Semi-coated aluminum positive electrode material, preparation method thereof and lithium ion battery

Abstract

The invention relates to a semi-coated aluminum positive electrode material, a preparation method thereof and a lithium ion battery, and the preparation method comprises the following steps: mixing a positive electrode material and aluminum acetate, then carrying out heating treatment in an oxygen-containing atmosphere, and cooling to obtain the semi-coated aluminum positive electrode material, the temperature of the heating treatment is 350 DEG C to 450 DEG C. The low atom mobility of aluminum acetate at 350-450 DEG C is utilized, so that aluminum oxide is scattered and densely distributed on the surface of the positive electrode material to achieve a semi-coating effect, and the thickness of an obtained coating layer can reach 100-200 nm. Therefore, compared with a fully-coated aluminum oxide coating, the semi-coated aluminum oxide coating can enable the surface of the positive electrode material to be partially exposed and is beneficial to reducing impedance, so that the energy density and the cycle performance of the lithium ion battery are improved; in addition, the thick aluminum oxide coating is closer to the electrolyte, so that the corrosion of fluoride in the electrolyte can be effectively resisted for a long time, and the stability of the positive electrode material is enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries and relates to a positive electrode material, in particular to a semi-coated aluminum positive electrode material and a preparation method thereof and a lithium ion battery. Background Art

[0002] Lithium-ion batteries are widely used in various fields, and finding a preparation method that combines high energy density, high cycle performance, low cost and safety is the main challenge currently faced. In this regard, high nickel cathode materials in lithium-ion batteries have shown breakthrough potential due to their high capacity. However, the highly active Ni 4+ This will make the ternary system structure unstable, leading to problems such as cation mixing, microcracks, electrolyte decomposition and transition metal dissolution. Among them, the interfacial reaction between the positive electrode and the electrolyte will seriously reduce the energy density and cycle performance of the battery, especially the decomposition of lithium salts in the electrolyte to generate fluoride to dissolve the transition metal on the surface of the positive electrode material; this process will release oxygen, leading to continuous electrolyte decomposition and destruction of the positive electrode material, causing the battery energy density and cycle performance to drop rapidly. Therefore, improving the stability of the high-nickel positive electrode can effectively improve its own capacity retention rate and improve the interfacial reaction with the electrolyte, so as to obtain a lithium-ion battery with high energy density, high cycle performance and safety.

[0003] Based on this, applying a surface coating to high-nickel positive electrode materials can directly prevent direct contact between the positive electrode and the electrolyte, and has become an effective strategy to prevent direct contact between the positive electrode and the electrolyte, which leads to the release of oxygen and decomposition of the positive electrode. Among various coatings, metal oxide coatings can effectively remove fluorides produced by the electrolyte and thus delay the decomposition of the positive electrode material. However, when fluorides are excessive, the metal oxide coating will be completely corroded, and the full coverage of the metal oxide coating will increase the resistance and reduce the ion and electron migration rate. Therefore, the thickness and coating morphology of the metal oxide coating need to be further optimized to reduce the resistance and improve the capacity and cycle performance. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a semi-coated aluminum positive electrode material and its preparation method and application. The present invention uses a semi-coated alumina coating to partially expose the surface of the positive electrode material, which helps to reduce impedance and thus improve the energy density and cycle performance of lithium-ion batteries.

[0005] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a method for preparing a semi-coated aluminum positive electrode material, the preparation method comprising the following steps:

[0007] Mix the cathode material with aluminum acetate, and then perform heat treatment in an oxygen-containing atmosphere. After cooling, the semi-coated aluminum cathode material is obtained;

[0008] The temperature of the heat treatment is 350°C - 450°C. For example, it can be 350°C, 360°C, 380°C, 400°C, 420°C or 450°C, but it is not limited to the listed values, and the other unlisted values within the numerical range are equally applicable.

[0009] In the present invention, the low atomic migration rate of aluminum acetate between 350°C and 450°C is utilized to make the alumina scatter densely on the surface of the cathode material to achieve a semi-coated effect, and the thickness of the coating layer can reach 100nm - 200nm. Thus, compared with the fully coated alumina coating, the semi-coated alumina coating can make part of the surface of the cathode material revealed, which helps to reduce the impedance, thereby improving the energy density and cycle performance of the lithium-ion battery; in addition, the thicker alumina coating is closer to the electrolyte, so it can effectively resist the erosion of fluoride in the electrolyte for a long time and enhance the stability of the cathode material.

[0010] Among them, the temperature needs to be strictly controlled at 350°C - 450°C. If the temperature is too low, it is not conducive to the formation of the alumina coating, resulting in poor coating stability and weak corrosion resistance, which is not conducive to the protection of the high-nickel cathode material and reduces the battery cycle performance; if the temperature is too high, the atomic migration rate increases, resulting in a uniformly fully covered alumina coating on the surface of the high-nickel cathode material, with a thinner coating layer and an increased impedance, so it is also not conducive to improving the cycle performance of the lithium-ion battery.

[0011] Preferably, the heating rate of the heat treatment is 10°C / min - 20°C / min.

[0012] Preferably, the holding time of the heat treatment is 3h - 5h.

[0013] Preferably, the volume percentage of oxygen in the oxygen-containing atmosphere is more than 80%.

[0014] Preferably, based on the total mass percentage of the cathode material and aluminum acetate being 100wt%, the mass percentage of aluminum acetate is 2wt% - 5wt%.

[0015] Preferably, the cathode material is a nickel-cobalt-manganese cathode material.

[0016] Preferably, the preparation method further includes grinding and sieving after cooling.

[0017] Preferably, the mesh number of the sieving is 150 mesh - 300 mesh.

[0018] In a second aspect, the present invention provides a semi-coated aluminum cathode material, which is prepared by the preparation method described in the first aspect.

[0019] In a third aspect, the present invention provides a lithium-ion battery, and the lithium-ion battery includes the semi-coated aluminum cathode material described in the second aspect.

[0020] The numerical ranges described in the present invention not only include the point values exemplified above, but also include any point values between the above numerical ranges that are not exemplified. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the ranges.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention utilizes the low atomic mobility of aluminum acetate between 350°C and 450°C, enabling the alumina to be densely distributed in scattered points on the surface of the cathode material to achieve a semi-coated effect, and the thickness of the coating layer can reach 100 nm - 200 nm. Thus, compared with the fully coated alumina coating, the semi-coated alumina coating can expose part of the surface of the cathode material, which helps to reduce the impedance, thereby improving the energy density and cycle performance of the lithium-ion battery; in addition, the thicker alumina coating is closer to the electrolyte, so it can effectively resist the erosion of fluoride in the electrolyte for a long time and enhance the stability of the cathode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the SEM diagram of the semi-coated aluminum cathode material obtained in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0025] An embodiment of the present invention provides a preparation method of a semi-coated aluminum cathode material, and the preparation method includes the following steps:

[0026] Mix the cathode material and aluminum acetate, and then perform heat treatment in an oxygen-containing atmosphere, and the semi-coated aluminum cathode material is obtained after cooling;

[0027] The temperature of the heat treatment is 350°C - 450°C, for example, it can be 350°C, 360°C, 380°C, 400°C, 420°C or 450°C, but is not limited to the listed values, and the other unlisted values within the numerical range are equally applicable.

[0028] The present invention utilizes the low atomic migration rate of aluminum acetate between 350°C and 450°C, enabling alumina to be densely distributed in scattered points on the surface of the cathode material to achieve a semi - coating effect, with the coating layer thickness reaching 100nm - 200nm. In this way, compared with the fully - coated alumina coating, the semi - coated alumina coating allows partial exposure of the cathode material surface, which helps reduce impedance, thereby improving the energy density and cycle performance of the lithium - ion battery; in addition, the thicker alumina coating is closer to the electrolyte, so it can effectively resist the erosion of fluorides in the electrolyte for a long time, enhancing the stability of the cathode material.

[0029] Among them, the temperature needs to be strictly controlled between 350°C and 450°C. If the temperature is too low, it is not conducive to the formation of the alumina coating, resulting in poor coating stability and weak corrosion resistance, which is not conducive to the protection of the high - nickel cathode material and reduces the battery cycle performance; if the temperature is too high, the atomic migration rate increases, causing a uniformly fully - covered alumina coating to form on the surface of the high - nickel cathode material, with a thinner coating layer thickness and an increased impedance, so it is also not conducive to improving the cycle performance of the lithium - ion battery.

[0030] In an embodiment, the heating rate of the heat treatment is 10°C / min - 20°C / min. For example, it can be 10°C / min, 12°C / min, 15°C / min, 16°C / min, 18°C / min, or 20°C / min, but it is not limited to the resins listed. The other unlisted values within the numerical range are equally applicable.

[0031] In an embodiment, the heat - preservation time of the heat treatment is 3h - 5h. For example, it can be 3h, 3.5h, 4h, 4.5h, or 5h, but it is not limited to the resins listed. The other unlisted values within the numerical range are equally applicable.

[0032] In an embodiment, the volume percentage of oxygen in the oxygen - containing atmosphere is above 80%. For example, it can be 80%, 85%, 90%, 95%, or 100%, but it is not limited to the resins listed. The other unlisted values within the numerical range are equally applicable.

[0033] The balance gas in the oxygen - containing atmosphere includes nitrogen and / or inert gas.

[0034] Optionally, the inert gas includes any one or at least two combinations of helium, neon, or argon. Typical but non - limiting combinations include the combination of helium and neon, the combination of neon and argon, the combination of helium and argon, or the combination of helium, neon, and argon.

[0035] In a certain embodiment, based on the total mass percentage of the positive electrode material and aluminum acetate being 100 wt%, the mass percentage of aluminum acetate is 2 wt% - 5 wt%. For example, it can be 2 wt%, 3 wt%, 4 wt% or 5 wt%, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0036] When the mass percentage of aluminum acetate is 2 wt% - 5 wt%, the thickness of the semi-coated alumina layer can be 100 nm - 200 nm. For example, it can be 100 nm, 120 nm, 150 nm, 160 nm, 180 nm or 200 nm, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0037] In a certain embodiment, the positive electrode material is a nickel cobalt manganese positive electrode material.

[0038] Optionally, the nickel cobalt manganese positive electrode material includes NCM622 and / or NCM811.

[0039] In a certain embodiment, the preparation method further includes grinding and sieving after cooling.

[0040] In a certain embodiment, the mesh number of the sieving is 150 mesh - 300 mesh. For example, it can be 150 mesh, 180 mesh, 200 mesh, 250 mesh or 300 mesh, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0041] A certain embodiment of the present invention provides a semi-coated aluminum positive electrode material, which is prepared by the preparation method described in any of the embodiments.

[0042] A certain embodiment of the present invention provides a lithium ion battery, which includes the semi-coated aluminum positive electrode material described in any of the embodiments.

[0043] Example 1

[0044] This example provides a preparation method for a semi-coated aluminum positive electrode material, and the preparation method includes the following steps:

[0045] (1) Ball mill and uniformly mix the positive electrode material NCM811 and aluminum acetate to obtain a mixed material; based on the total mass percentage of the positive electrode material and aluminum acetate being 100 wt%, the mass percentage of aluminum acetate is 2 wt%.

[0046] (2) In an aerobic atmosphere with an oxygen volume percentage of 80% and a nitrogen volume percentage of 20%, heat the mixed material at a heating rate of 10 °C / min to 400 °C and keep it warm for 4 h; after natural cooling, grind and crush it, and sieve it through a 300-mesh sieve to obtain the semi-coated aluminum positive electrode material.

[0047] The SEM image of the semi-coated aluminum cathode material obtained in this example is as follows Figure 1 shown. It shows that there are obvious dark area scatter points on the surface of the cathode material, which is the semi-coating effect of the alumina coating, and the coating thickness is 100 nm.

[0048] Example 2

[0049] This example provides a preparation method of a semi-coated aluminum cathode material, and the preparation method includes the following steps:

[0050] (1) Ball-mill and uniformly mix the cathode material NCM811 and aluminum acetate to obtain a mixed material; based on the total mass percentage of the cathode material and aluminum acetate being 100 wt%, the mass percentage of aluminum acetate is 5 wt%;

[0051] (2) In an aerobic atmosphere with an oxygen volume percentage of 80% and a nitrogen volume percentage of 20%, heat the mixed material at a heating rate of 10 °C / min to 400 °C, and keep it warm for 4 h; after natural cooling, grind and crush it, and pass through a 300-mesh sieve to obtain the semi-coated aluminum cathode material.

[0052] The coating thickness of the semi-coated aluminum cathode material obtained in this example is 200 nm.

[0053] Example 3

[0054] This example provides a preparation method of a semi-coated aluminum cathode material, and the preparation method includes the following steps:

[0055] (1) Ball-mill and uniformly mix the cathode material NCM811 and aluminum acetate to obtain a mixed material; based on the total mass percentage of the cathode material and aluminum acetate being 100 wt%, the mass percentage of aluminum acetate is 2 wt%;

[0056] (2) In an aerobic atmosphere with an oxygen volume percentage of 80% and a nitrogen volume percentage of 20%, heat the mixed material at a heating rate of 10 °C / min to 350 °C, and keep it warm for 5 h; after natural cooling, grind and crush it, and pass through a 150-mesh sieve to obtain the semi-coated aluminum cathode material.

[0057] The coating thickness of the semi-coated aluminum cathode material obtained in this example is 125 nm.

[0058] Example 4

[0059] This example provides a preparation method of a semi-coated aluminum cathode material, and the preparation method includes the following steps:

[0060] (1) The cathode material NCM811 and aluminum acetate are evenly mixed by ball milling to obtain a mixed material; based on the total mass percentage of the cathode material and aluminum acetate being 100 wt%, the mass percentage of aluminum acetate is 2 wt%.

[0061] (2) In an aerobic atmosphere with an oxygen volume percentage of 80% and a nitrogen volume percentage of 20%, the mixed material is heated to 450 °C at a heating rate of 20 °C / min and held for 3 h; after natural cooling, it is ground and crushed, and passed through a 300-mesh sieve to obtain the semi-coated aluminum cathode material.

[0062] The coating thickness of the semi-coated aluminum cathode material obtained in this example is 110 nm.

[0063] Example 5

[0064] This example provides a method for preparing a semi-coated aluminum cathode material, and the preparation method includes the following steps:

[0065] (1) The cathode material NCM811 and aluminum acetate are evenly mixed by ball milling to obtain a mixed material; based on the total mass percentage of the cathode material and aluminum acetate being 100 wt%, the mass percentage of aluminum acetate is 1 wt%.

[0066] (2) In an aerobic atmosphere with an oxygen volume percentage of 80% and a nitrogen volume percentage of 20%, the mixed material is heated to 400 °C at a heating rate of 10 °C / min and held for 4 h; after natural cooling, it is ground and crushed, and passed through a 300-mesh sieve to obtain the semi-coated aluminum cathode material.

[0067] The coating thickness of the semi-coated aluminum cathode material obtained in this example is 60 nm.

[0068] Example 6

[0069] This example provides a method for preparing a semi-coated aluminum cathode material, and the preparation method includes the following steps:

[0070] (1) The cathode material NCM811 and aluminum acetate are evenly mixed by ball milling to obtain a mixed material; based on the total mass percentage of the cathode material and aluminum acetate being 100 wt%, the mass percentage of aluminum acetate is 7 wt%.

[0071] (2) In an aerobic atmosphere with an oxygen volume percentage of 80% and a nitrogen volume percentage of 20%, the mixed material is heated to 400 °C at a heating rate of 10 °C / min and held for 4 h; after natural cooling, it is ground and crushed, and passed through a 300-mesh sieve to obtain the semi-coated aluminum cathode material.

[0072] The coating thickness of the semi-coated aluminum cathode material obtained in this example is 250 nm.

[0073] Comparative Example 1

[0074] This comparative example provides a method for preparing an all-coated aluminum cathode material, and the preparation method includes the following steps:

[0075] (1) Uniformly mix the cathode material NCM811 and aluminum acetate by ball milling to obtain a mixture; based on the total mass percentage of the cathode material and aluminum acetate being 100 wt%, the mass percentage of aluminum acetate is 2 wt%;

[0076] (2) In an aerobic atmosphere with an oxygen volume percentage of 80% and a nitrogen volume percentage of 20%, heat the mixture at a heating rate of 10 °C / min to 800 °C and hold for 4 h; after natural cooling, grind and crush, and pass through a 300-mesh sieve to obtain the all-coated aluminum cathode material.

[0077] The coating thickness of the all-coated aluminum cathode material obtained in this comparative example is 60 nm.

[0078] Comparative Example 2

[0079] This comparative example provides a method for preparing a cathode material, which is the same as Example 1 except that the heat treatment temperature is 300 °C.

[0080] Comparative Example 3

[0081] This comparative example provides a method for preparing a cathode material, which is the same as Example 1 except that the heat treatment temperature is 500 °C.

[0082] Performance Characterization

[0083] Assemble the above cathode material into a coin-type half-cell for electrochemical performance testing.

[0084] Mix the cathode material, conductive adhesive (CB), and binder in a mass ratio of 92:4:4, and then adjust the slurry of the mixture with NMP (N-methylpyrrolidone) at a liquid-solid mass ratio of 1:1.3; pour the slurry onto aluminum foil, keep it in a vacuum oven at 40 °C for 6 h, and then keep it at 110 °C for 12 h to remove NMP; then, punch the obtained electrode sheet into a 14-mm diameter circular sheet on a punching machine to prepare a positive electrode sheet. The electrolyte used is a mixed solution of 1 M LiPF6 dissolved in EC / EMC / EFC = 1 / 1 / 1 by volume, and the separator is a polyethylene porous film. The battery assembly sequence is: positive electrode case, positive electrode sheet, separator, electrolyte, lithium negative electrode, negative electrode case, and all operations are carried out in a glove box under argon protection.

[0085] The cyclic performance of the battery was tested by constant current charge and discharge. The test temperature was room temperature, and the voltage range was 2.8 - 4.2V. During the test, it was first cycled 5 times at a current density of 0.1C, then cycled 5 times at 0.3C, 0.5C, 1C, 2C, 5C, and 0.1C respectively, and finally a long cycle test of 200 cycles was carried out at 1C. The cyclic performance results are shown in Table 1.

[0086] Table 1

[0087]

[0088] As can be seen from Table 1, when the aluminum acetate content is between 2% and 5% and heat-treated at 350°C - 450°C, the cyclic performance of the battery can be effectively improved. Outside this range, it will lead to a significant reduction in the discharge specific capacity or little improvement in the cyclic performance; when heat-treated at a higher temperature, the formed fully coated aluminum coating will significantly reduce the discharge specific capacity and cyclic performance of the battery.

[0089] In summary, the present invention utilizes the low atomic mobility of aluminum acetate between 350°C and 450°C, enabling the alumina to be densely distributed in scattered points on the surface of the positive electrode material to achieve a semi-coated effect, and the thickness of the coating layer can reach 100nm - 200nm. In this way, compared with the fully coated alumina coating, the semi-coated alumina coating can expose part of the surface of the positive electrode material, which helps to reduce the impedance, thereby improving the energy density and cyclic performance of the lithium-ion battery; in addition, the thicker alumina coating is closer to the electrolyte, so it can effectively resist the erosion of fluorides in the electrolyte for a long time and enhance the stability of the positive electrode material.

[0090] The applicant declares that the above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A preparation method of a semi-coated aluminum positive electrode material, characterized in that, The preparation method includes the following steps: Mix the cathode material with aluminum acetate, and then conduct heat treatment in an oxygen-containing atmosphere. After cooling, the semi-coated aluminum cathode material is obtained; The temperature of the heat treatment is 350°C - 450°C.

2. The preparation method according to claim 1, characterized in that, The heating rate of the heat treatment is 10°C / min - 20°C / min.

3. The preparation method according to claim 1 or 2, characterized in that, The heat preservation time of the heat treatment is 3h - 5h.

4. The preparation method according to claim 1 or 2, characterized in that, The volume percentage of oxygen in the oxygen-containing atmosphere is more than 80%.

5. The preparation method according to claim 1, wherein Based on the total mass percentage of the cathode material and aluminum acetate being 100wt%, the mass percentage of aluminum acetate is 2wt% - 5wt%.

6. The preparation method according to claim 1, wherein The cathode material is a nickel cobalt manganese cathode material.

7. The preparation method according to claim 1, characterized in that The preparation method further includes grinding and sieving after cooling.

8. The preparation method according to claim 7, characterized in that, The mesh number of the sieving is 150 mesh - 300 mesh.

9. A semi-coated aluminum positive electrode material, characterized in that, The semi-coated aluminum cathode material is prepared by the preparation method according to any one of claims 1 - 8.

10. A lithium-ion battery, characterized in that, The lithium ion battery includes the semi-coated aluminum cathode material according to claim 9.

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