Amino acid type supramolecular gel polymer electrolyte as well as preparation method and application thereof

Abstract

The invention discloses an amino acid type supramolecular gel polymer electrolyte as well as a preparation method and application thereof, and belongs to the technical field of lithium battery electrolytes. The electrolyte is formed by in-situ polymerization of a precursor solution containing an amino acid N-carboxyl anhydride monomer, a lithium salt, an organic solvent and an organic alkali in the battery. The organic base initiates rapid ring opening polymerization of the NCA monomer, CO2 is released, and a polypeptide chain rich in amido bonds is generated; the polymer chains are crosslinked into a three-dimensional network through hydrogen bonds, ion-dipoles, pi-pi accumulation and other supramolecular actions, and the liquid electrolyte is cured into a gel state. A polymer formed by in-situ polymerization and a by-product CO2 cooperate to construct a stable interfacial film on the surfaces of the lithium negative electrode and the high-voltage positive electrode, so that dendritic crystal growth and transition metal dissolution are effectively inhibited, and the cycle stability of the battery is remarkably improved. The electrolyte prepared in the invention has the advantages of high ionic conductivity, excellent interfacial compatibility, simple and convenient in-situ forming process and the like, and has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery electrolyte technology, specifically relating to an amino acid-type supramolecular gel polymer electrolyte and its preparation method and application. Background Technology

[0002] Lithium metal batteries, due to their extremely high energy density, are considered important candidates for next-generation high-energy-density energy storage devices. However, the simultaneous use of lithium metal anodes and high-voltage cathodes (such as nickel-rich NCM811 or lithium-rich manganese-based cathodes) presents serious interfacial stability problems. Traditional liquid electrolytes are easily oxidized and decomposed at high voltages (>4.3~5.0V), and a non-uniform and unstable solid electrolyte interface (SEI) tends to form on the surface of the lithium anode, leading to low coulombic efficiency, lithium dendrite growth, and limited cycle life. Therefore, it is necessary to develop electrolytes with both high ionic conductivity and excellent interfacial stability to meet the requirements of both high-voltage cathodes and lithium metal anodes.

[0003] Gel polymer electrolytes (GPEs) have attracted widespread attention due to their improved safety and dimensional stability while maintaining the high ionic conductivity of liquid electrolytes. However, the interfacial compatibility of conventional GPEs at high voltages remains a bottleneck. For example, GPEs based on polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) can improve the cycle stability of lithium metal batteries by gelling high-concentration electrolytes, enabling stable cycling at 5V high-voltage cathodes. This strategy relies on an inert polymer scaffold to immobilize the electrolyte and utilizes a high-concentration lithium salt to form a stable interfacial film (rich in components such as LiF) to suppress side reactions. However, such inert polymers are not ion-conducting themselves and require pre-synthesis and film formation, making the preparation process relatively complex.

[0004] In recent years, in-situ polymerization methods have been proposed to directly solidify liquid precursors into gel electrolytes in batteries, thereby improving electrode / electrolyte interface contact and suppressing lithium dendrites. For example, existing technologies disclose a method for in-situ gelation initiated by the interaction of polyamides with the Lewis acid-base system of the liquid electrolyte in a battery, achieving gelation of the lithium anode surface and thus suppressing dendrite growth. Studies have found that some amino acids and their polymers can act as additives in electrolytes to improve the interface of lithium metal anodes. For example, using N-carboxylic anhydride (NCA) derivatives as electrolyte additives can release CO2 in situ in lithium-ion batteries and polymerize into peptides, thereby forming an effective SEI protective layer on the Si-based anode surface and significantly improving overall battery performance. These studies demonstrate that amino acid NCA monomers can undergo ring-opening polymerization under electrochemical conditions and achieve electrode surface protection through the synergistic effect of products and byproducts (such as CO2). However, to date, no literature reports the use of NCA monomers to prepare the bulk gel polymer electrolyte for lithium batteries. Current NCA polymerization is typically carried out in a vessel under an inert atmosphere (nitrogen or argon) for the synthesis of functional peptide materials. Traditional initiators (such as primary amines) lead to slow NCA polymerization, requiring several days to complete the reaction, and are extremely sensitive to trace amounts of water, necessitating operation in a glove box. This makes the direct application of NCA polymerization to battery systems challenging. However, recent research has revealed that strong base initiators such as lithium hexamethyldisilazane (LiHMDS) can initiate NCA ring-opening polymerization extremely rapidly at room temperature, completing the polymerization reaction within minutes to hours. The NCA polymerization mechanism initiated by LiHMDS is believed to be anionic ring-opening polymerization, offering fast polymerization rates and controllable molecular weight. Compared to traditional amine initiators, it is less sensitive to trace amounts of water and can even be carried out in open containers. This advancement makes it possible to introduce in-situ NCA polymerization into batteries.

[0005] In summary, developing a gel polymer electrolyte based on in-situ polymerization of NCA monomers is of great significance: it is expected to combine the safety and high ionic conductivity of traditional GPE, the interfacial stability of biomass polymers, and the close contact advantage of in-situ film formation, thereby meeting the compatibility requirements of high-voltage positive electrodes and lithium metal negative electrodes. Summary of the Invention

[0006] To address the aforementioned issues in the prior art, this invention discloses an amino acid-based supramolecular gel polymer electrolyte, its preparation method, and its applications. This aims to solve the technical problems in high-voltage lithium metal batteries, such as insufficient ionic conductivity, low lithium-ion transference number, and poor interfacial stability.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is to provide an amino acid-type supramolecular gel polymer electrolyte, which is formed by in-situ polymerization of a precursor solution containing an amino acid N-carboxyl ring anhydride monomer, lithium salt, organic solvent and organic base inside the battery.

[0008] The beneficial effects of this invention are as follows: the organic base, acting as an initiator, rapidly reacts with the monomer to open the cyclic anhydride, forming amino acid anions and initiating chain growth, thereby achieving the transformation of the liquid electrolyte to a gel state and forming a stable electrolyte / electrode interface. During the polymerization process, each mole of NCA monomer releases one molecule of CO2 gas. A small amount of CO2 can gradually dissolve in the electrolyte or diffuse to the negative electrode surface in the closed space of the battery and be reduced by lithium to inorganic components such as Li2CO3, thus forming a protective film rich in inorganic lithium carbonate in situ on the lithium negative electrode surface, which can construct an effective SEI and significantly improve cycle performance.

[0009] Based on the above technical solution, the present invention can be further improved as follows.

[0010] Furthermore, the anhydride monomers within the N-carboxyl ring of the amino acids are L-tryptophan-NCA (CAS: 1676-74-0), aspartic acid methyl ester-NCA (CAS: 21933-62-0), D-alanine-NCA (CAS: 4829-14-5), L-alanine-NCA, D,L-alanine-NCA, Z-alanine-NCA, Fmoc-D-alanine-NCA (CAS: 129288-35-3), Fmoc-L-alanine-NCA (CAS: 125814-20-2), ZL-alanine-NCA (CAS: 125814-23-5), and L-valine-NCA (CAS: 246). One or more of the following: L-leucine-NCA (CAS: 3190-70-3), D-lysine (TFA)-NCA (CAS: 1809273-81-1), L-phenylalanine-NCA (CAS: 14825-82-2), D-tyrosine-NCA (CAS: 183732-21-0), L-tyrosine-NCA (CAS: 3415-08-5), L-aspartic acid-4-benzyl ester-NCA (CAS: 13590-42-6), glutamic acid-5-benzyl ester-NCA (CAS: 3190-71-4), and glycine-NCA (CAS: 2185-00-4).

[0011] Furthermore, the lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium difluorooxalate borate (LiDFOB), lithium bis(trifluoroethyl)oxyborate (LiBOB), and lithium nitrate (LiNO3).

[0012] Furthermore, the organic solvent is one or more of the following: ether solvents, carbonate solvents, and amide solvents.

[0013] Furthermore, the ether solvents are tetraethylene glycol dimethyl ether (TEGDME), 1,2-dimethoxyethylene (DME), 1,2-dimethoxypropane (DMP), dimethoxymethane (DMM), 1,3-dioxolane (DOL), or diethylene glycol dimethyl ether (DEGDME); the carbonate solvents are propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), or methyl ethyl carbonate (EMC); and the amide solvents are N,N-dimethyltrifluoroacetamide (DTA), N,N-diethyltrifluoroacetamide (DRA), N-methylacetamide (NMA), or N,N-dimethylacetamide (DMA).

[0014] Furthermore, the organic base is one or more of hexamethyldisilazine lithium (LiHMDS), hexamethyldisilazine sodium (NaHMDS), triethylamine (TEA), and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU).

[0015] This invention also discloses a method for preparing an amino acid-type supramolecular gel polymer electrolyte, which includes the following steps: injecting a precursor solution containing an amino acid N-carboxyl ring anhydride monomer, lithium salt, organic solvent and organic base into a battery, and then allowing it to stand for 0.5 to 24 hours under anhydrous and oxygen-free conditions in the range of room temperature to 50°C to obtain the electrolyte.

[0016] This invention also discloses the application of amino acid-based supramolecular gel polymer electrolytes in the preparation of lithium batteries.

[0017] The beneficial effects of this invention are: 1. The amino acid-type polymer obtained after polymerization is a chain-like polymer containing a large number of amide bonds (-CO-NH-), namely a polypeptide or its derivative. This polymer chain forms abundant supramolecular interactions with itself and with residual liquid electrolyte molecules: hydrogen bonds can form between the amide groups of the main chain; polar amide groups and carbonyl groups can interact with lithium ions (Li... +The polymer and solvent molecules form ion-dipole interactions; π-π stacking occurs between aromatic side chains; and hydrogen bonds or electrostatic attraction may also form between side chains with polar groups. These non-covalent interactions act as "adhesives," linking the polymer chains and solvent-salt components into a three-dimensional network, making the electrolyte gel-like and possessing a certain mechanical strength. This invention does not require additional chemical cross-linking agents; it achieves self-support of the gel through the above physical processes, falling into the category of supramolecular gels. This gel is solid or semi-solid when at rest, but still contains a certain proportion of solvent, ensuring a high ion migration rate; at the same time, the polymer network restricts the fluidity of the solvent, improving safety and interfacial stability.

[0018] 2. The amino acid gel polymer electrolyte of the present invention has an ionic conductivity on the order of mS / cm at room temperature, reaching 1×10⁻⁶. -3 S / cm or higher. Lithium-ion transport number greater than 0.5. The high transport number is attributed to the drag effect of the polymer matrix on the anions: the polar groups on the polymer chain interact with the anions (such as TFSI). – This forms temporary bonds, reducing the migration rate of anions and thus increasing the net lithium-ion transport value. The upper limit of the electrochemical stability window, measured by linear sweep voltammetry, is approximately 4.6–4.8 V (vs. Li). + / Li). In this embodiment of the invention, tests were conducted between a stainless steel electrode and a lithium metal electrode, and a significant oxidation current was not observed until 4.7V. This indicates that the gel electrolyte of the present invention can operate stably without drastic decomposition at a high-voltage positive electrode (such as nickel-rich NCM811, charging cut-off voltage 4.3~4.5V). The good high-voltage stability is attributed to the high oxidation stability of the selected lithium salt and solvent, and also to the enhanced molecular stability due to the helical / ordered structure of the polymer backbone. In addition, the gel polymer electrolyte exhibits excellent interfacial stabilization for the lithium metal negative electrode. In long-term cycling and high-current deposition / stripping tests of symmetric batteries, there was little impedance growth and no dendrite short circuit occurred. This is due to the polymer formed by in-situ polymerization coating the lithium surface with a nitrogen- and oxygen-rich interfacial phase, which may contain inorganic lithium salts and organic polymer degradation products, together forming a stable composite SEI layer. In particular, since the polymer backbone contains nitrogen, a small amount of Li3N may be formed upon contact with lithium. This is a good ionic conductor with high mechanical strength, which can effectively suppress dendrite growth. Regarding the positive electrode, the electrolyte of this invention also exhibits good compatibility: the polymer maintains its structural integrity under high pressure, and it has a chelating effect on the dissolution of transition metals at the positive electrode, which can inhibit the migration of nickel and manganese ions after dissolution from the positive electrode and their deposition at the negative electrode. Therefore, the battery using the gel electrolyte of this invention has a stable positive electrode structure, and the deposition of precipitated metals on the negative electrode surface after cycling is significantly reduced, which contributes to a long cycle life.

[0019] 3. Excellent interfacial stability: The polymer and its byproducts (such as CO2) generated by in-situ polymerization form stable interfacial films (SEI and CEI) on the surfaces of the lithium anode and high-voltage cathode, suppressing side reactions and dendrite growth. During cycling, the impedance growth is small, the Li deposition morphology is dense, there is no dendrite short circuit, and the migration of transition metal ions in the cathode is restricted, significantly extending battery life.

[0020] 4. Good electrochemical stability window: The electrolyte remains stable at high potentials and can withstand voltages of approximately 4.7~5.0V, making it suitable for high-nickel ternary and lithium-rich manganese-based high-voltage cathode systems. At the same time, it does not cause severe side reactions to the lithium anode at low potentials.

[0021] 5. In-situ molding with excellent interfacial contact: The electrolyte, injected as a liquid precursor, gels in situ, tightly wetting and coating the electrode surface and porous membrane, reducing interfacial voids and lowering interfacial resistance. Compared to pre-prepared thin films and subsequent assembly, this method ensures complete contact between the electrode and electrolyte interfaces, reducing activation losses during initial cycles.

[0022] 6. Supramolecular network enhances mechanical properties: Hydrogen bonds and π-π interactions between polymer chains endow the gel with certain mechanical strength and elasticity, which can, to some extent, inhibit lithium dendrites from piercing the separator. Furthermore, this network possesses self-healing properties—minor local separations can self-recombine under non-covalent bonding, improving structural integrity during cycling.

[0023] 7. Simple Process: NCA monomers can be prepared by known methods or commercially available. They can be used by mixing with lithium salt solvents and initiators under dry conditions. Initiators such as LiHMDS initiate polymerization rapidly, completing the polymerization at room temperature without the need for UV or high-temperature curing or additional crosslinking agents, making the operation simple. The entire liquid injection and polymerization process can be carried out in the inert environment of standard battery assembly, making it compatible with existing battery production lines.

[0024] 8. Environmentally friendly and recyclable: The polymer backbone is derived from natural amino acids. During battery recycling, the polymer can be degraded into small-molecule amino acids or peptides through dissolution, enzymatic hydrolysis, or acid hydrolysis, achieving environmentally friendly electrolyte recovery. Compared to traditional, difficult-to-degrade synthetic polymers, it is more sustainable. Attached Figure Description

[0025] Figure 1 The figures show the charge-discharge curves of the button cell in Example 1 under constant current charging at 0.2C and constant current discharging at 0.3C at 30°C. Figure 2 The curves showing the cycle performance and coulombic efficiency of the button cell in Example 2; Figure 3 The figures show the charge-discharge curves of the button cell in Example 3 under constant current charging at 0.2C and constant current discharging at 0.3C at 0°C. Detailed Implementation

[0026] The specific embodiments of the present invention will be described in detail below with reference to examples.

[0027] Example 1 An amino acid-based supramolecular gel polymer electrolyte is prepared by the following steps: Preparation of the precursor solution: In a dry glove box, dissolve 13.8 mg LiNO3, 106.4 mg LiClO4, and 100.9 mg L-alanine-NCA in 0.5 mL of TEGDME in a glass sample vial and stir magnetically until homogeneous to obtain solution A. Dissolve 16.7 mg LiHMDS in 1 mL of TEGDME and stir magnetically until homogeneous to obtain solution B. Add 500 μL of solution B to solution A and stir slowly until homogeneous to obtain a light yellow, transparent precursor solution.

[0028] Battery assembly and polymerization: Using a 2032-type button cell casing, the NCM811 positive electrode (capacity load of 2.0 mAh / cm³) was assembled in an argon-filled glove box. -2 The battery consists of a 12mm diameter positive electrode, a PP separator (Celgard 2400), and a lithium metal anode (15mm diameter, 500µm thickness). 60µL of the precursor solution is injected into the battery casing using a pipette, ensuring complete wetting of the positive electrode and separator. After standing for 5 minutes, the battery is encapsulated. Following encapsulation, it is allowed to stand at room temperature for 12 hours for in-situ polymerization to obtain a transparent gel-like product.

[0029] Example 2 An amino acid-based supramolecular gel polymer electrolyte is prepared by the following steps: Preparation of the precursor solution: In a dry glove box, 0.25 g of L-phenylalanine-NCA monomer (white solid powder) and 0.25 g of L-tryptophan-NCA were dissolved in 4 mL of a mixed solvent of TEGDME and DTA (volume ratio 1:1) at a mass ratio of 1:1, and the solution was magnetically stirred until homogeneous to obtain solution A. LiTFSI and LiDFOB were dissolved in a mixed solvent of EC and DMC (volume ratio 1:1) at a molar ratio of 1:1, resulting in a lithium salt solution with a total lithium salt concentration of 1.0 M and containing 0.5 wt% LiNO3. 2.0 g of the lithium salt solution was added to solution A, followed by 0.3 mL of a 1.0 M LiHMDS solution (solvent: TEGDME), and the solution was slowly stirred until homogeneous to obtain a light yellow transparent precursor solution.

[0030] Battery assembly and polymerization: Using a 2032-type button cell casing, the NCM811 positive electrode (capacity load of 2.0 mAh / cm³) was assembled in an argon-filled glove box. -2The battery consists of a 12mm diameter positive electrode, a PP separator (Celgard 2400), and a lithium metal anode (15mm diameter, 500µm thickness). 60µL of the precursor solution is injected into the battery casing using a pipette, ensuring complete wetting of the positive electrode and separator. After standing for 5 minutes, the battery is encapsulated. Following encapsulation, it is allowed to stand at room temperature for 12 hours for in-situ polymerization to obtain a transparent gel-like product.

[0031] Example 3 An amino acid-based supramolecular gel polymer electrolyte is prepared by the following steps: Preparation of the precursor solution: In a dry glove box, 0.333 g of D,L-alanine-NCA and 0.167 g of glutamic acid-5-benzyl ester-NCA were dissolved in 4 mL of a mixed solvent of DME, EC, and DEC (volume ratio 2:1:1). The mixture was magnetically stirred until homogeneous to obtain solution A. LiFSI and LiTFSI were dissolved in a 1:1 molar ratio in a mixed solvent of DME, EC, and DEC (volume ratio 2:1:1). The resulting lithium salt solution had a total lithium salt concentration of 1.2 M and also contained 1 wt% LiNO3. 2.0 g of the lithium salt solution was added to solution A, followed by 0.3 mL of a 1.0 M LiHMDS solution (solvent: TEGDME). The mixture was slowly stirred until homogeneous to obtain a light yellow, transparent precursor solution.

[0032] Battery assembly and polymerization: Using a 2032-type button cell casing, the NCM811 positive electrode (capacity load of 2.0 mAh / cm³) was assembled in an argon-filled glove box. -2 The battery consists of a 12mm diameter positive electrode, a PP separator (Celgard 2400), and a lithium metal anode (15mm diameter, 500µm thickness). 60µL of the precursor solution is injected into the battery case using a pipette, ensuring complete wetting of the positive electrode and separator. After standing for 5 minutes, the battery is encapsulated. Following encapsulation, it is allowed to stand at room temperature for 8 hours for in-situ polymerization to obtain the slightly milky-white product.

[0033] Experimental Example After in-situ polymerization in Examples 1-3, the batteries were disassembled and observed, and no visible free liquid seepage was found. The NCM811||Li batteries assembled in Examples 1-3 were tested for cycle performance at 30°C within a charge / discharge voltage range of 2.8-4.3V. The charge / discharge rate and battery capacity were calculated based on the mass of NCM811. Constant current charging was performed at 0.2C (1C = 180mAh / g), and constant current discharging at 0.3C. The results are as follows. Figures 1-3 As shown. From Figure 1 As can be seen from Example 1, the battery exhibits minimal electrochemical performance degradation and excellent cycle stability after 10 cycles. Figure 2The initial discharge specific capacity was approximately 190 mAh / g, slowly increasing to approximately 200 mAh / g in the first 5 cycles, and then remaining relatively stable within 50 cycles with no significant decay. The coulombic efficiency was initially approximately 95%, stabilizing above 99% from the second cycle onwards, approaching 100%, indicating minimal charge loss per cycle. This demonstrates that the battery assembled in Example 2 exhibits excellent cycle life and high coulombic efficiency, high capacity retention after 50 cycles, and excellent reversibility. Figure 3 As can be seen from the data, the charge / discharge specific capacity of the battery assembled in Example 3 is close to 200mAh / g, and the voltage plateau is stable in the range of 3.7~4.2V without significant shift or capacity decay, demonstrating excellent long-cycle stability.

[0034] Although specific embodiments of the present invention have been described in detail with reference to examples, they should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims are still within the scope of protection of this patent.

Claims

1. An amino acid-based supramolecular gel polymer electrolyte, characterized in that: The electrolyte is formed by in-situ polymerization of a precursor solution containing an amino acid N-carboxyl ring anhydride monomer, lithium salt, organic solvent, and organic base inside the battery.

2. The amino acid-type supramolecular gel polymer electrolyte according to claim 1, characterized in that: The amino acid N-carboxyl ring anhydride monomer is one or more of the following: L-tryptophan-NCA, aspartic acid methyl ester-NCA, D-alanine-NCA, L-alanine-NCA, D,L-alanine-NCA, Z-alanine-NCA, Fmoc-D-alanine-NCA, Fmoc-L-alanine-NCA, ZL-alanine-NCA, L-valine-NCA, L-leucine-NCA, D-lysine (TFA)-NCA, L-phenylalanine-NCA, D-tyrosine-NCA, L-tyrosine-NCA, L-aspartic acid-4-benzyl ester-NCA, glutamic acid-5-benzyl ester-NCA, and glycine-NCA.

3. The amino acid-type supramolecular gel polymer electrolyte according to claim 1, characterized in that: The lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluorophosphate, lithium difluorooxalate borate, lithium bis(trifluoroethyl)oxyborate, and lithium nitrate.

4. The amino acid-type supramolecular gel polymer electrolyte according to claim 1, characterized in that: The organic solvent is one or more of ether solvents, carbonate solvents, and amide solvents.

5. The amino acid-type supramolecular gel polymer electrolyte according to claim 4, characterized in that: The ether solvent is tetraethylene glycol dimethyl ether, 1,2-dimethoxyethylene, 1,2-dimethoxypropane, dimethoxymethane, 1,3-dioxolane, or diethylene glycol dimethyl ether; the carbonate solvent is propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, or methyl ethyl carbonate; the amide solvent is N,N-dimethyltrifluoroacetamide, N,N-diethyltrifluoroacetamide, N-methylacetamide, or N,N-dimethylacetamide.

6. The amino acid-type supramolecular gel polymer electrolyte according to claim 1, characterized in that: The organic base is one or more of hexamethyldisilazine lithium, hexamethyldisilazine sodium, triethylamine and 1,8-diazabicyclo[5.4.0]undec-7-ene.

7. The method for preparing the amino acid-type supramolecular gel polymer electrolyte according to any one of claims 1 to 6, characterized in that, Includes the following steps: The precursor solution, containing amino acid N-carboxyl ring anhydride monomer, lithium salt, organic solvent and organic base, is injected into the battery and then allowed to stand for 0.5 to 24 hours under anhydrous and oxygen-free conditions within the range of room temperature to 50°C.

8. The application of the amino acid-type supramolecular gel polymer electrolyte according to any one of claims 1 to 6 in the preparation of lithium batteries.

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