Negative electrode, secondary battery, and electric device

Abstract

The embodiment of the invention provides a negative electrode, a secondary battery and electric equipment. The negative electrode has a special structure and parameter design, and compared with the prior art, under the condition that the same negative electrode active material is used, the negative electrode provided by the embodiment of the invention can be used for providing a secondary battery with better fast charging performance.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to negative electrodes, secondary batteries and electrical equipment. Background Art

[0002] As a key component of secondary batteries, the performance of the anode has a significant impact on their performance. With the development of new energy technologies, the market is demanding increasingly higher levels of fast-charging performance in secondary batteries, which requires improving the electronic and ionic conductivity of the anode. The industry generally improves the ionic and / or electronic conductivity of the anode by optimizing the anode active material, but rarely improves the fast-charging performance of the anode by optimizing the structure and parameter design of the anode active material layer. Summary of the Invention

[0003] In view of this, embodiments of the present application provide a negative electrode, a secondary battery, and an electrical device. The negative electrode has a unique structure and parameter design. Compared with related technologies, when using the same negative electrode active material, the negative electrode provided in the embodiments of the present application can be used to provide a secondary battery with better fast charging performance.

[0004] In a first aspect, an embodiment of the present application provides a negative electrode, comprising a current collector and a first active material layer and a second active material layer stacked on at least one side of the current collector, wherein the first active material layer is disposed away from the current collector;

[0005] Wherein, the first active material layer includes a first negative electrode active material and a first conductive agent, and the first conductive agent includes graphene; the graphene includes single-layer graphene or multi-layer graphene;

[0006] The first active material layer satisfies: 1.5≤D1k / (D0 2 L)≤25, where D1 is the particle size D50 of the first negative electrode active material, in μm; D0 is the particle size D50 of the graphene, in 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 sheets, in nm; k=3400 nm 2 .

[0007] Graphene particles have excellent electrolyte absorption and retention capabilities. The first active material layer is arranged away from the current collector and contains graphene particles, which can effectively improve the electrolyte's wetting of the negative electrode and the electrolyte's ability to retain liquid. Therefore, it can effectively reduce the reaction impedance of the negative electrode during the cycle, which is conducive to 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 meet a defined quantitative relationship. The two work together to build a more complete electronic conductivity network and a better ion transmission path in the first active material layer, thereby improving the fast charging capability of the negative electrode.

[0008] A second aspect of the present invention provides a secondary battery, comprising the negative electrode provided in the first aspect of the present invention. Due to the presence of the negative electrode provided in the first aspect of the present invention, the secondary battery can achieve better fast charging performance.

[0009] The third aspect of the embodiment of the present application provides an electric device, including the secondary battery provided in the embodiment of the present application. Due to the use of the secondary battery provided in the embodiment of the present application, the electric device has a good market prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 A schematic structural diagram of a negative electrode provided in one embodiment of the present application;

[0011] Figure 2 This is a simplified schematic diagram of the structure of the negative electrode provided in another embodiment of the present application. DETAILED DESCRIPTION

[0012] In order to meet 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 mostly 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 R&D investment, long R&D cycle, and is relatively difficult to implement. In fact, optimizing the structure and parameters of the negative electrode can also improve the fast charging performance of the negative electrode, and it can also be combined with the improvement of the negative electrode active material to further improve the fast charging performance of the negative electrode.

[0013] In order to optimize the fast charging performance of the negative electrode from the perspective of structural and parameter design, an embodiment of the present application provides a negative electrode, comprising a current collector and a first active material layer and a second active material layer stacked on at least one side of the current collector, wherein the first active material layer is disposed away from the current collector;

[0014] Wherein, the first active material layer includes a first negative electrode active material and a first conductive agent, and the first conductive agent includes graphene; the graphene includes single-layer graphene or multi-layer graphene;

[0015] The first active material layer satisfies: 1.5≤D1k / (D0 2 L)≤25 Formula (1), wherein D1 is the particle size D50 of the first negative electrode active material, in μm; D0 is the particle size D50 of the graphene, in μm; L is the thickness of the single-layer graphene, or L is the size of the multilayer graphene in the stacking direction of the graphene sheets, in nm; k=3400 nm 2 .

[0016] It should be noted that only the values of D1, D0, and L are substituted into formula (1) for calculation. For example, if the particle size D50(D1) of the first negative electrode active material is 2 μm, the particle size D50(D0) of the graphene particles is 1 μm, and L is 2.38 nm, then D1k / (D0 2 L)=2μm×3400nm 2 / (1μm 2 ×2.38nm)=2.857.

[0017] In the embodiment of the present application, a transmission electron microscope (TEM) can be used to test the thickness of a single-layer graphene, as well as the thickness of multilayer graphene in the stacking direction of graphite sheets. A laser particle size analyzer can be used to test the particle size D50 of graphene particles and the first negative electrode active material. In the embodiment of the present application, the particle size D50 refers to the particle size corresponding to when the cumulative volume percentage of the particles reaches 50%. Specifically, before the above-mentioned test, the negative electrode is also pretreated. Specifically, the pretreatment includes: peeling the first active material layer from the negative electrode, placing it in hydrochloric acid with stirring or ultrasound, drying the solid after solid-liquid separation, grinding the dried solid, and then dispersing it in a solvent (for example, ethanol, acetone, etc.), ultrasound-treating to obtain a suspension, and centrifuging the suspension to obtain the first negative electrode active material and graphene particles respectively.

[0018] In the examples of this application, please see Figure 1 The negative electrode 1 may be a current collector 10 having one side surface including the stacked first active material layer 21 and the second active material layer 22, and the other side surface having no material layer; or the other side surface having any negative electrode material layer known in the art. It may also be, for example Figure 2 As shown, both opposite sides of the current collector 10 include the first active material layer 21 and the second active material layer 22 stacked together.

[0019] Graphene particles have excellent electrolyte absorption and retention capabilities. The first active material layer is arranged away from the current collector and contains graphene particles, which can effectively improve the electrolyte's wetting of the negative electrode and the electrolyte's retention capacity. Therefore, it can effectively reduce the reaction impedance of the negative electrode during the cycle, which is conducive to improving the negative electrode's fast charging performance. 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 quantitative relationship defined by formula (1). The two work together to build a more complete electronic conductivity network and a better ion transmission path in the first active material layer, thereby improving the negative electrode's fast charging capability.

[0020] Specifically, D1k / (D0 2 The value of 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. 2 If the value of D1k / (D0 is too high (>25), it will seriously affect the construction of the electronic conductive network in the first active material layer, and if it is too low (<1.5), it will lead to a poor ion conductive network in the first active material layer. 2 If the value of D1k / (D0 2 Too high or too low a value of L) will lead to deterioration of battery performance.

[0021] It is understandable that rolling is generally required during the preparation of the negative electrode, and when the size parameters of the graphene particles and the first active material satisfy formula (1), during the above-mentioned rolling process, slippage is not easy to occur between the graphene particles and the first negative electrode active material, so that the pore structure of the first active material layer is better, which is more conducive to the adsorption and retention of the electrolyte, thereby facilitating ion transport during the charge and discharge cycle, and is conducive to fast charging performance. In some embodiments of the present application, the porosity of the first active material layer is greater than or equal to the porosity of the second active material layer. For example, the porosity of the first active material layer is 20%-40%, and the porosity of the second active material layer is 20%-30%. In an embodiment of the present application, a scanning electron microscope (SEM) can be used to test the porosity of the first active material layer and the second active material layer. Specifically, the surface of the negative electrode material layer (including the first active material layer and the second active material layer) is polished using argon ions, and then the negative electrode material layer is subjected to FIB cutting and imaging. 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 and the second active material layer, respectively. The porosity of the first active material layer and the second active material layer is tested using software. Specifically, the porosity of the first active material layer can be, for example, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, etc., and the porosity of the second active material layer can be, for example, 20%, 22%, 25%, 28%, 30%.

[0022] In some embodiments of the present application, graphene particles account for 0.1%-3% of the mass of the first negative electrode active material. In this way, the electrolyte retention capacity of the first active material layer can be ensured to be better, and it is also beneficial to ensure the good electronic conductivity of the first active material, thereby helping to ensure the fast charging performance of the negative electrode. Specifically, based on the mass of the first negative electrode active material, the mass proportion of graphene can be, for example, 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.

[0023] In the embodiments of the present application, the first negative electrode active material includes but is not limited to 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 includes one or more of graphite, hard carbon, soft carbon, and mesophase carbon microbeads; the silicon-based negative electrode active material includes one or more of silicon, silicon-carbon compounds, silicon-oxygen compounds, and silicon alloys; the phosphorus-based negative electrode active material includes one or more of black phosphorus, red phosphorus, and phosphorus-carbon compounds.

[0024] In some embodiments of the present application, the first conductive agent further includes other conductive agents, and the other conductive agents include, but are not limited to, one or more of conductive carbon black, carbon nanotubes, and carbon fibers.

[0025] 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. When the negative electrode is applied to the battery, it is beneficial to the performance of the battery. 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.

[0026] In some embodiments of the present application, 1μm ≤ D0 ≤ 15μm. That is, the particle size D50 of the graphene particles is 1μm - 15μm. Specifically, the particle size D50 of the graphene particles can be, for example, 1μm, 2μm, 5μm, 8μm, 10μm, 12μm, 15μm, etc. In some specific embodiments, 1μm ≤ D0 ≤ 6μm. In this way, the compounding effect with the first negative electrode active material is better, and it is also more beneficial to obtain a first active material layer with a suitable porosity, thereby being more beneficial to optimizing the fast charging performance of the negative electrode.

[0027] In some embodiments of the present application, 0.34nm ≤ L ≤ 3.4nm. It can be understood that when the graphene particles are single-layer graphene, L can be 0.34nm. When the graphene particles are multi-layer graphene, 0.68nm < L ≤ 3.4nm; that is, the size of the graphene particles in the stacking direction of the graphene sheets is in the range greater than 0.68nm to less than or equal to 3.4nm. In some specific embodiments, 1nm ≤ L ≤ 3.4nm. In this way, it is more beneficial to construct the conductive network in the negative electrode material layer. Specifically, L can be, for example, 0.34nm, 2.38nm, 2.72nm, 3.4nm, etc.

[0028] In some embodiments of the present application, 3μm ≤ D1 ≤ 25μm. That is, the particle size D50 of the first negative electrode active material is 3μm - 25μm. In this way, it is beneficial to cooperate with the graphene particles to construct a good electronic conductance network and ionic conductance network in the first active material layer, and the length of the deintercalation / insertion path of the active ions inside the particles of the first negative electrode active material can be controlled within a more appropriate range, which is beneficial to the rapid deintercalation / insertion of the active ions, thereby optimizing the fast charging performance. Specifically, the particle size D50 of the first negative electrode active material can be, for example, 3μm, 5μm, 7μm, 9μm, 10μm, 12μm, 15μm, 18μm, 20μm, 22μm, 25μm, etc.

[0029] In some embodiments of the present application, the second active material layer includes a second negative electrode active material and a second conductive agent. The second negative electrode active material includes, but is not limited to, one or more of the aforementioned carbon-based negative electrode active materials, silicon-based negative electrode active materials, and phosphorus-based negative electrode active materials. The second negative electrode active material may be the same as or different from the first negative electrode active material.

[0030] 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; in other words, the second active material layer does not contain graphene.

[0031] Considering that electron transport in the active material layer near the current collector region 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 proportion of the first conductive agent in the first active material layer is less than or equal to the mass proportion of the second conductive agent in the second active material layer. In some specific embodiments, the total mass of the first conductive agent in the first active material layer accounts for 0.1% to 3% by mass, and the total mass of the second conductive agent in the second active material layer accounts for 0.2% to 3% by mass. Specifically, the total mass of the second conductive agent in the second active material layer can be, for example, 0.2%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, etc.

[0032] In some embodiments of the present application, the single-surface density of the first active material layer is greater than or equal to the single-surface density of the second active material layer. In some embodiments of the present application, the single-surface density ratio of the first active material layer to the second active material layer is (1-7):1. The ratio of the single-surface density of the first active material layer to the second active material layer can be, for example, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1. In this way, during the charge and discharge cycle, it is more conducive to the transport of active ions in the second active material layer, and the compaction density of the negative electrode can also be taken into account, so that the comprehensive electrochemical performance of the negative electrode is better. In some specific embodiments, the single-surface density of the first active material layer is 40g / m 2 -140g / m 2 The single-surface density of the second active material layer is 20 g / m 2 -70g / m 2 In the embodiment of the present application, the single-surface density of the first active material layer = the mass of the first active material layer / the area of the first active material layer. Similarly, the single-surface density of the second active material layer = the mass of the second active material layer / the area of the second active material layer. Specifically, the single-surface density of the first active material layer can be, for example, 40 g / m 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 Specifically, the single-surface density of the second active material layer can be, for example, 20 g / m 2 , 30g / m 2 , 40g / m 2 , 50g / m 2 , 60g / m 2 , 70g / m 2 .

[0033] In some embodiments of the present application, the thickness of the first active material layer is 40μm-100μm, and the thickness of the second active material layer is 20μm-50μm. This is conducive to the absorption and retention of the electrolyte. In some embodiments of the present application, the sum of the thicknesses of the first active material layer and the second active material layer is 80μm-140μm. Specifically, the thickness of the first active material layer can be, for example, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, etc.; the thickness of the second active material layer can be, for example, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm.

[0034] In some specific embodiments, the thickness ratio of the second active material layer to the first active material layer is 1:(1-7). In some specific embodiments, the thickness ratio of the second active material layer to the first active material layer is 1:(1-3). This is beneficial to the electrochemical performance of the negative electrode. Specifically, the thickness ratio of the second active material layer to the first active material layer can be, for example, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, or 1:7.

[0035] In some embodiments of the present application, the first active material layer and the second active material layer may further include other auxiliary agents such as a binder, wherein the binder may be any binder suitable for a negative electrode that is well known to those skilled in the art.

[0036] In some embodiments of the present application, the method for preparing the negative electrode includes:

[0037] A second active coating layer and a first active coating layer are stacked on one side of the current collector, with the first active coating layer being disposed away from the current collector. The negative electrode provided in the embodiment of 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 having a particle size D50 of D1 μm and graphene particles having a particle size D50 of D0 μm and a thickness of L nm in a solvent, stirring, and obtaining a first negative electrode slurry; forming the first negative electrode slurry on the surface of the second active coating layer to obtain a first active coating layer, and the above D1, D0, and L satisfy the numerical values of: 1.5≤D1k / (D0 2 L)≤25.

[0038] In the embodiment of the present application, the second active coating layer and the first active coating layer can be formed on the surface of the current collector in sequence, or a double-layer coating process can be used to directly coat the surface of the current collector at one time to obtain a stacked first active material layer and a second active material layer.

[0039] In the embodiment of the present application, the above-mentioned current collector can be any current collector suitable for the negative electrode, including but not limited to copper foil, stainless steel foil, copper alloy foil, carbon-coated copper foil or copper-plated film.

[0040] The present invention also provides a secondary battery comprising the negative electrode provided in the present invention. Due to the presence of the negative electrode provided in the present invention, the secondary battery can have excellent fast charging performance.

[0041] In the embodiment of the present application, the secondary battery may be a lithium-ion battery, a sodium-ion battery, or other alkali metal ion battery.

[0042] In some embodiments of the present application, the secondary battery comprises a positive electrode, a negative electrode, and an electrolyte located between the positive electrode and the negative electrode. In some specific embodiments, the electrolyte comprises a liquid electrolyte.

[0043] In the embodiments of the present application, the positive electrode can be a known positive electrode in the industry suitable for a corresponding type of secondary battery. The electrolyte can also be a known electrolyte in the industry suitable for a corresponding type of secondary battery, and the present application does not impose any limitation on this.

[0044] 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 known separator in the industry, 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 triple-layer PP / PE / PP film, or a polymer separator, or a non-woven fabric.

[0045] The present application also provides an electrical device comprising a secondary battery provided in the present application. In some embodiments of the present application, the electrical device includes an electronic device, and the secondary battery provides power to the electronic device. Due to the use of the secondary battery provided in the present application, the electrical device has a promising market prospect.

[0046] In some embodiments of the present application, the above-mentioned electrical equipment includes but is not limited to vehicles, or 3C electronic consumer products such as mobile phones, laptops, tablets, smart watches, etc.

[0047] The technical solution of this application is further illustrated below with multiple embodiments.

[0048] Example 1

[0049] A negative electrode includes a current collector (specifically copper foil), wherein a first active material layer and a second active material layer are stacked on opposite sides of the current collector, wherein the first active material layer is arranged away from the current collector.

[0050] 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) in 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 in a mass ratio of 3:1, D1k / (D0 2 L)=2.5.

[0051] The second active material layer includes a second negative electrode active material (specifically, artificial graphite with a particle size D50 (D1) of 16 μm) in 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. The single-surface density of the first active material layer and the second active material layer is 60 g / m 2 .

[0052] Example 2

[0053] 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, L is 2.72 nm, and D1k / (D0 2 L) = 18.8. The second negative electrode active material is the same as the first negative electrode active material.

[0054] Example 3

[0055] The difference from Example 1 is that D1 of the first negative electrode active material is 13 μm, D0 of the graphene particles is 1 μm, L is 2.72 nm, and D1k / (D0 2L) = 16.3. The second negative electrode active material is the same as the first negative electrode active material.

[0056] Example 4

[0057] The difference from Example 1 is that D1 of the first negative electrode active material is 13 μm, D0 of the graphene particles is 1 μm, L is 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.

[0058] Furthermore, the single-side density of the first active material layer is 72 g / m 2 The single-surface density of the second active material layer is 48 g / m 2 (Area density per surface of the first active material layer:Area density per surface of the second active material layer=1.5:1).

[0059] Example 5

[0060] The difference from Example 4 is that the single-side density of the first active material layer is 48 g / m 2 The single-surface density of the second active material layer is 72 g / m 2 (The single-surface areal density of the first active material layer is: the single-surface areal density of the second active material layer = 1:1.5).

[0061] Example 6

[0062] The first active material layer includes a first negative electrode active material (specifically artificial graphite with a particle size D50 (D1) of 13 μm) in a mass ratio of 96:0.8:1:2, a first conductive agent, sodium carboxymethyl cellulose and a binder (styrene-butadiene rubber); wherein the first conductive agent is graphene particles (D0 = 1 μm, L = 2.72 nm) and conductive carbon black in a mass ratio of 5:1, D1k / (D0 2 L)=16.3.

[0063] The second active material layer includes a second negative electrode active material (specifically artificial graphite with a particle size D50 (D1) of 13 μm) in 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.

[0064] Furthermore, the single-side density of the first active material layer is 72 g / m 2 The single-surface density of the second active material layer is 48 g / m 2 (Area density per surface of the first active material layer:Area density per surface of the second active material layer=1.5:1).

[0065] Example 7

[0066] The difference from Example 6 is that the single-side density of the first active material layer is 48 g / m 2 The single-surface density of the second active material layer is 72 g / m 2 (The single-surface areal density of the first active material layer is: the single-surface areal density of the second active material layer = 1:1.5).

[0067] In order to highlight the beneficial effects of the embodiments of the present application, the following comparative examples are provided.

[0068] Comparative Example 1

[0069] A negative electrode includes a current collector (specifically, copper foil) and negative electrode material layers disposed on opposite sides of the current collector. The negative electrode material layers include a negative electrode active material (specifically, artificial graphite with a particle size D50 (D1) of 13 μm), conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber in a mass ratio of 96:1:1:2.

[0070] Comparative 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, L is 2.72 nm, and D1k / (D0 2 L) = 18.8. In addition, 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.

[0072] Comparative Example 3

[0073] The difference from Example 1 is that D1 of the first negative electrode active material is 16 μm, D0 of the graphene particles is 9 μm, L is 3.4 nm, and D1k / (D0 2 L)=0.2.

[0074] Comparative Example 4

[0075] The difference from Example 1 is that D1 of the first negative electrode active material is 16 μm, D0 of the graphene particles is 1 μm, L is 2.04 nm, and D1k / (D0 2 L)=26.66.

[0076] Electrochemical performance test

[0077] (1) Preparation of test cells: The positive electrode, the negative electrode of each embodiment and comparative example, a separator (specifically a PP separator), and an electrolyte were assembled into test cells with a capacity of 1.7 Ah. The positive electrode comprised an aluminum foil and a positive electrode material layer disposed on the surface of the aluminum foil. The positive electrode material layer comprised lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 97:1:2. The electrolyte was a 1 mol / L LiPF6 solution, and the solvent of the electrolyte was ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1:1.

[0078] (2) DC internal resistance (DCIR) test:

[0079] Each test battery was charged and discharged at 0.2C at 25°C to calibrate the capacity of each test battery;

[0080] Then charge at 0.2C to 50% SOC and 90% SOC;

[0081] Set the charge to 2C for 30 seconds, record the termination voltage and current of each process, and calculate DCIR: DCIR = (V1 - V2) / I. The results are summarized in Table 1. V1 is the voltage after 30 seconds of charging, V2 is the voltage at rest for 30 minutes after adjusting the battery to the target SOC, and I is the charging current.

[0082] Table 1

[0083]

[0084] From the data in Table 1, it can be found that when the negative electrode provided in the embodiment of the present application is used in a secondary battery, it can effectively reduce the DC internal resistance of the battery at different SOCs. It further shows that the negative electrode provided in the embodiment of the present application has a better electronic conductivity network and a better ion transport path, thereby improving the fast charging capability of the negative electrode. In addition, by comparing the data of Example 4 and Example 5, it can be found that when the ratio of the single-surface density of the first active material layer to the second active material layer is within the range further suggested in this application (Example 4), it is more conducive to optimizing the performance of the negative electrode, specifically, it is conducive to reducing the DC internal resistance of the negative electrode in the battery.

[0085] The above is an exemplary embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made thereto without departing from the principles of the present application. These improvements and modifications are also considered to be within the scope of protection of the present application.

Claims

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

2. The negative electrode according to claim 1, characterized in that The mass of the graphene particles accounts for 0.1%-3% of the mass of the first negative electrode active material; And / or, the first negative electrode active material includes 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 includes one or more of graphite, hard carbon, soft carbon, and mesophase carbon microbeads; the silicon-based negative electrode active material includes one or more of silicon, silicon-carbon compounds, silicon oxide compounds, and silicon alloys; the phosphorus-based negative electrode active material includes one or more of black phosphorus, red phosphorus, and phosphorus-carbon compounds.

3. The negative electrode according to claim 1 or 2, characterized in that 1μm≤D0≤15μm; 0.34nm≤L≤3.4nm.

4. The negative electrode according to any one of claims 1 to 3, characterized in that 3μm≤D1≤25μm.

5. The negative electrode according to any one of claims 1 to 4, characterized in that The first conductive agent further comprises one or more of conductive carbon black, carbon nanotubes and carbon fibers.

6. The negative electrode according to any one of claims 1 to 5, characterized in that The second active material layer includes a second negative electrode active material and a second conductive agent; the second active material layer does not contain the graphene particles.

7. The negative electrode according to claim 6, characterized in that 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.

8. The negative electrode according to any one of claims 1 to 7, characterized in that The single surface density of the first active material layer is greater than or equal to the single surface density of the second active material layer; the single surface density of the first active material layer is 40 g / m 2 -140 g / m 2 The single surface density of the second active material layer is 20 g / m 2 -70 g / m 2 ; And / or, the single-surface areal density ratio of the first active material layer to the second active material layer is (1-7):

1.

9. The negative electrode according to any one of claims 1 to 8, characterized in that 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%.

10. The negative electrode according to any one of claims 1 to 9, characterized in that The thickness of the first active material layer is 40 μm-100 μm, and the thickness of the second active material layer is 20 μm-50 μm; And / or, the thickness ratio of the first active material layer to the second active material layer is (1-5):

1.

11. A secondary battery, characterized in that: The negative electrode comprises the negative electrode according to any one of claims 1 to 10.

12. An electrical device, characterized in that: The secondary battery according to claim 11 is included.

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