Positive electrode sheet, battery positive electrode, secondary battery and electrical equipment

Abstract

The present disclosure relates to a positive electrode sheet, which 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 electrode active material and the conductive agent in the positive electrode sheet satisfy 6≤C≤50; C=D1k / (D0 2 Lγ); D1 is the average particle size of the positive electrode active material; k is 3400nm 2 ; D0 is the sheet diameter of graphene; γ is the ratio of the intensity of the D peak to the G peak in the Raman spectrum of graphene; L is the average thickness of graphene. The positive electrode material provided by the present disclosure can enhance the electrolyte infiltration effect of the positive electrode of the battery, improve the compaction and ion conductivity of the positive electrode of the lithium battery; can reduce the obstacle to ion diffusion, and effectively enhance the ion conductivity of the positive electrode; can reduce the amount of conductive agent added, optimize the performance of the battery to the greatest extent, and effectively improve the energy density and power performance of the prepared battery.

Description

Technical Field

[0001] The present disclosure relates to the field of secondary batteries, and in particular, to a positive electrode sheet, a battery positive electrode, a secondary battery and an electrical device. Background Art

[0002] Two-dimensional graphene materials can construct a conductive network of point-surface structures, so they can be used in lithium-ion batteries to accelerate the electron transfer during the charging and discharging process. At the same time, graphene has a high thermal conductivity (5300W / mK), which can quickly dissipate the heat generated by the rapid charging and discharging process of the battery, which is conducive to obtaining better battery performance.

[0003] However, in practical applications, the graphene prepared by the existing method is directly used as a conductive agent for lithium-ion batteries. In the case of a small amount of addition, the various parameters of the graphene material will greatly affect the performance of the prepared battery, making it difficult to effectively optimize the energy density and conductivity of the battery, thereby seriously affecting the battery performance. To overcome the above problems, one method is to optimize the performance of the ion battery by adjusting the weight ratio of the conductive agent in the positive electrode sheet, the weight ratio between the one-dimensional conductive material and the two-dimensional conductive material, the specific surface area of ​​the one-dimensional conductive material, and the secondary particle size distribution of the two-dimensional conductive material, so as to improve the low-temperature DC internal resistance, low-temperature charging and low-temperature rate discharge performance of the ion battery; another method is to use graphene with different sheet diameters to provide dimensional conductivity in the three-dimensional conductive network, with a very low steric effect, which can effectively improve the rate performance of the battery. However, both of the above methods cannot achieve the maximum optimization of battery performance, the graphene cannot be well matched with the main material, the graphene is inefficient, the addition amount is large, and the improvement of the energy density and power performance of the prepared battery is limited. Summary of the invention

[0004] The purpose of the present invention is to provide a positive electrode plate, a battery positive electrode, a secondary battery and an electrical device. The positive electrode plate provided by the present invention can enhance the electrolyte infiltration effect of the battery positive electrode, thereby reducing the obstacle to ion diffusion, and has better electrochemical performance when used in the battery.

[0005] In order to achieve the above-mentioned object, the first aspect of the present invention provides a positive electrode plate, wherein the positive electrode plate 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;

[0006] The positive electrode active material and the conductive agent in the positive electrode sheet satisfy 6≤C≤50; wherein C=D1k / (D0 2 Lγ);

[0007] Wherein, D1 is the average particle size of the positive electrode active material, in nm; k is the correction factor, 3400 nm2 ;

[0008] D0 is the average sheet diameter of the graphene, in nm; 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.

[0009] Optionally, D0 is 200~15000nm, L is 0.34~3.4nm, and γ is 0.01~0.5.

[0010] Optionally, 6≤C≤20.

[0011] Optionally, 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 %.

[0012] Optionally, the graphene accounts for 10-100wt% in the conductive agent.

[0013] Optionally, the positive electrode active material is selected from one or more of transition metal oxides, polyanionic compounds, organic polymers or Prussian blue materials.

[0014] Optionally, the positive electrode active material is selected from 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 olivine-structured lithium-containing phosphate.

[0015] Optionally, the conductive agent further includes a conductive filler, and the conductive filler is selected from one or more of conductive carbon black, carbon nanotubes, conductive graphite or carbon fiber.

[0016] Optionally, the positive electrode material layer further comprises a binder, the content of the binder is 0.5-3wt%; the binder is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene and hydrogenated nitrile rubber.

[0017] The second aspect of the present invention provides a positive electrode for a battery comprising the positive electrode sheet described in the first aspect of the present invention.

[0018] A third aspect of the present invention provides a secondary battery, wherein the secondary battery comprises the battery positive electrode provided by the second aspect of the present invention.

[0019] A fourth aspect of the present invention provides an electrical device, wherein the electrical device comprises the secondary battery provided by the third aspect of the present invention.

[0020] Through the above technical scheme, the present invention can optimize the matching relationship between the positive electrode active material and the graphene by coordinating and regulating the size of the positive electrode active material and the average sheet diameter, thickness and D / G ratio of the graphene according to the needs of different positive electrode systems, effectively enhance the electrolyte wetting effect of the battery positive electrode, and improve the compaction density and ion conductivity of the lithium battery positive electrode; and can reduce the obstacles to ion diffusion and effectively enhance the positive electrode ion conductivity; at the same time, the graphene used in this application has good conductivity, so that it is not easy to agglomerate in the positive electrode material, and can build a complete conductive structure, so as to achieve effective improvement of the short-range and long-range electron conductivity of the positive electrode; in addition, the use of the graphene of this application can effectively improve the use efficiency of the conductive agent, reduce the amount of conductive agent added, and optimize the battery performance of the battery to the greatest extent, and further effectively improve the energy density and power performance of the prepared battery.

[0021] Other features and advantages of the present disclosure will be described in detail in the following detailed description. DETAILED DESCRIPTION

[0022] The specific embodiments of the present disclosure are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure, and are not used to limit the present disclosure.

[0023] 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;

[0024] The positive electrode active material and the conductive agent in the positive electrode sheet satisfy 6≤C≤50; wherein C=D1k / (D0 2 Lγ);

[0025] Wherein, D1 is the average particle size of the positive electrode active material, in nm; k is the correction factor, 3400 nm 2 ;

[0026] D0 is the average sheet diameter of the graphene, in nm; 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.

[0027] The present disclosure can adjust the size of the positive electrode active material and the parameters such as the sheet diameter, thickness and D / G ratio of the graphene according to the needs of different positive electrode systems, clarify the matching relationship between the positive electrode active material and the graphene, and can partially or completely replace the traditional conductive agent with graphene, effectively enhance the electrolyte infiltration effect of the positive electrode of the lithium battery, improve the compaction and ion conductivity of the positive electrode of the battery; and can reduce the obstacles to ion diffusion and effectively enhance the ion conductivity of the positive electrode; at the same time, the graphene used in the present application has good conductivity, so that it is not easy to agglomerate in the positive electrode material, and can build a complete conductive structure, so as to effectively improve the short-range and long-range electron conductivity of the positive electrode; in addition, the use of the graphene of the present application can effectively improve the use efficiency of the conductive agent, reduce the amount of conductive agent added, optimize the battery performance of the battery to the greatest extent, and further effectively improve the energy density and power performance of the prepared battery.

[0028] In a preferred embodiment, 6≤C≤20.

[0029] In a specific implementation manner, D0 is 200-15000 nm, L is 0.34-3.4 nm, and γ is 0.01-0.5.

[0030] In the present disclosure, the average flake diameter of the graphene separated from the positive electrode sheet is tested by a scanning electron microscope. For example, the graphene is tested by a scanning electron microscope, and any 5 observation fields are randomly selected. The flake diameters of the graphene in each observation field are counted, and the average value of the flake diameters of the 5 different observation fields represents the average flake diameter of the graphene.

[0031] In the present disclosure, the average thickness of the graphene separated from the positive electrode sheet is tested by transmission electron microscopy. For example, the graphene is tested by transmission electron microscopy, and any 5 observation fields are randomly selected. The thickness of the graphene in each observation field is statistically analyzed, and the average value of the thicknesses of the 5 different observation fields represents the average thickness of the graphene.

[0032] In the present disclosure, the D / G ratio of graphene separated from the positive electrode sheet is tested using a Raman spectrometer.

[0033] The graphene meeting the parameter conditions used in preparing the positive electrode plate disclosed in the present invention can be obtained through screening, or can be directly purchased.

[0034] In a preferred embodiment, D0 is 500-3000 nm, L is 0.68-3.4 nm, and γ is 0.05-0.4. In a specific embodiment, D0 can be 500 nm, 880 nm, 3000 nm, 10000 nm, or a value between any two of them; L can be 2.38 nm, 2.72 nm, 3.4 nm, or a value between any two of them; γ can be 0.05, 0.166, 0.3, or a value between any two of them. In the above embodiment, for different positive electrode systems, graphene with appropriate size characteristics can be matched according to the average particle size D1 of the positive electrode active material, and the sheet diameter, thickness and D / G ratio of the graphene can be controlled within the preferred range of the present application, so that the positive electrode active material and the 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 ion conductivity of the lithium battery positive electrode, and can effectively reduce the obstacles to ion diffusion, further enhancing the positive electrode ion conductivity characteristics.

[0035] In a specific embodiment, the content of the positive electrode active material in the positive electrode material layer is 90-98wt%, preferably 95-97wt%, and the content of the conductive agent is 0.5-5wt%, preferably 0.5-3wt%.

[0036] In a specific embodiment, the positive electrode material layer further comprises a binder, and the content of the binder is 0.5-10wt%, preferably 0.5-3wt%.

[0037] In a specific embodiment, the proportion of the graphene in the conductive agent is 10~100wt%, preferably 40~100wt%. In the above embodiment, by regulating the size of the positive electrode active material and the parameters such as the sheet diameter, thickness and D / G ratio of the graphene, it is possible to partially or completely replace the traditional conductive agent with graphene, effectively enhance the electrolyte infiltration effect of the positive electrode of the lithium battery, improve the compaction density and ion conductivity of the positive electrode of the lithium battery; and reduce the obstacles to ion diffusion, effectively enhance the positive electrode ion conductivity; at the same time, the use of the graphene of the present application can effectively improve the use efficiency of the conductive agent, reduce the addition amount of the traditional conductive agent, and optimize the battery performance of the lithium battery to the greatest extent, and further effectively improve the energy density and power performance of the prepared battery.

[0038] In a specific embodiment, the positive electrode active material is selected from one or more of transition metal oxides, polyanionic compounds, organic polymers or Prussian blue materials, preferably transition metal oxides.

[0039] The type of positive electrode active material is conventional in the art. In a preferred embodiment, the positive electrode active material is selected from 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 olivine structure lithium phosphate. The average particle size of the positive electrode active material is within the conventional particle size range of the above materials.

[0040] In a specific embodiment, the conductive agent further comprises a conductive filler, and the conductive filler is selected from one or more of conductive carbon black, carbon nanotubes, conductive graphite or carbon fiber, preferably conductive carbon black.

[0041] In a specific embodiment, the adhesive is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene and hydrogenated nitrile rubber, preferably polyvinylidene fluoride.

[0042] A second aspect of the present disclosure provides a battery positive electrode comprising the positive electrode plate described in the first aspect of the present disclosure.

[0043] In the present disclosure, various parameters of graphene and positive electrode active material contained in the positive electrode of the lithium battery are tested by the following method, and the specific steps are as follows:

[0044] a. Separation of graphene in the positive electrode of lithium battery:

[0045] The positive electrode of the lithium battery was placed in an HCl solution, and after ultrasonic dissolution and dispersion for 1 hour, the dispersion was subjected to gradient centrifugation: centrifuged at an initial centrifugal speed of 2000 r / min for 10 min, and the supernatant was taken. The supernatant was then centrifuged at a speed of 500 r / min, and the bottom of the bottle was freeze-dried. The products after gradient centrifugation and freeze-drying were characterized by SEM, and the freeze-dried product with the highest graphene content was used as a benchmark to test the sheet diameter, thickness and Raman of the graphene.

[0046] b. Separation of positive electrode active materials in the positive electrode of lithium battery:

[0047] The positive electrode of the lithium battery was placed in an HCl solution, ultrasonically dissolved and dispersed for 1 hour, and then the dispersion was subjected to gradient centrifugation: after centrifugation at an initial centrifugal speed of 2000 r / min for 10 minutes, the precipitate was taken. The precipitate was then centrifuged and washed several times and then dried. The precipitate was subjected to a Malvern particle size test to obtain the average particle size of the positive electrode active material.

[0048] A third aspect of the present disclosure provides a secondary battery, wherein the secondary battery includes the battery positive electrode provided by the second aspect of the present disclosure.

[0049] In a specific embodiment, a lithium battery includes a positive electrode, a negative electrode, a separator and an electrolyte; in the present disclosure, the type of active material contained in the negative electrode is a conventional type known in the art.

[0050] A fourth aspect of the present disclosure provides an electrical device, wherein the electrical device includes the secondary battery provided by the third aspect of the present disclosure.

[0051] The present disclosure also provides an electrical device, which may be, for example, an electric tool, a digital product, a mobile phone, a laptop computer, or an electric car. The electrical device includes the lithium-ion battery provided by the present disclosure.

[0052] The present invention is further described below by way of examples, but the present invention is not limited thereto. The raw materials used in the examples can be obtained through commercial sources.

[0053] Example 1

[0054] The positive electrode active material, the conductive agent and the binder are mixed to obtain a positive electrode material, the positive electrode material and NMP are placed in a homogenizer and stirred into a positive electrode slurry, and the slurry is evenly coated on the surface of the aluminum foil to obtain a battery positive electrode, which is recorded as A1.

[0055] Among them, 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, the conductive agent and the 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 1140nm, the average sheet diameter D0 of the graphene is 880nm, the average thickness L of the graphene is 2.38nm, and γ is 0.12.

[0056] Example 2

[0057] The positive electrode active material, the conductive agent and the binder are mixed to obtain a positive electrode material, the positive electrode material and NMP are placed in a homogenizer and stirred into a positive electrode slurry, and the slurry is evenly coated on the surface of the aluminum foil to obtain a battery positive electrode, which is recorded as A2.

[0058] Among them, 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, the conductive agent and the 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 10000nm, the average sheet diameter D0 of the graphene is 10000nm, the average thickness L of the graphene is 3.4nm, and γ is 0.01.

[0059] Example 3

[0060] The positive electrode active material, the conductive agent and the binder are mixed to obtain a positive electrode material, the positive electrode material and NMP are placed in a homogenizer and stirred into a positive electrode slurry, and the slurry is evenly coated on the surface of the aluminum foil to obtain a battery positive electrode, which is recorded as A3.

[0061] Among them, 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, the conductive agent and the 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 800nm, the average sheet diameter D0 of the graphene is 880nm, the average thickness L of the graphene is 2.38nm, and γ is 0.12.

[0062] Example 4

[0063] The method of Example 1 is adopted, except that in step a, the positive electrode material satisfies C=45, and a positive electrode of a battery is obtained, which is recorded as A4.

[0064] Among them, the average particle size D1 of the positive electrode active material is 1140nm, the average sheet diameter D0 of the graphene is 500nm, the average thickness L of the graphene is 2.04nm, and γ is 0.166.

[0065] Example 5

[0066] The method of Example 1 is adopted, except that in step a, the content of graphene in the conductive agent is 100wt%, to obtain a battery positive electrode, which is recorded as A5.

[0067] Comparative Example 1

[0068] 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 a positive electrode of a battery, which is recorded as B1.

[0069] The average sheet diameter D0 of graphene is 10000 nm, the average thickness L of graphene is 2.38 nm, and γ is 0.01.

[0070] Comparative Example 2

[0071] 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 a positive electrode of a battery, which is recorded as B2.

[0072] The average sheet diameter D0 of graphene is 10000 nm, the average thickness L of graphene is 3.4 nm, and γ is 0.166.

[0073] Comparative Example 3

[0074] The positive electrode active material and method in Example 3 are used, except that in step a, the positive electrode material satisfies C=86, and a battery positive electrode is obtained, which is recorded as B3.

[0075] The average sheet diameter D0 of graphene is 880 nm, the average thickness L of graphene is 0.34 nm, and γ is 0.12.

[0076] Battery Preparation Examples 1~5

[0077] A negative electrode material is obtained by mixing a negative electrode active material, conductive carbon black, a thickener (CMC), and a binder (SBR), and the negative electrode material and deionized water are placed in a homogenizer and stirred into a negative electrode slurry, and the slurry is evenly coated on the surface of a copper foil to obtain a battery negative electrode; wherein the mass ratio of the negative electrode active material, the conductive carbon black, the thickener, and the binder is 96:1:1:2;

[0078] The battery positive electrodes A1-A5 prepared in Examples 1-5 were respectively assembled with the battery negative electrode and the polypropylene separator, and after injecting the electrolyte, forming and dividing the capacity, a laminated battery was prepared.

[0079] Battery comparison examples 1~3

[0080] A negative electrode material is obtained by mixing a negative electrode active material, conductive carbon black, a thickener (CMC), and a binder (SBR), and the negative electrode material and deionized water are placed in a homogenizer and stirred into a negative electrode slurry, and the slurry is evenly coated on the surface of a copper foil to obtain a battery negative electrode; wherein the mass ratio of the negative electrode active material, the conductive carbon black, the thickener, and the binder is 96:1:1:2;

[0081] The battery positive electrodes B1-B3 prepared in Comparative Examples 1-3 were respectively assembled with the battery negative electrode and the polypropylene separator, and after injecting the electrolyte, forming and dividing the capacity, a laminated battery was prepared.

[0082] Test Case

[0083] The various parameters of the graphene and positive electrode active material contained in the battery positive electrodes prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were tested by the following method. The results are listed in Table 1. The specific steps of the results are as follows:

[0084] (1) Separation of graphene from the positive electrode of lithium battery: The positive electrode of lithium battery was placed in HCl solution, ultrasonically dissolved and dispersed for 1 hour, and then the dispersion was subjected to gradient centrifugation: centrifuged at an initial centrifugal speed of 2000 r / min for 10 minutes, and the supernatant was taken. The supernatant was then centrifuged at a speed of 500 r / min, and the material at the bottom of the bottle was freeze-dried. The products after gradient centrifugation and freeze-drying were characterized by SEM, and the freeze-dried product with the highest graphene content was used as the benchmark to test the flake diameter, thickness and Raman of the graphene.

[0085] (2) Separation of positive electrode active materials in the positive electrode of lithium battery: The positive electrode of lithium battery is placed in HCl solution, ultrasonically dissolved and dispersed for 1 hour, and then the dispersion is subjected to gradient centrifugation: after centrifugation at an initial centrifugal speed of 2000 r / min for 10 minutes, the precipitate is taken. The precipitate is then centrifuged and washed multiple times and then dried. The precipitate is subjected to Malvern particle size test to obtain the average particle size of the positive electrode active material.

[0086] The average flake diameter of graphene is determined by the following method: the graphene obtained in the above step (1) is tested by a scanning electron microscope (equipment model: ZEISS GeminiSEM 300), the flake diameters of graphene in 5 different observation fields are selected for statistics, and then the average value of the flake diameters of all graphene is calculated as the average flake diameter of graphene.

[0087] The average thickness of graphene is determined by the following method: the graphene obtained in the above step (1) is tested by a transmission electron microscope (equipment model is Tecnai), the thickness of graphene in 5 different observation fields is selected for statistics, and then the average value of the thickness of all graphene is calculated as the average thickness of graphene.

[0088] The D / G ratio of graphene was tested using a Raman spectrometer (equipment model: Renishaw InVia).

[0089] The average particle size of the positive electrode active material was tested using a Malvern particle size analyzer (equipment model: Mastersizer 300). The results are listed in Table 1.

[0090] The DCIR of the laminated batteries prepared in Examples 1 to 5 and Comparative Examples 1 to 3 was tested using a Xinwei battery test cabinet (equipment model: BTS-5V12A), and the test method was as follows: (1) charge and discharge at 25°C 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, record the end voltage and end current of each process, and calculate the DCIR; the capacity test method was as follows: charge at 1 / 3C constant current and constant voltage at 25°C to 0.05C cutoff, then discharge at 1 / 3, repeat three times and record the third capacity. The results are listed in Table 2.

[0091] Table 1

[0092]

[0093] Table 2

[0094]

[0095] According to the test results in Table 2, it can be seen that the present disclosure can optimize the matching relationship between the positive electrode active material and the graphene by adjusting and coordinating the size of the positive electrode active material and the sheet diameter, thickness and D / G ratio of the graphene according to the needs of different positive electrode systems, and can achieve partial or complete replacement of the traditional conductive agent with graphene, effectively enhance the electrolyte infiltration effect of the battery positive electrode, improve the compaction and ion conductivity of the lithium battery positive electrode; and can reduce the obstacle to ion diffusion, enhance the positive electrode ion conductivity, so that the prepared battery has a low 50% DC internal resistance at 0.5C and 2C, and the battery capacity is improved, thereby optimizing the battery performance of the battery to the greatest extent.

[0096] It can be seen from the test results of Comparative Example 1 that 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 the graphene do not meet the parameter range specified in this application, the graphene and the main material cannot be well matched, and the utilization efficiency of the graphene is low. Therefore, compared with Example 1, the prepared battery has a higher 50% DC internal resistance at 0.5C and 2C, and the battery capacity is reduced.

[0097] It can be seen from the test results of Comparative Example 2 that, when Example 2 is compared with Comparative Example 2, the particle size of the positive electrode active material and the sheet diameter, thickness and D / G ratio of the graphene in Comparative Example 2 do not meet the parameter range specified in the present application, resulting in a poor match between the graphene and the main material. Therefore, the prepared battery has a higher 50% DC internal resistance at 0.5C and 2C than Example 1, and the battery rate performance is reduced.

[0098] It can be seen from the test results of Comparative Example 3 that the particle size of the positive electrode active material and the sheet diameter, thickness and D / G ratio of the graphene in Comparative Example 3 do not meet the parameter range specified in the present application, resulting in a poor match between the graphene and the main material. Therefore, compared with Example 1, the prepared battery has a higher 50% DC internal resistance at 0.5C and 2C, and the battery capacity is reduced.

[0099] The preferred embodiments of the present disclosure are described in detail above; however, the present disclosure is not limited to the specific details in the above embodiments. Within the technical concept of the present disclosure, a variety of simple modifications can be made to the technical solution of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0100] 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, the present disclosure will not further describe various possible combinations.

[0101] In addition, various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A positive electrode sheet, wherein: The positive electrode plate 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 positive electrode active material is selected from 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 phosphate containing an olivine structure; the conductive agent comprises graphene; the positive electrode material layer further comprises a binder, and the binder is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene and hydrogenated nitrile rubber; The positive electrode 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 nm; k is the correction factor, 3400nm 2 ; D0 is the average sheet diameter of the graphene, in nm; 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; Among them, D0 is 200~15000nm, L is 0.34~3.4nm, and γ is 0.01~0.5; The content of the conductive agent in the positive electrode material layer is 0.5-5wt%.

2. The positive electrode sheet according to claim 1, wherein: 6≤C≤20。 3. The positive electrode sheet according to claim 1, wherein: The content of the positive electrode active material in the positive electrode material layer is 90-98 wt %.

4. The positive electrode sheet according to claim 1, wherein: The graphene accounts for 10-100wt% of the conductive agent, and the content of the conductive agent is 0.5-3wt%.

5. The positive electrode sheet according to claim 1, wherein: The conductive agent also includes a conductive filler, and the conductive filler is selected from one or more of conductive carbon black, carbon nanotubes, conductive graphite or carbon fiber.

6. The positive electrode sheet according to claim 1, wherein: The content of the binder is 0.5-3wt%.

7. A battery positive electrode comprising the positive electrode sheet according to any one of claims 1 to 6.

8. A secondary battery, wherein: The secondary battery comprises the positive electrode of claim 7.

9. An electrical device, wherein: The electric device comprises the secondary battery according to claim 8.

Images