Positive electrode sheet and lithium ion battery

Abstract

The present invention relates to a positive electrode sheet and a lithium ion battery. The positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes lithium iron manganese phosphate and a ternary material; the ternary material includes a ternary single crystal material and a ternary polycrystalline material; the mass of the lithium iron manganese phosphate accounts for ≥50wt% of the mass of the positive electrode active material. In the present invention, by mixing ternary single crystals, ternary polycrystalline and lithium iron manganese phosphate in a certain proportion, the positive electrode sheet in which the lithium iron manganese phosphate accounts for more than 50wt% is optimized to optimize the discharge double platform voltage of lithium iron manganese phosphate, making the discharge voltage smoother, which is beneficial to the control of BMS; the presence of the ternary material not only solves the problem of the lithium iron manganese phosphate discharge double voltage platform, but also enhances the conductivity and power performance of the material.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion battery positive electrode materials and relates to a positive electrode sheet and a lithium ion battery. Background Art

[0002] With the widespread application of new energy vehicles, safe, reliable, high energy density and low cost lithium-ion batteries have become one of the research hotspots for scientific and technological workers, and the characteristics of positive electrode materials directly affect the safety performance and cost of the battery.

[0003] At present, lithium manganese iron phosphate positive electrode materials have obvious advantages in safety and low cost compared with ternary materials, and have achieved improved energy density compared with lithium iron phosphate materials. When the energy density of lithium iron phosphate materials is close to the theoretical limit, if lithium-ion batteries want to further develop and improve their specific energy density, lithium manganese iron phosphate materials have become one of the research focuses.

[0004] CN 109250698A discloses a high tap density lithium iron manganese phosphate positive electrode material and its preparation method and application. The positive electrode material is formed by mixing small-particle lithium iron manganese phosphate with a particle size of 0.3-0.8 μm and large-particle lithium iron manganese phosphate with a particle size of 3-5 μm in a mass ratio of 1-9:9-1. The preparation method includes: (1) preparation of dense lithium iron manganese phosphate; (2) preparation of large and small-particle lithium iron manganese phosphate slurry; (3) preparation of lithium iron manganese phosphate precursor powder; (4) preparation of lithium iron manganese phosphate finished product; the obtained material is applied to lithium battery positive electrode material.

[0005] CN 104124453A discloses a lithium iron manganese phosphate composite positive electrode material and a preparation method thereof, a lithium battery positive electrode and a lithium battery. The lithium iron manganese phosphate composite positive electrode material is nanometer-sized, and graphene is compounded in the lithium iron manganese phosphate substrate, and the mass of the graphene is 0.1% to 10% of the mass of the lithium iron manganese phosphate substrate. According to the molar ratio of each element of the lithium iron manganese phosphate, a nanometer-scale lithium source, a manganese source, an iron source, and a phosphorus source are added to a solvent for dissolution treatment to form a solution, and a complexing agent and a graphene solution are added to the solution in sequence, and then drying, grinding, sintering, annealing and other steps are performed. The lithium battery positive electrode and the lithium battery both contain the lithium iron manganese phosphate composite positive electrode material. The lithium iron manganese phosphate composite positive electrode material shortens the Li + The migration path of electrons is improved, thereby improving the conductivity of the material. The preparation method can ensure the stable performance of lithium manganese iron phosphate composite positive electrode material. The lithium battery has high discharge capacity and cycle capacity retention rate.

[0006] CN 114512649A A composite lithium iron manganese phosphate positive electrode material, the composite lithium iron manganese phosphate positive electrode material is a core-shell structure, which is composed of a core layer, a transition layer, an outer shell layer and a coating layer from the inside to the outside. The core layer is lithium manganese phosphate, the transition layer is lithium iron manganese phosphate, the outer shell layer is lithium iron phosphate, and the coating layer is carbon coating; the composite lithium iron phosphate positive electrode material is spherical or quasi-spherical particles, and its chemical composition is LiMn α Fe β PO4 / C; the inner core layer is xLiMnPO4 and the transition layer is yLiMn a Fe b PO4, the outer shell is zLiFePO4, where x+y+z=1, z≤0.05, x+ya=α, yb+z=β.

[0007] Although lithium manganese iron phosphate materials have such great advantages, they have major defects in practical applications. First, lithium manganese iron phosphate materials have dual voltage platforms during the discharge process, and the voltage difference between the two discharge platforms is large. In actual use, the existence of two voltage platforms will cause a cliff-like drop in voltage, making it difficult to collect BMS voltage; in addition, lithium manganese iron phosphate materials are doped with manganese, which reduces the conductivity of the material and has poor low-temperature discharge capabilities.

[0008] Therefore, how to solve the dual voltage platform problem of lithium manganese iron phosphate discharge is a technical problem that needs to be solved urgently. Summary of the invention

[0009] In order to solve the above technical problems, the present invention provides a positive electrode sheet and a lithium-ion battery. In the present invention, ternary single crystals, ternary polycrystals and lithium iron manganese phosphate are mixed in a certain proportion, wherein the positive electrode sheet with a lithium iron manganese phosphate content of more than 50wt% is optimized, and the discharge dual-platform voltage of lithium iron manganese phosphate is made smoother, which is beneficial to the control of BMS; the presence of the ternary material not only solves the problem of the dual voltage platform of lithium iron manganese phosphate discharge, but also enhances the conductivity and power performance of the material.

[0010] To achieve this object, the present invention adopts the following technical solutions:

[0011] In a first aspect, the present invention provides a positive electrode sheet, wherein the positive electrode sheet includes a positive electrode active material, wherein the positive electrode active material includes lithium manganese iron phosphate and a ternary material;

[0012] The ternary material includes ternary single crystal material and ternary polycrystalline material;

[0013] The mass of the lithium manganese iron phosphate accounts for ≥50wt% of the mass of the positive electrode active material, for example, it can be 50wt%, 60wt%, 70wt%, 80wt% or 95wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0014] In the present invention, by mixing ternary single crystals, ternary polycrystals and lithium iron manganese phosphate in a certain proportion, wherein the lithium iron manganese phosphate accounts for more than 50wt% of the positive electrode sheet, the discharge double platform voltage of lithium iron manganese phosphate is optimized, and the discharge voltage is smoother, which is beneficial to the control of BMS; the presence of the ternary material not only solves the problem of the lithium iron manganese phosphate discharge double voltage platform, but also enhances the conductivity and power performance of the material.

[0015] Preferably, the mass of the lithium manganese iron phosphate accounts for 60-80wt% of the mass of the positive electrode active material, for example, it can be 60wt%, 65wt%, 70wt%, 75wt% or 80wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0016] Preferably, the mass ratio of the ternary single crystal material to the ternary polycrystalline material is 0.25-0.4, for example, it can be 0.25, 0.28, 0.3, 0.35, 0.38 or 0.4, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0017] The blending of ternary single crystal materials and ternary polycrystalline materials can balance the dual platform voltages of lithium manganese iron phosphate. The special single crystal material can increase the discharge platform voltage of the mixed electrode, thereby further increasing the discharge platform voltage of the mixed material. The addition of polycrystalline reduces the transmission path of lithium ions, reduces resistance, and improves the material's power performance and low-temperature performance.

[0018] The positive electrode sheet provided by the present invention not only solves the application problem of lithium iron manganese phosphate materials, but also improves the performance of ternary materials and ensures the safety, reliability and low cost of the positive electrode materials.

[0019] Preferably, the ternary material includes any one of 8-series ternary materials, 7-series ternary materials or 6-series ternary materials, or a combination of at least two of them. Typical but non-limiting combinations include a combination of 8-series ternary materials and 7-series ternary materials, a combination of 7-series ternary materials and 6-series ternary materials, a combination of 8-series ternary materials and 6-series ternary materials, or a combination of 8-series ternary materials, 7-series ternary materials and 6-series ternary materials.

[0020] Preferably, the chemical formula of the lithium manganese iron phosphate is LiMn x Fe 1-xPO4, x is 0.3 to 0.7, for example, 0.3, 0.4, 0.5, 0.6 or 0.7, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0021] Preferably, the particle size of the lithium manganese iron phosphate is in the range of 1 to 5 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm or 5 μm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0022] Preferably, the particle size range of the ternary single crystal material is 3 to 40 μm, for example, 3 μm, 5 μm, 10 μm, 20 μm, 30 μm or 40 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] Preferably, the particle size of the ternary polycrystalline material is in the range of 1 to 16 μm, for example, 1 μm, 5 μm, 10 μm, 12 μm or 16 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] In a second aspect, the present invention provides a lithium-ion battery, wherein the lithium-ion battery contains the positive electrode sheet as described in the first aspect.

[0025] Preferably, the negative electrode material in the lithium-ion battery includes graphite and / or carbon-coated graphite.

[0026] Preferably, the lithium ion battery is a liquid battery.

[0027] Preferably, the organic solvent in the electrolyte used in the lithium ion battery includes any one of ethylene carbonate, ethyl methyl carbonate or dimethyl carbonate, or a combination of at least two of them. Typical but non-limiting combinations include a combination of ethylene carbonate and ethyl methyl carbonate, a combination of ethyl methyl carbonate and dimethyl carbonate, a combination of ethylene carbonate and dimethyl carbonate, or a combination of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate.

[0028] Compared with the prior art, the present invention has at least the following beneficial effects:

[0029] In the present invention, by mixing ternary single crystals, ternary polycrystals and lithium iron manganese phosphate in a certain proportion, wherein the lithium iron manganese phosphate accounts for more than 50wt% of the positive electrode sheet, the discharge double platform voltage of lithium iron manganese phosphate is optimized, and the discharge voltage is smoother, which is beneficial to the control of BMS; the presence of the ternary material not only solves the problem of the lithium iron manganese phosphate discharge double voltage platform, but also enhances the conductivity and power performance of the material. DETAILED DESCRIPTION

[0030] For the convenience of understanding the present invention, the present invention lists the following embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0031] Example 1

[0032] This embodiment provides a lithium-ion battery, which includes a positive electrode sheet and a negative electrode sheet.

[0033] The positive electrode sheet includes a positive electrode active material, which includes lithium iron manganese phosphate and a ternary material; the ternary material NCM (811) includes a ternary single crystal material and a ternary polycrystalline material with a mass ratio of 0.3; the particle size range of the ternary single crystal material is 3 to 40 μm, and the particle size range of the ternary polycrystalline material is 1 to 16 μm. x Fe 1-x The mass of PO4 (x is 0.5) accounts for 85 wt% of the mass of the positive electrode active material, and the particle size ranges from 1 to 5 μm.

[0034] The negative electrode material in the negative electrode sheet is graphite.

[0035] The organic solvent in the electrolyte used in the lithium ion battery includes ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate.

[0036] Example 2

[0037] This embodiment provides a lithium-ion battery, which includes a positive electrode sheet and a negative electrode sheet.

[0038] The positive electrode sheet includes a positive electrode active material, which includes lithium iron manganese phosphate and a ternary material; the ternary material NCM (712) includes a ternary single crystal material and a ternary polycrystalline material with a mass ratio of 0.28; the particle size range of the ternary single crystal material is 3 to 40 μm, and the particle size range of the ternary polycrystalline material is 1 to 16 μm. The lithium iron manganese phosphate (LiMn x Fe 1-x The mass of PO4 (x is 0.7) accounts for 80 wt% of the mass of the positive electrode active material, and the particle size ranges from 1 to 5 μm.

[0039] The negative electrode material in the negative electrode sheet is graphite.

[0040] The organic solvent in the electrolyte used in the lithium ion battery includes ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate.

[0041] Example 3

[0042] This embodiment provides a lithium-ion battery, which includes a positive electrode sheet and a negative electrode sheet.

[0043] The positive electrode sheet includes a positive electrode active material, which includes lithium iron manganese phosphate and a ternary material; the ternary material NCM (622) includes a ternary single crystal material and a ternary polycrystalline material with a mass ratio of 0.35; the particle size range of the ternary single crystal material is 3 to 40 μm, and the particle size range of the ternary polycrystalline material is 1 to 16 μm. The lithium iron manganese phosphate (LiMn x Fe 1-x The mass of PO4 (x is 0.3) accounts for 90wt% of the mass of the positive electrode active material, and the particle size ranges from 1 to 5μm.

[0044] The negative electrode material in the negative electrode sheet is graphite.

[0045] The organic solvent in the electrolyte used in the lithium ion battery includes ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate.

[0046] Example 4

[0047] This embodiment provides a lithium-ion battery, which includes a positive electrode sheet and a negative electrode sheet.

[0048] The positive electrode sheet includes a positive electrode active material, which includes lithium iron manganese phosphate and a ternary material; the ternary material NCM (811) includes a ternary single crystal material and a ternary polycrystalline material with a mass ratio of 0.25; the particle size range of the ternary single crystal material is 3 to 40 μm, and the particle size range of the ternary polycrystalline material is 1 to 16 μm. x Fe 1-x The mass of PO4 (x is 0.4) accounts for 50wt% of the mass of the positive electrode active material, and the particle size ranges from 1 to 5μm.

[0049] The negative electrode material in the negative electrode sheet is graphite.

[0050] The organic solvent in the electrolyte used in the lithium ion battery includes ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate.

[0051] Example 5

[0052] This embodiment provides a lithium-ion battery, which includes a positive electrode sheet and a negative electrode sheet.

[0053] The positive electrode sheet includes a positive electrode active material, which includes lithium iron manganese phosphate and a ternary material; the ternary material NCM (811) includes a ternary single crystal material and a ternary polycrystalline material with a mass ratio of 0.4; the particle size range of the ternary single crystal material is 3 to 40 μm, and the particle size range of the ternary polycrystalline material is 1 to 16 μm. x Fe 1-xThe mass of PO4 (x is 0.6) accounts for 50wt% of the mass of the positive electrode active material, and the particle size ranges from 1 to 5μm.

[0054] The negative electrode material in the negative electrode sheet is graphite.

[0055] The organic solvent in the electrolyte used in the lithium ion battery includes ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate.

[0056] Example 6

[0057] This embodiment provides a lithium-ion battery, which is different from Embodiment 1 in that the mass ratio of the ternary single crystal material to the ternary polycrystalline material is 0.2.

[0058] Example 7

[0059] This embodiment provides a lithium-ion battery, which is different from Embodiment 1 in that the mass ratio of the ternary single crystal material to the ternary polycrystalline material is 0.5.

[0060] Example 8

[0061] This embodiment provides a lithium-ion battery, which is different from the embodiment 1 in that the particle size of lithium manganese iron phosphate is in the range of 6 to 9 μm.

[0062] Example 9

[0063] This embodiment provides a lithium-ion battery, which is different from the embodiment 1 in that the particle size of the lithium manganese iron phosphate is in the range of 10 to 14 μm.

[0064] Example 10

[0065] This embodiment provides a lithium-ion battery, which is different from Embodiment 1 in that the particle size range of the ternary single crystal material is 41 to 45 μm.

[0066] Embodiment 11

[0067] This embodiment provides a lithium-ion battery, which is different from the embodiment 1 in that the particle size range of the ternary polycrystalline material is 17 to 20 μm.

[0068] Comparative Example 1

[0069] This comparative example provides a lithium-ion battery, which differs from Example 1 in that the ternary single crystal material is replaced by a ternary polycrystalline material of equal mass.

[0070] Comparative Example 2

[0071] This comparative example provides a lithium-ion battery, which differs from Example 1 in that the ternary polycrystalline material is replaced with a ternary single crystal material of equal mass.

[0072] Comparative Example 3

[0073] This comparative example provides a lithium ion battery, which is different from Example 1 in that the mass of lithium manganese iron phosphate is 45 wt % of the mass of the positive electrode active material.

[0074] The electrochemical performance of the lithium-ion battery obtained above was tested, and the test results are shown in Table 1.

[0075] Table 1

[0076]

[0077]

[0078] The following conclusions can be drawn from Table 1:

[0079] (1) It can be seen from Examples 1-5 and Comparative Examples 1-3 that in the present invention, by mixing ternary single crystals, ternary polycrystalline and lithium iron manganese phosphate in a certain proportion, wherein the lithium iron manganese phosphate accounts for more than 50wt% of the positive electrode sheet, the discharge double platform voltage of lithium iron manganese phosphate is optimized, making the discharge voltage smoother, which is beneficial to the control of the BMS; the presence of the ternary material not only solves the problem of the lithium iron manganese phosphate discharge double voltage platform, but also enhances the conductivity and power performance of the material.

[0080] In Comparative Example 3, since the mass of the ternary material is increased, the power performance is high, but the cost of the material in the positive electrode sheet is increased. From the comparison between Example 1 and Comparative Example 3, it can be seen that when the mass ratio of lithium manganese iron phosphate to the ternary material is improved, the advantages of both ensuring excellent power performance and reducing costs can be achieved.

[0081] (2) From the comparison between Examples 6 and 7 and Example 1, it can be seen that when the mass ratio of the ternary single crystal material to the ternary polycrystalline material is not in the range of 0.25 to 0.4, the positive electrode sheet is affected in solving the application problem of the lithium manganese iron phosphate material, which is not conducive to improving the performance of the ternary material, thereby making it impossible to ensure the safety, reliability and low cost of the positive electrode material.

[0082] (3) From the comparison between Examples 8 and 9 and Example 1, it can be seen that when the particle size range of lithium iron manganese phosphate is not within the preferred range of the present invention, the positive electrode sheet is affected to solve the application problem of lithium iron manganese phosphate material, thereby making it impossible to ensure the safety, reliability and low cost of the positive electrode material.

[0083] (4) From the comparison between Examples 10 and 11 and Example 1, it can be seen that when the particle size range of the ternary single crystal material or the ternary polycrystalline material is not within the preferred range of the present invention, it affects the ternary material's ability to solve the dual voltage platform problem of lithium manganese iron phosphate discharge, and is not conducive to enhancing the conductivity and power performance of the material.

[0084] In summary, in the present invention, ternary single crystals, ternary polycrystals and lithium iron manganese phosphate are mixed in a certain proportion, wherein the lithium iron manganese phosphate accounts for more than 50wt% of the positive electrode sheet, thereby optimizing the discharge dual-platform voltage of lithium iron manganese phosphate, making the discharge voltage smoother, which is beneficial to the control of BMS; the presence of ternary materials not only solves the problem of the dual voltage platform of lithium iron manganese phosphate discharge, but also enhances the conductivity and power performance of the material.

[0085] The present invention illustrates the detailed process equipment and process flow of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed process equipment and process flow, that is, it does not mean that the present invention must rely on the above-mentioned detailed process equipment and process flow to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A positive electrode sheet, characterized in that: The positive electrode sheet includes a positive electrode active material, the positive electrode active material is composed of lithium manganese iron phosphate and a ternary material; the ternary material is composed of a ternary single crystal material and a ternary polycrystalline material, and the mass ratio of the ternary single crystal material to the ternary polycrystalline material is 0.28 to 0.4; The mass of the lithium manganese iron phosphate accounts for ≥50wt% of the mass of the positive electrode active material.

2. The positive electrode sheet according to claim 1, characterized in that: The mass of the lithium manganese iron phosphate accounts for 60-80wt% of the mass of the positive electrode active material.

3. The positive electrode sheet according to claim 1, characterized in that: The ternary material includes any one of 8-series ternary materials, 7-series ternary materials or 6-series ternary materials, or a combination of at least two of them.

4. The positive electrode sheet according to claim 1, characterized in that: The chemical formula of the lithium iron manganese phosphate is LiMn x Fe 1- x PO4, x is 0.3~0.

7.

5. The positive electrode sheet according to claim 1, characterized in that: The particle size of the lithium manganese iron phosphate is in the range of 1 to 5 μm.

6. The positive electrode sheet according to claim 1, characterized in that: The grain size of the ternary single crystal material ranges from 3 to 40 μm.

7. The positive electrode sheet according to claim 1, characterized in that: The grain size of the ternary polycrystalline material ranges from 1 to 16 μm.

8. A lithium ion battery, characterized in that: The lithium-ion battery contains the positive electrode sheet as described in any one of claims 1 to 7.

9. The lithium-ion battery according to claim 8, characterized in that: The negative electrode material in the lithium ion battery includes graphite and / or carbon-coated graphite.

10. The lithium ion battery according to claim 8, characterized in that The lithium ion battery is a liquid battery.

11. The lithium ion battery according to claim 8, characterized in that: The organic solvent in the electrolyte used in the lithium ion battery includes any one of ethylene carbonate, ethyl methyl carbonate or dimethyl carbonate, or a combination of at least two of them.

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