Battery

Abstract

A battery. The battery comprises a negative electrode sheet, which comprises a silicon-based material, wherein the degree of sphericity of the silicon-based material is 0.66-0.99. The ratio S / H of the area S of a first surface of the battery to the thickness H of the battery is 800-3000, the unit of the area S of the first surface is mm2, the unit of the thickness H of the battery is mm, the first surface is a surface having the maximum area among six surfaces of the battery, and the thickness H of the battery is less than or equal to 3.5 mm. The battery can achieve a smaller thickness, a higher energy density, a lower thickness expansion rate and a higher cycle stability.

Description

Battery Technical Field

[0001] This disclosure relates to the field of battery technology, specifically to a battery.

[0002] Background of the Invention

[0003] With the continuous upgrading of the functions of 3C products such as smartphones and tablets, the market has placed higher demands on the battery life and size specifications of their components. The pursuit of thinner and lighter designs and higher energy density has become a core development direction for the battery industry. To improve battery energy density and reduce battery size, the most common solution is to use silicon-based materials with higher theoretical capacity to replace traditional graphite-based anode materials. However, silicon-based materials experience significant volume expansion (approximately 300%) during battery charge-discharge cycles, a problem that severely degrades the battery's thickness expansion rate and cycle stability.

[0004] Therefore, developing and disclosing a battery that combines ultra-thin size, high energy density, low expansion rate, and excellent cycle stability is of great practical significance. Summary of the Invention

[0005] The purpose of this disclosure is to overcome the aforementioned problems in the prior art and to provide a battery. The battery of this disclosure, by simultaneously controlling the ratio of the first surface area to the thickness of the battery, and the sphericity of the silicon-based material in the negative electrode, can simultaneously possess a thinner thickness, higher energy density, lower thickness expansion rate, and excellent cycle stability.

[0006] This disclosure provides a battery comprising a negative electrode sheet, the negative electrode sheet comprising a silicon-based material having a sphericity of 0.66-0.99; the ratio S / H of the area S of the first surface of the battery to the thickness H of the battery being S / H is 800-3000, and the unit of the area S of the first surface is mm. 2 The thickness H is in mm, and the first surface is the surface with the largest area among the six surfaces of the battery; the thickness H ≤ 3.5 mm.

[0007] With the silicon-based material used as the negative electrode active material, further adjusting the ratio of the battery's first surface area to its thickness can effectively improve the battery's energy density and cycle stability. The mechanism is as follows: reducing the battery thickness allows for a higher proportion of active material within the same volume or area, thus increasing the battery's energy density; however, excessively thin batteries can impair cycle stability. This disclosure has found that increasing the maximum surface area of ​​the battery helps improve cycle stability because a larger surface area allows more active material to participate in the charge-discharge reaction, thereby enhancing battery stability. Therefore, when the ratio of the battery's first surface area to its thickness is within a suitable range, a balance between energy density and cycle stability can be achieved. Furthermore, for wound batteries, adjusting this ratio can reduce the number of folds in the winding core, alleviate stress concentration in the curved area of ​​the winding core, improve the electrolyte wetting effect, and thus improve the battery's cycle expansion characteristics, enabling the battery to possess both a lower expansion rate and excellent cycle stability.

[0008] Building upon this, further control over the sphericity of silicon-based materials can further improve the cycle stability and thickness expansion rate of the battery. The main reason is that when the sphericity of the silicon-based material is within a specific range, it can evenly distribute pressure throughout the material when subjected to external pressure, preventing particle breakage due to stress concentration. Particle breakage exposes the inner surface of the silicon-based material to the electrolyte, leading to repeated SEI film formation and thus impairing the cycle stability of the battery. Furthermore, when the sphericity of the silicon-based material is within a specific range, it also results in a relatively smooth surface morphology, controlling surface defects (protrusions or depressions), which is beneficial for SEI film adhesion and avoids repeated SEI film growth caused by SEI film detachment. When the sphericity of the silicon-based material is large, for example, greater than 0.99, the surface becomes too smooth, which is detrimental to SEI film adhesion.

[0009] Compared with the prior art, the present disclosure has at least the following advantages through the above technical solution:

[0010] (1) The battery disclosed herein is an ultra-thin battery with high energy density.

[0011] (2) The battery disclosed herein has a low thickness expansion rate and high cycle stability.

[0012] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0013] Figure 1 shows a schematic diagram of the dimensions of a battery in an example of this disclosure; wherein, Figure 1(a) is a front view and Figure 1(b) is a side view.

[0014] Figure 2 shows a scanning electron microscope (SEM) image of a silicon-based material in an example of this disclosure.

[0015] Figure 3 shows the SEM image of the negative electrode sheet of the battery in Example 1 after 500 cycles.

[0016] Figure 4 shows the SEM image of the negative electrode of the battery in Comparative Example 1 after 500 cycles. Detailed Implementation

[0017] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure.

[0018] This disclosure provides a battery that may include a negative electrode. The negative electrode may include a silicon-based material, and the sphericity of the silicon-based material may be 0.66-0.99, for example, 0.66, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or 0.99. The ratio S / H of the area S of the first surface of the battery to the thickness H of the battery may be 800-3000 (for example, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, or 3000), and the unit of the area S of the first surface is mm. 2 The thickness H of the battery is in mm, and the first surface is the surface with the largest area among the six surfaces of the battery; the thickness H of the battery is ≤3.5mm (for example, 3.5mm, 3.4mm, 3.3mm, 3.2mm, 3.1mm, 3mm, 2.9mm, 2.8mm, 2.7mm, 2.6mm or 2.5mm).

[0019] In this disclosure, the area S of the first surface and the thickness H of the battery have conventional meanings in the art. The battery has six surfaces, as shown in Figure 1, which is a schematic diagram of the dimensions of a battery in an example of this disclosure; where Figure 1(a) is a front view and Figure 1(b) is a side view. As can be seen from the figures, the length of the battery is L, the width is W, and the thickness is H. The plane containing the length L and the width W is the surface with the largest area among the six surfaces of the battery, i.e., the first surface. The area S of the first surface can be obtained by measuring the length and width of the battery with a measuring tool, and multiplying the length by the width to obtain the area S of the first surface.

[0020] In this disclosure, the sphericity of the silicon-based material can be tested using conventional methods in the art. For example, after disassembling the battery, the negative electrode sheet is removed, cleaned with dimethyl carbonate (DMC), and dried. The negative electrode sheet is then polished along its thickness direction using an argon-ion polishing machine. The cross-sectional morphology of the negative electrode sheet is observed using a scanning electron microscope (SEM). In backscattered light mode, the white spherical particles are the silicon-based material particles. The lengths of the largest and smallest diameter points of the cross-section of the same silicon-based material particle are measured and denoted as d1 and d2, respectively. The ratio of d1 / d2 is the sphericity of the silicon-based material particle. At least 30 silicon-based material particles are selected for sphericity testing, and the average value is taken as the sphericity of the silicon-based material.

[0021] In one example, the ratio S / H of the area S of the first surface of the battery to the thickness H of the battery is 1500-2500.

[0022] In one example, the sphericity of the silicon-based material is 0.8-0.95.

[0023] In this disclosure, the surface of the silicon-based material may have recesses. Figure 2 shows a scanning electron microscope (SEM) image of a silicon-based material in an example of this disclosure. As can be seen from the figure, the surface of the silicon-based material has recesses, and the number of recesses on the silicon-based material particles is greater than or equal to one.

[0024] Constructing recesses on the surface of silicon-based materials can increase the specific surface area of ​​the silicon-based materials, which not only facilitates the contact and wetting between the silicon-based materials and the electrolyte, but also enhances the bonding effect between the silicon-based materials and various substances in the battery (such as conductive agents, binders, etc.), changing the bonding method from point contact to surface contact. The presence of recesses can increase the active sites on the surface of silicon-based materials, improve the adhesion of the SEI film on the surface of silicon-based materials, and help improve the cycle stability of the battery.

[0025] In this disclosure, the number of recesses can be 1 to 100, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90 or 100.

[0026] In one example, the number of recesses is 20 to 50.

[0027] In this disclosure, the number of recesses refers to the average number of recesses on a single silicon-based material particle; that is, the average number of recesses on the surface of each silicon-based material particle is 1 to 100, and does not imply that all silicon-based material particles have recesses on their surfaces. The number of recesses can be obtained by conventional methods in the art, such as using SEM. At least 10 silicon-based material particles are selected in the electron microscope image, and the number of recesses on each silicon-based material particle is counted. The number of recesses is then multiplied by 2 and the average is taken (wherein, multiplying by 2 is because the SEM image can only observe the front side of the silicon-based material particle, and the number of recesses on the back side is not directly observable, so it is assumed that the number of recesses on the back side is the same as the number of recesses on the front side, so the total number of observable surface recesses is multiplied by 2 to represent the total number of recesses on the surface of the entire silicon-based material particle). The number of recesses can then be obtained.

[0028] In this disclosure, the diameter of the recessed portion can be 0.1 μm-5 μm, for example, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm. The depth of the recessed portion can be 0.01 μm-5 μm, for example, 0.01 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm.

[0029] Under the premise that the number of recesses in silicon-based materials is within a certain range, further control of the diameter and depth of the recesses can effectively improve the cycle stability of the battery and reduce its thickness expansion rate. This is because when the diameter and depth of the recesses are within a specific range, it not only facilitates electrolyte wetting and storage but also enhances the adhesion between the silicon-based material surface and the SEI film, thereby improving the film formation stability of the SEI film on the silicon-based material surface. However, when the diameter of the recesses is too large (e.g., greater than 5 μm) and / or the depth is too deep (e.g., greater than 5 μm), it may cause severe damage to the surface structure of the silicon-based material, leading to... After charge-discharge cycles, the silicon-based material is prone to severe breakage, which exacerbates the side reactions with the electrolyte and is detrimental to improving the battery's cycle stability. In addition, if the broken silicon-based material produces sharp edges, it may puncture the separator, thereby causing a risk of internal short circuit in the battery. When the diameter of the recess is too small (e.g., less than 0.1 μm) and / or the depth is too shallow (e.g., less than 0.01 μm), the adhesion between the recess surface and the SEI film is insufficient. As the silicon-based material expands in volume during cycling, the SEI film on its surface may fall off, resulting in repeated growth of the SEI film, which is detrimental to improving the battery's thickness expansion rate and cycle stability.

[0030] In one example, the average diameter of the recess is 0.3 μm-3 μm. The average depth of the recess is 0.2 μm-2 μm.

[0031] In this disclosure, the diameter and depth of the recess have conventional meanings in the art. When the edge of the recess forms a "regular circle" on the silicon-based material surface, the diameter of the recess is the diameter of that regular circle; and when the edge of the recess forms a non-"regular circle" on the silicon-based material surface, the diameter of the recess is the equivalent diameter of a circle with the same area as the non-regular circle. The diameter of the recess can be obtained by conventional methods in the art, such as SEM, where at least 20 recesses (which can be on the same silicon-based material or on different silicon-based materials) are selected in the electron microscope image, and the diameter of each recess is measured and calculated, and the average value is taken. The depth of the recess refers to the vertical distance from the lowest point within the recess to the surface of the silicon-based material. The depth of the depression can be measured by conventional methods in the art, such as SEM. At least 20 depressions (which can be depressions on the same silicon substrate or depressions on different silicon substrates) are selected in the electron microscope image, and the depth of each depression is measured and the average value is taken.

[0032] In this disclosure, the silicon-based material may include at least one of elemental silicon, silicon-carbon, silicon-oxygen, and silicon alloys.

[0033] In one example, the silicon-based material includes silicon-carbon. The silicon-carbon may have a core-shell structure. The core of the core-shell structure includes a porous carbon matrix and silicon particles located in the pores within the porous carbon matrix, and the outer shell of the core-shell structure includes a carbon material.

[0034] In this disclosure, the average particle size of the silicon-carbon can be 5 μm-20 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 20 μm. The average particle size of the silicon particles can be 0.1 nm-2000 nm, for example, 0.1 nm, 0.5 nm, 1 nm, 5 nm, 10 nm, 50 nm, 100 nm, 500 nm, 1000 nm, or 2000 nm.

[0035] When the average particle size of silicon-carbon and silicon particles are within a specific range, it is beneficial to improve the electrochemical performance of silicon-based materials. When the average particle size of silicon-carbon and / or silicon particles is small, it means a larger specific surface area. This results in a larger contact area with the electrolyte, leading to greater consumption of active lithium during the first charging cycle, which is detrimental to improving battery cycle stability. Conversely, when the average particle size of silicon-carbon and / or silicon particles is large, it means a longer diffusion path for lithium ions within the silicon-based material, resulting in poorer kinetic performance of the negative electrode. Furthermore, a larger average particle size may lead to larger gaps between particles, lower material packing density, making it difficult to obtain a negative electrode with higher compaction density, resulting in a lower volumetric energy density of the battery.

[0036] In one example, the average particle size of the silicon particles is 1 nm to 50 nm.

[0037] In this disclosure, the average particle size of the silicon-carbon and the average particle size of the silicon particles can be obtained by methods conventional in the art. For example, the average particle size of the silicon-carbon is obtained by SEM, where at least 10 silicon-carbon particles are selected from the electron microscope image, the particle size of each silicon-carbon particle is measured, and the average value is taken. The average particle size of the silicon particles is obtained, for example, by transmission electron microscopy (TEM), where at least 20 silicon particles are selected from the electron microscope image, the particle size of each silicon particle is measured, and the average value is taken.

[0038] In this disclosure, the median particle size Dv50 of the silicon carbon can be 5μm-20μm, for example, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, or 20μm. The median particle size Dv50 of the silicon carbon can be obtained by methods conventional in the art, such as a laser particle size analyzer. In this disclosure, Dv50 is the particle size corresponding to the cumulative volume distribution reaching 50% after the particles are arranged in order of increasing particle size.

[0039] In this disclosure, the thickness of the outer shell can be 2nm-20nm, for example, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm or 20nm.

[0040] In one example, the average thickness of the shell is 5nm-10nm.

[0041] The outer shell of the silicon-carbon material effectively prevents direct contact between silicon and the electrolyte, thereby reducing side reactions and improving the stability of the negative electrode. Simultaneously, it inhibits silicon agglomeration, preventing stress concentration-induced failure of the silicon-based material and improving the battery's cycle stability. Furthermore, since silicon is a semiconductor, the conductivity of the porous carbon matrix combined with silicon is significantly reduced. The carbon-containing outer shell helps improve the overall conductivity of the silicon-carbon material, thus enhancing the battery's rate performance.

[0042] In this disclosure, the thickness of the shell can be tested using conventional methods in the art, such as using TEM, randomly selecting at least 50 silicon carbide particles, and selecting at least 3 sites on each silicon carbide particle, measuring the thickness of the shell at each site, and taking the average value.

[0043] In this disclosure, based on the total mass of the silicon and carbon, the content of the porous carbon matrix can be 38%-58% (e.g., 38%, 40%, 45%, 50% or 58%), the content of the silicon particles can be 40%-60% (e.g., 40%, 45%, 50%, 55% or 60%), and the content of the carbon material can be 2%-5% (e.g., 2%, 3%, 4% or 5%).

[0044] By adjusting the content of each component in silicon-carbon, it is beneficial to increase the battery's energy density while reducing the battery's thickness expansion rate.

[0045] In this disclosure, after 500 cycles at 45°C, a charge / discharge cutoff voltage of 2.5V-4.3V, 2C charging, and 0.7C discharging, the average thickness of the SEI film on the surface of the silicon-based material is 500nm-1000nm, for example, 500nm, 600nm, 700nm, 800nm, 900nm, or 1000nm.

[0046] In one example, after 500 cycles at 45°C, with a charge / discharge cutoff voltage of 2.5V-4.3V, 2C charging, and 0.7C discharging, the average thickness of the SEI film on the surface of the silicon-based material is 700nm-900nm.

[0047] In this disclosure, the average thickness of the SEI film on the surface of the silicon-based material can be tested by conventional methods in the art, such as cutting the negative electrode sheet using an argon ion mill to obtain a cross-sectional slice of the negative electrode sheet, and then using SEM (backscattered mode) to photograph the cross-sectional morphology of the negative electrode sheet. At least 5 silicon-based materials are selected, and at least 5 sites are selected on each silicon-based material. The thickness of the SEI film at each site is measured, and the average value is taken.

[0048] In this disclosure, the specific surface area of ​​the silicon-carbon can be 0.1 m². 2 / g-10m 2 / g, for example, 0.1m 2 / g, 0.5m 2 / g、1m 2 / g、2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g or 10m 2 / g. The pore volume of the silicon carbide can be 0.0005 cm³. 3 / g-0.002cm 3 / g, for example, 0.0005cm 3 / g, 0.001cm 3 / g or 0.002cm 3 / g.

[0049] When the specific surface area and pore volume of silicon-carbon meet certain ranges, the negative electrode active material can have a high specific capacity. At the same time, it can also reduce the contact between silicon-carbon and electrolyte, reduce the formation of SEI film, thereby improving the battery's initial efficiency and capacity retention.

[0050] In this disclosure, the specific surface area and pore volume of the silicon-carbon can be obtained by conventional methods in the art, such as by N2 isothermal adsorption-desorption determination and by fitting calculations using models such as BET and NLDFT.

[0051] In this disclosure, the true density of the silicon-carbon can be 1.5 g / cm³. 3 -2.4g / cm 3 For example, 1.5g / cm³ 3 1.6g / cm 3 1.7g / cm 3 1.8g / cm 3 1.9g / cm 3 2g / cm 3 2.1g / cm 3 2.2g / cm 3 2.3g / cm 3 Or 2.4g / cm 3 .

[0052] When the true density of silicon-carbon is within a specific range, it can ensure a high specific capacity of the negative electrode active material. Simultaneously, it can prevent the failure of the negative electrode active material due to excessive volume expansion of silicon. When the true density of silicon-carbon is low (e.g., less than 1.5 g / cm³), it can cause problems. 3 When the true density of silicon-carbon is high (e.g., greater than 2.4 g / cm³), it indicates that there are still many pores in the silicon-carbon matrix, and silicon has not been fully deposited inside the porous carbon matrix, resulting in a low specific capacity of silicon-carbon. 3 When the number of pores in silicon-carbon is low, it indicates that the silicon-carbon structure has a small number of pores. When the battery is charged, the silicon-lithium intercalation causes volume expansion. If the pore structure is insufficient to support the volume expansion of silicon, it will lead to the destruction of the structure of the negative electrode active material, which is not conducive to the cycle stability of the battery.

[0053] In this disclosure, the true density of the silicon-carbon can be obtained by methods conventional in the art, such as by gas displacement method.

[0054] In this disclosure, the difference between the mass content of silicon on the surface of the core and the mass content of silicon inside the core is ≤10%, for example, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5% or 0.1%.

[0055] When the difference between the mass content of silicon on the core surface and the mass content of silicon inside the core is within a specific range, it indicates that silicon can be uniformly deposited in the pores of the porous carbon matrix in silicon-carbon materials, and there is no silicon agglomeration on the core surface. When silicon is uniformly dispersed in the pores of the porous carbon matrix, the stress generated by the expansion of silicon during lithium intercalation can be uniformly distributed to various parts of the silicon-carbon material, thereby avoiding particle breakage failure due to excessive local stress. If silicon is enriched on the core surface of silicon-carbon materials, it will be detrimental to the overall electrochemical performance of the material. Compared with silicon deposited inside the porous carbon matrix, silicon enriched on the surface is more crystalline, and the reaction with lithium ions to form a silicon-lithium alloy is an irreversible process, which will lead to an excessively rapid rate decay in the later stages of battery cycling. In addition, the particle size of silicon agglomerates on the surface increases, and the lithium ion diffusion migration path becomes longer, resulting in poor battery rate performance. Therefore, avoiding silicon enrichment on the core surface can effectively improve the overall performance of silicon-carbon materials.

[0056] In this disclosure, the mass content of silicon on the surface of the core and the mass content of silicon inside the core can be obtained by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). In EDS point scanning mode, 5-10 points are selected both inside and on the surface of the silicon-carbon core, and the silicon content at each point is measured, with the average value taken. The terms "surface" and "interior" have their conventional meanings in the art, with "interior" referring to the non-"surface" region of the core.

[0057] In this disclosure, the negative electrode sheet includes a negative electrode current collector and a negative electrode active coating located on at least one side of the surface of the negative electrode current collector. The negative electrode active coating may include at least one of a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder. The negative electrode active material includes the silicon-based material. The negative electrode active material may also include a carbon-based material, such as at least one of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, and hard carbon. The negative electrode conductive agent may include conductive agents conventionally used in the art, such as at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, carbon nanotubes (including at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes), and carbon fibers. The negative electrode binder may include binders conventionally used in the art, such as at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene, and polyethylene oxide.

[0058] In this disclosure, based on the total mass of the negative electrode active coating, the content of the negative electrode active material can be 80 wt% to 99.8 wt% (e.g., 80 wt%, 82 wt%, 84 wt%, 86 wt%, 88 wt%, 90 wt%, 92 wt%, 94 wt%, 96 wt%, 98 wt%, 99 wt%, or 99.8 wt%), and the content of the negative electrode conductive agent can be 0.1 wt% to 10 wt% (e.g., 1 wt%). The content of the negative electrode binder can be 0.1% to 10% by weight (e.g., 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, or 0.1% by weight).

[0059] In this disclosure, the battery may further include a separator. The separator includes at least a substrate layer having polar groups. Introducing polar groups (e.g., carboxyl, hydroxyl, amino, etc.) into the substrate layer enhances the mechanical properties of the separator, allowing it to maintain high overall strength despite its thinness, thereby preventing battery deformation caused by an excessively thin separator. This effectively reduces the battery thickness, resulting in a higher volumetric energy density.

[0060] In this disclosure, the term "polar group" has its conventional meaning in the art and generally refers to a chemical group that has a significant electric dipole moment in a molecule. Whether the substrate layer has polar groups can be determined by conventional methods in the art, such as infrared spectroscopy.

[0061] In one example, the polar group includes at least one of hydroxyl, carboxyl, and amino groups.

[0062] In this disclosure, the thickness of the separator can be 3μm-9μm, for example, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, or 9μm. When the separator thickness is thin (e.g., less than 3μm), even if the substrate layer contains polar groups, it is difficult to effectively improve the mechanical strength of the separator, making the separator easily punctured, which will deteriorate the battery's self-discharge and storage performance. Furthermore, an excessively thin separator can easily lead to poor interfacial adhesion between the separator and the negative electrode active coating, making it prone to electrode powder shedding.

[0063] In this disclosure, the battery may further include an electrolyte. The electrolyte may include at least one of fluoroethylene carbonate (FEC), sulfur-containing additives, and lithium difluorophosphate (LiPO2F2).

[0064] FEC, sulfur-containing additives, and LiPO2F2 all contribute to the formation of the SEI film on the negative electrode. Among them, the SEI film formed by sulfur-containing additives mainly includes sulfur-containing organic compounds such as CH3CH(OSO2Li). In this case, the SEI film has better elasticity. Combined with the specific structure of silicon-based materials, it is more conducive to the stable adhesion of the SEI film to the surface of silicon-based materials, effectively avoiding the SEI film from detaching from the silicon-based material due to the large volume expansion caused by lithium insertion / extraction during charging and discharging.

[0065] In this disclosure, the sulfur-containing additive may include sulfur-containing additives conventionally used in the art, such as at least one of vinyl sulfite (ES), vinyl sulfate (DTD), 1,3-propanediol cyclosulfonate (PCS), 1,3-propanesulfonate lactone (PS), and 1,3-propenesulfonate lactone (PST).

[0066] In this disclosure, the FEC content in the electrolyte can be 5%-25% by mass, for example, 5%, 10%, 15%, 20%, or 25%. The sulfur-containing additive content in the electrolyte can be 0.1%-5% by mass, for example, 0.1%, 0.5%, 1%, 2%, 3%, 4%, or 5%. The LiPO2F2 content in the electrolyte can be 0.1%-1% by mass, for example, 0.1%, 0.5%, or 1%.

[0067] In this disclosure, the mass contents of FEC, the sulfur-containing additive, and LiPO2F2 in the electrolyte can be obtained by methods conventional in the art, such as gas chromatography-mass spectrometry.

[0068] In this disclosure, other components in the electrolyte, such as organic solvents and additives, can be added according to conventional methods in the art.

[0069] In this disclosure, the ratio of the volumetric energy density of the battery to the thickness of the battery is ≥240, for example, 240, 245, 250, 255, 260, 265, 270, 275, 280, 285, 290, 295, or 300. The unit of energy density is Wh / L, and the unit of thickness is mm.

[0070] By further adjusting the ratio of battery energy density to thickness, the battery can achieve higher space utilization.

[0071] In this disclosure, the battery further includes a positive electrode sheet. The positive electrode sheet includes a positive current collector and a positive active coating on at least one side surface of the positive current collector. The positive active coating includes a positive active material, which may include at least one of lithium cobalt oxide (LCO), nickel-cobalt-manganese ternary material (NCM), nickel-cobalt-aluminum ternary material (NCA), nickel-cobalt-manganese-aluminum quaternary material (NCMA), lithium iron phosphate (LFP), lithium manganese phosphate (LMP), lithium vanadium phosphate (LVP), lithium manganese oxide (LMO), lithium nickel oxide, lithium nickel manganese oxide binary material, lithium-rich manganese-based material, and lithium manganese iron phosphate.

[0072] In one example, the positive electrode active material comprises a first particle and a second particle. The first particle comprises a material with the chemical formula Li. a1 Ni b1 Co c1 Mn d1 M 1 e1 For O2, the following conditions apply: 0.8 ≤ a1 ≤ 1.3, 0.8 ≤ b1 ≤ 0.98, 0.02 ≤ c1 ≤ 0.2, 0.01 ≤ d1 ≤ 0.14, 0 <e1≤0.08,M 1 The first particle comprises at least one of Al, Zr, B, Y, Sr, W, Ti, Mg, and Nb, and is a single-crystal particle. The second particle comprises a particle with the chemical formula Li. a2 Ni b2 Co c2 Mn d2 M 2 e2 For O2, the following conditions apply: 0.9 ≤ a² ≤ 1.3, 0.8 ≤ b² ≤ 0.98, 0.02 ≤ c² ≤ 0.3, 0.01 ≤ d² ≤ 0.12, 0 <e2≤0.1,M 2 The second particle includes at least one of Al, Zr, B, Y, Sr, W, Ti, Mg, and Nb, and the second particle includes polycrystalline particles.

[0073] Single-crystal grains exhibit excellent structural stability due to the uniformity of their internal crystal structure and consistent grain orientation. Polycrystalline grains, on the other hand, have smaller primary grain sizes, significantly shortening the Li… + The transmission distance is beneficial to Li +The transfer of energy between silicon and the electrolyte improves the rate performance of the battery. Therefore, when single-crystal and polycrystalline particles are mixed, they exhibit better structural stability and rate performance. Furthermore, the side reaction activity between silicon and the electrolyte is strong at high temperatures, leading to significant volume expansion. However, when the positive electrode active material includes both single-crystal and polycrystalline particles, it exhibits a lower discharge temperature rise. Lowering the battery temperature during charging and discharging effectively suppresses silicon volume expansion, resulting in higher cycle performance and energy density. Therefore, when the positive electrode active material meets specific characteristics, its use in conjunction with the silicon-based material provided in this disclosure can further enhance the overall energy density and cycle performance of the battery.

[0074] This disclosure also provides a method for preparing the silicon-carbon, the method comprising the following steps:

[0075] S1: Mix the carbon source, catalyst, surfactant and solvent evenly, place them in the first reaction vessel, and carry out the first reaction;

[0076] S2: Take out the reaction product obtained in step S1, and perform the first washing and first drying;

[0077] S3: Mix the product obtained in step S2 with an alkaline substance and perform the first sintering;

[0078] S4: Perform first vapor deposition on the product obtained in step S3;

[0079] S5: Perform a second vapor deposition on the product obtained in step S4.

[0080] In this disclosure, in step S1, the carbon source includes, for example, at least one selected from resorcinol, formaldehyde, phenol, urea, and acrylic acid. The catalyst includes, for example, ammonia. The concentration of the ammonia can be 1 wt% to 5 wt% (e.g., 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%). The surfactant includes, for example, hexadecyltrimethylammonium bromide (CTAB). The solvent includes, for example, deionized water and / or ethanol.

[0081] In this disclosure, only the mass ratio of the carbon source to the surfactant needs to be adjusted; the mass of other materials (e.g., the catalyst and the solvent) is not limited. The mass ratio of the carbon source to the surfactant can be 1:(0.2-10), for example, 1:0.2, 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10.

[0082] The mixing temperature can be between 25°C and 45°C. The first reaction vessel includes, for example, an inner cylinder and an outer cylinder; the inner cylinder is, for example, made of polytetrafluoroethylene (PTFE), and the outer cylinder is, for example, made of stainless steel. The temperature of the first reaction can be between 80°C and 150°C, and the reaction time can be between 12 hours and 36 hours.

[0083] The particle size of silicon-carbon materials can be controlled by adjusting the concentration of the catalyst. The higher the catalyst concentration, the faster the nucleation rate, the more particles per unit volume, and the smaller the particle size.

[0084] In this disclosure, prior to step S2, the reaction vessel can be rinsed with cold water to rapidly cool it to room temperature.

[0085] In this disclosure, in step S2, the solvent used for the first cleaning can be deionized water. The temperature for the first drying can be 35°C-50°C.

[0086] In this disclosure, in step S3, the alkaline substance includes, for example, potassium hydroxide (KOH). The mass ratio of the product obtained in step S2 to the alkaline substance can be 1:(0.5-5), for example, 1:0.5, 1:1, 1:2, 1:3, 1:4 or 1:5.

[0087] In this disclosure, in step S3, the first sintering can be carried out in a tube furnace. The atmosphere for the first sintering is, for example, nitrogen. The first sintering can be completed in multiple steps, for example, in two steps. First, the temperature is increased to 400℃-600℃ at a heating rate of 5℃ / min-15℃ / min and held for 1h-4h; then, the temperature is increased to 700℃-900℃ at a heating rate of 5℃ / min-15℃ / min and held for 0.5h-3h.

[0088] Step S3 may further include: after the first sintering, cooling to room temperature, performing a second cleaning on the product, and performing a second drying at 50°C-70°C. The second cleaning may involve, for example, first washing the cooled product with dilute hydrochloric acid 1-4 times, then washing it with deionized water 1-4 times, followed by centrifugation and / or filtration.

[0089] In this disclosure, in step S4, a silicon source is used in the first vapor deposition. The silicon source may include at least one of silane, dichlorosilane, trichlorosilane, and tetrachlorosilane. The atmosphere for the first vapor deposition is an inert gas. The inert gas may include at least one of nitrogen, argon, and helium. The time for the first vapor deposition may be 1 h to 5 h, for example, 1 h, 2 h, 3 h, 4 h, or 5 h. The temperature for the first vapor deposition may be 400 °C to 600 °C, for example, 400 °C, 500 °C, or 600 °C. The heating rate for the first vapor deposition may be 5 °C / min to 15 °C / min, for example, 5 °C / min, 10 °C / min, or 15 °C / min.

[0090] In this disclosure, in step S5, a carbon source is used in the second vapor deposition. The carbon source may include at least one of methane, ethylene, and acetylene. The atmosphere for the second vapor deposition is an inert gas. The inert gas may include at least one of nitrogen, argon, and helium. The time for the second vapor deposition may be 0.5 h to 1.5 h, for example, 0.5 h, 1 h, or 1.5 h. The temperature for the second vapor deposition may be 400 °C to 800 °C, for example, 400 °C, 500 °C, 600 °C, 700 °C, or 800 °C.

[0091] It should be noted that the numerical designations such as "first" and "second" in this disclosure are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0092] The present disclosure will be described in detail below through embodiments. The embodiments described in this disclosure are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0093] In the following examples, unless otherwise specified, all materials used are commercially available analytical grade.

[0094] Preparation Example

[0095] The following preparation examples are used to illustrate the silicon-based materials of this disclosure.

[0096] Preparation Example 1

[0097] Silicon-based materials are prepared using the following method:

[0098] S1: Mix 120 mL of deionized water, 40 mL of ethanol, and 0.4 mL of ammonia solution (concentration 5 wt%) at 35 °C until homogeneous. Add CTAB and stir magnetically for 30 min. Then add m-diphenol and formaldehyde solution (concentration 35 wt%) separately. The molar ratio of CTAB to m-diphenol is 1:3, and the molar ratio of m-diphenol to formaldehyde solution (calculated as formaldehyde) is 1:1.5. Stir for 1 h. Pour the above mixture into a polytetrafluoroethylene inner sleeve, place the inner sleeve into a stainless steel outer sleeve, seal and tighten, and place in a 120 °C forced-air drying oven for 24 h. After the reaction is complete, rinse the outer sleeve with cold water and quickly cool to room temperature.

[0099] S2: Take out the reaction product obtained in step S1, wash it with deionized water, and dry it in a 40℃ forced-air drying oven to obtain phenolic resin microspheres.

[0100] S3: Mix the above phenolic resin microspheres and KOH at a mass ratio of 1:2, place them in a tube furnace, and heat them from room temperature to 500℃ at a heating rate of 10℃ / min under a nitrogen atmosphere and hold for 2 hours; then heat them to 800℃ at a heating rate of 10℃ / min and hold for 1 hour; after cooling to room temperature, take out the product, wash it twice with dilute hydrochloric acid (concentration of 0.5mol / L), then wash it twice with deionized water, centrifuge, filter, and dry at 50℃ to obtain porous phenolic resin microspheres.

[0101] S4: The above porous phenolic resin microspheres were placed in a tube furnace and heated from room temperature to 500°C at a heating rate of 10°C / min under a nitrogen atmosphere. A SiH4-N2 mixed gas with a flow rate of 60 sccm and a SiH4 volume content of 20% was introduced and kept for 3 hours.

[0102] S5: Increase the temperature to 550℃, introduce acetylene gas at a flow rate of 100 sccm, and maintain the temperature for 1 hour.

[0103] The prepared silicon-carbon material has a core-shell structure, with the core consisting of a porous carbon matrix and silicon particles, and the outer shell consisting of carbon material. The average particle size of the silicon-carbon material is 9.8 μm, the average particle size of the silicon particles is 12 nm, and the thickness of the outer shell is 7.5 nm. In the silicon-carbon material, the mass content of the porous carbon matrix is ​​48.0%, the mass content of the silicon particles is 49.6%, and the mass content of the carbon material is 2.4%. The surface of the silicon-carbon material has 22 depressions, with a diameter of 0.4 μm and a depth of 0.3 μm. The sphericity of the silicon-carbon material is 0.95.

[0104] Preparation Example 2

[0105] Silicon-based materials are prepared using the following method:

[0106] S1: Mix 120 mL of deionized water, 40 mL of ethanol, and 0.4 mL of ammonia solution (concentration 8 wt%) at 35 °C until homogeneous. Add CTAB and stir magnetically for 30 min. Then add m-diphenol and formaldehyde solution (concentration 35 wt%) separately. The molar ratio of CTAB to m-diphenol is 1:3, and the molar ratio of m-diphenol to formaldehyde solution (calculated as formaldehyde) is 1:1.5. Stir for 1 h. Pour the above mixture into a polytetrafluoroethylene inner sleeve, place the inner sleeve into a stainless steel outer sleeve, seal and tighten, and place in a 130 °C forced-air drying oven for 25 h. After the reaction is complete, rinse the outer sleeve with cold water and quickly cool to room temperature.

[0107] S2: Take out the reaction product obtained in step S1, wash it with deionized water, and dry it in a 40℃ forced-air drying oven to obtain phenolic resin microspheres.

[0108] S3: Mix the above phenolic resin microspheres and KOH at a mass ratio of 1:2, place them in a tube furnace, and heat them from room temperature to 500℃ at a heating rate of 10℃ / min under a nitrogen atmosphere and hold for 2 hours; then heat them to 800℃ at a heating rate of 10℃ / min and hold for 1 hour; after cooling to room temperature, take out the product, wash it twice with dilute hydrochloric acid, then wash it twice with deionized water, centrifuge, filter, and dry at 50℃ to obtain porous phenolic resin microspheres.

[0109] S4: The above porous phenolic resin microspheres were placed in a tube furnace and heated from room temperature to 500°C at a heating rate of 10°C / min under a nitrogen atmosphere. A SiH4-N2 mixed gas with a flow rate of 60 sccm and a SiH4 volume content of 20% was introduced and kept for 2 hours.

[0110] S5: Increase the temperature to 550℃, introduce acetylene gas at a flow rate of 100 sccm, and maintain the temperature for 1 hour.

[0111] The prepared silicon-carbon material has a core-shell structure, with the core consisting of a porous carbon matrix and silicon particles, and the outer shell consisting of carbon material. The average particle size of the silicon-carbon material is 5.6 μm, the average particle size of the silicon particles is 15 nm, and the thickness of the outer shell is 6.9 nm. In the silicon-carbon material, the mass content of the porous carbon matrix is ​​57.1%, the mass content of the silicon particles is 40.7%, and the mass content of the carbon material is 2.2%. The surface of the silicon-carbon material has 48 depressions, with a diameter of 0.7 μm and a depth of 0.5 μm. The sphericity of the silicon-carbon material is 0.81.

[0112] Preparation Example 3

[0113] Silicon-based materials are prepared using the following method:

[0114] S1: Mix 120 mL of deionized water, 40 mL of ethanol, and 0.4 mL of ammonia solution (concentration 2 wt%) at 35 °C until homogeneous. Add CTAB and stir magnetically for 30 min. Then add m-diphenol and formaldehyde solution (concentration 35 wt%) separately. The molar ratio of CTAB to m-diphenol is 1:3, and the molar ratio of m-diphenol to formaldehyde solution (calculated as formaldehyde) is 1:1.5. Stir for 1 h. Pour the above mixture into a polytetrafluoroethylene inner sleeve, place the inner sleeve into a stainless steel outer sleeve, seal and tighten, and place in a 125 °C forced-air drying oven for 26 h. After the reaction is complete, rinse the outer sleeve with cold water and quickly cool to room temperature.

[0115] S2: Take out the reaction product obtained in step S1, wash it with deionized water, and dry it in a 40℃ forced-air drying oven to obtain phenolic resin microspheres.

[0116] S3: Mix the above phenolic resin microspheres and KOH at a mass ratio of 1:2, place them in a tube furnace, and heat them from room temperature to 500℃ at a heating rate of 10℃ / min under a nitrogen atmosphere and hold for 2 hours; then heat them to 800℃ at a heating rate of 10℃ / min and hold for 1 hour; after cooling to room temperature, take out the product, wash it twice with dilute hydrochloric acid, then wash it twice with deionized water, centrifuge, filter, and dry at 50℃ to obtain porous phenolic resin microspheres.

[0117] S4: The above porous phenolic resin microspheres were placed in a tube furnace and heated from room temperature to 500°C at a heating rate of 10°C / min under a nitrogen atmosphere. A SiH4-N2 mixed gas with a flow rate of 60 sccm and a SiH4 volume content of 20% was introduced and kept for 4 hours.

[0118] S5: Increase the temperature to 550℃, introduce acetylene gas at a flow rate of 100 sccm, and maintain the temperature for 1 hour.

[0119] The prepared silicon-carbon material has a core-shell structure, with the core consisting of a porous carbon matrix and silicon particles, and the outer shell consisting of carbon material. The average particle size of the silicon-carbon material is 14.7 μm, the average particle size of the silicon particles is 20 nm, and the thickness of the outer shell is 9.6 nm. In the silicon-carbon material, the mass content of the porous carbon matrix is ​​39.1%, the mass content of the silicon particles is 58.3%, and the mass content of the carbon material is 2.6%. The surface of the silicon-carbon material has 36 depressions, with a diameter of 1.1 μm and a depth of 0.7 μm. The sphericity of the silicon-carbon material is 0.87.

[0120] Preparation Example 4

[0121] Used to verify the effect of whether there are depressions on the surface of silicon carbide materials.

[0122] The preparation was carried out in accordance with Example 1, except that the temperature in the drying oven in step S1 was changed to eliminate depressions on the surface of the silicon carbide material (by adjusting the temperature, the presence and number of depressions on the surface of the resin microspheres can be controlled; at higher temperatures, some functional groups on the surface of the resin microspheres decompose, leading to collapse and the formation of depressions), as detailed below:

[0123] The temperature in the drying oven in step S1 was adjusted from 120℃ to 90℃; and the molar ratio of CTAB to resorcinol was adjusted to 1:4 (the sphericity of the silicon carbide material was controlled to be 0.95 by adjusting the molar ratio of the two); the remaining parameters remained the same as in Preparation Example 1. The silicon carbide material surface had no depressions, and the sphericity of the silicon carbide material was 0.95.

[0124] Preparation Example 5

[0125] The examples prepared in this group are used to verify the effect of changing the number of "recesses".

[0126] The preparation examples in this group were carried out in accordance with Preparation Example 1, except that the number of depressions was adjusted by changing the temperature in the drying oven in step S1, as detailed below:

[0127] Preparation Example 5a

[0128] The temperature in the drying oven in step S1 was adjusted from 120℃ to 100℃, while the remaining parameters remained the same as in Preparation Example 1. Specifically, there were 6 depressions with a diameter of 0.4 μm and a depth of 0.2 μm; the sphericity of the silicon-carbon material was 0.98.

[0129] Preparation Example 5b

[0130] The temperature in the drying oven in step S1 was adjusted from 120℃ to 150℃, while the other parameters remained the same as in Preparation Example 1. The number of depressions was 88, with a diameter of 0.5 μm and a depth of 0.3 μm; the sphericity of the silicon-carbon material was 0.68.

[0131] Preparation Example 6

[0132] This is used to verify the effects of changes in the diameter and depth of the recess.

[0133] The preparation was carried out in accordance with Preparation Example 1, except that the diameter and depth of the depression were adjusted by changing the time the product was placed in the drying oven in step S1, as detailed below:

[0134] The reaction time in step S1, placed in the drying oven, was adjusted from 24 h to 28 h, while the remaining parameters remained the same as in Preparation Example 1. Specifically, the number of depressions was 24, with a diameter of 2.7 μm and a depth of 1.6 μm; the sphericity of the silicon-carbon material was 0.84.

[0135] The silicon-carbon materials prepared in the above examples all satisfy the following condition: specific surface area of ​​0.1 m². 2 / g-10m 2 / g; pore volume is 0.0005cm³ 3 / g-0.002cm 3 / g; true density is 1.5g / cm³ 3 -2.4g / cm 3 The difference between the mass content of silicon on the core surface and the mass content of silicon inside the core of the silicon-carbon material is ≤10%.

[0136] Comparative preparation example

[0137] Silicon-based materials are prepared using the following method:

[0138] Petroleum coke and KOH were mixed evenly at a mass ratio of 1:2, placed in a ceramic boat, and then placed in a tube furnace. Under a nitrogen atmosphere, the temperature was increased from room temperature to 800°C at a rate of 10°C / min and held for 2 hours. The mixture was then cooled to room temperature, washed twice with dilute hydrochloric acid (0.5 mol / L), and then washed twice with deionized water. The mixture was then centrifuged, filtered, and dried to obtain blocky porous activated carbon material. The blocky porous activated carbon material was placed in a tube furnace and heated from room temperature to 500°C at a rate of 10°C / min under a nitrogen atmosphere. A SiH4-N2 mixed gas with a flow rate of 60 sccm and a SiH4 volume content of 20% was introduced and held for 3 hours. The temperature was then increased to 700°C, and acetylene gas with a flow rate of 100 sccm was introduced and held for 1 hour.

[0139] The prepared silicon-carbon material has a core-shell structure, with the core consisting of a porous carbon material matrix and silicon particles, and the outer shell consisting of carbon material; the average particle size of the silicon-carbon material is 9.6 μm, and the sphericity of the silicon-carbon material is 0.42.

[0140] The following examples illustrate the battery of this disclosure.

[0141] Example 1

[0142] The battery is prepared according to the following method:

[0143] (1) Preparation of negative electrode sheet

[0144] The negative electrode active material (silicon-carbon material prepared in Preparation Example 1 and artificial graphite were mixed at a mass ratio of 2:8), sodium carboxymethyl cellulose, styrene-butadiene rubber, carbon black and single-walled carbon nanotubes were mixed evenly at a mass ratio of 85:2:5.5:7:0.5, deionized water was added, and the mixture was mixed evenly under the action of a vacuum stirrer to obtain a negative electrode slurry. The negative electrode slurry was evenly coated on copper foil, placed in an oven, dried at 80°C, and then rolled and slit to obtain a negative electrode sheet.

[0145] (2) Preparation of positive electrode sheet

[0146] The positive electrode active material (including a first particle and a second particle, wherein the first particle has the chemical formula LiNi) is used. 0.9 Co 0.04 Mn 0.04 Al 0.02 The O2 substance is a single crystal particle; the second particle is LiNi. 0.85 Co 0.08 Mn 0.04 Al 0.03 The substance containing O2 is a polycrystalline particle; the mass ratio of the first particle to the second particle is 85:15. Polyvinylidene fluoride, acetylene black, and single-walled carbon nanotubes are mixed evenly in a mass ratio of 96:2:1.5:0.5. N-methylpyrrolidone is added, and the mixture is mixed evenly under the action of a vacuum stirrer to obtain a positive electrode slurry. The positive electrode slurry is evenly coated on aluminum foil, placed in an oven, and dried at 120°C. After rolling and slitting, a positive electrode sheet is obtained.

[0147] (3) Preparation of electrolyte

[0148] In a glove box (H2O < 0.01 ppm, O2 < 0.01 ppm, Ar atmosphere), ethylene carbonate, propylene carbonate, and propyl propionate are mixed evenly in a mass ratio of 1:1:8 to form an organic solvent. Lithium hexafluorophosphate (14%), FEC (15%), PS (3%), and LiPO2F2 (0.5%) based on the total mass of the electrolyte are added to the organic solvent and stirred evenly. After passing the tests for moisture and free acid, the electrolyte is obtained.

[0149] (4) Battery fabrication

[0150] The negative electrode sheet, separator (7 μm thick, substrate layer is modified polyethylene with polar groups carboxyl, hydroxyl and amino) prepared in step (1) and the positive electrode sheet prepared in step (2) are stacked in sequence, with the separator between the positive electrode sheet and the negative electrode sheet; after winding, encapsulation, injection of electrolyte prepared in step (3), secondary sealing, formation and sorting, etc., the battery is obtained;

[0151] The area S of the first surface of the battery is 6254 mm². 2The thickness H is 3.15 mm, and the ratio of the area to the thickness of the first surface S / H is 1985.

[0152] Example 2

[0153] The procedure was carried out in accordance with Example 1, except that the area S of the first surface of the battery, the battery thickness H, and the composition of the electrolyte were changed, specifically as follows: the area S of the first surface of the battery was 4673 mm². 2 The thickness H is 3.08 mm, and the ratio of the area to the thickness of the first surface S / H is 1517; the mass content of FEC in the electrolyte is 13.4%, the mass content of PS is 3.7%, and the mass content of LiPO2F2 is 0.72%.

[0154] Example 3

[0155] The procedure was carried out in accordance with Example 1, except that the area S of the first surface of the battery, the battery thickness H, and the composition of the electrolyte were changed, specifically as follows: the area S of the first surface of the battery was 7081 mm². 2 The thickness H is 2.86 mm, and the ratio of the area to the thickness of the first surface S / H is 2476; the mass content of FEC in the electrolyte is 18.7%, the mass content of PS is 2.4%, and the mass content of LiPO2F2 is 0.25%.

[0156] Example 4 group

[0157] This set of examples is used to verify the impact of changes in "silicon-based materials".

[0158] This set of embodiments is based on Embodiment 1, except that the silicon-based material prepared in Embodiment 1 is adjusted as follows:

[0159] Example 4a: The silicon-carbon material prepared in Preparation Example 1 was replaced with the same mass of silicon-carbon material prepared in Preparation Example 2;

[0160] Example 4b: The silicon-carbon material prepared in Preparation Example 1 was replaced with the same mass of silicon-carbon material prepared in Preparation Example 3;

[0161] Example 4c: The silicon-carbon material prepared in Preparation Example 1 was replaced with the same mass of silicon-carbon material prepared in Preparation Example 4.

[0162] In Example 4d, the silicon-carbon material prepared in Preparation Example 1 was replaced with the same mass of silicon-carbon material prepared in Preparation Example 5a.

[0163] Example 4e: The silicon-carbon material prepared in Preparation Example 1 was replaced with the same mass of silicon-carbon material prepared in Preparation Example 5b.

[0164] In Example 4f, the silicon-carbon material prepared in Preparation Example 1 was replaced with the same mass of silicon-carbon material prepared in Preparation Example 6.

[0165] Example 5 group

[0166] This set of examples is used to verify the effect of changing the "ratio S / H of the first surface area to thickness of the battery".

[0167] This set of embodiments is based on Embodiment 1, except that the ratio S / H of the area of ​​the first surface to its thickness is adjusted by changing the area S of the first surface, as follows:

[0168] In Example 5a, the area S of the first surface of the battery is 2568 mm². 2 The thickness H is 3.18 mm, and the ratio of the area to the thickness of the first surface S / H is 808;

[0169] In Example 5b, the area S of the first surface of the battery is 9436 mm². 2 The thickness H is 3.16 mm, and the ratio of the area to the thickness of the first surface S / H is 2986.

[0170] Example 6

[0171] This was used to verify the impact of changes in the polar groups in the substrate layer of the diaphragm.

[0172] The procedure was carried out in accordance with Example 1, except that the composition of the substrate layer of the separator was changed and the thickness of the separator was increased (since the presence of polar groups can improve the mechanical strength of the separator, the thickness of the separator needs to be increased accordingly when there are no polar groups in the substrate layer), as detailed below:

[0173] The substrate layer of the diaphragm is a polyethylene film with a thickness of 8 μm; the thickness of H is 3.41 mm, and the ratio of the area to the thickness of the first surface is 1834.

[0174] Comparative Example 1

[0175] The procedure was carried out in accordance with Example 1, except that the silicon-carbon material prepared in Example 1 was replaced with the same mass of silicon-carbon material prepared in the comparative preparation example.

[0176] Comparative Example 2

[0177] The procedure is carried out in accordance with Example 1, except that the area S of the first surface of the battery is changed, specifically as follows: the area S of the first surface of the battery is 2047 mm². 2 The thickness H is 3.21 mm, and the ratio of the area to the thickness of the first surface S / H is 654.

[0178] Comparative Example 3

[0179] The procedure is carried out in accordance with Example 1, except that the thickness H of the battery is changed, specifically as follows: the area S of the first surface of the battery is 6256 mm². 2 The thickness H is 4.2 mm, and the ratio of the area to the thickness of the first surface S / H is 1490.

[0180] Test case

[0181] (1) Volumetric energy density test

[0182] The volumetric energy density of the batteries prepared in the examples and comparative examples was tested, and the specific testing methods are as follows:

[0183] At room temperature (25℃), using the LAND testing system:

[0184] 1- Charge at a constant current of 0.5C to 4.3V, then charge at a constant voltage of 0.02C, and let stand for 10 minutes;

[0185] 2- Discharge to 2.5V at 0.2C, let stand for 10 minutes, and record the charge during the discharge process as E;

[0186] 3- Charge the battery to 3.8V at 0.5C, measure the thickness of the battery using a PPG thickness gauge, and record it as c;

[0187] The volumetric energy density (VED) was calculated using the formula above, with units of Wh / L, where a, b, and c are the width, height, and thickness of the battery, respectively; the results are recorded in Table 1.

[0188] (2) Loop Test

[0189] The batteries prepared in the examples and comparative examples were subjected to cycle tests, and the specific test methods are as follows:

[0190] At high temperature (45℃), using the LAND testing system:

[0191] 1- Charge at a constant current of 2C to 4.3V, then charge at a constant voltage of 0.1C, and let stand for 10 minutes;

[0192] 2- Discharge to 2.5V at 0.7C and let stand for 10 minutes;

[0193] The weekly capacity retention rate of the battery was calculated based on the initial discharge capacity and weekly discharge capacity. Before the start of the cycle, the initial battery thickness was measured and recorded using a PPG thickness gauge. After every 100 cycles, the battery was fully charged, and the current thickness was measured again using the PPG thickness gauge. The thickness change rate was calculated based on the initial thickness. After 500 cycles, one battery was disassembled to measure the thickness of the SEI film on the surface of the silicon-based material. The results are recorded in Table 1. Figure 3 shows the SEM image of the negative electrode sheet of the battery in Example 1 after 500 cycles, and Figure 4 shows the SEM image of the negative electrode sheet of the battery in Comparative Example 1 after 500 cycles. It can be seen from the figures that the SEI film thickness on the surface of the silicon-carbon material in Example 1 is approximately 730 nm, while the SEI film thickness on the surface of the silicon-carbon material in Comparative Example 1 is approximately 1100 nm. The SEI film thickness on the surface of the silicon-carbon material in Example 1 is significantly smaller than that in Comparative Example 1. Furthermore, compared to the blocky silicon-carbon material in Comparative Example 1, the silicon-carbon material in Example 1 avoids sharp edges protruding and penetrating the separator, thus preventing self-discharge.

[0194] Table 1

[0195] As can be seen from Table 1, the battery disclosed herein, compared with the comparative example, can balance a thinner thickness, higher energy density, lower thickness expansion rate, and higher cycle stability.

[0196] The preferred embodiments of this disclosure have been described in detail above; however, this disclosure is not limited thereto. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in this disclosure and are all within the protection scope of this disclosure.

Claims

1. A battery, characterized in that, The battery includes a negative electrode, which is made of silicon-based material, and the sphericity of the silicon-based material is 0.66-0.

99. The ratio S / H of the area S of the first surface of the battery to the thickness H of the battery is 800-3000, and the unit of the area S of the first surface is mm. 2 The thickness H is in mm, and the first surface is the surface with the largest area among the six surfaces of the battery; the thickness H ≤ 3.5 mm.

2. The battery according to claim 1, characterized in that, The ratio of the area S of the first surface of the battery to the thickness H, S / H, is 1500-2500.

3. The battery according to claim 1 or 2, characterized in that, The sphericity of the silicon-based material is 0.8-0.

95.

4. The battery according to any one of claims 1-3, characterized in that, The silicon-based material has a recessed portion on its surface; Preferably, the number of recesses is 1 to 100; more preferably, it is 20 to 50. Preferably, the depth of the recess is 0.01μm-5μm; more preferably, it is 0.2μm-2μm. Preferably, the diameter of the recess is 0.1μm-5μm; more preferably, it is 0.3μm-3μm.

5. The battery according to any one of claims 1-4, characterized in that, The silicon-based material includes at least one of elemental silicon, silicon-carbon, silicon-oxygen, and silicon alloys; Preferably, the silicon-based material includes silicon-carbon.

6. The battery according to claim 5, characterized in that, The silicon-carbon structure includes a core-shell structure; the core of the core-shell structure includes a porous carbon matrix and silicon particles located in the internal channels of the porous carbon matrix, and the outer shell of the core-shell structure includes carbon material.

7. The battery according to claim 5 or 6, characterized in that, The average particle size of the silicon-carbon is 5μm-20μm.

8. The battery according to claim 6, characterized in that, The average particle size of the silicon particles is 0.1 nm-2000 nm; more preferably 1 nm-50 nm. And / or, the thickness of the outer shell is 2nm-20nm; more preferably 5nm-10nm.

9. The battery according to any one of claims 1-8, characterized in that, After 500 cycles at 45°C, with a charge / discharge cutoff voltage of 2.5V-4.3V, 2C charging, and 0.7C discharging, the average thickness of the SEI film on the surface of the silicon-based material is 500nm-1000nm; preferably 700nm-900nm.

10. The battery according to any one of claims 1-9, characterized in that, The battery further includes a separator, the separator comprising at least a substrate layer; the substrate layer having polar groups; the thickness of the separator being 3μm-9μm; Preferably, the polar group includes at least one of hydroxyl, carboxyl, and amino groups.

11. The battery according to any one of claims 1-10, characterized in that, The battery also includes an electrolyte, which includes at least one of fluoroethylene carbonate, sulfur-containing additives, and lithium difluorophosphate. Preferably, the fluoroethylene carbonate in the electrolyte contains 5%-25% by mass; Preferably, the sulfur-containing additive in the electrolyte has a mass content of 0.1%-5%; Preferably, the lithium difluorophosphate in the electrolyte has a mass content of 0.1%-1%.

12. The battery according to any one of claims 1-11, characterized in that, The ratio of the volumetric energy density of the battery to the thickness H is ≥240; the unit of the volumetric energy density is Wh / L, and the unit of the thickness H is mm.

13. The battery according to claim 5, characterized in that, The specific surface area of ​​the silicon-carbon is 0.1 m². 2 / g-10m 2 / g; And / or, the pore volume of the silicon carbide is 0.0005 cm³. 3 / g-0.002cm 3 / g.

14. The battery according to claim 5, characterized in that, The true density of the silicon-carbon is 1.5 g / cm³. 3 -2.4g / cm 3 .

15. The battery according to claim 5, characterized in that, The difference between the mass content of silicon on the surface of the silicon-carbon core and the mass content of silicon inside the silicon-carbon core is ≤10%.

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