Composite cathode material and preparation method thereof

Abstract

The application relates to the technical field of solid-state batteries, in particular to a composite positive electrode material and a preparation method thereof. The composite positive electrode material comprises an inner core, a catalytic layer and a coating layer which are sequentially coated on the surface of the inner core from inside to outside. The inner core comprises a positive electrode material, the positive electrode material is one or more of ternary materials or lithium-rich manganese-based materials; the catalytic layer comprises dicyanamide; and the coating layer comprises modified polyethylene oxide and LCSZM.LATP high-entropy solid melt electrolyte. The modified polyethylene oxide serves as a polymer electrolyte base material, and the LCSZM.LATP high-entropy solid melt electrolyte wraps the modified polyethylene oxide. Through the technical scheme, the service life and safety of the composite positive electrode material are improved, the possibility of lithium dendrite generation is reduced, and the power performance of the composite positive electrode material is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid-state batteries, and in particular relates to a composite positive electrode material and a preparation method thereof. Background Art

[0002] As China vigorously develops its new energy industry, the energy density of liquid lithium batteries is approaching its limit. The flammability of liquid electrolytes also poses safety risks. Solid-state batteries, with their superior safety and energy density, are widely recognized as the next generation of battery development.

[0003] Existing solid-state lithium metal electrolytes are primarily classified into three categories: polymer solid electrolytes, inorganic solid electrolytes, and composite solid electrolytes. Polymer-based solid electrolytes offer excellent mechanical flexibility and formability and are commonly used in thin-film electrolyte materials. However, their ionic conductivity is relatively low, typically failing to achieve the conductivity levels required for lithium metal batteries at room temperature. Furthermore, polymer electrolytes exhibit poor chemical stability at the lithium metal anode interface and are prone to side reactions with the lithium metal, forming an unstable interfacial layer that increases interfacial impedance and degrades battery performance. Consequently, composite solid electrolytes have become a research hotspot. Composite electrolytes enhance ionic conductivity by incorporating inorganic fillers, such as alumina and silica, or oxide-based solid electrolytes, into a polymer matrix. Furthermore, surface modification or the addition of a transition layer can enhance interfacial stability with the positive and negative electrodes. However, as the positive electrode material undergoes charge and discharge, the volume expansion rate can reach as high as 6.9% for high-nickel materials, while the volume expansion rate for lithium-rich manganese-based materials, due to irreversible phase transitions triggered by oxygen activity, is 5-8%. Due to this characteristic of the cathode material, the cathode material layer expands and contracts in a quasi-rigid interface manner. As the cycle progresses, gaps gradually appear between the cathode and electrolyte layers, causing poor interfacial contact, increased interfacial resistance, energy loss, and active lithium consumption. Lithium dendrites form and accumulate at the interfacial gaps, accelerating local degradation and ultimately leading to cell capacity decay or failure. Therefore, developing a modification technology that can effectively improve the interface characteristics between the cathode and solid electrolyte has become a hot topic and a difficult problem in current solid-state battery research. Summary of the Invention

[0004] To address the above problems, the present invention provides a composite cathode material and a preparation method thereof. The material consists of three layers: an outer coating layer comprising a modified polyethylene oxide (PEO) polymer electrolyte substrate encapsulating an LCSZM·LATP high-entropy solid solution electrolyte material; a middle layer comprising a dicyandiamide in-situ coated on the surface of the cathode material as a catalytic layer; and an inner layer comprising a ternary or lithium-rich manganese-based cathode material.

[0005] In a first aspect, the present invention provides a composite cathode material, comprising: a core, and a catalytic layer and a coating layer sequentially coated on the surface of the core from the inside out;

[0006] The core includes a positive electrode material, and the positive electrode material is one or more of a ternary material or a lithium-rich manganese-based material;

[0007] The catalytic layer includes dicyandiamide in situ coated on the surface of the core;

[0008] The coating layer includes modified polyethylene oxide and LCSZM·LATP high entropy solid solution electrolyte, wherein the modified polyethylene oxide serves as a polymer electrolyte substrate, and the LCSZM·LATP high entropy solid solution electrolyte wraps the modified polyethylene oxide; the molecular formula of the LCSZM·LATP high entropy solid solution electrolyte is Li a Al b Ti c (LiZrMoSrCo) x (PO4)3(1 <a,c<1.9,0<b,x<0.6),优选为Li 1.4 Al 0.3 Co 0.1 Zr 0.1 Ti 1.3 Mo 0.1 Sr 0.1 (PO4)3.

[0009] Optionally, the modified polyethylene oxide is formed by at least partial polymerization of polyethylene oxide and E12 epoxy resin.

[0010] In a second aspect, the present invention further provides a method for preparing a composite positive electrode material, for preparing the composite positive electrode material according to the first aspect, the method comprising:

[0011] Step 1: At a set pH, the cathode material is in situ coated with a cyanamide solution to form an intermediate product, wherein the core of the intermediate product is the cathode material and the catalytic layer is coated on the outer surface of the core;

[0012] Step 2, preparing modified polyethylene oxide;

[0013] Step 3: forming a coating layer composed of the modified polyethylene oxide and the LCSZM·LATP high entropy solid solution electrolyte on the outer surface of the intermediate product to obtain a composite positive electrode material; wherein the modified polyethylene oxide serves as a polymer electrolyte substrate, and the LCSZM·LATP high entropy solid solution electrolyte wraps the modified polyethylene oxide.

[0014] Optionally, the step 2, preparing modified polyethylene oxide, comprises:

[0015] Step 21: Mix polyethylene oxide and E12 epoxy resin and then perform pulse heating to allow the polyethylene oxide and the E12 epoxy resin to undergo a polymerization reaction to obtain the modified polyethylene oxide.

[0016] Optionally, step 21, mixing polyethylene oxide and E12 epoxy resin and then pulse heating, comprises:

[0017] Step 211: Add polyethylene oxide and E12 epoxy resin to a reactor, and control the temperature of the reactor to be between 25°C and 40°C. Add solvent to the reactor, dissolve the solvent, and then add hydroquinone, and stir evenly. The amount of hydroquinone added is 0.1% to 0.8% of the total mass of the polyethylene oxide and the E12 epoxy resin.

[0018] Step 212: After the temperature in the reactor is raised to a first temperature at a heating rate of 1°C / min-3°C / min, the MHHPA solution is added dropwise to the reactor for a first time;

[0019] Step 213: lowering the temperature in the reactor to a second temperature;

[0020] Step 214: cyclically execute steps 212 and 213 until the amount of the MHHPA solution added dropwise to the reactor reaches a preset mass, lowering the temperature of the solution in the reactor to 25-40° C. and stirring to obtain modified polyethylene oxide; wherein the mass of the MHHPA solution is 10%-35% of the mass of the E12 epoxy resin, preferably 22.5%.

[0021] Optionally, step 3, forming a coating layer composed of the modified polyethylene oxide and the LCSZM·LATP high entropy solid solution electrolyte on the outer surface of the intermediate product to obtain a composite positive electrode material, comprises:

[0022] The intermediate product and LCSZM·LATP high entropy solid solution electrolyte are added to the modified polyethylene oxide, and the mixture is dried in a vacuum oven at 50°C-80°C so that the cathode material, LCSZM·LATP high entropy solid solution electrolyte, and modified polyethylene oxide in the intermediate product form a point-like three-dimensional cross-linked structure to obtain the composite cathode material.

[0023] Optionally, the mass ratio of the polyethylene oxide to the E12 epoxy resin is 100:1-8:1.

[0024] Optionally, the mass of the cyanamide is 0.05%-0.5% of the mass of the positive electrode material.

[0025] Optionally, the mass ratio of the LCSZM·LATP high entropy solid solution electrolyte to the modified polyethylene oxide is 8:2-1:9; the total mass of the modified polyethylene oxide and the LCSZM·LATP high entropy solid solution electrolyte is 0.5%-5% of the mass of the positive electrode material.

[0026] The technical solution provided by the present invention has the following advantages compared with the prior art:

[0027] The present invention provides a composite positive electrode material and a preparation method thereof, wherein nano-Li a Al b Ti c (LiZrMoSrCo) x (PO4)3 material and modified PEO are composited as the coating layer of the positive electrode material. Dicyandiamide is used as a catalyst to catalyze the ring opening of the partially cross-linked E12 epoxy material with the PEO at 50-80°C, forming a point-like three-dimensional cross-linked structure on the surface of the positive electrode material. The outer coating layer is always tightly adhered to the surface of the positive electrode material during the expansion and contraction of the positive electrode material, and no gaps are formed between the electrolyte and the rigid positive electrode material, thereby reducing the possibility of lithium dendrite formation. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0029] In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0030] Figure 1 A schematic flow chart of a method for preparing a composite positive electrode material provided by the present invention;

[0031] Figure 2 This is the SEM image of the composite positive electrode material provided in Example 1. DETAILED DESCRIPTION

[0032] In order to more clearly understand the above-mentioned objectives, features and advantages of the present disclosure, the scheme of the present disclosure will be further described below. It should be noted that the embodiments of the present disclosure and the features therein can be combined with each other in the absence of conflict.

[0033] In the following description, many specific details are set forth to facilitate a full understanding of the present disclosure, but the present disclosure may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present disclosure, rather than all of the embodiments.

[0034] In a first aspect, the present invention provides a composite positive electrode material, comprising: a core, and a catalytic layer and a coating layer sequentially coated on the surface of the core from the inside out; the core comprises a positive electrode material, the positive electrode material being one or more of a ternary material or a lithium-rich manganese-based material; the catalytic layer comprises dicyandiamide in situ coated on the surface of the core; the coating layer comprises modified polyethylene oxide and LCSZM·LATP high entropy solid solution electrolyte, the modified polyethylene oxide serving as a polymer electrolyte substrate, the LCSZM·LATP high entropy solid solution electrolyte coating the modified polyethylene oxide; the molecular formula of the LCSZM·LATP high entropy solid solution electrolyte material is Li a Al b Ti c (LiZrMoSrCo) x (PO4)3(1 <a,c<1.9,0<b,x<0.6),优选为Li 1.4 Al 0.3 Co 0.1 Zr 0.1 Ti 1.3 Mo 0.1 Sr 0.1 (PO4)3.

[0035] Alternatively, the modified polyethylene oxide is formed by at least partial polymerization of polyethylene oxide and E12 epoxy resin.

[0036] In a second aspect, the present invention provides a method for preparing a composite positive electrode material, which is used to prepare the composite positive electrode material provided in the first aspect. Figure 1 A schematic diagram of a process for preparing a composite positive electrode material provided by the present invention is shown in FIG. Figure 1 As shown, the preparation method includes:

[0037] Step 1: At a set pH, the cathode material is in situ coated with a cyanamide solution to form an intermediate product, wherein the core of the intermediate product is the cathode material and the catalytic layer is coated on the outer surface of the core;

[0038] Step 2, preparing modified polyethylene oxide;

[0039] Step 3: forming a coating layer composed of modified polyethylene oxide and LCSZM·LATP high entropy solid solution electrolyte on the outer surface of the intermediate product to obtain a composite positive electrode material; wherein the modified polyethylene oxide serves as a polymer electrolyte substrate, and the LCSZM·LATP high entropy solid solution electrolyte wraps the modified polyethylene oxide.

[0040] Among them, the molecular formula of LCSZM·LATP high entropy solid solution electrolyte material is Li a Al b Ti c (LiZrMoSrCo) x (PO4)3(1 <a,c<1.9,0<b,x<0.6),优选为Li 1.4 Al 0.3 Co 0.1 Zr 0.1 Ti 1.3 Mo 0.1 Sr 0.1 (PO4)3.

[0041] The following is a specific process for preparing the composite positive electrode material:

[0042] Step 1: Add pure water and ammonia to a reactor, heat to 50°C, adjust the pH to between 9.5 and 10, add the cathode material, and while stirring, uniformly add a certain amount of cyanamide solution dropwise. Simultaneously, add ammonia to maintain the pH at the same level as the base solution. The reacted material is separated into a solid and liquid state to obtain an intermediate product. Step 2: Add PEO and E12 epoxy resin in appropriate proportions to a double-layer glass reactor. Use a thermostat to control the reactor temperature between 25 and 40°C. Add acetonitrile solvent and stir to dissolve. Then, add a certain amount of hydroquinone and stir evenly. The water jacket temperature is controlled by a thermostat. Raise the reactor temperature at 1°C / min to 80°C. Add a certain amount of MHHPA (methylhexahydrophthalic anhydride) solution dropwise while stirring. After reaching 80°C and holding for 5 seconds, stop adding the solution. Switch to 10°C cold water and cool the reactor until the temperature is below 60°C. Repeat the heating cycle to 80°C and hold for 5 seconds until all the MHHPA solution has been added. Cool to 25°C and continue stirring for 30-60 minutes to obtain modified polyethylene oxide. Step 3: Add a certain amount of high-entropy solid solution electrolyte LCSZM·LATP material and the intermediate product obtained in step 1 to the solution in step 2, stir evenly, pour into a vacuum rotary evaporator, stir to evaporate the liquid to dryness, and dry in a vacuum oven at 50°C-80°C for 4-8 hours to obtain the solid electrolyte composite coated modified positive electrode material provided by the present invention.

[0043] In order to better understand the present invention, examples and comparative examples are provided below.

[0044] Example 1: Add pure water and ammonia water to the reactor, heat to 50°C, adjust the pH value to between 9.7-10, and add 200g single crystal Li 1.2 Ni 0.13 Co 0.13 Mn 0.54O2 material, 0.4 g of monomethylamine solution dissolved in 50 mL of water was added at a constant speed during stirring, and ammonia water was added at the same time to keep the pH at 9.7. The completed reaction material was separated by solid-liquid separation to obtain an intermediate product. PEO and E12 epoxy resin were added to the double-layer glass reaction kettle in a mass ratio of 10:1, a total of 2.2 g, the temperature of the reaction kettle was controlled at 25°C by using a cold and hot integrated mold temperature controller, 30 g of acetonitrile solvent was injected, stirred and dissolved, and then 0.01 g of hydroquinone was added and stirred uniformly. The temperature of the water jacket was controlled by setting the cold and hot integrated mold temperature controller, and the temperature in the double-layer glass reaction kettle was raised to 80°C at a rate of 1°C per minute. After reaching 80°C, the MHHPA solution was added, and 5 seconds later, the temperature was switched to 10°C cold water, the MHHPA solution was stopped, and the temperature was lowered to below 60°C. After the temperature in the reaction kettle was lowered to below 60°C, the step of adding the MHHPA solution was repeated by raising the temperature to 80°C. The total amount of MHHPA solution added was 0.04 g. After the MHHPA solution was completely added, the solution was cooled to 25°C and stirred for 30 min. 2.2 g of Li 1.4 Al 0.3 Co 0.1 Zr 0.1 Ti 1.3 Mo 0.1 Sr 0.1 (PO4)3 material, and 200 g of the positive electrode material treated in step 1 was added, stirred uniformly, and injected into a vacuum rotary evaporator. The liquid was evaporated by stirring, transferred to a vacuum oven, and dried at 80°C for 6 h to obtain the modified polyethylene oxide and high-entropy solid solution Li 1.4 Al 0. 3Co 0.1 Zr 0.1 Ti 1.3 Mo 0.1 Sr 0.1 (PO4)3 coated solid electrolyte single crystal Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 material. Figure 2 The SEM image of the single crystal Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 material prepared in Example 1. Figure 2 It can be seen that the Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 material is a single crystal morphology.

[0045] Example 2: The same method as in Example 1 was used, except that the vacuum oven drying temperature was 70°C.

[0046] Example 3: The same operation as in Example 1 was performed, except that 2.2 g of PEO and E12 epoxy resin were added to a double-layer glass reactor in a mass ratio of 10:1, and the reactor temperature was controlled at 35°C using a hot and cold integrated mold temperature controller.

[0047] The comparative example is the original cathode material without coating, single crystal Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 material.

[0048] The composite cathode materials from Example 1 and the comparative example were thoroughly mixed with a conductive agent and a binder to form a cathode slurry. This slurry was then coated onto aluminum foil to form a cathode sheet. After drying, the sheet was assembled with a graphite anode and a solid electrolyte to produce a pouch-type solid-state battery. The electrochemical performance test results are listed in Table 1.

[0049] Table 1 Electrochemical performance test results of composite cathode materials

[0050] project Example 1 Example 2 Example 3 Comparative Example 0.1C discharge specific capacity (mAh / g) 289.6 296.3 291.1 285.1 1C discharge specific capacity (mAh / g) 266.9 275.0 271.2 211.5 2C discharge capacity / 1C discharge capacity (%) 87.7 89.5 85.3 59.2 Capacity retention rate after 100 cycles at 45°C (%) 89.5 91.8 90.2 73.6

[0051] As can be seen from Table 1, in the electrochemical performance test, the composite positive electrode material prepared by the present invention has a discharge specific capacity of more than 289.6 mAh / g at 0.1C, and a discharge specific capacity of more than 266.9 mAh / g at 1C, which is much larger than 211.5 mAh / g of the comparative example. The 100-cycle capacity retention rate at 45°C can be as high as more than 89.5%.

[0052] In summary, the present invention provides a composite cathode material and preparation method thereof. Modified polyethylene oxide and LCSZM·LATP high-entropy solid-solution electrolyte serve as the coating layer of the cathode material, and dicyandiamide serves as the catalytic layer. At 50°C-80°C, a partially cross-linked E12 epoxy resin material in the modified polyethylene oxide undergoes catalytic ring-opening on the surface of the cathode material, forming a point-like three-dimensional cross-linked structure on the surface of the cathode material. The rigid surface of the original cathode material is replaced with the flexible surface of the modified polyethylene oxide. This ensures that the coating layer remains tightly attached to the surface of the cathode material during expansion and contraction, preventing the formation of gaps between the LCSZM·LATP high-entropy solid-solution electrolyte and the rigid cathode material, thereby reducing the likelihood of lithium dendrite formation. Furthermore, the modified polyethylene oxide and LCSZM·LATP high-entropy solid-solution electrolyte in the coating layer improve the material's ionic conductivity, thereby enhancing the power performance of the composite cathode material.

[0053] The composite positive electrode material provided by the present invention comprises nano-Li a Al b Ti c(LiZrMoSrCo) x The (PO4)3 material and the modified PEO layer are composited as the coating layer of the positive electrode material. The coating layer is firmly attached to the surface of the positive electrode material through catalytic three-dimensional cross-linking, which improves the ionic conductivity of the material to a certain extent and significantly improves the power performance. The coating layer can shrink and expand with the positive electrode material, replacing the original positive electrode rigid surface with the flexible surface of the PEO material, reducing the possibility of gaps between the electrolyte layer and the positive electrode material layer to produce lithium dendrites, and improving the overall life and safety of the battery cell.

[0054] Although the present invention has been described above, the present invention is not limited to the above-mentioned specific embodiments. The above-mentioned specific embodiments are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can make many variations without departing from the purpose of the present invention, and these are all protected by the present invention.

Claims

1. A composite positive electrode material, characterized in that The composite positive electrode material comprises: a core, and a catalytic layer and a coating layer sequentially coated on the surface of the core from the inside to the outside; The core includes a positive electrode material, and the positive electrode material is one or more of a ternary material or a lithium-rich manganese-based material; The catalytic layer includes dicyandiamide in situ coated on the surface of the core; The coating layer includes modified polyethylene oxide and LCSZM·LATP high entropy solid solution electrolyte, wherein the modified polyethylene oxide serves as a polymer electrolyte substrate, and the LCSZM·LATP high entropy solid solution electrolyte wraps the modified polyethylene oxide; the molecular formula of the LCSZM·LATP high entropy solid solution electrolyte is Li a Al b Ti c (LiZrMoSrCo) x (PO4)3,1 <a,c<1.9,0<b,x<0.6。 2. The composite cathode material according to claim 1, characterized in that The modified polyethylene oxide is formed by at least partial polymerization of polyethylene oxide and E12 epoxy resin.

3. A method for preparing a composite positive electrode material, characterized in that: For preparing the composite positive electrode material according to any one of claims 1 to 2, the method comprises: Step 1: At a set pH, the cathode material is in situ coated with a cyanamide solution to form an intermediate product, wherein the core of the intermediate product is the cathode material and the catalytic layer is coated on the outer surface of the core; Step 2, preparing modified polyethylene oxide; Step 3: forming a coating layer composed of the modified polyethylene oxide and the LCSZM·LATP high entropy solid solution electrolyte on the outer surface of the intermediate product to obtain a composite positive electrode material; wherein the modified polyethylene oxide serves as a polymer electrolyte substrate, and the LCSZM·LATP high entropy solid solution electrolyte wraps the modified polyethylene oxide.

4. The method for preparing a composite positive electrode material according to claim 3, wherein: The step 2, preparing modified polyethylene oxide, comprises: Step 21: Mix polyethylene oxide and E12 epoxy resin and then perform pulse heating to allow the polyethylene oxide and E12 epoxy resin to undergo a polymerization reaction to obtain the modified polyethylene oxide.

5. The method for preparing a composite positive electrode material according to claim 4, wherein: The step 21 of mixing polyethylene oxide and E12 epoxy resin and then pulse heating the mixture comprises: Step 211: Add polyethylene oxide and E12 epoxy resin to a reactor, and control the temperature of the reactor to be between 25°C and 40°C. Add solvent to the reactor, dissolve the solvent, and then add hydroquinone, and stir evenly. The amount of hydroquinone added is 0.1% to 0.8% of the total mass of the polyethylene oxide and the E12 epoxy resin. Step 212: After the temperature in the reactor is raised to a first temperature at a heating rate of 1°C / min-3°C / min, the MHHPA solution is added dropwise to the reactor for a first time; Step 213: lowering the temperature in the reactor to a second temperature; Step 214: cyclically execute steps 212 and 213 until the amount of the MHHPA solution added dropwise to the reactor reaches a preset mass, lowering the temperature of the solution in the reactor to 25-40° C. and stirring to obtain modified polyethylene oxide; wherein the mass of the MHHPA solution is 10%-35% of the mass of the E12 epoxy resin.

6. The method for preparing a composite positive electrode material according to claim 3, wherein: The step 3, forming a coating layer composed of the modified polyethylene oxide and the LCSZM·LATP high entropy solid solution electrolyte on the outer surface of the intermediate product to obtain a composite positive electrode material, comprises: The intermediate product and LCSZM·LATP high entropy solid solution electrolyte are added to the modified polyethylene oxide, and the mixture is dried in a vacuum oven at 50°C-80°C so that the cathode material, LCSZM·LATP high entropy solid solution electrolyte, and modified polyethylene oxide in the intermediate product form a point-like three-dimensional cross-linked structure to obtain the composite cathode material.

7. The method for preparing a composite cathode material according to claim 4 or 5, characterized in that: The mass ratio of the polyethylene oxide to the E12 epoxy resin is 100:1-8:

1.

8. The method for preparing a composite cathode material according to claim 3, wherein: The mass of the cyanamide is 0.05%-0.5% of the mass of the positive electrode material.

9. The method for preparing a composite cathode material according to claim 3, wherein: The mass ratio of the LCSZM·LATP high entropy solid solution electrolyte to the modified polyethylene oxide is 8:2-1:9; the total mass of the modified polyethylene oxide and the LCSZM·LATP high entropy solid solution electrolyte is 0.5%-5% of the mass of the positive electrode material.

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