Received Date:
22 April 2024 Accepted Date:
20 June 2024 Revised Date:
15 June 2024 Available Online:
15 July 2025
Abstract:
Aqueous alkaline zinc batteries have received widespread attention owing to its higher electrode potential and faster reaction kinetics compared to in mild aqueous electrolyte. However, Zn metal anode in alkaline electrolyte usually suffers more severe corrosion, passivation, and hydrogen evolution reaction. Herein, an interface chemical regulation strategy employs to in-situ construct a Zn-Sn alloy layer during cycling. The K2[Sn(OH)6] has been introduced into the electrolyte as the deposition overpotential of Zn and Sn in alkaline electrolyte is approximate leading to their simultaneously plating. The Zn-Sn alloy layer not only prevents Zn anode corrosion and suppresses the dendrite growth but also promotes the reaction kinetics. Therefore, the ZnZn cell exhibits a long life of 400 h in alkaline electrolyte about 20 times of that in without K2[Sn(OH)6] electrolyte. Moreover, the NNCP@PQxZn full cell displays a superior cycle performance of 4000 cycles with 93% capacity retention at 2 A/g.
With the development of society, renewable energy storage system with high safety and reliability in large-scale application received intensely attentions [1-3]. The rechargeable aqueous batteries have the potential as candidates for next generation energy storage owing to the high ionic conductivity, low-cost and environmental-friendly [4-6]. Among them, the aqueous Zn batteries with alkaline electrolyte exhibit promising potential for their high theoretical capacity (820 mAh/g) and low redox potential (−1.26 V vs. SHE) [7-9]. However, the Zn metal anode usually suffers from severe hydrogen evolution, passivation and corrosion during continuously charging/discharging process [10-12], especially in alkaline electrolytes, as the redox potential of Zn is much lower than that of hydrogen evolution [13-16]. Therefore, regulating the Zn interface [17,18] which can protect Zn anode from dendrite growth and corrosion is of great significance for prolonging the life of alkaline aqueous batteries.
Many efforts have been made to solve it, such as surface coating of Zn anode [19-21], electrolyte optimization [22-24] and quasi-solid gel electrolyte [25,26]. Among them, introducing additives into electrolyte is one of the feasible ways due to its ease and effectiveness. Besides, tin (Sn) has high hydrogen evolution overpotential, corrosion resistance and non-toxicity [27,28]. On one hand, the Sn has stronger adsorption to Zn, which can reduce the nucleation barrier of Zn and promote Zn uniform deposition. On the other hand, Sn and Zn have similar redox potential, which can in-situ construct a Zn-Sn alloy on the surface of Zn anode during cycling. What is more, the alloy material usually has a high conductivity, which is conductive to accelerating the interface ion transfer kinetics, thereby promoting uniform deposition and avoiding dendrite growth [29]. For example, Peng et al. have proved that the Zn-Sn alloy electrodes through powder sintering technology have corrosion resistance in alkaline electrolytes [30]. Wang et al. proved that Zn-Sn alloy inhibited the hydrogen evolution and dendrite growth by doping the tin element on a 3D carbon cloth [31]. Therefore, in-situ constructing a Zn-Sn alloy layer based on interface chemical regulation will be an effective way to enhance the cycling life of Zn anode.
Herein, the Zn and Sn are co-deposited forming a Zn-Sn alloy layer on the surface of Zn anode by introducing K2[Sn(OH)6] into the electrolyte due to the closed redox potential of Zn and Sn. Sn has strong adsorption force for Zn, which can form many nucleation sites of Zn and contribute to the co-deposition of Zn and Sn. The high overpotential of hydrogen evolution and anti-corrosion of Sn in the alkaline electrolyte promote uniform plating of Zn and greatly inhibit the hydrogen evolution. As a result, the Zn||Zn cell achieves a stable long lifespan of 400 h in the alkaline aqueous electrolytes at 1 mA/cm2 and 1 mAh/cm2. The Zn||Zn cell still maintains a good cycling performance even at −25 ℃. Therefore, the full cell of N—NCP@PQx||Zn assembled by coupling the Zn with N—NCP@PQx cathode exhibits a long cycling performance of 4000 cycles.
Here, 200 mmol/L K2[Sn(OH)6] is dissolved into 4 mol/L KOH + 0.04 mol/L Zn(CH3COO)2 electrolyte to provide the Sn sources. In order to distinguish two kinds electrolyte, the pure 4 mol/L KOH + 0.04 mol/L Zn(CH3COO)2 electrolyte is denoted as without K2[Sn(OH)6] electrolyte, and the 200 mmol/L K2[Sn(OH)6] + 4 mol/L KOH + 0.04 mol/L Zn(CH3COO)2 electrolyte is denoted as with K2[Sn(OH)6] electrolyte. As depicted in Fig. 1a, the XRD pattern of Zn electrode after cycling 20 h is used to confirm the existence of Zn-Sn alloy layer. The peaks at 36.29°, 38.99° and 43.23° are indexed to be (002), (100) and (101) of Zn species (PDF #99–0110) [32,33]. Other newly emerged diffraction peaks in with K2[Sn(OH)6] electrolyte correspond to Sn (PDF #89–4898), especially at 30.6° and 32° (Fig. 1b) [34-36]. While in without K2[Sn(OH)6] electrolyte, no peaks of Sn can be detected. Significantly, the diffraction peaks of Sn are observed on both stripped side and plated side of Zn electrode (Fig. S1 in Supporting information), demonstrating that the Sn will plate onto the Zn electrode and protect the Zn electrode persistently. Raman spectrum (Fig. 1c) on the surface of Zn electrode after cycling 20 h shows the Sn-O stretching bands between 450 cm−1 and 800 cm−1 [37], proving the Sn deposition on the surface. The existence of O element is mainly due to that the Sn suffers surface oxidation during long-term cycling. The XPS results of Zn electrode after cycling 20 h in Zn||Zn cell also support the conclusion, as shown in Figs. 1d-i. The peaks located at 1022 and 1044 eV are ascribed to the Zn 2p3/2 and Zn 2p1/2 [38-40]. The Zn specie is still present even after etching 10 nm and 20 nm, which demonstrates Zn is deposited on the surface of Zn anode during plating. Additionally, the binding energies of 484.8, 493.3 and 499.4 eV are fitted to Sn 3d5/2, Sn 3d3/2 and Sn 3d1/2 [30]. The peaks at 486.5 eV and 496.6 eV are Sn-O bond. Obviously, the Sn is deposited together during Zn plating confirmed by etching different depth. Thus, it is concluded that the Zn and Sn will plate together at initial. The existence of Sn-O in O 1s spectrum (Fig. S2 in Supporting information) [41] is mainly due to the surface oxidation during measurement. All these above-mentioned results manifest the formation of Zn-Sn alloy.
Figure 1
Figure 1.
(a) XRD patterns of Zn electrode cycling 20 h in with K2[Sn(OH)6] electrolyte. (b) XRD patterns of Zn electrode between 25° to 35°. (c) Raman spectra of Zn electrode surface in different electrolytes. After cycling 20 h the electrodes with K2[Sn(OH)6] additive of XPS spectra of Zn 2p: (d) The surface; (e) After etching 10 nm; (f) After etching 20 nm. After cycling 20 h the electrodes with K2[Sn(OH)6] additive of XPS spectra of Sn 3d: (g) The surface; (h) After etching 10 nm; (i) After etching 20 nm.
As depicted in Figs. 2a and b, the in-situ optical microscopy was used to detect the plating behaviors of Zn electrode. A large number of bubbles and Zn dendrites appear on the Zn electrode surface after plating 5 min at a high current density of 10 mA/cm2 in without K2[Sn(OH)6] electrolyte, which is became more severe after plating 20 min. Compared that without K2[Sn(OH)6] electrolyte, the surface of Zn electrode is uniform and dense without dendrites and bubbles from beginning to ending during plating. The results further prove the effectiveness of Zn-Sn alloy layer in inhibiting dendrite growth and hydrogen evolution. The scanning electron microscopy (SEM) illustrates the morphological evolutions of Zn surface after plating/stripping at different current densities (1, 5, and 10 mA/cm2) and 1 mAh/cm2. As displayed in Fig. S3 (Supporting information), the Zn electrode in without K2[Sn(OH)6] electrolyte presents uneven morphology. With the current density further increased to 5 and 10 mA/cm2, a large number of flake-like dendrites with irregular shape cover the whole surface of Zn electrode. In comparison, the surface of Zn electrode is more even and smooth after cycling in with K2[Sn(OH)6] electrolyte. These results imply that the formation of Zn-Sn alloy layer has effect on inducing Zn uniform plating avoiding dendrite growth. In addition, as shown in Fig. 2c, the surface of Zn electrode after cycling 20 h in without K2[Sn(OH)6] electrolyte suffers severe corrosion covered with pothole. In contrast, the surface of Zn electrode after cycling 20 h in with K2[Sn(OH)6] electrolyte (Fig. 2f) is dense and uniform, even after cycling 40 h (Fig. S4 in Supporting information).
Figure 2
Figure 2.In situ optical microscopy images of Zn deposition during cycling: (a) In without K2[Sn(OH)6] electrolyte; (b) In with K2[Sn(OH)6] electrolyte. SEM images of Zn electrode in without K2[Sn(OH)6] electrolyte: (c) On the surface; (d) At the cross-section. SEM images of the surface of Zn electrode in with K2[Sn(OH)6] electrolyte: (f) On the surface; (g) At the cross-section. AFM images after cycling 20 h: (e) In without K2[Sn(OH)6] electrolyte; (h) In with K2[Sn(OH)6] electrolyte. (i-k) EDS elemental mapping of the Zn electrode after cycling 20 h.
Remarkably, the cross-sections of Zn electrode after cycling 20 h in Figs. 2d and g further reveal that the Zn electrode goes through a severe corrosion in without K2[Sn(OH)6] electrolyte. The morphology of Zn electrode after cycling 20 h was further studied by atomic force microscopy (AFM). It is obvious that the surface of Zn electrode in with K2[Sn(OH)6] electrolyte (the average surface roughness of 14.0 nm) is much smoother and more even than that in without K2[Sn(OH)6] electrolyte (the average surface roughness of 44.4 nm) after cycling 20 h (Figs. 2e and h, Fig. S5 in Supporting information). These results further demonstrate that Zn-Sn alloy layer inhibits corrosion and suppresses dendrite formation. TEM image in Fig. S6 (Supporting information) shows that the lattice spacing of the metal Sn phase ((200) plane) is 0.29 nm, and the metallic Zn phase is observed with a lattice spacing of 0.20 nm ((101) plane). The results of the TEM observation demonstrate the formation of Zn-Sn alloy. The element mapping images (EDS) in Figs. 2i-k show that the Zn and Sn element are homogeneously dispersed on the whole surface. EDS in Fig. S7 (Supporting information) also confirms the even distribution of Zn-Sn alloy layer at the cross-section, further indicating the co-deposition of Zn and Sn to form an alloy layer.
The linear sweep voltammetry (LSV) of Zn||Zn cell was performed to detect the electrochemical stability windows of different electrolytes (Fig. 3a). The lower potential (−0.273 eV) of Zn electrode in with K2[Sn(OH)6] electrolyte reveals that K2[Sn(OH)6] as an electrolyte additive has an effect on suppressing hydrogen evolution reaction. Tafel polarization curves of Zn||Zn symmetric cell in Fig. 3b show that the corrosion potential in with K2[Sn(OH)6] electrolyte is more positive than that in without K2[Sn(OH)6] electrolyte, indicating the enhancing corrosion resistance of Zn electrode. Additionally, as shown in Fig. 3c, the current density in without K2[Sn(OH)6] electrolyte increases continuously within 500 s indicating a 2D diffusion process occurred. In comparison, after introducing K2[Sn(OH)6] additive, the current density is increased in the first 100 s and then stabilized on a constant value, illustrating that the Zn-Sn alloy will inhibit 2D diffusion and induce the Zn uniform deposition. Comparing electrochemical impedance spectroscopy (EIS) in the temperature range of 0−60 ℃, it is found that the Zn||Zn symmetrical cell resistance decreases after the addition of K2[Sn(OH)6] (Fig. S8 in Supporting information). This indicates that the formation of the Zn-Sn alloy layer does not hinder ions conversion between the Zn electrode and the electrolyte. In addition, the charge transfer activation energy (Ea) can be used to evaluate electrode dynamics. As shown in Fig. S9 (Supporting information), the Ea (37.14 kJ/mol) with 200 mmol/L K2[Sn(OH)6] additive is significantly smaller than that without K2[Sn(OH)6] additive (44.78 kJ/mol). This indicates that the Zn-Sn alloy layer is conducive to the plating/stripping kinetics of Zn2+. The schematic illustrates that the addition of K2[Sn(OH)6] plays a crucial role in inhibiting corrosion and dendrites growth in alkaline electrolytes. The surface of the Zn electrode in without K2[Sn(OH)6] electrolyte produces many by-products and dendrites, and Zn electrode will be corroded (Fig. 3d). While the Zn electrode surface in with 200 mmol/L K2[Sn(OH)6] electrolyte in Fig. 3e will form a Zn-Sn alloy layer to prevent Zn corrosion. The reason why is that Zn and Sn will be co-deposited due to the similar reduction potential.
Figure 3
Figure 3.
(a) LSV curves of Zn||Zn cells; (b) Tafel plots of Zn electrode; (c) Chronoamperometric curves; Schematic diagram of morphology evolution of Zn deposition after long cycles. (d) In without K2[Sn(OH)6] electrolyte; (e) In with K2[Sn(OH)6] electrolyte.
Then, the electrochemical performance was conducted to detect the effectiveness of K2[Sn(OH)6] additive. First of all, the K2[Sn(OH)6] additive greatly enhances the cycling performance (Fig. 4a). Without K2[Sn(OH)6] additive, the Zn||Zn symmetric cell fails after cycling only 23 h, while the cell in saturated K2[Sn(OH)6] electrolyte exhibits a cycle life of 60 h. With the concentration of K2[Sn(OH)6] additive of 200 mmol/L, the cycling life is increased to 400 h, after which overpotential arises due to side reaction. It illustrates that K2[Sn(OH)6] additive has significant effect on enhancing the cycle life of Zn electrode in alkaline electrolyte. Besides, with the current density and capacity increasing to 10 mA/cm2 and 5 mAh/cm2, the cell in without K2[Sn(OH)6] electrolyte is failed after cycling 13 h. In contrast, the Zn||Zn cell in with 200 mmol/L K2[Sn(OH)6] electrolyte displays excellent cycling stability reaching 300 h (Fig. 4b). Moreover, the rate performance of Zn electrode at different current densities with the capacity of 1 mAh/cm2 (Fig. 4c), show that the cell in with K2[Sn(OH)6] electrolyte exhibits superior rate performance than that of in without K2[Sn(OH)6] electrolyte. The overpotential of the cell is slightly increased as the current densities increases (Fig. 4d), and the overpotential in with K2[Sn(OH)6] electrolyte is only 60 mV at 10 mA/cm2 and 1 mAh/cm2. However, the overpotential of the cell in Fig. S10 (Supporting information) is as large as several times than its, especially in high current density of 10 mA/cm2, suggesting the excellent reaction kinetics even under high current densities originating from the Zn-Sn alloy. Besides, even at 20 mA/cm2 and 5 mAh/cm2, the Zn||Zn cell can still maintain a long cycling life of 165 h (Fig. 4e). What is more, the fast reaction kinetics of Zn-Sn alloy endows the Zn||Zn cell with enhancing low temperature performance. At −25 ℃, the Zn||Zn cell exhibits a longer lifespan of 125 h in with K2[Sn(OH)6] electrolyte, as displayed in Fig. 4f. But the Zn||Zn cell in without K2[Sn(OH)6] electrolyte exhibits a much higher asymmetric potential and "died" soon. Therefore, the Zn-Sn alloy not only inhibits the corrosion and side reactions but also promotes the reaction kinetics.
Figure 4
Figure 4.
Cycling performance of Zn||Zn symmetric cell with different concentrations of K2[Sn(OH)6]. (a) At 1 mA/cm2 for 1 mAh/cm2; (b) At 10 mA/cm2 for 5 mAh/cm2; (c) Rate performance; (d) Capacity-voltage curves in with 200 mmol/L K2[Sn(OH)6] electrolyte; (e) At 20 mA/cm2 for 5 mAh/cm2; (f) At −25 ℃ at 1 mA/cm2 for 1 mAh/cm2.
To further verify the effectiveness of the Zn-Sn alloy layer in practice, the full cell of N—NCP@PQx||Zn is assembled by coupling Zn anode with N—NCP@PQx cathode using K2[Sn(OH)6] as electrolyte (Fig. 5a). The CV curves of N—NCP@PQx||Zn cell in Fig. 5b exhibit that the shapes of the CV curves remain well with increasing scanning rate in terms of electrode polarizations, manifesting that this N—NCP@PQx||Zn cell has excellent stability and reversibility. Thus, it is predictable that the N—NCP@PQx||Zn cell possesses excellent rate performance. The potential platform is well remained (Fig. 5c) demonstrating the favorable reversibility and rate performance. As shown in Fig. 5d, the specific capacitances of N—NCP@PQx||Zn cell are as high as 366 mAh/g at 2 A/g and 323 mAh/g even at 10 A/g. Besides the high specific capacity, the N—NCP@PQx||Zn cell also displays a long-cycling life, and it retains a high specific capacity of 222 mAh/g after 4000 cycles at 2 A/g (~93% of the initial capacity), as delivered in Fig. 5e. All these results indicate that the formation of Zn-Sn alloy layer can effectively prevent Zn corrosion and dendrite growth.
Figure 5
Figure 5.
The electrochemical performance of N—NCP@PQx||Zn cell in with K2[Sn(OH)6] electrolyte. (a) The schematic illustration of the full cell; (b) CV curves; (c) Rate performance; (d) The charge/discharge profiles; (e) Cycling performance.
In summary, a Zn-Sn alloy layer formed on the surface of Zn metal electrode after introducing K2[Sn(OH)6] into electrolyte as the overpotential of Zn and Sn is similar in electrolyte. On one hand, the Zn-Sn alloy layer covering on the surface of the Zn electrode can effectively avoid corrosion and dendrite growth. On the other hand, the Sn can decrease the nucleation energy barrier and promote the reaction kinetics. As a result, the cycle stability of the cell in with K2[Sn(OH)6] electrolyte reaches 400 h at 1 mA/cm2 and 1 mAh/cm2, which is about 20 times of in without K2[Sn(OH)6] electrolyte. The Zn||Zn symmetric cell also displays excellent rate performance and a low temperature resistance in with K2[Sn(OH)6] electrolyte owing to the promoting reaction kinetics. The assembled N—NCP@PQx||Zn full cell exhibits excellent long lifespan with capacity retention 93% after 4000 cycles at 2 A/g.
Declaration of competing interest
We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.
This work was supported by Joint Funds of the National Natural Science Foundation of China (No. U22A20140), University of Jinan Disciplinary Cross-Convergence Construction Project 2023 (No. XKJC-202309), Jinan City-School Integration Development Strategy Project (No. JNSX2023015), Independent Cultivation Program of Innovation Team of Ji'nan City (No. 202333042) and the Youth Innovation Group Plan of Shandong Province (No. 2022KJ095). Special thanks to the Optical microscopy (Yuescope, YM710R).
Supplementary materials
Supplementary material associated with this article can be found, in the online version, at doi: 10.1016/j.cclet.2024.110152.
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Figure 1
(a) XRD patterns of Zn electrode cycling 20 h in with K2[Sn(OH)6] electrolyte. (b) XRD patterns of Zn electrode between 25° to 35°. (c) Raman spectra of Zn electrode surface in different electrolytes. After cycling 20 h the electrodes with K2[Sn(OH)6] additive of XPS spectra of Zn 2p: (d) The surface; (e) After etching 10 nm; (f) After etching 20 nm. After cycling 20 h the electrodes with K2[Sn(OH)6] additive of XPS spectra of Sn 3d: (g) The surface; (h) After etching 10 nm; (i) After etching 20 nm.
Figure 2In situ optical microscopy images of Zn deposition during cycling: (a) In without K2[Sn(OH)6] electrolyte; (b) In with K2[Sn(OH)6] electrolyte. SEM images of Zn electrode in without K2[Sn(OH)6] electrolyte: (c) On the surface; (d) At the cross-section. SEM images of the surface of Zn electrode in with K2[Sn(OH)6] electrolyte: (f) On the surface; (g) At the cross-section. AFM images after cycling 20 h: (e) In without K2[Sn(OH)6] electrolyte; (h) In with K2[Sn(OH)6] electrolyte. (i-k) EDS elemental mapping of the Zn electrode after cycling 20 h.
Figure 3
(a) LSV curves of Zn||Zn cells; (b) Tafel plots of Zn electrode; (c) Chronoamperometric curves; Schematic diagram of morphology evolution of Zn deposition after long cycles. (d) In without K2[Sn(OH)6] electrolyte; (e) In with K2[Sn(OH)6] electrolyte.
Figure 4
Cycling performance of Zn||Zn symmetric cell with different concentrations of K2[Sn(OH)6]. (a) At 1 mA/cm2 for 1 mAh/cm2; (b) At 10 mA/cm2 for 5 mAh/cm2; (c) Rate performance; (d) Capacity-voltage curves in with 200 mmol/L K2[Sn(OH)6] electrolyte; (e) At 20 mA/cm2 for 5 mAh/cm2; (f) At −25 ℃ at 1 mA/cm2 for 1 mAh/cm2.
Figure 5
The electrochemical performance of N—NCP@PQx||Zn cell in with K2[Sn(OH)6] electrolyte. (a) The schematic illustration of the full cell; (b) CV curves; (c) Rate performance; (d) The charge/discharge profiles; (e) Cycling performance.
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