Composite positive electrode material and preparation method therefor, and secondary battery

Abstract

A composite positive electrode material and a preparation method therefor, and a secondary battery. The composite positive electrode material comprises: a positive electrode substrate; a fast-ion conductor coating layer covering the positive electrode substrate, wherein the fast-ion conductor coating layer has pores; and a carbon material located in the pores of the fast-ion conductor coating layer. The composite positive electrode material is a positive electrode material, having ion conductivity and electron conductivity, for an artificial CEI coating layer, and has high specific capacity; and a battery manufactured by using the composite positive electrode material has low internal resistance and a long cycle life.

Description

Composite cathode material, preparation method thereof and secondary battery TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy, in particular to a composite cathode material, a preparation method thereof and a secondary battery. BACKGROUND

[0002] Since the commercialization of lithium ion batteries, they have had a profound impact on people's lives and social development. For example, the high energy density and long life of lithium ion batteries have enabled the rapid development of portable electronic devices such as smartphones, laptops, and tablets, greatly improving people's mobility and work efficiency. Thanks to the miniaturization and high efficiency of lithium ion batteries, we can wear smartwatches, health monitoring devices, and other smart wearables to access the information we want anytime and anywhere. For another example, lithium ion batteries have driven the rapid development of electric vehicles, reducing dependence on fossil fuels and helping to reduce greenhouse gas emissions to combat global climate change. At the same time, lithium ion batteries play an important role in renewable energy storage systems such as solar and wind power, making the use of renewable energy more efficient and stable.

[0003] The future development direction of lithium ion batteries is high energy density and high safety. Artificial positive electrode solid electrolyte interface film (CEI) can effectively inhibit the side reactions that occur during the charging and discharging process of the electrode material, reduce the decomposition of the electrolyte, and thus prolong the service life of the battery. Especially under high voltage operation, it can inhibit the phase transition and internal stress increase of the positive electrode particles, and reduce the generation of particle microcracks. In summary, artificial CEI film is one of the important means to improve the safety and energy density of the battery.

[0004] Fast ion conductors are often used as one of the materials for CEI film, such as lithium aluminum titanium phosphate (LATP) and lithium lanthanum zirconium oxide (LLZO). However, such materials have low electronic conductivity, and coating on the surface of the positive electrode material will cause an increase in electrode resistance. SUMMARY

[0005] Therefore, the first aspect of the present application provides a composite cathode material, and the technical scheme is as follows:

[0006] A composite cathode material comprises:

[0007] a positive electrode substrate;

[0008] a fast ion conductor coating layer covering the positive electrode substrate, the fast ion conductor coating layer having pores;

[0009] a carbon material located in the pores of the fast ion conductor coating layer.

[0010] The second aspect of the present application provides a preparation method of a composite cathode material, and the technical scheme is as follows:

[0011] A preparation method of a composite positive electrode material, comprising the following steps:

[0012] mixing a positive electrode base material, a fast ion conductor and a pore-forming material, and allowing the fast ion conductor and the pore-forming material to coat the positive electrode base material to obtain a coated material;

[0013] heat-treating the coated material to remove the pore-forming material, to form a fast ion conductor coating layer with pores, to obtain a positive electrode precursor A;

[0014] mixing the positive electrode precursor A, a carbon source and water, to cause a hydrothermal reaction, to allow the carbon source to enter the pores, to obtain a positive electrode precursor B;

[0015] calcining the positive electrode precursor B to obtain the composite positive electrode material.

[0016] The third aspect of the application provides a secondary battery, and the technical scheme is as follows:

[0017] A secondary battery comprising the composite positive electrode material as described above.

[0018] Compared with the prior art, the application has the following beneficial effects:

[0019] In the application, the fast ion conductor is coated on the positive electrode base material, the fast ion conductor has high ion conductivity, which is conducive to improving the diffusion rate of lithium ions. At the same time, the fast ion coating layer has pores, and the pores contain carbon materials. On the one hand, the addition of carbon materials can improve the electronic conductivity of the material and solve the problem of increased resistance caused by the coating of the fast ion conductor. On the other hand, the carbon materials are located in the pores of the fast ion coating layer, which is more conducive to forming a complete electronic conduction path and reducing the resistance than directly coating the carbon materials on the fast ion coating layer without pores. On the other hand, compared with mixing the carbon materials with the fast ion conductor and then coating the mixture on the positive electrode base material, the carbon materials located in the pores of the fast ion coating layer can reduce the contact area between the carbon materials and the positive electrode base material, thereby reducing the reduction of transition metals in the positive electrode base material to metal by the carbon materials and the decline of the electrochemical performance. In summary, the composite positive electrode material of the application is a positive electrode material with an artificial CEI coating layer with ion conduction performance and electronic conduction performance, which has good capacity performance, low internal resistance of the prepared battery and long cycle life. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application, and more completely understand the present application and the beneficial effects thereof, the following will briefly introduce the drawings needed in the embodiment description. Obviously, the drawings in the following description only represent some of the embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort based on these drawings.

[0021] FIG. 1 is a schematic diagram of product conversion in the preparation process of the composite cathode material in an embodiment. DETAILED DESCRIPTION

[0022] The present application will be further described below in conjunction with specific embodiments. The present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terminology used in the specification of the present application is only for the purpose of describing specific embodiments and is not intended to limit the present application.

[0024] Terminology

[0025] Unless otherwise indicated or contradictory, the terms or phrases used herein have the following meanings:

[0026] In the present application, the terms "a plurality of", "a plurality of kinds", "a plurality of times", "a plurality of elements" and the like, if not specifically limited, refer to more than two or equal to two in number. For example, "one or more" means one or more than two. In the present application, the term "several" means at least one, for example, one, two, etc., unless otherwise specifically limited.

[0027] In the present application, the terms "optionally", "optional" and "optional" mean that it can or can not exist, that is, it means to select from any one of the two parallel schemes of "have" or "have". If there are multiple "options" in a technical solution, unless otherwise specified, and there is no contradictory or mutually restrictive relationship, each "option" is independent.

[0028] In the present application, the terms "first aspect", "second aspect", "third aspect", "fourth aspect" and the like, the terms "first", "second", "third", "fourth" and the like are only for the purpose of description, and cannot be understood as indicating or implying relative importance or quantity, nor can it be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first", "second", "third", "fourth" and the like only serve the purpose of non-exhaustive enumeration description, and should be understood as not constituting a closed limitation on the quantity.

[0029] In the present application, when referring to a numerical interval (i.e. a numerical range), unless otherwise specified, the optional numerical distribution within the numerical interval is considered to be continuous, and includes both numerical endpoints (i.e. the minimum and maximum values) of the numerical range, as well as every numerical value between the two numerical endpoints.

[0030] In the present application, unless otherwise specified, the temperature parameter allows for both constant temperature treatment, as well as a variation within a certain temperature interval. It should be understood that the constant temperature treatment allows for fluctuations within the accuracy range of the instrument control. Fluctuations within a range such as ±5°C, ±4°C, ±3°C, ±2°C, ±1°C are allowed.

[0031] In the present application, when referring to a percentage content, unless otherwise specified, both for solid-liquid mixing and solid-solid mixing, it refers to mass percentage, and for liquid-liquid mixing, it refers to volume percentage.

[0032] In the present application, when referring to a percentage concentration, unless otherwise specified, it refers to the final concentration. The final concentration refers to the proportion of the added component in the system after the component is added.

[0033] In the present application, % (w / w) and wt% both represent weight percentage, % (v / v) refers to volume percentage, and % (w / v) refers to mass volume percentage.

[0034] The first aspect of the present application provides a composite positive electrode material. In one embodiment, the composite positive electrode material comprises:

[0035] a positive electrode substrate;

[0036] a fast ion conductor coating layer covering the positive electrode substrate, the fast ion conductor coating layer having pores;

[0037] a carbon material located in the pores of the fast ion conductor coating layer.

[0038] The positive electrode substrate of the embodiment is coated with a fast ion conductor. The fast ion conductor has high ionic conductivity, which is conducive to improving the diffusion rate of lithium ions. At the same time, the fast ion coating layer has pores containing carbon materials. On the one hand, the addition of carbon materials can improve the electronic conductivity of the material and solve the problem of increased resistance caused by the coating of the fast ion conductor. On the other hand, the carbon materials in the pores of the fast ion coating layer are more conducive to forming a complete electronic conduction path and reducing resistance than the carbon materials directly coated on the fast ion coating layer without pores. On the other hand, compared with mixing the carbon materials with the fast ion conductor and then coating the positive electrode substrate, the carbon materials in the pores of the fast ion coating layer can reduce the contact area between the carbon materials and the positive electrode substrate, thereby reducing the reduction of transition metals in the positive electrode substrate to metal by the carbon materials and the decline of the electrochemical performance. In summary, the composite positive electrode material of the application is a positive electrode material with an artificial CEI coating layer having ion conduction performance and electronic conduction performance. The capacity is well developed, the battery resistance is low, and the cycle life is long.

[0039] Optionally, the positive electrode substrate comprises lithium cobaltate Li 1+z Co 1-n A n O2, ternary material Li 1+z Ni x Co y M 1-x-y-n A n O2, lithium-rich manganese-based mLi2MnO3·(1-m)Li 1+z Ni x Co y Mn 1-x-y-n A n O2, nickel-manganese spinel Li 1+z Ni 0.5-h Mn 1.5-l A n O4, lithium iron manganese phosphate Li 1+z Fe x Mn 1-x-n A n PO4, lithium manganate Li 1+z Mn 2-n A n O4, lithium iron phosphate Li 1+z Fe 1-n A n PO4, wherein 0≤z<0.1, 0≤n<0.1, 0

[0040] Optionally, the average particle size of the positive electrode substrate is 0.5 μm to 30 μm.

[0041] Optionally, the fast ion conductor of the fast ion conductor coating layer comprises Li 1+p Al p Ge 2-p (PO4)3, Li 3q La 2 / 3-q TiO3, LiZr 2-r Ti r (PO4)3, Li 1+m Al m Ti 2-m (PO4)3, Li 4-t Ge 1-t P t S4, Li 7-2n-j A n La3Zr 2-j B j O 12 , Li 7-2n-2j A n La3Zr 2-j C j O 12 , Li7P3P 11 , Li3PS4, wherein 0≤p≤2, 0≤q≤2 / 3, 0≤r≤2, 0≤m≤2, 0≤t≤1, 0≤n≤3, 0≤j≤2, A is at least one of Ge and Al, B is at least one of Nb and Ta, and C is at least one of Te and W.

[0042] The fast ion conductor coating layer forms a complete coating on the positive electrode substrate, and the coating is thin and has pores, which is conducive to improving the diffusion rate of lithium ions and the ion conductivity, and the carbon material is located in the pores, thereby avoiding the large-area contact between the carbon material and the positive electrode material and the reduction of transition metals in the positive electrode material.

[0043] Optionally, the porosity of the fast ion conductor coating layer is 11% to 50%. The pores of the fast ion conductor coating layer can be obtained by adding a pore-forming material in advance and then completely burning the pore-forming material.

[0044] Optionally, the thickness of the fast ion conductor coating layer is 50 nm to 500 nm.

[0045] Optionally, the mass of the fast ion conductor coating layer accounts for 1% to 6% of the mass of the composite positive electrode material.

[0046] Optionally, the mass of the carbon material accounts for 0.3% to 2% of the mass of the composite positive electrode material.

[0047] It can be understood that the particle size of the carbon material in the pores of the fast ion conductor coating layer is adapted to the pore size of the pores. In some examples, the particle size of the carbon material in the pores of the fast ion conductor coating layer is in the range of 1 nm to 500 nm.

[0048] In this embodiment, the composite positive electrode material further comprises a carbon coating layer, and the carbon coating layer coats the fast ion conductor coating layer.

[0049] Optionally, the thickness of the carbon coating layer is 0.37 nm to 100 nm. It can be understood that in this application, the thickness of the carbon coating layer refers to the distance from the outer surface of the non-porous region of the fast ion conductor coating layer to the outer surface of the carbon coating layer.

[0050] Optionally, the mass of the carbon coating layer accounts for 1% to 4% of the mass of the composite positive electrode material.

[0051] It can be understood that the carbon coating layer can be formed together with the carbon material in the pores of the fast ion conductor coating layer. For example, by calcining a carbon source.

[0052] The composite positive electrode material described above has ion conduction performance and electron conduction performance, low resistance, and high cycle performance retention rate. It can be used to prepare liquid lithium ion batteries, hybrid solid-liquid lithium ion batteries, hybrid solid-liquid metal lithium batteries, all-solid-state lithium ion batteries, and all-solid-state metal lithium batteries, which is beneficial to improve the safety and energy density of the batteries.

[0053] The second aspect of the application provides a preparation method of a composite positive electrode material. In one embodiment, referring to FIG. 1, the composite positive electrode material comprises the following steps:

[0054] S10, mixing the positive electrode substrate 11, the fast ion conductor, and the pore-forming material 12, and allowing the fast ion conductor and the pore-forming material 12 to coat the positive electrode substrate 11 to obtain a coated material.

[0055] Optionally, the pore-forming material comprises polyvinyl alcohol (PVA) resin. On the one hand, the polyvinyl alcohol resin can be completely burned in subsequent heat treatment, leaving pores; on the other hand, the polyvinyl alcohol resin can also act as a binder to help the fast ion conductor coat the positive electrode substrate.

[0056] Optionally, the particle size of the fast ion conductor is between 2 nm and 500 nm.

[0057] It can be understood that the mixing of the positive electrode substrate, the fast ion conductor, and the pore-forming material is solid-phase mixing. The mixing can be performed in a ball mill.

[0058] Optionally, the method of allowing the fast ion conductor and the pore-forming material to coat the positive electrode material comprises the following steps:

[0059] The mixed material of the positive electrode substrate, the fast ion conductor and the pore-forming material is subjected to mechanical fusion treatment. Optionally, the parameters of the mechanical fusion treatment include: a rotation speed of 2000 r / min to 4000 r / min. The fusion time is 10 min to 20 min.

[0060] It can be understood that the mechanical fusion treatment can be performed in a mechanical fusion machine.

[0061] S20, heat treating the coating material to remove the pore-forming material 12, form a fast ion conductor coating layer 14 with pores 13, and obtain a positive electrode precursor A.

[0062] Through the heat treatment, the polyvinyl alcohol resin is completely burned, leaving pores, and forming a fast ion conductor coating layer with pores.

[0063] Optionally, the heating rate of the heat treatment is 1 ℃ / min to 20 ℃ / min.

[0064] Optionally, the temperature of the heat treatment is 400 ℃ to 1200 ℃.

[0065] Optionally, the time of the heat treatment is 1 h to 10 h.

[0066] S30, mixing the positive electrode precursor A, a carbon source and water, and causing a hydrothermal reaction, so that the carbon source enters the pores, and a positive electrode precursor B is obtained.

[0067] In some examples, the amount of the carbon source is controlled so that the carbon source enters the pores, and the carbon source forms a carbon material after calcination, and the carbon material in the obtained composite positive electrode material is located in the pores of the fast ion conductor coating layer.

[0068] In some examples, the amount of the carbon source is controlled so that part of the carbon source enters the pores, and the remaining part of the carbon source coats the positive electrode precursor A. Please refer to FIG. 1, after subsequent calcination, part of the carbon material is located in the pores 13 of the fast ion conductor coating layer 14, and the remaining part forms a carbon coating layer above the fast ion conductor coating layer 14.

[0069] Optionally, the carbon source includes at least one of glucose and sucrose.

[0070] Optionally, the heating rate of the hydrothermal reaction is 1 ℃ / min to 20 ℃ / min.

[0071] Optionally, the temperature of the hydrothermal reaction is 140 ℃ to 180 ℃.

[0072] Optionally, the time of the hydrothermal reaction is 6 h to 10 h.

[0073] S40, calcining the positive electrode precursor B to obtain the composite positive electrode material, at this time, the composite positive electrode material.

[0074] By calcining, the carbon source is decomposed into carbon material,

[0075] Optionally, the heating rate of calcination is 1℃ / min-20℃ / min.

[0076] Optionally, the temperature of calcination is 600℃-800℃.

[0077] Optionally, the time of calcination is 2h-6h.

[0078] The preparation method of the composite positive electrode material is as follows: first, mixing the positive electrode substrate, the fast ion conductor and the pore-forming material, coating the fast ion conductor and the pore-forming material on the surface of the positive electrode substrate by a fusion coating machine, fusing the fast ion conductor and the positive electrode substrate by heat treatment, and completely burning the pore-forming material in the heat treatment to leave abundant pores in the fast ion conductor coating layer, obtaining a positive electrode precursor A, and then putting the positive electrode precursor A into a carbon source aqueous solution, and making the carbon source enter the pores by hydrothermal reaction, and then calcining the carbon source to form carbon material in the pores to obtain electron channels with small resistance.

[0079] The third aspect of the application provides a secondary battery, in one embodiment, the secondary battery comprises the composite positive electrode material as described above.

[0080] The secondary battery can be a liquid lithium ion battery, a hybrid solid-liquid lithium ion battery, a hybrid solid-liquid metal lithium battery, a full solid-state lithium ion battery, and a full solid-state metal lithium battery.

[0081] The following will be further described in combination with specific examples and comparative examples. The raw materials involved in the following specific examples and comparative examples, if not specifically stated, can be sourced from the market. The instruments used, if not specifically stated, can be sourced from the market. The processes involved, if not specifically stated, are commonly selected by those skilled in the art.

[0082] Example 1

[0083] The present embodiment provides a composite positive electrode material and a preparation method thereof, and the steps are as follows:

[0084] Step 1, 100g of LiFePO4(LFP), 5g of Li 1.4 Al 0.4 Ti 1.6 (PO4)3(LATP) and 5g of 10wt% PVA aqueous solution are placed in a ball mill to mix them thoroughly, and the mixed material is placed in a fusion machine at a rotation speed of 3000r / min for 15min to obtain a coated material of LATP and PVA coated LFP.

[0085] Step 2, the coated material of step 1 is placed in a muffle furnace, and heated to 700℃ at a rate of 5℃ / min, and kept for 4h, PVA is completely burned, leaving pores, forming a fast ionic conductor coating layer with pores, to obtain positive electrode precursor A.

[0086] Step 3, take 1g of positive electrode precursor A of step 2 and 30ml of 0.5mol / L glucose aqueous solution in an autoclave, and heat to 160℃ at a rate of 5℃ / min, and react for 8h, to obtain positive electrode precursor B.

[0087] Step 4, take the positive electrode precursor B of step 3 and place it in a tube furnace, and heat to 700℃ at a rate of 5℃ / min in an argon atmosphere, and keep for 4h, to finally obtain a composite positive electrode material.

[0088] Example 2

[0089] This example provides a composite positive electrode material and a preparation method thereof, which is basically the same as example 1, the main difference is that the amount of Li 1.4 Al 0.4 Ti 1.6 (PO4)3(LATP) is different. The steps are as follows:

[0090] Step 1, 100g of LiFePO4(LFP), 2g of Li 1.4 Al 0.4 Ti 1.6 (PO4)3(LATP) and 5g of 10wt% PVA aqueous solution are placed in a ball mill to mix them well, and the mixed material is placed in a fusion machine at a speed of 3000r / min for 15min, to obtain a coated material of LATP and PVA coated LFP.

[0091] Step 2, the coated material of step 1 is placed in a muffle furnace, and heated to 700℃ at a rate of 5℃ / min, and kept for 4h, PVA is completely burned, leaving pores, forming a fast ionic conductor coating layer with pores, to obtain positive electrode precursor A.

[0092] Step 3, take 1g of positive electrode precursor A of step 2 and 30ml of 0.5mol / L glucose aqueous solution in an autoclave, and heat to 160℃ at a rate of 5℃ / min, and react for 8h, to obtain positive electrode precursor B.

[0093] Step 4, take the positive electrode precursor B of step 3 and place it in a tube furnace, and heat to 700℃ at a rate of 5℃ / min in an argon atmosphere, and keep for 4h, to finally obtain a composite positive electrode material.

[0094] Example 3

[0095] The embodiment provides a composite positive electrode material and a preparation method thereof, which are basically the same as those in Embodiment 1, and the main difference lies in that the amount of Li 1.4 Al 0.4 Ti 1.6 (PO4)3(LATP) is different. The steps are as follows:

[0096] Step 1, 100g of LiFePO4(LFP), 6g of Li 1.4 Al 0.4 Ti 1.6 (PO4)3(LATP) and 5g of 10wt% PVA aqueous solution are placed in a ball mill to fully mix the three, and the mixed material is placed in a fusion machine at a rotation speed of 3000r / min for 15min to obtain a coated material of LATP and PVA coated LFP.

[0097] Step 2, the coated material in step 1 is placed in a muffle furnace and heated to 700℃ at a rate of 5℃ / min, and kept for 4h, PVA is completely burned, leaving pores, forming a fast ion conductor coating layer with pores, to obtain a positive electrode precursor A.

[0098] Step 3, 1g of the positive electrode precursor A in step 2 is taken and placed in a hydrothermal kettle with 30ml of 0.5mol / L glucose aqueous solution, and heated to 160℃ at a rate of 5℃ / min, and reacted for 8h to obtain a positive electrode precursor B.

[0099] Step 4, the positive electrode precursor B in step 3 is placed in a tube furnace and heated to 700℃ at a rate of 5℃ / min in an argon atmosphere, and kept for 4h, to finally obtain a composite positive electrode material.

[0100] Embodiment 4

[0101] The embodiment provides a composite positive electrode material and a preparation method thereof, which are basically the same as those in Embodiment 1, and the main difference lies in that the amount of PVA is different. The steps are as follows:

[0102] Step 1, 100g of LiFePO4(LFP), 5g of Li 1.4 Al 0.4 Ti 1.6 (PO4)3(LATP) and 10g of 10wt% PVA aqueous solution are placed in a ball mill to fully mix the three, and the mixed material is placed in a fusion machine at a rotation speed of 3000r / min for 15min to obtain a coated material of LATP and PVA coated LFP.

[0103] Step 2, the coated material of step 1 is placed in a muffle furnace, and heated to 700℃ at a rate of 5℃ / min, and kept for 4h, PVA is completely burned, leaving pores, forming a fast ionic conductor coating layer with pores, to obtain anode precursor A.

[0104] Step 3, take 1g of anode precursor A of step 2 and 30ml of 0.5mol / L glucose aqueous solution in an autoclave, heated to 160℃ at a rate of 5℃ / min, and reacted for 8h, to obtain anode precursor B.

[0105] Step 4, take the anode precursor B of step 3 and place it in a tube furnace, and heated to 700℃ at a rate of 5℃ / min in an argon atmosphere, and kept for 4h, to finally obtain a composite anode material.

[0106] Example 5

[0107] This example provides a composite anode material and a preparation method thereof, which is basically the same as example 1, the main difference is that the amount of PVA is different. The steps are as follows:

[0108] Step 1, 100g of LiFePO4(LFP), 5g of Li 1.4 Al 0.4 Ti 1.6 (PO4)3(LATP) and 2g of 10wt% PVA aqueous solution are placed in a ball mill to mix them well, and the mixed material is placed in a fusion machine at a speed of 3000r / min for 15min, to obtain a coated material of LATP and PVA coated LFP.

[0109] Step 2, the coated material of step 1 is placed in a muffle furnace, and heated to 700℃ at a rate of 5℃ / min, and kept for 4h, PVA is completely burned, leaving pores, forming a fast ionic conductor coating layer with pores, to obtain anode precursor A.

[0110] Step 3, take 1g of anode precursor A of step 2 and 30ml of 0.5mol / L glucose aqueous solution in an autoclave, heated to 160℃ at a rate of 5℃ / min, and reacted for 8h, to obtain anode precursor B.

[0111] Step 4, take the anode precursor B of step 3 and place it in a tube furnace, and heated to 700℃ at a rate of 5℃ / min in an argon atmosphere, and kept for 4h, to finally obtain a composite anode material.

[0112] Comparative Example 1

[0113] This comparative example provides a composite anode material and a preparation method thereof, which is basically the same as example 1, the main difference is that PVA is not added. The steps are as follows:

[0114] Step 1, 100 g of LiFePO4(LFP), 5 g of Li 1.4 Al 0.4 Ti 1.6 (PO4)3(LATP) and 5 g of water were placed in a ball mill to mix them well, and the mixed material was placed in a fusion machine at a rotation speed of 3000 r / min for 15 min to obtain a coated material of LATP-coated LFP.

[0115] Step 2, the coated material of step 1 was placed in a muffle furnace and heated to 700℃ at a rate of 5℃ / min, and kept for 4 h to obtain a positive electrode precursor A.

[0116] Step 3, 1 g of the positive electrode precursor A of step 2 was placed in a hydrothermal kettle with 30 ml of 0.5 mol / L glucose aqueous solution, and heated to 160℃ at a rate of 5℃ / min for 8 h to obtain a positive electrode precursor B.

[0117] Step 4, the positive electrode precursor B of step 3 was placed in a tube furnace and heated to 700℃ at a rate of 5℃ / min in an argon atmosphere, and kept for 4 h to finally obtain a composite positive electrode material.

[0118] Comparative Example 2

[0119] This comparative example provides a composite positive electrode material and a preparation method thereof, which are basically the same as those of Comparative Example 1, the main difference being that no carbon source is added. The steps are as follows:

[0120] Step 1, 100 g of LiFePO4(LFP), 5 g of Li 1.4 Al 0.4 Ti 1.6 (PO4)3(LATP) and 5 g of water were placed in a ball mill to mix them well, and the mixed material was placed in a fusion machine at a rotation speed of 3000 r / min for 15 min to obtain a coated material of LATP-coated LFP.

[0121] Step 2, the coated material of step 1 was placed in a muffle furnace and heated to 700℃ at a rate of 5℃ / min, and kept for 4 h to obtain a composite positive electrode material.

[0122] Comparative Example 3

[0123] This comparative example provides a composite positive electrode material and a preparation method thereof, which are basically the same as those of Example 1, the main difference being that no PVA is added, and the fast ion conductor is mixed with the carbon source. The steps are as follows:

[0124] 100 g of LiFePO4(LFP), 5 g of Li 1.4 Al 0.4 Ti 1.6The three were mixed thoroughly in a ball mill with 5 g of conductive carbon black, and the mixed material was placed in a fusion machine at a rotation speed of 3000 r / min for 15 min to obtain a coating material of LATP and carbon-coated LFP.

[0125] Test

[0126] Item 1. The porosity of the fast ion conductor coating layer on the surface of the positive electrode precursor A of each example was tested by BET, and the results are shown in Table 1.

[0127] Item 2. The composite positive electrode material was cut by argon ion cross-section polishing technology, and the cross-section of the composite positive electrode material of each example was observed by SEM+EDS. It was observed that in the composite positive electrode material of each example, part of the carbon material with an average particle size of 1 nm to 500 nm was located in the pores of the fast ion conductor coating layer, and the remaining carbon material coated the fast ion conductor coating layer to form a continuous carbon coating layer with a thickness of 0.37 nm to 100 nm.

[0128] Item 3. The mass percentages of the fast ion conductor, carbon material (carbon material located in the pores), and carbon coating layer in the composite positive electrode material of each example were tested by ICP, elemental analysis, and EDS, and the results are shown in Table 1.

[0129] Table 1

[0130] Item 4. The composite positive electrode materials obtained in each example and the comparative example were used to make a coin-type lithium ion battery, and performance tests were conducted. The components and mass ratio in the positive electrode active layer were as follows: composite positive electrode material: conductive additive: binder = 92:3:5, Celgard 2300 type separator was used, lithium metal was used as the negative electrode, EC / DMC+1M LiPF6 was used as the electrolyte, and carbon black was used as the conductive additive. The battery was cycled at 2-3.8V, 0.5C under the condition of 100 cycles.

[0131] The battery internal resistance was directly read out by a battery internal resistance meter, and the results are shown in Table 2.

[0132] The battery 100-week capacity retention rate Φ = ((1st week capacity-100th week capacity) / 1st week capacity) x 100%, and the results are shown in Table 2.

[0133] Table 2

[0134] As shown in Table 1, the composite positive electrode material of each example has good capacity release, low battery internal resistance, and long cycle life.

[0135] Any combination of the technical features in the above-described embodiments can be made, and for the sake of brevity, not all possible combinations are described, however, as long as there is no conflict, any combination of the technical features should be considered within the scope of the present disclosure.

[0136] The above-described embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the patent scope of the present application. It should be pointed out that, for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the patent protection scope of the present application should be subject to the appended claims.

Claims

1. A composite cathode material, characterized in that, include: Positive electrode substrate; A fast ion conductor coating layer is provided to coat the positive electrode substrate, and the fast ion conductor coating layer has pores. Carbon material is located in the pores of the fast ion conductor coating layer.

2. The composite cathode material according to claim 1, characterized in that, The porosity of the fast ion conductor coating is 11% to 50%.

3. The composite cathode material according to claim 2, characterized in that, The fast ion conductor coating layer includes at least one of the following features: (1) The thickness of the fast ion conductor coating layer is 50 nm to 500 nm; (2) The mass of the fast ion conductor coating layer accounts for 1% to 6% of the mass of the composite cathode material.

4. The composite cathode material according to claim 1, characterized in that, The carbon material accounts for 0.3% to 2% of the mass of the composite cathode material.

5. The composite cathode material according to any one of claims 1 to 4, characterized in that, It also includes a carbon coating layer that coats the fast ion conductor coating layer.

6. The composite cathode material according to claim 5, characterized in that, The carbon coating layer includes at least one of the following features: (1) The thickness of the carbon coating layer is 0.37 nm to 100 nm; (2) The mass of the carbon coating layer accounts for 1% to 4% of the mass of the composite cathode material.

7. The composite cathode material according to any one of claims 1 to 4 and 6, characterized in that, Includes at least one of the following features: (1) The average particle size of the positive electrode substrate is 0.5 μm to 30 μm; (2) The positive electrode substrate includes Li 1+z Co 1-n A n O2, Li 1+z Ni x Co y M 1-x-y-n A n O2、mLi2MnO3·(1-m)Li 1+z Ni x Co y Mn 1-x-y-n A n O2, Li 1+z Ni 0.5-h Mn 1.5-l A n O4, Li 1+z Fe x Mn 1-x-n A n PO4, Li 1+z Mn 2-n A n O4 and Li 1+z Fe 1-n A n One or more of PO4, wherein 0≤z<0.1, 0≤n<0.1, 0<x<1, 0<y<1, 0<x+y+n<1, 0<m<1, h+l=n, M is Mn or Al, and A is at least one element selected from Ti, Mg, Al, Zr, Nb, Ba, La, V, W, Ag, and Sn; (3) The fast ion conductor in the fast ion conductor coating layer includes Li 1+p Al p Ge 2-p (PO4)3, Li 3q La 2 / 3-q TiO3, LiZr 2-r Ti r (PO4)3, Li 1+m Al m Ti 2-m (PO4)3, Li 4-t Ge 1-t P t S4, Li 7-2n-j A n La3Zr 2-j B j O 12 Li 7-2n-2j A n La3Zr 2-j C j O 12 Li7P3P 11 One or more of Li3PS4, wherein 0≤p≤2, 0≤q≤2 / 3, 0≤r≤2, 0≤m≤2, 0≤t≤1, 0≤n≤3, 0≤j≤2, A is at least one element of Ge and Al, B is at least one element of Nb and Ta, and C is at least one element of Te and W.

8. A method for preparing a composite cathode material, characterized in that, Includes the following steps: A positive electrode substrate, a fast ion conductor, and a pore-forming material are mixed, and the fast ion conductor and the pore-forming material are used to coat the positive electrode substrate to obtain a coating material. The coating material is heat-treated to remove the pore-forming material, forming a porous fast ion conductor coating layer to obtain the positive electrode precursor A; The positive electrode precursor A, carbon source, and water are mixed to undergo a hydrothermal reaction, allowing the carbon source to enter the pores, thus obtaining the positive electrode precursor B. The positive electrode precursor B is calcined to obtain the composite positive electrode material.

9. The method for preparing the composite cathode material according to claim 8, characterized in that, The pore-forming material includes polyvinyl alcohol resin.

10. The method for preparing the composite cathode material according to claim 8, characterized in that, The amount of carbon source is controlled so that a portion of the carbon source enters the pores, and the remaining portion of the carbon source coats the positive electrode precursor A.

11. The method for preparing the composite cathode material according to claim 8, characterized in that, The carbon source includes at least one of glucose and sucrose.

12. The method for preparing the composite cathode material according to any one of claims 8 to 11, characterized in that, Includes at least one of the following features: (1) The heating rate of the heat treatment is 1℃ / min to 20℃ / min; (2) The heat treatment temperature is 400℃~1200℃; (3) The heat treatment time is 1 hour to 10 hours; (4) The heating rate of the hydrothermal reaction is 1℃ / min to 20℃ / min; (5) The temperature of the hydrothermal reaction is 140℃~180℃; (6) The hydrothermal reaction time is 6h to 10h; (7) The heating rate of calcination is 1℃ / min to 20℃ / min; (8) The calcination temperature is 600℃~800℃; (9) The calcination time is 2h to 6h.

13. A secondary battery, characterized in that, Includes the composite cathode material as described in any one of claims 1 to 7.

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