Inorganic-polymer composite solid electrolyte and method for preparing the same

Abstract

The application provides an inorganic-polymer composite solid electrolyte and a preparation method thereof. The composite solid electrolyte is prepared by taking low-toxicity and high-abundance Al2O3 or Li2O / Na2O as an oxygen source to prepare an inorganic glass phase (MACO), matching a PVDF-HFP polymer matrix and Li3PO4 / Na3PO4 ion dopant. The MACO chemical formula is MAlCl 4‑2x O x (M=Li / Na, 0.5

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid-state battery electrolyte, and particularly relates to an inorganic-polymer composite solid-state electrolyte and a preparation method thereof. BACKGROUND

[0002] With the rapid development of new energy automobile industry, higher requirements are put forward for the energy density, safety performance and cycle life of power batteries. Solid-state batteries are considered as the core development direction of the next generation of power batteries because they have the outstanding advantages of high energy density, no risk of liquid leakage and excellent safety performance by using solid-state electrolyte to replace traditional liquid electrolyte. However, the existing solid-state electrolyte technology still faces many key bottlenecks, which seriously restricts the practical process of solid-state batteries.

[0003] The existing solid-state electrolyte is mainly divided into three types: inorganic solid-state electrolyte, organic polymer electrolyte and inorganic-polymer composite solid-state electrolyte, but all of them have obvious defects:

[0004] The inorganic solid-state electrolyte (such as Li 6.4 La3Zr 1.4 Ta 0.6 O 12 ) has high chemical stability and certain ionic conductivity, but the material is extremely rigid, the interface contact performance with the electrode is poor, and a stacking pressure of several to several hundred megapascals needs to be applied to maintain effective electrode contact, which leads to complex battery pack design, increases the production cost, and significantly reduces the energy density of the battery, which is difficult to meet the practical application requirements of power batteries.

[0005] The organic polymer electrolyte (such as polyethylene oxide PEO) has good flexibility and can realize pressureless interface contact, but the room temperature ionic conductivity is extremely low (<10 -4 S / cm), and the high voltage resistance is poor (<4.0V), which cannot adapt to high-voltage positive electrode materials, limiting the improvement of battery energy density.

[0006] The existing super-fluid electrolyte (such as super-fluid inorganic electrolyte) has broken through the technical difficulty of high conductivity at room temperature (>10 mS / cm), but the mechanical strength of the pure inorganic system is seriously insufficient, and in the long-term cycle process of the battery, the interface is easy to crack due to the volume change of the electrode, leading to the performance degradation of the battery; another related technology uses viscoelastic inorganic glass as a solid-state electrolyte, but its oxygen source introduction depends on antimony trioxide (Sb2O3), and the toxicity of Sb element is high, and the cost controllability is poor, which is not conducive to large-scale industrial application.

[0007] The existing inorganic-polymer composite electrolyte generally has a trade-off between conductivity and mechanical properties: too high polymer content will significantly reduce the ionic conductivity, and too high inorganic phase content will lose the deformation ability, which is difficult to simultaneously meet the requirements of solid-state battery on the comprehensive performance of electrolyte. SUMMARY

[0008] The present application aims to solve the problems existing in the prior art and provides an inorganic-polymer composite solid-state electrolyte and a preparation method thereof.

[0009] To achieve the above-mentioned purpose, the application adopts the following technical scheme: an inorganic-polymer composite solid-state electrolyte, comprising the following components in terms of mass percentage: 50-80wt% of inorganic glass phase MACO, 15-40wt% of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and 1-5wt% of ion dopant; the chemical formula of the inorganic glass phase MACO is MAlCl 4-2X O X , wherein M is Li or Na, 0.5 + / Na + , and the oxygen source is Al2O3 or Li2O / Na2O; the ion dopant is Li3PO4, Na3PO4 or LiF.

[0010] Preferably, the room temperature ionic conductivity of the composite solid-state electrolyte is 2-5.5mS / cm, and the voltage resistance is ≥4.3V.

[0011] The application uses Al2O3 or Li2O / Na2O as the oxygen source to introduce oxygen atoms into MAlCl4 (M=Li / Na) through a melting reaction, and the reaction formula is as follows taking Li as an example:

[0012] LiCl + AlCl3+ Al2O3→MAlCl 4-2X O X (LACO).

[0013] Al2O3 has the advantages of low toxicity, high crustal abundance and low cost, and its cost is only 1 / 5 of that of Sb2O3, which can greatly reduce the production cost; at the same time, by adjusting the addition amount of Al2O3 (corresponding to x=0.6-0.9), the inorganic glass phase can be changed from "brittle" to "superfluid", ensuring that the electrolyte has good deformation ability at room temperature and can adapt to the volume change of the electrode.

[0014] The application selects polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) as the polymer matrix, and the fluorine atoms in the molecular structure can form a strong interaction with Li + / Na +Forming weak coordination: on the one hand, weak coordination can effectively avoid the agglomeration of inorganic phases in the composite system, ensuring the uniform dispersion of inorganic phases and providing continuous channels for ion transmission; on the other hand, the coordination strength is moderate and will not hinder the migration of Li + / Na + , ensuring that the ionic conductivity is not significantly affected. At the same time, the semi-crystalline structure of PVDF-HFP can significantly improve the tensile strength (>15 MPa) of the composite electrolyte, effectively solving the problem of insufficient mechanical strength and easy breakage of pure inorganic superfluid electrolyte, and realizing the synergistic optimization of conductivity and mechanical properties.

[0015] The application preferably uses Li3PO4 (for Li-based) or Na3PO4 (for Na-based) as an ion dopant, which mainly functions in two aspects: ①PO4 3- can form local "ion transmission nodes" with the Al-O-Al network in the inorganic glass phase, which can significantly shorten the hopping distance of Li + / Na + , optimize the ion transmission channel, and further improve the room temperature ionic conductivity of the electrolyte; ② the dopant can effectively inhibit the high-temperature crystallization of the inorganic phase, widen the superfluid temperature range (-40~80℃), improve the stability of the electrolyte at different working temperatures, and meet the use requirements of power batteries under complex working conditions.

[0016] Through a large number of experimental verifications, the optimal mass fraction of the ion dopant is 1~5wt%, when the doping amount is 3wt% (taking the Li-based system as an example), the room temperature ionic conductivity of the electrolyte reaches the maximum value, and excessive doping will cause PO4 3- agglomeration, which will hinder ion transmission and reduce conductivity.

[0017] A preparation method of an inorganic-polymer composite solid-state electrolyte, comprising the following steps:

[0018] S1: preparing an inorganic glass phase MACO:

[0019] MCl (LiCl / NaCl, purity 99.99%), AlCl3 (purity 99.99%) and oxygen-containing substances (Al2O3 or Li2O / Na2O) are mixed in a molar ratio of 1: (1~1.2): (0.1~0.3), placed in an alumina crucible, heated and melted at 180~220℃ for 2~4h, continuously stirred during the heating process to remove volatile components (such as HCl) generated during the reaction, and naturally cooled to room temperature to obtain a transparent MACO glass block;

[0020] S2: preparing a composite slurry:

[0021] PVDF-HFP (molecular weight 50-100 million) is dissolved in N-methyl pyrrolidone (NMP) to prepare a PVDF-HFP solution with a mass concentration of 10-15%;

[0022] The MACO glass bulk obtained in step S1 is crushed to obtain MACO glass powder with a particle size of 5-10 μm;

[0023] The MACO glass powder and the ion dopant are added to the PVDF-HFP solution, and stirring is performed at 60-80℃ for 3-5h to ensure uniform dispersion of the components and form a uniform composite slurry;

[0024] S3: coating, film forming and drying:

[0025] The composite slurry obtained in step S2 is coated on a polytetrafluoroethylene substrate;

[0026] First, pre-drying is performed at 80℃ for 2h to remove part of the solvent in the composite slurry coated on the polytetrafluoroethylene substrate; then, the film is transferred to a double-roller mill, and rolling is performed at a temperature of 50-70℃ and a pressure of 0.5-1 MPa to obtain a thin film with a thickness of 20 μm; finally, the film is transferred to a vacuum drying oven, and vacuum drying is performed at 120℃ for 6-8h to completely remove the residual NMP solvent on the polytetrafluoroethylene substrate, and finally an inorganic-polymer composite solid-state electrolyte film is obtained.

[0027] Preferably, the volatilized component in step S1 is HCl.

[0028] Preferably, the amount of NMP used in step S2 is 8 times the mass of PVDF-HFP.

[0029] A solid-state battery comprising a positive electrode, a negative electrode and an inorganic-polymer composite solid-state electrolyte; the positive electrode is selected from NCM622, Na3V2(PO4)3, and the negative electrode is selected from metal Li, metal Na or Li / Na alloy.

[0030] Compared with the prior art, the inorganic-polymer composite solid-state electrolyte of the present application has the following advantages and beneficial effects:

[0031] The safety and environmental protection are significantly improved: Al2O3 or Li2O / Na2O is used to replace the toxic Sb2O3 as the oxygen source, which completely avoids the toxicity risk of Sb element and reduces the harm of the material to the environment and human body; at the same time, Al2O3 has high crust abundance, and the cost is only 1 / 5 of that of Sb2O3, which greatly reduces the raw material cost of large-scale production and improves the market competitiveness of the product.

[0032] Synergistic optimization of conductivity and mechanical properties: The room-temperature ionic conductivity of the composite electrolyte can reach 20-55 mS / cm, close to the level of superfluid electrolyte, which can meet the high-power output demand of power batteries; at the same time, the tensile strength is increased to 15-25 MPa, effectively solving the core contradiction of "brittle" of pure inorganic electrolyte and "slow" of pure polymer electrolyte, realizing the synergistic unity of high conductivity and high mechanical strength.

[0033] Excellent interface compatibility: The inorganic-polymer composite solid-state electrolyte has good chemical compatibility with LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), Na3V2(PO4)3, etc. High-voltage cathodes have good chemical compatibility, and the battery capacity retention rate is still > 85% after cycling at 4.3V for several times, and the cycle stability is excellent; the metal Li + / Na + negative electrode also has good interface stability, and no obvious side reaction occurs.

[0034] Scalable preparation process: The present application adopts a melt blending-coating process, which does not require complex production equipment, is simple to operate, and can realize continuous production; the yield of the composite electrolyte film can reach 1000 m² / day at the laboratory scale, which can meet the large-scale production demand of power battery industrialization, and has broad industrial application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 It is a bending and stretching physical map of the composite electrolyte film;

[0036] Figure 2 It is a micro-morphology map of the polymer composite solid-state electrolyte;

[0037] Figure 3 It is a linear sweep voltammetry curve;

[0038] Figure 4 It is a cycle number-specific capacity / coulomb efficiency relationship diagram of Example 1;

[0039] Figure 5 It is a cycle number-specific capacity / coulomb efficiency relationship diagram of Example 2;

[0040] Figure 6 It is an electrochemical impedance spectroscopy (EIS) diagram of Example 1 and Example 2;

[0041] Figure 7 It is an electrochemical impedance spectroscopy (EIS) diagram of Example 3. DETAILED DESCRIPTION

[0042] In order to make the purpose, structure, characteristics and functions of the present application more comprehensible, the following detailed description is given in conjunction with the embodiments.

[0043] Please refer to Figures 1 to 7 The present application provides an inorganic-polymer composite solid electrolyte and a preparation method and application thereof.

[0044] Embodiment 1: Refer to Figure 3 , 4 , 6,

[0045] Li-based inorganic-polymer composite solid electrolyte (LACO-PVDF-HFP-Li3PO4):

[0046] In this embodiment, the meaning of inorganic glass phase MACO is as follows:

[0047] M is Li, abbreviated as L; A represents Al; C represents Cl, therefore, the abbreviation of the inorganic glass phase of this embodiment is LACO;

[0048] 1.1: Raw material ratio (by mass percentage and molar amount)

[0049] LiCl (0.1 mol), AlCl3 (0.11 mol), Al2O3 (0.02 mol), PVDF-HFP (molecular weight 800,000, 15wt%), Li3PO4 (3wt%), N-methyl pyrrolidone (NMP, solvent, the amount of which is 8 times the mass of PVDF-HFP); wherein the mass percentage of inorganic glass phase LACO is 72wt%.

[0050] 1.2: Preparation process:

[0051] Preparation of inorganic glass phase LACO:

[0052] LiCl, AlCl3 and Al2O3 are mixed uniformly according to the above molar ratio, placed in an alumina crucible, and put into a muffle furnace, heated and melted at 200℃ for 3h, and stirred every 30min during the melting process to fully remove the generated HCl; after melting, it is naturally cooled to room temperature to obtain a transparent LACO glass block, which is crushed and sieved to obtain LACO glass powder with a particle size of 5-10μm (chemical formula LiAlCl 2.5 O 0.75 , x=0.75); LiAlCl 2.5 O 0.75 is an inorganic glass solid electrolyte synthesized by replacing part of the chlorine atoms in lithium tetrachloroaluminate (LiAlCl4) with oxygen atoms, with an oxygen / aluminum ratio of 0.75:1.

[0053] Preparation of composite slurry:

[0054] PVDF-HFP was added to NMP solvent, stirred until completely dissolved, to prepare a PVDF-HFP solution with a mass concentration of 12%; the LACO glass powder and Li3PO4 dopant described above were added to the solution, placed in a 60°C constant temperature water bath, and stirred for 4h to form a uniformly dispersed composite slurry.

[0055] Coating, film forming and drying:

[0056] The composite slurry was uniformly coated on a polytetrafluoroethylene substrate by a coating machine, then placed in an 80°C oven for 2h of pre-drying to remove part of the NMP solvent; the pre-dried film was transferred to a double-roller mill and rolled at a temperature of 60°C and a pressure of 0.8MPa to obtain a uniform film with a thickness of 20μm; finally, the film was placed in a vacuum drying oven and vacuum dried at 120°C for 7h to completely remove the residual NMP solvent, obtaining a Li-based composite solid electrolyte film.

[0057] 1.3: Performance testing:

[0058] Room temperature (25 °C) ionic conductivity Linear sweep voltammetry, LSV Battery performance (Li / electrolyte / NCM622 battery, cathode loading 10 mg / cm 2 ​ 4.82 mS / cm 4.3-4.4V 1C cycle 500 times, capacity retention 87.3%

[0059] Room temperature ionic conductivity: tested by AC impedance method;

[0060] Voltage resistance performance: tested by linear sweep voltammetry (LSV), with a voltage resistance of 4.4V;

[0061] Interface compatibility and cycle stability: the electrolyte was applied to a solid-state battery with NCM622 as the positive electrode and metal Li as the negative electrode, and the battery was cycled at a voltage of 4.4V; after 500 cycles, the battery capacity retention rate was 87.3%; and no additional stacking pressure (<0.1MPa) was required during battery assembly, and the interface contact was good.

[0062] Example 2: According to the method of Example 1, Figure 3 、 5 、6,

[0063] Na-based inorganic-polymer composite solid electrolyte (NACO-PVDF-HFP-Na3PO4):

[0064] In this example, the meaning of the inorganic glass phase MACO is as follows:

[0065] M is Na, abbreviated as N; A represents Al; C represents Cl, so the abbreviation of the inorganic glass phase in this example is NACO;

[0066] 2.1: Raw material ratio (by mass percentage and molar amount):

[0067] NaCl (0.1 mol), AlCl3 (0.1 mol), Al2O3 (0.015 mol), PVDF-HFP (molecular weight 600,000, 20 wt%), Na3PO4 (2 wt%), N-methyl pyrrolidone (NMP, solvent, the amount is 8 times the mass of PVDF-HFP); wherein the mass ratio of the inorganic glass phase NaCO is 78 wt%.

[0068] 2.2: Preparation process

[0069] Preparation of inorganic glass phase NACO:

[0070] NaCl, AlCl3 and Al2O3 were mixed uniformly according to the above molar ratio, placed in an alumina crucible, and put into a muffle furnace, heated and melted at 190°C for 3.5h, stirred every 30min during the melting process, and removed the generated HCl; after natural cooling to room temperature, a transparent NACO glass bulk was obtained, which was crushed and sieved to obtain NACO glass powder with a particle size of 5-10μm (chemical formula: NaAlCl 2.7 O 0.65 , x=0.65); NaAlCl 2.7 O 0.65 is an inorganic glass solid electrolyte synthesized by replacing part of the chlorine atoms in sodium tetrachloroaluminate (NaAlCl4) with oxygen atoms, with an oxygen / aluminum ratio of 0.65:1

[0071] Preparation of composite slurry:

[0072] PVDF-HFP was added to NMP solvent and stirred until completely dissolved to prepare a PVDF-HFP solution with a mass concentration of 10%; the NACO glass powder and Na3PO4 dopant were added to the solution, and the mixture was stirred in a 70°C constant temperature water bath for 3.5h to form a uniformly dispersed composite slurry.

[0073] Coating, film forming and drying:

[0074] The composite slurry was uniformly coated on a polytetrafluoroethylene substrate and pre-dried at 80°C for 2h; then it was rolled in a double roller mill at a temperature of 55°C and a pressure of 0.6MPa to obtain a 20μm thick film; finally, it was vacuum dried at 120°C for 6.5h to remove residual NMP, obtaining a Na-based composite solid electrolyte film.

[0075] 2.3: Performance test:

[0076] Room temperature (25 °C) ionic conductivity Linear sweep voltammetry, LSV Battery performance (Na / electrolyte / Na3V2(PO4)3cell, cathode loading 10 mg / cm2) 2 ​ 3.95 mS / cm 4.3-4.4V 1C cycle 100 times, capacity retention 84.1%

[0077] Room temperature ionic conductivity: tested by AC impedance method;

[0078] Voltage resistance performance: tested by linear sweep voltammetry (LSV), the voltage resistance is 4.4V;

[0079] Interface compatibility and cycle stability: applied in a solid-state battery with Na3V2(PO4)3 as the positive electrode and metal Na as the negative electrode, the capacity retention rate of the battery is 84.1% after 100 cycles; good interface contact can be achieved without additional stacking pressure.

[0080] Example 3: Reference Figure 7 Effect of doping amount on conductivity (Li-based system):

[0081] To explore the optimal doping amount of the ion dopant Li3PO4, the mass percentage of LACO is fixed at 75wt%, the mass percentage of PVDF-HFP is fixed at 20wt%, and the doping amount of Li3PO4 is changed (1wt%, 3wt%, 5wt%). A series of Li-based composite solid electrolyte membranes are prepared according to the preparation method of Example 1, and their room temperature ionic conductivity is tested, and the results are shown in the following table:

[0082] From the above test results, it can be seen that the doping amount of Li3PO4 has a significant effect on the room temperature ionic conductivity of the composite electrolyte: as the doping amount increases from 1wt% to 3wt%, the ionic conductivity gradually increases, and when the doping amount is 3wt%, the conductivity reaches a maximum value of 5mS / cm; further increasing the doping amount to 5wt% reduces the conductivity.

[0083] This is because an appropriate amount of Li3PO4 can form a local "ion transmission node" with the Al-O-Al network in the inorganic glass phase, shortening the Li⁺ jumping distance and optimizing the ion transmission channel; while excessive doping will cause PO4³⁻ to agglomerate, hindering the migration of Li⁺, thereby reducing the conductivity. Therefore, the optimal doping amount of Li3PO4 is 3wt%.

[0084] The present application has been described by the above related embodiments, however, the above embodiments are only examples of implementing the present application. It must be pointed out that the disclosed embodiments do not limit the scope of the present application. On the contrary, modifications and improvements made without departing from the spirit and scope of the present application are within the scope of the patent protection of the present application.

Claims

1. An inorganic-polymer composite solid-state electrolyte, characterized by: By mass percentage, the following components are included: 50-80wt% of inorganic glass phase MACO, 15-40wt% of polyvinylidene fluoride-hexafluoropropylene copolymer PVDF-HFP, 1-5wt% of ion dopant; the chemical formula of the inorganic glass phase MACO is MAlCl 4-2X O X , wherein M is Li or Na, 0.5 2. The inorganic-polymer composite solid-state electrolyte of claim 1, wherein: The room temperature ionic conductivity of the composite solid electrolyte is 2-5.5 mS / cm, and the voltage resistance is greater than or equal to 4.3 V.

3. A method of producing the inorganic-polymer composite solid-state electrolyte according to any one of claims 1 to 2, characterized by: The method comprises the following steps: S1: preparing an inorganic glass phase MACO: MCl, AlCl3 and an oxygen-containing substance are mixed in a molar ratio of 1:(1-1.2):(0.1-0.3), placed in an alumina crucible, heated and melted at 180-220℃ for 2-4h, and stirred to remove volatile components during the process, and naturally cooled to room temperature to obtain a transparent MACO glass block; the MCl is LiCl or NaCl; the oxygen-containing substance is Al2O3 or Li2O / Na2O; S2: preparing a composite slurry: PVDF-HFP is dissolved in N-methyl pyrrolidone (NMP) to prepare a PVDF-HFP solution with a mass concentration of 10-15%; The MACO glass block obtained in step S1 is crushed into MACO glass powder; MACO glass powder and an ion dopant are added to the PVDF-HFP solution, and the mixture is stirred at 60-80℃ for 3-5h to form a uniform composite slurry; S3: coating, film forming and drying: The composite slurry obtained in step S2 is coated on a polytetrafluoroethylene substrate; First, pre-dry at 80℃ for 2h to remove part of the solvent on the polytetrafluoroethylene substrate; then transfer to a double-roller mill, and roll at a temperature of 50-70℃ and a pressure of 0.5-1MPa to obtain a thin film with a thickness of 20μm; finally, vacuum dry at 120℃ for 6-8h to completely remove the residual NMP on the polytetrafluoroethylene substrate, and finally obtain an inorganic-polymer composite solid electrolyte film.

4. The production method according to claim 3, characterized by: The volatilized component in step S1 is HCl.

5. The production method according to claim 4, characterized by: The amount of NMP used in step S2 is 8 times the mass of PVDF-HFP.

6. A solid state battery characterized by: A positive electrode, a negative electrode and the inorganic-polymer composite solid electrolyte of claim 1; the positive electrode is selected from NCM622, Na3V2(PO4)3, and the negative electrode is selected from metal Li, metal Na or Li / Na alloy.

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