Preparation method of DNA-chitosan composite modified layer, zinc negative electrode and zinc battery

Abstract

This invention provides a method for preparing a DNA-chitosan composite modified layer, a zinc anode, and a zinc battery, comprising: 1) treating a zinc substrate to be coated; 2) preparing a DNA solution and a chitosan solution separately, adding the DNA solution to the chitosan solution and stirring to composite, followed by static curing and degassing treatment to obtain a DNA-chitosan composite spin-coating solution; the composition is adjustable by adjusting the total concentration of the spin-coating solution and the molar ratio of DNA to chitosan; 3) adding the composite spin-coating solution dropwise to the surface of the zinc substrate to spin-coat a film, and obtaining a zinc anode with a DNA-chitosan composite modified layer on the surface after drying and curing. This invention utilizes the abundant nitrogen-containing bases and phosphate groups in DNA to provide zinc-loving sites, which, in synergy with the film-forming properties and amino coordination of chitosan, guide the uniform deposition of zinc ions, inhibit side reactions such as dendrite formation, hydrogen evolution, and corrosion, and significantly improve the coulombic efficiency and cycle life of aqueous zinc-ion batteries.

Description

Technical Field

[0001] This invention relates to the field of secondary aqueous metal battery technology, specifically to the surface modification of zinc anode in aqueous zinc-ion batteries, and to a method for preparing a DNA-chitosan composite modified layer, a zinc anode, and a zinc battery. Background Technology

[0002] As the global energy landscape accelerates its transition towards low-carbon energy, the development of high-efficiency and high-safety electrochemical energy storage technologies has become an urgent need. While lithium-ion batteries have achieved widespread commercialization in consumer electronics and new energy vehicles, the limited abundance and highly concentrated geographical distribution of lithium in the Earth's crust, coupled with the inherent thermal runaway risk of organic electrolyte systems and the rising cost of raw materials, make it difficult to fully meet the dual requirements of economic efficiency and intrinsic safety for large-scale grid-scale energy storage. Driven by this, aqueous zinc-ion batteries are emerging as a promising alternative: zinc metal possesses both high theoretical specific capacity (820 mAh g / g) and... -1 5855 mAh cm -3 With its low redox potential (−0.76 V vs. SHE), abundant crustal reserves, and mature smelting technology, coupled with the inherent safety characteristics of the non-flammable and non-toxic aqueous electrolyte system, this battery system demonstrates outstanding competitive advantages in large-scale stationary energy storage, flexible wearable electronics, and other application scenarios with stringent safety requirements.

[0003] However, the practical application of aqueous zinc-ion batteries has long been hampered by the complex interfacial thermodynamics and kinetics between the zinc metal anode and the aqueous electrolyte. Unlike the graphite anode in lithium-ion batteries, which can form a relatively stable solid electrolyte interphase (SEI), the zinc anode remains in a thermodynamically metastable state in weakly acidic to neutral aqueous electrolytes, facing a triple-coupling failure mechanism. First, at the deposition kinetics level, the unavoidable micro-roughness of the zinc foil surface causes local differences in electric field intensity, affecting the Zn... 2+First, reduction deposition preferentially occurs at protruding sites where electric field lines converge. This self-reinforcing "tip effect" drives dendrites to continuously extend in a direction perpendicular to the substrate, eventually piercing the separator and causing an internal short circuit in the battery. Simultaneously, some dendrites break off due to root dissolution during repeated deposition / stripping, forming electrochemically inert "dead zinc," causing irreversible loss of the negative electrode active material and continuous capacity decay. Second, at the thermodynamic level, the standard reduction potential of zinc is outside the electrochemical stability window of water. During charge and discharge, the hydrogen evolution reaction (HER) inevitably occurs as a competing parasitic reaction, directly consuming the electrolyte and generating bubbles that block ion transport channels, and causing a sharp increase in the local pH at the negative electrode / electrolyte interface. Third, the aforementioned localized alkalinization environment further induces non-uniform deposition of electronic insulating passivation byproducts such as basic zinc sulfate (Zn4SO4(OH)6·xH2O) and zinc oxide (ZnO) on the negative electrode surface. These byproduct coatings further exacerbate electric field distortion and ion transport blockage, continuously worsening dendrite growth and corrosion processes.

[0004] The dendrite growth, hydrogen evolution corrosion, and passivation mentioned above are not independent failure events, but rather deeply coupled through a positive feedback loop: the non-uniform growth of dendrites continuously exposes fresh, highly active zinc surfaces, accelerating the rates of hydrogen evolution and corrosion; the random accumulation of bubbles generated by hydrogen evolution and passivation products further distorts the surface electric field distribution and ion concentration gradient, providing a driving force for the abnormal nucleation of a new round of dendrites. This cascading degradation mechanism causes a cycle-by-cycle decrease in coulombic efficiency and a continuous increase in battery internal resistance, ultimately leading to premature battery failure. One of the core strategies to break this vicious cycle lies in the systematic functional reconstruction of the zinc anode / electrolyte interface—by introducing an artificial modification layer, a barrier is established at the physical level to prevent water molecules from directly contacting the zinc surface, and at the chemical level, controllable Zn is provided. 2+ Functional sites for transport flux and nucleation behavior, thereby simultaneously achieving a synergistic improvement in dendrite suppression, side reaction containment, and deposition / exfoliation reversibility.

[0005] Based on the aforementioned interface reconstruction approach, researchers have developed several technical routes: Inorganic coatings (metal oxides, carbon-based materials, metal alloy layers, etc.) can provide good mechanical rigidity and electronic / ionic conductivity, but they often rely on high-cost processes such as magnetron sputtering, atomic layer deposition, or high-temperature annealing, and the mechanical mismatch between the brittle coating and the flexible zinc substrate can easily induce cracking during cycling. Synthetic organic polymer coatings (such as polyvinylidene fluoride, polyacrylic acid, etc.) have good film-forming properties, but their limited range of functional groups makes them unsuitable for Zn... 2+The coordination regulation ability of Zn is limited. Against this backdrop, the construction of artificial interface protective layers using natural biomacromolecules has gradually gained attention due to its multiple engineering advantages. Natural biomacromolecules—such as chitosan, cellulose, proteins, and nucleic acids—are not only widely available, inexpensive, and environmentally friendly, but more importantly, their complex multi-level molecular configurations and diverse polar functional groups (hydroxyl, amino, carboxyl, phosphate groups, nitrogen-containing heterocycles, etc.) allow for molecular-scale interaction with Zn. 2+ It exhibits specific coordination and electrostatic interactions, precisely regulating the desolvation process of ions and deposition kinetics; at the same time, its flexible polymer chain network structure can effectively adapt to the volume fluctuations of the zinc anode during repeated stripping / deposition cycles.

[0006] Despite this, the application of single biomacromolecule systems in zinc anode modification still faces several bottlenecks. Most natural polymers are highly hydrophilic, easily undergoing excessive swelling in aqueous electrolytes, leading to a sharp decline in coating mechanical strength and an inability to effectively inhibit dendrite penetration. Furthermore, the interfacial adhesion between the single polymer coating and the zinc foil substrate is often weak, making it prone to peeling off during repeated charge-discharge stress cycles. Regarding coating preparation processes, existing methods generally suffer from numerous steps, difficulty in precisely controlling coating thickness and composition, and high equipment requirements, hindering their large-scale application. To overcome the inherent defects of single polymer systems, a strategy based on polyelectrolyte complexes (PECs) has a solid theoretical foundation: two biomacromolecules with opposite charges undergo molecular-level self-assembly driven by strong electrostatic complementarity, constructing a highly cross-linked three-dimensional PEC network at the interface. This network has a cross-linking density far exceeding that of single polymer coatings, fundamentally improving the coating's mechanical stability, anti-swelling ability, and interfacial adhesion.

[0007] Deoxyribonucleic acid (DNA) and chitosan form an ideal polyelectrolyte complex pair. As the only alkaline polysaccharide found in nature, chitosan undergoes protonation of its amino groups in the weakly acidic electrolyte environment commonly used in aqueous zinc-ion batteries, thus carrying a large positive charge. Simultaneously, the densely packed amino (-NH2) and hydroxyl (-OH) groups on its molecular chain can directly react with Zn. 2+Coordination occurs, endowing the coating with excellent film-forming properties and flexibility. DNA molecules, with their sugar-phosphate backbone exhibiting strong polyanionic characteristics, generate a strong charge-complementary driving force with protonated chitosan. After mixing, the two can form a highly dense cross-linked network at the molecular level through electrostatic self-assembly, significantly improving the coating's anti-swelling and mechanical robustness compared to any single-component system. At the electrochemical regulation level, this composite system integrates a very high density and diverse range of "zinc-loving sites": chitosan contributes amino and hydroxyl coordination centers, while DNA simultaneously provides heterocyclic coordination sites for phosphate groups and four nitrogenous bases (adenine A, thymine T, guanine G, and cytosine C). Compared to traditional polysaccharide systems with single functional groups, this multi-coordination environment can effectively competitively replace Zn. 2+ Water molecules in the solvation layer lower the desolvation energy barrier and accelerate interfacial charge transfer kinetics, while simultaneously reducing water molecule accumulation on the negative electrode surface from the source, thereby inhibiting water-related side reactions such as hydrogen evolution and corrosion. Furthermore, the highly ordered double-helix secondary structure unique to DNA is expected to exert a "molecular template" effect, inducing zinc ions to preferentially deposit along the thermodynamically most stable Zn(002) crystal plane through its regular molecular arrangement, forming a dense layered deposition morphology—a unique advantage not possessed by ordinary biopolymers with disordered structures. Therefore, constructing DNA and chitosan as a polyelectrolyte complex on the zinc negative electrode surface holds promise for achieving multifunctional synergistic optimization of the negative electrode interface in three dimensions: physical barrier, ion regulation, and crystal orientation guidance. Summary of the Invention

[0008] To address the aforementioned problems, this invention provides a method for preparing a DNA-chitosan composite modified layer on the surface of a zinc anode with adjustable components and controllable structure. By adjusting the total concentration of the composite solution and the molar ratio (N / P) of chitosan amino groups (N) to DNA phosphate groups (P), the composition and microstructure of the DNA-chitosan polyelectrolyte complex are systematically designed. This solves the problems of limited functional group types and difficulty in precisely controlling the composition and structure of existing single biopolymer coatings. At the same time, by utilizing the synergistic effect of DNA and chitosan, the zinc affinity of the anode surface is enhanced, and side reactions such as dendrite growth and hydrogen evolution / corrosion are suppressed, thus achieving the preparation of an ultra-long cycle stable metal battery anode.

[0009] The present invention adopts the following technical solution:

[0010] A method for preparing a DNA-chitosan composite modified layer includes the following steps:

[0011] Step 1) Substrate pretreatment: Cut zinc foil or zinc sheet to a predetermined size, and perform degreasing, decontamination, and drying treatments in sequence to obtain the zinc substrate to be coated. Specifically, wipe commercial zinc foil with organic solvents (such as ethanol or acetone) or ultrasonically clean it to remove surface oil and oxide layers, and then place it in a vacuum drying oven to dry for later use.

[0012] Step 2) Preparation of DNA-Chitosan Composite Spin-Coating Solution: Prepare DNA solution, chitosan solution, and pH=5 buffer solution separately. First, mix the chitosan solution and buffer solution to obtain Solution I. Then, add the DNA solution dropwise to Solution I and stir under set conditions to mix, allowing DNA and chitosan to combine through electrostatic interaction and hydrogen bonding to form a uniform and stable DNA-chitosan composite spin-coating precursor solution. After the DNA-chitosan composite spin-coating precursor solution is allowed to stand and defoam, the DNA-chitosan composite spin-coating solution is obtained for later use. The composition of the composite system can be adjusted by regulating the ratio of the number of moles of amino groups (N) in chitosan to the number of moles of phosphate groups (P) in DNA in the spin-coating solution.

[0013] Step 3) Spin-coating and post-treatment: The DNA-chitosan composite spin-coating solution prepared in Step 2) is dropwise added to the zinc substrate surface. Spin-coating is performed under the set spin-coating speed, acceleration, spin-coating time, and spin-coating times. After spin-coating, post-treatment such as drying and curing is performed to obtain a zinc negative electrode sheet with a DNA-chitosan composite modified layer on the surface. By adjusting the concentration of the spin-coating solution and the ratio of the molar number of amino groups (N) in chitosan to the molar number of phosphate groups (P) in DNA, a deoxyribonucleic acid-chitosan polymer coating is prepared to enhance the zinc affinity of the negative electrode surface and inhibit dendrite growth and side reactions such as hydrogen evolution / corrosion.

[0014] Furthermore, in step 1), the zinc foil has a thickness of 0.10 mm; the cutting size is a round piece with a diameter of 12 mm or a square piece with a side length of 10 mm; the organic solvent used for degreasing and decontamination is one or more of ethanol, acetone or isopropanol; the drying temperature is 50°C and the drying time is 12 h.

[0015] Furthermore, in step 2), the DNA is a sodium salt form of double-stranded deoxyribonucleic acid, derived from salmon sperm DNA, with a fragment length ranging from 200 to 2000 bp.

[0016] Furthermore, in step 2), the degree of deacetylation of chitosan is ≥95%, and the viscosity is 100-200 mPa.s.

[0017] Furthermore, in step 2), the solvent system of the chitosan solution is a 0.2M dilute acid aqueous solution; the solvent of the DNA solution is deionized water or buffer solution; and the pH range during compounding is 4.8 to 5.1.

[0018] Furthermore, in step 2), the ratio of the molar number of amino groups (N) in chitosan to the molar number of phosphate groups (P) in DNA is 1.2:1 to 5:1; the total concentration of the spin-coating solution is in the range of 0.8 to 2 mg / mL.

[0019] Furthermore, in step 2), the settling time of the composite spin coating liquid is 0.5 to 1 hour; the degassing treatment method is settling degassing or vacuum degassing, and the time is 10 to 30 minutes.

[0020] Furthermore, in step 3), the spin coating speed range is 2000-3000 rpm, the spin coating time range is 15-30 s, and the acceleration range is 1000-1500 rpm / s.

[0021] Furthermore, in step 3), the drying and curing temperature is 50-100℃, and the drying time is 12h.

[0022] Furthermore, the thickness of the DNA-chitosan composite modified layer is 50 nm to 350 nm, and it is characterized by cross-sectional scanning electron microscopy (SEM).

[0023] A zinc anode includes a zinc substrate and a DNA-chitosan composite modified layer covering the surface of the zinc substrate. The modified layer has a thickness of 50 nm to 350 nm, and the DNA and chitosan in the modified layer form a stable composite structure through electrostatic interaction and hydrogen bonding.

[0024] An aqueous zinc-ion battery includes a positive electrode, an electrolyte, a separator, and a zinc negative electrode, wherein the zinc negative electrode includes a zinc substrate and a DNA-chitosan composite modified layer covering the surface of the zinc substrate.

[0025] The beneficial effects of this invention are:

[0026] 1. This invention utilizes the complexation of DNA and chitosan, taking advantage of the abundant nitrogenous bases (adenine, guanine, etc.) and phosphate groups in the DNA molecule to provide numerous zinc-loving sites. These sites synergistically interact with the amino and hydroxyl groups on the chitosan molecular chain to effectively regulate Zn. 2+ Flux distribution makes zinc ions deposit more evenly on the negative electrode surface, thereby inhibiting dendrite growth.

[0027] 2. The DNA-chitosan composite layer prepared in this invention serves as an artificial solid interface layer, which can isolate the electrolyte from direct contact with the zinc anode and accelerate the reaction of Zn. 2+The desolvation process effectively suppresses side reactions such as hydrogen evolution and corrosion / passivation, significantly improving coulombic efficiency. In Zn-Cu half-cells, coulombic efficiency can reach over 99%, while cycle life is significantly extended compared to unmodified half-cells. The cycle life of Zn-Zn symmetric cells is significantly extended compared to blank zinc foil. Zn / / AC cells possess higher energy density and longer cycle life.

[0028] 3. The DNA and chitosan used in this invention are both natural biological macromolecules, widely available, environmentally friendly, and inexpensive, aligning with the concept of sustainable development. The modified zinc anode prepared in this invention significantly outperforms the unmodified blank zinc foil control in terms of symmetrical cell lifetime, half-cell coulombic efficiency, and full-cell cycle stability. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly described below. Obviously, the drawings described below only relate to some embodiments of the present invention and are not intended to limit the present invention.

[0030] Figure 1 The image shows the FTIR spectrum of the negative electrode modified with the DNA-chitosan composite layer, used to demonstrate the composition and structure of the DNA-chitosan composite layer and the interaction between DNA and chitosan.

[0031] Figure 2 XPS spectra of the negative electrode modified with the DNA-chitosan composite layer are used to demonstrate the composition and structure of the DNA-chitosan composite layer.

[0032] Figure 3 The graph shows the relationship between the thickness (a) and properties (b) of the DNA-chitosan composite modified layer and the ratio (N / P) of the molar number of amino groups (N) in chitosan to the molar number of phosphate groups (P) in DNA, which is used to demonstrate the adjustability of the coating composition.

[0033] Figure 4 The graph shows the relationship between the thickness (a) and properties (b) of the DNA-chitosan composite modified layer and the solution concentration, which is used to demonstrate the adjustability of the coating thickness.

[0034] Figure 5 For comparative examples and various embodiments, zinc foil was used as the negative electrode of a half-cell (Zn-Cu system) at 1 mA cm⁻¹. -2 -1mAh cm -2 The Coulomb efficiency versus cycle number curve is shown below.

[0035] Figure 6 To compare the zinc foil used as the negative electrode of the symmetrical battery (Zn-Zn system) in each embodiment at 1 mA cm⁻¹ -2 -1mAhcm -2The graph shows the cycle life / polarization voltage versus time.

[0036] Figure 7 The surface SEM images of zinc foil in the comparative and optimal embodiments after cycling in a symmetrical battery for a certain period of time are shown.

[0037] Figure 8 The image shows a comparison of the electrochemical impedance spectroscopy (EIS) and Tafel polarization curves between the comparative example and the optimal embodiment.

[0038] Figure 9 For comparative and optimal examples, zinc foil was used in full cells (Zn / / AC system) at 1 A·g -1 Cyclic performance versus rate performance curves at current density. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] The technical solution of the present invention will be further described clearly and completely below with reference to the embodiments and accompanying drawings:

[0041] Comparative Example 1

[0042] 1. Preparation of blank zinc anode

[0043] A 0.1 mm thick commercial zinc foil was wiped with ethanol to remove surface oil and impurities, and then dried in a vacuum drying oven at 60°C for 4 hours. The dried zinc foil was then cut into 12 mm diameter discs to obtain blank zinc negative electrodes.

[0044] 2. Preparation of activated carbon electrodes

[0045] Zinc iodide (ZnI2), activated carbon (AC), and polytetrafluoroethylene (PTFE) were mixed and ground in a mass ratio of 5:4:1. After adding an appropriate amount of ethanol and dispersing evenly, the mixture was rolled into a 500 μm sheet. After drying at 50°C overnight, a ZnI2 / / AC electrode was obtained.

[0046] 3. Zn-Cu half-cell cycle test

[0047] A CR-2032 coin cell was assembled using blank zinc foil and copper foil as the negative and positive electrodes, respectively, glass fiber as the separator, and 150 μL of 2 mol / L ZnSO4 aqueous solution as the electrolyte. The electrolyte was then applied at 1 mA cm⁻¹. -2 Current density, 1mAh cm-2 Cyclic testing was conducted under areal capacity conditions. From Figure 5 As can be seen from the data, the coulombic efficiency of the half-cell with blank zinc foil as the negative electrode is unstable, and the effective cycle count is about 100 times, which proves that its stability during the cycle is poor.

[0048] 4. Performance testing of Zn-Zn symmetric cells

[0049] Two blank zinc foils were assembled into a CR-2032 symmetrical battery for cycle stability testing. Glass fiber was used as the separator, and 150 μL of 2 mol / L ZnSO4 solution was used as the electrolyte. Test parameters were set as constant current charge-discharge with a current density of 1 mA cm⁻¹. -2 The surface capacity is 1mAh cm -2 . Figure 6 The results show that the effective cycling time of the blank zinc foil at the above current density is about 200 hours. It can be seen that the blank sample without coating protection fails in a short time and has poor stability.

[0050] 5. SEM morphology observation after cycling

[0051] Blank zinc foil was assembled into a symmetrical cell at 1 mA cm⁻¹. -2 After cycling at current densities for 20 hours and 50 hours, the zinc foil was disassembled, and its surface morphology was characterized using scanning electron microscopy (SEM). Figure 7 It is evident that a large number of byproducts and protruding flaky dendrites are generated on the surface of the zinc foil, resulting in a rough and uneven surface morphology.

[0052] 6. EIS and Tafel Testing

[0053] Blank zinc foil was assembled into a symmetrical cell for electrochemical impedance spectroscopy (EIS) testing. Figure 8 Electrochemical impedance spectroscopy showed that the impedance of the comparative sample was approximately 520 Ω.

[0054] 7. Full Battery Performance Test

[0055] A blank zinc foil was used as the negative electrode, and a ZnI2 / / AC electrode was used as the positive electrode to assemble a CR-2032 type button cell for full-cell cycle performance testing. Glass fiber was used as the separator, and the electrolyte was 2 mol / L ZnSO4. The test parameters were set to 1 A·g -1 Under constant current charging and discharging. For example... Figure 9 Full cells using blank zinc foil as the negative electrode have low capacity and a significant decay trend.

[0056] Example 1

[0057] 1. Matrix pretreatment

[0058] (1) Wipe the 0.1 mm thick commercial zinc foil with ethanol to remove surface oil stains, and then dry it in a vacuum drying oven at 60℃ for 4 hours. (2) Cut the dried zinc foil into round pieces with a diameter of 12 mm to obtain the zinc substrate to be coated.

[0059] 2. Preparation of DNA-Chitosan Composite Spin-Coating Solution

[0060] (1) Preparation of chitosan solution: Dissolve chitosan (degree of deacetylation ≥95%, viscosity 100-200 mPa.s) in 0.2M acetic acid aqueous solution, stir until completely dissolved, and prepare a chitosan solution with a concentration of 10 mg / mL. (2) Preparation of DNA solution: Dissolve salmon sperm DNA sodium salt in deionized water to prepare a DNA solution with a concentration of 5 mg / mL. (3) Preparation of pH=5 buffer solution: Mix 0.2M acetic acid solution and 0.2M sodium acetate solution in a volume ratio of 3:7, and then add deionized water to 20 ml to prepare a buffer solution with a pH of 5. (4) Composite: The DNA solution was added dropwise to the mixture of chitosan and buffer solution under stirring. The ratio of the molar number of amino groups (N) of chitosan to the molar number of phosphate groups (P) of DNA was 1.2:1 (R0), and the total concentration was 0.8 mg / mL (C0). After mixing, the mixture was stirred at room temperature for 1 h to ensure complete composite. After standing for 1 h, the mixture was degassed under vacuum for 30 min and filtered through a 0.25 μm filter membrane to obtain the DNA-chitosan composite spin-coating solution.

[0061] 3. Spin coating film formation and post-treatment

[0062] 120 μL of DNA-chitosan composite spin-coating solution was dropped onto the center of the zinc substrate surface and spin-coated at 2000 rpm (S0) for 30 s with an acceleration of 1000 rpm / s, for one spin coat. After spin-coating, the sample was dried on a 50℃ plate heating table for 1 h, followed by drying in a vacuum drying oven for 11 h to obtain a zinc negative electrode sheet with a DNA-chitosan composite modified layer on the surface.

[0063] 4. Coating Characterization

[0064] (1) Thickness measurement: The coating thickness was observed using cross-sectional SEM and was approximately 136.7 nm. (2) FTIR characterization: such as Figure 1 The amide vibration peak of chitosan can be seen in the image (approximately 1560 cm⁻¹). -1 The superposition peak of the stretching vibrations of all OH (hydroxyl) and NH (amine / amide) groups on DNA and chitosan molecules (at 3600 cm⁻¹). -1 Up to 3000cm -1 A significant, very broad, and smooth absorption band, with the peak centered at approximately 3400 cm⁻¹. -1(Nearby). This proves that the DNA-chitosan composite modified layer was successfully prepared. (3) XPS characterization: such as Figure 2 The presence of N 1s and P 2p signals confirms that DNA and chitosan coexist in the coating.

[0065] 5. Zn-Cu half-cell cycle test

[0066] Zinc foil and copper foil coated with the above-mentioned coating were used as the negative and positive electrodes, respectively. The battery assembly and testing conditions were the same as those in Comparative Example 1. Figure 5 As can be seen from the data, the Zn-Cu half-cell with zinc foil as the negative electrode prepared in Example 1 can stably reach more than 200 cycles, and the coulombic efficiency is about 99.8%, which is significantly better than that of Comparative Example 1.

[0067] 6. Performance testing of Zn-Zn symmetric cells

[0068] Two pieces of modified zinc foil prepared in Example 1 were assembled into a symmetrical battery, and the test conditions were the same as those in Comparative Example 1. Figure 6 The modified zinc foil was shown to have an effective cycle time of 300 hours at the above current density, indicating that the DNA-chitosan composite modified layer improved the cycle stability of the battery.

[0069] Example 2

[0070] 1. Matrix pretreatment

[0071] Same as Example 1.

[0072] 2. Preparation of DNA-Chitosan Composite Spin-Coating Solution

[0073] This example examines the coating performance under the condition of N / P=1:1. The preparation methods of chitosan solution and DNA solution are the same as in Example 1. When compounding, the ratio of the molar number of amino groups (N) of chitosan to the molar number of phosphate groups (P) of DNA is adjusted to 1:1, and the total concentration is 0.8 mg / mL. The remaining process steps are the same as in Example 1.

[0074] 3. Spin coating film formation and post-treatment

[0075] The spin coating speed was 2500 rpm, and the other spin coating parameters and drying and curing conditions were the same as in Example 1.

[0076] 4. Coating thickness characterization

[0077] Cross-sectional SEM observation was performed, by Figure 3 (a) The coating thickness was approximately 46.7 nm under the N / P = 1:1 condition. Compared with Example 1 (N / P = 1.2:1, thickness approximately 136.7 nm), the coating thickness was significantly reduced. This indicates that when the DNA content increases, the polyelectrolyte complex is prone to aggregation, leading to uneven film thickness distribution.

[0078] 5. Zn-Cu half-cell cycle test

[0079] Zinc foil and copper foil coated with the above-mentioned coating were used as the negative electrode and positive electrode, respectively. The battery assembly and testing conditions were the same as those in Comparative Example 1. Figure 3 As shown in (b), the Zn-Cu half-cell cycle count under the N / P=1:1 condition is approximately 100 cycles.

[0080] 6. Performance testing of Zn-Zn symmetric cells

[0081] Two pieces of modified zinc foil were assembled into a symmetrical battery, and the test conditions were the same as those in Comparative Example 1. Figure 3 As shown in (b), the cycle life of the symmetric cell under the N / P=1:1 condition is approximately 120 h. Compared with Example 1 (N / P=1.2:1, symmetric cell life approximately 300 h), the performance is reduced. The reason for this is that when N / P=1:1, the positive and negative charges between chitosan and DNA are nearly completely neutralized, making them prone to aggregation. This results in an uneven coating distribution, and the excessively uneven network structure increases the transport impedance of Zn²⁺, hindering ion diffusion kinetics and thus negatively impacting electrochemical performance.

[0082] Example 3

[0083] 1. Matrix pretreatment

[0084] Same as Example 1.

[0085] 2. Preparation of DNA-Chitosan Composite Spin-Coating Solution

[0086] This example examines the coating performance under the condition of N / P=5:1. The preparation methods of chitosan solution and DNA solution are the same as in Example 1. When compounding, the ratio of the molar number of amino groups (N) of chitosan to the molar number of phosphate groups (P) of DNA is adjusted to 5:1, the total concentration is 0.8 mg / mL, the spin coating speed is 2500 rpm, and the remaining process steps are the same as in Example 1.

[0087] 3. Spin coating film formation and post-treatment

[0088] The spin coating speed was 2500 rpm, and the rest was the same as in Example 1.

[0089] 4. Coating thickness characterization

[0090] Cross-sectional SEM observation was performed, by Figure 3(a) It is found that the coating thickness is approximately 248.6 nm under the condition of N / P=5:1. Compared with Example 1 (N / P=1.2:1, thickness approximately 136.7 nm), the coating thickness is significantly increased, indicating that when the chitosan content increases, the crosslinking density and solid content of the polyelectrolyte complex increase, and the coating deposited on the zinc substrate surface is correspondingly thicker.

[0091] 5. Zn-Cu half-cell cycle test

[0092] Zinc foil and copper foil coated with the above-mentioned coating were used as the negative and positive electrodes, respectively. The battery assembly and testing conditions were the same as those in Comparative Example 1. Figure 3 (b) It is found that the Zn-Cu half-cell cycle count under the condition of N / P=5:1 is about 600 times.

[0093] 6. Performance testing of Zn-Zn symmetric cells

[0094] Two modified zinc foils were assembled into a symmetrical battery, and the test conditions were the same as those in Comparative Example 1. Figure 3 (b) The cycle life of the symmetric battery under the N / P=5:1 condition was approximately 3120 h, significantly better than that of Example 1 (N / P=1.2:1, approximately 300 h) and Example 2 (N / P=1:1, approximately 120 h). The results indicate that increasing the N / P ratio to a relative excess of chitosan allows DNA to introduce more nitrogenous bases and phosphate groups into the complex, providing more abundant zinc-loving active sites, enhancing the affinity and adsorption capacity for Zn²⁺, more effectively and uniformly guiding zinc ion deposition, and inhibiting zinc dendrite growth, thereby significantly improving electrochemical cycling stability. Considering the results of Examples 1–3, N / P=5:1 is the optimal composition ratio.

[0095] Example 4

[0096] 1. Matrix pretreatment

[0097] Same as Example 1.

[0098] 2. Preparation of DNA-Chitosan Composite Spin-Coating Solution

[0099] Based on the optimal N / P ratio of 5:1 determined in Examples 1-3, two sets of samples were prepared in this example to investigate the effect of the concentration of the DNA-chitosan composite spin-coating solution on the coating performance. The concentration of the DNA-chitosan composite spin-coating solution in Example 4a was 1.0 mg / mL, and the concentration of the DNA-chitosan composite spin-coating solution in Example 4b was 2.0 mg / mL, with an N / P ratio of 5:1 in both cases. The remaining process steps were the same as in Example 1.

[0100] 3. Spin coating film formation and post-treatment

[0101] The spin coating speed was 2500 rpm, and the rest was the same as in Example 1.

[0102] 4. Coating thickness characterization

[0103] Figure 4 (a) shows the trend of coating thickness with varying concentration of the DNA-chitosan composite spin-coating solution under the optimal N / P ratio of 5:1. As the concentration of the DNA-chitosan composite spin-coating solution increases from 0.8 mg / mL to 2.0 mg / mL, the coating thickness monotonically increases—significantly from approximately 248.6 nm (0.8 mg / mL) to approximately 306.8 nm (1.0 mg / mL), and further increases to approximately 350 nm (2.0 mg / mL). Notably, the change in the concentration of the DNA-chitosan composite spin-coating solution not only affects the coating thickness but also the mass loading per unit area, i.e., alters the areal density of zinc-loving active sites in the coating. A higher areal mass loading means a more dense concentration of zinc-loving sites, such as nitrogenous bases and phosphate groups, provided by the DNA-chitosan complex per unit area, resulting in a stronger ability to regulate zinc ion deposition behavior.

[0104] 5. Zn-Cu half-cell cycle test

[0105] Zinc foil and copper foil coated with the above-mentioned coating were used as the negative and positive electrodes, respectively. The battery assembly and testing conditions were the same as those in Comparative Example 1. Figure 4 (b) It is found that the Zn-Cu half-cell of Example 4a (1.0 mg / mL) has about 2100 cycles, and the Zn-Cu half-cell of Example 4b (2.0 mg / mL) has about 600 cycles.

[0106] 6. Performance testing of Zn-Zn symmetric cells

[0107] Figure 4(b) This paper shows the changes in the cycle life of the Zn-Cu half-cell and the steady-state operation time of the Zn-Zn symmetric cell with the precursor concentration. Both parameters showed a trend of first increasing and then decreasing, reaching the optimal value at a concentration of 1.0 mg / mL for the DNA-chitosan composite spin-coating solution. Specifically, the number of half-cell cycles increased from approximately 600 cycles at 0.8 mg / mL to approximately 2100 cycles at 1.0 mg / mL, and then decreased back to approximately 600 cycles at 2.0 mg / mL; the steady-state operation time of the symmetric cell increased from approximately 3120 h to approximately 3800 h, and then decreased to approximately 1500 h. This indicates that at a concentration of 0.8 mg / mL, although the N / P ratio is optimal, the coating areal mass loading is low, and the density of zinc-affinity active sites per unit area is insufficient, making it difficult to fully regulate the deposition behavior of zinc ions. At a concentration of 1.0 mg / mL, the coating thickness and areal mass loading reach the optimal balance, and the composite coating forms a dense and uniform covering layer on the electrode surface. The areal density of zinc-affinity sites is sufficient to effectively guide the uniform deposition of zinc ions, while the coating thickness is moderate and does not excessively hinder ion transport. However, when the concentration reaches 2.0 mg / mL, although the areal mass loading further increases, the excessively thick coating increases the transport impedance of zinc ions, hinders ion diffusion kinetics, and weakens the electrochemical performance.

[0108] Example 5

[0109] 1. Matrix pretreatment: Same as in Example 1.

[0110] 2. Preparation of DNA-chitosan composite spin-coating solution: The composite spin-coating solution was prepared according to the optimal N / P ratio of 5:1 and the optimal concentration of DNA-chitosan composite spin-coating solution of 1.0 mg / mL. The remaining process steps were the same as in Example 1.

[0111] 3. Spin coating and post-treatment: The spin coating speed was 2500 rpm, and the other conditions were the same as in Example 1. The coating thickness was approximately 306.8 nm.

[0112] 4. Preparation of activated carbon electrodes

[0113] Zinc iodide (ZnI2), activated carbon (AC), and polytetrafluoroethylene (PTFE) were mixed and ground in a mass ratio of 5:4:1. After adding an appropriate amount of ethanol and dispersing evenly, the mixture was rolled into a 500 μm sheet. After drying at 50°C overnight, a ZnI2 / / AC electrode was obtained.

[0114] 5. Zn-Cu half-cell cycle test

[0115] The test conditions were the same as those for Comparative Example 1. From Figure 5As can be seen from the data, under optimal conditions, the modified zinc foil as the negative electrode can stably achieve a coulombic efficiency of over 99% for the Zn-Cu half-cell, with an effective cycle count of 2100, far exceeding the approximately 100 cycles of Comparative Example 1.

[0116] 6. Long-cycle testing of Zn-Zn symmetric cells

[0117] The test conditions were the same as those for Comparative Example 1. Figure 6 Prove that the modified zinc foil under optimal conditions operates at 1 mA cm⁻¹ -2 The effective cycle time at current density reached 3800 h, which is 19 times higher than that of Comparative Example 1 (approximately 200 h), indicating that the DNA-chitosan composite modified layer greatly improves the cycle stability of the battery.

[0118] 7. SEM morphology observation after cycling

[0119] A symmetric cell was assembled using modified zinc foil under optimal conditions, at 1 mA cm⁻¹. -2 1mAh cm -2 Loop under certain conditions. Figure 7 The SEM images show that after 20 h and 50 h of cycling, respectively, the zinc deposition on the DNA-CHI@Zn surface is uniform, with no obvious dendrites or corrosion pits, and the surface remains smooth. In contrast, the unmodified bare zinc anode (Bare Zn) showed a large number of scattered flaky zinc deposits on its surface after 20 h of cycling, and further deteriorated after 50 h of cycling, with the surface covered by coarse, disordered flaky dendrites, accompanied by obvious corrosion pits and cracks, and the surface roughness significantly increased.

[0120] 8. EIS and Tafel tests

[0121] Figure 8 Electrochemical impedance spectroscopy showed that the charge transfer resistance of the optimal embodiment was lower than that of Comparative Example 1, indicating that the DNA-chitosan composite modification layer promoted charge transfer kinetics. Tafel polarization curves showed that the corrosion current density of the optimal embodiment was lower than that of Comparative Example 1, and the corrosion potential shifted positively, indicating that the coating effectively inhibited zinc corrosion.

[0122] 9. Full Battery Performance Test

[0123] Using the modified zinc foil under optimal conditions as the negative electrode and the ZnI2 / / AC electrode as the positive electrode, CR-2032 coin cells were assembled for full-cell cycle performance testing. The test conditions were the same as those for the full-cell test in Comparative Example 1. Figure 9 The results show that the modified zinc foil as the negative electrode has a higher full cell capacity and excellent capacity retention after 8000 cycles, with a coulombic efficiency close to 100%, which is significantly better than Comparative Example 1.

[0124] In summary, this invention achieves precise tunability of the composition and microstructure of the DNA-chitosan composite modified layer by systematically controlling two key material parameters: the N / P ratio of DNA to chitosan and the concentration of the DNA-chitosan composite spin-coating solution. The results show that the N / P ratio determines the type and density of zinc-loving active sites in the composite; when N / P = 5:1, the DNA introduces the most abundant nitrogenous bases and phosphate groups, resulting in the best electrochemical performance. The concentration of the DNA-chitosan composite spin-coating solution affects the areal density of zinc-loving sites and the ion transport impedance by changing the coating thickness and areal mass loading; 1.0 mg / mL is the optimal concentration. The modified zinc anode prepared using the optimal material combination (N / P=5:1, concentration 1.0 mg / mL) determined based on the above principles exhibits comprehensive and excellent performance: the coulombic efficiency of the Zn-Cu half-cell remains stable above 99%, with an effective cycle life of 2100 cycles; the cycle life of the Zn-Zn symmetric cell reaches 3800 h, 19 times that of the blank zinc foil; the surface is smooth and dendrite-free after cycling; EIS and Tafel tests confirm that the coating reduces charge transfer resistance and inhibits corrosion; and the full cell maintains excellent capacity retention after 8000 cycles. These results fully demonstrate that the DNA-chitosan composite modified layer effectively inhibits dendrite growth and side reactions through physical barrier isolation, synergistic regulation of multiple zinc-loving sites, and crystal orientation guidance, significantly improving the long-cycle stability of aqueous zinc-ion batteries.

Claims

1. A method for preparing a DNA-chitosan composite modified layer, characterized in that, Includes the following steps: Step 1) Substrate pretreatment: Treat the zinc substrate to be coated; Step 2) Preparation of DNA-chitosan composite spin-coating solution: Prepare DNA solution, chitosan solution and buffer solution at pH=5 respectively. Mix chitosan solution and buffer solution to obtain solution I. Add DNA solution to solution I and stir to combine, to obtain DNA-chitosan composite spin-coating precursor solution. Then allow to stand for curing, degassing treatment and filter through a filter membrane to obtain DNA-chitosan composite spin-coating solution. Step 3) Spin-coating and post-treatment: The DNA-chitosan composite spin-coating solution is dropped onto the surface of the zinc substrate for spin-coating. After spin-coating, the substrate is dried and cured to obtain a zinc anode with a DNA-chitosan composite modified layer on the surface.

2. The preparation method according to claim 1, characterized in that, In step 2), the DNA is a sodium salt form of double-stranded deoxyribonucleic acid with a fragment length ranging from 200 to 2000 bp.

3. The preparation method according to claim 1, characterized in that, In step 2), the degree of deacetylation of chitosan is ≥95%, and the viscosity is 100-200 mPa.s.

4. The preparation method according to claim 1, characterized in that, In step 2), the solvent for the chitosan solution is a dilute acid aqueous solution with an acid concentration of 0.2M; the solvent for the DNA solution is deionized water or a buffer solution; and / or, the pH range of the solution during recombination is 4.8 to 5.

1.

5. The preparation method according to claim 1, characterized in that, In step 2), the ratio of the molar number of amino groups (N) in chitosan to the molar number of phosphate groups (P) in DNA is 1.2:1 to 5:1; and / or, the total concentration of the DNA-chitosan composite spin-coating solution is in the range of 0.8 to 2 mg / mL.

6. The preparation method according to claim 1, characterized in that, In step 2), the standing time of the DNA-chitosan composite spin-coating precursor solution is 0.5 to 1 hour; the degassing treatment method is standing degassing or vacuum degassing, and the degassing treatment time is 10 to 30 minutes.

7. The preparation method according to claim 1, characterized in that, In step 3), the drying and curing temperature is 50-100℃ and the drying time is 12h.

8. The preparation method according to claim 1, characterized in that, The thickness of the DNA-chitosan composite modified layer in step 3) is 50 nm to 350 nm.

9. A zinc negative electrode, characterized in that, The invention comprises a zinc substrate and a DNA-chitosan composite modified layer prepared by any one of claims 1 to 8, covering the surface of the zinc substrate, wherein the modified layer has a thickness of 50 nm to 350 nm, and the DNA and chitosan in the modified layer form a stable composite structure through electrostatic interaction and hydrogen bonding.

10. An aqueous zinc-ion battery, characterized in that, It includes a positive electrode, an electrolyte, a separator, and a zinc negative electrode as described in claim 9.

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