A solid electrolyte, a preparation method thereof, and an application thereof in a solid-state lithium battery

Abstract

The present application provides a composite solid electrolyte and a preparation method thereof. The composite solid electrolyte includes: Ce and Nb co-doped nanosheet barium titanate BaTiO3, a polymer matrix, and a lithium salt. The Ce and Nb co-doped nanosheet barium titanate BaTiO3 is prepared by microwave solvothermal method. The doping of Ce and Nb elements, on the one hand, enters the lattice of BaTiO3, which destroys the original lattice order of barium titanate, thus generating a large number of oxygen vacancy defects, and further greatly improving the ionic conductivity of the electrolyte. After the co-doped nanosheet barium titanate BaTiO3 overlaps with each other, a three-dimensional grid structure is formed, which greatly facilitates the shuttle of ions and constructs a long-range ion transfer channel, thereby improving the lithium ion conduction ability. In addition, the specific nanosheet structure can enhance the interfacial compatibility between the solid electrolyte and the electrode material, reduce the interfacial resistance, and effectively inhibit the growth of lithium dendrites.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a composite solid electrolyte and a preparation method thereof. Background Art

[0002] With the rapid development of new energy vehicles and 5G communication technologies, higher requirements are put forward for the safety, energy density and cycling performance of lithium-ion batteries. At present, the commercially available lithium-ion batteries mainly use liquid electrolytes. Liquid electrolytes have advantages such as high conductivity and excellent electrode wetting ability, but there are also safety problems such as easy leakage, corrosion and easy combustion. Compared with liquid electrolytes, solid electrolytes have the advantages of stable structure, good mechanical properties and non-flammability. Replacing liquid electrolytes with solid electrolytes can effectively solve the safety problems of liquid lithium batteries. According to the composition of solid electrolytes, they can be divided into inorganic solid electrolytes, polymer solid electrolytes and composite solid electrolytes.

[0003] Inorganic solid electrolytes have high ionic conductivity, wide electrochemical stability windows and high mechanical strength, but the solid / solid contact resistance between the electrode and the electrolyte is large, and the processing difficulty and cost are high. Polymer solid electrolytes have good flexibility, processability and contact interface properties, but the room-temperature ionic conductivity is low and they need to operate at high temperatures. Composite solid electrolytes are a promising alternative. Generally, they are obtained by compounding inorganic fillers and polymer solid electrolytes. They simultaneously have the high ionic conductivity of inorganic solid electrolytes and the good flexibility of polymer solid electrolytes, and have become one of the current research hotspots. The solid electrolyte obtained by adding inorganic fillers to the polymer solid electrolyte has excellent comprehensive properties. The inorganic fillers can play three roles: reducing the crystallinity, increasing the amorphous phase region, and facilitating the migration of lithium ions; fast lithium-ion channels can be formed near the filler particles; increasing the mechanical properties of the polymer matrix and making it easy to form a film. The composite solid electrolyte formed by comprehensively utilizing the high ionic conductivity and good mechanical strength of inorganic materials and the good interfacial compatibility and electrochemical stability of polymer materials can effectively improve the lithium-ion conductivity, inhibit the growth of lithium dendrites during battery operation, and improve the electrochemical stability, thermal stability and Coulomb efficiency of the battery. However, there are still a series of technical problems to be solved in the research of composite solid electrolytes. For composite solid electrolytes, how to prepare composite electrolytes with high ionic conductivity, wide electrochemical windows, high mechanical strength and taking into account interfacial contact and interfacial compatibility is the current research focus.

[0004] A composite solid electrolyte, a preparation method thereof, and an application thereof in an all-solid-state lithium battery are disclosed in the invention patent with the publication number CN107834104B. The composition includes: polyethylene oxide, polyvinylidene fluoride or its derivatives, a lithium salt, and inorganic nanoparticles. This composite solid electrolyte has high mechanical properties and excellent electrochemical stability. The assembled battery has stable cycling performance and high capacity utilization. However, the problem that inorganic nanoparticles are prone to agglomeration still exists.

[0005] An invention patent with the publication number CN117352827B discloses an organic-inorganic composite solid electrolyte constructed with Nb, Al double-doped garnet-type ceramic fiber-based composite solid electrolyte (LALZNO) nanofibers prepared by electrospinning technology as inorganic fillers, PVDF-HFP as a polymer matrix, and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as a lithium salt. The porous nanofiber rod-like structure LALZNO prepared by electrospinning and high-temperature calcination aims to improve the ionic conductivity and ion transference number of the polymer solid electrolyte, enhance the lithium cycling stability, and ultimately achieve the stable cycling of a lithium iron phosphate (LFP) battery. However, the preparation process of the above composite solid electrolyte is complex. Summary of the Invention

[0006] In view of the above technical problems, the present invention proposes a composite solid electrolyte and a preparation method thereof.

[0007] A composite solid electrolyte includes Ce, Nb double-doped barium titanate nanosheets BaTiO 3 and a polymer matrix, a lithium salt. The preparation method of the composite solid electrolyte includes the following steps:

[0008] (1) Add a titanium source and a barium source to ethanol, stir and mix evenly to obtain a mixed solution 1;

[0009] (2) Add a dopant Ce source and an Nb source to ethanol, continue to stir and mix evenly to obtain a mixed solution 2;

[0010] (3) Mix the mixed solutions 1 and 2, drop in a certain amount of ammonium nitrate to obtain a mixed solution 3. Place the mixed solution 3 in a microwave reaction kettle and react at 130 - 160 °C for 50 - 100 minutes. After the reaction ends, ultrasonically clean the product with deionized water and ethanol in sequence;

[0011] (4) Place the obtained product in a tube furnace and heat-treat it at 350 - 500 °C to obtain Ce, Nb double-doped barium titanate nanosheets BaTiO 3 ;

[0012] (5) Ce, Nb double-doped barium titanate nanosheets BaTiO 3, A polymer, a lithium salt, and a solvent are uniformly mixed in a mass ratio of (1 - 20):(30 - 90):(5 - 15) to obtain a mixed solution; the uniformly stirred mixed solution is coated into a film and dried to remove the solvent, thereby obtaining a composite solid electrolyte.

[0013] In some preferred embodiments of the present invention, the titanium source is one or more of titanium tetrachloride, isopropyl titanate, and tetrabutyl titanate; the barium source is one or more of barium nitrate and barium chloride;

[0014] In some preferred embodiments of the present invention, the molar ratio of the titanium source to the barium source is 1:1;

[0015] In some preferred embodiments of the present invention, the Ce source is cerium nitrate or cerium chloride; the Nb source is niobium nitrate, niobium acetate, or niobium oxalate;

[0016] In some preferred embodiments of the present invention, the molar ratio of the titanium source:Ce source:Nb source is 1:(0.01 - 0.03):(0.01 - 0.03);

[0017] In some preferred embodiments of the present invention, the molar ratio of the titanium source to ammonium nitrate is 1:(1 - 2);

[0018] In some preferred embodiments of the present invention, the lithium salt includes LiClO 4 , LiBF 4 , LiBOB, LiTFSI, or one or more thereof;

[0019] In some preferred embodiments of the present invention, the polymer is PEO or PVDF;

[0020] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0021] (1) The present application first proposes a Ce, Nb co-doped barium titanate nanosheet BaTiO 3 . The doping of Ce and Nb elements, on the one hand, enters the lattice of BaTiO 3 , which disrupts the original lattice order of barium titanate, thereby generating a large number of oxygen vacancy defects, and then improving the ionic conductivity of the electrolyte; in addition, it is found in the experimental process that Ce and Nb are beneficial to the formation of nanosheets;

[0022] (2) The co-doped barium titanate nanosheets BaTiO 3 form a three-dimensional grid structure after overlapping with each other, constructing a long-range ion transfer channel, which greatly facilitates the shuttle of ions, thereby improving the lithium ion conduction ability;

[0023] (3) The nano-sheet structure can enhance the interfacial compatibility between the solid electrolyte and the electrode material, reduce the interfacial resistance, and effectively inhibit the growth of lithium dendrites.

[0024] (4) The preparation process of the invention is simple in operation and convenient for large-scale industrial production. Description of the Drawings

[0025] Figure 1 SEM image of the double-doped nano-sheet barium titanate BaTiO of the present application 3 ;

[0026] Figure 2 Cycling performance graph of the coin cells assembled with the composite solid electrolyte membranes prepared in Example 1 and Comparative Examples 1-2 of the present application. Detailed Description of the Invention

[0027] The technical solutions of the present invention will be described clearly and completely below. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0028] Example 1

[0029] A composite solid electrolyte, the preparation method comprising the following steps:

[0030] (1) Add 0.2 mol of titanium tetrachloride and 0.2 mol of barium nitrate to 80 mL of ethanol, stir and mix evenly to obtain a mixed solution 1;

[0031] (2) Add 0.003 mol of cerium nitrate and 0.003 mol of niobium nitrate as dopants to 20 mL of ethanol, continue to stir and mix evenly to obtain a mixed solution 2;

[0032] (3) Mix the mixed solutions 1 and 2, add 0.2 mol of ammonium nitrate to obtain a mixed solution 3, place the mixed solution 3 in a microwave reaction kettle, and react at 150 °C for 60 minutes; after the reaction, ultrasonically clean the product with deionized water and ethanol in sequence;

[0033] (4) Place the obtained product in a tubular furnace and keep it at a constant temperature of 350 °C for 60 min to obtain Ce, Nb double-doped nano-sheet barium titanate BaTiO 3；

[0034] (5) Ce, Nb double-doped nano-sheet barium titanate BaTiO 3 , polymer PEO and lithium salt LiBF 4Mix 10:60:10 by mass ratio with 10 mL of acetonitrile thoroughly and uniformly to obtain a mixed solution; pour the well-stirred mixed solution into a polytetrafluoroethylene mold to form a film, and dry to remove the solvent to obtain the composite solid electrolyte.

[0035] Example 2

[0036] A composite solid electrolyte, the preparation method comprising the following steps:

[0037] (4) Add 0.2 mol of titanium tetrachloride and 0.2 mol of barium nitrate to 80 mL of ethanol, stir and mix evenly to obtain a mixed solution 1;

[0038] (5) Add 0.003 mol of cerium nitrate and 0.003 mol of niobium nitrate as dopants to 20 mL of ethanol, continue to stir and mix evenly to obtain a mixed solution 2;

[0039] (6) Mix the mixed solutions 1 and 2, add 0.2 mol of ammonium nitrate to obtain a mixed solution 3, place the mixed solution 3 in a microwave reactor, and react at 150 °C for 60 minutes; after the reaction is completed, ultrasonically clean the product with deionized water and ethanol in sequence;

[0040] (4) Place the obtained product in a tubular furnace and keep it at a constant temperature of 400 °C for 60 min to obtain Ce and Nb co-doped barium titanate nanosheets BaTiO 3；

[0041] (5) Ce and Nb co-doped barium titanate nanosheets BaTiO 3 , polymer PEO and LiBF 4 Mix 10:70:10 by mass ratio with 10 mL of acetonitrile thoroughly and uniformly to obtain a mixed solution; pour the well-stirred mixed solution into a polytetrafluoroethylene mold to form a film, and dry to remove the solvent to obtain the composite solid electrolyte.

[0042] Example 3

[0043] A composite solid electrolyte, the preparation method comprising the following steps:

[0044] (1) Add 0.2 mol of titanium tetrachloride and 0.2 mol of barium nitrate to 80 mL of ethanol, stir and mix evenly to obtain a mixed solution 1;

[0045] (2) Add 0.002 mol of cerium nitrate and 0.002 mol of niobium nitrate as dopants to 20 mL of ethanol, continue to stir and mix evenly to obtain a mixed solution 2;

[0046] (3) Mix the mixed solutions 1 and 2, add 0.2 mol of ammonium nitrate, and obtain mixed solution 3. Place mixed solution 3 into a microwave reactor and react at 150 °C for 60 minutes. After the reaction, ultrasonically clean the product successively with deionized water and ethanol;

[0047] (4) Place the obtained product in a tube furnace and keep it at a constant temperature of 400 °C for 60 min to obtain Ce and Nb co-doped barium titanate nanosheets BaTiO 3；

[0048] (5) Mix Ce and Nb co-doped barium titanate nanosheets BaTiO 3 , polymer PEO, and LiBF 4 in a mass ratio of 10:60:10 and mix them thoroughly with 10 mL of acetonitrile to obtain a mixed solution. Pour the well-stirred mixed solution into a polytetrafluoroethylene mold to form a film, and dry to remove the solvent to obtain the composite solid electrolyte.

[0049] Example 4

[0050] A composite solid electrolyte, the preparation method comprising the following steps:

[0051] (1) Add 0.2 mol of titanium tetrachloride and 0.2 mol of barium nitrate to 80 mL of ethanol, stir and mix evenly to obtain mixed solution 1;

[0052] (2) Add 0.002 mol of cerium nitrate and 0.002 mol of niobium nitrate as dopants to 20 mL of ethanol, and continue to stir and mix evenly to obtain mixed solution 2;

[0053] (3) Mix the mixed solutions 1 and 2, drop in 0.3 mol of ammonium nitrate, and obtain mixed solution 3. Place mixed solution 3 into a microwave reactor and react at 150 °C for 60 minutes. After the reaction, ultrasonically clean the product successively with deionized water and ethanol;

[0054] (4) Place the obtained product in a tube furnace and keep it at a constant temperature of 400 °C for 60 min to obtain Ce and Nb co-doped barium titanate nanosheets BaTiO 3；

[0055] (5) Mix Ce and Nb co-doped barium titanate nanosheets BaTiO 3 , polymer PEO, and LiBF 4 in a mass ratio of 10:60:10 and mix them thoroughly with 10 mL of acetonitrile to obtain a mixed solution. Pour the well-stirred mixed solution into a polytetrafluoroethylene mold to form a film, and dry to remove the solvent to obtain the composite solid electrolyte.

[0056] Comparative Example 1

[0057] A composite solid electrolyte, the preparation method comprising the following steps:

[0058] (1) Add 0.2 mol of titanium tetrachloride and 0.2 mol of barium nitrate to 80 mL of ethanol, stir and mix evenly to obtain mixture 1;

[0059] (2) Add 0.006 mol of niobium nitrate as a dopant to 20 mL of ethanol, continue to stir and mix evenly to obtain mixture 2;

[0060] (3) Mix mixtures 1 and 2, drop in 0.2 mol of ammonium nitrate to obtain mixture 3, place mixture 3 in a microwave reaction kettle, and react at 150 °C for 60 minutes; after the reaction is completed, ultrasonically clean the product with deionized water and ethanol in sequence;

[0061] (4) Place the obtained product in a tube furnace and keep it at a constant temperature of 350 °C for 60 min to obtain Nb-doped barium titanate BaTiO 3；

[0062] (5) Mix Nb-doped barium titanate BaTiO 3 , polymer PEO and LiBF 4 in a mass ratio of 10:60:10 and mix well with 10 mL of acetonitrile to obtain a mixed solution; pour the well-stirred mixed solution into a polytetrafluoroethylene mold to form a film, and dry to remove the solvent to obtain the composite solid electrolyte.

[0063] Comparative Example 2

[0064] A composite solid electrolyte, the preparation method comprising the following steps:

[0065] (1) Add 0.2 mol of titanium tetrachloride and 0.2 mol of barium nitrate to 80 mL of ethanol, stir and mix evenly to obtain mixture 1;

[0066] (2) Add 0.006 mol of cerium nitrate as a dopant to 20 mL of ethanol, continue to stir and mix evenly to obtain mixture 2;

[0067] (3) Mix mixtures 1 and 2, drop in 0.2 mol of ammonium nitrate to obtain mixture 3, place mixture 3 in a microwave reaction kettle, and react at 150 °C for 60 minutes; after the reaction is completed, ultrasonically clean the product with deionized water and ethanol in sequence;

[0068] (4) Place the obtained product in a tube furnace and keep it at a constant temperature of 350 °C for 60 min to obtain Ce-doped barium titanate BaTiO 3 ;

[0069] (5) Ce-doped barium titanate BaTiO 3, the polymer PEO and LiBF 4 Mix them thoroughly and evenly with 10 mL of acetonitrile according to the mass ratio of 10:60:10 to obtain a mixed solution; pour the well-stirred mixed solution into a polytetrafluoroethylene mold to form a film, and dry to remove the solvent to obtain a composite solid electrolyte.

[0070] Electrochemical performance test:

[0071] Coat and form a film, dry, and slice lithium iron phosphate, superconducting carbon black, and PVDF according to the mass ratio of 80:10:10 as the positive electrode, use metallic lithium as the negative electrode, and use the composite solid electrolyte membrane prepared in Example 1 and the composite solid electrolyte membranes prepared in Comparative Examples 1-2 as the separator and electrolyte of the battery respectively, and assemble them into a button-type lithium-ion battery in a glove box filled with argon. Use a Blue Electric Battery Program Control Tester to test the electrochemical performance of the battery. The results are shown in Table 1 and the appendix Figure 2 .

[0072] Table 1

[0073] <![CDATA[Room temperature ionic conductivity (10 -3 S / cm)]]> Example 1 5.1 Comparative Example 1 4.3 Comparative Example 2 4.8

[0074] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments or perform equivalent replacements on some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a composite solid electrolyte, characterized in that : The composite solid electrolyte includes Ce and Nb doped nanosheet barium titanate BaTiO3, a polymer matrix and a lithium salt; the preparation method includes the following steps: (1) adding a titanium source and a barium source into ethanol, stirring and mixing them uniformly to obtain a mixed solution 1; (2) Adding dopant Ce source and Nb source into ethanol, stirring and mixing evenly, to obtain mixed solution 2; the molar ratio of titanium source: Ce source: Nb source is 1: (0.01-0.03): (0.01-0.03); the molar ratio of titanium source: barium source is 1:1; (1) Solutions 1 and 2 are mixed, and a certain amount of ammonium nitrate is added to obtain a mixed solution 3, and the mixed solution 3 is placed in a microwave reactor and reacted at 130-160° C. for 50-100 minutes. After the reaction is completed, the product is ultrasonically cleaned with deionized water and ethanol in turn; (4) placing the obtained product in a tube furnace and heat treating it at 350-500°C for 1-2h to obtain Ce and Nb doped nanosheet barium titanate BaTiO3; (5) Ce and Nb doped nanosheet barium titanate BaTiO3, polymer and lithium salt are fully and evenly mixed with a solvent in a mass ratio of (1-20): (30-90): (5-15) to obtain a mixed solution; the mixed solution is coated to form a film, and the solvent is removed by drying to obtain a composite solid electrolyte.

2. According to the method for preparing a composite solid electrolyte according to claim 1, the titanium source is one or more of titanium tetrachloride, isopropyl titanate, and tetrabutyl titanate; the barium source is one or more of barium nitrate and barium chloride.

3. According to the method for preparing a composite solid electrolyte according to claim 1, the Ce source is cerium nitrate or cerium chloride; the Nb source is niobium nitrate, niobium acetate or niobium oxalate.

4. According to the method for preparing a composite solid electrolyte according to claim 1, the molar ratio of titanium source:ammonium nitrate is 1:(1-2).

5. The method for preparing a composite solid electrolyte according to claim 1, wherein the lithium salt comprises one or more of LiClO4, LiBF4, LiBOB, and LiTFSI.

6. The method for preparing a composite solid electrolyte according to claim 1, wherein the polymer is PEO or PVDF.

7. A composite solid electrolyte, characterized in that: Prepared by the method according to any one of claims 1 to 6.

8. Use of a composite solid electrolyte as claimed in claim 7, characterized in that: Apply it to solid-state batteries.

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