Positive electrode sheet, battery positive electrode, secondary battery, and electric device

Abstract

A positive electrode sheet, a battery positive electrode, a secondary battery and an electric device. The positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer, wherein the positive electrode material layer comprises a positive electrode active material and an electrically conductive agent, the electrically conductive agent comprising graphene. The positive electrode active material and the electrically conductive agent in the positive electrode sheet satisfy: 6≤C≤50, wherein C=D1k / (D0 2Lγ), where D1 is the average particle size of the positive electrode active material, with the units thereof being μm; k is 3400 nm2; D0 is the diameter of graphene sheets, with the unit thereof being μm; γ is the intensity ratio of peak D to peak G in a Raman spectrum of the graphene; and L is the average thickness of the graphene, with the unit thereof being nm.

Description

A positive electrode sheet, a battery positive electrode, a secondary battery, and an electric device

[0001] Cross Reference to Related Applications

[0002] The present disclosure claims priority to Chinese Patent Application No. CN202411055222.3, filed on August 2, 2024, the contents of which are incorporated herein in their entirety as part of the present disclosure. TECHNICAL FIELD

[0003] The present disclosure relates to the field of secondary batteries, in particular, to a positive electrode sheet, a battery positive electrode, a secondary battery, and an electric device. BACKGROUND

[0004] Two-dimensional graphene material can construct a conductive network of point-plane structure, and thus can be applied to lithium ion batteries to accelerate electron transmission in the charging and discharging process. Meanwhile, graphene has a high thermal conductivity coefficient (5300 W / mK), which can quickly dissipate the heat generated in the rapid charging and discharging process of the battery, and is beneficial to obtain more excellent battery performance.

[0005] However, in actual application, various parameters of graphene material will greatly affect the performance of the prepared battery, and it is difficult to effectively optimize the energy density and conductive performance of the battery, thereby seriously affecting the battery performance. Therefore, the prior art cannot achieve the maximum optimization of the battery performance, the graphene and the main material cannot be well matched, the use efficiency of the graphene is low, the addition amount is large, and the improvement of the energy density and power performance of the prepared battery is limited. SUMMARY

[0006] The purpose of the present disclosure is to provide a positive electrode sheet, a battery positive electrode, a secondary battery, and an electric device. The positive electrode sheet provided by the present disclosure can enhance the electrolyte wetting effect of the battery positive electrode, thereby reducing the hindrance to ion diffusion, and has more excellent electrochemical performance when used in a battery.

[0007] To achieve the above-mentioned purpose, the first aspect of the present disclosure provides a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer; the positive electrode material layer comprises a positive electrode active material and a conductive agent; the conductive agent comprises graphene;

[0008] The positive electrode active material and the conductive agent in the positive electrode sheet satisfy 6≤C≤50; wherein C=D1k / (D0 2 Lγ);

[0009] Wherein, D1 is the average particle size of the positive electrode active material, in units of μm; k is a correction coefficient, 3400nm 2D0 is an average flake size of the graphene, in units of μm; γ is a ratio of intensities of a D peak and a G peak in a Raman spectrum of the graphene; and L is an average thickness of the graphene, in units of nm.

[0010] In some embodiments, D0 is 0.2-15 μm, L is 0.34-3.4 nm, and γ is 0.01-0.5.

[0011] In some embodiments, 6≤C≤20.

[0012] In some embodiments, a content of the positive electrode active material in the positive electrode material layer is 90-98 wt%, and a content of the conductive agent is 0.5-10 wt%.

[0013] In some embodiments, a proportion of the graphene in the conductive agent is 10-100 wt%.

[0014] In some embodiments, the positive electrode active material includes one or more of a transition metal oxide, a polyanion compound, an organic polymer, or a Prussian blue type material.

[0015] In some embodiments, the positive electrode active material includes one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium-containing phosphate with an olivine structure.

[0016] In some embodiments, the conductive agent further includes a conductive filler, and the conductive filler includes one or more of conductive carbon black, carbon nanotubes, conductive graphite, or carbon fibers.

[0017] In some embodiments, the positive electrode material layer further includes a binder, and a content of the binder is 0.5-3 wt%, and the binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, and hydrogenated nitrile rubber.

[0018] A second aspect of the present disclosure provides a battery positive electrode including the positive electrode tab of the first aspect of the present disclosure.

[0019] A third aspect of the present disclosure provides a secondary battery including the battery positive electrode of the second aspect of the present disclosure.

[0020] A fourth aspect of the present disclosure provides an electrical device including the secondary battery of the third aspect of the present disclosure.

[0021] Through the above technical solutions, this disclosure provides a positive electrode sheet, a battery positive electrode, a secondary battery, and an electrical device. It can optimize the matching relationship between the positive electrode active material and graphene by coordinating and controlling parameters such as the size of the positive electrode active material and the average sheet diameter, thickness, and D / G ratio of graphene according to the needs of different positive electrode systems. This effectively enhances the electrolyte wetting effect of the battery positive electrode, improves the compaction density and ionic conductivity of the lithium battery positive electrode, and reduces the hindrance to ion diffusion, effectively enhancing the ion-conducting characteristics of the positive electrode. Simultaneously, the graphene used in this application has good conductivity, making it less prone to agglomeration in the positive electrode material, enabling the construction of a complete conductive structure and effectively improving the short-range and long-range ion-conducting capabilities of the positive electrode. Furthermore, the graphene used in this application can effectively improve the utilization efficiency of the conductive agent, reduce the amount of conductive agent added, and optimize the battery performance to the greatest extent, further effectively improving the energy density and power performance of the prepared battery.

[0022] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Detailed Implementation

[0023] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure.

[0024] The inventors of this disclosure have discovered that directly using graphene prepared by existing methods as a conductive agent in lithium-ion batteries, even with small amounts, significantly affects the battery's performance due to the substantial impact of graphene material parameters. This makes it difficult to effectively optimize the battery's energy density and conductivity, thus severely affecting battery performance. To overcome these problems, one approach is to optimize ion battery performance by controlling parameters such as the weight ratio of the conductive agent in the positive electrode, the weight ratio between one-dimensional and two-dimensional conductive materials, the specific surface area of ​​the one-dimensional conductive material, and the secondary particle size distribution of the two-dimensional conductive material. This improves the low-temperature DC internal resistance, low-temperature charging, and low-temperature rate discharge performance of the ion battery. Another approach involves using graphene with different sheet sizes to provide dimensional conductivity in a three-dimensional conductive network, exhibiting very low steric hindrance and effectively improving the battery's rate performance. However, neither of these methods can achieve maximum optimization of battery performance.

[0025] The first aspect of this disclosure provides a positive electrode sheet, wherein the positive electrode sheet includes a positive current collector and a positive electrode material layer; the positive electrode material layer includes a positive electrode active material and a conductive agent; the conductive agent comprises graphene;

[0026] The positive electrode active material and conductive agent in the positive electrode sheet satisfy 6 ≤ C ≤ 50; where C = D1k / (D0) 2 Lγ);

[0027] Where D1 is the average particle size of the positive electrode active material, in μm; k is a correction factor, 3400 nm. 2 D0 is the average sheet diameter of the graphene, in μm; γ is the ratio of the intensity of the D peak to the G peak in the Raman spectrum of the graphene; L is the average thickness of the graphene, in nm.

[0028] This disclosure provides a positive electrode sheet that can be controlled according to the needs of different positive electrode systems by adjusting the size of the positive electrode active material and parameters such as the sheet diameter, thickness, and D / G ratio of graphene. This clarifies the matching relationship between the positive electrode active material and graphene, enabling the partial or complete replacement of traditional conductive agents with graphene. This effectively enhances the electrolyte wetting effect of the lithium battery positive electrode, improves the compaction and ionic conductivity of the battery positive electrode, and reduces the hindrance to ion diffusion, effectively enhancing the ion-conducting characteristics of the positive electrode. Furthermore, the graphene used in this application possesses excellent conductivity, making it less prone to agglomeration in the positive electrode material, allowing for the construction of a complete conductive structure and effectively improving the short-range and long-range ion-conducting capabilities of the positive electrode. In addition, the graphene used in this application can effectively improve the utilization efficiency of conductive agents, reduce the amount of conductive agents added, and optimize battery performance to the greatest extent, further effectively improving the energy density and power performance of the prepared battery.

[0029] In a preferred embodiment, 6 ≤ C ≤ 20.

[0030] In one specific embodiment, D0 is 0.2–15 μm, L is 0.34–3.4 nm, and γ is 0.01–0.5.

[0031] In this disclosure, the average diameter of the graphene separated from the positive electrode is tested by scanning electron microscopy. For example, when performing scanning electron microscopy on the graphene, five random fields of view are selected, and the diameter of the graphene in each field of view is statistically analyzed. The average diameter of the graphene in the five different fields of view represents the average diameter of the graphene.

[0032] In this disclosure, the average thickness of the graphene separated from the positive electrode is tested by transmission electron microscopy. For example, when performing transmission electron microscopy on the graphene, five random fields of view are selected, and the thickness of the graphene in each field of view is statistically analyzed. The average thickness of the five different fields of view represents the average thickness of the graphene.

[0033] In this disclosure, the D / G ratio of the graphene separated from the positive electrode was measured using a Raman spectrometer.

[0034] The graphene meeting the parameter conditions used in the preparation of the positive electrode sheet disclosed herein can be obtained through screening or by direct purchase.

[0035] In a preferred embodiment, D0 is 0.5–3 μm, L is 0.68–3.4 nm, and γ is 0.05–0.4. In a specific embodiment, D0 can be 0.5 μm, 0.88 μm, 3 μm, 10 μm, or any value between two of them; L can be 2.38 nm, 2.72 nm, 3.4 nm, or any value between two of them; γ can be 0.05, 0.166, 0.3, or any value between two of them. In the above embodiments, for different positive electrode systems, graphene with suitable size characteristics can be matched according to the average particle size D1 of the positive electrode active material. By controlling the sheet diameter, thickness, and D / G ratio of graphene within the preferred range of this application, the positive electrode active material and graphene can be further effectively matched, thereby further enhancing the electrolyte wetting effect of the lithium battery positive electrode, further improving the compaction density and ionic conductivity of the lithium battery positive electrode, and effectively reducing the hindrance to ion diffusion, further enhancing the ion conduction characteristics of the positive electrode.

[0036] In one specific embodiment, the content of the positive electrode active material in the positive electrode material layer is 90-98 wt%, and in a preferred embodiment, the content of the positive electrode active material in the positive electrode material layer is 95-97 wt%. The content of the conductive agent in the positive electrode material layer is 0.5-5 wt%, and in a preferred embodiment, the content of the conductive agent in the positive electrode material layer is 0.5-3 wt%.

[0037] In one specific embodiment, the positive electrode material layer further comprises a binder, the content of which is 0.5 to 10 wt%; in a preferred embodiment, the content of which is 0.5 to 3 wt%.

[0038] In one specific embodiment, the proportion of graphene in the conductive agent is 10-100 wt%; in a preferred embodiment, the proportion of graphene in the conductive agent is 40-100 wt%. In the above embodiments, by controlling the size of the positive electrode active material and parameters such as the sheet diameter, thickness, and D / G ratio of graphene, it is possible to partially or completely replace traditional conductive agents with graphene, effectively enhancing the electrolyte wetting effect of the lithium battery positive electrode, improving the compaction density and ionic conductivity of the lithium battery positive electrode; and reducing the hindrance to ion diffusion, effectively enhancing the ion-conducting characteristics of the positive electrode; simultaneously, using the graphene of this application can effectively improve the utilization efficiency of the conductive agent, reduce the amount of traditional conductive agent added, and optimize the battery performance of the lithium battery to the greatest extent, further effectively improving the energy density and power performance of the prepared battery.

[0039] In one specific embodiment, the positive electrode active material includes one or more of transition metal oxides, polyanionic compounds, organic polymers, or Prussian blue materials; in a preferred embodiment, the positive electrode active material includes transition metal oxides.

[0040] In a preferred embodiment, the positive electrode active material includes one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium phosphates with an olivine structure.

[0041] In one specific embodiment, the conductive agent further includes a conductive filler, which includes one or more of conductive carbon black, carbon nanotubes, conductive graphite, or carbon fiber; in a preferred embodiment, the conductive filler includes conductive carbon black.

[0042] In one specific embodiment, the adhesive includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, and hydrogenated nitrile rubber; in a preferred embodiment, the adhesive includes polyvinylidene fluoride.

[0043] The second aspect of this disclosure provides a battery positive electrode comprising the positive electrode sheet described in the first aspect of this disclosure.

[0044] In this disclosure, the parameters of graphene and positive electrode active materials contained in the lithium battery positive electrode are tested using the following method, and the specific steps are as follows:

[0045] a. Separation of graphene from the positive electrode of lithium batteries:

[0046] The lithium battery positive electrode was placed in an HCl solution and ultrasonically dissolved and dispersed for 1 hour. The dispersion was then subjected to gradient centrifugation: centrifuged at an initial speed of 2000 rpm for 10 minutes, and the supernatant was collected. Subsequently, the supernatant was centrifuged at progressively increasing speeds of 500 rpm, and the bottom of the sample was freeze-dried. The products after gradient centrifugation and freeze-drying were characterized by SEM. Using the freeze-dried product with the highest graphene content as a benchmark, the graphene sheet diameter, thickness, and Raman spectroscopy were measured.

[0047] b. Separation of the positive electrode active material in the positive electrode of a lithium battery:

[0048] The lithium battery positive electrode was placed in an HCl solution and ultrasonically dissolved and dispersed for 1 hour. The dispersion was then subjected to gradient centrifugation: after centrifugation at an initial speed of 2000 r / min for 10 minutes, the precipitate was collected. The precipitate was then washed and dried after multiple centrifugations. Malvern particle size analysis was performed on the precipitate to obtain the average particle size of the positive electrode active material.

[0049] A third aspect of this disclosure provides a secondary battery, wherein the secondary battery includes the positive electrode of the battery provided in the second aspect of this disclosure.

[0050] In one specific embodiment, the secondary battery includes a lithium battery; the lithium battery includes a positive electrode, a negative electrode, a separator, and an electrolyte; in this disclosure, the negative electrode, separator, and electrolyte in the lithium battery can be of conventional types in the art. In one specific embodiment, the negative electrode comprises one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium phosphates with an olivine structure.

[0051] The fourth aspect of this disclosure provides an electrical device, wherein the electrical device includes a secondary battery provided in the third aspect of this disclosure.

[0052] This disclosure also provides an electrical device, including but not limited to power tools, digital products, mobile phones, laptops, and electric vehicles; the electrical device includes the lithium-ion battery provided in this disclosure.

[0053] The present disclosure is further illustrated by the following examples, but the present disclosure is not limited thereto. All raw materials used in the examples are commercially available.

[0054] Example 1

[0055] The positive electrode active material, conductive agent and binder are mixed to obtain the positive electrode material. The positive electrode material and NMP are placed in a homogenizer and stirred to form a positive electrode slurry, which is then uniformly coated on the surface of aluminum foil to obtain the battery positive electrode, denoted as A1.

[0056] The positive electrode active material is lithium iron phosphate, the conductive agent is conductive carbon black and graphene, and the binder is PVDF. The mass ratio of the positive electrode active material, conductive agent and binder is 96.5:1.5:2, and the proportion of graphene in the conductive agent is 20wt%. The positive electrode sheet satisfies C=17.52, the average particle size D1 of the positive electrode active material is 1.14μm, the average sheet diameter D0 of graphene is 0.88μm, the average thickness L of graphene is 2.38nm, and γ is 0.12.

[0057] Example 2

[0058] The positive electrode active material, conductive agent and binder are mixed to obtain the positive electrode material. The positive electrode material and NMP are placed in a homogenizer and stirred to form a positive electrode slurry, which is then uniformly coated on the surface of aluminum foil to obtain the battery positive electrode, denoted as A2.

[0059] The positive electrode active material is lithium cobalt oxide, the conductive agent is conductive carbon black and graphene, and the binder is PVDF. The mass ratio of the positive electrode active material, conductive agent and binder is 96.5:1.5:2, and the proportion of graphene in the conductive agent is 10wt%. The positive electrode material satisfies C=10, the average particle size D1 of the positive electrode active material is 10μm, the average sheet diameter D0 of the graphene is 10μm, the average thickness L of the graphene is 3.4nm, and γ is 0.01.

[0060] Example 3

[0061] The positive electrode active material, conductive agent and binder are mixed to obtain the positive electrode material. The positive electrode material and NMP are placed in a homogenizer and stirred to form a positive electrode slurry, which is then uniformly coated on the surface of aluminum foil to obtain the battery positive electrode, denoted as A3.

[0062] The positive electrode active material is lithium iron phosphate, the conductive agent is conductive carbon black and graphene, and the binder is PVDF. The mass ratio of the positive electrode active material, conductive agent and binder is 96.5:1.5:2, and the proportion of graphene in the conductive agent is 40wt%. The positive electrode material satisfies C=12.3, the average particle size D1 of the positive electrode active material is 0.8μm, the average sheet diameter D0 of the graphene is 0.88μm, the average thickness L of the graphene is 2.38nm, and γ is 0.12.

[0063] Example 4

[0064] The method of Example 1 is adopted, except that in step a, the positive electrode material satisfies C=45 to obtain the positive electrode of the battery, which is denoted as A4.

[0065] The average particle size D1 of the positive electrode active material is 1.14 μm, the average sheet diameter D0 of the graphene is 0.5 μm, the average thickness L of the graphene is 2.04 nm, and the γ is 0.166.

[0066] Example 5

[0067] The method of Example 1 was used, except that in step a, the content of graphene in the conductive agent was 100wt%, and the positive electrode of the battery was obtained, denoted as A5.

[0068] Comparative Example 1

[0069] The positive electrode active material and method in Example 1 are used, except that in step a, the positive electrode material satisfies C = 1.62 to obtain the battery positive electrode, denoted as B1.

[0070] The graphene has an average sheet diameter D0 of 10 μm, an average thickness L of 2.38 nm, and a γ of 0.01.

[0071] Comparative Example 2

[0072] The positive electrode active material and method in Example 2 are used, except that in step a, the positive electrode material satisfies C = 0.602 to obtain the battery positive electrode, denoted as B2.

[0073] The graphene has an average sheet diameter D0 of 10 μm, an average thickness L of 3.4 nm, and a γ of 0.166.

[0074] Comparative Example 3

[0075] The positive electrode active material and method in Example 3 are used, with the only difference being that in step a, the positive electrode material satisfies C=86 to obtain the battery positive electrode, denoted as B3.

[0076] The graphene has an average sheet diameter D0 of 0.88 μm, an average thickness L of 0.34 nm, and a γ of 0.12.

[0077] Battery fabrication examples 1-5

[0078] The negative electrode active material, conductive carbon black, thickener (CMC), and binder (SBR) are mixed to obtain the negative electrode material. The negative electrode material and deionized water are placed in a homogenizer and stirred to form a negative electrode slurry, which is then uniformly coated on the surface of copper foil to obtain the battery negative electrode. The mass ratio of the negative electrode active material, conductive carbon black, thickener, and binder is 96:1:1:2.

[0079] The positive electrodes A1 to A5 prepared in Examples 1 to 5 were assembled with the negative electrode and a polypropylene separator, respectively. After injecting electrolyte, forming and capacity testing, stacked batteries were prepared.

[0080] Battery Comparison Examples 1-3

[0081] The negative electrode active material, conductive carbon black, thickener (CMC), and binder (SBR) are mixed to obtain the negative electrode material. The negative electrode material and deionized water are placed in a homogenizer and stirred to form a negative electrode slurry, which is then uniformly coated on the surface of copper foil to obtain the battery negative electrode. The mass ratio of the negative electrode active material, conductive carbon black, thickener, and binder is 96:1:1:2.

[0082] The positive electrodes B1 to B3 prepared in Comparative Examples 1 to 3 were assembled with the negative electrode and polypropylene separator, respectively. After electrolyte injection, formation and capacity testing, stacked batteries were prepared.

[0083] Test case

[0084] The parameters of graphene and positive electrode active materials contained in the battery positive electrodes prepared in Examples 1-5 and Comparative Examples 1-3 were tested using the following methods, and the results are listed in Table 1. The specific steps for obtaining the results are as follows:

[0085] (1) Separation of graphene from lithium battery cathode: The lithium battery cathode was placed in HCl solution and ultrasonically dissolved and dispersed for 1 h. The dispersion was then subjected to gradient centrifugation: centrifuged at an initial speed of 2000 r / min for 10 min, and the supernatant was collected. Subsequently, the supernatant was centrifuged at a speed gradually increasing to 500 r / min, and the bottom of the bottle was collected for freeze-drying. The products after gradient centrifugation and freeze-drying were characterized by SEM. The freeze-dried product with the highest graphene content was used as the benchmark to measure the graphene sheet diameter, thickness, and Raman spectroscopy.

[0086] (2) Separation of positive electrode active material in lithium battery positive electrode: The lithium battery positive electrode was placed in HCl solution and ultrasonically dissolved and dispersed for 1 hour. The dispersion was then subjected to gradient centrifugation: after centrifugation at an initial speed of 2000 r / min for 10 min, the precipitate was collected. Subsequently, the precipitate was washed by centrifugation multiple times and then dried. Malvern particle size analysis was performed on the precipitate to obtain the average particle size of the positive electrode active material.

[0087] The average diameter of graphene was determined by the following method: the graphene obtained in step (1) was tested by scanning electron microscope (equipment model ZEISS GeminiSEM 300), the diameter of graphene in 5 different fields of view was statistically analyzed, and then the average diameter of all graphene was calculated as the average diameter of graphene.

[0088] The average thickness of graphene was determined by the following method: the graphene obtained in step (1) above was tested by transmission electron microscopy (equipment model Tecnai), the thickness of graphene in 5 different fields of view was statistically analyzed, and then the average thickness of all graphene was calculated as the average thickness of graphene.

[0089] The D / G ratio of graphene was measured using a Raman spectrometer (Renishaw InVia).

[0090] The average particle size of the positive electrode active material was measured using a Malvern particle size analyzer (Mastersizer300). The results are listed in Table 1.

[0091] The DCIR of the stacked batteries prepared in Examples 1-5 and Comparative Examples 1-3 was tested using a Xinwei battery test cabinet (equipment model BTS-5V12A). The test method is as follows: (1) Charge and discharge at 25℃ and 0.2C to calibrate the battery capacity; (2) Charge at 0.2C to 50% SOC; (3) Discharge at 0.5C and 2C for 30s respectively, record the termination voltage and termination current of each process, and calculate the DCIR; The capacity test method is as follows: Charge at 1 / 3C constant current and constant voltage at 25℃ to 0.05C cutoff, then discharge at 1 / 3, repeat three times and record the third capacity. The results are listed in Table 2.

[0092] Table 1

[0093] Table 2

[0094] As can be seen from the test results in Table 2, this disclosure can optimize the matching relationship between the positive electrode active material and graphene by coordinating and controlling parameters such as the size of the positive electrode active material and the sheet diameter, thickness, and D / G ratio of graphene according to the needs of different positive electrode systems. This enables the partial or complete replacement of traditional conductive agents with graphene, effectively enhancing the electrolyte wetting effect of the battery positive electrode, improving the compaction and ionic conductivity of the lithium battery positive electrode, and reducing the hindrance to ion diffusion, thereby enhancing the ion-conducting characteristics of the positive electrode. This results in a lower 50% DC internal resistance at 0.5C and 2C, increased battery capacity, and maximized optimization of battery performance.

[0095] As can be seen from the test results of Comparative Example 1, since the particle size of the positive electrode active material in the positive electrode material layer and the sheet diameter, thickness and D / G ratio of graphene do not meet the parameter range defined in this application, the graphene and the main material cannot be well matched, and the graphene utilization efficiency is low. Therefore, compared with Example 1, the battery prepared has a higher 50% DC internal resistance at 0.5C and 2C, and the battery capacity is reduced.

[0096] As can be seen from the test results of Comparative Example 2, compared with Comparative Example 2, the particle size of the positive electrode active material and the sheet diameter, thickness and D / G ratio of graphene in Comparative Example 2 do not meet the parameter range defined in this application, which leads to the graphene and the main material not being well matched. Therefore, the battery prepared has a higher 50% DC internal resistance at 0.5C and 2C compared with Example 1, and the battery rate performance is reduced.

[0097] The test results of Comparative Example 3 show that the particle size of the positive electrode active material, as well as the sheet diameter, thickness and D / G ratio of graphene in Comparative Example 3 do not meet the parameter range specified in this application, resulting in poor matching between graphene and the main material. Therefore, compared with Example 1, the battery prepared has a higher 50% DC internal resistance at 0.5C and 2C, and the battery capacity decreases.

[0098] The preferred embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0099] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0100] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A positive electrode sheet, wherein, The positive electrode tab comprises a positive electrode current collector and a positive electrode material layer; the positive electrode material layer comprises a positive electrode active material and a conductive agent; the conductive agent comprises graphene; The positive active material and the conductive agent in the positive electrode sheet satisfy 6≤C≤50; wherein C=D1k / (D0 2 Lγ); wherein D1 is the average particle size of the positive electrode active material, in units of μm; k is a correction coefficient, 3400 nm 2 ; D0 is the average flake diameter of the graphene, in units of μm; γ is the ratio of the intensity of the D peak to the G peak in the Raman spectrum of the graphene; L is the average thickness of the graphene, in units of nm.

2. The cathode sheet of claim 1, wherein, D0 is 0.2-15 μm, L is 0.34-3.4 nm, and γ is 0.01-0.

5.

3. The cathode sheet of claim 1 or 2, wherein, 6≤C≤20。 4. The positive electrode sheet according to any one of claims 1 to 3, wherein The content of the positive electrode active material in the positive electrode material layer is 90-98 wt%, and the content of the conductive agent is 0.5-10 wt%.

5. The positive electrode sheet according to any one of claims 1 to 4, wherein The proportion of the graphene in the conductive agent is 10-100 wt%.

6. The positive electrode sheet according to any one of claims 1 to 5, wherein The positive electrode active material comprises one or more of transition metal oxides, polyanion compounds, organic polymers, or Prussian blue materials.

7. The positive electrode sheet according to any one of claims 1 to 6, wherein The positive electrode active material comprises one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium-containing phosphate with an olivine structure.

8. The positive electrode sheet according to any one of claims 1 to 7, wherein The conductive agent further comprises a conductive filler, which comprises one or more of conductive carbon black, carbon nanotubes, conductive graphite, or carbon fibers.

9. The positive electrode plate of any one of claims 1-8, wherein, The positive electrode material layer further comprises a binder, the content of the binder being 0.5-3 wt%; the binder comprises one or more of polyvinylidene fluoride, polytetrafluoroethylene, and hydrogenated nitrile rubber.

10. A battery positive electrode comprising the positive electrode tab according to any one of claims 1-9.

11. A secondary battery, wherein, The secondary battery comprises the battery positive electrode according to claim 10.

12. An electrical device, comprising: The electric device comprises the secondary battery according to claim 11.

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