Pole piece, battery and electric equipment

Abstract

The invention discloses a pole piece, a battery and electric equipment, the pole piece comprises a pole piece main body and at least one tab connected with the pole piece main body, the pole piece main body comprises a current collector and an active material coated on the surface of the current collector, the pole piece main body comprises at least three areas in a first direction, active materials coated on at least two of the at least three areas are different; the active material of an intermediate region of the at least three regions includes secondary particles, where the secondary particles are formed of a plurality of primary particles. An electrode plate led out from the same side of a tab is divided into at least three areas, and at least two areas in the at least three areas are coated with different active materials; wherein an intermediate region is included, and an active material of the intermediate region includes secondary particles formed of a plurality of primary particles; the problem of uneven distribution of current density and electrode impedance in the electrode which is led out from the different side of the tab and is close to the tab side and the middle area can be solved, so that the electrochemical performance of the electrode is improved.

Description

Technical Field

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

[0002] In existing lithium iron phosphate batteries, the surface material of the positive electrode is uniformly distributed. For electrodes led out from opposite sides of the tab, the impedance of the electrode near the tab is lower, resulting in a higher current density; while the impedance in the middle of the electrode is higher, resulting in a lower current density. Furthermore, the difference in current density and impedance also leads to different amounts of heat generated by the electrodes.

[0003] Therefore, the positive electrode plates drawn from the same side of the tab have obvious problems with uneven current density and temperature distribution. Summary of the Invention

[0004] The summary section introduces a series of simplified concepts, which will be further explained in detail in the detailed description section. The summary section of this invention is not intended to limit the key features and essential technical features of the claimed technical solution, nor is it intended to determine the scope of protection of the claimed technical solution.

[0005] The present invention provides an electrode sheet, comprising an electrode sheet body and at least one tab connected to the electrode sheet body. The electrode sheet body includes a current collector and an active material coated on the surface of the current collector. The electrode sheet body includes at least three regions in a first direction, wherein at least two of the at least three regions are coated with different active materials. The active material in the middle region of the at least three regions includes secondary particles, wherein the secondary particles are formed by a plurality of primary particles.

[0006] For example, the secondary particles have a porous structure.

[0007] For example, the primary particle has a first size, and the secondary particle has a second size, the second size being at least 30 times the first size.

[0008] For example, when the first size and the second size are expressed in terms of median diameter, the median diameter of the secondary particle ranges from 6 μm to 9 μm, and the median diameter of the primary particle ranges from 70 nm to 130 nm.

[0009] For example, the first direction is the direction extending from the tab to the electrode sheet.

[0010] For example, the length of the intermediate region along the first direction is 25% to 35% of the length of the electrode body.

[0011] For example, the intermediate region covers the center point of the electrode body, and the distance between the intermediate region and both ends of the electrode body in the first direction is greater than 25% of the length of the electrode body; the center point is equidistant from both ends of the electrode in the first direction.

[0012] For example, the at least three regions further include a first region and a second region located on the electrode body, the first region and the second region being arranged along the first direction and located at opposite ends of the intermediate region, wherein the active material of the first region and the second region comprises particles having a third size.

[0013] For example, in the at least three regions, the particle size of the active material gradually increases from the middle region to the first region and the second region, respectively.

[0014] For example, the third size is larger than the first size and smaller than the second size, and when the third size is expressed as median diameter, the median diameter of the particles having the third size ranges from 0.6 μm to 1.2 μm.

[0015] For example, the active material includes a positive electrode active material.

[0016] For example, the positive electrode active material includes lithium iron phosphate.

[0017] For example, the electrode is used to form a battery with opposite tabs.

[0018] The present invention also provides a battery comprising the electrode sheet described in any of the above claims.

[0019] For example, the electrode includes a positive electrode and a negative electrode, and the tabs of the positive electrode and the negative electrode are led out in the same direction.

[0020] The present invention also provides an electrical device, including an electrode as described in any of the preceding claims or a battery as described in any of the preceding claims, and an electrical load, wherein the battery provides electrical energy to the electrical load.

[0021] According to the electrode, battery, and electrical device provided by the present invention, by dividing the electrode sheet led out from the same side of the tab into at least three regions, at least two of the at least three regions are coated with different active materials; including the middle region, the active material of the middle region includes secondary particles formed by a plurality of primary particles; the problem of uneven current density and electrode impedance distribution in the electrode led out from the opposite side of the tab in the region near the tab and the middle region can be improved, thereby improving the electrochemical performance of the electrode. Attached Figure Description

[0022] The following drawings, which are incorporated herein by reference as part of this invention, are provided for understanding the invention. The drawings illustrate embodiments of the invention and their descriptions, serving to explain the principles of the invention.

[0023] In the attached image:

[0024] Figure 1 This is a schematic diagram of the structure of an electrode sheet according to an embodiment of the present invention;

[0025] Figure 2 This is a schematic diagram of the structure of a battery according to an embodiment of the present invention.

[0026] Figure Labels

[0027] 10. Electrode body; 20. Electrode ear

[0028] 11. Area 1 12. Area 2

[0029] 13. Central Area Detailed Implementation

[0030] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without one or more of these details. In other instances, certain technical features well-known in the art have not been described in order to avoid obscuring the invention.

[0031] It should be understood that the invention can be embodied in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, for clarity, the dimensions and relative dimensions of layers and regions may be exaggerated. The same reference numerals denote the same elements throughout.

[0032] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0033] To fully understand this invention, detailed steps and structures will be presented in the following description to illustrate the technical solution proposed by this invention. Preferred embodiments of the invention are described in detail below; however, in addition to these detailed descriptions, the invention may have other embodiments.

[0034] For batteries with tabs on opposite sides, when the active material is uniformly distributed, there are significant issues with uneven current density and temperature along the tab extension direction. The current density is high in the areas near the tabs at both ends of the electrode, while the current density and impedance are low in the central area of ​​the electrode. Furthermore, the lower reaction temperature further exacerbates the uneven distribution of resistivity on the electrode surface, affecting battery performance.

[0035] To address the above problems, the present invention provides an electrode, such as... Figure 1 As shown, the electrode includes: an electrode body 10 and at least one tab 20 connected to the electrode body. The electrode body 10 includes a current collector and an active material coated on the surface of the current collector. The electrode body includes at least three regions in a first direction. At least two of the at least three regions are coated with different active materials. The active material in the middle region of the at least three regions includes secondary particles, wherein the secondary particles are formed by a plurality of primary particles.

[0036] For example, the electrode includes a positive electrode or a negative electrode; the electrode body 10 includes a current collector and an active material on the surface of the current collector; the tab 20 is made of a metal material, the single-layer metal material including aluminum foil or copper foil.

[0037] In one embodiment, the electrode is a positive electrode. Taking a lithium-ion battery as an example, the electrode body 10 of the positive electrode of a lithium-ion battery is typically composed of a positive active material (such as lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, ternary materials, etc.), a conductive agent (such as carbon nanotubes, conductive carbon black, graphene, etc.), and a binder (such as polyvinylidene fluoride PVDF, sodium carboxymethyl cellulose, and styrene-butadiene rubber), which is uniformly mixed and stirred into a paste. This paste is then uniformly coated onto both sides of the positive current collector (e.g., aluminum foil), dried under a nitrogen flow to remove organic dispersants, pressed into shape using a roller press, and then cut to the specified size according to design requirements. The tabs of the positive electrode extend from the positive current collector. The tabs of the positive electrode are typically made of aluminum foil, and their length and width can be designed as needed; this application does not impose any limitations on this.

[0038] In one embodiment, the electrode is a negative electrode. The negative electrode active material of the lithium-ion battery negative electrode mainly includes graphite, silicon-based materials, or lithium titanate. The negative electrode current collector can be copper foil. The fabrication process of the negative electrode is roughly the same as that of the positive electrode, and will not be described in detail here. The tabs of the negative electrode are led out from the negative electrode current collector. The tabs of the negative electrode are usually made of copper foil, and their length and width can be designed as needed; this application does not impose any limitations on this.

[0039] The electrode tab and the current collector can be integrally formed, which can be achieved by welding.

[0040] For example, the electrode body includes at least three regions in a first direction, and at least two of the at least three regions are coated with different active materials; the active material in the middle region of the at least three regions includes secondary particles, wherein the secondary particles are formed by a plurality of primary particles.

[0041] By dividing the electrode sheet led out from the same side of the tab into at least three regions, with at least two regions coated with different active materials, including the middle region, the problem of uneven current density and electrode impedance distribution in the electrode led out from the opposite side of the tab in the middle region can be improved, thereby enhancing the electrochemical performance of the electrode.

[0042] For example, the secondary particles have a porous structure.

[0043] Because secondary particles have a large number of pores, they can provide pathways for lithium-ion transport, thereby effectively improving the problem of uneven electrode current density distribution.

[0044] In one embodiment, such as Figure 1 As shown, the first direction is the direction extending from the tab 20 to the electrode 10. The electrode body 10 is sequentially divided into a first region 11, a middle region 13, and a second region 12 along the first direction extending from the tab 20 to the electrode 10. It should be noted that dividing the electrode body 10 into three regions is merely exemplary; it can also be divided into four, five, or even more regions, and this application does not impose any limitations on this. Furthermore, based on the above division of the electrode body 10 into multiple regions along the first direction, it can also be further divided into multiple regions along a second direction, where the second direction is perpendicular to or intersects the first direction.

[0045] Since the current density and temperature distribution of the electrode are uneven in the direction extending from the tab 20 to the electrode 10, the direction extending from the tab 20 to the electrode 10 is taken as the first direction. Based on this direction, the region is divided, which can effectively solve the problem of uneven current density and temperature distribution caused by the uniform distribution of the electrode surface material in this direction.

[0046] In one embodiment, the first direction includes a direction from the center point near the electrode body 10 to the direction away from the center point of the electrode body 10. The electrode body 10 is divided into multiple regions from the center point of the electrode body 10 outwards.

[0047] In one embodiment, the first direction includes a direction from high current density to low current density of the electrode body 10. The electrode body is divided into multiple regions according to the current density distribution. In one embodiment, the first direction includes a direction from high temperature to low temperature of the electrode body 10. The electrode body is divided into multiple regions according to the temperature distribution.

[0048] For example, the intermediate region covers the center point of the electrode body.

[0049] In one embodiment, such as Figure 1 As shown, the intermediate region 13 not only covers the center point of the electrode body 10, but the center point of the intermediate region 13 also coincides with the center point of the electrode body 10. In this case, the length of the first region 11 is equal to the length of the second region 12. In one embodiment, the intermediate region 13 may also only cover the center point of the electrode body 10, but the center point of the intermediate region 12 does not coincide with the center point of the electrode body 10. In this case, the length of the first region 11 is not equal to the length of the second region 12.

[0050] For example, the length of the intermediate region is 25% to 35% of the length of the electrode body, and the distance between the intermediate region and both ends of the electrode body in the first direction is greater than 25% of the length of the electrode body.

[0051] In one embodiment, when the length of the intermediate region 13 is relatively small, the current density distribution in the intermediate region is uneven, and the battery impedance is relatively high; when the length of the intermediate region 13 is relatively large, the battery energy density is relatively low. Therefore, the length of the intermediate region along the first direction is 25% to 35% of the length of the electrode body. Taking the length of the electrode body 10 as L as an example, the length of the intermediate region 13 ranges from 0.25L to 0.35L.

[0052] In one embodiment, when the length of the intermediate region 13 ranges from 0.25L to 0.35L, and the center point of the intermediate region 13 coincides with the center point of the electrode body 10, the lengths of both the first region 11 and the second region 12 are greater than 0.25L, and the center point is equidistant from both ends of the electrode in the first direction. When the center point of the intermediate region 13 does not coincide with the center point of the electrode body 10, to prevent the intermediate region 13 from being too close to the edge of the electrode body 10, the lengths of the first region 11 and the second region 12 need to be limited to be greater than 0.25L. In one embodiment, the length of the intermediate region 13 is 0.3L, and the lengths of the first region 11 and the second region 12 are both 0.35L. In another embodiment, the lengths of the first region 11, the intermediate region 13, and the second region 12 are 0.3L, 0.35L, and 0.35L, respectively.

[0053] In one embodiment, Table 1 shows the test results of battery performance when the length of the intermediate region is different.

[0054] The battery manufacturing process is as follows:

[0055] (1) Preparation of positive electrode sheet: Mix positive electrode active material, conductive agent (conductive carbon black), solvent (N-methylpyrrolidone), and binder (PVDF), wherein the mass ratio of positive electrode active material, conductive agent, binder and solvent is 100:1.5:2.5:50; prepare a positive electrode slurry with appropriate viscosity, coat it on the positive electrode current collector (aluminum foil), and dry to obtain positive electrode sheet; wherein, for the selection of positive electrode active material and coating position, please refer to Table 1-4;

[0056] (2) Preparation of negative electrode sheet: The negative electrode active material (graphite powder), conductive agent (conductive carbon black), binder (mixture of CMC and SBR), and solvent (water) are mixed to prepare a negative electrode slurry with appropriate viscosity. The mass ratio of positive electrode active material, conductive agent, binder and solvent is 100:0.8:2.5:50. The slurry is coated on the negative electrode current collector (copper foil) and dried to obtain the negative electrode sheet.

[0057] (3) Electrolyte: LiPF6 concentration of 1 mol / L electrolyte (solvent is 15% DMC + 40% EMC + 15% DEC + 30% EC by mass ratio);

[0058] (4) Preparation of lithium-ion batteries: The prepared positive electrode, separator (PP film) and negative electrode are stacked in sequence to assemble a soft pack battery, and the prepared electrolyte is injected. Electrochemical tests are performed, and the results are shown in Table 1-4.

[0059] Electrochemical performance testing:

[0060] (1) Current density difference test between the middle region of the electrode and the tab side (i.e., the near end region): Five different locations were selected in the near end region and the far end region to test the current density at the corresponding locations and calculate the average value; the current density difference J between the near end region and the near end region of the electrode is the current density difference between the far end region and the tab side of the electrode, as shown in Table 1-4; the current density test of the electrode is a routine test in this field and no specific restrictions are imposed.

[0061] (2) Battery energy density (Wh / L) test: Under 25℃ conditions, each lithium-ion battery was first charged at a 1 / 3C rate and then discharged at a 1 / 3C rate (voltage range of 2.2V-4.2V), and the actual discharge amount was recorded. The product of the actual discharge amount of the battery at 1 / 3C and the average voltage of the battery during discharge is the energy of the battery. The ratio of the energy of the battery to the volume of the battery is the energy density of the battery (Wh / L), as shown in Table 1-4.

[0062] (3) DC internal resistance at 50% SOC (mΩ): Discharge the battery to 50% SOC, let it rest for 2 hours, charge it at 1C for 30 seconds, let it rest for 2 hours, and discharge it at 1C for 30 seconds; calculate the DC internal resistance at 1C rate, as shown in Table 1-4.

[0063] (4) Capacity retention rate (%) after 500 cycles at 45℃: The battery is charged and discharged once at 0.5C / 0.5C to obtain the discharge capacity C1. Then the battery is placed in a 45℃ constant temperature chamber for 0.5C / 0.5C charge and discharge test. The discharge capacity C500 after the 500th cycle is recorded. The capacity retention rate after 500 cycles = C500 / C1*100%, as shown in Table 1-4.

[0064] Table 1 shows the battery performance test results when the length of the middle region is different. According to Table 1, when the length of the middle region is in the range of 0.25L to 0.35L, the DC internal resistance is smaller, the energy density is higher, and the battery performance is better. For example, when the length is 0.3L, the battery performance is optimal.

[0065] Table 1

[0066]

[0067] For example, the active material in the intermediate region comprises secondary particles with a porous structure, wherein the secondary particles are formed from a plurality of primary particles.

[0068] In one embodiment, taking lithium iron phosphate as an example of active material, the active material used in the intermediate region 13 is secondary particles with a second size, which are formed by agglomeration or sintering of primary particles with a first size. The size of the secondary particles (i.e., the second size) is larger than the size of the primary particles (i.e., the first size), and the size of the secondary particles is at least 30 times the size of the primary particles, typically 50 to 100 times.

[0069] Here, size refers to the particle size of the material. The particle size can be expressed as the median diameter D50, which is the particle size corresponding to 50% of the cumulative particle size distribution of a sample. It can be measured by laser particle size analysis.

[0070] Specifically, when the first and second dimensions are expressed in terms of median diameter, the median diameter of the secondary particles used to form the intermediate region 13 ranges from 6 μm to 9 μm, and the median diameter of the primary particles used to form the secondary particles ranges from 70 nm to 130 nm.

[0071] In one embodiment, Table 2 shows the test results of battery performance when the secondary particle sizes are different. When the primary particles are the same size, but the secondary particles they form are of different sizes, according to Table 2, the battery performance is optimal when the median diameter of the secondary particles is in the range of 6 μm to 9 μm, for example, 7 μm.

[0072] Table 2

[0073]

[0074] In one embodiment, Table 3 shows the test results of battery performance when the size of the primary particles is different. When the size of the secondary particles is the same, but the size of the primary particles used to form the secondary particles is different, according to Table 3, the battery performance is optimal when the median diameter of the primary particles is in the range of 70 nm to 130 nm, for example, 105 μm.

[0075] Table 3

[0076]

[0077] The secondary lithium iron phosphate particle material is composed of multiple small-diameter primary lithium iron phosphate particles with a large number of pore structures inside. The middle region adopts a porous electrode structure to provide a pathway for lithium-ion transport. Using materials with small primary particle sizes reduces battery impedance and effectively improves the problem of uneven current density distribution along the electrode length.

[0078] For example, the active materials in the first and second regions comprise particles having a third size.

[0079] Specifically, the particle size of the active material gradually increases from the intermediate region to the first region and the second region, respectively. Here, the particle size of the active material is the particle size of the primary particles.

[0080] Since materials with small particle sizes can reduce battery impedance, the resistance from the middle region to the first region and the second region can gradually decrease, thus solving the problem of uneven current density distribution.

[0081] The third size is larger than the first size and smaller than the second size. When the third size is expressed as median diameter, the median diameter of the particles having the third size ranges from 0.6 μm to 1.2 μm. The particles with the third size can be composed of primary particles or secondary particles; preferably, they are primary particles.

[0082] In one embodiment, the active material used to form the first region 11 and the second region 12 is a primary particle with a third size, the median diameter of which ranges from 0.6 μm to 1.2 μm. This size is smaller than the size of the secondary particle used to form the intermediate region 13 (i.e., the second size), but larger than the size of the primary particle used to form the secondary particle (i.e., the first size).

[0083] In one embodiment, the active material includes a positive electrode active material.

[0084] Specifically, the positive electrode active material includes lithium iron phosphate.

[0085] In one embodiment, the electrode is used to form an opposite-side tab battery.

[0086] The present invention also provides a battery comprising the electrodes described above.

[0087] In one embodiment, such as Figure 2 As shown, the battery includes a battery with tabs on opposite sides. The electrodes include a positive electrode and a negative electrode, with the tabs of the positive and negative electrodes extending in opposite directions.

[0088] Since the tabs of the unbalanced battery are distributed at opposite ends of the battery, the current distribution of the electrode body between the tabs of the unbalanced battery is that the current density is low and the impedance is high in the middle region, while the current density is high in the regions near the two ends of the tab. Therefore, when the above-mentioned electrodes are used to form an unbalanced battery, the middle region formed by secondary particles as active materials has good ion diffusion and electron transport channels. The primary particles used to form secondary particles reduce the battery impedance and can effectively improve the problem of uneven current distribution in the length direction of the unbalanced battery.

[0089] In one embodiment, each battery consists of one electrode core, and each electrode core consists of 34 positive electrode sheets and 35 negative electrode sheets, wherein the negative electrode excess ratio is 15% and the compaction is 1.60 g / cm³. 3 .

[0090] In one embodiment, Table 4 shows the performance test results of the battery formed using the electrode sheets described above. Schemes 14-15 serve as a blank control group. Scheme 14 does not use a partitioning method and all samples are coated with secondary particulate material; Scheme 15 does not use a partitioning method and all samples are coated with third-size particulate material.

[0091] Table 4

[0092]

[0093] The present invention also provides an electrical device, including an electrode as described in any of the preceding claims or a battery as described in any of the preceding claims, and an electrical load, wherein the battery provides electrical energy to the electrical load.

[0094] According to the electrode, battery, and electrical device provided by the present invention, the active material in the middle region of the electrode adopts a porous structure formed by secondary particles to provide a pathway for ion transport. The secondary particles are formed by multiple primary particles. The smaller particle size of the primary particles reduces the battery impedance, effectively improves the problem of uneven current distribution on the electrode surface, and improves battery performance.

[0095] The present invention has been described through the above embodiments. However, it should be understood that the above embodiments are for illustrative purposes only and are not intended to limit the invention to the scope of the described embodiments. Furthermore, those skilled in the art will understand that the present invention is not limited to the above embodiments, and many more variations and modifications can be made based on the teachings of the present invention, all of which fall within the scope of protection claimed by the present invention. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A pole piece, characterized in that, The electrode tab includes an electrode tab body and at least one tab connected to the electrode tab body, the electrode tab body includes a current collector and an active material coated on the surface of the current collector, the electrode tab body includes at least three regions in a first direction, at least two regions of the at least three regions are coated with different active materials; the active material of the middle region of the at least three regions includes secondary particles, wherein the secondary particles are formed by a plurality of primary particles.

2. The pole piece of claim 1, wherein The secondary particles have a porous structure.

3. The pole piece of claim 2, wherein The primary particles have a first size, and the secondary particles have a second size, the second size is at least 30 times the first size.

4. The pole piece of claim 2, wherein When the first size and the second size are represented by the median diameter, the median diameter of the secondary particles ranges from 6 μm to 9 μm, and the median diameter of the primary particles ranges from 70 nm to 130 nm.

5. The pole piece of claim 2, wherein The first direction is the direction extending from the tab to the electrode tab.

6. The pole piece of claim 5, wherein The length of the middle region in the first direction is 25% to 35% of the length of the electrode tab body.

7. The pole piece of claim 6, wherein The middle region covers the center point of the electrode tab body, and the distance between the middle region and both ends of the electrode tab body in the first direction is greater than 25% of the length of the electrode tab body. The center point is equidistant from both ends of the electrode tab in the first direction.

8. The pole piece of claim 2, wherein The at least three regions further include a first region and a second region respectively located on the electrode tab body, the first region and the second region are arranged along the first direction and are respectively located at both ends of the middle region, wherein the active material of the first region and the second region includes particles having a third size.

9. The pole piece of claim 8, wherein From the middle region to the first region and the second region respectively, the particle size of the active material gradually increases.

10. The pole piece of claim 9, wherein The third size is greater than the first size and less than the second size, when the third size is represented by the median diameter, the median diameter of the particles having the third size ranges from 0.6 μm to 1.2 μm.

11. The pole piece of claim 1, wherein The active material includes a positive electrode active material.

12. The pole piece of claim 11, wherein The positive electrode active material includes lithium iron phosphate.

13. The pole piece of claim 1, wherein The electrode tab is used to form a hetero-side tab battery.

14. A battery, characterized by The electrode tab includes the electrode tab of any one of claims 1-13.

15. The battery of claim 14, wherein the cathode comprises a lithium metal oxide. The electrode tab includes a positive electrode tab and a negative electrode tab, and the tab lead-out directions of the positive electrode tab and the negative electrode tab are opposite.

16. An electrical device, characterized by The battery of any one of claims 1-13 or the battery of claim 14 provides electrical energy for the electrical load.

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