Negative electrode, secondary battery, and electric device

Abstract

The present application provides a negative electrode, a secondary battery, and an electric device. The negative electrode has special structure and parameter design, and compared with the related art, when a same negative electrode active material is used, the negative electrode provided by the present application can be used for providing a secondary battery having better fast charging performance.

Description

Negative electrode, secondary battery and electric device

[0001] The present application claims priority to the Chinese patent application No. 202411364598.2, filed on September 27, 2024, entitled "Negative electrode, secondary battery and electric device", the whole content of which is incorporated herein by reference. TECHNICAL FIELD

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

[0003] As a key component of a secondary battery, the performance of the negative electrode has an important influence on the performance of the secondary battery. With the development of new energy technology, the market has higher and higher requirements for the fast charging performance of the secondary battery, which requires improving the electronic conductivity and ionic conductivity of the negative electrode. The industry generally improves the ionic conductivity and / or electronic conductivity of the negative electrode by optimizing the negative electrode active material, and rarely improves the fast charging performance of the negative electrode by optimizing the structure and parameter design of the negative electrode active material layer. SUMMARY

[0004] In view of this, the embodiments of the present application provide a negative electrode, a secondary battery and an electric device. The negative electrode has a special structure and parameter design, and compared with the related art, the negative electrode provided by the embodiments of the present application can be used to provide a secondary battery with better fast charging performance under the condition of using the same negative electrode active material.

[0005] The first aspect of the embodiments of the present application provides a negative electrode, comprising a current collector, and a first active material layer and a second active material layer which are stacked on at least one side surface of the current collector, the first active material layer is arranged away from the current collector;

[0006] The first active material layer comprises a first negative electrode active material and a first conductive agent, the first conductive agent comprises graphene; the graphene comprises single-layer graphene, or multi-layer graphene;

[0007] The first active material layer satisfies: 1.5≤D1k / (D0 2 L)≤25, wherein D1 is the particle size D50 of the first negative electrode active material, the unit is μm; D0 is the particle size D50 of the graphene, the unit is μm; L is the thickness of the single-layer graphene, or L is the size of the multi-layer graphene in the stacking direction of the graphene sheet layer, the unit is nm; k=3400nm 2 .

[0008] The graphene particles have good electrolyte absorption and retention capacity, the first active material layer is far away from the current collector and contains the graphene particles, which can effectively improve the electrolyte wettability of the negative electrode and the electrolyte retention capacity, thereby effectively reducing the reaction impedance of the negative electrode in the cycle process and improving the fast charging performance of the negative electrode. More importantly, the graphene particles have good electronic conductivity and certain ionic conductivity, and the particle size parameters of the graphene particles and the first negative active material satisfy the defined quantitative relationship, and the two can cooperate to build a more complete electronic conduction network and a better ion transmission path in the first active material layer, thereby improving the fast charging capacity of the negative electrode.

[0009] The negative electrode as described above, wherein the mass of the graphene particles accounts for 0.1%-3% of the mass of the first negative active material.

[0010] The negative electrode as described above, wherein the total mass of the first conductive agent accounts for 0.1%-3% of the total mass of the first active material layer.

[0011] The negative electrode as described above, wherein the first negative active material comprises one or more of a carbon-based negative active material, a silicon-based negative active material, and a phosphorus-based negative active material; the carbon-based negative active material comprises one or more of graphite, hard carbon, soft carbon, and mesocarbon microbeads; the silicon-based negative active material comprises one or more of silicon, silicon carbide, silicon oxide, and silicon alloy; and the phosphorus-based negative active material comprises one or more of black phosphorus, red phosphorus, and phosphorus carbide.

[0012] The negative electrode as described above, wherein 1 μm≤D0≤15 μm; and 0.34 nm≤L≤3.4 nm.

[0013] The negative electrode as described above, wherein 3 μm≤D1≤25 μm.

[0014] The negative electrode as described above, wherein the first conductive agent further comprises one or more of conductive carbon black, carbon nanotubes, and carbon fibers.

[0015] The negative electrode as described above, wherein the second active material layer comprises a second negative active material and a second conductive agent; and the second active material layer does not contain the graphene particles.

[0016] The negative electrode as described above, wherein the mass ratio of the first conductive agent in the first active material layer is less than or equal to the mass ratio of the second conductive agent in the second active material layer.

[0017] The negative electrode as described above, wherein the single-sided area density of the first active material layer is greater than or equal to the single-sided area density of the second active material layer; and the single-sided area density of the first active material layer is 40 g / m2 -140g / m 2 , the single surface density of the second active material layer is 20g / m 2 -70g / m 2 .

[0018] The negative electrode as described above, wherein the ratio of the single surface density of the first active material layer to the single surface density of the second active material layer is (1-7):1.

[0019] The negative electrode as described above, wherein the porosity of the first active material layer is greater than or equal to the porosity of the second active material layer; the porosity of the first active material layer is 20%-40%, and the porosity of the second active material layer is 20%-30%.

[0020] The negative electrode as described above, wherein the thickness of the first active material layer is 40μm-100μm, and the thickness of the second active material layer is 20μm-50μm.

[0021] The negative electrode as described above, wherein the thickness ratio of the first active material layer to the second active material layer is (1-5):1.

[0022] The negative electrode as described above, wherein the sum of the thickness of the first active material layer and the thickness of the second active material layer is 80μm-140μm.

[0023] The second aspect of the embodiments of the present application provides a secondary battery comprising the negative electrode provided by the first aspect of the embodiments of the present application. Since the secondary battery comprises the negative electrode provided by the first aspect of the embodiments of the present application, the secondary battery can achieve better fast charging performance.

[0024] The third aspect of the embodiments of the present application provides a power consuming device comprising the secondary battery provided by the embodiments of the present application. Since the power consuming device adopts the secondary battery provided by the embodiments of the present application, the power consuming device has a better market prospect. BRIEF DESCRIPTION OF DRAWINGS

[0025] Fig. 1 is a schematic structural diagram of a negative electrode provided by an embodiment of the present application;

[0026] Fig. 2 is a schematic structural diagram of a negative electrode provided by another embodiment of the present application;

[0027] Fig. 3 is a schematic structural diagram of a secondary battery and a power consuming device in an embodiment.

[0028] Legend: 10-collector; 21-first active material layer; 22-second active material layer; 3-power consuming device; 4-secondary battery. DETAILED DESCRIPTION

[0029] In order to cater to the needs of consumers, the industry is currently committed to improving the fast charging performance of secondary batteries, and improving the fast charging performance of the negative electrode is one of the important ways. At present, the industry improves the fast charging performance of the negative electrode by optimizing the electrical conductivity (including ionic conductivity and electronic conductivity) of the negative electrode active material; however, the performance optimization of the negative electrode active material requires large research and development investment, long research and development cycle, and relatively difficult landing. In fact, the structure and parameter optimization of the negative electrode can also improve the fast charging performance of the negative electrode, and can be combined with the improvement of the negative electrode active material to further improve the fast charging performance of the negative electrode.

[0030] In order to optimize the fast charging performance of the negative electrode from the structure and parameter design, the negative electrode provided by the embodiments of the present application comprises a current collector and a first active material layer and a second active material layer which are stacked on at least one side surface of the current collector, and the first active material layer is arranged away from the current collector;

[0031] The first active material layer comprises a first negative electrode active material and a first conductive agent, and the first conductive agent comprises graphene; the graphene comprises single-layer graphene or multi-layer graphene;

[0032] The first active material layer satisfies: 1.5≤D1k / (D0 2 L)≤25, wherein D1 is the particle size D50 of the first negative electrode active material, the unit is μm; D0 is the particle size D50 of the graphene, the unit is μm; L is the thickness of the single-layer graphene, or L is the size of the multi-layer graphene in the stacking direction of the graphene sheet layer, the unit is nm; k=3400 nm 2 .

[0033] It should be noted that only the values of D1, D0 and L are substituted into D1k / (D0 2 L) for calculation, for example: the particle size D50 (D1) of the first negative electrode active material is 2 μm, the particle size D50 (D0) of the graphene particle is 1 μm, the thickness of the single-layer graphene, or the size of the multi-layer graphene in the stacking direction of the graphene sheet layer (L) is 2.38 nm, then D1k / (D0 2 L) = 2 μm x 3400 nm 2 / (1 μm 2 x 2.38 nm) = 2.857.

[0034] In the embodiments of the present application, the thickness of single-layer graphene and the thickness of multi-layer graphene in the stacking direction of the graphite sheet can be tested by a transmission electron microscope (TEM). The particle size D50 of the graphene particles and the first negative electrode active material can be tested by a laser particle size analyzer. In the embodiments of the present application, the particle size D50 refers to the particle size corresponding to the cumulative volume percentage of 50% of the particles. Specifically, the negative electrode is pretreated before the above test. Specifically, the pretreatment includes: stripping the first active material layer from the negative electrode, stirring or ultrasonicating in hydrochloric acid, solid-liquid separation, drying the solid, grinding the dried solid, then dispersing in a solvent (for example, ethanol, acetone, etc.), ultrasonicating to obtain a suspension, and centrifuging the suspension to obtain the first negative electrode active material and the graphene particles, respectively.

[0035] In the embodiments of the present application, please refer to FIG. 1, which is a schematic diagram of the structure of the negative electrode provided by an embodiment. In FIG. 1, the negative electrode 1 can be a current collector 10, one side surface of which includes the first active material layer 21 and the second active material layer 22 which are stacked, and the other side surface is not provided with any material layer; or, the other side surface is provided with any negative electrode material layer known in the art. It can also be, as shown in FIG. 2, which is a schematic diagram of the structure of the negative electrode provided by another embodiment. In FIG. 2, the opposite two side surfaces of the current collector 10 each include the first active material layer 21 and the second active material layer 22 which are stacked.

[0036] The graphene particles have excellent electrolyte absorption and liquid retention capacity. The first active material layer 21 is arranged away from the current collector 10 and contains graphene particles, which can effectively improve the electrolyte infiltration of the negative electrode and the liquid retention capacity of the electrolyte, thereby effectively reducing the reaction impedance of the negative electrode in the cycle process and improving the fast charging performance of the negative electrode. More importantly, the graphene particles have excellent electronic conductivity and certain ionic conductivity. The particle size parameters of the graphene particles and the first negative electrode active material satisfy the above defined quantitative relationship, and the two cooperate with each other to build a more complete electronic conduction network and a more optimal ion transmission path in the first active material layer 21, thereby improving the fast charging capacity of the negative electrode.

[0037] Specifically, the value of D1k / (D0 2 L) can be, for example, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, etc. If D1k / (D0 2The value of D1k / (D0 2 The value of D1k / (D0 2 The value of D1k / (D0

[0038] It can be understood that the graphene particles and the first active material generally need to undergo rolling during the preparation of the negative electrode, and when the size parameters of the graphene particles and the first active material satisfy 1.5≤D1k / (D0 2 L)≤25, the graphene particles and the first negative electrode active material are not prone to slipping during the rolling, so that the pore structure of the first active material layer 21 is more optimal, which is more conducive to the adsorption and retention of the electrolyte, thereby facilitating ion transmission in the charging and discharging cycle and facilitating fast charging performance. In some embodiments of the present application, the porosity of the first active material layer 21 is greater than or equal to the porosity of the second active material layer 22. For example, the porosity of the first active material layer 21 is 20%-40%, and the porosity of the second active material layer 22 is 20%-30%. In the embodiments of the present application, the porosity of the first active material layer 21 and the second active material layer 22 can be tested by a scanning electron microscope (SEM). Specifically, the surface of the negative electrode material layer (including the first active material layer 21 and the second active material layer 22) is polished by argon ions, and then the negative electrode material layer is cut and imaged by FIB; the negative electrode material layer is cut along its thickness direction to obtain SEM photos of the cross sections of the first active material layer 21 and the second active material layer 22, and the porosity of the first active material layer 21 and the second active material layer 22 is tested by software. Specifically, the porosity of the first active material layer 21 may, for example, be 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, etc., and the porosity of the second active material layer 22 may, for example, be 20%, 22%, 25%, 28%, 30%, etc.

[0039] In some embodiments of the present application, the mass fraction of the graphene particles in the first negative electrode active material is 0.1%-3%. In this way, the electrolyte retention capacity of the first active material layer 21 can be ensured to be relatively optimal, and the electronic conductivity of the first active material can also be ensured to be good, thereby facilitating the fast charging performance of the negative electrode. Specifically, the mass fraction of the graphene may, for example, be 0.1%, 0.2%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.2%, 2.5%, 2.8%, 3.0%, etc., based on the mass of the first negative electrode active material.

[0040] In some embodiments of the present application, the first negative active material includes one or more of a carbon-based negative active material, a silicon-based negative active material, and a phosphorus-based negative active material. The carbon-based negative active material includes one or more of graphite, hard carbon, soft carbon, and mesocarbon microbeads. The silicon-based negative active material includes one or more of silicon, silicon carbide, silicon oxide, and silicon alloy. The phosphorus-based negative active material includes one or more of black phosphorus, red phosphorus, and phosphorus carbide.

[0041] In some embodiments of the present application, the first conductive agent further includes another conductive agent. The another conductive agent includes one or more of conductive carbon black, carbon nanotubes, and carbon fibers.

[0042] In some embodiments of the present application, the total mass of the first conductive agent accounts for 0.1%-3% of the total mass of the first active material layer 21. When the negative electrode is applied to a battery, the performance of the battery can be improved. Specifically, the total mass of the first conductive agent can account for 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, etc. of the total mass of the first active material layer 21.

[0043] In some embodiments of the present application, 1 μm≤D0≤15 μm. That is, the particle size D50 of the graphene particles is 1 μm-15 μm. Specifically, the particle size D50 of the graphene particles may, for example, be 1 μm, 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, etc. In some specific embodiments, 1 μm≤D0≤6 μm. In this way, the compounding effect with the first negative active material is better, and it is also more conducive to obtaining a first active material layer 21 with a suitable porosity, thereby more conducive to optimizing the fast-charging performance of the negative electrode.

[0044] In some embodiments of the present application, 0.34 nm≤L≤3.4 nm. It can be understood that when the graphene particles are single-layer graphene, L can be 0.34 nm. When the graphene particles are multi-layer graphene, 0.68 nm<L≤3.4 nm; that is, the size of the graphene particles in the stacking direction of the graphene sheets is in the range of greater than 0.68 nm to less than or equal to 3.4 nm. In some specific embodiments, 1 nm≤L≤3.4 nm. In this way, it is more conducive to the construction of a conductive network in the negative electrode material layer. Specifically, L may, for example, be 0.34 nm, 2.38 nm, 2.72 nm, 3.4 nm, etc.

[0045] In some embodiments of the present application, 3 pm≤D1≤25 pm. That is, the particle size D50 of the first negative active material is 3 pm-25 pm. In this way, it is beneficial to cooperate with graphene particles to build a good electron conduction network and ion conduction network in the first active material layer 21, and the length of the deintercalation path of active ions inside the particles of the first negative active material can be controlled within a more appropriate range, which is beneficial to realize the rapid deintercalation / intercalation of active ions, thereby optimizing the fast charging performance. Specifically, the particle size D50 of the first negative active material may, for example, be 3 pm, 5 pm, 7 pm, 9 pm, 10 pm, 12 pm, 15 pm, 18 pm, 20 pm, 22 pm, 25 pm, etc.

[0046] In some embodiments of the present application, the second active material layer 22 includes a second negative active material and a second conductive agent. The second negative active material includes, but is not limited to, one or more of the aforementioned carbon-based negative active materials, silicon-based negative active materials, and phosphorus-based negative active materials. The second negative active material can be the same as or different from the first negative active material.

[0047] In some embodiments of the present application, the second conductive agent includes, but is not limited to, one or more of conductive carbon black, carbon nanotubes, and carbon fibers. In some specific embodiments, the second conductive agent does not contain graphene particles; that is, the second active material layer does not contain graphene.

[0048] Considering that the electron transport in the active material layer near the current collector area is relatively difficult during the charge and discharge cycle, in order to balance the electronic conductivity and energy density of the negative electrode, in some embodiments of the present application, the mass fraction of the first conductive agent in the first active material layer 21 is less than or equal to the mass fraction of the second conductive agent in the second active material layer 22. In some specific embodiments, the mass fraction of the total mass of the first conductive agent in the first active material layer 21 is 0.1%-3%, and the mass fraction of the total mass of the second conductive agent in the second active material layer 22 is 0.2%-3%. Specifically, the mass fraction of the total mass of the second conductive agent in the second active material layer 22 may, for example, be 0.2%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, etc.

[0049] In some embodiments of the application, the areal density of the first active material layer 21 is greater than or equal to the areal density of the second active material layer 22. In some embodiments of the application, the ratio of the areal density of the first active material layer 21 to the areal density of the second active material layer 22 is (1-7): 1. For example, the ratio of the areal density of the first active material layer 21 to the areal density of the second active material layer 22 can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, etc. In this way, the transport of active ions in the second active material layer 22 is facilitated during charge and discharge cycles, while also taking into account the compaction density of the anode, thereby resulting in a more optimal overall electrochemical performance of the anode. In some specific embodiments, the areal density of the first active material layer 21 is 40 g / m2to 140 g / m2, and the areal density of the second active material layer 22 is 20 g / m2to 70 g / m2. 2 -140g / m 2 . 2 -70g / m 2 . In some embodiments of the application, the areal density of the first active material layer 21 is greater than or equal to the areal density of the second active material layer 22. In some embodiments of the application, the ratio of the areal density of the first active material layer 21 to the areal density of the second active material layer 22 is (1-7): 1. For example, the ratio of the areal density of the first active material layer 21 to the areal density of the second active material layer 22 can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, etc. In this way, the transport of active ions in the second active material layer 22 is facilitated during charge and discharge cycles, while also taking into account the compaction density of the anode, thereby resulting in a more optimal overall electrochemical performance of the anode. In some specific embodiments, the areal density of the first active material layer 21 is 40 g / m2to 140 g / m2, and the areal density of the second active material layer 22 is 20 g / m2to 70 g / m2. 2 、50g / m 2 、60g / m 2 、70g / m 2 、80g / m 2 、90g / m 2 、100g / m 2 、110g / m 2 、120g / m 2 、130g / m 2 、140g / m 2 . 2 、30g / m 2 、40g / m 2 、50g / m 2 、60g / m 2 、70g / m 2 .

[0050] In some embodiments of the present application, the thickness of the first active material layer 21 is 40-100 μm, and the thickness of the second active material layer 22 is 20-50 μm. In this way, the absorption and retention of the electrolyte are facilitated. In some embodiments of the present application, the sum of the thicknesses of the first active material layer 21 and the second active material layer 22 is 80-140 μm. Specifically, the thickness of the first active material layer 21 can be, for example, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, etc., and the thickness of the second active material layer 22 can be, for example, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, etc.

[0051] In some specific embodiments, the ratio of the thickness of the second active material layer 22 to the thickness of the first active material layer 21 is 1:(1-7). In some specific embodiments, the ratio of the thickness of the second active material layer 22 to the thickness of the first active material layer 21 is 1:(1-3). In this way, the electrochemical performance of the negative electrode is facilitated. Specifically, the ratio of the thickness of the second active material layer 22 to the thickness of the first active material layer 21 can be, for example, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, etc.

[0052] In some embodiments of the present application, the first active material layer 21 and the second active material layer 22 can further comprise a binder and other auxiliary agents. The binder can be any binder suitable for a negative electrode and known to those skilled in the art.

[0053] In some embodiments of the present application, the method for preparing the negative electrode comprises:

[0054] The second active coating layer and the first active coating layer are sequentially arranged on one side surface of the current collector 10, the first active coating layer is arranged away from the current collector, and the aforementioned negative electrode provided by the present application is obtained by rolling, drying, and slitting. The preparation of the first active coating layer comprises: mixing and dispersing a first negative electrode active material with a particle size D50 of D1 μm and graphene particles with a particle size D50 of D0 μm and a thickness of L nm in a solvent, stirring to obtain a first negative electrode slurry, and forming the first negative electrode slurry on the surface of the second active coating layer to obtain the first active coating layer, wherein D1, D0, and L satisfy the following condition: 1.5≤D1k / (D0 2 L)≤25.

[0055] In the present application, the second active coating layer and the first active coating layer can be sequentially formed on the surface of the current collector 10, or a double-layer coating process can be used to directly coat the first active material layer 21 and the second active material layer 22 arranged in layers on the surface of the current collector 10 at one time.

[0056] In the embodiments of the present application, the current collector 10 can be any current collector suitable for a negative electrode, including but not limited to a copper foil, a stainless steel foil, a copper alloy foil, a carbon-coated copper foil, a copper-plated film, and the like.

[0057] The embodiments of the present application also provide a secondary battery including the negative electrode provided by the embodiments of the present application. Due to the aforementioned negative electrode provided by the embodiments of the present application, the secondary battery can have a better fast-charging performance.

[0058] In the embodiments of the present application, the secondary battery can be a lithium ion battery, a sodium ion battery, or another alkali metal ion battery.

[0059] In some embodiments of the present application, the secondary battery includes a positive electrode, a negative electrode, and an electrolyte between the positive electrode and the negative electrode. In some specific embodiments, the electrolyte includes a liquid electrolyte.

[0060] In the embodiments of the present application, the positive electrode can be any positive electrode known in the art suitable for the corresponding type of secondary battery. The electrolyte can also be any electrolyte known in the art suitable for the corresponding type of secondary battery, which is not limited in the present application.

[0061] In some embodiments of the present application, a separator is further provided between the positive electrode and the negative electrode. The separator can be any separator known in the art, such as a single-layer polypropylene (PP) film, a single-layer polyethylene (PE) film, a double-layer PP / PE film, a double-layer PP / PP film, a three-layer PP / PE / PP polymer film, or a non-woven fabric, and the like.

[0062] The embodiments of the present application also provide an electric device 3 including the secondary battery 4 provided by the embodiments of the present application. In some embodiments of the present application, the electric device 3 includes an electronic device, and the secondary battery 4 supplies power to the electronic device. Due to the use of the secondary battery provided by the embodiments of the present application, the electric device has a good market prospect.

[0063] FIG. 3 is a structural schematic diagram of the secondary battery and the electric device in an embodiment of the present application. In FIG. 3, the secondary battery 4 is provided in the electric device 3.

[0064] In some embodiments of the present application, the electric device 4 includes but is not limited to a vehicle, or a 3C electronic consumer product such as a mobile phone, a notebook computer, a tablet computer, a smart watch, and the like.

[0065] The technical solutions of the present application are further described in the following embodiments.

[0066] Embodiment 1

[0067] A negative electrode includes a current collector (specifically, a copper foil), and a first active material layer and a second active material layer are respectively stacked on opposite sides of the current collector, wherein the first active material layer is away from the current collector.

[0068] The first active material layer includes a first negative electrode active material (specifically, artificial graphite with a particle size D50(D1) of 16 μm), a first conductive agent, sodium carboxymethyl cellulose, and a binder (styrene-butadiene rubber) at a mass ratio of 96:1:1:2; wherein the first conductive agent is graphene particles (D0=3 μm, L=2.38 nm) and conductive carbon black at a mass ratio of 3:1, D1k / (D0 2 L)=2.5.

[0069] The second active material layer includes a second negative electrode active material (specifically, artificial graphite with a particle size D50 of 16 μm), a second conductive agent, sodium carboxymethyl cellulose, and a binder (styrene-butadiene rubber) at a mass ratio of 96:1:1:2; wherein the second conductive agent is conductive carbon black. The single-sided area density of the first active material layer and the second active material layer is 60 g / m 2 2, the ratio of the single-sided area density of the first active material layer to the second active material layer is 1:1; the thickness of the first active material layer is 40 μm, and the thickness of the second active material layer is 38 μm, so the thickness ratio of the first active material layer to the second active material layer is 1.05:1; the porosity of the first active material layer is 32%, and the porosity of the second active material layer is 29%.

[0070] Example 2

[0071] The difference from Example 1 is that the D1 of the first negative electrode active material is 15 μm, the D0 of the graphene particles is 1 μm, the L is 2.72 nm, and the D1k / (D0 2 L) = 18.8. The second negative electrode active material is the same as the first negative electrode active material. The porosity of the first active material layer is 33%, and the porosity of the second active material layer is 29.5%.

[0072] Example 3

[0073] The difference from Example 1 is that the D1 of the first negative electrode active material is 13 μm, the D0 of the graphene particles is 1 μm, the L is 2.72 nm, and the D1k / (D0 2 L) = 16.3. The second negative electrode active material is the same as the first negative electrode active material. The porosity of the first active material layer is 34%, and the porosity of the second active material layer is 29.4%.

[0074] Example 4

[0075] The difference from Example 1 is that the first negative electrode active material has D1 of 13 pm, the graphene particles have D0 = 1 pm, L = 2.72 nm, and D1k / (D0 2 L) = 16.3. The second negative electrode active material is the same as the first negative electrode active material.

[0076] Also, the first active material layer has a single-sided area density of 72 g / m 2 , and the second active material layer has a single-sided area density of 48 g / m 2 (the single-sided area density of the first active material layer : the single-sided area density of the second active material layer = 1.5 : 1). The first active material layer has a porosity of 33.9%, and the second active material layer has a porosity of 30%.

[0077] Example 5

[0078] The difference from Example 4 is that the first active material layer has a single-sided area density of 48 g / m 2 , and the second active material layer has a single-sided area density of 72 g / m 2 (the single-sided area density of the first active material layer : the single-sided area density of the second active material layer = 0.67 : 1). The first active material layer has a porosity of 34%, and the second active material layer has a porosity of 29%.

[0079] Example 6

[0080] The difference from Example 1 is that the first active material layer includes the first negative electrode active material (specifically, artificial graphite having a particle size D50 (D1) of 13 pm) at a mass ratio of 96.2 : 0.8 : 1 : 2, a first conductive agent, sodium carboxymethyl cellulose, and a binder (styrene-butadiene rubber); wherein the first conductive agent is graphene particles (D0 = 1 pm, L = 2.72 nm) and conductive carbon black at a mass ratio of 5 : 1, and D1k / (D0 2 L) = 16.3.

[0081] The second active material layer includes the second negative electrode active material (specifically, artificial graphite having a particle size D50 of 13 pm) at a mass ratio of 96 : 1 : 1 : 2, a second conductive agent, sodium carboxymethyl cellulose, and a binder (styrene-butadiene rubber); wherein the second conductive agent is conductive carbon black.

[0082] Also, the first active material layer has a single-sided area density of 72 g / m 2 , and the second active material layer has a single-sided area density of 48 g / m 2 (the single-sided area density of the first active material layer : the single-sided area density of the second active material layer = 1.5 : 1). The first active material layer has a porosity of 33%, and the second active material layer has a porosity of 29.5%.

[0083] Example 7

[0084] The difference from Example 6 is that the areal density of the first active material layer is 48 g / m 2 The areal density of the second active material layer is 72 g / m 2 (the areal density of the first active material layer: the areal density of the second active material layer = 0.67:1). The porosity of the first active material layer is 33.2%, and the porosity of the second active material layer is 29%.

[0085] Example 8

[0086] The difference from Example 1 is that the thickness of the first active layer is 40 μm, and the thickness of the second active layer is 45 μm, so the thickness ratio of the first active material layer to the second active material layer is 0.89:1.

[0087] Example 9

[0088] The difference from Example 1 is that the mass ratio of graphene particles to conductive carbon black in the first conductive agent is 12:13, so the mass of graphene particles accounts for 0.05% of the mass of the first negative electrode active material. The porosity of the first active material layer is 29%, and the porosity of the second active material layer is 28.5%.

[0089] Example 10

[0090] The difference from Example 1 is that the second conductive agent in the second active material layer contains graphene particles, which have the same size as the graphene particles in the first conductive agent; and the mass ratio of graphene particles to conductive carbon black is 1:3. The porosity of the first active material layer is 32%, and the porosity of the second active material layer is 29.5%.

[0091] Example 11

[0092] The difference from Example 1 is that the mass ratio of each substance in the first active material layer is 95:2:1:2. The porosity of the first active material layer is 31%, and the porosity of the second active material layer is 29%.

[0093] In order to highlight the beneficial effects of the embodiments of the present application, the following comparative examples are set.

[0094] Comparative Example 1

[0095] A negative electrode includes a current collector (specifically, a copper foil), and a negative electrode material layer arranged on the opposite sides of the current collector. The negative electrode material layer includes a negative electrode active material (specifically, artificial graphite with a particle size D50 of 13 μm), conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber in a mass ratio of 96:1:1:2.

[0096] Comparative Example 2

[0097] The difference from Example 1 is that the D1 of the first negative active material is 15 pm, the D0 of the graphene particle is 1 pm, the L is 2.72 nm, and the D1k / (D0 2 L) = 18.8. Moreover, the relative positions of the first active material layer and the second active material layer are adjusted so that the first active material layer is disposed close to the current collector.

[0098] Comparative Example 3

[0099] The difference from Example 1 is that the D1 of the first negative active material is 16 pm, the D0 of the graphene particle is 9 pm, the L is 3.4 nm, and the D1k / (D0 2 L) = 0.2.

[0100] Comparative Example 4

[0101] The difference from Example 1 is that the D1 of the first negative active material is 16 pm, the D0 of the graphene particle is 1 pm, the L is 2.04 nm, and the D1k / (D0 2 L) = 26.66.

[0102] Electrochemical performance test

[0103] (1) Preparation of test batteries: the positive electrode, the negative electrode of each example and comparative example, and the separator (specifically, a PP separator), and the electrolyte were assembled into each test battery with a capacity of 1.7 Ah. The positive electrode comprises an aluminum foil and a positive electrode material layer disposed on the surface of the aluminum foil, and the positive electrode material layer comprises lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride at a mass ratio of 97:1:2. The electrolyte is a 1 mol / L LiPF6 solution, and the solvent of the electrolyte is a volume ratio of 1:1:1 of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate.

[0104] (2) DC internal resistance (DCIR) test:

[0105] Charge and discharge each test battery at 0.2C at 25°C to calibrate the capacity of each test battery;

[0106] Charge again at 0.2C to 50% SOC and 90% SOC;

[0107] Set the charging current to 2C for 30s, record the termination voltage and termination current of the above processes, calculate the DCIR, DCIR = (V1-V2) / I, and the results are summarized in Table 1. V1 is the voltage after charging for 30s, V2 is the voltage after adjusting the battery to the target SOC for 30 min, and I is the charging current.

[0108] Table 1

[0109] It can be found from the data in Table 1 that the negative electrode provided by the embodiments of the present application can effectively reduce the direct current resistance of the battery at different SOCs when applied in the secondary battery, which further indicates that the negative electrode provided by the embodiments of the present application has a more optimal electron conduction network and a more optimal ion transmission path, thereby improving the fast charging capability of the negative electrode. In addition, it can be found from the data of Comparative Example 4 and Example 5, and Example 6 and Example 7 that when the ratio of the single-sided area density of the first active material layer to the second active material layer is within the range further suggested by the present application (Example 4, Example 6), it is more beneficial to optimize the performance of the negative electrode, specifically to reduce the direct current resistance of the negative electrode in the battery.

[0110] The above is an exemplary embodiment of the present application. It should be noted that, for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, which are also considered within the scope of protection of the present application.

Claims

1. A negative electrode (1), wherein The negative electrode (1) comprises a current collector (10) and a first active material layer (21) and a second active material layer (22) stacked on at least one side surface of the current collector (10), wherein the first active material layer (21) is arranged away from the current collector (10). The first active material layer (21) comprises a first negative electrode active material and a first conductive agent, and the first conductive agent comprises graphene particles; the graphene particles comprise single-layer graphene or multi-layer graphene. The first active material layer (21) satisfies: 1.5 ≤ D1k / (D0 2 L) ≤ 25, where D1 is the particle size D50 of the first negative electrode active material, in units of μm; D0 is the particle size D50 of the graphene particle, in units of μm; L is the thickness of the single-layer graphene, or L is the size of the multi-layer graphene in the stacking direction of graphene sheets, in units of nm; k = 3400 nm 2 .

2. The negative electrode (1) according to claim 1, wherein The mass of the graphene particles accounts for 0.1%-3% of the mass of the first negative electrode active material.

3. The negative electrode (1) according to claim 1 or 2, wherein The total mass of the first conductive agent accounts for 0.1%-3% of the total mass of the first active material layer (21).

4. The negative electrode (1) according to any one of claims 1 to 3, wherein The first negative electrode active material comprises one or more of a carbon-based negative electrode active material, a silicon-based negative electrode active material, and a phosphorus-based negative electrode active material; the carbon-based negative electrode active material comprises one or more of graphite, hard carbon, soft carbon, and mesocarbon microbeads; the silicon-based negative electrode active material comprises one or more of silicon, silicon carbide, silicon oxide, and silicon alloy; and the phosphorus-based negative electrode active material comprises one or more of black phosphorus, red phosphorus, and phosphorus carbide.

5. The negative electrode (1) according to any one of claims 1 to 4, wherein 1μm≤D0≤15μm; 0.34nm≤L≤3.4nm.

6. The negative electrode (1) according to any one of claims 1 to 5, wherein 3μm≤D1≤25μm.

7. The negative electrode (1) according to any one of claims 1 to 6, wherein The first conductive agent further comprises one or more of conductive carbon black, carbon nanotubes, and carbon fibers.

8. The negative electrode (1) according to any one of claims 1 to 7, wherein The second active material layer (22) comprises a second negative electrode active material and a second conductive agent, and the second active material layer (22) does not contain the graphene particles.

9. The negative electrode (1) according to claim 8, wherein The mass ratio of the first conductive agent in the first active material layer (21) to the second conductive agent in the second active material layer (22) is less than or equal to 1.

10. The negative electrode (1) according to any one of claims 1 to 9, wherein the first active material layer (21) has a single-sided areal density greater than or equal to the single-sided areal density of the second active material layer (22); the single-sided areal density of the first active material layer (21) is 40 g / m 2 - 140 g / m 2 ; the single-sided areal density of the second active material layer (22) is 20 g / m 2 - 70 g / m 2 .

11. The negative electrode (1) according to any one of claims 1 to 10, wherein The single-side area density ratio of the first active material layer (21) to the second active material layer (22) is (1-7):

1.

12. The negative electrode (1) according to any one of claims 1 to 11, wherein The porosity of the first active material layer (21) is greater than or equal to the porosity of the second active material layer (22); the porosity of the first active material layer (21) is 20%-40%, and the porosity of the second active material layer (22) is 20%-30%.

13. The negative electrode (1) according to any one of claims 1 to 12, wherein The thickness of the first active material layer (21) is 40μm-100μm, and the thickness of the second active material layer (22) is 20μm-50μm.

14. The negative electrode (1) according to any one of claims 1 to 13, wherein The thickness ratio of the first active material layer (21) to the second active material layer (22) is (1-5):

1.

15. The negative electrode (1) according to any one of claims 1 to 14, wherein The sum of the thicknesses of the first active material layer (21) and the second active material layer (22) is 80μm-140μm.

16. A secondary battery (4), wherein The secondary battery (4) comprises the negative electrode (1) according to any one of claims 1-15.

17. An electrical consumer (3), wherein The secondary battery (4) comprises the negative electrode (1) according to any one of claims 1-15.

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