Positive plate and battery

Abstract

The invention provides a positive plate and a battery, the positive plate comprises a positive current collector and a positive coating located on at least one side surface of the positive current collector, the positive coating comprises a positive active layer and a first ceramic layer located between the outer edge of the positive plate and the positive active layer, the positive electrode active layer comprises a positive electrode active material and a conductive agent; the positive electrode active material comprises a single-crystal positive electrode ternary material and a polycrystal positive electrode ternary material; the positive plate meets the condition that x * y / A is greater than or equal to 0.8 and less than or equal to 1.2, A is the thickness of the area where the positive active layer on the positive plate is located, and the unit is metered by mu m; x is the compaction density of the positive electrode active layer, and the unit is g / cm < 3 >; y is the thickness of the first ceramic layer, and the unit is [mu] m. The power performance, the high-temperature storage performance and the safety performance of the battery can be improved at the same time.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a positive electrode sheet and a battery. Background Art

[0002] Batteries are common electrochemical devices with a wide range of applications. For example, lithium-ion batteries have the advantages of high energy density, low self-discharge, long life, near-zero memory, light weight, and environmental protection, and are widely used in portable devices, electric vehicles, aerospace, and other fields. With the development of science and technology, higher and higher requirements are placed on the high and low temperature performance and safety performance of batteries. Specifically, during the use of batteries, they usually face problems of mechanical abuse such as needle puncture. In the case of mechanical abuse, it is easy to cause the battery to catch fire or even explode, seriously affecting the safety of the battery during use. At the same time, when the battery encounters a high temperature environment, the high temperature environment will affect the capacity of the battery, thereby reducing the battery's capacity retention rate and worsening the battery's cycle life. This requires the battery to have good high-temperature storage performance. In addition to the corresponding requirements for the safety performance and high-temperature storage performance of the battery, higher and higher requirements are usually placed on the power performance of the battery, such as requiring the battery to have good low-temperature performance. However, in the relevant technology, how to balance the improvement of the safety performance, high-temperature storage performance, and power performance of the battery has always been a technical problem that needs to be solved in this field. Summary of the invention

[0003] The present invention provides a positive electrode sheet and a battery, which can improve the safety performance, high temperature storage performance and power performance of the battery, and effectively overcome the defects of the prior art.

[0004] In one aspect of the present invention, a positive electrode sheet is provided, comprising a positive electrode current collector and a positive electrode coating located on at least one side of the positive electrode current collector, wherein the positive electrode coating comprises a positive electrode active layer and a first ceramic layer located between the outer edge of the positive electrode sheet and the positive electrode active layer, wherein the positive electrode active layer comprises a positive electrode active material and a conductive agent; the positive electrode active material comprises a single crystal positive electrode ternary material and a polycrystalline positive electrode ternary material; the positive electrode sheet satisfies 0.8≤x*y / A≤1.2, wherein A is the thickness of the area where the positive electrode active layer is located on the positive electrode sheet, in μm; x is the compaction density of the positive electrode active layer, in g / cm 3 y is the thickness of the first ceramic layer, in μm.

[0005] According to one embodiment of the present invention, the ratio of the single crystal positive electrode ternary material to the polycrystalline positive electrode ternary material is 1: (0.05-0.5); and / or, the particle size Dv50 of the positive electrode active material is 3.5 μm to 7.5 μm; and / or, the average particle size of the single crystal positive electrode ternary material is 3.75 μm to 4.65 μm;

[0006] According to an embodiment of the present invention, the positive electrode active layer includes a conductive agent, and the conductive agent includes carbon nanotubes; preferably, the mass percentage content e of the carbon nanotubes in the positive electrode active layer is 0 < e ≤ 0.8%; preferably, the conductive agent further includes one or more of conductive carbon black, acetylene black, and conductive graphite.

[0007] According to an embodiment of the present invention, the positive electrode tab is provided on the positive electrode sheet and is connected to the positive electrode current collector, and the first ceramic layer is located on the side of the positive electrode sheet where the positive electrode tab is provided; according to an embodiment of the present invention, 2.7 g / cm 3 ≤ x ≤ 3.6 g / cm 3 ; and / or, 10 μm ≤ y ≤ 33 μm.

[0008] On the other hand, the present invention provides a battery including the above-mentioned positive electrode sheet.

[0009] According to an embodiment of the present invention, the above-mentioned battery further includes a negative electrode sheet, the negative electrode sheet includes a negative electrode coating, the negative electrode coating includes a negative electrode active material, and the ratio of the particle size Dv50 of the positive electrode active material to the particle size Dv50 of the negative electrode active material is 1:(1.6 - 2.8); preferably, the particle size Dv50 of the negative electrode active material is 5 μm to 10 μm.

[0010] According to an embodiment of the present invention, the above-mentioned battery further includes a separator, the separator includes a base film and a second ceramic layer located on the side of the base film facing the positive electrode sheet, and the ratio of the Fe element in the second ceramic layer to the Fe element in the positive electrode active material is 1:(1.2 - 2.5).

[0011] According to an embodiment of the present invention, the above-mentioned battery further includes a housing, a battery cell located in the housing, and a transfer tab connected to the battery cell and extending out of the housing. There is an ear glue between the transfer tab and the housing; preferably, the ratio of the width of the transfer tab to the width of the ear glue is 1:(1.2 - 1.5); preferably, the ratio of the width of the transfer tab to the width of the battery cell is 1:(8 - 20); preferably, the ear glue includes a polypropylene resin and a high-temperature resistant material, and the high-temperature resistant material includes one or more of polyethylene naphthalate, phenolic resin, urea resin, epoxy resin, and polyimide; preferably, the mass percentage content of the high-temperature resistant material in the ear glue is 5% - 20%; preferably, the ratio of the mass percentage content of the high-temperature resistant material in the ear glue to the thickness of the ear glue is (0.05 - 0.2):1.5, and the unit of the thickness of the ear glue is in mm;

[0012] According to one embodiment of the present invention, the dQ / dV curve of the battery has a first characteristic peak, a second characteristic peak and a third characteristic peak, the position of the first characteristic peak is (46%-52%) SOC, the position of the second characteristic peak is (57%-70%) SOC, and the position of the third characteristic peak is (70%-86%) SOC;

[0013] The ratio of the peak area P1 of the first characteristic peak to the peak area P2 of the second characteristic peak is 1:(2.0-3.0); the ratio of the peak area P1 of the first characteristic peak to the peak area P3 of the third characteristic peak is 1:(2.5-3.2).

[0014] In the present invention, single crystal positive electrode ternary material and polycrystalline positive electrode ternary material are simultaneously introduced into the positive electrode active layer as positive electrode active materials, and a first ceramic layer (ceramic edge) is arranged between the outer edge of the positive electrode sheet and the positive electrode active layer, and the compaction density x of the positive electrode active layer, the thickness y of the first ceramic layer, and the thickness A of the positive electrode sheet in the area where the positive electrode active layer is arranged on the positive electrode sheet are coordinated and regulated to satisfy 0.8≤x*y / A≤1.2. Under such a positive electrode composition system, the safety performance of the battery can be improved, and the battery can be prevented from catching fire, exploding, and other problems when encountering mechanical abuse such as needle puncture. At the same time, the high temperature storage performance of the battery can also be improved, so that the battery can still maintain a high capacity even when encountering a high temperature environment, thereby improving the service life (calendar life) of the battery. At the same time, the power performance (power discharge capacity) of the battery can also be improved, that is, the low temperature performance of the battery can be improved, and specifically, the cold start voltage of the battery in a low temperature environment can be improved, so that the battery has good safety performance, high temperature storage performance and power performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a front SEM image of a positive electrode sheet according to an embodiment of the present invention;

[0016] Figure 2 This is a cross-sectional SEM image of a positive electrode sheet according to an embodiment of the present invention;

[0017] Figure 3 dQ / dV curves of the batteries of Examples 1 and 13 of the present invention;

[0018] Figure 4 A schematic structural diagram of a positive electrode sheet according to an embodiment of the present invention;

[0019] Figure 5 Schematic diagram of the stacked structure of a positive electrode sheet, a separator and a negative electrode sheet in one embodiment of the present invention;

[0020] Figure 6 A schematic diagram of a battery structure according to an embodiment of the present invention;

[0021] Figure 7 FIG. 1 is a schematic structural diagram of a battery according to an embodiment of the present invention.

[0022] Explanation of the accompanying drawings: 1. positive electrode sheet; 110. positive electrode collector; 120. positive electrode active layer; 130. first ceramic layer; 11. positive electrode ear; 12: transfer ear; 2. negative electrode sheet; 210. negative electrode collector; 220. negative electrode coating; 3. diaphragm; 33. base film; 34. second ceramic layer; 31. first adhesive layer; 32. second adhesive layer; 4. battery cell; 5. shell; 50. cavity; 51. first side portion; 511. first main body portion; 512. first connecting portion; 52. second side portion; 521. second main body portion; 522. second connecting portion; 501. top edge seal; 502: side edge seal; 6. ear glue; a. first direction; b. second direction; c. third direction; y. thickness of the first ceramic layer; w. width of the first ceramic layer. DETAILED DESCRIPTION

[0023] In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below. The specific implementation methods listed below are only for describing the principles and features of the present invention. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0024] In the related technologies, how to improve the safety performance, high temperature storage performance and power performance of batteries has always been a technical problem that needs to be solved urgently in this field.

[0025] For example, with the widespread application of lithium-ion batteries, higher and higher requirements are placed on the power performance of lithium-ion batteries. For example, hybrid vehicles have both internal combustion engines and power batteries as drive systems. When the vehicle starts, a large starting current is required, and when braking, energy needs to be recovered in a short time. The power requirements for the battery are high. Therefore, it is urgent to develop high-output lithium-ion batteries.

[0026] Positive electrode materials are an important component of lithium-ion batteries, which affect the capacity, life, safety and power of lithium-ion batteries. Therefore, the development of positive electrode materials with high reversible discharge capacity, excellent cycle performance and high thermal stability is of great significance for improving the electrochemical performance of lithium-ion batteries.

[0027] According to the long-term research of the inventors of this application, power-type positive electrode materials are mostly secondary particles (i.e., polycrystalline positive electrode materials) tightly packed by primary particles. Although polycrystalline materials can exert certain power performance, they often have the problems of insufficient electrolyte infiltration, increased lithium ion diffusion path, large resistance, and in the repeated charge and discharge process, the volume change of the positive electrode active material forms stress, resulting in cracks or even pulverization inside the particles, which seriously affects the capacity, cycle performance and rate performance of the positive electrode material. At the same time, polycrystalline positive electrode material particles are secondary particles tightly packed by multiple primary particles, and their structural stability is poor. They are easily damaged by mechanical abuse such as needle puncture, affecting the safety of the battery.

[0028] According to the research of the inventors of this application, the development of positive electrode materials (such as ternary positive electrode materials) towards single crystallization can, on the one hand, make nano-crystal grains grow into micron-sized single crystal particles, which can reduce the specific surface area of ​​the material, thereby reducing its side reactions with the electrolyte and improving safety; on the other hand, after single crystallization, the grain boundaries and gaps between the primary grains are eliminated, which helps to increase the compaction density of the material, thereby increasing the volume energy density of the battery, and can also maintain the capacity of the battery to a certain extent. However, the kinetics of single crystal materials are slow, which hinders the lithiation process during discharge. This inherent low lithium chemical diffusion coefficient is a limiting factor in rate performance, and thus also limits the improvement of battery power performance.

[0029] Based on the above research findings, polycrystalline materials and single crystal materials each have their own advantages and can be used as feasible directions to improve battery performance. However, as mentioned above, polycrystalline materials and single crystal materials also have their own defects. How to overcome the adverse effects on battery performance caused by the inherent defects of polycrystalline materials and single crystal materials is still a technical problem that needs to be solved urgently.

[0030] In view of this, an embodiment of the present invention provides a positive electrode sheet 1, such as Figure 4 and Figure 5 As shown, the positive electrode sheet 1 includes a positive electrode collector 110, and a positive electrode active layer 120 located on at least one side surface of the positive electrode collector 110, the positive electrode active layer 120 includes a positive electrode active material and a conductive agent; the positive electrode active material includes a single crystal positive electrode material (a single crystal positive electrode material, hereinafter referred to as single crystal or single crystal material) and a polycrystalline positive electrode material (hereinafter referred to as polycrystalline or polycrystalline material); the positive electrode sheet satisfies 0.8≤x*y / A≤1.2, wherein A is the thickness of the area where the positive electrode active layer 120 is located on the positive electrode sheet 1 (that is, the thickness of the positive electrode sheet 1 in the area where the positive electrode active layer 120 is provided), in μm; x is the compaction density of the positive electrode active layer 120, in g / cm 3 y is the thickness of the first ceramic layer 130, in μm.

[0031] According to the research of the inventors, a mixture of single crystal and polycrystalline is used in the positive electrode active layer 120, and a first ceramic layer (ceramic edge) is arranged between the outer edge of the positive electrode sheet and the positive electrode active layer. At the same time, the compaction density x of the positive electrode active layer, the thickness y of the first ceramic layer, and the thickness A of the positive electrode sheet in the area where the positive electrode active layer is arranged on the positive electrode sheet are coordinated and regulated to satisfy 0.8≤x*y / A≤1.2. Under such a positive electrode system, the battery output rate can be stabilized, and the high temperature calendar life and needle puncture safety of the battery can be improved. The reason for the analysis is that, under the above-mentioned positive electrode system, on the one hand, the single crystal material has good structural stability, and will not be damaged when encountering mechanical abuse such as needle puncture, thereby improving the safety performance of the positive electrode sheet 1 and the battery, avoiding problems such as fire and explosion when encountering mechanical abuse such as needle puncture, and improving the high-temperature storage performance of the positive electrode sheet 1 and the battery. At the same time, the introduction of single crystal material also helps to improve the energy density of the positive electrode sheet 1 and the battery, and ensure the cycle life and other performance of the battery; on the other hand, such a positive electrode system overcomes the inherent defects of single crystal materials such as low lithium chemical diffusion coefficient, and can improve the power performance (power discharge capacity) of the battery cell 4; on the other hand, under the above-mentioned positive electrode system, polycrystalline material particles can exert good power performance, ensure the power performance of the battery, and overcome the influence of factors such as the polycrystalline structure of the polycrystalline material on the safety and other performance of the battery; on the other hand, in the above-mentioned mixed polycrystalline and single crystal positive electrode system, controlling the thickness of the ceramic layer can reduce the negative impact caused by the difference between single crystal and polycrystalline materials, stabilize the output power of the battery, and thus improve the battery cycle performance.

[0032] Therefore, in the embodiment of the present invention, under the above-mentioned positive electrode system, the advantages of single crystal materials and polycrystalline materials can be brought into play, and at the same time, the inherent defects of single crystal materials and polycrystalline materials that have an adverse effect on battery performance can be effectively overcome, thereby achieving the purpose of improving the battery's safety performance, high temperature storage performance, power performance and other performance.

[0033] Specifically, the positive electrode active material may include a ternary material, such as a nickel-cobalt-manganese ternary material (NCM). The single crystal positive electrode material may include a single crystal positive electrode ternary material, such as a single crystal nickel-cobalt-manganese ternary material, and may specifically include an NCM6 series single crystal ternary material (or NCM6 series single crystal positive electrode active material); the polycrystalline positive electrode material may include a polycrystalline positive electrode ternary material, such as a polycrystalline nickel-cobalt-manganese ternary material.

[0034] In an embodiment of the present invention, the above-mentioned single crystal material and polycrystalline material can be obtained by conventional methods in the art, for example, by first preparing a precursor and then sintering it at a high temperature. For example, NCM6 series single crystal ternary material can be obtained by obtaining a precursor solution through a co-deposition method and then preparing it through a multi-step high-temperature method.

[0035] In some embodiments, the preparation process of the single-crystalline ternary material may include: subjecting a mixture including a single-crystalline ternary material precursor and a lithium source to a first calcination to obtain a cathode material intermediate; and subjecting the cathode material intermediate to a second calcination to obtain the single-crystalline ternary material.

[0036] Specifically, the first calcination process includes: after holding the above mixture at a first temperature for a time t1, heating it to a second temperature and holding it at the second temperature for a time t2, and then cooling it to a third temperature and holding it at the third temperature for a time t3 to obtain the cathode material intermediate. Among them, during the process of holding at the first temperature for a time t1, dehydration and petrification of the mixture are mainly carried out. The first temperature can be 470 - 490 °C, such as 480 °C, and the time t1 can be 3.75 h - 4.25 h, such as 4 h; the process of holding at the second temperature for a time t2 is a short-time high-temperature sintering stage. The second temperature is 890 °C - 910 °C, such as 900 °C, and the time t2 is 1.75 h - 2.25 h, such as 2 h; the process of holding at the third temperature for a time t3 is a low-temperature holding stage. The third temperature is 790 °C - 810 °C, such as 800 °C, and the time t3 is 7.75 h - 8.25 h, such as 8 h.

[0037] Specifically, the temperature of the second calcination can be 740 °C - 760 °C, such as 750 °C, and the time of the second calcination can be 5.75 h - 6.25 h, such as 6 h.

[0038] Specifically, the above first calcination and second calcination processes can be carried out in an oxygen-containing atmosphere, specifically in air. For example, calcination is carried out using a muffle furnace. During the calcination process, the furnace lid of the muffle furnace is opened with a certain weight loss to enable the calcination material (such as the above mixture) to fully react with the oxygen in the air during the sintering process.

[0039] Specifically, the single-crystalline ternary material precursor is a hydroxide containing the transition metal elements of the single-crystalline ternary material. The transition metal elements, for example, include nickel element, cobalt element, and manganese element. The molar ratio between the transition metal elements in the single-crystalline ternary material precursor is basically equal to the molar ratio between the transition metal elements in the single-crystalline ternary material prepared using this single-crystalline ternary material precursor. For example, if the single-crystalline ternary material is lithium nickel cobalt manganate, its precursor can be a hydroxide containing nickel, cobalt, and manganese elements. This precursor is, for example, a Ni 0.6 Co 0.2 Mn 0.2 (OH)2 precursor (the single-crystalline ternary material prepared using the Ni 0.6 Co 0.2 Mn 0.2 (OH)2 precursor is NCM622).

[0040] Specifically, the single-crystalline ternary material precursor can be prepared by a co-precipitation method, and its preparation process may include: adding a precipitant and a chelating agent to an aqueous solution containing a transition metal source, followed by a precipitation reaction to obtain the single-crystalline ternary material precursor. Among them, during the precipitation reaction, when the pH of the reaction system reaches 10 to 12 (such as 11), the precipitation reaction ends, and the precipitate product is collected, which is the single-crystalline ternary material precursor.

[0041] Specifically, the temperature of the precipitation reaction can be 45 - 55 °C, such as 50 °C.

[0042] Specifically, the transition metal source may include compounds containing the transition metals in the single-crystalline ternary material, and specifically may include water-soluble salts containing transition metals, such as sulfates containing transition metals. This sulfate may include one or more of nickel sulfate, cobalt sulfate, and manganese sulfate. In specific implementation, the soluble salts of each transition metal can be mixed according to the stoichiometric ratio of the transition metal elements in the single-crystalline ternary material and dissolved in water to obtain an aqueous solution containing the transition metal source.

[0043] Specifically, the precipitant may include an inorganic base, and the inorganic base may include sodium hydroxide; the chelating agent may include ammonia water.

[0044] In addition, the lithium source may include lithium hydroxide (LiOH) and / or lithium salts. When the lithium source includes lithium hydroxide and lithium salts, the lithium salts can also be used as a flux. The lithium salts may specifically include lithium carbonate (Li2CO3).

[0045] In specific implementation, the single-crystalline ternary material precursor and the lithium source can be mixed to obtain a mixture; then the mixture is placed in a muffle furnace for the first calcination. During the first calcination, first heat up at a heating rate of 4 - 6 °C / min (such as 5 °C / min) to the first temperature, keep the temperature at the first temperature for a holding time t1, then heat up to the second temperature, heat at the second temperature for a heating time t2, and then cool down at a cooling rate of 2 - 4 °C / min (such as 3 °C / min) to the third temperature, keep the temperature at the third temperature for a holding time t3 to obtain the cathode material intermediate; then, water (specifically deionized water) can be used to wash the cathode material intermediate to remove impurities such as flux salts and residual lithium on its surface, and then dried, for example, dried at 70 - 90 °C (such as 80 °C) for 10 - 14 h (such as 12 h). Then, the obtained dried cathode material intermediate is placed in a muffle furnace for the second calcination. After the second calcination ends, the obtained second calcination product is ground and dispersed to obtain the single-crystalline ternary material.

[0046] Relatively speaking, the single-crystal material system performs more excellently in terms of safety performance and cycle performance, and the compaction density is also relatively high. Since the voltage of the single-crystal ternary material is higher, the overall energy density of the material will be higher than that of the polycrystalline material. However, the rate performance of the single-crystal ternary material is relatively poor compared with the polycrystalline material, and the production process is relatively complex, and the material price is relatively high. Considering these factors comprehensively in this application, the ratio of the single-crystal cathode material to the polycrystalline cathode material can be 1:(0.05 - 0.5), such as 1:0.05, 1:0.1, 1:0.15, 1:0.2, 1:0.25, 1:0.3, 1:0.35, 1:0.4, 1:0.45, 1:0.5 or the range composed of any two of them. This application is more conducive to improving the defect of the inherently low lithium chemical diffusion coefficient of the single crystal, obtaining a battery with excellent performance in terms of cycle, high-temperature storage, rate charge and discharge, safety, etc., and at the same time having advantages such as low cost.

[0047] In the embodiments of the present invention, the ratio of the single-crystal cathode material to the polycrystalline cathode material in the cathode active layer 120 can be measured by a scanning electron microscope (SEM). Specifically, during implementation, the cathode active layer 120 can be scraped off from the cathode current collector 110 to obtain cathode powder, and then through SEM analysis, the area S1 of the single-crystal material per unit area in the test field of view and the area S2 of the polycrystalline material per unit area in the test field of view are measured. Then, the ratio (S1 / S2) of S1 and S2 is the ratio of the single-crystal cathode material to the polycrystalline cathode material in the cathode active layer 120. Among them, there is no special limitation on the magnification during SEM analysis, as long as the single-crystal particles and polycrystalline particles can be seen. Specifically, during the test, for example, the cathode powder can be analyzed by SEM at a magnification of 100,000 times.

[0048] In some embodiments, the particle size Dv50 of the cathode active material can be 3.5 μm to 7.5 μm, such as 3.5 μm, 3.8 μm, 4 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.2 μm, 7.5 μm or the range composed of any two of them, which is conducive to improving the power performance of the battery while improving the safety and high-temperature storage performance of the battery. The reason for the analysis is that during low-temperature discharge, the cathode active material has a smaller particle size, resulting in a shorter lithium-ion diffusion path, a larger diffusion coefficient, a lower reduction amplitude of the battery voltage, and a longer time required for each particle to reach the lower cut-off voltage before reaching its available capacity. The discharge time at low temperature is long, and the available capacity is high, thereby improving the power performance of the battery.

[0049] Generally, the Dv90 of the above-mentioned positive electrode active material is less than or equal to 8 μm, that is, the particle size of the positive electrode active material is mainly concentrated below 8 μm. For example, its Dv90 can be 6.9 μm to 8.0 μm, and Dv10 is, for example, 1.8 μm to 2.6 μm.

[0050] In the embodiments of the present invention, the particle size Dv50 of the material represents the particle size at which the material particles reach 50% of the volume cumulative from the small particle size side in the particle size distribution based on volume. Dv90 represents the particle size at which the material particles reach 90% of the volume cumulative from the small particle size side in the particle size distribution based on volume; Dv10 represents the particle size at which the material particles reach 10% of the volume cumulative from the small particle size side in the particle size distribution based on volume. The particle sizes Dv50, Dv90, and Dv10 of the material can be measured by a laser particle size analyzer. For example, when measuring the particle sizes Dv50, Dv90, and Dv10 of the positive electrode active material in the positive electrode active layer 120, the positive electrode active layer 120 can be scraped from the surface of the positive electrode current collector 110, and organic substances such as binders therein can be removed by washing and other means. After removing the solvent used in the washing process by drying and other means, a solid particle product (the solid particle product is mainly the positive electrode active material) is obtained. Then, the volume particle size distribution of the solid particle product is measured by a laser particle size analyzer to obtain its particle sizes Dv50, Dv90, and Dv10, which are the particle sizes Dv50, Dv90, and Dv10 of the positive electrode active material.

[0051] In some embodiments, the average particle size of the single-crystal ternary positive electrode material can be 3.75 μm to 4.65 μm, such as 3.75 μm, 3.8 μm, 3.85 μm, 3.9 μm, 3.95 μm, 4 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.65 μm or the range composed of any two of them, which is beneficial to further take into account and improve the safety performance, high-temperature storage performance, and power performance of the battery. The reason for the analysis is that by controlling the average particle size of the single-crystal ternary positive electrode material within the above range, the single-crystal material can maintain a relatively small specific surface area, reduce the side reactions with the remaining electrolyte, and at the same time is more conducive to matching with materials such as the positive electrode material and carbon nanotubes for a long time, improving the compaction density of the positive electrode active layer 120, and forming a more suitable ion conduction network and conductive network, improving the energy density of the battery, reducing the internal resistance of the battery, and thus taking into account and improving the safety performance, high-temperature storage performance, and power performance of the battery.

[0052] Generally, the size of the single-crystal positive electrode material is less than or equal to 8 μm, that is, the particle size of the single-crystal positive electrode material is concentrated below 8 μm, and its size can specifically be 1.5 μm to 8 μm, that is, the particle size range of the single-crystal positive electrode material is concentrated between 1.5 μm and 8 μm.

[0053] In the embodiment of the present invention, the average particle size and size (particle size distribution range) of the single crystal positive electrode material in the positive electrode active layer 120 can be measured by a scanning electron microscope (SEM). For example, when testing the average particle size of the single crystal positive electrode material, the positive electrode active layer 120 can be scraped off from the positive electrode current collector 110 to obtain positive electrode powder, and then the diameter (particle size) of at least 20 single crystal positive electrode material particles in the test field can be measured by SEM analysis. Specifically, the diameter of 50 single crystal positive electrode material particles can be measured, and then the average value is statistically calculated, which is the average particle size of the single crystal positive electrode material in the positive electrode active layer 120. There is no special restriction on the magnification during SEM analysis, as long as the single crystal particles can be observed. In specific testing, the positive electrode powder can be SEM analyzed at a magnification of 100,000 times.

[0054] After further research, the above-mentioned positive electrode active layer includes a conductive agent, and the conductive agent may include carbon nanotubes (conductive carbon tubes). Under the above-mentioned positive electrode system, by introducing carbon nanotubes as a conductive agent in the positive electrode active layer 120, the fast charging ability and continuous discharge ability of the battery can be further improved, the battery ohmic and polarization internal resistance can be reduced, the battery discharge rate can be increased, and the inherent low diffusion coefficient and other defects of the single crystal material can be effectively compensated, and the power performance of the battery can be improved. The reason for the analysis is that the positive electrode active layer 120 simultaneously introduces single crystal materials and polycrystalline materials as positive electrode active materials, and introduces carbon nanotubes as a conductive agent, so that the positive electrode active layer 120 can form a suitable ion-conducting network and a conductive network, so that the positive electrode active layer 120 has a suitable ion transmission capacity and conductivity, while ensuring the capacity of the single crystal material and the polycrystalline material, the power performance of the positive electrode sheet 1 is improved, and at the same time, the stability of the positive electrode sheet 1 can be improved, and the side reactions of the positive electrode active material and other materials and the electrolyte in the positive electrode sheet 1 can be reduced, and the safety performance of the battery in the face of mechanical abuse such as acupuncture and the high temperature storage performance of the battery can be improved.

[0055] In some embodiments, the mass percentage of carbon nanotubes in the positive electrode active layer 120 can be e=0<e≤0.8%, for example, e is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8% or a range composed of any two of them, which is beneficial to further improve the safety performance, high temperature storage performance and power performance of the battery. The reason for this is that the introduction of carbon nanotubes as a conductive agent (e>0) in the positive electrode active layer 120 mixed with single crystal material and polycrystalline material can enhance the fast charging capability and continuous discharge capability of the battery, reduce the battery's ohmic and polarization internal resistance, increase the battery discharge rate, and improve the battery's power performance and other performance; at the same time, e is not higher than 0.8%, which can further inhibit the side reactions between the positive electrode material and the electrolyte and other materials, and further take into account the improvement of the battery's safety performance and high temperature storage performance.

[0056] In addition, the conductive agent in the positive electrode active layer 120 may further include other conductive agents in addition to carbon nanotubes. The other conductive agents may specifically include one or more of conductive carbon black, acetylene black, and conductive graphite.

[0057] In the embodiments of the present invention, a conventional positive electrode current collector 110 in the art may be used. For example, the positive electrode current collector 110 includes aluminum foil.

[0058] In the embodiments of the present invention, the first ceramic layer 130 is located on one side of the positive electrode active layer 120 close to the edge of the positive electrode current collector 110. That is, a first ceramic layer 130 (or ceramic edge) is further provided on the surface of the positive electrode current collector 110 where the positive electrode active layer 120 is provided. Setting the ceramic edge on the positive electrode current collector 110 can effectively reduce burrs (such as die-cutting burrs generated during the preparation of the positive electrode sheet 1) and the risk of the burr piercing the separator 3 and then causing a short circuit between the positive and negative electrodes. In particular, it can effectively avoid the occurrence of the most dangerous short-circuit mode between the positive electrode current collector 110 and the negative electrode, thereby further improving the safety performance of the battery.

[0059] Specifically, the first ceramic layer 130 may include a ceramic material and a binder. The ceramic material includes, but is not limited to, one or more of alumina, silicate, and silica. The binder includes, but is not limited to, one or more of polymer binders such as epoxy resin, polyurethane, and acrylate.

[0060] In the embodiments of the present invention, the first ceramic layer 130 may be formed in a preset area on the surface of the positive electrode current collector 110 by a conventional forming method of a ceramic film layer. For example, a ceramic slurry containing a ceramic material, a binder, a curing agent, and other materials is coated on the preset area on the surface of the positive electrode current collector 110, and after conventional processes such as drying and curing, the first ceramic layer 130 is formed. Among them, the curing agent is used to crosslink the binder, and the curing agent may include a resin-based hardener, such as phthalic anhydride.

[0061] In some embodiments, the mass percentage content of the ceramic material in the first ceramic layer 130 may be 25% - 45%, such as 35%.

[0062] In some embodiments, the mass percentage content of the binder in the first ceramic layer 130 may be 50% - 70%, such as 60%.

[0063] In some embodiments, the mass percentage content of the curing agent in the first ceramic layer 130 may be 3% - 7%, such as 5%.

[0064] Continue to refer to Figure 4The positive electrode sheet is also provided with a positive electrode ear (positive electrode soft ear) 11 connected to the positive electrode collector. The positive electrode ear 11 can be arranged at the end of at least one side in the length direction of the positive electrode sheet 1. The positive electrode ear 11 can be specifically formed by the positive electrode collector 110 extending outward in the direction away from the positive electrode active layer 120 in the length direction of the positive electrode sheet, but is not limited to this.

[0065] In some embodiments, Figure 4 As shown, the first ceramic layer 130 is located on the side of the positive electrode sheet 1 where the positive electrode tab 11 is provided. Specifically, in the direction from the first ceramic layer 130 to the positive electrode active layer 120, the first ceramic layer 130 is located between the positive electrode tab 11 and the positive electrode active layer 120. In comparison, the part of the positive electrode sheet 1 where the positive electrode tab 11 is provided is more prone to loosening and burrs due to the lead-out of the positive electrode tab 11. By providing the first ceramic layer 130 on the side of the positive electrode sheet 1 where the positive electrode tab 11 is led out, the risk of burrs and puncturing the diaphragm 3 and causing a short circuit between the positive and negative electrodes can be effectively reduced, and in particular, the most dangerous short circuit mode between the positive current collector 110 and the negative electrode can be effectively avoided, thereby further improving the safety performance of the battery.

[0066] like Figure 4 As shown, the first ceramic layer 130 can be in direct contact with the positive electrode active layer 120, that is, there is no other film structure or gap between the two.

[0067] In the embodiment of the present invention, the positive electrode active layer 120 may be disposed on one side surface of the positive electrode current collector 110 in the thickness direction, or the positive electrode active layer 120 may be disposed on both sides of the positive electrode current collector 110 in the thickness direction (i.e., the positive and negative surfaces of the positive electrode current collector 110). When the positive electrode active layer 120 is disposed on one side surface of the positive electrode current collector 110, the first ceramic layer 130 is disposed on the side surface of the positive electrode current collector 110 where the positive electrode active layer 120 is disposed; Figure 4 As shown, when the positive electrode active layer 120 is respectively provided on the front and back surfaces of the positive electrode collector 110, a first ceramic layer 130 may be respectively provided on the front and back surfaces of the positive electrode collector 110. For the positive electrode active layer 120 and the first ceramic layer 130 on each side surface of the positive electrode collector 110, the first ceramic layer 130 is located on one side of the positive electrode active layer 120 close to the edge of the positive electrode collector 110.

[0068] In some embodiments, the compaction density x of the positive electrode active layer 120 may be 2.7 g / cm 3 ~3.6g / cm 3 (i.e. 2.7 g / cm 3 ≤x≤3.6g / cm 3) In the blending system of single-crystal cathode materials and polycrystalline cathode materials, carbon nanotubes are introduced, and at the same time, the compaction density x of the cathode active layer 120 is controlled within the above range. A larger compaction density can increase the capacity of the battery, which is beneficial to improving the cycle performance of the battery. At the same time, it is beneficial to further avoid the destruction of the structure of the cathode active material, reduce the internal resistance of the battery, and improve the performance such as the power performance of the battery, thereby further improving the cycle characteristics, low-resistance characteristics, high-output power and other performances of the battery.

[0069] In some embodiments, the thickness y of the first ceramic layer 130 can be 10 μm to 33 μm (i.e., 10 μm ≤ y ≤ 33 μm), such as 10 μm, 13 μm, 15 μm, 18 μm, 20 μm, 23 μm, 25 μm, 28 μm, 30 μm, 33 μm or the range composed of any two of them, which is beneficial to avoiding burr short circuit and improving the battery safety performance, while further taking into account the higher energy density of the battery and improving the battery cycle performance.

[0070] In some embodiments, the width w of the first ceramic layer in the direction from the cathode active layer 120 to the first ceramic layer 130 can be 2 mm to 6 mm, such as 2 mm, 3 mm, 4 mm, 5 mm, 6 mm or the range composed of any two of them.

[0071] Specifically, the direction from the cathode active layer 120 to the first ceramic layer 130 (or the direction from the first ceramic layer 130 to the cathode active layer 120) is parallel to the length direction of the cathode plate.

[0072] In some embodiments, the thickness of the cathode active layer 120 can be 50 μm to 70 μm (i.e., 50 ≤ A ≤ 70), such as 50 μm, 53 μm, 55 μm, 58 μm, 60 μm, 63 μm, 65 μm, 68 μm, 70 μm or the range composed of any two of them.

[0073] Generally, the cathode active layer 120 further includes a binder, which can be a conventional binder material in the art. For example, the binder in the cathode active layer 120 includes one or more of polyvinylidene fluoride (PVDF), polyvinylidene difluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, etc.

[0074] Specifically, based on the total mass of the positive electrode active layer 120, the mass fraction of the positive electrode active material (i.e., the ratio of the total mass of the positive electrode active material to the total mass of the positive electrode active layer 120) can be 70% to 99%, such as 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99% or the range composed of any two of them. The mass fraction of the conductive agent can be 0.5% to 15%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or the range composed of any two of them. The mass fraction of the binder can be 0.5% to 15%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or the range composed of any two of them.

[0075] In the embodiment of the present invention, the positive electrode active layer 120 can be formed on the surface of the positive electrode current collector 110 by conventional methods in the art such as the coating method to obtain the positive electrode sheet 1. For example, materials such as the positive electrode active material, the conductive agent, and the binder can be placed in a solvent to make a positive electrode slurry. The solvent used includes, for example, N-methylpyrrolidone (NMP). Then, the positive electrode slurry is coated on the surface of the positive electrode current collector 110, and after processes such as drying and rolling, the positive electrode active layer 120 is formed on the surface of the positive electrode current collector 110 to obtain the positive electrode sheet 1. Among them, when forming the first ceramic layer 130 on the surface of the positive electrode current collector 110, the positive electrode slurry can be coated on a preset area of the surface of the positive electrode current collector 110, and the ceramic slurry for forming the first ceramic layer 130 can be coated on a preset area of the surface of the positive electrode current collector 110, and then dried and rolled uniformly to form the positive electrode active layer 120 and the first ceramic layer 130 on the surface of the positive electrode current collector 110 to obtain the positive electrode sheet 1. Among them, the processes such as drying and rolling involved are all conventional operations in the art and are not particularly limited herein.

[0076] The embodiment of the present invention also provides a battery, as Figures 5 to 7 shown. This battery includes the above-mentioned positive electrode sheet 1, and this battery has the corresponding advantages as the above-mentioned positive electrode sheet 1, which will not be elaborated here.

[0077] The battery in the embodiment of the present invention can be a lithium-ion battery, such as a lithium-ion power battery, etc. By adopting the above-mentioned positive electrode sheet 1, the power performance of the lithium-ion battery can be improved, and at the same time, the high-temperature storage performance and safety performance of the lithium-ion battery can be improved.

[0078] Generally, as Figure 6 and Figure 7As shown, the battery includes a housing 5 and a battery cell 4 located within the housing 5. Specifically, the battery may include an electrolyte, the battery cell 4, and the housing 5 that encapsulates the battery cell 4. The electrolyte is injected into the battery cell 4 within the housing 5. The battery cell 4 includes a positive electrode plate 1, a negative electrode plate 2, and a separator 3 located between the positive electrode plate 1 and the negative electrode plate 2. Among them, the battery cell 4 can be a wound battery cell 4, that is, the battery cell 4 is formed by winding the positive electrode plate 1, the separator 3, and the negative electrode plate 2 after being stacked; alternatively, the battery cell 4 can also be a laminated battery cell 4, that is, the battery cell 4 is formed by alternately stacking the positive electrode plate 1, the separator 3, and the negative electrode plate 2.

[0079] Specifically, the housing 5 can include a flexible packaging material (i.e., the battery is a soft-pack battery), and the flexible packaging material includes, for example, an aluminum-plastic film.

[0080] Specifically, the negative electrode plate 2 can include a negative electrode current collector 210 and a negative electrode coating 220 present on at least one surface of the negative electrode current collector 210. Specifically, the negative electrode coating 220 can be provided on one surface of the negative electrode current collector 210, or the negative electrode coating 220 can be provided on both the front and back surfaces of the negative electrode current collector 210 respectively.

[0081] Generally, the negative electrode plate 2 is also provided with a negative electrode tab (negative flexible tab) connected to the negative electrode current collector 210. The negative electrode tab can be provided at least one end of the negative electrode current collector 210 in the length direction. The negative electrode tab can extend outward from the negative electrode current collector, but is not limited thereto.

[0082] Specifically, the negative electrode coating 220 (or negative electrode active material layer) includes a negative electrode active material, and the negative electrode active material can include graphite, specifically including artificial graphite and / or natural graphite.

[0083] In some embodiments, the ratio of the particle size Dv50 of the positive electrode active material to the particle size Dv50 of the negative electrode active material can be 1:(1.6 - 2.8), such as 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, or the range composed of any two of them, which is beneficial for the battery to have good safety, high-temperature storage performance, and power performance.

[0084] In some embodiments, the particle size Dv50 of the negative electrode active material can be 5μm to 10μm, such as 5μm, 5.2μm, 5.5μm, 6μm, 7μm, 8μm, 9μm, 9.5μm, 9.8μm, 10μm, or the range composed of any two of them. By controlling the ratio of the particle size of the positive electrode active material to the particle size of the negative electrode active material within the above range, the battery polarization can be effectively reduced, and the electrochemical performance of the battery can be enhanced.

[0085] In addition, the negative electrode coating 220 (or the negative electrode active material layer) may further include materials such as a conductive agent and a binder, and these materials can all be conventional materials in the art. For example, the conductive agent may include at least one of conductive carbon black (SP), acetylene black, carbon nanotubes, conductive graphite, and graphene, and the binder may include one or more of carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyvinyl alcohol, and sodium polyacrylate.

[0086] Generally, in the negative electrode coating 220, the mass percentage content of the negative electrode active material can be 70% to 99%, such as 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or any range composed of any two of them. The mass fraction of the conductive agent can be 0.5% to 15%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any range composed of any two of them. The mass fraction of the binder can be 0.5% to 15%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any range composed of any two of them.

[0087] In the embodiments of the present invention, the negative electrode current collector 210 can be a conventional negative electrode current collector 210 in the art. For example, the negative electrode current collector 210 can include a copper foil.

[0088] The electrolyte in the embodiments of the present invention can be a conventional electrolyte in the art. For example, the electrolyte is a non-aqueous electrolyte, which can specifically include an organic solvent and an electrolyte salt (solute). The organic solvent includes, for example, one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC). The electrolyte salt can include a lithium salt, and the lithium salt can include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), and lithium hexafluoroarsenate (LiAsF6).

[0089] In addition, the separator 3 can be bonded to the positive electrode sheet 1 and the negative electrode sheet 2 respectively, that is, one side of the separator 3 is bonded to the positive electrode sheet 1 and the other side is bonded to the negative electrode sheet 2, which is beneficial to improving the structural stability of the battery cell 4 and further improving the battery performance.

[0090] Specifically, as Figure 5As shown, the separator 3 may include a base film 33, a first adhesive layer 31 on one side of the base film 33, and a second adhesive layer 32 on the other side of the base film 33. The first adhesive layer 31 is bonded to the positive electrode sheet 1, and the second adhesive layer 32 is bonded to the negative electrode sheet 2. That is, the first adhesive layer 31 and the second adhesive layer 32 are respectively the surface layers on the opposite sides in the thickness direction of the separator 3. The separator 3 is bonded to the positive electrode sheet 1 through the first adhesive layer 31 and bonded to the negative electrode sheet 2 through the second adhesive layer 32.

[0091] Among them, the base film 33 may be a conventional separator 3 material in the art. For example, the base film 33 includes one of a polypropylene (PP) film, a polyethylene (PE) film, a polypropylene / polyethylene (PP / PE) double-layer composite film, a polyimide electrospun film (PI), a polypropylene / polyethylene / polypropylene (PP / PE / PP) three-layer composite film, and a cellulose non-woven fabric film.

[0092] In addition, the first adhesive layer 31 may include a PVDF layer, that is, the material of the first adhesive layer 31 is PVDF, and it is mainly formed of PVDF.

[0093] In addition, the second adhesive layer 32 may include a PVDF layer, that is, the material of the second adhesive layer 32 is PVDF, and it is mainly formed of PVDF.

[0094] In some embodiments, the thickness of the first adhesive layer 31 may be 0.5 μm to 4 μm, such as 0.5 μm, 1 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, or a range composed of any two of them.

[0095] In some embodiments, the thickness of the second adhesive layer 32 may be 0.5 μm to 4 μm, such as 0.5 μm, 1 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, or a range composed of any two of them.

[0096] Specifically, the thickness of the first adhesive layer 31 and the thickness of the second adhesive layer 32 may be the same or different.

[0097] In addition, the separator 3 may include a second ceramic layer 34. Specifically, the second ceramic layer 34 may be located on the side of the base film 33 facing the positive electrode sheet 1, and the second ceramic layer 34 is located between the base film 33 and the first adhesive layer 31. By providing the second ceramic layer 34, it is beneficial to improve properties such as the heat resistance of the separator 3 and further improve the performance such as the safety of the battery.

[0098] Specifically, the second ceramic layer 34 includes a ceramic material, and the ceramic material in the second ceramic layer 34 may include alumina and / or boehmite. In some embodiments, the thickness of the second ceramic layer 34 may be 1 μm to 5 μm, such as 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or a range composed of any two of them.

[0099] According to the research of the inventors, the positive electrode active material usually contains metal elements such as Fe, and the second ceramic layer 34 can also contain iron (Fe) elements. The metal elements between the positive electrode active material of the positive electrode sheet 1 and the second ceramic layer 34 of the separator 3 will affect the battery performance. For example, when the iron element content is relatively high, the self-discharge rate of the battery will be high and the stability will be poor. The reason is that Fe impurity ions are gradually reduced and precipitated at the negative electrode, piercing the separator 3, resulting in an internal short circuit in the battery, thus causing a high self-discharge; when the Fe element content in the positive electrode active material of the positive electrode sheet 1 is low, the positive magnetic material is low, which will also affect the battery performance to a certain extent. Therefore, considering the above factors comprehensively, the ratio (mass ratio) of the Fe element in the second ceramic layer 34 to the Fe element in the positive electrode active material can be 1:(1.2 - 2.5).

[0100] In specific implementation, the ratio of the impurity ions of the positive electrode active material to the impurity ions of the separator 3 (mainly Fe ions) can be controlled within the above range by adjusting the synthesis process of the positive electrode active material (such as single crystal material) or introducing Fe elements during the preparation process of the second ceramic layer 34 and other conventional methods, so as to effectively improve the self-discharge ability of the battery cell 4 while ensuring the positive magnetic material.

[0101] In the embodiments of the present invention, the content of impurity elements such as Fe in the positive electrode active material and the second ceramic layer 34 of the separator 3 can be detected by ICP-MS, and the ratio (mass ratio) of the Fe element in the second ceramic layer 34 to the Fe element in the positive electrode active material can be measured.

[0102] In the embodiments of the present invention, as Figure 6 and Figure 7 shown, the above battery further includes a transfer tab 12 (or called a hard tab) connected to the battery cell 4 and extending out of the housing 5, and there is a tab glue 6 between the transfer tab 12 and the housing 5.

[0103] In the embodiments of the present invention, the battery can include a plurality of transfer tabs 12, at least one of which is a positive transfer tab (positive hard tab) connected to the positive electrode sheet 1, and at least one of which is a negative transfer tab (negative hard tab) connected to the negative electrode sheet 2. The tab glue 6 includes a first tab glue 6 provided between the positive transfer tab 12 and the housing 5 and a second tab glue provided between the negative transfer tab and the housing 5. That is, the tab glue 6 provided between the positive transfer tab and the housing 5 is the first tab glue, and the tab glue 6 provided between the negative transfer tab and the housing 5 is the second tab glue.

[0104] Specifically, when the battery includes a plurality of transfer tabs 12, these transfer tabs 12 can extend out of the housing 5 from the same side of the housing 5, for example, from the same side in the first direction a of the housing 5.

[0105] In some embodiments, as Figure 7 shown, the battery includes two transfer tabs 12, one of the transfer tabs 12 being a positive transfer tab and the other being a negative transfer tab. The positive transfer tab and the negative transfer tab extend out of the housing 5 from the same side of the housing 5 in the first direction a.

[0106] Specifically, as Figure 6 and Figure 7 shown, the housing 5 encloses a cavity 50, and the battery cell 4 is located in the cavity 50. Wherein, the housing 5 includes a first side portion 51 and a second side portion 52. The first side portion 51 includes a first main body portion 511 and a first connecting portion 512, and the second side portion 52 includes a second main body portion 521 and a second connecting portion 522. The first main body portion 511 and the second main body portion 521 are respectively located on opposite sides of the battery cell 4. The direction from the first main body portion 511 to the second main body portion 521 is parallel to the third direction c. The first connecting portion 512 and the second connecting portion 522 are connected, and specifically can be bonded by means such as hot pressing, thereby forming the sealing edges (top sealing edge 501 and side sealing edge 502) of the battery. Wherein, at the position where the transfer tab extends out, the first connecting portion 512 and the second connecting portion 522 are respectively located on opposite sides of the transfer tab. That is, for any transfer tab, one side of the transfer tab is bonded to the first connecting portion 512 through a tab adhesive 6, and the other side of the transfer tab is bonded to the second connecting portion 522 through another tab adhesive.

[0107] Specifically, the transfer tab 12 extends out of the housing 5 from one side of the housing 5 in the first direction a. The side of the housing 5 where the transfer tab 12 extends out is the top sealing edge 501 of the housing 5, that is, the transfer tab 12 extends out of the housing 5 from the top sealing edge 501 of the housing 5.

[0108] Generally, as Figure 6 and Figure 7 shown, the housing 5 includes side sealing edges 502, and the side sealing edges 502 are provided on opposite sides of the housing 5 in the second direction b.

[0109] In some embodiments, the tab adhesive 6 includes a polypropylene (PP) resin and a high-temperature resistant material, and the high-temperature resistant material includes one or more of polyethylene naphthalate, phenolic resin, urea-formaldehyde resin, heat-resistant epoxy, and polyimide.

[0110] Specifically, as a connecting component between the tab glue 6 and the housing 5 (such as an aluminum-plastic film) of the transfer tab 12, the tab glue 6 can improve the adhesion between the transfer tab 12 and the housing 5, enhance the battery sealing performance, and avoid problems such as liquid leakage. By using a high-bonding and high-temperature-resistant tab glue 6 and physically mixing pp resin with a high-temperature-resistant material to obtain the high-temperature-resistant tab glue 6, the melting point of the tab glue 6 is relatively high, which is more conducive to preventing the tab glue 6 from overheating and melting, and is beneficial to improving the safety performance of the battery. Among them, the higher the proportion of the high-temperature-resistant material in the tab glue 6, the stronger its high-temperature resistance. In some embodiments, the mass percentage content of the high-temperature-resistant material in the tab glue 6 is 5%-20%, which is beneficial to taking into account the improvement of the heat resistance of the tab glue 6 and the adhesion between the transfer tab 12 and the housing 5.

[0111] In some embodiments, the ratio of the mass percentage content of the high-temperature-resistant material in the tab glue 6 to the thickness of the tab glue 6 can be (0.05-0.2):1.5 (i.e., (5%-20%):1.5), such as 0.05:1.5, 0.08:1.5, 0.1:1.5, 0.13:1.5, 0.15:1.5, 0.18:1.5, 0.2:1.5 or the range composed of any two of them. The unit of the thickness of the tab glue 6 is in mm. The melting point and thickness of the tab glue 6 are relatively high, which can prevent the tab glue 6 from overheating and melting, and avoid problems such as short circuit and fire of the positive and negative electrodes of the battery. At the same time, due to the requirements for the encapsulation sealing performance of the housing 5 such as the aluminum-plastic film, the thickness of the tab glue 6 cannot be too thick. By coordinately regulating the content of the high-temperature-resistant material in the tab glue 6 and the thickness of the tab glue 6 to make it meet the above range, it can effectively prevent short circuit between the transfer tab 12 (metal strip) and the housing 5 (such as an aluminum-plastic film) during battery encapsulation, and during encapsulation, the tab glue 6 and the housing 5 are heat-sealed and bonded together to prevent liquid leakage, which can effectively improve the structural stability of the battery, improve the yield of formation (gas generation), and is beneficial to improving the long-term life of the battery.

[0112] In some embodiments, the ratio of the width of the transfer tab 12 to the width of the tab glue 6 is 1:(1.2-1.5), which is beneficial to further improving the safety performance of the battery while improving the power performance and high-temperature storage performance of the battery.

[0113] In some embodiments, the ratio of the width of the transfer tab 12 to the width of the battery cell 4 is 1:(8-20), which is beneficial to further improving the safety performance of the battery while improving the power performance and high-temperature storage performance of the battery.

[0114] Specifically, when the battery is discharged at a high rate, improving the conductivity of the tab can effectively improve the rate discharge performance of the battery at the initial stage of discharge. Generally speaking, the magnitude of the energized current is directly proportional to the cross-section of the wire (tab), that is, the larger the cross-sectional area of the wire, the larger the current that can pass through. For the tab glue 6, it is necessary to ensure the welding with the housing 5 and also ensure full coverage of the tab. By using the edge-sealing area of the tab glue 6 with the width ratio of the hard tab: tab glue 6: the width of the battery cell 4 being 1:(1.2 - 1.5):(8 - 20), the high-rate discharge capacity of the battery cell 4 can be effectively improved, thereby enhancing its power performance.

[0115] In the embodiment of the present invention, the width direction of the transfer tab 12, the width direction of the tab glue 6, and the width direction of the battery cell 4 are parallel to the second direction b. The second direction b intersects with the first direction a, and the two are perpendicular, for example. Specifically, the first direction a can be the length direction of the battery or the battery cell, and the second direction b is the width direction of the battery or the battery cell.

[0116] In addition, the third direction c intersects with the first direction a, and the two are specifically perpendicular to each other; the third direction c intersects with the second direction b, and the two are specifically perpendicular to each other. Specifically, the third direction c can be the thickness direction of the battery or the battery cell.

[0117] In addition, each peak on the dQ / dV curve of the battery represents an electrochemical reaction. The peak shift and the change in the capacity between peaks are used to estimate the contributions of different fatigue mechanisms, such as lithium inventory loss, active cathode loss, and anode loss. The peak point represents the phase change point of the material, and the area enclosed by the curve and the abscissa represents the capacity charged or discharged during the phase change process.

[0118] In the embodiment of the present invention, the positive electrode sheet 1 uses a blend of single crystal and polycrystal and introduces carbon nanotubes as a conductive agent, which can enhance the continuous discharge capacity of the positive electrode material, reduce the ohmic and polarization internal resistance of the battery, and effectively make up for the inherent defect of the low lithium chemical diffusion coefficient of the ternary single crystal material. In the dQ / dV curve, it is manifested as the shift of the peak position, which reflects the improvement of the discharge capacity at low SOC (State of Charge; representing the ratio of the remaining battery power to its rated capacity).

[0119] In the embodiments of the present invention, the dQ / dV curve of the battery has a first characteristic peak, a second characteristic peak, and a third characteristic peak. The position of the first characteristic peak is (46%-52%) SOC, the position of the second characteristic peak is (57%-70%) SOC, and the position of the third characteristic peak is (70%-86%) SOC. Among them, the ratio of the peak area P1 of the first characteristic peak to the peak area P2 of the second characteristic peak is 1:(2.0-3.0), and the ratio of the peak area P1 of the first characteristic peak to the peak area P3 of the third characteristic peak is 1:(2.5-3.2). That is to say, the ratio of the peak area P1 of the first characteristic peak, the peak area P2 of the second characteristic peak, and the peak area P3 of the third characteristic peak is 1:(2.0-3.0):(2.5-3.2).

[0120] In the embodiments of the present invention, the dQ / dV curve of the battery can be measured by conventional methods in the art, and then the peak positions, peak areas and other characteristics of its first characteristic peak, second characteristic peak and third characteristic peak can be obtained. Specifically, the dQ / dV curve is a relationship curve of dQ / dV and voltage V obtained by differentiating the ratio (dQ / dV) of the capacity (Q) and voltage (V) during the charging process of the battery (i.e., the dQ / dV-V curve). That is to say, the dQ / dV curve is the first-order differential curve of the battery charge-discharge curve (Q-V curve), and the Q-V curve is the charge-discharge curve with the capacity (Q) as the ordinate and the voltage (Voltage, unit V) as the abscissa. Specifically, during implementation, the battery can be subjected to charge-discharge tests at room temperature (25°C ± 2°C) to obtain the battery charge-discharge curve (i.e., the Q-V curve), and then the first-order differential is performed using origin software to obtain the dQ / dV curve of the battery. Integrations are respectively performed on the first characteristic peak, the second characteristic peak, and the third characteristic peak to measure the peak areas (integrated areas) of the respective characteristic peaks and their proportional relationships and other characteristics.

[0121] The battery of the embodiments of the present invention can be prepared by conventional methods in the art. For example, the positive electrode sheet 1 and the negative electrode sheet 2 are cut according to a preset shape and size. Then, after the positive electrode sheet 1, the separator 3, and the negative electrode sheet 2 are stacked in sequence, they are wound into a wound-type battery cell 4 or laminated into a laminated battery cell 4. Then, the battery cell 4 is hot-pressed to bond the separator 3 and the positive and negative electrode sheets 2, and then the battery cell 4 is encapsulated with a housing 5. Subsequently, after processes such as baking, liquid injection (i.e., injecting electrolyte into the housing 5), formation, secondary sealing, sorting, and OCV (open-circuit voltage test), the battery is manufactured. These steps / processes are all conventional operations in the art and are not particularly limited herein.

[0122] The battery of the embodiments of the present invention has good performance such as high cycle characteristics, low resistance, and high output power, greatly improving the safety performance, which is of great significance for improving the driving performance of electric vehicles. The present invention is further introduced below through specific embodiments.

[0123] Example 1

[0124] 1. Preparation of single-crystal cathode material (single-crystal ternary material NCM622)

[0125] Spherical Ni 0.6 Co 0.2 Mn 0.2 (OH)2 precursor is prepared by co-precipitation method: Mix NiSO4 . 6H2O, 6H2O, CoSO4 . 7H2O and MnSO4 . 5H2O according to the stoichiometric ratio of NCM622 to obtain an aqueous solution of transition metal sulfate; then pump it into a continuously stirred reaction kettle. At the same time, NaOH solution (4 mol / L) is used as a precipitant, and NH3 . H2O (4 mol / L) solution as a chelating agent are respectively added into the reaction kettle. The temperature is maintained at 50 ± 1 °C, and the stirring speed is maintained at 500 rpm. Under this condition, a precipitation reaction is carried out. When the pH value of the reaction system is 11 (the precipitation reaction time is about 30 min), the precipitation reaction ends, and Ni 0.6 Co 0.2 Mn 0.2 (OH)2 precursor is obtained;

[0126] Mix Ni 0.6 Co 0.2 Mn 0.2 (OH)2 precursor, LiOH . H2O and Li2CO3 in a crucible in a molar ratio of 1:1.5:0.25 to obtain a mixture; then carry out the first calcination of the mixture in a muffle furnace to obtain a cathode material intermediate; among them, during the first calcination, the furnace lid is always open to make the mixture react fully with oxygen in the air during the sintering process; during the first calcination, the heating rate is initially set at 5 °C / min, heated to 480 °C (the first temperature), keep the mixture at 480 °C for 4 hours (dehydration and petrification), then heated to 900 °C (the second temperature), heated at 900 °C for 2 hours (short-time high-temperature sintering stage), and then cooled to 800 °C at a rate of 3 °C / min, and kept at 800 °C for 8 hours (low-temperature heat preservation stage) to obtain the cathode material intermediate;

[0127] Rinse the cathode material intermediate with deionized water to remove the surface flux salts and residual lithium, and then place it in an oven at 80 °C and dry it for 12 hours; finally, put the dried material (i.e., the dried cathode material intermediate) into the muffle furnace again and heat-treat it at 750 °C for 6 hours (the second calcination), take out the heat-treated powder (i.e., the product of the second calcination) from the crucible, and grind it in a mortar to make it dispersed to obtain the single-crystal cathode material NCM622.

[0128] (1) Preparation of the positive electrode sheet

[0129] The single-crystal cathode material NCM622 and the polycrystalline material active substance NCM613 are mixed in a ratio of 1:0.25 to obtain the positive electrode active substance; the positive electrode active substance, conductive carbon black, carbon nanotubes, and PVDF are mixed in a mass ratio of 95:2.9:0.6:1.5, and after high-speed stirring, a uniformly dispersed mixture is obtained. NMP (N-methylpyrrolidone) is added thereto as a solvent to prepare a positive electrode slurry, and the solid content in the slurry is 60%; the positive electrode slurry is uniformly coated on both the front and back sides of the aluminum foil, and at the same time, a ceramic adhesive (the first ceramic layer) with an average thickness of 21.4 μm is coated on both sides, and the compaction density x is 3.2 g / cm 3 , to obtain the positive electrode sheet. Among them, the first ceramic layer is cured from alumina, epoxy resin, and phthalic anhydride in a mass ratio of 35:60:5, and the first ceramic layer is located on the side of the positive electrode sheet where the positive electrode tab (aluminum tab) is provided.

[0130] Among them, Figure 2 is a scanning electron microscope (SEM) image of the positive electrode sheet. The figure shows that the sum of the thicknesses of the aluminum foil and the first ceramic layer on both the front and back surfaces of the aluminum foil is about 56.5 μm. The thicknesses of the first ceramic layer on both sides are 21.1 μm and 21.8 μm respectively (the average thickness of the first ceramic layer is about 21.4 μm), the thickness of the aluminum foil is about 12.2 μm - 12.5 μm, and the sum of the thicknesses of the aluminum foil and the positive electrode coating on both the front and back surfaces of the aluminum foil (i.e., the thickness of the area where the positive electrode coating is located on the positive electrode sheet) A is about 68.5 μm. The thicknesses of the positive electrode coatings on both sides are 28.9 μm and 26.3 μm respectively.

[0131] In addition, the width 4 of the first ceramic layer in the direction from the positive electrode coating to the first ceramic layer is 4 mm.

[0132] Figure 1 is the front SEM image of the positive electrode sheet of Example 1. Its positive electrode active substance is composed of microsphere structures with a particle size distribution of 2.6 - 8 μm. After statistics, the particle size Dv10 of the positive electrode active substance is between 1.8 - 2.6 μm, Dv50 is about 4.2 μm, and Dv90 is between 6.9 - 8.0 μm. The particle size is small and concentrated below 8 μm.

[0133] (2) Preparation of the negative electrode sheet

[0134] Mix artificial graphite, SBR, and a conductive agent, and obtain a uniformly dispersed mixture containing negative electrode active material through high-speed stirring. In this mixture, the solid components include 95% artificial graphite, 2% conductive agent, and 3% binder SBR. Use water as a solvent to make a negative electrode paste, and the solid content in the negative electrode paste is 52 wt%. Coat the negative electrode paste evenly on both the front and back sides of the copper foil, and after drying and compressing with a roller press, obtain a negative electrode sheet.

[0135] (3) Preparation of pole ear glue (first pole ear glue, second pole ear glue)

[0136] Prepare a modified pp layer material: Mix pp resin and the high-temperature resistant material polyethylene naphthalate in a mass ratio of 9:1, and then add masterbatch to obtain the modified pp layer material; Prepare a semi-finished pole ear glue through co-extrusion casting.

[0137] (4) Assembly of the battery

[0138] After punching the positive electrode sheet and the negative electrode sheet, stack the positive electrode sheet, separator, and negative electrode sheet in sequence (the formed stacked structure is as Figure 5 shown), and form a bare battery core (wound battery core) through a winding process, and respectively turn out an aluminum pole ear (positive electrode pole ear) and a nickel-plated copper pole ear (negative electrode pole ear). Clamp the bare battery core with a glass clamp, and the force of the glass clamp is 100 MPa / m 2 , and bake it in a high-temperature vacuum at 85 °C for 24 hours, and then encapsulate it with an aluminum-plastic film; After encapsulation, carry out formation and aging on the battery to obtain a soft-packaged battery with a length × width × thickness of 110 mm × 110 mm × 245 mm (the battery structure is as Figure 6 and Figure 7 shown, and will not be elaborated).

[0139] Among them, there is a first pole ear glue between the positive electrode transfer pole ear that turns out the aluminum pole ear and the aluminum-plastic film (shell), and the thickness of the first pole ear glue is 1.5 mm. There is a second pole ear glue between the negative electrode transfer pole ear that turns out the nickel-plated copper pole ear and the aluminum-plastic film (shell), and the thickness of the second pole ear glue is 1.5 mm; The width of the positive electrode transfer pole ear is 9 mm, and the width of the negative electrode transfer pole ear is 9 mm.

[0140] Among them, the first pole ear glue and the second pole ear glue have the same composition, and they are both composed of PP resin and polyethylene naphthalate (high-temperature resistant material). During the encapsulation process of the battery core, the semi-finished pole ear glue is placed between the transfer pole ear and the shell, so that the transfer pole ear and the shell are bonded by the pole ear glue formed from the semi-finished pole ear glue after hot pressing.

[0141] The width of the transfer pole ear is 9 mm, the width of the pole ear glue is 12 mm, and the width ratio of the transfer pole ear to the pole ear glue is 1:1.33.

[0142] Among them, the separator includes a base film, a second ceramic layer provided on one surface of the base film facing the positive electrode sheet, a first adhesive layer provided on one surface of the second ceramic layer facing the positive electrode sheet, and a second adhesive layer provided on one surface of the base film facing the negative electrode sheet. The material of the second ceramic layer is boehmite, the thickness of the second ceramic layer is 2 μm, the materials of the first adhesive layer and the second adhesive layer are PVDF respectively, the thickness of the first adhesive layer is 2 μm, and the thickness of the second adhesive layer is 2 μm; the content of Fe element in the positive electrode active material is 30 ppb, and the ratio (mass ratio) of the Fe element in the second ceramic layer to the Fe element in the positive electrode active material is 1:1.8.

[0143] The difference between Example 2 and Example 1 is: (1) Preparation of the positive electrode sheet: The first conductive agent is conductive carbon black, with a proportion of 3.2%, and the second conductive agent is carbon nanotubes, with a proportion of 0.4%;

[0144] The difference between Example 3 and Example 1 is: (1) Preparation of the positive electrode sheet: The compaction density is 2.7 g / cm 3 ;

[0145] The difference between Example 4 and Example 1 is: (1) Preparation of the positive electrode sheet: Single crystal: Polycrystal (ratio) = 1:0.05;

[0146] The difference between Example 5 and Example 1 is: (1) Preparation of the positive electrode sheet: Single crystal: Polycrystal (ratio) = 1:0.5;

[0147] The difference between Example 6 and Example 1 is: (1) Preparation of the positive electrode sheet: Single crystal: Polycrystal (ratio) = 1:0.75;

[0148] The difference between Example 7 and Example 1 is: The ratio of the particle size Dv50 of the positive electrode active material to the particle size Dv50 of the negative electrode active material is 1:1.3;

[0149] The difference between Example 8 and Example 1 is: The ratio of the particle size Dv50 of the positive electrode active material to the particle size Dv50 of the negative electrode active material is 1:1.6, and the other conditions are the same;

[0150] The difference between Example 9 and Example 1 is: The ratio of the particle size Dv50 of the positive electrode active material to the particle size Dv50 of the negative electrode active material is 1:2.8, and the other conditions are the same;

[0151] The difference between Example 10 and Example 1 is: The ratio of the particle size Dv50 of the positive electrode active material to the particle size Dv50 of the negative electrode active material is 1:3;

[0152] The difference between Example 11 and Example 1 is: (1) Preparation of the positive electrode sheet: The coating thickness of the ceramic adhesive is 17.1 μm, and x*y / A is 0.8;

[0153] The difference between Example 12 and Example 1 is that: (1) Preparation of the positive electrode sheet: the coating thickness of the ceramic glue is 25.6 μm, and x*y / A is 1.2;

[0154] The difference between Example 13 and Example 1 is that: (2) Preparation of the positive electrode sheet: the conductive agent is all conductive carbon black, accounting for 3.6%;

[0155] The difference between Example 14 and Example 1 is that: (3) Preparation of the tab glue: the content of the high temperature resistant material in the tab glue is 3%;

[0156] The difference between Example 15 and Example 1 is that: (3) Preparation of the tab glue: the content of the high temperature resistant material in the tab glue is 5%;

[0157] The difference between Example 16 and Example 1 is that: (3) Preparation of the tab glue: the content of the high temperature resistant material in the tab glue is 20%;

[0158] The difference between Example 17 and Example 1 is that: (3) Preparation of the tab glue: the content of the high temperature resistant material in the tab glue is 23%;

[0159] The difference between Example 18 and Example 1 is that: (4) the width of the tab glue is 9 mm, and the ratio of the width of the transfer tab to the width of the tab glue is 1:1;

[0160] The difference between Example 19 and Example 1 is that: (4) the width of the tab glue is 10.8 mm, and the ratio of the width of the transfer tab to the width of the tab glue is 1:1.2;

[0161] The difference between Example 20 and Example 1 is that: (4) the width of the tab glue is 13.5 mm, and the ratio of the width of the transfer tab to the width of the tab glue is 1:1.5;

[0162] The difference between Example 21 and Example 1 is that: (4) the width of the tab glue is 16.2 mm, and the ratio of the width of the transfer tab to the width of the tab glue is 1:1.8;

[0163] The difference between Example 22 and Example 1 is that: (5) the width of the battery cell is 45 mm, and the ratio of the width of the transfer tab to the width of the battery cell is 1:5;

[0164] The difference between Example 23 and Example 1 is that: (5) the width of the battery cell is 72 mm, and the ratio of the width of the transfer tab to the width of the battery cell is 1:8;

[0165] The difference between Example 24 and Example 1 is that: (5) the width of the battery cell is 180 mm, and the ratio of the width of the transfer tab to the width of the battery cell is 1:20;

[0166] Example 25 is different from Example 1 in that: (5) the width of the battery cell is 225 mm, and the ratio of the width of the transfer tab to the width of the battery cell is 1:25;

[0167] Comparative Example 1 is different from Example 1 in that: (1) Preparation of the positive electrode sheet: all the positive electrode active materials are single crystals and do not contain polycrystals;

[0168] Comparative Example 2 is different from Example 1 in that: (1) Preparation of the positive electrode sheet: all the positive electrode active materials are polycrystals and do not contain single crystals;

[0169] Comparative Example 3 is different from Example 1 in that: (1) Preparation of the positive electrode sheet: the coating thickness of the ceramic adhesive is 10.7 μm, so x*y / A is 0.5;

[0170] Comparative Example 4 is different from Example 1 in that: (1) Preparation of the positive electrode sheet: the coating thickness of the ceramic adhesive is 32.1 μm, and x*y / A is 1.5;

[0171] Comparative Example 5 is different from Example 1 in that: (2) During the preparation of the positive electrode sheet, no ceramic adhesive is coated (i.e., no first ceramic layer is provided on the positive electrode sheet).

[0172] Among the examples and comparative examples, except for the above differences and the differences shown in Tables 1 to 3, the other conditions are basically the same. In each example and comparative example, the ratio of single crystal material to polycrystal material (single crystal: polycrystal), the mass percentage of carbon nanotubes in the positive electrode coating (carbon nanotube doping percentage) e, the average particle size of the single crystal positive electrode material, the particle size Dv50 of the positive electrode active material, the ratio of the particle size Dv50 of the positive electrode active material to the particle size Dv50 of the negative electrode active material (positive electrode particle size Dv50: negative electrode particle size Dv50), the thickness A of the region where the positive electrode active layer is located on the positive electrode sheet (positive electrode thickness A), the tap density x of the positive electrode active layer, the thickness y of the first ceramic edge, x*y / A, the mass ratio of the high-temperature resistant material in the tab adhesive (i.e., the mass ratio of the high-temperature resistant material in the first tab adhesive and the second tab adhesive respectively), the width of the tab adhesive, the width of the battery cell, the ratio of the width of the transfer tab to the width of the tab adhesive (i.e., the ratio of the width of the positive electrode transfer tab to the width of the first tab adhesive, the ratio of the width of the negative electrode transfer tab to the width of the second tab adhesive), the ratio of the width of the transfer tab to the width of the battery cell (i.e., the ratio of the width of the positive electrode transfer tab to the width of the battery cell, the ratio of the width of the negative electrode transfer tab to the width of the battery cell), and the peak area P1 of the first characteristic peak, the peak area P2 of the second characteristic peak, and the peak area P3 of the third characteristic peak in the dQ / dV curve of the battery are shown in Tables 1, 2, and 3 respectively.

[0173] The performance of the batteries prepared in each example was tested through the following processes respectively, and the results are shown in Table 3.

[0174] (1) Test of cold start of battery cells: Test the terminal voltage of the battery when discharging at a constant current of 10C0 for 0.5 s at -30°C and 50% SOC.

[0175] (2) The calendar life of the battery cells at 60°C is the capacity retention rate after storing the battery at 60°C for 60 days (i.e., the ratio of the capacity of the battery after storing at 60°C for 60 days to the capacity of the battery before storing under this condition). Among them, the capacities of the battery before and after storage are measured respectively according to the following process: In an environment of 25 ± 2°C, discharge the battery at a standard constant current of 1C to 2.8V, and leave it standing for 30 min; then charge it at a standard constant current and constant voltage of 1C to the charge limit voltage of 4.3V, with a cut-off current of 0.05C, and leave it standing for 30 min; then discharge it at a standard constant current to the discharge termination voltage of 4.3V to obtain the battery capacity.

[0176] (3) Test of the puncture passing rate:

[0177] In an environment of 25 ± 2°C, discharge the battery at a standard constant current of 1C to 2.8V, and leave it standing for 30 min; then charge it at a standard constant current and constant voltage of 1C to the charge limit voltage of 4.3V, with a cut-off current of 0.05C, and leave it standing for 30 min; then discharge it at a standard constant current to the discharge termination voltage of 4.3V to obtain the battery capacity C0; after fully charging the battery at 1C, then discharge it at 1C to 80% SOC (discharge until 20% of the C0 capacity is cut off), and use a high-temperature resistant steel needle with a diameter of ф3.00 mm (the conical angle of the needle tip is 45°C - 60°C, and the surface of the needle is smooth without rust, oxide layer and oil stain) to penetrate from a direction perpendicular to the battery plate at a speed of 80 mm ± 5 mm / s. The puncture position should be close to the geometric center of the punctured surface (the steel needle stays in the battery), observe for 1 h. If the battery cell does not catch fire or explode, it passes the puncture test; if the battery cell catches fire or explodes, it fails the test; test 100 battery cells through this process and calculate the puncture passing rate.

[0178] (4) dQ / dV curve:

[0179] Charge and discharge the battery at 1C / 1C to obtain the charge-discharge curve (i.e., the Q-V curve). The dQ / dV-V curve (i.e., the dQ / dV curve) is the first-order differential curve of the Q-V curve. The Q-V curve is the charge-discharge curve plotted with the capacity (Q) as the ordinate and the voltage (Voltage, unit V) as the abscissa. First, plot the Q-V curve, and then use the origin software to perform the first-order differential to obtain the dQ / dV curve of the battery. Among them, the process of charging and discharging the battery at 1C / 1C is: In an environment of 25 ± 2°C, discharge the battery at a standard constant current of 1C to 2.8V, and leave it standing for 30 min; then charge it at a standard constant current and constant voltage of 1C to the charge limit voltage of 4.3V, with a cut-off current of 0.05C, and leave it standing for 30 min; then discharge it at a standard constant current to the discharge termination voltage of 4.3V. Among them, Figure 3Shows the dQ / dV curves of the batteries of Example 1 and Example 13.

[0180] Table 1

[0181]

[0182] Table 2

[0183]

[0184] Table 3

[0185]

[0186]

[0187] As can be seen from Table 1, in Comparative Example 1, all single-crystal cathode materials are used as the cathode active material, and the battery has a low cold-start voltage and poor low-temperature power performance; in Comparative Example 2, all polycrystalline cathode materials are used as the cathode active material. Although the power performance of the battery is improved, the high-temperature storage performance and safety performance are poor, especially the safety performance deteriorates seriously.

[0188] In addition, in Comparative Example 5, the first ceramic layer is not provided on the cathode sheet, and the battery has a low needle-penetration passing rate (only 40%), and poor safety; although the first ceramic layer is provided on the cathode sheet in Comparative Example 3 and Comparative Example 4, but in Comparative Example 3, x*y / A < 0.8, and in Comparative Example 4, x*y / A > 1.2, neither of them can effectively balance the improvement of the power performance, high-temperature storage performance and safety performance of the battery (for example, the needle-penetration passing rate of Comparative Example 3 is only 50%, the 60°C calendar life of Comparative Example 4 is only 90.12%, and the cold-start voltage is also low. It is difficult for Comparative Example 3 and Comparative Example 4 to balance the improvement of the power performance, high-temperature storage performance and safety performance of the battery).

[0189] Compared with Comparative Examples 1 to 5, in Examples 1 to 28, by simultaneously blending single-crystal cathode material and polycrystalline cathode material in the cathode active layer, and setting the first ceramic layer (ceramic edge) between the outer edge of the cathode sheet and the cathode active layer, and simultaneously and coordinately regulating the compaction density x of the cathode active layer, the thickness y of the first ceramic layer, and the thickness A of the cathode sheet in the area where the cathode active layer is provided on the cathode sheet, so that 0.8 ≤ x*y / A ≤ 1.2, it is possible to balance the improvement of the safety performance (needle-penetration passing rate), high-temperature storage performance (60°C calendar life) and power performance (cold-start voltage) of the battery.

[0190] Further, it can be seen from Example 1, Examples 4 to 6 that, compared with Example 6, Examples 1, 4 and 5 can further improve the safety performance of the battery (the acupuncture passing rate is not less than 80%) on the basis of maintaining a relatively high cold start voltage and a calendar life at 60 °C by further controlling the ratio of the single crystal cathode material to the polycrystalline cathode material within the range of 1:(0.05 - 0.5).

[0191] Further, it can be seen from Example 1, Example 2 and Example 13 that carbon black is used as the conductive agent in Example 13, and carbon nanotubes are not introduced. Compared with Example 13, Examples 1 and 2 can more significantly improve the low-temperature power performance of the battery, while improving the high-temperature storage performance of the battery and taking into account maintaining good safety performance of the battery by further introducing carbon nanotubes into the positive electrode active layer on the basis of simultaneously using the single crystal cathode material and the polycrystalline cathode material and satisfying 0.8 ≤ x*y / A ≤ 1.2.

[0192] In addition, Examples 1, 2 and 3 further illustrate that, compared with Example 13, when the ratio of the peak area P1 of the first characteristic peak to the peak area P2 of the second characteristic peak of the batteries of Examples 1 and 2 is within the range of 1:(2.0 - 3.0), and the ratio of the peak area P1 of the first characteristic peak to the peak area P3 of the third characteristic peak is within the range of 1:(2.5 - 3.2), the low-temperature power performance of the battery can be more significantly improved, while the high-temperature storage performance of the battery is improved and good safety performance of the battery is taken into account.

[0193] Further, it can be seen from Example 1, Examples 4 to 10 that, compared with Example 6, Examples 7 and 10, Examples 1, 4, 5, 8 and 9 can further take into account improving the power performance, high-temperature storage performance and safety performance of the battery by further controlling the ratio of the particle size Dv50 of the positive electrode active material to the particle size Dv50 of the negative electrode active material within the range of 1:(1.6 - 2.8).

[0194] Further, it can be seen from Example 1, Examples 14 to 17 that, compared with Examples 14 and 17, in Examples 1, 15 to 17, by further controlling the mass ratio of the high-temperature resistant material in the tab glue within the range of 5% to 23%, it is possible to further improve the high-temperature storage performance and safety performance of the battery on the basis of maintaining good power performance of the battery. Among them, compared with Example 17, Example 16 can improve the power performance, high-temperature storage performance and safety performance of the battery (the power performance and safety performance are equivalent to those of Example 17, and the high-temperature storage performance is slightly higher than that of Example 17) by using a relatively small amount of high-temperature resistant material (the mass ratio of the high-temperature resistant material in the tab glue is within the range of 5% to 20%). Therefore, it is more preferable that the mass ratio of the high-temperature resistant material in the tab glue is 5% to 20%.

[0195] Further, it can be seen from Example 1, Examples 18 to 21 that in Examples 1, 19 and 20, by further controlling the ratio of the width of the transfer tab to the width of the tab glue within the range of 1:(1.2 - 1.5), it is beneficial to further balance and improve the power performance, high-temperature storage performance and safety performance of the battery.

[0196] Further, it can be seen from Example 1, Examples 22 to 25 that in Examples 1, 23 and 24, by further controlling the ratio of the width of the transfer tab to the width of the battery cell within the range of 1:(8 - 20), it is beneficial to further balance and improve the power performance, high-temperature storage performance and safety performance of the battery.

[0197] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode sheet, characterized in that: The invention comprises a positive electrode current collector and a positive electrode coating located on at least one side of the positive electrode current collector, wherein the positive electrode coating comprises a positive electrode active layer and a first ceramic layer located between the outer edge of the positive electrode sheet and the positive electrode active layer, wherein the positive electrode active layer comprises a positive electrode active material and a conductive agent; the positive electrode active material comprises a single crystal positive electrode ternary material and a polycrystalline positive electrode ternary material; The positive electrode sheet satisfies 0.8≤x*y / A≤1.2, wherein A is the thickness of the area where the positive electrode active layer is located on the positive electrode sheet, in μm; x is the compaction density of the positive electrode active layer, in g / cm 3 y is the thickness of the first ceramic layer, in μm.

2. The positive electrode sheet according to claim 1, characterized in that: The ratio of the single crystal positive electrode ternary material to the polycrystalline positive electrode ternary material is 1:(0.05-0.5); And / or, the particle size Dv50 of the positive electrode active material is 3.5 μm to 7.5 μm; And / or, the average particle size of the single crystal positive electrode ternary material is 3.75 μm to 4.65 μm.

3. The positive electrode sheet according to claim 1, characterized in that: The positive electrode active layer includes a conductive agent, and the conductive agent includes carbon nanotubes; Preferably, the mass percentage e of the carbon nanotubes in the positive electrode active layer is 0<e≤0.8%; Preferably, the conductive agent further includes one or more of conductive carbon black, acetylene black, and conductive graphite.

4. The positive electrode sheet according to claim 1, characterized in that: The positive electrode sheet is provided with a positive electrode tab connected to the positive electrode collector, and the first ceramic layer is located on a side of the positive electrode sheet where the positive electrode tab is provided.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: 2.7g / cm 3 ≤x≤3.6g / cm 3 ; And / or, 10μm≤y≤33μm.

6. A battery, characterized in that: The positive electrode sheet comprises the positive electrode sheet as described in any one of claims 1 to 5.

7. The battery according to claim 6, characterized in that Also included is a negative electrode sheet, the negative electrode sheet includes a negative electrode coating, the negative electrode coating includes a negative electrode active material, and the ratio of the particle size Dv50 of the positive electrode active material to the particle size Dv50 of the negative electrode active material is 1:(1.6-2.8); Preferably, the particle size Dv50 of the negative electrode active material is 5 μm to 10 μm.

8. The battery according to claim 6, characterized in that It also includes a diaphragm, which includes a base film and a second ceramic layer located on the side of the base film facing the positive electrode sheet, and the ratio of Fe element in the second ceramic layer to Fe element in the positive electrode active material is 1: (1.2-2.5).

9. The battery according to claim 6, characterized in that It also includes a shell, a battery cell located in the shell, and a transfer tab connected to the battery cell and extending out of the shell, wherein tab glue is provided between the transfer tab and the shell; Preferably, the ratio of the width of the transfer tab to the width of the tab glue is 1:(1.2-1.5); Preferably, the ratio of the width of the transfer tab to the width of the battery cell is 1:(8-20); Preferably, the ear glue comprises polypropylene resin and high temperature resistant material, and the high temperature resistant material comprises one or more of polyethylene naphthalate, phenolic resin, urea-formaldehyde resin, epoxy resin, and polyimide; Preferably, the mass percentage of the high temperature resistant material in the ear glue is 5%-20%; Preferably, the ratio of the mass percentage of the high temperature resistant material in the tab glue to the thickness of the tab glue is (0.05-0.2):1.5, and the thickness of the tab glue is measured in mm.

10. The battery according to any one of claims 6 to 9, characterized in that: The dQ / dV curve of the battery has a first characteristic peak, a second characteristic peak and a third characteristic peak, the first characteristic peak is located at (46%-52%) SOC, the second characteristic peak is located at (57%-70%) SOC, and the third characteristic peak is located at (70%-86%) SOC; The ratio of the peak area P1 of the first characteristic peak to the peak area P2 of the second characteristic peak is 1:(2.0-3.0); The ratio of the peak area P1 of the first characteristic peak to the peak area P3 of the third characteristic peak is 1:(2.5-3.2).

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