Negative pole piece, secondary battery and electric device

Abstract

The invention provides a negative pole piece, a secondary battery and an electric device. The negative electrode piece comprises a negative electrode current collector and a negative electrode film layer formed on at least one surface of the negative electrode current collector, the negative electrode film layer is provided with a first surface far away from the negative electrode current collector and a second surface opposite to the first surface, and the thickness of the negative electrode film layer is marked as H; the area from the first surface of the negative electrode film layer to the thickness range of 0.3 H is marked as the first area of the negative electrode film layer, the area from the second surface of the negative electrode film layer to the thickness range of 0.3 H is marked as the second area of the negative electrode film layer, and the first area comprises a spherical or / and sphere-like first silicon-based material. The negative pole piece can reduce the expansion rate of the negative pole piece, and improve the cycling stability and storage performance of the battery.

Description

Technical Field

[0001] This application relates to the technical field of secondary batteries, and particularly to a negative electrode sheet, a secondary battery, and an electrical device using the same. Background Art

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydroelectric, thermal, wind, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.

[0003] Silicon-based negative electrode active materials are an effective way to improve the capacity of secondary batteries. However, negative electrode sheets containing silicon-based materials have the disadvantages of high electrode sheet expansion rate, poor battery cycle life, and poor high-temperature storage performance. Therefore, existing negative electrode sheets containing silicon-based materials still need to be improved. Summary of the Invention

[0004] This application is made in view of the above problems, and its purpose is to provide a negative electrode sheet that can reduce its own expansion rate and improve the cycle stability and high-temperature storage performance of the battery.

[0005] In a first aspect of this application, a negative electrode sheet is provided. The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer formed on at least one surface of the negative electrode current collector. The negative electrode film layer has a first surface away from the negative electrode current collector and a second surface disposed opposite to the first surface. The thickness of the negative electrode film layer is denoted as H. The region within the thickness range from the first surface of the negative electrode film layer to 0.3H is denoted as the first region of the negative electrode film layer, and the region within the thickness range from the second surface of the negative electrode film layer to 0.3H is denoted as the second region of the negative electrode film layer. The first region includes spherical or / and quasi-spherical first silicon-based materials.

[0006] Currently, the mainstream negative electrode active materials of lithium-ion batteries are mainly artificial graphite and natural graphite. The theoretical specific capacity of silicon materials is much higher than that of graphite. Using silicon-based materials as negative electrode active materials can improve the energy density of secondary batteries. The first region in direct contact with the cold pressing roller and the electrolyte includes spherical or quasi-spherical silicon-based materials, which can broaden the compaction density window of the electrode sheet. The cold pressing pressure required under the same compaction density is smaller, reducing the probability of cracking of the silicon-based materials during cold pressing, facilitating the maintenance of the integrity of the silicon-based material particles, reducing the generation of new interfaces, and avoiding irreversible consumption of active ions caused by the contact between the active silicon exposed by the silicon-based materials and the electrolyte during the cycling process. Moreover, since the silicon-based materials are spherical or quasi-spherical, the stress concentration of the silicon-based materials during rolling and expansion can be reduced, further slowing down the cracking phenomenon of the silicon-based materials, thereby comprehensively reducing the expansion rate of the electrode sheet and improving the storage performance and cycle stability of the battery.

[0007] In any embodiment, the second region includes a second silicon-based material, and the average particle size of the second silicon-based material is smaller than the average particle size of the first silicon-based material.

[0008] For the first region where the negative electrode tab is in direct contact with the electrolyte, using the first silicon-based material with a large average particle size can reduce the specific surface area of the first silicon-based material, thereby reducing the loss of active ions caused by the direct contact and reaction between the silicon-based material and the electrolyte, decreasing the swelling rate of the tab, and improving the storage performance and cycle stability of the battery. For the second region of the negative electrode tab close to the current collector, using the second silicon-based material with a small average particle size, which has a short solid-phase ion transport distance, is beneficial to improving the transport performance of active ions and electrons, thus enhancing the fast charging performance of the battery. Moreover, the second silicon-based material with a small average particle size has a larger specific surface area, enhancing the interaction between the binder and the silicon-based material, thereby further reducing the swelling of the tab and improving the storage performance and cycle stability of the battery.

[0009] In any embodiment, the percentage of the mass of silicon element in the first silicon-based material relative to the total mass of the first silicon-based material is less than the percentage of the mass of silicon element in the second silicon-based material relative to the total mass of the second silicon-based material.

[0010] The low content of silicon element in the first silicon-based material in the first region in direct contact with the cold pressing roller and the electrolyte can reduce the content of silicon in contact with the electrolyte when the silicon-based material cracks, thereby slowing down the swelling of the tab and improving the cycle stability and storage performance of the battery. By using the second silicon-based material with a high silicon content in combination with the first silicon-based material with a low silicon content, it is beneficial for the battery to achieve low swelling, good cycle stability, and high energy density.

[0011] In any embodiment, the specific surface area of the first silicon-based material is smaller than the specific surface area of the second silicon-based material.

[0012] The first silicon-based material has a small specific surface area, which can reduce the loss of active ions caused by the reaction between the silicon-based material and the electrolyte, thereby slowing down the swelling of the tab and improving the cycle stability and storage performance of the battery. The second silicon-based material has a large specific surface area, which can enhance the interaction between the binder and the silicon-based material, thereby reducing the swelling of the tab. By using the first silicon-based material and the second silicon-based material in combination, the battery can achieve low swelling, excellent cycle stability, and storage performance.

[0013] In any embodiment, the crystallinity of the first silicon-based material is less than the crystallinity of the second silicon-based material.

[0014] The amorphous silicon-based material has better cycle stability compared to the crystalline silicon-based material. The low crystallinity of the first silicon-based material is beneficial to improving the cycle stability of the battery.

[0015] In any embodiment, a coin cell is used to perform a constant current charge-discharge test on the first silicon-based material, and a differential capacity curve in the lithium deintercalation stage is plotted to reflect the relationship between dQ / dV and the voltage V. It is stipulated that the maximum value of the differential value dQ / dV between 0.27 V and 0.34 V is denoted as V1, and the maximum value of the differential value dQ / dV between 0.43 V and 0.55 V is denoted as V2, and 1.55 ≤ V1 / V2 ≤ 1.75. Optionally, 1.60 ≤ V1 / V2 ≤ 1.72.

[0016] When V1 / V2 of the first silicon-based material is within the above range, a high voltage plateau is not likely to occur, which is beneficial to maintaining the structural stability of the silicon-based material and improving the cycle stability of the battery.

[0017] In any embodiment, the first silicon-based material and / or the second silicon-based material includes a silicon-carbon material, wherein the silicon-carbon material includes carbon matrix particles having a pore structure and nano-silicon-based materials disposed in the pore structure.

[0018] When the silicon-carbon material has a structure of carbon matrix particles having a pore structure and nano-silicon-based materials disposed in the pore structure, the carbon matrix particles having a pore structure have a certain inhibitory effect on the expansion of the nano-silicon-based materials during cycling, thereby improving the structural stability of the silicon-carbon material, taking into account excellent storage performance and cycle stability while increasing the battery capacity.

[0019] In any embodiment, the Dv50 of the first silicon-based material is 9 μm - 11 μm, and optionally 9.5 μm - 10 μm.

[0020] When the Dv50 of the first silicon-based material meets the above range, the loss of active ions caused by the direct contact and reaction between the silicon-based material and the electrolyte can be reduced, the expansion of the electrode sheet can be reduced, and the storage performance and cycle stability of the battery can be improved.

[0021] In any embodiment, the mass percentage of silicon element in the first silicon-based material relative to the total mass of the first silicon-based material is 40% - 60%, and optionally 45% - 50%.

[0022] When the mass percentage of silicon element in the first silicon-based material is within the above range, the content of silicon in contact with the electrolyte when the silicon-based material cracks can be reduced, the expansion of the electrode sheet can be slowed down, which is beneficial to maintaining the integrity of the silicon-based material particles, ensuring that the battery has excellent capacity while improving the cycle stability of the battery.

[0023] In any embodiment, the specific surface area of the first silicon-based material is 0.8 m 2 / g - 5 m 2 / g, and optionally 1.1 m 2 / g - 3.2 m 2 / g.

[0024] When the specific surface area of the first silicon-based material is within the above range, the loss of active ions caused by the reaction between the silicon-based material and the electrolyte can be reduced, the swelling of the electrode sheet can be reduced, and the cycle stability and storage performance of the battery can be improved.

[0025] In any embodiment, the second silicon-based material includes a massive morphology.

[0026] When the second silicon-based material has a massive morphology, while the battery has excellent performance, the manufacturing cost of the electrode sheet can be reduced.

[0027] In any embodiment, the Dv50 of the second silicon-based material is 5 μm - 6 μm, and can be optionally 5.2 μm - 5.6 μm.

[0028] When the Dv50 of the second silicon-based material is within the above range, it is beneficial to improve the transport performance of active ions and electrons, so that the fast charging performance of the battery is improved.

[0029] In any embodiment, the mass percentage of silicon element in the second silicon-based material relative to the total mass of the second silicon-based material is 45% - 65%, and can be optionally 47% - 55%.

[0030] When the mass percentage of silicon element in the second silicon-based material is within the above range, it is beneficial to improve the capacity of the battery.

[0031] In any embodiment, the specific surface area of the second silicon-based material is greater than or equal to 0.8 m 2 / g, and can be optionally 1.1 m 2 / g - 3.2 m 2 / g.

[0032] When the specific surface area of the second silicon-based material is within the above range, the interaction between the binder and the silicon-based material can be enhanced, thereby reducing the swelling of the electrode sheet.

[0033] In any embodiment, the second silicon-based material includes silicon grains, and the grain size of the silicon grains is less than or equal to 5 nm, and can be optionally 2 nm - 3 nm.

[0034] When the size of the silicon grains is within the above range, it can avoid excessive local silicon element enrichment caused by too large grain size, so as to prevent the situation of large swelling during lithium intercalation, which deteriorates the storage performance and cycle stability of the battery. By using the first silicon-based material and the second silicon-based material in combination, the deterioration of battery performance caused by crystallization due to easy silicon enrichment on the surface of the second silicon-based material with a smaller particle size can be alleviated.

[0035] In any embodiment, a coin cell is used to perform a constant current charge-discharge test on the second silicon-based material, and a differential capacity curve in the lithium extraction stage is plotted to reflect the relationship between dQ / dV and voltage V. It is specified that the maximum value of the differential value dQ / dV between 0.27 V and 0.34 V is denoted as VA, and the maximum value of the differential value dQ / dV between 0.43 V and 0.55 V is denoted as VB, where 0.8 ≤ VA / VB ≤ 1.3. Optionally, 0.8 ≤ VA / VB ≤ 1.0.

[0036] The surface of the silicon-based material with a smaller particle size is prone to silicon enrichment and crystallization, resulting in a high voltage plateau. By using the first silicon-based material and the second silicon-based material in combination, the deterioration of the material structure stability caused by the high voltage plateau generated by the second silicon-based material can be alleviated, and the storage performance and cycle stability of the battery can be improved.

[0037] In any embodiment, the first region further includes a first carbon material, and the Dv50 of the first carbon material is 14 μm - 19 μm.

[0038] In any embodiment, the second region further includes a second carbon material, and the first carbon material and / or the second carbon material includes at least one of artificial graphite, natural graphite, soft carbon, and hard carbon.

[0039] In any embodiment, the first carbon material includes artificial graphite.

[0040] Compared with natural graphite, artificial graphite can improve the compaction density of the electrode sheet, and has excellent cycle stability and storage performance, thereby reducing the expansion of the electrode sheet and improving the cycle stability and storage performance of the battery.

[0041] In any embodiment, the mass ratio of the first silicon-based material in the negative electrode film layer of the first region is less than the mass ratio of the second silicon-based material in the negative electrode film layer of the second region.

[0042] The low proportion of the first silicon-based material in the first region in direct contact with the cold pressing roller and the electrolyte can further reduce the content of silicon in contact with the electrolyte when the silicon-based material cracks, thereby slowing down the expansion of the electrode sheet and improving the cycle stability and storage performance of the battery.

[0043] The second aspect of the present application further provides a secondary battery, including the negative electrode sheet of the first aspect.

[0044] The third aspect of the present application further provides an electrical device, including the secondary battery of the second aspect. Description of the Drawings

[0045] Figure 1 is a schematic diagram of an embodiment of the negative electrode sheet of the present application;

[0046] Figure 2SEM image of the first silicon-based material according to an embodiment of the present application;

[0047] Figure 3 SEM cross-sectional image of the first region of the negative electrode film layer according to an embodiment of the present application;

[0048] Figure 4 SEM cross-sectional image of the second region of the negative electrode film layer according to an embodiment of the present application;

[0049] Figure 5 X-ray diffraction pattern of the first silicon-based material according to an embodiment of the present application;

[0050] Figure 6 X-ray diffraction pattern of the second silicon-based material according to an embodiment of the present application;

[0051] Figure 7 dQ / dV-V curve of the first silicon-based material according to an embodiment of the present application;

[0052] Figure 8 dQ / dV-V curve of the second silicon-based material according to an embodiment of the present application;

[0053] Figure 9 Schematic diagram of a secondary battery according to an embodiment of the present application;

[0054] Figure 10 is Figure 9 Exploded view of the secondary battery according to an embodiment of the present application shown;

[0055] Figure 11 Schematic diagram of a battery module according to an embodiment of the present application;

[0056] Figure 12 Schematic diagram of a battery pack according to an embodiment of the present application;

[0057] Figure 13 is Figure 12 Exploded view of the battery pack according to an embodiment of the present application shown;

[0058] Figure 14 Schematic diagram of an electrical device using the secondary battery according to an embodiment of the present application as a power source.

[0059] Explanation of reference numerals:

[0060] 1 Battery pack; 2 Upper box body; 3 Lower box body; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Cover plate; 10 Negative electrode tab, 101 Negative current collector, 102 Negative electrode film layer, 102a First surface, 102b Second surface, 1021 Second region, 1022 First region, 1023 Intermediate region. Detailed implementation manners

[0061] Hereinafter, embodiments of the negative electrode sheet, secondary battery, and electrical device of the present application will be specifically described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary details are omitted. For example, there are cases where details of well-known matters are omitted and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0062] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a specific range. The range defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In the present application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" represents that all real numbers between "0 - 5" have been fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when it is stated that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0063] If there is no special instruction, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0064] If there is no special instruction, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0065] Unless otherwise specified, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) carried out sequentially, or may also include steps (b) and (a) carried out sequentially. For example, when it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or may also include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0066] Unless otherwise specified, the terms "comprising" and "including" mentioned in this application are open-ended and can also be closed-ended. For example, the terms "comprising" and "including" may mean that other components not listed may also be included or comprised, or may only include or comprise the listed components.

[0067] Unless otherwise specified, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) while B is true (or exists); or both A and B are true (or exist).

[0068] Improving the energy density of batteries is a research hotspot in the field of lithium-ion batteries. Silicon has a theoretical specific capacity of up to 4200 mAh / g, making it the anode material of lithium-ion batteries with the highest specific capacity known so far. Moreover, it is rich in reserves and inexpensive. In recent years, extensive research has been conducted on using it to improve the energy density of batteries. The lithium storage mechanism of silicon anode materials is mainly through the formation of alloy phases with lithium ions. In practical applications, it has been found that the volume of the silicon anode material expands significantly after lithiation, resulting in high stress inside the battery, continuously squeezing the silicon anode material and causing cracking. Also, during the compaction process of the electrode sheet, cracking of some silicon anode materials will also occur. The silicon exposed to the electrolyte will continuously consume lithium ions in the electrolyte, leading to the deterioration of the battery's storage performance and cycle stability.

[0069] [Negative electrode sheet]

[0070] Based on this, this application provides a negative electrode sheet, such as Figure 1As shown, the negative electrode plate 10 includes a negative electrode current collector 101 and a negative electrode film layer 102 formed on at least one surface of the negative electrode current collector 101. The negative electrode film layer 102 has a first surface 102a far from the negative electrode current collector 101 and a second surface 102b oppositely arranged with respect to the first surface 102a. The thickness of the negative electrode film layer 102 is denoted as H, and the region within the thickness range from the first surface 102a of the negative electrode film layer 102 to 0.3H is denoted as the first region 1022 of the negative electrode film layer. The region within the thickness range from the second surface 102b of the negative electrode film layer 102 to 0.3H is denoted as the second region 1021 of the negative electrode film layer. The first region 1022 includes spherical or / and quasi-spherical first silicon-based materials.

[0071] In this application, the judgment method for spherical or quasi-spherical shapes can be tested by methods known in the art. As an example, a scanning electron microscope can be used to photograph and observe the silicon-based materials. Figure 2 is a scanning electron microscope image of a spherical silicon-based material sample, as Figure 2 shown, it can be clearly seen that the silicon-based material is spherical. Or use an argon ion beam to cut the electrode plate perpendicular to the large surface of the electrode plate to expose the cross-section, and photograph and observe the cross-section with a scanning electron microscope. The scanning electron microscope photograph of the first region of the negative electrode film layer is as Figure 3 shown, and spherical or quasi-spherical silicon-based materials can be observed in the first region of the negative electrode film layer.

[0072] In this article, "silicon-based materials" refers to at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

[0073] Currently, the mainstream negative electrode active materials for lithium-ion batteries are mainly artificial graphite and natural graphite. The theoretical specific capacity of silicon materials is much higher than that of graphite. Using silicon-based materials as negative electrode active materials can improve the energy density of secondary batteries. The first region in direct contact with the cold pressing roller and the electrolyte includes spherical or quasi-spherical silicon-based materials, which can broaden the compaction density window of the electrode plate, require less cold pressing pressure under the same compaction density, reduce the probability of cracking of the silicon-based materials during cold pressing, facilitate maintaining the integrity of the silicon-based material particles, reduce the generation of new interfaces, and avoid irreversible consumption of active ions caused by the contact between the active silicon exposed by the silicon-based materials and the electrolyte during the cycling process; moreover, the silicon-based materials are spherical or quasi-spherical, which can reduce the stress concentration of the silicon-based materials during rolling and expansion, further slow down the cracking phenomenon of the silicon-based materials, thereby comprehensively reducing the expansion rate of the electrode plate and improving the storage performance and cycling stability of the battery.

[0074] In some embodiments, the second region includes a second silicon-based material, and the average particle size of the second silicon-based material is smaller than the average particle size of the first silicon-based material.

[0075] In this application, the average particle size can be measured by methods known in the art. As an example, the electrode sheet is cut by an argon ion beam perpendicular to the large surface of the electrode sheet to expose the cross-section. The cross-section is photographed by a scanning electron microscope, and the particle sizes of the silicon-based materials in the first region and the second region are statistically analyzed using the major axis statistical method. Among them, the average particle size is the total particle size value divided by the total number of particles.

[0076] In the first region where the negative electrode sheet is in direct contact with the electrolyte, the first silicon-based material with a large average particle size is used, which can reduce the specific surface area of the first silicon-based material, thereby reducing the loss of active ions caused by the direct contact and reaction between the silicon-based material and the electrolyte, reducing the swelling rate of the electrode sheet, and improving the storage performance and cycle stability of the battery. In the second region of the negative electrode sheet close to the current collector, the second silicon-based material with a small average particle size is used, which has a short solid-phase ion transport distance, is beneficial to improving the transport performance of active ions and electrons, and improves the fast charging performance of the battery. Moreover, the second silicon-based material with a small average particle size has a larger specific surface area, enhancing the interaction between the binder and the silicon-based material, thereby further reducing the swelling of the electrode sheet and improving the storage performance and cycle stability of the battery.

[0077] In some embodiments, the percentage of the mass of silicon element in the first silicon-based material relative to the total mass of the first silicon-based material is less than the percentage of the mass of silicon element in the second silicon-based material relative to the total mass of the second silicon-based material.

[0078] In this application, the mass percentage of silicon element can be measured by methods known in the art. As an example, the silicon element content is determined by emission spectrum test (Inductively coupled plasma, ICP) as follows: taking the silicon-based material as a sample, digesting the sample with aqua regia and hydrofluoric acid HF, and taking the completely digested (digested for 0.5 h) solution for ICP test to obtain the mass percentage of silicon element of the silicon-based material.

[0079] The low silicon element content in the first silicon-based material in the first region in direct contact with the cold pressing roller and the electrolyte can reduce the content of silicon in contact with the electrolyte when the silicon-based material cracks, thereby slowing down the swelling of the electrode sheet and improving the cycle stability and storage performance of the battery. By combining the second silicon-based material with a high silicon content and the first silicon-based material with a low silicon content, it is beneficial for the battery to balance low swelling, good cycle stability and high energy density.

[0080] In some embodiments, the specific surface area of the first silicon-based material is less than the specific surface area of the second silicon-based material.

[0081] In this application, the specific surface area can be measured by methods known in the art. As an example, the gas adsorption method is used to measure the specific surface area, which is measured according to the test standard of GB / T 19587-2017. Specifically, the silicon-based material is taken as a sample, and the sample tube is immersed in liquid nitrogen at -196°C. The adsorption amount of nitrogen on the solid surface at different pressures is measured under a relative pressure of 0.05-0.30. Based on the BET multi-layer adsorption theory and its formula, the monolayer adsorption amount of the sample is obtained, and thus the specific surface area of the solid is calculated.

[0082]

[0083] Where n a is the amount of adsorbed gas, in mol / g; p / p 0 is the relative pressure; n m is the monolayer adsorption amount.

[0084] The first silicon-based material has a small specific surface area, which can reduce the loss of active ions caused by the reaction between the silicon-based material and the electrolyte, thereby slowing down the swelling of the electrode sheet and improving the cycle stability and storage performance of the battery. The second silicon-based material has a large specific surface area, which can enhance the interaction between the binder and the silicon-based material, thereby reducing the swelling of the electrode sheet. By using the first silicon-based material and the second silicon-based material in combination, the battery can achieve both low swelling and excellent cycle stability and storage performance.

[0085] In some embodiments, the crystallinity of the first silicon-based material is less than that of the second silicon-based material.

[0086] In this application, the crystallinity can be measured by methods known in the art. As an example, an X-ray diffractometer (D8 DISCOVER from Bruker) is used to measure the crystallinity of the silicon-based material. If no crystalline diffraction peak appears in the X-ray diffraction pattern, the material is determined to be an amorphous structure; if a sharp diffraction peak appears in the X-ray diffraction pattern, the material is determined to be a crystalline structure, and the crystallinity of the material is determined based on the intensity of the diffraction peak at the corresponding angle and the full width at half maximum of the diffraction peak. The stronger the diffraction peak and the smaller the full width at half maximum indicate the greater the crystallinity.

[0087] Amorphous silicon-based materials have better cycle stability than crystalline silicon-based materials. The low crystallinity of the first silicon-based material is beneficial to improving the cycle stability of the battery.

[0088] In some embodiments, a button cell is used to perform a constant current charge and discharge test on the first silicon-based material, and a differential capacity curve of the delithiation stage is drawn to reflect the relationship between dQ / dV and the voltage V. It is stipulated that the maximum value of the differential value dQ / dV between 0.27V-0.34V is recorded as V1, and the maximum value of the differential value dQ / dV between 0.43V-0.55V is recorded as V2, 1.55≤V1 / V2≤1.75, optionally, 1.60≤V1 / V2≤1.72.

[0089] In this article, the term "differential capacity curve" refers to the dQ / dV curve, which is an effective tool for analyzing the internal battery status of a battery. It is a method for obtaining the internal parameters and status of a battery without disassembling the battery. The dQ / dV curve is obtained by calculating the change in battery capacity within a constant voltage interval to obtain a dQ / dV-V curve.

[0090] In the present application, the dQ / dV curve can be tested by methods known in the art. As an example, the negative electrode material is mixed in a ratio of 8:1:1 among the active substance, the binder and the conductive carbon, and the slurry is coated on a copper foil to prepare a test electrode. Lithium metal is used for the electrode, and the constant current discharge is 0.05C to 5mV, the constant voltage discharge is 5mV to a current less than 50μm, and the constant current charge is 0.1C to 1.5V to obtain the constant current charging curve of the button battery. The constant current charging curve of 0.1C is subjected to differential capacity processing, and the capacity change within the constant voltage interval is calculated to obtain the dQ / dV-V curve.

[0091] In some embodiments, the value of V1 / V2 is 1.55, 1.60, 1.65, 1.7, 1.72, 1.75, or any value therebetween.

[0092] When V1 / V2 of the first silicon-based material is within the above range, a high voltage platform is not likely to appear, which is beneficial for the silicon-based material to maintain structural stability and improve the cycle stability of the battery.

[0093] In some embodiments, the first silicon-based material and / or the second silicon-based material comprises a silicon-carbon material, wherein the silicon-carbon material comprises carbon matrix particles having a pore structure, and nano-silicon-based materials disposed in the pore structure.

[0094] As used herein, the term "silicon-carbon material" refers to a material composed of two elements, silicon and carbon.

[0095] When the silicon-carbon material is a carbon matrix particle with a pore structure and a nano-silicon-based material is arranged in the pore structure, the carbon matrix particle with a pore structure has a certain inhibitory effect on the expansion of the nano-silicon-based material during the cycle process, thereby improving the structural stability of the silicon-carbon material, improving the battery capacity while taking into account excellent storage performance and cycle stability.

[0096] In some embodiments, the average pore diameter of the pore structure of the carbon matrix particles is 1.3 nm to 3.2 nm. Optionally, the average pore diameter of the pore structure of the carbon matrix particles is 1.6 nm to 2.4 nm.

[0097] In some embodiments, the average pore diameter of the pore structure of the carbon matrix particles is 1.3 nm, 1.5 nm, 1.7 nm, 1.9 nm, 2.1 nm, 2.3 nm, 2.5 nm, 2.7 nm, 2.9 nm, 3.2 nm, or any value therebetween.

[0098] The pores within this pore diameter range contribute to the adhesion of the nano-silicon-based material, and can effectively limit the expansion of the nano-silicon-based material within the pores. Moreover, the expanded silicon nanoparticles basically do not cause damage to the structure of the porous carbon matrix particles, thereby ensuring the structural stability of the silicon-carbon material. While reducing the expansion of the electrode sheet, the battery has excellent storage performance and cycle stability.

[0099] In some embodiments, the porosity of the carbon matrix particles is 70% to 89%, and may be optionally 78% to 84%.

[0100] In some embodiments, the porosity of the carbon matrix particles is 70%, 73%, 76%, 79%, 82%, 85%, 89%, or any value therebetween.

[0101] When the porosity of the carbon matrix particles meets the above range, the volume occupied by the pores in the carbon matrix particles is relatively high. The carbon matrix particles can cooperate with the nano-silicon-based material to improve the battery capacity. At the same time, the electrode sheet has low expansion, and the battery has excellent storage performance and cycle stability.

[0102] In some embodiments, the carbon matrix particles include hard carbon.

[0103] In some embodiments, the preparation method of the silicon-carbon material includes: providing a gas containing a silicon precursor to carbon matrix particles having a pore structure; generating a nano-silicon-based material disposed in the pore structure from the silicon precursor through chemical vapor deposition to obtain a carbon-silicon material.

[0104] In some embodiments, the silicon precursor is silane.

[0105] In some embodiments, the preparation method of the first silicon-based material includes: providing a gas containing a silicon precursor to spherical and / or quasi-spherical carbon matrix particles having a pore structure; generating a nano-silicon-based material disposed in the pore structure from the silicon precursor through chemical vapor deposition to obtain spherical and / or quasi-spherical carbon-silicon material.

[0106] In some embodiments, the Dv50 of the first silicon-based material is 9 μm - 11 μm, and can be optionally 9.5 μm - 10 μm.

[0107] In this document, the term "Dv50" refers to the particle size corresponding to when the volume distribution percentage reaches 50%.

[0108] In this application, Dv50 can be tested by methods known in the art. As an example, referring to GB / T19077-2016 Laser diffraction method for particle size distribution, it can be conveniently measured using a laser particle size analyzer, such as the Mastersizer 2000E type laser particle size analyzer of Malvern Instruments Limited, UK.

[0109] In some embodiments, the Dv50 of the first silicon-based material is 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm or any value therebetween.

[0110] When the Dv50 of the first silicon-based material meets the above range, it can reduce the loss of active ions caused by the direct contact and reaction between the silicon-based material and the electrolyte, reduce the swelling of the electrode sheet, and improve the storage performance and cycle stability of the battery.

[0111] In some embodiments, the mass percentage of silicon element in the first silicon-based material relative to the total mass of the first silicon-based material is 40% - 60%, and can be optionally 45% - 50%.

[0112] In some embodiments, the mass percentage of silicon element in the first silicon-based material relative to the total mass of the first silicon-based material is 40%, 45%, 50%, 55%, 60% or any value therebetween.

[0113] When the mass percentage of silicon element in the first silicon-based material is within the above range, it can reduce the content of silicon in contact with the electrolyte when the silicon-based material cracks, slow down the swelling of the electrode sheet, help maintain the integrity of the silicon-based material particles, and ensure that the battery has excellent capacity while improving the cycle stability of the battery.

[0114] In some embodiments, the specific surface area of the first silicon-based material is 0.8 m 2 / g - 5 m 2 / g, and can be optionally 1.1 m 2 / g - 3.2 m 2 / g.

[0115] In some embodiments, the specific surface area of the first silicon-based material is 0.8 m 2 / g, 1.4 m 2 / g, 1.8 m 2 / g, 2.2 m 2 / g, 2.6 m 2 / g, 3m 2 / g, 3.4m 2 / g, 3.8m 2 / g, 4.2m 2 / g, 4.6m 2 / g, 5m 2 / g or any value therebetween.

[0116] When the specific surface area of the first silicon-based material is within the above range, the loss of active ions caused by the reaction between the silicon-based material and the electrolyte can be reduced, the swelling of the electrode sheet can be reduced, and the cycle stability and storage performance of the battery can be improved.

[0117] In some embodiments, the second silicon-based material includes a massive morphology.

[0118] As used herein, the term "massive morphology" refers to a shape that is different from spherical or quasi-spherical shapes.

[0119] The electrode sheet is cut perpendicularly to the large surface of the electrode sheet by an argon ion beam to expose the cross-section, and the cross-section is photographed and observed by a scanning electron microscope. The scanning electron microscope photograph of the second region of the negative electrode film layer is as Figure 4 shown, and massive silicon-based materials can be observed in the second region of the negative electrode film layer.

[0120] When the second silicon-based material has a massive morphology, while the battery has excellent performance, the manufacturing cost of the electrode sheet can be reduced.

[0121] In some embodiments, the preparation method of the second silicon-based material includes: providing a gas containing a silicon precursor to massive carbon matrix particles having a carbon skeleton; generating nano-silicon-based materials attached to the carbon skeleton from the silicon precursor by chemical vapor deposition to obtain massive carbon-silicon materials.

[0122] In some embodiments, the Dv50 of the second silicon-based material is 5 μm - 6 μm, and may be optionally 5.2 μm - 5.6 μm.

[0123] In some embodiments, the Dv50 of the second silicon-based material is 5 μm, 5.1 μm, 5.2 μm, 5.3 μm, 5.4 μm, 5.5 μm, 5.6 μm, 5.7 μm, 5.8 μm, 5.9 μm, 6 μm or any value therebetween.

[0124] When the Dv50 of the second silicon-based material is within the above range, it is beneficial to improve the transport performance of active ions and electrons, and the fast charging performance of the battery is improved.

[0125] In some embodiments, the mass percentage of silicon element in the second silicon-based material relative to the total mass of the second silicon-based material is 45% - 65%, and may be optionally 47% - 55%.

[0126] In some embodiments, the mass percentage of silicon element in the second silicon-based material relative to the total mass of the second silicon-based material is 45%, 47%, 49%, 51%, 53%, 55%, 57%, 59%, 61%, 63%, 65% or any value therebetween.

[0127] When the mass percentage of silicon element in the second silicon-based material is within the above range, it is beneficial to improve the capacity of the battery.

[0128] In some embodiments, the specific surface area of the second silicon-based material is greater than or equal to 0.8 m 2 / g, and can be optionally 1.1 m 2 / g - 3.2 m 2 / g.

[0129] In some embodiments, the specific surface area of the second silicon-based material is 0.8 m 2 / g, 1.1 m 2 / g, 1.4 m 2 / g, 1.7 m 2 / g, 2 m 2 / g, 2.3 m 2 / g, 2.6 m 2 / g, 2.9 m 2 / g, 3.2 m 2 / g or any value therebetween.

[0130] When the specific surface area of the second silicon-based material is within the above range, the interaction between the binder and the silicon-based material can be enhanced, thereby reducing the swelling of the electrode sheet.

[0131] In some embodiments, the second silicon-based material includes silicon grains, and the grain size of the silicon grains is less than or equal to 5 nm, and can be optionally 2 nm - 3 nm.

[0132] In some embodiments, the grain size of the silicon grains is 1 nm, 2 nm, 3 nm, 4 nm, 5 nm or any value therebetween.

[0133] When the size of the silicon grains is within the above range, it can avoid excessive local silicon element enrichment caused by too large grain size, thereby preventing a large swelling during lithium intercalation and deteriorating the storage performance and cycle stability of the battery. By using the first silicon-based material and the second silicon-based material in combination, the deterioration of battery performance caused by crystallization due to easy silicon enrichment on the surface of the second silicon-based material with a smaller particle size can be alleviated.

[0134] In some embodiments, a coin cell is used to perform a constant current charge-discharge test on the second silicon-based material, and a differential capacity curve in the lithium deintercalation stage is plotted to reflect the relationship between dQ / dV and voltage V. It is specified that the maximum value of the differential value dQ / dV between 0.27 V and 0.34 V is denoted as VA, and the maximum value of the differential value dQ / dV between 0.43 V and 0.55 V is denoted as VB, where 0.8 ≤ VA / VB ≤ 1.3. Optionally, 0.8 ≤ VA / VB ≤ 1.0.

[0135] In some embodiments, the value of VA / VB is 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, or any value therebetween.

[0136] The surface of the silicon-based material with a smaller particle size is prone to silicon enrichment and crystallization, resulting in a high voltage plateau. By using the first silicon-based material and the second silicon-based material in combination, the deterioration of the material structure stability caused by the high voltage plateau generated by the second silicon-based material can be mitigated, and the storage performance and cycle stability of the battery can be improved.

[0137] In some embodiments, the first region further includes a first carbon material, and the Dv50 of the first carbon material is 14 μm - 19 μm.

[0138] In some embodiments, the Dv50 of the first carbon material is 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or any value therebetween.

[0139] In some embodiments, the second region further includes a second carbon material, and the first carbon material and / or the second carbon material includes at least one of artificial graphite, natural graphite, soft carbon, and hard carbon.

[0140] In some embodiments, the first carbon material includes artificial graphite.

[0141] Compared with natural graphite, artificial graphite can improve the compaction density of the electrode sheet and has excellent cycle stability and storage performance, thereby reducing the expansion of the electrode sheet and improving the cycle stability and storage performance of the battery.

[0142] In some embodiments, the mass ratio of the first silicon-based material in the negative electrode film layer of the first region is less than the mass ratio of the second silicon-based material in the negative electrode film layer of the second region.

[0143] The low proportion of the first silicon-based material in the first region that is in direct contact with the cold pressing roller and the electrolyte can further reduce the content of silicon in contact with the electrolyte when the silicon-based material cracks, thereby slowing down the expansion of the electrode sheet and improving the cycle stability and storage performance of the battery.

[0144] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector can include a polymer material substrate layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0145] In some embodiments, the negative electrode film layer may optionally further include a binder. The binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0146] In some embodiments, the negative electrode film layer may optionally further include a conductive agent. The conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0147] In some embodiments, the negative electrode film layer may optionally further include other additives, such as a thickening agent (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0148] In some embodiments, the negative electrode plate can be prepared in the following manner: dispersing the components for preparing the negative electrode plate described above, such as the first silicon-based material, the first carbon material, the conductive agent, the binder, and any other components, in a solvent (such as deionized water) to form a first negative electrode slurry; dispersing the second silicon-based material, the second carbon material, the conductive agent, the binder, and any other components in a solvent (such as deionized water) to form a second negative electrode slurry; extruding the first slurry and the second slurry simultaneously through a dual-chamber coating device. The second slurry is coated on the negative electrode current collector copper foil, and the first slurry is coated on the second slurry; after drying, cold pressing, and slitting, the negative electrode plate is obtained.

[0149] [Positive Electrode Plate]

[0150] The positive electrode plate generally includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0151] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on either or both of the two opposite surfaces of the positive electrode current collector.

[0152] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0153] In some embodiments, the positive electrode active material can be a positive electrode active material for batteries well-known in the art. As an example, the positive electrode active material can include at least one of the following materials: lithium phosphate with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials can also be used. These positive electrode active materials can be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides can include, but are not limited to, lithium cobalt oxide (such as LiCoO 2 ), lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 , LiMn 2 O 4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (which can also be abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (which can also be abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (which can also be abbreviated as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (which can also be abbreviated as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (which can also be abbreviated as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi0.85 Co 0.15 Al 0.05 O 2 ) and at least one of its modified compounds, etc. Examples of the lithium-containing phosphate with olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO 4 (which may also be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and at least one of a composite material of lithium manganese iron phosphate and carbon.

[0154] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0155] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0156] In some embodiments, the positive electrode plate can be prepared by the following method: dispersing the above components for preparing the positive electrode plate, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0157] [Electrolyte]

[0158] The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The present application does not specifically limit the type of the electrolyte, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid.

[0159] In some embodiments, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0160] In some embodiments, the electrolytic solution includes an ester solvent.

[0161] In some embodiments, the ester solvent may be selected from one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, and 1,4-butyrolactone.

[0162] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluoro bis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

[0163] In some embodiments, the electrolyte may optionally further include additives. For example, the additives may include anode film-forming additives, cathode film-forming additives, and may also include additives that can improve certain battery performance, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, and the like.

[0164] [Separator film]

[0165] In some embodiments, the secondary battery further includes a separator film. The present application does not particularly limit the type of the separator film, and any well-known porous structure separator film with good chemical stability and mechanical stability can be selected.

[0166] In some embodiments, the material of the separator film may be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator film is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0167] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator film may be made into an electrode assembly by a winding process or a stacking process.

[0168] In some embodiments, the secondary battery may include an outer package. The outer package can be used to encapsulate the above electrode assembly and electrolyte.

[0169] In some embodiments, the outer package of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery may also be a soft package, such as a pouch-type soft package. The material of the soft package may be plastic, and examples of the plastic may include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0170] In the present application, the shape of the secondary battery includes but is not limited to cylindrical, square, or any other arbitrary shape. For example,Figure 9 The secondary battery 5 is a square structure as an example.

[0171] In some embodiments, referring to Figure 10 , the outer package may include a housing 51 and a cover plate 53. Among them, the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode plate, the negative electrode plate and the separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and those skilled in the art can select according to specific actual needs.

[0172] In some embodiments, the secondary batteries can be assembled into a battery module. The number of secondary batteries included in the battery module may be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0173] Figure 11 The battery module 4 is an example. Referring to Figure 11 , in the battery module 4, a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other way. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

[0174] Optionally, the battery module 4 may further include a housing having a receiving space, and a plurality of secondary batteries 5 are received in the receiving space.

[0175] In some embodiments, the above battery module can be further assembled into a battery pack. The number of battery modules included in the battery pack may be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0176] Figure 12 and Figure 13 The battery pack 1 is an example. Referring to Figure 12 and Figure 13 , the battery pack 1 may include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can be covered on the lower box body 3 to form a closed space for receiving the battery module 4. The plurality of battery modules 4 can be arranged in the battery box in any way.

[0177] In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided by the present application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto.

[0178] As the electrical device, the secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0179] Figure 14 Take an electrical device as an example. The electrical device is a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the electrical device for the secondary battery, a battery pack or battery module can be used.

[0180] Another example of the device can be a mobile phone, tablet computer, laptop, etc. This device usually requires being thin and light, and a secondary battery can be used as the power source.

[0181] Embodiment

[0182] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application and should not be construed as a limitation to the present application. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the field or according to the product specifications. For the reagents or instruments not specified regarding the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0183] I. Preparation method

[0184] Preparation Example 1: Spherical silicon-carbon material A

[0185] A gas containing silane SiH 4 is introduced into spherical hard carbon particles with a pore structure. Through chemical vapor deposition, silicon is deposited in the pore structure of the hard carbon particles. Among them, the mass ratio of silicon in the silane to the hard carbon particles is 46:54. The Dv50 of the hard carbon particles is 8.8 μm, the porosity is 78.9%, and the average pore diameter is 2 nm. Then, a carbon layer accounting for 1% of the mass of the hard carbon particles after silicon deposition is coated on the outer surface of the hard carbon particles by chemical vapor deposition, and the gas source is acetylene gas, obtaining spherical silicon-carbon material A. The average particle size of spherical silicon-carbon material A is 9.5 μm, the silicon mass percentage content is 45.8%, and the specific surface area is 1.56 m 2 / g, the value of V1 / V2 in the differential capacity curve is 1.68. The X-ray diffraction pattern of spherical silicon carbide material A is as follows Figure 5 shown, and the differential capacity curve is as follows Figure 7 shown.

[0186] Preparation Example 2: Spherical silicon carbide material B

[0187] A gas containing silane SiH 4 was introduced into spherical hard carbon particles with a pore structure. Through chemical vapor deposition, silicon was deposited in the pore structure of the hard carbon particles. Among them, the mass ratio of silicon in silane to the hard carbon particles was 47:53. The Dv50 of the hard carbon particles was 4.3 μm, the porosity was 80.1%, and the average pore diameter was 2 nm. Then, a carbon layer accounting for 1% of the mass of the hard carbon particles after silicon deposition was coated on the outer surface of the hard carbon particles by chemical vapor deposition. The gas source was acetylene gas, and spherical silicon carbide material B was obtained. The average particle size of spherical silicon carbide material B was 5.2 μm, the silicon mass percentage content was 46.3%, and the specific surface area was 2.31 m 2 / g.

[0188] Preparation Example 3: Block-shaped silicon carbide material A

[0189] A gas containing silane SiH 4 was introduced into block-shaped hard carbon particles with a pore structure. Through chemical vapor deposition, silicon was deposited in the pore structure of the hard carbon particles. Among them, the mass ratio of silicon in silane to the hard carbon particles was 48:52. The Dv50 of the hard carbon particles was 4.3 μm, the porosity was 83.2%, and the average pore diameter was 2 nm. Then, a carbon layer accounting for 1% of the mass of the hard carbon particles after silicon deposition was coated on the outer surface of the hard carbon particles by chemical vapor deposition. The gas source was acetylene gas, and block-shaped silicon carbide material A was obtained. The average particle size of block-shaped silicon carbide material A was 5.2 μm, the silicon mass percentage content was 48.3%, and the specific surface area was 2.67 m 2 / g, and the value of V1 / V2 in the differential capacity curve was 0.89. The X-ray diffraction pattern of block-shaped silicon carbide material A is as follows Figure 6 shown, and the differential capacity curve is as follows Figure 8 shown. Block-shaped silicon carbide material A contains silicon grains, and the particle size of the silicon grains is 2.2 nm.

[0190] Preparation Example 4: Block-shaped silicon carbide material B

[0191] A gas containing silane SiH 4The gas is passed to the bulk hard carbon particles with a pore structure, and silicon is deposited in the pore structure of the hard carbon particles by chemical vapor deposition. Among them, the mass ratio of silicon in silane to the hard carbon particles is 47:53, the Dv50 of the hard carbon particles is 8.8 μm, the porosity is 82.1%, and the average pore diameter is 2 nm. Then, a carbon layer with a mass ratio of 1% of the mass of the hard carbon particles after silicon deposition is coated on the outer surface of the hard carbon particles by chemical vapor deposition, and the gas source is acetylene gas to obtain the bulk silicon-carbon material B. The average particle size of the bulk silicon-carbon material B is 9.5 μm, the silicon mass percentage content is 47.2%, and the specific surface area is 1.68 m 2 / g.

[0192] Preparation Example 5: Bulk silicon-carbon material C

[0193] Pass the gas containing silane SiH 4 to the bulk hard carbon particles with a pore structure, and deposit silicon in the pore structure of the hard carbon particles by chemical vapor deposition. Among them, the mass ratio of silicon in silane to the hard carbon particles is 46:54, the Dv50 of the hard carbon particles is 8.8 μm, the porosity is 80.5%, and the average pore diameter is 2 nm. Then, a carbon layer with a mass ratio of 1% of the mass of the hard carbon particles after silicon deposition is coated on the outer surface of the hard carbon particles by chemical vapor deposition, and the gas source is acetylene gas to obtain the bulk silicon-carbon material C. The average particle size of the bulk silicon-carbon material C is 9.5 μm, the silicon mass percentage content is 46.1%, and the specific surface area is 1.63 m 2 / g.

[0194] Example 1:

[0195] 1) Preparation of the negative electrode sheet

[0196] The spherical silicon-carbon material A and artificial graphite (average particle size of 15.6 μm) are mixed at a ratio of 0.16:0.84 as the first negative electrode active material. The first negative electrode active material, the conductive agent carbon nanotubes, the thickening agent sodium carboxymethyl cellulose (CMC-Na), and the binder styrene-butadiene rubber (SBR) are mixed at a mass ratio of 96.7:0.5:1.0:1.8, and deionized water is added, and the mixture is stirred in a vacuum mixer until the system becomes homogeneous to obtain the first slurry;

[0197] The bulk silicon-carbon material A and natural graphite (average particle size of 18.6 μm) are mixed at a ratio of 0.2:0.8 as the second negative electrode active material. The second negative electrode active material, the conductive agent carbon nanotubes, the thickening agent sodium carboxymethyl cellulose (CMC-Na), and the binder styrene-butadiene rubber (SBR) are mixed at a mass ratio of 95.5:0.7:2.0:1.8, and ionic water is added, and the mixture is stirred in a vacuum mixer until the system becomes homogeneous to obtain the second slurry;

[0198] Through a dual-chamber coating device, the first slurry and the second slurry are extruded simultaneously. The second slurry is coated on the negative current collector copper foil, and the first slurry is coated on the second slurry; after drying, cold pressing, and slitting, a negative electrode sheet is obtained. The coating weights of the first slurry and the second slurry are 4.2 mg / cm 2 and 6.3 mg / cm 2 .

[0199] 2) Preparation of the positive electrode sheet

[0200] The positive electrode active material lithium iron phosphate, conductive carbon black, and binder polyvinylidene fluoride (PVDF) are fully stirred and mixed evenly in an N-methylpyrrolidone solvent system at a weight ratio of 96:2:2 to obtain a positive electrode slurry; the above positive electrode slurry is uniformly coated on a positive current collector aluminum foil with a thickness of 13 μm, and the coating speed is 30 m / min; the temperature of the coating oven is between 110°C and 130°C, and then through cold pressing and slitting, a positive electrode sheet is obtained.

[0201] 3) Preparation of the electrolyte

[0202] In an argon atmosphere glove box (H 2 O content < 0.1 ppm, O 2 content < 0.1 ppm), the lithium salt lithium hexafluorophosphate LiPF 6 is dissolved in a mixed system of organic solvents ethylene carbonate (EC) and diethyl carbonate (DEC) (EC:DEC volume ratio is 3:7), and stirred evenly to obtain an electrolyte with a lithium salt concentration of 1 mol / L.

[0203] 4) Separator

[0204] A 9-μm polyethylene (PE) film is used as the separator.

[0205] 5) Preparation of the battery

[0206] The positive electrode sheet, separator, and composite negative electrode sheet are stacked in sequence, so that the separator is in the middle of the positive and negative electrode sheets to isolate the positive and negative electrode sheets, wound to obtain a bare battery cell, the electrode tabs are welded, and the battery cell is placed in an aluminum shell, then the electrolyte is injected and sealed, and through processes such as standing, cold pressing, formation, shaping, and capacity testing, the lithium-ion secondary battery prepared in Example 1 is obtained.

[0207] The batteries of Examples 2-3 are prepared in a similar manner to the battery of Example 1, except that the mass ratio of the first silicon-based material to the negative electrode active material in the first region and the mass ratio of the second silicon-based material to the negative electrode active material in the second region are adjusted, and the specific parameters are shown in Table 1.

[0208] The battery of Example 4 was prepared in a similar manner to the battery of Example 1, except that the first carbon material was natural graphite with a particle size of 18.6 um, and the specific parameters are shown in Table 1.

[0209] The batteries of Examples 4-7 were prepared in a similar manner to the battery of Example 1, except that the types of spherical silicon-carbon materials in the first region and / or massive silicon-carbon materials in the second region were adjusted, and the specific parameters are shown in Table 1.

[0210] The preparation method of the battery of Comparative Example 1 was similar to that of Example 1, except that the first silicon-based material was massive silicon-carbon material C, and the specific parameters are shown in Table 1.

[0211] Table 1

[0212]

[0213]

[0214] II. Test Methods

[0215] 1. Charging Time Test

[0216] The electrode sheet can be prepared into a button cell or a small laminated cell. At 35 °C, the battery is first charged and discharged at a current of 1C (i.e., the current value that completely discharges the theoretical capacity within 1 h). Specifically, the battery is charged at a constant current of 1C rate until the charging cut-off voltage of 2V, then charged at a constant voltage until the current ≤ 0.05C, left standing for 5 min, and then discharged at a constant current of 0.33C rate until the discharge cut-off voltage of 5 mV. Record its actual capacity as C0. Then the battery is successively charged at constant currents of 2.8C0, 3C0, 3.2C0, 3.5C0, 3.8C0, 4.1C0, 4.4C0, 4.7C0, 5C0, 5.3C0, 5.6C0, 5.9C0 until the full battery charging cut-off voltage V1 or the 0V negative electrode cut-off potential (whichever comes first). After each charging is completed, it is discharged at 1C0 until the full battery discharge cut-off voltage V2. Record the negative electrode potentials corresponding to 10%, 20%, 30%, ……, 80% SOC (State of Charge) at different charging rates, plot the charging rate-negative electrode potential curve at different SOC states, and after linear fitting, obtain the charging rate corresponding to the negative electrode potential of 0V at different SOC states. This charging rate is the charging window at this SOC state, denoted as C10%SOC, C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, C80%SOC respectively. According to the formula:

[0217] (60 / C20%SOC + 60 / C30%SOC + 60 / C40%SOC + 60 / C50%SOC + 60 / C60%SOC + 60 / C70%SOC + 60 / C80%SOC) × 10%

[0218] Calculate the charging time T of the battery from 10% SOC to 80% SOC, with the unit of min. The shorter this time is, the better the fast charging performance of the battery is.

[0219] 2. Based on the full charge expansion test of the cold-pressed electrode

[0220] After cold-pressing the negative electrode, use a micrometer to measure the thickness of 5 - 8 points on the electrode, take the average value, and record it as A1. Charge the battery to 4.25V, then charge at a constant voltage until the current ≤ 0.05C. Disassemble the negative electrode from the charged battery cell, measure the thickness of 5 - 8 points on the disassembled electrode, and take the average value as A2. Then the full charge expansion rate of the electrode is (A2 - A1) / A1 * 100%

[0221] 3. Storage performance test

[0222] Prepare the electrode into a stacked battery cell. The battery discharges at a constant current of 0.33C to the cut-off voltage of 2.5V, stands for 30 min, then charges at a constant current of 0.33C to the charging cut-off voltage of 4.25V, and then charges at a constant voltage until the current ≤ 0.05C. Stand for 30 min, and record the initial capacity as C0. Put the battery into a constant temperature oven at 60℃ for 60 days. After 60 days, take out the battery and let it stand at room temperature for 60 min, and conduct the capacity test. The specific process is as follows: discharge at a constant current of 0.33C to the cut-off voltage of 2.5V, stand for 30 min, then charge at a constant current of 0.33C to the charging cut-off voltage of 4.25V, and then charge at a constant voltage until the current ≤ 0.05C. Record the capacity as C1, and the storage capacity retention rate after 60 days is C1 / C0 * 100%.

[0223] 4. Normal temperature cycle performance test:

[0224] Test process: At 25℃, let the battery stand for 30 minutes, then charge it at a rate of 0.5C to a voltage of 4.2V, further charge it at a constant voltage of 4.2V until the current is 0.05C, stand for 5 minutes, and then discharge it at a rate of 0.5C to a voltage of 2.8V. The obtained capacity is recorded as the initial capacity C0, and this is one charge-discharge cycle process. Repeat the above steps for the same battery. Each time during the cycle, record the discharge capacity Cn. Then the battery capacity retention rate Pn after each cycle is Pn = Cn / C0 * 100%. Stop the test until Pn ≤ 80%, and record the number of cycles at this time.

[0225] III. Analysis of test results of each example and comparative example

[0226] Prepare the batteries of each example and comparative example respectively according to the above method, and measure various performance parameters. The results are shown in the following table.

[0227] As can be seen from Table 2, the shape of the silicon-based material in the first region of the negative electrode film layer is spherical, which can reduce the expansion rate of the electrode sheet after cold pressing and improve the high-temperature storage performance and cycle stability of the battery.

[0228] Table 2

[0229]

[0230] As can be seen from the comparison between Example 1 and Example 4 in Table 3, compared with natural graphite, the first graphite being artificial graphite is beneficial to improving the high-temperature storage performance, kinetic performance and cycle stability of the battery.

[0231] As can be seen from the comparison between Example 1 and Examples 5-7 in Table 3, when the large-particle-size first silicon-based material is used in combination with the small-particle-size second silicon-based material, the electrode sheet has a low expansion rate, and the battery has good cycle stability, high-temperature storage performance and fast charging performance.

[0232] Table 3

[0233]

[0234] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments with the same composition and the same effect as the technical idea within the technical solution scope of this application are included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that can be thought of by those skilled in the art to the embodiments, and other ways constructed by combining some constituent elements in the embodiments are also included in the scope of this application.

Claims

1. A negative electrode plate, characterized in that, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer formed on at least one surface of the negative electrode current collector. The negative electrode film layer has a first surface away from the negative electrode current collector and a second surface oppositely arranged with respect to the first surface. The thickness of the negative electrode film layer is denoted as H. The region within the thickness range from the first surface of the negative electrode film layer to 0.3H is denoted as the first region of the negative electrode film layer, and the region within the thickness range from the second surface of the negative electrode film layer to 0.3H is denoted as the second region of the negative electrode film layer. The first region includes spherical or / and spherical-like first silicon-based material.

2. The negative electrode plate according to claim 1, characterized in that, the second region includes a second silicon-based material, and the average particle size of the second silicon-based material is smaller than the average particle size of the first silicon-based material.

3. The negative electrode plate according to claim 2, characterized in that, the mass percentage of silicon element in the first silicon-based material relative to the total mass of the first silicon-based material is less than the mass percentage of silicon element in the second silicon-based material relative to the total mass of the second silicon-based material.

4. The negative electrode plate according to claim 2 or 3, characterized in that, the specific surface area of the first silicon-based material is smaller than the specific surface area of the second silicon-based material.

5. The negative electrode plate according to any one of claims 2 to 4, characterized in that, the crystallinity of the first silicon-based material is less than the crystallinity of the second silicon-based material.

6. The negative electrode plate according to any one of claims 1 to 5, characterized in that, a coin cell is used to perform a constant current charge-discharge test on the first silicon-based material, and a differential capacity curve in the lithium deintercalation stage is plotted to reflect the relationship between dQ / dV and voltage V. It is specified that the maximum value of the differential value dQ / dV between 0.27V - 0.34V is denoted as V1, and the maximum value of the differential value dQ / dV between 0.43V - 0.55V is denoted as V2, and 1.55 ≤ V1 / V2 ≤ 1.

75. Optionally, 1.60 ≤ V1 / V2 ≤ 1.

72.

7. The negative electrode plate according to any one of claims 2 to 6, characterized in that, the first silicon-based material and / or the second silicon-based material includes a silicon-carbon material, wherein the silicon-carbon material includes carbon matrix particles having a pore structure and nano-silicon-based materials disposed in the pore structure.

8. The negative electrode plate according to any one of claims 1 to 7, characterized in that, the first silicon-based material satisfies at least one of the following: (1) The Dv50 of the first silicon-based material is 9μm - 11μm, optionally 9.5μm - 10μm; (2) The mass percentage of silicon element in the first silicon-based material relative to the total mass of the first silicon-based material is 40% - 60%, optionally 45% - 50%; (3) The specific surface area of the first silicon-based material is 0.8 m 2 / g - 5 m 2 / g, and it can be optionally 1.1 m 2 / g - 3.2 m 2 / g.

9. The negative electrode plate according to any one of claims 2 to 8, characterized in that, the second silicon-based material satisfies at least one of the following: (1) The second silicon-based material includes a bulk morphology; (2) The Dv50 of the second silicon-based material is 5 μm - 6 μm, and can be optionally 5.2 μm - 5.6 μm; (3) The mass percentage of silicon element in the second silicon-based material relative to the total mass of the second silicon-based material is 45% - 65%, and can be optionally 47% - 55%; (4) The specific surface area of the second silicon-based material is greater than or equal to 0.8 m 2 / g, and can be optionally 1.1 m 2 / g - 3.2 m 2 / g; (5) The second silicon-based material includes silicon grains, and the grain size of the silicon grains is less than or equal to 5 nm, and can be optionally 2 nm - 3 nm; (6) A coin cell is used to perform a constant current charge-discharge test on the second silicon-based material, and a differential capacity curve in the lithium extraction stage is plotted to reflect the relationship between dQ / dV and voltage V. It is stipulated that the maximum value of the differential value dQ / dV between 0.27 V and 0.34 V is denoted as VA, and the maximum value of the differential value dQ / dV between 0.43 V and 0.55 V is denoted as VB, and 0.8 ≤ VA / VB ≤ 1.

3. Optionally, 0.8 ≤ VA / VB ≤ 1.

0.

10. The negative electrode sheet according to any one of claims 1 to 9, characterized in that, The first region further includes a first carbon material, and the Dv50 of the first carbon material is 14 μm - 19 μm.

11. The negative electrode sheet according to claim 10, characterized in that, The second region further includes a second carbon material, and the first carbon material and / or the second carbon material includes at least one of artificial graphite, natural graphite, soft carbon, and hard carbon.

12. The negative electrode sheet according to claim 10 or 11, characterized in that, The first carbon material includes artificial graphite.

13. The negative electrode sheet according to any one of claims 2 to 12, characterized in that, The mass ratio of the first silicon-based material in the negative electrode film layer of the first region is less than the mass ratio of the second silicon-based material in the negative electrode film layer of the second region.

14. A secondary battery, characterized in that, The secondary battery includes the negative electrode sheet according to any one of claims 1 to 13.

15. An electrical device, characterized in that, It includes the secondary battery according to claim 14.

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