Positive plate as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of batteries, and provides a positive plate and a preparation method and application thereof.According to the positive plate, the mass percent of a conductive agent in an active layer is marked as X, the numerical result of the DBP oil absorption value of the conductive agent is marked as A, and the numerical results of the pore size distribution proportions of the conductive agent with the pore size ranges of 0.5-1 nm and 0.5-2 nm are marked as B and C respectively, 1 > X * (A * (1 + B) * C) > 0.7. The electrolyte absorption and retention capabilities of the conductive agent to the electrolyte are simulated according to the pore size distribution of the conductive agent and the structure-activity relationship of the DBP oil absorption value, the relationship is further established with the addition amount of the conductive agent, and the method can be used for bidirectionally guiding and limiting the selection of the conductive agent and the control of the addition amount; therefore, the conductive agent in the positive electrode and the electrolyte are more efficiently matched, the liquid absorption and retention capabilities of the positive electrode are fully improved, and the energy and capacity performances are considered.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries and relates to a positive electrode sheet and a preparation method and application thereof. Background Art

[0002] With the continuous development of lithium-ion battery technology, olivine-structured cathode materials such as lithium iron phosphate (LiFePO4) and lithium iron manganese phosphate (LiFeMnPO4) have been widely used in power batteries and energy storage systems due to their excellent cycle stability, thermal safety and low cost, and have even occupied a mainstream position in the market. Although lithium iron phosphate itself has poor conductivity, it can be carbon-coated during synthesis or further post-processing to improve its electrochemical performance. With the continuous improvement of the carbon coating process, the dependence on traditional conductive agents such as carbon black in lithium iron phosphate cathodes has been reduced to a certain extent. Even so, the role of conductive agents in the cathode system cannot be ignored, especially in terms of their ability to absorb and retain electrolytes. This ability directly affects the ion transport behavior at the electrode interface, and thus affects the battery's rate performance, cycle life and internal resistance performance.

[0003] The reason why the conductive agent can adsorb and retain the electrolyte is closely related to its surface chemical properties and microscopic pore structure. Porous materials have a large specific surface area, and their pore size distribution can provide adsorption sites for electrolyte molecules. When the electrolyte enters the electrode sheet, the conductive agent absorbs it through physical adsorption or capillary action, and maintains a certain liquid electrolyte content during the subsequent charge and discharge process, thereby ensuring an effective migration path for the ions. If the conductive agent's ability to absorb liquid is insufficient, it may cause local drying of the electrode, resulting in obstruction of ion transmission and the formation of local high resistance areas, which in turn leads to problems such as capacity attenuation and decreased kinetic performance; if the liquid absorption is excessive, it may cause uneven distribution of the electrolyte in the electrode sheet, and even cause the electrode sheet to swell and aggravate interfacial side reactions, which is also not conducive to the long-term stable operation of the battery.

[0004] In order to adjust the liquid absorption capacity of the positive electrode, it is usually possible to increase the proportion of conductive agent added. However, this strategy will face obvious energy density loss problems in practical applications. Since the conductive agent itself does not participate in the electrochemical reaction, the increase in its mass ratio will directly reduce the proportion of active substances, thereby reducing the energy output per unit volume or unit mass. In addition, excessive conductive agent may also destroy the rheological properties of the electrode slurry, affect the coating uniformity, and thus affect the consistency and yield of the battery. Therefore, it is not possible to simply rely on increasing the amount of addition to improve the liquid absorption and liquid retention performance. Selecting or developing the most suitable conductive agent with the best liquid absorption efficiency and liquid retention capacity has become a problem that needs attention and solution.

[0005] There is a close relationship between the liquid absorption capacity of the conductive agent and its pore size distribution. For the adsorption process of small molecules, the most effective adsorption usually occurs in pores with a pore size between 1 and 3 times the molecular diameter, which is the so-called "specific adsorption" mechanism. Within this range, the van der Waals force between the molecule and the pore wall is the strongest, the adsorption energy is high, and thus the adsorption efficiency is the highest. When the pore diameter is much larger than the molecular size, although adsorption can still occur, due to the small contact area between the molecule and the pore wall, the adsorption strength is greatly reduced, and the adsorption efficiency is significantly reduced.

[0006] The liquid absorption and retention properties of conductive agents can be evaluated through standard tests. Currently, the DBP oil absorption value test method is widely used as a reference indicator, such as the test standard ASTM D2414 Standard Test Method for Carbon Black - Oil Absorption Number (OAN). This test method uses dibutyl phthalate (DBP) as a simulated liquid and indirectly reflects the adsorption capacity of its pore structure by measuring the amount of DBP adsorbed by a unit mass of conductive agent. However, this method has certain limitations: However, since the DBP molecule has a diameter of approximately 1 nm, the pore size range required for its specific adsorption is significantly different from that of common solvent molecules in actual electrolytes, such as dimethyl carbonate (DMC, molecular diameter approximately 0.5 nm) and diethyl carbonate (DEC, molecular diameter approximately 0.6 nm). Although the DBP absorption value test is simple and easy to operate, and the standards are unified, considering that the electrolyte system is often composed of multiple solvents and additives, the physical and chemical properties of each component, such as molecular size, polarity, viscosity, etc., are different, and their adsorption behavior on the surface of the conductive agent is also complex. Therefore, the result value based on the DBP oil absorption value cannot accurately reflect the adsorption capacity of the conductive agent for the actual electrolyte components, which makes it difficult to achieve the most appropriate amount of its addition in the positive electrode formula.

[0007] It can be seen that there is currently a lack of a more representative and closer to actual working conditions evaluation system that utilizes the conductive agent's liquid absorption capacity and combines it with material structure control methods to achieve efficient adaptation between the conductive agent and the electrolyte. This has become one of the core technical problems that need to be urgently solved in the current research and development of lithium-ion battery positive electrode materials.

[0008] At present, there is still a lack of a solution that is closer to actual working conditions and more representative, which can calibrate and utilize the relationship between the conductive agent's liquid absorption capacity and its addition amount, so as to select and add the most suitable conductive agent in the positive electrode sheet, so as to achieve efficient adaptation between the conductive agent and the electrolyte, fully improve the positive electrode's liquid absorption and liquid retention capacity, and take into account energy and capacity performance. Summary of the Invention

[0009] In view of the problems existing in the prior art, the present invention aims to provide a positive electrode sheet, a preparation method, and uses thereof. The mass percentage of the conductive agent in the active layer is denoted as X, the numerical result of the conductive agent's DBP oil absorption value is denoted as A, and the numerical results of the pore size distribution percentages of the conductive agent in the pore size ranges of 0.5-1 nm and 0.5-2 nm are denoted as B and C, respectively. In the positive electrode sheet, 1>X×(A×(1+B)×C)>0.7. The present invention simulates the conductive agent's ability to absorb and retain electrolyte liquid by analyzing the structure-activity relationship between the conductive agent's pore size distribution and DBP oil absorption value, and further establishes a relationship with the amount of conductive agent added. This can be used to provide bidirectional guidance and limitation for the selection of the conductive agent and the control of its addition amount, thereby achieving more efficient adaptation between the conductive agent and the electrolyte in the positive electrode, fully improving the positive electrode's ability to absorb and retain electrolyte liquid while taking into account both energy and capacity performance.

[0010] To achieve this object, the present invention adopts the following technical solutions:

[0011] In a first aspect, the present invention provides a positive electrode sheet, comprising a current collector and an active layer disposed on a surface of the current collector, wherein the active layer comprises a positive electrode active material, a conductive agent, and a binder;

[0012] The mass percentage of the conductive agent in the active layer is recorded as X, in units of %; the numerical result of the DBP oil absorption value of the conductive agent is recorded as A, in units of mL / 100 g; the numerical result of the pore size distribution ratio of the pore size range of 0.5 to 1 nm in the conductive agent is recorded as B, in units of %; the numerical result of the pore size distribution ratio of the pore size range of 0.5 to 2 nm in the conductive agent is recorded as C, in units of %;

[0013] Then, in the positive electrode sheet, 1>X×(A×(1+B)×C)>0.7.

[0014] The DBP oil absorption value described in the present invention refers to the volume of dibutyl phthalate (DBP) absorbed by a unit mass of conductive agent under certain conditions, but it cannot accurately reflect the conductive agent's ability to absorb electrolyte liquid. Considering that the pores of 0.5 to 1 nm and smaller in the conductive agent cannot make an effective contribution to the test of the DBP oil absorption value, which is reflected in the parameters of the DBP oil absorption value, it still has an adsorption effect on the components of the electrolyte of about 0.5 nm, such as solvent molecules. At the same time, the pore size of 0.5 to 2 nm can correspond to 1 to 3 times the electrolyte component molecules of about 0.5 to 0.6 nm in the electrolyte, that is, it corresponds to the pore size range for specific adsorption of the electrolyte. Based on this, the present invention first defines the product of the oil absorption value A and the conductive agent addition amount X (total conductive agent oil absorption value). The lower limit of the total conductive agent oil absorption value of this part is to ensure electrical performance, and the upper limit of the total conductive agent oil absorption value is to prevent excessive. However, as mentioned above, the oil absorption value A does not include the adsorption capacity of micropores below 1 nm. In this case, X×A is equivalent to the oil absorption value corresponding to the pore volume with a pore size of >1 nm. Furthermore, as mentioned above, considering that micropores of 0.5 to 1 nm still have the ability to adsorb electrolyte molecules, X×A×(1+B) is used to refer to the oil absorption value corresponding to the pore volume with a pore size of >0.5 nm. Furthermore, A×(1+B)×C refers to the oil absorption value corresponding to the pore volume with a pore size of 0.5 to 2 nm. This pore size range can form specific adsorption for electrolyte molecules. Therefore, by limiting the range of X×(A×(1+B)×C), the adsorption capacity of the conductive agent for electrolyte molecules can be better matched.

[0015] It can be understood that the calculation relationship of 1>X×(A×(1+B)×C)>0.7 can be used to guide and limit the selection of the conductive agent and the adjustment of the addition amount according to the actual design and needs of the positive electrode sheet. For example, when the required conductive agent addition amount X is determined in advance, it can be used to find the most suitable additive; or, for a certain conductive agent component that must be used, the result of (A×(1+B)×C) can be tested and calculated to obtain the range or specific value of the most suitable conductive agent addition amount X.

[0016] It should be noted that when the positive electrode sheet contains multiple conductive agents, the final calculated numerical result should be the weighted average of X×(A×(1+B)×C) calculated for each conductive agent, where the weight is the percentage of the mass of the conductive agent to the total mass of all conductive agents.

[0017] It should also be noted that the pore size distribution ratio described in the present invention is the ratio of the pore volume of a certain pore size (or pore size range) in the material to the total pore volume, which can usually be obtained by tests such as mercury intrusion porosimetry (MIP) or gas adsorption method (BET).

[0018] For example, a method for testing the pore size distribution ratio includes the following steps:

[0019] ① Place the sample at 250-300℃ for desorption for 6-8h, and the sample amount should be ≥250mg;

[0020] ② The nitrogen adsorption-desorption isotherm was tested at liquid nitrogen temperature (77K) using a BET surface analyzer, and the pore size range of the test was 0.35 to 500 nm.

[0021] ③ Pore size distribution calculation: generate the mesopore distribution curve by the BJH method, and calculate the total pore volume of 2-50nm by integration; construct theoretical adsorption isotherm sets (kernels) by QSDFT molecular simulation, match the experimental data to infer the pore size distribution and calculate the total pore volume of 0.35-2nm;

[0022] ④ In the present invention, the pore size distribution proportion B of 0.5-1 nm and the pore size distribution proportion C of 0.5-2 nm both fall within the test data of the micropore range below 2 nm, and can be calculated according to the micropore volume proportion algorithm:

[0023]

[0024] Supplementary explanation: Macropores larger than 50 nm will significantly reduce the adsorption efficiency due to their low specific surface area and weak adsorption properties. Therefore, the proportion of macropores is minimized during the design of conductive agents such as carbon black. Therefore, macropores larger than 50 nm are not considered in this calculation.

[0025] In the present invention, 1>X×(A×(1+B)×C)>0.7, which means that the calculated result of X×(A×(1+B)×C) can be 0.71, 0.73, 0.75, 0.77, 0.79, 0.8, 0.82, 0.84, 0.86, 0.88, 0.9, 0.91, 0.93, 0.95, 0.97 or 0.99, etc.

[0026] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0027] As a preferred technical solution of the present invention, the positive electrode active material includes lithium iron phosphate and / or lithium iron manganese phosphate.

[0028] Preferably, the conductive agent comprises carbon black.

[0029] Preferably, the carbon black includes at least one of acetylene black, Ketjen Black, conductive furnace black, such as SuperP, or thermal black.

[0030] As a preferred technical solution of the present invention, the value of X is 0.4% to 3.5%, for example, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, 3.2%, 3.3% or 3.5%, etc.

[0031] In the present invention, the addition amount of X in the range of 0.4% to 3.5% can ensure that the positive electrode sheet has both conductivity and liquid retention capabilities.

[0032] As a preferred technical solution of the present invention, the value of A is 180-400 mL / mg, for example, 180 mL / mg, 200 mL / mg, 220 mL / mg, 240 mL / mg, 260 mL / mg, 280 mL / mg, 300 mL / mg, 320 mL / mg, 340 mL / mg, 380 mL / mg or 400 mL / mg, etc.

[0033] In the present invention, when the A is lower than 180 mL / mg, the conductive agent's own liquid retention capacity is poor and does not meet the requirements of application in lithium-ion batteries. When the conductive agent is greater than 400 mL / mg, such as carbon black, the production yield will be greatly reduced, which is not conducive to controlling the use cost.

[0034] As a preferred technical solution of the present invention, the value of B is 10% to 30%, for example, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28% or 30%.

[0035] As a preferred technical solution of the present invention, the value of C is 15% to 50%, for example, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, 42%, 45%, 48% or 50%, etc.

[0036] As a preferred technical solution of the present invention, the mass percentage of the positive electrode active material in the active layer is 93.5% to 99.1%, for example, 93.5%, 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99% or 99.1%, etc.

[0037] Preferably, the binder accounts for 0.5% to 3% by mass of the active layer, for example, 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8% or 3%, etc.

[0038] Preferably, the binder includes at least one of polyvinylidene fluoride, polyacrylic acid, styrene-butadiene rubber or sodium carboxymethyl cellulose.

[0039] Preferably, the current collector comprises aluminum foil or carbon-coated aluminum foil.

[0040] In a second aspect, the present invention provides a method for preparing the positive electrode sheet according to the first aspect, the method comprising the following steps:

[0041] preparing a binder and a solvent into a glue solution;

[0042] The glue solution is mixed with the conductive agent, the positive electrode active material is added and mixed, and finally the solvent is added and dispersed to obtain a slurry;

[0043] The obtained slurry is coated on the surface of the current collector and baked to obtain a positive electrode sheet.

[0044] As a preferred technical solution of the present invention, the solvent includes N-methylpyrrolidone (NMP).

[0045] Preferably, the viscosity of the slurry is adjusted using the solvent before the coating.

[0046] Preferably, the coating method includes transfer coating and / or extrusion coating.

[0047] Preferably, the baking temperature is 90-105°C, for example, 90°C, 93°C, 95°C, 98°C, 100°C, 102°C or 105°C, and the baking time is 1-3 min, for example, 1 min, 1.2 min, 1.4 min, 1.6 min, 1.8 min, 2 min, 2.2 min, 2.4 min, 2.6 min, 2.8 min or 3 min, etc.

[0048] In a third aspect, the present invention provides a battery comprising the positive electrode sheet described in the first aspect.

[0049] It should be noted that due to space limitations and to avoid redundancy, the present invention does not exhaustively list all point values ​​within the above numerical range, but is not limited to the listed values. Other unlisted values ​​within the above numerical range are also applicable.

[0050] Compared with the existing technical solutions, the present invention has at least the following beneficial effects:

[0051] In the positive electrode sheet of the present invention, the mass percentage of the conductive agent in the active layer is recorded as X, the numerical result of the DBP oil absorption value of the conductive agent is recorded as A, and the numerical results of the pore size distribution ratio of the pore size range of 0.5-1nm and 0.5-2nm in the conductive agent are recorded as B and C respectively. Then, in the positive electrode sheet, 1>X×(A×(1+B)×C)>0.7. The present invention simulates the liquid absorption and liquid retention ability of the conductive agent for the electrolyte by the structure-activity relationship of the pore size distribution and DBP oil absorption value of the conductive agent, and further establishes a relationship with the addition amount of the conductive agent, which can be used to provide two-way guidance and limitation for the selection of the conductive agent and the control of the addition amount. When the positive electrode sheet meets the numerical range of this calculation relationship, an excellent conductive network can be built with the most appropriate addition amount without excessive conductive agent, thereby having excellent electronic conductivity and taking into account energy and capacity performance; at the same time, the positive electrode sheet also has good liquid absorption, liquid retention and infiltration effects on the electrolyte, so that the electrode sheet has excellent ionic conductivity. DETAILED DESCRIPTION

[0052] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0053] It should be apparent to those skilled in the art that the embodiments are only intended to help understand the present invention and should not be considered as specific limitations of the present invention.

[0054] Example 1

[0055] This embodiment provides a positive electrode sheet, comprising a current collector aluminum foil and an active layer disposed on the surface of the current collector, wherein the active layer comprises a positive electrode active material, lithium iron phosphate, a conductive agent, carbon black, and a binder, polyvinylidene fluoride;

[0056] The mass percentage of the conductive agent in the active layer is recorded as X, X=1.23%; the numerical result of the DBP oil absorption value of the conductive agent is recorded as A, A=300mL / 100g; the numerical result of the pore size distribution ratio of the pore size range of 0.5-1nm in the conductive agent is recorded as B, B=15%; the numerical result of the pore size distribution ratio of the pore size range of 0.5-2nm in the conductive agent is recorded as C, C=20%;

[0057] Then, in the positive electrode sheet, 1>X×(A×(1+B)×C)=0.849>0.7.

[0058] Example 2, Example 3 and Comparative Examples 1 to 4

[0059] Example 2, Example 3, and Comparative Examples 1 to 4 respectively provide a positive electrode sheet, in which the amount of the conductive agent added is adjusted and / or another new carbon black is used as the conductive agent. The specific adjustments are shown in Table 1. Except for the above, other conditions are exactly the same as those in Example 1.

[0060] Table 1

[0061] Group X A B C X×(A×(1+B)×C) Example 1 1.23％ 300mL / 100g 15.00％ 20.00％ 0.849 Example 2 1.02％ 300mL / 100g 15.00％ 20.00％ 0.704 Example 3 1.44％ 300mL / 100g 15.00％ 20.00％ 0.994 Example 4 3.33％ 180mL / 100g 11.00％ 15.00％ 0.998 Example 5 2.34％ 180mL / 100g 11.00％ 15.00％ 0.701 Example 6 2.84％ 180mL / 100g 11.00％ 15.00％ 0.851 Example 7 0.49％ 400mL / 100g 18.00％ 37.00％ 0.856 Example 8 0.57％ 400mL / 100g 18.00％ 37.00％ 0.995 Example 9 0.41％ 400mL / 100g 18.00％ 37.00％ 0.716 Comparative Example 1 2.00％ 300mL / 100g 15.00％ 20.00％ 1.380 Comparative Example 2 0.90％ 300mL / 100g 15.00％ 20.00％ 0.621 Comparative Example 3 4.60％ 180mL / 100g 11.00％ 15.00％ 1.379 Comparative Example 4 2.10％ 180mL / 100g 11.00％ 15.00％ 0.629 Comparative Example 5 0.79％ 400mL / 100g 18.00％ 37.00％ 1.380 Comparative Example 6 0.36％ 400mL / 100g 18.00％ 37.00％ 0.629

[0062] The positive electrode sheets of the above embodiments and comparative examples were obtained by the following preparation method, which includes:

[0063] 1) Prepare a positive electrode slurry according to the mass ratio of the positive electrode active material, conductive agent, binder and solvent NMP of 98.5-X:X:1.5:39: add the binder and a portion of the solvent to a double planetary mixer, mix at medium speed, and disperse for 3 hours to obtain a glue solution; add the glue solution and the conductive agent to a double planetary mixer, disperse at medium speed for 1-2 hours, add the positive electrode active material twice, and then add a portion of the solvent. After each addition, disperse at high speed for 2 hours. After the end, add an appropriate amount of solvent to adjust the slurry viscosity to a range suitable for coating;

[0064] 2) Then, the positive electrode is coated on one or both sides of the current collector by transfer coating or extrusion coating, and baked in an oven at a temperature of 90 to 105° C. for 2 minutes to obtain a positive electrode sheet.

[0065] Then, follow the steps below to assemble the obtained positive and negative electrode sheets, separators, and electrolytes into a battery:

[0066] 3) The negative electrode active material is graphite, the conductive agent is carbon black, the binder is CMC and SBR system, and the solvent is water. The mass ratio is 96.6:0.4:1:2:99. The negative electrode slurry is prepared: CMC and deionized water are added to a double planetary mixer and mixed at medium speed for 1-1.5 hours to obtain CMC glue; then the CMC glue and carbon black are added to the double planetary mixer and dispersed at medium speed for 1-2 hours. Then, graphite is added twice, and an appropriate amount of deionized water is added. The mixture is dispersed at high speed for 3-4 hours. SBR is added and stirred at low speed for 0.5 hours. During this period, an appropriate amount of deionized water is added to adjust the slurry viscosity to a range suitable for coating;

[0067] 4) Coating one or both sides of a copper foil or a carbon-coated copper foil by transfer coating or extrusion coating, and baking in an oven at a temperature of 50 to 80° C. for 2 minutes to obtain a negative electrode sheet.

[0068] 5) The separator is selected as PP base film or PE base film + PVDF glue, the electrolyte contains 1M LiPF6, and the solvent is ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) with a volume ratio of 1:1:1, and assembled into a CR2032 button battery.

[0069] The resulting batteries were tested using a multi-channel electrical performance tester, a high-precision thermostat with ±0.5°C temperature control, and an automated LIM system. Specific test items included: HPPC (Hybrid Pulse Power Characterization) charge-discharge testing at 25°C and -20°C; 3C rate charge-discharge testing at room temperature (25°C); 2C / 1C cycle testing at 25°C for 1000 cycles; and 2C / 1C cycle testing at 45°C for 1200 cycles. The relevant results are shown in Table 2.

[0070] Table 2

[0071]

[0072]

[0073] As can be seen from Table 2:

[0074] In Examples 1 to 9, even carbon blacks with significant differences in oil absorption can be used to construct positive electrode sheets that meet the characteristics of the present invention through the present invention, and the short-term and long-term electrical performance are basically the same; when Examples 1 to 3 are compared with Comparative Examples 1 and 2, or when Examples 4 to 6 are compared with Comparative Examples 3 and 4, or when Examples 7 to 9 are compared with Comparative Examples 5 and 6, the same type of carbon black is used and the addition amount is adjusted. When the upper limit of the specified range is exceeded, there is no further optimization effect on the electrical performance. On the contrary, the energy density is easily reduced due to excessive addition. When the carbon black addition amount is low, due to insufficient positive electrode kinetics, the DCR of room temperature and low temperature discharge deteriorates by 2.1% to 5.3%, and the cycle performance under 25°C cycling for 1000cls and 45°C cycling for 1200cls deteriorates significantly, both by more than 3.8%.

[0075] From the above, it can be seen that in the positive electrode sheet of the present invention, the mass percentage of the conductive agent in the active layer is recorded as X, the numerical result of the DBP oil absorption value of the conductive agent is recorded as A, and the numerical results of the pore size distribution ratio of the pore size range of 0.5-1nm and 0.5-2nm in the conductive agent are recorded as B and C respectively. Then, in the positive electrode sheet, 1>X×(A×(1+B)×C)>0.7. The present invention simulates the liquid absorption and liquid retention ability of the conductive agent for the electrolyte by the structure-activity relationship of the pore size distribution and DBP oil absorption value of the conductive agent, and further establishes a relationship with the addition amount of the conductive agent, which can be used to provide two-way guidance and limitation for the selection of the conductive agent and the control of the addition amount. When the positive electrode sheet meets the numerical range of this calculation relationship, an excellent conductive network can be built with the most appropriate addition amount without excessive conductive agent, thereby having excellent electronic conductivity and taking into account energy and capacity performance; at the same time, the positive electrode sheet also has good liquid absorption, liquid retention and infiltration effects on the electrolyte, so that the electrode sheet has excellent ionic conductivity.

[0076] The present invention uses the above-described embodiments to illustrate the features of the positive electrode sheet of the present invention and to provide exemplary processes for preparing the positive electrode sheet. However, the present invention is not limited to the aforementioned process equipment and process flow, and does not necessarily rely on the aforementioned detailed process equipment and process flow for implementation. Those skilled in the art should understand that any improvements to the present invention, equivalent replacements for various raw materials in the product of the present invention, additions of auxiliary components, and selection of specific process equipment, etc., fall within the scope of protection and disclosure of the present invention.

[0077] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0078] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0079] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A positive electrode sheet, characterized in that: The positive electrode sheet includes a current collector and an active layer provided on the surface of the current collector, wherein the active layer includes a positive electrode active material, a conductive agent and a binder; The mass percentage of the conductive agent in the active layer is recorded as X, in %; The numerical result of the DBP oil absorption value of the conductive agent is recorded as A, and the unit is mL / 100 g; the numerical result of the pore size distribution ratio of the pore size range of 0.5 to 1 nm in the conductive agent is recorded as B, and the unit is %; The numerical result of the pore size distribution ratio of the conductive agent with a pore size range of 0.5 to 2 nm is recorded as C, in units of %; Then, in the positive electrode sheet, 1>X×(A×(1+B)×C)>0.

7.

2. The positive electrode sheet according to claim 1, characterized in that The positive electrode active material includes lithium iron phosphate and / or lithium iron manganese phosphate; Preferably, the conductive agent comprises carbon black.

3. The positive electrode sheet according to claim 1 or 2, characterized in that: The value of X is 0.4% to 3.5%.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that: The value of A is 180-400 mL / mg.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The value of B is 10% to 30%.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The value of C is 15% to 50%.

7. The positive electrode sheet according to any one of claims 1 to 6, characterized in that: The mass percentage of the positive electrode active material in the active layer is 93.5% to 99.1%; Preferably, the binder accounts for 0.5% to 3% by mass of the active layer; Preferably, the binder comprises at least one of polyvinylidene fluoride, polyacrylic acid, styrene-butadiene rubber or sodium carboxymethyl cellulose; Preferably, the current collector comprises aluminum foil or carbon-coated aluminum foil.

8. A method for preparing a positive electrode sheet according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: preparing a binder and a solvent into a glue solution; The glue solution is mixed with the conductive agent, the positive electrode active material is added and mixed, and finally the solvent is added and dispersed to obtain a slurry; The obtained slurry is coated on the surface of the current collector and baked to obtain a positive electrode sheet.

9. The method for preparing a positive electrode sheet according to claim 8, wherein: The solvent includes N-methylpyrrolidone; Preferably, the viscosity of the slurry is adjusted using the solvent before coating; Preferably, the coating method includes transfer coating and / or extrusion coating; Preferably, the baking temperature is 90-105° C., and the baking time is 1-3 minutes.

10. A battery, characterized in that: A positive electrode sheet comprising the positive electrode sheet according to any one of claims 1 to 7.

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