Positive plate, preparation method thereof and battery

Abstract

The invention discloses a positive plate, a preparation method of the positive plate and a battery, and belongs to the technical field of batteries. The active layer is arranged on at least one side of the current collector, the active layer comprises at least two sub-active layers which are sequentially stacked on the current collector in the first direction, and each sub-active layer comprises an active substance and a conductive agent; wherein in the direction far away from the current collector, the mass ratio of the active substances in the different sub active layers is in an increasing trend, the mass ratio of the conductive agent is in a reducing trend, and the surface density of the sub active layers is in an increasing trend. Through mutual cooperation of gradient structures of surface densities, active substance mass ratios and conductive agent mass ratios in different sub-active layers, balance of structural stability and electrochemical performance of the positive plate is guaranteed, collaborative optimization of electron conduction, ion transmission and reaction kinetics is realized, and the battery is relatively good in fast charging performance and stability.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a positive electrode sheet and its preparation method, and a battery. Background Technology

[0002] With the rapid development of power batteries, higher demands are being placed on their fast-charging performance. The electrode is a crucial component of the battery, consisting of a current collector and an active material layer coated on it. The structure of the active material layer on the current collector affects lithium-ion diffusion and electrolyte wetting, thus impacting the battery's fast-charging performance. In related technologies, during battery charging and discharging, the electrolyte wetting effect on the active material layer on the current collector is poor in the direction away from the separator and closer to the current collector. Simultaneously, electron transport efficiency is limited on the side closer to the current collector, affecting the transport efficiency of lithium ions and electrons, resulting in poor fast-charging performance. Summary of the Invention

[0003] This application provides a positive electrode sheet and its preparation method, as well as a battery, aiming to solve the problem that the active layer on the current collector affects the wettability of the electrolyte and limits the electron transport efficiency, resulting in poor fast charging performance of the battery.

[0004] In a first aspect, this application provides a positive electrode sheet, comprising: Current collector; and An active layer is disposed on at least one side of the current collector. The active layer includes at least two sub-active layers that are sequentially stacked on the current collector along a first direction. Each sub-active layer includes an active material and a conductive agent. In the direction away from the current collector, the mass percentage of active material in different sub-active layers shows an increasing trend, the mass percentage of conductive agent shows a decreasing trend, and the areal density of the sub-active layer shows an increasing trend.

[0005] This application sets the active layer to include at least two sub-active layers sequentially stacked on the current collector along a first direction. In the direction away from the current collector, the mass percentage of active material in different sub-active layers tends to increase, the mass percentage of conductive agent tends to decrease, and the areal density of the sub-active layers tends to increase. When the positive electrode is applied to the battery, the areal density of the sub-active layer near the separator is larger, resulting in a thicker thickness (with unchanged porosity) or a smaller porosity (with unchanged thickness). However, its distance from the separator is smaller, so the wetting ability of the electrolyte is relatively better. Based on the better and more sufficient wetting of the sub-active layer by the electrolyte, the relatively larger proportion of active material can transport more lithium ions, and the transport path of lithium ions in the sub-active layer is shorter, improving the fast charging performance of the battery. At the same time, a relatively small proportion of conductive agent can better and more fully match the active material in the sub-active layer, so that lithium ions and electrons in the sub-active layer can be transported smoothly and efficiently. In the direction away from the separator, the areal density of different sub-active layers tends to decrease, resulting in a decreasing thickness or increasing porosity of the different sub-active layers. The smaller thickness or larger porosity allows for better electrolyte wetting. The interaction between the gradually increasing distance from the separator and the decreasing thickness or increasing porosity results in good electrolyte wetting of different sub-active layers. Furthermore, in the direction away from the separator, the mass proportion of active material in different sub-active layers tends to decrease, while the mass proportion of conductive agent tends to increase. That is, in the direction away from the separator, although the lithium ion transport path in different sub-active layers increases, the conductive network formed in different sub-active layers is richer. The interaction between the transport path length and the conductive network results in good lithium ion transport efficiency in different sub-active layers, thus improving the battery's fast-charging performance.

[0006] Optionally, the difference in the mass percentage of active material between adjacent sub-active layers is 0.1% to 0.5%; and / or, the difference in the mass percentage of conductive agent between adjacent sub-active layers is 0.1% to 0.5%; and / or, the difference in the areal density between adjacent sub-active layers is 5 g / m². 2 ~30g / m 2 .

[0007] This application achieves this by keeping the difference in the mass ratio of active material and conductive agent in adjacent sub-active layers and the difference in the areal density of adjacent sub-active layers within a suitable range. This suitable range of differences makes the gradient change of adjacent sub-active layers tend to be gentle, which not only alleviates the deviation in the wetting ability of the electrolyte in different sub-active layers, but also enables the continuous and efficient transport of electrons and lithium ions between different sub-active layers and reduces the internal resistance of the positive electrode; it also makes the bonding force of different sub-active layers stronger, improving the stability of the positive electrode and the battery.

[0008] Optionally, the active layer includes a first sub-active layer, a second sub-active layer, and a third sub-active layer sequentially stacked on the current collector along a first direction. In the first sub-active layer, the active material accounts for 96.5% to 96.8% of the mass of the first sub-active layer, and the conductive agent accounts for 1.6% to 1.9% of the mass of the first sub-active layer; and / or, in the second sub-active layer, the active material accounts for 96.8% to 97.1% of the mass of the second sub-active layer, and the conductive agent accounts for 1.3% to 1.6% of the mass of the second sub-active layer; and / or, in the third sub-active layer, the active material accounts for 97.1% to 97.4% of the mass of the third sub-active layer, and the conductive agent accounts for 1.0% to 1.3% of the mass of the third sub-active layer.

[0009] In this application, the active layer is configured to include a first sub-active layer, a second sub-active layer, and a third sub-active layer sequentially stacked on the current collector along a first direction. These three sub-active layers enrich the structure of the active layer while simplifying the preparation process of the positive electrode. By ensuring that the active materials and conductive agents in the first, second, and third sub-active layers are within suitable ranges, the synergistic effect between the different layers is fully utilized.

[0010] Optionally, the active layer includes a first sub-active layer, a second sub-active layer, and a third sub-active layer sequentially stacked on the current collector along a first direction, wherein the areal density of the first sub-active layer is 5 g / m². 2 ~15g / m 2 ; and / or, the areal density of the second sub-active layer is 15 g / m². 2 ~25g / m 2 ; and / or, the areal density of the third sub-active layer is 25 g / m². 2 ~50g / m 2 .

[0011] This application achieves this by ensuring that the areal density of the first, second, and third sub-active layers is within a suitable range. This not only makes the thickness of the first, second, and third sub-active layers suitable, resulting in a relatively short lithium-ion and electron transport path and improving lithium-ion and electron transport efficiency, but also ensures that the content of active materials and conductive agents in the first, second, and third sub-active layers is suitable, further promoting lithium-ion and electron transport and resulting in relatively high capacity and energy density of the positive electrode and the battery.

[0012] Optionally, the D50 particle size of the active material is 50 nm to 100 nm; and / or, the active material is at least one of lithium iron phosphate, lithium manganese iron phosphate, and lithium nickel cobalt manganese oxide; and / or, the thickness of the active layer is 20 μm to 30 μm.

[0013] This application achieves this by minimizing the D50 particle size of the active material or the thickness of the active layer, thus maintaining a low areal density and thickness. This results in higher lithium-ion and electron transport efficiency and lower transport resistance in the cathode, improving the battery's fast-charging performance. Simultaneously, it reduces heat generation and enhances battery stability. By rationally selecting the types of active materials, particularly those with good stability and high capacity, the capacity and energy density of both the cathode and the battery are relatively high.

[0014] Secondly, this application provides a method for preparing the positive electrode sheet provided in the first aspect of this application, wherein the positive electrode sheet is prepared by a dry spraying process.

[0015] This application employs a dry spraying process, which allows for better control of the thickness of the active layer in the positive electrode, thereby preparing a thinner active layer with a lower areal density. At the same time, the dry spraying process does not use solvents, reducing costs. In addition, the dry spraying process can more precisely control the proportion of different substances in the active layer.

[0016] Optionally, the method for preparing the positive electrode includes: At least two types of spray coatings are formulated from active substances, conductive agents, and binders, respectively. Different spray paints are sequentially sprayed on at least one side of the current collector, wherein the spraying distance is 150mm~300mm; After drying and rolling, the positive electrode sheet is obtained.

[0017] This application first prepares different spray coatings by uniformly mixing active materials, conductive agents, and binders. This process does not require the addition of solvents, and the solid active materials, conductive agents, and binders are directly mixed, providing favorable conditions for a dry spray coating process without slurry preparation. Then, different spray coatings are sequentially sprayed on at least one side of the current collector, controlling the spraying distance to be 150mm~300mm, so that the spray coating is more uniformly and densely sprayed on the current collector. After drying, the small amount of moisture that may have been introduced during the spraying process is removed, and after roll forming, a positive electrode sheet is obtained.

[0018] Optionally, the active material is lithium iron phosphate coated with metal-doped carbon, and the preparation method of lithium iron phosphate coated with metal-doped carbon includes: Iron source, lithium source, phosphorus source, carbon source, gas generating agent, first metal compound dopant and solvent are mixed, dried and sintered once to obtain a primary sintered material, wherein the temperature of the primary sintering is 350℃~400℃, and the first metal compound dopant is at least one of a compound including titanium, vanadium, magnesium and nickel. The primary sintering material is mixed with the second metal compound dopant, and then sintered a second time to obtain metal-doped carbon-coated lithium iron phosphate. The secondary sintering temperature is 550℃~700℃, and the second metal compound dopant is at least one of a compound including titanium, vanadium, magnesium, nickel, and aluminum.

[0019] In the preparation process of lithium iron phosphate, this application first uniformly disperses an iron source, a lithium source, a phosphorus source, a carbon source, a gas-generating agent, and a first metal compound dopant in a solvent. Then, a primary sintering is performed at a relatively low temperature of 350℃~400℃. The relatively low temperature results in a relatively low rate of solid-phase reaction, thus resulting in a smaller particle size of the obtained primary sinter. At the same time, the presence of the first metal compound dopant also refines the particle size of the primary sinter and improves its conductivity. The presence of the carbon source provides a reducing atmosphere for the reaction, preventing the formation of ferric iron. The gas-generating agent works synergistically with the carbon source to form a continuous, thin carbon coating layer on the surface of the primary sinter, achieving multi-layer carbon coating, refining the grain size of the primary sinter, and the gas generated by the gas-generating agent during the reaction forms continuous pores in the carbon coating layer. Next, a second sintering process is carried out. During the second sintering process, a second metal compound dopant is added, and the temperature of the second sintering is controlled at 550℃~700℃. The relatively low second sintering temperature ensures that the reaction is completed to obtain high-purity lithium iron phosphate with complete crystal structure. At the same time, the second metal compound dopant can further refine the particle size and further optimize the structure of the carbon coating layer, resulting in metal-doped carbon-coated lithium iron phosphate with small particle size, uniform particle size, and high conductivity.

[0020] Optionally, the amount of gas-generating agent added is 10% to 20% of the total mass of the iron source, lithium source, phosphorus source and carbon source; and / or, the amount of the first metal compound dopant added is 0.3% to 0.8% of the total mass of the iron source, lithium source, phosphorus source and carbon source; and / or, the amount of the second metal compound dopant added is 0.1% to 0.5% of the total mass of the iron source, lithium source, phosphorus source and carbon source.

[0021] This application optimizes the addition of a gas-generating agent by adjusting its dosage to achieve better synergy with the carbon source and create sufficient and uniform porosity within the carbon coating layer. By appropriately adjusting the dosage of the first metal compound dopant, the particle size of the primary sintering material is optimized, forming a preliminary coating layer and providing favorable conditions for preparing small-particle-size, highly conductive lithium iron phosphate. Furthermore, by appropriately adjusting the dosage of the second metal compound dopant, the particle size and conductivity of lithium iron phosphate are further optimized.

[0022] Optionally, before mixing the primary sintering material and the second metal compound dopant, the method further includes: pulverizing the primary sintering material to a D50 particle size of 0.2 μm to 0.5 μm; and / or mixing the primary sintering material and the second metal compound dopant, followed by secondary sintering to obtain metal-doped carbon-coated lithium iron phosphate, comprising: mixing the primary sintering material and the second metal compound dopant, followed by secondary sintering to obtain a crude product, pulverizing the crude product to a D50 particle size of 0.2 μm to 0.5 μm to obtain metal-doped carbon-coated lithium iron phosphate.

[0023] This application pulverizes the primary sintering material to a D50 particle size of 0.2μm~0.5μm, resulting in smaller and more uniform particle size, which provides favorable conditions for uniform secondary sintering. By pulverizing the coarse product from secondary sintering, the agglomerates are dispersed, resulting in uniform lithium iron phosphate particles, which provides favorable conditions for dry spraying to prepare the cathode sheet.

[0024] Thirdly, embodiments of this application provide a battery, including a positive electrode sheet provided in the first aspect of this application or a positive electrode sheet prepared by the method for preparing a positive electrode sheet provided in the second aspect of this application.

[0025] This application applies the positive electrode sheet provided in the first aspect of this application or the positive electrode sheet prepared in the second aspect of this application to a battery, thereby enabling faster lithium-ion and electron transport efficiency during the charging and discharging process, improving the fast charging performance of the battery. At the same time, the internal resistance of the electrode sheet is small, thereby reducing the heat generated during the charging and discharging process, and improving the stability and service life of the battery. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the positive electrode sheet provided in the application embodiment.

[0028] Figure Labels 100. Positive electrode sheet; 10. Active layer; 101. First sub-active layer; 102. Second sub-active layer; 103. Third sub-active layer; 20. Current collector. Detailed Implementation

[0029] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0030] This application provides a positive electrode 100, its preparation method, and a battery. Detailed descriptions are provided below. It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". The terms first, second, third, etc., are used merely as illustrative and do not impose numerical requirements or establish an order. Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0031] The technical solution of this application is as follows: Please see Figure 1 In a first aspect, embodiments of this application provide a positive electrode 100, which includes a current collector 20 and an active layer 10. The active layer 10 is disposed on at least one side of the current collector 20, and the active layer 10 includes components along a first direction ( Figure 1 At least two sub-active layers are sequentially stacked on the current collector 20 in the direction of the X-axis. Each sub-active layer includes an active material and a conductive agent. In the direction away from the current collector 20, the mass percentage of the active material in different sub-active layers tends to increase, the mass percentage of the conductive agent tends to decrease, and the areal density of the sub-active layers tends to increase.

[0032] In this application, firstly, by providing an active layer 10 on at least one side of the current collector 20, a basis for the electrochemical reaction of the battery is provided, ensuring smooth charging and discharging of the battery. Secondly, by configuring the active layer 10 as comprising at least two sub-active layers sequentially stacked on the current collector 20 along a first direction, each sub-active layer includes an active material and a conductive agent. The active material and conductive agent provide conditions for the transport of lithium ions and electrons. Specifically, in the direction away from the current collector 20, the mass percentage of active material in different sub-active layers tends to increase, the mass percentage of conductive agent tends to decrease, and the areal density of the sub-active layers tends to increase. When the positive electrode 100 is applied to the battery, the sub-active layer away from the current collector 20 is closer to the separator, that is, the areal density of the sub-active layer closer to the separator is larger, resulting in a thicker thickness (with unchanged porosity) or a smaller porosity (with unchanged thickness). However, its distance from the separator is smaller, resulting in less resistance and a shorter distance for the electrolyte to wet the sub-active layer. Therefore, the electrolyte's wetting ability is relatively good. At the same time, the active material in the sub-active layer has a larger mass ratio and the conductive agent has a smaller mass ratio. With the electrolyte wetting the sub-active layer better and more fully, the relatively larger proportion of active material can transport more lithium ions, and the lithium ion transport path in the sub-active layer is shorter, improving the battery's fast charging performance. Meanwhile, the relatively smaller proportion of conductive agent can better and more fully match the active material in the sub-active layer, allowing lithium ions and electrons in the sub-active layer to be transported smoothly and efficiently, further improving the battery's fast charging performance. In the direction away from the separator, the areal density of different sub-active layers decreases, leading to a decrease in the thickness or an increase in the porosity of these layers. Smaller thickness or higher porosity allows for better electrolyte wetting. The interaction of this increasing distance from the separator and the decreasing thickness or increasing porosity results in good electrolyte wetting of all sub-active layers. Furthermore, in the direction away from the separator, the mass percentage of active material in each sub-active layer decreases, while the mass percentage of conductive agent increases. This means that although the lithium-ion transport path increases in the sub-active layers, the resulting conductive network is richer, leading to higher electron transport efficiency. The interaction between the transport path length and the conductive network results in better lithium-ion transport efficiency in the sub-active layers, thus improving the battery's fast-charging performance. Moreover, with the smooth and rapid transport of lithium ions, the resistance of the positive electrode 100 is lower, resulting in less heat generated during battery charging and discharging, improving battery stability and lifespan. That is, this application ensures the structural stability and electrochemical performance balance of the positive electrode 100 by synergistically coordinating the gradient structures of areal density, active material mass ratio and conductive agent mass ratio in different sub-active layers, thereby achieving synergistic optimization of electron conduction, ion transport and reaction kinetics, resulting in better fast charging performance and stability of the battery.

[0033] In some embodiments, the difference in the mass percentage of active material in adjacent sub-active layers is 0.1% to 0.5%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, etc.; and / or, the difference in the mass percentage of conductive agent in adjacent sub-active layers is 0.1% to 0.5%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, etc.; and / or, the difference in areal density of adjacent sub-active layers is 5 g / m³. 2 ~40g / m 2 For example, it can be 5g / m 2 10g / m 2 15g / m 2 20g / m 2 25g / m 2 30g / m 2 35g / m 2 40g / m 2 It is understandable that each sub-active layer also includes a binder, and the areal density refers to the total mass of active material, conductive agent and binder per square meter in the sub-active layer.

[0034] In this application, by keeping the difference in the mass ratio of active material and conductive agent in adjacent sub-active layers and the difference in the areal density of adjacent sub-active layers within a suitable range, the gradient change of adjacent sub-active layers tends to be gentle, resulting in smaller performance deviations between different sub-active layers. This not only alleviates the deviation in the wetting ability of the electrolyte in different sub-active layers, enabling continuous and efficient transport of electrons and lithium ions between different sub-active layers and reducing the internal resistance of the positive electrode 100, but also strengthens the bonding force between different sub-active layers, improving the stability of the positive electrode 100 and the battery. Specifically, an appropriate difference in the mass ratio of active material ensures that the difference in the number of lithium ions transported in different sub-active layers is within a suitable range, thus ensuring relatively uniform lithium ion transport throughout the entire positive electrode 100; an appropriate difference in the mass ratio of conductive agent ensures that the difference in the number of electrons transported in different sub-active layers is within a suitable range, thus ensuring relatively uniform electron transport throughout the entire positive electrode 100, thereby promoting lithium ion transport; and an appropriate difference in areal density makes the gradient thickness structure or gradient pore structure formed in different sub-active layers more optimal, thereby better matching the transport of lithium ions and electrons and improving battery performance.

[0035] In some embodiments, the active layer 10 includes a first sub-active layer 101, a second sub-active layer 102, and a third sub-active layer 103 sequentially stacked on the current collector 20 along a first direction. In the first sub-active layer 101, the active material accounts for 96.5% to 96.8% of the mass of the first sub-active layer 101, for example, 96.5%, 96.6%, 96.7%, 96.8%, etc.; the conductive agent accounts for 1.6% to 1.9% of the mass of the first sub-active layer 101, for example, 1.6%, 1.65%, 1.7%, 1.75%, 1.8%, 1.85%, 1.9%, etc. It is understood that the remainder is a binder.

[0036] In this application, the active layer 10 is configured to include a first sub-active layer 101, a second sub-active layer 102, and a third sub-active layer 103 sequentially stacked on the current collector 20 along a first direction. This three-layer sub-active layer 10 provides a more complex structure while simplifying the fabrication process of the positive electrode 100. By ensuring that the proportion of active material in the first sub-active layer 101 is 96.5% to 96.8% of its mass, and the proportion of conductive agent is 1.6% to 1.9% of its mass, the relatively high proportion of conductive agent allows for the construction of a dense and uniform conductive network, improving the electron transport efficiency of the first sub-active layer 101. The appropriate proportion of active material ensures a moderate capacity for the first sub-active layer 101, avoiding any impact on the capacity of the positive electrode 100 and the battery. Simultaneously, the appropriate proportions of active material and conductive agent effectively mitigate self-discharge caused by excessive conductive agent, reducing its impact on the performance of the positive electrode 100 and the battery.

[0037] In some embodiments, in the second sub-active layer 102, the active material accounts for 96.8% to 97.1% of the mass of the second sub-active layer 102, for example, 96.8%, 96.9%, 97.0%, 97.1%, etc.; the conductive agent accounts for 1.3% to 1.6% of the mass of the second sub-active layer 102, for example, 1.3%, 1.35%, 1.4%, 1.45%, 1.5%, 1.55%, 1.6%, etc. It is understood that the balance is an adhesive.

[0038] In this application, the appropriate proportion of active material and conductive agent in the second sub-active layer 102 ensures the compatibility of lithium-ion and electron transport in the second sub-active layer 102. At the same time, the second sub-active layer 102, as an intermediate layer, can provide a buffer for the gradient changes of the first sub-active layer 101 and the third sub-active layer 103, making the gradient changes of the multilayer sub-active layers of the positive electrode 100 more continuous.

[0039] In some embodiments, in the third sub-active layer 103, the active material accounts for 97.1% to 97.4% of the mass of the third sub-active layer 103, for example, it can be 97.1%, 97.2%, 97.3%, 97.4%, etc.; the conductive agent accounts for 1.0% to 1.3% of the mass of the third sub-active layer 103, for example, it can be 1.0%, 1.05%, 1.1%, 1.15%, 1.2%, 1.25%, 1.3%, etc. It is understood that the balance is a binder.

[0040] In this application, by making the proportion of active material 97.1% to 97.4% of the mass of the third sub-active layer 103, the energy density and capacity of the positive electrode 100 and the battery can be improved. The appropriate proportion of conductive agent can provide a relatively rich conductive network for the third sub-active layer 103 while avoiding the impact of electron transport resistance on the performance of the positive electrode 100 and the battery.

[0041] In some embodiments, the active layer 10 includes a first sub-active layer 101, a second sub-active layer 102, and a third sub-active layer 103 sequentially stacked on the current collector 20 along a first direction, wherein the areal density of the first sub-active layer 101 is 5 g / m³. 2 ~15g / m 2 For example, it can be 5g / m 2 7g / m 2 9g / m 2 10g / m 2 11g / m 2 13g / m 2 15g / m 2 etc.; and / or, the areal density of the second sub-active layer 102 is 15 g / m². 2 ~25g / m 2 For example, it can be 15g / m 2 17g / m 2 19g / m 2 20g / m 2 21g / m 2 23g / m 2 25g / m 2 etc.; and / or, the areal density of the third sub-active layer 103 is 25 g / m³. 2 ~50g / m 2 For example, it can be 25g / m 2 30g / m 2 35g / m 2 40g / m 2 45g / m 2 50g / m 2 wait.

[0042] In this application, by ensuring that the areal density of the first sub-active layer 101, the second sub-active layer 102, and the third sub-active layer 103 is within a suitable range, not only are the thickness or porosity of the first sub-active layer 101, the second sub-active layer 102, and the third sub-active layer 103 suitable, resulting in a relatively short transport path for lithium ions and electrons and improving the transport efficiency of lithium ions and electrons, but also the content of active material and conductive agent in the first sub-active layer 101, the second sub-active layer 102, and the third sub-active layer 103 is suitable, further promoting the transport of lithium ions and electrons, and resulting in relatively high capacity and energy density of the positive electrode 100 and the battery. Furthermore, the suitable areal density of the first sub-active layer 101 ensures that its thickness or porosity is suitable, shortening the transport path of electrons from the active material to the current collector 20 and significantly reducing the internal resistance of the positive electrode 100. The second sub-active layer 102 can buffer the gradient changes of the first sub-active layer 101 and the third sub-active layer 103, making the gradient changes of the multi-layer sub-active layers of the cathode 100 more continuous. The appropriate areal density of the third sub-active layer 103 can carry more active materials, improving the capacity and energy density of the cathode 100 and the battery while ensuring the smooth transport of lithium ions and electrons.

[0043] In some embodiments, the D50 particle size of the active material is 50nm~100nm, for example, it can be 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, etc.

[0044] In this application, by setting the D50 particle size of the active material to 50nm~100nm, the nanoscale active material allows the areal density and thickness of the active layer 10 to be maintained at a low level. This results in higher lithium-ion and electron transport efficiency and lower transport resistance in the positive electrode 100, improving the fast-charging performance of the battery. At the same time, the battery generates less heat, improving battery stability. In addition, the smaller particle size of the active material provides favorable conditions for preparing a thinner positive electrode 100 (referring to the thickness of the active layer 10).

[0045] In some embodiments, the active material is at least one of lithium iron phosphate, lithium manganese iron phosphate, and lithium nickel cobalt manganese oxide.

[0046] In this application, by reasonably setting the types of active materials and selecting active materials with better stability and higher capacity, the capacity and energy density of the positive electrode 100 and the battery are relatively high.

[0047] For example, the conductive agent includes at least one of conductive carbon black, graphite, graphene, and carbon nanotubes.

[0048] For example, the adhesive includes at least one of polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF).

[0049] In some embodiments, the thickness of the active layer 10 is 20μm to 30μm, for example, it can be 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm, 30μm, etc.

[0050] In this application, by making the thickness of the active layer 10 20μm~30μm, the relatively small thickness results in a shorter lithium-ion transport path, lower lithium-ion transport resistance, and faster transport efficiency, thereby improving the fast-charging performance of the battery. Simultaneously, it reduces resistance and the heat generated during battery charging and discharging. Furthermore, the relatively thin active layer 10 results in a thinner positive electrode 100, allowing for a relatively larger number of positive electrode 100 sheets to be accommodated within the same battery casing volume, thus leading to higher energy density and capacity of the battery.

[0051] Typically, the preparation process of the positive electrode 100 involves first dispersing the active material in a solvent to prepare an active slurry, then applying the active slurry onto the current collector 20 using a wet coating process, followed by drying and rolling to obtain the electrode. However, due to the limitation of the thickness of the coating die pad used in the wet coating process, the coating thickness of the active slurry is relatively thick, resulting in a thicker active layer 10 with a higher areal density on the current collector 20. This affects the transport of lithium ions and electrons, and consequently, the fast-charging performance of the battery.

[0052] Secondly, embodiments of this application provide a method for preparing the positive electrode 100 provided in the first aspect of this application, wherein the positive electrode 100 is prepared by a dry spraying process.

[0053] In this application, a dry spraying process without slurry preparation is employed, allowing for better control of the thickness of the active layer 10 in the positive electrode 100. This results in a thinner active layer 10 with a lower areal density, leading to higher lithium-ion and electron transport efficiency and lower transport resistance in the positive electrode 100, thus improving the battery's fast-charging performance. Simultaneously, the battery generates less heat, enhancing its stability. Furthermore, the dry spraying process eliminates the need for solvents, reducing costs. Additionally, the dry spraying process allows for more precise control of the proportions of different substances in the active layer 10.

[0054] In some embodiments, the method for preparing the positive electrode 100 includes: At least two types of spray coatings are formulated from active substances, conductive agents, and binders, respectively. Different spray paints are sequentially sprayed on at least one side of the current collector 20, wherein the spraying distance is 150mm~300mm, for example, it can be 150mm, 200mm, 250mm, 300mm, etc. After drying and rolling, positive electrode 100 is obtained.

[0055] In this application, firstly, active materials, conductive agents, and binders are mixed evenly to prepare different spray coatings. This process does not require the addition of solvents; the solid active materials, conductive agents, and binders are directly mixed, providing favorable conditions for a dry spray coating process without slurry preparation. Then, different spray coatings are sequentially sprayed on at least one side of the current collector 20, controlling the spraying distance to be 150mm~300mm, thereby making the spray coating more uniform and dense on the current collector 20. Next, it is dried to remove any small amount of moisture that may have been introduced during the spraying process, and after roll forming, a positive electrode sheet 100 is obtained.

[0056] For example, in the step of sequentially spraying different paints on at least one side of the current collector 20, the spraying distance is 250 mm.

[0057] In some embodiments, the active material is lithium iron phosphate coated with metal-doped carbon, and the preparation method of lithium iron phosphate coated with metal-doped carbon includes: Iron source, lithium source, phosphorus source, carbon source, gas-generating agent, first metal compound dopant and solvent are mixed, dried and sintered once to obtain a primary sintered material. The primary sintering temperature is 350℃~400℃, for example, 350℃, 360℃, 370℃, 380℃, 390℃, 400℃, etc., and the sintering time is 3h~6h, for example, 3h, 4h, 5h, 6h, etc., and the first metal compound dopant is at least one of compounds including titanium, vanadium, magnesium and nickel. The primary sintering material and the second metal compound dopant are mixed and then sintered a second time to obtain metal-doped carbon-coated lithium iron phosphate. The secondary sintering temperature is 550℃~700℃, for example, 550℃, 570℃, 590℃, 600℃, 610℃, 630℃, 650℃, 670℃, 690℃, 700℃, etc., and the sintering time is 4h~7h, for example, 4h, 5h, 6h, 7h, etc., and the second metal compound dopant is at least one of the compounds including titanium, vanadium, magnesium, nickel, and aluminum.

[0058] In this application, by setting the active material as metal-doped carbon-coated lithium iron phosphate, the lithium iron phosphate exhibits high structural stability and long cycle life, thereby improving the stability and lifespan of the battery. In the preparation process of metal-doped carbon-coated lithium iron phosphate, an iron source, lithium source, phosphorus source, carbon source, gas-generating agent, first metal compound dopant, and solvent are first mixed to ensure uniform dispersion of these components in the solvent. Then, a primary sintering is performed at a relatively low temperature of 350℃~400℃. This relatively low temperature results in a relatively low rate of solid-phase reaction, leading to a smaller particle size in the obtained primary sintered material. Simultaneously, the presence of the first metal compound dopant also refines the particle size of the primary sintered material. It also improves the conductivity of the primary sinter; the presence of the carbon source can provide a reducing atmosphere for the reaction, avoid the formation of ferric iron, and provide favorable conditions for the preparation of high-purity lithium iron phosphate; the gas-generating agent can work synergistically with the carbon source to form a continuous and thin carbon coating layer on the surface of the primary sinter, achieving multi-layer carbon coating, refining the grains of the primary sinter, avoiding the agglomeration and growth of the primary sinter particles, and the gas generated by the gas-generating agent during the reaction will form continuous pores in the carbon coating layer, which is conducive to electrolyte wetting and improves conductivity. At the same time, the gas-generating agent can decompose residual trace carbon. Next, a second sintering process is performed, during which a second metal compound dopant is added, and the sintering temperature is controlled at 550℃~700℃. This relatively low sintering temperature ensures complete reaction to obtain high-purity, well-formed lithium iron phosphate, while the second metal compound dopant further refines the particle size and optimizes the structure of the carbon coating layer. This results in metal-doped carbon-coated lithium iron phosphate with smaller, more uniform particle size and higher conductivity, providing a basis for dry spraying. In other words, this application prepares nanoscale lithium iron phosphate through metal doping and low-temperature sintering coating processes. The resulting lithium iron phosphate has a diameter of no more than 100 nm and possesses high electrical performance. These nanoscale lithium iron phosphate particles can be used in dry spraying processes to form a thinner, lower-area-density active layer 10 on the positive electrode 100.

[0059] For example, the step of mixing an iron source, a lithium source, a phosphorus source, a carbon source, a gas-generating agent, a first metal compound dopant, and a solvent, followed by drying and a single sintering to obtain a primary sintered material includes: mixing the iron source, lithium source, phosphorus source, carbon source, gas-generating agent, first metal compound dopant, and solvent, grinding the mixture in a sand mill to a particle size of 0.3μm to 0.6μm, for example, 0.3μm, 0.4μm, 0.5μm, 0.6μm, etc., followed by spray drying and a single sintering to obtain a primary sintered material.

[0060] For example, the lithium source includes at least one of lithium carbonate, lithium oxide, lithium nitrate, lithium oxalate, lithium acetate, and lithium hydroxide.

[0061] For example, the iron source includes at least one of iron oxide, ferrous oxalate, ferrous sulfate, ferrous chloride, ferrous acetate, ferrous hydroxide, and ferrous hydroxide.

[0062] For example, the phosphorus source includes one or more of iron phosphate, phosphoric acid, ammonium phosphate, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, lithium phosphate, lithium monohydrogen phosphate, and lithium dihydrogen phosphate.

[0063] For example, the carbon source includes one or more of glucose, sucrose, maltose, starch, cellulose, polyethylene glycol, polyvinyl chloride, and polypyrrole.

[0064] For example, the solvent is at least one of water and ethanol.

[0065] In some embodiments, the amount of gas-generating agent added is 10% to 20% of the total mass of the iron source, lithium source, phosphorus source and carbon source, for example, it can be 10%, 12%, 14%, 15%, 16%, 18%, 20%, etc.; and / or, the amount of the first metal compound dopant added is 0.3% to 0.8% of the total mass of the iron source, lithium source, phosphorus source and carbon source, for example, it can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, etc.; and / or, the amount of the second metal compound dopant added is 0.1% to 0.5% of the total mass of the iron source, lithium source, phosphorus source and carbon source, for example, it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, etc.

[0066] In this application, by rationally setting the amount of gas-generating agent added, its synergistic effect with the carbon source is better achieved, forming sufficient and uniform pores in the carbon coating layer. By rationally setting the amount of the first metal compound dopant added, the particle size of the primary sintering material can be fully optimized, and a preliminary coating layer can be formed, providing favorable conditions for the preparation of small-particle-size, highly conductive lithium iron phosphate. By rationally setting the amount of the second metal compound dopant added, the particle size and conductivity of lithium iron phosphate are further optimized.

[0067] In some embodiments, before mixing the primary sintering material and the second metal compound dopant, the method further includes: pulverizing the primary sintering material to a D50 particle size of 0.2 μm to 0.5 μm, for example, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, etc.

[0068] In this application, by crushing the primary sintering material to a D50 particle size of 0.2μm~0.5μm, the particle size of the primary sintering material is small and more uniform, which provides favorable conditions for the uniformity of the secondary sintering.

[0069] For example, the primary sintering material is pulverized to a D50 particle size of 0.3 μm.

[0070] In some embodiments, mixing a primary sintering material with a second metal compound dopant and then sintering it a second time to obtain lithium iron phosphate includes: mixing a primary sintering material with a second metal compound dopant and then sintering it a second time to obtain a crude product; pulverizing the crude product to a D50 particle size of 0.2 μm to 0.5 μm, for example, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, etc., to obtain lithium iron phosphate.

[0071] In this application, the agglomerates are dispersed by crushing the crude product from secondary sintering, resulting in uniform lithium iron phosphate particles, which provides favorable conditions for the dry spraying preparation of the positive electrode 100.

[0072] For example, the crude product is pulverized to a D50 particle size of 0.3 μm.

[0073] Thirdly, embodiments of this application provide a battery, including a positive electrode 100 prepared by the method of preparing the positive electrode 100 provided in the first aspect of this application or the positive electrode 100 provided in the second aspect of this application.

[0074] In this application, by applying the positive electrode 100 provided in the first aspect of this application or the positive electrode 100 prepared in the second aspect of this application to a battery, the lithium ion and electron transport efficiency of the battery is faster during charging and discharging, thereby improving the fast charging performance of the battery. At the same time, the internal resistance of the electrode is smaller, thereby reducing the heat generated during charging and discharging, and improving the stability and service life of the battery.

[0075] The present application will be specifically described below through specific embodiments. These embodiments are only some embodiments of the present application and are not intended to limit the present application. Unless otherwise specified, the raw materials used in the following embodiments are all commercially available products.

[0076] Example 1 This embodiment provides a positive electrode 100, which includes an aluminum foil and an active layer 10. The aluminum foil has a thickness of 10 μm, and the active layer 10 has a thickness of 25 μm. The active layer 10 includes a first sub-active layer 101, a second sub-active layer 102, and a third sub-active layer 103 sequentially stacked on a current collector 20 along a first direction. The first sub-active layer 101, the second sub-active layer 102, and the third sub-active layer 103 all include metal-doped carbon-coated lithium iron phosphate, conductive carbon black, and PVDF. The D50 particle size of the metal-doped carbon-coated lithium iron phosphate is 100 nm. The areal density of the first sub-active layer 101 is 10 g / m³. 2 In the first sub-active layer 101, the mass percentage of metal-doped carbon-coated lithium iron phosphate is 96.7%, the mass percentage of conductive carbon black is 1.7%, and the mass percentage of PVDF is 1.6%; the areal density of the second sub-active layer 102 is 20 g / m³. 2In the second sub-active layer 102, the mass percentage of metal-doped carbon-coated lithium iron phosphate is 97.0%, the mass percentage of conductive carbon black is 1.4%, and the mass percentage of PVDF is 1.6%; the areal density of the third sub-active layer 103 is 40 g / m³. 2 In the third active layer 103, the mass percentage of metal-doped carbon-coated lithium iron phosphate is 97.2%, the mass percentage of conductive carbon black is 1.2%, and the mass percentage of PVDF is 1.6%.

[0077] The preparation method of the positive electrode 100 includes: (1) Preparation of metal-doped carbon-coated lithium iron phosphate: (11) Weigh iron phosphate, lithium carbonate, and glucose according to the molar ratio of lithium, iron, phosphorus, and carbon as 1.02:1.0:1.0:0.1. At the same time, control the amount of ammonium acetate added to be 15% of the total mass of iron source, lithium source, phosphorus source, and carbon source, and control the amount of titanium oxide added as the first metal compound dopant to be 0.5% of the total mass of iron source, lithium source, phosphorus source, and carbon source. Mix iron phosphate, lithium carbonate, glucose, ammonium acetate, titanium oxide, and water evenly, then grind them to a particle size of 0.5 μm through a sand mill, spray dry them, and then put them into a sintering furnace under a protective atmosphere (e.g., nitrogen or argon) for a first sintering. The temperature of the first sintering is 400℃ and the sintering time is 4h. After cooling, the first sintered material is obtained. (12) The obtained primary sintering material is crushed to a D50 particle size of 0.3 μm. The crushed primary sintering material and the second metal compound dopant ammonium metavanadate are mixed evenly. The amount of ammonium metavanadate added is controlled to be 0.3% of the total mass of iron source, lithium source, phosphorus source and carbon source. The mixture is injected into a sintering furnace under a protective atmosphere (e.g. nitrogen, argon) for secondary sintering. The temperature of the secondary sintering is 600℃ and the sintering time is 5h. After cooling, a crude product is obtained. The crude product is crushed to a D50 particle size of 0.3 μm to obtain metal-doped carbon-coated lithium iron phosphate.

[0078] (2) Prepare the first spray coating material according to the ratio of metal-doped carbon-coated lithium iron phosphate, conductive carbon black and PDVF in the first sub-active layer 101. Use a powder spraying machine to control the spraying distance to 250mm and spray the first spray coating material on one side of the aluminum foil. Control the surface density of the first sub-active layer 101 to the required surface density.

[0079] (3) Prepare a second spray coating material according to the ratio of metal-doped carbon-coated lithium iron phosphate, conductive carbon black and PDVF in the second sub-active layer 102. Use a powder spraying machine to control the spraying distance to 250mm and spray the second spray coating material onto the first sub-active layer 101. Control the surface density of the second sub-active layer 102 to the required surface density.

[0080] (4) Prepare the third spray coating material according to the ratio of metal-doped carbon-coated lithium iron phosphate, conductive carbon black and PDVF in the third sub-active layer 103. Use a powder spraying machine to control the spraying distance to 250mm and spray the third spray coating material onto the second sub-active layer 102. Control the surface density of the third sub-active layer 103 to the required surface density.

[0081] (5) The aluminum foil coated with the coating material is placed in an oven to dry, and then rolled to obtain the positive electrode 100. The positive electrode 100 is cut into pieces with a length of 300 mm and a width of 90 mm. The positive electrode 100 can be directly used in square short-blade aluminum-cased batteries.

[0082] Example 2 This embodiment provides a positive electrode 100. Compared with Embodiment 1, the only difference is that in the first sub-active layer 101, the mass ratio of metal-doped carbon-coated lithium iron phosphate is 96.8%, and the mass ratio of conductive carbon black is 1.6%. The rest is the same as in Embodiment 1, and will not be repeated here.

[0083] Example 3 This embodiment provides a positive electrode 100. Compared with Embodiment 1, the only difference is that in the first sub-active layer 101, the mass ratio of metal-doped carbon-coated lithium iron phosphate is 96.5%, and the mass ratio of conductive carbon black is 1.9%. The rest is the same as in Embodiment 1, and will not be repeated here.

[0084] Example 4 This embodiment provides a positive electrode 100. Compared with Embodiment 1, the only difference is that in the first sub-active layer 101, the mass ratio of metal-doped carbon-coated lithium iron phosphate is 96.4%, and the mass ratio of conductive carbon black is 2%. The rest is the same as in Embodiment 1, and will not be repeated here.

[0085] Example 5 This embodiment provides a positive electrode 100. Compared with Embodiment 1, the only difference is that in the second sub-active layer 102, the mass ratio of metal-doped carbon-coated lithium iron phosphate is 96.8%, and the mass ratio of conductive carbon black is 1.6%. The rest is the same as in Embodiment 1, and will not be repeated here.

[0086] Example 6 This embodiment provides a positive electrode 100. Compared with Embodiment 1, the only difference is that in the second sub-active layer 102, the mass ratio of metal-doped carbon-coated lithium iron phosphate is 97.1%, and the mass ratio of conductive carbon black is 1.3%. The rest is the same as in Embodiment 1, and will not be repeated here.

[0087] Example 7 This embodiment provides a positive electrode 100. Compared with Embodiment 1, the only difference is that in the third sub-active layer 103, the mass ratio of metal-doped carbon-coated lithium iron phosphate is 97.1%, and the mass ratio of conductive carbon black is 1.3%. The rest is the same as in Embodiment 1, and will not be repeated here.

[0088] Example 8 This embodiment provides a positive electrode 100. Compared with Embodiment 1, the only difference is that in the third sub-active layer 103, the mass ratio of metal-doped carbon-coated lithium iron phosphate is 97.4%, and the mass ratio of conductive carbon black is 1.0%. The rest is the same as in Embodiment 1, and will not be repeated here.

[0089] Example 9 This embodiment provides a positive electrode 100. Compared with Embodiment 1, the only difference is that in the third sub-active layer 103, the mass ratio of metal-doped carbon-coated lithium iron phosphate is 97.5%, and the mass ratio of conductive carbon black is 0.9%. The rest is the same as in Embodiment 1, and will not be repeated here.

[0090] Example 10 This embodiment provides a positive electrode 100, which differs from Embodiment 1 only in that, in the first sub-active layer 101, the mass percentage of lithium iron phosphate coated with metal-doped carbon is 96.75%, and the mass percentage of conductive carbon black is 1.65%; in the second sub-active layer 102, the mass percentage of lithium iron phosphate coated with metal-doped carbon is 96.8%, and the mass percentage of conductive carbon black is 1.6%; and in the third sub-active layer 103, the mass percentage of lithium iron phosphate coated with metal-doped carbon is 97.2%, and the mass percentage of conductive carbon black is 1.2%. The other contents are the same as in Embodiment 1 and will not be repeated here.

[0091] Example 11 This embodiment provides a positive electrode 100, which differs from Embodiment 1 only in that, in the first sub-active layer 101, the mass percentage of lithium iron phosphate coated with metal-doped carbon is 96.7%, and the mass percentage of conductive carbon black is 1.7%; in the second sub-active layer 102, the mass percentage of lithium iron phosphate coated with metal-doped carbon is 97.05%, and the mass percentage of conductive carbon black is 1.35%; and in the third sub-active layer 103, the mass percentage of lithium iron phosphate coated with metal-doped carbon is 97.1%, and the mass percentage of conductive carbon black is 1.3%. The other contents are the same as in Embodiment 1 and will not be repeated here.

[0092] Example 12 This embodiment provides a positive electrode 100, which differs from Embodiment 1 only in that the areal density of the first sub-active layer 101 is 5 g / m². 2 The thickness of the active layer 10 is 23 μm, and the rest is the same as in Example 1, so it will not be described again here.

[0093] Example 13 This embodiment provides a positive electrode 100, which differs from Embodiment 1 only in that the areal density of the first sub-active layer 101 is 15 g / m². 2 The thickness of the active layer 10 is 27 μm, and the rest is the same as in Example 1, so it will not be described again here.

[0094] Example 14 This embodiment provides a positive electrode 100, which differs from Embodiment 1 only in that the areal density of the second sub-active layer 102 is 15 g / m². 2 The thickness of the active layer 10 is 23 μm, and the rest is the same as in Example 1, so it will not be described again here.

[0095] Example 15 This embodiment provides a positive electrode 100, which differs from Embodiment 1 only in that the areal density of the second sub-active layer 102 is 25 g / m². 2 The thickness of the active layer 10 is 27 μm, and the rest is the same as in Example 1, so it will not be described again here.

[0096] Example 16 This embodiment provides a positive electrode 100, which differs from Embodiment 1 only in that the areal density of the third sub-active layer 103 is 25 g / m³. 2 The thickness of the active layer 10 is 20 μm, and the rest is the same as in Example 1, so it will not be described again here.

[0097] Example 17 This embodiment provides a positive electrode 100, which differs from Embodiment 1 only in that the areal density of the third sub-active layer 103 is 50 g / m³. 2 The thickness of the active layer 10 is 29 μm, and the rest is the same as in Example 1, so it will not be described again here.

[0098] Example 18 This embodiment provides a positive electrode 100, which differs from Embodiment 1 only in that the areal density of the first sub-active layer 101 is 10 g / m². 2 The areal density of the second sub-active layer 102 is 15 g / m². 2 The areal density of the third sub-active layer 103 is 35 g / m³. 2 The thickness of the active layer 10 is 27 μm, and the rest is the same as in Example 1, so it will not be described again here.

[0099] Example 19 This comparative example provides a positive electrode 100, which differs from Example 1 only in that the areal density of the first sub-active layer 101 is 12 g / m². 2The areal density of the second sub-active layer 102 is 15 g / m². 2 The areal density of the third sub-active layer 103 is 25 g / m³. 2 The thickness of the active layer 10 is 19 μm, and the rest is consistent with Example 1, so it will not be repeated here.

[0100] Example 20 This embodiment provides a positive electrode 100, which differs from Embodiment 1 only in that the particle size of the lithium iron phosphate coated with metal-doped carbon is 50nm. The rest is the same as Embodiment 1 and will not be described again here.

[0101] Example 21 This embodiment provides a positive electrode 100, which differs from Embodiment 1 only in that the particle size of the lithium iron phosphate coated with metal-doped carbon is 200nm. The rest is the same as in Embodiment 1 and will not be described again here.

[0102] Comparative Example 1 This comparative example provides a positive electrode 100, which differs from Example 1 only in that, in the second sub-active layer 102, the mass percentage of lithium iron phosphate coated with metal-doped carbon is 97.2%, and the mass percentage of conductive carbon black is 1.2%. In the third sub-active layer 103 and the first sub-active layer 101, the mass percentage of lithium iron phosphate coated with metal-doped carbon is 97%, and the mass percentage of conductive carbon black is 1.4%. The rest is consistent with Example 1 and will not be repeated here.

[0103] Comparative Example 2 This comparative example provides a positive electrode 100, which differs from Example 1 only in that, in the first sub-active layer 101, the mass percentage of lithium iron phosphate coated with metal-doped carbon is 97.2%, and the mass percentage of conductive carbon black is 1.2%; in the second sub-active layer 102, the mass percentage of lithium iron phosphate coated with metal-doped carbon is 97%, and the mass percentage of conductive carbon black is 1.4%; and in the third sub-active layer 103, the mass percentage of lithium iron phosphate coated with metal-doped carbon is 96.7%, and the mass percentage of conductive carbon black is 1.7%. The other contents are the same as in Example 1 and will not be repeated here.

[0104] Comparative Example 3 This comparative example provides a positive electrode 100, which differs from Example 1 only in that the areal density of both the first sub-active layer 101 and the second sub-active layer 102 is 20 g / m². 2 The thickness of the active layer 10 is 29 μm, and the rest is the same as in Example 1, so it will not be described again here.

[0105] Comparative Example 4 This comparative example provides a positive electrode 100, which differs from Example 1 only in that the areal density of both the second sub-active layer 102 and the third sub-active layer 103 is 40 g / m². 2 The thickness of the active layer 10 is 32 μm, and the rest is the same as in Example 1, so it will not be repeated here.

[0106] Comparative Example 5 This comparative example provides a positive electrode 100, which differs from Example 1 only in that the areal density of the first sub-active layer 101 is 10 g / m². 2 The areal density of the second sub-active layer 102 is 40 g / m². 2 The areal density of the third sub-active layer 103 is 20 g / m³. 2 Everything else is the same as in Example 1, and will not be repeated here.

[0107] Comparative Example 6 This comparative example provides a positive electrode 100, which differs from Example 1 only in that the areal density of the first sub-active layer 101 is 40 g / m². 2 The areal density of the second sub-active layer 102 is 20 g / m². 2 The areal density of the third sub-active layer 103 is 10 g / m³. 2 Everything else is the same as in Example 1, and will not be repeated here.

[0108] Comparative Example 7 This comparative example provides a positive electrode 100, which differs from Example 1 only in that the positive electrode 100 includes an aluminum foil and an active layer 10. The aluminum foil has a thickness of 10 μm, and the active layer 10 has a thickness of 25 μm. The active layer 10 comprises metal-doped carbon-coated lithium iron phosphate, conductive carbon black, and PVDF. The D50 particle size of the metal-doped carbon-coated lithium iron phosphate is 100 nm. The areal density of the active layer 10 is 10 g / m³. 2 In the active layer 10, the mass percentage of metal-doped carbon-coated lithium iron phosphate is 97%, the mass percentage of conductive carbon black is 1.4%, the mass percentage of PVDF is 1.6%, and the other components are consistent with those in Example 1, and will not be repeated here.

[0109] The positive electrode sheets 100 of Examples 1-21 and Comparative Examples 1-7 were assembled into batteries and their performance was tested. The results are shown in Table 1.

[0110] The battery assembly process is as follows: Graphite, acetylene black, and sodium carboxymethyl cellulose are weighed in a mass percentage ratio of 97.2%:1.3%:1.5% and dispersed in deionized water to prepare a negative electrode slurry with a solid content of 50%. The negative electrode slurry is coated on both sides of a copper foil, and after baking and rolling, a negative electrode sheet is obtained. The positive electrode sheets from Examples 1-21 and Comparative Examples 1-7 are cut into 100 pieces and stacked with a separator and negative electrode sheets using a stacking machine to form a core package. The core package is placed in an aluminum shell, and the electrode tabs are welded to the cover plate posts. After a first injection of electrolyte, high-temperature formation is performed, followed by a second injection of electrolyte. After sealing with nails, capacity testing is conducted, and the battery is then coated and produced. The battery has a defined length of 310 mm, a width of 100 mm, and a thickness of 30 mm.

[0111] It is understood that the parameters of the spraying equipment used for the first sub-active layer 101, the second sub-active layer 102, and the third sub-active layer 103 in the above embodiments and comparative examples are the same, that is, the porosity of the first sub-active layer 101, the second sub-active layer 102, and the third sub-active layer 103 is the same, and the areal density is mainly controlled by the thickness of the first sub-active layer 101, the second sub-active layer 102, and the third sub-active layer 103. With the battery volume remaining constant, although the thickness of the positive electrode sheet 100 varies in different embodiments and comparative examples, resulting in variations in the number of stacked sheets accommodated in the battery casing, the variation in the stacked sheet thickness is relatively small, and the thickness of the active layer 10 in the entire battery remains essentially unchanged.

[0112] DCR testing: The resistance of the battery at 50% SOC and 1C discharge was tested at 25℃ using the discharge method. Fast charging time test: the time it takes to charge the battery from 10% SOC to 80% SOC; Energy density was measured using an electrochemical workstation.

[0113] Table 1

[0114] As shown in Table 1, Examples 1-4, the battery performance changes when the mass ratio of metal-doped carbon-coated lithium iron phosphate and conductive carbon black in the first sub-active layer 101 is changed. When the mass ratio of metal-doped carbon-coated lithium iron phosphate in the first sub-active layer 101 is between 96.5% and 96.8%, the battery performance is relatively good. When the mass ratio of metal-doped carbon-coated lithium iron phosphate in the first sub-active layer 101 is low, on the one hand, the gradient structure of the positive electrode 100 changes significantly, thus affecting the synergistic effect between different sub-active layers; on the other hand, the adaptability of the proportion of metal-doped carbon-coated lithium iron phosphate and conductive carbon black in the first sub-active layer 101 is poor, thus affecting the battery performance.

[0115] Data from Examples 1 and 5-6 show that when the proportions of metal-doped carbon-coated lithium iron phosphate and conductive carbon black in the second sub-active layer 102 vary within a certain range, the overall performance of the battery is better.

[0116] Data from Examples 1 and 7-9 show that when the mass percentage of metal-doped carbon-coated lithium iron phosphate in the third sub-active layer 103 is between 97.1% and 97.4%, a good gradient change can be achieved between the different sub-active layers of the positive electrode 100 within this range. Simultaneously, a suitable proportion of conductive carbon black in the third sub-active layer 103 can form a relatively dense and uniform conductive network, thereby improving lithium-ion transport efficiency. A suitable proportion of metal-doped carbon-coated lithium iron phosphate enables the battery to achieve a good energy density. However, when the mass percentage of metal-doped carbon-coated lithium iron phosphate in the third sub-active layer 103 is too high, the integrity of the electron transport network in the third sub-active layer 103 is poor, and the metal-doped carbon-coated lithium iron phosphate agglomerates, thus affecting battery performance.

[0117] The data from Examples 10-11 further illustrate that when the difference in the metal-doped carbon coating of lithium iron phosphate or conductive carbon black in adjacent sub-active layers is too small, the performance of the battery will be affected to some extent. This is mainly because a small deviation makes the composition of adjacent sub-active layers tend to be the same, resulting in weak capillary action when the electrolyte is wetting between lithium iron phosphate layers, leading to poor wetting effect. When the electrolyte diffuses between capillaries, a suitable gradient structure can increase the pressure difference between adjacent sub-active layers, thereby promoting electrolyte wetting and improving battery performance.

[0118] Data from Examples 1 and 12-17 show that when the areal density of different sub-active layers varies within a certain range, the thicknesses of the first sub-active layer 101, the second sub-active layer 102, and the third sub-active layer 103 become suitable, resulting in relatively short transport paths for lithium ions and electrons, thus improving the transport efficiency of lithium ions and electrons and consequently enhancing battery performance. Data from Examples 18-19 show that when the areal density difference between adjacent sub-active layers is too large or too small, the battery performance is adversely affected, further demonstrating that a suitable gradient of areal density variation can achieve better synergy among different sub-active layers, thereby improving battery performance.

[0119] As can be seen from the data of Examples 1 and 20-21, when the D50 particle size of the metal-doped carbon-coated lithium iron phosphate is less than 100 nm, the distribution of the metal-doped carbon-coated lithium iron phosphate and the conductive carbon black is more uniform, and the conductive carbon black on the surface of the metal-doped carbon-coated lithium iron phosphate is more concentrated, thereby improving the transmission efficiency of lithium ions and electrons and improving the performance of the battery.

[0120] As can be seen from the data of Comparative Examples 1-2 and Comparative Example 7, when the gradient changes of the metal-doped carbon-coated lithium iron phosphate and conductive carbon black in different sub-active layers are different from or have no gradient change trend in the embodiments of this application, the battery performance is significantly worse. This is mainly because the positive electrode 100 of Comparative Examples 1-2 and Comparative Example 7 cannot effectively wet the electrolyte in different layers, thereby affecting the electron transport efficiency and ion transport efficiency, resulting in poor battery performance.

[0121] As can be seen from the data of Comparative Examples 3 to 6, when the variation of areal density in different sub-active layers is different from the gradient variation trend of the embodiments of this application, the performance of the battery is significantly worse, which further illustrates that the gradient structure of this application can alleviate the reduction in battery performance caused by the deviation of electrolyte wetting ability in different sub-active layers.

[0122] In summary, this application achieves a high-performance battery by utilizing the specific gradient structure formed by different sub-active layers and the synergistic effect of the proportion and areal density of lithium iron phosphate coated with metal-doped carbon and conductive carbon black in different sub-active layers.

[0123] The above provides a detailed description of a positive electrode 100, its preparation method, and the battery provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A positive electrode (100), characterized in that, include: Current collector(20); and An active layer (10) is disposed on at least one side of the current collector (20). The active layer (10) includes at least two sub-active layers that are sequentially stacked on the current collector (20) along a first direction. Each sub-active layer includes an active material and a conductive agent. In the direction away from the current collector (20), the mass percentage of the active material in different sub-active layers tends to increase, the mass percentage of the conductive agent tends to decrease, and the areal density of the sub-active layer tends to increase.

2. The positive electrode (100) according to claim 1, characterized in that, In adjacent sub-active layers, the difference in the mass percentage of the active substance is 0.1% to 0.5%; and / or, In adjacent sub-active layers, the difference in the mass percentage of the conductive agent is 0.1% to 0.5%; and / or, The difference in areal density between adjacent sub-active layers is 5 g / m². 2 ~30g / m 2 .

3. The positive electrode (100) according to claim 1 or 2, characterized in that, The active layer (10) comprises a first sub-active layer (101), a second sub-active layer (102), and a third sub-active layer (103) sequentially stacked on the current collector (20) along a first direction. In the first sub-active layer (101), the active substance accounts for 96.5% to 96.8% of the mass of the first sub-active layer (101), and the conductive agent accounts for 1.6% to 1.9% of the mass of the first sub-active layer (101); and / or, In the second sub-active layer (102), the active material accounts for 96.8% to 97.1% of the mass of the second sub-active layer (102), and the conductive agent accounts for 1.3% to 1.6% of the mass of the second sub-active layer (102); and / or, In the third sub-active layer (103), the active substance accounts for 97.1% to 97.4% of the mass of the third sub-active layer (103), and the conductive agent accounts for 1.0% to 1.3% of the mass of the third sub-active layer (103).

4. The positive electrode (100) according to claim 1 or 2, characterized in that, The active layer (10) includes a first sub-active layer (101), a second sub-active layer (102), and a third sub-active layer (103) sequentially stacked on the current collector (20) along a first direction. The areal density of the first sub-active layer (101) is 5 g / m³. 2 ~15g / m 2 ; and / or, The areal density of the second sub-active layer (102) is 15 g / m². 2 ~25g / m 2 ; and / or, The areal density of the third sub-active layer (103) is 25 g / m³. 2 ~50g / m 2 .

5. The positive electrode sheet (100) according to any one of claims 1 to 4, characterized in that, The D50 particle size of the active material is 50 nm to 100 nm; and / or, The active material is at least one selected from lithium iron phosphate, lithium manganese iron phosphate, and lithium nickel cobalt manganese oxide; and / or, The thickness of the active layer (10) is 20μm~30μm.

6. A method for preparing a positive electrode sheet (100) according to any one of claims 1 to 5, characterized in that, The positive electrode (100) is prepared by dry spraying process.

7. The method for preparing the positive electrode sheet (100) according to claim 6, characterized in that, include: At least two spray coatings are formulated from active substances, conductive agents, and binders, respectively. Different spray coatings are sequentially sprayed on at least one side of the current collector (20), wherein the spraying distance is 150mm~300mm; After drying and rolling, the positive electrode sheet (100) is obtained.

8. The positive electrode (100) according to claim 7, characterized in that, The active material is lithium iron phosphate coated with metal-doped carbon, and the preparation method of the lithium iron phosphate coated with metal-doped carbon includes: Iron source, lithium source, phosphorus source, carbon source, gas generating agent, first metal compound dopant and solvent are mixed, dried and sintered once to obtain a primary sintered material, wherein the temperature of the primary sintering is 350℃~400℃, and the first metal compound dopant is at least one of a compound including titanium, vanadium, magnesium and nickel. The primary sintering material and the second metal compound dopant are mixed and then sintered a second time to obtain the metal-doped carbon-coated lithium iron phosphate. The temperature of the second sintering is 550℃~700℃, and the second metal compound dopant is at least one of a compound including titanium, vanadium, magnesium, nickel, and aluminum.

9. The positive electrode (100) according to claim 8, characterized in that, The amount of the gas-generating agent added is 10% to 20% of the total mass of the iron source, the lithium source, the phosphorus source, and the carbon source; and / or, The amount of the first metal compound dopant added is 0.3% to 0.8% of the total mass of the iron source, the lithium source, the phosphorus source, and the carbon source; and / or, The amount of the second metal compound dopant added is 0.1% to 0.5% of the total mass of the iron source, the lithium source, the phosphorus source and the carbon source.

10. The positive electrode (100) according to claim 8, characterized in that, Before mixing the primary sintered material and the second metal compound dopant, the method further includes: pulverizing the primary sintered material to a D50 particle size of 0.2 μm to 0.5 μm; and / or, The step of mixing the primary sintering material with the second metal compound dopant and then sintering it a second time to obtain the lithium iron phosphate includes: mixing the primary sintering material with the second metal compound dopant and then sintering it a second time to obtain a crude product; and then pulverizing the crude product to a D50 particle size of 0.2 μm to 0.5 μm to obtain the lithium iron phosphate.

11. A battery, characterized in that, The positive electrode (100) includes the positive electrode (100) prepared by the preparation method of the positive electrode (100) according to any one of claims 1 to 5 or the positive electrode (100) according to any one of claims 6 to 10.

Images