Composite current collector, preparation method thereof and non-cathode metal battery

Abstract

The invention relates to the technical field of battery materials, and discloses a composite current collector, a preparation method thereof and a negative-electrode-free metal battery. The composite current collector comprises a base material and a functional layer covering the surface of the base material, and the functional layer comprises barium titanate accounting for 85-95% of the mass of the functional layer, an adhesive accounting for 2-5% of the mass of the functional layer and a conductive agent accounting for 0-10% of the mass of the functional layer. The barium titanate in the functional layer has ferroelectricity, and an electric field generated during charging and discharging of the battery can trigger polarization change in the barium titanate, so that bound charges in the barium titanate can be activated, and the surface of the barium titanate is charged; the protons generated by the organic solvent in the electrolyte are generated at the positive electrode and can be dissociated to the negative electrode to generate hydrogen, and bound charges generated by barium titanate just neutralize the protons on the surface of the negative electrode, so that the process of inhibiting gas production is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, in particular to a composite current collector, a preparation method thereof and a metal anode-free battery. BACKGROUND

[0002] The metal anode-free battery is a battery with lithium iron phosphate, ternary, layered oxide material, prussian blue analog material, polyanion as the positive electrode, and carbon-coated metal foil fluid as the negative electrode. The battery mainly uses ether as the solvent, adds metal salt (such as fluorine salt, boron salt and perchlorate salt) electrolyte and various additives (such as film forming type, flame retardant type and overcharge protection type), and forms an electrolyte. Although the metal anode-free battery has the advantages of good low-temperature performance, low cost and high energy density, its gas production seriously hinders its development.

[0003] In view of this, the present application is proposed. SUMMARY

[0004] The purpose of the present application is to provide a composite current collector, a preparation method thereof and a metal anode-free battery, aiming to improve at least one problem mentioned in the background art.

[0005] The present application is realized as follows: In a first aspect, the present application provides a composite current collector, comprising a substrate and a functional layer covering the surface of the substrate. The functional layer comprises 85-95% of barium titanate, 2-5% of an adhesive and 0-10% of a conductive agent by mass of the functional layer.

[0006] In an optional embodiment, the adhesive is a silicate. Optionally, the silicate is at least one selected from sodium silicate and potassium silicate.

[0007] In an optional embodiment, the functional layer further comprises a conductive agent, and the conductive agent accounts for 2.5-10% of the mass of the functional layer. Optionally, the conductive agent is at least one selected from Ks-6, Ks-12 and CNT.

[0008] In an optional embodiment, at least one of the following features (1) and (2) is further included: (1) The thickness of the functional layer is 5-15 μm. (2) The substrate is a copper foil.

[0009] In a second aspect, the present application provides a preparation method of the composite current collector, comprising: Coating the coating material on the surface of the substrate, and calcining in an inert atmosphere to form the functional layer on the surface of the substrate. In an optional embodiment, the preparation method of the coating material comprises: The dispersion liquid is prepared by mixing raw materials with anhydrous ethanol, the raw materials including titanate, barium salt and binder; An acid liquid with pH of 3-4 is provided; The acid liquid is added dropwise into the dispersion liquid under stirring, and the temperature is controlled at 80-95℃, and the stirring is continued until a colloidal mixture is obtained; The volume ratio of the acid liquid to the dispersion liquid is 0.07-0.1:1.

[0010] In an optional embodiment, the titanate is at least one of tetrabutyl titanate and tetraisopropyl titanate; Optionally, the barium salt is barium acetate; Optionally, the acid liquid is an aqueous solution of acetic acid; Optionally, the dispersion liquid further includes a conductive agent, and the mass ratio of the conductive agent to the titanate is 0.02-0.05:1; Optionally, the mass ratio of the anhydrous ethanol to the titanate is 40-65:1.

[0011] In an optional embodiment, the dispersion liquid further includes a dispersant, and the mass ratio of the dispersant to the titanate is 0.01-0.05:1; Optionally, the dispersant is at least one of sodium carboxymethyl cellulose, sodium carboxymethyl starch, polyacrylic acid and sodium polyacrylate.

[0012] In an optional embodiment, the calcination temperature is 700-800℃, and the calcination time is 5-10h; Optionally, after the calcination, annealing is further included for 1.5-2.5h; Optionally, the inert atmosphere is argon atmosphere.

[0013] In a third aspect, the application provides a metal anode-free battery including the composite current collector according to any one of the preceding embodiments or prepared by the preparation method according to any one of the preceding embodiments.

[0014] The application has the following beneficial effects: The composite current collector provided by the embodiments of the application has a functional layer on the surface, and the functional layer contains barium titanate. The barium titanate has ferroelectricity, and the electric field generated during the charging and discharging of the battery can induce the polarization change in the barium titanate. In this way, the bound charges in the barium titanate can be activated, and the surface of the barium titanate is charged. The protons generated by the organic solvent in the electrolyte are generated at the positive electrode and will be separated to the negative electrode to generate hydrogen. The bound charges generated by the barium titanate neutralize the protons on the surface of the negative electrode, so that the process of generating gas is inhibited. DETAILED DESCRIPTION

[0015] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. If specific conditions are not specified in the embodiments, the conventional conditions or the conditions suggested by the manufacturers are adopted. If the manufacturers of the reagents or instruments are not specified, the conventional products that can be purchased in the market are adopted.

[0016] The features and performances of the present application will be further described in detail below in combination with the embodiments.

[0017] The embodiments of the present application provide a composite current collector, comprising a substrate and a functional layer covering the surface of the substrate. The functional layer comprises 85-95% (for example, 85%, 90% or 95%) of barium titanate, 2-5% (for example, 2%, 3%, 4% or 5%) of a bonding agent and 0-10% (for example, 0%, 2%, 4%, 6%, 8% or 10%) of a conductive agent.

[0018] The composite current collector provided by the embodiments of the present application has the barium titanate in the functional layer on the surface, the barium titanate has ferroelectricity, the electric field generated during the charging and discharging of the battery can induce the polarization change in the barium titanate, so that the bound charges in the barium titanate are activated, and the surface of the barium titanate is charged; the protons generated by the organic solvent in the electrolyte are generated at the positive electrode and will be separated to the negative electrode to generate hydrogen, and the bound charges generated by the barium titanate neutralize the protons on the surface of the negative electrode, so that the process of inhibiting gas generation is achieved.

[0019] Therefore, the barium titanate in the functional layer of the composite current collector reduces the gas generation of the battery, and has the effects of prolonging the cycle life and improving the safety.

[0020] Optionally, the functional layer comprises 86-95% of barium titanate, 2.5-4.5% (for example, 2%, 3%, 4% or 5%) of a bonding agent and 0-4.5% of a conductive agent.

[0021] Optionally, the bonding agent is a silicate.

[0022] Specifically, the silicate is at least one selected from sodium silicate and potassium silicate. These silicates have the characteristics of high temperature resistance.

[0023] Optionally, the functional layer further comprises a conductive agent, and the conductive agent accounts for 3.5-10% (for example, 5%, 8% or 10%) of the mass of the functional layer, preferably 2.5-4.5%. The addition of the conductive agent is used to improve the conductivity of the current collector.

[0024] Optionally, the conductive agent is selected from at least one of Ks-6 (Ks-6 is a graphite flake with a particle size of D90 at 6 microns), Ks-12 (is a graphite flake with a particle size of D90 at 12 microns), and CNT. The above-mentioned several conductive agents are high-temperature-resistant conductive agents.

[0025] Optionally, to ensure better performance of the composite current collector applied to the anode-free battery, the thickness of the functional layer is 5-15 μm (for example, 5 μm, 10 μm, or 15 μm); Optionally, the substrate is a copper foil or other common current collector material.

[0026] The preparation method of the composite current collector provided by the embodiments of the present application comprises: coating the coating material to the surface of the substrate, and calcining under an inert atmosphere to form the functional layer on the surface of the substrate. Specifically, the preparation method comprises: S1, providing a dispersion liquid The raw materials are mixed with anhydrous ethanol to obtain a dispersion liquid. The raw materials include titanate, barium salt, adhesive, conductive agent, and dispersant.

[0027] The conductive agent is added to improve the conductivity of the current collector; the dispersant is added to improve the uniform dispersion of each component in the dispersion liquid.

[0028] The conductive agent and the adhesive are selected from high-temperature-resistant materials to avoid subsequent decomposition by calcination.

[0029] The ratio of the amounts of the titanate and the barium salt is just enough to ensure complete reaction.

[0030] Optionally, the titanate is selected from at least one of tetrabutyl titanate and tetraisopropyl titanate.

[0031] Optionally, the barium salt is barium acetate.

[0032] Optionally, the mass ratio of the conductive agent to the titanate is 0.02-0.05:1 (for example, 0.02:1, 0.03:1, 0.04:1, or 0.05:1).

[0033] Optionally, the mass ratio of the dispersant to the titanate is 0.01-0.05:1 (for example, 0.01:1, 0.02:1, 0.03:1, 0.04:1, or 0.05:1). The dispersant in the above ratio range can uniformly disperse each component.

[0034] Optionally, the dispersant is selected from at least one of sodium carboxymethyl cellulose, sodium carboxymethyl starch, polyacrylic acid, and sodium polyacrylate.

[0035] Optionally, the mass ratio of the anhydrous ethanol to the titanate is 40-65:1 (e.g., 40:1, 50:1, 60:1, or 65:1). The amount of anhydrous ethanol in the above ratio range can ensure that a dispersion liquid with a suitable concentration is obtained.

[0036] S2, providing an acid liquid The acid and deionized water are mixed to obtain an acid liquid with a pH of 3-4.

[0037] The acid functions to inhibit the strong hydrolysis of the titanate, thereby prolonging the hydrolysis time of the titanate.

[0038] Optionally, the acid is acetic acid. The acetic acid can be completely carbonized in the subsequent calcination process, without introducing impurity elements, thereby further improving the electrochemical performance of the current collector when applied to a negative electrode-free metal battery.

[0039] Optionally, the barium salt is barium acetate.

[0040] S3, obtaining a coating material The acid liquid is added dropwise to the dispersion liquid under stirring, and the temperature is controlled at 80-95°C (e.g., 80°C, 85°C, 90°C, or 95°C), and the stirring is continued until a colloidal mixture is obtained.

[0041] In this step, the titanate and the barium salt react with each other to form barium titanate, and the solution system gradually changes into a gel.

[0042] The coating material is prepared by in-situ generation of barium titanate and gelation. The presence of the gel can effectively prevent the agglomeration of the tiny barium titanate, thereby ensuring that the barium titanate can be uniformly coated on the current collector. This in-situ generation of barium titanate improves the electrochemical performance of the prepared current collector.

[0043] Optionally, the stirring time is 11-20 h (e.g., 11 h, 15 h, 18 h, or 20 h). Optionally, the volume ratio of the acid liquid to the dispersion liquid is 0.07-0.1:1 (e.g., 0.07:1, 0.08:1, or 0.1:1). The above ratio can ensure that the titanate is sufficiently hydrolyzed.

[0044] S4, coating The above colloidal coating material is uniformly coated on the surface of the substrate. The coated substrate is calcined at 700-800°C (e.g., 700°C, 750°C, or 800°C) under an inert atmosphere for 5-10 h (e.g., 5 h, 8 h, or 10 h), and then annealed for 1.5-2.5 h (e.g., 1.5 h, 2 h, or 2.5 h).

[0045] After rolling, a current collector with a functional layer is obtained.

[0046] Optionally, the inert atmosphere is an argon atmosphere.

[0047] The negative electrode-free metal battery provided by the embodiment of the application comprises the composite current collector provided by the embodiment of the application or the composite current collector prepared by the preparation method provided by the embodiment of the application.

[0048] Embodiment 1 7.5 g of tetrabutyl titanate (molecular weight 340), 5.61 g of barium acetate (molecular weight 255), 0.2 g of sodium silicate (molecular weight 122), 0.3 g of CMC (molecular weight 17000), 0.2 g of Ks-6 / Ks-12 / CNT (molecular weight 12) and 400 g of anhydrous ethanol (molecular weight 46) are uniformly mixed to obtain a dispersion liquid; Acetic acid and deionized water are uniformly mixed to obtain an acid liquid with a pH of 3.5; Under stirring, the acid liquid is added dropwise into the dispersion liquid, the volume ratio of the acid liquid to the dispersion liquid is 0.08:1, the reaction temperature is controlled at 85°C, and stirring is performed for 12 h to obtain a colloidal coating material; The coating material is coated on the surface of an aluminum foil with a thickness of 12 µm, then calcination is performed at 750°C for 8 h under an argon atmosphere, followed by annealing for 2 h, and finally rolling to obtain a composite current collector with a functional layer.

[0049] The thickness of the functional layer in the obtained composite current collector is 10 microns, the proportion of barium titanate in the functional layer is 90%, the proportion of sodium silicate is 3.5%, the proportion of the conductive agent is 3.5%, and the balance is the product after carbonization of the dispersant or impurities.

[0050] Embodiment 2 7.5 g of tetrabutyl titanate, 5.61 g of barium acetate, 0.22 g of sodium silicate and 0.3 g of CMC are uniformly mixed with 400 g of anhydrous ethanol to obtain a dispersion liquid; Acetic acid and deionized water are uniformly mixed to obtain an acid liquid with a pH of 3.5; Under stirring, the acid liquid is added dropwise into the dispersion liquid, the volume ratio of the acid liquid to the dispersion liquid is 0.07:1, the reaction temperature is controlled at 85°C, and stirring is performed for 12 h to obtain a colloidal coating material; The coating material is coated on the surface of a copper foil with a thickness of 8 µm, then calcination is performed at 750°C for 8 h under an argon atmosphere, followed by annealing for 2 h, and finally rolling to obtain a composite current collector with a functional layer.

[0051] The thickness of the functional layer in the obtained composite current collector is 10 microns, the proportion of barium titanate in the functional layer is 95%, the proportion of sodium silicate is 4.0%, and the balance is the product after carbonization of the dispersant or impurities.

[0052] Embodiment 3 7.5g tetrabutyl titanate, 5.61g barium acetate, 0.14g sodium silicate, 0.2g CMC, 0.14g Ks-6 / Ks-12 / CNT and 400g anhydrous ethanol were mixed to obtain a dispersion liquid; Acetic acid and deionized water were mixed to obtain an acid solution with a pH of 4; The acid solution was added dropwise to the dispersion liquid under stirring, the volume ratio of the acid solution to the dispersion liquid was 0.18:1, and the reaction temperature was controlled at 80℃, and stirring was performed for 20h to obtain a colloidal coating material; The coating material was coated on the surface of an 8µm copper foil, and then calcined at 700℃ for 10h under an argon atmosphere, followed by annealing for 2.5h, and finally roll-pressed to obtain a composite current collector with a functional layer.

[0053] The thickness of the functional layer in the obtained composite current collector was 15 microns, the proportion of barium titanate in the functional layer was 93%, the proportion of sodium silicate was 2.5%, the proportion of the conductive agent was 2.5%, and the balance was the product after carbonization of the dispersant or impurities.

[0054] Example 4 7.5g tetrabutyl titanate, 5.61g barium acetate, 0.27g sodium silicate, 0.4g CMC, 0.27g Ks-6 / Ks-12 / CNT and 400g anhydrous ethanol were mixed to obtain a dispersion liquid; Acetic acid and deionized water were mixed to obtain an acid solution with a pH of 3; The acid solution was added dropwise to the dispersion liquid under stirring, and the reaction temperature was controlled at 95℃, and stirring was performed for 11h to obtain a colloidal coating material; The coating material was coated on the surface of an 8µm copper foil, and then calcined at 800℃ for 5h under an argon atmosphere, followed by annealing for 1.5h, and finally roll-pressed to obtain a composite current collector with a functional layer.

[0055] The thickness of the functional layer in the obtained composite current collector was 5 microns, the proportion of barium titanate in the functional layer was 86%, the proportion of sodium silicate was 4.5%, the proportion of the conductive agent was 4.5%, and the balance was the product after carbonization of the dispersant or impurities.

[0056] Example 5 This example is basically the same as Example 2, except that 7.5g tetrabutyl titanate and 5.61g barium acetate are replaced by 5.13g nano-sized barium titanate fine powder (particle size 50~100nm).

[0057] Comparative Example 1 This comparative example is basically the same as Example 2, except that tetrabutyl titanate and barium acetate are not included in the raw materials.

[0058] Comparative Example 2 The comparative example is the copper foil used as the substrate in Example 2.

[0059] Comparative Example 3 The comparative example is basically the same as Example 2, except that the acid solution is replaced with an equal amount of deionized water.

[0060] Experimental Example The composite current collectors prepared in each of the examples and comparative examples are assembled into a negative electrode-free sodium metal battery or a negative electrode-free lithium metal battery.

[0061] Negative electrode-free sodium metal battery: A positive electrode sheet is provided, which uses a carbon-coated aluminum foil as a current collector. The positive electrode sheet is prepared by mixing sodium iron phosphate pyrophosphate, conductive carbon black, PVDF, and PVP in a ratio of 95:2:2:1, adding them into a solvent (NMP) to obtain a positive electrode slurry, and coating the positive electrode slurry onto the surface of the carbon-coated aluminum foil. An electrolyte is provided, which is 1M sodium salt (LiPF6) + solvent (diethylene glycol dimethyl ether). The separator is a 20-micron PP separator. The current collector is the current collector prepared or provided in each of the examples or comparative examples.

[0062] The electrochemical performance of the negative electrode-free sodium metal battery is tested. The test methods are: charge-discharge capacity, initial coulombic efficiency, 5C capacity retention rate (compared with 0.5C normal cycle, the percentage of capacity compared with 0.5C cycle), capacity retention rate after 100 cycles of charge-discharge at 0.1C / 0.1C, gas production, and capacity retention rate after 300 cycles of charge-discharge at 0.5C / 1C.

[0063] Negative electrode-free lithium metal battery: A positive electrode sheet is provided, which uses a carbon-coated aluminum foil as a current collector. The positive electrode sheet is prepared by mixing NCM811, conductive carbon black, PVDF, and PAA in a ratio of 95:2:2:1, adding them into a solvent (NMP) to obtain a positive electrode slurry, and coating the positive electrode slurry onto the surface of the carbon-coated aluminum foil. An electrolyte is provided, which is 1M lithium salt (LiPF6) + solvent (diethylene glycol dimethyl ether). The separator is a 20-micron PP separator. The current collector is the current collector prepared or provided in each of the examples or comparative examples.

[0064] The electrochemical performance of the negative electrode-free metal battery is tested. The test methods are: charge-discharge capacity, initial coulombic efficiency, 5C capacity retention rate (compared with 0.5C normal cycle, the percentage of capacity compared with 0.5C cycle), capacity retention rate after 100 cycles of charge-discharge at 0.1C / 0.1C, gas production, and capacity retention rate after 300 cycles of charge-discharge at 0.5C / 1C. The test results are recorded in Table 1.

[0065] Example 1 is the test result used in sodium battery; Other examples and comparative examples are the test results used in lithium battery.

[0066] Test results of each example and comparative example in Table 1

[0067] As can be seen from Table 1, the composite current collector prepared by each example of the present application has a lower gas production when applied in sodium battery or lithium battery. The gas production and electrochemical performance of examples 2 to 5 are obviously better than those of comparative examples 1 and 2, which indicates that the composite current collector provided by the present application has good electrochemical performance when applied in metal anode-free battery. Comparing comparative example 3 with example 2, the gas production inhibition of comparative example 3 is obviously worse, which indicates that if the acid solution is not used to inhibit the hydrolysis of titanate during the preparation process, the stability of barium titanate precursor is poor, so that the current collector with good electrochemical performance cannot be prepared. Comparing example 5 with example 2, the cycle performance of example 5 is poor, which indicates that the performance of the current collector prepared by the method of generating barium titanate in the gel formation process is better than that of the current collector prepared by the method of directly mixing nano barium titanate with other raw materials to form a gel to form a functional layer.

[0068] In summary, due to the presence of barium titanate in the functional layer of the composite current collector provided by the present application, the battery gas production is reduced, which prolongs the cycle life and improves the safety.

[0069] The above only describes the preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A composite current collector, characterized in that, Includes a substrate and a functional layer covering the surface of the substrate; The functional layer comprises 85-95% barium titanate, 2-5% adhesive, and 0-10% conductive agent by mass.

2. The composite current collector according to claim 1, characterized in that, The adhesive is a silicate; Optionally, the silicate is selected from at least one of sodium silicate and potassium silicate.

3. The composite current collector according to claim 1, characterized in that, The functional layer further includes a conductive agent, which accounts for 2.5% to 10% of the mass of the functional layer. Optionally, the conductive agent is selected from at least one of Ks-6, Ks-12 and CNT.

4. The composite current collector according to claim 1, characterized in that, It also includes at least one of the following features (1) and (2): (1) The thickness of the functional layer is 5~15μm; (2) The substrate is copper foil.

5. A method for preparing a composite current collector as described in any one of claims 1 to 4, characterized in that, include: The coating material is applied to the surface of the substrate and calcined in an inert atmosphere to form the functional layer on the surface of the substrate.

6. The preparation method according to claim 5, characterized in that, The preparation method of the coating material includes: A dispersion is provided by uniformly mixing raw materials with anhydrous ethanol to obtain a dispersion, wherein the raw materials include titanate, barium salt and the binder; Provide an acidic solution with a pH of 3-4; Under stirring conditions, the acid solution is added dropwise to the dispersion, and the temperature is controlled at 80~95℃. Stirring is continued until a colloidal mixture is obtained. The volume ratio of the acid solution to the dispersion is 0.07~0.1:

1.

7. The preparation method according to claim 6, characterized in that, The titanate is selected from at least one of tetrabutyl titanate and tetraisopropyl titanate; Optionally, the barium salt is barium acetate; Optionally, the acid solution is an aqueous solution of acetic acid; Optionally, the dispersion further includes a conductive agent, wherein the mass ratio of the conductive agent to the titanate is 0.02~0.05:1; Optionally, the mass ratio of the anhydrous ethanol to the titanate is 40-65:

1.

8. The preparation method according to claim 7, characterized in that, The dispersion also includes a dispersant, wherein the mass ratio of the dispersant to the titanate is 0.01~0.05:1; Optionally, the dispersant is selected from at least one of sodium carboxymethyl cellulose, sodium carboxymethyl starch, polyacrylic acid, and sodium polyacrylate.

9. The preparation method according to claim 5, characterized in that, The calcination temperature is 700~800℃, and the calcination time is 5~10h; Optionally, annealing for 1.5 to 2.5 hours is also included after calcination; Optionally, the inert atmosphere is an argon atmosphere.

10. A negative electrode-free metal battery, characterized in that, The composite current collector includes the composite current collector as described in any one of claims 1 to 4 or the composite current collector prepared by the preparation method described in any one of claims 5 to 9.

Images