Secondary battery and electronic device

Abstract

Provided in the present application are a secondary battery and an electronic device. The secondary battery comprises an electrode assembly, wherein the electrode assembly comprises a negative electrode sheet, a positive electrode sheet and a separator; the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector; the negative electrode material layer comprises a silicon-carbon material; the silicon-carbon material comprises a substrate, a silicon coating layer and a carbon coating layer; the substrate comprises porous carbon and nano-silicon particles; the pores of the porous carbon contain the nano-silicon particles; and the silicon coating layer is arranged between the substrate and the carbon coating layer. Having the above characteristics, the silicon-carbon material can improve the dynamic performance and cycle performance of the secondary battery, and also enables the secondary battery to have a relatively high energy density.

Description

Secondary battery and electronic device

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on March 29, 2024, with application number 202410381093.0 and invention name “A Secondary Battery and Electronic Device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of electrochemical technology, and in particular to a secondary battery and an electronic device. Background Art

[0003] With the widespread use of secondary batteries, people have an increasing demand for their cycle performance and kinetic performance.

[0004] Silicon, with its high theoretical specific capacity, has attracted considerable attention for its application research. However, during lithium insertion, silicon experiences a volume expansion of approximately 300%, which can cause the solid electrolyte interface (SEI) to rupture and form a new interface. This leads to continuous side reactions between the electrolyte and the silicon, consuming the electrolyte. This can also cause the silicon to pulverize and break, forming a larger interface, exacerbating electrolyte consumption and impacting the cycling performance of lithium-ion batteries. Furthermore, silicon's poor electronic conductivity can also affect the kinetic performance of lithium-ion batteries. Summary of the Invention

[0005] The purpose of this application is to provide a secondary battery and electronic device that can improve the dynamic performance and cycle performance of the secondary battery while also making the secondary battery have a higher energy density. The specific technical solution is as follows:

[0006] The first aspect of the present application provides a secondary battery comprising an electrode assembly, the electrode assembly comprising a negative electrode plate, a positive electrode plate, and a separator, the negative electrode plate comprising a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, the negative electrode material layer comprising a silicon-carbon material, the silicon-carbon material comprising a substrate, a silicon coating layer, and a carbon coating layer, the substrate comprising porous carbon and nano-silicon particles, the porous carbon having nano-silicon particles in its pores, and the silicon coating layer disposed between the substrate and the carbon coating layer. The silicon-carbon material satisfies the above-mentioned characteristics, can improve the kinetic performance and cycle performance of the secondary battery, and also provide the secondary battery with a higher energy density.

[0007] In one embodiment of the present application, the secondary battery is discharged at a 10C rate at -20°C, and the difference between the initial discharge voltage E0 and the valley voltage E1 during the discharge process is ΔE, with 0.1V≤ΔE≤0.6V. Using the silicon-carbon material of the present application, a rapid lithium ion transport channel is constructed on the particle surface and within the particle by the silicon material, which further improves the kinetic performance of the silicon-carbon material. When the silicon-carbon material is applied to a secondary battery, the secondary battery is discharged at a 10C rate at -20°C. The difference ΔE between the initial discharge voltage E0 and the valley voltage E1 during the discharge process is within the range of the present application, indicating that the secondary battery has good kinetic performance.

[0008] In one embodiment of the present application, the thickness of the silicon coating layer is H1nm, and the thickness of the carbon coating layer is H2nm, 1≤H1≤100, 5≤H2≤100. The silicon coating layer is used to construct a fast lithium ion transmission channel between the outer carbon coating layer and the inner nano-silicon particles. When the thickness of the silicon coating layer is within the scope of the present application, the sub-outer silicon coating layer can be more fully connected with the nano-silicon particles deposited in the pores, so that the lithium ion transmission effect of the constructed channel is better; the silicon coating layer has a suitable thickness, which is also beneficial to the transmission of lithium ions to the interior of the particles, further improving the kinetic performance of the secondary battery. When the thickness of the carbon coating layer is within the scope of the present application, the carbon coating layer has a suitable thickness, which can provide better electronic conductivity, and can also reduce the contact between the electrolyte and the silicon coating layer to a certain extent, reduce the occurrence of side reactions, and improve the cycle performance of the secondary battery; at the same time, it is also beneficial to the transmission of lithium ions and electrons to the interior of the particles, further improving the kinetic performance of the secondary battery.

[0009] In one embodiment of the present application, based on the mass of the silicon-carbon material, the mass percentage of silicon in the silicon-carbon material is W1%, the mass percentage of carbon in the silicon-carbon material is W2%, 40≤W1≤70, and 30≤W2≤60. By regulating the mass percentage of silicon and carbon in the silicon-carbon material within the scope of the present application, it is beneficial to form a silicon coating layer of moderate thickness on the surface of the substrate, so that the sub-outer silicon coating layer is more fully connected to the nano-silicon particles deposited in the pores, further improving the lithium ion transmission effect of the constructed channel, thereby improving the kinetic performance of the secondary battery, and at the same time, it can also improve the gram capacity and first efficiency of the silicon-carbon material, so that the secondary battery has a higher energy density.

[0010] In one embodiment of the present application, in the first-cycle delithiation dQ / dV curve of the silicon-carbon material, a first delithiation peak exists in the range of 0.25V to 0.32V, and a second delithiation peak exists in the range of 0.35V to 0.45V. The peak intensity of the first delithiation peak is I1, and the peak intensity of the second delithiation peak is I2, and 0.1≤I1 / I2≤3. The value of I1 / I2 can reflect the thickness of the silicon coating layer. When the value of I1 / I2 is within the range of this application, the silicon coating layer has a suitable thickness, so that the sub-outer silicon coating layer is more fully connected to the nano-silicon particles deposited in the pores, further improving the lithium ion transport effect of the constructed channel; it is also beneficial for the transmission of lithium ions to the interior of the particles, further improving the kinetic performance of the secondary battery.

[0011] In one embodiment of the present application, the reversible capacity of the silicon-carbon material at 0.05C is D0 mAh / g, and 1500≤D0≤2500. Silicon material has a high specific capacity, and the reversible capacity of the silicon-carbon material at 0.05C of the present application is within the scope of the present application. The silicon-carbon material has a high reversible capacity, so that the secondary battery has a high energy density.

[0012] In one embodiment of the present application, the silicon-carbon material satisfies at least one of the following characteristics: (1) the thickness of the silicon coating layer is H1 nm, the thickness of the carbon coating layer is H2 nm, 3≤H1≤80, 10≤H2≤50; (2) based on the mass of the silicon-carbon material, the mass percentage of silicon element in the silicon-carbon material is W1%, the mass percentage of carbon element in the silicon-carbon material is W2%, 45≤W1≤65, 35≤W2≤55; (3) in the first-cycle delithiation dQ / dV curve of the silicon-carbon material, there is a first delithiation peak in the range of 0.25 V to 0.32 V, and a second delithiation peak in the range of 0.35 V to 0.45 V, the peak intensity of the first delithiation peak is I1, the peak intensity of the second delithiation peak is I2, 0.2≤I1 / I2≤2.

[0013] In one embodiment of the present application, the negative electrode material layer further comprises a carbon material, and the carbon material satisfies at least one of the following characteristics: (1) the carbon material comprises at least one of natural graphite, artificial graphite or hard carbon; (2) the particle size Dv50 of the carbon material satisfies: 5 μm ≤ Dv50 ≤ 18 μm; (3) the specific surface area BET of the carbon material satisfies: 0.5 m 2 / g≤BET≤3m 2 / g; (4) In the Raman spectrum of carbon materials, at 1300cm -1 to 1400cm -1 There is a peak intensity of I in the range D The first characteristic peak at 1550 cm -1 to 1650cm -1 There is a peak intensity of I in the range G The second characteristic peak, 0.1<ID / I G <0.4. The negative electrode material layer also includes carbon material. Carbon material has good electronic conductivity and ionic conductivity, which is conducive to the transmission of electrons and lithium ions. It can also buffer the volume expansion of silicon material during the process of lithium removal and lithium insertion, which can further improve the dynamic performance and cycle performance of the secondary battery.

[0014] In one embodiment of the present application, based on the sum of the masses of the carbon material and the silicon-carbon material, the ratio of the mass percentage of the carbon material to the mass percentage of the silicon-carbon material is 1 to 20. The carbon material can improve the kinetic performance and cycle performance of the secondary battery, and the silicon-carbon material can improve the energy density of the secondary battery. By regulating the ratio of the mass percentage of the carbon material to the mass percentage of the silicon-carbon material within the scope of the present application, the secondary battery can have a higher energy density in addition to having good kinetic performance and cycle performance.

[0015] In one embodiment of the present application, the electrode assembly further includes a positive electrode tab and a negative electrode tab. The positive electrode plate includes a first hollow foil region and a positive electrode material layer region, with the positive electrode tab disposed in the first hollow foil region. The negative electrode plate includes a second hollow foil region and a negative electrode material layer region, with the negative electrode tab disposed in the second hollow foil region. With the structure of the electrode assembly configured as described above, current can be transmitted through the hollow current collector, maximizing the uniformity of current density distribution in the plate, reducing polarization of the secondary battery, and further improving the dynamic performance and cycle performance of the secondary battery.

[0016] In one embodiment of the present application, the negative electrode sheet includes a first edge and a second edge facing each other along its width after expansion. From the first edge to the second edge, the negative electrode sheet is sequentially provided with a second hollow foil region and a negative electrode material layer region. The negative electrode sheet is provided with the above-described structure, and the positive electrode sheet is also provided with the above-described structure. The electrode assembly adopts a full-tab structure, allowing current to be transmitted through the hollow current collector. This maximizes the uniformity of the current density distribution in the sheet, reduces polarization of the secondary battery, and can further improve the dynamic performance and cycle performance of the secondary battery.

[0017] The second aspect of the present application provides an electronic device, which includes the secondary battery in any of the aforementioned embodiments. Therefore, the electronic device provided by the present application has good dynamic performance and cycle performance, and also has a high energy density.

[0018] Beneficial effects of this application:

[0019] The present application provides a secondary battery and electronic device. The secondary battery includes an electrode assembly, the electrode assembly including a negative electrode plate, a positive electrode plate, and a separator. The negative electrode plate includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The negative electrode material layer includes a silicon-carbon material. The silicon-carbon material includes a substrate, a silicon coating layer, and a carbon coating layer. The substrate includes porous carbon and nano-silicon particles, the porous carbon has nano-silicon particles in its pores, and the silicon coating layer is disposed between the substrate and the carbon coating layer. The silicon-carbon material meets the above-mentioned characteristics and can improve the kinetic performance and cycle performance of the secondary battery, while also enabling the secondary battery to have a higher energy density.

[0020] Of course, it is not necessary to achieve all of the above advantages at the same time when implementing any product or method of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0022] FIG1 is a schematic structural diagram of the silicon-carbon material of Comparative Example 1;

[0023] FIG2 is a schematic structural diagram of a silicon-carbon material according to an embodiment of the present application;

[0024] FIG3 is a schematic structural diagram of a negative electrode sheet according to an embodiment of the present application;

[0025] FIG4 is a schematic structural diagram of the negative electrode sheet of Example 1-17. DETAILED DESCRIPTION

[0026] The following will be combined with the accompanying drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0027] It should be noted that, in the specific embodiments of the present application, lithium-ion batteries are used as an example of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries.

[0028] The present application provides a secondary battery, which includes an electrode assembly, the electrode assembly includes a negative electrode plate, a positive electrode plate and a separator, the negative electrode plate includes a negative electrode collector and a negative electrode material layer provided on at least one surface of the negative electrode collector, the negative electrode material layer includes a silicon-carbon material, the silicon-carbon material includes a substrate, a silicon coating layer and a carbon coating layer, the substrate includes porous carbon and nano-silicon particles, the porous carbon has nano-silicon particles in its pores, and the silicon coating layer is provided between the substrate and the carbon coating layer. The above-mentioned "negative electrode material layer provided on at least one surface of the negative electrode collector" means that the negative electrode material layer can be provided on one surface of the negative electrode collector along its own thickness direction, or on two surfaces of the negative electrode collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the negative electrode collector or a partial area of ​​the negative electrode collector. This application is not particularly limited, as long as the purpose of this application can be achieved.

[0029] Existing silicon-carbon materials generally adopt the structure shown in FIG1 , where the silicon-carbon material 10 includes a substrate 11 and a carbon coating 12. The substrate 11 includes porous carbon 111 and nano-silicon particles 112. The carbon coating 12 is provided on the entire surface of the substrate 11. In the above-mentioned silicon-carbon material, pores are reserved to accommodate the expansion of the nano-silicon particles after lithium insertion. However, due to the presence of pores, lithium ions need to first penetrate the carbon coating and then diffuse through the pores to the nano-silicon particles, and then react with the nano-silicon particles to insert lithium. In the delithiation process, the opposite is true. The lithium released from the Li-Si alloy is first transferred to the pores and then diffuses through the pores to the surface of the silicon-carbon material particles, and finally penetrates the carbon coating and diffuses into the electrolyte. In the above-mentioned delithiation and insertion processes, since the transmission speed of lithium ions in the pores is relatively slow, the delithiation and insertion kinetics of the silicon-carbon material will deteriorate.

[0030] The inventors have found that by optimizing the silane deposition process, a silicon coating layer is formed on the surface of the substrate. Due to the characteristics of the silane deposition reaction, the nano-silicon particles deposited in the porous carbon will grow outward along the pore wall, so the outer silicon coating layer will form a connection with the nano-silicon particles deposited in the pores. After that, a carbon coating treatment is performed to form a carbon coating layer on the surface of the silicon coating layer. The structure of the prepared silicon-carbon material is shown in Figure 2. The silicon-carbon material 10 includes a substrate 11, a silicon coating layer 13 and a carbon coating layer 12. The substrate 11 includes porous carbon 111 and nano-silicon particles 112. The nano-silicon particles 112 are arranged in the pores of the porous carbon 111, and the silicon coating layer 13 is arranged between the substrate 11 and the carbon coating layer 12. During the lithium insertion process, lithium ions penetrate the outermost carbon coating layer and come into direct contact with the silicon coating layer, and a reaction occurs to insert lithium. The lithium ions then continue to diffuse in the Li-Si alloy into the interior of the particles, causing the silicon material inside the particles to insert lithium. The delithiation process is the opposite. The lithium ions diffuse out through the Li-Si alloy and then penetrate the carbon coating layer to diffuse into the electrolyte. In the silicon-carbon material of the present application, during the delithiation and lithium insertion process, lithium ions diffuse through the Li-Si alloy. Compared with the existing diffusion through the pore structure, this can further increase the diffusion rate of lithium ions inside the particles, improve the delithiation and lithium insertion kinetics of the silicon-carbon material, and improve the kinetic performance and cycle performance of the secondary battery. At the same time, the secondary battery also has a higher energy density (ED).

[0031] In one embodiment of the present application, the secondary battery is discharged at a rate of 10C at -20°C, and the difference between the initial discharge voltage E0 and the valley voltage E1 during the discharge process is ΔE, and 0.1V≤ΔE≤0.6V. Exemplarily, the value of ΔE can be 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, 0.34, 0.36, 0.38, 0.4, 0.42, 0.44, 0.46, 0.48, 0.5, 0.52, 0.54, 0.56, 0.58, 0.6, or a range consisting of any two of the above values. When a secondary battery is placed in a -20°C environment and discharged at a 10C rate, there is an initial discharge voltage E0 at the beginning of the discharge. The secondary battery continues to discharge and the voltage continues to decrease. However, due to the high impedance of the secondary battery at this time, a large amount of heat is also generated during external discharge, which increases the temperature of the secondary battery. This in turn reduces the impedance of the secondary battery caused by the low temperature, reduces the polarization of the secondary battery, and increases the voltage. This process of the secondary battery voltage first decreasing and then increasing is reflected in the discharge curve of the secondary battery as a voltage trough with a trough voltage E1. The difference between the initial discharge voltage E0 and the trough voltage E1 during the discharge process is ΔE. ΔE can reflect the kinetic properties of the material. The better the kinetic properties of the material, the smaller the ΔE. The silicon-carbon material of this application further improves its kinetic performance by constructing a rapid lithium-ion transport channel on the particle surface and within the particle. When the silicon-carbon material is applied to a secondary battery, the secondary battery is discharged at a 10C rate at -20°C. The difference ΔE between the initial discharge voltage E0 and the valley voltage E1 during discharge is within the range of this application, indicating that the secondary battery has good kinetic performance. In this application, low temperature refers to temperatures below -20°C.

[0032] In one embodiment of the present application, the thickness of the silicon coating layer is H1 nm, the thickness of the carbon coating layer is H2 nm, 1≤H1≤100, preferably, 3≤H1≤80, illustratively, the value of H1 can be 1, 3, 5, 7, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, or a range consisting of any two of the above values. 5≤H2≤100, preferably, 10≤H2≤50, illustratively, the value of H2 can be 5, 7, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, or a range consisting of any two of the above values. The silicon coating layer is used to construct a fast lithium ion transmission channel between the outer carbon coating layer and the inner nano-silicon particles. When the thickness of the silicon coating layer is within the scope of this application, the connection between the second outer silicon coating layer and the nano-silicon particles deposited in the pores can be more complete, so that the lithium ion transmission effect of the constructed channel is better; the silicon coating layer has an appropriate thickness, which is also conducive to the transmission of lithium ions into the interior of the particles, further improving the kinetic performance of the secondary battery. When the thickness of the carbon coating layer is within the scope of this application, the carbon coating layer has an appropriate thickness, which can provide good electronic conductivity and can also reduce the contact between the electrolyte and the silicon coating layer to a certain extent, reduce the occurrence of side reactions, and improve the cycle performance of the secondary battery; at the same time, it is also conducive to the transmission of lithium ions and electrons into the interior of the particles, further improving the kinetic performance of the secondary battery.

[0033] In one embodiment of the present application, based on the mass of the silicon-carbon material, the mass percentage of silicon in the silicon-carbon material is W1%, the mass percentage of carbon in the silicon-carbon material is W2%, 40≤W1≤70, preferably, 45≤W1≤65, illustratively, the value of W1 can be 40, 43, 45, 47, 49, 50, 53, 55, 57, 59, 60, 63, 65, 67, 69, 70 or a range consisting of any two of the above values. 30≤W2≤60, preferably, 35≤W2≤55, illustratively, the value of W2 can be 30, 33, 35, 37, 39, 40, 43, 45, 47, 49, 50, 53, 55, 57, 59, 60 or a range consisting of any two of the above values. By regulating the mass percentage of silicon and carbon in the silicon-carbon material within the scope of this application, it is beneficial to form a silicon coating layer of moderate thickness on the surface of the substrate, so that the sub-outer silicon coating layer is more fully connected with the nano-silicon particles deposited in the pores, further improving the lithium ion transmission effect of the constructed channel, thereby improving the kinetic performance of the secondary battery, and at the same time, it can also increase the gram capacity and first efficiency of the silicon-carbon material, so that the secondary battery has a higher energy density.

[0034] In one embodiment of the present application, in the first-cycle delithiation dQ / dV curve of the silicon-carbon material, a first delithiation peak exists in the range of 0.25V to 0.32V, and a second delithiation peak exists in the range of 0.35V to 0.45V. The peak intensity of the first delithiation peak is I1, and the peak intensity of the second delithiation peak is I2. 0.1≤I1 / I2≤3, preferably, 0.2≤I1 / I2≤2. Exemplarily, the value of I1 / I2 can be 0.1, 0.2, 0.3, 0.5, 0.7, 0.9, 1, 1.3, 1.5, 1.7, 1.9, 2, 2.3, 2.5, 2.7, 2.9, 3, or a range consisting of any two of the above values. In this application, the first-cycle discharge specific capacity of the silicon-carbon material is used as the horizontal coordinate and the voltage is used as the vertical coordinate to obtain the first-cycle discharge curve of the silicon-carbon material. The first-cycle discharge specific capacity of the silicon-carbon material is the first-cycle delithiation specific capacity. Then, the first-order derivative of the first-cycle delithiation specific capacity Q with respect to the voltage V is taken, and then the voltage V is plotted to obtain the differential capacity curve, i.e., the dQ / dV curve. The value of I1 / I2 can reflect the thickness of the silicon coating layer. When the value of I1 / I2 is within the range of this application, the silicon coating layer has an appropriate thickness, so that the sub-outer silicon coating layer is more fully connected to the nano-silicon particles deposited in the pores, further improving the lithium ion transport effect of the constructed channel; it is also beneficial for the transmission of lithium ions to the interior of the particles, further improving the kinetic performance of the secondary battery.

[0035] In one embodiment of the present application, the reversible capacity of the silicon-carbon material at 0.05C is D0 mAh / g, and 1500≤D0≤2500. For example, the value of D0 can be 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, or a range consisting of any two of the above values. The silicon material has a high specific capacity, and the reversible capacity of the silicon-carbon material of the present application at 0.05C is within the scope of the present application. The silicon-carbon material has a high reversible capacity, so that the secondary battery has a high energy density.

[0036] In one embodiment of the present application, the negative electrode material layer also includes a carbon material. The carbon material has good electronic conductivity and ionic conductivity, which is conducive to the transmission of electrons and lithium ions. It can also buffer the volume expansion of the silicon material during the delithiation and insertion of lithium, and can further improve the kinetic performance and cycle performance of the secondary battery.

[0037] In one embodiment of the present application, the carbon material comprises at least one of natural graphite, artificial graphite, or hard carbon. The carbon material has excellent electronic and ionic conductivity, facilitating electron and lithium ion transport, and can further enhance the kinetic and cycling performance of the secondary battery.

[0038] In one embodiment of the present application, the particle size Dv50 of the carbon material satisfies: 5μm≤Dv50≤18μm. For example, the value of Dv50 can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, or a range consisting of any two of the above values. By regulating the particle size Dv50 of the carbon material within the scope of this application, the particle size of the carbon material is relatively small, which can shorten the transmission path of lithium ions and improve the kinetic performance of the carbon material, thereby further improving the kinetic performance of the secondary battery.

[0039] In the present application, Dv50 means the particle size at which the volume accumulation reaches 50% from the smallest particle size in the volume-based particle size distribution of the material.

[0040] In one embodiment of the present application, the BET specific surface area of ​​the carbon material satisfies: 0.5 m 2 / g≤BET≤3m 2 / g. For example, the BET value can be 0.5, 0.7, 0.9, 1, 1.1, 1.3, 1.5, 1.7, 1.9, 2, 2.1, 2.3, 2.5, 2.7, 2.9, 3, or a range consisting of any two of the above values. By regulating the specific surface area of ​​the carbon material within the scope of this application, the carbon material can have a suitable specific surface area and particle size, which can shorten the transmission path of lithium ions and improve the kinetic performance of the carbon material, thereby further improving the kinetic performance of the secondary battery.

[0041] In one embodiment of the present application, in the Raman spectrum of the carbon material, at 1300 cm -1 to 1400cm -1 There is a peak intensity of I in the range D The first characteristic peak at 1550 cm -1 to 1650cm -1 There is a peak intensity of I in the range G The second characteristic peak, 0.1<I D / I G <0.4. For example, I D / I G The value of can be 0.11, 0.13, 0.15, 0.17, 0.19, 0.2, 0.21, 0.23, 0.25, 0.27, 0.29, 0.3, 0.31, 0.33, 0.35, 0.37, 0.39 or a range consisting of any two of the above values. In the Raman spectrum of the carbon material, I D / I G The value of is within the scope of this application, I D / I G The value of is relatively small, the kinetic performance of the carbon material is good, and the secondary battery can have good kinetic performance.

[0042] In one embodiment of the present application, based on the sum of the masses of the carbon material and the silicon-carbon material, the ratio of the mass percentage of the carbon material to the mass percentage of the silicon-carbon material (W Gr / W Si ) is 1 to 20. For example, W Gr / W Si The value of can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or a range consisting of any two of the above values. Carbon materials can improve the kinetic performance and cycle performance of secondary batteries, and silicon-carbon materials can improve the energy density of secondary batteries. By regulating the ratio of the mass percentage of carbon materials to the mass percentage of silicon-carbon materials within the scope of this application, the secondary battery can have a higher energy density in addition to having good kinetic performance and cycle performance.

[0043] In one embodiment of the present application, the electrode assembly further comprises a positive electrode tab and a negative electrode tab. The positive electrode sheet comprises a first hollow foil area and a positive electrode material layer area, with the positive electrode tab being arranged in the first hollow foil area. The negative electrode sheet comprises a second hollow foil area and a negative electrode material layer area, with the negative electrode tab being arranged in the second hollow foil area. For ease of understanding, a two-dimensional rectangular coordinate system is established with the width direction of the unfolded negative electrode sheet as the Y direction and the length direction of the unfolded negative electrode sheet as the X direction. It can be understood that the size of the second hollow foil area along the Y direction is the width of the second hollow foil area. As shown in FIG3 , the negative electrode sheet 100 comprises a second hollow foil area 110 and a negative electrode material layer area 120, with the negative electrode tab being arranged in the second hollow foil area 110. The above-mentioned “negative electrode tab being arranged in the second hollow foil area” means that an empty current collector is retained without a material layer during coating, and the empty current collector is transformed into a full tab structure through a flattening process after winding, that is, the entire second hollow foil area is the negative electrode tab. It is understood that the positive electrode sheet has the same structure as the negative electrode sheet. The positive electrode sheet includes a first hollow foil area and a positive electrode material layer area, and the positive electrode tab is arranged in the first hollow foil area. The structure of the electrode assembly is arranged as above, and the current can be transmitted through the hollow current collector, thereby maximizing the uniformity of the current density distribution in the electrode sheet, reducing the polarization of the secondary battery, and further improving the dynamic performance and cycle performance of the secondary battery. In the present application, the width w1 of the second hollow foil area 110 is 5mm to 20mm.

[0044] In one embodiment of the present application, as shown in FIG3 , along the width direction of the unfolded negative electrode sheet 100, i.e., the Y direction, the negative electrode sheet 100 includes a first edge 101 and a second edge 102 opposite each other. From the first edge 101 to the second edge 102, the negative electrode sheet 100 is sequentially provided with a second hollow foil region 110 and a negative electrode material layer region 120. The negative electrode sheet is provided with the above structure, and the positive electrode sheet is also provided with the above structure. The electrode assembly adopts a full-ear structure, and current can be transmitted through the hollow current collector, thereby maximizing the uniformity of the current density distribution in the sheet, reducing the polarization of the secondary battery, and further improving the dynamic performance and cycle performance of the secondary battery.

[0045] In one embodiment of the present application, the positive electrode sheet includes a third edge and a fourth edge facing each other along its unfolded width. From the third edge to the fourth edge, the positive electrode sheet is sequentially provided with a first hollow foil region and a positive electrode material layer region. The positive electrode sheet is provided with the above-described structure, and the negative electrode sheet is also provided with the above-described structure. The electrode assembly adopts a full-tab structure, allowing current to be transmitted through the hollow current collector, maximizing the uniformity of the current density distribution in the sheet, reducing the polarization of the secondary battery, and further improving the dynamic performance and cycle performance of the secondary battery.

[0046] This application does not specifically limit the method for preparing porous carbon. For example, the method may include, but is not limited to, the following steps: carbonizing a carbon raw material under an inert atmosphere, followed by cooling and crushing to obtain carbonaceous particles; placing the carbonaceous particles in a rotary kiln, introducing CO2 gas to activate and create pores, and then cooling to obtain porous carbon particles; and airflow-pulverizing and classifying the porous carbon particles to obtain porous carbon. This application does not specifically limit the carbon raw material, as long as the objectives of this application can be achieved. For example, the carbon raw material may include, but is not limited to, phenolic resin or coconut shell. This application does not specifically limit the inert atmosphere, as long as the objectives of this application can be achieved. For example, the inert atmosphere may include nitrogen or argon. This application does not specifically limit the temperature T1 and time t1 of the carbonization treatment, as long as the objectives of this application can be achieved. For example, T1 may range from 700°C to 1100°C, and t1 may range from 4 hours to 8 hours. This application does not specifically limit the particle size Dv50 of the carbonaceous particles, as long as the objectives of this application can be achieved. For example, the particle size Dv50 of the carbonaceous particles can be less than 80 μm. The present application has no particular restrictions on the temperature T2 and time t2 of the activation pore-forming treatment, as long as the purpose of the present application can be achieved. For example, T2 can be 650°C to 1200°C, and t2 can be 4h to 8h. The present application has no particular restrictions on the particle size Dv50 of the porous carbon, as long as the purpose of the present application can be achieved. For example, the particle size Dv50 of the porous carbon can be less than 9 μm.

[0047] The present application does not particularly limit the preparation method of silicon-carbon materials. For example, the preparation method of silicon-carbon materials may include but is not limited to the following steps: placing the porous carbon prepared above in a fluidized bed chemical vapor deposition furnace, heating and keeping the temperature under an inert atmosphere, and then introducing a silicon source to perform silicon grain vapor deposition to obtain porous carbon with surface-deposited silicon; then stopping the introduction of the silicon source, continuing to introduce an inert gas and heating and keeping the temperature, and then introducing a carbon source to perform surface passivation treatment to obtain passivated silicon-carbon; placing the above-mentioned passivated silicon-carbon in a rotary kiln, heating and keeping the temperature under an inert atmosphere, and then introducing a carbon source to perform surface coating treatment, and then naturally cooling to room temperature and sieving to obtain the desired silicon-carbon material. The present application does not particularly limit the silicon source, as long as the purpose of the present application can be achieved. For example, the silicon source may include but is not limited to silane (SiH4), disilane (Si2H6) or trichlorosilane (SiHCl3). Preferably, the silicon source may include silane. The present application has no particular restrictions on the temperature T3 and time t3 of the silicon grain vapor deposition process, as long as the purpose of the present application can be achieved. For example, T3 can be 400°C to 600°C, and t3 can be 3h to 9h. The present application has no particular restrictions on the gas flow rate v1 of the silicon source, as long as the purpose of the present application can be achieved. For example, v1 can be 2L / min to 6L / min. The present application has no particular restrictions on the carbon source, as long as the purpose of the present application can be achieved. For example, the carbon source can include but is not limited to acetylene, methane, ethylene or propane, and preferably, the carbon source can include acetylene. The present application has no particular restrictions on the temperature T4 and time t4 of the surface passivation treatment process, as long as the purpose of the present application can be achieved. For example, T4 can be 400°C to 750°C, and t4 can be 0.2h to 2h. The present application has no particular restrictions on the gas flow rate v2 of the carbon source during the surface passivation treatment process, as long as the purpose of the present application can be achieved. For example, v2 can be 0.5L / min to 3L / min. The present application does not particularly limit the temperature T5 and time t5 of the surface coating process, as long as the purpose of this application can be achieved. For example, T5 can be 420°C to 800°C, and t5 can be 1 hour to 6 hours. The present application does not particularly limit the gas flow rate v3 of the carbon source introduced during the surface coating process, as long as the purpose of this application can be achieved. For example, v3 can be 1 L / min to 4 L / min.

[0048] The present application does not particularly limit the method for controlling the thickness of the silicon coating layer, as long as the objectives of the present application can be achieved. For example, the thickness of the silicon coating layer can be controlled by adjusting the silicon source introduction time. For example, when the silicon source aeration rate remains unchanged, extending the silicon source introduction time increases the thickness of the silicon coating layer; shortening the silicon source introduction time decreases the thickness of the silicon coating layer.

[0049] The present application does not particularly limit the method for controlling the thickness of the carbon coating layer, as long as the objectives of the present application can be achieved. For example, the thickness of the carbon coating layer can be controlled by adjusting the carbon source introduction time. For example, when the carbon source aeration rate remains unchanged, extending the carbon source introduction time increases the thickness of the carbon coating layer; shortening the carbon source introduction time decreases the thickness of the carbon coating layer.

[0050] The present application does not particularly limit the method for regulating the mass percentage of silicon in the silicon-carbon material, as long as the purpose of the present application can be achieved. For example, the thickness of the silicon coating layer can be regulated by regulating the silicon source introduction time, thereby regulating the mass percentage of silicon in the silicon-carbon material. For example, when the silicon source ventilation rate remains unchanged, extending the silicon source introduction time increases the thickness of the silicon coating layer and increases the mass percentage of silicon in the silicon-carbon material; shortening the silicon source introduction time reduces the thickness of the silicon coating layer and reduces the mass percentage of silicon in the silicon-carbon material.

[0051] The present application does not particularly limit the method for regulating the mass percentage of carbon in the silicon-carbon material, as long as the purpose of the present application can be achieved. For example, the thickness of the carbon coating layer can be regulated by regulating the carbon source introduction time, thereby regulating the mass percentage of carbon in the silicon-carbon material. For example, when the carbon source ventilation rate remains unchanged, extending the carbon source introduction time increases the thickness of the carbon coating layer and increases the mass percentage of carbon in the silicon-carbon material; shortening the carbon source introduction time reduces the thickness of the carbon coating layer and reduces the mass percentage of carbon in the silicon-carbon material.

[0052] The present application does not particularly limit the method for regulating the value of I1 / I2, as long as the purpose of the present application can be achieved. For example, the thickness of the silicon coating layer can be regulated by regulating the silicon source introduction time, thereby regulating the value of I1 / I2. For example, when the silicon source ventilation rate remains unchanged, extending the silicon source introduction time increases the thickness of the silicon coating layer and reduces the value of I1 / I2; shortening the silicon source introduction time reduces the thickness of the silicon coating layer and increases the value of I1 / I2.

[0053] The present application does not particularly limit the method for regulating the reversible capacity of the silicon-carbon material at 0.05°C, as long as the purpose of the present application can be achieved. For example, the reversible capacity of the silicon-carbon material at 0.05°C can be regulated by regulating the mass percentage of silicon in the silicon-carbon material. For example, as the mass percentage of silicon increases, the reversible capacity increases; and as the mass percentage of silicon decreases, the reversible capacity decreases.

[0054] The present application does not particularly limit the method for regulating the particle size Dv50 and specific surface area of ​​the carbon material, as long as the purpose of the present application can be achieved. For example, the particle size Dv50 and specific surface area of ​​the carbon material can be regulated by grinding the carbon material. For example, when other conditions remain unchanged, the grinding time is extended, the particle size Dv50 of the carbon material decreases, and the specific surface area of ​​the carbon material increases; the grinding time is shortened, the particle size Dv50 of the carbon material increases, and the specific surface area of ​​the carbon material decreases. For example, commercially available carbon materials with different particle sizes Dv50 can be selected, and the particle size Dv50 of the carbon material can be tested in combination with the test method of "Particle Size Test" in this application, and the carbon material with the required particle size Dv50 can be selected. For example, commercially available carbon materials with different specific surface areas can be selected, and the specific surface area of ​​the carbon material can be tested in combination with the test method of "Specific Surface Area Test" in this application, and the carbon material with the required specific surface area can be selected.

[0055] This application is about carbon materials D / I G There is no particular limitation on the way to control the value of , as long as the purpose of this application can be achieved. For example, the I of the carbon material can be controlled by controlling the graphitization degree of the carbon material. D / I G For example, the graphitization degree of carbon materials increases, I D / I G The value of increases; the graphitization degree of carbon material decreases, I D / I G The value of decreases.

[0056] The present application does not particularly limit the method for regulating the ratio of the mass percentage of the carbon material to the mass percentage of the silicon-carbon material, as long as the purpose of the present application can be achieved. For example, the ratio of the mass percentage of the carbon material to the mass percentage of the silicon-carbon material can be regulated by regulating the mass percentage of the added carbon material and the mass percentage of the silicon-carbon material.

[0057] The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or a composite current collector (such as a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.).

[0058] The negative electrode material layer of the present application includes a negative electrode active material, and the negative electrode active material includes a silicon-carbon material and / or a carbon material. The negative electrode material layer of the present application also includes a negative electrode conductive agent and a negative electrode binder. The present application has no particular restrictions on the negative electrode conductive agent and the negative electrode binder in the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the negative electrode conductive agent may include but is not limited to at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials or conductive polymers. The above-mentioned conductive carbon black may include but is not limited to Super P, acetylene black or Ketjen black. The above-mentioned carbon nanotubes may include but is not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder and / or metal fibers. Specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymer may include but is not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. The negative electrode binder may include, but is not limited to, at least one of polyacrylic acid, polyacrylate, polyimide, polyamide, polyamideimide, polyvinylidene fluoride (PVDF), polystyrene butadiene copolymer (styrene butadiene rubber, SBR), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose, or potassium hydroxymethyl cellulose. The present application does not particularly limit the mass ratio of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved.

[0059] The present application does not particularly limit the thickness of the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 16 μm. The present application does not particularly limit the thickness of the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the single-sided negative electrode material layer is 25 μm to 150 μm.

[0060] Optionally, the negative electrode plate may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. The present application does not particularly limit the composition of the conductive layer, and it can be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. The present application does not particularly limit the conductive agent and binder in the conductive layer, and it can be at least one of the above-mentioned negative electrode conductive agent and the above-mentioned negative electrode binder. The present application does not particularly limit the mass ratio of the conductive agent and binder in the conductive layer, and those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved.

[0061] In this application, a positive electrode sheet includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The phrase "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be disposed on one surface of the positive electrode current collector along its thickness direction, or on both surfaces of the positive electrode current collector along its thickness direction. It should be noted that the "surface" here can refer to the entire area of ​​the positive electrode current collector or a portion of the positive electrode current collector. This is not particularly limited in this application, as long as the purpose of this application can be achieved.

[0062] The present application has no particular limitation on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector).

[0063] The positive electrode material layer of the present application includes a positive electrode active material, and the positive electrode active material includes a substance that can reversibly embed and extract active ions such as lithium ions. The positive electrode material layer can be one layer or more layers, and each layer in the multilayer positive electrode material layer can contain the same or different positive electrode active materials. The present application has no special restrictions on the positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include but is not limited to lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium iron manganese phosphate or lithium titanate. The above-mentioned lithium nickel cobalt manganese oxide may include LiNi 0.95 Co 0.03 Mn 0.02 O2(Ni95),LiNi 0.91 Co 0.03 Mn 0.06 O2(Ni91), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622),LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523) or LiNi 1 / 3 Co 1 / 3 Mn 1 / 3At least one of O2 (NCM111). The positive electrode material layer of the present application also includes a positive electrode conductor and a positive electrode binder. The present application has no special restrictions on the positive electrode conductor and the positive electrode binder in the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the positive electrode conductor may include at least one of the above-mentioned negative electrode conductors; the positive electrode binder may include at least one of the above-mentioned negative electrode binders. The present application has no special restrictions on the mass ratio of the positive electrode active material, the positive electrode conductor, and the positive electrode binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved.

[0064] The present application does not particularly limit the thickness of the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 6 μm to 16 μm. The present application does not particularly limit the thickness of the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the single-sided positive electrode material layer is 25 μm to 120 μm.

[0065] Optionally, the positive electrode sheet may further include a conductive layer, which is located between the positive electrode current collector and the positive electrode material layer. The present application does not particularly limit the composition of the conductive layer, and it can be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. The present application does not particularly limit the conductive agent and binder in the conductive layer, and it can be at least one of the above-mentioned positive electrode conductive agent and the above-mentioned positive electrode binder. The present application does not particularly limit the mass ratio of the conductive agent and the binder in the conductive layer, and those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved.

[0066] In the present application, the diaphragm is used to separate the positive electrode plate and the negative electrode plate, prevent the internal short circuit of the secondary battery, allow the electrolyte ions to pass freely, and do not affect the electrochemical charge and discharge process. The present application has no special restrictions on the diaphragm, as long as it can achieve the purpose of the present application. For example, the material of the diaphragm may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid; the type of diaphragm may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane.

[0067] In the present application, the separator may include a substrate and a surface treatment layer. The substrate may be a non-woven fabric or a composite film having a porous structure, and the material of the substrate may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic material. For example, the inorganic layer includes inorganic particles and a separator binder. The present application does not particularly limit the above-mentioned inorganic particles, and for example, it may include at least one of aluminum oxide, 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, or barium sulfate. The present application does not particularly limit the above-mentioned separator binder, and for example, it may be at least one of the aforementioned negative electrode binders. The polymer layer includes a polymer, and the polymer material includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinyl pyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene). The present application does not particularly limit the thickness of the separator, as long as the purpose of the present application can be achieved. For example, the thickness of the separator can be 5 μm to 20 μm.

[0068] The secondary battery of the present application also includes an electrolyte. The electrolyte includes a lithium salt. The present application does not particularly limit the type of lithium salt, and lithium salts known in the art can be used. For example, the lithium salt can include but is not limited to at least one of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2, LiTFSI), lithium bis(fluorosulfonyl)imide (Li(N(SO2F)2), LiFSI), lithium difluorophosphate (LiPO2F2), lithium bis(oxalatoborate) (LiB(C2O4)2, LiBOB) or lithium difluorooxalatoborate (LiBF2(C2O4), LiDFOB). The present application does not particularly limit the mass percentage of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. The electrolyte also includes a non-aqueous organic solvent. The present application does not particularly limit the non-aqueous organic solvent, as long as the purpose of the present application can be achieved. For example, the non-aqueous organic solvent can include at least one of a carbonate compound, a carboxylate compound, an ether compound or other organic solvents. Above-mentioned carbonate compound can include but not limited to at least one in linear carbonate compound, cyclic carbonate compound or fluorinated carbonate compound.Above-mentioned linear carbonate compound can include but not limited to at least one in dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) or ethyl methyl carbonate (EMC).Above-mentioned cyclic carbonate compound can include but not limited to at least one in ethylene carbonate (EC), vinylene carbonate, propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The above-mentioned fluorinated carbonate compound may include but is not limited to fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate or at least one of trifluoromethylethylene carbonate. The above-mentioned carboxylate compound may include but is not limited to at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate or propyl propionate. The above-mentioned ether compound may include but is not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The above-mentioned other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate or phosphate ester.The present application has no particular limitation on the mass percentage of the non-aqueous organic solvent in the electrolyte, as long as the purpose of the present application can be achieved.

[0069] The secondary battery of this application also includes a packaging bag for containing the electrode assembly and electrolyte, as well as other components of the secondary battery known in the art. This application does not limit these other components. This application does not specifically limit the packaging bag and can be any packaging bag known in the art, as long as it can achieve the purpose of this application. For example, an aluminum-plastic film packaging bag can be used.

[0070] The present application does not particularly limit the type of secondary battery, which may include any device that generates an electrochemical reaction. In the present application, secondary batteries may include, but are not limited to: lithium metal secondary batteries, lithium ion secondary batteries (lithium ion batteries), lithium polymer secondary batteries or lithium ion polymer secondary batteries (lithium ion polymer batteries), etc. The present application does not particularly limit the lithium ion secondary battery. For example, the lithium ion secondary battery may be a soft pack battery, a square steel shell battery or a cylindrical steel shell battery. Preferably, the lithium ion secondary battery may be a cylindrical steel shell battery.

[0071] The preparation process of the secondary battery of this application is well known to those skilled in the art and is not particularly limited in this application. For example, it may include, but is not limited to, the following steps: stacking the positive electrode sheet, separator, and negative electrode sheet in sequence, and winding and folding them as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, as needed, overcurrent protection components, guide plates, etc. may be placed in the packaging bag to prevent pressure buildup and overcharging and discharging within the secondary battery.

[0072] The second aspect of the present application provides an electronic device, which includes the secondary battery according to any one of the aforementioned embodiments. Therefore, the electronic device provided by the present application has good dynamic performance and cycle performance, and also has a high energy density.

[0073] The present application does not particularly limit the type of electronic device, and the electronic device may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0074] Example

[0075] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0076] Test methods and equipment:

[0077] ΔE test:

[0078] The lithium-ion battery is discharged at a rate of 10C to 2.0V at -20°C. At the beginning of discharge, there is an initial discharge voltage E0, and the voltage continues to decrease. Subsequently, the voltage increases. The process in which the lithium-ion battery voltage first decreases and then increases is reflected in the discharge curve of the lithium-ion battery as a voltage trough. There is a trough voltage E1, and the difference between the initial discharge voltage E0 and the trough voltage E1 during the discharge process is ΔE.

[0079] In this application, the better the dynamic performance of the material, the smaller the ΔE.

[0080] Thickness test of silicon coating and carbon coating:

[0081] The silicon-carbon material was sliced ​​with the help of a focused ion beam (FIB), and then the thickness of the silicon coating layer and the carbon coating layer of the silicon-carbon material was observed under a high-resolution transmission electron microscope (HRTEM, model JEM-F200) at a magnification of 500,000 times.

[0082] Mass percentage test of elements in silicon-carbon materials:

[0083] Using an elemental analyzer, the silicon-carbon material is heated to 500°C in a muffle furnace and then concentrated nitric acid is added for digestion. After dilution, the mass percentage of silicon is tested using an elemental analyzer. The mass percentage of carbon in the silicon-carbon material = 100% - the mass percentage of silicon.

[0084] Reversible capacity test:

[0085] The silicon-carbon material in this application was used as the negative electrode active material, Super P as the conductive agent, and polyacrylic acid as the binder. The mass ratio of the negative electrode active material, Super P, and polyacrylic acid was 80:10:10. The negative electrode active material, Super P, polyacrylic acid, and deionized water were thoroughly mixed to obtain a negative electrode slurry with a solid content of 35 wt%. The negative electrode slurry was evenly coated on copper foil and dried to obtain a negative electrode sheet. The negative electrode sheet was cut into small discs with a diameter of 14 mm, a lithium sheet with a diameter of 16 mm was used as the counter electrode, and the separator and electrolyte in Example 1-1 were used to assemble a button cell for testing. The button battery was kept at a constant temperature of 25°C for 12 hours, discharged at a constant current of 0.05C to 5.0mV, allowed to stand for 5 minutes, then discharged at a constant current of 10μA to 5.0mV, allowed to stand for 5 minutes, and then discharged at a constant current of 5μA to 5.0mV; charged at a constant current of 0.05C to 2.0V, and the charge specific capacity of the button battery at this time was recorded, which was recorded as the reversible capacity D0 at 0.05C.

[0086] Particle size test:

[0087] The particle size of the carbon material was measured using a Malvern particle size tester (model: MasterSizer 2000). 0.02 g of the carbon material was added to a 50 mL clean beaker, along with 20 mL of dispersant ethanol. The mixture was ultrasonically cleaned in a 120 W ultrasonic cleaner for 30 minutes to completely disperse the carbon material in the ethanol, thereby obtaining a sample dispersion. The sample dispersion was then tested using a Malvern particle size tester to obtain the particle size Dv50 of the carbon material.

[0088] Specific surface area test:

[0089] In accordance with the national standard “Determination of the specific surface area of ​​solid substances by gas adsorption BET method” (GB / T 19587-2017), the specific surface area of ​​carbon materials was tested by nitrogen adsorption method using a specific surface area analyzer (model: TristarⅡ3020M).

[0090] Raman spectroscopy test:

[0091] The Raman spectrum of carbon materials was measured using a laser microconfocal Raman spectrometer (model HR Evolution, HORIBA Scientific Instruments Division). The Raman spectrum of carbon materials was 1350 cm -1 The peak intensity at I D , at 1580cm -1 The peak intensity at I G . I of carbon materials D / I G The value of is obtained by the following method: take the obtained carbon material, test 100 points, and obtain 100 corresponding I D / I GThe value of 100 I D / I G The average value of the values ​​is the I D / I G value.

[0092] Discharge temperature rise test:

[0093] After attaching a temperature-sensing wire to the surface of the lithium-ion battery, let it stand at 25°C for 30 minutes, then discharge it at a rate of 10C to 2.5V. Record the temperature change curve during the discharge process, including the initial discharge temperature T0 and the maximum temperature Tmax. The discharge temperature rise = Tmax-T0.

[0094] In this application, the better the kinetic performance of the material, the smaller the temperature rise when discharged at a rate of 10C at 25°C.

[0095] Cyclic performance test:

[0096] At 25°C, the lithium-ion battery was charged to 4.25V at a constant current of 1.2C, then charged to 0.02C at a constant voltage of 4.25V. After standing for 5 minutes, it was discharged to 2.5V at a constant current of 8C. This was the first cycle, and the discharge capacity was recorded. The lithium-ion battery was cycled according to the above process. When the cycle reached 300 cycles (cls), the test was stopped and the capacity retention rate was calculated as an indicator for evaluating the cycle performance of the lithium-ion battery.

[0097] Capacity retention rate after 300 cls of cycles (%) = (discharge capacity after 300 cls of cycles / discharge capacity at the first cycle) × 100%.

[0098] Example 1-1

[0099] <Preparation of Porous Carbon>

[0100] (1) The phenolic resin was carbonized under a nitrogen atmosphere, and after cooling, the phenolic resin was taken out and the carbonized block was crushed into carbonaceous particles with a particle size Dv50 of 70 μm; wherein the carbonization temperature T1 was 900°C and the carbonization time t1 was 6 h;

[0101] (2) placing the carbonaceous particles in a rotary kiln, introducing CO2 gas, performing activation pore-forming treatment, and taking them out after cooling to obtain porous carbon particles; wherein the activation pore-forming treatment temperature T2 is 850°C, and the activation pore-forming treatment time t2 is 6 hours;

[0102] (3) The porous carbon particles are subjected to air flow pulverization and classification to obtain porous carbon with a particle size Dv50 of about 8 μm.

[0103] <Preparation of Silicon Carbon Material>

[0104] (1) Vapor deposition of silicon grains: 1 kg of the porous carbon was placed in a fluidized bed chemical vapor deposition furnace. The temperature was raised to 490°C (T3) at a rate of 5°C / min under nitrogen atmosphere. After holding the temperature for 30 min, silane gas was introduced at a gas flow rate of 3 L / min (V1). The gas was continuously ventilated and held at temperature for 5 h to obtain porous carbon with silicon deposited on the surface.

[0105] (2) Surface passivation treatment: After the silane gas is introduced in step (1), nitrogen gas is continuously introduced and the temperature is raised to 530°C (T4) at a rate of 2°C / min. After holding the temperature for 30 min, acetylene gas is introduced at a gas flow rate of 1 L / min (V2), and the temperature is held for 1 h (T4). The mixture is then naturally cooled to obtain passivated silicon carbon with silicon grains having completed surface passivation distributed in the porous carbon.

[0106] (3) Surface coating treatment: The passivated silicon carbon was placed in a rotary kiln and heated to 530°C (T5) at a rate of 8°C / min under a nitrogen atmosphere. After keeping the temperature for 30 minutes, acetylene gas was introduced at a gas flow rate of 2 L / min (v3). The temperature was kept at t5 for 3 hours. Then, the introduction of acetylene gas and heating were stopped. The product was naturally cooled to room temperature and then taken out. After screening, the desired silicon carbon material was obtained.

[0107] <Preparation of negative electrode sheet>

[0108] After artificial graphite, silicon-carbon material, lithium carboxymethyl cellulose and carbon nanotubes are uniformly mixed, 50wt% (based on the total mass of the added polyacrylic acid) of polyacrylic acid and deionized water are added to prepare a slurry with a solid content of 62wt%, and then kneaded for 90min; the remaining 50wt% of polyacrylic acid and deionized water are added to prepare a slurry with a solid content of 50wt%, and then dispersed for 30min; deionized water is added to prepare a slurry with a solid content of 42wt%, and the mixture is further dispersed for 40min, and then vacuum degassed for 30min to obtain a negative electrode slurry. Among them, the mass ratio of artificial graphite, silicon-carbon material, polyacrylic acid, lithium carboxymethyl cellulose and carbon nanotubes is 87.2:10:2:0.4:0.4; based on the sum of the mass of artificial graphite and silicon-carbon material, the ratio of the mass percentage of carbon material to the mass percentage of silicon-carbon material (W Gr / W Si ) is 8.72; the particle size Dv50 of artificial graphite is 12 μm and the specific surface area BET is 1.26 m 2 / g、I D / I G is 0.32.

[0109] The negative electrode slurry prepared above was evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 6 μm using an extrusion coater and dried at 90°C to obtain a coating mass of 100 mg / 1540.25 mm2 The negative electrode sheet with negative electrode material layer coated on one side is then repeated on the other side of the copper foil to obtain a negative electrode sheet with negative electrode material layer coated on both sides. After drying at 90℃, it is cold pressed and then slit to obtain negative electrode sheets with specifications of 78mm×875mm for future use. The compacted density of the negative electrode material layer after cold pressing is 1.65g / cm 3 The structure of the prepared negative electrode sheet is shown in FIG3 . Along the Y direction, from the first edge to the second edge, the negative electrode sheet is sequentially provided with a second empty foil area and a negative electrode material layer area. The width of the second empty foil area is 12 mm.

[0110] <Preparation of positive electrode sheet>

[0111] Lithium nickel cobalt manganese oxide (Ni91), PVDF, Super P, and carbon nanotubes were mixed in a mass ratio of 97.6:1.3:0.6:0.5, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 76 wt%. The mixture was then dispersed for 40 minutes and vacuum degassed to obtain a positive electrode slurry.

[0112] The positive electrode slurry prepared above was evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 13 μm and dried at 90°C to obtain a coating mass of 245 mg / 1540.25 mm 2 The positive electrode sheet with a single-sided positive electrode material layer is then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided positive electrode material layer. After drying at 90°C, it is cold pressed and then slit to obtain a positive electrode sheet with a specification of 74mm×867mm for use. The compacted density of the positive electrode material layer after cold pressing is 3.60g / cm 3 The structure of the prepared positive electrode sheet is the same as that of the negative electrode sheet shown in Figure 3. Along the width direction of the unfolded positive electrode sheet, the positive electrode sheet includes a third edge and a fourth edge that are opposite to each other. From the third edge to the fourth edge, the positive electrode sheet is sequentially provided with a first empty foil area and a positive electrode material layer area. The width of the first empty foil area is 15 mm.

[0113] <Preparation of Electrolyte>

[0114] In an argon atmosphere glove box with a water content of less than 10 ppm, DMC, DEC, and EC were mixed in a mass ratio of 1:1:1 to obtain a base organic solvent. Lithium salt LiPF6 was then added to the base organic solvent, dissolved, and mixed thoroughly. Vinylene carbonate was then added to obtain an electrolyte. The electrolyte solution contained 12.5% ​​lithium salt by mass, 2% vinylene carbonate by mass, and the remainder consisting of the base organic solvent.

[0115] <Diaphragm>

[0116] PVDF and alumina were mixed in a 9:1 mass ratio, and NMP was added as a solvent to prepare a slurry with a solid content of 12 wt%. The mixture was then stirred to obtain an inorganic layer slurry. The inorganic layer slurry was evenly coated on one surface of a 7 μm thick PP film substrate. After drying, a separator with a single-sided inorganic layer coated with a thickness of 2 μm was obtained.

[0117] <Preparation of lithium-ion batteries>

[0118] The prepared positive electrode sheet, separator, negative electrode sheet, and separator are stacked in order, with the separator positioned between the positive and negative electrode sheets to act as a barrier. The electrode assembly is then wound to form an electrode. The uncoated foil area on the end of the electrode assembly is flattened, welded to a current collector, and then placed in a case. The battery is then dried in an 85°C vacuum oven for 12 hours to remove moisture. The prepared electrolyte is then injected, and the battery undergoes vacuum packaging, standing, formation, capacity testing, and high-temperature aging to produce a lithium-ion battery. The electrode assembly utilizes a full-tab structure.

[0119] Example 1-2 to Example 1-7

[0120] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0121] Example 1-8 to Example 1-10

[0122] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-2.

[0123] Examples 1-11

[0124] Except that the mass ratio of artificial graphite, silicon-carbon material, polyacrylic acid, lithium carboxymethyl cellulose, and carbon nanotubes is adjusted to 76.2:20:2.4:0.6:0.8 in <Preparation of Negative Electrode>, the rest is the same as Example 1-9.

[0125] Examples 1-12

[0126] Except that the mass ratio of artificial graphite, silicon-carbon material, polyacrylic acid, lithium carboxymethyl cellulose, and carbon nanotubes is adjusted to 92.4:5:1.8:0.4:0.4 in <Preparation of Negative Electrode>, the rest is the same as Example 1-9.

[0127] Example 1-13 to Example 1-16

[0128] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-9.

[0129] Examples 1-17

[0130] In addition to the bipolar ear structure adopted by the electrode assembly in the preparation of lithium-ion batteries, the structure of the negative electrode sheet in the electrode assembly is shown in FIG4 , where the negative electrode sheet 100 includes a negative electrode material layer region 120 and a negative electrode ear 121 , and the structure of the positive electrode sheet in the electrode assembly is the same as that shown in FIG4 , where the positive electrode sheet includes a positive electrode material layer and a positive electrode ear.

[0131] The same applies to Examples 1-9.

[0132] Comparative Example 1

[0133] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-9.

[0134] Comparative Example 2

[0135] Except that the surface coating treatment is not performed in <Preparation of Silicon Carbon Material>, the rest is the same as Example 1-9.

[0136] The preparation parameters, material performance parameters and electrical performance parameters of each embodiment and comparative example are shown in Tables 1 and 2.

[0137] Table 1

[0138] Note: In Table 1, “ / ” indicates no relevant preparation parameters.

[0139] Table 2

[0140] Note: In Table 2, “ / ” indicates no relevant preparation parameters.

[0141] Referring to Table 1 and Table 2, it can be seen from Examples 1-1 to 1-17 and Comparative Examples 1 to 2 that when the silicon-carbon material meets the above characteristics, the energy density of the lithium-ion battery is higher, the ΔE is smaller, the discharge temperature rise at 25°C / 10C is smaller, and the capacity retention rate after 300cls of cycling is higher, indicating that the lithium-ion battery of the present application has good kinetic performance and cycling performance, as well as a higher energy density.

[0142] It can be seen from Examples 1-1 to 1-5 that the main parameter that changes is the silane introduction time. At the same silane aeration rate, the longer the silane introduction time, the more silicon is introduced into the porous carbon. However, the pore volume of the porous carbon is fixed. When silane is continued to be introduced into it after the internal pore deposition is completed, the silane will decompose on the surface of the particles, and then form a coating layer of different thicknesses on the surface of the particles. Generally, the longer the silane introduction time, the thicker the silicon coating layer formed on the surface, and the higher the mass percentage of silicon element in the silicon-carbon material after deposition. Similarly, since the active silicon is the main component that exerts the activity of lithium removal and lithium insertion in the silicon-carbon material, the reversible capacity of the silicon-carbon material also increases with the increase of the mass percentage of silicon element. In the first-cycle delithiation dQ / dV curve of the silicon-carbon material, there is a first delithiation peak between 0.25V and 0.32V and a second delithiation peak between 0.35V and 0.45V, wherein the intensity of the second delithiation peak is closely related to the size of the silicon grains in the silicon-carbon material. Since the average pore diameter of the pore structure in the porous carbon used in this application is less than 2nm, the size of the silicon grains in the silicon-carbon material is mainly directly related to the thickness of the silicon coating layer on the surface of the silicon-carbon material. The thicker the silicon coating layer, the higher the degree of crystallization of the corresponding silicon-carbon material, the stronger the peak intensity of the second delithiation peak in the dQ / dV curve, and the smaller the peak intensity ratio I1 / I2 of the corresponding first delithiation peak to the second delithiation peak. Corresponding to this application, the longer the silane introduction time, the smaller I1 / I2. Since artificial graphite and silicon-carbon material were added at a fixed ratio of 87.2:10 during the preparation of the negative electrode sheets in Examples 1 to 1-5, the higher the reversible capacity of the silicon-carbon material, the higher the reversible capacity of the corresponding negative electrode sheet, and the higher the energy density of the corresponding lithium-ion battery. In Examples 1-1 to 1-3, as the thickness of the silicon coating layer increased, ΔE and the 25°C 10C discharge temperature rise both decreased, and the kinetic performance of the lithium-ion battery improved. Compared with Example 1-2, in Example 1-3, the thickness of the silicon coating layer was significantly increased, and the silicon content was also increased. The increased silicon content leads to greater expansion and increased side reactions with the electrolyte, resulting in relatively poor cycling performance. In Example 1-4, the silane injection time was short and the thickness of the silicon coating layer was small, resulting in relatively poor lithium ion transport in the transmission channels constructed by the silicon material on the particle surface and inside the particles. As a result, the kinetic performance of the lithium-ion battery was poor, the lithium-ion battery had greater polarization, and its cycling performance was relatively poor. In Examples 1-5, the silane injection time was long and the thickness of the silicon coating layer was large, which made lithium ion shuttling difficult, resulting in poor kinetic performance. In addition, the relatively high silicon content also resulted in poor electronic conductivity, resulting in relatively poor cycling performance of the lithium-ion battery. The preparation parameters of the silicon-carbon material are within the range of this application, and the thickness of the silicon coating layer is within the range of this application. The lithium-ion battery has good kinetic performance and cycling performance, and also has a high energy density.

[0143] From Examples 1-1, 1-6, and 1-7, it can be seen that when the silane aeration rate is increased and the silane introduction time is shortened, under these reaction conditions, silane is more easily deposited on the surface of the material, so the surface silicon coating layer is thicker, which also causes the silane utilization rate to decrease, resulting in a decrease in the mass percentage of silicon element in the silicon-carbon material and a decrease in the reversible capacity. However, due to the thicker thickness of the surface silicon coating layer, the value of I1 / I2 becomes smaller, and due to the decrease in its reversible capacity, the actual energy density of the lithium-ion battery is ultimately reduced. However, due to the reasonable thickening of the silicon coating layer, its kinetic performance will improve, and ΔE and 25°C 10C discharge temperature rise will both be reduced. At the same time, due to the improvement in kinetic performance, the polarization of the lithium-ion battery during the cycle becomes smaller, which can improve the consumption of electrolyte by the negative electrode, resulting in a slight improvement in the cycle performance of the lithium-ion battery. On the contrary, when the silane aeration rate is reduced and the silane introduction time is extended, more silane is adsorbed and deposited in the pores inside the porous carbon, which reduces the thickness of the silicon coating layer on the particle surface. However, the utilization rate of silane will be slightly improved, resulting in a certain increase in the mass percentage of silicon element in the silicon-carbon material and the reversible capacity of the silicon-carbon material, and a slight increase in the energy density of the lithium-ion battery. At the same time, the reduction in the thickness of the surface silicon coating layer will lead to an increase in the I1 / I2 value, and the kinetic properties of the silicon-carbon material will also deteriorate slightly, resulting in an increase in the ΔE and 25℃10C discharge temperature rise of the lithium-ion battery. The cycle performance will also deteriorate slightly due to the increase in the polarization of the lithium-ion battery.

[0144] From Examples 1-2, 1-8 to 1-10, it can be seen that the parameter that is changed is the acetylene introduction time, that is, the coating time of the carbon coating layer. As the coating time increases, the thickness of the carbon coating layer will also increase. Compared with Examples 1-2 and 1-9, Example 1-8 has an increased thickness of the carbon coating layer due to the extended coating time, which leads to an increase in the mass percentage of carbon elements in the silicon-carbon material and a decrease in the mass percentage of silicon elements. The reversible capacity of the silicon-carbon material and the energy density of the lithium-ion battery are reduced. At the same time, due to the thicker thickness of the carbon coating layer, it is more difficult for lithium ions to pass through the carbon coating layer, resulting in a deterioration in the kinetic performance of the silicon-carbon material, an increase in ΔE, and a 25°C 10C discharge temperature rise, and a deterioration in the cycle performance. Compared with Example 1-2 and Example 1-9, Example 1-10 has a further shortened coating time, which leads to poor conductivity of the silicon-carbon material and hindered electron transport in the negative electrode sheet, thereby causing poor kinetic performance of the lithium-ion battery, increased ΔE and 25°C 10C discharge temperature rise, and increased consumption of electrolyte due to the thinning of the carbon coating layer, resulting in poor cycle performance of the lithium-ion battery.

[0145] As can be seen from Examples 1-9, 1-11, and 1-12, the primary change is the amount of silicon added to the negative electrode. Increasing the silicon addition reduces the mass percentage ratio of artificial graphite to silicon-carbon material in the negative electrode, improving the energy density of the lithium-ion battery. However, the increased silicon content hinders electron transport and lithium ion diffusion in the negative electrode, deteriorating the kinetic performance of the lithium-ion battery, increasing ΔE and the 25°C / 10C discharge temperature rise. Furthermore, increased silicon content exacerbates electrolyte consumption by the negative electrode, leading to poor cycling performance. Reducing the silicon addition has the opposite effect, reducing the energy density of the lithium-ion battery, but improving both kinetic and cycling performance.

[0146] From Example 1-9, Example 1-13 to Example 1-16, it can be seen that the performance index of artificial graphite is mainly changed. In Example 1-13, the particle size of artificial graphite is D / I G The results show that the kinetic performance is poor and the cycle performance is also poor. D / I G , and its kinetic performance and cycle performance are the best. In Examples 1-9 and 1-16, the particle size of the carbon material remains unchanged, and the specific surface area of ​​the carbon material in Example 1-16 is relatively large. D / I G The kinetic performance of Example 1-16 is slightly better, but due to the large specific surface area, there are more active sites and more side reactions, which will lead to poor cycle performance of the lithium ion battery. In Examples 1-9 and 1-14, the particle size of the carbon material remains unchanged. D / I G The smaller the particle size, the better the dynamic performance and the better the cycle performance.

[0147] Compared with Example 1-9, Example 1-17 adopts a bipolar tab structure. In this type of structure, when the lithium-ion battery is discharged, electrons can only move to the electrode through the two tabs, resulting in a higher current density near the tabs and poor current density distribution uniformity in the pole piece. The negative pole piece contains silicon material, which leads to a slightly higher sheet resistance of the negative pole piece. Therefore, the more concentrated the current density distribution, the greater the polarization of the lithium-ion battery, resulting in a larger ΔE and poorer cycle performance. In Example 1-9, by retaining an empty current collector without a material layer during coating and converting the empty current collector into a full-tab structure through a flattening process after winding, current can be transmitted through the empty current collector, which can further improve the uniformity of the current density distribution in the pole piece, reduce the polarization of the lithium-ion battery, and improve the dynamic performance and cycle performance of the lithium-ion battery.

[0148] In Comparative Example 1, the silane introduction time is further shortened to control the absence of a silicon coating on the surface of the material. At this time, lithium ions can only diffuse into the interior of the particles through the pores after passing through the carbon coating, resulting in poor kinetic performance of the lithium-ion battery.

[0149] The material of Comparative Example 2 has no carbon coating layer, resulting in poor electron conductivity of the material, which in turn causes the lithium-ion battery to have a large impedance and poor dynamic performance. During the cycle, direct contact of silicon with the electrolyte will also cause rapid consumption of the electrolyte, resulting in poor cycle performance of the lithium-ion battery.

[0150] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article comprising a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, or article.

[0151] Each embodiment in this specification is described in a related manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0152] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery, comprising an electrode assembly, the electrode assembly comprising a negative electrode plate, a positive electrode plate and a separator, the negative electrode plate comprising a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, the negative electrode material layer comprising a silicon-carbon material, the silicon-carbon material comprising a substrate, a silicon coating layer and a carbon coating layer, the substrate comprising porous carbon and nano-silicon particles, the porous carbon having the nano-silicon particles in its pores, and the silicon coating layer disposed between the substrate and the carbon coating layer.

2. The secondary battery according to claim 1, wherein The secondary battery is discharged at a rate of 10C at -20°C, and the difference between the initial discharge voltage E0 and the valley voltage E1 during the discharge process is ΔE, where 0.1V≤ΔE≤0.6V.

3. The secondary battery according to claim 1, wherein The thickness of the silicon coating layer is H1 nm, the thickness of the carbon coating layer is H2 nm, 1≤H1≤100, 5≤H2≤100.

4. The secondary battery according to claim 1, wherein Based on the mass of the silicon-carbon material, the mass percentage of silicon element in the silicon-carbon material is W1%, the mass percentage of carbon element in the silicon-carbon material is W2%, 40≤W1≤70, 30≤W2≤60.

5. The secondary battery according to any one of claims 1 to 4, wherein In the first-cycle delithiation dQ / dV curve of the silicon-carbon material, there is a first delithiation peak in the range of 0.25V to 0.32V, and a second delithiation peak in the range of 0.35V to 0.45V. The peak intensity of the first delithiation peak is I1, and the peak intensity of the second delithiation peak is I2, 0.1≤I1 / I2≤3.

6. The secondary battery according to any one of claims 1 to 4, wherein The reversible capacity of the silicon-carbon material at 0.05C is D0 mAh / g, and 1500≤D0≤2500.

7. The secondary battery according to any one of claims 1 to 4, wherein The silicon-carbon material satisfies at least one of the following characteristics: (1) The thickness of the silicon coating layer is H1 nm, the thickness of the carbon coating layer is H2 nm, 3≤H1≤80, 10≤H2≤50; (2) Based on the mass of the silicon-carbon material, the mass percentage of silicon in the silicon-carbon material is W1%, the mass percentage of carbon in the silicon-carbon material is W2%, 45≤W1≤65, 35≤W2≤55; (3) In the first-cycle delithiation dQ / dV curve of the silicon-carbon material, there is a first delithiation peak in the range of 0.25V to 0.32V, and a second delithiation peak in the range of 0.35V to 0.45V. The peak intensity of the first delithiation peak is I1, and the peak intensity of the second delithiation peak is I2, 0.2≤I1 / I2≤2.

8. The secondary battery according to any one of claims 1 to 4, wherein The negative electrode material layer further includes a carbon material, and the carbon material satisfies at least one of the following characteristics: (1) The carbon material comprises at least one of natural graphite, artificial graphite or hard carbon; (2) The particle size Dv50 of the carbon material satisfies the following conditions: 5 μm ≤ Dv50 ≤ 18 μm; (3) The specific surface area of ​​the carbon material satisfies BET: 0.5 m 2 / g≤BET≤3m 2 / g; (4) In the Raman spectrum of the carbon material, at 1300 cm -1 to 1400cm -1 There is a peak intensity of I in the range D The first characteristic peak at 1550 cm -1 to 1650cm -1 There is a peak intensity of I in the range G The second characteristic peak, 0.1<I D / I G <0.

4.

9. The secondary battery according to claim 8, wherein Based on the sum of the mass of the carbon material and the silicon-carbon material, the ratio of the mass percentage of the carbon material to the mass percentage of the silicon-carbon material is 1 to 20.

10. The secondary battery according to any one of claims 1 to 4, wherein The electrode assembly also includes a positive electrode tab and a negative electrode tab. The positive electrode plate includes a first empty foil area and a positive electrode material layer area, and the positive electrode tab is arranged in the first empty foil area. The negative electrode plate includes a second empty foil area and a negative electrode material layer area, and the negative electrode tab is arranged in the second empty foil area.

11. The secondary battery according to claim 10, wherein Along the width direction of the unfolded negative electrode sheet, the negative electrode sheet includes a first edge and a second edge opposite to each other. From the first edge to the second edge, the negative electrode sheet is sequentially provided with the second empty foil area and the negative electrode material layer area. 12 . An electronic device comprising the secondary battery according to claim 1 .

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