Polymer composite electrolyte and preparation method and application thereof

Abstract

The invention provides a polymer composite electrolyte and a preparation method and application thereof, and belongs to the technical field of sodium metal batteries. Comprising 20-30% of a long-chain ether polymer, 20-40% of a sodium salt, 10-40% of an ether solvent and 10-50% of an inorganic filler. The ionic conductivity of the polymer composite electrolyte is 0.1-5 mS / cm, the sodium ion transference number is 0.5-0.9, and the working temperature is 0-60 DEG C. When the electrolyte is applied to the negative-electrode-free sodium metal battery, the incombustibility of the electrolyte can be realized, the safety of the battery is greatly improved, and the stable circulation of the negative-electrode-free sodium metal battery is realized.

Description

TECHNICAL FIELD

[0001] The application relates to a polymer composite electrolyte and a preparation method and application thereof, and belongs to the technical field of sodium metal batteries. BACKGROUND

[0002] Sodium metal is considered as a key negative material for further improving the energy density of sodium ion batteries due to its high theoretical specific capacity (1166 mA h g -1 ) and low reduction potential (-2.71 V vs. H2 / H + ). However, metal sodium is very active and difficult to be prepared in large quantities for use as a negative electrode in actual production process, so the development of a negative electrode-free sodium battery is an important direction for the development of sodium ion batteries. The negative electrode-free sodium battery is a rechargeable battery matched with a sodium-containing positive electrode, which only relies on a negative electrode current collector and does not use sodium metal or conventional negative electrode materials such as hard carbon materials before battery assembly.

[0003] However, the existing liquid battery system uses electrolytes such as carbonate and ether organic solvents, which have safety hazards such as easy volatilization and easy leakage. Using a solid-state electrolyte to replace the traditional organic electrolyte is an effective path for developing a solid-state negative electrode-free sodium battery and improving the safety of the battery. The polymer composite electrolyte has the advantages of both polymer electrolytes and inorganic solid-state electrolytes and is considered as one of the most commercially valuable solid-state electrolytes. Compared with inorganic solid-state electrolytes, the polymer composite electrolyte has good flexibility and processability, and the interface contact between the electrode and the electrolyte is good; compared with pure polymer solid-state electrolytes, the gel polymer solid-state electrolyte has higher room temperature ionic conductivity. However, there is no polymer composite electrolyte that can realize stable cycling of a negative electrode-free sodium metal battery. SUMMARY

[0004] Therefore, the application provides a polymer composite electrolyte which not only has non-flammable performance and good safety when applied to a battery, but also endows the corresponding negative electrode-free sodium metal battery with good cycle stability, room temperature ionic conductivity and high sodium ion transference number.

[0005] Specifically, the application is realized by the following scheme: A polymer composite electrolyte comprises the following components in the following mass ratio: a long-chain ether polymer: 20-30 %, a sodium salt: 20-40 %, an ether solvent: 10-40 %, an inorganic filler: 10-50 %.

[0006] The ionic conductivity of the polymer composite electrolyte is 0.1-1 mS / cm, the sodium ion transference number is 0.5-0.9, and the working temperature is 0-60℃.

[0007] Further, as preferred: The long-chain ether polymer is at least one of polyethylene oxide, poly-1,3-dioxolane, polytetrahydrofuran, and cellulose nanofiber.

[0008] The sodium salt is at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium tetrakis(3,5-di(trifluoromethyl)phenyl)borate, and sodium perchlorate. Preferably, sodium hexafluorophosphate or sodium tetrafluoroborate is used as the sodium salt.

[0009] The ether solvent is at least one of triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dibutyl ether, diethylene glycol diisopropyl ether, triethylene glycol diethyl ether, tetraethylene glycol diethyl ether, triethylene glycol dipropyl ether, and tetraethylene glycol dipropyl ether, etc.

[0010] The inorganic filler is at least one of nano-aluminum oxide, nano-barium titanate, nano-silicon dioxide, nano-zirconium oxide, montmorillonite, molecular sieve, carbon nitride, etc. inert fillers with high surface activity, and Na-β-Al2O3, sodium ion fast conductor, sulfide inorganic solid electrolyte, halide inorganic solid electrolyte, etc. sodium ion-conducting active inorganic fillers.

[0011] The above polymer composite electrolyte can be prepared according to the following steps: Step one, mix and disperse the inorganic filler and the dispersion solvent in proportion to obtain an inorganic filler dispersion liquid; Step two, dissolve the long-chain ether polymer in the volatile solvent to obtain solution one, dissolve the sodium salt in the ether solvent to obtain solution two; mix solution one and solution two to obtain an electrolyte precursor solution; Step three, add the inorganic filler dispersion liquid to the electrolyte precursor solution, mix uniformly, and then shape to obtain the polymer composite electrolyte.

[0012] Preferably: In step one, The dispersion mass ratio of the inorganic filler and the dispersion solvent is 1-10: 1-100.

[0013] The dispersion solvent is an easily volatile solvent such as acetone, ketone, ethanol, etc.

[0014] The dispersion includes but is not limited to stirring, ultrasonic, nodular, etc.

[0015] In step two, The concentration of the long-chain ether polymer in solution one is 1-200 g / L.

[0016] The volatile solvent is tetrahydrofuran, acetone or dichloromethane.

[0017] The concentration of the sodium salt in solution two is 0.5-2 mol / L.

[0018] The mass ratio of solution one to solution two is 0.1-10:1.

[0019] In step three, The mass ratio of the inorganic filler dispersion liquid added to the electrolyte precursor solution is 1-10:1-100.

[0020] The forming is by pouring, electrospinning or casting film forming.

[0021] The above polymer composite electrolyte can be applied to the anode-free sodium metal battery as an electrolyte, and the forming position is on the surface of the anode current collector, and then the anode-free sodium metal battery is assembled with the positive electrode.

[0022] Preferably, The active material of the positive electrode is one of polyanions (such as sodium iron phosphate pyrophosphate NFPP, sodium vanadium phosphate NVP, sodium iron sulfate NFS, etc.), layered oxides (such as sodium copper iron manganese acid, sodium nickel iron manganese acid, sodium chromate, sodium nickel manganese acid, etc.), prussian blue active material (such as iron-based prussian blue, manganese-based prussian blue, iron-manganese-based prussian blue, etc.).

[0023] The anode current collector is at least one of aluminum foil, porous aluminum foil, carbon-coated aluminum foil, copper foil, porous copper foil, carbon-coated copper foil, etc.

[0024] The assembled battery forms include but are not limited to button, laminated or wound batteries, etc.

[0025] The quasi-solid anode-free sodium metal battery provided by the application provides sodium source with a composite positive electrode, avoids the use of metal sodium, and the electrolyte is in a quasi-solid form, avoiding the introduction of volatile liquid electrolyte, which gives the quasi-solid anode-free sodium metal battery a high specific energy of 180 Wh / kg or more. While realizing high specific energy and stable cycle, the preparation process is carried out at room temperature, the composition does not contain flammable and volatile substances, and high safety production can be realized, which shows more excellent comprehensive performance in the field of anode-free sodium battery. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the application.

[0027] Figure 1 A photograph of a polymer composite electrolyte prepared in the present application; Figure 2 A combustion test of a polymer composite electrolyte prepared in the present application; Figure 3 A graph of the ion conductivity-temperature relationship of a polymer composite electrolyte prepared in the present application; Figure 4 A chronopotentiometry test graph of a polymer composite electrolyte prepared in the present application, in which the small graph is a Nyquist impedance spectrum before and after the test; Figure 5 A schematic diagram of a structure of a sodium metal battery without a negative electrode assembled with an electrolyte of the present application, Figure legend: 1. positive electrode; 2. electrolyte; 3. negative electrode current collector; Figure 6 A half-cell first cycle charge-discharge curve graph of a sodium metal battery without a negative electrode assembled with the electrolyte of Example 1; Figure 7 A full-cell cycle performance curve graph of a sodium metal battery without a negative electrode assembled with the electrolyte of Example 1; DETAILED DESCRIPTION

[0028] In order to make the technical problems to be solved, technical solutions and beneficial effects of the present application more clear and explicit, the technical solutions in the embodiments of the present application will be further described in detail below in combination with the drawings in the embodiments of the present application. It should be understood that the specific embodiments described here are only used to explain the present application and not to limit the technical solutions of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0029] Example 1

[0030] The polymer composite electrolyte of the present embodiment is composed of polyethylene oxide, sodium hexafluorophosphate, triethylene glycol dimethyl ether and nano-aluminum oxide as main raw materials, and its preparation process is as follows: First step, preparation of inorganic filler dispersion liquid The nano-aluminum oxide and ethanol are configured into a slurry in a mass ratio of 2:8, and the inorganic filler dispersion liquid is obtained by stirring; Second step, preparation of electrolyte precursor solution S1, polyethylene oxide is dissolved in tetrahydrofuran to form a solution one with a concentration of 100 g / L.

[0031] S2, sodium hexafluorophosphate is dissolved in triethylene glycol dimethyl ether to form a solution two with a concentration of 1 mol / L.

[0032] S3, mixing solution one and solution two according to a mass ratio of 2:1 to obtain an electrolyte precursor solution.

[0033] Step 3, preparing a polymer composite electrolyte The inorganic filler dispersion liquid obtained in step 1 is added to the electrolyte precursor solution obtained in step 2, and after uniform mixing, a film is obtained by casting, as shown in Figure 1 The added mass ratio of the inorganic filler dispersion liquid to the electrolyte precursor solution is 1:5.

[0034] As can be seen from Figure 1 It can be seen that: the prepared polymer composite electrolyte has the characteristics of uniform film formation, transparency, smooth surface, certain flexibility and mechanical strength, etc.

[0035] The polymer composite electrolyte obtained by the above method is subjected to a combustion test, and the results are shown in Figure 2 As can be seen from Figure 2 , the polymer composite electrolyte can be ignited when placed in the flame of an alcohol lamp (left side of Figure 2 ), but it is extinguished when removed from the flame (right side of Figure 2 ), proving that the polymer composite electrolyte provided by the present application has good flame retardancy.

[0036] The polymer composite electrolyte obtained by the above method is subjected to an ion conductivity determination experiment (by testing the impedance spectrum of a stainless steel | polymer composite electrolyte | stainless steel battery at different temperatures), and the results are shown in Figure 3 As can be seen from Figure 3 , the ion conductivity of the polymer composite electrolyte is higher than 0.1 mS / cm in the temperature range of 0-60℃, 0.94 mS / cm at room temperature, and up to 2 mS / cm at 60℃, which has good ion migration performance, so its working temperature range is 0-60℃.

[0037] The polymer composite electrolyte obtained by the above method is subjected to a cation migration number determination experiment (by testing the chronopotentiogram of a sodium metal | polymer composite electrolyte | sodium metal battery and the impedance spectrum before and after testing), and the results are shown in Figure 4 As can be seen from Figure 4 , the polymer composite electrolyte has a cation migration number of 0.64 calculated by the Bruce-Vincent formula.

[0038] The above polymer composite electrolyte is applied to a negative electrode-free sodium battery, and the negative electrode-free sodium metal battery includes a positive electrode, a polymer composite electrolyte and a negative electrode current collector, and the process is as follows: Full cell cathode: NFPP (Na4Fe3(PO4)2P2O7), acetylene black, carbon nanotube (CNT), polyvinylidene fluoride (PVDF) were mixed according to the mass ratio of 95:1:1:3 to form a slurry, the slurry was coated on the surface of carbon-coated aluminum foil (thickness d1=14 um), dried to obtain a composite cathode material, and the thickness D1 of the dried composite cathode material was 180 um.

[0039] Half cell cathode: Commercialized metal sodium sheet (thickness d2=70 um).

[0040] 3) Anode current collector: Commercialized carbon-coated aluminum foil (thickness d3=14 um), the coating layer includes graphite, graphene, hard carbon, soft carbon, carbon black, conductive carbon, carbon nanotube, carbon fiber, etc.

[0041] 4) The mixed solution of the inorganic filler dispersion liquid and the electrolyte precursor solution in the third step was cast into a film on the surface of the anode current collector to obtain an electrolyte-anode current collector composite layer (thickness D3=100 um).

[0042] 5) In a glove box, the cathode and the electrolyte-anode current collector composite layer were assembled to obtain a negative electrode-free sodium metal battery, as shown in Figure 5 .

[0043] (1) The first cycle charge-discharge experiment of the half cell of the above negative electrode-free sodium metal battery was carried out (discharged at a current density of 1.8 mA / cm 2 for 1 hour and then charged to the cut-off voltage of 0.5 V), and the results are shown in Figure 6 . The first cycle charge-discharge performance of the half cell of the negative electrode-free sodium metal battery was that the charge-discharge efficiency was 99.3%. It is proved that the electrolyte used in this embodiment has significant advantages in the deposition and stripping of sodium metal.

[0044] (2) The full cell cycle performance experiment of the above negative electrode-free sodium metal battery was carried out (cyclic voltage range 1.5-3.5 V, 0.2 C rate constant current charge-discharge for 2 cycles, and then 1 C rate constant current charge-discharge cycle test), and the results are shown in Figure 7 . Under the condition of 1 C, when the cycle was 140 times, the coulombic efficiency could still be maintained at about 100%, the discharge specific capacity was maintained at 100 mAh / g, and the capacity retention rate was 101.2%. It is proved that the battery of the present application has good cycle performance.

[0045] Comparative Example 1

[0046] This comparative example and example 1 are the same in setting, the difference is that NaPF6 / diethylene glycol dimethyl ether (G2) is used as the electrolyte and a common commercial PP separator is used as the separator to form the electrolyte.

[0047] As can be seen from Comparative Example 1 and Comparative Example 2, the scheme of the present application has significant advantages in intrinsic safety, cycle stability and cation transference number, which are specifically shown as follows: The separator was taken out after being soaked in the electrolyte for 30 s and was burned on an alcohol lamp. The result showed that the separator was directly ignited and continued to burn after being removed from the fire, proving that the separator did not have flame-retardant properties with the electrolyte.

[0048] The cation transference number determination experiment was performed on the electrolyte of Comparative Example 1 (by testing the chronopotentiogram of the sodium metal | electrolyte | sodium metal battery and the impedance spectrum before and after the test), and the Bruce-Vincent formula was used to calculate that the electrolyte of Comparative Example 1 had a cation transference number of 0.31.

[0049] The full battery without a negative electrode was assembled and subjected to charge-discharge cycle experiments. Under the condition of 1C, when the cycle was 140 times, the coulombic efficiency could be maintained at about 100%, the discharge specific capacity was maintained at 98.4 mAh / g, and the capacity retention rate was 99.5%.

[0050] Example 2

[0051] The settings of this example and Example 1 were the same, except that in S1, the polyethylene oxide was replaced by poly-1,3-dioxolane (the corresponding scheme is denoted as Example 2-1), polytetrahydrofuran (the corresponding scheme is denoted as Example 2-2), and cellulose nanofiber (the corresponding scheme is denoted as Example 2-3).

[0052] Comparative Example 2

[0053] The settings of this comparative example and Example 1 were the same, except that the polymers used were replaced by polyvinylidene fluoride (the corresponding scheme is denoted as Comparative Example 2-1) and vinylidene fluoride-hexafluoropropylene copolymer (the corresponding scheme is denoted as Comparative Example 2-2).

[0054] As can be seen from Example 1, Example 2 and Comparative Example 2, the groups contained in the polymer have a greater impact on the performance of the full battery without a negative electrode, but have no effect on the ionic conductivity, cation transference number and intrinsic safety, which are specifically shown in Table 1.

[0055] Table 1: Effect comparison of Example 1, Example 2 and Comparative Example 2 .

[0056] Example 3 The present embodiment is the same as the setting of example 1, the difference is that in S2, triethylene glycol dimethyl ether is replaced by tetraethylene glycol dimethyl ether (the corresponding scheme is recorded as example 3-1), diethylene glycol dibutyl ether (the corresponding scheme is recorded as example 3-2), diethylene glycol diisopropyl ether, triethylene glycol diethyl ether (the corresponding scheme is recorded as example 3-3), tetraethylene glycol diethyl ether, triethylene glycol dipropyl ether, tetraethylene glycol dipropyl ether.

[0057] Comparative example 3

[0058] The present comparative example is the same as the setting of example 1, the difference is that the solvent used is ethylene carbonate (the corresponding scheme is recorded as comparative example 3-1), propylene carbonate, fluorinated ethylene carbonate (the corresponding scheme is recorded as comparative example 3-2), and other commonly used carbonate solvents or ethylene glycol dimethyl ether (the corresponding scheme is recorded as comparative example 3-3), diethylene glycol dimethyl ether and other low-boiling ether solvents.

[0059] It can be seen from example 1, example 3 and comparative example 3 that the type of solvent in the polymer composite electrolyte has a greater influence on the ionic conductivity, the performance of the anode-free sodium metal half-cell and the full cell, but has no effect on the cation transference number and the intrinsic safety, which is shown in Table 2.

[0060] Table 2: Effect comparison of example 1, example 3 and comparative example 3 .

[0061] Example 4

[0062] The present embodiment is the same as the setting of example 1, the difference is that in the polymer composite electrolyte, nano-aluminum oxide is replaced by nano-silicon dioxide, molecular sieve, carbon nitride, NASICON electrolyte, etc. After replacing the inorganic filler, the performance of the composite electrolyte is within the measurement error range, and the inorganic fillers of the present application can all realize the formation of the composite electrolyte with relatively no effect. After replacing different inorganic fillers, the polymer composite electrolyte can still achieve high ionic conductivity, high cation transference number, intrinsic safety, and excellent performance of the anode-free sodium metal half-cell and full cell.

[0063] The above-described embodiments only express several possible implementation manners of the present application, which are described in detail, but should not be understood as limiting the scope of the present patent. The embodiments are not used to limit the protection scope in the claims of the present application. For those skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, and any equivalent implementation or change made without departing from the present application should be included in the present application.

Claims

1. A polymer composite electrolyte, characterized by, The components include the following mass ratios: a long-chain ether polymer: 20-30 %, a sodium salt: 20-40 %, an ether solvent: 10-40 %, an inorganic filler: 10-50 %, The polymer composite electrolyte has an ionic conductivity of 0.1-1 mS / cm, a sodium ion transference number of 0.5-0.9, and a working temperature of 0-60 ℃.

2. The polymer composite electrolyte according to claim 1, wherein: The long-chain ether polymer is at least one of polyethylene oxide, poly-1,3-dioxolane, polytetrahydrofuran, and cellulose nanofiber.

3. The polymer composite electrolyte according to claim 1, wherein: The sodium salt is at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium tetrakis(3,5-di(trifluoromethyl)phenyl)borate, and sodium perchlorate.

4. The polymer composite electrolyte according to claim 1, wherein: The ether solvent is at least one of triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dibutyl ether, diethylene glycol diisopropyl ether, triethylene glycol diethyl ether, tetraethylene glycol diethyl ether, triethylene glycol dipropyl ether, and tetraethylene glycol dipropyl ether.

5. The polymer composite electrolyte according to claim 1, wherein: The inorganic filler is at least one of nano-aluminum oxide, nano-barium titanate, nano-silicon dioxide, nano-zirconium oxide, montmorillonite, molecular sieve, carbon nitride, Na-β-Al2O3, sodium ion fast conductor, sulfide inorganic solid-state electrolyte, and halide inorganic solid-state electrolyte.

6. A method of preparing the polymer composite electrolyte of claim 1, characterized by, The steps are as follows: Step one: mixing and dispersing the inorganic filler and the dispersing solvent in a proportion to obtain an inorganic filler dispersion liquid; Step two: dissolving the long-chain ether polymer in a volatile solvent to obtain solution one, and dissolving the sodium salt in an ether solvent to obtain solution two; mixing solution one and solution two to obtain an electrolyte precursor solution; Step three: adding the inorganic filler dispersion liquid to the electrolyte precursor solution, uniformly mixing, and then forming to obtain a polymer composite electrolyte.

7. The method of claim 6, wherein: In step one, the dispersion mass ratio of the inorganic filler and the dispersing solvent is 1-10: 1-100.

8. The method of claim 6, wherein: In step two, the concentration of solution one is 1-200 g / L, the concentration of solution two is 0.5-2 mol / L, and the mixing mass ratio of solution one and solution two is 0.1-10:

1.

9. The method of claim 6, wherein: In step three, the forming is performed by pouring, electrospinning, or casting film forming.

10. Use of the polymer composite electrolyte of claim 1 in a negative electrode-free sodium metal battery.

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