Negative electrode sheet, secondary battery, battery assembly, and electric device

Abstract

A negative electrode sheet (10), a secondary battery (100), a battery assembly (200), and an electric device (300). The negative electrode sheet (10) comprises a current collector (11) and a negative electrode material (12) provided on at least one surface of the current collector (11). The negative electrode material (12) comprises negative electrode active materials (1) and a conductive agent (2). The conductive agent (2) comprises carbon nanotubes (21) and graphene sheets (22). The average tube diameter of the carbon nanotubes (21) ranges from 20 nm to 80 nm, and the average sheet diameter of the graphene sheets (22) ranges from 0.5 μm to 5 μm.

Description

Negative electrode sheet, secondary battery, battery assembly and electric device

[0001] The present application claims priority to the Chinese patent application No. 202411393910.0, filed on September 29, 2024, the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present disclosure relates to the technical field of batteries, and in particular to a negative electrode sheet, a secondary battery, a battery assembly and an electric device. BACKGROUND

[0003] Secondary batteries are widely used in electric vehicles, electric motorcycles, aerospace and other fields. As the application range of secondary batteries becomes more and more extensive, higher requirements are put forward for the performance of secondary batteries. SUMMARY

[0004] The present disclosure provides a negative electrode sheet, a secondary battery, a battery assembly and an electric device to solve the problem that the internal resistance of the secondary battery is large when the surface density of the battery electrode sheet is increased, affecting the charging speed of the secondary battery.

[0005] In a first aspect, a negative electrode sheet is provided. The negative electrode sheet includes a current collector and a negative electrode material disposed on at least one surface of the current collector. The negative electrode material includes a negative electrode active material and a conductive agent. The conductive agent includes carbon nanotubes and graphene sheets. The average tube diameter of the carbon nanotubes ranges from 20 nm to 80 nm; and the average sheet diameter of the graphene sheets ranges from 0.5 μm to 5 μm.

[0006] The negative electrode material provided by some embodiments of the present disclosure is used in the negative electrode sheet of a secondary battery. The average tube diameter of the carbon nanotubes in the conductive agent ranges from 20 nm to 80 nm, which can make the carbon nanotubes form a continuous conductive network and improve the diffusion rate of active ions in the carbon nanotubes in the secondary battery. The sheet diameter of the graphene sheets in the conductive agent ranges from 0.5 μm to 5 μm, which can improve the dispersibility of the graphene sheets in the negative electrode material and the close connection performance with other components of the negative electrode material, and is used to improve the compaction performance and flexibility of the negative electrode sheet. Further, by setting the average tube diameter of the carbon nanotubes to range from 20 nm to 80 nm and the average sheet diameter of the graphene sheets to range from 0.5 μm to 5 μm, the carbon nanotubes with linear structure and the graphene sheets with sheet layer structure can complement each other, forming a winding and surrounding conductive network, so that the negative electrode material forms a more uniform and dense microstructure, the transmission and diffusion rate of active ions between and inside the carbon nanotubes is improved, the compaction performance and flexibility of the negative electrode sheet are improved, the internal resistance of the secondary battery is reduced, and thus the charging and discharging performance of the battery is improved.

[0007] In some embodiments, the average tube length of the carbon nanotubes ranges from 0.5 μm to 30 μm.

[0008] In some embodiments, the ratio of the mass of the carbon nanotubes to the mass of the graphene sheets ranges from 0.1 to 10.

[0009] In some embodiments, the ratio of the mass of the carbon nanotubes to the mass of the graphene sheets ranges from 0.1 to 3.

[0010] In some embodiments, the ratio of the mass of the carbon nanotubes to the mass of the negative electrode active material ranges from 0.0008 to 0.03.

[0011] In some embodiments, the ratio of the mass of the carbon nanotubes to the mass of the negative electrode active material ranges from 0.0008 to 0.02.

[0012] In some embodiments, the conductive agent further includes at least one of conductive carbon black and carbon fiber material.

[0013] In some embodiments, the negative electrode material further includes a thickening agent and a binder. The ratio of the sum of the mass of the thickening agent and the mass of the binder to the sum of the mass of the negative electrode active material, the mass of the conductive agent, the mass of the thickening agent, and the mass of the binder ranges from 0.025 to 0.035.

[0014] In a second aspect, a secondary battery is provided. The secondary battery includes a positive electrode tab and the negative electrode tab described above. The positive electrode tab is disposed apart from the negative electrode tab.

[0015] It can be understood that the secondary battery provided by the above-described embodiments can achieve the beneficial effects described above with reference to the negative electrode tab, which will not be described herein again.

[0016] In a third aspect, a battery assembly is provided. The battery assembly includes the secondary battery described above and an assembly housing. The secondary battery is disposed in the assembly housing.

[0017] It can be understood that the battery assembly provided by the above-described embodiments can achieve the beneficial effects described above with reference to the negative electrode tab, which will not be described herein again.

[0018] In a fourth aspect, an electric device is provided. The electric device includes at least one of the secondary battery described above and the battery assembly described above.

[0019] It can be understood that the electric device provided by the above-described embodiments can achieve the beneficial effects described above with reference to the negative electrode tab, which will not be described herein again. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of some embodiments of the present disclosure, the following will briefly introduce the drawings needed to be used in the embodiments. Obviously, the drawings in the following description only constitute some embodiments of the present disclosure, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0021] FIG. 1 is a schematic diagram of a negative electrode tab according to some embodiments;

[0022] FIG. 2 is a schematic diagram of a negative electrode material according to some embodiments;

[0023] FIG. 3 is a block diagram of a secondary battery according to some embodiments;

[0024] FIG. 4 is a block diagram of a battery assembly according to some embodiments;

[0025] FIG. 5 is a block diagram of an electric device according to some embodiments;

[0026] FIG. 6 is a flowchart of a method of manufacturing a secondary battery according to some embodiments. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present disclosure will be described clearly and completely in the following with reference to the drawings in the embodiments of the present disclosure. Obviously, the described embodiments only constitute some embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present disclosure.

[0028] In the description of the present disclosure, it should be understood that the terms "upper", "lower", "left", "right", "front", "back", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or relative position relationship shown in the drawings, and are only for the purpose of facilitating the description of the present disclosure and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present disclosure. Unless otherwise specified, the above orientation description can be flexibly arranged in the actual application process under the condition of meeting the relative position relationship shown in the drawings.

[0029] The terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present disclosure, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0030] In the description of the present disclosure, it should be noted that unless specifically defined and limited otherwise, the terms "mount", "connected", "connection", "communicate" should be interpreted broadly, for example, can be fixed connection, can also be detachable connection, or integral connection. It can be directly connected, or indirectly connected through an intermediate medium, and it can be internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present disclosure can be understood according to the specific circumstances.

[0031] In some embodiments of the present disclosure, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, article or apparatus including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent to such a process, article or apparatus. Without more limitations, the element defined by the sentence "including a" does not exclude the presence of additional identical elements in the process, article or apparatus including the element.

[0032] In some embodiments of the present disclosure, the word "exemplary" or "for example" is used to mean serving as an example, instance or illustration. Any embodiment or design described as "exemplary" or "for example" in some embodiments of the present disclosure should not be construed as being more preferred or advantageous than other embodiments or designs. Rather, the use of "exemplary" or "for example" is intended to present concepts in a concrete manner.

[0033] In the description of the present disclosure, features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0034] In order to make the technical problems, technical solutions and beneficial effects solved by the present disclosure clearer, some embodiments of the present disclosure are further described in detail below in combination with the drawings and examples. It should be understood that the embodiments described herein are only used to explain the present disclosure, and not to limit the present disclosure.

[0035] In the related art, as the surface density of the battery pole piece of the secondary battery increases, the internal resistance of the secondary battery increases significantly, which reduces the conductivity of the secondary battery, thereby reducing the charging speed of the secondary battery and affecting the charging performance of the secondary battery.

[0036] To solve the above problems, some embodiments of the present disclosure provide a negative pole piece, a secondary battery, a battery assembly and a power consumption device.

[0037] In some embodiments, the secondary battery comprises: a positive electrode sheet, a negative electrode sheet, a shell, an electrolyte, and a separator. The positive electrode sheet, the negative electrode sheet, the electrolyte, and the separator are placed in the shell. During the charging and discharging process of the secondary battery, active ions are embedded and de-embedded between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent short circuiting of the positive and negative electrodes, and can allow active ions to pass through.

[0038] The speed of active ions embedding and de-embedding between the positive electrode sheet and the negative electrode sheet has an important influence on the charging performance of the secondary battery. The faster the diffusion rate of active ions, the faster the charging speed of the secondary battery, and vice versa. The slower the diffusion rate of active ions, the slower the charging speed of the secondary battery.

[0039] Exemplarily, the negative electrode sheet is loaded with a negative electrode material, which has an important influence on the charging speed of the secondary battery. The influence of the negative electrode material on the charging speed of the secondary battery can include the following three aspects.

[0040] Firstly, the negative electrode material can affect the diffusion rate of active ions. As the main storage place of active ions, the faster the speed of active ions embedding and de-embedding the negative electrode material, the faster the diffusion rate of active ions, which can reduce the transmission resistance of active ions in the material, reduce the contact resistance of the negative electrode material, and further reduce the internal resistance of the secondary battery, thereby improving the charging speed of the secondary battery.

[0041] Secondly, the negative electrode material can affect the compaction performance of the negative electrode sheet. The compaction performance of the negative electrode sheet can affect the conduction performance of active ions. Higher compaction performance can make the internal resistance of the secondary battery smaller, thereby reducing the internal resistance of the secondary battery to improve the charging speed of the secondary battery.

[0042] Thirdly, the negative electrode material can affect the flexibility of the negative electrode sheet. During the charging and discharging process of the secondary battery, the negative electrode sheet may be broken or pulverized due to volume change. The flexibility of the negative electrode sheet can alleviate the stress on the negative electrode sheet due to volume change, maintain the structural stability of the negative electrode sheet, and reduce the problem of breaking or pulverization of the negative electrode sheet, thereby maintaining the stable interface contact of the negative electrode sheet and helping to reduce the internal resistance of the secondary battery.

[0043] Based on this, the negative electrode tab 10 is provided in some embodiments of the present disclosure. As shown in FIG. 1, the negative electrode tab 10 includes a current collector 11 and a negative electrode material 12 disposed on at least one surface of the current collector 11. As shown in FIG. 2, the negative electrode material 12 includes a negative electrode active material 1 and a conductive agent 2. The conductive agent 2 includes carbon nanotubes 21 and graphene sheets 22. The average tube diameter of the carbon nanotubes 21 ranges from 20 nm to 80 nm; and the average sheet diameter of the graphene sheets 22 ranges from 0.5 μm to 5 μm.

[0044] The current collector 11 mainly functions to collect and conduct current. During the charging and discharging process of the secondary battery, the current collector 11 is responsible for effectively conducting the current generated on the negative electrode material 12 to the external circuit.

[0045] It should be noted that the active material is an important component of the negative electrode tab 10. During the charging and discharging process of the secondary battery, the negative electrode active material 1 plays an important role in transferring electrons; and the negative electrode active material 1 can reversibly de-intercalate active ions and store energy, which is a key material for the secondary battery.

[0046] Exemplarily, the negative electrode active material 1 includes a carbon material. For example, the carbon material can be natural graphite, artificial graphite, hard carbon, secondary silicon-carbon, etc.

[0047] The conductive agent 2 can reduce the contact resistance of the negative electrode tab 10, thereby accelerating the movement rate of electrons and improving the charging and discharging efficiency of the secondary battery. During the multiple charging and discharging process of the secondary battery, the intercalation and de-intercalation of active ions can cause the volume expansion of the negative electrode material 12, which reduces the conductivity of the negative electrode material 12. The conductive agent 2 can help alleviate the volume expansion of the negative electrode material 12, thereby improving the cycle performance of the secondary battery.

[0048] Exemplarily, the average tube diameter of the carbon nanotubes 21 can be 20 nm, 35 nm, 50 nm, 65 nm, or 80 nm, etc.

[0049] Exemplarily, the average sheet diameter of the graphene sheets 22 can be 0.5 μm, 1 μm, 1.5 μm, 2.5 μm, 3.5 μm, or 5 μm, etc.

[0050] Based on this scheme, first, the carbon nanotubes 21 have a high specific surface area, which can provide a large number of active ion active sites, which is beneficial to the intercalation and de-intercalation of active ions. In addition, the cylindrical configuration of the carbon nanotubes 21 can enable active ions to intercalate from both the outer wall and the inner wall, thereby effectively improving the diffusion ability of active ions in the negative electrode material 12, enhancing the conductivity of the negative electrode tab 10, and helping to reduce the internal resistance of the secondary battery. In addition, the carbon nanotubes 21 have good flexibility, and the compressed carbon nanotubes 21 form wave-shaped knots that can elastically relax and recover to their original shape after unloading, which can resist distortion caused by torsional force.

[0051] When the average tube diameter of the carbon nanotubes 21 is relatively large, for example, greater than 80 nm, voids can be formed in the negative electrode sheet 10, resulting in a relatively small compaction performance of the negative electrode sheet 10. In addition, the relatively large tube diameter can also make the distribution of the carbon nanotubes 21 in the negative electrode sheet 10 uneven, further affecting the compaction performance of the negative electrode sheet 10. When the average tube diameter of the carbon nanotubes 21 is relatively small, for example, less than 5 nm, the carbon nanotubes 21 can only coat the surface of the negative electrode material 12, and cannot form an effective three-dimensional conductive network, which cannot form sufficient contact points, affecting the transport and diffusion of active ions between and inside the carbon nanotubes 21, and thus cannot achieve good connection of the negative electrode conductive path.

[0052] Secondly, the high electrical conductivity of the graphene sheets 22 enables electrons to be transmitted in the negative electrode sheet 10 more quickly, and the graphene sheets 22 have a two-dimensional layered structure and a large specific surface area, and can form a relatively dense network structure with the carbon nanotubes 21, thereby improving the compaction density of the negative electrode sheet 10, and further enabling the internal resistance of the secondary battery to be relatively small. In addition, the graphene sheets 22 have excellent flexibility, and can maintain the integrity and stability of their structure even when subjected to external forces. During the charging and discharging process of the secondary battery, the negative electrode sheet 10 can resist volume changes and prevent the negative electrode sheet 10 from breaking or pulverizing. In addition, the graphene sheets 22 can act as a “bridge” in the negative electrode material 12, connecting negative electrode materials 12 of different components to form a more stable three-dimensional network structure, thereby further improving the flexibility of the negative electrode sheet 10.

[0053] However, when the average sheet diameter of the graphene sheets 22 is relatively large, for example, greater than 5 pm, the graphene sheets 22 can form relatively large agglomerates in the negative electrode material 12, and the dispersibility is reduced, thereby increasing the number of voids in the negative electrode material on the negative electrode sheet 10 and reducing the compaction performance of the negative electrode sheet 10. In addition, the graphene sheets 22 with an excessively large average sheet diameter can increase the brittleness of the negative electrode sheet 10 and reduce the flexibility of the negative electrode sheet 10, and the negative electrode sheet 10 can break or pulverize due to volume changes during the charging and discharging process of the secondary battery.

[0054] When the average sheet diameter of the graphene sheets 22 is relatively small, for example, less than 0.5 pm, it can affect the formation of a continuous and uniform contact network between the components of the negative electrode material 12, resulting in insufficient compaction of the graphene sheets 22 in the negative electrode material 12, and thus affecting the compaction performance of the negative electrode sheet 10. In addition, the graphene sheets 22 with a relatively small average sheet diameter can increase the contact resistance between the graphene sheets 22, resulting in an increase in the internal resistance of the negative electrode sheet 10.

[0055] In summary, on the one hand, by setting the average tube diameter of the carbon nanotubes 21 in the range of 20 nm to 80 nm, the multiple carbon nanotubes 21 can be more easily contacted and overlapped with each other to form a continuous conductive network, so that the active ions can be more easily transported and diffused between and inside the multiple carbon nanotubes 21, thereby improving the diffusion rate of the active ions in the carbon nanotubes 21 and reducing the internal resistance of the secondary battery. Further, the carbon nanotubes 21 can also improve the compaction performance of the negative electrode sheet 10, further reduce the internal resistance of the secondary battery, and improve the stability of the secondary battery. By setting the average sheet diameter of the graphene sheets 22 in the range of 0.5 μm to 5 μm, the dispersibility of the graphene sheets 22 in the negative electrode material 12 can be improved to improve the close connection performance of the graphene sheets 22 with other components in the negative electrode material 12, thereby improving the compaction performance and flexibility of the negative electrode sheet 10.

[0056] On the other hand, by setting the average tube diameter of the carbon nanotubes 21 in the range of 20 nm to 80 nm and the average sheet diameter of the graphene sheets 22 in the range of 0.5 μm to 5 μm, the carbon nanotubes 21 with linear structure and the graphene sheets 22 with sheet structure can be mutually complementary to form a conductive network that is intertwined and surrounded, so that the negative electrode material 12 forms a more uniform and dense microstructure, which can further improve the rate of transport and diffusion of active ions between and inside the carbon nanotubes 21, and improve the compaction performance and flexibility of the negative electrode sheet 10, further reduce the internal resistance of the secondary battery, and thereby improve the charging performance of the secondary battery.

[0057] Exemplarily, the conductive agent 2 on the surface and cross-section of the negative electrode sheet 10 can be directly characterized by a Focused Ion Beam-Scanning Electron Microscope (FIB-SEM).

[0058] Exemplarily, the carbon nanotubes 21 can be prepared by a moving bed / fixed bed growth process.

[0059] Exemplarily, the carbon nanotubes 21 can be prepared by a fixed bed growth process using a nickel-based catalyst.

[0060] Exemplarily, the average tube diameter of the carbon nanotubes 21 and the average sheet diameter of the graphene sheets 22 can be tested by a Scanning Electron Microscope (SEM) and a Transmission Electron Microscope (TEM), and the test standard can refer to the national standard GB / T 30544.13-2018. The method is as follows: after separation, dilute with ethanol, disperse in a micro-grid copper mesh, and randomly select 100 carbon nanotubes 21 for tube diameter statistics, and take the average value.

[0061] Exemplarily, the carbon nanotubes 21 and graphene sheets 22 in the negative electrode material 12 on the negative electrode sheet 10 are separated, and the average tube length of the carbon nanotubes 21 and catalyst information are tested.

[0062] Exemplarily, the separation of the carbon nanotubes 21 and graphene sheets 22 in the negative electrode material 12 on the negative electrode sheet 10 can be performed by the following steps. The negative electrode sheet 10 is placed in a hydrogen chloride (HCl) solution of a certain concentration, and the current collector 11 (for example, a copper foil) and other soluble components in the sheet are removed by stirring or ultrasonic acceleration of dissolution, and then the solution is separated from the insoluble components by filtration or centrifugation. The insoluble components are dried and ground to be particle-free, and then mixed with an appropriate amount of solvent or dispersant, placed in an ultrasonic bath or treated with an ultrasonic probe to form a uniform suspension.

[0063] During the ultrasonic treatment, due to the different characteristics of the negative electrode active material 1 and the carbon nanotubes 21, a small amount of aggregation and dispersion will occur. After the ultrasonic treatment is completed, the sample is centrifuged, and the centrifugal speed is adjusted to separate the carbon nanotubes 21, graphene sheets 22 and negative electrode active material 1, which are then tested by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The method is as follows: after separation, ethanol is used for dilution, and the carbon nanotubes 21 are dispersed on a micro-grid copper mesh. 100 carbon nanotubes 21 are randomly selected for tube length statistics, and the average value is taken.

[0064] In some embodiments, the average tube length of the carbon nanotubes 21 ranges from 0.5 μm to 30 μm.

[0065] Exemplarily, the average tube length of the carbon nanotubes 21 can be 0.5 μm, 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm or 30 μm, etc.

[0066] When the average tube length of the carbon nanotubes 21 is relatively long, for example, the average tube length of the carbon nanotubes 21 is greater than 30 μm, the carbon nanotubes 21 will have a large degree of bending, which will increase the instability of the internal structure of the carbon nanotubes 21 when subjected to external forces. The relatively long average tube length of the carbon nanotubes 21 can also cause discontinuity of the conductive network, increasing the internal resistance of the negative electrode sheet 10. The relatively long average tube length of the carbon nanotubes 21 causes the presence of pores in the negative electrode material 12, which reduces the compaction performance of the negative electrode sheet 10.

[0067] When the average tube length of the carbon nanotubes 21 is relatively short, for example, the average tube length of the carbon nanotubes 21 is less than 0.5 μm, the electrons will encounter more obstacles or deviate from the original path when transmitting in the negative electrode material 12, which will affect the embedding and de-embedding speed of the active ions, and ultimately affect the charging performance of the secondary battery.

[0068] Therefore, by setting the average tube length of the carbon nanotubes 21 in the range of 0.5 μm to 20 μm, the resistance of the electron transmission inside the negative electrode material 12 can be reduced, so that the negative electrode material 12 can provide a better electron transmission path, an effective conductive network can be formed, the diffusion of the active ions in the negative electrode material 12 is more rapid and uniform, the internal resistance of the negative electrode plate 10 is reduced, and thus the internal resistance of the secondary battery is reduced, so as to improve the charging performance of the secondary battery.

[0069] In some embodiments, the ratio of the mass of the carbon nanotubes 21 to the mass of the graphene sheets 22 is in the range of 0.1 to 10.

[0070] For example, the ratio of the mass of the carbon nanotubes 21 to the mass of the graphene sheets 22 can be 0.1, 2, 4, 6, 8, or 10, etc.

[0071] By setting the ratio of the mass of the carbon nanotubes 21 to the mass of the graphene sheets 22 in the range of 0.1 to 10, the conductive network of the negative electrode plate 10 can be made more dense, so that the electron transmission is more efficient, thereby improving the diffusion performance of the active ions, reducing the contact resistance inside the negative electrode material 12, improving the electrical conductivity, and thus reducing the internal resistance of the secondary battery; the compaction performance and flexibility of the negative electrode plate 10 can also be improved, a more stable and continuous conductive channel is formed, and the internal resistance of the secondary battery is further reduced.

[0072] In some embodiments, the ratio of the mass of the carbon nanotubes 21 to the mass of the graphene sheets 22 is in the range of 0.1 to 3.

[0073] By setting the ratio of the mass of the carbon nanotubes 21 to the mass of the graphene sheets 22 in the range of 0.1 to 3, the conductive network of the negative electrode plate 10 can be made more dense, and the internal resistance of the secondary battery is further reduced.

[0074] In some embodiments, the ratio of the mass of the carbon nanotubes 21 to the mass of the negative electrode active material 1 is in the range of 0.0008 to 0.03.

[0075] For example, the ratio of the mass of the carbon nanotubes 21 to the mass of the negative electrode active material 1 can be 0.0008, 0.001, 0.0015, 0.002, 0.0025, or 0.03, etc.

[0076] By setting the ratio of the mass of the carbon nanotubes 21 to the mass of the negative electrode active material 1 in the range of 0.0008 to 0.03, the carbon nanotubes 21 can be more effectively filled in the gaps between the negative electrode active material 1 particles to form a more dense conductive channel, which helps the rapid transmission of electrons in the negative electrode material 12, and also ensures that the secondary battery maintains stable performance during the charging and discharging process, and further reduces the internal resistance of the secondary battery.

[0077] In some embodiments, the ratio of the mass of the carbon nanotubes 21 to the mass of the negative active material 1 ranges from 0.0008 to 0.002.

[0078] By setting the ratio of the mass of the carbon nanotubes 21 to the mass of the negative active material 1 to range from 0.0008 to 0.02, the rapid transmission of electrons in the negative material 12 can be further facilitated, and the internal resistance of the secondary battery can be further reduced.

[0079] In some embodiments, the conductive agent 2 further includes at least one of conductive carbon black and carbon fiber material.

[0080] It can be understood that any one or more of the above-mentioned conductive agents 2 can improve the charging performance of the secondary battery.

[0081] In some embodiments, the negative material 12 further includes a thickening agent and a binder; the ratio of the sum of the mass of the thickening agent and the mass of the binder to the sum of the mass of the negative active material 1, the mass of the conductive agent 2, the mass of the thickening agent, and the mass of the binder ranges from 0.025 to 0.035.

[0082] Exemplarily, the ratio of the sum of the mass of the thickening agent and the mass of the binder to the sum of the mass of the negative active material 1, the mass of the conductive agent 2, the mass of the thickening agent, and the mass of the binder can be 0.025, 0.03, or 0.035, etc.

[0083] The main role of the thickening agent is to increase the viscosity of the negative slurry and improve the rheological properties of the negative slurry, so that the negative material 12 is more easily shaped, thereby improving the formability and adhesion of the negative electrode sheet 10.

[0084] The main role of the binder is to adhere the negative material 12 to the current collector 11 and maintain the integrity and stability of the structure of the negative electrode sheet 10. The binder can also improve the wettability of the electrolyte and promote the transmission of active ions at the interface between the negative electrode and the electrolyte.

[0085] In the second aspect, as shown in FIG. 3, some embodiments of the present disclosure further provide a secondary battery 100. The secondary battery 100 includes a positive electrode sheet and the negative electrode sheet 10 in any one of the above-mentioned embodiments. The positive electrode sheet and the negative electrode sheet 10 are arranged in a spaced manner.

[0086] Exemplarily, the positive electrode sheet includes a positive current collector 11 and a positive material arranged on at least one surface of the positive current collector 11.

[0087] Exemplarily, the positive current collector 11 can adopt a metal foil or a composite current collector 11. For example, as the metal foil, an aluminum foil can be adopted. The composite current collector 11 can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer.

[0088] Exemplarily, the positive electrode material includes a positive electrode active material, a conductive agent 2, and a binder.

[0089] Exemplarily, the positive electrode active material can employ a positive electrode active material for a battery known in the art. For example, the positive electrode active material can include at least one of a lithium-containing phosphate of an olivine structure, a lithium transition metal oxide, or a modified compound of each thereof. However, the present disclosure is not limited to these materials, and other conventional materials that can be used as a positive electrode active material for a battery can also be used. Some embodiments of the present disclosure are exemplified with a lithium iron phosphate (LiFeP04) as the positive electrode active material.

[0090] Exemplarily, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene-fluorotetrafluoroethylene-propylene terpolymer, a vinylidene-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, or a fluorine-containing acrylate resin.

[0091] For example, the conductive agent 2 can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes 21, graphene sheets 22, or carbon nanofibers.

[0092] In some embodiments, the negative electrode sheet 10 can be prepared by dispersing the components for preparing the negative electrode sheet 10, for example, the negative electrode active material 1, the conductive agent 2, the thickening agent, and the binder, in a solvent to form a negative electrode slurry, coating the negative electrode slurry on the negative electrode current collector 11, and then performing processes such as drying and cold pressing to obtain the negative electrode sheet 10.

[0093] In some embodiments, the electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet 10. The present disclosure does not limit the type of electrolyte, which can be selected as needed. For example, the electrolyte can be in a liquid state, a gel state, or a full solid state.

[0094] In some embodiments, the electrolyte includes an electrolyte salt and a solvent.

[0095] Exemplarily, the electrolyte salt can be lithium hexafluorophosphate.

[0096] Exemplarily, the solvent can be a combination of dimethyl carbonate and ethyl methyl carbonate.

[0097] In some embodiments, the secondary battery further includes a separator film, and the present disclosure does not particularly limit the type of the separator film, which can be any known porous structure separator film having good chemical stability and mechanical stability.

[0098] In some embodiments, the material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The separator film can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

[0099] In some embodiments, the positive electrode tab, the negative electrode tab 10, and the separator film can be made into an electrode assembly through a winding process or a stacking process.

[0100] The shape of the secondary battery according to the present disclosure is not particularly limited, and can be cylindrical, square, or any other shape. For example, FIG. 1 is a secondary battery of a square structure as an example.

[0101] In a third aspect, as shown in FIG. 4, some embodiments of the present disclosure further provide a battery assembly 200. The battery assembly 200 includes a secondary battery 100 as in the above embodiments and an assembly housing. The secondary battery is arranged in the assembly housing.

[0102] In a fourth aspect, as shown in FIG. 5, some embodiments of the present disclosure further provide a power consuming device 300. The power consuming device 300 includes at least one of a secondary battery 100 as in the above embodiments or a battery assembly 200 as in the above embodiments. In FIG. 5, the power consuming device 300 is taken as an example including the secondary battery 100 and the battery assembly 200.

[0103] The secondary battery or the battery assembly can be used as a power source of the power consuming device, or can be used as an energy storage unit of the power consuming device. The power consuming device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc., but is not limited thereto.

[0104] As the power consuming device, the secondary battery or the battery assembly can be selected according to the use requirement thereof.

[0105] As another example of the power consuming device, it can be a mobile phone, a tablet computer, a notebook computer, etc. The power consuming device usually requires thinness, and the secondary battery can be used as a power source.

[0106] The following experiments are taken as examples to further describe some embodiments of the present disclosure in detail.

[0107] Embodiment 1

[0108] As shown in FIG. 6, the preparation method of the secondary battery includes steps S11-S14.

[0109] S11: Add the positive active material, the conductive agent and the binder in a mass ratio of 97:1:2 into a solvent to form a mixture, mix and stir the mixture into a positive slurry by using a homogenizer, and uniformly coat the positive slurry on an aluminum foil to form a positive electrode sheet.

[0110] Illustratively, the positive active material is selected from lithium iron phosphate.

[0111] Illustratively, the conductive agent is selected from conductive carbon black.

[0112] Illustratively, the binder is selected from polyvinylidene fluoride.

[0113] Illustratively, the solvent is selected from methylpyrrolidone.

[0114] S12: Mix the negative active material 1, the conductive agent 2, the thickening agent and the binder in a mass ratio of 96:1:1:2, stir to form a negative slurry by using a homogenizer, and single-layer coat the negative slurry on a copper foil to form a negative electrode sheet 10.

[0115] Illustratively, the negative active material 1 is selected from artificial graphite.

[0116] Illustratively, the thickening agent is selected from sodium carboxymethyl cellulose.

[0117] Illustratively, the binder is selected from butadiene styrene rubber.

[0118] Illustratively, the conductive agent 2 is selected from carbon nanotubes 21, graphene sheets 22 and carbon black.

[0119] The mass ratio of the carbon nanotubes 21, the graphene sheets 22 and the carbon black is 1:1:10; the average tube diameter of the carbon nanotubes 21 is 20 nm, and the average tube length is 20 μm; the average sheet diameter of the graphene sheets 22 is 0.5 μm.

[0120] S13: Mix ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate in a volume ratio of 1:1:1, then add lithium hexafluorophosphate and mix and stir to form a lithium hexafluorophosphate electrolyte with a molar concentration of 1M.

[0121] S14: Stack the positive electrode sheet formed in step S11, the separator and the negative electrode sheet 10 formed in step S12 to assemble a 1.7 Ah secondary battery, and the electrolyte is the electrolyte prepared in step S13.

[0122] Illustratively, the material of the separator is selected from polypropylene.

[0123] Example 2

[0124] The preparation method of the secondary battery of Example 2 is the same as that of Example 1, except that the mass ratio of the carbon nanotube 21, the graphene sheet 22 and the carbon black in the conductive agent 2 of S12 is 2:2:10; the average tube diameter of the carbon nanotube 21 is 80 nm, and the average tube length is 0.5 μm; and the average sheet diameter of the graphene sheet 22 is 5 μm.

[0125] Example 3

[0126] The preparation method of the secondary battery of Example 3 is the same as that of Example 1, except that the mass ratio of the carbon nanotube 21, the graphene sheet 22 and the carbon black in the conductive agent 2 of S12 is 2:2:6; the average tube diameter of the carbon nanotube 21 is 40 nm, and the average tube length is 2 μm; and the average sheet diameter of the graphene sheet 22 is 1 μm.

[0127] Example 4

[0128] The preparation method of the secondary battery of Example 4 is the same as that of Example 1, except that the mass ratio of the carbon nanotube 21, the graphene sheet 22 and the carbon black in the conductive agent 2 of S12 is 1:10:1.

[0129] Example 5

[0130] The preparation method of the secondary battery of Example 5 is the same as that of Example 1, except that the mass ratio of the carbon nanotube 21, the graphene sheet 22 and the carbon black in S12 is 9:3:1.

[0131] Example 6

[0132] The preparation method of the secondary battery of Example 6 is the same as that of Example 1, except that the mass ratio of the carbon nanotube 21, the graphene sheet 22 and the carbon black in S12 is 1:5:5.

[0133] Example 7

[0134] The preparation method of the secondary battery of Example 7 is the same as that of Example 1, except that the conductive agent 2 composed of the carbon nanotube 21 and the graphene sheet 22, in which the mass ratio of the carbon nanotube 21 and the graphene sheet 22 is 1:1, is used to replace the conductive agent 2 composed of the carbon nanotube 21, the graphene sheet 22 and the carbon black in S12 in equal amount.

[0135] Comparative Example 1

[0136] The preparation method of the secondary battery of Comparative Example 1 is the same as that of Example 1, except that the conductive agent 2 of S12 is conductive carbon black.

[0137] Comparative Example 2

[0138] The preparation method of the secondary battery of Comparative Example 2 is the same as that of Example 1, except that the mass ratio of the negative active material 1, the conductive agent 2, the thickening agent and the binder in S12 is 95:2:1:2, and the conductive agent 2 is conductive carbon black.

[0139] Comparative Example 3

[0140] The preparation method of the secondary battery of Comparative Example 3 is the same as that of Example 1, except that the average tube diameter of the carbon nanotube 21 is 7 nm and the average tube length is 20 μm; and the average sheet diameter of the graphene sheet 22 is 0.5 μm in S12.

[0141] Comparative Example 4

[0142] The preparation method of the secondary battery of Comparative Example 4 is the same as that of Example 1, except that the average tube diameter of the carbon nanotube 21 is 90 nm and the average tube length is 20 μm; and the average sheet diameter of the graphene sheet 22 is 0.5 μm in S12.

[0143] Comparative Example 5

[0144] The preparation method of the secondary battery of Comparative Example 5 is the same as that of Example 1, except that the average tube diameter of the carbon nanotube 21 is 20 nm and the average tube length is 20 μm; and the average sheet diameter of the graphene sheet 22 is 0.2 μm in S12.

[0145] Comparative Example 6

[0146] The preparation method of the secondary battery of Comparative Example 6 is the same as that of Example 1, except that the average tube diameter of the carbon nanotube 21 is 20 nm and the average tube length is 20 μm; and the average sheet diameter of the graphene sheet 22 is 10 μm in S12.

[0147] The following describes the performance test data of the batteries provided by Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2.

[0148] Direct current internal resistance (DCIR) test, the test method is as follows:

[0149] (1) At a temperature of 25℃, 0.2C charging and discharging is carried out to calibrate the battery capacity;

[0150] (2) Charged at 0.2C to 50% state of charge and 90% state of charge;

[0151] (3) Set 2C charging for 30s, record the termination voltage and termination current of each process, and calculate the DCIR. The results are shown in Table 1.

[0152] Table 1 Direct current internal resistance (mΩ) of the secondary battery of the examples and comparative examples

[0153] As can be seen from Table 1, the direct current internal resistance of the secondary battery provided by Examples 1-7 is less than that of the secondary batteries provided by Comparative Examples 1-6, indicating that the secondary battery formed by the negative electrode sheet 10 provided by some embodiments of the present disclosure has good charging performance.

[0154] The direct current internal resistance of the secondary battery provided by Examples 4 and 5 is less than that of the secondary battery provided by Example 1, indicating that when the ratio of the mass of the carbon nanotube 21 to the mass of the graphene sheet 22 is in the range of 0.1-3, the secondary battery has good charging performance.

[0155] The direct current internal resistance of the secondary battery provided by Comparative Example 1 is less than that of the secondary batteries provided by Comparative Examples 3-6, indicating that in some embodiments of the present disclosure, the conductive agent in which the average tube diameter of the carbon nanotube 21 is in the range of 20-80 nm and the average sheet diameter of the graphene sheet 22 is in the range of 0.5-5 μm can be used in the secondary battery to reduce the internal resistance of the secondary battery, which is related to the fact that the average tube diameter of the carbon nanotube 21 is in the range of 5-80 nm and the average sheet diameter of the graphene sheet 22 is in the range of 0.5-5 μm, which can improve the ion diffusion performance, compaction performance, and flexibility of the negative electrode sheet 10.

[0156] The above is only a specific embodiment of the present disclosure, but the protection scope of the present disclosure is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present disclosure, which should be covered within the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure should be subject to the protection scope of the claims.

Claims

1. A negative electrode sheet comprising: A current collector and a negative electrode material provided on at least one surface of the current collector; The negative electrode material includes a negative electrode active material and a conductive agent; The conductive agent includes carbon nanotubes and graphene sheets; The average tube diameter of the carbon nanotubes ranges from 20 nm to 80 nm; The average sheet diameter of the graphene sheets ranges from 0.5 μm to 5 μm.

2. The negative electrode sheet according to claim 1, wherein The average tube length of the carbon nanotubes ranges from 0.5 μm to 30 μm.

3. The negative electrode sheet according to claim 1 or 2, wherein The ratio of the mass of the carbon nanotubes to the mass of the graphene sheets ranges from 0.1 to 10.

4. The negative electrode sheet according to claim 3, wherein The ratio of the mass of the carbon nanotubes to the mass of the graphene sheets ranges from 0.1 to 3.

5. The negative electrode sheet according to any one of claims 1 to 4, wherein The ratio of the mass of the carbon nanotubes to the mass of the negative electrode active material ranges from 0.0008 to 0.

03.

6. The negative electrode sheet according to any one of claims 1 to 5, wherein The ratio of the mass of the carbon nanotubes to the mass of the negative electrode active material ranges from 0.0008 to 0.

02.

7. The negative electrode sheet according to any one of claims 1 to 6, wherein The conductive agent further includes at least one of conductive carbon black or carbon fiber material.

8. The negative electrode sheet according to any one of claims 1 to 7, further comprising: A thickening agent and a binder; the ratio of the sum of the mass of the thickening agent and the mass of the binder to the mass of the negative electrode material ranges from 0.025 to 0.

035.

9. A secondary battery, comprising: The negative electrode sheet according to any one of claims 1 to 8; and A positive electrode sheet disposed apart from the negative electrode sheet.

10. A battery assembly, comprising: The secondary battery according to claim 9; and An assembly housing in which the secondary battery is disposed.

11. An electrical device comprising: At least one of the secondary battery according to claim 9 or the battery assembly according to claim 10.

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