Polydopamine modified cellulose nanocrystal composite diaphragm, preparation method thereof and application of polydopamine modified cellulose nanocrystal composite diaphragm in battery

Abstract

The invention discloses a polydopamine modified cellulose nanocrystal composite diaphragm. According to the lithium metal battery composite diaphragm provided by the invention, the modified layer of the diaphragm has good electrolyte permeability and an ordered nanopore structure, and can guide uniform lithium ion flux. According to the present invention, the CNC is coated with the polydopamine, and has the extremely high mechanical property, such that the growth of the lithium dendrites can be effectively inhibited, the metal ions coating the CNC are chelated with the polydopamine, the alloying SEI layer can be formed on the lithium metal surface, the metal ions dissolved in the positive electrode can be adsorbed, and the cycle performance and the safety performance of the battery can be ultimately improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and particularly relates to a polydopamine-modified cellulose nanocrystal composite separator and a preparation method thereof and an application thereof in a battery. Background Art

[0002] The interfacial instability between the lithium metal anode and the electrolyte, the drastic growth of lithium dendrites, the generation of "dead lithium", and the uncontrolled volume change lead to the rapid loss of capacity during the charge and discharge cycles of the battery, restricting the practical application of the lithium metal anode. In addition to solving the limitations of the lithium metal anode, a great deal of research work must be devoted to studying the cathode to achieve a high-energy-density lithium metal full battery with long cycles. In recent years, cathode materials with a high nickel (Ni) content (LiNi x M 1-x O2, M = Mn, Co, x≥0.6) have been applied to lithium metal full batteries. However, these cathode materials are usually affected by the dissolution of transition metal ions into the electrolyte, and then an irreversible deposition layer is formed on the anode, resulting in an undesirable loss of capacity during the charge and discharge cycles. Considering that the metal ions dissolved from the cathode tend to migrate to the counter anode through the ion conduction channels of the separator, great attention must be paid to the good potential of the separator in solving the problem of chemical crosstalk.

[0003] Cellulose nanocrystals (CNCs) are a kind of nanoscale cellulose extracted from natural fibers. It not only has the characteristics of nanoparticles but also has extremely high mechanical strength and optical properties. Cellulose nanocrystals can self-assemble into a cholesteric liquid crystal structure and can serve as a lithium ion transport channel. Summary of the Invention

[0004] Aiming at the deficiencies in the prior art, one of the purposes of the present invention is to provide a polydopamine-modified cellulose nanocrystal composite separator. The modified layer of this separator has good electrolyte permeability and an ordered nanoporous structure, which can guide a uniform lithium ion flux. And it has extremely high mechanical properties, which can effectively inhibit the growth of lithium dendrites. The metal ion-chelated polydopamine coated on the CNCs can form an alloyed SEI on the surface of the lithium metal and can adsorb the metal ions dissolved from the cathode, ultimately improving the cycle performance and safety performance of the battery, etc.

[0005] Another purpose of the present invention is to provide a lithium metal negative electrode battery containing the polydopamine-modified cellulose nanocrystal composite separator.

[0006] Another purpose of the present invention is to provide a preparation method of a lithium metal battery composite separator. This method has a simple process, low cost, and is easy to produce.

[0007] The purpose of the present invention is achieved through the following technical solutions.

[0008] A composite separator for a lithium metal battery, the composite separator includes a base film, and at least one side of the base film has a modified layer, and the modified layer is a porous structure self-assembled by cellulose nanocrystals with a coating layer.

[0009] The coating layer is polydopamine chelating metal ions;

[0010] The metal ions are one or more of zinc ions, indium ions, and tin ions;

[0011] The porous structure is arranged in layers, the molecules within the layers are arranged parallel to the long axis direction of the molecules, the layers are parallel to each other, and the molecules of each layer are helically twisted along the normal direction to form a continuous chiral nematic space structure.

[0012] The preparation method of the polydopamine-modified cellulose nanocrystal composite separator shown in the present invention is as follows:

[0013] (1) Mix and stir a Triss-HCl solution and an aqueous sulfonated CNC solution for 12 h and sonicate for 12 h to obtain a uniform viscous solution;

[0014] (2) Add dopamine hydrochloride and metal chloride to the Triss-HCl solution and stir until completely dissolved.

[0015] (3) Quickly add the solution in step (2) to the suspension in step (1), and then stir at room temperature.

[0016] (4) Centrifuge the solution after stirring in step (3) three times quickly, add deionized water to obtain a CNC@PDA suspension with a certain concentration, drop a certain amount of it into the template on the separator, and dry it naturally to obtain the composite separator.

[0017] Furthermore, in step (1), the concentration of the Triss solution is 10 M - 20 M, the concentration of the sulfonated CNC is 6 wt% to 10 wt%, and the volume ratio of their mixture is 8:1 to 4:1.

[0018] Furthermore, in step (2), the mass ratio of dopamine hydrochloride to metal chloride is 1:2 to 1:4. Add the Triss-HCl solution to make it completely dissolve.

[0019] Furthermore, the metal chloride in step (2) is one or several of zinc chloride, tin chloride, and indium chloride.

[0020] Furthermore, in step (3), after the solutions are mixed, the concentration of dopamine hydrochloride in the Triss-HCl solution is 0.1 - 0.5 mg / ml.

[0021] Further, in step (3), the stirring time is 6 - 24 h.

[0022] Further, in step (4), the concentration of the suspension after adding deionized water is 1 wt% to 4 wt%.

[0023] Beneficial effects:

[0024] (1) For the composite separator of the lithium metal battery described in the present invention, the modified layer has good electrolyte permeability and an ordered nanoporous structure, enabling Li + to flow uniformly towards the lithium metal negative electrode, achieving the effects of preventing the generation of lithium dendrites and reducing the interfacial impedance, thereby improving the cycle performance and safety performance of the battery, etc.

[0025] (2) The high mechanical modulus of the modified layer slows down the growth of Li dendrites on the lithium metal anode, improving the electrochemical performance of the battery.

[0026] (3) The metal ion chelated polydopamine coated on the CNC forms an alloyed SEI layer on the surface of the lithium metal negative electrode, reducing the overpotential during cycling and achieving uniform lithium deposition.

[0027] (4) Polydopamine can adsorb the metal ions dissolved from the positive electrode, avoiding the adverse effects of chemical crosstalk.

[0028] (5) The preparation method of the modified separator in the present invention has a simple process, low cost and is easy to scale up production. Description of the drawings

[0029] Figure 1 It is a scanning electron microscope (SEM) image of the composite separator of the lithium metal battery prepared in Example 1.

[0030] Figure 2 It is an X-ray photoelectron spectroscopy (XPS) image of the composite separator of the lithium metal battery in Example 1. Specific embodiments

[0031] The present invention will be further described below in conjunction with the drawings and specific embodiments. Among them, the methods are conventional methods unless otherwise specified, and the raw materials can be obtained from public commercial channels unless otherwise specified.

[0032] The information of the main reagents and instruments involved in the following examples is shown in Table 1 in detail.

[0033] Table 1

[0034]

[0035]

[0036] Assembly and testing of lithium-lithium batteries in the following examples and comparative examples: Both the positive and negative electrodes are lithium metal sheets. The electrolyte consists of 1 mol / L lithium hexafluorophosphate and a mixed solvent of ethylene carbonate and diethyl carbonate with a volume ratio of 1:1. A Celgard separator is used to form a CR2025 type lithium-lithium battery in a glove box; an electrochemical performance test is carried out on the assembled lithium-lithium battery using a Blue Energy test system, and the test temperature is 30 °C.

[0037] Example 1

[0038] (1) Mix 72 ml of 10 M Tris-HCl solution and 16 ml of 8% sulfonated CNC aqueous solution and stir for 12 h, then sonicate for 12 h; a uniform viscous solution is obtained.

[0039] (2) Add 9.52 mg of dopamine hydrochloride and 19 mg of zinc chloride salt to 7.2 ml of 10 M Tris-HCl solution and stir until completely dissolved.

[0040] (3) Quickly add the solution in step (2) to the suspension in step (1), and then stir at room temperature for 18 h.

[0041] (4) Centrifuge the solution after stirring in step (3) three times quickly, add deionized water to obtain a 2 wt% CNC@PDA suspension, drop it into a 7 cm * 7 cm template on the separator, and dry naturally for 24 h to obtain a composite separator.

[0042] From Figure 1 the SEM images, it can be seen that the prepared modified layer is a porous structure with a thickness of 600 nm. From the contact angle test, it can be known that the prepared polydopamine-modified cellulose nanocrystal composite separator has better electrolyte wettability.

[0043] Assemble two lithium-lithium symmetric batteries, the difference is only that: a composite separator is assembled on one lithium metal, and the other does not have a composite separator. The two lithium-lithium symmetric batteries are subjected to a cycling test at a current density of 1.0 mAh / cm 2 . When the lithium metal sheet does not have a composite separator, the cycle life of the prepared symmetric battery is less than 150 h; when the lithium metal negative electrode sheet has a composite separator, the cycle life of the prepared symmetric battery is not less than 800 h. This shows that the polydopamine-modified cellulose nanocrystal layer on the separator can greatly improve the cycling performance and can significantly extend the cycle life of the battery.

[0044] Example 2

[0045] (1) Mix 72 ml of 10 M Tris-HCl solution and 16 ml of 8% sulfonated CNC aqueous solution, stir for 12 h, and sonicate for 12 h to obtain a homogeneous viscous solution.

[0046] (2) Add 9.52 mg of dopamine hydrochloride and 19 mg of tin chloride salt to 7.2 ml of 10 M Tris-HCl solution, and stir until completely dissolved.

[0047] (3) Quickly add the solution in step (2) to the suspension in step (1), and then stir at room temperature for 18 h.

[0048] (4) Centrifuge the solution after stirring in step (3) three times quickly, add deionized water to obtain a 2 wt% CNC@PDA suspension, drop it into a 7 cm * 7 cm template on the diaphragm, and dry it naturally for 24 h to obtain a composite diaphragm.

[0049] The prepared modified layer is a porous structure with a thickness of 600 nm. It can be seen from the contact angle test that the prepared polydopamine-modified cellulose nanocrystal composite diaphragm has better electrolyte wettability.

[0050] Assemble two lithium-lithium symmetric cells, the only difference being that one lithium metal is equipped with a composite diaphragm and the other is not. The two lithium-lithium symmetric cells are subjected to a cycling test at a current density of 1.0 mAh / cm 2 When the lithium metal sheet does not have a composite diaphragm, the cycle life of the prepared symmetric cell is less than 150 h; when the lithium metal negative electrode sheet has a composite diaphragm, the cycle life of the prepared symmetric cell is not less than 850 h. This shows that the polydopamine-modified cellulose nanocrystal layer on the diaphragm can greatly improve the cycling performance and significantly extend the cycle life of the battery.

[0051] Example 3

[0052] (1) Mix 72 ml of 10 M Tris-HCl solution and 16 ml of 8% sulfonated CNC aqueous solution, stir for 12 h, and sonicate for 12 h to obtain a homogeneous viscous solution.

[0053] (2) Add 9.52 mg of dopamine hydrochloride and 19 mg of indium chloride salt to 7.2 ml of 10 M Tris-HCl solution, and stir until completely dissolved.

[0054] (3) Quickly add the solution in step (2) to the suspension in step (1), and then stir at room temperature for 18 h.

[0055] (4) Centrifuge the solution after stirring in step (3) three times rapidly, add deionized water to obtain a 2 wt% concentration CNC@PDA suspension, drop it into a 7 cm * 7 cm template on the separator, and dry it naturally for 24 h to obtain a composite separator.

[0056] The prepared modified layer is a porous structure with a thickness of 600 nm. From the contact angle test, it can be seen that the prepared polydopamine-modified cellulose nanocrystal composite separator has better electrolyte wettability.

[0057] Assemble two lithium-lithium symmetric cells, the only difference being that one lithium metal is equipped with a composite separator and the other is not. The two lithium-lithium symmetric cells are subjected to cyclic tests at a current density of 1.0 mAh / cm 2 When the lithium metal sheet does not have a composite separator, the cycle life of the prepared symmetric cell is less than 150 h; when the lithium metal negative electrode sheet has a composite separator, the cycle life of the prepared symmetric cell is not less than 750 h. This shows that the polydopamine-modified cellulose nanocrystal layer on the separator greatly improves the cycling performance and can significantly extend the cycle life of the battery.

[0058] Example 4

[0059] (1) Mix and stir 72 ml of a 10 M Tris-HCl solution and 16 ml of an 8% sulfonated CNC aqueous solution for 12 h and sonicate for 12 h to obtain a uniform viscous solution;

[0060] (2) Add 19 mg of dopamine hydrochloride and 19 mg of zinc chloride salt to 7.2 ml of a 10 M Tris-HCl solution and stir until completely dissolved.

[0061] (3) Rapidly add the solution in step (2) to the suspension in step (1), and then stir at room temperature for 18 h.

[0062] (4) Centrifuge the solution after stirring in step (3) three times rapidly, add deionized water to obtain a 2 wt% concentration CNC@PDA suspension, drop it into a 7 cm * 7 cm template on the separator, and dry it naturally for 24 h to obtain a composite separator.

[0063] The prepared modified layer is a porous structure with a thickness of 800 nm. From the contact angle test, it can be seen that the prepared polydopamine-modified cellulose nanocrystal composite separator has better electrolyte wettability.

[0064] Assemble two lithium-lithium symmetric cells, the only difference being that one lithium metal is equipped with a composite separator and the other is not. The two lithium-lithium symmetric cells are subjected to cyclic tests at a current density of 1.0 mAh / cm 2The cyclic test was carried out at a current density of []. When the lithium metal sheet did not have a composite separator, the cycle life of the prepared symmetric battery was less than 150 h; when the lithium metal negative electrode sheet had a composite separator, the cycle life of the prepared symmetric battery was not less than 770 h. This shows that the polydopamine-modified cellulose nanocrystal layer on the separator can greatly improve the cycling performance and significantly extend the cycle life of the battery.

[0065] Example 5

[0066] (1) Mix 72 ml of 10 M Tris-HCl solution and 16 ml of 8% sulfonated CNC aqueous solution, stir for 12 h, and sonicate for 12 h to obtain a homogeneous viscous solution.

[0067] (2) Add 19 mg of dopamine hydrochloride and 19 mg of tin chloride salt to 7.2 ml of 10 M Tris-HCl solution and stir until completely dissolved.

[0068] (3) Quickly add the solution in step (2) to the suspension in step (1), and then stir at room temperature for 18 h.

[0069] (4) Centrifuge the solution after stirring in step (3) three times quickly, add deionized water to obtain a 2 wt% concentration of CNC@PDA suspension, drop it into a 7 cm×7 cm template on the separator, and dry it naturally for 24 h to obtain a composite separator.

[0070] The prepared modified layer is a porous structure with a thickness of 800 nm. It can be seen from the contact angle test that the prepared polydopamine-modified cellulose nanocrystal composite separator has better electrolyte wettability.

[0071] Assemble two lithium-lithium symmetric batteries, the difference is only that: one lithium metal is equipped with a composite separator, and the other does not have a composite separator. The two lithium-lithium symmetric batteries were subjected to a cyclic test at a current density of 1.0 mAh / cm 2 The cyclic test was carried out at a current density of []. When the lithium metal sheet did not have a composite separator, the cycle life of the prepared symmetric battery was less than 150 h; when the lithium metal negative electrode sheet had a composite separator, the cycle life of the prepared symmetric battery was not less than 750 h. This shows that the polydopamine-modified cellulose nanocrystal layer on the separator can greatly improve the cycling performance and significantly extend the cycle life of the battery.

[0072] Example 6

[0073] (1) Mix 72 ml of 10 M Tris-HCl solution and 16 ml of 8% sulfonated CNC aqueous solution, stir for 12 h, and sonicate for 12 h to obtain a homogeneous viscous solution.

[0074] (2) Add 19 mg of dopamine hydrochloride and 19 mg of indium chloride salt to 7.2 ml of a 10 M Tris-HCl solution, and stir until completely dissolved.

[0075] (3) Quickly add the solution from step (2) to the suspension in step (1), and then stir at room temperature for 18 h.

[0076] (4) Centrifuge the solution after stirring in step (3) three times quickly, add deionized water to obtain a 2 wt% concentration of CNC@PDA suspension, drop it into a 7 cm * 7 cm template on the diaphragm, and dry naturally for 24 h to obtain a composite diaphragm.

[0077] The prepared modified layer is a porous structure with a thickness of 800 nm. From the contact angle test, it can be seen that the prepared polydopamine-modified cellulose nanocrystal composite diaphragm has better electrolyte wettability.

[0078] Assemble two lithium-lithium symmetric cells, the only difference being that one lithium metal is equipped with a composite diaphragm and the other is not. The two lithium-lithium symmetric cells are subjected to a cycling test at a current density of 1.0 mAh / cm 2 When the lithium metal sheet does not have a composite diaphragm, the cycle life of the prepared symmetric cell is less than 150 h; when the lithium metal negative electrode sheet has a composite diaphragm, the cycle life of the prepared symmetric cell is not less than 725 h. This shows that the polydopamine-modified cellulose nanocrystal layer on the diaphragm can greatly improve the cycling performance and significantly extend the cycle life of the battery.

[0079] Example 7

[0080] (1) Mix 72 ml of a 10 M Tris-HCl solution and 16 ml of an 8% sulfonated CNC aqueous solution, stir for 12 h, and ultrasonicate for 12 h to obtain a homogeneous viscous solution;

[0081] (2) Add 9.52 mg of dopamine hydrochloride and 19 mg of zinc chloride salt to 7.2 ml of a 10 M Tris-HCl solution, and stir until completely dissolved.

[0082] (3) Quickly add the solution from step (2) to the suspension in step (1), and then stir at room temperature for 6 h.

[0083] (4) Centrifuge the solution after stirring in step (3) three times quickly, add deionized water to obtain a 2 wt% concentration of CNC@PDA suspension, drop it into a 7 cm * 7 cm template on the diaphragm, and dry naturally for 24 h to obtain a composite diaphragm.

[0084] The prepared modified layer is a porous structure with a thickness of 400 nm. From the contact angle test, it can be seen that the prepared polydopamine-modified cellulose nanocrystal composite separator has better electrolyte wettability.

[0085] Two lithium-lithium symmetric cells were assembled, with the only difference being that one lithium metal was equipped with the composite separator and the other was not. The two lithium-lithium symmetric cells were subjected to cyclic tests at a current density of 1.0 mAh / cm 2 . When the lithium metal sheet did not have the composite separator, the cycle life of the prepared symmetric cell was less than 150 h; when the lithium metal negative electrode sheet had the composite separator, the cycle life of the prepared symmetric cell was not less than 700 h. This shows that the polydopamine-modified cellulose nanocrystal layer on the separator can greatly improve the cycling performance and significantly extend the cycle life of the battery.

Claims

1. A preparation method of a polydopamine-modified cellulose nanocrystal composite separator, characterized in that, The composite separator includes a base film, and at least one side of the base film has a modified layer, and the modified layer is a porous structure self-assembled by cellulose nanocrystals with a coating layer.

2. The polydopamine-modified cellulose nanocrystal composite separator according to claim 1, wherein The coating layer is polydopamine chelating metal ions.

3. The polydopamine-modified cellulose nanocrystal composite separator according to claim 1, wherein The metal ions are one or more of zinc ions, indium ions, and tin ions.

4. A method for preparing the composite separator according to any one of claims 1 to 3, characterized in that, It includes the following steps: S1: Mix and stir the Triss-HCl solution and the sulfonated CNC aqueous solution for 12 h and sonicate for 12 h to obtain a uniform viscous solution; S2: Add hydrochloric acid dopamine and metal chloride salts to the Triss-HCl solution and stir until completely dissolved; S3: Rapidly add the solution of S2 to the suspension in step S1, and then stir at room temperature; S4: Centrifuge the solution after stirring in S3 three times rapidly, add deionized water to obtain a CNC@PDA suspension with a certain concentration, drop a certain amount of it into the template on the separator, and dry it naturally to obtain the composite separator.

5. The preparation method of the polydopamine-modified cellulose nanocrystal composite separator according to claim 4, characterized in that, In S1, the concentration of the Triss solution is 10M-20M, the concentration of sulfonated CNC is 6wt% to 10wt%, and the volume ratio of their mixture is 8:1 to 4:

1.

6. The preparation method of the polydopamine-modified cellulose nanocrystal composite separator according to claim 4, characterized in that, The metal chloride salt in S2 is one or several of zinc chloride, tin chloride, and indium chloride. Further preferably, the mass ratio of hydrochloric acid dopamine to metal chloride salt in S2 is 1:2 to 1:

4.

7. The preparation method of the polydopamine-modified cellulose nanocrystal composite separator according to claim 4, characterized in that, The concentration of hydrochloric acid dopamine in the Triss-HCl solution after mixing the solutions in S3 is 0.1-0.5 mg / ml. Further preferably, the stirring time of the solution in S3 is 6-24 h.

8. The preparation method of the polydopamine-modified cellulose nanocrystal composite separator according to claim 4, characterized in that, The concentration of the suspension after adding deionized water in S4 is 1wt% to 4wt%.

9. A battery, an electrochemical device, or an electrical equipment using the composite separator according to any one of claims 1-3 and the composite separator prepared by the preparation method according to any one of claims 4-8.

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