A positive electrode plate and a fast charge and discharge type battery

Abstract

The present invention belongs to the technical field of lithium batteries, and particularly relates to a positive electrode plate and a fast charge and fast discharge type battery. The positive electrode plate includes a current collector and a first active material layer provided on the current collector; the first active material layer includes a first conductive agent, a first positive electrode active material, and a second positive electrode active material, and the positive electrode plate satisfies the formula: 59 < (a*d - b*d)2 - 2abc < 740; The positive electrode plate provided by the embodiment of the present invention not only ensures sufficient contact between particles without blocking the ion movement channels by limiting the tap density of the first positive electrode active material, the tap density of the second active material, and the oil absorption value of the conductive agent, but also can greatly increase the structural stability of the positive and negative electrodes during the cycling process by setting the conductive agent within the range of the oil absorption value, thereby improving the cycle life of the battery, enhancing the fast charge and fast discharge performance of the battery, and meeting the fast charge and fast discharge requirements of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and particularly relates to a positive electrode plate and a fast charge and discharge type battery. Background Art

[0002] Lithium-ion secondary batteries are widely used in most mobile terminal devices and new energy vehicles. Compared with nickel-metal hydride, nickel-cadmium, and lead-acid batteries, they have the advantages of high working voltage, high specific energy, and long cycle life. In recent years, with the rapid development of power tools, drones, and new energy vehicles, especially with the mass application of lithium-ion batteries in HEV hybrid vehicles, higher requirements have been put forward for the charging and discharging power of lithium-ion secondary batteries.

[0003] However, the existing lithium-ion power batteries generally have the following deficiencies or problems: First, the cycle life of the battery is short. Especially after the batteries are grouped, some of them reach the end of their life in less than three years. Second, the allowable charging and discharging current is small, resulting in too long charging time for the battery pack.

[0004] Currently, the improvement of fast charging performance is mainly achieved from the material system, such as the improvement of graphite compaction, kinetics, and the matching of formulations. However, if it is necessary to meet the requirements of fast discharge while satisfying fast charging, simply considering from the perspective of the material system can no longer meet the needs of fast charge and discharge. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: aiming at the problem that the existing power batteries can no longer meet the requirements of fast charge and discharge when considered from the perspective of the material system, to provide a positive electrode plate and a fast charge and discharge type battery.

[0006] To solve the above technical problem, on the one hand, an embodiment of the present invention provides a positive electrode plate, including a current collector and a first active material layer disposed on the current collector;

[0007] The first active material layer includes a first conductive agent, a first positive electrode active material, and a second positive electrode active material, and the positive electrode plate satisfies the formula: 59 < (a*d - b*d) 2 - 2abc < 740;

[0008] Wherein, a is the compaction density of the first positive electrode active material, with the unit of g / cm 3 ; b is the compaction density of the second positive electrode active material, with the unit of g / cm 3 ; c is the particle size of the first positive electrode active material, with the unit of μm; d is the oil absorption value of the first conductive agent, with the unit of cm 3 .

[0009] Optionally, the tap density a of the first positive electrode active material is 4.15 - 4.35 g / cm 3 , the tap density b of the second positive electrode active material is 3.85 - 4.15 g / cm 3 , the particle size c of the first positive electrode active material is 5 - 25 μm, and the oil absorption value d of the first conductive agent is 30 - 100 cm 3 .

[0010] Optionally, the first positive electrode active material is a high-tap-density positive electrode material, the second positive electrode active material is a fast-charging positive electrode material, and the doping ratio of the first positive electrode active material and the second positive electrode active material is (1:9) - (9:1).

[0011] Optionally, the positive electrode sheet further includes a second active material layer, the second active material layer is disposed on the surface of the current collector facing away from the first active material layer, and the ratio of the thicknesses of the first active material layer and the second active material layer is (3:7) - (7:3).

[0012] Optionally, the second active material layer includes a second conductive agent, a third positive electrode active material, and a fourth positive electrode active material, the third positive electrode active material is lithium iron manganese phosphate, the fourth positive electrode active material is a fast-charging positive electrode material, and the doping ratio of the third positive electrode active material and the fourth positive electrode active material is (1:9) - (9:1).

[0013] Optionally, the first positive electrode active material, the second positive electrode active material, and the fourth positive electrode active material independently represent LiNi 1-x-y-z Co x Mn y Al z O2, where: 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1 and 0 ≤ x + y + z ≤ 1.

[0014] Optionally, the first positive electrode active material is high-tap-density lithium cobalt oxide, the second positive electrode active material is fast-charging lithium cobalt oxide, and the fourth positive electrode active material is fast-charging lithium cobalt oxide.

[0015] Optionally, the first conductive agent and the second conductive agent are independently selected from one or more of conductive carbon black, carbon nanotubes, acetylene black, conductive graphite, carbon fiber, and graphene.

[0016] Optionally, the first conductive agent includes conductive carbon black and / or carbon nanotubes, the percentage of the conductive carbon black in the total mass of the first active material layer is 0.1 - 2.5%, and the percentage of the carbon nanotubes in the total mass of the first active material layer is 0.1 - 2%;

[0017] The second conductive agent includes single-walled carbon nanotubes and / or flake graphite. The percentage of the single-walled carbon nanotubes in the total mass of the second active material layer is 0-1%, and the percentage of the flake graphite in the total mass of the second active material layer is 0-5%.

[0018] On the other hand, an embodiment of the present invention provides a fast charge and fast discharge type battery, including the positive electrode plate as described above.

[0019] The positive electrode plate provided by the embodiment of the present invention not only ensures sufficient contact between particles without blocking the ion movement channels by defining the tap density of the first positive active material, the tap density of the second active material, and the oil absorption value of the conductive agent, but also can greatly increase the structural stability of the positive and negative electrodes during the cycling process by setting the conductive agent within the range of the oil absorption value, thereby improving the cycle life of the battery, enhancing the fast charge and fast discharge performance of the battery, and meeting the fast charge and fast discharge requirements of the battery. Description of the Drawings

[0020] Figure 1 It is a schematic diagram of the positive electrode plate provided by an embodiment of the present invention.

[0021] The reference numerals in the specification are as follows:

[0022] 1. Current collector; 2. First active material layer; 3. Second active material layer. Detailed Embodiments

[0023] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] As Figure 1 shown, a positive electrode plate provided by an embodiment of the present invention includes a current collector 1 and a first active material layer 2 provided on the current collector 1. The first active material layer 2 includes a first conductive agent, a first positive active material, and a second positive active material. The positive electrode plate needs to satisfy the formula: 59 < (a*d - b*d) 2 - 2abc < 740. Wherein, a is the tap density of the first positive active material, with the unit of g / cm 3 ; b is the tap density of the second positive active material, with the unit of g / cm 3 ; c is the particle size D50 of the first positive active material, with the unit of μm; d is the oil absorption value of the first conductive agent, with the unit of cm 3 .

[0025] Specifically, the compaction density is closely related to the specific capacity, efficiency, internal resistance, and battery cycle performance of the sheet. The compaction density is related to the particle size and density of the particles. If the compaction density is too large, the distance between particles decreases, the contact becomes closer, the electron conductivity increases, which can improve the volumetric energy density and gravimetric energy density of the electrode. However, the amount of electrolyte absorbed decreases, the ion movement channels decrease or are blocked, which is not conducive to the rapid movement of a large number of ions, thus limiting its high-current discharge and reducing the discharge capacity. If the compaction density is too small, the distance between particles increases, the ion channels increase, and the liquid absorption capacity of the electrolyte increases, which is conducive to the rapid movement of ions. However, due to the too large particle spacing, the contact probability and contact area between particles decrease, which is not conducive to electron conduction, the conductivity decreases, affecting the high-current discharge and increasing the discharge polarization. Therefore, it is necessary to design an appropriate compaction density range to ensure the full infiltration of the electrolyte, sufficient contact between particles without blocking the ion movement channels, and at the same time ensure good electron conductivity and rapid ion movement during high-current discharge, reduce the discharge polarization, and increase the discharge platform voltage.

[0026] The conductive agent is used to increase the conductivity of electrons and lithium ions. By forming a conductive network on the surface of the active material, it can accelerate the electron transfer rate. At the same time, it can absorb and retain the electrolyte, providing more electrolyte interfaces for lithium ions, thereby improving the battery charging efficiency and extending the battery service life. The oil absorption value is the determining factor affecting the ionic conductivity of the conductive agent. When the oil absorption value of the conductive agent is larger, it is easier to form aggregates with a large number of particles and a complex structure, thus enhancing the conductivity.

[0027] The positive electrode sheet provided by the embodiment of the present invention has a first active material layer 2 coated on the positive electrode current collector 1. There are two active materials in the first active material layer 2. By using a formula to limit the compaction density of the first positive electrode active material, the compaction density of the second active material, and the oil absorption value of the conductive agent, it can not only ensure sufficient contact between particles without blocking the ion movement channels, but also greatly increase the structural stability of the positive and negative electrodes during the cycling process by setting the conductive agent within the oil absorption value range, thereby improving the battery cycle life, enhancing the fast charge and fast discharge performance of the battery, and meeting the fast charge and fast discharge requirements of the battery.

[0028] In one embodiment, the compaction density a of the first positive electrode active material is 4.15 - 4.35 g / cm 3 , the compaction density b of the second positive electrode active material is 3.85 - 4.15 g / cm 3 , the particle size c of the first positive electrode active material is 5 - 25 μm, and the oil absorption value d of the first conductive agent is 30 - 100 cm 3Within the above-mentioned range of compaction density, in the first active material layer 2 after rolling, the contact between active material particles is tight, the distance and gap between particles are small, the electron conductivity is strong, which is conducive to electron conduction. When a sufficient amount of electrolyte is injected, the electrolyte will penetrate into the gaps between particles and reach a saturated state, enabling full infiltration of the positive electrode plate. The particle size D50 within the above range can increase the specific surface area of the active material in the positive electrode plate, and it is not prone to agglomeration, which may cause a decrease in electron conductivity and an increase in the internal resistance of the lithium-ion battery. Within the above-mentioned oil absorption value range, the conductive agent has good ionic conductivity, forms a conductive chain structure, accelerates the electron migration rate, and thus improves the charge and discharge performance.

[0029] In one embodiment, the compaction density a of the first positive electrode active material is 4.20 - 4.30 g / cm 3 , the compaction density b of the second positive electrode active material is 3.90 - 4.10 g / cm 3 , the particle size c of the first positive electrode active material is 8 - 20 μm, and the oil absorption value d of the first conductive agent is 40 - 80 cm 3 .

[0030] In one embodiment, the first positive electrode active material is a high-compaction positive electrode material, the second positive electrode active material is a fast-charging positive electrode material, and the doping ratio of the first positive electrode active material and the second positive electrode active material is (1:9) - (9:1). The high-compaction positive electrode material has advantages such as high compaction and high energy density, and the fast-charging positive electrode material enables the battery to have excellent rate performance. By doping the high-compaction positive electrode material and the fast-charging positive electrode material, the compaction density of the positive electrode plate can be increased, and its volumetric energy density and rate performance can be improved.

[0031] In one embodiment, the first positive electrode active material and the second positive electrode active material independently represent LiNi 1-x-y-z Co x Mn y Al z O2, where: 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1 and 0 ≤ x + y + z ≤ 1. The first positive electrode active material and the second positive electrode active material are independently selected from lithium cobalt oxide, lithium manganate, nickel cobalt manganese ternary material or nickel cobalt aluminum ternary material.

[0032] In one embodiment, the first positive electrode active material is high-compaction lithium cobalt oxide, and the second positive electrode active material is fast-charging lithium cobalt oxide.

[0033] In one embodiment, the first conductive agent is selected from one or more of conductive carbon black, carbon nanotubes, acetylene black, conductive graphite, carbon fiber, and graphene.

[0034] In one embodiment, the first conductive agent includes conductive carbon black and / or carbon nanotubes. The percentage of the conductive carbon black in the total mass of the first active material layer 2 is 0.1 - 2.5%, and the percentage of the carbon nanotubes in the total mass of the first active material layer 2 is 0.1 - 2%. Further, the first conductive agent at least includes conductive carbon black, and the oil absorption value d of the conductive carbon black is 30 - 100 cm 3 .

[0035] In one embodiment, the positive electrode plate further includes a second active material layer 3. The second active material layer 3 is disposed on the surface of the current collector 1 facing away from the first active material layer 2. The first active material layer 2 and the second active material layer 3 are respectively coated on the opposite two side surfaces of the current collector 1, and the ratio of the thicknesses of the first active material layer 2 and the second active material layer 3 is (3:7) - (7:3).

[0036] In one embodiment, the second active material layer 3 includes a second conductive agent, a third positive electrode active material, and a fourth positive electrode active material. The third positive electrode active material is lithium iron manganese phosphate, and the fourth positive electrode active material is a fast-charging type positive electrode material. The doping ratio of the third positive electrode active material and the fourth positive electrode active material is (1:9) - (9:1).

[0037] In one embodiment, the fourth positive electrode active material is LiNi 1-x-y-z Co x Mn y Al z O2, where: 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1 and 0 ≤ x + y + z ≤ 1. The fourth positive electrode active material is selected from lithium cobalt oxide, lithium manganese oxide, nickel cobalt manganese ternary material, or nickel cobalt aluminum ternary material.

[0038] In one embodiment, the fourth positive electrode active material is fast-charging type lithium cobalt oxide.

[0039] In one embodiment, the second conductive agent is selected from one or more of conductive carbon black, carbon nanotubes, acetylene black, conductive graphite, carbon fiber, and graphene.

[0040] In one embodiment, the second conductive agent includes single-walled carbon nanotubes and / or flake graphite. The percentage of the single-walled carbon nanotubes in the total mass of the second active material layer 3 is 0 - 1%, and the percentage of the flake graphite in the total mass of the second active material layer 3 is 0 - 5%.

[0041] In one embodiment, the positive electrode sheet further includes a binder. The binder is a component that helps the combination between the positive electrode active material and the conductive agent and also helps the combination between the positive electrode active material and the current collector. The bonding method is not limited and can be selected according to the existing technical requirements in the art. For example, the binder can be polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), styrene-butadiene rubber, or fluororubber.

[0042] The conductive agent, binder, first positive electrode active material, and second positive electrode active material are dispersed in a solvent and stirred evenly to form a positive electrode paste. The solvent is not limited and conventional solvents can be selected.

[0043] On the other hand, the present invention provides a fast charge and discharge type battery, including the positive electrode sheet as described above.

[0044] In one embodiment, the battery further includes a negative electrode sheet, a battery case, and an electrolyte filled in the battery case. The negative electrode sheet can be prepared by coating a negative electrode active material layer on the current collector of the negative electrode. The negative electrode active material layer can be formed by coating a negative electrode paste including a negative electrode active material, a binder, a conductive agent, and a solvent on the negative electrode current collector, and then drying and rolling the coated negative electrode current collector.

[0045] The above battery case, electrolyte, negative electrode active material, conductive agent, and binder are not limited and can be selected according to the existing technical requirements in the art.

[0046] The present invention is further described below through examples.

[0047] Example 1

[0048] 1. Preparation of the positive electrode sheet

[0049] The positive electrode active materials high-compaction lithium cobaltate and fast-charge type lithium cobaltate, conductive carbon black, and polyvinylidene fluoride (PVDF) are mixed according to a mass ratio, and then they are dispersed in the solvent N-methyl-2-pyrrolidone (NMP). After stirring evenly, the paste is coated on the front surface of the current collector 1 to obtain the first active material layer 2.

[0050] Among them, the compaction density of the high-compaction lithium cobaltate is 4.15 g / cm 3 , the particle size D50 is 5 μm, the compaction density of the fast-charge type lithium cobaltate is 4 g / cm 3 , and the oil absorption value of the conductive carbon black is 100 cm 3 .

[0051] Mix the cathode active materials lithium iron manganese phosphate and fast-charging lithium cobalt oxide, single-walled carbon nanotubes, flake graphite, and polyvinylidene fluoride (PVDF) according to the mass ratio, and then disperse them in the solvent N-methyl-2-pyrrolidone (NMP). After stirring evenly, coat the slurry on the back of the current collector 1 to obtain the second active material layer 3. After drying, rolling, and vacuum drying, a cathode electrode sheet is obtained, and the thickness of the cathode electrode sheet is in the range of 120-150 μm.

[0052] 2. Preparation of the anode electrode sheet

[0053] Mix the anode active material artificial graphite, conductive carbon black Super-P, binder, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) according to the mass ratio, and then disperse them in deionized water to obtain an anode slurry. Coat the slurry on both sides of the copper foil, and after drying, rolling, and vacuum drying, an anode electrode sheet is obtained, and the thickness of the anode electrode sheet is 120-150 μm.

[0054] 3. Preparation of the battery cell

[0055] Wind the above-mentioned cathode electrode sheet, anode electrode sheet, and polypropylene separator respectively to obtain a lithium-ion battery cell.

[0056] Example 2

[0057] It is basically the same as the preparation process in Example 1, except that the tap density of the high-tap-density lithium cobalt oxide is 4.15 g / cm 3 , the particle size D50 is 5 μm, the tap density of the fast-charging lithium cobalt oxide is 3.86 g / cm 3 , and the oil absorption value of the conductive carbon black is 80 cm 3 .

[0058] Example 3

[0059] It is basically the same as the preparation process in Example 1, except that the tap density of the high-tap-density lithium cobalt oxide is 4.15 g / cm 3 , the particle size D50 is 10 μm, the tap density of the fast-charging lithium cobalt oxide is 3.86 g / cm 3 , and the oil absorption value of the conductive carbon black is 80 cm 3 .

[0060] Example 4

[0061] It is basically the same as the preparation process in Example 1, except that the tap density of the high-tap-density lithium cobalt oxide is 4.15 g / cm 3 , the particle size D50 is 12 μm, the tap density of the fast-charging lithium cobalt oxide is 3.86 g / cm 3 , and the oil absorption value of the conductive carbon black is 80 cm 3 .

[0062] Example 5

[0063] It is basically the same as the preparation process in Example 1, except that the tap density of the high tap density lithium cobalt oxide is 4.25 g / cm 3 , the particle size D50 is 12 μm, the tap density of the fast charging type lithium cobalt oxide is 3.95 g / cm 3 , and the oil absorption value of the conductive carbon black is 75 cm 3 .

[0064] Example 6

[0065] It is basically the same as the preparation process in Example 1, except that the tap density of the high tap density lithium cobalt oxide is 4.25 g / cm 3 , the particle size D50 is 10 μm, the tap density of the fast charging type lithium cobalt oxide is 4 g / cm 3 , and the oil absorption value of the conductive carbon black is 100 cm 3 .

[0066] Example 7

[0067] It is basically the same as the preparation process in Example 1, except that the tap density of the high tap density lithium cobalt oxide is 4.25 g / cm 3 , the particle size D50 is 8 μm, the tap density of the fast charging type lithium cobalt oxide is 3.9 g / cm 3 , and the oil absorption value of the conductive carbon black is 60 cm 3 .

[0068] Example 8

[0069] It is basically the same as the preparation process in Example 1, except that the tap density of the high tap density lithium cobalt oxide is 4.25 g / cm 3 , the particle size D50 is 15 μm, the tap density of the fast charging type lithium cobalt oxide is 3.95 g / cm 3 , and the oil absorption value of the conductive carbon black is 100 cm 3 .

[0070] Example 9

[0071] It is basically the same as the preparation process in Example 1, except that the tap density of the high tap density lithium cobalt oxide is 4.35 g / cm 3 , the particle size D50 is 20 μm, the tap density of the fast charging type lithium cobalt oxide is 3.95 g / cm 3 , and the oil absorption value of the conductive carbon black is 90 cm 3 .

[0072] Example 10

[0073] Basically the same as the preparation process in Example 1, except that the tap density of the high tap density lithium cobalt oxide is 4.35 g / cm 3 , the D50 particle size is 5 μm, the tap density of the fast charging type lithium cobalt oxide is 3.85 g / cm 3 , and the oil absorption value of the conductive carbon black is 31 cm 3 .

[0074] Example 11

[0075] Basically the same as the preparation process in Example 1, except that the tap density of the high tap density lithium cobalt oxide is 4.35 g / cm 3 , the D50 particle size is 8 μm, the tap density of the fast charging type lithium cobalt oxide is 3.95 g / cm 3 , and the oil absorption value of the conductive carbon black is 60 cm 3 .

[0076] Example 12

[0077] Basically the same as the preparation process in Example 1, except that the tap density of the high tap density lithium cobalt oxide is 4.35 g / cm 3 , the D50 particle size is 5 μm, the tap density of the fast charging type lithium cobalt oxide is 4.15 g / cm 3 , and the oil absorption value of the conductive carbon black is 90 cm 3 .

[0078] Example 13

[0079] Basically the same as the preparation process in Example 1, except that the tap density of the high tap density lithium cobalt oxide is 4.35 g / cm 3 , the D50 particle size is 10 μm, the tap density of the fast charging type lithium cobalt oxide is 3.85 g / cm 3 , and the oil absorption value of the conductive carbon black is 50 cm 3 .

[0080] Comparative Example 1

[0081] Basically the same as the preparation process in Example 4, except that the D50 particle size of the high tap density lithium cobalt oxide is 25 μm.

[0082] Comparative Example 2

[0083] Basically the same as the preparation process in Example 4, except that the tap density of the fast charging type lithium cobalt oxide is 4.15 g / cm 3 .

[0084] Comparative Example 3

[0085] Basically the same as the preparation process in Example 6, except that the tap density of the high tap density lithium cobalt oxide is 4.15 g / cm3 。

[0086] Comparative Example 4

[0087] It is basically the same as the preparation process in Example 10, except that the particle size D50 of the high-compaction lithium cobaltate is 15 μm, and the compaction density of the fast-charging lithium cobaltate is 4 g / cm 3 。

[0088] Comparative Example 5

[0089] It is basically the same as the preparation process in Example 11, except that the compaction density of the high-compaction lithium cobaltate is 4.25 g / cm 3 , and the compaction density of the fast-charging lithium cobaltate is 4.15 g / cm 3 。

[0090] Comparative Example 6

[0091] It is basically the same as the preparation process in Example 12, except that the particle size D50 of the high-compaction lithium cobaltate is 2 μm.

[0092] Comparative Example 7

[0093] It is basically the same as the preparation process in Example 1, except that the compaction density of the high-compaction lithium cobaltate is 4.5 g / cm 3 , and the compaction density of the fast-charging lithium cobaltate is 3.8 g / cm 3 , and the oil absorption value of the conductive carbon black is 40 cm 3 。

[0094] Performance Test

[0095] The following performance tests were carried out on the lithium-ion batteries prepared in the above Examples 1 to 13 and Comparative Examples 1 to 7:

[0096] 1) Test of constant current ratio

[0097] The battery was charged at a constant current of 1C / 2C / 3C to 4.2V with constant voltage, and the ratio of the capacity charged at a constant current to the total charging capacity was calculated.

[0098] The calculation formula of the constant current ratio is as follows:

[0099] Constant current ratio = constant current charge capacity / (constant current charge capacity + constant voltage charge capacity) * 100%.

[0100] 2) Cycle performance test

[0101] At room temperature, the formed battery was charged at a constant current of 1C to 4.2V with constant voltage, the cut-off current was 0.01C, and then discharged at a constant current of 1C to 3.0V. After such charge / discharge cycles were carried out N times, the capacity retention rate after the Nth cycle was calculated to evaluate its cycle performance.

[0102] The calculation formula for the capacity retention rate of the normal temperature 1C cycle for N times is as follows:

[0103] The capacity retention rate (%) of the Nth cycle = (the discharge capacity of the Nth cycle / the discharge capacity of the first cycle) × 100%.

[0104] The obtained test results are filled in Table 1.

[0105] Table 1 Test results of Examples 1-13 and Comparative Examples 1-7

[0106]

[0107]

[0108] From the test results of Examples 1 to 13 and Comparative Examples 1-7 in Table 1, it can be seen that within the value ranges of a, b, c, and d, and when satisfying the relationship of 59 < (a*d - b*d) 2 - 2abc < 740, the battery has good fast charge and fast discharge performance.

[0109] From the comparison of Comparative Examples 1-5, it can be seen that the tap density of the high tap density lithium cobaltate satisfies the range of 4.15 - 4.35 g / cm 3 range, the particle size D50 satisfies the range of 5 - 25 μm, the tap density of the fast charging type lithium cobaltate satisfies the range of 3.85 - 4.15 g / cm 3 range, the oil absorption value of the conductive carbon black satisfies the range of 30 - 100 cm 3 range, but when the calculation result of its relationship formula is not within the range of 59 - 740, its rate performance and cycle performance are significantly reduced, and it cannot meet the fast charge and fast discharge performance of the battery.

[0110] From the comparison of Comparative Example 6 with the examples, it is found that the particle size D50 of the high tap density lithium cobaltate exceeds the range of 5 - 25 μm. Although the calculation result of its relationship formula is within the range of 59 - 740, its rate performance and cycle performance are poor and it cannot meet the fast charge and fast discharge performance. This is because the particle size D50 of the high tap density lithium cobaltate is too small, resulting in a decrease in the distance between particles, closer contact, a decrease in the amount of electrolyte absorbed, and a reduction or blockage of the ion movement channels, which is not conducive to the rapid movement of a large number of ions, thus restricting its high current discharge.

[0111] From the comparison of Comparative Example 7 with the examples, it is found that the tap density of the high tap density lithium cobaltate is 4.5 g / cm 3 , exceeding the range of 4.15 - 4.35 g / cm 3 range, the tap density of the fast charging type lithium cobaltate is 3.8 g / cm 3 , exceeding the range of 3.85 - 4.15 g / cm 3In the range, although the calculation result of its relational expression is within the range of 59 - 740, its rate performance and cycle performance are poor and cannot meet the fast charge and fast discharge performance. This is because the tap density of the high-compaction lithium cobaltate is too large, resulting in a decrease in the distance between particles and closer contact, leading to a decrease in the amount of electrolyte absorbed, a reduction or blockage of ion movement channels, and being unfavorable for the rapid movement of a large number of ions. The tap density of the fast-charging lithium cobaltate is too small. Although it is conducive to the rapid movement of ions, due to the too large distance between particles, the contact probability and contact area between particles are reduced, which is unfavorable for electron conduction, thus resulting in the fast charge and fast discharge performance of the battery being affected and unable to meet the requirements.

[0112] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A positive electrode sheet, characterized in that, It includes a current collector and a first active material layer disposed on the current collector; The first active material layer includes a first conductive agent, a first positive electrode active material, and a second positive electrode active material; the first positive electrode active material is a high-compaction positive electrode material, and the second positive electrode active material is a fast-charging positive electrode material; Among them, the tap density of the first positive electrode active material is a g / cm 3 ; the tap density of the second positive electrode active material is b g / cm 3 ; the particle size of the first positive electrode active material is c μm; the oil absorption value of the first conductive agent is d cm 3 ; The positive electrode sheet satisfies the formula: 59 < (a*d - b*d)² - 2abc < 608.7; The positive electrode sheet further includes a second active material layer, and the second active material layer is disposed on the surface of the current collector facing away from the first active material layer; the second active material layer includes a second conductive agent, a third positive electrode active material, and a fourth positive electrode active material, the third positive electrode active material is lithium iron phosphate manganese, and the fourth positive electrode active material is a fast-charging positive electrode material; The tap density of the first positive electrode active material is 4.15 - 4.35 g / cm 3 , and the tap density of the second positive electrode active material is 3.85 - 4.15 g / cm 3 , the particle size of the first positive electrode active material is 5 - 25 μm, and the oil absorption value of the first conductive agent is 30 - 100 cm 3 .

2. The positive electrode sheet according to claim 1, characterized in that, The doping ratio of the first positive electrode active material and the second positive electrode active material is (1:9) - (9:1).

3. The positive electrode sheet according to claim 1, characterized in that, The ratio of the thickness of the first active material layer to the second active material layer is (3:7) - (7:3).

4. The positive electrode sheet according to claim 3, wherein The doping ratio of the third positive electrode active material and the fourth positive electrode active material is (1:9) - (9:1).

5. The positive electrode sheet according to claim 4, wherein, The first positive electrode active material, the second positive electrode active material, and the fourth positive electrode active material are independently representative of LiNi 1-x-y-z Co x Mn y Al z O2, where: 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1 and 0 ≤ x + y + z ≤ 1.

6. The positive electrode sheet according to claim 5, characterized in that, The first positive electrode active material is high-compaction lithium cobaltate, the second positive electrode active material is fast-charging lithium cobaltate, and the fourth positive electrode active material is fast-charging lithium cobaltate.

7. The positive electrode sheet according to claim 6, wherein, The first conductive agent and the second conductive agent are independently selected from one or more of conductive carbon black, carbon nanotubes, conductive graphite, carbon fiber, and graphene.

8. The positive electrode sheet according to claim 7, characterized in that, The first conductive agent includes conductive carbon black and / or carbon nanotubes, the percentage of the conductive carbon black in the total mass of the first active material layer is 0.1 - 2.5%, and the percentage of the carbon nanotubes in the total mass of the first active material layer is 0.1 - 2%; The second conductive agent includes single-walled carbon nanotubes and / or flake graphite, the percentage of the single-walled carbon nanotubes in the total mass of the second active material layer is 0 - 1%, and the percentage of the flake graphite in the total mass of the second active material layer is 0 - 5%.

9. A fast charge and fast discharge type battery, characterized in that, It includes the positive electrode sheet according to any one of claims 1 - 8.

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