Preparation and application of ultrathin organic-inorganic composite solid electrolyte membrane

Abstract

The application relates to a preparation and application of an ultrathin organic-inorganic composite solid electrolyte film, belonging to the technical field of lithium ion battery electrolytes. First, a high-molecular polymer and highly-dispersed inorganic nanoparticles are selected, an ultrathin composite electrolyte self-supporting base film with controllable thickness is prepared through a flow casting method, then a high-ionic-conductivity carbonate-based polymer electrolyte is selected, and an ultrathin organic-inorganic composite electrolyte film is prepared through a solution casting method. The ultrathin organic-inorganic composite electrolyte film prepared in the application can be reduced to below 10 microns in thickness, and simultaneously has high ionic conductivity, a wide electrochemical stability window and excellent mechanical performance. The preparation process of the application is simple, convenient for large-scale production, and suitable for commercial lithium ion solid batteries.

Description

TECHNICAL FIELD

[0001] The present application relates to a lithium ion battery solid-state electrolyte, in particular to the preparation and application of an ultrathin organic-inorganic composite solid-state electrolyte film, and belongs to the technical field of lithium ion battery electrolytes. BACKGROUND

[0002] Lithium ion batteries as a new type of electrochemical energy storage device have been widely used in mobile electronic devices, electric vehicles, and emergency power supplies, and are gradually being used in energy storage power stations, rail transportation, and aerospace. So far, most commercial lithium ion batteries use conventional organic liquid electrolytes, such as ethylene carbonate and propylene carbonate. However, lithium ion batteries using organic liquid electrolytes have significant safety problems, which seriously hinder the further popularization and wider application of lithium ion batteries. The main reason is that organic electrolytes usually have high chemical activity, volatility, flammability, and explosion safety defects. Therefore, using solid-state electrolytes instead of traditional organic electrolytes is one of the effective ways to solve the above-mentioned safety problems of lithium ion batteries. At the same time, solid-state electrolytes also have the advantages of high ionic conductivity, wide electrochemical window, wide working temperature, and arbitrary cutting or changing.

[0003] For solid-state electrolytes, the diffusion time of Li + is closely related to the thickness of the solid-state electrolyte. According to the equation τ = l 2 / D, where τ is the diffusion time, l is the thickness of the solid-state electrolyte, and D is the diffusion constant, it can be seen that reducing the thickness l of the solid-state electrolyte film can effectively shorten the transmission distance and transmission time of lithium ions. In addition, reducing the thickness of the solid-state electrolyte can also help to improve the energy density and power density of the solid-state battery. Moreover, reducing the thickness of the solid-state electrolyte can reduce the manufacturing cost of the solid-state battery, which is of great significance to promote the commercialization of the battery. It should be noted that in addition to reducing the thickness of the solid-state electrolyte film, the structure of the electrolyte also needs to be designed to achieve interface matching with the positive and negative electrode materials. For example, the oxidation resistance of the solid-state electrolyte film needs to be considered on the positive electrode side, and the ability to inhibit lithium dendrite growth is required on the negative electrode side, especially when using lithium metal as the negative electrode. Chinese patent (CN202111078836.X) discloses a solid-state electrolyte film prepared by using cellulose aerogel as the skeleton and gel-like guar gum electrolyte as the filler. Through step 1, cellulose aerogel is prepared; step 2, gel-like guar gum electrolyte is prepared; step 3, solid-state electrolyte film is prepared: the gel-like guar gum electrolyte is doped into the cellulose aerogel to prepare a solid-state electrolyte. In a thin film all-solid-state battery, due to the low ionic conductivity, narrow electrochemical window, and serious interface problem between the electrolyte and the electrode material of the solid-state electrolyte, the all-solid-state battery cannot match high-voltage positive electrode materials, has poor cycle performance, low battery power density, and its application is limited to a certain extent. SUMMARY

[0004] In view of the problems in the prior art, the present application provides a method for preparing an ultra-thin organic-inorganic composite solid electrolyte film by combining a casting method with a solution casting method, and a lithium ion secondary full solid-state battery constructed by using the thin film electrolyte.

[0005] The technical solution of the present application is as follows:

[0006] First, a high molecular polymer (20wt%-80wt%) and highly dispersed inorganic nanoparticles (20wt%-80wt%, adding up to 100% with the high molecular polymer) are dispersed in an organic solvent, an ultra-thin composite electrolyte self-supporting base film with controllable thickness and a large number of internal pores is prepared by a casting method, then a high ionic conductivity carbonate-based polymer electrolyte precursor solution is selected, and the solution is poured into the inside of the base film to reach a saturated state by a solution casting method, and an ultra-thin organic-inorganic composite electrolyte film is obtained after high temperature (60-120℃) polymerization.

[0007] The selected high molecular polymer includes but is not limited to one or more of polyethylene oxide (PEO) and its derivatives, polyvinylidene fluoride (PVDF) and its derivatives, polyacrylonitrile (PAN) and its derivatives, polysiloxane and its derivatives, etc.

[0008] The highly dispersed inorganic nanoparticles include but are not limited to garnet-type Li7La3Zr2O 12 and doped and modified solid electrolyte nanoparticles, perovskite-type LiLaTiO3 and doped and modified solid electrolyte nanoparticles, NASICON-type Li 1+x Al x Ti 2-x (PO4)3 and doped and modified solid electrolyte nanoparticles, LISICON-type Li 14 Zn(GeO4)4 and doped and modified solid electrolyte nanoparticles, spinel-type LiTaSiO5 and doped and modified solid electrolyte nanoparticles, sulfide Li 10 GeP2S 12 solid electrolyte nanoparticles, halide Li3InCl6 solid electrolyte nanoparticles, montmorillonite nanoparticles, silicon dioxide nanoparticles, zirconium dioxide nanoparticles, barium titanate nanoparticles, calcium carbonate nanoparticles, aluminum oxide nanoparticles, titanium dioxide nanoparticles, silicon carbide nanoparticles, Li 14Zn(GeO4)4 nanoparticles, LiZr2(PO4)3 nanoparticles, LiPON nanoparticles, and one or more of the like nanoparticles.

[0009] Carbonate-based polymer electrolyte precursors, which are precursors capable of forming carbonate-based polymer electrolytes, including but not limited to one or more of the following polymer precursors: polycarbonate precursor solution (carbonate + lithium salt + initiator), polyvinyl carbonate precursor solution (carbonate + lithium salt + initiator), polyvinylidene carbonate precursor solution (vinylidene carbonate + lithium salt + initiator), polyallyl methyl carbonate precursor solution (allyl methyl carbonate + lithium salt + initiator), polyvinylidene precursor solution (vinylidene carbonate + lithium salt + initiator), polyfluorovinyl carbonate precursor solution (fluorovinyl carbonate + lithium salt + initiator), and the like.

[0010] The prepared ultra-thin organic-inorganic composite electrolyte film can be reduced to a thickness of less than 10 μm and has good mechanical properties.

[0011] The prepared ultra-thin organic-inorganic composite electrolyte film has high room temperature ionic conductivity (> 1.0 x 10 -3 S / cm), a wide electrochemical stability window (> 5.5 V (vs. Li + / Li)) and a high ion transference number (> 0.65) and good stability with a lithium metal electrode.

[0012] A lithium ion secondary full solid-state battery is constructed using the solid-state electrolyte thin film described in the present application.

[0013] The lithium ion battery positive active material is one or more of lithium cobaltate (LiCoO2), lithium nickelate (LiNiO2), lithium ion fluorophosphate, lithium manganate, lithium-rich manganese-based layered oxide, lithium iron manganese phosphate, lithium nickel cobalt aluminum (NCA), lithium nickel cobalt manganate, lithium iron phosphate (LiFeO4), lithium vanadium phosphate (Li3V2(PO4)3); the negative active material is one or more of metal lithium, lithium alloy, graphite, hard carbon, lithium metal nitride, antimony oxide, carbon germanium composite material, carbon silicon composite material, lithium titanate, lithium titanium oxide. The initiator or catalyst is one of the following: dibutyl tin dilaurate, bis(acetylacetone) dibutyl tin, azobis diisopropyl cyanide (ABVN), azobis diisobutyronitrile (AIBN), dimethyl azobis isobutyrate (AIBME), benzoyl peroxide (BPO), platinum gold water (Pt);

[0014] The preparation of the lithium ion battery positive electrode material comprises the following steps: grinding and mixing 50-90% by mass fraction of the positive electrode active material, 5-30% by mass fraction of the conductive agent acetylene black; adding 1-15% by mass fraction of polyvinylidene fluoride (PVDF), 1-15% of polycarbonate-based organic-inorganic composite solid electrolyte (the above-mentioned substances add up to 100%) and 1-methyl-2-pyrrolidone (NMP) for grinding and mixing; coating on the surface of an aluminum foil and drying; the metal lithium or metal lithium alloy can be directly used as the corresponding negative electrode material; the preparation of other negative electrode materials comprises the following steps: grinding and mixing 50-90% by mass fraction of the negative electrode active material, 5-30% by mass fraction of the conductive agent acetylene black, adding 5-25% by mass fraction of polyvinylidene fluoride (PVDF) (the above-mentioned substances add up to 100%) and 1-methyl-2-pyrrolidone (NMP) for grinding and mixing; coating on the surface of a copper foil and drying.

[0015] The lithium ion battery assembly comprises button cells and soft package cells, and the internal stacking sequence of the solid-state battery is positive electrode-the ultra-thin organic-inorganic composite solid electrolyte film of the application-negative electrode.

[0016] The innovation and practicability of the application lie in that:

[0017] 1. The thickness of the ultra-thin organic-inorganic composite solid electrolyte film prepared by the application can be reduced to below 10 microns, while good flexibility and mechanical processing performance are maintained.

[0018] 2. The ultra-thin organic-inorganic composite solid electrolyte film prepared by the application has good electrochemical performance, high room temperature ionic conductivity (>1.0×10 -3 S / cm), wide electrochemical stability window (>5.5V (vs. Li + / Li)) and high ion transference number (>0.65), and good stability with lithium metal electrode.

[0019] 3. The ultra-thin organic-inorganic composite solid electrolyte film prepared by the application has simple preparation process and can be mass-produced. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 It is the optical morphology picture of the base film in Example 2 of the ultra-thin organic-inorganic composite solid electrolyte film.

[0021] Figure 2 The cobaltate lithium positive electrode solid-state battery charge-discharge curve assembled according to Example 6 is obtained from the ultra-thin organic-inorganic composite solid electrolyte film of Example 2. DETAILED DESCRIPTION

[0022] The application will be described in detail below through specific examples, and the examples are provided for better understanding of the application, but are not intended to limit the scope of the application.

[0023] Preparation of electrolyte:

[0024] Example 1

[0025] First, 1 g of polyvinylidene fluoride (PVDF) was dispersed and dissolved in NMP organic solvent, fully stirred to completely dissolve, and an equal amount of garnet-type Li7La3Zr2O12 was added. 6.6 La 2.9 Ca 0.1 Zr 1.75 W 0.25 O 12 The solid electrolyte nanoparticles were stirred vigorously for 12 h and ultrasonically for 2 h to obtain a slurry with uniformly dispersed particles. An ultrathin composite electrolyte base film was prepared by a casting method, and an ultrathin electrolyte base film was obtained. Then, a high-ionic-conductivity poly(ethylene carbonate) electrolyte precursor solution (ethylene carbonate (76%) + LiTFSI (23.99%) + azobisisobutyronitrile (0.01%)) was selected, and it was poured into the ultrathin electrolyte base film by a solution pouring method. An ultrathin organic-inorganic composite electrolyte film with excellent performance was obtained by high-temperature curing at 80°C.

[0026] Example 2

[0027] First, 1 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) was dispersed and dissolved in NMP organic solvent, fully stirred to completely dissolve, and an equal amount of garnet-type Li7La3Zr2O12 was added. 6.6 La 2.9 Ca 0.1 Zr 1.75 W 0.25 O 12 The solid electrolyte nanoparticles were stirred vigorously for 12 h and ultrasonically for 2 h to obtain a slurry with uniformly dispersed particles. An ultrathin composite electrolyte base film was prepared by a casting method, and an ultrathin electrolyte base film was obtained. Then, a high-ionic-conductivity poly(ethylene carbonate) electrolyte precursor solution (ethylene carbonate (76%) + LiTFSI (23.99%) + azobisisobutyronitrile (0.01%)) was selected, and it was poured into the ultrathin electrolyte base film by a solution pouring method. An ultrathin organic-inorganic composite electrolyte film with excellent performance was obtained by high-temperature curing at 80°C.

[0028] Example 3

[0029] Firstly, 1 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) is dispersed and dissolved in NMP organic solvent, fully stirred to completely dissolve, and 1 g of silica nanoparticles is added and stirred vigorously for 12 h and ultrasonic for 2 h to obtain a slurry with uniformly dispersed particles. An ultra-thin composite electrolyte base film is prepared by a casting method, and a thin film electrolyte base film is obtained. A polyvinyl ethylene carbonate electrolyte precursor solution (vinyl ethylene carbonate (76%) + LiTFSI (23.99%) + azobisisobutyronitrile (0.01%)) is poured into the thin film electrolyte base film by a solution pouring method, and an ultra-thin organic-inorganic composite electrolyte film with excellent performance is obtained by high-temperature curing.

[0030] Example 4

[0031] Firstly, 1 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) is dispersed and dissolved in NMP organic solvent, fully stirred to completely dissolve, and 1 g of silica nanoparticles is added and stirred vigorously for 12 h and ultrasonic for 2 h to obtain a slurry with uniformly dispersed particles. An ultra-thin composite electrolyte base film is prepared by a casting method, and a thin film electrolyte base film is obtained. A polyvinyl ethylene carbonate electrolyte precursor solution (vinyl ethylene carbonate (76%) + LiTFSI (23.99%) + azobisisobutyronitrile (0.01%)) is poured into the thin film electrolyte base film by a solution pouring method, and an ultra-thin organic-inorganic composite electrolyte film with excellent performance is obtained by high-temperature curing.

[0032] Example 5

[0033] Firstly, 1 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) is dispersed and dissolved in NMP organic solvent, fully stirred to completely dissolve, and 1 g of silica nanoparticles is added and stirred vigorously for 12 h and ultrasonic for 2 h to obtain a slurry with uniformly dispersed particles. An ultra-thin composite electrolyte base film is prepared by a casting method, and a thin film electrolyte base film is obtained. A polyvinyl ethylene carbonate electrolyte precursor solution (vinyl ethylene carbonate (76%) + LiTFSI (23.99%) + azobisisobutyronitrile (0.01%)) is poured into the thin film electrolyte base film by a solution pouring method, and an ultra-thin organic-inorganic composite electrolyte film with excellent performance is obtained by high-temperature curing. 6.6 La 2.9 Ca 0.1 Zr 1.75 W 0.25 O 12 Firstly, 1 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) is dispersed and dissolved in NMP organic solvent, fully stirred to completely dissolve, and 1 g of silica nanoparticles is added and stirred vigorously for 12 h and ultrasonic for 2 h to obtain a slurry with uniformly dispersed particles. An ultra-thin composite electrolyte base film is prepared by a casting method, and a thin film electrolyte base film is obtained. A polyvinyl ethylene carbonate electrolyte precursor solution (vinyl ethylene carbonate (76%) + LiTFSI (23.99%) + azobisisobutyronitrile (0.01%)) is poured into the thin film electrolyte base film by a solution pouring method, and an ultra-thin organic-inorganic composite electrolyte film with excellent performance is obtained by high-temperature curing.

[0034] Electrolyte thickness: The thickness of the ultra-thin organic-inorganic composite electrolyte film is measured by a micrometer (accuracy 0.01 mm), and the average value is obtained by measuring 3 points on the film.

[0035] Ionic conductivity: The polymer electrolyte was sandwiched by two stainless steel shims, and the impedance was measured by assembling a R2032 coin cell according to the formula where L is the thickness of the polymer electrolyte, S is the area of the stainless steel shim, and R is the measured impedance value.

[0036] Electrochemical window: The polymer electrolyte was sandwiched by stainless steel and lithium sheet, and the linear voltammetry scan (LSV) measurement was performed by assembling a R2032 coin cell with a starting voltage of 2.8 V and a maximum potential of 6.5 V at a scan rate of 1 mV / S.

[0037] Example 6

[0038] 240 mg of lithium cobaltate cathode and 45 mg of conductive agent acetylene black were uniformly ground for 40 min; 15 mg of binder polyvinylidene fluoride, 15 mg of electrolyte mixture, and 150 μL of 1-methyl-2 pyrrolidone were uniformly ground for 40 min; coated on the surface of an aluminum foil, dried at 80°C under vacuum conditions for 8 h; the electrode sheet was cut into a round sheet with R = 12 mm, and the above-mentioned Example 2 ultra-thin organic-inorganic composite electrolyte film was used to assemble a solid-state lithium ion battery with metal lithium as the anode. The assembled solid-state battery can be charged to 4.6 V, and can be stably cycled for 200 cycles at a room temperature charge cut-off voltage of 4.5 V, with a capacity retention rate of 74% or more.

[0039] Table 1

[0040]

Claims

1. A method for preparing an ultrathin organic-inorganic composite solid electrolyte membrane, characterized in that, The process includes the following steps: First, a polymer and highly dispersed inorganic nanoparticles are dispersed in an organic solvent. An ultrathin composite electrolyte self-supporting base membrane with controllable thickness and numerous internal pores is prepared by casting. Then, a carbonate-based polymer electrolyte precursor solution with high ionic conductivity is injected into the base membrane until saturation is achieved via solution casting. After high-temperature polymerization at 60-120℃, an ultrathin organic-inorganic composite electrolyte membrane is obtained. The polymer comprises 20 wt%-80 wt%, and the highly dispersed inorganic nanoparticles comprise 20 wt%-80 wt%, with the total weight of the inorganic nanoparticles and polymer being 100%. The selected polymer is selected from one or more of polyethylene oxide (PEO) and its derivatives, polyvinylidene fluoride (PVDF) and its derivatives, polyacrylonitrile (PAN) and its derivatives, and polysiloxane and its derivatives. The selected organic solvent is one or more of the following: N-methylpyrrolidone (NMP), ethylene carbonate, propylene carbonate, butenyl carbonate, dimethyl carbonate, ethylene carbonate, methyl ethyl carbonate, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, acetonitrile, 1,2-dimethoxyethylene, tetraethylene glycol dimethyl ether, triethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and dimethyl sulfoxide; Highly dispersed inorganic nanoparticles were selected from garnet-type Li7La3Zr2O 12 and doped modified solid electrolyte nanoparticles, perovskite-type LiLaTiO3 and doped modified solid electrolyte nanoparticles, NASICON-type Li 1+x Al x Ti 2-x (PO4)3 and doped modified solid electrolyte nanoparticles, LISICON-type Li 14 Zn(GeO4)4 and doped modified solid electrolyte nanoparticles, litholytic LiTaSiO5 and doped modified solid electrolyte nanoparticles, sulfide Li 10 GeP2S 12 Solid electrolyte nanoparticles, halide Li3InCl6 solid electrolyte nanoparticles, montmorillonite nanoparticles, silica nanoparticles, zirconium dioxide nanoparticles, barium titanate nanoparticles, calcium carbonate nanoparticles, alumina nanoparticles, titanium dioxide nanoparticles, silicon carbide nanoparticles, Li 14 One or more of Zn(GeO4)4 nanoparticles, LiZr2(PO4)3 nanoparticles, and LiPON nanoparticles; The prepared ultrathin organic-inorganic composite electrolyte membrane has a thickness of less than 10 μm.

2. The method for preparing an ultrathin organic-inorganic composite solid electrolyte membrane according to claim 1, characterized in that, The carbonate-based polymer electrolyte precursor is a precursor capable of forming a carbonate-based polymer electrolyte, selected from one or more of the following: polycarbonate precursor solution, polyvinyl carbonate precursor solution, polyethylene carbonate precursor solution, polyallyl methyl carbonate precursor solution, polyvinyl carbonate precursor solution, and polyfluoroethylene carbonate precursor solution. The polycarbonate precursor solution includes carbonate + lithium salt + initiator; the polyvinyl carbonate precursor solution includes carbonate + lithium salt + initiator; the polyethylene carbonate precursor solution includes polyvinyl carbonate + lithium salt + initiator; the polyallyl methyl carbonate precursor solution includes allyl methyl carbonate + lithium salt + initiator; the polyvinyl carbonate precursor solution includes polyvinyl carbonate + lithium salt + initiator; and the polyfluoroethylene carbonate precursor solution includes fluoroethylene carbonate + lithium salt + initiator.

3. An ultrathin organic-inorganic composite solid electrolyte membrane prepared according to any one of claims 1-2.

4. An ultrathin organic-inorganic composite solid electrolyte membrane prepared according to any one of claims 1-2, having a room temperature ionic conductivity >1.0 × 10⁻⁶. -3 S / cm, electrochemical stability window > 5.5V (vs. Li + / Li), ion transference number >0.

65.

5. A lithium-ion rechargeable all-solid-state battery, characterized in that, The ultrathin organic-inorganic composite solid electrolyte membrane prepared by the method described in any one of claims 1-2.

6. A lithium-ion secondary all-solid-state battery according to claim 5, characterized in that, The positive electrode active material of the lithium-ion battery is one or more of lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium-ion fluorophosphate, lithium manganese oxide, lithium-rich manganese base oxide, lithium iron manganese phosphate, lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide, lithium iron phosphate (LiFeO4), and lithium vanadium phosphate (Li3V2(PO4)3); the negative electrode active material is one or more of lithium metal, lithium alloy, graphite, hard carbon, lithium metal nitride, antimony oxide, carbon germanium composite material, carbon silicon composite material, lithium titanate, and lithium titanium oxide; the initiator or catalyst is one of the following: dibutyltin dilaurate, bis(acetylacetonate) dibutyltin, azobisisoheptanenitrile (ABVN), azobisisobutyronitrile (AIBN), dimethyl azobisisobutyrate (AIBME), benzoyl peroxide (BPO), and platinum solution (Pt). The preparation of positive electrode materials for lithium-ion batteries includes the following steps: grinding and mixing 50-90% by mass of positive electrode active material and 5-30% by mass of conductive agent acetylene black; adding 1-15% by mass of polyvinylidene fluoride (PVDF), 1-15% by mass of polycarbonate-based organic-inorganic composite solid electrolyte, and 1-methyl-2-pyrrolidone (NMP) and grinding and mixing; coating on the surface of aluminum foil and drying; lithium metal and lithium metal alloys are directly used as the corresponding negative electrode materials; or the preparation of other negative electrode materials includes the following steps: grinding and mixing 50-90% by mass of negative electrode active material and 5-30% by mass of conductive agent acetylene black; adding 5-25% by mass of polyvinylidene fluoride (PVDF) and 1-methyl-2-pyrrolidone (NMP) and grinding and mixing; coating on the surface of copper foil and drying; Lithium-ion battery assembly includes coin cells and pouch cells. The internal stacking order of solid-state batteries is positive electrode - ultra-thin organic-inorganic composite solid electrolyte membrane - negative electrode.

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