A solid-state battery cathode material, cathode sheet, preparation method and application

Abstract

This invention discloses a solid-state battery cathode material comprising 75-85 parts lithium iron phosphate, 5-10 parts polyvinyl alcohol, 5-10 parts composite solid electrolyte Li7O2Br3, and 2-5 parts graphene. The polyvinyl alcohol is a high molecular weight polyvinyl alcohol with a molecular weight of 100,000-2,000,000. The invention also discloses a cathode sheet, its preparation method, and its application in lithium batteries. This invention utilizes polyvinyl alcohol as a binder to interact with the anti-perovskite structure of Li7O2Br3, thereby improving ionic conductivity, discharge capacity, and the recyclability of the active material. This solves the problems of relatively low ionic conductivity, low discharge capacity, and severe pollution during active material recovery in composite electrodes.

Description

Technical Field

[0001] This invention patent belongs to the field of electrochemical energy storage, specifically relating to a solid-state battery cathode material, as well as cathode sheet, preparation method, and application in lithium batteries. Background Technology

[0002] Lithium-ion batteries, with their superior energy density, excellent cycle life, and lack of memory effect, have become leading commercially available high-efficiency energy storage devices, widely used in all aspects of our daily lives and various production activities. However, despite their excellent performance, the safety hazards posed by the flammable organic electrolytes used in commercial lithium-ion batteries remain a significant challenge for their large-scale applications, particularly in electric vehicles and energy storage power stations. This safety hazard cannot be ignored, as it limits the wider application and development of lithium-ion batteries.

[0003] All-solid-state lithium-ion batteries fundamentally solve the safety hazards of lithium-ion batteries by using solid electrolytes instead of traditional organic liquid electrolytes. Currently, the research focus of the scientific community on all-solid-state lithium-ion batteries is mainly on solid electrolytes, and remarkable results have been achieved. Solid electrolytes in many systems have demonstrated performance as high as 10... - 4 With a lithium-ion conductivity of S / cm, this performance basically meets the requirements of all-solid-state lithium-ion batteries for electrolyte conductivity.

[0004] The positive electrode of a lithium-ion battery is carefully composed of a positive electrode active material, an inorganic solid-state electrolyte, and conductive additives. The inorganic solid-state electrolyte is cleverly introduced, providing an efficient transport channel for lithium ions; while the addition of conductive additives ensures unimpeded electron transport. This design not only significantly increases the contact area between the electrolyte and the positive electrode active material, effectively solving interface problems, but also shortens the migration distance of lithium ions within the positive electrode active material, especially in materials with low lithium-ion conductivity. This innovative design ensures that the positive electrode active material can fully undergo redox reactions during battery charging and discharging, thereby greatly improving battery performance. Industry experts generally believe that adopting this positive electrode structure is an indispensable key to achieving the widespread application of all-solid-state lithium-ion batteries.

[0005] Currently reported oxide electrolyte system cathodes, whether thin-film or thick-film, are generally limited to a thickness of less than 10 μm. This thickness limitation severely affects the areal capacity of the cathode, thus restricting the energy density of all-solid-state batteries. More critically, these reported cathodes do not incorporate conductive additives in their design, which greatly limits their electrochemical performance under high-rate, high-current charge-discharge conditions. Current electrodes also face challenges of low ionic conductivity and low discharge capacity. Due to insufficient ionic conductivity, the migration efficiency of lithium ions in the electrode material is limited, affecting the charge-discharge rate and capacity of the battery. Furthermore, the presence of water-insoluble binders in the electrodes hinders the recovery and reuse of active materials, increasing production costs and environmental burden.

[0006] Therefore, to improve the performance and sustainability of all-solid-state lithium-ion batteries, this invention conducts in-depth research and improvements on issues such as electrode ionic conductivity, discharge capacity, and active material recovery. By optimizing the composition and structure of electrode materials and introducing high-performance conductive additives and binders, the current problems with electrodes are solved, promoting the development and application of all-solid-state lithium-ion battery technology. Summary of the Invention

[0007] In order to overcome the shortcomings of the existing technology, one of the objectives of this invention is to provide a solid-state battery cathode material.

[0008] The technical solution adopted by the present invention to solve its technical problem is: a solid-state battery cathode material, which, by weight fraction, contains 75-85 parts of lithium iron phosphate, 5-10 parts of polyvinyl alcohol, 5-10 parts of composite solid electrolyte Li7O2Br3 and 2-5 parts of conductive agent graphene, wherein the polyvinyl alcohol is a high molecular weight polyvinyl alcohol with a molecular weight of 100,000-2,000,000.

[0009] Furthermore, the composite solid electrolyte Li7O2Br3 is obtained by ball milling and pressure sintering of Li2O and LiBr as raw materials, with the pressure sintering pressure being 4... -10 The sintering temperature is 550–900℃. The composite solid electrolyte Li7O2Br3 obtained by the above method is not a pure compound. Sintering under pressure can yield an anti-perovskite solid electrolyte with a purity of 61–72% for Li7O2Br3, which can improve the ionic conductivity of the anti-perovskite solid electrolyte. Ball milling can control the particle size of lithium iron phosphate, ensuring uniform mixing and dispersion of lithium iron phosphate, composite solid electrolyte, and graphene.

[0010] Furthermore, by weight, the lithium iron phosphate comprises 83 parts, polyvinyl alcohol comprises 8 parts, the composite solid electrolyte Li7O2Br3 comprises 7 parts, and graphene comprises 2 parts.

[0011] The second objective of this invention is to provide a solid-state battery positive electrode sheet, comprising an aluminum foil current collector, wherein the aluminum foil current collector is coated with the aforementioned positive electrode material.

[0012] The third objective of this invention is to provide a method for preparing a positive electrode sheet for a solid-state battery, comprising the following steps:

[0013] (1) Weigh 75-85 parts of lithium iron phosphate, 5-10 parts of composite solid electrolyte Li7O2Br3 and 2-5 parts of graphene and dry mix them. After adding a small amount of N-methylpyrrolidone, the mixture is ball-milled at a rotation speed of 350-400 r / min and a revolution speed of 2-5 r / min for 2-8 h to obtain the original slurry.

[0014] (2) Weigh polyvinyl alcohol and add it to the original slurry. Continue ball milling and mixing. Use a high-shear emulsifier to stir at high speed to obtain the slurry. Use an AFA-automatic coating machine to coat the slurry onto aluminum foil and dry it at 40-80℃ to obtain the sheet.

[0015] (3) Roll the sheet using a roller press and punch it into a round electrode using a punching machine.

[0016] The fourth objective of this invention is to provide the above-mentioned solid-state battery positive electrode sheet for use in lithium batteries.

[0017] The beneficial technical effects obtained by this invention are as follows:

[0018] This invention is the first to add a composite solid electrolyte, Li7O2Br3, to the positive electrode of a solid-state battery. Li7O2Br3 possesses good mechanical strength and non-flammability, effectively suppressing lithium dendrite growth and reducing the risk of short circuits and thermal runaway. Furthermore, the high ionic conductivity of Li7O2Br3 helps improve the ionic conductivity of the positive electrode. Adding Li7O2Br3 increases ionic conductivity and reduces interfacial resistance, thereby improving the discharge capacity and cycle performance of the solid-state battery. Lithium iron phosphate has a high discharge plateau voltage and low internal resistance, providing stable power output. This invention utilizes the synergistic effect of high molecular weight polyvinyl alcohol and Li7O2Br3 to reduce the crystallinity of the solid electrolyte and improve the migration ability of ions within it. Improving ionic conductivity can also enhance the flexibility and processability of solid-state electrolytes, making the fabrication of solid-state batteries more convenient. Polyvinyl alcohol contains a large number of hydroxyl functional groups, which can effectively form ion channels with lithium ions, thereby improving the ionic conductivity of the cathode. High molecular weight polyvinyl alcohol can improve the adhesion between cathode materials, increase density, and reduce the likelihood of cracking. Furthermore, polyvinyl alcohol is more soluble in aqueous solutions than binders such as polytetrafluoroethylene, facilitating the recycling of subsequent materials. The addition of high molecular weight polyvinyl alcohol can reduce the crystallinity of solid-state electrolytes, improve the migration ability of ions within them, thereby increasing ionic conductivity. It can also improve the flexibility and processability of solid-state electrolytes, making the fabrication of solid-state batteries more convenient.

[0019] This invention improves ionic conductivity by adjusting specific composition and content. The improved ionic conductivity helps reduce battery internal resistance, allowing more lithium ions to be inserted into and extracted from LFP during charging and discharging, thereby increasing discharge capacity. The synergistic effect of solid electrolyte and PVA also helps reduce battery self-discharge and maintain battery capacity during storage. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments.

[0021] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. It should be understood that the following description is merely illustrative and is not intended to limit the invention.

[0022] Unless otherwise specified, the raw materials and equipment used in this invention can be purchased from the market or are commonly used in the field. Unless otherwise specified, the methods in the embodiments are conventional methods in the field.

[0023] The following description, in conjunction with specific implementation methods, provides further details. Example 1

[0024] This embodiment discloses a solid-state battery positive electrode sheet, which is prepared by the following steps: 83 parts by weight of lithium iron phosphate, 7 parts by weight of composite solid electrolyte Li7O2Br3 and 2 parts by weight of graphene are weighed, mixed and dry-mixed, and a small amount of N-methylpyrrolidone is added and ball-milled to obtain a raw slurry; then 8 parts by weight of polyvinyl alcohol are added to the raw slurry, and ball-milling is continued, and high-speed stirring is performed using a high-shear emulsifier to obtain a slurry; the prepared slurry is coated onto prepared aluminum foil using an AFA-automatic coating machine and dried at 50°C; the dried electrode sheet is rolled using a roller press, and the electrode sheet is punched into small round pieces of the required size and shape using a punching machine, which is the solid-state battery positive electrode material.

[0025] Ionic conductivity and discharge capacity tests: The obtained positive electrode sheet was cut and then assembled into a coin cell with the negative lithium sheet and electrolyte. The full-charge EIS impedance diagram, discharge capacity, first efficiency and 100-cycle retention rate at 1C were tested at 3-4.35V. The ionic conductivity of the positive electrode material was also tested. The test results are shown in Table 1 below. Example 2

[0026] This embodiment discloses a solid-state battery positive electrode sheet, which is prepared by the following steps: 75 parts by weight of lithium iron phosphate, 10 parts by weight of composite solid electrolyte Li7O2Br3 and 5 parts by weight of graphene are weighed and mixed, and then dry-mixed. A small amount of N-methylpyrrolidone is added and the mixture is ball-milled to obtain a raw slurry. Then, 10 parts by weight of polyvinyl alcohol are added to the raw slurry and ball-milled and mixed. The mixture is stirred at high speed using a high-shear emulsifier to obtain a slurry. The prepared slurry is coated onto a prepared aluminum foil using an AFA-automatic coating machine and dried at 40°C. The dried electrode sheet is rolled using a roller press and punched into small round sheets of the required size and shape using a punching machine, which is the solid-state battery positive electrode material. Example 3

[0027] This embodiment discloses a solid-state battery positive electrode sheet, which is prepared by the following steps: 85 parts by weight of lithium iron phosphate, 5 parts by weight of composite solid electrolyte Li7O2Br3 and 5 parts by weight of graphene are weighed, mixed and dry-mixed, and a small amount of N-methylpyrrolidone is added and ball-milled to obtain a raw slurry; then 5 parts by weight of polyvinyl alcohol are added to the raw slurry, and ball-milling is continued, and high-speed stirring is performed using a high-shear emulsifier to obtain a slurry; the prepared slurry is coated onto prepared aluminum foil using an AFA-automatic coating machine and dried at 80°C; the dried electrode sheet is rolled using a roller press, and the electrode sheet is punched into small round pieces of the required size and shape using a punching machine, which is the solid-state battery positive electrode material.

[0028] Comparative Example 1: Weigh out 83 parts by weight of lithium iron phosphate and 7 parts by weight of garnet-type oxide solid electrolyte Li7La3Zr2O.12 Mix 2 parts graphene and dry mix, add a small amount of N-methylpyrrolidone and ball mill to obtain the original slurry; then weigh 8 parts polyvinyl alcohol and add it to the original slurry, continue ball milling and mixing, and use a high-shear emulsifier for high-speed stirring to obtain the slurry; use an AFA-automatic coating machine to coat the prepared aluminum foil, and dry it at 50°C; roll the dried electrode sheet with a roller press, and use a punching machine to punch the electrode sheet into small round sheets of the required size and shape, which are the solid-state battery cathode materials.

[0029] Comparative Example 2: 83 parts by weight of lithium iron phosphate and 7 parts by weight of LISICON type solid electrolyte Li 3.25 GeP 0.7 S4 and 2 parts graphene are mixed and dry-mixed. A small amount of N-methylpyrrolidone is added and ball-milled to obtain the original slurry. Then, 8 parts of polyvinyl alcohol are weighed and added to the original slurry. The mixture is ball-milled and mixed, and stirred at high speed using a high-shear emulsifier to obtain the slurry. The prepared slurry is coated onto the prepared aluminum foil using an AFA-automatic coating machine and dried at 50°C. The dried electrode is rolled using a roller press, and the electrode is punched into small round pieces of the required size and shape using a punching machine, which is the solid-state battery cathode material.

[0030] Comparative Example 3: By weight, 83 parts of lithium iron phosphate and 2 parts of graphene were weighed and mixed, and then dry-mixed. A small amount of N-methylpyrrolidone was added and the mixture was ball-milled to obtain the original slurry. Then, 15 parts of polyvinyl alcohol were weighed and added to the original slurry, and the mixture was ball-milled and mixed. The mixture was stirred at high speed using a high-shear emulsifier to obtain the slurry. The prepared slurry was coated onto the prepared aluminum foil using an AFA-automatic coating machine and dried at 50°C. The dried electrode was rolled using a roller press, and the electrode was punched into small round pieces of the required size and shape using a punching machine, which is the solid-state battery cathode material.

[0031] Comparative Example 4: 83 parts by weight of lithium iron phosphate, 15 parts by weight of composite solid electrolyte Li7O2Br3, and 2 parts by weight of graphene were weighed and mixed, then dry-mixed. A small amount of N-methylpyrrolidone was added and the mixture was ball-milled. The mixture was then stirred at high speed using a high-shear emulsifier to obtain a slurry. The prepared slurry was coated onto prepared aluminum foil using an AFA-automatic coating machine and dried at 50°C. The dried electrode was then rolled using a roller press, and the electrode was punched into small round pieces of the required size and shape using a punching machine, which are the solid-state battery cathode materials. The physical performance parameters of the examples and comparative examples are shown in the table below.

[0032] .

[0033] As can be seen from the data in the table above, Examples 1 to 3 compared the effects of different contents of polyvinyl alcohol and composite solid electrolyte on the ionic conductivity and discharge capacity of the positive electrode sheet.

[0034] Comparing the data from Example 1 and Comparative Examples 1-2, it can be found that the ionic conductivity and discharge capacity obtained by using different types of solid electrolytes in combination with lithium iron phosphate vary, with 7 parts of Li7O2Br3 showing the best performance.

[0035] The data comparison of Example 1 and Comparative Examples 3-4 further verifies the influence of different composition contents on the performance of solid-state electrodes.

[0036] Furthermore, this invention uses polyvinyl alcohol as a binder, and water can be used directly as a solvent for the recovery of active materials, which is beneficial for green recycling.

[0037] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A solid-state battery cathode material, characterized in that: It contains 75-85 parts of lithium iron phosphate, 5-10 parts of polyvinyl alcohol, 5-10 parts of Li7O2Br3 and 2-5 parts of graphene, wherein the polyvinyl alcohol is a high molecular weight polyvinyl alcohol with a molecular weight of 100,000-2,000,000.

2. The solid-state battery cathode material according to claim 1, characterized in that, The Li7O2Br3 mentioned above is obtained by ball milling and pressure sintering of Li2O and LiBr as raw materials. The pressure sintering pressure is 4. -10 Gpa, sintering temperature is 550~900℃.

3. A solid-state battery cathode material according to claim 1 or 2, characterized in that, The composition of the lithium iron phosphate is 83 parts, the polyvinyl alcohol is 8 parts, the composite solid electrolyte Li7O2Br3 is 7 parts, and the graphene is 2 parts.

4. A positive electrode sheet for a solid-state battery, characterized in that: It includes an aluminum foil current collector, wherein the aluminum foil current collector is coated with the positive electrode material as described in claim 1.

5. A method for preparing a solid-state battery positive electrode sheet as described in claim 4, characterized in that, Includes the following steps: (1) Lithium iron phosphate, Li7O2Br3 and graphene were dry mixed, and N-methylpyrrolidone was added. The mixture was then ball-milled at a rotation speed of 350-400 r / min and a revolution speed of 2-5 r / min for 2-8 h to obtain the original slurry. (2) Weigh polyvinyl alcohol and add it to the original slurry. Continue ball milling and mixing. Use a high-shear emulsifier to stir at high speed to obtain the slurry. Use an AFA-automatic coating machine to coat the slurry onto aluminum foil and dry it at 40-80℃ to obtain the sheet. (3) Roll the sheet using a roller press and punch it into a round electrode using a punching machine to obtain the positive electrode of the solid battery.

6. A solid-state battery positive electrode as described in claim 4 for use in a lithium battery.