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Adv. Funct. Mater.｜Spray-printed MXene to construct Janus separator for accelerating zinc ion flux to stabilize zinc metal anode
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Detailed
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Research abstract
In recent years, aqueous zinc-ion batteries have received extensive attention due to their low cost and high safety. Meanwhile, zinc has a lower redox potential (–0.76 V vs. hydrogen-labeled electrode) and a higher specific capacity (820 mAh g–1; 5855 mAh cm–3). However, problems such as dendrite growth and corrosion on the negative electrode side of aqueous Zn-ion batteries will reduce the battery cycle performance; when the dendrite growth pierces the separator and touches the counter electrode, the battery will short-circuit.
In order to solve the above problems, the usual strategies include the construction of artificial interface layer, separator modification, design of three-dimensional host, electrolyte modification and alloying treatment. However, few reported works so far start from the nature of zinc dendrite generation, that is, narrowing the rate difference between the zinc ion mass transfer process and the redox Faradaic process. The abundant surface functional groups of Ti3C2Tx MXene are expected to desolvate and accelerate zinc ion diffusion. More importantly, Ti3C2Tx has good electrical conductivity. When the two-dimensional Ti3C2Tx sheet is covered on the surface of the insulating fiber, microscopic dipoles will be generated under external field conditions due to the difference in conductivity, which makes the dielectric constant of the overall fiber material. increase. Due to the Maxwell-Wagner effect, this will lead to a uniform and field-strength electric field in the direction of the zinc ion mass transfer to accelerate the zinc ion migration process, thereby improving the kinetic mismatch between the mass transfer process and the Faraday process on the zinc anode side.
Recently, the team of Professor Sun Jingyu of Soochow University used the spray printing method to uniformly cover the Ti3C2Tx MXene material on one side of a commercial glass fiber separator (GF). By changing the concentration of the MXene ink, a modified separator with tunable dielectric constant was obtained. (MXene-GF). The optimized MXene-GF has a higher dielectric constant than the commercial separator, which helps to construct a uniform built-in electric field through the Maxwell-Wagner effect to accelerate the zinc ion migration process, thereby slowing the zinc dendrite kinetically production. In this study, it was found that with the increase of MXene ink concentration, the dielectric constant of the separator first increased and then decreased. When the MXene ink concentration was 3.0 mg mL–1, the modified separator had the highest dielectric constant. In addition to the enhanced dielectric constant helping to build a uniform positive built-in electric field to accelerate the Zn ion migration, the Zn ion diffusion and desolvation processes were also facilitated by the presence of abundant functional groups on the MXene surface. Correspondingly, the corrosion resistance of the zinc electrode has also been improved. Symmetric cells were assembled using MXene-GF, and cycle lifetimes of 1180 h and 1200 h were obtained at 1 mA cm–2/1 mAh cm–2 and 5 mA cm–2/1 mAh cm–2, respectively. The full cell assembled using MXene-GF can achieve high capacity retention at 5.0 A g–1 cycle.
This work was published online in the internationally renowned journal Advanced Functional Materials (IF 18.808), with the title: Printing-Scalable Ti3C2Tx MXene-Decorated Janus Separator with Expedited Zn2+ Flux toward Stabilized Zn Anodes. Sun Jingyus group of master student Su Yiwen and postdoctoral fellow Liu Bingzhi First author.
Graphical guide
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Figure 1. a) Schematic diagram of the preparation and function of the MXene-GF separator. b) Digital photographs of commercial GF and MXene-GF. Illustration: Printing inks used. c) Schematic diagram of polarized charge distribution in different separators. d) Digital photograph of MXene-GF material with a diameter of 11 cm.
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Figure 2. a) AFM image of Ti3C2Tx MXene nanosheets showing a typical thickness of 2 nm. b) TEM and c) HRTEM images of Ti3C2Tx MXene nanosheets. d) SEM image of MXene-GF. e) High-resolution XPS C 1s spectrum of MXene-GF. f) XRD spectra of MXene-GF and GF. g) Digital photographs showing the contact angles of droplets on GF and MXene-GF. h) Hysteresis loops of GF and MXene-GF.
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Figure 3. a) Cycling performance comparison of symmetric cells based on different MXene-GF separators at 5 mA cm−2/5 mAh cm−2. b) Cycling performance of MXene-GF and GF-based symmetric cells at 1 mA cm−2/1 mAh cm−2. c) Rate performance of symmetric cells based on MXene-GF and GF. SEM images of d) bare Zn and e) protected Zn after 20 cycles at 1 mA cm−2/1 mAh cm−2. f) Coulombic efficiencies of Ti-Zn cells based on different separators at 2 mA cm−2/0.5 mAh cm−2. g) XRD patterns of Zn with and without MXene-GF protection at 1 mA cm−2/1 mAh cm−2 after 20 cycles. h) Tafel curves of symmetric cells based on GF and MXene-GF.
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Figure 4. EIS spectra of a) MXene-GF and b) GF at different temperatures. c) The corresponding fitted Arrhenius curve. d) In situ optical observation of the electrodeposition morphology changes of GF/MXene-GF-equipped zinc flakes at 5 mA cm–2. Scale bar: 100 μm. e) Chronoamperometric curves of MXene-GF at a potential of 10 mV. Inset: corresponding EIS spectra before and after chronoamperometry. COMSOL simulation of electric field distributions for f) GF and g) MXene-GF. h) Galvanostatic cycling performance of GF and MXene-GF-based symmetric cells at 1 mA cm−2/1 mAh cm−2 in a lean electrolyte (0.01 M ZnSO4).
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Figure 5. Electrochemical performance of zinc-ion full cells assembled with MXene-GF separators. a) Schematic diagram of the zinc-ion full cell assembled with GF/MXene-GF separator. b) CV curves at a scan rate of 0.1 mV s−1. c) The CV curves of MXene-GF full cells are provided at different scan rates. d) Fit the linear curve of the b value. e) Rate performance of full cells based on GF and MXene-GF. f) Cycling performance of the full cell for 1000 cycles at 5.0 A g−1. g) The power supply photos of the pouch battery with MXene-GF as separator under different bending states.
Summarize
In this paper, a novel MXene-GF Janus separator was constructed by spray printing. The designed MXene-GF separator endows Zn anode with two unique advantages: i) the dielectric constant of MXene-GF is significantly higher than that of intrinsic GF, which helps to construct a directional built-in electric field via the Maxwell-Wagner effect to accelerate Zn2+ migration; ii) The abundant surface functional groups of MXene help to reduce the desolvation energy, accelerate Zn2+ diffusion and suppress SO42– anion flux, thus facilitating dendrite-free Zn deposition and alleviating the corrosion degree of Zn electrodes. In terms of battery performance, the symmetric battery assembled with MXene-GF achieved a cycle life of 1180 hours at 1 mA cm−2/1 mAh cm−2. Meanwhile, the application of MXene-GF in full cells can achieve good rate and cycle performance. The reported membrane engineering strategy is expected to provide new ideas for the construction of dendrite-free metal anodes.
Literature link
https://doi.org/10.1002/adfm.202204306
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