Secondary battery and electronic apparatus

Abstract

A secondary battery and an electronic apparatus. The secondary battery comprises a negative electrode sheet, which comprises a silicon-based negative electrode material. The secondary battery satisfies: 0.3≤α≤0.8, wherein α represents the ratio of I1 to I2 in a differential capacity curve of the secondary battery, I1 represents the peak intensity of a characteristic peak of the differential capacity curve of the secondary battery at 3.9±0.05 V, and I2 represents the peak intensity of a characteristic peak of the differential capacity curve of the secondary battery at 3.75±0.05 V. Therefore, the present application enables the secondary battery to have a certain cycle performance and expansion performance, and also facilitates an improvement in the reversible capacity, high-temperature storage performance and volumetric energy density of the secondary battery.

Description

Secondary battery and electronic device TECHNICAL FIELD

[0001] The present application relates to the field of electrochemical energy storage, and in particular to a secondary battery and an electronic device. BACKGROUND

[0002] Graphite is the most widely used negative electrode material, which has the advantages of high efficiency, stable charge and discharge platform, etc. However, the lower specific capacity hinders the further application of graphite. Compared with graphite, elemental silicon is considered as an ideal negative electrode material that can replace graphite due to its higher theoretical specific capacity and suitable working voltage.

[0003] However, as a semiconductor material, silicon has low electrical conductivity and will experience a huge volume expansion during alloying / de-alloying, resulting in poor cycle performance and high-temperature storage performance of the secondary battery.

[0004] SUMMARY

[0005] The present application provides a secondary battery and an electronic device.

[0006] The first aspect of the present application provides a secondary battery, comprising a negative electrode sheet, the negative electrode sheet comprising a silicon-based negative electrode material. The secondary battery satisfies: 0.3≤α≤0.8, α represents the ratio of I1 and I2 in the differential capacity curve of the secondary battery, I1 represents the peak intensity of the characteristic peak of the differential capacity curve of the secondary battery at 3.9±0.05V, and I2 represents the peak intensity of the characteristic peak of the differential capacity curve of the secondary battery at 3.75±0.05V.

[0007] In the present application, the dQ / dV curve of the secondary battery during charging has redox peaks at 3.9±0.05V and 3.75±0.05V, which can reflect the electrochemical reaction occurring in the secondary battery. The ratio α of I1 and I2 can reflect the size of the reversible capacity of the secondary battery. When the α value is within the above range, the occurrence of lithium extraction is facilitated, the internal dynamics of the secondary battery is good, thereby facilitating the improvement of the reversible capacity of the secondary battery, and also reducing the volume expansion effect, and also facilitating the reduction of the occurrence of interface side reactions and the loss of active lithium, reducing the internal resistance of the secondary battery during charging and discharging, thereby facilitating the improvement of the rate performance, cycle performance, expansion performance and high-temperature storage performance of the secondary battery, and further facilitating the simultaneous improvement of the reversible capacity, high-temperature storage performance and volume energy density of the secondary battery when the secondary battery has good cycle performance and expansion performance.

[0008] Based on the first aspect, in some embodiments, 0.41≤α≤0.7. This is conducive to further simultaneously improving the rate performance, cycle performance, expansion performance and high-temperature storage performance of the secondary battery.

[0009] In some embodiments based on the first aspect, 0.35≤I3 / I2≤0.66, I3 represents the peak intensity of the characteristic peak of the differential capacity curve of the lithium stripping of the secondary battery at 3.82±0.05 V. This is conducive to further improving the cycle performance and swelling performance of the secondary battery.

[0010] In some embodiments based on the first aspect, along the thickness direction of the negative electrode tab, the region 1.5 μm inward from the edge of the section of the silicon-based negative electrode material is a first region, and the region 1.5 μm outward from the center of the section of the silicon-based negative electrode material is a second region. The difference between the content of silicon in the first region and the second region is less than 10% based on the mass of the silicon-based negative electrode material. By measuring the content of silicon in the first region and the second region respectively, and calculating the difference T between the content of silicon in the first region and the second region, the distribution of silicon in the silicon-based negative electrode material can be reflected. When the difference between the content of silicon in the first region and the second region is within the above range, the silicon is uniformly distributed in the silicon-based negative electrode material, which is conducive to improving the uniformity of lithium ion transmission, fully utilizing the contribution of silicon, improving the reversible capacity of the secondary battery, and also improving the uniformity of the overall stress of the silicon-based negative electrode material during charging and discharging, and improving the interface stability of the silicon-based negative electrode material, so as to improve the first coulomb efficiency, energy density, cycle performance and swelling performance of the secondary battery.

[0011] In some embodiments based on the first aspect, the content of silicon is 20 wt% to 60 wt% based on the mass of the silicon-based negative electrode material. This is conducive to fully utilizing the capacity contribution of silicon in the silicon-based negative electrode material, and also conducive to relieving the volume expansion of the silicon-based negative electrode material during charging and discharging, so that the secondary battery has excellent specific capacity, cycle performance and swelling performance.

[0012] In some embodiments based on the first aspect, the particle size Dv10 of the silicon-based negative electrode material is 2.0 μm to 7.0 μm, and the particle size Dv99 is 12.0 μm to 26.0 μm. This is conducive to making the silicon-based negative electrode material have a suitable specific surface area, and shortening the transmission path of electrons and lithium ions, so as to improve the first coulomb efficiency and kinetic performance of the secondary battery.

[0013] In some embodiments based on the first aspect, the compaction density of the negative electrode tab under a mass of 5 tons is 1.5 g / cm 3 to 1.9 g / cm 3 . This is conducive to making the contact between the silicon-based negative electrode materials in the negative electrode tab more close, increasing the electron conduction and rapid movement of lithium ions, reducing the degree of discharge polarization of the secondary battery, and improving the large-current discharge and rate performance of the secondary battery.

[0014] In some embodiments of the first aspect, the particle elastic modulus of the silicon-based negative electrode material is 3 GPa to 6 GPa. This helps to improve the pressure resistance of the silicon-based negative electrode material, improve the compaction density of the silicon-based negative electrode material and the structural stability of the silicon-based negative electrode material, thereby helping to improve the energy density and cycle performance of the secondary battery.

[0015] In some embodiments of the first aspect, the silicon-based negative electrode material comprises a porous carbon matrix, the volume fraction of ultramicropores in the porous carbon matrix is 7% or less, the volume fraction of micropores in the porous carbon matrix is 80% to 92%, and the pore volume of the porous carbon matrix is 0.6 cm 3 / g to 1.0 cm 3 / g. The volume fraction of ultramicropores, the volume fraction of micropores and the pore volume in the porous matrix are in a suitable range, which helps to further improve the cycle performance, rate performance and swelling performance of the silicon-based negative electrode material.

[0016] In some embodiments of the first aspect, the size of the silicon grains in the silicon-based negative electrode material is 0.5 nm to 4 nm. This helps to reduce the volume expansion of the silicon grains in the silicon-based negative electrode material during the charging and discharging process, reduces the cracking or pulverization of the negative electrode sheet, makes the silicon-based negative electrode material have good electrical conductivity, reduces the internal resistance of the negative electrode sheet, and helps to improve the cycle performance and swelling performance of the secondary battery and reduce the internal resistance of the secondary battery.

[0017] In some embodiments of the first aspect, the negative electrode sheet comprises a negative electrode active material, the negative electrode active material comprises the silicon-based negative electrode material and graphite, and the mass fraction of the silicon-based negative electrode material in the negative electrode active material is 2% to 20%. The cooperation of the added graphite and the silicon-based negative electrode material helps to alleviate the volume expansion of the negative electrode active material as a whole, improves the stability and rate performance of the negative electrode active material; the mass fraction of the silicon-based negative electrode material is in the above range, which helps to improve the energy density of the secondary battery while improving the swelling performance of the secondary battery. In some embodiments, the graphite comprises at least one of natural graphite and artificial graphite.

[0018] In some embodiments of the first aspect, at 25±1°C, using 3C step charging and 0.5C discharging, when the number of charging and discharging cycles of the secondary battery is greater than or equal to 500 cycles, the ratio of the swelling rate of the negative electrode sheet to the swelling rate of the secondary battery is 0.4 to 3.5. The ratio of the swelling rates of the above negative electrode sheet and the secondary battery can reflect the influence of the swelling rate of the negative electrode sheet on the swelling rate of the secondary battery, and in this range, the influence of the swelling rate of the negative electrode sheet on the secondary battery is small during the cycle charging and discharging process of the secondary battery, thereby improving the cycle performance and swelling performance of the secondary battery.

[0019] The second aspect of the present application provides an electronic device comprising a secondary battery. In the secondary battery, a represents the ratio of I1 and I2 in the dQ / dV curve of the secondary battery, and a is in a suitable range, which is beneficial to improving the reversible capacity, high-temperature storage performance and volume energy density of the secondary battery when the secondary battery has good cycle performance and expansion performance, thereby improving the service life, charging and discharging efficiency and high-temperature performance applicability of the electronic device. BRIEF DESCRIPTION OF DRAWINGS

[0020] The above and / or additional aspects and advantages of the present application will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings, in which:

[0021] FIG. 1 is a differential capacity curve of a secondary battery prepared in Example 1.

[0022] FIG. 2 is a scanning electron microscope image of a silicon-based negative electrode material prepared in Example 1.

[0023] FIG. 3 is a cross-section of a silicon-based negative electrode material in Example 1, and an elemental distribution energy spectrum map of silicon elements on the cross-section.

[0024] FIG. 4 is an X-ray diffraction pattern of a silicon-based negative electrode material prepared in Example 1.

[0025] FIG. 5 is a differential capacity curve of a secondary battery prepared in Comparative Example 3. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Unless otherwise defined, all the technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing the specific embodiments and are not intended to limit the present application.

[0027] Hereinafter, the embodiments of the present application will be described in detail. However, the present application can be embodied in many different forms, and should not be interpreted as being limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided so that the present application can be thoroughly and completely conveyed to those skilled in the art.

[0028] An embodiment of the present application provides a secondary battery, which comprises a shell, an electrode assembly and an electrolyte. The electrode assembly and the electrolyte are both located in the shell.

[0029] The shell can be a packaging bag obtained by packaging with a packaging film (such as an aluminum plastic film), such as a soft package battery. In other embodiments, the secondary battery can also be a steel shell battery, an aluminum shell battery, etc.

[0030] The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator disposed between the positive and negative electrode. The electrode assembly can be a stacked structure, formed by layering the positive electrode, separator, and negative electrode. In other embodiments, the electrode assembly can also be a wound structure, formed by winding the stacked positive electrode, separator, and negative electrode.

[0031] Negative electrode sheet

[0032] The negative electrode includes silicon-based negative electrode materials. The secondary battery satisfies: 0.3 ≤ α ≤ 0.8, where α represents the ratio of I1 to I2 in the differential capacity curve of the secondary battery, i.e., I1 / I2. I1 represents the peak intensity of the characteristic peak of the differential capacity curve of the secondary battery at 3.9 ± 0.05 V, and I2 represents the peak intensity of the characteristic peak of the differential capacity curve of the secondary battery at 3.75 ± 0.05 V.

[0033] The first derivative of the constant-current charging capacity Q of the secondary battery with respect to voltage V is calculated, and then plotted against voltage V to obtain the differential capacity curve (dQ / dV curve). Figure 1 shows the differential capacity curve of the secondary battery in Example 1. The differential capacity curve reflects the capacity contained in the secondary battery within a unit voltage range. If the capacity is high at a certain voltage plateau, it means that a large amount of capacity is contributed within a very small voltage fluctuation range, which will show a characteristic peak on the curve. Each characteristic peak represents an electrochemical reaction.

[0034] In this application, the dQ / dV curve of the secondary battery exhibits redox peaks at 3.9±0.05V and 3.75±0.05V, reflecting the electrochemical reactions occurring in the secondary battery. The ratio α of I1 to I2 reflects the reversible capacity of the secondary battery. An α value within the aforementioned range favors lithium insertion / extraction, resulting in good internal kinetic performance of the secondary battery, thus improving its reversible capacity. Furthermore, it reduces volume expansion, minimizes interfacial side reactions and active lithium loss, and reduces internal resistance during charge / discharge. This improves the rate performance, cycle performance, expansion performance, and high-temperature storage performance of the secondary battery. Consequently, while achieving good cycle and expansion performance, it also simultaneously enhances the reversible capacity, high-temperature storage performance, and volumetric energy density of the secondary battery.

[0035] If α is large, the I1 / I2 ratio is large, resulting in less lithium intercalation in the silicon-based anode material, which is detrimental to capacity utilization and reduces the energy density of the secondary battery. If α is small, the I1 / I2 ratio is small, leading to significant volume expansion during lithium intercalation. This makes the silicon-based anode material prone to cracking, allowing electrolyte to penetrate and etch the material, resulting in severe interfacial side reactions, increased internal resistance, and increased consumption of active lithium, thus affecting the cycle performance, expansion performance, rate performance, and specific capacity of the secondary battery. In some embodiments, α can be 0.3, 0.35, 0.39, 0.4, 0.41, 0.45, 0.49, 0.53, 0.56, 0.59, 0.62, 0.66, 0.7, 0.71, 0.75, 0.79, 0.8, or any value within the range of any two of the above values.

[0036] In some embodiments, 0.41≤α≤0.7 is beneficial for further improving the rate performance, cycle performance, expansion performance and high-temperature storage performance of the secondary battery simultaneously.

[0037] In some embodiments, 0.36 ≤ I3 / I2 ≤ 0.60, where I3 represents the peak intensity of the characteristic peak of the dQ / dV curve of the secondary battery at 3.82 ± 0.05 V. The I3 / I2 ratio also affects the specific capacity, cycle performance, and expansion performance of the silicon-based anode material. An I3 / I2 ratio within the above range is beneficial for maintaining good specific capacity, cycle performance, and expansion performance of the silicon-based anode material. If the I3 / I2 ratio is large, the specific capacity of the silicon-based anode material is small, which is detrimental to improving the energy density of the secondary battery. If the I3 / I2 ratio is small, the silicon-based anode material will experience significant volume expansion during lithium intercalation, which will reduce the cycle performance and expansion performance of the secondary battery. In some embodiments, the I3 / I2 ratio can be 0.36, 0.4, 0.43, 0.46, 0.5, 0.53, 0.56, 0.6, or any value within the range of any two of the above values.

[0038] In some embodiments, the negative electrode sheet is sliced ​​along its thickness direction. The region 1.5 μm inward from the edge of the cut surface of the silicon-based negative electrode material is designated as the first region, and the region 1.5 μm outward from the center of the cut surface of the silicon-based negative electrode material is designated as the second region. Based on the mass of the silicon-based negative electrode material, the difference T between the silicon content in the first region and the second region is less than 10%.

[0039] The silicon content in the first and second regions described above can be tested using a scanning electron microscope (SEM), as shown in Figure 3. By measuring the silicon content in the first and second regions of the silicon-based anode material using SEM and calculating the difference T between them, the distribution of silicon in the anode material can be observed. The silicon content in the first region is greater than or equal to that in the second region, or the silicon content in the second region is greater than that in the first region. When the difference T between the silicon content in the first and second regions is within this range, silicon is uniformly distributed in the silicon-based anode material. This is beneficial for improving the uniformity of lithium-ion transport, fully utilizing the contribution of silicon in the anode material, increasing the reversible capacity of the secondary battery, increasing the lithium-ion transport rate, and also improving the uniformity of the overall stress on the silicon-based anode material during charging and discharging, as well as improving the interfacial stability of the silicon-based anode material. Ultimately, this contributes to improving the initial coulombic efficiency, energy density, cycle performance, and expansion performance of the secondary battery. In some embodiments, the difference T between the silicon content in the first region and the second region can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 9.5%, or any value within the range of any two of the above values.

[0040] In some embodiments, the silicon content is between 20 wt% and 60 wt% based on the mass of the silicon-based anode material. A silicon content within this range is beneficial for fully utilizing the capacity contribution of silicon in the silicon-based anode material and also helps mitigate the volume expansion of the silicon-based anode material during charge and discharge, resulting in a secondary battery with excellent specific capacity, cycle performance, and expansion resistance. In some embodiments, the silicon content can be 20 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, or any value within the range of any two of the above values.

[0041] In some embodiments, the particle size Dv10 of the silicon-based anode material is 2.0 μm to 7.0 μm, and the particle size Dv99 is 12.0 μm to 26.0 μm. The particle size distribution range of Dv10 and Dv99 within this range is beneficial for the silicon-based anode material to have a suitable specific surface area and for shortening the electron and lithium-ion transport paths, thereby improving the initial coulombic efficiency and kinetic performance of the secondary battery. Simultaneously, Dv10 within this suitable particle size distribution range also facilitates the filling of the gaps between the smaller silicon-based anode material particles with larger particle sizes, increasing the compaction density of the anode sheet and thus improving the volumetric energy density of the secondary battery. Furthermore, the particle size distribution range of Dv10 and Dv99 within this suitable range also improves the uniform dispersion of the configured anode slurry. In some embodiments, the particle size Dv10 of the silicon-based anode material can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, or any value within the range of any two of the above values. The particle size Dv99 of the silicon-based anode material can be 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, or any value within the range of any two of the above values.

[0042] Wherein, Dv10 represents the particle size that, in the volume-based particle size distribution of silicon-based anode materials, reaches 10% of the total volume from the smallest particle size, that is, the volume of silicon-based anode materials smaller than this particle size accounts for 10% of the total volume of silicon-based anode material particles. DV99 represents the particle size that, in the volume-based particle size distribution of silicon-based anode materials, reaches 99% of the total volume from the smallest particle size.

[0043] In some embodiments, the compaction density of the negative electrode sheet at a mass of 5 tons is 1.5 g / cm³. 3 Up to 1.9 g / cm 3 This design facilitates closer contact between the silicon-based negative electrode material and the negative electrode sheet, increasing electron conduction and the rapid movement of lithium ions, reducing the polarization degree of the secondary battery during discharge, and improving the high-current discharge capability of the secondary battery. Furthermore, in secondary batteries, it helps maintain the electrolyte level within a suitable range, allowing for proper electrolyte wetting of both the positive and negative electrode sheets, reducing the decomposition and gas generation of excess electrolyte during charging and discharging, improving the contact between the positive and negative electrode sheets, and enhancing the cycle performance and safety of the secondary battery. In some embodiments, the compaction density of the negative electrode sheet at a mass of 5 tons is 1.5 g / cm³. 3 1.6g / cm 3 1.7g / cm 3 1.8g / cm 3 1.9g / cm3 Or it can be any value within the range of any of the above numerical values.

[0044] In some embodiments, the particle elastic modulus of the silicon-based anode material is between 3 GPa and 6 GPa. This is beneficial for improving the voltage resistance, compaction density, and structural stability of the silicon-based anode material, thereby improving the energy density and cycle performance of the secondary battery. In some embodiments, the particle elastic modulus of the silicon-based anode material can be 3 GPa, 4 GPa, 5 GPa, 6 GPa, or any value within the range of any of the above values.

[0045] In some embodiments, the silicon-based anode material comprises a porous carbon matrix. The volume fraction of ultramicropores (pore size less than or equal to 0.7 nm) in the porous carbon matrix is ​​less than 7%, the volume fraction of micropores (pore size less than or equal to 2 nm) in the porous carbon matrix is ​​80% to 92%, and the pore volume of the porous carbon matrix is ​​0.6 cm³. 3 / g to 1.0cm 3 / g. In porous carbon matrices, a suitable range of the volume ratio of micropores, the volume ratio of micropores, and the size of the pores ensures uniform silicon deposition, promotes silicon capacity utilization, and improves the cycle performance, rate performance, and expansion performance of silicon-based anode materials. A high volume ratio of micropores in a porous carbon matrix hinders silicon deposition, affecting the amount of silicon deposited and consequently impacting the cycle performance, rate performance, and expansion performance of the secondary battery. Similarly, a low volume ratio of micropores, as the primary sites for silicon deposition, also hinders silicon deposition. Low pore volumes in porous carbon matrices limit the available space for silicon, further reducing the amount of silicon deposited. Conversely, high pore volumes result in a porous carbon matrix with a loose carbon skeleton, making it prone to cracking under stress (such as the force generated by silicon volume expansion during charging and discharging in a secondary battery). This reduces the voltage withstand capability of the silicon-based anode material and affects its stability.

[0046] In some embodiments, the size of the silicon grains in the silicon-based anode material is from 0.5 nm to 4 nm. A suitable size range for the silicon grains helps reduce the volume expansion of the silicon grains during charge and discharge, reducing cracking or pulverization of the anode sheet. This results in good conductivity of the silicon-based anode material, reduces the internal resistance of the anode sheet, and improves the cycle performance and expansion performance of the secondary battery, while also reducing its internal resistance. In some embodiments, the size of the silicon grains in the silicon-based anode material is 0.5 nm, 0.7 nm, 0.8 nm, 1 nm, 1.2 nm, 1.5 nm, 1.7 nm, 1.9 nm, 2.3 nm, 2.7 nm, 2.8 nm, 3 nm, 3.2 nm, 3.5 nm, 3.7 nm, 3.8 nm, 4 nm, or any value within a range of the above values.

[0047] In some embodiments, the negative electrode sheet includes a negative electrode active material, which includes a silicon-based negative electrode material and graphite. Based on the mass of the negative electrode active material, the mass percentage of the silicon-based negative electrode material is 2% to 20%, and the mass percentage of graphite is 80% to 98%. Graphite has a certain degree of flexibility, and the addition of graphite, combined with the silicon-based negative electrode material, helps to alleviate the overall volume expansion of the negative electrode active material and improve its stability and rate performance. The mass percentage of the silicon-based negative electrode material within the above range helps to improve the expansion performance of the secondary battery while increasing its energy density. In some embodiments, the mass percentage of the silicon-based negative electrode material in the negative electrode active material can be 2%, 3%, 5%, 7%, 10%, 12%, 14%, 17%, 20%, or any value within the range of any of the above values. The mass percentage of graphite can be 80%, 82%, 85%, 87%, 90%, 92%, 95%, 98%, or any value within the range of any of the above values.

[0048] In some implementations, graphite includes at least one of natural graphite and synthetic graphite.

[0049] In some embodiments, at 25±1℃, using 3C stepped charging and 0.5C discharging, when the number of charge-discharge cycles of the secondary battery is greater than or equal to 500 cycles, the ratio of the expansion rate of the negative electrode to the expansion rate of the secondary battery is 0.4 to 3.5. This ratio of the expansion rate of the negative electrode to the secondary battery reflects the influence of the expansion rate of the negative electrode on the expansion rate of the secondary battery. Within this range, the influence of the expansion rate of the negative electrode on the secondary battery is minimized during the cyclic charge-discharge process, thereby improving the cycle performance and expansion performance of the secondary battery. In some embodiments, the ratio of the expansion rate of the negative electrode to the expansion rate of the secondary battery can be 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.5, 2.6, 2.8, 3, 3.2, 3.5, or any value within the range of any of the above values.

[0050] The preparation method of the silicon-based anode material in this application includes:

[0051] (1) Preparation of porous carbon matrix: The carbonized porous carbon raw material is activated, for example, using potassium hydroxide. A mixture of potassium hydroxide and the carbonized porous carbon raw material at a mass ratio of (3–3.5):1 is used for activation at a reaction temperature of 600℃–950℃ and a reaction time of 1.0 h–2.5 h, yielding a pore volume greater than 0.55 cm³. 3 / g porous carbon matrix.

[0052] Porous carbon raw materials can be selected from at least one of biochar, resin carbon, or coke.

[0053] (2) First deposition of silicon: Dry the porous carbon matrix prepared in step (1), place the treated porous carbon material in a chemical vapor deposition furnace, heat it to 450℃~500℃ under argon protective atmosphere, introduce a mixture of silane / carbon source (volume ratio of silane and carbon source 4:1) under a slightly positive gas phase pressure, and introduce argon at 10L / min as an inert gas. In the mixed gas and argon atmosphere, the volume ratio of silane / carbon source is 5%~30%, set the total gas flow rate to 10.5L / min~13L / min and continue the reaction for 1h~4h, so that the elemental nano-silicon and carbon buffer medium are adsorbed and deposited in the porous carbon pores.

[0054] (3) Secondary silicon deposition: In the same chemical vapor deposition furnace, the temperature inside the deposition furnace is reduced to 360-450°C under the protective atmosphere of argon. Under the slightly positive pressure of the gas phase, silane is used as the silicon source and argon is introduced at a rate of 10 L / min as the inert gas. In the mixed gas composed of silane and argon, the volume ratio of silane is 8%-50%. The total gas flow rate is set to 8.6 L / min-16 L / min and the reaction is continued for 5-12 hours, so that the elemental nano-silicon is adsorbed and deposited in the porous carbon pores.

[0055] (4) Preparation of carbon coating layer: In the same chemical vapor deposition furnace, continue to heat to 500℃~650℃ under argon protective atmosphere, and introduce a mixed gas containing argon with a carbon source ratio of 20%~100% under slightly positive gas phase pressure. Set the total gas flow rate to 1L / min~20L / min and continue the reaction for 3h~9h, so that acetylene-derived carbon is deposited on the outer surface of the material described in step 3) and forms a carbon coating layer.

[0056] 5) Grind and sieve the deposited sample obtained in step 4) to obtain silicon-based anode material.

[0057] The carbon source is alkynes such as acetylene and propyne, olefins such as ethylene and propylene, and alkanes such as methane and hexane, as well as mixtures of these gases.

[0058] In the above-described process for preparing silicon-based anode materials, the porous carbon matrix undergoes two silicon deposition processes in a chemical vapor deposition furnace. During the second silicon deposition process, the reaction temperature is lowered to slow down the decomposition of silane and improve the uniformity of elemental silicon deposition on the porous carbon matrix, which is beneficial for improving the cycle performance and expansion performance of the silicon-based anode material.

[0059] In the above preparation method, the pore volume of the porous carbon matrix, the flow rate and time of the first silane / carbon source mixed gas, and the temperature and time of the second deposition of elemental silicon are all related to the α ratio in the secondary battery assembled with silicon-based anode material as the anode active material. The introduction of the first silane / carbon source mixed gas can add a buffer medium (such as silicon carbide) to the pores of the porous carbon matrix. If the flow rate of the first silane / carbon source mixed gas is high or the introduction time is long, the α value will decrease, which will significantly reduce the amount of silicon deposited in the second deposition, which is not conducive to improving the specific capacity of the silicon-based anode material.

[0060] The pore volume of the porous carbon matrix, the temperature of the second silicon deposition, and the deposition time all affect the amount and uniformity of silicon deposition. Increasing the temperature or extending the deposition time decreases the α value, potentially increasing the amount of silicon deposited or causing uneven deposition, leading to increased volume expansion or uneven stress on the silicon-based anode material. If the pore volume of the porous carbon matrix is ​​large, the α value decreases, increasing the silicon content and resulting in greater volume expansion of silicon during charge and discharge. This increases the forces acting on the porous carbon matrix framework, reducing the stress on the silicon-based anode material and making the cycle performance and expansion performance of the secondary battery more prone to degradation, as well as reducing high-temperature storage performance. Conversely, if the pore volume of the porous carbon matrix is ​​too small, the second silicon deposition temperature is too low, and the deposition time is too short, the α value increases, reducing the amount of silicon deposited. This results in a low specific capacity of the silicon-based anode material, which is detrimental to improving the energy density of the secondary battery.

[0061] In some embodiments, the negative electrode sheet further includes a negative current collector, which includes: copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.

[0062] In some embodiments, the negative electrode active material further includes a binder and a conductive agent. In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0063] In some embodiments, the conductive agent includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0064] Positive electrode sheet

[0065] The positive electrode sheet includes a positive current collector and a positive active material layer. The positive active material layer includes a positive active material, a binder, and a conductive agent.

[0066] According to some embodiments of this application, the positive current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used. The composite current collector can be formed by forming a metallic material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate.

[0067] According to some embodiments of this application, the positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel manganese aluminum oxide, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel-type lithium manganese oxide, spinel-type lithium nickel manganese oxide, and lithium titanate. The positive electrode sheet in the secondary battery includes at least one of lithium cobalt oxide or ternary positive electrode material. Preferably, the positive electrode active material includes lithium cobalt oxide or lithium nickel cobalt manganese oxide.

[0068] In some embodiments, the binder comprises an adhesive polymer, such as at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber, or polyurethane. In some embodiments, the polyolefin binder comprises at least one of polyethylene, polypropylene, polyolefin ester, polyenol, or polyacrylic acid. In some embodiments, the conductive agent comprises a carbon-based material, such as carbon black, acetylene black, Ketjen black, or carbon fiber; a metal-based material, such as metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; a conductive polymer, such as a polyphenylene derivative; or a mixture thereof.

[0069] Separating membrane

[0070] The material and shape of the separator used in the secondary battery of this application are not particularly limited, and can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0071] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be selected.

[0072] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixture of polymer and inorganic materials. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate.

[0073] The binder is selected from at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer contains a polymer, the polymer material of which is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0074] electrolyte

[0075] According to some embodiments of this application, the electrolyte includes an organic solvent, a lithium salt, and optional additives.

[0076] The organic solvent in the electrolyte of this application may be any organic solvent known in the prior art that can be used as an electrolyte solvent. There are no limitations on the electrolyte used in the electrolyte according to this application; it may be any electrolyte known in the prior art. The additives in the electrolyte according to this application may be any additives known in the prior art that can be used as electrolyte additives. In some embodiments, the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), or ethyl propionate.

[0077] In some embodiments, the organic solvent includes ether solvents, such as at least one selected from 1,3-dioxapentane (DOL) and dimethyl glycol ether (DME). In some embodiments, the lithium salt includes at least one selected from organic lithium salts or inorganic lithium salts. In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(fluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalatoborate)borate LiB(C2O4)2 (LiBOB), or lithium difluorooxalatoborate LiBF2(C2O4) (LiDFOB). In some embodiments, the additive includes at least one selected from fluoroethylene carbonate and adiponitrile.

[0078] According to some embodiments of this application, the secondary battery of this application includes, but is not limited to, lithium-ion batteries or sodium-ion batteries. In some embodiments, the secondary battery includes a lithium-ion battery.

[0079] This application also applies secondary batteries to electronic devices to power loads within those devices. The aforementioned electronic devices include secondary batteries that satisfy the following condition: 0.3 ≤ α ≤ 0.8, where α represents the ratio of I1 to I2 in the dQ / dV curve of the secondary battery. A suitable α value is beneficial for improving the specific capacity, cycle performance, expansion performance, high-temperature storage performance, and volumetric energy density of the secondary battery, thereby enhancing the lifespan, charge / discharge efficiency, and high-temperature suitability of the electronic device.

[0080] The electronic devices or apparatus described in this application are not particularly limited. In some embodiments, the electronic devices described in this application include, but are not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0081] The present application will be described below through specific embodiments and comparative examples. Those skilled in the art should understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0082] Example 1

[0083] Preparation of silicon-based anode materials:

[0084] 1) Potassium hydroxide and carbonized porous carbon raw material were mixed at a mass ratio of 3.2:1 and activated at a reaction temperature of 780℃ for 1.5 h to obtain a pore volume of 0.85 cm³. 3 / g of porous carbon.

[0085] 2) Dry the porous carbon obtained in step 1). Place the dried porous carbon material in a chemical vapor deposition furnace and heat it to 460°C under an argon protective atmosphere. A mixture of silane / acetylene (volume ratio of 4:1) is introduced under a slightly positive gas phase pressure. Argon is introduced at a flow rate of 10 L / min as an inert gas. In the atmosphere of the mixed gas and argon, the volume ratio of silane / acetylene is 6%. The total gas flow rate is set to 10.6 L / min and the reaction is continued for 1.5 h to allow elemental nano-silicon and carbon buffer medium to be adsorbed and deposited in the pores of the porous carbon.

[0086] 3) In the same chemical vapor deposition furnace, the argon protective atmosphere is lowered to 420°C. Under a slightly positive gas phase pressure, silane is used as the silicon source, and argon gas is introduced at a rate of 10 L / min as an inert gas. In the atmosphere of silane and argon, the volume ratio of silane is 20%. The total gas flow rate is set to 12.5 L / min and the reaction is continued for 9 hours, so that elemental nano-silicon is adsorbed and deposited in the porous carbon pores.

[0087] 4) In the same chemical vapor deposition furnace, continue to heat to 550°C under an argon protective atmosphere, and introduce a mixed gas containing argon with 50% acetylene carbon source under a slightly positive gas phase pressure. Set the total gas flow rate to 5 L / min and continue the reaction for 5.6 h to allow acetylene-derived carbon to be deposited on the outer surface of the material described in step 3) and form a carbon coating layer.

[0088] 5) Grind and sieve the deposited sample obtained in step 4) to obtain silicon-based anode material.

[0089] Preparation of lithium-ion batteries:

[0090] (1) Preparation of the positive electrode sheet: LiCoO2, conductive carbon black, and polyvinylidene fluoride (PVDF) were thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of approximately 95%:2.5%:2.5% to obtain a positive electrode slurry. The obtained positive electrode slurry was coated onto a positive electrode current collector aluminum foil, dried, and cold-pressed to obtain the positive electrode. The compacted density was 3.3 g / cm³. 3 Moisture content must be ≤200ppm.

[0091] (2) Preparation of negative electrode sheet: artificial graphite, silicon-based negative electrode material, conductive agent (conductive carbon black), Artificial graphite and silicon-based anode material are mixed in a weight ratio of approximately 77%:8%:5%:10% (artificial graphite: silicon-based anode material = 16:1 to 13:4), and an appropriate amount of water is added. The mixture is kneaded until the solid content is approximately 55-70 wt%. An appropriate amount of water is added to adjust the viscosity of the slurry to approximately 5000 Pa·s, thus preparing the anode slurry. The prepared anode slurry is coated onto the copper foil of the anode current collector, dried, and cold-pressed to obtain the anode sheet. The compacted density is 1.65 g / cm³. 3Moisture content must be ≤200ppm.

[0092] (3) Preparation of electrolyte: Under dry argon atmosphere, LiPF6 was added to a solvent composed of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) in a weight ratio of about 1:1:1 and mixed evenly. The concentration of LiPF6 was about 1.15 mol / L. Then, about 12.5 wt% of fluoroethylene carbonate (FEC) was added and mixed evenly to obtain the electrolyte.

[0093] (4) Preparation of the separator: PE film is used as the separator.

[0094] (5) Preparation of lithium-ion batteries: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain bare cells. The bare cells are placed in outer packaging, electrolyte is injected, and the packaging is completed. After formation, degassing, and edge trimming processes, a lithium-ion full battery is obtained.

[0095] Examples 2 to 13

[0096] Examples 2 to 13 are largely the same as Example 1, except that the preparation method of silicon-based anode material was adjusted according to Table 1 to obtain different silicon-based anode materials. The relevant test data of silicon-based anode materials and lithium-ion batteries are shown in Tables 2 to 3.

[0097] Comparative Examples 1 to 7

[0098] Comparative Examples 1 to 7 are largely the same as Example 1, except that the preparation method of the silicon-based anode material was adjusted according to Table 1. The relevant test data of the silicon-based anode material and the lithium-ion battery are shown in Tables 2 to 3.

[0099] Table 1

[0100] The particle elastic modulus, scanning electron microscopy (SEM) values, Dv10 / Dv99, silicon grain size, and pore volume of the silicon-based anode materials prepared in Examples 1 to 13 and Comparative Examples 1 to 7 were measured. The test data are recorded in Tables 2 and 3.

[0101] Test method:

[0102] (1) Elastic modulus of particles

[0103] The hardness and elastic modulus of individual silicon-based anode material particles were tested using a nanoindenter (Hysitron TI 950), according to the JB / T 12721-2016 standard. Before testing, the silicon-based anode material powder was dispersed in epoxy resin and cured. The cured resin was then cut using ion polishing, and individual particles were indented using a nanoindenter. The indentation depth on the particle surface was monitored, and the elastic modulus of the particle was calculated. The elastic modulus of five particles from the same sample were tested in parallel, and the average value was taken to obtain the particle elastic modulus of the silicon-based anode material.

[0104] (2) Point scanning electron microscopy energy dispersive spectroscopy of the cross section

[0105] Silicon-based anode material, binder (PAA), and deionized water were mixed in a mass ratio of 5:4:8 to form an electrode sheet. After drying, the electrode sheet was cut into a cross-section using ion polishing. This cross-section was then used as the test section of the sample and transferred to a field emission scanning electron microscope (FET) for focusing and testing. During testing, at least 10 points were taken on the cross-section within 1.5 μm of the outer surface of the particle, and another 1.5 μm from the center of the cross-section to the outer surface. The silicon content in the silicon-based anode material was measured, and the scanned values ​​were then averaged. The difference in silicon content between the two average values ​​was obtained by subtracting the average values ​​from each.

[0106] (3) Characterization methods for Dv10 and Dv99

[0107] Add 0.02g of the silicon-based anode material powder sample from each example and comparative example to a 50ml clean beaker, add 20ml of deionized water, and then add a surfactant to completely disperse the powder sample in the water. Sonicate in a 120W ultrasonic cleaner for 5 minutes. Use a MasterSizer 2000 device to test the silicon-based anode material from a detection angle of 0° to 135°. According to the particle size distribution laser diffraction method GB / T 19077-2016, the particle size distribution is measured. In the volume-based particle size distribution of the material, starting from the smallest particle size, the particle size reaching 10% of the volume accumulation is Dv10, and the particle size reaching 99% of the volume accumulation is Dv99.

[0108] (4) Silicon grain size

[0109] XRD analysis of the material was performed using an X-ray powder diffractometer (POWDIX 600 / 300). The size of the silicon grains in the silicon-based anode material could be calculated using the Scherrer equation: D = Kλ / βcosθ, where K is the Scherrer constant, D is the size of the silicon grains, B is the measured half-width at half-maximum (FWHM) of the diffraction peak, θ is the Bragg diffraction angle, and γ is the X-ray wavelength.

[0110] (5) Pore volume test

[0111] Porous carbon matrix solid powder was placed in a sample tube and degassed under vacuum at 100°C for 12 hours. The adsorption capacity of the porous carbon matrix for nitrogen under different pressures was measured using an ASAP1460 physical adsorption analyzer, and adsorption and desorption isotherms were plotted. The pore shape was determined based on the shape of the hysteresis loop, and the pore size distribution curve of the micropores was fitted using a DFT model. The pore volume and pore size distribution of the porous carbon matrix were then calculated.

[0112] (6) Scanning electron microscopy test

[0113] A JEOL-JSM-6700F scanning electron microscope was used to test silicon-based anode materials at a voltage of 5 kV and a current of 0.8 nA.

[0114] (7) Mass percentage of silicon-based anode materials

[0115] The silicon content 'a' in silicon-based anode materials was characterized using ICP (inductively coupled plasma spectroscopy) technology.

[0116] Lithium-ion battery related tests

[0117] (1) Testing of the compaction density of the negative electrode sheet

[0118] The coated negative electrode sheet is dried, rolled under a 5-ton weight, and then punched into small round pieces with a diameter of 14mm using a punching machine. The mass of these small round pieces is weighed and recorded. The cold-pressed density is calculated based on the formula: negative electrode sheet coating weight / cold-pressed thickness.

[0119] (2) First Coulomb Efficiency Test of Full Cell

[0120] A lithium-ion battery is charged to 4.48V at 0.5C, and the initial charge capacity is recorded as C. Then, the lithium-ion battery is discharged to 3.0V at 0.5C, and the initial discharge capacity is recorded as D. Calculate the initial coulombic efficiency CE of the full cell using the following formula: CE = D / C.

[0121] (3) Cyclic performance test

[0122] Using a battery performance testing machine (model CT-4080-5V12A), the lithium-ion battery under test was left to stand for 5 minutes at test temperatures of 25℃ / 45℃, and the initial thickness MMC0 of the lithium-ion battery was recorded. The lithium-ion battery was then charged at a constant current of 3C to 4.25V, then at 2C to 4.4V, then at 1C to 4.48V, and finally charged at a constant voltage of 4.48V to 0.05C, and the discharge capacity C4 of the lithium-ion battery was recorded. After standing for 5 minutes, it was discharged at a constant current of 0.5C to 3.0V, and then stood for 5 minutes. After 400 cycles of the above 3C charge / 0.5C discharge cycle, the thickness MMC1 and discharge capacity C5 of the lithium-ion battery were recorded.

[0123] 400-cycle capacity retention rate (%) = C5 / C1 × 100%;

[0124] Expansion rate (%) after 400 cycles = (MMC1 - MMC0) / MMC0 × 100%.

[0125] (4) Discharge rate performance test

[0126] At 25℃, the capacitor was discharged to 3.0V at 0.2C, allowed to stand for 5 minutes, charged to 4.48V at 0.5C, and then charged at a constant voltage to 0.05C, allowed to stand for 5 minutes. The discharge rate was adjusted, and discharge tests were conducted at 0.2C, 0.5C, 1C, 1.5C, and 2.0C respectively. The discharge capacity was obtained for each rate. The capacity obtained at each rate was compared with the capacity obtained at 0.2C. The rate performance was obtained by comparing the ratio of 2C to 0.2C.

[0127] (5) Test of the expansion ratio of the negative electrode sheet and the lithium-ion battery after 500 cycles

[0128] The lithium-ion batteries under test were divided into two groups. One group was cycled 500 times according to the steps in the cycle performance and expansion performance test process described above. The initial thickness of the lithium-ion battery was MMC0, and the thickness after 500 cycles was MMC2. Then, the lithium-ion batteries that had been fully discharged after 500 cycles were disassembled, and the thickness H1 of the negative electrode was measured. The other group was directly disassembled, and the initial thickness H0 of the negative electrode was measured. The expansion ratio R of the negative electrode to the lithium-ion battery after 500 cycles was R = (MMC2 - MMC0) / (H1 - H0).

[0129] (6) DCR test

[0130] At 25℃, charge at 1C to 4.48V, then charge at a constant voltage to 0.05C and let stand for 5 minutes. Discharge at 0.5C to 3.0V, let stand for 5 minutes, and set the cutoff capacity as C1. Charge at 1C to 4.48V, then charge at a constant voltage to 0.05C and let stand for 120 minutes. Discharge at 1C for 360 seconds, let stand for 120 minutes, then discharge at 0.1C for 10 seconds. Repeat this process 11 times, letting stand for 20 minutes after each cycle. This yields the internal resistance (DCR) of the lithium-ion battery at 20% SOC.

[0131] (7) High-temperature storage performance test

[0132] At 25℃, discharge to 3.0V at 0.5C and let stand for 5 minutes. Then charge to 4.48V at 0.5C, and then charge at a constant voltage to 0.05C and let stand for 5 minutes. Then discharge to 3.0V at 0.5C and let stand for 5 minutes. Repeat the above steps three times, and then store at 80℃ for 24 hours. Measure the following thermal parameters: initial, before storage - after pretreatment, lithium-ion battery thickness (PPG), OCV / IMP, and after 24 hours of storage. 24-hour expansion rate = PPG at 24 hours / initial PPG-1. PPG-1 is the thickness of the lithium-ion battery after three cycles, and PPG at 24 hours refers to the thickness of the lithium-ion battery after 24 hours of storage at 80℃.

[0133] (8) Differential capacity curve test of lithium-ion batteries

[0134] The differential capacity curve test of lithium-ion batteries is based on the above cycle performance test (3). The cycle number corresponding to the minimum absolute value of the starting current under constant current discharge state in the first two hundred cycles is selected. Then, the first derivative of the constant current charging capacity Q of the secondary battery under this corresponding cycle number is obtained with respect to the voltage V. Then, the voltage V is plotted to obtain the differential capacity curve (dQ / dV curve).

[0135] Table 2

[0136] Table 3

[0137] Referring to Figure 2, it can be seen that the silicon-based anode material has uniform particle size and good dispersion.

[0138] Refer to Figure 4, which shows the XRD pattern of the silicon-based anode material.

[0139] Referring to Figure 5, which shows the differential capacity curve in Comparative Example 3, the calculated α value is 0.82, which corresponds to a decrease in the cycle performance, rate performance, and expansion performance of the secondary battery.

[0140] Referring to Tables 1 and 2, compared to Comparative Examples 1 to 7, the secondary batteries in Examples 1 to 13, with α values ​​within a suitable range, all exhibit excellent reversible capacity. Furthermore, these secondary batteries demonstrate improved high-temperature storage performance while maintaining good initial coulombic efficiency, rate performance, cycle performance, and expansion performance. In the examples, when the α value is between 0.41 and 0.7, the corresponding secondary batteries show superior rate performance, cycle performance, expansion performance, and high-temperature storage performance. This indicates that within the aforementioned α value range, lithium insertion / extraction is facilitated, which improves the initial coulombic efficiency of the secondary battery. It also reduces the volume expansion effect, enhancing the reversible capacity, cycle performance, and expansion performance of the secondary battery. Moreover, within this range, it also helps reduce the internal resistance during charging and discharging, thus improving high-temperature storage performance.

[0141] In Examples 1 to 13, the cycle performance and expansion performance of the secondary battery were improved when I3 / I2 was within a suitable range. Furthermore, in Examples 1 to 13, the silicon content in the first and second regions of the silicon-based anode material differed only slightly, indicating a relatively uniform distribution of silicon in the silicon-based anode material, which is beneficial for improving the initial coulombic efficiency, cycle performance, and expansion performance of the silicon-based anode material.

[0142] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Therefore, any equivalent variations made in accordance with this application are still within the scope of this application.

Claims

1. A secondary battery comprising a negative electrode sheet, wherein, The negative electrode sheet includes a silicon-based negative electrode material, and the secondary battery satisfies 0.3≤α≤0.8, where α represents a ratio of I1 and I2 in a differential capacity curve of the secondary battery, I1 represents a peak intensity of a characteristic peak of the differential capacity curve of the secondary battery at 3.9±0.05 V, and I2 represents a peak intensity of a characteristic peak of the differential capacity curve of the secondary battery at 3.75±0.05 V.

2. The secondary battery according to claim 1, wherein 0.41≤α≤0.7。 3. The secondary battery according to claim 1 or 2, wherein 0.36≤I3 / I2≤0.60, where I3 represents a peak intensity of a characteristic peak of the differential capacity curve of the secondary battery at 3.82±0.05 V.

4. The secondary battery according to any one of claims 1 to 3, wherein Slicing along a thickness direction of the negative electrode sheet, a region 1.5 μm inward from a section edge of the silicon-based negative electrode material is a first region, and a region 1.5 μm outward from a center of the section of the silicon-based negative electrode material is a second region, and a difference between contents of silicon elements in the first region and the second region is less than 10% based on a mass of the silicon-based negative electrode material.

5. The secondary battery according to any one of claims 1 to 4, wherein The negative electrode sheet satisfies at least one of the following conditions: (1) the content of the silicon element accounts for 20 wt% to 60 wt% based on a mass of the silicon-based negative electrode material; (2) Dv10 of the silicon-based negative electrode material is 2.0 μm to 7.0 μm, and Dv99 is 12.0 μm to 26.0 μm; (3) the compaction density of the negative electrode plate under 5 tons of mass is 1.5 g / cm 3 to 1.9 g / cm 3 ; (4) a particle elastic modulus of the silicon-based negative electrode material is 3 GPa to 6 Gpa.

6. The secondary battery according to any one of claims 1 to 5, wherein The silicon-based negative electrode material comprises a porous carbon matrix, the volume ratio of ultra-micropores in the porous carbon matrix is 7% or less, the volume ratio of micropores in the porous carbon matrix is 80% to 92%, and the pore volume of the porous carbon matrix is 0.6 cm 3 / g to 1 cm 3 / g.

7. The secondary battery according to any one of claims 1 to 6, wherein A size of a silicon crystal grain in the silicon-based negative electrode material is 0.5 nm to 4 nm.

8. The secondary battery according to any one of claims 1 to 7, wherein The negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes the silicon-based negative electrode material and graphite, and a mass of the silicon-based negative electrode material accounts for 2% to 20% based on a mass of the negative electrode active material.

9. The secondary battery according to any one of claims 1 to 8, wherein When a charge-discharge cycle number of the secondary battery is greater than or equal to 500 cycles at 25±1℃, using 3C step charging and 0.5C discharging, a ratio of an expansion rate of the negative electrode sheet to an expansion rate of the secondary battery is 0.4 to 3.

5.

10. An electronic device, wherein, The secondary battery includes the secondary battery according to any one of claims 1 to 9.

Images