Introduction

With the gradual consumption of traditional fossil energy and the increase of environmental problems, the development of green and sustainable energy has become particularly important [1]. People are working hard to develop a series of clean and renewable energy sources, such as solar, water, and wind power; however, most of them are limited by their geographical features and instability [2]. Therefore, the growing of advanced energy storage systems for reliably store and efficiently use these intermittent clean energy sources is becoming particularly urgent [3,4,5]. In various rechargeable batteries, lithium-ion batteries (LIBs) have received the most extensive attention in the energy storage field for decades due to its excellent energy density and longer energy lifetime [6,7,8]. However, the further development of LIBs is hindered by its high price, poisonous electrolytes, low ionic conductivity of organic electrolytes, as well as the safety and environmental issues [9,10,11,12].

In recent years, aqueous rechargeable batteries are considered a promising alternative to solve these problems because of high ionic conductivity (~ 1 S cm−1), high safety, and ecological friendliness [13, 14]. Particularly, zinc (Zn) presents one of the most promising alternatives given its high-safety, huge cost competitiveness, high specific capacity (820 mAh g−1), high abundance, and eco-friendliness [15,16,17], showing unparalleled advantages in matching with aqueous electrolytes. Thus, aqueous zinc-ion batteries (AZIBs) have attracted great attention as emerging energy storage systems. Despite some encouraging achievements in this field [18,19,20], finding a suitable cathode with satisfactory stability remains a significant challenge.

Benefiting from the special crystal structure, multiple valence states of Mn and good Zn2+ storage capacity and manganese oxide (MnO2) as a cathode material have received intensive attention for AZIBs [21, 22]. Nevertheless, MnO2 have the low conductivity, lattice distortion, and irreversible dissolution problems and cannot play their best performance [23, 24]. To overcome these problems and improve the electrochemical performance of MnO2, one promising approach is to use another type of nanomaterial to design and fabricate hierarchical MnO2 core–shell nanostructures [25,26,27]. The core–shell structure of 2-dimensional (2D) nanosheets grown on the surface of 1D MnO2 nanowires has attracted widespread attention because the core–shell can not only form ordered and open structures, but also be reinforced by strong mechanical underpinning [25]. The potential synergistic effect of the good conductivity and short ion diffusion path of 1D nanowires coupled with the large surface area and ion adsorption of 2D nanosheets exhibited an extremely high energy density, remarkable rate performance, and impressive cycle stability [28]. Furthermore, another alternative method to enhance the cycle stability of MnO2 is to adjust the components of MnO2. The introduction of the other elements can adjust or change the ionic/electronic transfer, adsorption property, and structure stability of active materials towards Zn2+ storage [29,30,31]. The heterostructure formed by the core–shell structure not only reduces the ion diffusion resistance and promotes rapid redox reactions, but also provides more sites for electrochemical reactions [32, 33]. Inspired by this, we believe that the core–shell structure constructed by combining 1D MnO2 nanowires or nanotubes with heteroatom doped metal oxides can achieve excellent electrochemical performance of AZIBs.

In this work, we combined the advantages of MnO2 nanotubes and heteroatom doped metal oxides to design and prepare a α-MnO2@LaxMn1-xO2-δ core–shell structure as a cathode material for AZIBs. The α-MnO2@LaxMn1-xO2-δ not only shortens the diffusion path of Zn2+ and offer an effective electron transfer pathway, but also enhances the capacitive process and stabilizes the composite structure. The α-MnO2@LaxMn1-xO2-δ exhibits a high discharge capacity of 248 mAh g−1 at a current density of 0.3 A g−1 and ultrastable cycle retention of 98% after 100 cycles. Moreover, the α-MnO2@LaxMn1-xO2-δ cathode delivers 90% of the initial capacity after 1500 cycles at 1 A g−1. These impressive results could be attributed to the high ion diffusion rate of α-MnO2@LaxMn1-xO2-δ, and the unique structure of α-MnO2@LaxMn1-xO2-δ improves the structural stability of the active material, thus enhancing the transmission capacity and transmission capacity of H+ and Zn2+ ions. Herein, we provide new insights for the development of high-performance cathode materials for AZIBs.

Experimental

Synthesis of α-MnO2 nanotubes

MnO2 cathode was prepared using a facile one-step hydrothermal method [34]. In detail, 1 mL of concentrated HCl (AR, 98%) was added to 45 mL of aqueous solution, and then 2.5 mmoL KMnO4 (AR, 98%) were added to the above solution and stirred for 0.5 h to form a uniform purple suspension, followed by pouring the uniform purple suspension into a Teflon-lined stainless-steel autoclave, and heating it at 140 °C for 12 h. Finally, the obtained products were centrifuged and washed with water and ethanol for several times and dried at 60 °C for 24 h.

Synthesis of α-MnO2@LMO

Typically, 20 mg of α-MnO2 nanotubes were poured into 40 mL of water and sonicated for 10 min. The mass ratio of KMnO4: La(NO3)3⋅6H2O = 2:1 was added to the above solution followed by magnetic stirring for 2 h. The resulting solution was then transferred into a Teflon-lined stainless-steel autoclave under the heat-treatment at 160 °C for 2 h. The obtained precipitate was centrifuged and washed with water and ethanol for several times. Finally, α-MnO2@LMO was obtained by drying at 60 °C for 24 h. Except for different feed ratios, all other conditions are completely the same for different ratios of KMnO4 and La(NO3)3⋅6H2O. The mass ratio parameters are shown in the Table S1.

Material characterizations

The powder X-ray diffraction (XRD) patterns of the samples were recorded using a Ultima IV powder diffractometer with Cu-Ka radiation source (λ = 1.5418 Å). The microstructures of as-prepared samples were observed by the field emission scanning electron microscope (FESEM, JSM-7800F, JEOL, Japan), a transmission electron microscopy (TEM), and a high-resolution TEM (JEM2100F). X-ray photoelectron spectroscopy (XPS) (Thermo SCIENTIFIC ESCALAB 250xi) was performed to evaluate the valence state and the surface chemistry of the samples.

Electrochemical measurements

In order to estimate the electrochemical behavior of α-MnO2 and α-MnO2@LMO, CR2025 coin-type cells were assembled using the active materials (α-MnO2 or α-MnO2@LMO) as the cathode and Zn plate as the anode, respectively. The electrolyte solution consists of 2 M ZnSO4 and 0.1 M MnSO4. The working electrode was prepared by uniformly mingling a mixed slurry containing the α-MnO2 or α-MnO2@LMO (70 wt%), poly(tetrafluoroethylene) (PVDF) (10 wt%), and Ketjen black (20 wt%) in N-methyl-2-pyrrolidinone (NMP) onto the carbon paper, and then vacuum-dried at 60 °C for 12 h. The mass loading of electroactive materials was controlled at 1.5 ~ 2.0 mg cm−2. Cyclic voltammetry (CV) were conducted using CS310M electrochemical workstation at a sweep rate of 0.1 mV/s from 1.0 to 1.8 V vs. Zn2+/Zn. The electrochemical impedance spectroscopy (EIS) was recorded over a frequency range from 0.01 Hz to 100 kHz with a signal amplitude of 5 mV. Galvanostatic charge/discharge measurements were carried on Neware battery testing equipment (NEWARE, CT-4008 T). The discharge and charge cut-off voltages are 1.0 V and 1.8 V vs. Zn2+/Zn, respectively. The current densities of rate performance were 0.1, 0.3, 0.5, 1, 2, and 5 A g−1, respectively. Additionally, the galvanostatic intermittent titration technique (GITT) was measured on Neware battery testing equipment at controllable current densities. The diffusion coefficient (DGITT) can be calculated by the following expression [35, 36].

$${D}_{GITT}=\frac{4}{\mathrm{\pi \tau }} {\left(\frac{{{\text{m}}}_{{\text{B}}}{{\text{V}}}_{{\text{M}}}}{{{\text{M}}}_{{\text{B}}}{\text{S}}}\right)}^{2}{\left(\frac{{\Delta {\text{E}}}_{{\text{s}}}}{{\Delta {\text{E}}}_{{\text{t}}}}\right)}^{2}$$

where τ represents the constant current pulse time (s). MB (g mol−1), VM (cm3 mol−1), and mB (g) are the molar mass, the molar volume, and the mass of the active materials. S (cm2) is the contact area between the electrolyte and the electrode. ΔEt (V) and ΔEs (V) represent the change of battery voltage and the changes in quasi-balanced voltage, respectively. It should be noted that all specific capacities and energy densities are calculated based on the mass of the active materials.

Results and discussion

Characterization of structure and morphology

The synthesis process of the active materials in this study is schematically shown in Fig. 1a We first prepared 1D α-MnO2 nanotubes through a one-step hydrothermal method. Subsequently, α-MnO2@LMO was prepared by in situ growth of LaxMn1-xO2-δ on the surface of α-MnO2 nanotubes using hydrothermal method. The crystallography of multiple electrode materials was studied using XRD, as shown in Fig. 1b and Fig. 1c. As observed in XRD spectrum, the product obtained in the first step was dominated by α-MnO2 phases, and XRD analysis indicates that two strong peaks at 12.7°, 18.1°, and 37.6° matched well with the (110) planes, (200) planes, and the (121) planes of α-MnO2 (JCPDS#72–1982), respectively (Fig. 1b). The XRD patterns show that the phase composition of α-MnO2@LMO is still α-MnO2 phases; however, the diffraction peak of α-MnO2@LMO shifted towards to the higher diffraction angles compared with the α-MnO2 sample. According to Bragg’s equation, the angle increases, and the cell parameters decrease. These results indicate that the lattice of the α-MnO2 core was compressed, thus being beneficial for electron transfer in the reaction process [37]. The SEM images of α-MnO2 and α-MnO2@LMO are displayed in Fig. 1d and Fig. 1e. As is shown in Fig. 1d, the high magnification SEM image of α-MnO2 clearly exhibit the typical 1D nanotube structure. By contrast, Fig. 1e and 1f shows the uniform growth of a layer of LaxMn1-xO2-δ nanosheets on the surface of α-MnO2 nanotubes, showing the core–shell structure of α-MnO2@LMO. This indicates that LaxMnyO2 was successfully loaded onto the α-MnO2 surface. This corresponds to the XRD results. The EDS spectrum demonstrated the uniform distribution of La, Mn, and O elements in the LaxMn1-xO2-δ nanosheets (Fig. S1a). The TEM image in Fig. S1b proves that LMO nanosheets uniformly distributed on the surface of α-MnO2 nanotubes. The HRTEM image in Fig. 1g shows that the lattice spacings of ∼0.18 nm and ∼0.26 nm correspond to the (-114) planes and the (200) planes of δ-MnO2, respectively [38].

Fig. 1
figure 1figure 1

a Schematic diagram of the preparation processes and structure of α-MnO2@LMO. b, c X-ray diffractometer (XRD) spectrum of α-MnO2 and α-MnO2@LMO. d FESEM image of α-MnO2. e FESEM image of α-MnO2@LMO. f, g HRTEM of α-MnO2@LMO. h XPS wide spectrum of the α-MnO2@LMO. i La 3d spectrum. j Mn 2p spectrum. k O 1 s spectrum

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X-ray photoelectron spectroscopy (XPS) was performed to assess the surface chemical state of α-MnO2@LMO. The full spectrum of the prepared α-MnO2@LMO sample is shown in Fig. 1 h, confirming the presence of the elements La, Mn, and O. The high-resolution La 3d spectrum of the sample is shown in Fig. 1i. There are two satellite peaks at binding energies 838.53 and 855.3 eV which are usually reported for the La 3d [39]. And two main peaks at 835.3 eV and 852 eV, which respectively correspond to the La 3d5/2 and La 3d3/2, indicating the existence of La3+ [40]. The high-resolution Mn 2p spectrum of the sample is shown in Fig. 1j. The Fig. 1j exhibits characteristic spin orbit peaks of Mn 2p3/2 and Mn 2p1/2 at 642.1 eV and 653.8 eV, respectively, as well as spin energy difference of 11.7 eV, indicating the existence of Mn4+ [41, 42]. In the Fig. 1k, the O 1 s single peak of α-MnO2@LMO can be deconvoluted into three subpeaks, showing lattice oxygen (OL) at 529.7 eV, oxygen deficiency (Od) at 531.2 eV, and the structural or physically absorbed water (Ow) at 533.1 eV [43].

Electrochemical performance and kinetics investigation

In this study, we controlled the content of LMO by changing the feeding mass ratio for secondary hydrothermal. We recorded the α-MnO2@LMO with different feeding mass ratio as α-MnO2@LMO (10:1), α-MnO2@LMO (5:1), α-MnO2@LMO (2:1), and α-MnO2@LMO (1:1), respectively (Table S1). we used 2 M ZnSO4 and 0.1 M MnSO4 as the electrolyte and assembled α-MnO2@LMO with different mass ratio into batteries for electrochemical performance test. As shown in Fig. S2, after 100 cycles at a current density of 0.3 A g−1, the battery exhibited the best discharge capacity and cycle stability with the α-MnO2@LMO (2:1). Therefore, we adopted α-MnO2@LMO (2:1) as the separator all through our study. In view of this, α-MnO2 or α-MnO2@LMO was applied as the cathode to investigate the electrochemical behaviors in AZIBs. In order to further characterize the electrochemical excellence of α-MnO2@LMO, we have prepared LaxMn1-xO2-δ(LMO) without combining α-MnO2 in the same preparation steps. And it was performed the charging circulation performance test under the current density of 0.3A g−1 and 1 A g−1, respectively. The CV curves were first conducted from the potential range of 1.0 to 1.8 V (vs. Zn/Zn2+) at a scan rate of 0.1 mV s−1, as in Fig. 2a. Figure 2a presents the comparative CV curves of the α-MnO2@LMO samples. By comparison, the α-MnO2@LMO electrode displays higher redox peak currents densities than that of the α-MnO2 electrode (Fig. S3), clearly revealing that the electrochemical reactivity of the α-MnO2@LMO electrode was significantly improved after formation of α-MnO2@LMO core–shell structure. The obvious cathodic peaks located at 1.39 V and 1.28 V were attributed to the intercalation of H+ and Zn2+ along with the reduction of high valence Mn to lower valence states [44]. The anodic peaks at 1.56 V and 1.60 V corresponded to the cations extraction process [45]. Figure 2b shows a typical electrostatic charge–discharge (GCD) curve for the first 100 cycles at 0.3 A g−1. Relative to the initial α-MnO2 and LMO, the core–shell material α-MnO2@ LMO requires an activation process and has a stable mass specific capacity of 240 mAh g−1, which may be related to the lamellar structure (LMO) in the surface coating of α-MnO2 [46]. Figure 2c and 2d show the charging/discharging curves of the first 100 cycles at 0.3A g−1 current density, and it can be seen that the α-MnO2@LMO//Zn cell has better capacity retention and stable H+ and Zn2+ embedding platform. Figure S4 shows the α-MnO2@LMO//Zn battery had large H+ and Zn2+ reaction contribution compared with α-MnO2//Zn battery, which was consistent with the enhanced current density in CV curves. The rate performances of α-MnO2 electrode and α-MnO2@LMO electrode at current densities of 0.1, 0.3, 0.5, 1, 2, and 5 A g−1 are presented in Fig. 2e. The excellent rate capability was associated with fast ion diffusion kinetics in the crystal. The GCD curves of α-MnO2@LMO//Zn batteries at different current densities are shown in Fig. 2f. When the current density was restored from 5 to 0.1 A g−1, the discharge capacity still reached 225 mAh g−1, displaying that the outstanding rate performance of α-MnO2@LMO electrode was owing to the formation of α-MnO2@LMO core–shell structure, which enhances the conductivity and diffusion kinetics of the active material. The cycling performance of α-MnO2 and α-MnO2@LMO was investigated for 300 cycles at 0.3 A g−1, respectively (Fig. S5). The α-MnO2 battery possesses a lower capacity retention (63%) of the specific capacity after 100 cycles, while that of α-MnO2@LMO battery is 220 mAh g−1 with capacity retention rate of up to 92% after 300 cycles. The long-term cycling stability performance of all samples at a high current density of 1 A g−1 has also been evaluated, as in Fig. 2g. It can be seen that α-MnO2@LMO battery displays a relatively stable and reversible discharging capacity of 115 mAh g−1 even after 1500 cycles. Additionally, a capacity retention of 90% was maintained. However, the specific capacity and capacity retention of α-MnO2 battery after 1500 cycles are only 50 mAh g−1 and 20%, respectively. The comparison of electrochemical performance shows that α-MnO2@LMO battery has significant advantages compared with those reported in literature (Table. S1). These results indicate that LaxMn1-xO2-δ on the surface of α-MnO2 nanotubes stabilizes the structure of α-MnO2 and inhibits the dissolution of Mn4+ ions.

Fig. 2
figure 2

Electrochemical performance of α-MnO2//Zn, α-MnO2@LMO//Zn, and LMO//Zn batteries in 2 M ZnSO4 + 0.1 M MnSO4 electrolyte. a α-MnO2@LMO//Zn battery CV curves at 0.1 mV s −1. b Cycling performance at 0.3 A g−1. c, d GCD curves of different cycles at 0.3 A g−1. e Rate performance from 0.1 to 5 A g−1. f GCD curves at different current densities of α-MnO2@LMO//Zn battery. g Long-term cycling performance at 1 A g−1

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To further explore the kinetics behaviors of α-MnO2 and α-MnO2@LMO electrode, CV curves were recorded at different scan rates (0.1 ~ 1 mV s−1) to analyze the energy storage behavior (Fig. 3a and S6). The results of Fig. 3a and S6 indicate that as the scanning rate increases, the CV profiles of α-MnO2 and α-MnO2@LMO electrode both maintain similar shapes, indicating good reversibility [47]. Generally, the capacity contribution of an electrode is composed of surface induced pseudo-capacitance and diffusion controlled battery capacity [48]. The electrochemical kinetic process can be analyzed by the following equation:

$$i=a{v}^{b}$$
(1)

where there is a power-law relationship between the peak current i and scanning rate v. The a and b represent adjustable parameters. The logarithms on both sides of Eq. (1) can be taken as Eq. (2):

Fig. 3
figure 3

Kinetic study of α-MnO2@LMO//Zn and α-MnO2//Zn batteries. a CV curves of α-MnO2@LMO//Zn batteries at different scan rates. b log (i) versus log (ν) plots at four peaks of the α-MnO2@LMO electrode. c Corresponding percent of capacitive contribution of the α-MnO2@LMO electrodes. d The EIS spectra before cycles. e GITT curves of α-MnO2@LMO//Zn. f Ion diffusion coefficients of two materials

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$${\text{log}}\left(i\right)=blog\left(v\right)+{\text{log}}(a)$$
(2)

In general, the variation range of b value is from 0.5 to 1. When the value of b approaches 0.5, the main kinetic process is controlled by ion diffusion, while b value close to 1.0 indicates the surface capacitance control process [34]. Figure 3b is the relationship between log i and log ν for α-MnO2@LMO//Zn batteries. And linear fitting of log i and log ν in Eq. (2) can obtain the value of b. Based on this, the b values calculated are 0.82 (peak 1), 0.53 (peak 2), 0.79 (peak 3), and 0.66 (peak 4), respectively, showing that the Zn storage behavior is influenced by the synergistic control of ion diffusion and capacitance contribution. Subsequently, we quantified the contribution rate of the pseudocapacitance using Eq. (3):

$$i\left(v\right)={k}_{1}v+{k}_{2}{v}^{1/2}$$
(3)

where k1ν and k2ν refer to the capacitive contribution and the diffusion-controlled contribution, respectively. The capacitance contribution value gradually increases with the scanning rate increases in Fig. 3c. From the fitting results, the higher capacitance contribution accelerates the electrochemical reaction kinetics of the electrode, resulting in superior rate performance. The above results indicate an improved kinetics of Zn2+ intercalation/deintercalation for α-MnO2@LMO electrode [49], which may be due to its unique core–shell structure provide additional active sites.

The EIS were applied to estimate the transfer process of the charge before cycles, as shown in Fig. 3d. The semicircle diameter of α-MnO2@LMO electrode is obviously lower than that of α-MnO2 electrode, showing that α-MnO2@LMO electrode possess faster charge transfer ability and better conductivity. From the electrochemical impedance spectroscopy (EIS) of MnO2@LMO//Zn batteries after 200 cycles are shown in the Fig. S7, showing that the charge transfer impedance of the cells decreased during the cycling test, which suggests α-MnO2@LMO structure with a small polarization during the electrochemical reaction.

The Zn2+ ion diffusion coefficients were calculated using the galvanostatic intermittent titration technique (GITT) for further evaluating the reaction kinetics of α-MnO2//Zn and α-MnO2@LMO//Zn batteries. GITT result is obtained by discharging or charging for 2 min at a current density of 0.3 A g−1 in the second cycle and then by relaxation for 2 h to achieve voltage balance. The above operation was repeated for the full voltage window. The gradual change of the potential in Fig. 3e and Fig. S8 is considered to ionic diffusion, while the sudden change is attributed to the ohmic resistance and the charge transfer [50]. The corresponding ion diffusion coefficient Dion is calculated according to the Eq. (4) [51, 52]:

$${{\varvec{D}}}_{{\varvec{i}}{\varvec{o}}{\varvec{n}}}=\frac{4}{\mathrm{\pi \tau }} {(\frac{{{\varvec{n}}}_{{\varvec{B}}}{{\varvec{V}}}_{{\varvec{M}}}}{{\varvec{S}}})}^{2}{(\frac{{\Delta {\varvec{E}}}_{{\varvec{s}}}}{{\Delta {\varvec{E}}}_{\uptau }})}^{2}$$
(4)

where τ is the pulse time, nB is the number of moles, VM is the molar volume of the active material, and S is the surface of the electrode in contact with the electrolyte. ΔEs and ΔEτ represent the voltage change caused by pulse and the voltage change of galvanostatic charge and discharge, respectively. Figure 3f shows that the Dion of α-MnO2@LMO//Zn battery was calculated to be as 10–10 to 10–13 cm2 s−1, which is greater than 10–11 to 10–14 cm2 s−1 for α-MnO2//Zn battery. The enhanced electrochemical reaction kinetics may be the relatively stable core–shell structure of α-MnO2@LMO.

Electrochemical mechanism

In order to expound the high stability of α-MnO2@LMO battery, the evolution of chemical component of α-MnO2@LMO electrode after 200 cycles at 1 A g−1 was characterized by ex situ SEM and XRD (Fig. 4a). The SEM image in Fig. 4a shows the transformation of the electrode into a sheet-like structure due to the insertion/extraction of H+ and Zn2+ ions at 200 cycles of a fully charged α-MnO2@LMO. At the same time, in Fig. 4b, it is found that when the α-MnO2@LMO//Zn cell was fully discharged after 200 cycles, the surface of the cathode structure was covered with a large sheet of material, which is believed to be zinc hydroxide sulfate (ZHS), which can be further supported by the XRD results in Fig. 4c. When fully discharged to 1.0 V at a current density of 1 A g−1, the diffraction peaks occur at about 12.3°, 32.7°, 51.5°, and 58.4°, which are well matched with the ZHS characteristic peaks (JCPDS No.44–0674). Zn4SO4(OH)6·5H2O is produced due to the local increase in OH− concentration caused by the intercalation of H+ in the electrolyte (MnO2 + H+  + e−  ↔ MnOOH) [53, 54], while the ZHS diffraction peaks are significantly weakened or even disappeared in the fully charged state (Fig. 4c). The characteristic peaks at 34.7°, 36.2°, and 62.5° of the α-MnO2@LMO cathode in the fully discharged state in the 200th cycle were well matched with ZnMn2O4 (JCPDS No.19–1459); however, the characteristic peaks of ZnMn2O4 were significantly weakened in the fully charged state, indicating that it had good reversibility.

Fig. 4
figure 4

a FESEM image of the α-MnO2@LMO electrode in the fully charged state after 200 cycles at 1 A g−1. b FESEM image of the α-MnO2@LMO electrode in the fully discharged state after 200 cycles at 1 A g−1. c XRD spectra of the α-MnO2@LMO electrode in the fully charged/discharged state after 200 cycles at 1 A g−1

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Conclusion

In conclusion, a unique α-MnO2 nanotubes@LaxMnyO2 nanosheets core–shell hierarchical nanostructure has been successfully constructed by a facile and effective two-step hydrothermal reaction. Benefiting from the synergistic effect of the core-shells nanostructure, the constructed hierarchical α-MnO2@LMO core–shell nanostructures exhibit good rate capacity and superior cycling stability as electrodes for rechargeable AZIBs. The α-MnO2@LMO has excellent stable cycling performance with only 2% capacity degradation after 100 cycles. Moreover, the α-MnO2@LMO cathode delivers a specific capacity of 115 mAh g−1 with 90% of the initial capacity after 1500 cycles at 1 A g−1. The excellent electrochemical performance of the α-MnO2@LMO cathode is attributed to the unique core–shell structure and synergistic effects of Mn-based materials with two different dimensions. Additionally, the analysis of the reaction mechanism proves the co-insertion/extraction reaction process of H+ and Zn2+ and the stable phase structure. This study provides a potential solution for designing nanomaterials with unique core–shell to enhance the use of Mn-based materials for AZIBs.