A solid-state lithium battery composite positive electrode material capable of realizing capacity breakthrough, a preparation method thereof and a full-solid-state lithium ion battery

Abstract

The application belongs to the technical field of solid-state batteries, and provides a solid-state lithium battery composite positive electrode material capable of realizing capacity breakthrough, a preparation method and a full solid-state lithium ion battery. The composite positive electrode material is prepared by using anhydrous lithium hydroxide and ferric chloride as reaction raw materials, through manual grinding, low-temperature heating treatment and mechanical mixing methods. The method provided by the application has low raw material cost and simple process, and the prepared active precursor material has high ionic conductivity and can contribute to its own capacity, so as to realize the capacity breakthrough of the solid-state lithium battery composite positive electrode material and improve the energy density of the battery system.

Description

Technical Field

[0001] This technical invention belongs to the field of solid-state battery technology, and specifically relates to a solid-state lithium battery composite positive electrode material and a preparation method and an all-solid-state lithium-ion battery that can achieve a breakthrough in capacity. Background Art

[0002] Since the introduction of rechargeable lithium-ion batteries to the consumer market in the early 1990s, they have transformed the global communications sector with the revolution in portable electronics. They are a mature and efficient energy storage technology in terms of energy and power density, service life and design flexibility. At present, the commercial application of lithium-ion batteries has largely solved the energy storage problems facing the world. With the increase in application requirements, batteries with high energy density, stable electrochemical properties, safety and low cost have become the focus of research at this stage. Commercial lithium batteries are generally composed of an organic liquid electrolyte, a positive electrode and a negative electrode. Since most liquid organic electrolytes are flammable, traditional lithium-ion laboratories are at risk of fire or even explosion during overcharging, leakage and heating. In addition, most practical applications of liquid lithium batteries have reached 230 Wh kg −1 , which is very close to its theoretical energy density (300 Wh kg −1 ).

[0003] All-solid-state lithium batteries use non-flammable solid electrolytes and high-voltage cathode materials, and their theoretical energy density can exceed 700 Wh kg −1 , currently reaching 300-400 Wh kg −1 Compared with the lithium negative electrode with high theoretical capacity (3860 mAhg -1 ) and silicon anode (4200 mAh g -1 ), the positive electrode materials with low theoretical specific capacity have always been the key to limiting the development of energy density of solid-state battery systems.

[0004] Traditional oxide positive electrode materials (LiCoO2, LiFePO4, NCM111) have low inherent ionic conductivity and cannot construct an effective ion transmission path on the positive electrode side of the all-solid-state lithium battery. Therefore, it is necessary to add a supporting electrolyte with high ionic conductivity on the positive electrode side to artificially construct an ion transmission channel. However, the inactive supporting electrolyte will reduce the mass proportion of the active oxide positive electrode material, thereby reducing the energy density of the battery system, causing the public to have capacity anxiety about battery life. Therefore, replacing the inactive supporting electrolyte with an active electrolyte material that has ion conductivity and can carry out charge and discharge reactions can solve the capacity anxiety problem of the current commercial oxide positive electrode materials to a certain extent.

[0005] In summary, it is particularly important to develop an active positive electrode electrolyte material which has high ionic conductivity and can realize the charge and discharge electrochemical process, and to realize fast ion conduction to avoid the addition of supporting electrolyte and to contribute to the capacity itself during battery discharge to realize the capacity breakthrough of the composite positive electrode material of the solid-state lithium battery. SUMMARY

[0006] In view of this, the purpose of the present application is to develop a solid-state lithium battery composite positive electrode material which can realize capacity breakthrough. The composite positive electrode material of the present application can contribute additional capacity during battery charge and discharge by introducing a precursor material which has high ionic conductivity and can realize reversible charge and discharge process during the manufacturing process, thereby greatly improving the energy density of the battery system.

[0007] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0008] The present application provides a preparation method of a solid-state lithium battery composite positive electrode material which can realize capacity breakthrough, comprising: S1, grinding anhydrous lithium hydroxide and anhydrous ferric chloride in an inert atmosphere to obtain a mixed powder; S2, heating the powder in the inert atmosphere to obtain a positive electrode precursor material; S3, mechanically ball milling commercial carbon-coated lithium iron phosphate positive electrode material (C@LiFePO4), the precursor material and the conductive additive in a certain proportion in the inert atmosphere to obtain a solid-state battery composite positive electrode material.

[0009] The specific implementation scheme is as follows:

[0010] (1) Under the protection of inert atmosphere, grind the lithium hydroxide and ferric chloride material uniformly to obtain a mixed powder;

[0011] The molar ratio of the mixed lithium hydroxide and ferric chloride is 1-2:1, preferably the ratio is 1-1.5:1, and more preferably 1.2-1.5:1;

[0012] (2) Under the protection of inert atmosphere, heat the mixed powder to obtain a positive electrode precursor material;

[0013] The heating treatment temperature is 40-120℃, preferably the temperature is 50-80℃, more preferably 60-70℃, and the treatment time is 1-24h, preferably 1-16h, and more preferably 12-14h;

[0014] (3) Under the protection of inert atmosphere, mechanically ball mill mix the positive electrode material, the positive electrode precursor material and the conductive additive to obtain a solid-state battery composite positive electrode material.

[0015] Further, the lithium hydroxide and the ferric chloride are both anhydrous materials.

[0016] The inert atmosphere gas is one or more of nitrogen and argon. Preferably, the inert atmosphere is high-purity argon, the purity of which is greater than 99.99%, and the contents of oxygen and water are respectively less than 0.1 ppm.

[0017] Furthermore, lithium hydroxide and ferric chloride are fully ground, and the container mortar used is a mortar that has been dried.

[0018] The time for grinding and mixing lithium hydroxide and ferric chloride is 5-30 minutes, preferably 15-20 minutes.

[0019] Before the mechanical ball milling, the ball milling jar and the ball milling beads are dried in an oven, and then the materials are added to perform a sealed ball milling operation.

[0020] Furthermore, the ball milling beads for the mechanical ball milling mixture include two or more types of ball milling beads with different diameters, and the rotation speed of the mechanical ball milling mixture is 100-500 rpm, preferably 200-300 rpm.

[0021] Furthermore, when two types of ball milling beads with different diameters are used, the ball milling beads include two types with diameters of 8-10 mm and 4-5 mm, and the mass ratio of the ball milling beads is 1-5:1, preferably 1-3:1, and more preferably 2-2.5:1.

[0022] Furthermore, the mechanical ball milling mixing procedure includes forward rotation, pause, reverse rotation, pause, and the like, and the cycle operation is performed in this synthesis order; the time of each cycle operation is 1 to 9 hours, preferably 6 to 9 hours, more preferably 8 to 9 hours; the number of cycles is 1 to 18 times, preferably 6 to 18 times, more preferably 15 to 18 times.

[0023] Furthermore, the positive electrode material is a carbon-coated lithium iron phosphate (C@LiFePO4) material, with a carbon content of 1-10 wt.%, preferably 1-5 wt.%, and more preferably 2-3 wt.%.

[0024] The conductive additive is one or more of acetylene black, activated carbon, carbon nanotubes, graphene, carbon nanofibers, BP2000, KB600, KB300, XC-72, and SuperP.

[0025] Furthermore, the mass ratio of the composite positive electrode material is carbon-coated lithium iron phosphate material: precursor: conductive additive = 40~70:57~27:3, preferably 50~70:47~27:3, more preferably 65-68:32-37:3.

[0026] Furthermore, the composite positive electrode material prepared by the preparation method.

[0027] Furthermore, an all-solid-state lithium-ion battery is provided, with a lithium sheet as the negative electrode, lithium phosphorus sulfur chloride (Li6PS5Cl) and lithium zirconium chloride (Li2ZrCl6, CN202010972122.2) as the solid electrolyte layer, and the composite positive electrode material prepared by the preparation method as the positive electrode material.

[0028] The beneficial effects of the present invention are:

[0029] The composite cathode material prepared by the present invention has a simple preparation process, and the desired product can be obtained by simple hand grinding, low-temperature treatment and ball milling mixing. The raw materials are inexpensive and are expected to be widely used.

[0030] The precursor material prepared by the present invention has high electrical conductivity and can carry out normal battery charge and discharge processes without adding a supporting electrolyte, thereby avoiding the addition of an inactive supporting electrolyte. Therefore, the discharge specific capacity of the prepared composite positive electrode material can be increased by at least 25% compared with traditional composite positive electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Flow chart of the method for preparing composite positive electrode materials.

[0032] Figure 2 This is the X-ray diffraction pattern of the precursor material prepared in Example 1.

[0033] Figure 3 X-ray diffraction pattern of the precursor material prepared in Comparative Example 1.

[0034] Figure 4 X-ray diffraction pattern of the precursor material prepared for Comparative Example 2.

[0035] Figure 5 EIS spectra of the precursor materials prepared in Example 1, Comparative Example 1, and Comparative Example 2.

[0036] Figure 6 This is the EIS spectrum of the precursor material prepared in Comparative Example 3.

[0037] Figure 7 EIS spectra of the precursor materials prepared in Comparative Examples 5 and 6.

[0038] Figure 8 EIS spectra of the precursor materials prepared in Comparative Examples 7, 8, and 9.

[0039] Figure 9 Electrochemical performance curves of composite cathode materials prepared in Example 2 and Comparative Example 3 in solid-state lithium batteries.

[0040] Figure 10 The cycle performance diagram of the composite positive electrode material prepared in Example 2 and Comparative Example 3 in a solid-state lithium battery. DETAILED DESCRIPTION

[0041] The present invention is described in detail below with reference to the embodiments, but the embodiments of the present invention are not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments obtained without creative work all fall within the scope of protection of the present invention.

[0042] The present invention significantly increases the battery's charge and discharge capacity by adding a composite cathode material prepared from an electrochemical reaction precursor that has ion conductivity. By manually grinding and low-temperature processing, the lithium content can be further controlled to achieve an ionic conductivity of 5 mS cm at room temperature. -1 The composite cathode material prepared by mixing the above precursor materials with commercial carbon-coated lithium iron phosphate cathode materials can be used in solid-state lithium batteries. This can avoid the addition of inactive supporting electrolytes, increase the proportion of active materials in the composite cathode material, achieve a breakthrough in the discharge capacity of the composite cathode material, and improve the overall energy density of the battery system.

[0043] Based on the above findings, the first embodiment of the present invention provides a method for preparing a solid-state lithium battery composite positive electrode material that can achieve a breakthrough in capacity. Figure 1 , including: S1, grinding anhydrous lithium hydroxide and anhydrous ferric chloride in an inert atmosphere to obtain a mixed powder; S2, low-temperature heating the powder in the inert atmosphere to obtain a precursor; S3, ball-milling the precursor material and a commercial carbon-coated lithium iron phosphate positive electrode material conductive additive in the inert atmosphere to obtain a composite positive electrode material.

[0044] The raw materials in S1 are lithium hydroxide (LiOH, anhydrous grade, 99.9%) and ferric chloride (FeCl3, anhydrous grade, 99.9%).

[0045] Preferably, the optimal time for manual grinding in S1 is 30 minutes, until the white powder of LiOH is evenly distributed.

[0046] Preferably, the molar ratio of the raw materials is LiOH:FeCl3=1.2:1, and the corresponding amounts are LiOH (0.1505g) and FeCl3 (0.8495g). In this formulation, the obtained precursor material has the best room temperature ion conductivity.

[0047] Preferably, the optimal temperature for low temperature treatment in S2 is 60°C and the treatment time is 12h;

[0048] The specific steps for mechanical ball milling are to add C@LiFePO4:precursor:conductive additive in a weight ratio of 65:32:3 to a ball mill jar in a glove box, which is then tightly sealed. The jar is then placed and secured in a ball mill. The mill is set to run for 5 minutes forward, 10 minutes rest, and 5 minutes reverse, 10 minutes rest, with the speed set at 200 rpm. After the ball milling process is complete, the composite cathode material is prepared.

[0049] Based on the above embodiment, the stoichiometric ratio of lithium hydroxide and ferric chloride is 1-2:1.

[0050] Based on the above embodiment, the ball milling beads synthesized by mechanical ball milling include at least two types of diameters, and the rotation speed of the mechanical ball milling synthesis is 100-500 rpm, and the time is 1-48 hours.

[0051] Based on the above embodiment, the mechanical ball milling synthesis procedure includes forward rotation, pause, reverse rotation, pause, and the like, and the cycle operation is performed in this order.

[0052] Based on the above embodiment, the zirconium dioxide ball milling beads include two types of diameters: 10 mm and 5 mm, and the mass ratio of the ball milling beads is 2-5:1.

[0053] Based on the above embodiment, the inert atmosphere is high-purity argon gas, the purity of the high-purity argon gas is ≥99.999%, and the oxygen and water contents are less than 0.01 ppm.

[0054] High-purity argon has the function of protecting the inert atmosphere in the glove box. The oxygen and water content is less than 0.01 ppm, which can reduce the influence of moisture absorption on the electrochemical properties of the material.

[0055] Based on the above embodiment, a conductive additive is added, which is one of carbon nanotubes, graphene, carbon nanofibers, BP2000, KB600, KB300, XC-72, SuperP, acetylene black, and activated carbon. The addition of the conductive additive is to build an electron transport network within the positive electrode material, thereby reducing the polarization problem caused by the low electronic conductivity of the positive electrode material.

[0056] On the basis of the above embodiment, the process further includes drying the ball mill jar and the ball mill beads in an oven before mechanical ball milling synthesis, and then adding materials and sealing the jar.

[0057] Before mechanical ball milling, the jar and beads must be dried in a 60°C oven for 12 hours to remove any moisture from the jar and beads. This allows for the addition of materials and subsequent mechanical milling. Moisture from the jar and beads can cause the raw materials and final product to absorb moisture, leading to hydrolysis and ultimately affecting the product's properties.

[0058] The solid-state lithium battery composite positive electrode material prepared by the manual grinding, low-temperature processing and mechanical mixing method has a very high active material ratio, avoids the addition of a supporting electrolyte, and improves the energy density of the battery system. In addition, the composite positive electrode material prepared by the above method does not need high-temperature processing, the process is simple, and the production energy consumption is reduced.

[0059] The following specific examples will be described in detail.

[0060] The instrument and equipment for testing and assembling the solid-state full battery of the precursor material ion conductivity include a general cylindrical mold (Φ10 mm), a solid-state battery test mold (Φ10 mm), a manual tablet press, a multi-channel electrochemical workstation, and a battery detection system. The solid-state full battery assembly process is used in a dry inert atmosphere (high-purity argon) glove box, in which the oxygen and water contents are both below 0.1 ppm.

[0061] Example 1

[0062] In a dry high-purity argon (in which the oxygen and water contents are both below 0.1 ppm) glove box, 0.1505 g of lithium hydroxide and 0.8495 g of iron chloride (LiOH: FeCl3 addition molar ratio is 1.2:1) were weighed and placed in an agate mortar for manual grinding for 30 minutes. Then, the ground material was heated to 60℃ and kept for 12h in the glove box to obtain the precursor material.

[0063] The agate mortar was dried in a 60℃ oven for 12 hours before use. Example 2

[0064] In a dry high-purity argon (in which the oxygen and water contents are both below 0.1 ppm) glove box, C@LiFePO4 (carbon content about 2 wt.%) from Shanghai Aladdin Biochemical Technology Co., Ltd., the precursor material prepared in Example 1, and conductive additive KB600 were added in a weight ratio of 65:32:3 in a ball milling tank, and the ball milling tank was strictly sealed in the glove box. The ball milling machine was set to operate for 5 minutes in the forward direction, 10 minutes of intermittent; 5 minutes in the reverse direction, 10 minutes of intermittent mode, and the rotation speed was set to 200 revolutions per minute. Each cycle of operation was 9h; the number of cycles was set to 18 times. After the ball milling program was completed, the composite positive electrode material was prepared.

[0065] Before mechanical ball milling mixing, the ball milling tank and ball milling beads need to be dried in a 60℃ oven for 12 hours;

[0066] The ball milling beads include two types of diameters, 10mm and 5mm, and the mass ratio of the ball milling beads is 2:1.

[0067] Comparative Example 1

[0068] The process and conditions were the same as those in Example 1, except that the molar ratio of LiOH:FeCl3 added to the prepared precursor material was 0.8:1 (the amount of ferric chloride used was 0.8495 g).

[0069] Comparative Example 2

[0070] The process and conditions were the same as those in Example 1, except that the molar ratio of LiOH:FeCl3 added to the prepared precursor material was 3:1 (the amount of ferric chloride used was 0.8495 g).

[0071] Comparative Example 3

[0072] The process and conditions are the same as those in Example 1. The difference from Example 1 is that the raw materials are replaced with LiCl and Fe(OH)3, and the molar ratio of the added amounts in the prepared precursor material is 1.2:1.

[0073] Comparative Example 4

[0074] The process and conditions are the same as those in Example 2. The difference from Example 2 is that lithium zirconium chloride is used instead of the precursor material, and the molar ratio of C@LiFePO4, Li2ZrCl6 and conductive additive added to the prepared composite positive electrode material is 65:32:3.

[0075] Comparative Example 5

[0076] The process and conditions were the same as those in Example 1, except that all the precursor raw materials were replaced with LiOH in an amount of 0.1505 g.

[0077] Comparative Example 6

[0078] The process and conditions are the same as those in Example 1. The difference from Example 1 is that all the precursor raw materials are replaced with FeCl3, and the added amount is 0.8495g.

[0079] Comparative Example 7

[0080] The process and conditions are the same as those in Example 1. The difference from Example 1 is that the prepared precursor raw materials are LiOH and FeCl2, and the molar ratio of LiOH:FeCl2 added is 0.8:1 (the amount of ferrous chloride used is 0.8495 g).

[0081] Comparative Example 8

[0082] The process and conditions are the same as those in Example 1. The difference from Example 1 is that the prepared precursor raw materials are LiOH and FeCl2, and the molar ratio of LiOH:FeCl2 added is 1.2:1 (the amount of ferrous chloride used is 0.8495g).

[0083] Comparative Example 9

[0084] The process and conditions are the same as those in Example 1. The difference from Example 1 is that the prepared precursor raw materials are LiOH and FeCl2, and the molar ratio of LiOH:FeCl2 added is 3:1 (the amount of ferrous chloride used is 0.8495 g).

[0085] Figure 2 The X-ray diffraction patterns of Example 1 and Comparative Examples 1 and 2 are shown. The horizontal axis of the X-ray diffraction pattern represents the diffraction angle 2θ, and the vertical axis represents the diffraction intensity. It can be seen that the Example 1 material exhibits only a diffraction peak of the lithium chloride crystalline phase within the diffraction range; whereas the Comparative Example 1 sample exhibits a diffraction peak of the raw material ferric chloride, and the Comparative Example 2 sample exhibits a diffraction peak of hydrated lithium chloride. This indicates that the Example 1 material has a reasonable reaction degree and can produce an ideal reaction product.

[0086] Preparation and testing of material sheets of Example 1 and Comparative Examples 1, 2, and 3

[0087] 100 mg of each of the materials obtained in Example 1 and Comparative Examples 1, 2, and 3 were added to a conventional hollow cylindrical mold (inner diameter Φ10 mm). A manual tablet press was applied with a pressure of 500 MPa and the tablets were cold pressed for 1 minute. Ionic conductivity was then measured using a Biologic multi-channel electrochemical workstation at a test frequency of 7 MHz to 1 Hz and a bias voltage of 100 mV.

[0088] Figure 5 The electrochemical impedance spectroscopy of the precursor materials of Example 1 and Comparative Examples 1 and 2 of the present invention is shown in Figure 1. The horizontal axis is the real impedance and the vertical axis is the imaginary impedance. It can be confirmed that the conductivity of Example 1 at room temperature is 5 mS cm -1 , which is significantly higher than the conductivity of comparative example 1 (0.6 mS cm -1 The conductivity of Comparative Example 2 is 0.2 mS cm -1 , which shows that the ion conductivity of the sample in Example 1 is stronger and is at the same level as the currently advanced inactive solid supporting electrolyte. It can replace the inactive supporting electrolyte under the same conditions to ensure the ion conductivity in the composite positive electrode material. Figure 6 This is the electrochemical impedance spectroscopy of the precursor material of Comparative Example 3 of the present invention. The results show that the ion conductivity of the comparative example synthesized is about 0, which is unable to conduct ions normally and therefore cannot be used as an active material with ion conductivity. In addition, Figure 7 and Figure 8 The precursor materials prepared in Comparative Examples 5, 6, 7, 8, and 9 are similar to those in Comparative Example 3, and their ion conductivity is approximately 0. Normal ion conduction cannot be achieved in the composite positive electrode, and therefore cannot be used as precursor materials that can achieve a capacity breakthrough.

[0089] Assembly and testing of solid-state full batteries based on composite cathode materials

[0090] 50 mg of lithium zirconium chloride Li2ZrCl6 solid electrolyte was added to a hollow cylindrical mold (inner diameter Φ10mm) battery core, 50 MPa pressure was applied, and cold pressing was maintained for 1 minute; then 50 mg of Li6PS5Cl solid electrolyte was added to the battery core, 100 MPa pressure was applied, and cold pressing was maintained for 1 minute; subsequently, 3 mg of the composite positive electrode material prepared by the above process was added to one side of the lithium zirconium chloride electrolyte, 500 MPa pressure was applied, and cold pressing was maintained for 1 minute; lithium sheet was added to one side of the lithium phosphorus sulfur chloride electrolyte sheet, and aluminum foil and copper foil were added to the positive and negative electrode sides respectively. After assembling the battery, the battery mold was kept under 100 MPa pressure and electrochemical testing was performed using a blue battery tester. In this test, the applied current density was 0.1 mA cm -2 .

[0091] Figure 9 and Figure 10 The electrochemical performance curves and cycle performance diagrams of solid-state full batteries based on composite cathode materials provided in Example 2 and Comparative Example 3 of the present invention. The specific capacity of the composite cathode material in Example 2 can reach 190 mAh g -1 LFP This indicates that the cathode precursor can not only conduct ions during battery charge and discharge, but also provide an additional capacity of approximately 40 mAhg -1 LFP Among them, the positive electrode material obtained in Comparative Example 3 has only C@LiFePO4 as the active material for charge and discharge, so the specific capacity of the composite positive electrode material is 150 mAh g -1 LFP Based on the above results, the discharge capacity of Example 2 is greater than that of Comparative Example 4 by more than 25%.

[0092] In addition, both composite cathode materials can undergo stable electrochemical cycling and have commercial application prospects. In summary, it can be concluded that the composite cathode material prepared in Example 1 has higher capacity and energy density.

[0093] The method provided by the present invention has low raw material cost, simple process and the prepared active precursor material has high ionic conductivity and can contribute its own capacity, thereby achieving a capacity breakthrough of solid-state lithium battery composite positive electrode materials and improving the energy density of the battery system.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a solid-state lithium battery composite cathode material capable of achieving a breakthrough in capacity, characterized in that: The steps include: (1) Under an inert atmosphere, lithium hydroxide and ferric chloride are ground and mixed to obtain a mixed powder; The molar ratio of the lithium hydroxide and ferric chloride is 1 to 2:1; (2) heating the mixed powder under inert atmosphere to obtain a cathode precursor material; The heating treatment temperature is 40-120°C and the treatment time is 1-24 hours; (3) Under the protection of an inert atmosphere, the positive electrode material, the positive electrode precursor material and the conductive additive are mechanically ball-milled to obtain a solid-state battery composite positive electrode material.

2. The method for preparing a solid-state lithium battery composite positive electrode material capable of achieving a breakthrough in capacity according to claim 1, characterized in that: The lithium hydroxide and ferric chloride are both anhydrous materials; The inert atmosphere gas is one or more of nitrogen and argon, the purity of the argon is greater than 99.99%, and the contents of oxygen and water are respectively less than 0.1 ppm.

3. The method for preparing a solid-state lithium battery composite positive electrode material capable of achieving a breakthrough in capacity according to claim 1, characterized in that: Grind lithium hydroxide and ferric chloride thoroughly using a dried mortar. The time for grinding and mixing lithium hydroxide and ferric chloride is 5-30 minutes; Before the mechanical ball milling, the ball milling jar and the ball milling beads are dried in an oven, and then the materials are added to perform a sealed ball milling operation.

4. The method for preparing a solid-state lithium battery composite cathode material capable of achieving a breakthrough in capacity according to claim 1, characterized in that: The ball milling beads for the mechanical ball milling mixture include two or more types of ball milling beads with different diameters, and the rotation speed of the mechanical ball milling mixture is 100-500 rpm.

5. The method for preparing a solid-state lithium battery composite cathode material capable of achieving a breakthrough in capacity according to claim 4, characterized in that: When two types of ball milling beads with different diameters are used, the ball milling beads include two types with diameters of 8-10 mm and 4-5 mm, and the mass ratio of the ball milling beads is 1-5:

1.

6. The method for preparing a solid-state lithium battery composite cathode material capable of achieving a breakthrough in capacity according to claim 1, characterized in that: The mechanical ball milling mixing procedure includes forward rotation, pause, reverse rotation, pause, and a cyclic operation in this synthesis order; the time of each cycle operation is 1 to 9 hours; and the number of cycles is 1 to 18 times.

7. The method for preparing a solid-state lithium battery composite cathode material capable of achieving a breakthrough in capacity according to claim 1, characterized in that: The positive electrode material is a carbon-coated lithium iron phosphate material with a carbon content of 1-10 wt.%; The conductive additive is one or more of acetylene black, activated carbon, carbon nanotubes, graphene, carbon nanofibers, BP2000, KB600, KB300, XC-72, and SuperP.

8. The method for preparing a solid-state lithium battery composite cathode material capable of achieving a breakthrough in capacity according to claim 1, characterized in that: The mass ratio of the composite positive electrode material is carbon-coated lithium iron phosphate material: precursor: conductive additive = 40~70:57~27:

3.

9. A composite positive electrode material prepared by the method for preparing a solid-state lithium battery composite positive electrode material capable of achieving a breakthrough in capacity according to any one of claims 1 to 8.

10. An all-solid-state lithium-ion battery, characterized in that: A lithium sheet is used as the negative electrode, lithium phosphorus sulfur chlorine and lithium zirconium chloride are used as the solid electrolyte layer, and a composite positive electrode material prepared by the preparation method according to any one of claims 1 to 8 is used as the positive electrode material.

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