Polymer-based composite solid electrolyte, preparation method and lithium solid-state battery

Abstract

The invention relates to a polymer-based composite solid electrolyte, a preparation method and a lithium solid-state battery. The polymer-based composite solid electrolyte is prepared from the following components in parts by mass: 5 to 15 parts of polymer, 5 to 15 parts of lithium salt and 0.5 to 2.5 parts of composite filler, the composite filler comprises barium titanate, and the surface of the barium titanate is coated with lithium tungstate. The polymer-based composite solid electrolyte disclosed by the invention has relatively high ionic conductivity and electrochemical stability, the ionic conductivity of the polymer-based composite solid electrolyte is up to 2.86 mS / cm, and an electrochemical stability window is up to 5.4 V. Meanwhile, the interface between the polymer-based composite solid electrolyte and the electrode is more stable, and the cycle performance is excellent.

Description

Technical Field

[0001] The present invention relates to a polymer-based composite solid electrolyte, a preparation method and a lithium solid-state battery, belonging to the technical field of solid-state batteries. Background Art

[0002] Although traditional liquid lithium-ion batteries are widely used in various fields, including electric vehicles, energy storage systems, and consumer electronics, their energy density is approaching its limit, and their safety deficiencies are becoming increasingly prominent. In recent years, solid-state batteries have become a hot topic of research, offering numerous advantages, including high energy density and enhanced safety. The core of solid-state batteries is the solid electrolyte. Common solid-state electrolytes include sulfide electrolytes, oxide electrolytes, halide electrolytes, and polymer electrolytes. Among them, polymer solid electrolytes have attracted increasing attention due to their excellent flexibility and processability. However, polymer solid electrolytes also suffer from relatively low room-temperature ionic conductivity and poor mechanical properties. Currently, a common strategy to improve the performance of polymer electrolytes is to add inorganic fillers. Common inorganic fillers include Al2O3, SiO2, TiO2, and BaTiO3. While these fillers can generally improve certain properties of polymer electrolytes, the addition of a single inorganic filler has limited effect and is unlikely to enhance the overall performance of solid-state batteries.

[0003] Chinese invention patent application CN201410683144.1 discloses an all-solid-state polymer electrolyte comprising polyethylene oxide (PEO), a lithium salt, inorganic nanoparticles, and an ionic liquid. The ratio of the lithium salt to the PEO mass is 0.1 to 0.5, and the sum of the inorganic nanoparticles and the ionic liquid mass is 10% to 30% of the mass of the all-solid-state polymer electrolyte. The lithium salt comprises one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, and lithium bis(oxalatoborate); and the inorganic nanoparticles comprise one or more of nano-alumina, nano-silicon oxide, nano-zirconium oxide, and nano-barium titanate. In this patent, the nano-inorganic particles are used to improve mechanical properties, while the room-temperature ionic liquid provides electrical conductivity. The combined action of the two gives the all-solid-state polymer electrolyte excellent mechanical strength and high ionic conductivity. However, ionic liquids are liquid and will not evaporate even after long-term baking, resulting in the risk of leakage in all-solid-state polymer electrolytes, which may affect the normal performance of the polymer electrolytes. In addition, ionic liquids are relatively expensive, which increases the cost of all-solid-state polymer electrolytes.

[0004] Chinese invention patent application CN202010141024.4 discloses a composite solid electrolyte, the components of which include polyethylene oxide, polymer, electrolyte, inorganic filler particles and solvent, the polymer being one or more of polyethylene glycol (PEG), polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC) and polyvinyl pyrrolidone (PVP), the electrolyte being one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium hexafluorophosphate (LiPF6) and lithium perchlorate (LiClO4), and the inorganic filler particles being one or more of titanium dioxide (TiO2), silicon dioxide (SiO2), aluminum oxide (Al2O3) and barium titanate (BaTiO3). However, the room temperature ionic conductivity of this composite solid electrolyte can only reach 3.83×10 -5 S / cm, there is still much room for improvement. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, one of the objects of the present invention is to provide a polymer-based composite solid electrolyte with high ionic conductivity; the second object of the present invention is to provide a method for preparing a polymer-based composite solid electrolyte; and the third object of the present invention is to provide a lithium solid-state battery.

[0006] In order to solve the above technical problems, the technical solutions of the present invention are as follows: A polymer-based composite solid electrolyte comprises, by weight, 5-15 parts of a polymer, 5-15 parts of a lithium salt and 0.5-2.5 parts of a composite filler; the composite filler comprises barium titanate, the surface of which is coated with lithium tungstate.

[0007] Optionally, the polymer-based composite solid electrolyte includes 8-12 parts of polymer, 8-12 parts of lithium salt and 0.8-2.2 parts of composite filler.

[0008] Furthermore, the polymer-based composite solid electrolyte comprises 9.5-10.5 parts of polymer, 9.5-10.5 parts of lithium salt and 1-2 parts of composite filler; and / or, the polymer-based composite solid electrolyte is in a film-like form with a thickness of 20-150 μm, further 40-130 μm, and further 50-100 μm.

[0009] Furthermore, the polymer-based composite solid electrolyte includes 9.8-10.2 parts of polymer, 9.8-10.2 parts of lithium salt and 1.2-1.7 parts of composite filler.

[0010] Furthermore, in the composite filler, the mass ratio of lithium tungstate to barium titanate is 5-20:100, further 8-18:100, preferably 10-15:100, further preferably 11-14:100, and even more preferably 12-13:100.

[0011] Furthermore, the preparation method of the composite filler comprises the following steps: adding barium titanate powder to a mixed solution, dispersing the mixture by ultrasonication, allowing the mixture to stand under negative pressure, drying the solvent, calcining, grinding, and sieving to obtain the composite filler; The mixed solution contains tungstate and lithium ions; in the mixed solution, the molar ratio of tungstate to lithium ions is 1:2; and the solvent of the mixed solution is water.

[0012] Barium titanate is insoluble in the above solvent and can be used as a core. In the above process, the in-situ generated lithium tungstate can be loaded onto the barium titanate, so that the lithium tungstate is coated on the barium titanate to obtain a composite filler.

[0013] Optionally, the pH value of the mixed solution is 7.0±0.3, further 7.0±0.1.

[0014] During in-depth research, the applicant unexpectedly discovered that the composite filler described in the present invention can effectively improve the ionic conductivity of the polymer-based composite solid electrolyte and widen its electrochemical window, and enable the assembled lithium solid-state battery to exhibit better cycle performance; however, when lithium tungstate or lithium titanate is used as a filler alone or when lithium tungstate and lithium titanate are simply compounded as a filler, the above-mentioned improvement effect cannot be achieved.

[0015] Optionally, during ultrasonic dispersion, the ultrasonic power is 350-450W.

[0016] Optionally, the particle size of the barium titanate powder is less than 300 nm.

[0017] Optionally, the barium titanate powder is nano barium carbonate powder.

[0018] Optionally, ultrasonic dispersion is performed for 30-90 min, further, ultrasonic dispersion is performed for 45-75 min.

[0019] Optionally, the mixture is allowed to stand under negative pressure (optionally -0.15-0.01 MPa) for 8-12 hours.

[0020] Optionally, grind for 0.3-0.8 h.

[0021] Furthermore, first let it stand at -0.01-0.06Mpa for 1-3 hours, then let it stand at -0.09-0.07Mpa for 2-4 hours, and then let it stand at -0.11-0.09Mpa for 4-6 hours.

[0022] Optionally, the calcination is performed at 600-700° C. for 2-6 hours, and further, the calcination is performed at 620-670° C. for 3-5 hours.

[0023] Further, a water-soluble tungsten source and a water-soluble lithium source are dissolved in water to obtain a mixed solution; wherein the water-soluble tungsten source is ammonium dodecotungstate ((NH4)10 W 12 O 41 ), ammonium metatungstate ((NH4)6H2W 12 O 40 ) and the water-soluble lithium source is one or more of lithium acetate and lithium hydroxide. This allows for the preparation of composite fillers without introducing impurity elements, thereby contributing to the production of polymer-based composite solid electrolytes of superior quality.

[0024] Furthermore, the polymer is one or more of polyvinylidene fluoride, poly(vinylidene fluoride-hexafluoropropylene) copolymer, and poly(vinylidene fluoride-trifluoroethylene) copolymer.

[0025] Optionally, the weight average molecular weight of the polymer is 300,000-1,000,000, further 400,000-900,000, and further 500,000-800,000.

[0026] Furthermore, the lithium salt is one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium difluorooxalatoborate, and lithium bis(oxalatoborate).

[0027] Optionally, the polymer-based solid electrolyte further includes a polar solvent.

[0028] Optionally, the room temperature ionic conductivity of the polymer-based composite solid electrolyte is ≥1 mS / cm, preferably ≥1.5 mS / cm, more preferably ≥2 mS / cm, and even more preferably ≥2.5 mS / cm.

[0029] Optionally, the electrochemical stability window of the polymer-based composite solid electrolyte is ≥5V, preferably ≥5.2V, and more preferably ≥5.4V.

[0030] Based on the same inventive concept, the present invention also provides: a method for preparing the polymer-based composite solid electrolyte as described above, comprising the following steps: S1. Mix the polymer, lithium salt, composite filler, and polar solvent in a ratio of 5-15 g: 5-15 g: 0.5-2.5 g: 20-100 mL to obtain a polymer solution; S2. Applying the polymer solution on a template, drying, and demoulding to obtain a polymer-based composite solid electrolyte.

[0031] Furthermore, in S1, the polymer, lithium salt, composite filler and polar solvent are uniformly mixed in a ratio of 8-12 g: 8-12 g: 0.8-2.2 g: 30-90 mL.

[0032] Furthermore, in S1, the polymer, lithium salt, composite filler and polar solvent are uniformly mixed in a ratio of 9-11 g:9-11 g:1-2 g:40-80 mL. Further, the polymer, lithium salt, composite filler and polar solvent are uniformly mixed in a ratio of 9.5-10.5 g:9.5-10.5 g:1.2-1.8 g:50-70 mL.

[0033] Furthermore, in S1, the polar solvent is one or more of N-methylpyrrolidone, acetone, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0034] Furthermore, in S1, the polymer, the composite lithium salt, the filler, and the polar solvent are mixed and stirred at 45-85° C. for 4-12 hours to obtain a polymer solution. Alternatively, the polymer, the lithium salt, and the polar solvent are first mixed uniformly, and then the composite filler is added and mixed uniformly to obtain a polymer solution.

[0035] Furthermore, in S2, the template is a glass plate.

[0036] Optionally, in S2, a doctor blade is used for coating to form a film.

[0037] Furthermore, the gap of the scraper is 200-1000 μm.

[0038] Optionally, in S2, drying is performed at 25-80°C for 0.5-8h, and further drying is performed at 35-65°C for 1.5-6h.

[0039] Based on the same inventive concept, the present invention also provides: a lithium solid-state battery, comprising a negative electrode plate stacked in sequence, a polymer-based composite solid electrolyte as described above or a polymer-based composite solid electrolyte prepared by the preparation method as described above, and a positive electrode plate.

[0040] Optionally, the active material of the positive electrode plate is a conventional commercial lithium-ion battery positive electrode material, and the other components are a binder, a conductive agent and / or a functional additive.

[0041] Optionally, the negative electrode plate is a common commercial negative electrode such as graphite, silicon carbon, or lithium metal.

[0042] Optionally, the lithium solid-state battery is stably cycled for 500 cycles at a rate of 0.5C at room temperature, and the capacity retention rate is as high as ≥89%, preferably ≥90%, and more preferably ≥95%.

[0043] Compared with the prior art, the present invention has the following beneficial effects: (1) The polymer-based composite solid electrolyte of the present invention has high ionic conductivity and electrochemical stability. The ionic conductivity of the polymer-based composite solid electrolyte is as high as 2.86mS / cm, and the electrochemical stability window is up to 5.4V. At the same time, the interface between the polymer-based composite solid electrolyte and the electrode is also more stable, and the cycling performance is excellent.

[0044] (2) The polymer-based composite solid electrolyte of the present invention is used to assemble a lithium solid-state battery, which can be stably cycled for 500 cycles at a rate of 0.5C at room temperature, with a capacity retention rate of up to 89.4%, showing good prospects for industrial application.

[0045] (3) The preparation process of the present invention is simple and efficient, which is conducive to promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 is a SEM image of the composite filler in Example 1 of the present invention.

[0047] Figure 2 1 is an elemental analysis energy spectrum of the composite filler in Example 1 of the present invention.

[0048] Figure 3 These are photos of the polymer-based composite solid electrolyte membranes prepared in Example 1 and Comparative Example 3 of the present invention.

[0049] Figure 4 1-2 and Comparative Examples 1 and 3 of the present invention are graphs showing the test results of the ionic conductivity of the polymer-based composite solid electrolytes prepared.

[0050] Figure 5 Graphs showing the test results of the electrochemical windows of the polymer-based composite solid electrolytes prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention.

[0051] Figure 6 1 is a graph showing the cycle performance test results of the button batteries prepared in Example 1 and Comparative Examples 1 and 3 of the present invention. DETAILED DESCRIPTION

[0052] The present invention will be described in detail below with reference to the embodiments. It should be noted that the embodiments and features of the embodiments of the present invention can be combined with each other without conflict.

[0053] Example 1 The preparation method of the polymer-based composite solid electrolyte of this embodiment includes the following steps: (1) Add 25.35g (0.1 / 12mol) ammonium dodecotungstate and 13.2g (0.2mol) lithium acetate to 100mL water and stir for 2h to dissolve. Then add ammonia water to adjust the pH value of the solution to 7.0±0.1 and stir for 0.5h. Then add 218.45g barium titanate powder (insoluble in water) to the solution and treat it with 400W ultrasonic wave for 1h (control the temperature with ice bath <30℃). Then put it into a vacuum oven, evacuate to -0.05Mpa and let it stand for 2h, then evacuate to -0.08Mpa and let it stand for 3h, and then evacuate to -0.1Mpa and let it stand for 5h. Dry the solvent in a blast oven at 100℃, then place it in a tube furnace and calcine at 650℃ for 4h, then grind it in an agate mortar for 0.5h and sieve it with a 100-mesh sieve. Take the sieve to obtain a composite filler.

[0054] (2) In an argon atmosphere glove box, weigh 1 g of poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) with a weight average molecular weight of 400,000, 1 g of lithium bis(trifluoromethylamide)imide (LiTFSI), 2 mL of N,N-dimethylformamide (DMF), and 5 mL of acetone, then place the above substances in a serum bottle and magnetically stir at 600 rpm at 60°C until they are completely dissolved; then take 0.15 g of the composite filler obtained in step (1) and add it to the serum bottle, ultrasonically disperse it for 30 minutes, and stir it at 800 rpm at 60°C for 8 hours to obtain a polymer solution.

[0055] (3) The polymer solution was cast on a glass plate, and a film was formed by scraping with a scraper with a gap of 1000 μm. The film was then placed in a vacuum oven, and allowed to stand at room temperature for 0.5 h, and then heated to 45 ° C and baked for 2 h. The film was peeled off to obtain a polymer-based composite solid electrolyte membrane (see Figure 3 ).

[0056] The resulting polymer-based composite solid electrolyte membrane was cut into 19 mm diameter discs, and its room temperature ionic conductivity and electrochemical window were tested using an electrochemical workstation. The test results are shown in Table 1.

[0057] Button cells were assembled in the order of stacking the negative electrode sheet (lithium sheet, 0.45 mm thick and 15.4 mm in diameter), the polymer-based composite solid electrolyte membrane, and the positive electrode sheet, and the cycle performance of the battery was tested. The test results are shown in Table 1.

[0058] The preparation method of the positive electrode sheet is as follows: the positive electrode material (6 series ternary, purchased from Henan Tianli, chemical formula is LiNi 0.6 Mn 0.2 Co 0.2O2), conductive agent (SP), binder (PVDF5130), and NMP (N-methylpyrrolidone) are mixed evenly in a mass ratio of 9:0.5:0.5:10, and then coated on the aluminum current collector (aluminum foil) with a scraper with a gap of 100μm. Place it in a vacuum oven at 80℃ and dry it for 8h, then take it out and cut it into small circles with a diameter of 12mm to obtain the positive electrode sheet.

[0059] Depend on Figure 1 and Figure 2 It can be seen that the composite filler of Example 1 is in the form of nanoparticles, and elements such as titanium, barium, tungsten, and oxygen are evenly distributed. The distribution density of titanium, barium, and oxygen is relatively large, and the distribution density of tungsten is relatively small. This is related to the relatively small amount of ammonium dodecotungstate and lithium acetate added in step (1), which also shows that lithium tungstate is successfully coated on the surface of barium titanate.

[0060] Example 2 Example 1 was repeated, except that in step (2), 0.05 g of the composite filler was added.

[0061] Example 3 Example 1 was repeated, except that in step (2), 0.25 g of the composite filler was added.

[0062] Comparative Example 1 Example 1 was repeated, except that step (1) was omitted and the composite filler was replaced with an equal mass of barium titanate in step (2).

[0063] Comparative Example 2 Example 1 was repeated, except that step (1) was omitted and the composite filler was replaced with lithium tungstate of equal mass in step (2).

[0064] Comparative Example 3 Example 1 was repeated, except that step (1) was omitted and the composite filler was replaced by lithium tungstate powder and barium titanate powder in step (2), wherein the ratio of the added lithium tungstate powder and barium titanate powder was consistent with the ratio of lithium tungstate to lithium titanate in the composite filler in Example 1.

[0065] The performance test results of each embodiment and comparative example are shown in Table 1.

[0066] Table 1 Comparison of performance test results of various embodiments and comparative examples

[0067] As shown in Table 1, when barium titanate and lithium tungstate are used alone as fillers, the polymer-based composite solid electrolytes prepared have low ionic conductivity, a narrow electrochemical window, and poor cycling performance of the assembled batteries (see Comparative Examples 1 and 2). When barium titanate and lithium tungstate are simply compounded as fillers, the polymer-based solid electrolytes prepared also have low ionic conductivity, even lower than that obtained when barium titanate is used alone as a filler (see Comparative Examples 1-3). This indicates that the simply compounded barium titanate and lithium tungstate exhibit an antagonistic effect, which is not conducive to improving the ionic conductivity of the polymer-based solid electrolyte. When the composite filler of the present invention is used, the prepared polymer-based composite solid electrolyte exhibits significantly higher ionic conductivity, in which case barium titanate and lithium tungstate exhibit a synergistic effect. Furthermore, the prepared polymer-based composite solid electrolyte has a wider electrochemical window, and the assembled battery also exhibits significantly better cycling performance. The possible reason is that the simply compounded barium titanate and lithium tungstate are in a mutually dispersed state in the polymer-based composite solid electrolyte. Since the addition amount of both is not high, it is difficult for the two to exert a synergistic effect. Therefore, when barium titanate and lithium tungstate are simply compounded as fillers, the ionic conductivity, electrochemical window and cycle performance of the corresponding battery of the obtained polymer-based composite solid electrolyte are relatively poor, which are close to or even worse than the relevant indicators when barium titanate and lithium tungstate are used as fillers alone. When the composite filler of the present invention is used, the surface of the barium titanate is coated with lithium tungstate. In the polymer-based composite solid electrolyte, the barium titanate and lithium tungstate are in contact with each other, and the two can fully exert a synergistic effect, so that the polymer-based composite solid electrolyte exhibits excellent ionic conductivity and electrochemical window, and the assembled battery exhibits excellent cycle performance.

[0068] The contents illustrated in the above embodiments should be understood as these embodiments are only used to more clearly illustrate the present invention, and are not used to limit the scope of the present invention. After reading the present invention, various equivalent modifications of the present invention by those skilled in the art shall fall within the scope defined by the claims attached to this application.

Claims

1. A polymer-based composite solid electrolyte, characterized in that: The composition comprises 5-15 parts of polymer, 5-15 parts of lithium salt and 0.5-2.5 parts of composite filler by mass; the composite filler comprises barium titanate, and the surface of the barium titanate is coated with lithium tungstate.

2. The polymer-based composite solid electrolyte according to claim 1, characterized in that The polymer-based composite solid electrolyte comprises 8-12 parts of polymer, 8-12 parts of lithium salt and 0.8-2.2 parts of composite filler; and / or the polymer-based composite solid electrolyte is in a film shape with a thickness of 20-150 μm.

3. The polymer-based composite solid electrolyte according to claim 1, characterized in that In the composite filler, the mass ratio of lithium tungstate to barium titanate is 5-20:

100.

4. The polymer-based composite solid electrolyte according to any one of claims 1 to 3, characterized in that: The preparation method of the composite filler comprises the following steps: adding barium titanate powder to a mixed solution, performing ultrasonic dispersion, allowing the mixture to stand under negative pressure, drying the solvent, calcining, grinding, and sieving to obtain the composite filler; The mixed solution contains tungstate and lithium ions; in the mixed solution, the molar ratio of tungstate to lithium ions is 1:2; and the solvent of the mixed solution is water.

5. The polymer-based composite solid electrolyte according to claim 4, characterized in that A water-soluble tungsten source and a water-soluble lithium source are dissolved in water to obtain a mixed solution; wherein the water-soluble tungsten source is one or more of ammonium dodecotungstate and ammonium metatungstate; and the water-soluble lithium source is one or more of lithium acetate and lithium hydroxide.

6. The polymer-based composite solid electrolyte according to any one of claims 1 to 3, characterized in that: The polymer is one or more of polyvinylidene fluoride, poly(vinylidene fluoride-hexafluoropropylene) copolymer, and poly(vinylidene fluoride-trifluoroethylene) copolymer; the lithium salt is one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium difluorooxalatoborate, and lithium bisoxalatoborate.

7. The method for preparing a polymer-based composite solid electrolyte according to any one of claims 1 to 6, wherein: The steps include: S1. Mix the polymer, lithium salt, composite filler, and polar solvent in a ratio of 5-15 g: 5-15 g: 0.5-2.5 g: 20-100 mL to obtain a polymer solution; S2. Applying the polymer solution on a template, drying, and demoulding to obtain a polymer-based composite solid electrolyte.

8. The preparation method according to claim 7, characterized in that In S1, the polar solvent is one or more of N-methylpyrrolidone, acetone, N,N-dimethylformamide, and N,N-dimethylacetamide.

9. The preparation method according to claim 7, characterized in that In S2, the template is a glass plate.

10. A lithium solid-state battery, characterized in that: It comprises a negative electrode sheet stacked in sequence, a polymer-based composite solid electrolyte as described in any one of claims 1 to 6 or a polymer-based composite solid electrolyte prepared by the preparation method as described in any one of claims 7 to 9, and a positive electrode sheet.

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