A positive electrode sheet, a method for manufacturing the same, and a lithium ion battery

Abstract

The application provides a positive electrode sheet, a preparation method thereof and a lithium ion battery. The positive electrode sheet comprises: a positive current collector, the positive current collector comprising a first surface and a second surface; a first positive electrode, the first positive electrode being formed on the first surface, and the material of the first positive electrode comprising lithium iron manganese phosphate and a first conductive agent; and a second positive electrode, the second positive electrode being formed on the second surface, and the material of the second positive electrode comprising a ternary positive electrode material and a second conductive agent; wherein the mass fraction of the first conductive agent in the material of the first positive electrode is greater than the mass fraction of the second conductive agent in the material of the second positive electrode. The application sets the coating layers containing different kinds of positive electrode materials on both sides of the positive current collector, and further adjusts the content of the corresponding components, thereby improving the fast charging performance of the lithium ion battery and being beneficial to the BMS control.

Description

Technical Field

[0001] This invention belongs to the field of cathode material technology, specifically relating to a cathode sheet, its preparation method, and a lithium-ion battery. Background Technology

[0002] Compared to ternary cathode materials and other cathode materials with layered structures, cathode materials with olivine structures, such as lithium manganese iron phosphate (LMFP) and lithium iron phosphate (LFP), have better safety and stability performance and have broad application prospects in the field of power batteries.

[0003] Compared to lithium iron phosphate (LFP), lithium manganese iron phosphate (LMP) combines high voltage, high energy density, and good low-temperature performance. However, the presence of two voltage plateaus during charge and discharge increases the complexity of the battery management system. Furthermore, LMP has a relatively low constant current ratio (approximately 85%), which hinders its fast-charging performance. These factors limit the further application of LMP in power batteries. To address these issues, existing technologies disclose methods such as blending LMP with ternary cathode materials or using a double-layer coating of LMP and ternary cathode materials.

[0004] In addition, the viscosity of the electrode slurry prepared by mixing lithium manganese iron phosphate material with ternary cathode material changes significantly over time, making it difficult to meet the needs of industrial production, while the production cost of the double-layer coating preparation process is too high.

[0005] Therefore, there is an urgent need to develop a low-cost lithium iron phosphate cathode suitable for large-scale industrial production, with a simple preparation method. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a positive electrode sheet, its preparation method, and a lithium-ion battery. The present invention solves the technical problems of lithium manganese iron phosphate having dual voltage plateaus and low constant current ratio by setting coatings containing different types of positive electrode materials on both sides of the positive electrode current collector and further controlling the content of the corresponding components. This improves the fast-charging performance of lithium-ion batteries and facilitates BMS control.

[0007] To achieve this objective, the present invention employs the following technical solution:

[0008] In a first aspect, the present invention provides a positive electrode sheet, the positive electrode sheet comprising:

[0009] A positive current collector, wherein the positive current collector includes a first surface and a second surface;

[0010] A first positive electrode, formed on the first surface, wherein the material of the first positive electrode includes lithium manganese iron phosphate and a first conductive agent; and

[0011] The second positive electrode is formed on the second surface, and the material of the second positive electrode includes a ternary positive electrode material and a second conductive agent;

[0012] Wherein, the mass fraction of the first conductive agent in the material of the first positive electrode is greater than the mass fraction of the second conductive agent in the material of the second positive electrode.

[0013] This invention addresses the issue of significant viscosity variations in electrode slurries prepared by mixing lithium manganese iron phosphate (LFP) and ternary cathode materials by applying coatings containing different types of cathode materials to both sides of the cathode current collector. This prevents the slurry from failing to meet the requirements for industrial production due to its viscosity changing over time. Furthermore, this invention controls the mass fraction of the first conductive agent in the first cathode material to be greater than that of the second conductive agent in the second cathode material. This is because ternary cathode materials have stronger conductivity than LFP materials. Therefore, adding a larger mass fraction of the first conductive agent to the first cathode material improves its conductivity, resulting in similar conductivity between the first and second cathodes. This extends battery life and solves the technical problems of LFP's dual voltage plateau and low constant current ratio, thereby improving the fast-charging performance of lithium-ion batteries and facilitating BMS control.

[0014] Preferably, the first conductive agent and the second conductive agent each independently comprise any one or a combination of at least two of vapor-grown carbon fiber (VGCF), carbon nanotubes, Super P, or acetylene black.

[0015] In this invention, the first conductive agent and the second conductive agent can be the same or different, and this invention does not impose too many restrictions.

[0016] Preferably, the first conductive agent is a combination of vapor-grown carbon fiber (VGCF), carbon nanotubes, Super P and acetylene black.

[0017] In this invention, a combination of vapor-grown carbon fiber, carbon nanotubes, Super P and acetylene black is preferred as the first conductive agent. In this way, the conductivity of the positive electrode can be further improved by using long-range and short-range conductive agents in combination, thereby improving the power performance of the battery.

[0018] Preferably, the mass ratio of the vapor-grown carbon fiber (VGCF), carbon nanotubes, Super P and acetylene black is (1-5):(1-5):(1-6):(1-6), for example, it can be 1:1:1:1, 1:2:1:2, 2:1:2:1, 3:2:4:5, 3:3:5:5, 5:5:6:6, etc.

[0019] Preferably, the mass fraction of the first conductive agent in the material of the first positive electrode is 0.8% to 2%, for example, it can be 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, etc.

[0020] Preferably, the second conductive agent is a combination of vapor-grown carbon fiber (VGCF), carbon nanotubes, Super P and acetylene black.

[0021] In this invention, a combination of vapor-grown carbon fibers, carbon nanotubes, Super P and acetylene black is preferred as the second conductive agent. In this way, the conductivity of the positive electrode can be further improved by using long-range and short-range conductive agents in combination, thereby improving the power performance of the battery.

[0022] Preferably, the mass ratio of the vapor-grown carbon fiber (VGCF), carbon nanotubes, Super P and acetylene black is (1-5):(1-5):(1-6):(1-6), for example, it can be 1:1:1:1, 1:2:1:2, 2:1:2:1, 3:2:4:5, 3:3:5:5, 5:5:6:6, etc.

[0023] Preferably, the mass fraction of the second conductive agent in the material of the second positive electrode is 0.8% to 1.2%, for example, it can be 0.8%, 0.85%, 0.88%, 0.9%, 0.95%, 1%, 1.2%, etc.

[0024] Preferably, the first positive electrode further includes a first binder, and the second positive electrode further includes a second binder.

[0025] Preferably, the first adhesive and the second adhesive each independently comprise polyvinylidene fluoride and / or sodium carboxymethyl cellulose.

[0026] Preferably, the mass fraction of the first binder in the material of the first positive electrode is 1.5% to 2.0%, for example, it can be 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, etc.

[0027] Preferably, the mass fraction of the second binder in the material of the second positive electrode is 1.5% to 2.0%, for example, it can be 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, etc.

[0028] In this invention, the first positive electrode further includes a first dispersant, and the second positive electrode further includes a second dispersant.

[0029] In this invention, the mass fraction of the first dispersant in the material of the first positive electrode is 0.1% to 2.0%, for example, it can be 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, etc.

[0030] In this invention, the mass fraction of the second dispersant in the material of the second positive electrode is 0.1% to 2.0%, for example, it can be 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, etc.

[0031] It should be noted that the types of the first and second dispersants in this invention are not limited in detail, and their main purpose is to achieve the technical effect of uniform mixing of the positive electrode material.

[0032] Preferably, the thickness of the first positive electrode is 50-90 μm, for example, it can be 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, etc.

[0033] Preferably, the thickness of the second positive electrode is 50-90 μm, for example, it can be 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, etc.

[0034] Preferably, the lithium manganese iron phosphate is lithium manganese iron phosphate with a core-shell coating structure.

[0035] In this invention, compared with ordinary lithium manganese iron phosphate materials, the dissolution of manganese ions in lithium manganese iron phosphate materials with core-shell coating structure is suppressed, thus it has higher stability and cycle performance. For example, it can be lithium manganese iron phosphate coated with carbon (as shell layer) (as core layer), or lithium manganese iron phosphate coated with metal oxide or metal nitride (as shell layer) (as core layer).

[0036] Preferably, the ternary cathode material is a single-crystal ternary cathode material.

[0037] In this invention, the single-crystal ternary cathode material has better overcharge resistance, which is beneficial for long-term battery cycle charging and discharging and improves battery life.

[0038] In this invention, the single-crystal ternary cathode material can be, for example, a 4-9 series single-crystal ternary cathode material. Preferably, the single-crystal ternary cathode material can be, for example, an 8 series ternary cathode material. This is beneficial to ensure that the battery has a high energy density.

[0039] Preferably, the mass ratio of the ternary cathode material to the lithium manganese iron phosphate is 1:(1-4), more preferably 1:(1.4-1.6), for example, it can be 1:1, 1:1.2, 1:1.3, 1:1.4, 1:1.42, 1:1.45, 1:48, 1:5, 1:52, 1:55, 1:58, 1:1.6, 1:2, 1:3, 1:4, etc.

[0040] In this invention, by adjusting the mass ratio of ternary cathode material to lithium manganese iron phosphate, an excessively high mass ratio affects the cost of electrode production and the safety of the battery, while an excessively low mass ratio cannot solve the dual-voltage plateau problem.

[0041] In a second aspect, the present invention provides a method for preparing a positive electrode sheet according to the first aspect, the method comprising the following steps:

[0042] A positive current collector is provided, the positive current collector including a first surface and a second surface;

[0043] A first positive electrode is formed on the first surface, the material of the first positive electrode comprising lithium manganese iron phosphate and a first conductive agent; and

[0044] A second positive electrode is formed on the second surface, wherein the material of the second positive electrode includes a ternary positive electrode material and a second conductive agent;

[0045] Wherein, the mass fraction of the first conductive agent in the material of the first positive electrode is greater than the mass fraction of the second conductive agent in the material of the second positive electrode.

[0046] Thirdly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising:

[0047] A positive electrode sheet, wherein the positive electrode sheet is the positive electrode sheet according to the first aspect, or the positive electrode sheet is a positive electrode sheet prepared according to the preparation method according to the second aspect;

[0048] The negative electrode includes a negative current collector and a first negative electrode and a second negative electrode formed on two opposing surfaces of the negative current collector; and

[0049] A diaphragm is disposed between the positive electrode and the negative electrode.

[0050] Preferably, the lithium-ion battery includes at least one electrode unit and at least one second electrode unit, wherein the first electrode unit and the second electrode unit are alternately arranged, the first electrode unit includes a first positive electrode, the separator and the first negative electrode arranged in sequence, and the second electrode unit includes a second positive electrode, the separator and the second negative electrode arranged in sequence;

[0051] Preferably, the ratio of the capacity of the first negative electrode per unit area to the capacity of the first positive electrode per unit area is equal to the ratio of the capacity of the second negative electrode per unit area to the capacity of the second positive electrode per unit area.

[0052] It should be noted that the materials of the first and second negative electrodes may include, for example, graphite, silicon carbide composite materials or other negative electrode materials commonly used in the art, and the present invention does not limit them.

[0053] In this invention, to form a complete battery, a separator, a positive current collector, and a negative current collector may be provided between the first electrode unit and the second electrode unit. It should be noted that in some embodiments, different first electrode units and second electrode units can be composed of the same positive electrode sheet, the same negative electrode sheet, and the same separator. For example, when the lithium-ion battery is a wound structure battery, the battery actually includes only one positive electrode sheet, one separator, and one negative electrode sheet. However, through winding, multiple alternating structures of the aforementioned first electrode units and second electrode units can be formed inside the battery. The number of first electrode units and second electrode units depends on the number of turns. In some embodiments, different first electrode units and second electrode units can be composed of different positive electrode sheets, different negative electrode sheets, and the same separator. For example, when the lithium-ion battery is a stacked structure battery, the battery includes multiple positive electrode sheets, multiple negative electrode sheets, and one separator. By folding the separator and alternately arranging the positive and negative electrode sheets, multiple electrode units can also be formed inside the battery.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] This invention provides a positive electrode sheet, which avoids the problem of large viscosity changes over time in the electrode slurry prepared after mixing lithium manganese iron phosphate and ternary positive electrode materials by forming coatings containing different types of positive electrode materials on both sides of the positive electrode current collector. This makes it difficult to meet the requirements of industrial production. Furthermore, this invention controls the mass fraction of the first conductive agent in the first positive electrode material to be greater than the mass fraction of the second conductive agent in the second positive electrode material. This is because ternary positive electrode materials have stronger conductivity than lithium manganese iron phosphate materials. Therefore, adding a larger mass fraction of the first conductive agent to the first positive electrode material improves the conductivity of the first positive electrode, making the first and second positive electrodes have similar conductivity, thereby extending battery life. This solves the technical problems of lithium manganese iron phosphate having dual voltage plateaus and low constant current ratio, thus improving the fast charging performance of lithium-ion batteries and facilitating BMS control. Attached Figure Description

[0056] Figure 1 A schematic diagram of the internal structure of the battery provided for Application Example 1;

[0057] Figure 2 This is a graph showing the viscosity variation of different cathode slurries.

[0058] Figure 3 The discharge performance diagrams are for the batteries assembled in Example 1 and Comparative Example 2.

[0059] Among them, 10-positive electrode sheet, 101-first positive electrode, 102-aluminum foil, 103-second positive electrode, 20-separator, 30-negative electrode sheet, 301-first negative electrode, 302-copper foil, 303-second negative electrode. Detailed Implementation

[0060] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be considered as specific limitations thereof.

[0061] Example 1

[0062] This embodiment provides a positive electrode sheet, such as Figure 1 As shown, the positive electrode includes:

[0063] Aluminum foil, comprising a first surface and a second surface;

[0064] The first positive electrode, formed on the first surface, comprises, by weight (100%), 97% lithium manganese iron phosphate with a core-shell coated structure, 0.2% dispersant (YTF003, purchased from Shenzhen TeYi Company), a first conductive agent (0.25% by weight of vapor-grown carbon fiber, 0.25% by weight of carbon nanotubes, 0.3% by weight of Super P and 0.3% by weight of acetylene black), and 1.7% polyvinylidene fluoride binder, wherein the thickness of the first positive electrode is 70 μm; and

[0065] The second cathode, formed on the second surface, comprises, by mass percentage (100%), 97.3% single-crystal ternary cathode material LiNi. 0.8 Co 0.1 Mn 0.1 The mixture consists of O2, 0.2% dispersant (model YTF003, purchased from Shenzhen Teyi Company), a second conductive agent (mass fractions of vapor-grown carbon fiber, carbon nanotubes, Super P and acetylene black of 0.1%, 0.1%, 0.3% and 0.3% respectively), and 1.7% polyvinylidene fluoride binder, wherein the thickness of the second positive electrode is 70 μm.

[0066] The mass ratio of the single-crystal ternary cathode material to the lithium manganese iron phosphate with a core-shell coating structure is 3:7.

[0067] This embodiment also provides a method for preparing the above-mentioned positive electrode sheet, which includes the following steps:

[0068] An aluminum foil is provided, the aluminum foil comprising a first surface and a second surface;

[0069] A first positive electrode slurry with lithium manganese iron phosphate having a core-shell coating structure, a first dispersant, a first conductive agent, and polyvinylidene fluoride binder are mixed with N-methylpyrrolidone to prepare a first positive electrode slurry with lithium manganese iron phosphate having a core-shell coating structure as the main positive electrode material. The first positive electrode slurry is then coated on the first surface of an aluminum foil to form a first positive electrode.

[0070] A second positive electrode slurry with a single-crystal ternary positive electrode material, a second dispersant, a second conductive agent, and a polyvinylidene fluoride binder is prepared by mixing with N-methylpyrrolidone. The second positive electrode slurry is then coated on the second surface of an aluminum foil to form a second positive electrode.

[0071] Example 2

[0072] This embodiment provides a positive electrode sheet, which includes:

[0073] Aluminum foil, comprising a first surface and a second surface;

[0074] The first positive electrode, formed on the first surface, comprises, by weight (100%), 97.3% lithium manganese iron phosphate with a core-shell coating, 0.1% dispersant (YTF003, purchased from Shenzhen TeYi Company), a first conductive agent (vapor-grown carbon fiber, carbon nanotubes, Super P, and acetylene black, with mass fractions of 0.25%, 0.25%, 0.3%, and 0.3%, respectively), and 1.5% polyvinylidene fluoride binder, wherein the thickness of the first positive electrode is 50 μm; and

[0075] The second cathode, formed on the second surface, comprises, by mass percentage (100%), 97.4% single-crystal ternary cathode material LiNi. 0.8 Co 0.1 Mn 0.1 The mixture consists of O2, 0.1% dispersant (model YTF003, purchased from Shenzhen Teyi Company), a second conductive agent (mass fractions of vapor-grown carbon fiber, carbon nanotubes, Super P and acetylene black of 0.25%, 0.25%, 0.25% and 0.25% respectively), and 1.5% polyvinylidene fluoride binder, wherein the thickness of the second positive electrode is 50 μm.

[0076] The mass ratio of the single-crystal ternary cathode material to the lithium manganese iron phosphate with a core-shell coating structure is 1:1.

[0077] This embodiment also provides a method for preparing the above-mentioned positive electrode sheet, which includes the following steps:

[0078] An aluminum foil is provided, the aluminum foil comprising a first surface and a second surface;

[0079] A first positive electrode slurry with lithium manganese iron phosphate having a core-shell coating structure, a first dispersant, a first conductive agent, and polyvinylidene fluoride binder are mixed with N-methylpyrrolidone to prepare a first positive electrode slurry with lithium manganese iron phosphate having a core-shell coating structure as the main positive electrode material. The first positive electrode slurry is then coated on the first surface of an aluminum foil to form a first positive electrode.

[0080] A second positive electrode slurry with a single-crystal ternary positive electrode material, a second dispersant, a second conductive agent, and a polyvinylidene fluoride binder is prepared by mixing with N-methylpyrrolidone. The second positive electrode slurry is then coated on the second surface of an aluminum foil to form a second positive electrode.

[0081] Example 3

[0082] This embodiment provides a positive electrode sheet, which includes:

[0083] Aluminum foil, comprising a first surface and a second surface;

[0084] The first positive electrode, formed on a first surface, comprises, by weight (100%), 94.9% lithium manganese iron phosphate with a core-shell coating, 2% dispersant (YTF003, purchased from Shenzhen TeYi Company), a first conductive agent (0.25% by weight of vapor-grown carbon fiber, 0.25% by weight of carbon nanotubes, 0.3% by weight of Super P and 0.3% by weight of acetylene black), and 2% polyvinylidene fluoride binder, wherein the thickness of the first positive electrode is 80 μm; and

[0085] The second cathode, formed on the second surface, comprises, by mass percentage (100%), 95.1% single-crystal ternary cathode material LiNi. 0.8 Co 0.1 Mn 0.1 The mixture consists of O2, 2% dispersant (model YTF003, purchased from Shenzhen Teyi Company), a second conductive agent (mass fractions of vapor-grown carbon fiber, carbon nanotubes, Super P and acetylene black of 0.15%, 0.15%, 0.3% and 0.3% respectively), and 2% polyvinylidene fluoride binder, wherein the thickness of the second positive electrode is 80 μm.

[0086] The mass ratio of single-crystal ternary cathode material to lithium manganese iron phosphate with a core-shell coating structure is 1:4.

[0087] This embodiment also provides a method for preparing the above-mentioned positive electrode sheet, which includes the following steps:

[0088] An aluminum foil is provided, the aluminum foil comprising a first surface and a second surface;

[0089] A first positive electrode slurry with lithium manganese iron phosphate having a core-shell coating structure, a first dispersant, a first conductive agent, and polyvinylidene fluoride binder are mixed with N-methylpyrrolidone to prepare a first positive electrode slurry with lithium manganese iron phosphate having a core-shell coating structure as the main positive electrode material. The first positive electrode slurry is then coated on the first surface of an aluminum foil to form a first positive electrode.

[0090] A second positive electrode slurry with a single-crystal ternary positive electrode material, a second dispersant, a second conductive agent, and a polyvinylidene fluoride binder is prepared by mixing with N-methylpyrrolidone. The second positive electrode slurry is then coated on the second surface of an aluminum foil to form a second positive electrode.

[0091] Example 4

[0092] The difference between this embodiment and Embodiment 1 is that the mass ratio of the single-crystal ternary cathode material to the lithium manganese iron phosphate with a core-shell coating structure is 1:0.5, while all other aspects are the same as in Embodiment 1.

[0093] Example 5

[0094] The difference between this embodiment and Embodiment 1 is that the mass ratio of the single-crystal ternary cathode material to the lithium manganese iron phosphate with a core-shell coating structure is 1:8, while all other aspects are the same as in Embodiment 1.

[0095] Comparative Example 1

[0096] This comparative example provides a positive electrode plate, which includes:

[0097] Aluminum foil, and;

[0098] The positive electrode is formed on the surface of an aluminum foil. Based on the total mass of the positive electrode (100%), the materials include 50% lithium manganese iron phosphate with a core-shell coating structure and 47.2% single-crystal ternary positive electrode material LiNi. 0.8 Co 0.1 Mn 0.1 O2, conductive agent (0.25%, 0.25%, 0.3%, and 0.3% by mass of vapor-grown carbon fiber, carbon nanotube, Super P, and acetylene black, respectively), and 1.7% polyvinylidene fluoride binder.

[0099] This comparative example also provides a method for preparing the above-mentioned positive electrode sheet, which includes the following steps:

[0100] Aluminum foil is available;

[0101] Lithium manganese iron phosphate with a core-shell coating structure and LiNi single-crystal ternary cathode material 0.8 Co 0.1 Mn 0.1 O2, conductive agent, and polyvinylidene fluoride binder are mixed with N-methylpyrrolidone to prepare a positive electrode slurry, and the positive electrode slurry is coated on the surface of aluminum foil to form a positive electrode.

[0102] Comparative Example 2

[0103] The difference between this comparative example and Example 1 is that the single-crystal ternary cathode material LiNi in the second cathode is used. 0.8 Co 0.1 Mn 0.1 O2 was replaced with lithium manganese iron phosphate with a core-shell coating structure, and everything else was the same as in Example 1.

[0104] Application Examples 1 to 5 and Comparative Application Examples 1 to 2

[0105] Lithium-ion batteries were prepared using the positive electrode sheets provided in Examples 1 to 5 and Comparative Examples 1 to 2, and the preparation methods are as follows:

[0106] Preparation of the positive electrode sheet: The above-mentioned positive electrode sheet.

[0107] Preparation of negative electrode sheet: The negative electrode active material graphite, conductive agent carbon black, styrene-butadiene rubber binder and sodium carboxymethyl cellulose thickener are mixed in a mass ratio of 96.7:0.6:1.5:1.2. Deionized water is added and the mixture is stirred and mixed thoroughly to form a uniform negative electrode slurry. The slurry is coated on copper foil, dried and rolled to obtain the negative electrode sheet.

[0108] Preparation of lithium-ion batteries: The positive electrode, separator and negative electrode are wound in sequence to obtain the cell; the cell is packaged with aluminum-plastic film, baked to remove water and injected with electrolyte, and then subjected to vacuum sealing, resting, formation, secondary sealing and shaping processes to obtain the lithium-ion battery.

[0109] In summary, viscosity tests were conducted on the positive electrode slurries of Example 1 and Comparative Example 1, and the test results are shown in [reference needed]. Figure 2The test results show that, compared to the existing technology that uses a mixture of lithium manganese iron phosphate and ternary cathode materials to prepare the cathode slurry, the present invention, by preparing lithium manganese iron phosphate cathode slurry and ternary cathode material cathode slurry separately, significantly reduces the viscosity of the slurry over time. This is beneficial for the stability of the cathode slurry during the cathode coating process, and thus facilitates the large-scale industrial production of batteries. The batteries assembled in Example 1 and Comparative Example 2 were discharged at a rate of 0.33C; the test results are shown below. Figure 3 The test results show that, compared with the existing lithium manganese iron phosphate battery system, the present invention eliminates the dual voltage plateau by introducing ternary cathode material, which is beneficial to the control of the BMS system.

[0110] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in 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 by, The positive electrode tab comprises: a positive electrode current collector comprising a first surface and a second surface; a first positive electrode formed on the first surface, a material of the first positive electrode comprising lithium iron manganese phosphate and a first conductive agent; and a second positive electrode formed on the second surface, a material of the second positive electrode comprising a ternary positive electrode material and a second conductive agent; wherein a mass fraction of the first conductive agent in the material of the first positive electrode is greater than a mass fraction of the second conductive agent in the material of the second positive electrode; the first conductive agent is a combination of vapor grown carbon fiber, carbon nanotube, Super P and acetylene black, and a mass ratio of the vapor grown carbon fiber, the carbon nanotube, the Super P and the acetylene black is (1-5):(1-5):(1-6):(1-6).

2. The cathode electrode of claim 1, wherein, the second conductive agent comprises any one or a combination of at least two of vapor grown carbon fiber, carbon nanotube, Super P or acetylene black.

3. The cathode electrode of claim 1, wherein, the mass fraction of the first conductive agent in the material of the first positive electrode is 0.8-2%.

4. The cathode electrode of claim 2, wherein, the second conductive agent is a combination of vapor grown carbon fiber, carbon nanotube, Super P and acetylene black.

5. The cathode electrode of claim 4, wherein, a mass ratio of the vapor grown carbon fiber, the carbon nanotube, the Super P and the acetylene black is (1-5):(1-5):(1-6):(1-6).

6. The cathode sheet of claim 1, wherein, the mass fraction of the second conductive agent in the material of the second positive electrode is 0.8-1.2%.

7. The cathode sheet of claim 1, wherein, the first positive electrode further comprises a first binder, and the second positive electrode further comprises a second binder.

8. The cathode electrode of claim 7, wherein, the first binder and the second binder each independently comprise polyvinylidene fluoride and / or sodium carboxymethyl cellulose.

9. The cathode electrode of claim 7, wherein, the mass fraction of the first binder in the material of the first positive electrode is 1.5-2.0%.

10. The cathode electrode of claim 7, wherein, the mass fraction of the second binder in the material of the second positive electrode is 1.5-2.0%.

11. The cathode electrode of claim 1, wherein, a thickness of the first positive electrode is 50-90 μm.

12. The cathode sheet of claim 1, wherein, a thickness of the second positive electrode is 50-90 μm.

13. The cathode sheet of claim 1, wherein, the lithium iron manganese phosphate is lithium iron manganese phosphate with a core-shell coating structure.

14. The cathode sheet of claim 1, wherein, the ternary positive electrode material is single-crystal ternary positive electrode material.

15. The cathode sheet of claim 1, wherein, a mass ratio of the ternary positive electrode material to the lithium iron manganese phosphate is 1:(1-4).

16. The cathode sheet of claim 15, wherein, a mass ratio of the ternary positive electrode material to the lithium iron manganese phosphate is 1:(1.4-1.6).

17. A method of making the positive electrode sheet of any one of claims 1-16, characterized by, The method comprises the following steps: providing a positive electrode current collector comprising a first surface and a second surface; forming a first positive electrode on the first surface, a material of the first positive electrode comprising lithium iron manganese phosphate and a first conductive agent; and forming a second positive electrode on the second surface, a material of the second positive electrode comprising a ternary positive electrode material and a second conductive agent; wherein a mass fraction of the first conductive agent in the material of the first positive electrode is greater than a mass fraction of the second conductive agent in the material of the second positive electrode.

18. A lithium-ion battery, characterized by, The lithium ion battery comprises: a positive electrode tab, the positive electrode tab being the positive electrode tab according to any one of claims 1-16, or the positive electrode tab being prepared by the preparation method according to claim 17; The negative electrode sheet includes a negative current collector and first and second negative electrodes respectively formed on opposite surfaces of the negative current collector; and A separator is disposed between the positive electrode sheet and the negative electrode sheet.

19. The lithium-ion battery of claim 18, wherein, The lithium ion battery includes at least one first electrode unit and at least one second electrode unit, the first electrode unit and the second electrode unit are arranged alternately, the first electrode unit includes the first positive electrode, the separator and the first negative electrode arranged in sequence, and the second electrode unit includes the second positive electrode, the separator and the second negative electrode arranged in sequence.

20. The lithium-ion battery of claim 19, wherein, The ratio of the capacity of the first negative electrode per unit area to the capacity of the first positive electrode per unit area is equal to the ratio of the capacity of the second negative electrode per unit area to the capacity of the second positive electrode per unit area.

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