Positive pole piece, lithium ion battery and electric device

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a positive pole piece, which comprises a positive current collector and a positive coating coated on at least one side surface of the positive current collector, and the positive coating comprises a positive active material; wherein the porosity, the specific surface area and the compaction density of the positive pole piece meet preset conditions, and the average particle size and the porosity of the positive active material meet preset conditions. Therefore, ion conduction and electron conduction can be effectively balanced, so that the rate capability and the cycle performance of the lithium ion battery are comprehensively improved. The invention also discloses a lithium ion battery and a power utilization device.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, specifically to a positive electrode, a lithium-ion battery, and an electrical device. Background Technology

[0002] Currently, with the widespread application of lithium-ion batteries in new energy vehicles, energy storage systems, and portable electronic devices, the requirements for their energy density, rate performance, and cycle performance are continuously increasing. Among these, the positive electrode, as an important component of lithium-ion batteries, plays a significant role in the battery's rate performance and cycle performance.

[0003] In related technologies, the performance of lithium-ion batteries is generally improved by optimizing the positive electrode active material in the positive electrode sheet. For example, appropriate elements are doped into the particles of the positive electrode active material, or elements are coated onto the particles of the positive electrode active material; or the element ratio of the positive electrode active material is adjusted.

[0004] In the process of implementing the embodiments of this disclosure, at least the following problems were found in the related art:

[0005] Although optimizing the positive electrode active material can improve the performance of lithium-ion batteries, it is still difficult to achieve a balance between ion conduction and electron conduction, which affects the rate performance or cycle performance of lithium-ion batteries.

[0006] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0007] To provide a basic understanding of some aspects of the disclosed embodiments, a brief summary is given below. This summary is not intended as a general commentary, nor is it intended to identify key / important components or describe the scope of protection of these embodiments, but rather as a prelude to the detailed description that follows.

[0008] This disclosure provides a positive electrode, a lithium-ion battery, and an electrical device that can effectively balance ion conduction and electron conduction, thereby comprehensively improving the rate performance and cycle performance of the lithium-ion battery.

[0009] In some embodiments, the positive electrode sheet includes a positive current collector and a positive electrode coating coated on at least one surface of the positive current collector, the positive electrode coating including a positive electrode active material; wherein, the positive electrode sheet satisfies the following condition:

[0010]

[0011] Where A is the porosity of the positive electrode, B is the specific surface area of ​​the positive electrode, and P is the compaction density of the positive electrode.

[0012] The positive electrode active material satisfies the following conditions:

[0013]

[0014] Among them, D 50 denoted as the average particle size of the positive electrode active material, and E is the specific surface area of ​​the positive electrode active material.

[0015] In some embodiments, the positive electrode sheet satisfies the following conditions:

[0016]

[0017] In some embodiments, the porosity A of the positive electrode sheet is 15% to 38%.

[0018] In some embodiments, the specific surface area B of the positive electrode is 0.8 cm². 2 / g~2.2g / cm 2 / g.

[0019] In some embodiments, the compaction density P of the positive electrode sheet is 3.0 g / cm³. 3 ~3.8g / cm 3 .

[0020] In some embodiments, the positive electrode active material satisfies the following conditions:

[0021]

[0022] In some embodiments, the average particle size D of the positive electrode active material 50 The size ranges from 3μm to 15μm.

[0023] In some embodiments, the specific surface area E of the positive electrode active material is 0.3 cm². 2 / g~1.2g / cm 2 / g.

[0024] In some embodiments, the positive electrode sheet and the positive electrode active material further satisfy the following conditions:

[0025] And 0.6 ≤ c ≤ 1.8;

[0026] in,

[0027] In some embodiments, the positive electrode coating further includes a positive electrode conductive agent and a positive electrode binder. By mass percentage, the positive electrode active material accounts for 94%–97%, the first positive electrode conductive agent accounts for 0.5%–1.1%, the second positive electrode conductive agent accounts for 1.1%–2.6%, and the positive electrode binder accounts for 1.5%–3%. The first and second positive electrode conductive agents are selected from one or more of multi-walled carbon nanotubes, single-walled carbon nanotubes, carbon black, and acetylene black. The positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0028] In some embodiments, the lithium-ion battery includes a negative electrode and a positive electrode as described in the foregoing embodiments.

[0029] In some embodiments, the electrical device includes a lithium-ion battery for providing power as described in the foregoing embodiments.

[0030] The positive electrode, lithium-ion battery, and power-consuming device provided in this disclosure can achieve the following technical effects:

[0031] By properly matching the parameters of the positive electrode sheet, the parameters of the positive electrode active material, and the relationship between the positive electrode sheet and the positive electrode active material, it is possible to ensure that the positive electrode sheet has a certain porosity and specific surface area, which is conducive to the rapid insertion and extraction of active ions, while also having a certain structural stability. This further ensures the cycle performance and rate performance of the lithium-ion battery, and also ensures that the lithium-ion battery has a high energy density.

[0032] The above general description and the description below are exemplary and illustrative only and are not intended to limit this application. Attached Figure Description

[0033] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations and drawings do not constitute a limitation on the embodiments. Elements having the same reference numerals in the drawings are shown as similar elements. The drawings are not to be scaled. And wherein:

[0034] Figure 1 This is a schematic diagram of the structure of a lithium-ion battery provided in an embodiment of this disclosure;

[0035] Figure 2 This is a schematic diagram of the structure of a lithium-ion battery provided in an embodiment of this disclosure;

[0036] Figure 3 This is a schematic diagram of a lithium-ion battery provided in an embodiment of this disclosure.

[0037] Figure label:

[0038] 1-Positive terminal; 10-Cell; 11-Positive terminal post; 12-Negative terminal; 2-Shell; 3-Negative electrode plate; 4-Separator; 5-Positive electrode plate. Detailed Implementation

[0039] To provide a more detailed understanding of the features and technical content of the embodiments of this disclosure, the implementation of the embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. The accompanying drawings are for illustrative purposes only and are not intended to limit the embodiments of this disclosure. In the following technical description, for ease of explanation, several details are used to provide a full understanding of the disclosed embodiments. However, one or more embodiments may still be implemented without these details. In other cases, well-known structures and devices may be simplified in their depiction to simplify the drawings.

[0040] The terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this disclosure are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this disclosure described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0041] In this disclosure, the terms "upper," "lower," "inner," "middle," "outer," "front," and "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for better description of the embodiments of this disclosure and their implementations, and are not intended to limit the indicated devices, elements, or components to having a specific orientation, or to require them to be constructed and operated in a specific orientation. Furthermore, some of the aforementioned terms may be used to indicate other meanings besides orientation or positional relationship; for example, the term "upper" may in some cases indicate a dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in the embodiments of this disclosure according to the specific circumstances.

[0042] Furthermore, the terms "set up," "connect," and "fix" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this disclosure according to the specific circumstances.

[0043] Unless otherwise stated, the term "multiple" means two or more.

[0044] In this embodiment of the disclosure, the character " / " indicates that the objects before and after it are in an "or" relationship. For example, A / B means: A or B.

[0045] The term "and / or" describes an association between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or A and B.

[0046] It should be noted that, unless otherwise specified, the embodiments and features described in the present disclosure can be combined with each other.

[0047] This disclosure provides a positive electrode sheet, including a positive current collector and a positive electrode coating coated on at least one surface of the positive current collector, wherein the positive electrode coating includes a positive electrode active material; wherein the positive electrode sheet satisfies the following conditions:

[0048]

[0049] Where A is the porosity of the positive electrode, B is the specific surface area of ​​the positive electrode, and P is the compaction density of the positive electrode.

[0050] The positive electrode active material must meet the following conditions:

[0051]

[0052] Among them, D 50 denoted as the average particle size of the positive electrode active material, and E is the specific surface area of ​​the positive electrode active material.

[0053] In this embodiment, the porosity A, specific surface area B, and compaction density P of the positive electrode are three interrelated and mutually restrictive key parameters. Optimizing any one parameter alone makes it difficult to achieve excellent overall performance. For example, increasing the compaction density P will affect the porosity A, thereby hindering ion transport; conversely, increasing the porosity A without sufficient electrode specific surface area B as support makes the electron conduction network under high compaction density more fragile, thus affecting energy density and electron conduction.

[0054] In the formula for positive electrode sheets, porosity A defines the volume fraction of pores within the positive electrode sheet that are not filled with solid material, serving as channels for lithium-ion transport. Here, higher porosity A indicates wider ion transport paths and higher electrolyte retention, significantly reducing ion migration resistance and concentration polarization during charge and discharge, thus positively impacting the battery's rate performance and low-temperature performance. However, porosity A is fundamentally contradictory to energy density and electronic conductivity. Excessively high porosity A directly reduces the amount of active material per unit volume, sacrificing the battery's volumetric energy density. Simultaneously, it may sparse the contact points between active material particles and the conductive agent, weakening the continuity of the electronic conductivity network and leading to increased ohmic resistance.

[0055] In the formula for positive electrode sheets, the compaction density P is a direct indicator of the degree of compaction of the positive electrode sheet and has a decisive impact on battery performance. Increasing the compaction density P forces the active material and conductive agent particles into closer contact, greatly improving the electronic conductivity network, reducing electron transport impedance, and thus improving the battery's power density. Simultaneously, a higher compaction density P allows for more active material to be filled within a limited volume, directly increasing the battery's volumetric energy density. On the other hand, increasing the compaction density P is achieved through mechanical rolling, a process that inevitably compresses and reduces the porosity of the positive electrode sheet. When the compaction density P is too high, it leads to narrow and tortuous ion transport channels, a sharp decrease in ionic conductivity, and severe polarization. This not only limits capacity utilization but also causes localized stress concentration during cycling due to uneven lithium ion insertion / extraction, accelerating active particle breakage and performance degradation, and increasing the risk of thermal runaway.

[0056] In the formula satisfied by the positive electrode active material, the focus is on optimizing the reaction kinetics and stability of the positive electrode active particles themselves. Here, the average particle size D of the positive electrode active material... 50 It is positively correlated with the lithium-ion solid-phase diffusion path, i.e., the average particle size D 50 The smaller the particle size, the faster the ion diffusion and the better the rate performance, but the specific surface area E of the positive electrode active material increases accordingly. Specific surface area E is positively correlated with reactivity and the degree of side reactions; that is, the larger the specific surface area E, the more initial reaction interfaces there are, and the more intense the side reactions with the electrolyte. Thus, the average particle size D is determined using the above formula. 50 By adjusting the specific surface area E to a reasonable range, it can be ensured that the positive electrode active material has a short ion diffusion path, but will not cause rapid capacity decay due to excessive surface activity.

[0057] Therefore, by using the positive electrode sheet provided in this embodiment, and by reasonably matching the parameters of the positive electrode sheet, the parameters of the positive electrode active material, and the relationship between the positive electrode sheet and the positive electrode active material, it is possible to ensure that the positive electrode sheet has a certain porosity and specific surface area, which is conducive to the rapid insertion and extraction of active ions, while also having a certain structural stability. This further ensures the cycle performance and rate performance of the lithium-ion battery, and also ensures that the lithium-ion battery has a high energy density.

[0058] In this embodiment of the disclosure, the average particle size of the positive electrode active material refers to the particle size value corresponding to when the particle size distribution of the positive electrode active material reaches 50%.

[0059] In some embodiments, the positive electrode sheet satisfies the following condition:

[0060]

[0061] In some embodiments, the porosity A of the positive electrode sheet is 15% to 38%.

[0062] In some specific embodiments, the porosity A of the positive electrode sheet is 20% to 32%.

[0063] In some embodiments, the specific surface area B of the positive electrode is 0.8 cm². 2 / g~2.2g / cm 2 / g.

[0064] In some specific embodiments, the specific surface area B of the positive electrode is 1.1 cm². 2 / g~1.8g / cm 2 / g.

[0065] In some embodiments, the compaction density P of the positive electrode sheet is 3.0 g / cm³. 3 ~3.8g / cm 3 .

[0066] In some specific embodiments, the compaction density P of the positive electrode sheet is 3.4 g / cm³. 3 ~3.7g / cm 3 .

[0067] In some embodiments, the positive electrode active material satisfies the following conditions:

[0068]

[0069] In some embodiments, the average particle size D of the positive electrode active material 50 The size ranges from 3μm to 15μm.

[0070] In some embodiments, the specific surface area E of the positive electrode active material is 0.3 cm². 2 / g~1.2g / cm 2 / g.

[0071] In some specific embodiments, the specific surface area E of the positive electrode active material is 0.3 cm². 2 / g~1.0g / cm 2 / g.

[0072] In some embodiments, the positive electrode sheet and the positive electrode active material satisfy the following conditions:

[0073] And 0.6 ≤ c ≤ 1.8;

[0074] in,

[0075] In the embodiments of this disclosure, 'a' can represent the macroscopic structural features of the positive electrode sheet, and 'b' can represent the microscopic intrinsic features of the positive electrode active material. By matching the characteristics of the positive electrode sheet and the positive electrode active material through the above formula, the lithium-ion battery can achieve optimal performance.

[0076] In some embodiments, the positive electrode coating further includes a positive electrode conductive agent and a positive electrode binder. By mass percentage, the positive electrode active material accounts for 94%–97%, the first positive electrode conductive agent accounts for 0.5%–1.1%, the second positive electrode conductive agent accounts for 1.1%–2.6%, and the positive electrode binder accounts for 1.5%–3%. The first and second positive electrode conductive agents are selected from one or more of multi-walled carbon nanotubes, single-walled carbon nanotubes, carbon black, and acetylene black. The positive electrode active material includes lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0077] This disclosure also provides a lithium-ion battery, including a negative electrode and a positive electrode as described in the foregoing embodiments.

[0078] The specific structure of the positive electrode sheet is as described in the above embodiments. Since this lithium-ion battery adopts all the technical solutions of all the above embodiments, it has at least all the technical effects brought about by the technical solutions of the above embodiments, and will not be described in detail here.

[0079] In this embodiment of the disclosure, the lithium-ion battery further includes a casing, in which a positive electrode and a negative electrode are encapsulated. Figures 1 to 3 As shown, the lithium-ion battery specifically includes a cylindrical casing 2, which houses the battery cells. The top is the positive terminal 1, and the bottom is the negative terminal 12. A positive electrode post 11 is disposed on the positive terminal 1. Specifically, Figure 2 A schematic diagram of the lithium-ion battery structure in this application is shown. Figure 3 A schematic diagram of the lithium-ion battery described in this application is shown. The positive electrode 5, negative electrode 3, and separator 4 are shown as follows: Figure 3The layers are stacked and then wound to form... Figure 2 The cylindrical battery cell 10 shown is initially wound to the electrode end at the cylindrical axis, and ends to the electrode end on the outer surface of the cylinder after winding. The positive electrode 5 includes a strip-shaped positive electrode foil, a positive electrode coating on the surface of the strip-shaped positive electrode foil, and a first empty foil area. The negative electrode 3 includes a strip-shaped negative electrode foil, a negative electrode coating on the surface of the strip-shaped negative electrode foil, and a second empty foil area. The first and second empty foil areas are perpendicular to the winding direction and are formed into the top or bottom end face of the lithium-ion battery by methods such as flattening or folding.

[0080] Based on this, the present disclosure provides a method for preparing a lithium-ion battery, comprising:

[0081] Preparation of positive electrode sheet: Mix positive electrode coating material and coat it on both sides of the positive electrode current collector. After drying and cold pressing, the positive electrode sheet is obtained.

[0082] Preparation of negative electrode sheet: Mix negative electrode coating material and coat it on both sides of the negative electrode current collector. After drying and cold pressing, the negative electrode sheet is obtained.

[0083] Battery cell preparation: The positive and negative electrode sheets are rolled and slit respectively, and then wound together with the separator to obtain the battery cell;

[0084] Assembling lithium-ion batteries: The tabs of the lithium-ion battery are welded to the electrical connectors, installed into the battery casing, and electrolyte is injected, sealed, and formed to obtain the lithium-ion battery.

[0085] Furthermore, embodiments of this disclosure provide an electrical device including a lithium-ion battery for providing power as described in this application.

[0086] The present invention will be further explained and illustrated below with reference to embodiments.

[0087] Example 1

[0088] This embodiment 1 provides a method for preparing a lithium-ion battery as follows:

[0089] Preparation of positive electrode sheet: Select positive electrode active materials lithium nickel cobalt manganese oxide (NMC811), multi-walled carbon nanotubes (MWCNT), carbon black (Super-P) and polyvinylidene fluoride (PVDF) and mix them thoroughly in an N-methylpyrrolidone solvent system at a mass percentage of 96:0.7:1.8:1.5 to obtain a positive electrode slurry with a solid content of 60%. Coat the positive electrode slurry onto both sides of aluminum foil, and after drying, cold pressing, slitting and cutting, obtain the positive electrode sheet.

[0090] Among them, the average particle size D of the positive electrode active material 50The diameter is 10 μm, and the specific surface area (BET) of the positive electrode active material is 0.6 cm². 2 / g; the porosity of the positive electrode is 25%, and the specific surface area (BET) of the positive electrode is 1.5 cm². 2 / g, the compacted density of the positive electrode sheet is 3.5g / cm³. 3 .

[0091] Preparation of negative electrode sheet: Select artificial graphite, silicon, acetylene black, sodium carboxymethyl cellulose (CMC) and polyacrylic acid (PAA), mix them thoroughly in deionized water at a mass percentage of 93:3:1:1:2 to obtain a negative electrode slurry with a solid content of 40%. Coat the negative electrode slurry onto both sides of copper foil, and after drying, cold pressing, slitting and cutting, obtain the negative electrode sheet.

[0092] Electrolyte preparation: Ethyl carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Fully dried lithium salt lithium hexafluorophosphate (LiPF6) is dissolved in the mixed organic solvent to obtain an electrolyte with a concentration of 1 mol / L.

[0093] Preparation of the diaphragm: A high-porosity diaphragm was selected. The thickness of the polyethylene (PE) base membrane in the diaphragm was 3 μm, the thickness of the ceramic coating on both sides of the base membrane was 1 μm, the thickness of the polyvinylidene fluoride (PVDF) coating was 1 μm, and the air permeability of the diaphragm was 120 s / 100 mL.

[0094] Assembling the lithium-ion battery: After the positive and negative electrode sheets are rolled and slit, they are wound together with the separator to obtain a cylindrical battery core. The battery core is then welded to the electrical connector and installed into the battery casing. After completing the liquid injection, sealing, and formation processes, the lithium-ion battery of Example 1 is obtained.

[0095] Example 2

[0096] Example 2 provides a lithium-ion battery. The difference between this example and Example 1 is that the porosity of the positive electrode is 20%. Everything else is the same as in Example 1.

[0097] Example 3

[0098] Example 3 provides a lithium-ion battery. The difference between this example and Example 1 is that the porosity of the positive electrode is 30%. Everything else is the same as in Example 1.

[0099] Example 4

[0100] Example 4 provides a lithium-ion battery. The difference between this example and Example 1 is that the specific surface area of ​​the positive electrode is 1.1 cm².2 / g. Everything else is the same as in Example 1.

[0101] Example 5

[0102] Example 5 provides a lithium-ion battery. The difference between this example and Example 1 is that the specific surface area of ​​the positive electrode is 1.8 cm². 2 / g. Everything else is the same as in Example 1.

[0103] Example 6

[0104] Example 6 provides a lithium-ion battery. The difference between this example and Example 1 is that the compaction density of the positive electrode sheet is 3.4 g / cm³. 3 Everything else is the same as in Example 1.

[0105] Example 7

[0106] Example 7 provides a lithium-ion battery. The difference between this example and Example 1 is that the compaction density of the positive electrode sheet is 3.6 g / cm³. 3 Everything else is the same as in Example 1.

[0107] Example 8

[0108] Example 8 provides a lithium-ion battery. The difference between this example and Example 1 is that the average particle size D of the positive electrode active material is... 50 The value is 8 μm. Everything else is the same as in Example 1.

[0109] Example 9

[0110] Example 9 provides a lithium-ion battery. The difference between this example and Example 1 is that the average particle size D of the positive electrode active material is... 50 The value is 12 μm. Everything else is the same as in Example 1.

[0111] Example 10

[0112] Example 10 provides a lithium-ion battery. The difference between this example and Example 1 is that the specific surface area of ​​the positive electrode active material is 0.4 cm². 2 / g. Everything else is the same as in Example 1.

[0113] Example 11

[0114] Example 11 provides a lithium-ion battery. The difference between this example and Example 1 is that the specific surface area of ​​the positive electrode active material is 0.8 cm². 2 / g. Everything else is the same as in Example 1.

[0115] Example 12

[0116] Example 12 provides a lithium-ion battery. The difference between this example and Example 1 is that the positive electrode active material is lithium nickel cobalt manganese oxide (NCM523). Everything else is the same as in Example 1.

[0117] Example 13

[0118] Example 13 provides a lithium-ion battery. The difference between this example and Example 1 is that the positive electrode active material is lithium cobalt oxide (LCO). Everything else is the same as in Example 1.

[0119] Comparative Example 1

[0120] Comparative Example 1 provides a lithium-ion battery. The difference between this comparative example and Example 1 is that the porosity of the positive electrode is 12%. Everything else is the same as Example 1.

[0121] Comparative Example 2

[0122] Comparative Example 2 provides a lithium-ion battery. The difference between this comparative example and Example 1 is that the specific surface area of ​​the positive electrode is 2.5 cm². 2 / g. Everything else is the same as in Example 1.

[0123] Comparative Example 3

[0124] Comparative Example 3 provides a lithium-ion battery. The difference between this comparative example and Example 1 is that the average particle size D of the positive electrode active material is... 50 The value is 16 μm. Everything else is the same as in Example 1.

[0125] Comparative Example 4

[0126] Comparative Example 4 provides a lithium-ion battery. The difference between this comparative example and Example 1 is that the specific surface area of ​​the positive electrode active material is 1.4 cm². 2 / g. Everything else is the same as in Example 1.

[0127] Comparative Example 5

[0128] Comparative Example 5 provides a lithium-ion battery. The difference between this comparative example and Example 1 is that the compaction density of the positive electrode sheet is 3 g / cm³. 3 Everything else is the same as in Example 1.

[0129] The lithium-ion batteries of Examples 1 to 13 and Comparative Examples 1 to 5 were tested accordingly.

[0130] This embodiment provides a method for testing the rate performance of a lithium-ion battery. The lithium-ion battery is placed in a constant temperature chamber at 25°C for 4 hours. The positive electrode material is a ternary material, and the voltage window is 2.5-4.2V. For different positive electrode materials, the voltage window needs to be adjusted accordingly. Then, the test is carried out according to the following steps:

[0131] Under a discharge rate of 0.1C, constant current discharge is carried out until 2.5V is cut off, and then left to stand for 10 minutes;

[0132] Under a charging rate of 0.1C, charge at a constant current to 4.2V and then charge at a constant voltage to 0.01C cutoff, and let stand for 10 minutes.

[0133] Under a discharge rate of 0.1C, the capacitor is discharged at a constant current until it is cut off at 2.5V, and then left to stand for 10 minutes. At this point, the capacity value is recorded as C0.

[0134] Under a charging rate of 0.1C, charge at a constant current to 4.2V and then charge at a constant voltage to 0.01C cutoff, and let stand for 10 minutes.

[0135] Under a discharge rate of 0.5C, constant current discharge is carried out until 2.5V is cut off, and then left to stand for 10 minutes.

[0136] Under a charging rate of 0.1C, charge at a constant current to 4.2V and then charge at a constant voltage to 0.01C cutoff, and let stand for 10 minutes.

[0137] Under a discharge rate of 1C, discharge at a constant current until the cutoff voltage of 2.5V, and let stand for 10 minutes.

[0138] Under a charging rate of 0.1C, charge at a constant current to 4.2V and then charge at a constant voltage to 0.01C cutoff, and let stand for 10 minutes.

[0139] Under a 2C discharge rate, discharge at a constant current until the cutoff voltage is 2.5V, and then let stand for 10 minutes.

[0140] Under a charging rate of 0.1C, charge at a constant current to 4.2V and then charge at a constant voltage to 0.01C cutoff, and let stand for 10 minutes.

[0141] Under 3C discharge rate conditions, constant current discharge is performed until 2.5V cutoff, and then left to stand for 10 minutes;

[0142] Under a charging rate of 0.1C, charge at a constant current to 4.2V and then charge at a constant voltage to 0.01C cutoff, and let stand for 10 minutes.

[0143] Under a 4C discharge rate, discharge at a constant current until the cutoff voltage is 2.5V, and then let stand for 10 minutes.

[0144] Under a charging rate of 0.1C, charge at a constant current to 4.2V and then charge at a constant voltage to 0.01C cutoff, and let stand for 10 minutes.

[0145] Under a 5C discharge rate, discharge at a constant current until the cutoff voltage is 2.5V, and then let stand for 10 minutes.

[0146] Under a charging rate of 0.1C, charge at a constant current to 4.2V and then charge at a constant voltage to 0.01C cutoff, and let stand for 10 minutes.

[0147] Under a discharge rate of 6C, constant current discharge is applied until 2.5V is cut off, and the mixture is left to stand for 10 minutes.

[0148] Under a charging rate of 0.1C, charge at a constant current to 4.2V and then charge at a constant voltage to 0.01C cutoff, and let stand for 10 minutes.

[0149] Under an 8C discharge rate, discharge at a constant current until the cutoff voltage is 2.5V, then let stand for 10 minutes.

[0150] Here, the rate performance of a single battery, i.e., the capacity retention rate, is obtained by the ratio of the discharge capacity of each rate discharge to the first discharge capacity C0.

[0151] This embodiment also provides a method for testing the cycle performance of a lithium-ion battery. The lithium-ion battery is placed in a constant temperature chamber at 25°C for 4 hours. The positive electrode material is a ternary material, and the voltage window is 2.5-4.2V. For different positive electrode materials, the voltage window needs to be adjusted accordingly. Then, the test is carried out according to the following steps:

[0152] Under a discharge rate of 0.1C, the sample was discharged at a constant current until it was cut off at 2.5V, and then left to stand for 5 minutes.

[0153] Under a charging rate of 0.2C, constant current charging is performed until 4.2V is cut off, and constant voltage charging is performed until 0.05C is cut off, and then the mixture is left to stand for 5 minutes.

[0154] Under a discharge rate of 0.2C, the capacitor is discharged at a constant current until it is cut off at 2.5V, and then left to stand for 5 minutes. The capacitance value C1 at this time is then read.

[0155] Charging steps: Under a 1C charging rate, charge at a constant current to 4.2V, and then charge at a constant voltage to 0.05C cutoff. Let stand for 5 minutes.

[0156] Discharge procedure: Under the condition of 2C discharge rate, discharge at constant current until 2.5V cutoff, and let stand for 5 minutes.

[0157] Repeat the above charging and discharging steps 600 times.

[0158] Here, the battery discharge capacity C after 600 cycles is... 600 The ratio of the discharge capacity C1 of the first cycle to the single cell's cycle performance, i.e., cycle retention rate, is obtained.

[0159] After performing the above tests on Examples 1 to 13 and Comparative Examples 1 to 5, the corresponding data were obtained.

[0160] The capacity retention and cycle retention rates measured in Examples 1 to 7 are shown in Table 1 below:

[0161] a b c Capacity retention Cycle retention rate Example 1 3.5 2.94 3.97 80％ 80％ Example 2 2.93 2.94 3.65 75％ 80％ Example 3 4.11 2.94 4.58 85％ 75％ Example 4 2.57 2.94 3.58 78％ 85％ Example 5 4.2 2.94 4.68 82％ 75％ Example 6 3.4 2.94 3.78 81％ 78％ Example 7 3.6 2.94 4.01 79％ 82％

[0162] Table 1

[0163] Table 1 shows that by comparing Examples 1 to 7, the value of 'a' changes by adjusting the parameters of the positive electrode. In Example 1, the porosity of the positive electrode is 25% and the specific surface area is 1.5 m². 2 / g, compacted density is 3.5g / cm³ 3 At this point, a balance between ion conduction and electronic conduction can be achieved, enabling the capacity retention and cycle retention of lithium-ion batteries to both reach 80%.

[0164] In the porosity of the positive electrode, as the porosity increases, for example in Example 3 where the value of 'a' is 4.11, the ion channels increase, resulting in a capacity retention rate of 85% for the lithium-ion battery. Conversely, as the porosity decreases, for example in Example 2 where the value of 'a' is 2.93, electron conduction is enhanced, stabilizing the cycle retention rate of the lithium-ion battery at 80%.

[0165] In the specific surface area of ​​the positive electrode, as the specific surface area of ​​the positive electrode increases, for example, in Example 5, the value of a is 4.2. At this time, the number of reaction sites increases, and the capacity retention rate of the lithium-ion battery increases to 82%. However, the side reactions also increase, and the cycle retention rate of the lithium-ion battery decreases to 75%. Conversely, as the specific surface area of ​​the positive electrode decreases, for example, in Example 4, the value of a is 2.57. At this time, the number of reaction sites decreases, and the capacity retention rate of the lithium-ion battery decreases to 78%. However, the side reactions decrease, and the cycle retention rate of the lithium-ion battery increases to 85%.

[0166] In the compaction density of the positive electrode sheet, appropriately increasing the compaction density of the positive electrode sheet, such as in Example 7 where the value of a is 3.6, increases the ion diffusion resistance, causing a slight decrease in the capacity retention rate of the lithium-ion battery. However, the higher compaction density can improve the compactness of the structure, thereby increasing the cycle retention rate of the lithium-ion battery to 82%.

[0167] The capacity retention and cycle retention rates measured according to Examples 1, 8 to 11 are shown in Table 2 below:

[0168] a b c Capacity retention Cycle retention rate Example 1 3.5 2.94 3.97 80％ 80％ Example 8 3.5 3.45 3.96 82％ 75％ Example 9 3.5 2.56 4.29 78％ 85％ Example 10 3.5 3.23 3.79 78％ 85％ Example 11 3.5 2.7 4.07 82％ 75％

[0169] Table 2

[0170] Table 2 shows that by comparing Example 1 with Examples 8 to 11, it can be seen that by adjusting the parameters of the positive electrode active material, the value of b changes, thereby altering the capacity retention rate and cycle retention rate of the lithium-ion battery.

[0171] In the particle size of the positive electrode active material, as the particle size decreases, for example in Example 8 where the value of b is 3.96, the ion diffusion path becomes shorter and the interfacial reaction accelerates, resulting in an increase in the capacity retention rate of the lithium-ion battery to 82%. However, the smaller particle size increases interfacial side reactions, causing the cycle retention rate of the lithium-ion battery to decrease to 75%. As the particle size of the positive electrode active material increases, for example in Example 9 where the value of b is 4.29, the ion diffusion path becomes longer and the interfacial reaction slows down, causing the capacity retention rate of the lithium-ion battery to decrease to 78%. However, the larger particle size reduces interfacial side reactions, resulting in an increase in the cycle retention rate of the lithium-ion battery to 85%.

[0172] In the specific surface area of ​​the positive electrode active material, as the specific surface area of ​​the positive electrode active material decreases, for example, in Example 10, the value of b is 3.79. At this time, the number of reaction sites decreases, the rate performance decreases, and the capacity retention rate of the lithium-ion battery decreases to 78%. However, the small particle size increases the interfacial side reactions, which reduces the cycle retention rate of the lithium-ion battery to 75%. As the specific surface area of ​​the positive electrode active material increases, for example, in Example 11, the value of b is 4.07. The number of reaction sites increases, the rate performance improves, and the capacity retention rate of the lithium-ion battery increases to 82%.

[0173] The capacity retention and cycle retention rates measured according to Examples 1, 12, and 13 are shown in Table 3 below:

[0174] a b c Capacity retention Cycle retention rate Example 1 3.5 2.94 3.97 80％ 80％ Example 12 3.5 2.94 3.97 80％ 85％ Example 13 3.5 2.94 3.97 70％ 85％

[0175] Table 3

[0176] Table 3 shows that by comparing Example 1 with Examples 12 and 13, it can be seen that in Examples 12 and 13, the materials of the positive electrode active material were changed to NCM523 and LCO, respectively. When the materials of the positive electrode active material meet the above conditions, they all have good capacity retention and cycle retention.

[0177] The capacity retention and cycle retention rates measured according to Example 1 and Comparative Examples 1 to 5 are shown in Table 4 below:

[0178] a b c Capacity retention Cycle retention rate Example 1 3.5 2.94 3.97 80％ 80％ Comparative Example 1 2.07 2.94 3.08 60％ 70％ Comparative Example 2 5.83 2.94 6.49 85％ 50％ Comparative Example 3 3.5 2.04 5 65％ 80％ Comparative Example 4 3.5 2.17 4.52 83％ 40％ Comparative Example 5 3 2.94 3.33 82％ 75％

[0179] Table 4

[0180] In Table 4, by comparing Example 1 and Comparative Examples 1 to 5, it can be seen that in Comparative Example 1, the porosity of its positive electrode sheet is 12%, which results in insufficient ion transport channels, causing the capacity retention of the lithium-ion battery to decrease to 60%.

[0181] In Comparative Example 2, the specific surface area of ​​its positive electrode is 2.5 m². 2 / g, which will exacerbate surface side reactions and reduce the cycle retention rate of lithium-ion batteries to 50%.

[0182] In Comparative Example 3, the average particle size of the positive electrode active material is 16 μm, which would result in an excessively long lithium-ion diffusion distance, causing the capacity retention of the lithium-ion battery to decrease to 65%.

[0183] In Comparative Example 4, the specific surface area of ​​the positive electrode active material particles was 1.4 m². 2 / g, which will cause excessive surface reaction, reducing the cycle retention rate of lithium-ion batteries to 40%.

[0184] In Comparative Example 5, the compaction density of the positive electrode sheet was 3.0 g / cm³. 3 Although it meets the preset conditions for the positive electrode, it is not well matched with the positive electrode active material, resulting in a decline in overall performance.

[0185] In summary, by properly matching the parameters of the positive electrode sheet, the parameters of the positive electrode active material, and the relationship between the positive electrode sheet and the positive electrode active material, it is possible to ensure that the positive electrode sheet has a certain porosity and specific surface area, which is conducive to the rapid insertion and extraction of active ions, while also having a certain structural stability. This further ensures the cycle performance and rate performance of the lithium-ion battery, and also ensures that the lithium-ion battery has a high energy density.

[0186] The foregoing description and accompanying drawings fully illustrate embodiments of the present disclosure to enable those skilled in the art to practice them. Other embodiments may include structural and other changes. The embodiments represent only possible variations. Individual components and functions are optional unless explicitly required, and the order of operation may vary. Parts and features of some embodiments may be included or substituted for parts and features of other embodiments. Embodiments of the present disclosure are not limited to the structures described above and shown in the accompanying drawings, and various modifications and changes may be made without departing from its scope. The scope of the present disclosure is limited only by the appended claims.

Claims

1. A positive electrode plate, characterized in that, The device includes a positive current collector and a positive electrode coating applied to at least one surface of the positive current collector, wherein the positive electrode coating includes a positive electrode active material; wherein the positive electrode sheet satisfies the following conditions: Where A is the porosity of the positive electrode, B is the specific surface area of ​​the positive electrode, and P is the compaction density of the positive electrode. The positive electrode active material satisfies the following conditions: Among them, D 50 denoted as the average particle size of the positive electrode active material, and E is the specific surface area of ​​the positive electrode active material.

2. The positive electrode sheet according to claim 1, characterized in that, The positive electrode sheet satisfies the following conditions:

3. The positive electrode sheet according to claim 2, characterized in that, The positive electrode sheet has a porosity A of 15%–38% and a specific surface area B of 0.8 cm². 2 / g~2.2g / cm 2 / g, compacted density P is 3.0g / cm³ 3 ~3.8g / cm 3 .

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that, The positive electrode active material satisfies the following conditions:

5. The positive electrode sheet according to claim 4, characterized in that, The average particle size D of the positive electrode active material 50 The size ranges from 3μm to 15μm.

6. The positive electrode sheet according to claim 4, characterized in that, The specific surface area E of the positive electrode active material is 0.3 cm². 2 / g~1.2g / cm 2 / g.

7. The positive electrode sheet according to any one of claims 1 to 3, characterized in that, The positive electrode sheet and the positive electrode active material satisfy the following conditions: And 0.6 ≤ c ≤ 1.8; in, 8. The positive electrode sheet according to any one of claims 1 to 3, characterized in that, The positive electrode coating further includes a positive electrode conductive agent and a positive electrode binder. Calculated by mass percentage, the positive electrode active material accounts for 94%–97%, the first positive electrode conductive agent accounts for 0.5%–1.1%, the second positive electrode conductive agent accounts for 1.1%–2.6%, and the positive electrode binder accounts for 1.5%–3%. The first and second positive electrode conductive agents are selected from one or more of multi-walled carbon nanotubes, single-walled carbon nanotubes, carbon black, and acetylene black, respectively. The positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

9. A lithium-ion battery, characterized in that, It includes a negative electrode and a positive electrode as described in any one of claims 1 to 8.

10. An electrical appliance, characterized in that, Includes the lithium-ion battery for providing power as described in claim 9.

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