Composite electrolyte, preparation method thereof and lithium ion battery

Abstract

The application provides a composite electrolyte and a preparation method thereof and a lithium ion battery. Components of the composite electrolyte include a polymer solid-state electrolyte, a lithium salt, an ionic liquid, butanedinitrile and ceramic powder. The composite electrolyte provided by the application is prepared by incorporating the ionic liquid into a porous film, so that the prepared composite electrolyte has high ionic conductivity, mechanical properties and excellent electrode / electrolyte interface wettability, and the interface is prevented from generating a double electric layer. On the other hand, under high temperature, the micropores of the electrolyte are deformed and enlarged, the ionic liquid is released and immersed into the gap of the positive electrode material, and then the surface of the active material particles is passivated, so that the high-temperature lattice oxygen evolution phenomenon of the positive electrode material is effectively inhibited, and the high-temperature safety of the electrode is improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a composite electrolyte and its preparation method, and a lithium-ion battery. Background Technology

[0002] With the increasing prominence of fossil fuel consumption and environmental pollution, a vast market has emerged for the rise of new energy vehicles, leading to unprecedented attention on power lithium batteries. However, on the one hand, the organic liquid electrolytes currently used in commercial power lithium batteries have drawbacks such as flammability, volatility, and leakage, posing significant safety hazards. On the other hand, traditional liquid lithium batteries have been developed for over thirty years, and their related materials and technologies have reached a bottleneck, with energy density also reaching its limit, making it difficult to meet the long-range requirements of new energy vehicles.

[0003] Solid-state electrolytes are renowned for their high safety, excellent thermal and electrochemical stability, wide electrochemical window, and superior mechanical properties, making them highly regarded by both academia and industry. Solid-state electrolytes can suppress lithium dendrite formation and mitigate ongoing side reactions between metallic lithium and the electrolyte, thus enabling the use of lithium metal anodes and significantly improving the energy density of lithium-ion batteries. This makes solid-state lithium metal batteries one of the most likely next-generation lithium battery systems to replace current liquid lithium batteries. Similarly, solid-state electrolytes with high oxidation potential can reduce side reactions at the high-voltage cathode interface, resulting in more stable cycle performance. Furthermore, the production processes of solid-state electrolytes are more flexible and diverse, leading to a wider range of applications.

[0004] Existing research indicates that the application of ionic liquids in batteries is advantageous. However, the current practice is to directly mix ionic liquids with battery components. This mixing method prevents the ionic liquids in the battery from forming effective interactions with the battery components. Furthermore, since the ionic liquids are liquid, they will separate from the electrodes and solid electrolytes during use, resulting in low bonding strength.

[0005] Meanwhile, the pore structures formed in existing polymer solid electrolytes are difficult to reach the nanoscale and are unevenly dispersed, which is not conducive to maintaining the overall performance of the solid electrolyte layer. Summary of the Invention

[0006] To address one or more of the aforementioned technical problems in the prior art, this application provides a composite electrolyte and its preparation method, as well as a lithium-ion battery, to solve the problems of low room-temperature ionic conductivity, poor interface compatibility, and difficulty in passivating single-crystal LiCoO2 and polycrystalline LiNi in the prior art. x Co y Mn zThe surface of positive electrode material particles such as O2 cannot suppress the high-temperature lattice oxygen evolution phenomenon of positive electrode materials.

[0007] To achieve the above objectives, the technical solution adopted by this application to solve its technical problem is as follows:

[0008] In a first aspect, this application provides a composite electrolyte, the components of which include:

[0009] Polymer solid electrolytes, lithium salts, ionic liquids, succinic acid;

[0010] The composite electrolyte comprises a pore structure with a pore size of less than 200 nm; preferably, the pore size is less than 100 nm; preferably, the pore size is less than 80 nm.

[0011] In one specific embodiment, the ionic liquid is dispersed in the pore structure; preferably, the ionic liquid is uniformly dispersed in the pore structure.

[0012] In one specific embodiment, the polymer solid electrolyte comprises at least a partially crystalline polymer and consists of at least two phases: crystalline and amorphous.

[0013] The crystalline polymer refers to a polymer that has the property of crystallization. In actual polymer solid electrolytes, it has two phases: crystalline and amorphous.

[0014] In one specific embodiment, the polymer solid electrolyte can form a porous structure under the action of succinic anionizer.

[0015] In one specific embodiment, the composite electrolyte further includes ceramic powder;

[0016] Preferably, the ceramic powder is a fast ion conductor;

[0017] Preferably, the fast ion conductor is one or more of the following: oxide solid electrolyte, sulfide solid electrolyte, halide solid electrolyte, boride solid electrolyte, nitride solid electrolyte, and hydride solid electrolyte;

[0018] More preferably, the oxide solid electrolyte comprises LLZTO powder and / or LATP powder.

[0019] In one specific embodiment, the particle size of the ceramic powder is less than 1 μm; preferably, the particle size of the ceramic powder is less than 500 nm; more preferably, the particle size of the ceramic powder is smaller than the pore size of the pore structure.

[0020] In one specific embodiment, the ionic liquid includes one or more of imidazole, pyrrolidine, pyridine, morpholine, piperidine, quaternary ammonium, quaternary phosphorus, and guanidine ionic liquids.

[0021] In one specific embodiment, the polymer solid electrolyte includes one or more of polyethylene oxide, polyvinylidene fluoride, polymethyl methacrylate, polyvinylidene fluoride cohexafluoropropylene, polyurethane acrylate, polyethylene glycol, and polyvinyl alcohol.

[0022] In one specific embodiment, the lithium salt includes one or a mixture of several of lithium bis(trifluoromethanesulfonate)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, and lithium bis(fluorosulfonate)imide.

[0023] In one specific embodiment, the components of the composite electrolyte, calculated by mass percentage, include:

[0024] The composition includes 30-60 wt% polymer solid electrolyte, 1-10 wt% ionic liquid, 15-30 wt% lithium salt, 10-30 wt% succinic anionylene, and 10-30 wt% ceramic powder.

[0025] Preferably, the proportion of succinic anion is 15-25 wt%.

[0026] Secondly, corresponding to the above-mentioned composite electrolyte, this application also provides a method for preparing a composite electrolyte, the method comprising:

[0027] The polymer solid electrolyte, the first part of the ionic liquid, and the lithium salt are dispersed in an organic solvent according to a preset ratio and mixed to obtain a first mixture;

[0028] A first preset mass of succinic anion is added to the first mixture, and the mixture is then mixed to obtain a second mixture;

[0029] A second preset mass of ceramic powder is added to the second mixture, and the mixture is then mixed to obtain a third mixture;

[0030] The third mixture was dried and prepared into a membrane to obtain a polymer solid electrolyte membrane;

[0031] The polymer solid electrolyte membrane is immersed in the second part of the ionic liquid to obtain a composite electrolyte.

[0032] Thirdly, corresponding to the above-mentioned composite electrolyte, this application also provides a lithium-ion battery, the lithium-ion battery including a positive electrode, a negative electrode, and the above-mentioned composite electrolyte.

[0033] The beneficial effects of the technical solutions provided in this application are:

[0034] The composite electrolyte and its preparation method, as well as the lithium-ion battery provided in this application, are composed of a polymer solid electrolyte, a lithium salt, an ionic liquid, succinic acid, and ceramic powder. This application utilizes the pore-forming effect of succinic acid on the crystalline polymer. Succinic acid is mixed with the polymer solid electrolyte, and a polymer solid electrolyte membrane containing uniform nanopores is prepared through appropriate process parameters. The nanopores in the polymer solid electrolyte membrane are uniformly distributed, resulting in a more uniform micron-sized pore structure compared to existing technologies. Furthermore, the pore-forming process of succinic acid on the polymer solid electrolyte is uniform during crystallization, forming a pinhole-like porous structure. Simultaneously, by immersing the polymer solid electrolyte membrane in the ionic liquid, the ionic liquid can better composite with the nanopore structure, and the ionic liquid's integration with the battery prevents leakage.

[0035] Furthermore, the composite electrolyte provided in this application has high ionic conductivity and mechanical properties, as well as excellent electrode / electrolyte interface wettability, avoiding the formation of a double layer at the interface. On the other hand, under high temperature conditions, the micropores of the composite electrolyte provided in this application deform and enlarge, and the ionic liquid is released and penetrates into the gaps of the positive electrode material, thereby passivating the surface of the active material particles, effectively suppressing the high-temperature lattice oxygen evolution phenomenon of the positive electrode material, and improving the high-temperature safety of the electrode. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 Here is a SEM image of the composite electrolyte prepared in Example 1;

[0038] Figure 2 SEM image of the composite electrolyte prepared in Example 3;

[0039] Figure 3 The image shows the SEM image of the composite electrolyte prepared in Comparative Example 1. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0041] As described in the background section, existing electrolytes each have their own drawbacks. On the one hand, existing solid electrolytes such as inorganic ceramic electrolytes, polymer solid electrolytes, and organic-inorganic composite electrolytes mostly suffer from low room temperature ionic conductivity and poor interfacial compatibility. Similarly, all-solid-state ceramic electrolytes also suffer from poor interfacial compatibility, which easily leads to the formation of a double-layer effect at the electrode / electrolyte interface. On the other hand, existing solid electrolyte systems are difficult to passivate materials such as single-crystal LiCoO2 and polycrystalline LiNi. x Co y Mn z O2 and other positive electrode material particles cannot suppress the high-temperature lattice oxygen evolution phenomenon of the positive electrode material, causing the battery cell to generate oxygen rapidly during the heating process, resulting in gas bulging of the battery cell.

[0042] To address one or more of the aforementioned problems, this application creatively proposes a novel porous inorganic-organic composite electrolyte prepared by solution casting. This electrolyte possesses high ionic conductivity, ion transference number, and a wide electrochemical stability window, making it compatible with high-voltage cathode materials (including but not limited to modified lithium cobalt oxide, ternary nickel-cobalt-aluminum, nickel-cobalt-manganese, and lithium-rich manganese). Furthermore, at high temperatures, the electrolyte's micropores deform and enlarge, releasing ionic liquid that penetrates into the gaps between cathode materials, thereby passivating the surface of active material particles and improving the high-temperature safety of the electrode.

[0043] The following are optional technical solutions for this application, but are not intended to limit the technical solutions provided in this application. The technical objectives and beneficial effects of this application can be better achieved through the following optional technical solutions.

[0044] The composite electrolyte provided in this application embodiment is in the form of a jelly and includes a polymer solid electrolyte, a lithium salt, an ionic liquid, and succinic acid.

[0045] The composite electrolyte comprises a pore structure with a pore size of less than 200 nm; preferably, the pore size is less than 100 nm; preferably, the pore size is less than 80 nm.

[0046] The ionic liquid is dispersed in the pore structure, preferably, the ionic liquid is uniformly dispersed in the pore structure.

[0047] Preferably, the polymer solid electrolyte comprises at least a partially crystalline polymer and consists of at least two phases: crystalline and amorphous.

[0048] Preferably, the polymer solid electrolyte can form a porous structure under the action of succinic anionizer.

[0049] Preferably, the composite electrolyte further includes ceramic powder;

[0050] Preferably, the ceramic powder is a fast ion conductor;

[0051] Preferably, the fast ion conductor is one or more of the following: oxide solid electrolyte, sulfide solid electrolyte, halide solid electrolyte, boride solid electrolyte, and nitride solid electrolyte.

[0052] In a preferred embodiment of this application, the particle size of the ceramic powder is less than 1 μm; preferably, the particle size of the ceramic powder is less than 500 nm, such as 50 nm, 80 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, etc.; more preferably, the particle size of the ceramic powder is smaller than the pore size of the pore structure.

[0053] As a preferred embodiment, in this application embodiment, the components of the composite electrolyte, calculated by mass percentage, include:

[0054] The composition includes 30-60 wt% polymer solid electrolyte, 1-12 wt% ionic liquid, 15-30 wt% lithium salt, 10-30 wt% succinic anionylene, and 10-30 wt% ceramic electrolyte powder.

[0055] Specifically, the content of each component in the composite electrolyte can be adjusted according to factors such as battery usage, design, and actual formulation system. In practice, polymer solid electrolyte, lithium salt, ionic liquid, succinic acid, and ceramic powder are prepared according to the above proportions for use in subsequent preparation processes.

[0056] Optionally, this application does not particularly limit the mass ratio of lithium salt. The main function of lithium salt is to improve the ionic conductivity of the composite electrolyte. Without departing from the inventive concept of this application, the mass ratio of lithium salt can be 20%, 25%, 30%, 35%, 40%, 45%, or 50%, etc. Preferably, the mass ratio of lithium salt is 20%.

[0057] Optionally, the mass percentage of succinic anion can be 10%, 15%, 20%, 25%, 30%, etc., and preferably, the mass percentage of succinic anion is 15-25 wt%.

[0058] Specifically, succinic anhydride is an organic compound, a colorless and odorless waxy solid, slightly soluble in water, ethanol, benzene, diethyl ether, and carbon disulfide, and soluble in acetone, chloroform, and dioxane, etc. It is a commonly used raw material for organic synthesis. In the embodiments of this application, the addition of succinic anhydride can suppress the crystalline phase of the crystalline polymer, and when the added succinic anhydride reaches a certain proportion, a porous structure can be formed. Generally speaking, the mass percentage of succinic anhydride needs to reach more than 10% to form a porous structure; if the succinic anhydride content is too high, the porosity will be too large.

[0059] This is merely speculation, and not intended to limit the scope of protection, but the introduction of succinic acid may reduce the proportion of crystalline phase in crystalline polymers, thereby creating a porous structure.

[0060] Optionally, the mass percentage of ceramic powder can be 10%, 12.5%, 15%, 17.5%, 20%, 22.5%, 25%, or 30%, etc.

[0061] Specifically, ionic liquids exist in a liquid state at or near room temperature and possess several excellent properties, such as non-flammability, negligible vapor pressure, thermal stability, high ionic conductivity, and a wide electrochemical stability window. By adding ionic liquids and utilizing their properties, the resulting composite electrolytes can exhibit high ionic conductivity, ion transference number, and a wide electrochemical stability window. This allows them to be matched with high-voltage cathode materials. Furthermore, at high temperatures, the micropores of the composite electrolyte deform and enlarge, allowing the ionic liquid to be released and penetrate into the gaps between the cathode materials. This passivates the surface of the active material particles, suppresses high-temperature lattice oxygen evolution in the cathode material, and improves the high-temperature safety of the electrode.

[0062] In this application, the pore structure obtained by the pore-forming effect of succinic acid is at the nanoscale, which allows the ionic liquid to be uniformly dispersed in the pore structure of the composite electrolyte. If the pore structure size is too large, the ionic liquid will agglomerate in the pore structure, resulting in uneven dispersion. Furthermore, the pore structure has a smaller "retention" effect on the ionic liquid, which is not conducive to the retention of the ionic liquid in the composite electrolyte.

[0063] In a preferred embodiment, the ionic liquid in this application includes one or a mixture of several of imidazole, pyrrolidine, pyridine, morpholine, piperidine, quaternary ammonium, quaternary phosphorus, and guanidine ionic liquids. It should be noted that this application does not specifically limit the ionic liquid; any known ionic liquid can be used as the ionic liquid in this application without departing from the inventive concept.

[0064] In a preferred embodiment of this application, the polymer solid electrolyte comprises one or a mixture of several of polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polyvinylidene fluoride cohexafluoropropylene (PVDF-HFP), polyurethane acrylate (PUA), polyethylene glycol (PEG), and polyvinyl alcohol (PVA).

[0065] Preferably, the polymer solid electrolyte is a mixture of polyvinylidene fluoride cohexafluoropropylene (PVDF-HFP) and polyethylene glycol (PEG).

[0066] More preferably, the mass ratio of polyvinylidene fluoride cohexafluoropropylene (PVDF-HFP) to polyethylene glycol (PEG) is 5:1.

[0067] In a preferred embodiment, the suitable lithium salt in this application typically has an inert anion. A non-limiting list of lithium salts that can be dissolved in organic solvents or mixtures of organic solvents to form a non-aqueous liquid electrolyte solution includes: lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrachloroaluminate (LiAlCl4), lithium iodide (Li1), lithium bromide (LiBr), lithium thiocyanate (LiSCN), lithium tetrafluoroborate (LiBF4), lithium difluorooxalate borate (LiBF2(C2O4))(LiODFB), lithium tetraphenylborate (LiB(C6H5)), and lithium tetraphenylborate (LiB(C6H5)). 4) Lithium bis(oxalate)borate (LiB(C2O4)2)(LiBOB), lithium tetrafluorooxalate phosphate (LiPF4(C2O4))(LiFOP), lithium nitrate (LiNO3), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonylimide) (LITFSI)(LiN(CF3SO2)2), lithium bis(fluorosulfonylimide) (LiN(FSO2)2)(LIFSI), and combinations thereof. In some variations, the lithium salt is selected from lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonylimide) (LiTFSI)(LiN(CF3SO2)2), lithium bis(fluorosulfonylimide) (LiN(FSO2)2)(LiFSI), lithium fluoroalkylphosphonate (LiFAP), lithium phosphate (Li3PO4), and combinations thereof.

[0068] In a preferred embodiment of this application, the ceramic powder contains a fast ion conductor; preferably, the fast ion conductor is at least one of oxide electrolyte, sulfide electrolyte, boride solid electrolyte, nitride solid electrolyte, halide solid electrolyte, and hydride solid electrolyte.

[0069] In one implementation, the oxide solid electrolyte may comprise one or more garnet ceramics, LIS ICON type oxides, NASICON type oxides, and perovskite type ceramics. For example, one or more garnet ceramics may be selected from the group consisting of: Li 6.5 La3Zr 1.75 Te 0.25 O 12 Li7La3Zr2O 12 Li 6.2 Ga 0.3 La 2.9 Rb 0.05 Zr2O 12 Li 6.85 La 2.9 Ca 0.1 Zr 1.75 Nb 0.25 O 12 Li 6.25 Al 0.25 La3Zr2O 12 Li 6.75 La3Zr 1.75 Nb 0.25 O 12 And combinations thereof. One or more LI SICON-type oxides may be selected from the group consisting of: Li 14 Zn(GeO4)4, Li 3+x (P 1-x Si x O4 (where 0 < x < 1), Li 3+x Ge x V 1-x O4 (where 0 < x < 1) and combinations thereof. One or more NASICON-type oxides may be defined by LiMM′(PO4)3, where M and M′ are independently selected from Al, Ge, Ti, Sn, Hf, Zr, and La. For example, in some variants, one or more NASICON-type oxides may be selected from the group consisting of: Li 1+x Al x Ge 2-x (PO4)3(LAGP) (where 0 ≤ x ≤ 2), Li 1+x Al x Ti 2-x (PO4)3(LATP) (where 0 ≤ x ≤ 2), Li 1+x Y x Zr 2-x (PO4)3(LYZP) (where 0≤x≤2), Li 1.3 Al 0.3 Ti 1.7(PO4)3, LiTi2(PO4)3, LiGeTi(PO4)3, LiGe2(PO4)3, LiHf2(PO4)3, and combinations thereof. One or more perovskite ceramics may be selected from the group consisting of: Li a.3 La 0.53 TiO3, LiSr 1.65 Zr 1.3 Ta 1.7 O9、Li 2x-y Sr 1-x Ta y Zr 1-y O3 (where x = 0.75y and 0.60 < y < 0.75), Li 3 / 8Sr 7 / 16 Nb 3 / 4Zr 1 / 4 O3 (where 0 < x < 0.25) and combinations thereof. In one variant, one or more oxide-based materials may have a value greater than or equal to about 10. -5 S / cm to less than or equal to approximately 10 -1 Ionic conductivity in S / cm.

[0070] In one embodiment, the sulfide solid electrolyte may include one or more sulfide-based materials selected from the following: Li2S-P2S5, Li2S-P2S5-MS X (where M is Si, Ge, and Sn and 0 ≤ x ≤ 2), Li 3.4 Si 0.4 P 0.6 S4, Li 10 GeP2s 11.700.3 Li 9.6 P3S 12 Li7P3S 11 Li9P3S9O3, Li 10.35 Si 1.35 P 1.65 S 12 Li 9.81 Sn 0.81 P 2.19 S 12 Li 10 (Si 0.5 Ge 0.5 P2S 12 Li (Ge 0.5 Sn 0.5 P2S 12 Li(Si) 0.5 Sn 0.5 PS 12 Li 10GeP2S 12 (LGPS), Li6PS5X (where X is Cl, Br, or I), Li7P2S8I, Li 10.35 Ge 1.35 P 1.65 S 12 Li 3.25 Ge 0.25 P 0.75 S4, Li 10 SnP2S 12 Li 10 SiP2S 12 Li 9.54 Si 1.74 P 1.44 S 11.7 CI 0.3 (1-x)P2S 5-x Li₂S (where 0.5 ≤ x ≤ 0.7) and combinations thereof. In one variant, one or more sulfide-based materials may have a content greater than or equal to about 10. -7 Ionic conductivity from S / cm to less than or equal to about 1 S / cm.

[0071] In one embodiment, the halide solid electrolyte may include one or more halide-based materials selected from the following: Li₂CdCl₄, Li₂MgCl₄, Li₂CdI₄, Li₂ZnI₄, Li₃OCl, LiI, Li₅ZnI₄, Li₃OCl 1-x Br x (where 0 < x < 1) and their combinations. In one variant, one or more halide-based materials may have a value greater than or equal to about 10. -8 S / cm to less than or equal to approximately 10 -1 Ionic conductivity in S / cm.

[0072] In one embodiment, the boride solid electrolyte may include one or more borate-based materials selected from Li₂B₄O₇, Li₂O-(B₂O₃)-(P₂O₅), and combinations thereof. In one variation, the one or more borate-based materials may have a content greater than or equal to about 10 -7 S / cm to less than or equal to approximately 10 -2 Ionic conductivity in S / cm.

[0073] As one implementation, the nitride solid electrolyte may include one or more nitride-based materials selected from the following: Li a N, Li7PN4, LiSi2N3, and combinations thereof. In one variant, one or more nitride-based materials may have a density greater than or equal to about 10. -9Ionic conductivity from S / cm to less than or equal to about 1 S / cm.

[0074] In one implementation, the hydride solid electrolyte may include one or more hydride-based materials selected from the group consisting of: Li a AlH6, LiBH4, LiBH4-LiX (where X is one of Cl, Br, and I), LiNH2, Li2NH, LiBH4-LiNH2, and combinations thereof. In one variant, one or more hydride-based materials may have a content greater than or equal to about 10. -7 S / cm to less than or equal to approximately 10 -2 Ionic conductivity in S / cm.

[0075] In one embodiment, the solid electrolyte particles may be quasi-solid electrolytes comprising a mixture of the non-aqueous liquid electrolyte solution and the solid electrolyte system detailed above, for example, including one or more ionic liquids and one or more metal oxide particles (such as alumina (Al2O3) and / or silicon dioxide (SiO2)).

[0076] In a preferred embodiment of this application, the particle size of the ceramic powder is less than 1 μm, preferably less than 500 nm; more preferably, the particle size of the ceramic powder is smaller than the pore size of the pore structure.

[0077] Corresponding to the above-mentioned composite electrolyte, this application provides a method for preparing a composite electrolyte, the method comprising:

[0078] S1. The polymer solid electrolyte, the first part of the ionic liquid, and the lithium salt are dispersed in an organic solvent according to a preset ratio and mixed to obtain a first mixture;

[0079] S2. Add a first preset mass of succinic anion to the first mixture and mix to obtain a second mixture;

[0080] S3. Add the second preset mass of ceramic powder to the second mixture and mix to obtain a third mixture;

[0081] S4. The third mixture is dried and prepared into a membrane to obtain a polymer solid electrolyte membrane;

[0082] S5. Immerse the polymer solid electrolyte membrane in the second part of the ionic liquid to obtain a composite electrolyte.

[0083] Preferably, in step S1, a predetermined ratio of polymer solid electrolyte, lithium salt and ionic liquid is dispersed in an organic solvent and mixed to obtain a first mixture.

[0084] Preferably, 30-60 wt% of a polymer solid electrolyte, 1-12 wt% of an ionic liquid (i.e., the first part of the ionic liquid), and 15-30 wt% of a lithium salt are dissolved in an organic solvent and magnetically stirred at room temperature for 12 hours to obtain a first mixture; a first predetermined mass of succinic anion is added to the first mixture and magnetically stirred at 50°C for 8-12 hours to obtain a second mixture; a second predetermined mass of ceramic powder is added to the second mixture and magnetically stirred at room temperature for 12 hours to obtain a third mixture; the third mixture is placed in a predetermined mold and dried at room temperature for 12 hours, and then dried again at 60°C for 12 hours to obtain a polymer solid electrolyte membrane; the polymer solid electrolyte membrane is immersed in the second part of the ionic liquid for 12-20 hours to obtain a composite electrolyte.

[0085] It is understandable that the content of ionic liquid in the final composite electrolyte should be the sum of the contents of all ionic liquids in steps S1 and S5.

[0086] In one implementation, the first part of the ionic liquid and the second part of the ions can be of the same or different types.

[0087] In this application, no specific limitation is made to the organic solvent. Any known organic solvent may be used in this application without departing from the inventive concept. Preferably, the organic solvent is N,N-dimethylformamide (DMF), and the mass ratio of the organic solvent to the polymer solid electrolyte is preferably 3-5:1.

[0088] Specifically, the addition of succinic acid can suppress the proportion of the crystalline phase of the polymer solid electrolyte, forming a porous structure.

[0089] It should be noted that in this embodiment, the specific addition mass of ceramic powder is not limited. Without violating the inventive concept of this application, the user can set the first preset mass and the second preset mass according to actual needs.

[0090] Specifically, the pre-set mold includes, but is not limited to, a polytetrafluoroethylene mold. The third mixture is placed in the polytetrafluoroethylene mold and dried at room temperature, and then dried again at 60-80°C for 10-24 hours to obtain a porous electrolyte membrane. The porous electrolyte membrane is then immersed in the ionic liquid and soaked for 12-20 hours to obtain a jelly-like composite electrolyte.

[0091] This application does not impose any special requirements on the drying process. Any known drying process can be used in this application without departing from the inventive concept. The examples provided are merely illustrative and not intended to limit the scope of protection. Drying can be performed by methods such as baking. It is understood that this application does not impose special limitations on the drying temperature, drying time, and other related process parameters. Any technical solution obtained by adjusting these parameters without requiring inventive effort is within the scope of protection of this application, provided it does not depart from the inventive concept.

[0092] Corresponding to the above-mentioned composite electrolyte, this application provides a lithium-ion battery, which includes a positive electrode, a negative electrode, and the above-mentioned composite electrolyte, wherein the negative electrode is a lithium metal negative electrode.

[0093] The composite electrolyte of this application, on the one hand, improves the stability of lithium metal while maintaining high lithium-ion conductivity. Due to its stability to lithium metal, it is particularly suitable for lithium metal anode systems. On the other hand, under high temperature conditions, the micropores of the electrolyte itself deform and enlarge, and the ionic liquid is released and penetrates into the gaps of the cathode material, thereby passivating the surface of the active material particles, effectively suppressing the high-temperature lattice oxygen evolution phenomenon of the cathode material, and improving the high-temperature safety of the electrode.

[0094] The negative electrode sheet involved in this application can be a lithium foil, or it can be composed of a current collector and a negative electrode active material containing metallic lithium.

[0095] Optionally, the lithium foil can be lithium metal or a lithium alloy; preferably, the lithium alloy can be one of aluminum-lithium alloy, lithium-tin alloy, lithium-lead alloy, or lithium-silicon alloy.

[0096] As an alternative to the negative electrode, the current collector and the negative electrode active material containing lithium metal can be conventional negative electrodes in the prior art; the current collector can be copper foil, and the negative electrode active material can be lithium metal or lithium alloy. Preferably, the lithium alloy can be one of aluminum-lithium alloy, lithium-tin alloy, lithium-lead alloy, and lithium-silicon alloy.

[0097] Preferably, the negative electrode active material can be combined with a binder to form an active material layer, said binder being one or more selected from polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, sodium carboxymethyl cellulose, hydroxyethyl cellulose, and polyvinyl alcohol. The amount of binder used can be its conventional amount. The amount of binder relative to 100 parts by weight of the negative electrode active material can be 2-50% by weight.

[0098] As a preferred embodiment, in this application embodiment, the positive electrode sheet includes a positive current collector and a positive active material layer. The positive current collector may be a metal foil, metal mesh or wire mesh, or mesh metal containing aluminum or any other suitable conductive material known to those skilled in the art.

[0099] In a preferred embodiment, the positive electrode sheet in this application is formed of a plurality of positive electrode active particles comprising one or more transition metal cations, such as manganese (Mn), nickel (Ni), cobalt (Co), chromium (Cr), iron (Fe), vanadium (V), and combinations thereof. In some embodiments, the positive electrode active material layer further comprises an electrolyte, such as a plurality of electrolyte particles.

[0100] The positive electrode active material includes one of layered oxide cathodes, spinel cathodes, and polyanion cathodes. For example, a layered oxide cathode (e.g., rock salt layered oxide) comprises one or more lithium-based positive electrode active materials selected from: LiCoO2, LiNi x Mn y Co 1-x-y O2 (where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1), LiNi 1-x-y Co x Al y O2 (where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1), LiNi x Mn 1-x O2 (where 0 ≤ x ≤ 1), and Li 1+x MO2 (where M is one of Mn, Ni, Co and Al, 0≤x≤1).

[0101] In one specific embodiment, one or more lithium-based cathode active materials may optionally be coated and / or doped. Furthermore, in some embodiments, one or more lithium-based cathode active materials may optionally be mixed with one or more conductive materials that provide an electronic conduction path and / or at least one polymeric binder material that improves the structural integrity of the cathode. For example, the cathode active material layer may comprise more than or equal to about 30 wt% to less than or equal to about 98 wt% of one or more lithium-based cathode active materials; more than or equal to about 0 wt% to less than or equal to about 30 wt% of conductive materials; and more than or equal to about 0 wt% to less than or equal to about 20 wt% of binder, and in some aspects, optionally more than or equal to about 1 wt% to less than or equal to about 20 wt% of binder.

[0102] In a preferred embodiment of this application, the positive electrode active material layer may optionally be mixed with an adhesive such as polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), nitrile rubber (NBR), styrene-ethylene-butene-styrene copolymer (SEBS), styrene-butadiene-styrene copolymer (SBS), lithium polyacrylate (LiPAA), sodium polyacrylate (NaPAA), sodium alginate, lithium alginate, and combinations thereof.

[0103] In a preferred embodiment, the conductive material in this application may include carbon-based materials, powdered nickel or other metal particles, or conductive polymers. Carbon-based materials may include particles such as carbon black, graphite, acetylene black (e.g., KETCHENTM black or DENKATM black), carbon fibers and nanotubes, graphene, etc. Examples of conductive polymers include polyaniline, polythiophene, polyacetylene, polypyrrole, etc.

[0104] Example 1

[0105] This application provides a composite electrolyte, the preparation process of which is as follows:

[0106] 40 wt% polymer solid electrolyte, 10 wt% ionic liquid and 20 wt% lithium salt were dispersed in an organic solvent and magnetically stirred at room temperature for 12 h to obtain a first mixture, wherein the polymer solid electrolyte was a mixture of PVDF-HFP and PEG in a mass ratio of 5:1, the lithium salt was LiTFSI, and the organic solvent was N,N-dimethylformamide (DMF) in a mass ratio of 5:1 to the polymer solid electrolyte.

[0107] Add 20 wt% succinate to the first mixture and stir magnetically at 50 °C for 8-12 h to obtain the second mixture;

[0108] 10 wt% of ceramic powder was added to the second mixture and magnetically stirred at room temperature for 12 h to obtain a third mixture, wherein the ceramic electrolyte powder was LLZO with a particle size of 500 nm.

[0109] The third mixture was placed in a polytetrafluoroethylene mold and dried at room temperature for 12 hours, and then dried again at 60°C for 12 hours to obtain a polymer solid electrolyte membrane.

[0110] The polymer solid electrolyte membrane was immersed in 10 wt% ionic liquid for 12 h to obtain a composite electrolyte, wherein the ionic liquid was 1-butyl-3-methylimidazolium chloride.

[0111] Example 2

[0112] This application provides a composite electrolyte, the preparation process of which is as follows:

[0113] 45 wt% polymer solid electrolyte, 10 wt% ionic liquid and 20 wt% lithium salt were dispersed in an organic solvent and magnetically stirred at room temperature for 12 h to obtain a first mixture, wherein the polymer solid electrolyte membrane was a mixture of PVDF-HFP and PEG in a mass ratio of 5:1, the lithium salt was LiTFSI, and the organic solvent was N,N-dimethylformamide (DMF) in a mass ratio of 5:1 to the polymer solid electrolyte.

[0114] 15 wt% succinate was added to the first mixture, and the mixture was magnetically stirred at 50 °C for 8-12 h to obtain the second mixture;

[0115] 10 wt% of ceramic powder was added to the second mixture and magnetically stirred at room temperature for 12 h to obtain a third mixture, wherein the ceramic electrolyte powder was LLZO with a particle size of 500 nm.

[0116] The third mixture was placed in a polytetrafluoroethylene mold and dried at room temperature for 12 hours, and then dried again at 60°C for 12 hours to obtain a polymer solid electrolyte membrane.

[0117] The polymer solid electrolyte membrane was immersed in 10 wt% ionic liquid for 18 h to obtain a composite electrolyte, wherein the ionic liquid was 1-butyl-3-methylimidazolium chloride.

[0118] Example 3

[0119] This application provides a composite electrolyte, the preparation process of which is as follows:

[0120] 52 wt% polymer solid electrolyte, 10 wt% ionic liquid and 20 wt% lithium salt were dispersed in an organic solvent and magnetically stirred at room temperature for 12 h to obtain a first mixture, wherein the polymer solid electrolyte membrane was a mixture of PVDF-HFP and PEG in a mass ratio of 5:1, the lithium salt was LiTFSI, and the organic solvent was N,N-dimethylformamide (DMF) in a mass ratio of 5:1 to the polymer solid electrolyte.

[0121] Add 8 wt% succinic anion to the first mixture and stir magnetically at 50°C for 8-12 h to obtain the second mixture;

[0122] 10 wt% of ceramic electrolyte powder was added to the second mixture and magnetically stirred at room temperature for 12 h to obtain a third mixture, wherein the ceramic powder was LLTO with a particle size of 650 nm.

[0123] The third mixture was placed in a polytetrafluoroethylene mold and dried at room temperature for 12 hours, and then dried again at 60°C for 12 hours to obtain a polymer solid electrolyte membrane.

[0124] Example 4

[0125] This application provides a composite electrolyte, the preparation process of which is as follows:

[0126] 40 wt% polymer solid electrolyte, 10 wt% ionic liquid and 20 wt% lithium salt were dispersed in an organic solvent and magnetically stirred at room temperature for 12 h to obtain a first mixture, wherein the polymer solid electrolyte was PVDF, the lithium salt was LiTFSI, the organic solvent was N,N-dimethylformamide (DMF) and the mass ratio of organic solvent to polymer was 5:1.

[0127] Add 20 wt% succinate to the first mixture and stir magnetically at 50 °C for 8-12 h to obtain the second mixture;

[0128] 10 wt% of ceramic powder was added to the second mixture and magnetically stirred at room temperature for 12 h to obtain a third mixture, wherein the ceramic powder was LLTO with a particle size of 650 nm.

[0129] The third mixture was placed in a polytetrafluoroethylene mold and dried at room temperature for 12 hours, and then dried again at 60°C for 12 hours to obtain a polymer solid electrolyte membrane.

[0130] The polymer solid electrolyte membrane was immersed in 10 wt% ionic liquid for 18 h to obtain a composite electrolyte, wherein the ionic liquid was 1-(3-aminopropyl)imidazole chloride.

[0131] Example 5

[0132] This application provides a composite electrolyte, the preparation process of which is as follows:

[0133] 40 wt% polymer solid electrolyte, 10 wt% ionic liquid and 20 wt% lithium salt were dispersed in an organic solvent and magnetically stirred at room temperature for 12 h to obtain a first mixture, wherein the polymer solid electrolyte was PMMA, the lithium salt was LiTFSI, the organic solvent was N,N-dimethylformamide (DMF) and the mass ratio of organic solvent to polymer was 5:1.

[0134] Add 20 wt% succinate to the first mixture and stir magnetically at 50 °C for 8-12 h to obtain the second mixture;

[0135] 10 wt% of ceramic powder was added to the second mixture and magnetically stirred at room temperature for 12 h to obtain a third mixture, wherein the ceramic electrolyte powder was LLT0 and its particle size was 650 nm.

[0136] The third mixture was placed in a polytetrafluoroethylene mold and dried at room temperature for 12 hours, and then dried again at 60°C for 12 hours to obtain a polymer solid electrolyte membrane.

[0137] The polymer solid electrolyte membrane was immersed in 10 wt% ionic liquid for 18 h to obtain a composite electrolyte, wherein the ionic liquid was 1-(3-aminopropyl)imidazole chloride.

[0138] Comparative Example 1

[0139] The difference from Example 1 is that succinic anhydride is not added.

[0140] Battery manufacturing

[0141] A lithium-ion battery is prepared by stacking the positive electrode, the negative electrode, and the composite electrolyte prepared in the examples and comparative examples.

[0142] The positive electrode consists of 96 wt% LiFePO4, 2 wt% super-P, and 2 wt% PVDF.

[0143] The negative electrode is composed of 94% wt graphite, 2 wt% super-P, 2 wt% SBR, and 2 wt% CMC.

[0144] 1. 500-cycle performance test method:

[0145] Cycle performance tests were performed on the lithium-ion batteries obtained in the examples and comparative examples:

[0146] Temperature 25℃±2℃

[0147] ① Charge to the termination voltage at 1C or the specified current, cut off current 0.05C, and let stand for 30 minutes;

[0148] ② Discharge at 1C until the final discharge voltage (2.75V), record the discharge capacity, and let stand for 30 minutes;

[0149] Repeat steps ①-② until the cycle is completed 500 times, and record the final capacity retention rate.

[0150]

[0151] The experimental data above show that the lithium-ion battery prepared using the method described in this application effectively improves the battery's cycle performance.

[0152] Figure 1 This is a SEM image of the polymer solid electrolyte membrane prepared in Example 1. Figure 2 This is a SEM image of the polymer solid electrolyte membrane prepared in Example 3. Figure 3 The image shows a SEM image of the polymer solid electrolyte membrane prepared in Comparative Example 1. Figure 1 and Figure 2 The comparison shows that, under the same polymer matrix, the polymer film prepared by adding succinic anionylene in Example 1 has a rich porous structure with uniform pore size. According to the scale bar, the pore diameter is less than 100 nm. In contrast, in Comparative Example 1, since no succinic anionylene was added, the polymer film prepared did not form a porous structure, and the final result was a dense polymer solid electrolyte film. Comparing Examples 1-3, it can be seen that when the content of succinic anionylene is too low, it is insufficient to generate a porous structure in the polymer solid electrolyte film, thereby affecting the battery performance.

[0153] Based on the battery cycle data, due to the positive pore-forming effect of succinate on the polymer solid electrolyte, uniformly dispersed nanopores are formed within the polymer solid electrolyte membrane. The ionic liquid is dispersed in the nanopores and uniformly dispersed in the solid electrolyte, which effectively improves the overall cycle performance of the battery. In contrast, in the comparative example without succinate, the ionic liquid has a smaller effect on battery performance improvement, and the difference is significant compared to the example with succinate.

[0154] In the description of this application, it should be understood that the terms "vertical," "parallel," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0155] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0156] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A composite electrolyte, characterized in that, The components of the composite electrolyte include: Polymer solid electrolytes, lithium salts, ionic liquids, succinic acid; The polymer solid electrolyte can form a nanoscale porous structure under the action of succinic acid; The composite electrolyte includes a porous structure with a pore size of less than 100 nm. The ionic liquid is dispersed in the pore structure; The succinic anion has a mass percentage of 10% to 30% in the composite electrolyte. The ionic liquid includes one or more of the following: imidazole, pyrrolidine, pyridine, morpholine, piperidine, quaternary ammonium, quaternary phosphorus, and guanidine ionic liquids; The polymer solid electrolyte includes one or more of polyethylene oxide, polyvinylidene fluoride, polymethyl methacrylate, polyvinylidene fluoride cohexafluoropropylene, polyurethane acrylate, polyethylene glycol, and polyvinyl alcohol.

2. The composite electrolyte according to claim 1, characterized in that, The ionic liquid is uniformly dispersed in the pore structure.

3. The composite electrolyte according to claim 1, characterized in that, The polymer solid electrolyte comprises at least a partially crystalline polymer and consists of at least two phases: crystalline and amorphous.

4. The composite electrolyte according to claim 1, characterized in that, The composite electrolyte also includes ceramic powder.

5. The composite electrolyte according to claim 4, characterized in that, The ceramic powder includes fast ion conductors.

6. The composite electrolyte according to claim 5, characterized in that, The fast ion conductor is one or more of the following: oxide solid electrolyte, sulfide solid electrolyte, halide solid electrolyte, boride solid electrolyte, and nitride solid electrolyte.

7. The composite electrolyte according to claim 4, characterized in that, The particle size of the ceramic powder is less than 1 μm.

8. The composite electrolyte according to claim 7, characterized in that, The particle size of the ceramic powder is less than 500 nm.

9. The composite electrolyte according to claim 8, characterized in that, The particle size of the ceramic powder is smaller than the pore size of the pore structure.

10. The composite electrolyte according to claim 1, characterized in that, The aperture is less than 80 nm.

11. A method for preparing the composite electrolyte as described in any one of claims 1 to 10, characterized in that, The preparation method includes: The polymer solid electrolyte, the first part of the ionic liquid, and the lithium salt are dispersed in an organic solvent according to a preset ratio and mixed to obtain a first mixture; A first preset mass of succinic anion is added to the first mixture, and the mixture is then mixed to obtain a second mixture; A second preset mass of ceramic powder is added to the second mixture, and the mixture is then mixed to obtain a third mixture; The third mixture was dried and prepared into a membrane to obtain a polymer solid electrolyte membrane; The polymer solid electrolyte membrane is immersed in the second part of the ionic liquid to obtain a composite electrolyte.

12. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, and a composite electrolyte as described in any one of claims 1 to 10.

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