Positive electrode sheet and battery

Abstract

The application provides a positive electrode sheet and a battery, the positive electrode sheet comprising a positive electrode current collector and a positive electrode active material coating arranged on at least one surface of the positive electrode current collector; the positive electrode active material coating comprising a positive electrode active material, a conductive material and a binder; wherein the relationship between the compaction density PD of the positive electrode sheet and the content W of the conductive material and the content of the binder satisfies: 0.27<=W / (PD*Wd)<=1.12. d The content of the binder satisfies: 0.27<=W / (PD*Wd)<=1.12. n The content of the binder satisfies: 0.27<=W / (PD*Wd)<=1.12. n When the content of the conductive material and the binder and the compaction density of the positive electrode sheet provided by the application satisfy the above relationship and range, the battery using the positive electrode sheet has better conductive performance and cycle capacity.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a positive electrode and a battery. Background Technology

[0002] Currently, the demand for long-range new energy vehicles is driving increasingly higher requirements for battery energy density. Using thick electrodes with high-load-density active materials is one of the most practical strategies. However, during long-term cycling, thick electrodes experience severe electrochemical performance degradation, resulting in unsatisfactory power performance and increasingly poor capacity retention. Due to differences in the fundamental properties of thick electrode materials, such as conductivity and particle size, this cycling degradation phenomenon is particularly pronounced in lithium manganese iron phosphate (LFP) batteries (compared to ternary and lithium iron phosphate materials). Therefore, current LFP thick electrode batteries suffer from poor conductivity and severe degradation in the later stages of cycling. Summary of the Invention

[0003] The embodiments of the present invention provide a positive electrode and a battery that have both good conductivity and high cycle life.

[0004] To achieve the above objectives, according to a first aspect of this application, a positive electrode sheet is provided, comprising a positive current collector and a positive active material coating disposed on at least one surface of the positive current collector;

[0005] The positive electrode active material coating includes a positive electrode active material, a conductive material, and a binder;

[0006] The compaction density PD of the positive electrode sheet is related to the content W of the conductive material. d and the content W of the adhesive n The relation satisfies: 0.27 ≤ W n / (PD*Wd)≤1.12.

[0007] In some embodiments, the conductive material includes a primary conductive agent and an auxiliary conductive agent, wherein the primary conductive agent is granular and the auxiliary conductive agent has a linear structure.

[0008] In some embodiments, the primary conductive agent comprises carbon black, and the secondary conductive agent comprises at least one of carbon nanotubes and carbon nanofibers.

[0009] In some embodiments, the conductive material comprises carbon black and carbon nanotubes, wherein the mass percentage a of the carbon black ranges from 0.3% to 1.8%, the mass percentage b of the carbon nanotubes ranges from 0.2% to 0.8%, and a > b.

[0010] In some embodiments, the conductive material comprises carbon black and carbon nanofibers, wherein the mass percentage a of the carbon black ranges from 0.3% to 1.8%, the mass percentage c of the carbon nanofibers ranges from 0.2% to 0.8%, and a > c.

[0011] In some embodiments, the conductive material includes carbon black, carbon nanotubes, and carbon nanofibers, wherein the mass percentage a of the carbon black ranges from 0.3% to 1.8%, the mass percentage b of the carbon nanotubes ranges from 0.2% to 0.8%, the mass percentage c of the carbon nanofibers ranges from 0.2% to 0.8%, and a ≥ b ≥ c.

[0012] In some embodiments, the thickness of the positive electrode sheet is d, 200 μm ≤ d ≤ 250 μm; the areal density of the positive electrode sheet is SD, 480 g / m³. 2 ≤SD≤560g / m 2 The compaction density of the positive electrode sheet is PD, 2.3 g / cm³. 3 ≤PD≤2.5g / cm 3 .

[0013] In some embodiments, the positive electrode active material includes lithium manganese iron phosphate.

[0014] In some embodiments, in the positive electrode active material coating, the mass percentage of the positive electrode active material ranges from 96% to 98%, the mass percentage of the conductive material ranges from 0.8% to 1.8%, and the mass percentage of the binder ranges from 1.2% to 2.2%.

[0015] According to a second aspect of this application, a battery is provided, comprising a positive electrode as described in the first aspect.

[0016] This application provides a positive electrode sheet and a battery. The positive electrode sheet includes a positive active material coating, which comprises a positive active material, a conductive material, and a binder. The compaction density PD of the positive electrode sheet is related to the content W of the conductive material. d and the content of adhesive W n The relation satisfies: 0.27 ≤ W n / (PD*Wd)≤1.12. This application combines the compaction density PD of the positive electrode and the content of conductive material W. d The content of adhesive W n The cooperative relationship between them, when W n / (PD*W dWhen the concentration of the positive electrode active material coating is between 0.27 and 1.12, the coating has a suitable compaction density, a suitable content of conductive material and a suitable content of binder, so that the battery using this positive electrode has both good conductivity and high cycle capability. Attached Figure Description

[0017] 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 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.

[0018] Figure 1 This is a schematic diagram of the structure of a positive electrode sheet provided in an embodiment of this application. Detailed Implementation

[0019] 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 a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the protection scope of this application.

[0020] This application provides a positive electrode sheet, which includes a positive current collector and a positive active material coating disposed on at least one surface of the positive current collector; the positive active material coating includes a positive active material, a conductive material, and a binder; wherein, the compaction density PD of the positive electrode sheet is related to the content W of the conductive material. d and the content of adhesive W n The relation satisfies: 0.27 ≤ W n / (PD*Wd)≤1.12.

[0021] Please see Figure 1 This is a schematic diagram of a positive electrode sheet provided in an embodiment of this application. The positive electrode sheet 10 includes a positive current collector 1, which has a first surface 11 and a second surface 12 facing away from each other. A positive active material coating 2 is located on the first surface 11 and / or the second surface 12. In this application, the material of the positive current collector 1 can be a metal, such as aluminum or copper, but is not limited thereto. The positive active material coating 2 is formed on the first surface 11 and / or the second surface 12 of the positive current collector 1 through processes such as coating, drying, and rolling. Specifically, as shown... Figure 1 As shown, the positive electrode sheet 10 can be coated on both sides of the positive current collector 1 by a single-layer coating process, that is, the positive active material coating 2 on the first surface 11 and the second surface 12 of the positive current collector 1 is a single-layer film.

[0022] The compaction density (PD) of the positive electrode sheet refers to the ratio of the areal density (SD) of the positive electrode sheet after compaction to the thickness (d) of the positive electrode sheet, PD = SD / d, where d does not include the thickness of the positive electrode current collector. The compaction density (PD) has a significant impact on battery performance, closely related to the specific capacity, efficiency, internal resistance, and cycle performance of the battery. Generally, a higher compaction density results in a higher battery capacity; therefore, compaction density is considered an important reference indicator for the energy density of electrode materials. However, both excessively high and low compaction densities are detrimental to lithium-ion intercalation and extraction. Excessive compaction density leads to greater compression between electrode material particles, resulting in smaller porosity and fewer channels for ion transport. This reduces the electrode's ability to absorb electrolyte, making it difficult for the electrolyte to wet the electrode, leading to greater polarization loss and battery degradation during cycling, and a significant increase in internal resistance. Conversely, insufficient compaction density increases ion transport distance and hinders capacity improvement. Therefore, a suitable compaction density can increase battery capacity, reduce internal resistance, decrease polarization loss, and extend battery cycle life. In this application, the compaction density (PD) of the positive electrode sheet ranges from 2.3 g / cm³. 3 ≤PD≤2.5g / cm 3 When the compaction density (PD) of the positive electrode is within the above range, the battery has a high capacity without affecting the dynamic performance.

[0023] The areal density (SD) of the positive electrode refers to the density of the positive electrode active material coating per unit area of ​​the positive electrode current collector. In this application, the areal density (SD) of the positive electrode refers to the bifacial areal density, and the range of the areal density (SD) of the positive electrode is 480 g / m². 2 ≤SD≤560g / m 2 When the areal density (SD) of the positive electrode is within the above-mentioned range, the battery has good range. When the areal density (SD) is too low, the battery capacity is too small, resulting in insufficient range; when the areal density (SD) is too high, there are problems with dynamics and manufacturing costs increase.

[0024] In this application, the thickness d of the positive electrode sheet is in the range of 200μm≤d≤250μm. The positive electrode sheet of this application is a thick electrode. Using a thick electrode can improve the energy density of the battery and improve the battery life.

[0025] In existing technologies, thick electrodes suffer from poor conductivity and severe degradation in the later stages of cycling. This application addresses these issues by adjusting the compaction density (PD) of the positive electrode and the content (W) of the conductive material. d The content of adhesive W n The coordination relationship between them ensures that 0.27 ≤ W n / (PD*Wd)≤1.12, when W n / (PD*W dWhen the concentration of the positive electrode is between 0.27 and 1.12, the positive electrode sheet has a suitable compaction density, a suitable content of conductive material and binder. This can improve the capacity and conductivity of the positive electrode sheet while also ensuring the adhesion between the positive electrode sheet and the positive current collector, thereby improving the cycle capability of the battery under thick electrodes and enhancing the overall performance of the battery.

[0026] In this application, the positive electrode active material coating includes a positive electrode active material, a conductive material, and a binder, wherein the mass percentage W of the positive electrode active material is... h The range is 96%–98%, and the mass percentage of conductive material W d The range is 0.8% to 1.8%, W (by mass) of the adhesive. n The range is 1.2% to 2.2%. The total mass percentage of the positive electrode active material coating, the mass percentage of the conductive material, and the mass percentage of the binder, W, constitutes the total mass percentage of the positive electrode active material. h +W d +W n =100%. When the contents of the positive electrode active material, conductive material, and binder are within the above range, the positive electrode sheet has good conductivity and the battery has good cycle capability.

[0027] In this application, the positive electrode active material can be lithium manganese iron phosphate (LMFP). In the prior art, thick LMFP electrodes suffer from poor conductivity and severe degradation in the later stages of cycling. This application addresses these issues by adjusting the compaction density (PD) of the positive electrode sheet and the content of conductive material (W). d The content of adhesive W n Satisfying 0.27≤W n The relationship of / (PD*Wd)≤1.12 gives thick electrode lithium manganese iron phosphate batteries better conductivity and cycle life.

[0028] In this application, the conductive material includes a primary conductive agent and an auxiliary conductive agent. The primary conductive agent is particulate, such as carbon black, acetylene black, and Ketjen black. The auxiliary conductive agent has a linear structure, which can be a long-chain structure or a tubular structure. These linear conductive agents have a large aspect ratio. Long-chain conductive agents include carbon nanofibers, and tubular conductive agents include carbon nanotubes. The primary conductive agent, being particulate, has strong conductivity and good dispersibility. The auxiliary conductive agent, being linear, can form a network structure, constructing conductive pathways. By adding a linear auxiliary conductive agent to the primary conductive agent, the primary and auxiliary conductive agents together form a conductive network, which helps to improve the overall conductivity of the conductive material, thereby improving the conductivity of the positive electrode.

[0029] In some embodiments, the primary conductive agent includes carbon black, and the secondary conductive agent includes at least one of carbon nanotubes and carbon nanofibers. The carbon black has a particle size ranging from 10 nm to 50 nm. Carbon black possesses high conductivity, and its small particle size, large specific surface area, and easy dispersion are beneficial for improving conductivity and electrochemical performance. Carbon nanotubes have a hollow structure, with a diameter ranging from 1 nm to 20 nm and a length ranging from 0.5 μm to 15 μm. Carbon nanotubes can withstand volume changes in the positive electrode active material during battery expansion, reducing particle breakage and structural damage. Carbon nanofibers have a linear, non-hollow structure, with a diameter ranging from 60 nm to 200 nm and a length ranging from 30 μm to 100 μm. They can bridge the gaps between positive electrode active material particles, ensuring electron and ion transport. Both carbon nanotubes and carbon nanofibers are linear structures that can form a network structure, together with the primary conductive agent, forming a conductive network, which is beneficial for improving the overall conductivity of the conductive material, thereby enhancing the conductivity of the positive electrode.

[0030] In one embodiment, the conductive material includes carbon black and carbon nanotubes, wherein the mass percentage a of carbon black ranges from 0.3% to 1.8%, the mass percentage b of carbon nanotubes ranges from 0.2% to 0.8%, and a > b.

[0031] In this embodiment, carbon nanotubes can form a conductive network with carbon black, and the hollow structure of carbon nanotubes can serve as a particle transport channel, effectively improving the conductivity of the conductive material. The content of carbon nanotubes must be less than the content of carbon black. Excessive carbon nanotube content can lead to decreased porosity of the conductive material, poor electrolyte wetting, and reduced dispersibility, making it prone to aggregation. This increases local charge and side reactions, ultimately negatively impacting conductivity.

[0032] In one embodiment, the conductive material includes carbon black and carbon nanofibers, wherein the mass percentage a of carbon black ranges from 0.3% to 1.8%, the mass percentage c of carbon nanofibers ranges from 0.2% to 0.8%, and a > c.

[0033] In this embodiment, carbon nanofibers can form a conductive network with carbon black. Carbon nanofibers, with their long-chain structure, more easily form a network structure, constructing conductive pathways between carbon black particles and effectively improving the conductivity of the conductive material. The content of carbon nanofibers must be less than the content of carbon black. Excessive carbon nanofiber content can lead to reduced porosity of the conductive material, poor electrolyte wetting, and difficulty in dispersing the active material and carbon black, resulting in agglomeration and ultimately affecting conductivity.

[0034] In one embodiment, the conductive material includes carbon black, carbon nanotubes, and carbon nanofibers, wherein the mass percentage a of carbon black ranges from 0.3% to 1.8%, the mass percentage b of carbon nanotubes ranges from 0.2% to 0.8%, and the mass percentage c of carbon nanofibers ranges from 0.2% to 0.8%, and a ≥ b ≥ c.

[0035] In this embodiment, carbon nanotubes, carbon nanofibers, and carbon black together form a conductive network. Carbon nanotubes have better conductivity, higher strength, and greater flexibility than carbon nanofibers, which can prevent failure caused by volume expansion and contraction of the cathode material during charging and discharging. Carbon nanofibers have slightly lower conductivity and stability than carbon nanotubes, but they have a larger diameter and longer length, and can be combined with carbon nanotubes to further improve the conductivity of the conductive material and enhance its overall performance.

[0036] In this application, the binder is used to increase the adhesion between the various materials of the positive electrode active material coating and the adhesion between the positive electrode active material coating and the positive electrode current collector, thereby improving the stability and lifespan of the battery. The binder may be one or more of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), etc.

[0037] This application also provides a method for preparing a positive electrode sheet, comprising:

[0038] Positive electrode active material, conductive material and binder are added to solvent and mixed to form positive electrode slurry;

[0039] The positive electrode slurry is coated onto at least one surface of the positive electrode current collector, and then dried and rolled to form a positive electrode sheet;

[0040] Among them, the compaction density PD of the positive electrode sheet is related to the content of conductive material W. d and the content of adhesive W n The relation satisfies: 0.27 ≤ W n / (PD*Wd)≤1.12.

[0041] This application also provides a battery, which includes a battery casing and an electrolyte, a negative electrode, a separator, and a positive electrode as described above, located within the battery casing.

[0042] The battery casing has a receiving cavity, in which the negative electrode, separator, and positive electrode are sequentially stacked, and the electrolyte is contained within the receiving cavity. The battery casing can be made of metal, such as aluminum or steel.

[0043] The negative electrode sheet includes a negative current collector and a negative active material coating disposed on at least one surface of the negative current collector. The negative active material coating may include graphite, a conductive agent, a binder, etc. The conductive agent may be carbon black, acetylene black, Ketjen black, etc., and the binder may be styrene-butadiene rubber (SBR) solution, polyacrylate solution, etc.

[0044] The positive electrode and battery of this application will be further described below through specific embodiments.

[0045] 1. Battery manufacturing methods

[0046] (1) Preparation of positive electrode sheet

[0047] S11, The positive electrode active material, conductive material and binder are combined in W... h :W d :W n The mass ratio of the mixture was added to N-methylpyrrolidone (NMP) and mixed thoroughly to obtain a positive electrode slurry; and

[0048] S12. A single layer of positive electrode slurry is coated onto the two surfaces of the positive electrode current collector, and after drying, a positive electrode sheet is obtained by a rolling process. The areal density of the positive electrode sheet is SD, and the compaction density of the positive electrode sheet is PD.

[0049] (2) Preparation of negative electrode sheet

[0050] S21. Graphite, carbon black, and styrene-butadiene rubber (SBR) are mixed in a mass ratio of 97.3:1.5:1.2 and added to a solvent, then stirred until homogeneous to obtain a negative electrode slurry; and

[0051] S22. The negative electrode slurry is coated in a single layer onto the two surfaces of the negative electrode current collector, and after drying, the negative electrode sheet is obtained by a rolling process.

[0052] S3, Battery Preparation

[0053] After vacuum drying, the positive electrode, separator, and negative electrode are assembled and then cut, die-cut, and slit before being placed inside the battery casing. Electrolyte is then injected under high temperature and negative pressure to assemble a square aluminum-cased battery.

[0054] Batteries corresponding to Examples 1 to 8 were prepared using the battery preparation method described above. The preparation methods for the positive electrode, negative electrode, and battery in Examples 1 to 8 are the same and will not be repeated here. The differences between Examples 1 to 8 lie only in the ratio of the positive active material, conductive material, and binder in the positive electrode, as well as the composition and ratio of the conductive agent or the compaction density. See the following examples and Table 1 for details.

[0055] Example 1:

[0056] The positive electrode active material is lithium manganese iron phosphate (LMFP), the conductive materials are carbon black, carbon nanotubes and carbon nanofibers, and the binder is polyvinylidene fluoride (PVDF).

[0057] The mass ratio of positive electrode active material, conductive material and binder W h :W d :W n =97:1.3:1.7; The mass ratio of carbon black, carbon nanotubes, and carbon nanofibers in the conductive material is a:b:c = 0.6:0.4:0.3;

[0058] The areal density of the positive electrode is SD = 500 g / m². 2 The compaction density PD of the positive electrode sheet is 2.3 g / cm³. 3 .

[0059] Example 2:

[0060] The positive electrode active material is lithium manganese iron phosphate (LMFP), the conductive materials are carbon black, carbon nanotubes and carbon nanofibers, and the binder is polyvinylidene fluoride (PVDF).

[0061] The mass ratio of positive electrode active material, conductive material and binder W h :W d :W n = 96.2:1.8:2; The mass ratio of carbon black, carbon nanotubes, and carbon nanofibers in the conductive material is a:b:c = 0.8:0.6:0.4;

[0062] The areal density of the positive electrode is SD = 500 g / m². 2 The compaction density PD of the positive electrode sheet is 2.45 g / cm³. 3 .

[0063] Example 3:

[0064] The positive electrode active material is lithium manganese iron phosphate (LMFP), the conductive material is carbon black, and the binder is polyvinylidene fluoride (PVDF).

[0065] The mass ratio of positive electrode active material, conductive material and binder W h :W d :W n = 97:1.3:1.7;

[0066] The areal density of the positive electrode is SD = 500 g / m². 2 The compaction density PD of the positive electrode sheet is 2.3 g / cm³. 3 .

[0067] Example 4:

[0068] The positive electrode active material is lithium manganese iron phosphate (LMFP), the conductive materials are carbon black and carbon nanotubes, and the binder is polyvinylidene fluoride (PVDF).

[0069] The mass ratio of positive electrode active material, conductive material and binder W h :W d :W n =97:1.3:1.7; The mass ratio of carbon black to carbon nanotubes in conductive materials is a:b = 0.7:0.6;

[0070] The areal density of the positive electrode is SD = 500 g / m². 2 The compaction density PD of the positive electrode sheet is 2.3 g / cm³. 3 .

[0071] Example 5:

[0072] The positive electrode active material is lithium manganese iron phosphate (LMFP), the conductive materials are carbon black and carbon nanotubes, and the binder is polyvinylidene fluoride (PVDF).

[0073] The mass ratio of positive electrode active material, conductive material and binder W h :W d :W n =97:1.3:1.7; The mass ratio of carbon black to carbon nanotubes in conductive materials is a:b = 0.5:0.8;

[0074] The areal density of the positive electrode is SD = 500 g / m². 2 The compaction density PD of the positive electrode sheet is 2.3 g / cm³. 3 .

[0075] Example 6:

[0076] The positive electrode active material is lithium manganese iron phosphate (LMFP), the conductive materials are carbon black, carbon nanotubes and carbon nanofibers, and the binder is polyvinylidene fluoride (PVDF).

[0077] The mass ratio of positive electrode active material, conductive material and binder W h :W d :W n =97:1.3:1.7; The mass ratio of carbon black, carbon nanotubes, and carbon nanofibers in conductive materials is a:b:c = 0.3:0.4:0.6;

[0078] The areal density of the positive electrode is SD = 500 g / m². 2 The compaction density PD of the positive electrode sheet is 2.3 g / cm³. 3 .

[0079] Example 7:

[0080] The positive electrode active material is lithium manganese iron phosphate (LMFP), the conductive materials are carbon black, carbon nanotubes and carbon nanofibers, and the binder is polyvinylidene fluoride (PVDF).

[0081] The mass ratio of positive electrode active material, conductive material and binder W h :W d :W n =97:1.8:1.2; The mass ratio of carbon black, carbon nanotubes, and carbon nanofibers in the conductive material is a:b:c = 0.8:0.6:0.4;

[0082] The areal density of the positive electrode is SD = 500 g / m². 2 The compaction density PD of the positive electrode sheet is 2.45 g / cm³. 3 .

[0083] Example 8:

[0084] The positive electrode active material is lithium manganese iron phosphate (LMFP), the conductive materials are carbon black, carbon nanotubes and carbon nanofibers, and the binder is polyvinylidene fluoride (PVDF).

[0085] The mass ratio of positive electrode active material, conductive material and binder W h :W d :W n = 97.22:0.78:2; The mass ratio of carbon black, carbon nanotubes, and carbon nanofibers in the conductive material is a:b:c = 0.38:0.2:0.2;

[0086] The areal density of the positive electrode is SD = 500 g / m². 2 The compaction density PD of the positive electrode sheet is 2.2 g / cm³. 3 .

[0087] 2. Battery performance testing

[0088] 1) DC Internal Resistance (DCIR) Test

[0089] Test method: Constant current and constant voltage charging, current is 0.33C, constant voltage is 4.2V, cut-off current is 0.05C (C is the battery design capacity), after resting for 0.5h, discharge at 0.1C for 0.5Q, rest for 1h, record the voltage at this time as V0, then discharge at 1C for 30s, record the voltage V1 and current I at the end of the discharge, then DCR=(V0-V1) / I, the unit is mΩ.

[0090] The DC internal resistance (DCIR) of the batteries in Examples 1 to 8 was tested, and the test results are shown in Table 1.

[0091] 2) Cyclic performance test

[0092] Test method: The battery was placed at 25℃ for 30 minutes; then charged with constant current and constant voltage (C = 0.33C, 4.2V, cutoff current = 0.05C, where C is the battery design capacity). Three cycles were performed, and the capacity of the last cycle was recorded as Q (calibrated capacity). After a 1-hour rest, constant current and constant voltage charging was performed again (1Q, 4.2V, cutoff current = 0.05Q). After another 1-hour rest, constant current discharge was performed (1Q), for a total of 500 cycles. The stability of the material was evaluated by the cycle capacity retention rate after 500 cycles. The battery cycle performance test results for Examples 1 to 8 are shown in Table 1.

[0093] Table 1

[0094]

[0095] In Table 1, the positive electrode active material represents lithium manganese iron phosphate, the binder represents polyvinylidene fluoride, conductive agent a represents carbon black, conductive agent b represents carbon nanotubes, and conductive agent c represents carbon nanofibers.

[0096] As can be seen from the data in Table 1, W in Examples 1 to 6 n / (PD*W d The calculated values ​​are all in the range of 0.27 to 1.12. (W in Example 7) n / (PD*W d The calculated value is lower than the above range, W in Example 8 n

[0097] / (PD*W d The calculated value is higher than the above range.

[0098] Example 1 is the preferred formulation of this application. The battery in Example 1 has a high capacity retention rate of 96.1% and a relatively low DC internal resistance, which proves that the battery in Example 1 has high cycle capability and good conductivity.

[0099] Compared to Example 1, Example 2 increased the conductive agent content and compaction density. The DC internal resistance of Example 2 decreased, demonstrating that increasing the conductive agent content improves battery conductivity. However, the battery capacity retention rate of Example 2 decreased slightly, indicating that further increasing the compaction density does not further increase battery capacity. This may be because higher compaction density leads to greater compression between electrode material particles, resulting in smaller electrode porosity and fewer channels for ion transport, leading to greater polarization loss during battery cycling and affecting cycle performance. Nevertheless, the battery of Example 2 still exhibits high cycle capability and good conductivity overall.

[0100] Compared to Example 1, Example 3's conductive material contains only carbon black. The DC internal resistance of the battery in Example 3 is increased and the capacity retention rate is reduced. This is because the conductive material in Example 3 lacks a conductive network formed by a linear conductive agent, resulting in reduced conductivity and cycle performance.

[0101] Compared to Example 3, Example 4 incorporates carbon nanotubes into its conductive material. This results in a lower DC internal resistance and increased capacity retention. This is because the carbon nanotubes and carbon black form a conductive network, enhancing the conductivity of the conductive material and improving its cycle performance.

[0102] Compared to Example 4, Example 5 has a lower carbon black content than carbon nanotube content in its conductive material. This results in an increased DC internal resistance and a decreased capacity retention rate. This is because the excessive carbon nanotube content makes it difficult to disperse the positive electrode active material particles and carbon black particles, leading to agglomeration, which in turn affects the conductivity and cycle performance.

[0103] Compared to Example 1, the conductive material in Example 6 has a lower carbon black content than carbon nanotube content, and a lower carbon black content than carbon nanofiber content. The DC internal resistance of Example 6 is increased and the capacity retention rate is reduced. This is because the carbon black content is too low, which reduces the conductivity. In addition, the excessive carbon nanotube and carbon nanofiber content makes it difficult to disperse the positive electrode active material particles and carbon black particles, resulting in agglomeration, reduced conduction efficiency, and overall decreased conductivity, which in turn affects the conductivity and cycle performance.

[0104] In the scheme of Example 7, W n / (PD*W d With a particle size of ≤0.27, its compacted density increases to 2.45 g / cm³. 3 The binder content was too low, making coating difficult and failing to produce the positive electrode sheet, thus rendering the solution ineffective.

[0105] In the scheme of Example 8, W n / (PD*W d With a value ≥1.12, the binder content increases and the conductive agent content decreases. The DC internal resistance of Example 8 increases significantly, the capacity retention rate is as low as 92.1%, and the conductivity and cycling performance are poor. This system is difficult to meet the requirements for long-term cycling.

[0106] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0107] The embodiments, implementation methods, and related technical features of this application can be combined and substituted for each other without conflict.

[0108] The above are merely preferred embodiments of this application and are not intended to limit this application in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of this application without departing from the scope of the technical solution of this application shall still fall within the scope of the technical solution of this application.

Claims

1. A positive electrode plate, characterized in that, It includes a positive current collector and a positive active material coating disposed on at least one surface of the positive current collector; The positive electrode active material coating includes a positive electrode active material, a conductive material, and a binder; The positive electrode active material includes lithium manganese iron phosphate, and the conductive material includes a main conductive agent and an auxiliary conductive agent. The main conductive agent is granular, and the auxiliary conductive agent has a linear structure. The compaction density PD of the positive electrode sheet is related to the content W of the conductive material. d and the content W of the adhesive n The relation satisfies: 0.27 ≤ W n / (PD*W d The compaction density of the positive electrode sheet is 2.3 g / cm³, with a density ≤1.

12. 3 ≤PD≤2.45g / cm 3 The conductive material has a mass percentage range of 0.8% to 1.8%, and the adhesive has a mass percentage range of 1.2% to 2.2%. The thickness of the positive electrode sheet is d, where 200μm≤d≤250μm; The main conductive agent includes carbon black, and the auxiliary conductive agent includes at least one of carbon nanotubes and carbon nanofibers. When the conductive material includes carbon black and carbon nanotubes, the mass percentage of carbon black is a, the mass percentage of carbon nanotubes is b, and a > b; When the conductive material includes carbon black and carbon nanofibers, the mass percentage of carbon black is a, the mass percentage of carbon nanofibers is c, and a > c; When the conductive material includes carbon black, carbon nanotubes, and carbon nanofibers, the mass percentage of the carbon black is a, the mass percentage of the carbon nanotubes is b, and the mass percentage of the carbon nanofibers is c, where a ≥ b ≥ c.

2. The positive electrode sheet according to claim 1, characterized in that, The conductive material includes carbon black and carbon nanotubes, wherein the mass percentage a of the carbon black ranges from 0.3% to 1.8%, and the mass percentage b of the carbon nanotubes ranges from 0.2% to 0.8%.

3. The positive electrode sheet according to claim 1, characterized in that, The conductive material includes carbon black and carbon nanofibers, wherein the mass percentage a of the carbon black ranges from 0.3% to 1.8%, and the mass percentage c of the carbon nanofibers ranges from 0.2% to 0.8%.

4. The positive electrode sheet according to claim 1, characterized in that, The conductive material includes carbon black, carbon nanotubes, and carbon nanofibers, wherein the mass percentage a of the carbon black ranges from 0.3% to 1.8%, the mass percentage b of the carbon nanotubes ranges from 0.2% to 0.8%, and the mass percentage c of the carbon nanofibers ranges from 0.2% to 0.8%.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that, The areal density of the positive electrode sheet is SD, 480g / m²≤SD≤560g / m².

6. The positive electrode sheet according to any one of claims 1 to 4, characterized in that, In the positive electrode active material coating, the mass percentage of the positive electrode active material ranges from 96% to 98%.

7. A battery, characterized in that, Including the positive electrode sheet as described in any one of claims 1 to 6.

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