A hybrid positive electrode for solid-state batteries, a corresponding battery and a method of preparation

Abstract

The application belongs to a kind of mixed positive electrode for solid-state battery, the corresponding battery and preparation method, wherein the preparation method of the mixed positive electrode for solid-state battery comprises the following steps: mixing iodine-containing material and lithium battery positive electrode material according to a certain proportion, grinding uniformly, mixing the mixed material, conductive carbon material and binder, solvent to prepare a uniform slurry, coating on aluminum foil, vacuum drying, to obtain an iodine ion added mixed positive electrode; under the action of iodine, it can not only promote the internal charge transfer of the electrode, but also effectively promote the transmission of lithium ions, effectively improve the cycle rate performance of the solid-state battery, and the preparation method is simple and suitable for large-scale industrial application.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of new energy batteries, and particularly relates to a preparation method of a mixed positive electrode for a solid-state battery, a mixed positive electrode prepared by the method, and a corresponding battery. BACKGROUND

[0002] All-solid-state lithium batteries (ASSLBs) are promising energy storage devices, but their energy and power densities are still inferior to those of lithium-ion batteries (LIBs) with liquid electrolytes (LEs). Although improving the ionic conductivity of solid-state electrolytes (SSEs) is key to improving the performance of ASSLBs, the mass transport within the entire battery is still insufficient. During battery operation, the ion-permeable network in the composite positive electrode is crucial for maintaining the electrochemical reactions of the positive active material (CAM).

[0003] In traditional LIBs, the porous nature of the positive electrode allows LEs to easily penetrate, ensuring good ion transport. However, in composite positive electrodes, SSEs have difficulty establishing continuous ion transport channels, leading to low CAM utilization and limited capacity output. In addition, there is a large energy barrier for lithium ion transport at the interface, and incompatible solid-solid contact and side reactions further increase impedance, reducing capacity retention. Therefore, to ensure high-performance ASSLBs, it is crucial to design the microstructure of the solid-state positive electrode to establish an efficient ion-permeable network.

[0004] Although additional ion diffusion paths can be provided by controlling crystal structures, surface modification, pore adjustment, and ion conduction path optimization to help establish an efficient ion-permeable network, these solid-state positive electrodes still face the challenges of low CAM load (typically less than 5 mg cm -2 ) and poor rate performance. For the practical application of ASSLBs, designing a composite positive electrode that can operate at high load and appropriate current density is a key problem that must be solved. However, increasing the CAM load will bring performance limitations related to ion permeation in the solid-state positive electrode. Increasing the positive electrode thickness / or shortening the charge / discharge interval will exacerbate the ion concentration gradient along the depth of the positive electrode, leading to increased polarization and insufficient utilization of CAM. In view of the current problems of solid-state batteries, such as poor electrochemical performance at high load positive electrodes, slow mass transport within the electrode, etc.

[0005] Typical prior art records: Traditional lithium-ion battery positive electrode materials, such as lithium iron phosphate (LiFePO4) and ternary materials (NCM, NCA), have been widely used in liquid electrolyte batteries. However, these materials exhibit certain limitations in solid-state batteries, mainly due to the large interfacial resistance between the solid-state electrolyte and the positive electrode material, which affects the transmission efficiency of lithium ions.

[0006] J. Am. Chem. Soc. 2022, 144, 32, 14638–14646Iodine ions (I⁻) have been studied as additives in liquid batteries to some extent, which can improve the electrochemical performance of the battery to some extent. For example, some studies have shown that lithium iodide (LiI) can be used as an electrolyte additive to improve the cycle stability of lithium-ion batteries, but its application in solid-state battery cathodes has not been fully studied.

[0007] The prior art describes the addition of additives to improve the performance of the cathode: CN202311665592.4, some research work attempts to add conductive additives or ion conductors to the cathode material to improve the overall performance of the battery. For example, adding conductive materials such as carbon nanotubes and graphene can improve the conductivity of the cathode, thereby improving the rate performance of the battery. The effect of these additives is limited, and the cost of materials and the complexity of the preparation process are increased.

[0008] Through the interface modification technology CN202210142540.8, by introducing an interface modification layer (such as coating a thin film with high conductivity) at the interface between the solid-state electrolyte and the cathode material, the interface resistance can be effectively reduced, and the transmission efficiency of lithium ions can be improved. This coating technology is costly and difficult to be widely used.

[0009] CN201910385205.9 proposes to use composite cathode materials to synergistically improve battery performance, for example, lithium iron phosphate and lithium cobaltate are combined to take advantage of the safety of the former and the high energy density of the latter. Although this method improves the performance of the battery to some extent, it still has shortcomings in improving the cycle rate performance, and the material selection and composite process need to be carefully controlled.

[0010] The present application aims to provide a mixed cathode for solid-state batteries that can promote charge transfer within the electrode and effectively promote the transmission of lithium ions, effectively improving the cycle rate performance of solid-state batteries, and the preparation method is simple and suitable for large-scale industrial application. SUMMARY

[0011] To overcome the shortcomings of existing solid-state batteries, such as poor battery performance, complex preparation process, and high cost, the present application provides a mixed cathode for solid-state batteries, a corresponding battery, and a preparation method.

[0012] In a first aspect, the present application provides a preparation method for a mixed cathode for solid-state batteries, the synthesis method comprising the following steps:

[0013] (1) selecting a certain amount of iodine-containing material A1 and lithium battery cathode material A2;

[0014] Mixing A1 and A2 to obtain a mixed material A.

[0015] Further, the iodine-containing element material A1 is one or more of methylamine hydroiodide, tetrabutylammonium triiodide, imidazole hydroiodide, 1-iodoferrocene, iodinated polyacrylonitrile, lithium iodide, sodium iodide, potassium iodide, iodomethane; the lithium battery positive electrode material A2 is one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium manganate, etc.; and the mass ratio of the iodine-containing material A1 and the lithium battery positive electrode material A2 is 0.1-10.

[0016] (2) The mixture A is ground in a corundum mortar to form fine particles to obtain a mixed material C.

[0017] Further, the grinding time of the mixture A in the corundum mortar in step (2) is 1-6 hours.

[0018] (3) The mixed material C, a conductive agent D, a binder E, and a solvent F are ground in a ball mill to obtain a mixed slurry G.

[0019] Further, the grinding time in step (3) is 1-6 hours.

[0020] (4) The mixed slurry G is coated on a carbon-coated aluminum foil, and the coating thickness is 10-100 microns.

[0021] (5) The coated aluminum foil is dried in a vacuum environment at a drying temperature of 50-110°C to obtain an iodine-containing added mixed positive electrode.

[0022] Further, the drying time in step (5) is 6-12 hours.

[0023] Further, the conductive agent in step (3) is one or more of graphite, carbon nanotubes, acetylene black, and graphene.

[0024] Further, the binder E in step (3) is one or more of polyvinylidene fluoride, butadiene rubber, carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, and polyacrylate.

[0025] Further, the solvent in step (3) is one or more of N,N-dimethylformamide, acetonitrile, tetrahydrofuran, ethylene glycol dimethyl ether, N-methylpyrrolidone, anisole, dimethyl sulfoxide, and acetone.

[0026] Further, the mass ratio of the mixed material C, the conductive agent D, and the binder E in step (1) is 8:1:1.

[0027] Further, the ball milling adopts a planetary ball mill, at a rotation speed of 100-1000 r / min, ball milling for 1-6 hours, preferably, at a rotation speed of 200-800 r / min, ball milling for 2-5 hours; at a rotation speed of 400-600 r / min, ball milling for 4-6 hours.

[0028] In a second aspect, the present application further provides a hybrid cathode for solid-state batteries, prepared by the method of the first aspect.

[0029] In a third aspect, the present application further provides a battery, comprising the hybrid cathode of the second aspect and a lithium metal negative electrode and a polyethylene oxide solid-state electrolyte.

[0030] Further, the battery can be stably cycled at least 1000 times at a 2C high rate in a test voltage range of 2.0-3.8 V, and can be stably operated at least 50 cycles at a 0.1C rate. -2 Further, the battery can be stably cycled at least 1000 times at a 2C high rate in a test voltage range of 2.0-3.8 V, and can be stably operated at least 50 cycles at a 0.1C rate.

[0031] The present application has the following advantages:

[0032] 1) The present application improves the ion transport and charge transfer in the interior of the hybrid cathode material of the solid-state battery by introducing iodine-containing materials, which is beneficial to comprehensively improving the electrochemical performance of the solid-state battery.

[0033] 2) The present application improves the long cycle and rate performance of the hybrid cathode material of the solid-state battery by introducing iodine-containing materials. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 SEM image of the hybrid cathode of the iodine-containing material prepared in Example 2;

[0035] Figure 2 Cycle test chart of battery performance comparison of different examples;

[0036] Figure 3 Long cycle test chart of the solid-state battery of Example 2 at a 2C high rate;

[0037] Figure 4 Cycle test chart of the solid-state battery of Example 2 at a 0.1C rate under high load;

[0038] Figure 5 Electrochemical impedance test chart of the hybrid cathode of the iodine-containing material and the non-iodine-containing material. DETAILED DESCRIPTION

[0039] In order to better understand the present application, the following examples are further illustrations of the present application, but the content of the present application is not limited to the following examples. Example 1

[0040] (1) Lithium iodide and lithium iron phosphate were mixed in a mass ratio of 1:100 in a agate mortar, and ground for 30 min to obtain mixed material A.

[0041] (2) Mixed material A was ground in a agate mortar for 4 hours to ensure that the materials were fully and uniformly mixed to form fine particles, obtaining mixed material C.

[0042] (3) Mixed material C, conductive agent acetylene black, binder polyvinylidene fluoride, solvent N-methyl pyrrolidone were mixed in a mass ratio of 8:1:1:10 in a ball mill for 3 hours to obtain mixed slurry G.

[0043] (4) The mixed slurry G was coated on a carbon-coated aluminum foil with a coating thickness of about 50 microns to ensure uniform distribution.

[0044] (5) The coated aluminum foil was dried in a vacuum environment at a drying temperature of 80°C for 8 hours to ensure complete evaporation of the solvent, obtaining an iodine-containing added mixed positive electrode.

[0045] (6) Polyethylene oxide and lithium trifluoromethylsulfonylimide were weighed in a molar ratio of 16:1, dissolved in an appropriate amount of acetonitrile, stirred at 60°C for 12 h until the slurry became viscous. Then the slurry was put into a polytetrafluoroethylene mold, and then transferred to a vacuum drying oven and dried at 80°C for 12 h. The dried product was cut into a size of 16 mm in diameter with a cutting machine and used as a solid-state electrolyte film.

[0046] (7) A 2025 type button solid-state battery was assembled in a super-purified glove box (water and oxygen content was less than 0.1 ppm) with lithium metal sheet as the negative electrode, the mixed positive electrode containing iodine element material prepared in steps 1-5 as the positive electrode, and the solid-state electrolyte film prepared in step 6 as the electrolyte. Example 2

[0047] (1) Methylamine hydroiodide and lithium iron phosphate were mixed in a mass ratio of 1:7 in a agate mortar, and ground for 30 min to obtain mixed material A.

[0048] (2) Mixed material A was ground in a agate mortar for 4 hours to ensure that the materials were fully and uniformly mixed to form fine particles, obtaining mixed material C.

[0049] (3) Mixed material C, conductive agent acetylene black, binder polyvinylidene fluoride, solvent N-methyl pyrrolidone were mixed in a mass ratio of 8:1:1:20 in a ball mill for 6 hours to obtain mixed slurry G.

[0050] (4) The mixed slurry G is applied to the carbon-coated aluminum foil with a coating thickness of about 25 microns to ensure uniform distribution.

[0051] (5) The coated aluminum foil is dried in a vacuum environment, usually at a drying temperature of 60°C for 12 hours to ensure complete evaporation of the solvent, obtaining an iodine-containing mixed positive electrode.

[0052] (6) Polyethylene oxide and lithium trifluoromethyl sulfonimide are weighed according to a molar ratio of 16:1, dissolved in an appropriate amount of acetonitrile, stirred at 60°C for 12 hours until the slurry becomes viscous. Then the slurry is put into a polytetrafluoroethylene mold, and then transferred to a vacuum drying oven, dried at 80°C for 12 hours. The dried product is cut into a size of 16mm in diameter with a film cutter for standby, obtaining a polyethylene oxide polymer solid-state electrolyte film.

[0053] (7) The other assembly steps of the solid-state battery are the same as in Example 1. Example 3

[0054] (1) Iodine-containing material methylamine hydroiodide and lithium iron phosphate positive electrode material are weighed in a mass ratio of 100:1 and mixed in a agate mortar, and ground for 30 minutes to obtain mixed material A.

[0055] (2) The mixed material A is ground in a agate mortar for 8 hours to ensure that the materials are fully and uniformly mixed to form fine particles, obtaining mixed material C.

[0056] (3) Mixed material C, conductive agent acetylene black, binder polyvinylidene fluoride, and solvent N-methyl pyrrolidone are weighed in a mass ratio of 8:1:1:5 in a ball mill and ground for 10 hours to obtain mixed slurry G.

[0057] (4) The mixed slurry G is applied to the carbon-coated aluminum foil with a coating thickness of about 15 microns to ensure uniform distribution.

[0058] (5) The coated aluminum foil is dried in a vacuum environment, usually at a drying temperature of 60°C for 12 hours to ensure complete evaporation of the solvent, obtaining an iodine-containing mixed positive electrode.

[0059] (6) Polyethylene oxide and lithium trifluoromethyl sulfonimide are weighed according to a molar ratio of 16:1, dissolved in an appropriate amount of acetonitrile, stirred at 60°C for 12 hours until the slurry becomes viscous. Then the slurry is put into a polytetrafluoroethylene mold, and then transferred to a vacuum drying oven, dried at 80°C for 12 hours. The dried product is cut into a size of 16mm in diameter with a film cutter for standby, obtaining a polyethylene oxide polymer solid-state electrolyte film.

[0060] (7) The other assembly steps of the solid-state battery are the same as in Example 1. Comparative Example 1

[0061] (1) Lithium battery cathode material lithium iron phosphate was weighed and mixed in a agate mortar, and ground for 30 min to obtain mixed material A.

[0062] (2) Mixed material A was ground in a agate mortar for 4 hours to ensure that the materials were fully and uniformly mixed, and fine particles were formed to obtain mixed material C.

[0063] (3) Mixed material C, conductive agent acetylene black, binder polyvinylidene fluoride, and solvent N-methyl pyrrolidone were mixed in a mass ratio of 8:1:1:20 in a ball mill for 6 hours to obtain mixed slurry G.

[0064] (4) The mixed slurry G was coated on a carbon-coated aluminum foil with a coating thickness of about 25 microns to ensure uniform distribution.

[0065] (5) The coated aluminum foil was dried in a vacuum environment, usually at a drying temperature of 60°C for 12 hours to ensure complete evaporation of the solvent, and a mixed cathode was obtained.

[0066] (6) Polyethylene oxide and lithium trifluoromethyl sulfonimide were weighed in a molar ratio of 16:1, dissolved in an appropriate amount of acetonitrile, and stirred at 60°C for 12 h until the slurry became viscous. Then the slurry was put into a polytetrafluoroethylene mold and transferred to a vacuum drying oven, dried at 80°C for 12 h. The dried sample was cut into a size of 16 mm in diameter with a cutting machine and used as a polyethylene oxide polymer solid electrolyte membrane.

[0067] (7) The other assembly steps of the solid-state battery were the same as in Example 1.

[0068] Performance test

[0069] The 2025 type button solid-state batteries assembled with the mixed cathodes prepared in Examples 1, 2, 3 and Comparative Example 1 were tested for cycle performance on a Blue Electric Cell Tester, wherein the test voltage range was 2.0~3.8V, and the constant current charge and discharge test was carried out at a rate of 0.5C. Figure 2 It can be seen that after 100 cycles, the batteries of Example 2, Examples 1, 2, 3 and Comparative Example 1 have discharge specific capacities of 2.9, 27.9, 165.6, 2.8 mAh / g, respectively, and it can be seen that Example 2 has good cycle stability. In addition, the battery prepared in Example 2 can be stably cycled for 1000 times at a large rate of 2C, and can be stably operated for 50 cycles at a high surface capacity of 7.1 mg cm -2 0.1C rate.

[0070] Table 1

[0071] In addition, as Figure 5The impedance test of ion-electron type symmetric battery was also used to test the ion / electron conductivity of the calculated mixed electrode, and the results are shown in Table 1. The mixed positive electrode of Example 2 added with iodine-containing material has larger ion and electron conductivity than Comparative Example 1, which shows that the addition of appropriate amount of iodine-containing element material as in the present application builds fast lithium ion transmission and fast charge transfer inside the mixed positive electrode, improves the long cycle and rate performance of the solid battery composite positive electrode.

[0072] The above-described embodiments are only preferred technical solutions of the present application and should not be regarded as limitations of the present application. The embodiments in the present application and the features in the embodiments can be combined with each other as long as there is no conflict. The protection scope of the present application should be based on the technical solutions claimed in the claims, including equivalent replacement solutions of the technical features claimed in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present application.

Claims

1. A method for producing a hybrid positive electrode for a solid-state battery, characterized by, The synthesis method comprises the following steps: (1) selecting a certain amount of iodine-containing material A1 and lithium battery positive electrode material A2; Mixing A1 and A2 to obtain a mixed material A; (2) grinding the mixture A in a agate mortar to obtain a fine particle, and obtaining a mixed material C; (3) grinding the mixed material C, conductive agent D, binder E and solvent F in a ball mill to obtain a mixed slurry G; (4) coating the mixed slurry G on a carbon-coated aluminum foil, and the coating thickness is 10-100 microns; (5) drying the coated aluminum foil in a vacuum environment at a temperature of 50-110°C to obtain an iodine-containing added mixed positive electrode; The iodine-containing material A1 is one or more of methylamine hydroiodide, tetrabutylammonium triiodide, imidazole hydroiodide, 1-iodoferrocene and iodinated polyacrylonitrile; the lithium battery positive electrode material A2 is one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide and lithium manganate; the mass ratio of the iodine-containing material A1 and the lithium battery positive electrode material A2 is 0.1-10.

2. The method of claim 1, wherein the mixed cathode for the solid-state battery is prepared by mixing the cathode active material, the solid-state electrolyte, and the conductive agent. The grinding time in step (2) is 1-6 hours, the grinding time in step (3) is 1-6 hours, and the drying time in step (5) is 6-12 hours. 3.The method of claim 1, wherein the method further comprises: mixing the lithium transition metal oxide and the solid electrolyte to form a mixture; and compressing the mixture to form the mixed cathode. The conductive agent is one or more of graphite, carbon nanotubes, acetylene black and graphene.

4. The method of claim 1, wherein the mixed cathode for the solid-state battery is prepared by mixing the cathode active material, the solid-state electrolyte, and the conductive agent. The binder E in step (3) is one or more of polyvinylidene fluoride, butadiene rubber, carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile and polyacrylate.

5. The method of claim 1, wherein the mixed cathode for the solid-state battery is prepared by mixing the cathode active material, the solid-state electrolyte, and the conductive agent. The solvent is one or more of N,N-dimethylformamide, acetonitrile, tetrahydrofuran, ethylene glycol dimethyl ether, N-methyl pyrrolidone, anisole, dimethyl sulfoxide and acetone.

6. The method of claim 1, wherein the mixed cathode for the solid-state battery is prepared by mixing the cathode active material, the solid-state electrolyte, and the conductive agent. The mass ratio of the mixed material C, the conductive agent D and the binder E in step (1) is 8:1:

1.

7. A hybrid cathode for solid-state batteries, characterized by: Prepared by the method of any one of claims 1-6.

8. A battery, characterized by The battery comprises the mixed positive electrode of claim 7 and a negative electrode composed of lithium metal and a polyethylene oxide solid-state electrolyte.

9. The battery of claim 8, wherein: at a test voltage range of 2.0-3.8 V, stable cycling at 2C high rate for at least 1000 times, and stable operation at high surface capacity of 5.6 mg cm -2 and 0.5C rate for at least 50 cycles.

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