Negative electrode film layer, negative electrode sheet, secondary battery and electric device

Abstract

A negative electrode film layer, a negative electrode sheet, a secondary battery and an electric device. The negative electrode film layer comprises a first active material layer and a second active material layer which are arranged in a stacked manner, wherein the material of the first active material layer comprises a first silicon-oxygen material, and the material of the second active material layer comprises a second silicon-oxygen material; and the chemical formula of the first silicon-oxygen material is SixOy, and the chemical formula of the second silicon-oxygen material is SimOn, where x<y, and m＞n.

Description

Negative electrode film, negative electrode sheet, secondary battery and electrical device

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese patent application No. CN202410800097.8, filed on June 19, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to a negative electrode film, a negative electrode sheet, a secondary battery, and an electrical device. Background Technology

[0004] Lithium-ion batteries have outstanding features such as light weight, high energy density, no pollution, and long service life, and are widely used in new energy vehicles.

[0005] To fabricate higher-capacity lithium-ion batteries, higher-capacity positive and negative electrode materials are needed. For negative electrode materials, the specific capacity of traditional graphite is difficult to further improve, thus necessitating the development of new high-capacity materials. Silicon-based materials, with a specific capacity ten times that of graphite, are considered the most promising negative electrode materials. However, pure silicon materials are prone to volume expansion and contraction during lithium insertion / extraction, leading to severe performance degradation such as pulverization and peeling. While silicon-oxygen materials are beneficial in suppressing volume expansion, their specific capacity and initial efficiency are significantly lower than those of pure silicon. Therefore, it is difficult to reconcile capacity improvement and cycle stability in silicon-based materials. Summary of the Invention

[0006] The purpose of this disclosure is to provide a negative electrode film, a negative electrode, a secondary battery, and an electrical device that combine high energy density and electrode stability.

[0007] To achieve the above objectives, a first aspect of this disclosure provides a negative electrode film layer comprising a first active material layer and a second active material layer stacked thereon, wherein the first active material layer is made of a first silicon-oxygen material, and the second active material layer is made of a second silicon-oxygen material; wherein the chemical formula of the first silicon-oxygen material is Si. x O y The chemical formula of the second silicon-oxygen material is Si. m O n x <y,m>n。

[0008] Optionally, the ratio of x to y is 1:(1.1 to 2); and / or the ratio of m to n is 1:(0.6 to 0.9).

[0009] Optionally, the D50 particle size of the first silicon oxide material is smaller than the D50 particle size of the second silicon oxide material.

[0010] Optionally, the D50 particle size of the first silicon oxide material is 4 to 8 μm, preferably 6 to 6.5 μm; and / or, the D50 particle size of the second silicon oxide material is 8 to 16 μm, preferably 12 to 15 μm.

[0011] Optionally, the electrochemical capacity of the first silicon oxide material and the second silicon oxide material is independently 800 to 2600 mAh / g.

[0012] Optionally, the initial efficiency of the first silicon oxide material is 75-92%, preferably 76-85%; and / or, the initial efficiency of the second silicon oxide material is 75-92%, preferably 83-90%.

[0013] Optionally, the material of the first active material layer may further include the second silicon-oxygen material; and / or, the material of the second active material layer may further include the first silicon-oxygen material.

[0014] Optionally, the first active material layer further comprises first graphite, a first binder, and a first conductive agent. Based on 100 parts by weight of the first active material layer, the content of the first silicon oxide material is 5-40 parts by weight, the content of the first graphite is 50-90 parts by weight, the content of the first binder is 0.5-4 parts by weight, and the content of the first conductive agent is 0.5-6 parts by weight; and / or,

[0015] The second active material layer also includes a second graphite, a second binder, and a second conductive agent. Based on 100 parts by weight of the second active material layer, the content of the second silicon oxide material is 5 to 40 parts by weight, the content of the second graphite is 50 to 90 parts by weight, the content of the second binder is 0.5 to 4 parts by weight, and the content of the second conductive agent is 0.5 to 6 parts by weight.

[0016] Optionally, the electrochemical capacities of the first graphite and the second graphite are each independently 355–365 mAh / g; and / or,

[0017] The D50 particle size of the first graphite and the second graphite is independently 15–19 μm; and / or,

[0018] The initial efficiency of the first graphite and the second graphite is independently 92-95%.

[0019] Optionally, the first adhesive and the second adhesive each independently comprise at least one of polyacrylic acid, sodium carboxymethyl cellulose, and styrene-butadiene rubber; and / or,

[0020] The first conductive agent and the second conductive agent are each independently conductive carbon black and / or carbon nanotubes.

[0021] Optionally, the weight ratio of the first active material layer to the second active material layer is (0.1-3):1.

[0022] In a second aspect, this disclosure provides a negative electrode sheet, comprising a negative current collector and a negative electrode film layer as described in the first aspect of this disclosure, wherein the negative electrode film layer is disposed on at least one surface of the negative current collector.

[0023] Optionally, the first active material layer is disposed on at least one side surface of the negative electrode current collector, and the second active material layer is disposed on the first active material layer.

[0024] In a third aspect, this disclosure provides a secondary battery including the negative electrode sheet described in the second aspect of this disclosure.

[0025] In a fourth aspect, this disclosure provides an electrical device including the secondary battery described in the third aspect of this disclosure.

[0026] Through the above technical solution, the negative electrode film layer disclosed herein has a double-layer active material structure, and the silicon-oxygen materials in the two active material layers have different silicon-oxygen atom ratios. The negative electrode sheet prepared using this negative electrode film layer is beneficial to improving the electrode stability of the secondary battery, and exhibits excellent electrical performance and long-term performance while maintaining a high energy density.

[0027] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0028] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0029] Figure 1 is a schematic diagram of the structure of the negative electrode film layer according to a specific embodiment of the present disclosure.

[0030] Figure 2 is a schematic diagram of the structure of a negative electrode sheet according to a specific embodiment of the present disclosure.

[0031] Figure 3 is a schematic diagram of the negative electrode sheet according to another specific embodiment provided in this disclosure.

[0032] Explanation of reference numerals in the attached figures: 1—first active material layer, 2—second active material layer, 3—negative electrode current collector. Detailed Implementation

[0033] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0034] In a first aspect, this disclosure provides a negative electrode film layer. Referring to FIG1, the negative electrode film layer includes a first active material layer 1 and a second active material layer 2 stacked thereon. The first active material layer 1 is made of a first silicon-oxygen material, and the second active material layer 2 is made of a second silicon-oxygen material. The chemical formula of the first silicon-oxygen material is Si. x O y The chemical formula of the second silicon-oxygen material is Si. m O n Where x and m represent the number of silicon atoms in the silicon-oxygen material, and y and n represent the number of oxygen atoms in the silicon-oxygen material, and x <y,m>n。

[0035] The negative electrode film layer disclosed herein has a bilayer active material structure. The first silicon-oxygen material has fewer silicon atoms than oxygen atoms, which can reduce the expansion effect of the electrode while increasing the electrode capacity, thereby avoiding separation of the electrode from the current collector due to large changes in the volume of the active material. The second silicon-oxygen material has more silicon atoms than oxygen atoms, which is beneficial to further increase the electrode capacity and significantly increase the lithium storage capacity of the electrode, thereby improving the energy density of the cell. In addition, since both active materials contain silicon-oxygen materials, it helps to reduce the stress difference between different layers during charging and discharging, avoids the phenomenon of interlayer delamination, further improves the stability of the electrode, and extends the service life of the battery.

[0036] In a preferred embodiment, the first silicon-oxygen material Si x O y The ratio of x to y is 1:(1.1~2), and / or, the second silicon-oxygen material Si m O n The ratio of m to n is 1:(0.6~0.9). Using two silicon-oxygen materials with the above-mentioned silicon-oxygen atomic ratio is beneficial to further improve the energy density and long-term performance of the battery.

[0037] The particle size of the first silicon oxide material and the second silicon oxide material can be adjusted within a certain range, and they can have the same or different particle size ranges.

[0038] In a preferred embodiment, the D50 particle size of the first silicon oxide material is smaller than that of the second silicon oxide material. By controlling the D50 particle size of the first silicon oxide material to be smaller than that of the second silicon oxide material, the structural stability of the negative electrode film and the migration of lithium ions in the negative electrode film can be further increased, thereby improving the energy density and rate charge / discharge capability of the battery.

[0039] In a preferred embodiment, the D50 particle size of the first silicon oxide material is 4-8 μm, more preferably 6-6.5 μm; the D50 particle size of the second silicon oxide material is 8-16 μm, more preferably 12-15 μm; thus, the D50 particle sizes of the two silicon oxide materials are controlled within the above ranges, so that the film layer forms a better micro-pore structure, which is beneficial to further improve the liquid phase transport capability of the negative electrode film layer and improve the rate charge and discharge capability of the cell.

[0040] The first silicon-oxygen material and the second silicon-oxygen material can possess high electrochemical capacity and initial efficiency, thereby enabling the battery to exhibit excellent electrical performance. Electrochemical capacity refers to the amount of charge that the material can release or absorb during charge and discharge; initial efficiency refers to the ratio of the battery's discharge capacity to its charge capacity achieved during the first charge-discharge cycle. Specifically, the electrochemical capacity of each of the first silicon-oxygen material and the second silicon-oxygen material can independently be 800–2600 mAh / g. The initial efficiency of the first silicon-oxygen material can be 75–92%, preferably 76–85%; the initial efficiency of the second silicon-oxygen material can be 75–92%, preferably 83–90%.

[0041] In one specific embodiment, the material of the first active material layer may further include the second silicon-oxygen material Si. m O n At this time, in the first active material layer, the first silicon-oxygen material Si x O y With the second silicon-oxygen material Si m O n The weight ratio can be 1:(0.5~1.5). In one specific embodiment, the material of the second active material layer may further include the first silicon-oxygen material Si. x O y At this time, in the second active material layer, the first silicon-oxygen material Si x O y With the second silicon-oxygen material Si m O n The weight ratio can be 1:(0.5~1.5). Introducing a portion of the second silicon-oxygen material into the first active material layer, and / or introducing a portion of the first silicon-oxygen material into the second active material layer, is beneficial to improving the overall performance of the electrode.

[0042] According to this disclosure, the material of the first active material layer may further include first graphite, first binder, and first conductive agent. The proportions of each component can be adjusted within a certain range. Specifically, based on 100 parts by weight of the first active material layer, the content of the first silicon oxide material (or the first silicon oxide material and the second silicon oxide material) can be 5 to 40 parts by weight, the content of the first graphite can be 50 to 90 parts by weight, the content of the first binder can be 0.5 to 4 parts by weight, and the content of the first conductive agent can be 0.5 to 6 parts by weight. Preferably, based on 100 parts by weight of the first active material layer, the content of the first silicon oxide material (or the first silicon oxide material and the second silicon oxide material) is 5 to 15 parts by weight, the content of the first graphite is 80 to 90 parts by weight, the content of the first binder is 2 to 4 parts by weight, and the content of the first conductive agent is 1 to 1.5 parts by weight.

[0043] The material of the second active material layer may further include second graphite, second binder, and second conductive agent. The proportions of each component can be adjusted within a certain range. Specifically, based on 100 parts by weight of the second active material layer, the content of the second silicon oxide material (or the first silicon oxide material and the second silicon oxide material) can be 5 to 40 parts by weight, the content of the second graphite can be 50 to 90 parts by weight, the content of the second binder can be 0.5 to 4 parts by weight, and the content of the second conductive agent can be 0.5 to 6 parts by weight. Preferably, based on 100 parts by weight of the second active material layer, the content of the second silicon oxide material (or the first silicon oxide material and the second silicon oxide material) is 10 to 20 parts by weight, the content of the second graphite is 75 to 85 parts by weight, the content of the second binder is 2 to 4 parts by weight, and the content of the second conductive agent is 1 to 1.5 parts by weight.

[0044] The first graphite and the second graphite can each be natural graphite and / or artificial graphite. The D50 particle size of the first graphite and the second graphite can each independently be 15–19 μm, preferably 16–18 μm. Further, the electrochemical capacity of the first graphite and the second graphite can each independently be 355–365 mAh / g, preferably 355–360 mAh / g. The initial efficiency of the first graphite and the second graphite can each independently be 92–95%.

[0045] The first adhesive and the second adhesive may be of the same or different types. Specifically, the first adhesive and the second adhesive may each independently include at least one of polyacrylic acid, sodium carboxymethyl cellulose, and styrene-butadiene rubber. In one specific embodiment, the first adhesive and the second adhesive may each independently be a mixture of polyacrylic acid, sodium carboxymethyl cellulose, and styrene-butadiene rubber, in which case the weight ratio of polyacrylic acid, sodium carboxymethyl cellulose, and styrene-butadiene rubber may be 1:(0.1~1):(0.1~1.5).

[0046] The first conductive agent and the second conductive agent may be the same or different. Specifically, the first conductive agent and the second conductive agent may each be independently conductive carbon black and / or carbon nanotubes.

[0047] According to this disclosure, the amounts of the first active material layer and the second active material layer can be adjusted within a certain range to form a double-layer negative electrode film structure with a certain thickness. Specifically, the weight ratio of the first active material layer to the second active material layer can be (0.1-3):1, preferably (0.8-1.2):1.

[0048] In a second aspect, this disclosure provides a negative electrode sheet, referring to Figures 2 and 3, comprising a negative current collector 3 and a negative electrode film layer as described in the first aspect of this disclosure, the negative electrode film layer being disposed on at least one surface of the negative current collector 3.

[0049] The negative electrode film layer extends in the same direction as the negative electrode current collector 3, so that the first active material layer 1 and the second active material layer 2 are stacked on at least one side surface of the negative electrode current collector 3. The vertical order of the first active material layer 1 and the second active material layer 2 is not limited; that is, the structure of the negative electrode sheet can be as shown in Figure 2, in which case the first active material layer 1 is close to the negative electrode current collector 3; or, the structure of the negative electrode sheet can be as shown in Figure 3, in which case the second active material layer 2 is close to the negative electrode current collector 3. When the negative electrode film layer is disposed on both opposite sides of the negative electrode current collector 3, the vertical order of the two active material layers in the two negative electrode film layers can be the same or different.

[0050] In a preferred embodiment, the first active material layer 1 is disposed on at least one side surface of the negative electrode current collector 3, that is, the first active material layer 1 is close to the negative electrode current collector 3, and the second active material layer 2 is disposed on the first active material layer 1, that is, the second active material layer 2 is far away from the negative electrode current collector 3. This results in the silicon-oxygen material in the active material layer close to the negative electrode current collector 3 having a smaller silicon-oxygen atomic ratio, while the silicon-oxygen material in the active material layer far away from the negative electrode current collector 3 has a larger silicon-oxygen atomic ratio. This effectively avoids electrode peeling caused by the volume expansion effect of the active material, and at the same time helps to improve the battery capacity, enabling the battery to have excellent electrical performance and long-term performance.

[0051] This disclosure does not impose any special restrictions on the preparation method of the negative electrode sheet. Well-known processes and equipment in the art can be used to coat the materials of the first active material layer and the second active material layer (and solvents can be added to the aforementioned components if necessary) onto the surface of the negative electrode current collector 3, respectively or simultaneously, to obtain the negative electrode sheet.

[0052] In a third aspect, this disclosure provides a secondary battery, including the negative electrode sheet described in the second aspect of this disclosure. This disclosure does not impose any particular limitation on the specific structure of the secondary battery, which may include other structures commonly found in the art, such as a positive electrode, a separator, and an electrolyte. The positive electrode material may be a high-nickel ternary material, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, etc.

[0053] The secondary battery disclosed herein has high energy density and high electrode stability. Under normal temperature, high temperature and fast charging cycle conditions, it can exhibit good cycle stability and reliability, maintain high energy conversion efficiency and long service life. When used in new energy vehicles, it can provide longer driving range and longer power support, reduce battery replacement frequency and maintenance costs, and provide a reliable power source for the development and popularization of the new energy field.

[0054] In a fourth aspect, this disclosure provides an electrical device including the secondary battery described in the third aspect of this disclosure. The electrical device may be, for example, a power battery or an energy storage cabinet.

[0055] The present disclosure is further illustrated by the following examples, but is not intended to limit the scope of the disclosure.

[0056] All raw materials and reagents used in the examples and comparative examples are commercially available products.

[0057] In this embodiment, the testing and calculation methods for the silicon content and oxygen content of the silicon-oxygen material are as follows: 0.05g of silicon-oxygen material sample is weighed into a nickel bag, and the sample is melted using an inert gas-protected pulse electrode. The oxygen content (denoted as w1, %) is measured by infrared absorption method; 0.05g of silicon-oxygen material sample and 1.5-1.8g of tungsten-tin granules are weighed into a ceramic crucible, mixed evenly, and tested by oxygen combustion in a high-frequency infrared carbon-sulfur analyzer. The carbon content (denoted as w2, %) is measured, and the silicon content w3 is calculated as (1-w1-w2)×100%.

[0058] The D50 particle size of the silicon-oxygen material was obtained by laser particle size analyzer.

[0059] Example 1

[0060] In this embodiment, the first silicon-oxygen material is Si1O. 1.5 Its D50 particle size is 6μm, its electrochemical capacity is 1250mAh / g, and its initial efficiency is 78%; the second silicon-oxygen material is Si1O. 0.7 The D50 particle size of the graphite is 13 μm, the electrochemical capacity is 1850 mAh / g, and the first-time efficiency is 88%; the D50 particle size of graphite is 17 μm, the electrochemical capacity is 355 mAh / g, and the first-time efficiency is 94%.

[0061] The following mixture was prepared by feeding graphite, first silica material, conductive carbon black (SP), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polyacrylic acid (PAA) in a weight ratio of 85.95:9.55:1:0.7:0.8:2; water (H2O) and N-methylpyrrolidone (NMP) were added as solvents, with the amounts being 68% and 3% of the total weight of graphite and first silica material, respectively, to obtain a mixed slurry for the first active material layer.

[0062] The following mixture was prepared by feeding graphite, second silica material, conductive carbon black (SP), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polyacrylic acid (PAA) in a weight ratio of 81.175:14.325:1:0.7:0.8:2; water (H2O) and N-methylpyrrolidone (NMP) were added as solvents, accounting for 68% and 3% of the total weight of graphite and second silica material, respectively, to obtain a mixed slurry for the second active material layer.

[0063] By adjusting the coating process, the weight ratio (dry weight after drying) of the first active material layer to the second active material layer coated on the surface of the negative electrode current collector (double-sided coating) is controlled to be 1:1, and the mixed slurry of the first active material layer is brought into contact with the surface of the negative electrode current collector. After rolling and cutting, the negative electrode sheet of this embodiment is obtained. The negative electrode sheet includes a negative electrode film layer with a thickness of 108 μm (single-sided), and its structure is shown in Figure 2 (only the single-sided negative electrode film layer is shown).

[0064] Example 2

[0065] The negative electrode sheet was prepared according to the method of Example 1, except that the weight ratio of the first active material layer to the second active material layer (dry weight) was 3:7.

[0066] Example 3

[0067] The negative electrode sheet was prepared according to the method of Example 1, except that the weight ratio of the first active material layer to the second active material layer (dry weight) was 7:3.

[0068] Example 4

[0069] The negative electrode sheet was prepared according to the method of Example 1, except that the mixed slurry of the second active material layer was brought into contact with the surface of the negative electrode current collector. The structure of the negative electrode sheet in this example is shown in Figure 3 (only one side of the negative electrode film layer is shown).

[0070] Example 5

[0071] The negative electrode sheet was prepared according to the method in Example 1, except that the first silicon-oxygen material was Si1O. 2.2 Its D50 particle size is 6μm, its electrochemical capacity is 900mAh / g, and its initial efficiency is 75%; the second silicon-oxygen material is Si1O. 0.5 Its D50 particle size is 13μm, its electrochemical capacity is 2200mAh / g, and its initial efficiency is 90%.

[0072] Example 6

[0073] The negative electrode sheet was prepared according to the method in Example 1, except that the first silicon-oxygen material was Si1O. 1.05 Its D50 particle size is 6μm, its electrochemical capacity is 1400mAh / g, and its initial efficiency is 79%; the second silicon-oxygen material is Si1O. 0.95 Its D50 particle size is 13μm, its electrochemical capacity is 1600mAh / g, and its initial efficiency is 88%.

[0074] Example 7

[0075] The negative electrode sheet was prepared according to the method in Example 1, except that the first silicon-oxygen material was Si1O. 1.5 Its D50 particle size is 8μm, its electrochemical capacity is 1250mAh / g, and its initial efficiency is 78%; the second silicon-oxygen material is Si1O. 0.7 Its D50 particle size is 9μm, its electrochemical capacity is 1850mAh / g, and its initial efficiency is 88%.

[0076] Example 8

[0077] The negative electrode sheet was prepared according to the method in Example 1, except that the first silicon-oxygen material was Si1O. 1.5 Its D50 particle size is 7μm, its electrochemical capacity is 1100mAh / g, and its initial efficiency is 75%; the second silicon-oxygen material is Si1O. 0.7 Its D50 particle size is 13μm, its electrochemical capacity is 1950mAh / g, and its initial efficiency is 91%.

[0078] Example 9

[0079] The negative electrode was prepared according to the method of Example 1, except that the D50 particle size of the graphite was 19 μm, the electrochemical capacity was 365 mAh / g, and the initial efficiency was 95%.

[0080] Example 10

[0081] The negative electrode sheet was prepared according to the method of Example 1, except that the feeding ratio of the mixed slurry of the first active material layer was graphite: first silica material: conductive carbon black (SP): sodium carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR): polyacrylic acid (PAA) = 76.4:19.1:1:0.7:0.8:2 (weight ratio); and the feeding ratio of the mixed slurry of the second active material layer was graphite: second silica material: conductive carbon black (SP): sodium carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR): polyacrylic acid (PAA) = 89.725:5.775:1:0.7:0.8:2 (weight ratio).

[0082] Example 11

[0083] The negative electrode sheet was prepared according to the method of Example 1, except that the first active material layer also included a second silica material, and the feeding ratio of the mixed slurry was graphite: first silica material: second silica material: conductive carbon black (SP): sodium carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR): polyacrylic acid (PAA) = 85.95: 4.05: 5.55: 1: 0.7: 0.8: 2 (weight ratio); the second active material layer also included the first silica material, and the feeding ratio of the mixed slurry was graphite: first silica material: second silica material: conductive carbon black (SP): sodium carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR): polyacrylic acid (PAA) = 81.175: 8.320: 6.005: 1: 0.7: 0.8: 2 (weight ratio).

[0084] Comparative Example 1

[0085] The negative electrode sheet was prepared according to the method of Example 1, except that only the mixed slurry of the first active material layer was coated on the surface of the negative current collector. The prepared negative electrode sheet included a negative electrode film layer (single-sided) with a thickness of 108 μm, which contained only the first active material layer.

[0086] Comparative Example 2

[0087] The negative electrode sheet was prepared according to the method of Example 1, except that only the mixed slurry of the second active material layer was coated on the surface of the negative electrode current collector. The prepared negative electrode sheet included a negative electrode film layer (single-sided) with a thickness of 108 μm, which contained only the second active material layer.

[0088] Test case

[0089] Full cells were prepared using the negative electrode sheets of the examples and comparative examples under the same conditions, and their performance was tested under the same conditions.

[0090] Preparation of positive electrode sheet: The active material nickel cobalt manganese ternary material (NCM), conductive agent (Ketjen black), and binder polyvinylidene fluoride (PVDF) are thoroughly mixed in an N-methylpyrrolidone (NMP) solvent system at a weight ratio of 97:1.5:1.5. The mixture is then coated onto aluminum foil (double-sided coating). After rolling and slitting, the positive electrode sheet is obtained.

[0091] Preparation of electrolyte: The lithium salt is 1M lithium hexafluorophosphate (LiPF6), and the organic solvent is ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) mixed in a weight ratio of 3:4:3. 5% fluoroethylene carbonate (FEC) is added as a film-forming additive.

[0092] The positive electrode, negative electrode and PE ceramic separator are wound to form a core, which is then packaged with aluminum-plastic film, baked in a vacuum for 48 hours to remove moisture, injected with electrolyte, and after formation and capacity testing, a soft-pack secondary battery is made.

[0093] The room temperature cycle performance, high temperature cycle performance, and 35℃ fast charge cycle performance of the prepared soft-pack secondary battery were tested. The test methods are as follows, and the results are shown in Table 1.

[0094] 25℃ 1.0C / 1.0C ambient temperature cycle test: At 25℃, charge at a constant current of 1.0C to 4.25V, charge at a constant voltage of 4.25V to the cutoff current of 0.05C, and then discharge the battery at a constant current of 1.0C. The discharge capacity is recorded as C0. Then, repeat the charge and discharge at 0.5C0 / 1C0 until the capacity retention rate reaches 80%, and record the number of cycles.

[0095] 45℃ 1.0C / 1.0C High Temperature Cycling Test: Charge the battery at 45℃ with a constant current of 1.0C to 4.25V, then charge it at a constant voltage of 4.25V until the cutoff current is 0.05C. Then discharge the battery with a constant current of 1.0C, and record the discharge capacity as C0. Then repeat the charge and discharge at 0.5C0 / 1C0 until the capacity retention rate reaches 80%, and record the number of cycles.

[0096] 35℃ Fast Charging Cycle Test: At 35℃, the battery was charged at a constant current of 0.33C0 for 13.635 min; 4C0 for 1.5 min; 3.5C0 for 1.2 min; 3C0 for 3 min; 2.5C0 for 3.63 min; 2C0 for 2.4 min; 1.5C0 for 2 min; and 1C0 for 6 min (each current setting included time and voltage jump, with a jump limit of 4.25V). The battery was then charged at a constant current and voltage of 0.33C0 at 4.25V with a cutoff current of 0.05C0. Afterward, the battery was discharged at a constant current of 1.0C to 2.75V. This charging and discharging process was repeated until the capacity retention reached 80%, and the number of cycles was recorded.

[0097] The energy density of the prepared soft-pack secondary battery was tested by weighing the battery (m), charging and discharging it for 3 cycles at 0.33C, and taking the discharge energy (W) of the last cycle. The energy density of the battery is W / m, and the unit is Wh / kg. The results are shown in Table 1.

[0098] Table 1

[0099] As shown in Table 1, the negative electrode prepared in the examples has more cycles at room temperature, more cycles at high temperature, and more cycles at 35°C fast charging, exhibiting superior long-term cycle performance while also having higher energy density.

[0100] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0101] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0102] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A negative electrode film layer, characterized in that, The active material includes a first active material layer and a second active material layer stacked together. The first active material layer is made of a first silicon-oxygen material, and the second active material layer is made of a second silicon-oxygen material. The first silicon-oxygen material has the chemical formula Si. x O y The chemical formula of the second silicon-oxygen material is Si. m O n x <y,m>n。 2. The negative electrode film layer according to claim 1, wherein, The ratio of x to y is 1:(1.1 to 2); and / or the ratio of m to n is 1:(0.6 to 0.9).

3. The negative electrode film layer according to claim 1 or 2, wherein, The D50 particle size of the first silicon oxide material is smaller than that of the second silicon oxide material.

4. The negative electrode film layer according to any one of claims 1 to 3, wherein, The D50 particle size of the first silicon oxide material is 4–8 μm, preferably 6–6.5 μm; and / or, The D50 particle size of the second silicon oxide material is 8-16 μm, preferably 12-15 μm.

5. The negative electrode film layer according to any one of claims 1 to 4, wherein, The electrochemical capacities of the first silicon-oxygen material and the second silicon-oxygen material are each independently 800–2600 mAh / g.

6. The negative electrode film layer according to any one of claims 1 to 5, wherein, The initial efficiency of the first silicon-oxygen material is 75-92%, preferably 76-85%; and / or, The initial efficiency of the second silicon-oxygen material is 75-92%, preferably 83-90%.

7. The negative electrode film layer according to any one of claims 1 to 6, wherein, The material of the first active material layer further includes the second silicon-oxygen material; and / or, the material of the second active material layer further includes the first silicon-oxygen material.

8. The negative electrode film layer according to any one of claims 1 to 7, wherein, The first active material layer further comprises first graphite, first binder, and first conductive agent. Based on 100 parts by weight of the first active material layer, the content of the first silicon-oxygen material is 5-40 parts by weight, the content of the first graphite is 50-90 parts by weight, the content of the first binder is 0.5-4 parts by weight, and the content of the first conductive agent is 0.5-6 parts by weight; and / or, The second active material layer also includes a second graphite, a second binder, and a second conductive agent. Based on 100 parts by weight of the second active material layer, the content of the second silicon oxide material is 5 to 40 parts by weight, the content of the second graphite is 50 to 90 parts by weight, the content of the second binder is 0.5 to 4 parts by weight, and the content of the second conductive agent is 0.5 to 6 parts by weight.

9. The negative electrode film layer according to claim 8, wherein, The electrochemical capacities of the first graphite and the second graphite are each independently 355–365 mAh / g; and / or, The D50 particle size of the first graphite and the second graphite is independently 15–19 μm; and / or, The initial efficiency of the first graphite and the second graphite is independently 92-95%.

10. The negative electrode film layer according to claim 8 or 9, wherein, The first adhesive and the second adhesive each independently comprise at least one of polyacrylic acid, sodium carboxymethyl cellulose, and styrene-butadiene rubber; and / or, The first conductive agent and the second conductive agent are each independently conductive carbon black and / or carbon nanotubes.

11. The negative electrode film layer according to any one of claims 1 to 10, wherein, The weight ratio of the first active material layer to the second active material layer is (0.1-3):

1.

12. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and a negative electrode film layer as described in any one of claims 1 to 11, wherein the negative electrode film layer is disposed on at least one side surface of the negative electrode current collector.

13. The negative electrode sheet according to claim 12, wherein, The first active material layer is disposed on at least one side surface of the negative electrode current collector, and the second active material layer is disposed on the first active material layer.

14. A secondary battery, characterized in that, Includes the negative electrode sheet as described in claim 12 or 13.

15. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 14.

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