An organic conjugated polymer and a preparation method thereof, and a zinc ion battery

Abstract

The application belongs to the technical field of battery materials, and discloses an organic conjugated polymer, a preparation method thereof and a zinc ion battery. The organic conjugated polymer comprises a main chain and a side chain. The main chain comprises a sulfur-containing polythiophene structure, and the side chain comprises a glycol structure. The organic conjugated polymer can protect the zinc anode by adjusting zinc deposition, inhibiting zinc dendrite growth and inhibiting adverse side reactions, so as to improve the electrochemical performance of the aqueous rechargeable zinc ion battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and particularly relates to an organic conjugated polymer and a preparation method thereof and a zinc ion battery. BACKGROUND

[0002] Zinc anode with high safety, cost-effectiveness, environmental friendliness, and relatively high theoretical capacity (820 mAh g -1 or 5855 mAh cm -3 ) and low redox potential (vs. standard hydrogen electrode -0.76 V) makes aqueous rechargeable zinc ion batteries (ZIBs) have great potential in large-scale energy storage applications, and are also widely used in flexible wearable electronic devices. However, problems related to zinc dendrite growth, competitive hydrogen evolution reaction, continuous zinc corrosion and by-product accumulation (for example, zinc hydroxysulfate or ZHS in acidic electrolyte, ZHS refers to Zn4SO4(OH)6 containing H2O, and the Chinese name is basic zinc sulfate) seriously threaten the capacity and cycle stability of ZIBs.

[0003] Notably, both zinc dendrite formation and side reactions are closely related to the zinc anode surface, therefore, various coating strategies have been proposed in the prior art to protect the zinc anode. For example, a layer of TiN is deposited on the surface of the zinc anode, which suppresses the growth of zinc dendrites by adjusting the zinc ion flux and promoting its uniform deposition. In addition, the preferentially oriented TiN (200) protective coating has been shown to have a thermodynamic advantage for the lateral growth of ZHS, which is more electrochemically reversible than the vertically arranged ZHS nanosheet. Benefiting from excellent corrosion resistance, good structural and chemical stability, metal oxides (for example, Al2O3, ZrO2 and TiO2) are also adopted as protective barriers for guiding zinc anode electrodeposition, resisting zinc corrosion, and inhibiting hydrogen evolution reaction (HER). However, the rigid interface with the zinc anode produced by inorganic materials cannot adapt to the volume change of zinc metal during repeated charge and discharge processes, eventually leading to cracks in the coating and loss of protection function. Polymers with high flexibility and adjustable mechanical properties are an ideal choice to overcome the shortcomings of inorganic materials. For example, a self-adapting polydimethylsiloxane (PDMS) / TiO 2-xThe coating stabilizes the zinc metal surface and suppresses the growth of dendrites. In addition, due to the higher tensile strength and modulus, as well as excellent thermochemical stability, polyacrylonitrile (PAN) and its mixture with zinc salt (PANZ) can help to accommodate the volume change during continuous zinc plating and stripping processes. Despite some promising results based on polymer coatings, issues related to zinc anodes still exist, especially the problems generated during long-term cycling. This is mainly due to two limitations of most commonly used polymers: (1) low electronic and ionic conductivity, and (2) poor structural adjustability. The conductive properties of the coating are closely related to the electron transport and zinc ion diffusion, which determine the electrochemical deposition and stripping state of the zinc anode. Therefore, polymer coatings with poor electronic and ionic conductivity have a negative effect on the zinc electrodeposition and electrochemical reaction kinetics of ZIBs, which will lead to rapid growth of zinc dendrites after repeated charge and discharge processes. Since the zinc anode surface has an important influence on the side reactions, its surface properties (e.g., hydrophilicity and zinc affinity) need to be highly optimized, but the molecular structure of most polymers used as zinc anode protective layers (e.g., PVP polyvinylpyrrolidone and PAN) is difficult to adjust to improve the electrochemical performance of ZIBs.

[0004] Therefore, there is an urgent need for a new substance to protect the zinc anode and thus improve the electrochemical performance of ZIBs. SUMMARY

[0005] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application proposes an organic conjugated polymer and a preparation method thereof, and a zinc ion battery. The organic conjugated polymer according to the present application can protect the zinc anode by adjusting zinc deposition, suppressing zinc dendrite growth and suppressing undesirable side reactions, thereby improving the electrochemical performance of ZIBs.

[0006] Compared to existing polymers, the organic conjugated polymer of this invention exhibits mixed ionic and electronic conductivity, improving electrodeposition kinetics and the stability of the zinc anode. Furthermore, the sulfur-containing backbone of the polythiophene in the organic conjugated polymer of this invention can chemically interact with zinc ions, promoting the dissolution of zinc ions from the hydrated structure and facilitating the formation of unique channels. This simultaneously accelerates zinc ion transport and regulates the electrodeposition of the zinc anode. Moreover, by adjusting the side chains from the alkyl group to the hydrophilic glycol group, the organic conjugated polymer of this invention yields polythiophene poly(2-(4,4′-bis(2-methoxyethoxy)-5'-methyl-[2,2'-thiophene]-5-yl)-5-methylthiophene (abbreviated as pgBTTT), which exhibits better hydrophilicity than poly[2,5-bis(3-dodecylthiophene-2-yl)thiophene] (abbreviated as pBTTT). Therefore, pgBTTT has higher film-forming performance than pBTTT. Therefore, the electrochemical performance of ZIBs based on the pgBTTT zinc anode protective layer is significantly improved, and a zinc-zinc symmetric cell is used at 2 mA cm⁻¹. -2 Stable cycling for over 1700 hours under certain conditions. A complete cell using NH4VO4 (NVO) as the cathode at 0.2 A g... -1 It has a higher specific capacity (over 520mAh g) -1 For example, 528mAh g -1 Improved rate performance and long-term cycling stability (low decay rate of less than 0.019% per cycle after 1000 cycles, for example, 0.0183%).

[0007] The first aspect of the present invention provides an organic conjugated polymer and a method for preparing the same.

[0008] Specifically, an organic conjugated polymer includes a main chain and side chains; the main chain includes a sulfur-containing polythiophene structure, and the side chains include glycol structures.

[0009] Preferably, the general structural formula of the organic conjugated polymer is shown below:

[0010] Where n is a positive integer greater than 0.

[0011] Preferably, n is a positive integer between 1 and 1000; more preferably, n is a positive integer between 100 and 1000, for example, n is 50, 100, 200, 300, 400, 500, 600, 800, or 1000.

[0012] Preferably, the number-average molecular weight (Mn) of the organic conjugated polymer is 10,000 to 50,000, more preferably 10,000 to 25,000, for example 10,000, 20,000, 30,000, 40,000, or 50,000.

[0013] Preferably, the number average molecular weight (Mw) of the organic conjugated polymer is 20,000 to 80,000, further preferably 20,000 to 50,000, for example 20,000, 30,000, 40,000, 50,000, 60,000, 70,000.

[0014] The second aspect of the present application provides a method for preparing an organic conjugated polymer.

[0015] Specifically, a method for preparing an organic conjugated polymer comprises the following steps:

[0016] reacting halogen and methoxyethoxy containing dithiophene with tin containing thiophene to obtain the organic conjugated polymer.

[0017] Preferably, the halogen and methoxyethoxy containing dithiophene comprises 5,5'-dibromo-4,4'-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-2,2'-bithiophene; and / or, the tin containing thiophene comprises 2,5-bis(trimethylstannyl)thieno[3,2-b]thiophene.

[0018] Preferably, the halogen and methoxyethoxy containing dithiophene comprises 5,5'-dibromo-4,4'-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-2,2'-bithiophene; and / or, the tin containing thiophene comprises 2,5-bis(trimethylstannyl)thieno[3,2-b]thiophene.

[0019] Preferably, the mass ratio of the 5,5'-dibromo-4,4'-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-2,2'-bithiophene to the 2,5-bis(trimethylstannyl)thieno[3,2-b]thiophene is 100:(50-100), further preferably 100:(60-80).

[0020] Preferably, the temperature of the reaction is 90-100℃, and the reaction time is 7-9 hours.

[0021] Preferably, Pd2(dba)3(tris(dibenzylideneacetone)dipalladium), tri(o- methylphenyl)phosphine, 2-(tributylstannyl)thiophene and 2-bromothiophene are also used in the preparation of the organic conjugated polymer.

[0022] Preferably, the method for preparing the organic conjugated polymer comprises the following steps:

[0023] The 5,5'-dibromo-4,4'-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-2,2'-bithiophene, 2,5-bis(trimethyltin)thiophene[3,2-b]thiophene, Pd2(dba)3 and tri(o-methylphenyl)phosphine are dissolved in an organic solvent to obtain a reaction mixture, the reaction mixture is purged with argon, then the reaction is heated, after the reaction is completed, the obtained mixture is cooled to room temperature, an organic solvent and 2-(tributyltin)thiophene are added, the reaction is continued, then 2-bromothiophene is added to react, cooled to room temperature, and the solid is collected to obtain the organic conjugated polymer.

[0024] Preferably, the mass ratio of 5,5'-dibromo-4,4'-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-2,2'-bithiophene, Pd2(dba)3 and tri(o-methylphenyl)phosphine is 100:(1.5-2.8):(2.5-3.8).

[0025] Preferably, the mass ratio of 5,5'-dibromo-4,4'-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-2,2'-bithiophene, 2-(tributyltin)thiophene and 2-bromothiophene is 100:(0.1-1.0):(0.1-1.5), and further preferably 100:(0.1-0.5):(0.4-1.0).

[0026] Preferably, the temperature of the continued reaction is 100-120°C, and the reaction time is 10-15 minutes.

[0027] Preferably, the temperature of the reaction of adding 2-bromothiophene to react is 100-120°C, and the reaction time is 10-15 minutes.

[0028] Preferably, the 5,5'-dibromo-4,4'-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-2,2'-bithiophene is obtained by reacting 2-bromo-3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)thiophene, silver nitrate, potassium fluoride, bis(benzonitrile)palladium dichloride (PdCl2(PhCN)2).

[0029] Preferably, the 2-bromo-3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)thiophene is obtained by reacting 3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)thiophene, N-bromosuccinimide (NBS).

[0030] Preferably, the 3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)thiophene is obtained by reacting triethylene glycol monomethyl ether, 3-(2-methoxyethoxy)thiophene, p-toluenesulfonic acid (PTSA).

[0031] The third aspect of the present application provides an application of the organic conjugated polymer.

[0032] A zinc anode with a protective layer on the surface, wherein the protective layer contains the organic conjugated polymer.

[0033] A method for preparing a zinc anode with a protective layer on the surface, comprising the following steps:

[0034] The zinc foil is cleaned and dried, and then coated with an organic solution containing the organic conjugated polymer on the surface of the zinc foil, and the zinc anode with a protective layer on the surface is obtained after drying.

[0035] A zinc ion battery comprising the zinc anode.

[0036] Preferably, the zinc ion battery is a zinc-zinc symmetric battery or a battery with NH4VO4 as the cathode.

[0037] Preferably, the zinc ion battery further comprises an electrolyte containing zinc ions, a separator.

[0038] Compared with the prior art, the present application has the following advantages:

[0039] (1) The organic conjugated polymer has mixed ionic and electronic conductivity, which improves the electrodeposition kinetics and the stability of the zinc anode. The sulfur-containing main chain of the polythiophene in the organic conjugated polymer can interact with zinc ions, promoting the dissolution of zinc ions from the hydrated structure and the formation of unique channels, which can simultaneously accelerate the transport of zinc ions and regulate the electrodeposition of the zinc anode. In addition, by adjusting the side chain from an alkyl group to a hydrophilic glycol group, the polythiophene poly(2-(4,4'-bis(2-methoxyethoxy)-5'-methyl-[2,2'-thiophene]-5-yl)-5-methylthiophene) (abbreviated as pgBTTT) shows better hydrophilicity than poly[2,5-bis(3-dodecylthiophene-2-yl)thiophene] (abbreviated as pBTTT), and therefore, pgBTTT has higher film formation performance than pBTTT. Therefore, the electrochemical performance of the ZIBs based on the pgBTTT zinc anode protective layer is significantly improved, and the zinc-zinc symmetric battery is stably cycled for more than 1700 hours under the condition of 2mA cm -2 -1 The complete battery with NH4VO4 (NVO) as the cathode has a higher specific capacity (more than 520mAh g -1 , for example 528mAh g -1 ), improved rate performance and long-term cycle stability (low decay rate per cycle is less than 0.019% after 1000 cycles, for example 0.0183%).​

[0040] (2) The organic conjugated polymer according to the present application is applied to a zinc anode as a protective layer, and has ion and electron conductivity at the same time, and the reaction kinetics of zinc plating and stripping is promoted, thereby improving the reversibility and rate capability of zinc ion batteries (ZIBs). In addition, the glycolated side chain endows the protective layer with increased hydrophilicity, ensuring sufficient penetration of aqueous electrolyte. In addition, the chemical interaction between the sulfur-containing polythiophene main chain and zinc ions can promote the specific transport of zinc ions. These factors work together to result in a high-performance zinc anode, especially with long-term stability and improved rate performance. The conjugated polymer with mixed conductivity and high structural flexibility is expected to be applied to the fields of energy conversion and storage and electrochemical catalysis as a modification layer or directly as an electrode. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 Process schematic diagram of spin-coating zinc foil with the organic conjugated polymer of Example 1 and Comparative Example 1;

[0042] Figure 2 SEM and water contact angle diagrams of the zinc anode corresponding to the organic conjugated polymer of Example 1 and Comparative Example 1;

[0043] Figure 3 Battery cycle stability diagram corresponding to the organic conjugated polymer of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0044] In order to make the skilled in the art more clearly understand the technical solutions of the present application, the following examples are listed for illustration. It should be pointed out that the following examples do not constitute a limitation on the scope of protection required by the present application.

[0045] The raw materials, reagents or devices used in the following examples, if not specifically stated, can be obtained from conventional commercial channels, or can be obtained by existing known methods.

[0046] Example 1: Preparation of an organic conjugated polymer

[0047] The synthesis route of the organic conjugated polymer (named pgBTTT) of this example is as follows:

[0048]

[0049] The preparation method of the organic conjugated polymer of this example comprises the following steps:

[0050] 3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)thiophene (6): Triethylene glycol monomethyl ether (8.63 g), 3-(2-methoxyethoxy)thiophene (4 g) and p-toluenesulfonic acid (667 mg) were mixed in a round bottom flask, 150 mL of toluene was added and the reaction was carried out under reflux conditions overnight. The reaction mixture was cooled to room temperature and then quenched with saturated sodium bromide solution, the mixture was extracted with ethyl acetate three times, the organic phase was collected, dried over magnesium sulfate, filtered and concentrated under vacuum to obtain the pure product as a yellow viscous oil (3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)thiophene, 5.60 g, 65% yield);

[0051] The NMR characterization results of 3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)thiophene are: 1 HNMR (400 MHz, CDC13): δ 7.15 (dd, 1H, J = 5.1, 3 Hz), 6.72 (dd, 1H, J = 5, 1.7 Hz), 6.25 (dd, 1H, J = 3.1, 1.6 Hz), 4.12 (t, 2H, J = 4.8 Hz), 3.82 (t, 2H, J = 4.7 Hz), 3.71 (dd, 2H, J = 6.3, 3.5 Hz), 3.70 (m, 4H), 3.52 (dd, 2H, J = 5.3, 3.6 Hz), 3.38 (s, 3H).

[0052] 2-bromo-3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)thiophene (7): 3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)thiophene (3.2 g) was dissolved in THF (100 mL), cooled to -30 °C, N-bromosuccinimide (2.32 g) was added and stirred for 3 hours, then the resulting mixture was heated to room temperature and quenched with saturated sodium sulfite solution, then the mixture was extracted with diethyl ether, dried over magnesium sulfate and concentrated under reduced pressure, the crude product was purified by silica gel flash column chromatography to obtain the pure product as a yellow oil (2-bromo-3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)thiophene, 3.45 g, 82% yield).

[0053] The NMR characterization results of 2-bromo-3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)thiophene are: 1HNMR (500 MHz, CDC13): δ (ppm) 7.15 (d, 1H, J = 5.9 Hz), 6.77 (d, 1H, J = 6.0 Hz), 4.14 (t, 2H, J = 4.0 Hz), 3.80 (t, 2H, J = 4.0 Hz), 3.72 (m, 2H), 3.67-3.61 (m, 4H), 3.55 (m, 2H), 3.37 (s, 3H).

[0054] 5,5'-Dibromo-4,4'-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-2,2'-bithiophene (8) was prepared: 2-Bromo-3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)thiophene (1 g) was taken in anhydrous DMSO (dimethylsulfoxide, 10 mL) and degassed with nitrogen gas for 3 times, silver nitrate (1.042 g), potassium fluoride (356 mg) and bis(benzonitrile)dichloropalladium (PdCl2(PhCN)2) (35 mg) were added and the resulting mixture was stirred at 90 °C overnight, then cooled to room temperature and quenched with water, the aqueous phase was extracted with ethyl acetate, the organic layer was washed with water and brine, then dried over magnesium sulfate, the crude product was purified by silica gel flash column chromatography using ethyl acetate as eluent to get the white solid product (5,5'-Dibromo-4,4'-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-2,2'-bithiophene, 0.60 g, yield 60 %);

[0055] The results of the nuclear magnetic resonance characterization of 5,5'-dibromo-4,4'-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-2,2'-bithiophene are: 1 H NMR (500 MHz, CDC13): δ (ppm) 6.82 (s, 2H), 4.23 (t, 4H, J = 4.8 Hz), 3.87 (t, 4H, J = 4.8 Hz), 3.78 (dd, 4H, J = 5.9, 3.6 Hz), 3.72-3.61 (m, 8H), 3.57 (dd, 4H, J = 5.7, 3.7), 3.39 (s, 6H).

[0056] Preparation of organic conjugated polymer pgBTTT: 5,5'-dibromo-4,4'-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-2,2'-bithiophene (100 mg), 2,5-bis(trimethyltin)thiophene [3,2-b]thiophene (71.73 mg), Pd2(dba)3(2.8 mg) and tri(o-methylphenyl)phosphine (3.74 mg) were dissolved in a microwave vial with 5.0 mL of anhydrous DMF (dimethylformamide), the resulting mixture was purged with argon and then heated to 100°C for 9 hours, after the mixture was cooled to room temperature, 0.2 mL of degassed DMF and 2-(tributyltin)thiophene (0.05 mg) were added, and the reaction was stirred at 120°C for 15 minutes, 2-bromothiophene (0.1 mg) was added (2-(tributyltin)thiophene and 2-bromothiophene were used as end-capping reagents for polymer synthesis to improve the structural stability of the polymer material), and the reaction was stirred at 120°C for 15 minutes, and then the reaction mixture was cooled to room temperature, and the solid was collected and subjected to Soxhlet extraction with methanol (Soxhlet extraction for 16 hours), acetone (Soxhlet extraction for 16 hours), hexane (Soxhlet extraction for 16 hours), THF (Soxhlet extraction for 16 hours) and chloroform (Soxhlet extraction for 16 hours), the organic conjugated polymer pgBTTT was dissolved in the chloroform fraction, the organic conjugated polymer pgBTTT was precipitated in methanol, and was collected and dried under high vacuum to a blue solid (organic conjugated polymer pgBTTT, 35 mg, yield 36%).

[0057] The nuclear magnetic resonance characterization results of the organic conjugated polymer pgBTTT are as follows: 1 H NMR (500 MHz, CDCl3): δ (ppm) 6.98 (br s), 4.18 (br s), 3.67 (br m), 3.56 (br s), 3.38 (br s);

[0058] The Mn of the organic conjugated polymer pgBTTT of this example is 13900 Da, and the Mw is 23600 Da.

[0059] Comparative Example 1

[0060] The following polymer (named pBTTT) was prepared according to the preparation method of Reference Example 1:

[0061]

[0062] Comparative Example 2

[0063] The polythiophene with an alcohol amine group in the side chain prepared in CN105860033A Example 2.

[0064] Product effect test

[0065] 1. Preparation of zinc anode

[0066] A method for preparing a zinc anode with a surface protection layer, comprising the following steps:

[0067] Firstly, the zinc foil is treated with 2 mol / L hydrochloric acid to remove the oxide layer on the surface of the zinc foil, then the treated zinc foil is immersed in a deionized water solution and subjected to ultrasonic treatment, and finally dried with nitrogen for use;

[0068] The organic conjugated polymers pgBTTT and pBTTT obtained in Example 1 and Comparative Example 1 are respectively prepared into 5 mg / ml chloroform solutions, and then the two solutions are respectively spin-coated on the surface of the zinc foil at a rotation speed of 500 rpm, the spin-coating time is 60 seconds, and dried to obtain a zinc anode with a surface protection layer (zinc anode of Example 1, zinc anode of Comparative Example 1) with a thickness layer of about 300-500 nm.

[0069] 2. Preparation of NH4VO4 cathode

[0070] Preparation of NH4VO4 cathode, comprising the following steps:

[0071] The synthesis process of NH4VO4 is as follows: firstly, NH4VO3 (0.64 g) is dissolved in 80 mL of distilled water, and then H2C2O4 (0.828 g) is slowly added to the solution until it turns light green, then the light green solution is transferred to a 100 mL pressure cooker and subjected to hydrothermal reaction at 180°C for 3 hours, after the hydrothermal reaction, the product is washed with distilled water and ethanol for 3 times respectively, finally, the obtained NVO is freeze-dried and stored under dry conditions for later use;

[0072] Firstly, the synthesized NVO, Super P conductive carbon black and polyvinylidene fluoride are mixed in NMP (N-methyl pyrrolidone) at a mass ratio of 8:1:1 to obtain a slurry, which is coated on a titanium foil and dried at 80°C overnight to obtain a NH4VO4 cathode.

[0073] 3. Preparation of zinc-zinc symmetric battery

[0074] The preparation process of zinc-zinc symmetric battery is as follows: taking the zinc anode with a surface protection layer, then assembling it in CR2025 coin type battery mode, using ZnSO4 aqueous solution (2M) as electrolyte solution, and using glass fiber separator to separate the zinc anode and NH4VO4 cathode to obtain a zinc-zinc symmetric battery. Constant current test is carried out on LAND system, the potential range is 0.4 to 1.4V, and the current density is 2-10A g -1 .

[0075] Figure 1 Process schematic diagram for spin-coating zinc foil with organic conjugated polymer of Example 1 and Comparative Example 1.Figure 1 "pBTTT" corresponds to the organic conjugated polymer prepared in Comparative Example 1, "pgBTTT" corresponds to the organic conjugated polymer prepared in Example 1, "Pure zinc" means pure zinc, "Spin coating" means spin coating, "Zinc plating" means zinc plating, "Dendritic zinc" means dendritic zinc, "Smoothly deposited zinc" means smoothly deposited zinc.

[0076] In Figure 1 The molecular structures of the synthesized pBTTT and pgBTTT are shown in FIG. 1. They share the same thiophene backbone, in which the conjugated structure is beneficial for electron transport, while the side chains of pgBTTT are glycol groups, which have better hydrophilicity than the alkyl side chains of pBTTT. In addition, the arrangement of the side chains of pgBTTT can reduce the disorder of the backbone and enhance the pi-stacking, thus facilitating ion transport. To ensure the uniform and consistent coating of the organic conjugated polymer on the zinc anode surface, a simple spin coating method was adopted, and the resulting structures are denoted as Zn@pBTTT (Comparative Example 1 zinc anode) and Zn@pgBTTT (Example 1 zinc anode), respectively. Due to the above advantages, including improved mixed electronic and ionic conductivity, hydrophilicity and film-forming ability, the zinc anode coated with the pgBTTT layer is expected to have higher stability, which can avoid the influence of zinc dendrite growth and adverse side reactions in aqueous electrolyte medium Figure 1 ).

[0077] By pgBTTT, as a protective layer of zinc anode, it is expected to integrate three important features: (1) mixed electronic and ionic conductivity means promoting the simultaneous transport of electrons and zinc ions, which is beneficial for the smooth electrochemical plating and stripping of zinc anode, thus pgBTTT helps to avoid the growth of zinc dendrites; (2) the sulfur-containing polythiophene backbone can chemically interact with zinc ions, providing traction for the desorption of zinc ions from their hydration structure and generating dedicated channels, which not only can promote the diffusion of zinc ions, but also can prevent water from directly contacting the zinc anode to some extent, thus preventing adverse side reactions caused by aqueous electrolyte, and (3) glycol side chains can improve the hydrophilicity and film-forming ability of the protective layer, so as to ensure the coating of a complete and dense protective layer on the zinc anode with high electrolyte permeability. In summary, the pgBTTT protective layer can simultaneously solve the problems of zinc dendrite growth, competitive HER, zinc corrosion and byproduct accumulation, thus it is expected to further improve the cycle durability and energy density of ZIBs.

[0078] Due to the good film-forming ability, the pgBTTT protective layer was uniformly and densely coated on the zinc anode surface after spin-coating, however, the surface coated with pBTTT protective layer was uneven, presenting randomly distributed string-like particles and agglomerates, which was harmful to achieve smooth deposition of zinc and prevent undesirable side reactions.

[0079] Figure 2 SEM images and water contact angle images of zinc anodes corresponding to the organic conjugated polymers of Example 1, Comparative Example 1.

[0080] Before coating, the zinc foil surface had many chaotic processing scratches, which was not conducive to the smooth deposition of zinc Figure 2 The SEM image of the zinc surface in Figure c is shown in the middle. Therefore, interfacial engineering (e.g., protective layer coating) is crucial for stabilizing zinc anodes. Figure 2 The SEM image of the zinc electrode coated with pgBTTT material is shown in Figure a. From the figure, it can be seen that the pgBTTT protective layer coated on the zinc anode surface looks like a combination of many dense micron-sized particles, which is likely due to the tight and regular arrangement of pgBTTT chains. The size of these polymer combinations ranges from one to two microns. However, the cross-sectional morphology results show that the coated pgBTTT is a uniform layer with a porous surface (pore size at the micron level), which is conducive to stable zinc deposition. Figure 2 The SEM image of the zinc electrode coated with pBTTT material is shown in Figure b. In contrast, the roughness of the pBTTT layer is much higher, with disordered polymer agglomerates of various shapes. The exposed zinc area lacks polymer coating, which can lead to direct contact between the zinc anode and the aqueous electrolyte, resulting in undesirable side reactions and zinc dendrite growth. In addition, due to the improvement of film-forming ability, there is almost no gap formed between the zinc anode and the pgBTTT protective layer, which helps to reduce the transmission resistance of ions and electrons, thereby improving the electrochemical reaction kinetics. On the contrary, there is a clear gap between the pBTTT coating layer and the zinc metal, which can be peeled off from the zinc anode surface during repeated zinc plating and stripping processes. In addition, pgBTTT tends to form a thicker and denser coating on the zinc anode surface compared to pBTTT under the same spin-coating experimental conditions. As discussed earlier, the hydrophilicity of the protective layer plays a key role in the zinc ion transport behavior and the electrochemical performance of ZIBs, so corresponding water contact angle measurements were carried out to test this special surface property. Figure 2Figs. d, e, and f are schematic diagrams of the contact angle of the zinc electrode coated with pgBTTT, the zinc electrode coated with pBTTT, and the pure zinc electrode, respectively. The results show that Zn@pgBTTT exhibits the best hydrophilicity, with the minimum water contact angle of 55.7°, while the values of Zn@pBTTT and pure zinc are 75.2° and 96.4°, respectively. In short, the optimized glycolated side chain of pgBTTT endows it with ideal morphological structure and surface properties to achieve a stable zinc anode.

[0081] Figure 3 Fig. 2 is a graph of the cycle stability of the batteries corresponding to the organic conjugated polymers of Example 1 and Comparative Example 1. Figure 3 “Voltage” in Fig. 2 represents voltage, and “Time” represents time.

[0082] The symmetric cell is a typical prototype for studying the electrochemical performance of zinc anodes, which is not interfered by the cathode and the complex electrode / electrolyte interface. By performing the corresponding charge-discharge results at a constant current of 2 mA cm -2 , 1 mAh cm -2 , it can be seen that the zinc anode coated with the pgBTTT protective layer exhibits the best cycle stability, which can be stably operated for 1700 hours Figure 3 (a) in Fig. 2). In contrast, Zn@pBTTT and pure zinc (Zn) can only be cycled for less than 700 and 300 hours, respectively. In addition, although the initial deposition overpotential of Zn@pgBTTT, Zn@pBTTT, and pure zinc is similar, about 70 mV, after long-term cycling, the overpotential value of Zn@pgBTTT decreases to about 30 mV Figure 3 (c) in Fig. 2), which indicates that the pgBTTT protective layer can improve the deposition kinetics of the zinc anode. On the contrary, Zn@pBTTT shows serious voltage fluctuation during the cycle process, especially after 600 hours, the overpotential exceeds 1 V, and it dies immediately. As for the pure zinc anode, an internal short circuit occurs after about 250 hours of cycling, mainly due to the penetration of the grown zinc dendrites through the separator. Subsequently, galvanostatic charge-discharge experiments at different current densities from 1 to 10 mA cm -2 , 1 mAh cm -2 were carried out to evaluate the rate capability of the zinc anode. As shown in Figure 3 , the deposition overpotential of Zn@pgBTTT is stable and shows a slow increasing trend with the increase of the current density, and when the current density returns to 1 mA cm -2 , it can be further stably cycled for more than 100 hours. In contrast, Zn@pBTTT not only shows a larger deposition overpotential when the current density increases to 5 mA cm -2 or higher, but also shows a large fluctuation in the overpotential when the current density returns to 1 mA cm -2The latter is easier to die. Although the pure zinc anode shows a smaller deposition overpotential at a relatively low current density, its deposition overpotential starts to fluctuate and rises to more than 1 V at 10 mA cm -2 , and moreover, after returning to 1 mA cm -2 , the deposition overpotential value is much higher than the initial value, and the corresponding symmetric cell dies soon. Figure 3 Figure b characterizes the cycle stability of two types of materials when the current density is reduced from 10 mA cm -2 to 1 mA cm -2 . The deposition overpotential of Zn@pgBTTT shows a slow growth trend with the increase of current density, and its stable cycle is more than 100 hours.

[0083] To further study the effect of current density on the cycle stability of zinc anode, the symmetric cell with a current density of 5 mA cm -2 and 1 mAh cm -2 was tested by constant current cycle. The results show that compared with Zn@pBTTT and pure zinc, Zn@pgBTTT has better operation stability (more than 500 hours) and smaller deposition overpotential, which further proves the protection ability of pgBTTT protective layer to zinc anode. In general, the pgBTTT protective layer can ensure reversible zinc deposition and stripping during long-term cycling, and improve the rate capability in the current density range of 1-10 mA cm -2 .

[0084] The molecular skeleton selected by Comparative Example 2 is a single thiophene, while the molecular skeleton selected by the present application is a combined unit skeleton of thiophene- thiophene-thiophene, which has a longer conjugation length and is more conducive to charge transmission, and has a higher carrier mobility and ion mobility. In terms of side chains, the present application optimizes the length of the side chain and confirms that the side chain containing four oxygen atoms has the best performance. In addition, the present application applies this type of material to the field of energy storage aqueous zinc battery and provides battery characterization data, expanding the application scenarios of this type of material.

Claims

1. A zinc anode provided with a surface protection layer, characterized in that The protective layer contains an organic conjugated polymer, and the structural general formula of the organic conjugated polymer is as shown in the following formula: where n is a positive integer greater than 0.

2. Zinc anode according to claim 1, characterized in that The n is a positive integer between 1-1000.

3. Zinc anode according to claim 1, characterized in that The number average molecular weight Mn of the organic conjugated polymer is 10,000-50,000.

4. The zinc anode according to claim 1, characterized in that The weight average molecular weight Mw of the organic conjugated polymer is 20,000-80,000.

5. Zinc anode according to any one of claims 1 to 4, characterized in that The preparation method of the organic conjugated polymer comprises the following steps: The halogen and methoxyethoxy containing bithiophene is reacted with tin thiophene to obtain the organic conjugated polymer.

6. Zinc anode according to claim 5, characterized in that The halogen and methoxyethoxy containing bithiophene comprises 5,5'-dibromo-4,4'-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-2,2'-bithiophene; And / or, the tin thiophene comprises 2,5-bis(trimethylstannyl)thiophene[3,2-b]thiophene.

7. Zinc anode according to claim 6, characterized in that The 5,5'-dibromo-4,4'-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-2,2'-bithiophene and 2,5-bis(trimethylstannyl)thiophene[3,2-b]thiophene are reacted to obtain the organic conjugated polymer; And / or, the mass ratio of the 5,5'-dibromo-4,4'-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-2,2'-bithiophene to 2,5-bis(trimethylstannyl)thiophene[3,2-b]thiophene is 100:(50-100); And / or, the temperature of the reaction is 90-100℃, and the reaction time is 7-9 hours; And / or, in the process of preparing the organic conjugated polymer, tris(dibenzylideneacetone)dipalladium, tri(o-methylphenyl)phosphine, 2-(tributylstannyl)thiophene and 2-bromothiophene are also used.

8. A zinc-ion battery, characterized in that, The zinc anode comprises the zinc anode according to any one of claims 1-7.

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