Solid-liquid mixed electrolyte based on bifunctional quaternary ammonium salt modification and preparation method thereof

Abstract

The invention relates to a solid-liquid mixed electrolyte based on bifunctional quaternary ammonium salt modification and a preparation method of the solid-liquid mixed electrolyte, and belongs to the technical field of lithium ion batteries. Wherein the bifunctional quaternary ammonium salt monomer is hexadecyl dimethyl allyl ammonium chloride. According to the structure, stable embedding of quaternary ammonium cations in a polymer main chain is realized, the dissociation capacity of lithium salt and the transference number of lithium ions are remarkably improved, and meanwhile, anion migration and interface side reaction are inhibited. The electrolyte has excellent rate capability and cycling stability, and is suitable for a high-voltage lithium ion battery system.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a solid-liquid mixed electrolyte modified based on a bifunctional quaternary ammonium salt and a preparation method thereof, which is suitable for high-voltage and high-rate lithium-ion battery systems. Background Art

[0002] Traditional liquid electrolytes pose safety risks due to flammability and leakage, while solid electrolytes, while safe, suffer from large interfacial impedance and low ionic conductivity. In recent years, solid-liquid hybrid electrolytes, combining the advantages of both, have become a research hotspot. However, existing in-situ polymerization precursors (such as ether or carbonate monomers) have problems such as low lithium ion transference numbers (<0.4) and numerous interfacial side reactions, making it difficult to meet the requirements of high voltage (>4.3V) and long cycle times.

[0003] Research has shown that quaternary ammonium monomers can promote the dissociation of lithium salts through "ion-dipole" interactions, but their dispersion stability in polymer matrices is poor and they are prone to phase separation. Therefore, a new electrolyte design is urgently needed to achieve stable embedding of functional components at the molecular level while optimizing lithium ion transport kinetics. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the present invention provides a solid-liquid mixed electrolyte with high ion migration number and high interface stability, which solves the problems of anion migration and phase separation through the copolymerization design of bifunctional quaternary ammonium salt and acrylate monomer.

[0005] In order to solve the above technical problems, the technical solution proposed in this application is:

[0006] The invention provides a solid-liquid hybrid electrolyte modified by a bifunctional quaternary ammonium salt, comprising a polymer matrix formed by in-situ polymerization of a bifunctional quaternary ammonium salt monomer and methyl methacrylate (MMA), wherein the bifunctional quaternary ammonium salt monomer is hexadecyldimethylallylammonium chloride (C16DMAAC).

[0007] Furthermore, the molar ratio of C16DMAAC to MMA is 1:10 to 1:2.

[0008] Furthermore, the polymer matrix further comprises a lithium salt, wherein the lithium salt is at least one of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and lithium hexafluorophosphate (LiPF6), and the concentration thereof is 0.5-2.0 mol / L.

[0009] Furthermore, at 25° C., the lithium ion transference number in the electrolyte is ≥0.6, and the ionic conductivity is ≥1×10-3S / cm.

[0010] Furthermore, the interface impedance between the electrolyte and the lithium metal negative electrode at a voltage of 4.5V is ≤50Ω·cm 2 .

[0011] On the other hand, the present application also claims a method for preparing the electrolyte as described in any of the foregoing items, comprising the following steps:

[0012] (a) Dissolving C16DMAAC and MMA monomers in a polar solvent to form a homogeneous precursor solution;

[0013] (b) adding a free radical initiator and a lithium salt to the solution of step (a) and mixing them uniformly;

[0014] (c) The mixed solution is injected into the battery casing and heated to induce an in-situ polymerization reaction to form a gel electrolyte.

[0015] Furthermore, the free radical initiator is azobisisobutyronitrile (AIBN) or benzoyl peroxide (BPO), and the added amount is 0.5%-3% of the total weight of the monomers.

[0016] Furthermore, the polar solvent is at least one of propylene carbonate (PC) and γ-butyrolactone (GBL).

[0017] On the other hand, the present application also claims protection for a lithium-ion battery comprising a positive electrode, a negative electrode, a separator and the electrolyte described in any one of the above items.

[0018] Furthermore, the positive electrode active material is a high voltage ternary material LiNi 0.5 Mn 1.5 At least one of O4 and lithium cobalt oxide (LiCoO2), with an operating voltage ≥ 4.3V.

[0019] Compared with the prior art, the present invention has achieved the following beneficial technical effects:

[0020] This invention forms a coacervate polymer electrolyte by copolymerizing a bifunctional quaternary ammonium salt (C16DMAAC) with methyl methacrylate (MMA). This significantly improves the lithium ion transference number and ionic conductivity, inhibits anion migration and interfacial side reactions, and is suitable for high-voltage positive electrodes (≥4.5V). An in-situ thermal polymerization method enhances the stability of the electrolyte-electrode interface, achieving a capacity decay of <10% after 1000 cycles and reducing the risk of lithium dendrites. The quaternary ammonium salt is chemically embedded in the main chain to prevent phase separation, with a thermal decomposition temperature >250°C, improving safety. DETAILED DESCRIPTION

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0022] The present invention provides a solid-liquid hybrid electrolyte modified by a bifunctional quaternary ammonium salt, comprising a polymer matrix formed by in-situ polymerization of a bifunctional quaternary ammonium salt monomer and methyl methacrylate (MMA), wherein the bifunctional quaternary ammonium salt monomer is hexadecyldimethylallylammonium chloride (C16DMAAC). Preferably, the molar ratio of C16DMAAC to MMA is 1:10 to 1:2. The present application uses C16DMAAC and MMA as comonomers to form a polymer matrix by free radical polymerization. The quaternary ammonium cations of C16DMAAC provide lithium salt dissociation sites, and the long alkyl chains inhibit anion migration; the ester groups of MMA enhance the flexibility of the polymer chain and the compatibility with the electrode interface.

[0023] In one embodiment of the present application, the polymer matrix further comprises a lithium salt, and the lithium salt is at least one of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and lithium hexafluorophosphate (LiPF6), with a concentration of 0.5-2.0 mol / L.

[0024] The preparation method of the solid-liquid mixed electrolyte modified by a bifunctional quaternary ammonium salt of the present application comprises the following steps:

[0025] (a) Dissolving C16DMAAC and MMA monomers in a polar solvent to form a homogeneous precursor solution;

[0026] (b) adding a free radical initiator and a lithium salt to the solution of step (a) and mixing them uniformly;

[0027] (c) The mixed solution is injected into the battery casing and heated to induce an in-situ polymerization reaction to form a gel electrolyte.

[0028] This application uses a one-step in-situ polymerization process to directly form a gel electrolyte inside the battery, avoiding phase separation.

[0029] Preferably, the free radical initiator is azobisisobutyronitrile (AIBN) or benzoyl peroxide (BPO), and the added amount is 0.5%-3% of the total weight of the monomers.

[0030] Preferably, the polar solvent is at least one of propylene carbonate (PC) and γ-butyrolactone (GBL).

[0031] The present application also discloses a lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and the aforementioned solid-liquid mixed electrolyte modified with a bifunctional quaternary ammonium salt.

[0032] In this battery, the positive electrode active material is a high voltage ternary material LiNi 0.5 Mn 1.5 At least one of O4 and lithium cobalt oxide (LiCoO2), with an operating voltage ≥ 4.3V.

[0033] Example 1:

[0034] C16DMAAC and MMA (molar ratio 1:5) were dissolved in propylene carbonate (PC), and 1.0 M LiTFSI and 1% AIBN were added;

[0035] Injected into soft-pack batteries, polymerized at 70°C for 6 hours to form a transparent gel;

[0036] Tests show that at room temperature (25 degrees), the ion migration number is 0.68 and the ion conductivity is 1.2×10 -3 S / cm, interface impedance 40Ω·cm 2 .

[0037] Example 2:

[0038] The molar ratio of C16DMAAC to MMA was adjusted to 1:8, and the rest was the same as in Example 1;

[0039] The obtained electrolyte has a discharge capacity retention rate of 92% at a 5C rate and a capacity decay of 8% after 1000 cycles.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A solid-liquid mixed electrolyte modified with a bifunctional quaternary ammonium salt, characterized in that: The invention comprises a polymer matrix formed by in-situ polymerization of a bifunctional quaternary ammonium salt monomer and methyl methacrylate (MMA), wherein the bifunctional quaternary ammonium salt monomer is hexadecyldimethylallylammonium chloride (C16DMAAC).

2. The electrolyte according to claim 1, characterized in that The molar ratio of C16DMAAC to MMA is 1:10 to 1:

2.

3. The electrolyte according to claim 1, characterized in that The polymer matrix further comprises a lithium salt, which is at least one of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and lithium hexafluorophosphate (LiPF6), with a concentration of 0.5-2.0 mol / L.

4. The electrolyte according to claim 1, characterized in that At 25° C., the lithium ion transference number in the electrolyte is ≥0.6, and the ionic conductivity is ≥1×10-3 S / cm.

5. The electrolyte according to claim 1, characterized in that The electrolyte has an interface impedance of ≤50Ω·cm with the lithium metal negative electrode at a voltage of 4.5V. 2 .

6. A method for preparing the electrolyte according to any one of claims 1 to 5, characterized in that: The following steps are involved: (a) Dissolving C16DMAAC and MMA monomers in a polar solvent to form a homogeneous precursor solution; (b) adding a free radical initiator and a lithium salt to the solution of step (a) and mixing them uniformly; (c) The mixed solution is injected into the battery casing and heated to induce an in-situ polymerization reaction to form a gel electrolyte.

7. The preparation method according to claim 6, characterized in that The free radical initiator is azobisisobutyronitrile (AIBN) or benzoyl peroxide (BPO), and the added amount is 0.5%-3% of the total weight of the monomers.

8. The preparation method according to claim 6, characterized in that The polar solvent is at least one of propylene carbonate (PC) and gamma-butyrolactone (GBL).

9. A lithium-ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and the electrolyte according to any one of claims 1 to 5.

10. The lithium-ion battery according to claim 9, characterized in that The positive electrode active material is a high voltage ternary material LiNi 0.5 Mn 1.5 At least one of O4 and lithium cobalt oxide (LiCoO2), with an operating voltage ≥ 4.3V.