Ionic liquid gel for interface buffer layer, modified positive electrode, preparation method of ionic liquid gel and modified positive electrode, and sulfide all-solid-state lithium battery

Abstract

The invention discloses ionic liquid gel for an interface buffer layer, a modified positive electrode, a preparation method of the ionic liquid gel and the modified positive electrode and a sulfide all-solid-state lithium battery. The ionic liquid gel is arranged on the surface of a positive pole piece to serve as a buffer interface so as to modify a positive pole material, the ionic liquid gel is composed of organic-inorganic mixed matrix ionic gel, and the organic-inorganic mixed matrix ionic gel comprises an organic matrix, an inorganic matrix, ionic liquid and lithium bis (trifluoromethane sulfonimide). The ionic liquid gel can modify the positive electrode material to achieve the effect of inhibiting side reaction of the positive electrode material caused by direct contact with sulfide electrolyte.

Description

Technical Field

[0001] This invention relates to the field of sulfide all-solid-state lithium battery technology, and in particular to an ionic liquid gel for an interface buffer layer and a modified cathode, its preparation method, and a sulfide all-solid-state lithium battery. Background Technology

[0002] Lithium-ion batteries (LIBs) have been widely used in portable electronics, electric vehicles, grid energy storage, and many other fields, but the energy density of commercial LIBs is nearing its limit. Furthermore, leakage and thermal instability of the highly flammable liquid electrolyte have caused serious safety issues for commercial LIBs. To address these problems, all-solid-state battery (ASSB) technology is widely considered one of the most promising candidate technologies.

[0003] Currently, the most prominent type of solid electrolyte is sulfide-based materials. Sulfide solid electrolytes possess high ionic conductivity and good mechanical ductility, facilitating close contact with electrode materials. However, sulfides are prone to oxidative decomposition when in contact with high-voltage cathodes (such as high-nickel NCM), forming interfacial layers (such as Li₂S and P₂S₅) that lead to capacity decay. Therefore, establishing a stable chemical / electrochemical interface between the cathode material and the sulfide solid electrolyte is crucial.

[0004] Currently, oxides are commonly used as a typical coating material for modifying cathode materials, thereby improving the cycle stability of the battery. Extensively studied oxide coating materials include MgO, Al2O3, SiO2, TiO2, ZnO, CeO2, and Co3O4. These oxides are themselves insulating or semiconductor materials; excessively thick coatings can hinder the growth of Li. + Diffusion and electronic conduction lead to increased interfacial impedance, reducing rate performance. Furthermore, oxides (such as Al₂O₃ and Li₂ZrO₃) and sulfide electrolytes (such as Li₆PS₅Cl and Li₂) can also affect interfacial performance. 10 GeP2S 12 Li₂O and Li₂S have poor chemical / electrochemical stability and readily form high-resistivity interface layers (such as Li₂O and Li₂S), leading to impeded ion transport. Li₂O and Li₂S oxides and sulfides... + Large differences in chemical potential make it easy for Li to form at the interface. + The depletion region (space charge layer) significantly increases interfacial resistance, ultimately leading to increased battery polarization and limiting rate performance and capacity. Even after coating, sulfides can still directly contact the cathode material through coating defects during long-term cycling, forming harmful phases (such as Ni3S2, P2S). x This leads to accelerated capacity decay and reduced coulomb efficiency.

[0005] Sulfide-based all-solid-state batteries face interfacial challenges due to the electrical, electrochemical, chemical, and mechanical incompatibilities between the electrodes and solid-state electrolytes, including space charge layer effects, interfacial side reactions, and mechanical instabilities. These interfacial problems lead to the formation of Li at the positive electrode. + Depletion layers or low-conductivity cathode material / electrolyte interfaces significantly hinder Li + and e - The transport of sulfide solid electrolytes undergoes side reactions at the interface with the cathode material, generating byproducts such as Li₂S and P₂S₅. These byproducts have extremely low ionic conductivity, which hinders the transport of Li₂S at the cathode-electrolyte interface. + The transmission of these signals leads to increased polarization and capacity decay. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings and defects of the prior art by providing an ionic liquid gel for an interface buffer layer, a modified positive electrode, its preparation method, and a sulfide-based all-solid-state lithium battery. The ionic liquid gel of this invention can modify the positive electrode, thereby suppressing side reactions that occur when the positive electrode directly contacts the sulfide electrolyte.

[0007] One object of the present invention is to provide an ionic liquid gel for use as an interface buffer layer, which is used to modify the positive electrode material by being placed on the surface of the positive electrode as a buffer interface. The gel is composed of an organic-inorganic mixed matrix ionic gel, wherein the organic-inorganic mixed matrix ionic gel includes an organic matrix, an inorganic matrix and an ionic liquid, and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0008] Preferably, the anion of the ionic liquid comprises bis(trifluoromethanesulfonyl)imide (TFSI). - ), BF4 - and PF6 - The cations of the ionic liquid include imidazole, pyrrole, and short-chain aliphatic quaternary ammonium salts, which are large organic ions.

[0009] Preferably, the ionic liquid is selected from N-methoxyethyl-N-methylpyrrolidone bis(trifluoromethanesulfonyl)imine ([Pyr1(2O1)]TFSI), N-hexyl-N-methylpyrrolidone bis(trifluoromethanesulfonyl)imine, and N-butyl-N-methylpyrrolidone bis(trifluoromethanesulfonyl)imine (Pyr 14 One or more of TFSI, preferably Pyr 14 TFSI.

[0010] Preferably, the inorganic matrix is ​​selected from one or more of SiO2, TiO2, and Al2O3.

[0011] Preferably, the organic matrix is ​​selected from one or more of PVDF-HFP, PEO, PMMA, PVC, and PAN.

[0012] A second objective of this invention is to provide a method for preparing an ionic liquid gel for an interface buffer layer, comprising the following steps:

[0013] The lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added to the ionic liquid and heated to obtain a homogeneous solution. The organic matrix was dissolved in the solvent, added to the homogeneous solution and stirred to dissolve. The inorganic matrix precursor was added to the above solution by a one-pot sol-gel method and reacted under stirring. The inorganic matrix was generated in situ and uniformly dispersed in the solution to obtain an organic-inorganic mixed matrix ionic liquid gel.

[0014] Preferably, the molar ratio of lithium bis(trifluoromethanesulfonylimide) to the ionic liquid is 0.05 to 0.1;

[0015] Preferably, in the organic-inorganic mixed matrix ionic liquid gel, the organic matrix, inorganic matrix, and lithium bis(trifluoromethanesulfonyl)imide ionic liquid each account for 15%-30%, 5%-15%, and 60%-80% by mass percentage.

[0016] The preferred ionic liquid is Pyr. 14 TFSI, to prevent the introduction of an ionic liquid layer from reducing Li + The transmission effect, during fabrication, is achieved using an ionic liquid (Pyr). 14 A small amount of LiTFSI was added to TFSI; first, LiTFSI was dissolved in an ionic liquid (Pyr). 14 TFSI) (LiTFSI: Pyr 14 TFSI = 0.05~0.1 molar ratio, preferably 0.05), forming 0.15M~0.2M LiTFSI-Pyr 14 TFSI (preferably 0.15M) homogeneous solution modifies nickel-cobalt-manganese / nickel-cobalt-aluminum ternary cathode materials (preferably Li[Ni 0.8 Co 0.1 Mn 0.1 O2).

[0017] A third objective of this invention is to provide an ionic liquid gel interface buffer layer modified positive electrode, comprising a positive electrode sheet formed by pressing a positive electrode material, a binder, and a conductive agent, wherein the surface of the positive electrode sheet has the interface buffer layer using an ionic liquid gel as the interface buffer layer.

[0018] Preferably, the cathode material is selected from one or more of layered transition metal oxide lithium cobalt oxide, polyanionic lithium iron phosphate, spinel lithium manganese oxide, lithium-rich manganese-based cathode material, nickel-cobalt-manganese ternary cathode material, and nickel-cobalt-aluminum ternary cathode material; more preferably, nickel-cobalt-manganese ternary cathode material.

[0019] Preferably, the chemical formula of the nickel-cobalt-manganese / nickel-cobalt-aluminum ternary cathode material is Li[Ni] 1-x-y Co x M2 y O2 and M2 include one or more of Al and Mn, 0 < x ≤ 0.2, 0 < y ≤ 0.2, with Mn being the preferred element.

[0020] The fourth objective of this invention is to provide a method for preparing a positive electrode modified by an ionic liquid gel interface buffer layer, wherein the positive electrode material, binder, and conductive agent are weighed according to a preset ratio and then ground in a mortar to obtain a positive electrode mixture; the positive electrode mixture is pressed into a positive electrode sheet, and the organic-inorganic mixed matrix ionic liquid gel is cast onto the surface of the positive electrode sheet and left to stand to form a gel film (coating), thereby obtaining a positive electrode material modified by an ionic liquid gel interface coating.

[0021] In this invention, the ionic liquid gel coating serves as an ion-conducting interface buffer layer. The coexistence of electrostatic charge, aromatic groups, and alkyl segments in its ionic structure enables the ionic liquid to have good affinity for both inorganic and organic materials, and to achieve good interfacial compatibility with the cathode material.

[0022] The fifth objective of this invention is to provide a sulfide-based all-solid-state lithium battery comprising the ionic liquid gel interface buffer layer modified cathode.

[0023] Ionic liquids possess unique properties such as ultra-low volatility, good thermal stability, low flammability, tunable polarity and acidity / alkalinity, and ionic conductivity. These properties give them great promise in various chemical processes, with energy storage being one of the most promising areas. The low volatility and low flammability of ionic liquids make them significantly safer than molecular solvents. Their wide electrochemical window and good thermal stability further enhance their feasibility. The coexistence of electrostatic charges, aromatic groups, and alkyl segments in their ionic structures gives ionic liquids good affinity for both inorganic and organic materials, which is beneficial for preparing composite battery cathode materials, improving interfacial properties, and generating ordered nanostructures. Ionic liquids are confined as dispersed or liquid phases within or dispersed throughout a continuous solid phase, including inorganic, organic, and organic-inorganic hybrid matrices, thus achieving ionic liquid gelation. Ionic liquid gels are mainly prepared through five methods: sol-gel, solvent casting, matrix swelling in ionic liquids, hot pressing, and in-situ polymerization. The incorporated ionic liquid acts as both a plasticizer and a charge carrier, and the conductivity of the ionic liquid gel can reach 10 at 25 °C. -2 S cm -1 Compared to solid electrolytes (10 -8 ~10 -5 S cm -1 The efficiency is significantly improved, and the ionic liquid gel exhibits better mechanical flexibility and better electrode / electrolyte interface contact. Furthermore, due to the Li... + Diffusion can occur through ionic liquid gel channels, and the ionic gel buffer layer can enhance Li... + migration rate.

[0024] Inorganic matrices are generally advantageous in terms of thermal stability, mechanical strength, and safety, and silica is the most commonly used inorganic matrix for confining ionic liquids. Silica-based ionogels can be readily obtained via in-situ sol-gel and in-situ gel methods, exhibiting not only superior safety but also relatively high ionic conductivity and good mechanical strength. However, the relatively low dielectric constant of silica particles makes it difficult for ionogels to dissociate lithium salts, and also hinders the dissociation of lithium salts by Li. + Conductivity is hindered. The organic polymer matrix primarily uses polymers including polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyethylene oxide (PEO), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), and polyacrylonitrile (PAN). However, the neutral structure of these polymers results in weak interactions with ionic liquids, leading to poor compatibility and a tendency for phase separation. Furthermore, their neutral structure imbues them with inherent inertness, thus limiting the conductivity of the constructed ionic gel.

[0025] This invention synthesizes ionic gels by confining ionic liquids within an organic-inorganic hybrid matrix, thus combining the advantages of both inorganic and organic matrices. Introducing inorganic nanoparticles into the polymer ionic gel improves its mechanical properties while maintaining its flexibility.

[0026] This invention employs an ionic liquid coating as an interfacial buffer layer to modify the cathode material. The ionic liquid coating blocks the interdiffusion of elements between the electrode and the electrolyte, balances the chemical potential at the interface, suppresses the formation of a space charge layer, and inhibits the occurrence of side reactions. It can also serve as a Li-rich coating. + The ion transport channels enhance Li + The improved mobility enables favorable interfacial dynamics, effectively enhancing the battery's coulombic efficiency, rate performance, and cycle stability.

[0027] This invention modifies the cathode material using an ionic liquid gel buffer interface layer, reducing direct contact between the high-nickel cathode material and the sulfide solid electrolyte. This alleviates interfacial contact issues between the high-nickel cathode material and the electrolyte layer, resolving a series of interface problems arising from direct contact, including interfacial side reactions and impaired ion conduction. It also addresses the problems of high impedance due to the electronic insulation of oxide coatings and avoids side reactions caused by direct contact between the high-nickel cathode material and the sulfide solid electrolyte. The ionic liquid gel coating acts as a buffer layer, providing a "soft" buffer space that blocks interdiffusion of elements between the electrode and electrolyte, balances the chemical potential at the interface, and suppresses the formation of a space charge layer, thereby improving battery cycle stability. The interface buffer layer, as a Li-rich... + The ion transport channels enhance Li + The high mobility of the ionic liquid enables favorable interfacial dynamics, effectively improving the coulombic efficiency, rate performance, and cycle stability of the battery. Furthermore, the good wettability of the ionic liquid can appropriately alleviate the problem of high interfacial impedance. Attached Figure Description

[0028] Figure 1 This is a rate performance diagram of a sulfide-based all-solid-state lithium battery according to an embodiment of the present invention. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0030] This invention provides an ionic liquid gel for an interface buffer layer, which is used to be placed on the surface of a positive electrode sheet as a buffer interface to modify the positive electrode material. It is composed of an organic-inorganic mixed matrix ionic gel; the organic-inorganic mixed matrix ionic gel includes an organic matrix, an inorganic matrix and an ionic liquid, and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0031] In a preferred embodiment of the present invention, the anion of the ionic liquid comprises bis(trifluoromethanesulfonyl)imide (TFSI). - ), BF4 - and PF6 - The cations of the ionic liquid include imidazole, pyrrole, and short-chain aliphatic quaternary ammonium salts, which are large organic ions.

[0032] In a preferred embodiment of the present invention, the ionic liquid is selected from N-methoxyethyl-N-methylpyrrolidine-onium bis(trifluoromethanesulfonyl)imine ([Pyr1(2O1)]TFSI), N-hexyl-N-methylpyrrolidine-onium bis(trifluoromethanesulfonyl)imine, and N-butyl-N-methylpyrrolidine-onium bis(trifluoromethanesulfonyl)imine (Pyr 14 One or more of TFSI, preferably Pyr 14 TFSI.

[0033] In a preferred embodiment of the present invention, the inorganic matrix is ​​selected from one or more of SiO2, TiO2, and Al2O3. In a preferred embodiment of the present invention, the organic matrix is ​​selected from one or more of PVDF-HFP, PEO, PMMA, PVC, and PAN.

[0034] An embodiment of the present invention provides a method for preparing an interfacial buffer layer ionic liquid gel, comprising the following steps: adding lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to an ionic liquid and heating to obtain a homogeneous solution; dissolving an organic matrix in a solvent, adding the homogeneous solution and stirring to dissolve; adding an inorganic matrix precursor to the above solution using a one-pot sol-gel method, reacting under stirring, wherein the inorganic matrix is ​​generated in situ and uniformly dispersed in the solution to obtain an organic-inorganic mixed matrix ionic liquid gel.

[0035] Wherein, the molar ratio of lithium bis(trifluoromethanesulfonyl)imide to ionic liquid is 0.05~0.1; preferably, in the organic-inorganic mixed matrix ionic liquid gel, the organic matrix, inorganic matrix, lithium bis(trifluoromethanesulfonyl)imide-ionic liquid each account for 15%-30%, 5%-15%, and 60%-80% by mass percentage.

[0036] The ionic liquid is preferably Pyr. 14 TFSI, to prevent the introduction of an ionic liquid layer from reducing Li +The transmission effect, during fabrication, is achieved using an ionic liquid (Pyr). 14 A small amount of LiTFSI was added to TFSI; first, LiTFSI was dissolved in an ionic liquid (Pyr). 14 TFSI) (LiTFSI: Pyr 14 TFSI = 0.05~0.1 molar ratio, preferably 0.05), forming 0.15M~0.2M LiTFSI-Pyr 14 TFSI (preferably 0.15M) homogeneous solution modifies nickel-cobalt-manganese / nickel-cobalt-aluminum ternary cathode materials (preferably Li[Ni 0.8 Co 0.1 Mn 0.1 O2).

[0037] An embodiment of the present invention provides an ionic liquid gel interface buffer layer modified positive electrode, comprising a positive electrode sheet formed by pressing a positive electrode material, a binder, and a conductive agent, wherein the positive electrode sheet has an interface buffer layer using an ionic liquid gel as the interface buffer layer.

[0038] In a preferred embodiment of the present invention, the cathode material is selected from one or more of layered transition metal oxide lithium cobalt oxide, polyanionic lithium iron phosphate, spinel lithium manganese oxide, lithium-rich manganese-based cathode material, nickel-cobalt-manganese ternary cathode material, and nickel-cobalt-aluminum ternary cathode material; preferably, a nickel-cobalt-manganese ternary cathode material is used. 1-x-y Co x M2 y O2 and M2 include one or more of Al and Mn, 0 < x ≤ 0.2, 0 < y ≤ 0.2, with Mn being the preferred element.

[0039] An embodiment of the present invention provides a method for preparing a positive electrode modified by an ionic liquid gel interface buffer layer. The positive electrode material, binder and conductive agent are weighed according to a preset ratio and then ground in a mortar to obtain a positive electrode mixture. The positive electrode mixture is pressed into a positive electrode sheet, and the ionic liquid gel is cast onto the surface of the positive electrode sheet and left to stand to form a gel film (coating), thereby obtaining a positive electrode material modified by an ionic liquid gel interface coating.

[0040] In this invention, the ionic liquid gel coating serves as an ion-conducting interface buffer layer. The coexistence of electrostatic charge, aromatic groups, and alkyl segments in its ionic structure enables the ionic liquid to have good affinity for both inorganic and organic materials, and it can achieve good interfacial compatibility with the cathode material.

[0041] This invention provides a sulfide-based all-solid-state lithium battery, comprising a positive electrode modified by the ionic liquid gel interface buffer layer.

[0042] Below, we select PVDF as the preferred organic matrix, SiO2 as the inorganic matrix, and Pyr as the ionic liquid. 14 TFSI describes the embodiments of this application.

[0043] Example 1

[0044] 1. LiTFSI-Pyr 14 Preparation of homogeneous TFSI solution:

[0045] Take 0.007 mol LiTFSI and add it to 0.14 mol Pyr 14 0.15 M LiTFSI-Pyr was obtained by heating at 70 °C for 3 h in TFSI. 14 TFSI homogeneous solution.

[0046] 2. Preparation of ionic liquid gels:

[0047] Dissolve PVDF-HFP in NMP solvent, then add LiTFSI-Pyr 14 A homogeneous TFSI solution was prepared and dissolved by stirring. A SiO2 precursor (tetraethyl orthosilicate, TEOS) was added to the solution using a one-pot sol-gel method, and the reaction was carried out for 8 hours with stirring. SiO2 was directly generated in situ and uniformly dispersed in the solution. An organic-inorganic mixed matrix ionogel was synthesized, in which PVDF-HFP:SiO2:LiTFSI-Pyr 14 The mass ratio of TFSI is 30%:10%:60%.

[0048] 3. Preparation of high-nickel cathode materials modified by ionic liquid gel interface layer:

[0049] The cathode material Li[Ni 0.9 Co 0.05 Mn 0.05 O2, binder PVDF, and conductive agent Super P were weighed in a ratio of 80%:10%:10% (wt%) and ground in a mortar for 1 hour to obtain a positive electrode mixture. 200 mg of the positive electrode mixture was weighed and placed in a pressure battery mold with a diameter of 10 mm. The powder was rotated and flattened by rotating a stainless steel column and pressed into a sheet on a tablet press at a pressure of 360 MPa for 2 minutes. 20 µL of the above ionic liquid gel was cast onto the pressed positive electrode sheet and allowed to stand for 2 hours to form a gel film, thus obtaining a high-nickel positive electrode material modified with an ionic liquid gel interface coating.

[0050] Example 2

[0051] The mass ratio of PVDF-HFP:SiO2:LiTFSI-Pyr14TFSI is 22.5%:7.5%:70%, and the other steps are the same as in Example 1.

[0052] Example 3

[0053] The mass ratio of PVDF-HFP:SiO2:LiTFSI-Pyr14TFS is 15%:5%:80%, and the other steps are the same as in Example 1.

[0054] Example 4

[0055] The mass ratio of PVDF-HFP:SiO2:LiTFSI-Pyr14TFS is 15%:15%:70%, and the other steps are the same as in Example 1.

[0056] Example 5

[0057] The mass ratio of PVDF-HFP:SiO2:LiTFSI-Pyr14TFS is 20%:10%:70%, and the other steps are the same as in Example 1.

[0058] Comparative Example 1

[0059] PVDF-HFP: LiTFSI-Pyr without added inorganic matrix 14 The mass ratio of TFSI to the two is 30%:70%, and the other steps are the same as in Example 1.

[0060] Comparative Example 2

[0061] Without adding an organic polymer matrix, SiO2: LiTFSI-Pyr 14 The mass ratio of TFSI to the two is 30%:70%, and the other steps are the same as in Example 1.

[0062] Comparative Example 3

[0063] The cathode was not modified with an ionic liquid gel interface layer; the other steps were the same as in Example 1.

[0064] The battery mold assembly and charge / discharge performance testing were conducted as follows:

[0065] 1. Battery assembly:

[0066] In an argon-filled glove box, 150 mg of LiPSCl electrolyte powder was placed in a 10 mm diameter pressure battery mold. A rotating stainless steel column was used to flatten the electrolyte powder, which was then pressed into a sheet on a tablet press at a pressure of 120 MPa for 2 minutes. The freshly pressed ionic liquid-modified high-nickel cathode material was placed in the mold, and a 10 mm diameter aluminum (Al) foil was placed on the surface of the composite cathode sheet as the cathode current collector. A silicon (Si) anode was placed on the other side of the LiPSCl electrolyte sheet, and a copper (Cu) foil was used as the current collector. After assembly, a pressure of 50 MPa was applied to obtain a sulfide all-solid-state lithium-ion battery.

[0067] 2. Test conditions:

[0068] The battery was tested for charge and discharge at 4.3V and 2.5V respectively, and its performance was tested for 100 charge and discharge cycles at 0.1C.

[0069] Table 1 Performance of Sulfide All-Solid-State Lithium-ion Batteries

[0070]

[0071] As shown in Table 1, comparing Examples 1-3, with a constant PVDF-HFP:SiO2 ratio (3:1), the charge / discharge specific capacity initially increased and then decreased with increasing ionic liquid content. This trend is attributed to the increased ionic liquid gel content and decreased mass ratio of the inorganic-organic mixed matrix. Furthermore, during the in-situ sol-gel SiO2 formation process, a continuous SiO2 network is expected to form, which can generate SiO2 / [Pyr] 14 [TFSI] Dual continuous interface, thereby improving ionic conductivity. If the inorganic-organic mixed matrix has a low mass, it is insufficient to form a continuous network structure, resulting in slow ion transport and reduced charge / discharge capacity. When the ionic liquid gel content is low, the amorphous state of the ionic liquid gel also affects the capacity. Therefore, when the ionic liquid gel content is moderate, with a mass percentage of 70%, it has a better ion transport channel, and the charge / discharge capacity can be fully utilized. Example 2 has the optimal ratio, with a discharge specific capacity of 191.79 mAh / g and a high coulombic efficiency, with an initial efficiency of over 85%. After 100 cycles, the discharge capacity remains above 98%.

[0072] Comparing Examples 2, 4, and 5, it can be seen that when the ionic liquid gel content is constant, adjusting the PVDF-HFP:SiO2 ratio results in optimal performance when the SiO2 content is 10%, achieving a discharge specific capacity of 193.82 mAh / g. This is because with a low SiO2 content, a discontinuous SiO2 network structure is formed, and the interface buffer layer is amorphous, affecting ion transport performance and preventing the full utilization of the charge / discharge specific capacity. With a high SiO2 content, the relatively low dielectric constant of the SiO2 particles makes it difficult for the ionic gel to dissociate the lithium salt, and also affects the Li... + Conduction is hindered, resulting in reduced discharge capacity and decreased cycle stability.

[0073] Comparing Examples 1-5 with Comparative Examples 1-2, it can be seen that when only PVDF-HFP or only SiO2 is added, the discharge specific capacity is significantly reduced. This is because the relatively low dielectric constant of pure SiO2 particles makes it difficult for the ion gel to dissociate the lithium salt, and also affects the Li... + Conductivity is hindered because the neutral structure of the simple organic polymer matrix results in weak interaction with the ionic liquid, leading to poor compatibility and easy phase separation. This limits the conductivity of the constructed ionic gel. Both of these factors contribute to a decrease in discharge capacity, as well as a decline in cycle and rate performance. Comparing Examples 1-5 with Comparative Example 3, it is evident that Comparative Example 3, which directly contacts the cathode material with a sulfide solid electrolyte, suffers from solid-solid interface problems, including side reactions, high interfacial impedance, and poor ion transport performance. Consequently, the battery's cycle and rate performance are significantly worse than that of the cathode material modified with the ionic liquid gel interface layer.

[0074] It can be seen that ionic liquids play multiple roles in the formation of mixed ion and electronic conductivity networks, including enhancing solid / solid interface contact, providing ion migration channels, and providing a "soft" buffer space for volume expansion during cycling. The interface buffer layer modified cathode material of this application is one of the effective strategies to improve the thermal and structural stability of the cathode material and sulfide electrolyte interface. This method can form a protective layer on the electrode material surface, which has many beneficial effects on the electrode material, including improving the ionic conductivity of the cathode material, promoting electron transfer, and Li... + Diffusion, stabilizing surface structure, and preventing direct contact between cathode material and electrolyte are all benefits of interfacial buffer layers. These layers enable favorable interfacial dynamics, effectively improving the battery's coulombic efficiency, rate performance, and cycle stability. Ionic liquids play multiple roles in forming mixed ionic and electronic conductive networks, including enhancing solid / solid interface contacts, providing ion migration channels, and offering a "soft" buffer for volume expansion during cycling.

[0075] This invention addresses the problems of electronic insulation, impeded ion transport, and high impedance properties associated with oxide coatings by providing an ionic liquid gel interfacial buffer layer to modify cathode materials. Furthermore, it avoids side reactions arising from direct contact between high-nickel cathode materials and sulfide solid electrolytes. The ionic liquid gel coating serves as an interfacial buffer layer, blocking interdiffusion of elements between the electrode and electrolyte, balancing the chemical potential at the interface, and suppressing the formation of a space charge layer. This interfacial buffer layer acts as a Li-rich... + The ion transport channels enhance Li + By increasing the mobility of the cells and achieving favorable interface dynamics, this strategy effectively improves the coulombic efficiency, rate performance, and cycle stability of the cells.

[0076] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention.

[0077] Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of the equivalents of the claims be included within the invention.

[0078] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An ionic liquid gel for the interface buffer layer, characterized in that, Used as a buffer interface on the surface of the positive electrode to modify the positive electrode material, it is composed of an organic-inorganic mixed matrix ion gel, which includes an organic matrix, an inorganic matrix and an ionic liquid, and lithium bis(trifluoromethanesulfonyl)imide.

2. The ionic liquid gel for the interface buffer layer according to claim 1, characterized in that, The anions of the ionic liquid include bis(trifluoromethylsulfonyl)imide and BF4. - and PF6 - The cations of the ionic liquid include imidazole, pyrrole, and short-chain aliphatic quaternary ammonium salts, which are large organic ions.

3. The ionic liquid gel for the interface buffer layer according to claim 2, characterized in that, The ionic liquid is selected from one or more of N-methoxyethyl-N-methylpyrrolidine-onium bis(trifluoromethanesulfonyl)imine, N-hexyl-N-methylpyrrolidine-onium bis(trifluoromethanesulfonyl)imine, and N-butyl-N-methylpyrrolidine-onium bis(trifluoromethanesulfonyl)imine.

4. The ionic liquid gel for the interface buffer layer according to claim 1, characterized in that, The inorganic matrix is ​​selected from one or more of SiO2, TiO2, and Al2O3; Preferably, the organic matrix is ​​selected from one or more of PVDF-HFP, PEO, PMMA, PVC, and PAN.

5. A method for preparing the ionic liquid gel for the interface buffer layer according to any one of claims 1-4, characterized in that, Including the following steps: The lithium bis(trifluoromethanesulfonyl)imide was added to an ionic liquid and heated to obtain a homogeneous solution; The organic matrix is ​​dissolved in a solvent and added to the homogeneous solution and stirred to dissolve. The precursor of the inorganic matrix is ​​added to the above solution by a one-pot sol-gel method and reacted under stirring. The inorganic matrix is ​​generated in situ and uniformly dispersed in the solution to obtain an organic-inorganic mixed matrix ionic liquid gel. Preferably, the molar ratio of lithium bis(trifluoromethanesulfonylimide) to the ionic liquid is 0.05 to 0.1; Preferably, in the organic-inorganic mixed matrix ionic liquid gel, the organic matrix, inorganic matrix, and lithium bis(trifluoromethanesulfonyl)imide ionic liquid each account for 15%-30%, 5%-15%, and 60%-80% by mass percentage.

6. A positive electrode modified with an ionic liquid gel interface buffer layer, characterized in that, It includes a positive electrode sheet formed by pressing a positive electrode material, a binder, and a conductive agent, wherein the surface of the positive electrode sheet has an interface buffer layer as described in any one of claims 1-4, using an ionic liquid gel as the interface buffer layer.

7. The positive electrode modified with an ionic liquid gel interface buffer layer according to claim 6, characterized in that, The cathode material is selected from one or more of the following: layered transition metal oxide lithium cobalt oxide, polyanionic lithium iron phosphate, spinel lithium manganese oxide, lithium-rich manganese-based cathode material, nickel-cobalt-manganese ternary cathode material, and nickel-cobalt-aluminum ternary cathode material; preferably, nickel-cobalt-manganese ternary cathode material.

8. The positive electrode modified with an ionic liquid gel interface buffer layer according to claim 7, characterized in that, The chemical formula of the nickel-cobalt-manganese / nickel-cobalt-aluminum ternary cathode material is Li[Ni 1-x-y Co x M2 y O2, M2 includes one or more of Al and Mn, 0 < x ≤ 0.2, 0 < y ≤ 0.

2.

9. A method for preparing the ionic liquid gel interface buffer layer modified positive electrode according to any one of claims 6-8, characterized in that, The positive electrode material, binder, and conductive agent are weighed according to a preset ratio and then ground in a mortar to obtain a positive electrode mixture. The positive electrode mixture is pressed into a positive electrode sheet, and the organic-inorganic mixed matrix ionic liquid gel is cast onto the surface of the positive electrode sheet and left to stand to form a gel film, thus obtaining an ionic liquid gel interface coating modified positive electrode.

10. A sulfide-based all-solid-state lithium battery, characterized in that, The positive electrode comprises the ionic liquid gel interface buffer layer as described in any one of claims 6-8.

Images