ] However, most reported α ‐MnO 2 suffer from poor electric conductivity (≈10 −5 to 10 −6 S cm −1 ), structural damage, and dissolution caused by unstable crystal structure and the Jahn–Teller distortion of Mn 3+ ions, eventually resulting in inferior rate performance and rapid capacity attenuation during cycling.…”

“…[ 28 ] However, most reported α ‐MnO 2 suffer from poor electric conductivity (≈10 −5 to 10 −6 S cm −1 ), structural damage, and dissolution caused by unstable crystal structure and the Jahn–Teller distortion of Mn 3+ ions, eventually resulting in inferior rate performance and rapid capacity attenuation during cycling. [ 27 , 29 , 30 , 31 ]…”

Design Strategies for High‐Energy‐Density Aqueous Zinc Batteries

“…It is worth mentioning that the oxygen vacancies in CMO can reduce the local oxygen mobility to inhibit the OER and the low-valence manganese oxides can endow CMO with more active electron transfer dynamics. [54] In addition, the type of manganese and zinc salts also affects the electrochemical process in the Zn//MnO 2 batteries.D ifferent from the MnSO 4 electrolyte,i nt he mild acetate-based electrolyte,Mn 2+ ions are directly transformed into MnO 2 without disproportionation to Mn 3+ during the charging process,d ue to the coordination effect of CH 3 COO À ,w hich effectively promotes the reversibility of the MnO 2 /Mn 2+ conversion reaction (Figure 8b). [56] Meanwhile,t he mild acetate-based electrolyte has excellent compatibility and stability for the zinc anode.…”