In-situ phase separation copolymer solid electrolyte and preparation method thereof

Abstract

The application discloses an in-situ phase separation copolymer solid electrolyte and a preparation method thereof. An alkenyl monomer capable of forming strong hydrogen bonding is used as a hard segment monomer, and acrylamide is used as a representative, and the PAAm segment formed after copolymerization can form strong hydrogen bonding and provide mechanical support as a hard phase; an alkenyl monomer containing ether in the side chain is used as a soft segment monomer, and methoxy poly(ethylene glycol) acrylate is used as a representative, and the PMPEGA segment formed after copolymerization has long side chain ether, can enrich solvent and lithium salt, and can quickly conduct lithium ions as an ion conducting phase. The two kinds of monomers and lithium salt can be dissolved in different solvent systems, and the copolymer electrolyte can be generated by in-situ thermal initiation polymerization in the battery or by photo initiation polymerization on the electrode surface. The in-situ phase separation copolymer solid electrolyte prepared by the application simultaneously realizes high ion conductivity and high mechanical strength, the preparation method is simple and easy to implement, and is suitable for the current commercial liquid battery production process of 'assembling first and then injecting liquid'.

Description

Technical Field

[0001] This invention belongs to the field of solid electrolytes, specifically, it relates to an in-situ phase separation copolymer solid electrolyte and its preparation method. Background Technology

[0002] Solid-state lithium metal batteries, using lithium metal with ultra-high specific capacity (3860 mAh / g) as the negative electrode and matched with an ultra-thin, high-performance solid electrolyte, can achieve a target of 500 Wh / kg. Solid-state electrolytes replace easily leaking, flammable, and explosive liquid electrolytes, potentially leading to breakthroughs in both battery safety and energy density.

[0003] The key issues restricting the development of high-energy solid-state lithium batteries are: (1) High ionic conductivity and high mechanical strength of electrolytes cannot be achieved simultaneously: Inorganic solid electrolytes have high ionic conductivity, but are hard and brittle; The complexation-decomplexation ion conduction mechanism of polymer electrolytes requires the polymer ion conduction region to be in a high elastic state, which limits the simultaneous improvement of ionic conductivity and strength, and limits the energy density and safety performance of solid-state batteries; (2) High cost of electrolyte preparation process: Inorganic solid electrolytes require high temperature synthesis and GPa-level high pressure compaction; Most polymer electrolytes are prepared by solvent evaporation of "polymer-lithium salt solution", which needs to be carried out under oxygen- and moisture-proof conditions, which is time-consuming, energy-consuming, and pollutes the environment. The mechanical strength is also difficult to meet the requirements of large-scale roll-to-roll preparation, and is not suitable for existing lithium battery production lines.

[0004] Solid-state electrolytes can be classified into inorganic solid-state electrolytes, solid polymer electrolytes, and organic-inorganic composite electrolytes. Inorganic solid-state electrolytes mainly fall into two categories: oxide electrolytes and sulfide electrolytes. Their advantage lies in their high ionic conductivity, comparable to that of liquid electrolytes. However, these inorganic solid-state electrolytes generally suffer from the following disadvantages: ① Poor chemical stability: sensitive to water and oxygen, and unstable with metallic lithium; ② Significant electrode interface problems: inorganic solid-state electrolytes are hard and brittle, resulting in poor contact between the positive and negative electrodes, easily leading to cracks and pores at the interface, hindering lithium-ion transport and inducing lithium dendrite growth; ③ High cost and difficult manufacturing: inorganic electrolytes are expensive; they lack flexibility and require GPa-level pressure to ensure the battery's internal compactness. Organic-inorganic composite electrolytes, on the other hand, have significant differences in the properties of the two phases, presenting new interface problems. Particle agglomeration often occurs, leading to low ionic conductivity and poor yield. The lithium anode / electrolyte interface still suffers from differences in hard and soft contact and uneven ion conduction, causing lithium dendrite growth. In comparison, polymer electrolytes have advantages in all three aspects: ① Chemical stability is better than inorganic solid electrolytes: relatively inert and insensitive to water and oxygen; ② High electrode interface compatibility: polymer electrolytes have viscoelasticity and can form an adaptive electrode / electrolyte interface; ③ Low manufacturing cost, with the potential to achieve roll-to-roll mass production: polymer electrolytes are lightweight, and the monomer raw materials are usually cheap and widely available; they have good mechanical flexibility and are easy to form films, and roll-to-roll preparation is suitable for the current commercial battery production process of "assembly first, then electrolyte injection".

[0005] Chinese invention patent application number 2022106485496, entitled "A Polyurethane-Based Polymer Solid Electrolyte Material and Its Preparation Method and Application," utilizes hard and soft segments to create a polyurethane-based polymer solid electrolyte material through hydrogen bonding. However, the polyurethane diblock or triblock copolymer electrolyte in this patent involves at least several steps, including a reaction with solvents to obtain such a copolymer, followed by melting or solvent blending with lithium salts to obtain the polymer electrolyte, and then a third step of non-in-situ assembly with a battery to form a solid-state battery. The entire process is extremely time-consuming and labor-intensive, and diisocyanates are very expensive, requiring a series of cumbersome steps such as solvent treatment. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing in-situ phase separation copolymer solid electrolytes in a one-pot, one-step process. This invention can generate solid batteries through in-situ polymerization inside the battery, avoiding battery short circuits, and is low in cost and simple in procedure. At the same time, it solves the contradiction between high ionic conductivity and high mechanical strength.

[0007] The above-mentioned objective of the present invention is achieved by the following technical methods:

[0008] To achieve in-situ preparation of polymer electrolytes with high ionic conductivity and high mechanical strength separation, this invention employs an in-situ one-pot one-step method. It utilizes the differences in reaction rates and compatibility between soft and hard segment monomers under different salt / solvent systems to design and prepare phase-separated polymer electrolytes through thermally initiated polymerization and photoinitiated polymerization.

[0009] The in-situ phase-separated copolymer solid electrolyte of the present invention uses an alkenyl monomer capable of forming strong hydrogen bonds as the hard segment monomer, preferably acrylamide (AAm). After copolymerization, the PAAm segments formed by AAM can form strong hydrogen bonds, displacing the solvent and lithium salt, and providing mechanical support as the hard phase. An alkenyl monomer with ether-containing side chains is used as the soft segment monomer, preferably methoxy poly(ethylene glycol) acrylate (MPEGA). After copolymerization, the PMPEGA segments formed by PMPEGA have long side-chain ethers, and the large steric hindrance reduces the regularity of the chain segments, resulting in a high proportion of free volume and thus lowering the glass transition temperature. T g This compound can enrich solvent and lithium salt, serving as an ion-conducting phase for rapid lithium ion transport. Both monomers and the lithium salt are soluble in different solvent systems, allowing for one-pot, one-step in-situ thermally initiated polymerization inside the battery or photoinitiated polymerization on the electrode surface to generate P(AAM-). co -MPEGA) copolymer electrolyte. The composition and naming of this copolymer electrolyte are as follows: P(AAM) 0.8 - co -MPEGA 0.2 )+ 70 wt% 1M LiTFSI / FEC, abbreviated as AM-87@FEC, where A and M are the first letters of the two monomers, 8 represents that the hard segment AAm accounts for 80 wt% in the polymer, and 7 represents that 1 MLiTFSI / FEC accounts for 70 wt% in the entire polymer electrolyte.

[0010] An in-situ phase separation copolymer solid electrolyte is formed by dissolving two types of monomers and a lithium salt in a solvent system and polymerizing them by thermal or photoinitiation in the presence of a crosslinking agent. The monomers are alkenyl monomers that can form strong hydrogen bonds as hard segment monomers and alkenyl monomers with ether-containing side groups as soft segment monomers.

[0011] Preferably, in the above-mentioned in-situ phase-separated copolymer solid electrolyte, the hard segment monomer is as shown in formula (I):

[0012]

[0013] Preferably, in the above-mentioned in-situ phase-separated copolymer solid electrolyte, the soft segment monomer is as shown in formula (II), where x is the number of chains, taking a value of 1-50:

[0014]

[0015] Preferably, in the above-mentioned in-situ phase-separated copolymer solid electrolyte, the solvent is a nitrile solvent, an ether solvent, a carbonate solvent, or a phosphate solvent.

[0016] Preferably, in the above-mentioned in-situ phase-separated copolymer solid electrolyte, the lithium salt is as shown in formula (Ⅲ):

[0017]

[0018] Preferably, in the above-mentioned in-situ phase-separated copolymer solid electrolyte, the copolymer formed by the hard segment and the soft segment accounts for 25-90% of the mass percentage of the in-situ phase-separated copolymer solid electrolyte.

[0019] Preferably, in the above-mentioned in-situ phase-separated copolymer solid electrolyte, the proportion of the hard segment monomer to the total mass of the soft segment and hard segment monomer is 5-100%.

[0020] Preferably, in the above-mentioned in-situ phase separation copolymer solid electrolyte, the crosslinking agent contains two or more carbon-carbon double bonds and can react to form a crosslinking network, such as containing dienyl, trienyl or tetraenyl monomers.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The in-situ phase-separated copolymer solid electrolyte prepared by this invention simultaneously achieves high ionic conductivity and high mechanical strength. The AM-87@FEC electrolyte exhibits an ionic conductivity as high as 1.6 mS / cm at 28℃, a tensile strength of 5.07 MPa, a compressive strength of 10.86 MPa, and an elastic modulus of 22.79 MPa; the AM-67@SN electrolyte exhibits an ionic conductivity as high as 1.5 mS / cm at 28℃, a tensile strength of 3.96 MPa, a compressive strength of 7.10 MPa, and an elastic modulus of 76.4 MPa; the AM-87@SN electrolyte also achieves an ionic conductivity of 0.61 mS / cm at 28℃, a tensile strength of 5.04 MPa, and an elastic modulus of 124 MPa. Among these, the high-modulus polymer electrolyte plays a crucial role in suppressing lithium dendrite growth and also reduces the risk of short circuits, ensuring battery safety.

[0023] 2. The preparation method of the present invention is simple and easy to implement. The copolymer electrolyte can be obtained by in-situ polymerization inside the battery through a one-pot one-step method, which is suitable for the current commercial liquid battery production process of "assembly first, then liquid injection". Attached Figure Description

[0024] Figure 1The flowcharts are for the preparation of Examples 2, 3 and 4.

[0025] Figure 2 The impedance diagram is the one measured for the AM-xy@SN copolymer solid electrolyte in Example 5.

[0026] Figure 3 This is a graph showing the ionic conductivity of the AM-xy@SN copolymer solid electrolyte obtained in Example 5.

[0027] Figure 4 This is a graph showing the ionic conductivity of the AM-xy@LDN copolymer solid electrolyte obtained in Example 5.

[0028] Figure 5 This is a graph showing the ionic conductivity of the AM-xy@FEC copolymer solid electrolyte obtained in Example 5.

[0029] Figure 6 The tensile strength diagram of AM-xy@SN measured in Example 6 is shown.

[0030] Figure 7 The tensile strength diagram of AM-xy@FEC measured in Example 6 is shown.

[0031] Figure 8 The tensile strength-ionic conductivity relationship of AM-xy@SN obtained in Examples 5 and 6 is shown in the figure.

[0032] Figure 9 The tensile strength-ionic conductivity relationship of AM-xy@FEC obtained in Examples 5 and 6 is shown in the figure.

[0033] Figure 10 The AM-xy@FEC spline diagram used in Example 6 for measuring tensile strength is shown.

[0034] Figure 11 This is a diagram of the AM-xy@FEC sample used to measure compressive strength in Example 7.

[0035] Figure 12 The graph shows a comparison of the tensile strength, compressive strength, elastic modulus, and ionic conductivity of AM-xy@FEC obtained in Examples 5, 6, and 7.

[0036] Figure 13 This is a comparison chart of the tensile strength, elastic modulus, and ionic conductivity of AM-xy@SN obtained in Examples 5 and 6. Detailed Implementation

[0037] The following lists some of the in-situ phase separation copolymer solid electrolytes involved in this invention, as well as the performance test results, and provides a more detailed description of this invention, but it is not limited to the compounds listed.

[0038] Example 1 illustrates the preparation of electrolytes in different solvent systems.

[0039] Example 1: Succinate electrolyte (IL) was used as a representative of nitrile electrolytes; ethylene glycol dimethyl ether electrolyte (LDN) was used as a representative of ether electrolytes; and fluoroethylene carbonate electrolyte (1M LiTFSI FEC) was used as a representative of carbonate electrolytes. The formulations are shown in Table 1.

[0040]

[0041] The following operations were all performed in an argon atmosphere glove box. Lithium salt and solvent were added in proportion to a 20mL brown glass bottle with a stir bar, and stirred in the dark until completely dissolved to obtain an electrolyte.

[0042] Examples 2-4 illustrate the preparation of copolymer solid electrolytes.

[0043] Example 2: Preparation of copolymer solid electrolyte based on nitrile electrolyte, taking the copolymer solid electrolyte of succinic acid electrolyte (AM-xy@SN) as an example: acrylamide (AAm) is used as hard segment monomer, methoxy poly(ethylene glycol) acrylate (MPEGA) is used as soft segment monomer, and the formulation is shown in Table 2.

[0044]

[0045] Note: 651-CL-IL is a diluent. Since the crosslinking agent and initiator used in the experiment are present in small amounts, it is difficult to obtain the appropriate amount directly. By using the dilution sampling method, the crosslinking agent and initiator are diluted into the electrolyte, so that the appropriate amount can be obtained more accurately. The operation of taking 651-CL-LDN and 651-CL-FEC in the following text is the same as above.

[0046] The following operations are all performed in a glove box. IL, MPEGA and AAM are added to a 20mL brown glass bottle with a stir bar in the proportions in the table above. The mixture is stirred in the dark until it is completely dissolved. Diluent is added before sample preparation or battery assembly. After it is dropped into the mold or onto the lithium sheet when assembling the battery, photopolymerization is initiated under 365nm ultraviolet light to obtain copolymer solid electrolyte (AM-xy@SN).

[0047] Example 3: Preparation of copolymer solid electrolyte based on ether electrolyte (AM-xy@DME): The formulation is shown in Table 3.

[0048]

[0049] Except for the changes in electrolyte and diluent, the dosage and operating procedures of all other reagents are the same as in Example 2.

[0050] Example 4: Preparation of carbonate-based copolymer solid electrolyte (AM-xy@FEC): The formulation is shown in Table 4.

[0051]

[0052] The following operations were all performed in a glove box. 1M LiTFSI FEC, MPEGA, and AAM were added to a 20mL brown glass bottle with a stir bar according to the proportions in the table above. The mixture was heated at 80°C, and the bottle was continuously removed to dissolve the solids on the bottle wall into the solvent until all AAM was dissolved. Before preparing the sample or assembling the battery, a diluent was added. After the solution was dropped into the mold or onto the lithium sheet when assembling the battery, photopolymerization was initiated under 365nm ultraviolet light to obtain the copolymer solid electrolyte (AM-xy@FEC).

[0053] Example 5 shows the ionic conductivity test of in-situ phase-separated copolymer solid electrolytes in different solvent systems at different temperatures (ring mold).

[0054] Example 5: Ionic conductivity test based on AM-67@SN as an all-solid copolymer electrolyte (EIS AM-67@SN). The following test method can avoid the problem of high ionic conductivity caused by the electrolyte being compressed.

[0055] The following operations are performed in three steps. Step 1: Prepare a PET film with a thickness of approximately 100 μm using a PET film containing single-sided hot melt adhesive. l Limiters () ɸ A 19*3.5mm ring was used to place the membrane into a 2025-type positive electrode shell, which was then placed in a 100℃ oven to ensure the mold adhered firmly to the positive electrode shell. The second step (in a glove box): an electrolyte solution was dropped into the ring, and polymerization was carried out under ultraviolet light to obtain a copolymer solid electrolyte (AM-67@SN). After the light irradiation, the smoother side of a 1.5mm steel sheet was placed over the electrolyte, followed by a spring sheet, and finally the negative electrode shell. The third step: the membrane was removed from room temperature (28℃). o C) to high temperature (80) o C) Test its impedance ( R And calculate its ionic conductivity (σ) according to the formula.

[0056] The contact area (S) between the copolymer solid electrolyte (AM-67@SN) and the steel sheet is 1.13 cm². 2 .

[0057] The formula for calculating the ionic conductivity is as follows: .

[0058] As attached Figure 2 The impedance diagrams of the AM-67@SN copolymer solid electrolyte were measured at different temperatures. The ionic conductivity was calculated and the results are shown in Table 5. It can be found that the ionic conductivity of AM-67@SN reaches 1.5 mS / cm at room temperature of 28℃.

[0059]

[0060] Appendix Figure 3 Appendix Figure 4 and attached Figure 5 The graphs show the changes in ionic conductivity as a function of temperature under different solvents. It can be observed that, except for the pure soft segment case where ionic conductivity is relatively high, the in-situ phase-separated copolymer solid electrolytes prepared from AM-87@FEC, AM-66@SN, AM-67@SN, AM-87@SN, AM-69@LDN, AM-79@LDN, AM-88@LDN, and AM-89@LDN exhibit high ionic conductivity.

[0061] Example 6 shows the tensile strength test of solid electrolyte samples of in-situ phase-separated copolymers in different solvent systems.

[0062] Example 6: Tensile strength test of solid electrolyte specimens based on AM-67@SN in-situ phase-separated copolymer.

[0063] The following operation is performed in two steps, both in an argon-atmospheric glove box. Step 1: Drop as little electrolyte solution as possible into the mold (to simulate the thickness of the electrolyte solution in the battery. If the sample is too thick, it may have defects, affecting the experimental results). Photopolymerize using UV-light to obtain a copolymer solid electrolyte sample (AM-67@SN). After the photopolymerization is complete, place it in a sealed bag for storage. Step 2: Perform tensile strength testing.

[0064] As attached Figure 6 and attached Figure 7 It can be found that the samples prepared by AM-87@FEC, AM-67@SN, and AM-87@SN have stronger mechanical strength compared to other ratios, while AM-xy@LDN is too brittle to be prepared into samples for testing.

[0065] Example 7 is a test of the compressive strength of in-situ phase-separated copolymer solid electrolyte samples in different solvent systems.

[0066] Example 7: Compressive strength test of solid electrolyte sample based on AM-87@FEC in situ phase separation copolymer.

[0067] The following operations are performed in three steps. Step 1: Prepare several syringes and cut off a portion of the needle plug near the needle shaft to create a mold. Step 2 (performed in a glove box): Add approximately 3 mL (10 mm high) of electrolyte solution to the syringe and perform photopolymerization using UV light to obtain a copolymer solid electrolyte sample (AM-87@FEC). After photopolymerization, place it in a sealed bag for storage. Step 3: Perform compressive strength tests from 0% to 50% compressive strain.

[0068] As attached Figure 10 and attached Figure 11 In this study, phase separation can be examined by observing the transparency of samples with different proportions. It was found that as the content of hard segment AAM increases, the polymer electrolyte formed becomes less transparent, and the transition from micro-phase separation to macro-phase separation becomes more obvious.

[0069] As attached Figure 12 and attached Figure 13 It can be found that the in-situ phase-separated copolymer solid electrolytes prepared by AM-87@FEC, AM-67@SN, and AM-87@SN simultaneously achieve high ionic conductivity and high mechanical strength.

Claims

1. An in-situ phase-separated copolymer solid electrolyte, characterized in that: This solid electrolyte uses an alkenyl monomer capable of forming strong hydrogen bonds as the hard segment monomer and an alkenyl monomer with ether-containing side groups as the soft segment monomer. These two monomers and a lithium salt are dissolved in a solvent system and polymerized by thermal or photoinitiation in the presence of a crosslinking agent. The hard segment monomer is shown in formula (I), and the soft segment monomer is shown in formula (II), where x is the number of chains, ranging from 1 to 50. The solvent is a nitrile solvent, an ether solvent, a carbonate solvent, or a phosphate solvent. 。 2. The in-situ phase-separated copolymer solid electrolyte according to claim 1, characterized in that, The lithium salt is shown in formula (Ⅲ): 。 3. The in-situ phase-separated copolymer solid electrolyte according to claim 1, characterized in that, The copolymer formed by the hard segment and the soft segment accounts for 25-90% of the mass percentage of the in-situ phase-separated copolymer solid electrolyte.

4. The in-situ phase-separated copolymer solid electrolyte according to claim 1, characterized in that, The hard segment monomer accounts for 5-100% of the total mass of the soft segment and hard segment monomer.

5. The in-situ phase-separated copolymer solid electrolyte according to claim 1, characterized in that, The crosslinking agent contains two or more carbon-carbon double bonds.

Images