High-loading positive electrode sheet and preparation method, high-specific-energy battery

Abstract

The application belongs to the technical field of lithium ion batteries, and relates to a high-load positive electrode sheet, a preparation method and a high-specific-energy battery. The positive electrode sheet is a double-layer structure electrode, which comprises a current collector and a first electrode layer and a second electrode layer along the direction away from the current collector. The first electrode layer has small-granularity single-crystal ternary material with smaller specific gravity than large-granularity polycrystal ternary material, and the second electrode layer has small-granularity single-crystal ternary material with larger specific gravity than large-granularity polycrystal ternary material. The double-structure electrode sheet Li + The migration path is tortuous and the gradient distribution is achieved, and the small and large particles are synergistically used to realize a fast electrolyte diffusion channel and a lithium ion diffusion channel. The first electrode layer serves as a fast transmission layer, and the second electrode layer serves as a reaction balance layer, so that the concentration polarization problem in the thick electrode is effectively solved, the capacity of the positive electrode is helped to be exerted, and the energy density of the battery is improved. Meanwhile, the prepared positive electrode slurry is heated to realize high solid content, reduce the solvent usage amount, prevent cracking in the coating of the high-load electrode sheet, the first electrode layer and the second electrode layer are simultaneously coated by using a double-layer coating die, integrated preparation is realized, and the interface resistance is reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a positive electrode sheet and a preparation method. BACKGROUND

[0002] High specific energy batteries can store more energy under the same volume or weight. With the popularization of new energy vehicles and the demand for long driving range, it is urgent to improve the density of power batteries. To improve the energy density of lithium ion batteries, high-capacity positive and negative electrode materials and reduced use of battery auxiliary materials are generally used to improve the energy density of the battery. Since the specific capacity of the negative electrode material is much larger than that of the positive electrode, the main reason for restricting the energy density of the lithium battery is the positive electrode. To reduce the proportion of battery auxiliary materials, high-load positive electrode sheets need to be developed. However, the high-load positive electrode sheet has a large thickness, and the lithium ion transmission path is long, resulting in large concentration difference polarization in the vertical axis, and the battery capacity is not easy to develop. Secondly, thick electrodes are prone to cracking during slurry coating, causing uneven surface of the electrode sheet and affecting performance development.

[0003] Patent CN109560249A discloses a double-layer structure positive electrode sheet, which adopts a double-layer pore structure with gradually increasing porosity in the positive active unit, i.e. the porosity of the second electrode material layer > the porosity of the first electrode material layer, which improves the wettability of the electrolyte in the positive electrode material, the effective diffusion coefficient of lithium ions and the utilization rate of the positive active material, and further improves the actual specific capacity of the positive electrode material. The invention only increases the electrolyte wettability by controlling the porosity, which cannot solve the problem of concentration difference polarization caused by the long ion migration path of high-load thick electrodes.

[0004] Patent CN111640912A discloses a preparation method of a positive electrode sheet. The positive active material includes at least two kinds of lithium nickel cobalt manganese oxide LiNi x Co y Mn 1-x-y O2 with different morphologies and average particle sizes D50. By adjusting the proportion of single-crystal primary particles and multi-crystal material and the nickel content, the positive electrode sheet has good thermal stability and excellent kinetic performance, and the lithium ion secondary battery based on the positive electrode sheet has the characteristics of long cycle at room temperature and high temperature. The invention controls the size of single-crystal and multi-crystal material particles, coats a single-layer uniform structure electrode, and the electrode sheet does not have a tortuous gradient distribution, which cannot solve the problem of high-load thick electrodes.

[0005] Patent CN118630149A discloses a high-energy-density pole piece preparation method. The invention coats a polymer film on the surface of the conductive layer to obtain a lightweight current collector; uses the lightweight current collector to coat active substances to prepare a high-energy-density pole piece; the difference from the traditional current collector is that a lightweight, high-conductive carbon material is used as a lightweight conductive substance, which reduces the weight more obviously. However, for reducing the weight of the auxiliary current collector to improve the battery energy density, it is very limited, and there is no explanation of the large problem of battery internal resistance caused by high-load electrodes.

[0006] Patent CN118352468A discloses a preparation method of a high-face-load electrode. The invention is to realize high active material utilization rate of the high-face-load electrode through regulation of electrode coating composition and molding process. The mixed and uniform active material, conductive agent, electrolyte and part of the photopolymerization initiator form a coating on the current collector through in-situ solidification, wherein the electrolyte contains a polymerizable monomer, which forms a macromolecular network under the action of ultraviolet light, visible light or heat, which can improve the binding force between active material particles through physical interlocking, thereby improving the structural integrity of the electrode and helping to improve the electrode surface capacity. SUMMARY

[0007] In view of the problems existing in the high-load positive pole piece, the present application provides a high-load positive pole piece and a preparation method thereof, and a high-specific-energy battery. By adjusting the proportion of small-particle single-crystal and large-particle polycrystal ternary material in the first and second electrode layers of the positive pole piece, a high-load positive pole piece with tortuous gradient distribution is prepared, realizing fast electrolyte diffusion channel and lithium ion diffusion channel, effectively reducing the concentration polarization problem in thick electrodes, helping to exert the capacity of the positive electrode, and improving the energy density of the battery. At the same time, high compaction of the pole piece can be realized to improve the volume energy density. At the same time, the prepared positive electrode slurry is heated to realize high solid content, reduce the amount of solvent used, prevent cracking in the coating of high-load pole pieces, and realize simultaneous coating of the first and second electrode layers by a double-layer coating die to realize integrated preparation and reduce the interface resistance.

[0008] In order to achieve the above-mentioned purposes, the technical scheme of the present application is as follows:

[0009] A high-load positive pole piece, the positive pole piece comprising a current collector and a positive electrode layer, the positive electrode layer comprising a first electrode layer and a second electrode layer away from the current collector; the positive electrode layer comprises active material, conductive agent and binder; the active material comprises single-crystal ternary positive electrode material and polycrystal ternary positive electrode material, the particle size of the single-crystal ternary positive electrode material in the active material is smaller than that of the polycrystal ternary positive electrode material; the proportion of single-crystal ternary positive electrode material in the first electrode layer is smaller than that of polycrystal ternary positive electrode material, and the proportion of single-crystal ternary positive electrode material in the second electrode layer is greater than that of polycrystal ternary positive electrode material.

[0010] Preferably, the mass ratio of the polycrystal ternary cathode material to the single crystal ternary cathode material in the first electrode layer is (2-9):1; and the mass ratio of the single crystal ternary cathode material to the polycrystal ternary cathode material in the second electrode layer is (2-9):1.

[0011] Preferably, the mass ratio of the active material, the conductive agent and the binder is (92-98):(1.5-4):(0.5-4).

[0012] Preferably, the ternary cathode material is LiNi x Co y Mn 1−x−y O2, wherein 0

[0013] Preferably, the D 50 particle size of the single crystal ternary cathode material is 1-6 μm; and the D 50 particle size of the polycrystal ternary cathode material is 10-20 μm.

[0014] Preferably, the conductive agent is any one or a combination of several of conductive carbon black, acetylene black, ketjen black, carbon nanotube, graphene and carbon fiber.

[0015] The binder is any one or a combination of several of polyvinylidene fluoride, sodium hydroxymethyl cellulose, sodium alginate and polyethylene oxide.

[0016] Preferably, the coating surface density of the first electrode layer is 20-25 mg / cm 2 ; and the coating surface density of the second electrode layer is 15-20 mg / cm 2 .

[0017] Preferably, the preparation method of the high-loading cathode electrode sheet comprises the following steps:

[0018] (1) adding the active material, the conductive agent and the binder into a solvent and performing heating homogenization to prepare the first electrode layer slurry and the second electrode layer slurry, respectively;

[0019] (2) performing first electrode layer coating and second electrode layer coating on the first electrode layer slurry and the second electrode layer slurry of step (1), respectively.

[0020] Preferably, the temperature of the heating homogenization in step (1) is 30-50℃; the solid content of the slurry is 75-85 wt%; the viscosity is 5000-8000 mPa.s; and the solvent is N-methyl pyrrolidone.

[0021] Preferably, the step (2) is performed by using a double-layer coating die to coat the first electrode layer and the second electrode layer simultaneously;

[0022] A high specific energy battery, the positive electrode sheet of the battery is the high-load positive electrode sheet, the negative electrode sheet is a silicon-based negative electrode sheet or a lithium metal electrode sheet; the positive and negative electrode sheets are laminated, packaged, liquid injected, formed, and prepared into a high specific energy soft package battery.

[0023] The present application has the following beneficial effects:

[0024] 1. The present application provides a high-load positive electrode sheet and a preparation method, by adjusting the proportion of small particle single crystal and large particle polycrystal ternary material in the first and second electrode layers of the positive electrode sheet, realizing the tortuosity gradient distribution of the high-load positive electrode sheet. + Fast transmission; the large particle active material in the second electrode layer with high tortuosity can realize deep delithiation at low Li + Concentration, achieve reaction equilibrium, thereby solving the concentration polarization problem of high-load electrodes during charging and discharging, fully exerting the capacity of the positive electrode sheet, and improving the energy density of the battery.

[0025] 2. The second electrode layer of the present application mainly uses small particle single crystal ternary material, realizes high compaction of the electrode sheet, reduces the ion migration path in the high compaction electrode sheet, reduces the internal resistance of the electrode sheet, and improves the performance of the battery.

[0026] 3. The present application uses a heating homogenization method to realize the preparation of high solid content slurry, reduces the amount of organic solvent used, and prevents cracking in the coating of high-load electrode sheets.

[0027] 4. The positive electrode sheet prepared by the method of the present application is applied to a high specific energy battery, and the single-sided coating density can reach 40 mg / cm 2 , realizes the preparation of high-load active material and thick electrode sheet, and at the same time achieves the effect of high battery energy density, and the energy density of the prepared battery can reach 360 Wh / Kg, which is much higher than the data of the comparative example (290 Wh / Kg). BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0029] Figure 1 This is a schematic diagram of the positive electrode structure of the present invention.

[0030] Figure 2 The discharge curves of the pouch batteries in Examples 1-3 and Comparative Example 1 are shown. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] The ternary cathode material used in this embodiment of the invention was purchased from Beijing Easpring Material Technology Co., Ltd.

[0033] Example 1

[0034] The positive electrode and the soft-pack battery in this embodiment are prepared by the following steps:

[0035] (1) The single-crystal ternary cathode material in the active material is LiNi. 0.93 Co 0.05 Mn 0.02 O2 and polycrystalline ternary cathode material are LiNi 0.9 Co 0.06 Mn 0.04 O2; D in single-crystal and polycrystalline materials 50 The particle sizes are 4μm and 13μm, respectively. The active material, conductive agent conductive carbon black and binder polyvinylidene fluoride are mixed in a ratio of 97:3:1 and heated to 35℃ to prepare the first and second layers of positive electrode slurry, respectively. The mass ratio of single crystal to polycrystalline active material in the first and second layers is 1:9 and 9:1, respectively. The viscosity of the slurry is adjusted to 7000mPa.s by adding solvent N-methylpyrrolidone, and the solid content is 78%.

[0036] (2) Apply the slurry prepared in step (1) to a double-layer coating die with a first electrode layer density of 20 mg / cm³. 2 Density of the second electrode layer: 15 mg / cm³ 2 Simultaneously, coating is performed, and the resulting positive electrode sheet has the following structure: Figure 1 As shown.

[0037] (3) Using the high-load positive electrode sheet prepared above, and the negative electrode sheet is a silicon-oxygen 550 negative electrode sheet; the 40Ah soft pack battery is prepared by stacking (15 layers of positive electrode and 16 layers of negative electrode), encapsulation, liquid injection (liquid injection coefficient 2.0g / Ah), formation, capacity testing and other processes.

[0038] Example 2

[0039] The positive electrode tab and soft package battery of the present example are prepared by the following steps:

[0040] (1) The single-crystal ternary material in the active material is LiNi 0.93 Co 0.05 Mn 0.02 O2, and the polycrystalline ternary material is LiNi 0.9 Co 0.06 Mn 0.04 O2; the D 50 particle sizes of the single-crystal and polycrystalline materials are 3 μm and 15 μm, respectively; the active material, the conductive agent, conductive carbon black, and the binder, polyvinylidene fluoride, are mixed in a ratio of 96:2.5:1.5, heated at 40°C, and used to prepare the first layer and the second layer of the positive electrode slurry, wherein the mass ratio of the single-crystal and polycrystalline active materials in the first layer and the second layer is 1:4 and 4:1, respectively; the solvent, N-methyl pyrrolidone, is added to adjust the viscosity of the slurry to 6000 mPa.s, and the solid content is 80%.

[0041] (2) The slurry prepared in step (1) is coated using a double-layer coating die at a first electrode layer area density of 22 mg / cm 2 and a second electrode layer area density of 16 mg / cm 2 at the same time.

[0042] (3) The high-load positive electrode tab prepared above and a silicon-oxygen 550 negative electrode tab are used to perform the processes of lamination (15 layers of positive electrode and 16 layers of negative electrode), packaging, liquid injection (liquid injection coefficient 2.0 g / Ah), formation, and capacity grading to prepare a 40 Ah soft package battery.

[0043] Example 3

[0044] The positive electrode tab and soft package battery of the present example are prepared by the following steps:

[0045] (1) The single-crystal ternary material in the active material is LiNi 0.93 Co 0.05 Mn 0.02 O2, and the polycrystalline ternary material is LiNi 0.9 Co 0.06 Mn 0.04 O2; the D 50 particle sizes of the single-crystal and polycrystalline materials are 2 μm and 14 μm, respectively; the active material, the conductive agent, conductive carbon black, and the binder, polyvinylidene fluoride, are mixed in a ratio of 97.5:1.5:1, heated at 45°C, and used to prepare the first layer and the second layer of the positive electrode slurry, wherein the mass ratio of the single-crystal and polycrystalline active materials in the first layer and the second layer is 3:7 and 7:3, respectively; the solvent, N-methyl pyrrolidone, is added to adjust the viscosity of the slurry to 5500 mPa.s, and the solid content is 82%.

[0046] (2) The slurry prepared in step (1) is coated simultaneously using a double-layer coating die according to a first electrode layer density of 22 mg / cm 2 and a second electrode layer density of 18 mg / cm 2 .

[0047] (3) The high-load positive electrode plate prepared above is used, and a silicon-oxygen 550 negative electrode plate is used; the processes of lamination (15 layers of positive electrode and 16 layers of negative electrode), packaging, liquid injection (liquid injection coefficient 2.0 g / Ah), formation, and capacity grading are performed to prepare a 40 Ah soft package battery.

[0048] Example 4

[0049] The positive electrode plate and the soft package battery of the present example are prepared by the following steps:

[0050] (1) The single-crystal ternary positive electrode material in the active material is LiNi 0.8 Co 0.1 Mn 0.1 O2, and the polycrystal ternary positive electrode material is LiNi 0.92 Co 0.04 Mn 0.04 O2; the D 50 particle sizes of the single-crystal and polycrystal materials are 4 μm and 13 μm, respectively; the active material, the conductive agent (mass ratio of Ketjen black and carbon nanotube 1:1), and the binder (mass ratio of polyvinylidene fluoride and polyethylene oxide 1:1) are mixed in a proportion of 98:1.5:0.5, heated at 35°C, and used for the preparation of the first layer and the second layer of positive electrode slurry, wherein the mass ratio of the single-crystal and polycrystal active materials of the first layer and the second layer is 1:2 and 2:1, respectively; the solvent N-methyl pyrrolidone is added to adjust the viscosity of the slurry to 6000 mPa.s, and the solid content is 83%.

[0051] (2) The slurry prepared in step (1) is coated simultaneously using a double-layer coating die according to a first electrode layer density of 20 mg / cm 2 and a second electrode layer density of 15 mg / cm 2 .

[0052] (3) The high-load positive electrode plate prepared above is used, and a silicon-oxygen 550 negative electrode plate is used; the processes of lamination (15 layers of positive electrode and 16 layers of negative electrode), packaging, liquid injection (liquid injection coefficient 2.0 g / Ah), formation, and capacity grading are performed to prepare a 40 Ah soft package battery.

[0053] Example 5

[0054] The positive electrode plate and the soft package battery of the present example are prepared by the following steps:

[0055] (1) The single-crystal ternary cathode material in the active material is LiNi 0.93 Co 0.05 Mn 0.02 O2, and the polycrystal ternary cathode material is LiNi 0.9 Co 0.06 Mn 0.04 O2; the D 50 particle sizes of the single-crystal and polycrystal materials are 1 μm and 10 μm respectively; the active material, the conductive agent (acetylene black and carbon fiber with a mass ratio of 7:3) and the binder polyethylene oxide are mixed in a proportion of 92:4:4 and heated at 30°C to prepare a first layer and a second layer of cathode slurry respectively, wherein the mass ratio of the single-crystal and polycrystal active materials in the first layer and the second layer is 1:9 and 9:1 respectively; the solvent N-methyl pyrrolidone is added to adjust the viscosity of the slurry to 5000 mPa.s, and the solid content is 75%.

[0056] (2) The slurry prepared in step (1) is coated using a double-layer coating die at a first electrode layer area density of 20 mg / cm 2 and a second electrode layer area density of 15 mg / cm 2 at the same time.

[0057] (3) The high-load cathode electrode sheet prepared above is used, and a silicon-oxygen 550 negative electrode sheet is used as a negative electrode sheet; a laminated sheet (15 layers of positive electrodes and 16 layers of negative electrodes) is prepared, and the laminated sheet is packaged, liquid injected (liquid injection coefficient 2.0 g / Ah), formed, and subjected to a capacity distribution process to prepare a 40 Ah soft package battery.

[0058] Example 6

[0059] The positive electrode sheet and the soft package battery of this example are prepared by the following steps:

[0060] (1) The single-crystal ternary cathode material in the active material is LiNi 0.93 Co 0.05 Mn 0.02 O2, and the polycrystal ternary cathode material is LiNi 0.9 Co 0.06 Mn 0.04 O2; the D 50 particle sizes of the single-crystal and polycrystal materials are 6 μm and 20 μm respectively; the active material, the conductive agent (graphene and Ketjen black with a mass ratio of 3:7) and the binder sodium carboxymethyl cellulose are mixed in a proportion of 97:3:1 and heated at 50°C to prepare a first layer and a second layer of cathode slurry respectively, wherein the mass ratio of the single-crystal and polycrystal active materials in the first layer and the second layer is 1:9 and 9:1 respectively; the solvent N-methyl pyrrolidone is added to adjust the viscosity of the slurry to 8000 mPa.s, and the solid content is 85%.

[0061] (2) Apply the slurry prepared in step (1) to a double-layer coating die with a first electrode layer density of 25 mg / cm³. 2 The density of the second electrode layer is 20 mg / cm³. 2 Coating is performed simultaneously.

[0062] (3) Using the high-load positive electrode sheet prepared above, and the negative electrode sheet is a silicon-oxygen 550 negative electrode sheet; the 40Ah soft pack battery is prepared by stacking (15 layers of positive electrode and 16 layers of negative electrode), encapsulation, liquid injection (liquid injection coefficient 2.0g / Ah), formation, capacity testing and other processes.

[0063] Comparative Example 1

[0064] The positive electrode and pouch cell of this comparative example were prepared by the following steps:

[0065] (1) The active material single crystal ternary material LiNi 0.93 Co 0.05 Mn 0.02 O2 and polycrystalline ternary material LiNi 0.9 Co 0.06 Mn 0.04 O2, conductive carbon black (conductive agent), and polyvinylidene fluoride (PVDF) (binder) were mixed in a ratio of 97.5:1.5:1 and heated to 45°C to prepare a slurry. The mass ratio of single-crystal to polycrystalline active material was 1:1; the Dcrystal of the single-crystal to polycrystalline material was... 50 The particle sizes were 2 μm and 14 μm, respectively; the viscosity of the slurry was adjusted to 6500 mPa·s by adding the solvent N-methylpyrrolidone, and the solid content was 80%.

[0066] (2) The slurry prepared in step (1) is subjected to a surface density of 40 mg / cm³. 2 Perform a single-layer coating.

[0067] (3) Using the high-load positive electrode sheet prepared above, and the negative electrode sheet is a silicon-oxygen 550 negative electrode sheet; the 40Ah soft pack battery is prepared by stacking (15 layers of positive electrode and 16 layers of negative electrode), encapsulation, liquid injection (liquid injection coefficient 2.0g / Ah), formation, capacity testing and other processes.

[0068] Comparative Example 2

[0069] The positive electrode and pouch cell of this comparative example were prepared by the following steps:

[0070] (1) The active material single crystal ternary material LiNi 0.93 Co 0.05 Mn 0.02 O2, conductive agent conductive carbon black, and binder polyvinylidene fluoride were mixed in a ratio of 96:2.5:1.5 and heated to 45°C to prepare the positive electrode slurry. The single-crystal material D... 50The particle size is 2 μm respectively; the solvent N-methyl pyrrolidone is added to adjust the slurry viscosity to 8000 mPa.s, and the solid content is 75%.

[0071] (2) The prepared slurry in step (1) is coated by using a surface density of 40 mg / cm 2 to perform single-layer coating.

[0072] (3) The high-load positive electrode plate prepared above is used, and the negative electrode plate is a silicon oxide 550 negative electrode plate; a 40 Ah soft package battery is prepared by performing processes such as lamination (15 layers of positive electrode and 16 layers of negative electrode), packaging, liquid injection (liquid injection coefficient 2.0 g / Ah), formation, and capacity distribution.

[0073] Comparative Example 3

[0074] The positive electrode plate and the soft package battery of the present comparative example are prepared by the following steps:

[0075] (1) The active substance polycrystalline ternary material LiNi 0.9 Co 0.06 Mn 0.04 O2, conductive agent conductive carbon black, and binder polyvinylidene fluoride are mixed in a ratio of 97.5:1.5:1, heated at 45°C to prepare slurry, and the D 50 The particle size is 14 μm respectively; the solvent N-methyl pyrrolidone is added to adjust the slurry viscosity to 5000 mPa.s, and the solid content is 85%.

[0076] (2) The prepared slurry in step (1) is coated by using a surface density of 40 mg / cm 2 to perform single-layer coating.

[0077] (3) The high-load positive electrode plate prepared above is used, and the negative electrode plate is a silicon oxide 550 negative electrode plate; a 40 Ah soft package battery is prepared by performing processes such as lamination (15 layers of positive electrode and 16 layers of negative electrode), packaging, liquid injection (liquid injection coefficient 2.0 g / Ah), formation, and capacity distribution.

[0078] Comparative Example 4

[0079] The positive electrode plate and the soft package battery of the present comparative example are prepared by the following steps:

[0080] (1) The active substance polycrystalline ternary material LiNi 0.93 Co 0.05 Mn 0.02 O2, conductive agent conductive carbon black, and binder polyvinylidene fluoride are mixed in a ratio of 97.5:1.5:1, heated at 45°C to prepare slurry, and the D 0.9 Co 0.06 Mn 0.04 O2; the D 50The particle sizes are 2 μm and 14 μm respectively; the active material, the conductive agent, conductive carbon black, and the binder, polyvinylidene fluoride, are mixed in a ratio of 97.5:1.5:1, heated at 45°C, and used to prepare the first layer and the second layer of the positive electrode slurry, wherein the mass ratio of the single crystal and the polycrystal of the active material in the first layer and the second layer is 7:3 and 3:7 respectively; the solvent N-methyl pyrrolidone is added to adjust the viscosity of the slurry to 6000 mPa.s, and the solid content is 83%.

[0081] (2) The slurry prepared in step (1) is coated using a double-layer coating die according to the first electrode layer density of 22 mg / cm 2 and the second electrode layer density of 18 mg / cm 2 at the same time.

[0082] (3) The high-load positive electrode plate prepared above is used, and the negative electrode plate is a silicon-oxygen 550 negative electrode plate; the processes of lamination (15 layers of positive electrode and 16 layers of negative electrode), packaging, liquid injection (liquid injection coefficient 2.0 g / Ah), formation, and capacity determination are performed to prepare a 40 Ah soft package battery.

[0083] The batteries prepared in Examples 1-6 and Comparative Examples 1-4 are different only in the positive electrode layer, and the processes of the negative electrode and the packaging are the same. The electrode parameters and the soft package battery data of Examples 1-3 and Comparative Example 1-4 are shown in Table 1:

[0084] Table 1 Soft package battery data of Examples 1-3 and Comparative Example 1-4

[0085]

[0086] Comparative Example 1-3 is different from Example 1-3 in that it uses a single-layer structure positive electrode, and the rest of the processes for preparing the battery are the same. According to the data in Table 1, the electrode and the battery prepared in Example 3 using the method of the present application exhibit higher specific capacity and battery energy density (such as Figure 2The reason is that the present application realizes the tortuosity gradient distribution of the high-loading positive electrode sheet by adjusting the proportion of small-particle single-crystal and large-particle polycrystal ternary materials in the first and second electrode layers of the positive electrode sheet. The low tortuosity of the first electrode layer realizes fast transmission, and the high tortuosity of the second electrode layer realizes reaction balance, thereby solving the concentration polarization problem of the high-loading electrode in the charging and discharging, making the capacity of the positive electrode sheet fully play, and improving the energy density of the battery. The second electrode layer mainly uses small-particle single-crystal ternary materials to realize high compaction of the electrode sheet, the high-compaction electrode sheet reduces the ion migration path, reduces the internal resistance of the electrode sheet, and improves the performance of the battery. The compounding of polycrystal and single-crystal ternary materials realizes the synergistic effect of particles, reduces the volume expansion in the charging and discharging process of the electrode sheet, and improves the capacity play of the battery. Comparative Example 2 and Comparative Example 3 respectively use pure single-crystal and pure polycrystal positive active materials relative to Example 3, and coat the positive electrode into a single-layer structure, so that the positive electrode sheet does not have a tortuosity gradient structure, and therefore the prepared battery has low energy density and low positive electrode capacity play. + The migration rate is less than the interface reaction rate, causing large concentration polarization, and the ion migration path of the first electrode layer is short and does not play a role in reaction balance, so the capacity play of the electrode is low.

[0087] The above description of the present application is only the preferred embodiment of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A high-load positive electrode, characterized in that, The positive electrode sheet includes a current collector and a positive electrode layer. The positive electrode layer includes a first electrode layer and a second electrode layer along a direction away from the current collector. The positive electrode layer contains an active material, a conductive agent, and a binder. The active material includes monocrystalline ternary positive electrode material and polycrystalline ternary positive electrode material. The particle size of the monocrystalline ternary positive electrode material is smaller than that of the polycrystalline ternary positive electrode material. The specific gravity of the monocrystalline ternary positive electrode material in the first electrode layer is less than that of the polycrystalline ternary positive electrode material, and the specific gravity of the monocrystalline ternary positive electrode material in the second electrode layer is greater than that of the polycrystalline ternary positive electrode material.

2. The high-load positive electrode sheet according to claim 1, characterized in that: The mass ratio of polycrystalline ternary cathode material to single-crystal ternary cathode material in the first electrode layer is (2~9):1; the mass ratio of single-crystal ternary cathode material to polycrystalline ternary cathode material in the second electrode layer is (2~9):

1.

3. The high-load positive electrode sheet according to claim 1, characterized in that: The single-crystal ternary cathode material D 50 Particle size of 1~6μm; polycrystalline ternary cathode material D 50 The particle size is 10~20μm.

4. The high-load positive electrode sheet according to any one of claims 1-3, characterized in that: The mass ratio of the active material, conductive agent, and binder is (92~98):(1.5~4):(0.5~4).

5. The high-load positive electrode sheet according to claim 4, characterized in that: The ternary cathode material is LiNi. x Co y Mn 1−x−y O2, where 0 <x<1,0<y<1-x。 6. The high-load positive electrode sheet according to claim 4, characterized in that: The conductive agent is any one or a combination of several of the following: conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, and carbon fiber. The adhesive is any one or a combination of several of polyvinylidene fluoride, sodium hydroxymethyl cellulose, sodium alginate, and polyethylene oxide.

7. The high-load positive electrode sheet according to claim 4, characterized in that: The surface density of the first electrode layer coating is 20~25 mg / cm³. 2 The surface density of the second electrode layer coating is 15~20 mg / cm³. 2 .

8. The method for preparing the high-load positive electrode sheet according to any one of claims 1-7, characterized in that, Includes the following steps: (1) Add active material, conductive agent and binder to solvent and heat to homogenize, so as to prepare first electrode layer slurry and second electrode layer slurry respectively; (2) The first electrode layer slurry and the second electrode layer slurry in step (1) are respectively coated with the first electrode layer and the second electrode layer.

9. The method for preparing a high-load positive electrode sheet according to claim 8, characterized in that, The temperature of heating the homogenized slurry in step (1) is 30~50℃; the solid content of the slurry is 75~85wt%; the viscosity is 5000~8000 mPa.s; and the solvent is N-methylpyrrolidone.

10. A high-energy-density battery, characterized in that, The positive electrode of the battery is the high-load positive electrode as described in any one of claims 1-7, and the negative electrode is a silicon-based negative electrode or a lithium metal electrode; the high-energy-density soft-pack battery is prepared by stacking, packaging, liquid injection, formation and capacity testing of the positive and negative electrodes.

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