Lithium-ion battery composite positive electrode material, and preparation method therefor and use thereof

Abstract

A lithium-ion battery composite positive electrode material, and a preparation method therefor and the use thereof. The lithium-ion battery composite positive electrode material comprises a positive electrode matrix material and a composite polymer coating layer coating the surface of the positive electrode matrix material. The composite polymer coating layer is obtained by means of a cross-linking reaction of an ionic conductive polymer and PEDOT:PSS. The ionic conductive polymer comprises any one or a combination of at least two of PEO, PEG or PEI. By means of cross-linking the ionic conductive polymer and PEDOT:PSS, a uniform and compact composite polymer coating layer is formed, thereby reducing the crystallinity of the ionic conductive polymer, and modifying a sulfonic acid group of PEDOT:PSS, such that the synergistic effect of the ionic conductive polymer and PEDOT:PSS achieves an electron-ion dual-function channel conductive effect. The composite polymer coating layer effectively improves the electron transport rate and reaction kinetics of the positive electrode material.

Description

A lithium-ion battery composite positive electrode material and its preparation method and application Technical Field

[0001] The present disclosure belongs to the field of battery technology, and particularly relates to a lithium-ion battery composite positive electrode material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries (LIBs) have been widely used commercially due to their high voltage, high specific energy, and long cycle life, becoming the mainstream technology in the new generation of energy storage batteries. Among the various lithium-ion batteries, lithium iron phosphate (LiFePO4) has advantages such as low raw material costs, a high operating voltage platform, thermal stability, and excellent electrochemical cycling performance. It not only holds a large market share in power batteries, but also has explosive growth in demand in areas such as base station energy storage and new energy. However, LiFePO4 is limited by its stable olivine crystal structure, which means that lithium ions can only diffuse in one-dimensional channels, resulting in slow electron transmission rates. These problems have greatly restricted the future commercial development of lithium iron phosphate batteries.

[0003] There are many methods for modifying lithium iron phosphate, among which coating is the most common, simple and practical method, and the required coating raw materials are widely available and low in cost. The carbon-coated LiFePO4 positive electrode material not only improves its disadvantage of poor conductivity, but also optimizes the particle size and morphology. The patent with publication number CN105244481B synthesizes in-situ carbon-coated lithium iron phosphate (LiFePO4 / C) positive electrode material by liquid phase-ball milling method, which can improve the electrochemical performance and effectively inhibit the agglomeration and excessive growth of LiFePO4. However, this carbon coating strategy also has its limitations. The carbon material itself has a low mass density, and after coating, it has a side effect on the solid-solid contact between the positive electrode materials, increases the gap between the particles, and reduces the tap density of the material. To this end, researchers began to turn their attention to using a conductive flexible coating to stabilize the contact between positive electrode particles. The patent with publication number CN102185140B uses a surfactant as a template to allow conductive polymer monomers to be in situ polymerized on the surface of lithium iron phosphate and grow into a nano-network structure to act as a coating. This coating method mostly only uses a single electronic conductive polymer for coating, which has almost no effect on improving the ionic conductivity of lithium iron phosphate.

[0004] Therefore, designing a flexible coating layer that is both electronically and ionically conductive to stabilize the contact between positive electrode particles, improve the electrical conductivity of the material, and give full play to the electrical properties of the positive electrode material is one of the key research directions that needs to be urgently studied.

[0005] Summary of the Invention

[0006] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0007] In response to the shortcomings of the prior art, the present disclosure aims to provide a composite positive electrode material for lithium-ion batteries, a preparation method thereof, and applications thereof. The present disclosure forms a uniform and dense composite polymer coating layer by coating the positive electrode substrate material with an ion-conductive polymer and PEDOT:PSS cross-linking. The cross-linking effect reduces the crystallinity of the ion-conductive polymer and modifies the sulfonic acid groups of PEDOT:PSS. The synergistic effect of the two further improves the conductivity of PEDOT:PSS-PEO, achieving an electron-ion dual-functional channel conduction effect. The composite polymer coating layer not only improves the electron transport rate and reaction kinetics of the positive electrode material, but also improves the contact between the positive electrode particles by taking into account the flexibility of the coating layer, significantly improving the electrical performance of the positive electrode material.

[0008] To achieve this purpose, the present disclosure adopts the following technical solutions:

[0009] In a first aspect, the present disclosure provides a lithium-ion battery composite positive electrode material, the lithium-ion battery composite positive electrode material comprising a positive electrode base material and a composite polymer coating layer coated on the surface of the positive electrode base material;

[0010] The composite polymer coating layer is obtained by cross-linking reaction between an ion conductive polymer and PEDOT:PSS;

[0011] The ion conductive polymer includes any one of PEO, PEG or PEI or a combination of at least two of them.

[0012] The present invention uses an ion-conducting polymer and PEDOT:PSS cross-linked to coat the cathode substrate material, forming a uniform and dense composite polymer coating. The cross-linking effect reduces the crystallinity of the ion-conducting polymer and modifies the sulfonic acid groups of PEDOT:PSS. The synergistic effect of the two further enhances the conductivity of PEDOT:PSS-PEO, achieving electron-ion dual-functional channel conduction. This composite polymer coating not only improves the electron transport rate and reaction kinetics of the cathode material, but also improves the contact between the cathode particles by taking into account the flexibility of the coating, significantly enhancing the electrical performance of the cathode material.

[0013] In this disclosure, an electronically conductive polymer, PEDOT:PSS, undergoes a crosslinking reaction with an ionically conductive polymer. The protonated hydroxyl groups in the ionically conductive polymer react with the sulfonic acid in the PSS to form a hydrophobic sulfonate. The presence of the hydrophobic group reduces the adsorption of moisture from the positive electrode active material, preventing residual moisture in the positive electrode from reacting with the electrolyte and damaging the SEI film, thereby effectively improving the battery's coulombic efficiency and cycle performance. Furthermore, the crosslinked polymer not only isolates the electrolyte from contact but also maintains a certain degree of flexibility, stabilizing contact between the positive electrode particles and fully utilizing the performance of the positive electrode material.

[0014] It should be noted that PEO refers to polyethylene oxide, a crystalline, thermoplastic water-soluble polymer; PEG refers to polyethylene glycol, an addition polymer of polyethylene oxide and water; PEI refers to polyetherimide, an amorphous high-performance polymer; PEDOT:PSS is composed of two substances, PEDOT and PSS. PEDOT is a polymer of EDOT (3,4-ethylenedioxythiophene monomer) and PSS is polystyrene sulfonate.

[0015] As an optional technical solution of the present disclosure, the composite polymer coating layer is a mesh structure.

[0016] In the present disclosure, the composite polymer coating layer has a network structure and can uniformly and tightly coat the lithium iron phosphate.

[0017] In one embodiment, the ion conducting polymer is PEO.

[0018] As an optional technical solution of the present disclosure, the thickness of the composite polymer coating is 2-20 nm, for example, it can be 2 nm, 4 nm, 6 nm, 8 nm, 10 nm, 12 nm, 14 nm, 16 nm, 18 nm or 20 nm.

[0019] In the present disclosure, if the thickness of the composite polymer coating layer is too small, the coating layer cannot completely isolate the electrolyte; if the thickness of the composite polymer coating layer is too large, it will seriously affect the lithium ion transmission and thus affect the battery performance.

[0020] As an optional technical solution of the present disclosure, the particle size D50 of the positive electrode matrix material is 0.8-2.5 μm, for example, it can be 0.8 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.4 μm or 2.5 μm, etc.

[0021] In one embodiment, the positive electrode matrix material includes lithium iron phosphate.

[0022] It should be noted that lithium iron phosphate is limited by its own stable olivine crystal structure. Lithium ions can only diffuse in one-dimensional channels and the electron transmission rate is slow. To address this problem, the present disclosure modifies the lithium iron phosphate material and greatly optimizes its performance.

[0023] In a second aspect, the present disclosure provides a method for preparing the composite positive electrode material for a lithium-ion battery as described in the first aspect, the preparation method comprising the following steps:

[0024] The ion conductive polymer, PEDOT:PSS, a positive electrode matrix material and a solvent are mixed and heat treated to obtain the lithium ion battery composite positive electrode material.

[0025] The preparation method provided by the present disclosure has simple process, low cost, and can be applied to large-scale industrial production.

[0026] As an optional technical solution of the present disclosure, the molar ratio of the ion conductive polymer and PEDOT:PSS is (1-5):(5-9), wherein the selection range of the ion conductive polymer "1-5" can be, for example, 1, 2, 3, 4 or 5, and the selection range of PEDOT:PSS "5-9" can be, for example, 5, 6, 7, 8 or 9.

[0027] In the present disclosure, if the molar ratio of the ion conductive polymer to PEDOT:PSS is too small, the ion conductive polymer is too little and cannot play the expected ion conductive role; if the molar ratio of the ion conductive polymer to PEDOT:PSS is too large, the ion conductive polymer is too much, which will affect the transmission rate of electronic conduction.

[0028] As an optional technical solution of the present disclosure, the preparation method of the positive electrode base material includes:

[0029] The raw materials of the positive electrode matrix material and the carbon source are mixed, pre-sintered and sintered once, and then sintered twice to obtain the positive electrode matrix material.

[0030] The present invention adds a carbon source during the preparation of the positive electrode matrix material and removes it in the subsequent process. This process is beneficial for the carbon source to act as a reducing agent during high-temperature roasting, which can reduce Fe3+ to Fe2+, avoid the formation of impurities, and improve product purity.

[0031] In one embodiment, based on the total mass of the raw materials of the positive electrode matrix material, the mass fraction of the carbon source is 3-15%, for example, 3%, 5%, 7%, 9%, 11%, 13% or 15%.

[0032] In the present disclosure, the mass fraction of the carbon source is 3-15%. Within this range, the carbon source can play the greatest role. Too little carbon source cannot completely reduce the divalent iron, and too much carbon source will affect the thickness of the coating layer, which is not conducive to later removal.

[0033] In one embodiment, the pre-calcination temperature is 200-400°C, for example, 200°C, 250°C, 300°C, 350°C or 400°C, and the holding time is 2-6h, for example, 2h, 3h, 4h, 5h or 6h.

[0034] The present disclosure pre-sinters the mixture of the raw material of the positive electrode matrix material and the carbon source within the above parameter range, which can promote the formation of nuclear crystals of lithium iron phosphate and close adhesion with the carbon source.

[0035] In one embodiment, the pre-firing is performed in a protective atmosphere, and the gas in the protective atmosphere includes argon or nitrogen.

[0036] In one embodiment, the primary sintering temperature is 600-750°C, for example, 600°C, 650°C, 700°C or 750°C, and the holding time is 4-10h, for example, 4h, 5h, 6h, 7h, 8h, 9h or 10h.

[0037] In the present disclosure, a single sintering at 600-750° C. for 4-10 hours can help the lithium iron phosphate recrystallize, reduce defects and form spherical particles with better crystal form.

[0038] In one embodiment, the primary sintering is performed in a protective atmosphere, and the gas in the protective atmosphere includes argon.

[0039] In one embodiment, the secondary sintering temperature is 400-700°C, for example, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C or 700°C, and the holding time is 0.5-2h, for example, 0.5h, 1h, 1.5h or 2h.

[0040] In the present disclosure, a secondary sintering at 400-700° C. for 0.5-2 h can allow the carbon in the lithium iron phosphate to react with substances in the atmosphere and be released, leaving more reaction sites.

[0041] In one embodiment, the secondary sintering is performed in a carbon dioxide atmosphere.

[0042] In the present disclosure, the positive electrode matrix material is placed in a carbon dioxide atmosphere for secondary sintering. The reaction between carbon and carbon dioxide can generate carbon monoxide, thereby effectively removing carbon residues on the surface and exposing more reaction sites. This not only allows the dual conductive polymer and lithium iron phosphate to be more tightly bonded, but also avoids repeated coating to reduce the tap density.

[0043] As an optional technical solution of the present disclosure, the method of mixing PEO, PEDOT:PSS, positive electrode matrix material and solvent includes:

[0044] PEO, PEDOT:PSS and a solvent are mixed once to obtain a polymer solution, and then the polymer solution and the positive electrode matrix material are mixed twice.

[0045] In the present disclosure, the above-mentioned mixing method is adopted to facilitate uniform wrapping of the polymer on the positive electrode matrix material.

[0046] In one embodiment, based on the mass of the positive electrode matrix material, the mass fraction of the mixture of the ion conductive polymer and PEDOT:PSS is 1-10%, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc.

[0047] In the present disclosure, if the mass fraction of the mixture of the ion conductive polymer and PEDOT:PSS is too low, the thickness of the coating layer is too small and effective coating cannot be performed; if the mass fraction of the mixture of the ion conductive polymer and PEDOT:PSS is too high, the thickness of the coating layer will be too large, which is not conducive to the transmission of lithium ions in the battery and affects the electrical performance of the battery.

[0048] In one embodiment, the primary mixing process is accompanied by stirring, and the stirring time is 2-4 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours or 4 hours.

[0049] The present invention performs stirring during a mixing process, which can make the materials mixed more fully.

[0050] In one embodiment, the secondary mixing process is accompanied by stirring, and the stirring time is 1-3 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours or 3 hours.

[0051] The present invention performs stirring during the secondary mixing process, which can make the materials mixed more fully.

[0052] In one embodiment, the heat treatment temperature is 80-130°C, for example, 80°C, 90°C, 100°C, 110°C, 120°C or 130°C, and the heat treatment time is 2-8h, for example, 2h, 3h, 4h, 5h, 6h, 7h or 8h, etc.

[0053] In the present disclosure, if the heat treatment temperature is too low, the cross-linking reaction temperature cannot be reached, and the mixed polymer can only become a mixture rather than a cross-linked product; if the heat treatment temperature is too high, the polymer will degrade and the structure will change, affecting its own properties.

[0054] In one embodiment, the heat treatment is accompanied by stirring.

[0055] In one embodiment, after the heat treatment is completed, filtering and drying steps are further performed.

[0056] In the present disclosure, the steps of filtering and drying can help remove the solvent in the lithium iron phosphate to avoid affecting its electrical properties.

[0057] In one embodiment, the drying temperature is 50-90°C, for example, 50°C, 60°C, 70°C, 80°C or 90°C, and the drying time is 6-36h, for example, 6h, 12h, 18h, 24h, 30h or 36h.

[0058] As an optional technical solution of the present disclosure, the preparation method includes the following steps:

[0059] (1) ball-milling the raw materials of the positive electrode matrix material and the carbon source for 2-5 hours, then drying the obtained mixture to obtain a precursor powder, pre-calcining the precursor powder at 200-400°C for 2-6 hours in a protective atmosphere, then sintering the precursor powder at 600-750°C for 4-10 hours in a protective atmosphere, and then sintering the obtained product for a second time in a carbon dioxide atmosphere at a temperature of 400-700°C for 0.5-2 hours to obtain a positive electrode matrix material;

[0060] The raw materials of the positive electrode matrix material include a lithium source, a phosphorus source and an iron source. The mass fraction of the carbon source is 3-15% based on the total mass of the lithium source, the phosphorus source and the iron source.

[0061] (2) stirring and mixing PEO, PEDOT:PSS and a solvent for 2-4 hours to obtain a polymer solution, and then stirring and mixing the polymer solution and the positive electrode matrix material for a second time for 1-3 hours, and obtaining the lithium ion battery composite positive electrode material after heat treatment, filtering and drying;

[0062] Among them, the molar ratio of PEO and PEDOT:PSS is (1-5):(5-9), based on the mass of the positive electrode matrix material, the total mass fraction of the mixture of PEO and PEDOT:PSS is 1-10%, the heat treatment temperature is 80-130°C, the heat treatment time is 2-8h, and the drying temperature is 50-90°C and the time is 6-36h.

[0063] It should be noted that the present disclosure does not limit the specific type of lithium source, and illustratively, it may be lithium carbonate, lithium hydroxide or lithium acetate, etc.; the present disclosure does not limit the specific type of phosphorus source, and illustratively, it may be ammonium dihydrogen phosphate, lithium dihydrogen phosphate, iron phosphate or phosphoric acid, etc.; the present disclosure does not limit the specific type of iron source, and illustratively, it may be iron phosphate, iron oxide, iron sulfate, or ferroferric oxide, etc.; the present disclosure does not limit the specific type of carbon source, and illustratively, it may be glucose, sucrose, phenolic resin, starch, dextrin, citric acid, oxalic acid, cellulose or vitamins, etc.

[0064] In a third aspect, the present disclosure provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery includes the lithium-ion battery composite positive electrode material as described in the first aspect.

[0065] The numerical range described in the present disclosure includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present disclosure no longer exhaustively lists the specific point values ​​included in the range.

[0066] Compared with the prior art, the present disclosure has the following beneficial effects:

[0067] (1) The present invention uses an ion-conducting polymer and PEDOT:PSS cross-linked to coat the cathode substrate material, forming a uniform and dense composite polymer coating. The cross-linking effect reduces the crystallinity of the ion-conducting polymer and modifies the sulfonic acid groups of PEDOT:PSS. The synergistic effect of the two further enhances the conductivity of PEDOT:PSS-PEO, achieving electron-ion dual-functional channel conduction. This composite polymer coating not only improves the electron transport rate and reaction kinetics of the cathode material, but also improves the contact between the cathode particles by taking into account the flexibility of the coating layer, significantly enhancing the electrical performance of the cathode material.

[0068] (2) In the process of cross-linking the PEDOT:PSS and ion-conductive polymers used in the present disclosure, the protonated hydroxyl groups in the ion-conductive polymer react with the sulfonic acid in the PSS to form hydrophobic sulfonate groups. The presence of the hydrophobic groups can reduce the adsorption of moisture from the positive electrode active material to the environment, preventing the residual moisture in the positive electrode sheet from reacting with the electrolyte to destroy the SEI film, thereby effectively improving the coulombic efficiency and cycle performance of the battery. In addition, the cross-linked polymer can not only isolate the contact with the electrolyte, but also maintain a certain degree of flexibility to stabilize the contact between the positive electrode particles, giving full play to the performance of the positive electrode material.

[0069] (3) The preparation method provided by the present disclosure has simple process, low cost, and can be applied to large-scale industrial production.

[0070] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0072] FIG1 is a SEM image of the lithium-ion battery composite positive electrode material prepared in Example 3 of the present disclosure. DETAILED DESCRIPTION

[0073] The technical solution of the present disclosure is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present disclosure and should not be regarded as specific limitations of the present disclosure.

[0074] Example 1

[0075] This embodiment provides a lithium-ion battery composite positive electrode material, which includes a positive electrode base material and a composite polymer coating layer coated on the surface of the positive electrode base material;

[0076] The composite polymer coating layer is a network structure obtained by the cross-linking reaction of PEO and PEDOT:PSS;

[0077] The positive electrode matrix material is lithium iron phosphate, the particle size D50 of the positive electrode matrix material is 2.04 μm, and the thickness of the composite polymer coating layer is 10 nm.

[0078] This embodiment also provides a method for preparing the above-mentioned lithium-ion battery composite positive electrode material, which comprises the following steps:

[0079] (1) Lithium carbonate and iron phosphate are used as raw materials for the positive electrode matrix material, and are ball-milled for 2 hours in a molar ratio of Li:Fe=1.02:1 with deionized water as the medium. After being mixed evenly, glucose is added and the ball-milling is continued for 3 hours until uniform. The obtained mixture is then spray-dried to obtain a precursor powder. The precursor powder is pre-calcined at 350°C for 3 hours in an argon atmosphere. After the pre-calcination, the powder is taken out and ball-milled for 2 hours. Then, the powder is sintered at 700°C for 5 hours in an argon atmosphere. The obtained product is then sintered twice in a carbon dioxide atmosphere at a temperature of 550°C for 1 hour to obtain lithium iron phosphate, a positive electrode matrix material;

[0080] Wherein, based on the mass of the raw material of the positive electrode matrix material, the mass fraction of the glucose is 10%;

[0081] (2) PEO and PEDOT:PSS were mixed at a molar ratio of 1:9, and then dispersed in deionized water with a total mass fraction of 5% of the mass of lithium iron phosphate, stirred and mixed for 2 hours to obtain a polymer solution, and then lithium iron phosphate was immersed in the polymer solution and stirred and mixed for a second time for 2 hours, and then heated to 100°C for stirring heat treatment for 4 hours;

[0082] The mixed solution obtained after the heat treatment was filtered to obtain a solid product, which was then vacuum-dried at 60° C. for 12 h to obtain the lithium-ion battery composite positive electrode material, namely, PEDOT:PSS-PEO-coated lithium iron phosphate.

[0083] Example 2

[0084] The difference between this embodiment and embodiment 1 is that the molar ratio of PEO and PEDOT:PSS in step (2) is adjusted to 3:7.

[0085] The rest of the preparation methods and parameters remained the same as in Example 1.

[0086] Example 3

[0087] The difference between this embodiment and embodiment 1 is that the molar ratio of PEO and PEDOT:PSS in step (2) is adjusted to 1:1.

[0088] The rest of the preparation methods and parameters remained the same as in Example 1.

[0089] FIG1 shows an SEM image of the composite cathode material for lithium-ion batteries prepared in this embodiment. As can be seen from the image, after magnification 5000 times, it can be seen that the surface of lithium iron phosphate is evenly coated with a layer of PEDOT:PSS-PEO material.

[0090] Example 4

[0091] This embodiment provides a lithium-ion battery composite positive electrode material, which includes a positive electrode base material and a composite polymer coating layer coated on the surface of the positive electrode base material;

[0092] The composite polymer coating layer is a network structure obtained by the cross-linking reaction of PEO and PEDOT:PSS;

[0093] The positive electrode matrix material is lithium iron phosphate, the particle size D50 of the positive electrode matrix material is 1.96 μm, and the thickness of the composite polymer coating layer is 7 nm.

[0094] This embodiment also provides a method for preparing the above-mentioned lithium-ion battery composite positive electrode material, which comprises the following steps:

[0095] (1) Lithium carbonate and iron phosphate are used as raw materials for the positive electrode matrix material, and are ball-milled for 2 hours in a molar ratio of Li:Fe=1.02:1 with deionized water as the medium. After being mixed evenly, glucose is added and the ball-milling is continued for 3 hours until uniform. The obtained mixture is then spray-dried to obtain a precursor powder. The precursor powder is pre-calcined at 200°C for 6 hours in an argon atmosphere. After the pre-calcination, the powder is taken out and ball-milled for 2 hours. Then, the powder is sintered at 600°C for 10 hours in an argon atmosphere. The obtained product is then sintered twice in a carbon dioxide atmosphere at a temperature of 400°C for 2 hours to obtain lithium iron phosphate, a positive electrode matrix material;

[0096] Wherein, based on the mass of the raw material of the positive electrode matrix material, the mass fraction of the glucose is 5%;

[0097] (2) PEO and PEDOT:PSS were mixed in a molar ratio of 3:7, and then dispersed in deionized water with a total mass fraction of 1% of the mass of lithium iron phosphate, and stirred and mixed for 3 hours to obtain a polymer solution. The lithium iron phosphate was then immersed in the polymer solution and stirred and mixed for a second time for 1 hour, and then heated to 80°C for stirring heat treatment for 8 hours;

[0098] The mixed solution obtained after the heat treatment was filtered to obtain a solid product, which was then vacuum-dried at 70° C. for 18 h to obtain the lithium-ion battery composite positive electrode material, namely, PEDOT:PSS-PEO-coated lithium iron phosphate.

[0099] Example 5

[0100] This embodiment provides a lithium-ion battery composite positive electrode material, which includes a positive electrode base material and a composite polymer coating layer coated on the surface of the positive electrode base material;

[0101] The composite polymer coating layer is a network structure obtained by the cross-linking reaction of PEO and PEDOT:PSS;

[0102] The positive electrode matrix material is lithium iron phosphate, the particle size D50 of the positive electrode matrix material is 2.02 μm, and the thickness of the composite polymer coating layer is 14 nm.

[0103] This embodiment also provides a method for preparing the above-mentioned lithium-ion battery composite positive electrode material, which comprises the following steps:

[0104] (1) Lithium carbonate and iron phosphate are used as raw materials for the positive electrode matrix material, and are ball-milled for 2 hours in a molar ratio of Li:Fe=1.02:1 with deionized water as the medium. After being mixed evenly, glucose is added and the ball-milling is continued for 3 hours until uniform. The obtained mixture is then spray-dried to obtain a precursor powder. The precursor powder is pre-calcined at 400°C for 2 hours in an argon atmosphere. After the pre-calcination, the precursor powder is taken out and ball-milled for 2 hours. Then, the precursor powder is sintered at 750°C for 4 hours in an argon atmosphere. The obtained product is then sintered twice in a carbon dioxide atmosphere at a temperature of 700°C for 0.5 hours to obtain lithium iron phosphate, a positive electrode matrix material;

[0105] Wherein, based on the mass of the raw material of the positive electrode matrix material, the mass fraction of the glucose is 15%;

[0106] (2) PEO and PEDOT:PSS were mixed in a molar ratio of 3:7, and then dispersed in deionized water with a total mass fraction of 10% of the mass of lithium iron phosphate, and stirred and mixed for 4 hours to obtain a polymer solution. The lithium iron phosphate was then immersed in the polymer solution and stirred and mixed for a second time for 3 hours, and then heated to 120°C for stirring and heat treatment for 2 hours;

[0107] The mixed solution obtained after the heat treatment was filtered to obtain a solid product, which was then vacuum-dried at 80° C. for 8 h to obtain the lithium-ion battery composite positive electrode material, namely, PEDOT:PSS-PEO-coated lithium iron phosphate.

[0108] Example 6

[0109] The difference between this embodiment and embodiment 1 is that the thickness of the composite polymer coating layer is 1 nm by adjusting the total mass fraction of the mixture of PEO and PEDOT:PSS in step (2).

[0110] The rest of the preparation methods and parameters remained the same as in Example 1.

[0111] Example 7

[0112] The difference between this embodiment and embodiment 1 is that the thickness of the composite polymer coating layer is 25 nm by adjusting the total mass fraction of the mixture of PEO and PEDOT:PSS in step (2).

[0113] The rest of the preparation methods and parameters remained the same as in Example 1.

[0114] Example 8

[0115] The difference between this embodiment and embodiment 1 is that the molar ratio of PEO and PEDOT:PSS in step (2) is 1:10.

[0116] The rest of the preparation methods and parameters remained the same as in Example 1.

[0117] Example 9

[0118] The difference between this embodiment and embodiment 1 is that the molar ratio of PEO and PEDOT:PSS in step (2) is 6:5.

[0119] The rest of the preparation methods and parameters remained the same as in Example 1.

[0120] Example 10

[0121] The difference between this embodiment and embodiment 1 is that the atmosphere for the secondary sintering in step (1) is a nitrogen atmosphere.

[0122] The rest of the preparation methods and parameters remained the same as in Example 1.

[0123] Example 11

[0124] The difference between this embodiment and embodiment 1 is that the temperature of the heat treatment in step (2) is 50°C.

[0125] The rest of the preparation methods and parameters remained the same as in Example 1.

[0126] Example 12

[0127] The difference between this embodiment and embodiment 1 is that the temperature of the heat treatment in step (2) is 150°C.

[0128] The rest of the preparation methods and parameters remained the same as in Example 1.

[0129] Comparative Example 1

[0130] This comparative example provides a method for preparing a lithium iron phosphate positive electrode material, the preparation method comprising the following steps:

[0131] Lithium carbonate and iron phosphate are used as raw materials for the positive electrode matrix material. They are ball-milled for 2 hours with deionized water as the medium according to the molar ratio of Li:Fe=1.02:1. After being mixed evenly, glucose is added and the ball-milling is continued for 3 hours until uniform. The obtained mixture is then spray-dried to obtain a precursor powder. The precursor powder is pre-calcined at 350°C for 3 hours in an argon atmosphere. After the pre-calcination is completed, it is taken out and ball-milled for 2 hours, and then sintered once at 700°C for 5 hours in an argon atmosphere to obtain a carbon-coated lithium iron phosphate positive electrode material.

[0132] Comparative Example 2

[0133] The difference between this comparative example and Example 1 is that PEO is replaced by polyethylene succinate.

[0134] The rest of the preparation methods and parameters remained the same as in Example 1.

[0135] Comparative Example 3

[0136] The difference between this comparative example and Example 1 is that PEDOT:PSS is replaced by polyaniline.

[0137] The rest of the preparation methods and parameters remained the same as in Example 1.

[0138] Performance Testing

[0139] The positive electrode materials prepared in the above examples and comparative examples were made into button batteries and subjected to electrochemical performance tests. The specific steps are as follows:

[0140] The positive electrode materials prepared in the above examples and comparative examples were uniformly mixed with the conductive agent acetylene black and the adhesive polyvinylidene fluoride in an N-methylpyrrolidone solvent at a mass percentage of 90:5:5. The obtained positive electrode slurry was coated on an aluminum foil and dried in a vacuum drying oven. After drying, the battery was assembled in an argon glove box and pressed into positive electrode sheets using a tablet press. The negative electrode was a metal lithium sheet. The electrolyte was 1 M LiPF6-EC:DMC (volume ratio of 1:1), and a polypropylene porous membrane was used as a separator.

[0141] The test results are shown in Table 1.

[0142] Table 1

[0143] analyze:

[0144] As can be seen from the table above, the present disclosure forms a uniform and dense composite polymer coating by cross-linking the positive electrode substrate material with an ion-conductive polymer and PEDOT:PSS. The cross-linking effect reduces the crystallinity of the ion-conductive polymer and modifies the sulfonic acid groups of PEDOT:PSS. The synergistic effect of the two further improves the conductivity of PEDOT:PSS-PEO, achieving electron-ion dual-functional channel conduction. This composite polymer coating not only improves the electron transport rate and reaction kinetics of the positive electrode material, but also improves the contact between the positive electrode particles by taking into account the flexibility of the coating layer, significantly enhancing the electrical performance of the positive electrode material.

[0145] It can be seen from the data results of Example 1 and Examples 6-7 that if the thickness of the composite polymer coating layer is too small, the coating is incomplete, resulting in a decrease in electrical performance; if the thickness of the composite polymer coating layer is too large, the lithium ion transmission distance is increased, the volume of the positive electrode material increases, and the proportion of active material is low, resulting in a decrease in battery capacity.

[0146] It can be seen from the data results of Example 1 and Examples 8-9 that if the molar ratio of PEO and PEDOT:PSS is too small, the ion conductive part accounts for a small proportion, thereby reducing the utilization of the conductivity of lithium ions; if the molar ratio of PEO and PEDOT:PSS is too large, the ion conductive part accounts for a large proportion, which will cause the conductivity of the positive electrode material to deteriorate.

[0147] It can be seen from the data results of Example 1 and Example 10 that if the atmosphere of the secondary sintering is a nitrogen atmosphere, it is difficult to remove the carbon on the surface of the positive electrode substrate material, resulting in both carbon coating and conductive polymer coating in the coating layer. The overall coating layer is too thick, affecting the transmission of lithium ions.

[0148] The data results of Examples 1 and 11-12 indicate that if the heat treatment temperature is too low, a cross-linking reaction cannot occur, resulting in PEO and PEDOT:PSS failing to enhance each other's ionic and electronic conductivity, and instead simply coating the lithium iron phosphate as a mixture. If the heat treatment temperature is too high, the polymer may degrade and structurally break, causing a decrease in the polymer's own electrical conductivity, which in turn affects the battery's electrical performance.

[0149] It can be seen from the data results of Example 1 and Comparative Example 1 that the carbon-coated lithium iron phosphate positive electrode material is lower than the lithium-ion battery composite positive electrode material prepared in the present application in terms of conductivity and rate performance. Although both of them have the same coating layer that plays a conductive role, the carbon coating does not provide support for the ion conductive part.

[0150] From the data results of Example 1 and Comparative Examples 2-3, it can be seen that if PEO is replaced with polyethylene succinate, or PEDOT:PSS is replaced with polyaniline, the expected ideal dual conductive channel coating of lithium iron phosphate cannot be achieved. This is because no cross-linking reaction occurs between them, and thus the conductivity cannot be synergistically improved.

Claims

1. A lithium-ion battery composite positive electrode material, comprising a positive electrode matrix material and a composite polymer coating layer coated on the surface of the positive electrode matrix material; The composite polymer coating layer is obtained by cross-linking reaction between an ion conductive polymer and PEDOT:PSS; The ion conductive polymer includes any one of PEO, PEG or PEI or a combination of at least two of them.

2. The lithium-ion battery composite positive electrode material according to claim 1, wherein The composite polymer coating layer is a mesh structure.

3. The lithium ion battery composite positive electrode material according to claim 1 or 2, wherein: The ion conductive polymer is PEO.

4. The lithium ion battery composite positive electrode material according to any one of claims 1 to 3, wherein: The thickness of the composite polymer coating layer is 2-20 nm.

5. The lithium-ion battery composite positive electrode material according to any one of claims 1 to 4, wherein: The particle size D50 of the positive electrode matrix material is 0.8-2.5 μm.

6. The lithium-ion battery composite positive electrode material according to any one of claims 1 to 5, wherein: The positive electrode matrix material includes lithium iron phosphate.

7. A method for preparing a lithium ion battery composite positive electrode material according to any one of claims 1 to 6, the preparation method comprising the following steps: The ion conductive polymer, PEDOT:PSS, a positive electrode matrix material and a solvent are mixed and heat treated to obtain the lithium ion battery composite positive electrode material.

8. The preparation method according to claim 7, wherein: The molar ratio of the ion conductive polymer to PEDOT:PSS is (1-5):(5-9).

9. The preparation method according to claim 7 or 8, wherein: The preparation method of the positive electrode matrix material comprises: The raw material of the positive electrode matrix material and the carbon source are mixed, pre-sintered and first sintered, and then second sintered to obtain the positive electrode matrix material.

10. The preparation method according to any one of claims 7 to 9, wherein: Based on the total mass of the raw materials of the positive electrode matrix material, the mass fraction of the carbon source is 3-15%.

11. The preparation method according to claim 9, wherein: The pre-burning temperature is 200-400° C., and the heat preservation time is 2-6 hours.

12. The preparation method according to any one of claims 9 to 11, wherein: The primary sintering temperature is 600-750° C., and the heat preservation time is 4-10 hours.

13. The preparation method according to any one of claims 9 to 12, wherein: The secondary sintering temperature is 400-700° C., and the heat preservation time is 0.5-2h.

14. The preparation method according to claims 9-13, wherein: The secondary sintering is performed in a carbon dioxide atmosphere.

15. The preparation method according to any one of claims 7 to 14, wherein: The method of mixing the ion conductive polymer, PEDOT:PSS, the positive electrode matrix material and the solvent comprises: The ion conductive polymer, PEDOT:PSS and a solvent are mixed once to obtain a polymer solution, and then the polymer solution and a positive electrode matrix material are mixed for a second time; Optionally, based on the mass of the positive electrode matrix material, the mass fraction of the mixture of the ion conductive polymer and PEDOT:PSS is 1-10%; Optionally, the heat treatment temperature is 80-130° C., and the heat treatment time is 2-8 hours; Optionally, after the heat treatment is completed, filtering and drying steps are further performed.

16. The preparation method according to any one of claims 7 to 15, wherein: The preparation method comprises the following steps: (1) The raw materials of the positive electrode matrix material and the carbon source are ball-milled for 2-5 hours, and then the resulting mixture is subjected to The precursor powder is dried to obtain a precursor powder, the precursor powder is pre-sintered at 200-400° C. for 2-6 hours in a protective atmosphere, and then the precursor powder is sintered at 600-750° C. for 4-10 hours in a protective atmosphere, and the obtained product is sintered twice in a carbon dioxide atmosphere at a temperature of 400-700° C. for 0.5-2 hours to obtain a positive electrode matrix material; The raw materials of the positive electrode matrix material include a lithium source, a phosphorus source and an iron source. The mass fraction of the carbon source is 3-15% based on the total mass of the lithium source, the phosphorus source and the iron source. (2) stirring and mixing PEO, PEDOT:PSS and a solvent for 2-4 hours to obtain a polymer solution, and then stirring and mixing the polymer solution and the positive electrode matrix material for a second time for 1-3 hours, and obtaining the lithium ion battery composite positive electrode material after heat treatment, filtering and drying; Among them, the molar ratio of PEO and PEDOT:PSS is (1-5):(5-9), based on the mass of the positive electrode matrix material, the total mass fraction of the mixture of PEO and PEDOT:PSS is 1-10%, the heat treatment temperature is 80-130°C, the heat treatment time is 2-8h, the drying temperature is 50-90°C, and the time is 6-36h.

17. A lithium ion battery, wherein the positive electrode of the lithium ion battery comprises the lithium ion battery composite positive electrode material according to any one of claims 1 to 6.

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