Composite solid electrolyte diaphragm, preparation method and lithium ion battery

Abstract

The present invention discloses a composite solid electrolyte membrane, comprising a bacterial cellulose membrane, fluorinated metal modified PEO electrolyte particles and functional group modified particles, wherein the fluorinated metal modified PEO electrolyte particles and the functional group modified particles are loaded in the three-dimensional network structure of the bacterial cellulose membrane, the functional group modified particles are functional group modified silica particles and functional group modified LATP particles, the functional group modified silica particles uniformly wrap the functional group modified LATP particles, and the fluorinated metal of the fluorinated metal modified PEO electrolyte particles is combined with the functional group of the functional group modified particles through a coordination bond. The present invention also discloses a preparation method thereof and a battery having the electrolyte membrane. The present invention improves the ionic conductivity of the electrolyte membrane.

Description

Technical Field

[0001] The invention relates to an electrolyte and a preparation method thereof and a battery, belonging to the technical field of lithium ion batteries. Background Art

[0002] Solid electrolytes are materials that can conduct ions in a solid state and are widely used in various electronic devices and energy storage systems, such as batteries, capacitors, and fuel cells.

[0003] Solid electrolytes are divided into two categories: inorganic and organic polymers. Among them, polymer solid electrolytes have attracted much attention due to their soft and lightweight properties. Among the many polymer electrolytes, polymer polyethylene oxide (PEO) electrolyte has become one of the most widely studied solid electrolytes due to its excellent interface contact and easy operation. Its good interface contact properties help to reduce the resistance inside the battery, while its softness and lightness provide greater flexibility for battery design; at room temperature, PEO electrolytes are often semi-crystalline, which leads to lower ionic conductivity and insufficient lithium ion migration number; inorganic solid electrolytes, such as LATP, have excellent ionic conductivity and lithium ion migration number, strong mechanical properties, but have poor wettability with the electrode interface and high interface contact impedance.

[0004] However, the direct mixing of LATP and the polymer polyethylene oxide cannot give full play to the advantages of LATP's high ionic conductivity, but instead affects the overall mechanical properties. Summary of the invention

[0005] In view of the above-mentioned defects of the prior art, the present invention provides a composite solid electrolyte diaphragm to improve the ion conductivity of the diaphragm and ensure that the mechanical properties of the diaphragm meet the battery requirements. The present invention also provides a method for preparing the composite solid electrolyte diaphragm and a lithium ion battery using the composite solid electrolyte diaphragm.

[0006] The technical solution of the present invention is as follows: a composite solid electrolyte membrane, comprising a bacterial cellulose membrane, metal fluoride-modified PEO electrolyte particles and functional group modified particles, wherein the metal fluoride-modified PEO electrolyte particles and the functional group modified particles are loaded in the three-dimensional network structure of the bacterial cellulose membrane, the functional group modified particles are functional group modified silica particles and functional group modified LATP particles, the functional group modified silica particles uniformly wrap the functional group modified LATP particles, and the metal fluoride of the metal fluoride-modified PEO electrolyte particles is bonded to the functional groups of the functional group modified particles through coordination bonds.

[0007] Furthermore, the metal fluoride is aluminum fluoride or copper fluoride.

[0008] Furthermore, the functional group is an amino group or a hydroxyl group.

[0009] Furthermore, the mass ratio of the fluorinated metal modified PEO electrolyte particles to the functional group modified particles is 1:(0.5-2).

[0010] Furthermore, the mass proportion of the functional group modified silica particles in the functional group modified particles is 1% to 20%.

[0011] Furthermore, the particle size of the functional group-modified silica particles is 1 to 100 nm, for example, 1 nm, 2 nm, 5 nm, 10 nm, 15 nm, 20 nm, 30 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm.

[0012] Furthermore, the particle size of the functional group-modified LATP particles is 0.01 to 1 μm, for example, 0.01 μm, 0.05 μm, 0.08 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.8 μm, or 1 μm.

[0013] Furthermore, the particle size of the metal fluoride-modified PEO electrolyte particles is 0.01-1 μm, and the surface of the metal fluoride-modified PEO electrolyte particles is provided with pores whose size is larger than the particle size of the functional group-modified silica particles.

[0014] Another technical solution of the present invention is: a method for preparing a composite solid electrolyte membrane, comprising the steps of:

[0015] The PEO electrolyte is dissolved in an organic solvent, and then the metal powder is fluorinated, and the mixture is stirred until the metal powder is evenly dispersed in the PEO electrolyte solution, and the metal fluoride-modified PEO electrolyte particles are obtained by evaporating the solvent;

[0016] Fluorinated metal modified PEO electrolyte particles, functional group modified silica particles and functional group modified LATP particles are dispersed in an organic solvent to form a dispersion, a bacterial cellulose membrane is immersed in the dispersion and the particles are diffused into the bacterial cellulose membrane with the assistance of ultrasound to obtain a composite diaphragm wet film, and then the solvent is removed under vacuum, and then the composite solid electrolyte diaphragm is obtained after pressing with a roller press.

[0017] Another technical solution of the present invention is: a lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte and the aforementioned composite solid electrolyte membrane.

[0018] Compared with the prior art, the advantages of the technical solution provided by the present invention are:

[0019] 1. The present invention proposes that the bacterial cellulose membrane is a three-dimensional network structure, which has a porous microstructure and a high liquid absorption capacity, and the surface of the membrane adsorbs fluorinated metal-modified PEO electrolyte particles, and the metal ions M + The presence of ions tends to destroy the nearby Li-O coordination environment and form MO bonds; + Li + PEO-TFSI - Therefore, when introducing M + After that, the original Li-O bonding force becomes weaker, and Li + It can migrate more efficiently in PEO-MF2.

[0020] 2. The electrochemical oxidation potential of the electrolyte is closely related to its highest occupied molecular orbital (HOMO) energy level. PEO electrolytes should be resistant to oxidation at high potential positive electrodes to avoid electrolyte decomposition, and the electrolyte must form a stable SEI when reduced on the electrode surface. In addition, the electrolyte should be non-flammable to ensure battery safety. In general, the addition of electron-withdrawing fluorine groups reduces the HOMO-lowest unoccupied molecular orbital (LUMO) energy, promotes the formation of a thin and stable inorganic SEI layer, inhibits the dissolution of metal ions from the electrode into the electrolyte, inhibits dendrite growth, increases oxidation stability, and ultimately improves battery safety and cycle performance. Further, fluorination can increase the polarity of the solid electrolyte by changing the local environment around the ionic species and improving ion transport, thereby improving the ionic conductivity of the composite solid electrolyte.

[0021] 3. Functional group modified silica particles and functional group modified LATP particles. This system exhibits high thermal stability and dimensional stability on a macro scale. Functional group modified silica particles and functional group modified LATP particles can spontaneously form hydrogen bonds to form a better and regular network on the surface of bacterial cellulose, which is beneficial to promote ion transport. At the same time, the continuous ion conduction network provides a fast lithium ion conduction channel inside the fiber, improves the diffusion coefficient of ions, and acts as a scaffold to provide mechanical support for the solid polymer electrolyte.

[0022] 4. The functional groups of the functional group-modified silica particles in the present invention are selected to be strongly polar groups, have good interfacial wettability, and are smaller in size than the functional group-modified LATP particles. In terms of microstructure, the functional group-modified silica particles are evenly wrapped around the functional group-modified LATP particles to form a continuous wetting phase, providing a fast channel for the migration and conduction of ions.

[0023] 5. The metal fluoride in the fluoride-modified PEO electrolyte particles is a Lewis acid, which is easy to undergo Lewis acid-base reaction with amino or hydroxyl groups, thereby making the metal fluoride-modified PEO electrolyte particles and functional group-modified particles on the surface of bacterial cellulose more closely connected, thereby improving the ionic conductivity in the composite solid electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a morphology picture of the composite solid electrolyte membrane sample prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with examples. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading this description, various equivalent modifications to this description by those skilled in the art fall within the scope defined by the claims attached to this application.

[0026] The preparation of metal fluoride modified PEO electrolyte particles was carried out by the following method:

[0027] The commercially available polymer polyethylene oxide (PEO) electrolyte (EO to Li molar ratio of 16) is dissolved in acetone by solution casting, and stirred to fully dissolve the PEO electrolyte (heating can also be used to accelerate dissolution, 30-50°C) to form a uniform solution. Secondly, metal fluoride is added to the above solution, and stirring or ultrasound can be used to ensure that the metal fluoride is fully dispersed in the solution. The above solution is transferred into the mold again, and the mold is placed in a well-ventilated environment (acetone can evaporate at room temperature) to allow the solvent to evaporate slowly and the solution to gradually solidify. It can also be heated to a certain temperature (about 30°C, too high a temperature will affect the curing effect). After curing, the material is taken out of the mold, and then ground and dried to ensure that good quality metal fluoride-modified PEO electrolyte particles are obtained.

[0028] Copper fluoride powder with a mass fraction of 0.5% was added to the acetone solution of polymer polyethylene oxide (PEO) electrolyte to prepare copper fluoride modified PEO electrolyte particles. Aluminum fluoride powder with a mass fraction of 0.5% was added to the acetone solution of polymer polyethylene oxide (PEO) electrolyte to prepare aluminum fluoride modified PEO electrolyte particles.

[0029] The functional group-modified silica particles were prepared by the following method:

[0030] 0.3 g of stearic acid, 30 ml of anhydrous ethanol and 5 g of nano-silicon dioxide were added to distilled water, mixed, and stirred to react to form an initial solution; 0.3 g of stearic acid was dissolved in anhydrous ethanol to prepare a stearic acid ethanol solution; the stearic acid ethanol solution was added to the above initial solution and stirred for 3 hours to allow the substances to fully react and mix; after the stirring was completed, the solution was heated until the ethanol was completely volatilized, and after the volatilization was completed, it was baked at 80°C for 30 minutes and ground for 10 minutes to obtain hydroxyl-modified silica particles.

[0031] 10 g of porous silica was suspended in an ethanol solvent and stirred to mix evenly to obtain a porous silica suspension; 0.35 g of aminopropyltriethoxysilane was dissolved in ethanol to form an aminopropyltriethoxysilane solution; the aminopropyltriethoxysilane solution was added to the silica suspension while stirring, and the reaction was stirred at 25° C. for 8 hours to obtain an amino-modified silica solution; the amino-modified silica solution was heated and dried at 50° C. for 4 hours, and then washed and dried to obtain amino-modified silica particles.

[0032] The functional group-modified LATP particles were prepared by the following method:

[0033] 0.3g of stearic acid, 30ml of anhydrous ethanol and 5g of nano-LATP were added to distilled water and mixed, and stirred to react to form an initial solution; 0.3g of stearic acid was dissolved in anhydrous ethanol to prepare a stearic acid ethanol solution; 3. The stearic acid ethanol solution was added to the above initial solution and stirred for 3h to allow the substances to fully react and mix; after the stirring was completed, the solution was heated until the ethanol was completely volatilized, and after the volatilization was completed, it was baked at 70°C for 30 minutes and ground for 10 minutes to obtain hydroxyl-modified LATP particles.

[0034] 10g of LATP was suspended in an ethanol solvent and stirred to mix evenly to obtain a LATP suspension; 0.35g of aminopropyltriethoxysilane was dissolved in ethanol to form an aminopropyltriethoxysilane solution; the aminopropyltriethoxysilane solution was added to the LATP suspension while stirring, and the reaction was stirred at 25°C for 8h to obtain an amino LATP solution; the amino LATP solution was heated and dried at 50°C for 4h, and then washed and dried to obtain amino-modified LATP particles.

[0035] Example 1

[0036] A bacterial cellulose membrane with a size of 10 cm × 10 cm and a thickness of 2.0 mm, copper fluoride-modified PEO electrolyte particles with a particle size of 0.5 μm after grinding and screening, and functional group-modified particles were mixed in 500 ml of acetone at a mass ratio of 6:2:2, wherein the functional group-modified particles included amino-modified silica particles with a particle size of 50 nm after grinding and screening and hydroxyl-modified LATP particles with a particle size of 0.5 μm after grinding and screening at a mass ratio of 5:95. Then, ultrasonic treatment was performed for 120 min, and the wet composite membrane was taken out and dried at 40 ° C for 12 h. After roller pressing, a composite solid electrolyte membrane with a three-dimensional network structure was obtained.

[0037] The morphology of the composite solid electrolyte membrane obtained in this embodiment is as follows Figure 1 As shown, copper fluoride-modified PEO electrolyte particles, amino-modified silica particles, and hydroxyl-modified LATP particles are all loaded in the three-dimensional network structure of the bacterial cellulose membrane to form an ion transport network.

[0038] Example 2

[0039] The amino-modified silica particles were replaced by hydroxy-modified silica particles, and the hydroxy-modified LATP particles were replaced by amino-modified LATP particles. The rest was the same as in Example 1.

[0040] Example 3

[0041] The copper fluoride modified PEO electrolyte particles were replaced with aluminum fluoride modified PEO electrolyte particles, and the rest was the same as in Example 1.

[0042] Example 4

[0043] The mass ratio of the bacterial cellulose membrane, the copper fluoride modified PEO electrolyte particles and the functional group modified particles added into acetone is 8:1:1, and the rest is the same as in Example 1.

[0044] Example 5

[0045] The amino-modified silica particles are selected from particles with a particle size of 70 nm after grinding and screening, and the hydroxyl-modified LATP particles are selected from particles with a particle size of 0.3 μm after grinding and screening. The rest is the same as in Example 1.

[0046] Example 6

[0047] The amino-modified silica particles are selected from particles with a particle size of 30 nm after grinding and screening, and the hydroxyl-modified LATP particles are selected from particles with a particle size of 1 μm after grinding and screening. The rest is the same as in Example 1.

[0048] Example 7

[0049] The mass ratio of amino-modified silica particles to hydroxyl-modified LATP particles in the functional group-modified particles is 1:9, and the rest is the same as in Example 1.

[0050] Example 8

[0051] The mass ratio of amino-modified silica particles to hydroxyl-modified LATP particles in the functional group-modified particles is 2:8, and the rest is the same as in Example 1.

[0052] Comparative Example 1

[0053] The amino-modified silica particles were replaced with ordinary silica particles, and the rest was the same as in Example 1.

[0054] Comparative Example 2

[0055] The hydroxyl-modified LATP particles were replaced with non-modified LATP particles, and the rest was the same as in Example 1.

[0056] Comparative Example 3

[0057] The functional group-modified particles only used hydroxyl-modified LATP particles, and the rest were the same as in Example 1.

[0058] Comparative Example 4

[0059] The functional group-modified particles only used amino-modified silica particles, and the rest were the same as in Example 1.

[0060] Comparative Example 5

[0061] A bacterial cellulose membrane with a size of 10 cm × 10 cm and a thickness of 2.0 mm and functional group-modified particles were mixed in 500 ml of acetone at a mass ratio of 6:4, wherein the functional group-modified particles included amino-modified silica particles with a particle size of 50 nm after grinding and screening and hydroxyl-modified LATP particles with a particle size of 0.5 μm after grinding and screening at a mass ratio of 5:95. Then, ultrasonic treatment was performed for 120 min, and the wet composite membrane was taken out and dried at 40 ° C for 12 h. After roller pressing, a composite solid electrolyte membrane with a three-dimensional network structure was obtained.

[0062] Comparative Example 6

[0063] After mixing polyolefin resin (PP) with copper fluoride modified PEO electrolyte particles and functional group modified particles, heat and melt (180°C) and extrude into thick sheets (extrusion speed is 50 rpm, extrusion pressure is 8MPa), then uniaxially stretch at a certain temperature (90°C, stretch ratio is 5, stretching speed is 3m / min) to orient the polymer molecular chains and form a microporous structure. Then, heat setting treatment (heat setting is 80°C, time is 5 minutes), and finally cut to obtain lithium-ion battery separators.

[0064] Comparative Example 7

[0065] The amino-modified silicon dioxide particles are selected from particles with a particle size of 0.5 μm after grinding and screening, and the rest are the same as in Example 1.

[0066] Comparative Example 8

[0067] The hydroxyl-modified LATP particles are selected from particles with a particle size of 50 nm after grinding and screening, and the rest is the same as in Example 1.

[0068] The following tests were performed on the diaphragms prepared in the above embodiments and comparative examples:

[0069] Permeability test: When the composite solid electrolyte membrane is fixed, a certain air pressure is applied to one side of the membrane. Due to the micropores on the membrane, the air pressure will gradually decrease until it is equal to the atmospheric pressure. By comparing the time taken for the pressure to drop from the initial pressure to the final pressure, the air permeability of the membrane can be known.

[0070] High temperature shrinkage rate: Take a sample of 10 cm × 10 cm and record the longitudinal length l of each sample 原始 , placed at 130 ℃ for 10h, test the longitudinal length l of each sample 保温 , calculate the shrinkage rate, shrinkage rate = (l 保温 / l 原始 )×100%.

[0071] Wetting angle test: Place the diaphragm horizontally, take a drop of electrolyte and drop it on the surface of the diaphragm, leave it for 1 minute to allow the electrolyte to penetrate into a certain stable state, then use a digital camera to take a picture of the droplet in the horizontal direction, and measure the wetting angle of the electrolyte and diaphragm in the data photo. ImageJ image processing software can be used for measurement.

[0072] The diaphragms prepared in the above-mentioned embodiments and comparative examples were made into batteries according to the following method and tested:

[0073] (1) NCM811, conductive carbon black and polyvinylidene fluoride were weighed in a weight ratio of 7:2:1 and added to N-methylpyrrolidone to prepare a positive electrode slurry; (2) The positive electrode slurry was then coated on an aluminum foil, and the positive electrode sheet was prepared after drying, rolling, slitting and sheeting in sequence; (3) Graphite, conductive carbon black and acrylonitrile multipolymer were weighed in a weight ratio of 7:2:1 and added to N-methylpyrrolidone to prepare a negative electrode slurry; (4) The negative electrode slurry was coated on a copper foil, and the negative electrode sheet was prepared after drying, rolling, slitting and sheeting in sequence; (5) The prepared positive electrode sheet and negative electrode sheet, and the separators prepared in each embodiment and comparative example were stacked, and then the electrolyte was injected to assemble an aluminum shell battery.

[0074] Ionic conductivity ceshi: Calculate the ionic conductivity according to the formula σ = L / (A × Rb), and perform impedance test at room temperature 25°C, where σ is the ionic conductivity in S / cm; L is the thickness of the tablet in cm; A is the area of ​​the tablet in cm 2 ; Rb is the body impedance of the sample to be tested, in Ω. Where L is 0.015cm, A is 2.84cm 2 , calculate the value of σ.

[0075] Electrochemical performance test: The above battery was subjected to a cycle performance test with a voltage window of 2.8 to 4.2 V and a test condition of 0.1C. The capacity retention rate of the battery after 3000 cycles was tested.

[0076] The test results are as follows

[0077]

[0078] From the above results, we can see that:

[0079] Compared with Example 1, Comparative Example 1 and Comparative Example 2: Hydrogen bonds cannot be spontaneously formed between the functional group-modified silica particles and the non-modified LATP particles, as well as between the ordinary silica particles and the functional group-modified LATP particles, and a good and regular network cannot be formed on the surface of the bacterial cellulose to promote ion transport. Therefore, the ionic conductivity of the membrane is poor, and a continuous wetting phase cannot be formed, so the wetting angle of the membrane is poor.

[0080] Compared with Example 1, Comparative Examples 3 and 4 lack the functional group-modified silica particles or the functional group-modified LATP particles, and thus the mechanical properties of the diaphragm are lower and the wettability of the diaphragm is poor.

[0081] Compared with Example 1, Comparative Example 5 does not add PEO electrolyte, the entire interface is not soft and light enough, the flexibility is poor, so the ionic conductivity is low and the cycle retention rate of the battery is poor.

[0082] Compared with Example 1, Comparative Example 6 does not add bacterial cellulose membrane, and cannot provide a three-dimensional network structure as a whole, resulting in poor air permeability and buffering properties of the diaphragm, which affects the cycle retention rate of the battery.

[0083] Compared with Example 1, Comparative Examples 7 and 8 show that the functional group-modified silica particles cannot be evenly wrapped around the functional group-modified LATP particles in the microstructure to form a continuous wetting phase, which affects the wettability and ionic conductivity of the diaphragm, thereby affecting the electrical cycle performance.

Claims

1. A composite solid electrolyte membrane, characterized in that: The invention comprises a bacterial cellulose membrane, fluorinated metal-modified PEO electrolyte particles and functional group-modified particles, wherein the fluorinated metal-modified PEO electrolyte particles and the functional group-modified particles are loaded in the three-dimensional network structure of the bacterial cellulose membrane, the functional group-modified particles are functional group-modified silica particles and functional group-modified LATP particles, the functional group-modified silica particles uniformly wrap the functional group-modified LATP particles, the fluorinated metal of the fluorinated metal-modified PEO electrolyte particles and the functional group-modified particles are loaded in the three-dimensional network structure of the bacterial cellulose membrane, the functional group-modified particles are functional group-modified silica particles and functional group-modified LATP particles, the functional group-modified silica particles uniformly wrap the functional group-modified LATP particles, the fluorinated metal of the fluorinated metal-modified PEO electrolyte particles and the functional group-modified particles are loaded in the three-dimensional network structure of the bacterial cellulose membrane, the functional group-modified particles are functional group-modified silica particles and functional group-modified LATP particles, the functional group-modified silica particles uniformly wrap the functional group-modified LATP particles, the functional group-modified LATP particles are uniformly wrapped with ... The functional groups of the functional group modified particles are bonded by coordination bonds; the metal fluoride is aluminum fluoride or copper fluoride, the mass proportion of the functional group modified silica particles in the functional group modified particles is 1% to 20%, the particle size of the functional group modified silica particles is 1 to 100 nm, the particle size of the functional group modified LATP particles is 0.01 to 1 μm, the functional group modified silica particles are amino modified silica particles, and the functional group modified LATP particles are hydroxyl modified LATP particles.

2. The composite solid electrolyte membrane according to claim 1, characterized in that: The mass ratio of the fluorinated metal modified PEO electrolyte particles to the functional group modified particles is 1:(0.5-2).

3. The composite solid electrolyte membrane according to claim 1, characterized in that: The particle size of the metal fluoride modified PEO electrolyte particles is 0.01-1 μm, and the surface of the metal fluoride modified PEO electrolyte particles is provided with pores whose size is larger than the particle size of the functional group modified silica particles.

4. A method for preparing a composite solid electrolyte membrane according to any one of claims 1 to 3, characterized in that: Includes steps: The PEO electrolyte is dissolved in an organic solvent, and then a metal fluoride powder is added and stirred until the metal fluoride powder is evenly dispersed in the PEO electrolyte solution, and metal fluoride-modified PEO electrolyte particles are obtained by evaporating the solvent; The fluorinated metal modified PEO electrolyte particles, functional group modified silica particles and functional group modified LATP particles are dispersed in an organic solvent to form a dispersion, the bacterial cellulose membrane is immersed in the dispersion and the particles are diffused into the bacterial cellulose membrane with the assistance of ultrasound to obtain a composite membrane wet film, and then the solvent is removed under vacuum at 40°C, and then the composite solid electrolyte membrane is obtained after pressing with a roller press.

5. A lithium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, an electrolyte and a composite solid electrolyte membrane as claimed in any one of claims 1 to 3.

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