Negative electrode sheet, secondary battery, and electric device

Abstract

A negative electrode sheet, a secondary battery, and an electric device. The negative electrode sheet 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 has a first surface away from the negative electrode current collector and a second surface 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 to 0.3 H of the negative electrode film layer is denoted as a first region of the negative electrode film layer; the region within the thickness range from the second surface to 0.3 H of the negative electrode film layer is denoted as a second region of the negative electrode film layer; the first region comprises a spherical or / and spheroid first silicon-based material. The negative electrode sheet can reduce its own expansion rate and improve the cycle stability and storage performance of the battery.

Description

Negative electrode sheet, secondary battery and electrical device

[0001] Cross-references

[0002] This application claims priority to Chinese Patent Application No. 202311640889.5, filed on November 30, 2023, entitled “Negative Electrode Sheet, Secondary Battery and Electrical Device,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The present application relates to the technical field of secondary batteries, and in particular to a negative electrode plate, a secondary battery, and an electrical device. Background Art

[0004] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0005] Silicon-based negative electrode active materials are an effective way to increase the capacity of secondary batteries. However, negative electrode plates containing silicon-based materials face the disadvantages of high plate expansion rate, poor battery cycle life, and poor high-temperature storage performance. Therefore, existing negative electrode plates containing silicon-based materials still need to be improved.

[0006] Summary of the Invention

[0007] The present application is made in view of the above-mentioned problems, and its purpose is to provide a negative electrode plate that can reduce its own expansion rate and improve the cycle stability and high-temperature storage performance of the battery.

[0008] A first aspect of the present application provides a negative electrode plate, which 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 having a first surface away from the negative electrode current collector and a second surface arranged opposite to the first surface, the thickness of the negative electrode film layer is recorded as H, the area within the thickness range from the first surface of the negative electrode film layer to 0.3H is recorded as the first area of ​​the negative electrode film layer, and the area within the thickness range from the second surface of the negative electrode film layer to 0.3H is recorded as the second area of ​​the negative electrode film layer, and the first area includes a spherical or / and quasi-spherical first silicon-based material.

[0009] Currently, the mainstream negative electrode active materials for lithium-ion batteries are mainly artificial graphite and natural graphite. However, 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 area in direct contact with the cold pressing roller and the electrolyte includes spherical or quasi-spherical silicon-based materials, which can widen the compaction density window of the electrode. The cold pressing pressure required at the same compaction density is smaller, reducing the probability of cracking of the silicon-based material during the cold pressing process. This is beneficial for maintaining the integrity of the silicon-based material particles, reducing the formation of new interfaces, and avoiding irreversible active ion consumption caused by contact between the exposed active silicon of the silicon-based material and the electrolyte during the cycle. The spherical or quasi-spherical shape of the silicon-based material can reduce stress concentration in the silicon-based material during rolling and expansion, further mitigating the cracking of the silicon-based material, thereby comprehensively reducing the expansion rate of the electrode and improving the storage performance and cycle stability of the battery.

[0010] 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.

[0011] The first area of ​​the negative electrode plate that is in direct contact with the electrolyte uses a first silicon-based material with a large average particle size. This can reduce the specific surface area of ​​the first silicon-based material, thereby reducing the loss of active ions caused by the reaction after direct contact between the silicon-based material and the electrolyte, reducing the expansion rate of the plate, and improving the storage performance and cycle stability of the battery. The second area of ​​the negative electrode plate close to the current collector uses a second silicon-based material with a small average particle size. The second silicon-based material has a shorter solid-phase ion transmission distance, which is beneficial to improving the transmission performance of active ions and electrons, thereby improving the fast charging performance of the battery. The second silicon-based material with a small average particle size has a larger specific surface area, which enhances the interaction between the binder and the silicon-based material, thereby further reducing the expansion of the plate and improving the storage performance and cycle stability of the battery.

[0012] In any embodiment, the mass percentage of silicon 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 in the second silicon-based material relative to the total mass of the second silicon-based material.

[0013] The low silicon content of the first silicon-based material in the first region, which directly contacts the cold press rollers and the electrolyte, reduces the amount of silicon exposed to the electrolyte when the silicon-based material cracks. This slows electrode expansion and improves the battery's cycling stability and storage performance. Combining a high-silicon-content second silicon-based material with a low-silicon-content first silicon-based material facilitates a battery with low expansion, good cycling stability, and high energy density.

[0014] 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.

[0015] The first silicon-based material has a smaller 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 the expansion of the electrode and improving the battery's cycling stability and storage performance. The second silicon-based material has a larger specific surface area, which can enhance the interaction between the binder and the silicon-based material, thereby reducing the expansion of the electrode. The combination of the first and second silicon-based materials can achieve a battery with low expansion and excellent cycling stability and storage performance.

[0016] In any embodiment, the first silicon-based material has a lower crystallinity than the second silicon-based material.

[0017] 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.

[0018] In any embodiment, a constant current charge and discharge test is performed on the first silicon-based material using a button cell, and a differential capacity curve of the delithiation stage is drawn to reflect the relationship between dQ / dV and voltage V. It is stipulated that the maximum value of the differential value dQ / dV between 0.27V-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.

[0019] When the V1 / V2 of the first silicon-based material is within the above range, a high voltage platform is unlikely to appear, which is beneficial for the silicon-based material to maintain structural stability and improve the cycle stability of the battery.

[0020] In any embodiment, 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.

[0021] When the silicon-carbon material is a carbon matrix particle with a pore structure and a nano-silicon-based material 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, thereby improving the structural stability of the silicon-carbon material, improving the battery capacity while taking into account excellent storage performance and cycle stability.

[0022] In any embodiment, Dv50 of the first silicon-based material is 9 μm-11 μm, and optionally 9.5 μm-10 μm.

[0023] When the Dv50 of the first silicon-based material meets the above range, it can reduce the loss of active ions caused by the reaction after direct contact between the silicon-based material and the electrolyte, reduce the expansion of the electrode, and improve the storage performance and cycle stability of the battery.

[0024] 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%.

[0025] 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, slowing down the expansion of the electrode, 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.

[0026] In any embodiment, the specific surface area of ​​the first silicon-based material is 0.8 m 2 / g-5m 2 / g, optional 1.1m 2 / g-3.2m 2 / g.

[0027] 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 expansion of the electrode can be reduced, and the cycle stability and storage performance of the battery can be improved.

[0028] In any embodiment, the second silicon-based material comprises a bulk morphology.

[0029] The second silicon-based material has a block morphology, which not only ensures excellent battery performance but also reduces the manufacturing cost of the electrode.

[0030] In any embodiment, Dv50 of the second silicon-based material is 5 μm-6 μm, and optionally 5.2 μm-5.6 μm.

[0031] When the Dv50 of the second silicon-based material is within the above range, it is beneficial to improve the transmission performance of active ions and electrons, thereby improving the fast charging performance of the battery.

[0032] 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 optionally 47%-55%.

[0033] 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.

[0034] In any embodiment, the specific surface area of ​​the second silicon-based material is greater than or equal to 0.8 m 2 / g, optional 1.1m 2 / g-3.2m 2 / g.

[0035] When the specific surface area of ​​the second silicon-based material is within the above range, the interaction between the adhesive and the silicon-based material can be enhanced, thereby reducing the expansion of the pole piece.

[0036] 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.

[0037] Keeping silicon grains within the aforementioned range can avoid excessive local silicon enrichment caused by overly large grains, which can lead to significant expansion during lithium insertion and deteriorate the battery's storage performance and cycling stability. Combining the first and second silicon-based materials can mitigate the degradation of battery performance caused by the crystallization of silicon on the surface of the smaller second silicon-based material.

[0038] In any embodiment, a constant current charge and discharge test is performed on the second silicon-based material using a button battery, and a differential capacity curve of the delithiation stage is drawn to reflect the relationship between dQ / dV and voltage V. It is stipulated that the maximum value of the differential value dQ / dV between 0.27V-0.34V is recorded as VA, and the maximum value of the differential value dQ / dV between 0.43V-0.55V is recorded as VB, 0.8≤VA / VB≤1.3, optionally, 0.8≤VA / VB≤1.0.

[0039] Silicon-based materials with smaller particle sizes are prone to silicon-rich crystallization, resulting in a high-voltage platform. By combining the first and second silicon-based materials, the deterioration of the material structure stability caused by the high-voltage platform generated by the second silicon-based material can be mitigated, improving the battery's storage performance and cycle stability.

[0040] In any embodiment, the first region further includes a first carbon material, and the Dv50 of the first carbon material is 14 μm to 19 μm.

[0041] 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.

[0042] In any embodiment, the first carbon material includes artificial graphite.

[0043] Compared with natural graphite, artificial graphite can improve the compaction density of the electrode and has excellent cycle stability and storage performance, thereby reducing the expansion of the electrode and improving the cycle stability and storage performance of the battery.

[0044] In any embodiment, the mass proportion of the first silicon-based material in the negative electrode film layer in the first region is smaller than the mass proportion of the second silicon-based material in the negative electrode film layer in the second region.

[0045] The first silicon-based material in the first area in direct contact with the cold pressing roller and the electrolyte has a low proportion, which 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 and improving the cycle stability and storage performance of the battery.

[0046] A second aspect of the present application further provides a secondary battery comprising the negative electrode sheet of the first aspect.

[0047] The third aspect of the present application further provides an electrical device comprising the secondary battery of the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] FIG1 is a schematic diagram of an embodiment of a negative electrode sheet of the present application;

[0049] FIG2 is a scanning electron microscope image of a first silicon-based material according to an embodiment of the present application;

[0050] FIG3 is a scanning electron microscope image of a cross section of a first region of a negative electrode film layer according to an embodiment of the present application;

[0051] FIG4 is a scanning electron microscope image of a cross section of the second region of the negative electrode film layer according to one embodiment of the present application;

[0052] FIG5 is an X-ray diffraction pattern of a first silicon-based material according to an embodiment of the present application;

[0053] FIG6 is an X-ray diffraction pattern of a second silicon-based material according to an embodiment of the present application;

[0054] FIG7 is a dQ / dV-V curve of a first silicon-based material according to an embodiment of the present application;

[0055] FIG8 is a dQ / dV-V curve of a second silicon-based material according to an embodiment of the present application;

[0056] FIG9 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0057] FIG10 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG9 ;

[0058] FIG11 is a schematic diagram of a battery module according to an embodiment of the present application;

[0059] FIG12 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0060] FIG13 is an exploded view of the battery pack according to one embodiment of the present application shown in FIG12 ;

[0061] FIG. 14 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0062] Explanation of the accompanying drawings: 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 cover plate; 10 negative electrode sheet, 101 negative electrode current collector, 102 negative electrode film layer, 102a first surface, 102b second surface, 1021 second region, 1022 first region, 1023 middle region. DETAILED DESCRIPTION

[0063] Below, the embodiments of the negative electrode sheet, secondary battery and electric device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the 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 described in the claims.

[0064] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0065] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0066] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0067] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0068] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0069] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0070] Improving battery energy density is a research hotspot in the field of lithium-ion batteries. Silicon has a theoretical gram capacity of up to 4200mAh / g, making it the lithium-ion battery anode material with the highest known specific capacity. It is also abundant in reserves and inexpensive, and its use in improving battery energy density has been widely studied in recent years. The lithium storage mechanism of silicon anode materials is mainly through the formation of an alloy phase with lithium ions. In actual applications, it has been found that the volume of silicon anode materials expands significantly after lithiation, resulting in high stress inside the battery. Continuous squeezing of the silicon anode material causes cracking, and the compaction process of the pole piece can also cause cracking of some silicon anode materials. Silicon exposed to the electrolyte will continuously consume lithium ions in the electrolyte, leading to deterioration of battery storage performance and cycle stability.

[0071] [Negative electrode]

[0072] Based on this, the present application provides a negative electrode plate, as shown in Figure 1, 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 away from the negative electrode current collector 101 and a second surface 102b arranged opposite to the first surface 102a, the thickness of the negative electrode film layer 102 is recorded as H, the area within the thickness range from the first surface 102a of the negative electrode film layer 102 to 0.3H is recorded as the first area 1022 of the negative electrode film layer, and the area within the thickness range from the second surface 102b of the negative electrode film layer 102 to 0.3H is recorded as the second area 1021 of the negative electrode film layer, and the first area 1022 includes a spherical or / and spherical-like first silicon-based material.

[0073] In this application, the determination of spherical or quasi-spherical shapes can be performed using methods known in the art. As an example, a scanning electron microscope can be used to photograph and observe the silicon-based material. Figure 2 is a scanning electron microscope image of a spherical silicon-based material sample. As shown in Figure 2, the silicon-based material is clearly spherical. Alternatively, an argon ion beam can be used to cut the electrode perpendicular to its large surface to expose a cross-section, which is then photographed and observed using a scanning electron microscope. A scanning electron microscope image of the first region of the negative electrode film is shown in Figure 3. Spherical or quasi-spherical silicon-based material can be observed in the first region of the negative electrode film.

[0074] Herein, “silicon-based material” refers to at least one of elemental silicon, silicon-oxygen compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

[0075] Currently, the mainstream negative electrode active materials for lithium-ion batteries are mainly artificial graphite and natural graphite. However, 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 area in direct contact with the cold pressing roller and the electrolyte includes spherical or quasi-spherical silicon-based materials, which can widen the compaction density window of the electrode. The cold pressing pressure required at the same compaction density is smaller, reducing the probability of cracking of the silicon-based material during the cold pressing process. This is beneficial for maintaining the integrity of the silicon-based material particles, reducing the formation of new interfaces, and avoiding irreversible active ion consumption caused by contact between the exposed active silicon of the silicon-based material and the electrolyte during the cycle. The spherical or quasi-spherical shape of the silicon-based material can reduce stress concentration in the silicon-based material during rolling and expansion, further mitigating the cracking of the silicon-based material, thereby comprehensively reducing the expansion rate of the electrode and improving the storage performance and cycle stability of the battery.

[0076] In some embodiments, the second region includes a second silicon-based material, and an average particle size of the second silicon-based material is smaller than an average particle size of the first silicon-based material.

[0077] In the present application, the average particle size can be tested by methods known in the art. As an example, an argon ion beam is used to cut the pole piece perpendicular to the large surface of the pole piece to expose the cross section, which is photographed using a scanning electron microscope. The particle size of the silicon-based material in the first region and the second region is statistically analyzed using the length diameter statistical method; wherein the average particle size is the total particle size value divided by the total number of particles.

[0078] The first area of ​​the negative electrode plate that is in direct contact with the electrolyte uses a first silicon-based material with a large average particle size. This can reduce the specific surface area of ​​the first silicon-based material, thereby reducing the loss of active ions caused by the reaction after direct contact between the silicon-based material and the electrolyte, reducing the expansion rate of the plate, and improving the storage performance and cycle stability of the battery. The second area of ​​the negative electrode plate close to the current collector uses a second silicon-based material with a small average particle size. The second silicon-based material has a shorter solid-phase ion transmission distance, which is beneficial to improving the transmission performance of active ions and electrons, thereby improving the fast charging performance of the battery. The second silicon-based material with a small average particle size has a larger specific surface area, which enhances the interaction between the binder and the silicon-based material, thereby further reducing the expansion of the plate and improving the storage performance and cycle stability of the battery.

[0079] In some embodiments, the mass percentage of silicon 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 in the second silicon-based material relative to the total mass of the second silicon-based material.

[0080] In the present application, the mass percentage of silicon element can be tested by methods known in the art. As an example, the silicon element content is determined by emission spectroscopy (Inductively coupled plasma, ICP), specifically as follows: a silicon-based material is taken as a sample, the sample is digested with aqua regia and hydrofluoric acid HF, and the completely digested solution (digestion for 0.5h) is taken for ICP testing to obtain the mass percentage of silicon element in the silicon-based material.

[0081] The low silicon content of the first silicon-based material in the first region, which is in direct contact with the cold press rollers and the electrolyte, reduces the amount of silicon that comes into contact with the electrolyte when the silicon-based material cracks, thereby slowing electrode expansion and improving the battery's cycling stability and storage performance. Combining a high-silicon-content second silicon-based material with a low-silicon-content first silicon-based material helps achieve a battery with low expansion, good cycling stability, and high energy density.

[0082] In some embodiments, the specific surface area of ​​the first silicon-based material is smaller than the specific surface area of ​​the second silicon-based material.

[0083] In this application, the specific surface area can be tested by methods known in the art. As an example, the specific surface area is tested by a gas adsorption method according to the GB / T19587-2017 test standard, specifically as follows: a silicon-based material is taken as a sample, the sample tube is immersed in liquid nitrogen at -196°C, and the adsorption amount of nitrogen on the solid surface at different pressures is measured at a relative pressure of 0.05-0.30. The monolayer adsorption amount of the sample is obtained based on the BET multilayer adsorption theory and its formula, thereby calculating the specific surface area of ​​the solid.

[0084] where n a is the amount of adsorbed gas, unit is mol / g; p / p0 is the relative pressure; n m is the monolayer adsorption capacity.

[0085] The first silicon-based material has a smaller 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 the expansion of the electrode and improving the battery's cycling stability and storage performance. The second silicon-based material has a larger specific surface area, which can enhance the interaction between the binder and the silicon-based material, thereby reducing the expansion of the electrode. The combination of the first and second silicon-based materials can achieve a battery with low expansion, excellent cycling stability, and storage performance.

[0086] In some embodiments, the first silicon-based material has less crystallinity than the second silicon-based material.

[0087] In this application, crystallinity can be tested using methods known in the art. As an example, an X-ray diffractometer (Bruker D8 DISCOVER) is used to test the crystallinity of silicon-based materials. If no crystalline diffraction peak appears in the X-ray diffraction pattern, the material is determined to have an amorphous structure; if a sharp diffraction peak appears in the X-ray diffraction pattern, the material is determined to have a crystalline structure. The crystallinity of the material is determined based on the diffraction peak intensity at the corresponding angle and the half-maximum width of the diffraction peak. Stronger diffraction peaks and smaller half-maximum widths indicate greater crystallinity.

[0088] 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.

[0089] In some embodiments, a constant current charge-discharge test is performed on the first silicon-based material using a button cell. A differential capacity curve is plotted during the delithiation stage to reflect the relationship between dQ / dV and voltage V. The maximum differential value dQ / dV between 0.27V and 0.34V is designated as V1, the maximum differential value dQ / dV between 0.43V and 0.55V is designated as V2, and 1.55≤V1 / V2≤1.75. In some embodiments, 1.60≤V1 / V2≤1.72.

[0090] In this article, the term "differential capacity curve" refers to the dQ / dV curve, which is an effective tool for analyzing the internal battery state. It is a method for obtaining internal battery parameters and status without disassembling the battery. The dQ / dV curve is obtained by calculating the change in battery capacity within a constant voltage interval.

[0091] In the present application, the dQ / dV curve can be tested using methods known in the art. As an example, the negative electrode material is mixed in a ratio of 8:1:1 of active material, binder, and conductive carbon, and the slurry is coated on a copper foil to prepare a test electrode. Lithium metal is used for the electrode, and 0.05C constant current discharge is performed to 5mV, 5mV constant voltage discharge is performed to a current less than 50μm, and 0.1C constant current charge is performed to 1.5V to obtain the constant current charging curve of the button battery. The 0.1C constant current charging curve is subjected to differential capacity processing, and the capacity change within the constant voltage interval is calculated to obtain the dQ / dV-V curve.

[0092] In some embodiments, the value of V1 / V2 is any value among 1.55, 1.60, 1.65, 1.7, 1.72, 1.75, or a range consisting of any two values ​​therein.

[0093] When the V1 / V2 of the first silicon-based material is within the above range, a high voltage platform is unlikely to appear, which is beneficial for the silicon-based material to maintain structural stability and improve the cycle stability of the battery.

[0094] 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.

[0095] As used herein, the term "silicon-carbon material" refers to a material composed of two elements: silicon and carbon.

[0096] When the silicon-carbon material is a carbon matrix particle with a pore structure and a structure of a nano-silicon-based material 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, thereby improving the structural stability of the silicon-carbon material, improving the battery capacity while taking into account excellent storage performance and cycle stability.

[0097] In some embodiments, the average pore size of the carbon matrix particle pore structure is 1.3 nm to 3.2 nm. In some embodiments, the average pore size of the carbon matrix particle pore structure is 1.6 nm to 2.4 nm.

[0098] In some embodiments, the average pore size 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, or a range consisting of any two values ​​therein.

[0099] The pores in this pore size range are conducive to the adhesion of nano-silicon-based materials and can effectively limit the expansion of nano-silicon-based materials in the pores. 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 and reducing the expansion of the electrode. At the same time, the battery has excellent storage performance and cycle stability.

[0100] In some embodiments, the carbon matrix particles have a porosity of 70% to 89%. In some embodiments, the carbon matrix particles have a porosity of 78% to 84%.

[0101] In some embodiments, the porosity of the carbon matrix particles is 70%, 73%, 76%, 79%, 82%, 85%, 89%, or any value therebetween, or a range consisting of any two values ​​therein.

[0102] When the porosity of the carbon matrix particles meets the above range, the volume of the carbon matrix particles occupied by the pores is relatively high. The carbon matrix particles can work synergistically with the nano-silicon-based materials to improve the battery capacity while the electrode has low expansion, and the battery has excellent storage performance and cycle stability.

[0103] In some embodiments, the carbon matrix particles comprise hard carbon.

[0104] In some embodiments, a method for preparing a silicon-carbon material includes: providing a gas containing a silicon precursor to carbon matrix particles having a porous structure; and generating a nano-silicon-based material disposed in the porous structure from the silicon precursor by chemical vapor deposition to obtain a carbon-silicon material.

[0105] In some embodiments, the silicon precursor is silane.

[0106] 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-based particles having a pore structure; generating a nano-silicon-based material arranged in the pore structure from the silicon precursor through chemical vapor deposition to obtain a spherical and / or quasi-spherical carbon silicon material.

[0107] In some embodiments, the first silicon-based material has a Dv50 of 9 μm to 11 μm. In some embodiments, the first silicon-based material has a Dv50 of 9.5 μm to 10 μm.

[0108] As used herein, the term "Dv50" refers to the particle size at which the volume distribution percentage reaches 50%.

[0109] In the present application, Dv50 can be tested by methods known in the art. As an example, referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method, it is conveniently measured using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer produced by Malvern Instruments Ltd. in the United Kingdom.

[0110] In some embodiments, Dv50 of the first silicon-based material is any value among 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, or a range consisting of any two values ​​therein.

[0111] When the Dv50 of the first silicon-based material meets the above range, it can reduce the loss of active ions caused by the reaction after direct contact between the silicon-based material and the electrolyte, reduce the expansion of the electrode, and improve the storage performance and cycle stability of the battery.

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

[0113] In some embodiments, the percentage of silicon element mass in the first silicon-based material relative to the total mass of the first silicon-based material is any value therebetween, or a range consisting of any two values ​​therein.

[0114] 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, slowing down the expansion of the electrode, 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.

[0115] In some embodiments, the specific surface area of ​​the first silicon-based material is 0.8 m2 / g-5m 2 In some embodiments, the specific surface area of ​​the first silicon-based material is 1.1 m 2 / g-3.2m 2 / g.

[0116] In some embodiments, the specific surface area of ​​the first silicon-based material is 0.8 m 2 / g, 1.4m 2 / g, 1.8m 2 / g, 2.2m 2 / g, 2.6m 2 / g、3m 2 / g, 3.4m 2 / g, 3.8m 2 / g, 4.2m 2 / g, 4.6m 2 / g、5m 2 / g any value or a range consisting of any two values ​​therebetween.

[0117] 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 expansion of the electrode can be reduced, and the cycle stability and storage performance of the battery can be improved.

[0118] In some embodiments, the second silicon-based material comprises a bulk morphology.

[0119] As used herein, the term "blocky morphology" refers to a shape other than a spherical or spherical-like shape.

[0120] An argon ion beam was used to cut the electrode perpendicular to the large surface of the electrode to expose the cross section, which was then photographed using a scanning electron microscope. A scanning electron microscope photograph of the second region of the negative electrode film layer is shown in FIG4 . Blocky silicon-based materials can be observed in the second region of the negative electrode film layer.

[0121] The second silicon-based material has a block morphology, which not only ensures excellent battery performance but also reduces the manufacturing cost of the electrode.

[0122] In some embodiments, the preparation method of the second silicon-based material includes: providing a gas containing a silicon precursor to bulk carbon-based particles having a carbon skeleton; and generating a nano-silicon-based material attached to the carbon skeleton from the silicon precursor through chemical vapor deposition to obtain a bulk carbon silicon material.

[0123] In some embodiments, the second silicon-based material has a Dv50 of 5 μm to 6 μm. In some embodiments, the second silicon-based material has a Dv50 of 5.2 μm to 5.6 μm.

[0124] In some embodiments, 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, or a range consisting of any two values ​​therein.

[0125] When the Dv50 of the second silicon-based material is within the above range, it is beneficial to improve the transmission performance of active ions and electrons, thereby improving the fast charging performance of the battery.

[0126] In some embodiments, the mass percentage of silicon in the second silicon-based material relative to the total mass of the second silicon-based material is 45%-65%. In some embodiments, the mass percentage of silicon in the second silicon-based material relative to the total mass of the second silicon-based material is 47%-55%.

[0127] In some embodiments, the percentage of the mass of the 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 other value therebetween, or a range consisting of any two values ​​therein.

[0128] 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.

[0129] In some embodiments, the specific surface area of ​​the second silicon-based material is greater than or equal to 0.8 m 2 In some embodiments, the specific surface area of ​​the second silicon-based material is 1.1 m 2 / g-3.2m 2 / g.

[0130] In some embodiments, the specific surface area of ​​the second silicon-based material is 0.8 m 2 / g, 1.1m 2 / g, 1.4m 2 / g, 1.7m 2 / g, 2m 2 / g, 2.3m 2 / g, 2.6m 2 / g, 2.9m 2 / g, 3.2m 2 / g any value or a range consisting of any two values ​​therebetween.

[0131] When the specific surface area of ​​the second silicon-based material is within the above range, the interaction between the adhesive and the silicon-based material can be enhanced, thereby reducing the expansion of the pole piece.

[0132] 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. In some embodiments, the grain size of the silicon grains is 2 nm to 3 nm.

[0133] 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, or a range consisting of any two values ​​therein.

[0134] Keeping silicon grains within the aforementioned range can avoid excessive local silicon enrichment caused by overly large grains, which can lead to significant expansion during lithium insertion and deteriorate the battery's storage performance and cycling stability. Combining the first and second silicon-based materials can mitigate the degradation of battery performance caused by the crystallization of silicon on the surface of the smaller second silicon-based material.

[0135] In some embodiments, a constant current charge-discharge test is performed on the second silicon-based material using a button cell, and a differential capacity curve is plotted during the delithiation stage to reflect the relationship between dQ / dV and voltage V. The maximum differential value dQ / dV between 0.27V and 0.34V is designated as VA, and the maximum differential value dQ / dV between 0.43V and 0.55V is designated as VB, with 0.8≤VA / VB≤1.3. In some embodiments, 0.8≤VA / VB≤1.0.

[0136] In some embodiments, the value of VA / VB is any value among 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, or a range consisting of any two values ​​therein.

[0137] Silicon-based materials with smaller particle sizes are prone to silicon-rich crystallization, resulting in a high-voltage platform. By combining the first and second silicon-based materials, the deterioration of the material structure stability caused by the high-voltage platform generated by the second silicon-based material can be mitigated, improving the battery's storage performance and cycle stability.

[0138] 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.

[0139] 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, or a range consisting of any two values ​​therein.

[0140] In some embodiments, the second region further includes a second carbon material, and the first carbon material and / or the second carbon material include at least one of artificial graphite, natural graphite, soft carbon, and hard carbon.

[0141] In some embodiments, the first carbon material includes artificial graphite.

[0142] Compared with natural graphite, artificial graphite can improve the compaction density of the electrode and has excellent cycle stability and storage performance, thereby reducing the expansion of the electrode and improving the cycle stability and storage performance of the battery.

[0143] In some embodiments, the mass proportion of the first silicon-based material in the negative electrode film layer in the first region is smaller than the mass proportion of the second silicon-based material in the negative electrode film layer in the second region.

[0144] The first silicon-based material in the first area in direct contact with the cold pressing roller and the electrolyte has a low proportion, which 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 and improving the cycle stability and storage performance of the battery.

[0145] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0146] In some embodiments, the negative electrode film layer may further include a binder. The binder may 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).

[0147] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0148] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0149] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the first silicon-based material, the first carbon material, the conductive agent, the binder, and any other components, are dispersed in a solvent (such as deionized water) to form a first negative electrode slurry; the second silicon-based material, the second carbon material, the conductive agent, the binder, and any other components are dispersed in a solvent (such as deionized water) to form a second negative electrode slurry; the first slurry and the second slurry are extruded 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; and the negative electrode sheet is obtained after drying, cold pressing, and slitting.

[0150] [Positive electrode]

[0151] The positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0152] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0153] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (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.).

[0154] In some embodiments, the positive electrode active material may adopt the positive electrode active material for batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates 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 traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), 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 O2 (also referred to as NCM 333 ), LiNi0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0155] 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), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0156] In some embodiments, the positive electrode film layer may further include a conductive agent. For 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.

[0157] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0158] [Electrolytes]

[0159] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0160] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0161] In some embodiments, the electrolyte includes an ester solvent.

[0162] In some embodiments, the ester solvent can be selected from one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl 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.

[0163] 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 difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0164] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0165] [Isolation film]

[0166] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0167] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0168] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0169] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0170] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0171] In this application, the shape of the secondary battery includes but is not limited to cylindrical, square or any other shape. For example, FIG9 shows a secondary battery 5 with a square structure as an example.

[0172] In some embodiments, referring to Figure 10, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination 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 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0173] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0174] Figure 11 shows an example battery module 4. Referring to Figure 11 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured together using fasteners.

[0175] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0176] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0177] Figures 12 and 13 illustrate an example battery pack 1. Referring to Figures 12 and 13 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0178] In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may 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 and satellites, energy storage systems, etc., but is not limited thereto.

[0179] As an electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0180] Figure 14 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0181] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0182] Example

[0183] The following examples are provided. The examples described below are exemplary and are intended only to explain the present application and are not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature within the art or in the product specifications are used. Reagents or instruments not specified by manufacturer are commercially available conventional products.

[0184] 1. Preparation method

[0185] Preparation Example 1: Spherical silicon carbon material A

[0186] A gas containing silane SiH4 is introduced into spherical hard carbon particles with a porous structure, and silicon is deposited in the porous structure of the hard carbon particles by chemical vapor deposition. The mass ratio of silicon in silane to hard carbon particles is 46:54, the Dv50 of the hard carbon particles is 8.8um, the porosity is 78.9%, and the average pore size is 2nm. Chemical vapor deposition is then used to coat the surface of the hard carbon particles with a carbon layer that accounts for 1% of the mass of the hard carbon particles after silicon deposition, wherein the gas source is acetylene gas, to obtain spherical silicon-carbon material A. The average particle size of spherical silicon-carbon material A is 9.5μm, the silicon mass percentage is 45.8%, and the specific surface area is 1.56m 2 / g, and the value of V1 / V2 in the differential capacity curve is 1.68. The X-ray diffraction pattern of the spherical silicon-carbon material A is shown in FIG5 , and the differential capacity curve is shown in FIG7 .

[0187] Preparation Example 2: Spherical silicon carbon material B

[0188] A gas containing silane SiH4 is introduced into spherical hard carbon particles with a porous structure, and silicon is deposited in the porous structure of the hard carbon particles by chemical vapor deposition. Among them, the mass ratio of silicon in silane to hard carbon particles is 47:53, the Dv50 of the hard carbon particles is 4.3um, the porosity is 80.1%, and the average pore size is 2nm. Then, a carbon layer accounting for 1% of the mass of the hard carbon particles after silicon deposition is coated on the surface of the hard carbon particles by chemical vapor deposition, wherein the gas source is acetylene gas, to obtain spherical silicon-carbon material B. The average particle size of spherical silicon-carbon material B is 5.2μm, the silicon mass percentage is 46.3%, and the specific surface area is 2.31m 2 / g.

[0189] Preparation Example 3: Bulk Silicon Carbon Material A

[0190] A gas containing silane SiH4 is introduced into the bulk hard carbon particles with a porous structure, and silicon is deposited in the porous structure of the hard carbon particles by chemical vapor deposition. The mass ratio of silicon in silane to hard carbon particles is 48:52, the Dv50 of the hard carbon particles is 4.3um, the porosity is 83.2%, and the average pore size is 2nm. Chemical vapor deposition is then used to coat the surface of the hard carbon particles with a carbon layer that accounts for 1% of the mass of the hard carbon particles after silicon deposition, wherein the gas source is acetylene gas, to obtain bulk silicon-carbon material A. The average particle size of bulk silicon-carbon material A is 5.2μm, the silicon mass percentage is 48.3%, and the specific surface area is 2.67m 2 / g, and the V1 / V2 value in the differential capacity curve is 0.89. The X-ray diffraction pattern of bulk silicon-carbon material A is shown in Figure 6, and the differential capacity curve is shown in Figure 8. Bulk silicon-carbon material A contains silicon crystals with a particle size of 2.2 nm.

[0191] Preparation Example 4: Bulk Silicon Carbon Material B

[0192] A gas containing silane SiH4 is introduced into the bulk hard carbon particles with a porous structure, and silicon is deposited in the porous structure of the hard carbon particles by chemical vapor deposition. Among them, the mass ratio of silicon in silane to hard carbon particles is 47:53, the Dv50 of the hard carbon particles is 8.8um, the porosity is 82.1%, and the average pore size is 2nm. Then, a carbon layer accounting for 1% of the mass of the hard carbon particles after silicon deposition is coated on the surface of the hard carbon particles by chemical vapor deposition, wherein the gas source is acetylene gas, to obtain bulk silicon-carbon material B. The average particle size of bulk silicon-carbon material B is 9.5μm, the silicon mass percentage is 47.2%, and the specific surface area is 1.68m 2 / g.

[0193] Preparation Example 5: Bulk Silicon Carbon Material C

[0194] A gas containing silane SiH4 is introduced into the bulk hard carbon particles with a porous structure, and silicon is deposited in the porous structure of the hard carbon particles by chemical vapor deposition. Among them, the mass ratio of silicon in silane to hard carbon particles is 46:54, the Dv50 of the hard carbon particles is 8.8um, the porosity is 80.5%, and the average pore size is 2nm. Then, a carbon layer accounting for 1% of the mass of the hard carbon particles after silicon deposition is coated on the surface of the hard carbon particles by chemical vapor deposition, wherein the gas source is acetylene gas, to obtain bulk silicon-carbon material C. The average particle size of bulk silicon-carbon material C is 9.5μm, the silicon mass percentage is 46.1%, and the specific surface area is 1.63m 2 / g.

[0195] Example 1:

[0196] 1) Preparation of negative electrode sheet

[0197] Spherical silicon-carbon material A and artificial graphite (average particle size of 15.6 μm) were mixed in a ratio of 0.16:0.84 to form the first negative electrode active material. The first negative electrode active material, conductive carbon nanotubes, thickener sodium carboxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber (SBR) were mixed in a mass ratio of 96.7:0.5:1.0:1.8, deionized water was added, and the mixture was stirred in a vacuum mixer until the mixture was homogeneous to obtain a first slurry.

[0198] Block silicon-carbon material A and natural graphite (average particle size 18.6 μm) were mixed in a ratio of 0.2:0.8 to form the second negative electrode active material. The second negative electrode active material, conductive carbon nanotubes, thickener sodium carboxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber (SBR) were mixed in a mass ratio of 95.5:0.7:2.0:1.8. Deionized water was added and the mixture was stirred in a vacuum mixer until the mixture was homogeneous, yielding a second slurry.

[0199] The first slurry and the second slurry are extruded 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 sheet is obtained. The coating weight of the first slurry and the second slurry is 4.2 mg / cm 2 and 6.3mg / cm 2 .

[0200] 2) Preparation of positive electrode sheet

[0201] The positive electrode active material lithium iron phosphate, conductive carbon black, and binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in an N-methylpyrrolidone solvent system in a weight ratio of 96:2:2 to obtain a positive electrode slurry; the above positive electrode slurry is evenly coated on a positive electrode current collector aluminum foil with a thickness of 13 μm at a coating speed of 30 m / min; the temperature of the coating oven is 110°C-130°C, and then the positive electrode sheets are obtained through cold pressing and slitting.

[0202] 3) Preparation of electrolyte

[0203] In an argon atmosphere glove box (H2O content <0.1ppm, O2 content <0.1ppm), lithium salt lithium hexafluorophosphate LiPF6 was dissolved in a mixed system of organic solvents ethylene carbonate (EC) and diethyl carbonate (DEC) (EC:DEC volume ratio of 3:7) and stirred evenly to obtain an electrolyte with a lithium salt concentration of 1 mol / L.

[0204] 4) Isolation film

[0205] A 9 μm polyethylene (PE) film was used as the separator.

[0206] 5) Preparation of batteries

[0207] The positive electrode sheet, the separator, and the composite negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to isolate the positive and negative electrode sheets. The bare battery cell is wound, the tabs are welded, and the battery cell is placed in an aluminum shell. The electrolyte is then injected and sealed. After standing, cold pressing, formation, shaping, capacity testing and other processes, the lithium-ion secondary battery prepared in Example 1 is obtained.

[0208] The preparation method of the battery of Example 2-3 is similar to that of 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. The specific parameters are shown in Table 1.

[0209] The preparation method of the battery of Example 4 is similar to that of the battery of Example 1, except that the first carbon material is natural graphite with a particle size of 18.6 μm. The specific parameters are shown in Table 1.

[0210] The batteries of Examples 5-7 were prepared in a similar manner to that of Example 1, except that the types of spherical silicon-carbon materials in the first region and / or bulk silicon-carbon materials in the second region were adjusted. Specific parameters are shown in Table 1.

[0211] The battery preparation method of Comparative Example 1 is similar to that of Example 1, except that the first silicon-based material is a bulk silicon-carbon material C. The specific parameters are shown in Table 1.

[0212] Table 1

[0213] 2. Test Method

[0214] 1. Charging time test

[0215] The electrode can be prepared into a button battery or a small stacked battery cell. At 35°C, the battery is charged and discharged for the first time at a current of 1C (i.e., the current value that completely discharges the theoretical capacity within 1 hour). Specifically, the battery is charged at a constant current rate of 1C to a charge cut-off voltage of 2V, then charged at a constant voltage to a current ≤0.05C, left to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to a discharge cut-off voltage of 5mV. Its actual capacity is recorded as C0. Then the battery is charged with a constant current of 2.8C0, 3C0, 3.2C0, 3.5C0, 3.8C0, 4.1C0, 4.4C0, 4.7C0, 5C0, 5.3C0, 5.6C0, and 5.9C0 in sequence to the full battery charge cut-off voltage V1 or the negative electrode cut-off potential of 0V (whichever is reached first). After each charge is completed, it is discharged with 1C0 to the full battery discharge cut-off voltage V2. The SOC (State of Charge) of the battery is recorded at different charge rates when it is charged to 10%, 20%, 30%, ..., 80%. The charge rate-negative electrode potential curve under different SOC states is drawn. After linear fitting, the charge rate corresponding to the negative electrode potential of 0V under different SOC states is obtained. The charge rate is the charging window under the SOC state, which is recorded as C10% SOC, C20% SOC, C30% SOC, C40% SOC, C50% SOC, C60% SOC, C70% SOC, and C80% SOC respectively. According to the formula:

[0216] (60 / C20%SOC+60 / C30%SOC+60 / C40%SOC+60 / C50%SOC+60 / C60%SOC+60 / C70%SOC+60 / C80%SOC)×10%

[0217] The charging time T for charging the battery from 10% SOC to 80% SOC is calculated in minutes. The shorter the time, the better the fast charging performance of the battery.

[0218] 2. Based on the cold pressure electrode full charge expansion test

[0219] After the negative electrode is cold pressed, 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 it at a constant voltage until the current is ≤0.05C. After charging, disassemble the battery cell to remove the negative electrode, measure the thickness of 5-8 points on the disassembled electrode, and take the average value as A2. The full charge expansion rate of the electrode is (A2-A1) / A1*100%.

[0220] 3. Storage performance test

[0221] The electrode was prepared into a laminated cell. The battery was discharged at a constant current rate of 0.33C to a cutoff voltage of 2.5V, allowed to stand for 30 minutes, and then charged at a constant current rate of 0.33C to a charge cutoff voltage of 4.25V. After that, it was charged at a constant voltage until the current was ≤0.05C. After standing for 30 minutes, the initial capacity was recorded as C0. The battery was placed in a constant temperature box at 60°C for 60 days. After 60 days, the battery was taken out and allowed to stand at room temperature for 60 minutes for capacity testing. The specific process was as follows: discharge at a constant current rate of 0.33C to a cutoff voltage of 2.5V, allowed to stand for 30 minutes, and then charged at a constant current rate of 0.33C to a charge cutoff voltage of 4.25V. After that, it was charged at a constant voltage until the current was ≤0.05C. The capacity was recorded as C1, and the 60-day storage capacity retention rate was C1 / C0*100%.

[0222] 4. Normal temperature cycle performance test:

[0223] Test process: At 25°C, let the battery rest for 30 minutes, then charge at a rate of 0.5C to a voltage of 4.2V. Further charge at a constant voltage of 4.2V to a current of 0.05C, let it rest for 5 minutes, and then discharge at a rate of 0.5C to a voltage of 2.8V. The resulting capacity is recorded as the initial capacity C0. This is one charge and discharge cycle. Repeat the above steps for the same battery, recording the discharge capacity Cn after each cycle. The battery capacity retention rate after each cycle is Pn = Cn / C0*100%, until Pn≦80%, stop the test, and record the number of cycles at this time.

[0224] 3. Analysis of test results of various embodiments and comparative examples

[0225] Batteries of various examples and comparative examples were prepared according to the above methods, and various performance parameters were measured. The results are shown in the table below.

[0226] As can be seen from Table 2, the silicon-based material in the first region of the negative electrode film layer is spherical in shape, which can reduce the expansion rate of the electrode after cold pressing and improve the high-temperature storage performance and cycle stability of the battery.

[0227] Table 2

[0228] From the comparison of Example 1 and Example 4 in Table 3, it can be seen that compared with natural graphite, the first graphite being artificial graphite is beneficial to improving the high-temperature storage performance, dynamic performance and cycle stability of the battery.

[0229] From the comparison of Example 1 and Examples 5-7 in Table 3, it can be seen that when the first silicon-based material with a large particle size is used in combination with the second silicon-based material with a small particle size, the electrode has a low expansion rate, and the battery has good cycle stability, high-temperature storage performance and fast charging performance.

[0230] Table 3

[0231] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present application, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present application. In addition, within the scope of the subject matter of the present application, various modifications that can be conceived by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements in the embodiments are also included in the scope of the present 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 arranged opposite to the first surface, the thickness of the negative electrode film layer is recorded as H, the area within the thickness range from the first surface of the negative electrode film layer to 0.3H is recorded as the first area of ​​the negative electrode film layer, and the area within the thickness range from the second surface of the negative electrode film layer to 0.3H is recorded as the second area of ​​the negative electrode film layer, and the first area includes a spherical or / and spherical-like first silicon-based material.

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

3. The negative electrode sheet according to claim 2, characterized in that: The mass percentage of silicon 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 in the second silicon-based material relative to the total mass of the second silicon-based material.

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

6. The negative electrode sheet according to any one of claims 1 to 5, characterized in that: A constant current charge and discharge test of the first silicon-based material is carried out using a button cell, and a differential capacity curve of the delithiation 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 0.27V-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.

7. The negative electrode sheet according to any one of claims 2 to 6, characterized in that: 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.

8. The negative electrode sheet 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 9 μm-11 μm, and can be 9.5 μm-10 μm; (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%, and can be 45%-50%; (3) The specific surface area of ​​the first silicon-based material is 0.8 m 2 / g-5m 2 / g, optional 1.1m 2 / g-3.2m 2 / g.

9. The negative electrode sheet 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 comprises a block morphology; (2) The Dv50 of the second silicon-based material is 5 μm-6 μm, and can be 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 47%-55%; (4) The specific surface area of ​​the second silicon-based material is greater than or equal to 0.8 m 2 / g, optional 1.1m 2 / g-3.2m 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 2 nm to 3 nm; (6) A constant current charge and discharge test is performed on the second silicon-based material using a button cell, and a differential capacity curve in the lithium removal stage is plotted to reflect the relationship between dQ / dV and voltage V. The maximum value of the differential value dQ / dV between 0.27 V and 0.34 V is designated as VA, and The maximum value of the differential value dQ / dV between 0.43V and 0.55V is recorded as VB, 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 also 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 also 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 proportion of the first silicon-based material in the negative electrode film layer in the first region is smaller than the mass proportion of the second silicon-based material in the negative electrode film layer in the second region.

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

15. An electrical device, characterized in that: Includes the secondary battery as claimed in claim 14.

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