A modified composite solid electrolyte membrane and a method for preparing the same

Abstract

The application relates to the technical field of solid-state batteries, in particular to a modified composite solid-state electrolyte film and a preparation method thereof. The modified composite solid-state electrolyte film comprises an electrolyte base material and a dopant for shaping the electrolyte base material; wherein the electrolyte base material comprises modified polyethylene oxide, the modified polyethylene oxide is polyethylene oxide connected with a functional resin, the functional resin is E12 epoxy resin, and the dopant comprises lithium salt and LCSZM.LATP high-entropy solid melt electrolyte. Through the technical scheme, the possibility of chain degradation caused by the gap between the interfaces is avoided as much as possible, the ion transmission and the stability of the mechanical structure are improved, and the solid-solid interface adhesion degree is enhanced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of solid-state batteries, and particularly relates to a modified composite solid-state electrolyte film and a preparation method thereof. BACKGROUND

[0002] With the vigorous development of new energy industry in China, the energy density of liquid lithium battery has reached the limit. The flammable nature of liquid electrolyte poses a safety hazard. Solid-state batteries have become the recognized direction of the next generation of battery development due to their higher safety and energy density.

[0003] Existing solid-state lithium metal electrolytes are mainly divided into three categories: polymer solid-state electrolyte, inorganic solid-state electrolyte and composite solid-state electrolyte. Polymer-based solid-state electrolyte has good mechanical flexibility and formability, and is often used in thin film electrolyte materials. However, the ion conductivity is relatively low, and it is usually difficult to achieve the required conductivity level of lithium metal battery at room temperature. Moreover, the chemical stability of polymer electrolyte at the lithium metal negative electrode interface is poor, and it is easy to react with lithium metal to form an unstable interface layer, resulting in increased interface impedance and decreased battery performance. Therefore, composite solid-state electrolyte has gradually become a research hotspot. Composite electrolyte introduces inorganic fillers (such as aluminum oxide, silicon dioxide, etc.), oxide solid-state electrolyte, etc. into the polymer matrix to improve the ion conductivity, and can also improve the stability of the negative electrode interface through surface modification or the addition of a transition layer. However, away from liquid substances, as the charging and discharging process proceeds, the positive and negative electrode material layers expand and contract in a rigid interface manner, resulting in the gradual appearance of gaps between the positive and negative electrode interfaces and the electrolyte layer, causing poor interface contact, increased interface resistance, internal heating of the battery cell during high-power use, energy loss, consumption of active lithium, and the formation of lithium dendrites or local accelerated degradation, ultimately leading to capacity attenuation or failure of the battery cell. SUMMARY

[0004] To solve the above problems, the present application provides a modified composite solid-state electrolyte film and a preparation method thereof. The polyethylene oxide (PEO) substrate is modified by introducing a functional epoxy compound (E12 epoxy resin), which enables the modified PEO material to adhere to the positive or negative electrode layer at multiple points under specific process conditions, allowing the electrolyte layer to be in close contact with the positive and negative electrode layers, and enabling the PEO material to exhibit its flexible electrolyte properties. The PEO layer is forced to shrink and expand with the positive and negative electrodes, reducing the likelihood of a chain reaction of degradation caused by the appearance of gaps between the interfaces. The modified PEO material is then combined with lithium salt and modified oxide solid-state electrolyte filler to form a modified polymer solid-state electrolyte film, which is bonded to the positive and negative electrode layers under specific conditions. This not only improves ion transport and mechanical structure, but also enhances the adhesion of the solid-solid interface, reducing the likelihood of gaps occurring at the interface.

[0005] In order to achieve the above technical advantages, the application uses E12 epoxy resin as a triggerable functional adhesive, a catalyst induces partial ring opening of the epoxy resin, pulse heating reaction, uses the ether bond (-O-) oxygen atom in the PEO material as a nucleophile to attack the carbon atom after the ring opening of the epoxy group, forms a new C-O bond, and crosslinks the PEO and the E12 epoxy resin. The modified PEO is mixed with fillers, lithium salts, oxide electrolytes and other materials as a substrate, and is poured into an electrolyte membrane.

[0006] In a first aspect, the application provides a modified composite solid-state electrolyte membrane, comprising:

[0007] An electrolyte substrate and a dopant shaped to the electrolyte substrate; wherein the electrolyte substrate comprises a modified polyethylene oxide, the modified polyethylene oxide is polyethylene oxide connected to a functional resin, the functional resin is E12 epoxy resin, and the dopant comprises a lithium salt and a LCSZM.LATP high-entropy solid melt electrolyte; the molecular formula of the LCSZM.LATP high-entropy solid melt electrolyte is Li a Al b Ti c ·(LiZrMoSrCo) x (PO4)3(1<a, c<1.9, 0<b, x<0.6), preferably Li 1.4 Al 0.3 Co 0.1 Zr 0.1 Ti 1.3 Mo 0.1 Sr 0.1 (PO4)3.

[0008] In a second aspect, the application also provides a preparation method of a modified composite solid-state electrolyte membrane, for preparing a modified composite solid-state electrolyte membrane, the method comprising:

[0009] Step 1, mixing polyethylene oxide and E12 epoxy resin, and then performing temperature reciprocating pulse heating to control the degree of polyethylene oxide and E12 epoxy resin connection reaction, and obtaining modified polyethylene oxide;

[0010] Step 2, adding lithium salt and LCSZM.LATP high-entropy solid melt electrolyte to the modified polyethylene oxide, stirring and evaporating to obtain a gel, extruding the gel to shape, and placing it in a vacuum oven at 50-60°C for 4-12h, and then gradually rolling to obtain a modified composite solid-state electrolyte membrane.

[0011] Optionally, the step 1, after mixing the polyethylene oxide and the E12 epoxy resin, temperature reciprocating pulse heating, comprises:

[0012] Step 11, polyethylene oxide and E12 epoxy resin are added into a reaction kettle, and the temperature in the reaction kettle is controlled between 25-40℃, solvent is added into the reaction kettle, after dissolution, hydroquinone is added, and stirring is uniform;

[0013] Step 12, after the temperature in the reaction kettle is increased to the first temperature at a temperature increasing rate of 1-3℃ / min, methylhexahydrophthalic anhydride solution is added into the reaction kettle dropwisely for a set time;

[0014] Step 13, the temperature in the reaction kettle is decreased to the second temperature;

[0015] Step 14, step 12 and step 13 are cyclically executed until the amount of the methylhexahydrophthalic anhydride solution added into the reaction kettle reaches the preset mass, the temperature of the solution in the reaction kettle is decreased to 25-40℃ and stirring is performed, and modified polyethylene oxide is obtained.

[0016] Optionally, the mass ratio of the polyethylene oxide and the E12 epoxy resin is 100:1-8:1.

[0017] Optionally, the added amount of the hydroquinone is 0.1%-0.8% of the total mass of the polyethylene oxide and the E12 epoxy resin, preferably 0.5%.

[0018] Optionally, the mass of the methylhexahydrophthalic anhydride solution is 10%-35% of the mass of the E12 epoxy resin, preferably 22.5%.

[0019] Optionally, the lithium salt is one or more of LiTFSI, LiFSI, LiDFP, LiBOB, LiDFOB and LiFTFSI.

[0020] Optionally, the mass of the lithium salt is 5%-20% of the mass of the modified polyethylene oxide.

[0021] The technical solution provided by the present application has the following advantages compared with the prior art:

[0022] The application provides a modified composite solid-state electrolyte film and a preparation method thereof, uses a pulse heating mode to control the ring opening rate of an epoxy compound, uses hydroquinone as a polymerization inhibitor to control the polymerization rate of the ether bond of PEO and the self-polymerization of the epoxy compound, ensures the polymerization degree of E12 epoxy resin and PEO, and keeps part of the epoxy groups of E12 from playing a bonding role under specific conditions in the presence of an initiator. BRIEF DESCRIPTION OF DRAWINGS

[0023] The drawings incorporated in the specification hereof and forming a part thereof illustrate embodiments consistent with the present disclosure and together with the description serve to explain the principles of the present disclosure.

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or the prior art, the drawings required to be used in the embodiments or the prior art description will be briefly introduced hereinafter, and obviously, other drawings can also be obtained by those skilled in the art without any creative labor under the premise of these drawings.

[0025] Figure 1 A flowchart of a preparation method of a modified composite solid-state electrolyte film provided by the application is shown in the figure.

[0026] Figure 2 An SEM image of a solid-state electrolyte film provided by example 1 is shown in the figure. DETAILED DESCRIPTION

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or the prior art, the drawings required to be used in the embodiments or the prior art description will be briefly introduced hereinafter, and obviously, other drawings can also be obtained by those skilled in the art without any creative labor under the premise of these drawings.

[0028] In the following description, many specific details are set forth in order to provide a thorough understanding of the present disclosure, but the present disclosure can also be implemented in other ways different from those described herein; obviously, the examples in the specification are only some of the embodiments of the present disclosure, not all the embodiments.

[0029] In order to solve the problem of poor electrical performance of the solid-state battery, the application provides a modified composite solid-state electrolyte film and a preparation method thereof. The ring-opening rate of the epoxy compound is controlled by using a pulse heating method, the ether bond polymerization rate of the epoxy compound and the self-polymerization of the epoxy compound are controlled by using hydroquinone as a polymerization inhibitor. While ensuring the ether bond polymerization degree of the E12 epoxy resin and the PEO, the partial epoxy group of the E12 can play a cohesive role under specific conditions in the presence of an initiator. Meanwhile, the high-entropy solid-solution electrolyte LCSZM.LATP is used as a filler to enhance the mechanical strength and ionic conductivity of the electrolyte film. After the solid-state electrolyte film is prepared, the initiator generated in situ under the action of a specific coating can quickly adhere in a specific temperature environment, tightly contact the contact interface or the positive electrode surface, and not produce gaps with the positive and negative electrodes due to expansion and contraction during charging and discharging. At the same time, the formation of lithium deposition and lithium dendrites can be inhibited, the growth rate of the interface contact resistance can be reduced, and the capacity decay of the battery can be delayed.

[0030] In order to better understand the application, the following provides examples and comparative examples.

[0031] Example 1: 22 g of PEO and E12 epoxy resin in a mass ratio of 10:1 were added to a double-layer glass reaction kettle, a cold-hot integrated mold temperature machine was used to control the temperature of the reaction kettle at 25°C, 150 g of acetonitrile solvent was injected, stirring and dissolving, then 0.1 g of hydroquinone was added and stirred uniformly. The temperature of the water jacket was controlled by setting the mold temperature machine, and the temperature in the reaction kettle was increased to 80°C at a rate of 1°C per minute. After reaching 80°C, the MHHPA (methylhexahydrophthalic anhydride) solution was added dropwise, 5 s later the cold water was switched to 10°C, the dropwise addition of the MHHPA solution was stopped, and the stirring was continued. After the temperature in the reaction kettle was lowered to below 60°C, the step of adding the MHHPA solution dropwise was repeated. The total amount of the MHHPA solution added was 0.5 g. After the addition of the MHHPA solution was completed, the solution was cooled to room temperature, and stirring was continued for 30 min. 22 g of Li 1.4 Al 0.3 Co 0.1 Zr 0.1 Ti 1.3 Mo 0.1 Sr 0.1 (PO4)3 material and 2 g of LiTFSI were added and stirred, and a vacuum rotary evaporator was used to evaporate the liquid to form a gel. The gel was transferred to a mold for extrusion and shaping, and was baked in a vacuum oven at 50-60°C for 4-12 h. The modified composite solid-state electrolyte film was obtained by gradually rolling to 30 μm, and the film was cut to assemble a battery. Figure 2 The morphology of the solid-state electrolyte film prepared in Example 1 is shown in FIG. 1.

[0032] The positive electrode material LiNi 0.85 Co0.05 Mn 0.1 O2 material was made into a positive electrode sheet with a mass ratio of positive electrode material: conductive agent (carbon black): binder (polyvinylidene fluoride) = 94:2:4, 2-ethyl-4-methylimidazole was sprayed, the negative electrode used a copper lithium alloy with the same surface sprayed with 2-ethyl-4-methylimidazole, the positive electrode, the modified composite solid electrolyte film, and the negative electrode were stacked and hot-pressed at 70°C for 1h, the modified composite solid electrolyte film was completely bonded with the positive and negative electrodes. The universal tensile testing machine was used to detect the interfacial peeling force, the capacity and cycle performance of the battery were tested.

[0033] Example 2: The preparation steps were the same as those of Example 1, except that Li 1.4 Al 0.3 Co 0.1 Zr 0.1 Ti 1.3 Mo 0.1 Sr 0.1 The addition amount of the (PO4)3 material was 60g.

[0034] Example 3: The preparation steps were the same as those of Example 1, except that Li 1.4 Al 0.3 Co 0.1 Zr 0.1 Ti 1.3 Mo 0.1 Sr 0.1 The addition amount of the (PO4)3 material was 2g.

[0035] The comparative example was a non-modified PEO film.

[0036] The results of the physical and chemical tests and the electrochemical tests of the comparative example, Example 1, Example 2, and Example 3 are shown in Table 1.

[0037] Table 1 Performance comparison of examples and comparative examples

[0038] Item Comparative Example Example 1 Example 2 Example 3 Puncture strength (N / um) 0.18 0.54 0.71 0.32 Room temperature conductivity (S / cm) 1.02 x 10 -5 ]]> 2.23 x 10 -4 ]]> 5.32 x 10 -4 ]]> 0.95 x 10 -4 ]] Peeling force between electrolyte membrane and positive electrode (N / mm) 0.28 — — — 0.1C initial discharge specific capacity (mAh / g) 163.5 176.5 179.6 172.3 0.1C initial efficiency (%) 76.3 84.27 86.31 81.5 100 cycle capacity retention rate (%) 61.5 92.6 94.1 90.8

[0039] It should be noted that since the stripping force of the current collector is less than the stripping force of the positive electrode and the electrolyte film, the universal tensile testing machine cannot measure the accurate stripping force of the modified composite solid electrolyte film and the positive and negative electrodes.

[0040] As shown in Table 1, the puncture strength and room temperature conductivity of Examples 1, 2, and 3 have been significantly improved compared to the comparative example. In the electrochemical performance test, the 0.1C discharge specific capacity of the modified composite solid electrolyte prepared by the present application is close to 180mAh / g, the 0.1C initial efficiency can reach more than 81%, and the 100-cycle capacity retention rate can reach more than 90%.

[0041] In summary, the application provides a modified composite solid-state electrolyte membrane and a preparation method thereof, uses E12 epoxy resin as a triggerable functional adhesive, induces partial ring opening of the epoxy resin by MHHPA, controls the pulse heating reaction, uses the ether bond (-O-) oxygen atom in the polyethylene oxide material as a nucleophile to attack the carbon atom after ring opening of the epoxy group, forms a new C-O bond, crosslinks PEO and E12 epoxy resin, uses hydroquinone as a polymerization inhibitor to control the polymerization rate of the polyethylene oxide ether bond and the self-polymerization of the epoxy compound. Mix the modified polyethylene oxide as a substrate with lithium salt and LCSZM·LATP high-entropy solid melt electrolyte, pour into an electrolyte membrane, use LCSZM·LATP high-entropy solid melt electrolyte as a filler to enhance the mechanical strength and ionic conductivity of the electrolyte membrane. The prepared modified composite solid-state electrolyte membrane can quickly adhere under the action of a specific coating or in-situ generated initiator in a specific temperature environment, tightly contact the contact interface or the positive electrode surface, and exhibit the flexible electrolyte characteristics of the polyethylene oxide material. The polyethylene oxide layer is forced to shrink and expand with the expansion and contraction of the positive and negative electrodes, no gap is generated with the expansion and contraction of the positive and negative electrodes during charging and discharging, lithium deposition and lithium dendrite formation are inhibited, the interface contact resistance growth rate is reduced, and the battery capacity decay is delayed.

[0042] The modified PEO membrane prepared by the method provided by the application can improve ionic conductivity while achieving multi-point adhesion with the positive and negative electrode layers, tightly contacting the electrode layers, fully exhibiting the flexible electrolyte characteristics of PEO, and shrinking and expanding with the expansion and contraction of the positive and negative electrodes during charging and discharging. The application of the application can inhibit the generation of gaps in the rigid interface, cause poor interface contact, lithium dendrites, and other problems, and improve the service life of the solid-state battery.

[0043] Although the application has been described above, the application is not limited to the specific embodiments described above, which are merely illustrative and not limiting. Those skilled in the art can make many modifications under the guidance of the application without departing from the spirit of the application, and these modifications are all within the protection scope of the application.

Claims

1. A modified composite solid electrolyte membrane, characterized in that, include: An electrolyte substrate and a dopant for shaping the electrolyte substrate; wherein the electrolyte substrate comprises modified polyethylene oxide, the modified polyethylene oxide being a polyethylene oxide graft-polymerized functional resin, and the functional resin being E12 epoxy resin. The preparation method of the modified polyethylene oxide includes: mixing polyethylene oxide and E12 epoxy resin, and then subjecting the mixture to pulse heating with repeated temperature changes to control the degree of grafting reaction between the polyethylene oxide and the E12 epoxy resin, thereby obtaining the modified polyethylene oxide. The process of mixing polyethylene oxide and E12 epoxy resin and then subjecting them to pulse heating with cyclic temperature reciprocation includes: Step 11: Add polyethylene oxide and E12 epoxy resin to the reactor and control the temperature inside the reactor between 25°C and 40°C. Add solvent to the reactor, dissolve the resin, then add hydroquinone and stir until homogeneous. Step 12: After raising the temperature inside the reactor to the first temperature at a heating rate of 1℃ / min-3℃ / min, add methylhexahydrophthalic anhydride solution dropwise into the reactor for a set time. Step 13: Reduce the temperature inside the reactor to the second temperature; Step 14: Repeat steps 12 and 13 until the amount of the methylhexahydrophthalic anhydride solution added to the reactor reaches the preset mass. Then, lower the temperature of the solution in the reactor to 25-40°C and stir to obtain modified polyethylene oxide. The dopant includes lithium salt and LCSZM·LATP high-entropy solid solution electrolyte; the molecular formula of the LCSZM·LATP high-entropy solid solution electrolyte is Li. a Al b Ti c ·(LiZrMoSrCo) x (PO4)3,1 <a,c<1.9,0<b,x<0.6。 2. A method for preparing a modified composite solid electrolyte membrane, characterized in that, The method for preparing the modified composite solid electrolyte membrane as described in claim 1 includes: Step 1: After mixing polyethylene oxide and E12 epoxy resin, the mixture is subjected to pulse heating with repeated temperature changes to control the degree of grafting reaction between the polyethylene oxide and the E12 epoxy resin, and to obtain modified polyethylene oxide. Step 2: Add lithium salt and LCSZM·LATP high-entropy solid solution electrolyte to the modified polyethylene oxide, stir and evaporate to dryness in an evaporator to obtain a colloid, extrude and shape the colloid, place it in a vacuum oven at 50℃-60℃ for 4h-12h and then roll it step by step to obtain a modified composite solid electrolyte membrane. Step 1, which involves mixing polyethylene oxide and E12 epoxy resin and then subjecting the mixture to pulse heating with cyclic temperature reciprocation, includes: Step 11: Add polyethylene oxide and E12 epoxy resin to the reactor and control the temperature inside the reactor between 25°C and 40°C. Add solvent to the reactor, dissolve the resin, then add hydroquinone and stir until homogeneous. Step 12: After raising the temperature inside the reactor to the first temperature at a heating rate of 1℃ / min-3℃ / min, add methylhexahydrophthalic anhydride solution dropwise into the reactor for a set time. Step 13: Reduce the temperature inside the reactor to the second temperature; Step 14: Repeat steps 12 and 13 until the amount of the methylhexahydrophthalic anhydride solution added to the reactor reaches the preset mass. Then, lower the temperature of the solution in the reactor to 25-40°C and stir to obtain modified polyethylene oxide.

3. The method for preparing the modified composite solid electrolyte membrane according to claim 2, characterized in that, The mass ratio of the polyethylene oxide to the E12 epoxy resin is 100:1-8:

1.

4. The method for preparing the modified composite solid electrolyte membrane according to claim 2, characterized in that, The amount of hydroquinone added is 0.1%-0.8% of the total mass of the polyethylene oxide and the E12 epoxy resin.

5. The method for preparing the modified composite solid electrolyte membrane according to claim 2, characterized in that, The mass of the methylhexahydrophthalic anhydride solution is 10%-35% of the mass of the E12 epoxy resin.

6. The method for preparing the modified composite solid electrolyte membrane according to claim 2, characterized in that, The lithium salt is one or more of LiTFSI, LiFSI, LiDFP, LiBOB, LiDFOB, and LiFTFSI.

7. The method for preparing the modified composite solid electrolyte membrane according to claim 2, characterized in that, The mass of the lithium salt is 5%-20% of the mass of the modified polyethylene oxide.

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