A negative electrode sheet, a lithium ion battery, and an electric device

Abstract

The present disclosure relates to a negative electrode sheet, a lithium ion battery and an electric device, the negative electrode sheet comprising a current collector and an active layer arranged on the surface of the current collector; the active layer comprises an inner active layer and an outer active layer arranged in a stack, the outer active layer being arranged on the side of the inner active layer away from the current collector; the inner active layer comprises a first active material; the outer active layer comprises a second active material; wherein the first active material comprises silicon monoxide and / or stannous oxide, and the second active material comprises silicon. The negative electrode sheet provided by the present disclosure can improve the capacity performance and cycle performance of the lithium battery, reduce the risk of active material falling off, and reduce the material cost.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of lithium batteries, in particular, to a negative electrode sheet, a lithium ion battery and an electric device. BACKGROUND

[0002] The negative electrode material is one of the important raw materials of the lithium ion battery, and plays a key role in the lithium ion battery. The negative electrode material is accompanied by the "insertion-removal" of lithium ions during the charging and discharging process. The reversible reaction capability of the "insertion-removal" of lithium ions directly determines the reversible capacity, cycle performance and the like of the lithium ion battery. Based on the requirement of new energy vehicles on the energy density of the power battery material, the silicon-based negative electrode is an important technical direction to solve the low capacity of the graphite-based negative electrode material (the theoretical specific capacity is only 372 mAh / g).

[0003] However, the volume expansion effect (about 400%) of the silicon-based negative electrode material in the charging and discharging cycle process limits the use of silicon. First, during the lithiation process, the volume increase causes the breakage and pulverization of the silicon particles themselves, and reduces the contact between the silicon materials and between the active layer and the current collector, and further causes the active layer to separate from the current collector; second, the volume expansion causes the destruction of the SEI interface, and the continuous generation of new SEI film causes the continuous consumption of active lithium and additives in the battery.

[0004] At present, the existing modification methods such as pore making, coating, element doping and nanocrystallization of silicon materials have limited volume expansion inhibition ability at the electrode sheet level, and cannot solve the problem of active material falling off. SUMMARY

[0005] The purpose of the present disclosure is to provide a negative electrode sheet and a preparation method thereof, so as to reduce the risk of active material falling off in the negative electrode sheet, improve the performance of silicon in the negative electrode sheet, and improve the capacity and cycle performance of the battery.

[0006] In order to achieve the above purpose, the first aspect of the present disclosure provides a negative electrode sheet, which comprises a current collector and an active layer arranged on the surface of the current collector; the active layer comprises an inner active layer and an outer active layer arranged in layers, and the outer active layer is arranged on the side of the inner active layer away from the current collector; the inner active layer comprises a first active material; the outer active layer comprises a second active material; wherein the first active material comprises silicon monoxide and / or stannous oxide, and the second active material comprises silicon.

[0007] Optionally, the first active material further comprises a first carbon material; the content of the silicon monoxide and / or stannous oxide is 50-99% by weight based on the total weight of the first active material, and the content of the first carbon material is 1-50% by weight.

[0008] The second active material further comprises a second carbon material; the content of the silicon is 50-99% by weight, and the content of the second carbon material is 1-50% by weight, based on the total weight of the second active material.

[0009] Optionally, the content of the silicon is 15-50% by weight, and the content of the silicon monoxide and / or stannous oxide is 15-50% by weight, based on the total weight of the inner active layer and the outer active layer in the negative electrode plate.

[0010] Optionally, the inner active layer further comprises a first conductive material and a first binder material, and the outer active layer further comprises a second conductive material and a second binder material.

[0011] Optionally, the content of the first active material is 80-96% by weight, the content of the first conductive material is 1-10% by weight, and the content of the first binder material is 3-10% by weight, based on the total weight of the inner active layer.

[0012] The content of the second active material is 80-96% by weight, the content of the second conductive material is 1-10% by weight, and the content of the second binder material is 3-10% by weight, based on the total weight of the outer active layer.

[0013] Optionally, the first carbon material and the second carbon material are each independently selected from one or more of natural graphite, artificial graphite, hard carbon, soft carbon, and mesocarbon microbeads;

[0014] The first conductive material and the second conductive material are each independently selected from one or more of conductive carbon black, conductive graphite, carbon nanotubes, and graphene;

[0015] The first binder material and the second binder material are each independently selected from one or more of styrene-butadiene rubber, carboxymethyl cellulose, and polyacrylic acid.

[0016] Optionally, the D50 of the silicon monoxide and / or stannous oxide in the inner active layer is 1-20 μm. 50 The D50 of the first carbon material is 1-20 μm. 50 The D50 of the silicon in the outer active layer is 1-30 μm. 50 The D50 of the silicon monoxide and / or stannous oxide in the outer active layer is 1-20 μm. 50 The D50 of the second carbon material is 1-30 μm.

[0017] Optionally, the thickness of the negative electrode plate is 36-144 μm.

[0018] Optionally, the thickness ratio of the outer active layer to the inner active layer is 0.5-2:1.

[0019] Optionally, the ratio of the thickness of the inner active layer to the thickness of the current collector is 1-5:1.

[0020] The second aspect of the present disclosure provides a lithium ion battery comprising the negative electrode sheet of the first aspect of the present disclosure.

[0021] The third aspect of the present disclosure provides a power-using device comprising the lithium ion battery of the second aspect of the present disclosure.

[0022] Through the above technical solution, the present disclosure provides a negative electrode sheet, a lithium ion battery and a power-using device. The negative electrode sheet is provided with a double-layer active layer containing active materials with different expansion coefficients. A first active material (such as silicon monoxide and / or stannous oxide) with a smaller expansion coefficient is used as an inner active layer, and a second active material (such as silicon) with a larger expansion coefficient is used as an outer active layer, so as to obtain a silicon-based negative electrode sheet with an expansion gradient, in which the expansion of silicon in the outer layer is greater than the expansion of silicon monoxide and / or stannous oxide in the inner layer. In the application of the negative electrode sheet in a battery, the inner layer has a smaller expansion coefficient, which can avoid the peeling of the inner active layer in contact with the current collector, so that the inner active layer maintains good contact with the current collector and reduces the risk of material falling off. Moreover, the present disclosure does not inhibit the expansion of the inner active layer and the outer active layer, but allows both the inner active layer and the outer active layer to expand. The second active material silicon has a larger expansion coefficient, which can leave expansion space for the expansion of the inner layer active material silicon monoxide and / or stannous oxide, so that the inner active layer part adhered to the outer active layer can expand along with the expansion of the outer active layer, avoiding the separation phenomenon of the two active layer adhered parts caused by too large expansion difference, thereby reducing the risk of peeling of the inner and outer active layers and significantly improving the cycle performance. The negative electrode sheet provided by the present disclosure can effectively apply high silicon content and improve the performance of silicon (the less silicon that falls off in the active layer, the more silicon that does not fall off, and the more silicon that can be used), and the present disclosure simultaneously introduces silicon monoxide and / or stannous oxide and silicon for use together, which can achieve high capacity and high initial efficiency in battery applications.

[0023] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0024] The accompanying drawings are included to provide a further understanding of the present disclosure and constitute a part of the specification, which together with the following detailed description, serve to explain the present disclosure. In the drawings:

[0025] Figure 1 A structural schematic diagram of the negative electrode sheet provided by the present disclosure is shown in FIG. 1.

[0026] Reference Signs

[0027] 1-Current collector, 2-Inner active layer, 3-Outer active layer, 4-First active material, 5-Second active material. Detailed Implementation

[0028] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure.

[0029] The first aspect of this disclosure provides a negative electrode plate, such as... Figure 1 As shown, the negative electrode includes a current collector 1 and an active layer disposed on the surface of the current collector; the active layer includes an inner active layer 2 and an outer active layer 3 stacked together, the outer active layer 3 being disposed on the side of the inner active layer 2 away from the current collector 1; the inner active layer includes a first active material 4, and the outer active layer includes a second active material 5; wherein the first active material includes one or both of silicon suboxide and / or tin suboxide, the second active material includes silicon, and the coefficient of thermal expansion of the first active material is less than the coefficient of thermal expansion of the second active material.

[0030] This disclosure provides a negative electrode sheet with a double active layer containing active materials with different coefficients of thermal expansion. A first active material with a smaller coefficient of thermal expansion (such as silicon suboxide and / or tin suboxide) is used as the inner active layer, and a second active material with a larger coefficient of thermal expansion (such as silicon) is used as the outer active layer, resulting in a silicon-based negative electrode sheet with an expansion gradient. The expansion of silicon in the outer layer is greater than that of silicon suboxide and / or tin suboxide in the inner layer. In battery applications, the smaller coefficient of thermal expansion in the inner layer prevents the inner active layer in contact with the current collector from peeling off. The inner active layer maintains good contact with the current collector, reducing the risk of material detachment. Furthermore, this disclosure does not suppress the expansion of the inner and outer active layers, but rather allows both to expand. The second active material, silicon, has a large coefficient of expansion, providing expansion space for the inner active materials, silicon suboxide and / or tin suboxide. This allows the portion of the inner active layer bonded to the outer active layer to expand along with it, avoiding separation caused by excessive expansion differences between the two active layers. This further reduces the risk of delamination between the inner and outer active layers, significantly improving cycle performance. The negative electrode sheet provided by this disclosure is effectively suitable for high silicon content, improving silicon performance (the less silicon detached from the active layer and the more silicon remaining, the more silicon can function). This disclosure also introduces the use of silicon suboxide and / or tin suboxide in conjunction with silicon, achieving high capacity and high first-efficiency in battery applications.

[0031] In a preferred embodiment, the first active material is silicon suboxide, and the second active material is silicon. Using a combination of silicon suboxide and silicon in the negative electrode can achieve better results.

[0032] In one embodiment, the inner active layer is disposed on the surface of the current collector.

[0033] In one embodiment, the first active material further comprises a first carbon material; the content of the silicon monoxide and / or tin monoxide is 50-99% by weight, and the content of the first carbon material is 1-50% by weight, based on the total weight of the first active material; the content of the silicon monoxide and / or tin monoxide in the first active material can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 99% by weight, but is not limited to the above specific values, and is preferably 60-80% by weight; wherein the content of the silicon monoxide and / or tin monoxide being 1-50% by weight includes the following three cases: the inner active layer only contains silicon monoxide, and the content of the silicon monoxide is 50-99% by weight; the inner active layer only contains tin monoxide, and the content of the tin monoxide is 50-99% by weight; or the inner active layer contains silicon monoxide and tin monoxide, and the total content of the silicon monoxide and tin monoxide is 50-99% by weight; the content of the first carbon material can be 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50% by weight, but is not limited to the above specific values, and is preferably 20-40% by weight; the content ratio of the silicon monoxide and / or tin monoxide and the first carbon material in the first active material provided in this embodiment can effectively improve the performance of the negative electrode sheet.

[0034] In one embodiment, the second active material further comprises a second carbon material; the content of the silicon is 50-99% by weight, and the content of the second carbon material is 1-50% by weight, based on the total weight of the second active material; in the outer active layer of the present disclosure, the content of the silicon can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 99% by weight, but is not limited to the above specific values, and is preferably 60-80% by weight; the content of the second carbon material can be 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50% by weight, but is not limited to the above specific values, and is preferably 20-40% by weight; the content ratio of the silicon and the second carbon material in the outer active layer provided in this embodiment can effectively improve the performance of the negative electrode sheet.

[0035] In one embodiment, the content of silicon is 15-50% by weight, and the content of the silicon monoxide and / or stannous oxide is 15-50% by weight, based on the total weight of the inner active layer and the outer active layer in the negative electrode plate. In the present disclosure, the content of silicon or the content of the silicon monoxide and / or stannous oxide in the negative electrode plate can each independently be 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50% by weight, but is not limited to the above specific values. Preferably, the content of silicon is 15-35% by weight, and the content of the silicon monoxide and / or stannous oxide is 15-35% by weight, based on the total weight of the inner active layer and the outer active layer in the negative electrode plate, wherein the “silicon monoxide and / or stannous oxide” also includes the three cases of “only including silicon monoxide, only including stannous oxide, or including both silicon monoxide and stannous oxide”. In the prior art electrode plate arrangement, an increase in the content of silicon leads to an increased risk of detachment of the elemental silicon active material, and therefore in order to overcome this phenomenon, it is necessary to reduce the content of elemental silicon, but at the same time this also brings the effect that the battery cannot exhibit high capacity, while the negative electrode plate provided by the present disclosure can have a high content of silicon active material while avoiding the peeling of silicon, thereby helping to improve the capacity of the negative electrode plate.

[0036] In one embodiment, the inner active layer further comprises a first conductive material and a first binder material, and the outer active layer further comprises a second conductive material and a second binder material.

[0037] In one embodiment, the content of the first active material is 80-96% by weight, including but not limited to 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, or 96% by weight, based on the total weight of the inner active layer; the content of the first conductive material is 1-10% by weight, including but not limited to 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% by weight; the content of the first binder material is 3-10% by weight, including but not limited to 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% by weight; and optionally, the content of the silicon monoxide and / or stannous oxide is 40-96% by weight, based on the total weight of the inner active layer; wherein the “silicon monoxide and / or stannous oxide” also includes the three cases of “only including silicon monoxide, only including stannous oxide, or including both silicon monoxide and stannous oxide”.

[0038] The content of the second active material is 80-96 wt%, including but not limited to 80 wt%, 82 wt%, 84 wt%, 86 wt%, 88 wt%, 90 wt%, 92 wt%, 94 wt%, or 96 wt%; the content of the second conductive material is 1-10 wt%, including but not limited to 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%; the content of the second binding material is 3-10 wt%, including but not limited to 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%; and optionally, the content of silicon is 40-96 wt% based on the total weight of the outer active layer. Within the ranges provided in the embodiments, the content ratio of each component in the inner active layer and the outer active layer can enable the negative electrode sheet to have excellent comprehensive performance.

[0039] In some embodiments, the first carbon material and the second carbon material are each independently selected from one or more of natural graphite, artificial graphite, hard carbon, soft carbon, and mesocarbon microbeads.

[0040] The first conductive material and the second conductive material are each independently selected from one or more of conductive carbon black, conductive graphite, carbon nanotubes, and graphene.

[0041] The first binding material and the second binding material are each independently selected from one or more of styrene-butadiene rubber, carboxymethyl cellulose, and polyacrylic acid. Each of the substances used in the present disclosure can be purchased through commercial channels or prepared by known methods.

[0042] In some embodiments, the D50 of the silicon oxide and / or stannous oxide in the inner active layer is 1-20 pm. 50 The D50 of the first carbon material is 1-20 pm. 50 The D50 of the silicon in the outer active layer is 1-30 pm. 50 The D50 of the second carbon material is 1-20 pm. 50 The D50 of the second carbon material is 1-30 pm. The D50 of 1-20 pm includes but is not limited to 1 pm, 2 pm, 4 pm, 6 pm, 8 pm, 10 pm, 12 pm, 14 pm, 16 pm, 18 pm, 20 pm, and the D50 of 1-30 pm includes but is not limited to 1 pm, 2 pm, 4 pm, 6 pm, 8 pm, 10 pm, 12 pm, 14 pm, 16 pm, 18 pm, 20 pm, 22 pm, 24 pm, 26 pm, 28 pm, 30 pm. The negative electrode sheet provided in the present disclosure uses micrometer-level particles in the inner active layer and the outer active layer, which can reduce the cost of materials.

[0043] In an embodiment, the thickness of the negative electrode tab is 36-144 μm, including but not limited to 36 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 144 μm. The negative electrode tab provided by the present disclosure has a suitable thickness, so that the battery has good capacity performance and cycle effect.

[0044] In a preferred embodiment, the thickness ratio of the outer active layer to the inner active layer is 0.5-2:1, including but not limited to 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1.0:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1. The thickness ratio of the outer active layer to the inner active layer of the negative electrode tab is within the range of the present embodiment, and the negative electrode tab can have more excellent battery performance in battery applications, such as excellent capacity, first coulombic efficiency, and cycle stability.

[0045] In a preferred embodiment, the thickness ratio of the inner active layer to the current collector is 1-5:1, including but not limited to 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1. The thickness ratio of the inner active layer to the current collector of the negative electrode tab is within the range of the present embodiment, and the negative electrode tab can simultaneously have excellent capacity, first coulombic efficiency, and cycle stability in battery applications.

[0046] The negative electrode tab provided by the present disclosure can be prepared by a method comprising the following steps:

[0047] The first active material is mixed with the first dispersion solvent to obtain a first slurry; the second active material is mixed with the second dispersion solvent to obtain a second slurry; the expansion coefficient of the first active material is less than the expansion coefficient of the second active material; wherein the first active material includes one or both of silicon monoxide and stannous oxide, preferably silicon monoxide; the second active material includes silicon;

[0048] The first slurry is coated on the surface of the current collector by using a double-layer coating process, and the second slurry is coated on the surface of the first slurry coating;

[0049] The coated current collector is subjected to drying treatment and rolling treatment.

[0050] The present disclosure uses the technical means of double-layer coating to simultaneously coat two layers of slurry (the first slurry and the second slurry) on the negative electrode current collector to form an inner active layer with low expansion capacity and an outer active layer with high expansion capacity, thereby preparing a negative electrode tab, which has a simple process.

[0051] In a preferred embodiment, the content of silicon monoxide and / or tin monoxide in the first active material is 50-99% by weight, and the content of the first carbon material is 1-50% by weight;

[0052] In the second active material, the content of silicon is 50-99% by weight, and the content of the second carbon material is 1-50% by weight.

[0053] In an embodiment, the D50 of the first active material in the first slurry is 1-20 μm, and the D50 of the first carbon material is 1-30 μm. 50 In an embodiment, the D50 of the first active material in the first slurry is 1-20 μm, and the D50 of the first carbon material is 1-30 μm. 50 In an embodiment, the D50 of the first active material in the first slurry is 1-20 μm, and the D50 of the first carbon material is 1-30 μm. 50 In an embodiment, the D50 of the first active material in the first slurry is 1-20 μm, and the D50 of the first carbon material is 1-30 μm. 50 In an embodiment, the D50 of the first active material in the first slurry is 1-20 μm, and the D50 of the first carbon material is 1-30 μm.

[0054] In an embodiment, the first slurry further comprises a first conductive material and a first binding material, and the second slurry further comprises a second conductive material and a second binding material.

[0055] In a preferred embodiment, the solid content in the first slurry is 40-50% by weight, and the solid content in the second slurry is 40-50% by weight.

[0056] In an embodiment, the content of the first active material is 80-96% by weight, the content of the first conductive material is 1-10% by weight, and the content of the first binding material is 3-10% by weight, based on the solid content in the first slurry.

[0057] In an embodiment, the content of the second active material is 80-96% by weight, the content of the second conductive material is 1-10% by weight, and the content of the second binding material is 3-10% by weight, based on the solid content in the second slurry.

[0058] In a specific embodiment, the first carbon material and the second carbon material are each independently selected from one or more of natural graphite, artificial graphite, hard carbon, soft carbon, and mesocarbon microbeads;

[0059] The first conductive material and the second conductive material are each independently selected from one or more of conductive carbon black, conductive graphite, carbon nanotubes, and graphene;

[0060] The first binding material and the second binding material are each independently selected from one or more of styrene-butadiene rubber, carboxymethyl cellulose, and polyacrylic acid;

[0061] The first dispersion solvent and the second dispersion solvent are water.

[0062] In one embodiment, the weight ratio of the first paste and the second paste dressing is 0.5-2:1, preferably 1-5:1. By controlling the weight ratio of the first paste and the second paste dressing, the thickness ratio of the inner active layer and the outer active layer can be controlled.

[0063] In one embodiment, the double-layer coating process, drying treatment, and roll forming treatment are performed using conventional equipment and conventional process conditions.

[0064] A second aspect of this disclosure provides a lithium-ion battery comprising the negative electrode sheet described in the first aspect of this disclosure.

[0065] The lithium-ion battery disclosed herein can be assembled using conventional assembly methods and conventional materials in the art.

[0066] A third aspect of this disclosure provides an electrical device that includes the lithium-ion battery provided in the second aspect of this disclosure.

[0067] The electrical equipment disclosed herein may include electric vehicles, power banks, mobile phones, laptops, etc.

[0068] The present disclosure is further described in detail below through examples. All raw materials used in the examples are commercially available.

[0069] In the following examples and comparative examples, conductive carbon black was used as the conductive agent and SBR was used as the binder.

[0070] D of the graphite carbon material added to the inner and outer active layers 50 Within the range of 10-25 μm.

[0071] Example 1

[0072] (1) Silicon suboxide material (D 50 A slurry A with a solid content of 45 wt% was obtained by dispersing graphite, conductive agent, and binder in deionized water at a weight ratio of 50:30:10:10. In the obtained inner active layer, the content of the first active material (silicon suboxide and graphite) was 80 wt% based on the total weight of the inner active layer (the content of silicon suboxide was 50 wt% based on the total weight of the inner active layer); the content of silicon suboxide was 62.5 wt% and the content of graphite was 37.5 wt% based on the total weight of the first active material.

[0073] (2) Silicon material (D 50silicon and graphite) in the inner active layer is 80% by weight (the content of silicon is 50% by weight in the total weight of the inner active layer); the content of silicon is 62.5% by weight and the content of graphite is 37.5% by weight in the total weight of the first active material;

[0074] (3) The slurry A and the slurry B are uniformly coated on the surface of the negative current collector by using a double-layer coating device at a coating amount ratio of 1:1, so that the thickness ratio of the inner active layer to the outer active layer is 1:1. After drying, rolling and die cutting, a negative electrode sheet F1 is obtained.

[0075] The thickness of the current collector is 9 μm, the thickness of the inner active layer is 18 μm, the thickness of the outer active layer is 18 μm, and the total thickness of the negative electrode sheet is 45 μm. The thickness ratio of the outer active layer to the inner active layer is 1:1.

[0076] Example 2

[0077] (1) The silicon monoxide material (D 50 The thickness of the current collector is 9 μm, the thickness of the inner active layer is 18 μm, the thickness of the outer active layer is 18 μm, and the total thickness of the negative electrode sheet is 45 μm. The thickness ratio of the outer active layer to the inner active layer is 1:1.

[0078] (2) The silicon material (D 50 The thickness of the current collector is 9 μm, the thickness of the inner active layer is 18 μm, the thickness of the outer active layer is 18 μm, and the total thickness of the negative electrode sheet is 45 μm. The thickness ratio of the outer active layer to the inner active layer is 1:1.

[0079] (3) The slurry A and the slurry B are uniformly coated on the surface of the negative current collector by using a double-layer coating device at a coating amount ratio of 1:1, so that the thickness ratio of the inner active layer to the outer active layer is 1:1. After drying, rolling and die cutting, a negative electrode sheet F1 is obtained.

[0080] The thickness of the current collector is 9 μm, the thickness of the inner active layer is 18 μm, and the thickness of the outer active layer is 18 μm.

[0081] Example 3

[0082] (1) The silicon oxide material (D 50 The thickness of the current collector is 9 μm, the thickness of the inner active layer is 18 μm, and the thickness of the outer active layer is 18 μm.

[0083] (2) The silicon material (D 50 The thickness of the current collector is 9 μm, the thickness of the inner active layer is 18 μm, and the thickness of the outer active layer is 18 μm.

[0084] (3) The slurry A and the slurry B are uniformly coated on the surface of the negative electrode current collector by using a double-layer coating device at a coating amount ratio of 1:1, so that the thickness ratio of the inner active layer to the outer active layer is 1:1. After drying, rolling, and die cutting, the negative electrode sheet F3 is obtained.

[0085] The thickness of the current collector is 9 μm, the thickness of the inner active layer is 18 μm, and the thickness of the outer active layer is 18 μm.

[0086] Example 4

[0087] (1) The silicon oxide material (D 50 The thickness of the current collector is 9 μm, the thickness of the inner active layer is 18 μm, and the thickness of the outer active layer is 18 μm.

[0088] (2) The silicon material (D 50silicon and graphite) was 80% by weight (based on the total weight of the inner active layer, the content of silicon was 60% by weight); based on the total weight of the second active material, the content of silicon was 75% by weight, and the content of graphite was 25% by weight;

[0089] (3) The slurry A and the slurry B were uniformly coated on the surface of the negative current collector by using a double-layer coating device at a coating amount ratio of 1:1, so that the thickness ratio of the inner active layer and the outer active layer was 1:1. After drying, rolling and die cutting, the negative electrode sheet F4 was obtained.

[0090] The thickness of the current collector was 9 μm, the thickness of the inner active layer was 18 μm, and the thickness of the outer active layer was 18 μm.

[0091] Example 5

[0092] (1) The silicon monoxide material (D 50 The silicon monoxide material (D

[0093] (2) The silicon material (D 50 The silicon monoxide material (D

[0094] (3) The slurry A and the slurry B were uniformly coated on the surface of the negative current collector by using a double-layer coating device at a coating amount ratio of 0.5:1, so that the thickness ratio of the inner active layer and the outer active layer was 0.5:1. After drying, rolling and die cutting, the negative electrode sheet F5 was obtained.

[0095] The thickness of the current collector was 9 μm, the thickness of the inner active layer was 12 μm, and the thickness of the outer active layer was 24 μm.

[0096] Example 6

[0097] (1) Silicon suboxide material (D 50 A slurry A with a solid content of 45 wt% was obtained by dispersing graphite, conductive agent, and binder in deionized water at a weight ratio of 50:30:10:10. In the obtained inner active layer, the content of the first active material (silicon suboxide and graphite) was 80 wt% based on the total weight of the inner active layer (the content of silicon suboxide was 50 wt% based on the total weight of the inner active layer); the content of silicon suboxide was 62.5 wt% and the content of graphite was 37.5 wt% based on the total weight of the first active material.

[0098] (2) Elemental silicon material (D 50 A slurry B with a solid content of 45 wt% was obtained by dispersing graphite, conductive agent, and binder in deionized water at a weight ratio of 50:30:10:10 (5 μm). In the obtained outer active layer, based on the total weight of the outer active layer, the content of the second active material (silicon and graphite) was 80 wt% (based on the total weight of the outer active layer, the silicon content was 50 wt%); based on the total weight of the second active material, the silicon content was 62.5 wt% and the graphite content was 37.5 wt%.

[0099] (3) Using a double-layer coating equipment, slurry A and slurry B are uniformly coated on the surface of the negative electrode current collector at a coating ratio of 2:1, so that the thickness ratio of the inner active layer to the outer active layer is 2:1. After drying, rolling and die cutting, the negative electrode sheet F6 is obtained.

[0100] The thickness of the current collector is 9 μm, the thickness of the inner active layer is 24 μm, and the thickness of the outer active layer is 12 μm.

[0101] Example 7

[0102] This Example 1 follows the preparation method described in Example 1, except that:

[0103] In step (1), no graphite is added to the slurry used to prepare the inner active layer, meaning that the active material of the inner active layer is only silicon suboxide: silicon suboxide material (D... 50 A slurry A with a solid content of 45% by weight was obtained by dispersing a conductive agent and a binder (5μm) in deionized water at a weight ratio of 80:10:10. In the obtained inner active layer, the content of the first active material (silicon suboxide material) was 80% by weight based on the total weight of the inner active layer, and the content of silicon suboxide was 100% by weight based on the total weight of the first active material.

[0104] The remaining steps are the same as in Example 1, resulting in negative electrode F7;

[0105] The thickness of the current collector is 9 pm, the thickness of the inner active layer is 18 pm, the thickness of the outer active layer is 18 pm, the total thickness of the negative electrode sheet is 45 pm, and the thickness ratio of the outer active layer to the inner active layer is 1:1.

[0106] Example 8

[0107] This example refers to the preparation method in Example 1, and the difference from Example 1 is only that:

[0108] No graphite is added in the slurry for preparing the outer active layer in step (2), that is, the active material of the outer active layer is only silicon: the silicon material (D 50 The thickness of the current collector is 9 pm, the thickness of the inner active layer is 18 pm, the thickness of the outer active layer is 18 pm, the total thickness of the negative electrode sheet is 45 pm, and the thickness ratio of the outer active layer to the inner active layer is 1:1.

[0109] The remaining steps are the same as those in Example 1, and a negative electrode sheet F8 is obtained.

[0110] The thickness of the current collector is 9 pm, the thickness of the inner active layer is 18 pm, the thickness of the outer active layer is 18 pm, the total thickness of the negative electrode sheet is 45 pm, and the thickness ratio of the outer active layer to the inner active layer is 1:1.

[0111] Example 9

[0112] This example refers to the preparation method in Example 1, and the difference from Example 1 is that the thickness ratio of the inner active layer to the outer active layer is controlled to be 0.2:1:

[0113] That is, in step (3), the slurry A and the slurry B are uniformly coated on the surface of the negative electrode current collector by using a double-layer coating device at a coating amount ratio of 0.2:1, so that the thickness ratio of the outer active layer to the inner active layer is 0.2:1, and after drying, rolling and die cutting, a negative electrode sheet F9 is obtained.

[0114] The thickness of the current collector is 9 pm, the thickness of the outer active layer is 9 pm, and the thickness of the inner active layer is 45 pm.

[0115] Example 10

[0116] This example refers to the preparation method in Example 1, and the difference from Example 1 is that the thickness ratio of the inner active layer to the outer active layer is controlled to be 3:1:

[0117] That is, in step (3), slurry A and slurry B are uniformly coated on the surface of the negative current collector in a coating amount ratio of 3:1 using a double-layer coating device, so that the thickness ratio of the outer active layer and the inner active layer is 3:1, and after drying, rolling and die cutting, a negative electrode sheet F10 is obtained.

[0118] The thickness of the current collector is 9 μm, the thickness of the inner active layer is 4.5 μm, and the thickness of the outer active layer is 4.5 μm. A negative electrode sheet F11 is obtained, and the total thickness of the negative electrode sheet is 18 μm.

[0119] Example 11

[0120] This example refers to the preparation method in Example 1, and differs from Example 1 in that the thickness ratio of the inner active layer to the current collector is controlled to be 6:1:

[0121] The thickness of the current collector is 9 μm, the thickness of the inner active layer is 54 μm, and the thickness of the outer active layer is 54 μm. A negative electrode sheet F12 is obtained, and the total thickness of the negative electrode sheet is 117 μm.

[0122] Example 12

[0123] This example refers to the preparation method in Example 1, and differs from Example 1 in that the thickness ratio of the inner active layer to the current collector is controlled to be 6:1:

[0124] The thickness of the current collector is 9 μm, the thickness of the inner active layer is 54 μm, and the thickness of the outer active layer is 54 μm. A negative electrode sheet F12 is obtained, and the total thickness of the negative electrode sheet is 117 μm.

[0125] Example 13

[0126] This example refers to the preparation method in Example 1, and differs from Example 1 in that the silicon monoxide is replaced by stannous oxide, and the rest of the process is the same as Example 1. A negative electrode sheet F13 is obtained;

[0127] The thickness of the current collector is 9 μm, the thickness of the inner active layer is 54 μm, and the thickness of the outer active layer is 54 μm. A negative electrode sheet F12 is obtained, and the total thickness of the negative electrode sheet is 117 μm.

[0128] Comparative Example 1

[0129] This comparative example refers to the preparation method in Example 1, and differs from Example 1 in that a slurry A containing silicon monoxide is used for double-layer coating, i.e. the active material in the inner active layer and the outer active layer is all silicon monoxide, and the inner active layer and the outer active layer obtained are a whole active layer of silicon monoxide as the active material, and the thickness of the whole active layer of silicon monoxide is the same as the total thickness of the inner active layer and the outer active layer in Example 1. A negative electrode sheet D-1 is obtained.

[0130] Comparative Example 2

[0131] The present comparative example refers to the preparation method in Example 1, and differs from Example 1 in that: the slurry B containing silicon is used for double-layer coating, i.e. the active material in the inner active layer and the outer active layer is silicon, the obtained inner active layer and outer active layer are a whole active layer with silicon as the active material, and the thickness of the silicon whole active layer is the same as the total thickness of the inner active layer and the outer active layer in Example 1, obtaining the negative electrode sheet D-2.

[0132] Comparative Example 3

[0133] The present comparative example refers to the preparation method in Example 1, and differs from Example 1 in that:

[0134] The slurry B is used for inner active layer coating, and the slurry A is used for outer active layer coating, obtaining a negative electrode sheet in which the expansion coefficient of the inner active layer is greater than that of the outer active layer, obtaining the negative electrode sheet D-3.

[0135] The composition and thickness data of the inner active layer and the outer active layer of the negative electrode material obtained in the above examples and comparative examples are listed in Table 1 below.

[0136] Table 1

[0137] In Table 1, the silicon content and silicon monoxide content marked with “*” are based on the total weight of the inner active layer and the outer active layer in the negative electrode sheet.

[0138] Test Example

[0139] The present test example is used to illustrate the effect of the negative electrode material prepared in the above examples and comparative examples in the application of lithium ion batteries.

[0140] Specifically, the soft package battery is assembled in the following manner: the negative electrode sheets prepared in the examples and comparative examples are cut into 80x60 sheets, nickel-cobalt-manganese (811) ternary is used as the positive electrode, PE / PP film is used as the ion exchange film, LiPF6 is used as the electrolyte, and aluminum plastic film is used as the shell, and the soft package battery is assembled.

[0141] The assembled soft package battery is subjected to electrochemical performance testing (including initial charge-discharge capacity, coulombic efficiency, capacity retention rate, etc.). The battery testing method includes: placing the obtained soft package battery in a blue electric test cabinet for charge-discharge testing, the charge-discharge rate is 0.5C, the voltage range is 2.5-4.2V, and the specific capacity of the battery is obtained by testing; the same method is used for 300 cycles to obtain the cycle performance of the battery. The test results of the soft package battery are listed in Table 2 below.

[0142] Table 2

[0143]

[0144] According to the data in Table 2 above, it can be seen that:

[0145] Compared with Comparative Example 1 (containing only silicon monoxide active layer), Comparative Example 2 (containing only silicon active layer) and Comparative Example 3 (the expansion coefficient of the inner active layer is greater than that of the outer active layer), the negative electrode material provided in Examples 1-13 can simultaneously obtain high capacity, high initial efficiency and excellent cycle capacity retention rate, and has better comprehensive performance.

[0146] Comparing Example 1 with Examples 7-8, it can be seen that the inner active layer and the outer active layer in Example 1 add graphite, and the negative electrode in Example 1 has a higher cycle capacity retention rate.

[0147] Comparing Example 1 with Examples 9-10, it can be seen that the thickness ratio of the outer active layer to the inner active layer in Example 1 is within the range of “0.5-2:1”, and the negative electrode material provided in Example 1 can simultaneously have higher initial coulombic efficiency and cycle capacity retention rate.

[0148] Comparing Example 1 with Examples 11-12, it can be seen that the thickness ratio of the inner active layer to the current collector in Example 1 is within the range of “1-5:1”, and the negative electrode material provided in Example 1 can simultaneously have high capacity and high initial efficiency, and also have excellent cycle capacity retention rate.

[0149] The negative electrode material of Comparative Example 1 has all active layers of silicon monoxide, low capacity and small expansion, so it does not fall off; compared with the negative electrode materials obtained from Comparative Examples 2-3, the negative electrode of Examples 1-13 has the structure of the inner and outer active layers provided in the present disclosure, and the negative electrode of Examples 1-13 can also reduce the risk of active material falling off.

[0150] The above describes the preferred embodiments of the present disclosure, but the present disclosure is not limited to the specific details in the above-described embodiments, and various simple modifications can be made to the technical solutions of the present disclosure within the technical concept of the present disclosure, and these simple modifications all belong to the protection scope of the present disclosure.

[0151] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0152] In addition, various different embodiments of the present disclosure can also be combined in any appropriate manner, as long as it does not deviate from the idea of the present disclosure, it should also be considered as disclosed in the present disclosure.

Claims

1. A negative electrode sheet, characterized by, The negative electrode sheet comprises a current collector and an active layer arranged on the surface of the current collector; the active layer comprises an inner active layer and an outer active layer arranged in a stack, the outer active layer being arranged on the side of the inner active layer away from the current collector; the inner active layer comprises a first active material; the outer active layer comprises a second active material; the first active material has a smaller expansion coefficient than the second active material; the first active material comprises silicon monoxide and / or stannous oxide, and the second active material comprises silicon; the content of the silicon is 15-30% by weight and the content of the silicon monoxide and / or stannous oxide is 15-30% by weight, based on the total weight of the inner active layer and the outer active layer in the negative electrode sheet; D50 of the silicon oxide and / or stannous oxide in the inner active layer is 0.1-5 μm 50 D50 of the silicon in the outer active layer is 1-20 μm 50 D50 of the silicon in the outer active layer is 1-20 μm The thickness ratio of the inner active layer to the current collector is 1-5:

1.

2. The negative electrode sheet according to claim 1, characterized by, The first active material further comprises a first carbon material; the content of the silicon monoxide and / or stannous oxide is 50-99% by weight and the content of the first carbon material is 1-50% by weight, based on the total weight of the first active material; The second active material further comprises a second carbon material; the content of the silicon is 50-99% by weight and the content of the second carbon material is 1-50% by weight, based on the total weight of the second active material.

3. The negative electrode sheet according to claim 2, characterized by The inner active layer further comprises a first conductive material and a first binder material, and the outer active layer further comprises a second conductive material and a second binder material.

4. The negative electrode sheet according to claim 3, characterized by The content of the first active material is 80-96% by weight, the content of the first conductive material is 1-10% by weight, and the content of the first binder material is 3-10% by weight, based on the total weight of the inner active layer; The content of the second active material is 80-96% by weight, the content of the second conductive material is 1-10% by weight, and the content of the second binder material is 3-10% by weight, based on the total weight of the outer active layer.

5. The negative electrode sheet according to claim 3, wherein The first carbon material and the second carbon material are each independently selected from one or more of natural graphite, artificial graphite, hard carbon, soft carbon, and mesocarbon microbeads; The first conductive material and the second conductive material are each independently selected from one or more of conductive carbon black, conductive graphite, carbon nanotubes, and graphene; The first binder material and the second binder material are each independently selected from one or more of styrene-butadiene rubber, carboxymethyl cellulose, and polyacrylic acid.

6. The negative electrode sheet according to claim 2, wherein D50 of the first carbon material is 1-30 μm 50 D50 of the second carbon material is 1-30 μm 50 D50 of the second carbon material is 1-30 μm.

7. The negative electrode sheet according to claim 1, wherein The thickness of the negative electrode sheet is 36-144 μm.

8. The negative electrode sheet according to claim 1, wherein The thickness ratio of the outer active layer to the inner active layer is 0.5-2:

1.

9. A lithium-ion battery, characterized by The negative electrode sheet of any one of claims 1-8.

10. An electric device, characterized by The lithium ion battery of claim 9.

Images