Electrochemical device, preparation method thereof and electronic device

Abstract

The invention provides an electrochemical device, a preparation method thereof and an electronic device. The electrochemical device comprises an electrode assembly, and the electrode assembly comprises a positive pole piece, an isolating membrane and a negative pole piece which are arranged in sequence; the negative electrode plate comprises a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector, and the negative electrode material layer comprises silicon-based particles; wherein the depth of the silicon-based particles embedded into the isolating membrane is A [mu] m, the thickness of the isolating membrane is H [mu] m, 0 < = A < = 5, and 0% < = A / H < = 50%. The electrochemical device provided by the invention has good cycle performance and relatively low self discharge.

Description

Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to an electrochemical device and a preparation method thereof, and an electronic device. Background Art

[0002] The positive electrode active materials (such as lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide) and silicon-based negative electrode materials used in electrochemical devices have high hardness and irregular shapes. During the production process of electrochemical devices, the positive electrode active materials and silicon-based negative electrode materials are prone to damage the isolation membrane under high pressure; at the same time, under high voltage, the sharp corners of the positive electrode active material and silicon-based negative electrode material particles may cause tip discharge, damaging the isolation membrane, thereby causing the isolation membrane to lose its function of isolating the positive and negative electrode sheets. These problems will lead to higher self-discharge of electrochemical devices, faster capacity decay, shorter service life, and also pose certain safety risks.

[0003] Therefore, during the fabrication of electrochemical devices, a ceramic layer is typically applied to the surface of the separator's base membrane to reduce damage from positive electrode active materials, silicon-based negative electrode materials, or other particles. However, the interaction between ceramic particles is weak, limiting their protective effect on the base membrane. Furthermore, ceramic particles are also relatively hard, potentially damaging the base membrane under significant pressure. Summary of the Invention

[0004] The purpose of the present application is to provide an electrochemical device and a preparation method thereof, and an electronic device, so as to reduce the self-discharge of the electrochemical device and improve the cycle performance of the electrochemical device.

[0005] It should be noted that in the invention content of this application, lithium-ion batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0006] The first aspect of the present application provides an electrochemical device, comprising an electrode assembly, the electrode assembly comprising a positive electrode sheet, a separator, and a negative electrode sheet arranged in sequence. The negative electrode sheet comprises a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector. The negative electrode material layer comprises silicon-based particles. The depth of the silicon-based particles embedded in the separator is A μm, the thickness of the separator is H μm, 0≤A≤5, 0%≤A / H≤50%. By regulating the values ​​of A and A / H within the above ranges, it is beneficial to reduce the risk of the separator being punctured by silicon-based particles, thereby reducing the risk of self-discharge and thermal runaway caused by the separator being punctured by silicon-based particles. At the same time, it is beneficial to reduce damage to the separator caused by the expansion of silicon-based particles during the cycle, reduce the self-discharge of the electrochemical device, and reduce the capacity loss of the electrochemical device during the cycle, thereby improving the cycle performance and safety performance of the electrochemical device.

[0007] In some embodiments of the present application, 0≤A≤2. When the value of A is within the above range, the self-discharge of the electrochemical device can be further reduced, and the cycle performance and safety performance of the electrochemical device can be improved.

[0008] In some embodiments of the present application, 0%≤A / H≤20%. When the value of A / H is within the above range, the self-discharge of the electrochemical device can be further reduced, and the cycle performance and safety performance of the electrochemical device can be improved.

[0009] In some embodiments of the present application, the voltage drop per unit time of the electrochemical device is K mV / h, 0≤K≤0.06, preferably, 0≤K≤0.04. When the value of K is within the above range, it indicates that the self-discharge of the electrochemical device is low, which can reduce the capacity loss of the electrochemical device during the cycle process, and the electrochemical device has good cycle performance.

[0010] In some embodiments of the present application, the 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 positive electrode material layer includes a positive electrode active material. The depth of the positive electrode active material embedded in the separator is B μm, and 0% ≤ B / H ≤ 50%. When the value of B / H is within the above range, the ratio of the depth of the positive electrode active material embedded in the separator to the total thickness of the separator is small, and the degree of embedding of the positive electrode active material in the separator is small, which helps reduce the risk of the separator being punctured by the positive electrode active material. In turn, it reduces the risk of self-discharge and thermal runaway caused by puncture of the separator by the positive electrode active material, thereby reducing the self-discharge of the electrochemical device. At the same time, lower self-discharge can reduce the capacity loss of the electrochemical device during cycling, thereby improving the cycling performance and safety performance of the electrochemical device.

[0011] In some embodiments of the present application, 0% ≤ (A + B) / H ≤ 60%. When the value of (A + B) / H is within the above range, the ratio of the depth of the positive electrode active material and the silicon-based particles embedded in the separator to the total thickness of the separator is small, and the degree of embedding of the positive electrode active material and the silicon-based particles in the separator is small. While the separator has an isolation effect, the risk of self-discharge and thermal runaway caused by the separator being punctured by particles of the positive electrode active material or the silicon-based particles is reduced, thereby reducing the self-discharge of the electrochemical device, reducing the capacity loss of the electrochemical device during the cycle process, and improving the cycle performance and safety performance of the electrochemical device.

[0012] In some embodiments of the present application, the separator includes a base membrane, the base membrane includes an observation area, the size of the observation area is 25 μm × 40 μm, and the ratio of the damaged area of ​​the base membrane in the observation area to the area of ​​the observation area is C%, and 0≤C≤40. When the value of C is within the above range, the base membrane is less damaged by the embedding or extrusion of the positive electrode active material and the silicon-based particles, and the degree of embedding of the positive electrode active material and the silicon-based particles into the separator is less. While the separator has an isolation effect, the risk of self-discharge and thermal runaway caused by the separator being punctured by the particles of the positive electrode active material or the silicon-based particles is reduced, thereby reducing the self-discharge of the electrochemical device, reducing the capacity loss of the electrochemical device during the cycle process, and improving the cycle performance and safety performance of the electrochemical device.

[0013] In some embodiments of the present application, the silicon-based particles include at least one of silicon-carbon particles or silicon-oxygen particles. Preferably, the silicon-based particles include silicon-carbon particles. When the silicon-based particles are selected from the above materials, they are beneficial for increasing the energy density of the electrochemical device and can also provide the electrochemical device with a lower cycle expansion rate, thereby improving the cycle performance of the electrochemical device.

[0014] In some embodiments of the present application, the mass percentage of the silicon-based particles is W based on the mass of the negative electrode material layer. Si %,1≤W Si ≤45. When W Si When the value of is within the above range, it is beneficial to improve the energy density of the electrochemical device, and can make the electrochemical device have a lower cycle expansion rate, thereby improving the cycle performance of the electrochemical device.

[0015] In some embodiments of the present application, the Dv50 of the silicon-based particles is D1 μm, the Dv90 of the silicon-based particles is D2 μm, 3≤D1≤12, and 4≤D2≤14. When the values ​​of D1 and D2 are within the above ranges, by regulating the particle size of the silicon-based particles, the particle size distribution of the silicon-based particles is narrow, which can reduce the degree of damage to the isolation membrane caused by the silicon-based particles, reduce the self-discharge of the electrochemical device, reduce the capacity loss of the electrochemical device during the cycle, improve the safety performance of the electrochemical device, and at the same time, the electrochemical device has good cycle performance.

[0016] In some embodiments of the present application, the ratio of the shortest diameter to the longest diameter of a single silicon-based particle is L, and 0.6≤L≤1. When the value of L is within the above range, the self-discharge of the electrochemical device can be further reduced, the capacity loss of the electrochemical device during the cycle process can be reduced, and the cycle performance and safety performance of the electrochemical device can be improved.

[0017] In some embodiments of the present application, the Dv90 of the positive electrode active material is D3μm, 4≤D3≤14, and D3≤2H. By regulating the Dv90 and D3 values ​​of the positive electrode active material to satisfy the above relationship with the 2H value, the particle size distribution of the positive electrode active material is narrow, which can reduce the degree of damage to the separator by the positive electrode active material, thereby reducing the self-discharge of the electrochemical device, reducing the capacity loss of the electrochemical device during the cycle process, and improving the cycle performance and safety performance of the electrochemical device.

[0018] In some embodiments of the present application, the separator includes a base film, a ceramic layer, and an adhesive layer, wherein the ceramic layer is disposed between the base film and the adhesive layer. The base film has a thickness of h μm, where 2 ≤ h ≤ 7. When the value of h is within the above range, the thinner thickness can reduce the space occupied by the separator in the electrochemical device, increase the content of the electrode active material in the electrochemical device, and thus increase the energy density of the electrochemical device; at the same time, it can shorten the transfer path of lithium ions and improve the cycling performance of the electrochemical device. Preferably, 2 ≤ h ≤ 5. When h meets this range, the cycling performance and self-discharge phenomenon of the electrochemical device can be better improved.

[0019] In some embodiments of the present application, the puncture strength of the base film is P1 gf, the unit puncture strength of the base film is P2 gf / μm, 220 ≤ P1 ≤ 900, 55 ≤ P2 ≤ 160; preferably, 260 ≤ P1 ≤ 900. When the values ​​of P1 and P2 are within the above ranges, it indicates that the base film also has good puncture resistance, reduces the self-discharge of the electrochemical device, and improves the safety performance of the electrochemical device.

[0020] In some embodiments of the present application, the diameter of the fibers of the base membrane is d μm, with 0.05 ≤ d ≤ 0.3. When the value of d is within the above range, the thicker base membrane fibers can improve the puncture resistance of the base membrane and the overall mechanical strength of the separator, thereby reducing the risk of internal short circuits caused by puncture of the separator by silicon-based particles or positive electrode active materials, thereby reducing the self-discharge of the electrochemical device and improving the safety performance of the electrochemical device.

[0021] In some embodiments of the present application, the base film has a crystallinity of V%, with a range of 60 ≤ V ≤ 80. When the value of V is within the above range, the base film has a high degree of crystallinity and strong rigidity, which can further improve the puncture resistance of the base film, thereby reducing the risk of internal short circuit caused by puncture of the separator by silicon-based particles or positive electrode active materials, thereby reducing the self-discharge of the electrochemical device and improving the safety performance of the electrochemical device.

[0022] In some embodiments of the present application, the ceramic layer includes inorganic particles, and the inorganic particles include at least one of aluminum oxide, boehmite, barium titanate, barium sulfate, titanium dioxide, melamine cyanurate, triphenyl phosphate, melamine polyphosphate, or ammonium polyphosphate; preferably, the inorganic particles include at least one of melamine cyanurate, triphenyl phosphate, or melamine polyphosphate. When the inorganic particles are selected from the above materials, using the above materials in the ceramic layer can improve the heat resistance, oxidation resistance, and electrolyte wetting properties of the separator, and the application of the ceramic particles in the ceramic layer can improve the mechanical properties of the separator, reduce the embedding degree of silicon-based particles and positive electrode active materials, thereby reducing the self-discharge of the electrochemical device, reducing the capacity loss of the electrochemical device during cycling, and improving the cycling performance and safety performance of the electrochemical device.

[0023] In some embodiments of the present application, the peel strength between the ceramic layer and the base film is FN / m, 6≤F≤100. When the value of F is within the above range, the ceramic layer is not easily detached when the separator is squeezed by silicon-based particles or positive electrode active material particles during long-term cycling of the electrochemical device, thereby improving the protective effect of the ceramic layer on the base film, further reducing the self-discharge of the electrochemical device and improving the safety performance of the electrochemical device.

[0024] The second aspect of the present application provides a method for preparing an electrochemical device in any of the aforementioned embodiments, comprising the following steps: preparing a positive electrode sheet, a negative electrode sheet, and a separator, stacking the negative electrode sheet, the separator, and the positive electrode sheet in order, assembling an electrode assembly, placing the electrode assembly in a packaging bag, and packaging and shaping the electrochemical device; wherein, during the shaping process, the electrochemical device is subjected to a pressure of P3 MPa, and the pressure time of the electrochemical device is t min, 1.2≤P3≤2.2, 20≤t≤120. When the value of P3 and the value of t are regulated within the above range, the adhesive layer can exert a better adhesive effect while reducing damage to the separator, thereby reducing the self-discharge of the electrochemical device, reducing the capacity loss of the electrochemical device during the cycle, and improving the cycle performance and safety performance of the electrochemical device.

[0025] The third aspect of the present application provides an electronic device, which includes the electrochemical device in any of the aforementioned embodiments, or includes the electrochemical device prepared by the preparation method in any of the aforementioned embodiments. The electronic device of the present application has good performance.

[0026] Beneficial effects of this application:

[0027] The present application provides an electrochemical device, a preparation method thereof, and an electronic device. The electrochemical device includes an electrode assembly, the electrode assembly including, in sequence, a positive electrode sheet, a separator, and a negative electrode sheet; the negative electrode sheet includes a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector, the negative electrode material layer including silicon-based particles; wherein the silicon-based particles are embedded in the separator to a depth of A μm, the separator thickness is H μm, 0≤A≤5, and 0%≤A / H≤50%. By regulating the values ​​of A and A / H within the above ranges, the risk of the separator being punctured by silicon-based particles is reduced, thereby reducing the risk of self-discharge and thermal runaway caused by the separator being punctured by silicon-based particles; and at the same time, it is beneficial to reduce damage to the separator caused by expansion of silicon-based particles during cycling, reduce self-discharge of the electrochemical device, and reduce capacity loss of the electrochemical device during cycling, thereby improving the cycling performance and safety performance of the electrochemical device.

[0028] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. 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.

[0030] Figure 1 A schematic diagram of a cross section of a separator embedded with silicon-based particles and a positive electrode active material along a thickness direction according to an embodiment of the present application;

[0031] Figure 2 A scanning electron microscope image of a portion of the surface of a base film according to an embodiment of the present application;

[0032] Figure 3 A topographical diagram of a cross section along the thickness direction of an isolation film embedded with silicon-based particles according to an embodiment of the present application;

[0033] Figure 4 This is a scanning electron microscope image of a portion of the surface of the base film according to one embodiment of the present application. DETAILED DESCRIPTION

[0034] The following will be combined with the embodiments of the present application and the accompanying drawings to clearly and completely describe the technical solutions in this application. Obviously, the embodiments described 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.

[0035] It should be noted that, in the specific embodiments of the present application, a lithium-ion battery is used as an example of an electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to a lithium-ion battery.

[0036] The first aspect of the present application provides an electrochemical device, which includes an electrode assembly, and the electrode assembly includes a positive electrode sheet, a separator and a negative electrode sheet arranged in sequence; the negative electrode sheet includes a negative electrode collector and a negative electrode material layer arranged on at least one surface of the negative electrode collector; the above-mentioned "negative electrode material layer arranged on at least one surface of the negative electrode collector" means that the negative electrode material layer can be arranged on one surface of the negative electrode collector along the thickness direction, or on two surfaces of the negative electrode collector along the thickness direction. It should be noted that the "surface" here can be the entire area of ​​the surface of the negative electrode collector, or a partial area of ​​the surface of the negative electrode collector. This application has no special restrictions, as long as the purpose of this application can be achieved. The negative electrode material layer includes silicon-based particles, such as Figure 1 As shown, the depth of silicon-based particles 12 embedded in isolation film 11 is A μm, the thickness of the isolation film is H μm, 0 ≤ A ≤ 5, 0% ≤ A / H ≤ 50%; preferably, 0 ≤ A ≤ 2, 0% ≤ A / H ≤ 20%. For example, the value of A can be 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or a range consisting of any two thereof; the value of A / H can be 0%, 10%, 20%, 30%, 40%, 50%, or a range consisting of any two thereof.

[0037] The inventors have discovered that when the value of A and / or A / H is too high, for example, when the value of A is greater than 5 and the value of A / H is greater than 50%, the silicon-based particles cause significant damage to the separator, which can easily lead to self-discharge or thermal runaway of the electrochemical device, reducing the safety performance of the electrochemical device. Self-discharge can also lead to increased capacity loss of the electrochemical device and reduced cycling performance of the electrochemical device. By regulating the values ​​of A and A / H within the above ranges, the risk of the separator being punctured by silicon-based particles is reduced, thereby reducing the risk of self-discharge and thermal runaway caused by puncture of the separator by silicon-based particles. It also helps to reduce damage to the separator caused by the expansion of silicon-based particles during cycling, reduce the self-discharge of the electrochemical device, and reduce the capacity loss of the electrochemical device during cycling, thereby improving the cycling performance and safety of the electrochemical device.

[0038] In some embodiments of the present application, 3≤H≤15. For example, the value of H can be 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or a range consisting of any two values ​​therein.

[0039] In some embodiments of the present application, the voltage drop per unit time of the electrochemical device is K mV / h, 0≤K≤0.06, preferably, 0≤K≤0.04. For example, the value of K can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, or a range consisting of any two values ​​therein. The value of K reflects the self-discharge of the electrochemical device, and the smaller the value of K, the lower the self-discharge of the electrochemical device. When the value of K is within the above range, it indicates that the self-discharge of the electrochemical device is low, which can reduce the capacity loss of the electrochemical device during the cycle, and the electrochemical device has good cycle performance.

[0040] In some embodiments of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector. The above-mentioned "positive electrode material layer provided on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be provided on one surface of the positive electrode current collector along the thickness direction, or on two surfaces of the positive electrode current collector along the thickness direction. It should be noted that the "surface" here can be the entire area of ​​the surface of the positive electrode current collector or a partial area of ​​the surface of the positive electrode current collector. This application has no special restrictions as long as the purpose of this application can be achieved. The positive electrode material layer includes positive active materials, such as Figure 1 As shown, the depth of the positive electrode active material 13 embedded in the separator 11 is Bμm, and 0% ≤ B / H ≤ 50%. For example, the value of B / H can be 0%, 10%, 20%, 30%, 40%, 50%, or a range consisting of any two of these values. When the value of B / H is within the above range, the ratio of the depth of the positive electrode active material embedded in the separator to the total thickness of the separator is small, and the degree of embedding of the positive electrode active material in the separator is small, which helps to reduce the risk of the separator being punctured by the positive electrode active material. In turn, it reduces the risk of self-discharge and thermal runaway caused by the separator being punctured by the positive electrode active material. At the same time, lower self-discharge can reduce the capacity loss of the electrochemical device during the cycle process, thereby improving the cycle performance and safety performance of the electrochemical device.

[0041] In some embodiments of the present application, 0≤B≤5. For example, the value of B can be 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or a range consisting of any two values ​​therein.

[0042] In some embodiments of the present application, 0%≤(A+B) / H≤60%. For example, the value of (A+B) / H can be 0%, 10%, 20%, 30%, 40%, 50%, 60% or a range consisting of any two values ​​therein. The value of (A+B) / H reflects the embedding of the isolation membrane by silicon-based particles and positive electrode active materials. When the value of (A+B) / H is within the above range, the ratio of the depth of the positive electrode active material and the silicon-based particles embedded in the isolation membrane to the total thickness of the isolation membrane is small, and the degree to which the positive electrode active material and the silicon-based particles are embedded in the isolation membrane is small. While the isolation membrane has an isolation effect, it reduces the risk of self-discharge and thermal runaway caused by the isolation membrane being punctured by particles of the positive electrode active material or silicon-based particles, thereby reducing the self-discharge of the electrochemical device, reducing the capacity loss of the electrochemical device during the cycle, and improving the cycle performance and safety performance of the electrochemical device.

[0043] In some embodiments of the present application, the isolation film includes a base film, the base film includes an observation area, the size of the observation area is 25 μm×40 μm, and the ratio of the damaged area of ​​the base film in the observation area to the area of ​​the observation area is C%, and 0≤C≤40. For example, the value of C can be 0, 5, 10, 15, 20, 25, 30, 35, 40, or a range consisting of any two of these values. Figure 2 As shown, due to the embedding of silicon-based particles or positive electrode active materials into the separator, the base membrane is squeezed or embedded into the base membrane, resulting in damage to the base membrane surface. The damaged area reflects the embedding of the separator into the silicon-based particles and the positive electrode active material. When the value of C is within the above range, the base membrane is less damaged by the embedding or squeezing of the positive electrode active material and silicon-based particles, and the degree of embedding of the positive electrode active material and silicon-based particles into the separator is less. While the separator provides an isolation effect, the risk of self-discharge and thermal runaway caused by puncture of the separator by positive electrode active material particles or silicon-based particles is reduced. This reduces the self-discharge of the electrochemical device, reduces the capacity loss of the electrochemical device during cycling, and improves the cycling performance and safety of the electrochemical device.

[0044] In some embodiments of the present application, the silicon-based particles include at least one of silicon-carbon particles or silicon-oxygen particles. Preferably, the silicon-based particles include silicon-carbon particles. In the present application, based on the mass of the silicon-carbon particles, the mass percentage of silicon in the silicon-carbon particles is 15% to 45%, and the mass percentage of carbon in the silicon-carbon particles is 55% to 85%. Based on the mass of the silicon-oxygen particles, the mass percentage of silicon in the silicon-oxygen particles is 25% to 50%, and the mass percentage of oxygen in the silicon-oxygen particles is 50% to 75%. When the silicon-based particles are selected from the above materials, it is beneficial to improve the energy density of the electrochemical device, and can make the electrochemical device have a lower cycle expansion rate, thereby improving the cycle performance of the electrochemical device.

[0045] In some embodiments of the present application, the mass percentage of the silicon-based particles is W based on the mass of the negative electrode material layer. Si %,1≤W Si ≤45. For example, W Si The value of can be 1, 5, 10, 15, 20, 25, 30, 35, 40, 45 or a range consisting of any two of them. Si When the value of is within the above range, it is beneficial to improve the energy density of the electrochemical device, and can make the electrochemical device have a lower cycle expansion rate, thereby improving the cycle performance of the electrochemical device.

[0046] In some embodiments of the present application, the Dv50 of the silicon-based particles is D1μm, the Dv90 of the silicon-based particles is D2μm, 3≤D1≤12, 4≤D2≤14. For example, the value of D1 can be 3, 5, 7, 9, 11, 12, or a range consisting of any two of these values; the value of D2 can be 4, 4.2, 4.5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or a range consisting of any two of these values. When the values ​​of D1 and D2 are within the above ranges, by controlling the particle size of the silicon-based particles, the particle size distribution of the silicon-based particles is narrow, which can reduce the degree of damage to the isolation membrane caused by the silicon-based particles, reduce the self-discharge of the electrochemical device, reduce the capacity loss of the electrochemical device during the cycle, improve the safety performance of the electrochemical device, and at the same time, the electrochemical device has good cycle performance.

[0047] In this application, Dv50 means the particle size at which 50% of the volume is accumulated, measured from the smallest particle size, in the volume-based particle size distribution of the material; Dv90 means the particle size at which 90% of the volume is accumulated, measured from the smallest particle size, in the volume-based particle size distribution of the material.

[0048] In some embodiments of the present application, D2≤2H. By regulating the value of D2 and the value of 2H to satisfy the above relationship, the particle size distribution of the silicon-based particles is narrow, which can reduce the degree of damage to the separator by the silicon-based particles, reduce the self-discharge of the electrochemical device, reduce the capacity loss of the electrochemical device during the cycle, improve the safety performance of the electrochemical device, and at the same time, the electrochemical device has good cycle performance.

[0049] The present application does not specifically limit the method for regulating the Dv50 and Dv90 of silicon-based particles, as long as the objectives of the present application can be achieved. For example, commercially available silicon-based particles with different Dv50 or Dv90 values ​​can be selected and the Dv50 or Dv90 values ​​of the silicon-based particles can be measured using the "Particle Size Test" method described in this application to select silicon-based particles with the desired Dv50 or Dv90.

[0050] In some embodiments of the present application, the ratio of the shortest diameter to the longest diameter of a single silicon-based particle is L, and 0.6≤L≤1. For example, the value of L can be 0.6, 0.7, 0.8, 0.9, 1, or a range consisting of any two of these values. The shortest diameter is the shortest distance of a single silicon-based particle in the radial direction, and the longest diameter is the longest distance of a single silicon-based particle in the radial direction. The closer the value of L is to 1, the closer the three-dimensional size of the silicon-based particle is to a circle. When the value of L is within the above range, the possibility of the presence of sharp corners in silicon-based particles can be reduced, and silicon-based particles with relatively regular shapes cause less damage to the isolation membrane, thereby reducing the risk of self-discharge and thermal runaway caused by puncturing the isolation membrane of silicon-based particles, thereby further reducing the self-discharge of the electrochemical device, reducing the capacity loss of the electrochemical device during the cycle, and improving the cycle performance and safety performance of the electrochemical device.

[0051] The present application does not particularly limit the method for regulating the ratio L of the shortest diameter to the longest diameter of a single silicon-based particle, as long as the objectives of the present application can be achieved. For example, commercially available silicon-based particles having different L values ​​can be selected, and the ratio L of the shortest diameter to the longest diameter of a single silicon-based particle can be tested in conjunction with the test method for "Testing the Ratio L of the Shortest Diameter to the Longest Diameter of a Single Silicon-Based Particle" in this application to select silicon-based particles with the desired L value.

[0052] In some embodiments of the present application, the positive electrode active material includes at least one of lithium cobalt oxide, lithium manganese oxide, a ternary positive electrode material containing nickel, cobalt, and manganese, or a ternary positive electrode material containing nickel, manganese, and aluminum. Preferably, the positive electrode active material includes lithium cobalt oxide. These materials have high specific capacity and high voltage resistance. When selected from these materials, the positive electrode active material can improve the energy density and cycle performance of the electrochemical device.

[0053] In some embodiments of the present application, the Dv90 of the positive electrode active material is D3μm, 4≤D3≤14, and D3≤2H. For example, the value of D3 can be 4, 6, 8, 10, 12, 14, or a range consisting of any two of these values. By regulating the Dv90 and D3 values ​​of the positive electrode active material to satisfy the above relationship with the value of 2H, the particle size distribution of the positive electrode active material is narrow, which can reduce the degree of damage to the separator by the positive electrode active material, thereby reducing the self-discharge of the electrochemical device, reducing the capacity loss of the electrochemical device during the cycle process, and improving the cycle performance and safety performance of the electrochemical device.

[0054] This application does not specifically limit the method for regulating the Dv90 of the positive electrode active material, as long as it can achieve the objectives of this application. For example, commercially available positive electrode active materials with different Dv90 values ​​can be selected and tested for Dv90 using the "Particle Size Test" method in this application to select a positive electrode active material with the desired Dv90 value.

[0055] In some embodiments of the present application, the isolation membrane includes a base membrane, a ceramic layer and an adhesive layer, the ceramic layer is arranged between the base membrane and the adhesive layer, and the thickness of the base membrane is hμm, 2≤h≤7. For example, the value of h can be 2, 3, 4, 5, 6, 7 or a range consisting of any two values ​​therein. When the value of h is within the above range, the thinner thickness can reduce the space occupied by the isolation membrane in the electrochemical device, increase the content of the positive electrode active material and silicon-based particles in the electrochemical device, thereby increasing the energy density of the electrochemical device; at the same time, it can shorten the transfer path of lithium ions and improve the cycle performance of the electrochemical device. Preferably, 2≤h≤5, when h meets this range, the cycle performance and self-discharge phenomenon of the electrochemical device can be better improved.

[0056] In some embodiments of the present application, the separator includes a ceramic layer, two adhesive layers, and a base film. Along the thickness of the separator, the ceramic layer is disposed on one side of the base film, the adhesive layers are disposed on both sides of the base film, and the ceramic layer is disposed between the adhesive layers and the base film. In some embodiments of the present application, the side of the base film on which the ceramic layer is disposed faces the positive electrode sheet.

[0057] In some embodiments of the present application, the isolation membrane includes two ceramic layers, two bonding layers and a base membrane. Along the thickness direction of the isolation membrane, the ceramic layers are arranged on both sides of the base membrane, the bonding layers are arranged on both sides of the base membrane, and the ceramic layer is arranged between the bonding layers and the base membrane.

[0058] In some embodiments of the present application, the puncture strength of the base film is P1 gf, the unit puncture strength of the base film is P2gf / μm, 220≤P1≤900, 55≤P2≤160; preferably, 260≤P1≤900. For example, the value of P1 can be 220, 260, 300, 400, 500, 600, 700, 800, 900, or a range consisting of any two values ​​therein; the value of P2 can be 55, 70, 85, 100, 115, 130, 145, 160, or a range consisting of any two values ​​therein. When the values ​​of P1 and P2 are within the above ranges, it indicates that the base film has good puncture resistance, which is beneficial to reducing the risk of internal short circuit caused by puncturing the isolation membrane by silicon-based particles or positive electrode active materials, thereby reducing the self-discharge of the electrochemical device and improving the safety performance of the electrochemical device.

[0059] In some embodiments of the present application, the diameter of the fibers of the base membrane is d μm, 0.05 ≤ d ≤ 0.3. For example, the value of d can be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, or a range consisting of any two of these values. When the value of d is within the above range, the thicker base membrane fibers can improve the puncture resistance of the base membrane and the mechanical strength of the separator as a whole, which is beneficial to reduce the risk of internal short circuit caused by puncture of the separator by silicon-based particles or positive electrode active materials, thereby reducing the self-discharge of the electrochemical device and improving the safety performance of the electrochemical device.

[0060] In some embodiments of the present application, the crystallinity of the base film is V%, and 60≤V≤80. For example, the value of V can be 60, 65, 70, 75, 80, or a range consisting of any two of these values. When the value of V is within the above range, the base film has a high degree of crystallinity and strong rigidity, which can further improve the puncture resistance of the base film, thereby reducing the risk of internal short circuit caused by puncture of the separator by silicon-based particles or positive electrode active materials, thereby reducing the self-discharge of the electrochemical device and improving the safety performance of the electrochemical device.

[0061] In some embodiments of the present application, the material of the base film includes at least one of polypropylene, polyethylene, polyimide, aramid, or polyvinylidene fluoride.

[0062] In some embodiments of the present application, the ceramic layer includes inorganic particles, and the inorganic particles include at least one of aluminum oxide, boehmite, barium titanate, barium sulfate, titanium dioxide, melamine cyanurate, triphenyl phosphate, melamine polyphosphate, or ammonium polyphosphate; preferably, the inorganic particles include at least one of melamine cyanurate, triphenyl phosphate, or melamine polyphosphate. When the inorganic particles are selected from the above materials, using the above materials in the ceramic layer can improve the heat resistance, oxidation resistance, and electrolyte wetting properties of the separator. In addition, the application of the inorganic particles in the ceramic layer can improve the mechanical properties of the separator, reduce the embedding degree of silicon-based particles and positive electrode active materials, thereby reducing the self-discharge of the electrochemical device, reducing the capacity loss of the electrochemical device during cycling, and improving the cycling performance and safety performance of the electrochemical device.

[0063] In some embodiments of the present application, the Dv50 of the inorganic particles is D4 μm, 0.2 ≤ D4 ≤ 1.5. For example, the value of D4 can be 0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.5, or a range consisting of any two of these values. When the value of D4 is within the above range, the packing density between the particles can be increased, forming a denser ceramic layer on the surface of the base film, enhancing the protection of the base film, reducing the occurrence of short circuits in the electrochemical device, thereby further reducing the self-discharge of the electrochemical device and improving the safety performance of the electrochemical device.

[0064] The present application does not specifically limit the method for regulating the Dv50 of the inorganic particles, as long as the objectives of the present application can be achieved. For example, commercially available inorganic particles with different Dv50 values ​​can be selected and the Dv50 values ​​of the inorganic particles can be measured using the "Particle Size Test" method described in this application to select inorganic particles with the desired Dv50 value.

[0065] In some embodiments of the present application, the ceramic layer further includes a first binder, the first binder including at least one of polyacrylic acid, polyvinyl alcohol, styrene-acrylate emulsion, styrene-butadiene rubber emulsion, polymethyl methacrylate, or polyethyl methacrylate. When the first binder is selected from the above materials, it is beneficial to improve the adhesion of the entire ceramic layer, improve the adhesion between the ceramic layer and the base film, improve the peel strength between the ceramic layer and the base film, improve the mechanical properties of the separator, and reduce the embedding degree of silicon-based particles and positive electrode active materials, thereby further reducing the self-discharge of the electrochemical device and improving the safety performance of the electrochemical device.

[0066] In some embodiments of the present application, based on the mass of the ceramic layer, the mass percentage of the first binder is 1% to 8%. For example, the mass percentage of the first binder can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or a range consisting of any two of these values. By regulating the mass percentage of the first binder within the above range, it is beneficial to improve the overall adhesion of the ceramic layer, improve the adhesion between the ceramic layer and the base film, improve the peel strength between the ceramic layer and the base film, improve the mechanical properties of the separator, reduce the degree of embedding of silicon-based particles and positive electrode active materials, thereby further reducing the self-discharge of the electrochemical device and improving the safety performance of the electrochemical device.

[0067] In some embodiments of the present application, the peel strength between the ceramic layer and the base film is FN / m, 6≤F≤100. For example, the value of F can be 6, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or a range consisting of any two of these values. When the value of F is within the above range, it is beneficial for the electrochemical device to be less likely to fall off when the separator is squeezed by silicon-based particles or positive electrode active material particles during long-term cycling, thereby improving the protective effect of the ceramic layer on the base film, thereby further reducing the self-discharge of the electrochemical device and improving the safety performance of the electrochemical device.

[0068] In the present application, the ceramic layer further includes a thickener and a wetting agent. The thickener may include, but is not limited to, at least one of carboxymethyl cellulose, sodium carboxymethyl cellulose (CMC), or lithium carboxymethyl cellulose. The wetting agent may include, but is not limited to, at least one of polyoxyethylene ether, ammonium polyacrylate, ammonium carboxylate, or phenyl polyoxyethylene ether. The present application does not particularly limit the mass ratio of the inorganic particles, the first binder, the thickener, and the wetting agent in the ceramic layer. Those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved.

[0069] In some embodiments of the present application, the bonding layer includes a second binder and a first additive. The present application does not particularly limit the types of the second binder and the first additive, as long as the purpose of the present application can be achieved. For example, the second binder can include but is not limited to polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyamide-imide, polyvinylidene fluoride, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber (SBR), acrylic acid (ester) styrene-butadiene rubber, epoxy resin or nylon at least one. The first additive can include but is not limited to an acrylate solution having a solid content of 20wt% to 50wt%. The present application does not particularly limit the mass ratio of the second binder and the first additive in the bonding 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.

[0070] The present application does not particularly limit the preparation method of the base film, as long as the purpose of the present application can be achieved. For example, the preparation method of the base film may include but is not limited to the following steps: (1) uniformly mixing a first polyethylene material, a second polyethylene material, and a polypropylene material in a mass ratio of (10 to 25): (65 to 87): (3 to 10) to obtain a base film raw material; and uniformly mixing a second additive and a first solvent in a mass ratio of (0.05 to 0.8): (99.2 to 99.95) to obtain a base film solvent. Wherein, the first polyethylene material may include but is not limited to polyethylene resin with a viscosity average molecular weight of 200,000 to 500,000; the second polyethylene material may include but is not limited to polyethylene resin with a viscosity average molecular weight of 600,000 to 2,000,000; the polypropylene material may include but is not limited to polypropylene with a melting point of 162°C to 176°C; the second additive may include but is not limited to at least one of tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]pentaerythritol, tris(2,4-di-tert-butylphenyl)phosphite, β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 2,5-di-tert-butylhydroquinone or 2,5-di-tert-butylhydroquinone; the first solvent may include but is not limited to at least one of paraffin oil or mineral oil. (2) The mixed base film raw material and base film solvent are added to the extruder system respectively, extruded through a T-die, and cast on a casting roller to obtain a first porous film; wherein the mass ratio of the base film raw material to the base film solvent is (15:35) to (65:85). (3) The first porous membrane is stretched transversely at a stretching ratio of 5 to 15 times, and then stretched longitudinally for the first time at a stretching ratio of 5 to 15 times, and then extracted with dichloromethane, and then stretched longitudinally for the second time at a stretching ratio of 0.5 to 5 times, and finally dried with hot air at a temperature of 110°C to 130°C to obtain a second porous membrane, which is then heat-set and rolled up to obtain a base membrane.

[0071] The present application does not impose any particular restrictions on the preparation method of the isolation membrane, as long as the purpose of the present application can be achieved. For example, in some embodiments, the preparation method of the isolation membrane may include but is not limited to the following steps: (1) adding the second binder and the first additive to the second solvent and mixing them evenly to obtain a bonding layer slurry; (2) adding inorganic particles, the first binder and the thickener to the second solvent and mixing them evenly to obtain a ceramic layer slurry; (3) coating the ceramic layer slurry on one surface of the base membrane of the isolation membrane, drying it, forming a ceramic layer on one surface of the base membrane, coating the bonding layer slurry on the surface of the ceramic layer away from the base membrane, drying it, to obtain an isolation membrane with a single-sided coating of a ceramic layer and a bonding layer; (4) repeating the above steps on the other surface of the base membrane to obtain the isolation membrane. The second solvent can be independently selected from at least one of deionized water, N-methylpyrrolidone (NMP) or dimethylacetamide (DMAC).

[0072] For example, in some embodiments, the preparation method of the isolation membrane may include but is not limited to the following steps: (1) adding the second binder and the first additive to the second solvent and mixing them evenly to obtain a bonding layer slurry; (2) adding inorganic particles, the first binder and the thickener to the second solvent and mixing them evenly to obtain a ceramic layer slurry; (3) coating the ceramic layer slurry on one surface of the base membrane of the isolation membrane, and after drying, forming a ceramic layer on one surface of the base membrane; coating the bonding layer slurry on the surface of the ceramic layer, and after drying, forming a bonding layer on the surface of the ceramic layer away from the base membrane; coating the bonding layer slurry on the other surface of the base membrane, and after drying, forming a bonding layer on the other surface of the base membrane, thereby obtaining an isolation membrane.

[0073] In this application, the thickness h of the base film can be controlled by methods known to those skilled in the art, as long as the objectives of this application are achieved. For example, the thickness h of the base film can be controlled by adjusting the extrusion rate of the extruder. When the extrusion rate increases, the thickness h of the base film increases; when the extrusion rate decreases, the thickness h of the base film decreases.

[0074] In the present application, the diameter d of the fibers of the base membrane can be controlled by methods known to those skilled in the art, as long as the objectives of the present application are achieved. For example, the diameter d of the fibers of the base membrane can be controlled by controlling the viscosity-average molecular weight of the first polyethylene material and / or the viscosity-average molecular weight of the second polyethylene material. When the viscosity-average molecular weight of the first polyethylene material and / or the viscosity-average molecular weight of the second polyethylene material is increased, the diameter d of the fibers of the base membrane increases; when the viscosity-average molecular weight of the first polyethylene material and / or the viscosity-average molecular weight of the second polyethylene material is decreased, the diameter d of the fibers of the base membrane decreases.

[0075] In this application, the crystallinity V of the base film can be controlled by methods known to those skilled in the art, as long as the objectives of this application can be achieved. For example, the crystallinity V of the base film can be controlled by controlling the viscosity-average molecular weight of the first polyethylene material, the viscosity-average molecular weight of the second polyethylene material, or the stretch ratio. When the viscosity-average molecular weight of the first polyethylene material is increased, the viscosity-average molecular weight of the second polyethylene material is increased, or the stretch ratio is increased, the crystallinity V of the base film increases; when the viscosity-average molecular weight of the first polyethylene material is decreased, the viscosity-average molecular weight of the second polyethylene material is decreased, or the stretch ratio is decreased, the crystallinity V of the base film decreases.

[0076] In this application, the thickness H of the isolation membrane is controlled by means known to those skilled in the art, as long as the objectives of this application can be achieved. For example, the thickness H of the isolation membrane can be controlled by controlling the thickness of the base membrane, the thickness of the ceramic layer, or the thickness of the bonding layer. When the thickness of the base membrane, the thickness of the ceramic layer, or the bonding layer increases, the thickness H of the isolation membrane increases; when the thickness of the base membrane, the thickness of the ceramic layer, or the bonding layer decreases, the thickness H of the isolation membrane decreases.

[0077] 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, lithium-copper composite current collector, carbon-copper composite current collector, nickel-copper composite current collector or titanium-copper composite current collector, etc.

[0078] In the present application, the negative electrode material layer also includes a carbon material, which may include but is not limited to at least one of graphite, hard carbon, soft carbon or mesophase microcarbon beads. In some embodiments of the present application, the negative electrode material layer may also include a conductive agent, a second binder and a thickener. The present application does not particularly limit the types of the conductive agent, the second binder and the thickener, as long as the purpose of the present application can be achieved. For example, the second binder and the thickener may be at least one of the aforementioned second binders and thickeners. The conductive agent may include but is not limited to at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, a metal material or a conductive polymer. The above-mentioned conductive carbon black may include but is not limited to at least one of Super P, acetylene black or Ketjen black. The above-mentioned carbon nanotubes may include but is not limited to at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to at least one of vapor-grown carbon fibers (VGCF) or nanocarbon fibers. The above-mentioned metal material may include but is not limited to at least one of metal powder or metal fiber. 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 present application has no particular restrictions on the mass ratio of silicon-based particles, carbon material, conductive agent, second binder and thickener in the negative electrode material layer, and those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. In some embodiments of the present application, the negative electrode material layer includes silicon-based particles, carbon material, second binder and thickener, and the mass ratio of silicon-based particles, carbon material, second binder and thickener in the negative electrode material layer is (1 to 45): (47 to 97.3): (1.5 to 8): (0.2 to 1).

[0079] The present application has no particular limitation on the thickness of the negative electrode current collector and 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 negative electrode current collector is 4 μm to 15 μm, and the thickness of the single-sided negative electrode material layer is 30 μm to 100 μm.

[0080] Optionally, the negative electrode sheet may further include a conductive layer positioned between the negative electrode current collector and the negative electrode material layer. This application does not specifically limit the composition of the conductive layer; it may be any conductive layer commonly used in the art. For example, the conductive layer may include a conductive agent and a second binder. This application does not specifically limit the conductive agent and second binder in the conductive layer, as long as they can achieve the objectives of this application. For example, it may be at least one of the aforementioned conductive agent and second binder.

[0081] The present application does not particularly limit the positive electrode current collector, as long as it can achieve the purpose of the present application. For example, a metal foil or a composite current collector can be used. For example, the metal foil may include but is not limited to aluminum foil; the composite current collector can be obtained by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate.

[0082] In the present application, the positive electrode material layer may further include a conductive agent and a second binder. The present application does not particularly limit the types of the conductive agent and the second binder, as long as the purpose of the present application can be achieved. For example, it can be at least one of the aforementioned conductive agent and the aforementioned second binder. The present application does not particularly limit the mass ratio of the positive electrode active material, the conductive agent, and the second binder in the positive 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.

[0083] The thickness of the positive electrode current collector and the positive electrode material layer is not particularly limited in this application, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, and the thickness of the single-sided positive electrode material layer is 30 μm to 80 μm.

[0084] Optionally, the positive electrode sheet may further include a conductive layer positioned between the positive electrode current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and may be any commonly used conductive layer in the art. The conductive layer includes a conductive agent and a second binder. The present application does not particularly limit the conductive agent and second binder in the conductive layer; for example, the conductive agent and second binder may be at least one of the aforementioned conductive agent and second binder.

[0085] In the present application, the electrolyte includes a lithium salt and a non-aqueous solvent. The present application has no particular restrictions on the lithium salt, as long as the purpose of the present application can be achieved. For example, the lithium salt may include but is not limited to at least one of LiPF6, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiC(SO2CF3)3 or Li2SiF6. The present application has no particular restrictions on the mass percentage of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. For example, based on the mass of the electrolyte, the mass percentage of the lithium salt is 8% to 20%. The present application has no particular restrictions on the non-aqueous solvent, as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent may include but is not limited to at least one of a carbonate compound, a carboxylate compound, an ether compound or other organic solvents. The above-mentioned carbonate compound may include but is not limited to at least one of a chain carbonate compound, a cyclic carbonate compound or a fluorinated carbonate compound. The above-mentioned linear carbonate compound may include but is not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC) or methylethyl carbonate (MEC). The above-mentioned cyclic carbonate compound may include but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinylethylene carbonate (VEC). The above-mentioned fluorocarbonate compound may include but is not limited to at least one of 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 trifluoromethylethylene carbonate. The 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, propyl propionate, γ-butyrolactone, decanoic acid, valerolactone, or caprolactone. The ether compound may include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The other organic solvent may include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. The present application does not particularly limit the mass percentage of the non-aqueous solvent in the electrolyte, as long as the purpose of the present application can be achieved.

[0086] In the present application, the electrochemical device further includes a housing for accommodating a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte, as well as other components known in the field of electrochemistry. This application does not limit the above-mentioned other components. This application does not particularly limit the housing, and it can be a housing known in the art, as long as it can achieve the purpose of this application. For example, the housing can be a hard shell housing or a flexible shell. The material of the hard shell housing can be metal. This application does not limit the type of metal, and a metal hard shell housing known in the art can be used, as long as it can achieve the purpose of this application. The flexible shell can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0087] The present application does not particularly limit the type of electrochemical device, and the electrochemical device may include any device that generates an electrochemical reaction. In the present application, the electrochemical device may include, but is not limited to, a lithium metal electrochemical device, a lithium ion electrochemical device (lithium ion battery), a lithium polymer electrochemical device, or a lithium ion polymer electrochemical device (lithium ion polymer battery).

[0088] The second aspect of the present application provides a method for preparing an electrochemical device in any of the aforementioned embodiments, comprising the following steps: preparing a positive electrode sheet, a negative electrode sheet, and a separator, stacking the negative electrode sheet, the separator, and the positive electrode sheet in order, assembling an electrode assembly, placing the electrode assembly in a packaging bag, and obtaining an electrochemical device after packaging and shaping; wherein, during the shaping process, the electrochemical device is subjected to a pressure of P3 MPa, the pressure time of the electrochemical device is t min, 1.2≤P3≤2.2, 20≤t≤120. For example, the value of P3 can be 1.2, 1.4, 1.6, 1.8, 2, 2.2, or a range consisting of any two of these values; the value of t can be 20, 40, 60, 80, 100, 120, or a range consisting of any two of these values. During the preparation of the electrochemical device, in order to achieve better interfacial contact between the positive electrode sheet and the separator and / or between the negative electrode sheet and the separator, the shaping process under a certain pressure and pressure time can allow the adhesive layer of the separator to play a better bonding role. However, if the pressure is too high or the pressure time is too long, the silicon-based particles, the positive electrode active material or other foreign matter will cause damage to the separator, resulting in a deterioration of the isolation effect of the separator, thereby increasing the self-discharge of the electrochemical device. When the value of P3 and the value of t are adjusted within the above range, the adhesive layer can play a better bonding role while reducing damage to the separator, thereby reducing the self-discharge of the electrochemical device, reducing the capacity loss of the electrochemical device during the cycle, and improving the safety performance and cycle performance of the electrochemical device.

[0089] In this application, the assembly process of the electrode assembly is well known to those skilled in the art and is not particularly limited in this application. For example, the assembly process of the electrode assembly may include, but is not limited to, the following steps: stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and performing winding, folding, and other operations as needed to obtain a wound electrode assembly. Alternatively, stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and then securing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly.

[0090] In this application, the depth A of the silicon-based particles embedded in the isolation film can be controlled by means known to those skilled in the art, as long as the purpose of this application can be achieved. For example, the mass percentage of silicon-based particles W Si , Dv50 of silicon-based particles, Dv90 of silicon-based particles, the ratio L of the shortest diameter to the longest diameter of a single silicon-based particle, the thickness h of the base membrane, the diameter d of the fiber of the base membrane, the crystallinity V of the base membrane, the compressive pressure P3 of the electrochemical device or the compressive time t of the electrochemical device will affect the value of A.

[0091] In this application, the depth B of the cathode active material embedded in the separator is controlled by methods known to those skilled in the art, as long as the objectives of this application are achieved. For example, the value of B may be affected by the Dv90 of the cathode active material, the thickness h of the base membrane, the diameter d of the fibers of the base membrane, the crystallinity V of the base membrane, the compressive pressure P3 of the electrochemical device, or the compressive time t of the electrochemical device.

[0092] The present application does not particularly limit the method for regulating the value of A / H, as long as the purpose of the present application can be achieved. For example, the value of A / H can be regulated by regulating the values ​​of A and H, and the regulation method is as described above.

[0093] The present application does not particularly limit the method for regulating the value of B / H, as long as the purpose of the present application can be achieved. For example, the value of B / H can be regulated by regulating the values ​​of B and H, and the regulation method is as described above.

[0094] The present application does not particularly limit the method for regulating the value of (A+B) / H, as long as the purpose of the present application can be achieved. For example, the value of (A+B) / H can be regulated by regulating the values ​​of A, B, and H, as described above.

[0095] The third aspect of the present application provides an electronic device, which includes the electrochemical device in any of the aforementioned embodiments, or includes the electrochemical device prepared by the preparation method in any of the aforementioned embodiments. The electronic device of the present application has good performance.

[0096] The electronic device of the present application is not particularly limited and can 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.

[0097] Example

[0098] 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.

[0099] Test methods and equipment:

[0100] Particle size test:

[0101] Instrument used: The test equipment used is Mastersizer 3000 produced by Malvern.

[0102] The particle size test method refers to the national standard GB / T 19077-2016. The specific process is: weigh 1g of silicon-based particles and mix them evenly with 20mL of deionized water to obtain a silicon-based particle solution sample. After placing it in an ultrasonic device for 5 minutes, the sample is poured into the sampling system Hydro 2000SM for testing. During the test, when the laser beam passes through the silicon-based particle solution sample, the particle size measurement is completed by measuring the intensity of the scattered light, and then the data is used to analyze and calculate the particle size distribution of the scattering spectrum. A silicon-based particle solution sample is tested three times, and the average value of the three tests is finally taken to measure the Dv50 and Dv90 of the silicon-based particles, that is, D1 and D2.

[0103] 1 g of inorganic particles were weighed and mixed evenly with 20 mL of deionized water to obtain an inorganic particle solution sample. The Dv50 of the inorganic particles, i.e., D4, was obtained by testing according to the above method.

[0104] 1 g of the positive electrode active material was weighed and dispersed in 20 mL of N-methylpyrrolidone and mixed evenly to obtain a positive electrode active material solution sample. The Dv50 of the positive electrode active material, ie, D3, was obtained by testing according to the above method.

[0105] Depth test of silicon-based particles or positive electrode active materials embedded in the isolation film:

[0106] The lithium-ion battery in each embodiment or comparative example was discharged at a constant current of 0.05 C to 3.0 V at 25±5° C.

[0107] The discharged lithium-ion battery was disassembled, and the composite sample of the separator and the negative electrode was taken. The composite sample was plasma cut longitudinally along the thickness direction and polished using argon ion polishing technology to obtain a flat cross section. The cross section morphology was then photographed using a scanning electron microscope (model OXFORD·EDS), as shown in the figure. Figure 3 As shown, the thickness of the isolation film at 10 locations is observed and measured, and the average value is the isolation film thickness H. Then, the position where the silicon-based particles are embedded in the isolation film is found in the cross-sectional topography image, and the maximum distance from the position where the silicon-based particles are embedded in the isolation film to the isolation film surface is measured, which is the depth of the silicon-based particles embedded in the isolation film. The average value of the embedding depths of the 10 silicon-based particles is taken to obtain A, and A / H is calculated.

[0108] Take a composite sample of the separator and the positive electrode sheet, plasma-cut the composite sample longitudinally along the thickness direction, polish it using argon ion polishing technology to obtain a flat cross-section, and then use a scanning electron microscope (model OXFORD·EDS) to capture the cross-sectional topography. Observe and measure the thickness of the separator at 10 locations, and take the average value to obtain the separator thickness H. Then, find the position where the positive electrode active material is embedded in the separator in the cross-sectional topography, measure the maximum distance from the position where the positive electrode active material is embedded in the separator to the separator surface, and calculate the depth B of the positive electrode active material embedded in the separator.

[0109] The ratio of the sum of the depth of silicon-based particles and positive electrode active materials embedded in the isolation membrane to the thickness of the isolation membrane (A+B) / H test:

[0110] Take the lithium ion battery in each embodiment or comparative example and discharge it at a constant current of 0.05C to 3.0V at 25±5°C;

[0111] The discharged lithium-ion battery was disassembled, and a composite sample of the positive electrode sheet, separator, and negative electrode sheet was obtained. The composite sample was plasma-sectioned longitudinally along the thickness direction and polished using argon ion polishing technology to obtain a flat cross-section. The cross-sectional topography was then photographed using a scanning electron microscope (OXFORD EDS). The separator thickness was observed and measured at 10 locations, and the average value was taken to obtain the separator thickness H. The locations where the silicon-based particles and the positive electrode active material were embedded in the separator were then located in the cross-sectional topography. The maximum distance from the location where the silicon-based particles were embedded in the separator to the separator surface was measured, which was the embedding depth of the silicon-based particles in the separator. The embedding depths of the 10 silicon-based particles were averaged to obtain A. The maximum distance from the location where the positive electrode active material was embedded in the separator to the separator surface was measured, which was the embedding depth of the positive electrode active material in the separator. The embedding depth of the positive electrode active material in the separator was averaged to obtain B. (A + B) / H was calculated.

[0112] Test C of the ratio of the damaged area of ​​the basement membrane in the observation area to the area of ​​the observation area:

[0113] Take the lithium ion battery in each embodiment or comparative example and discharge it at a constant current of 0.05C to 3.0V at 25±5°C;

[0114] The discharged lithium-ion battery was disassembled in a drying room (humidity controlled at <2%), and the ceramic layer and adhesive layer on the isolation membrane were cleaned in an ultrasonic cleaner using N-methylpyrrolidone to obtain a base membrane. The base membrane was dried and cut into 1 cm × 1 cm base membrane samples, which were then sprayed with gold. The surface morphology of the base membrane samples was photographed using a scanning electron microscope (model OXFORD·EDS). The scanning electron microscope image of the surface of a portion of the base membrane in one embodiment of the present application is shown in FIG. Figure 2 As shown. Figure 2 In the figure, the dark gray area in the center of the basement membrane surface is the concave area, that is, the damaged area of ​​the basement membrane, and the area of ​​the damaged area is the damaged area.

[0115] The damaged area Sμm of the basement membrane was measured in an observation area of ​​25μm×40μm. 2 , the ratio of the damaged area of ​​the basement membrane in the observation area to the area of ​​the observation area C (%) = S / 1000×100%.

[0116] The ratio of the shortest diameter to the longest diameter of a single silicon-based particle, L, is tested:

[0117] Conductive adhesive was applied to the sample table, and a powdered sample of the silicon-based particles in each embodiment or comparative example was spread flat on the conductive adhesive. The unadhered powder was blown away with an ear bulb, and gold was sprayed. The surface morphology of the silicon-based particles was photographed using a scanning electron microscope (model OXFORD·EDS) at an acceleration voltage of 10 kV, an emission current of 10 mA, and a magnification of 3000 times. The longest and shortest diameters of a single silicon-based particle were measured, and the ratio of the shortest diameter to the longest diameter of a single silicon-based particle, L, was calculated. The shortest and longest diameters of 10 silicon-based particles were observed and measured, and the ratio of the shortest diameter to the longest diameter of the 10 silicon-based particles was calculated. The average value was the ratio of the shortest diameter to the longest diameter of the single silicon-based particle, L.

[0118] Base film thickness test:

[0119] Take the lithium ion battery in each embodiment or comparative example and discharge it at a constant current of 0.05C to 3.0V at 25±5°C;

[0120] The discharged lithium-ion battery was disassembled in a drying room (humidity controlled at <2%), the separator was removed, and the ceramic layer and the adhesive layer on the separator were cleaned in an ultrasonic cleaner using N-methylpyrrolidone to obtain a base film. After the base film was dried, the thickness of the base film at 10 locations was measured using a 10,000-degree thickness gauge, and the average value was the thickness h of the base film.

[0121] Puncture strength of basement membrane, unit puncture strength test:

[0122] Take the lithium ion battery in each embodiment or comparative example and discharge it at a constant current of 0.05C to 3.0V at 25±5°C;

[0123] The discharged lithium-ion battery was disassembled in a drying room (humidity controlled at <2%). The separator was removed and the ceramic layer and adhesive layer on the separator were cleaned in an ultrasonic cleaner using N-methylpyrrolidone to obtain a base membrane. After drying, the base membrane was measured at 10 locations using a 10,000-degree thickness gauge. The average value was the base membrane thickness h. The dried base membrane was fixed to a test fixture with a 10mm hole in the center. A hemispherical steel nail with a diameter of 1mm was lowered at a speed of 120mm / min. The maximum force required to puncture the base membrane was determined as the base membrane puncture strength P1. The unit puncture strength P2 (gf / μm) of the base membrane was calculated as P1 / h.

[0124] Diameter test of base membrane fibers:

[0125] The base film prepared in each embodiment or comparative example was cut into base film samples of 1 cm×1 cm, sprayed with gold, and the surface morphology of the base film samples was photographed at a magnification of 30,000 times using a scanning electron microscope (model OXFORD·EDS). Figure 4As shown, the diameters of the basement membrane fibers at 9 positions within the field of view are measured, and the average value is taken to obtain the diameter d of the basement membrane fibers.

[0126] Crystallinity test:

[0127] The crystallinity of the base films prepared in each embodiment or comparative example was tested using a differential scanning calorimeter (NETZSCH DSC214). The base film sample was placed in a crucible and heated from 30°C to 300°C at a rate of 10°C / min under a nitrogen atmosphere to obtain a differential scanning calorimetry (DSC) curve of the base film sample. The melting endothermic curve of the base film sample was integrated to obtain the melting enthalpy H of the base film sample in J / g. The crystallinity V (%) of the base film = H / (melting enthalpy of 100% polyethylene crystallization × mass percentage of polyethylene in the base film + melting enthalpy of 100% polypropylene crystallization × mass percentage of polypropylene in the base film).

[0128] Peel strength test:

[0129] Take the lithium ion battery in each embodiment or comparative example and discharge it at a constant current of 0.05C to 3.0V at 25±5°C;

[0130] Disassemble the discharged lithium-ion battery in a dry room (humidity controlled at <2%), remove the separator, clean it with dimethylacetamide (DAMC), and then dry it. Cut the dried separator into separator samples with a width of 20 mm, and take at least 5 parallel samples for each lithium-ion battery. Attach one side of the separator sample to a steel plate with double-sided tape, and install the steel plate on the fixed fixture at the bottom of the high-speed rail tensile testing machine. Confirm that the bottom layer of the separator sample on the steel plate is firmly bonded to the steel plate. Tear about 1 cm along the interface between the separator sample and the double-sided tape at one end of the sample in the longitudinal direction. Clamp one corner of the torn separator on the movable fixture at the top of the high-speed rail tensile testing machine, and the sample is ready. Test: Stretch at an angle of 180° and a stretching speed of 50 mm / min until the interface between the separator and the double-sided tape is completely pulled apart. After pulling apart, the ceramic layer and the adhesive layer are bonded to the double-sided tape surface, and the other side of the pulled interface is at least partially exposed base film. Record the average load force (N) during the stretching process and divide it by the sample width (20 mm) to determine the peel strength between the ceramic layer and the base film. Then, average the peel strengths of five parallel samples to obtain the peel strength (F) between the ceramic layer and the base film, expressed in N / m. The time difference between disassembling the lithium-ion battery and completing the test for each separator sample was kept within one hour.

[0131] Voltage drop per unit time test:

[0132] Take the lithium ion battery in each embodiment or comparative example and fully charge it at 25±5°C. The specific steps are: charge the lithium ion battery at a constant current of 0.5C to 4.5V, and then charge it at a constant voltage of 4.5V to 0.05C.

[0133] Discharge a fully charged lithium-ion battery at a constant current of 0.2C to 3.95V at 25±5°C. Measure the actual voltage of the lithium-ion battery at this point, recorded as M1 in mV. Then, place the lithium-ion battery at 45±5°C for 48 hours, recording the actual rest time T1 in hours. Place the lithium-ion battery at 25±5°C for another 48 hours, recording the actual rest time T2 in hours. Measure the voltage of the lithium-ion battery after rest, recorded as M2 in mV. Voltage drop per unit time (K, mV / h) = (M1 - M2) / (T1 + T2).

[0134] The voltage drop per unit time K is used to characterize the self-discharge of the lithium-ion battery, thereby characterizing the safety performance of the lithium-ion battery. The lower the voltage drop per unit time K, the better the safety performance of the lithium-ion battery.

[0135] Cycle capacity retention test:

[0136] Take the lithium-ion battery in each example or comparative example and charge it at 25°C at a constant current of 0.5C to 4.5V, then charge it at a constant voltage of 4.5V to 0.05C. After standing for 5 minutes, discharge it at a constant current of 0.5C to 3.0V. The discharge capacity obtained in this step is recorded as the initial discharge capacity. A charge and discharge cycle test is performed according to the above steps. After 1000 cycles, the discharge capacity at the 1000th cycle is obtained. Cycle capacity retention (%) = (discharge capacity at the 1000th cycle / initial discharge capacity) × 100%.

[0137] "1C" is the current value that fully discharges the capacity of each lithium-ion battery within 1 hour, "0.5C" is the current value that fully discharges the capacity of each lithium-ion battery within 2 hours, and "0.05C" is the current value that fully discharges the capacity of each lithium-ion battery within 20 hours.

[0138] The cycle capacity retention rate is used to characterize the cycle performance of lithium-ion batteries. The higher the cycle capacity retention rate, the better the cycle performance of the lithium-ion battery.

[0139] Example 1-1

[0140] <Preparation of negative electrode sheet>

[0141] Silicon-based particles, silicon-carbon particles, carbon material graphite, second binder polyacrylic acid, second binder styrene-butadiene rubber (SBR), and thickener carboxymethyl cellulose (CMC) were mixed in a mass ratio of 20:75.5:3:1:0.5, dissolved in deionized water as a negative electrode solvent, and mixed evenly to prepare a negative electrode material layer slurry with a solid content of 70wt%. The negative electrode material layer slurry was evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 6μm, and dried at 85℃ for 4h to obtain a negative electrode sheet coated with a negative electrode material layer on one side. The coating weight of the negative electrode material layer was 90mg / 1540.25mm 2 . Then repeat the above steps on the other surface of the copper foil to obtain a negative electrode pole piece coated with a negative electrode material layer on both sides. After cold pressing, cutting and slitting, dry it under vacuum conditions at 120°C for 12 hours to obtain a negative electrode pole piece with a specification of 76.6mm×875mm for standby use. Among them, the mass percentage of silicon element in the silicon-carbon particles is 20%, the mass percentage of carbon element in the silicon-carbon particles is 80%, the Dv50 of the silicon-based particles is 6μm, the Dv90 of the silicon-based particles is 10μm, the ratio L of the shortest diameter to the longest diameter of a single silicon-based particle is 0.8, and the compaction density of the negative electrode pole piece is 1.7g / cm 3 .

[0142] <Preparation of positive electrode sheet>

[0143] The positive electrode active material lithium cobalt oxide LiCoO2, the conductive agent Super P and the second binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 96.3:2.2:1.5, and the positive electrode solvent N-methylpyrrolidone was added and stirred evenly to obtain a positive electrode material layer slurry with a solid content of 75wt%. The positive electrode material layer slurry was evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 8μm and dried at 85℃ to obtain a positive electrode sheet with a single-sided positive electrode material layer. The coating weight of the positive electrode material layer was 110mg / 1540.25mm 2 Then repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a positive electrode material layer on both sides. After cold pressing, cutting, and slitting, it is dried under vacuum conditions at 85°C for 4 hours to obtain a positive electrode sheet with a specification of 74mm×867mm for use. Among them, the Dv90 of lithium cobalt oxide is 12μm, and the compaction density of the positive electrode sheet is 4.15g / cm 3 .

[0144] <Preparation of base film>

[0145] (1) A first polyethylene material having a viscosity-average molecular weight of 300,000 polyethylene resin, a second polyethylene material having a viscosity-average molecular weight of 1,000,000 polyethylene resin, and a polypropylene having a melting point of 165° C. are mixed in a mass ratio of 10:85:5 to obtain a base film raw material; a second additive, pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and a first solvent, paraffin oil, are mixed in a mass ratio of 0.3:99.7 to obtain a base film solvent.

[0146] (2) adding the mixed base film raw material and base film solvent to the extruder system respectively, extruding through a T-shaped die, and cooling the cast sheet on a casting roller to obtain a first porous membrane; wherein the mass ratio of the base film raw material to the base film solvent is 25:75.

[0147] (3) The first porous membrane is stretched transversely at a stretching ratio of 8 times, and then stretched longitudinally for the first time at a stretching ratio of 9 times, and then extracted with dichloromethane, and then stretched longitudinally for the second time at a stretching ratio of 2 times, and finally dried with hot air at a temperature of 120°C to obtain a second porous membrane. After heat setting and winding, a base membrane is obtained.

[0148] <Preparation of Separator>

[0149] (1) The second binder polyvinylidene fluoride and the first additive acrylate solution with a solid content of 40 wt% were added to deionized water in a mass ratio of 80:20 and mixed evenly to obtain a bonding layer slurry with a solid content of 12 wt%.

[0150] (2) Adding inorganic particles of boehmite, a first binder of acrylic emulsion, a thickener of sodium carboxymethyl cellulose, and a wetting agent of phenyl polyoxyethylene ether into deionized water in a mass ratio of 94.5:4:1:0.5 and mixing them evenly to obtain a ceramic layer slurry with a solid content of 40 wt%; wherein the Dv50 of the inorganic particles is 0.5 μm.

[0151] (3) A ceramic layer slurry is applied on one surface of the base film of the isolation film by a micro-concave coating method. After oven drying, a ceramic layer is formed on one surface of the base film. An adhesive layer slurry is applied on the surface of the ceramic layer away from the base film by a micro-concave coating method. After oven drying, an isolation film with a single-sided ceramic layer and an adhesive layer is obtained. The adhesive layer slurry is applied on the other surface of the base film by a micro-concave coating method. After oven drying, an isolation film with a single-sided ceramic layer and a double-sided adhesive layer is obtained. The thickness of the single-sided ceramic layer is 3 μm and the surface density is 2.4 g / m 2 The thickness of the single-sided adhesive layer is 1 μm and the surface density is 0.18 g / m 2 .

[0152] <Preparation of Electrolyte>

[0153] In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 1:1:1:1 to obtain a base solvent. Lithium salt LiPF6 was added to the base solvent and stirred to obtain an electrolyte. The lithium salt content was 12.5% ​​by weight and the base solvent content was 87.5% by weight based on the mass of the electrolyte.

[0154] <Preparation of lithium-ion batteries>

[0155] The positive electrode sheet after welding the tabs, the separator, the negative electrode sheet after welding the tabs, and the separator are stacked in order, so that the separator is located between the positive and negative electrode sheets to act as an insulator, and the side of the separator base film with the ceramic layer facing the positive electrode sheet, and then wound to obtain an electrode assembly. The electrode assembly is placed in an aluminum-plastic film and placed in an 80°C vacuum oven to dry for 12 hours to remove moisture. The prepared electrolyte is injected, and a lithium-ion battery is obtained through a vacuum packaging, standing, formation, and shaping process. During the shaping process, the compressive pressure P3 of the lithium-ion battery is 1.8MPa, and the pressure time t of the lithium-ion battery is 65min.

[0156] Example 1-2

[0157] Except that the mass ratio of silicon-based particles silicon-carbon particles, carbon material graphite, second binder polyacrylic acid, second binder styrene-butadiene rubber (SBR) and thickener carboxymethyl cellulose (CMC) is adjusted to 1:94.8:1:3:0.2 in <Preparation of negative electrode plate>, the rest is the same as Example 1-1.

[0158] Examples 1-3

[0159] Except that the mass ratio of silicon-based particles silicon-carbon particles, carbon material graphite, second binder polyacrylic acid, second binder styrene-butadiene rubber (SBR) and thickener carboxymethyl cellulose (CMC) is adjusted to 45:47:5:2:1 in <Preparation of negative electrode plate>, the rest is the same as Example 1-1.

[0160] Example 1-4 to Example 1-6

[0161] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0162] Examples 1-7

[0163] Except for adjusting the mass ratio of silicon-based particles silicon-carbon particles, carbon material graphite, second binder polyacrylic acid, second binder styrene-butadiene rubber (SBR) and thickener carboxymethyl cellulose (CMC) to 45:47:5:2:1 in <Preparation of Negative Electrode>, and adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0164] Example 1-8 to Example 1-12

[0165] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0166] Examples 1-13

[0167] In addition to adjusting the extrusion rate of the extruder in the preparation of the isolation film so that the thickness of the base film h is as shown in Table 1, the surface density of the ceramic layer is adjusted to 3.2 g / m 2 , so that the thickness of the single-sided ceramic layer is 4 μm, and the relevant preparation parameters are adjusted according to Table 1, the rest are the same as Example 1-1.

[0168] Examples 1-14

[0169] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0170] Examples 1-15

[0171] Except that the mass ratio of silicon-based particles silicon-carbon particles, carbon material graphite, second binder polyacrylic acid, second binder styrene-butadiene rubber (SBR) and thickener carboxymethyl cellulose (CMC) is 5:90.8:1:3:0.2 in <Preparation of negative electrode plate>, the thickness h of the base film is shown in Table 1 by adjusting the extrusion amount of the extruder in <Preparation of isolation membrane>, the diameter d of the fiber of the base film and the crystallinity V of the base film are shown in Table 1 by adjusting the viscosity-average molecular weight of the second polyethylene material, and the relevant preparation parameters are adjusted according to Table 1, the rest are the same as Example 1-1.

[0172] Example 1-16 to Example 1-18

[0173] Except that the extrusion volume of the extruder was adjusted in the preparation of the isolation film so that the thickness h of the base film was as shown in Table 1, and the relevant preparation parameters were adjusted according to Table 1, the rest were the same as in Example 1-1.

[0174] Example 1-19 to Example 1-20

[0175] Except that in <Preparation of Isolation Film>, the thickness h of the base film is as shown in Table 1 by regulating the extrusion volume of the extruder, the diameter d of the fiber of the base film and the crystallinity V of the base film are as shown in Table 1 by regulating the viscosity-average molecular weight of the second polyethylene material, and the relevant preparation parameters are regulated according to Table 1, the rest are the same as Example 1-1.

[0176] Example 1-21 to Example 1-24

[0177] The preparation method was the same as Example 1-1 except that the viscosity average molecular weight of the second polyethylene material was adjusted in <Preparation of Separator> so that the diameter d of the fibers of the base film and the crystallinity V of the base film were as shown in Table 1.

[0178] Example 1-25 to Example 1-28

[0179] Except that the stretching ratio was adjusted in <Preparation of Separator> so that the crystallinity V of the base film was as shown in Table 1, the rest was the same as Example 1-1.

[0180] Examples 1-29

[0181] Except that the mass ratio of silicon-based particles silicon-carbon particles, carbon material graphite, second binder polyacrylic acid, second binder styrene-butadiene rubber (SBR) and thickener carboxymethyl cellulose (CMC) is adjusted to 0.5:95.3:1:3:0.2 in <Preparation of negative electrode plate>, the thickness h of the base film is as shown in Table 1 by adjusting the extrusion amount of the extruder in <Preparation of isolation membrane>, and the relevant preparation parameters are adjusted according to Table 1, the rest are the same as Example 1-1.

[0182] Examples 1-30

[0183] Except that the extrusion volume of the extruder was adjusted in the preparation of the isolation film so that the thickness h of the base film was as shown in Table 1, and the relevant preparation parameters were adjusted according to Table 1, the rest were the same as in Example 1-1.

[0184] Examples 1-31

[0185] Except that the mass ratio of silicon-based particles silicon-carbon particles, carbon material graphite, second binder polyacrylic acid, second binder styrene-butadiene rubber (SBR) and thickener carboxymethyl cellulose (CMC) is 10:85.8:1:3:0.2 in <Preparation of negative electrode plate>, the extrusion amount of the extruder is adjusted to make the thickness h of the base film as shown in Table 1 in <Preparation of isolation membrane>, and the relevant preparation parameters are adjusted according to Table 1, the rest are the same as Example 1-1.

[0186] Example 2-1

[0187] Except that the silicon oxide particles are used as silicon-based particles according to Table 2 in <Preparation of Negative Electrode Plate>, the rest is the same as Example 1-1; wherein, based on the mass of the silicon oxide particles, the mass percentage of silicon element is 30%, and the mass percentage of oxygen element is 70%.

[0188] Example 2-2 to Example 2-4

[0189] Except that the types of inorganic particles were adjusted according to Table 2 in <Preparation of Separator>, the rest were the same as Example 1-1.

[0190] Example 2-5 to Example 2-8

[0191] Except that the compressive pressure P3 and the compressive time t of the lithium ion battery are regulated according to Table 2 in <Preparation of lithium ion battery>, the rest is the same as Example 1-1.

[0192] Examples 2-9

[0193] Except that in step (2) of <Preparation of Isolation Film> the mass ratio of inorganic particles, first binder, thickener and wetting agent is adjusted to 97.5:1:1:0.5 so that the peel strength F between the ceramic layer and the base film is as shown in Table 2, the rest is the same as Example 1-1.

[0194] Example 2-10

[0195] Except that in step (2) of <Preparation of Isolation Film> the mass ratio of inorganic particles, first binder, thickener and wetting agent is adjusted to 90.5:8:1:0.5 so that the peel strength F between the ceramic layer and the base film is as shown in Table 2, the rest is the same as Example 1-1.

[0196] Example 2-11

[0197] Except that in step (2) of <Preparation of Isolation Film> the mass ratio of inorganic particles, first binder, thickener and wetting agent is adjusted to 98:0.5:1:0.5 so that the peel strength F between the ceramic layer and the base film is as shown in Table 2, the rest is the same as Example 1-1.

[0198] Comparative Example 1-1

[0199] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0200] Comparative Example 1-2

[0201] Except that the mass ratio of silicon-based particles silicon-carbon particles, carbon material graphite, second binder polyacrylic acid, second binder styrene-butadiene rubber (SBR) and thickener carboxymethyl cellulose (CMC) is adjusted to 50:41:5:3:1 in <Preparation of negative electrode plate>, the rest is the same as Example 1-1.

[0202] Comparative Examples 1-3

[0203] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0204] Comparative Examples 1-4

[0205] Except for adjusting the mass ratio of silicon-based particles silicon-carbon particles, carbon material graphite, second binder polyacrylic acid, second binder styrene-butadiene rubber (SBR) and thickener carboxymethyl cellulose (CMC) to 25:70.5:3:1:0.5 in <Preparation of Negative Electrode>, and adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0206] Comparative Examples 1-5

[0207] Except for adjusting the mass ratio of silicon-based particles silicon-carbon particles, carbon material graphite, second binder polyacrylic acid, second binder styrene-butadiene rubber (SBR) and thickener carboxymethyl cellulose (CMC) to 50:47:1:1:1 in <Preparation of negative electrode plate>, and adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0208] Comparative Example 2-1 to Comparative Example 2-6

[0209] Except that the compressive pressure P3 and the compressive time t of the lithium ion battery are regulated according to Table 2 in <Preparation of lithium ion battery>, the rest is the same as Example 1-1.

[0210] The preparation parameters and performance tests of each embodiment and comparative example are shown in Table 1 and Table 2.

[0211]

[0212]

[0213]

[0214] As can be seen from Examples 1-1 to 1-31 and Comparative Examples 1-1 to 1-5, when the values ​​of A and A / H are within the ranges of this application, the resulting lithium-ion batteries have a low voltage drop per unit time, K, and a high cycle capacity retention rate, indicating that the safety and cycle performance of the lithium-ion batteries of this application are improved. The values ​​of A and A / H for Comparative Examples 1-1 to 1-3 are outside the ranges of this application, the value of A for Comparative Example 1-4 is outside the range of this application, and the value of A / H for Comparative Example 1-5 is outside the range of this application. The resulting lithium-ion batteries have a high voltage drop per unit time, K, and a low cycle capacity retention rate, indicating that the safety and cycle performance of the lithium-ion batteries of the comparative examples are poor.

[0215] The depth B and B / H of the positive electrode active material embedded in the isolation membrane usually affect the safety performance and cycle performance of the electrochemical device. It can be seen from Examples 1-1, 1-10 to 1-31 that when the values ​​of B and B / H are within the range of this application, the obtained lithium-ion battery has a lower voltage drop per unit time K and a higher cycle capacity retention rate, indicating that the cycle performance and safety performance of the lithium-ion battery of this application are improved.

[0216] The ratio C of the damaged area of ​​the base film in the observation region to the area of ​​the observation region usually affects the safety performance and cycle performance of the electrochemical device. It can be seen from Examples 1-1 to 1-31 that when the value of C is within the range of this application, the obtained lithium-ion battery has a lower voltage drop per unit time K and a higher cycle capacity retention rate, indicating that the cycle performance and safety performance of the lithium-ion battery of this application are improved.

[0217] Mass percentage of silicon-based particles W Si It usually affects the cycle performance of the electrochemical device. From Examples 1-1 to 1-3 and 1-29, it can be seen that when the mass percentage of silicon-based particles W Si When within the scope of the present application, the obtained lithium-ion battery has a low voltage drop K per unit time and a high cycle capacity retention rate, indicating that the cycle performance of the lithium-ion battery of the present application is improved while having good safety performance.

[0218] The Dv50 and Dv90 of silicon-based particles usually affect the safety performance and cycle performance of electrochemical devices. It can be seen from Examples 1-1, 1-4 to 1-7, and 1-30 that when the Dv50 and Dv90 of the silicon-based particles are within the range of this application, the obtained lithium-ion battery has a lower voltage drop per unit time K and a higher cycle capacity retention rate, indicating that the cycle performance of the lithium-ion battery of this application is improved and has good safety performance.

[0219] The ratio L of the shortest diameter to the longest diameter of a single silicon-based particle usually affects the safety performance and cycle performance of the electrochemical device. It can be seen from Examples 1-1, 1-7 to 1-9, and 1-31 that when the value of L is within the range of this application, the obtained lithium-ion battery has a lower voltage drop per unit time K and a higher cycle capacity retention rate, indicating that the cycle performance and safety performance of the lithium-ion battery of this application are improved.

[0220] The Dv90 of the positive electrode active material usually affects the safety performance and cycle performance of the electrochemical device. It can be seen from Examples 1-1, 1-10 to 1-15 that when the Dv90 of the positive electrode active material is within the range of this application, the obtained lithium-ion battery has a lower voltage drop per unit time K and a higher cycle capacity retention rate, indicating that the cycle performance and safety performance of the lithium-ion battery of this application are improved.

[0221] The thickness h of the base film usually affects the cycle performance of the electrochemical device. It can be seen from Examples 1-1, 1-13, 1-15 to 1-20, and 1-30 to 1-31 that when the thickness h of the base film is within the range of this application, the obtained lithium-ion battery has a lower voltage drop per unit time K and a higher cycle capacity retention rate, indicating that the cycle performance of the lithium-ion battery of this application is improved and has good safety performance.

[0222] The diameter d of the fibers of the base membrane usually affects the safety performance of the electrochemical device. It can be seen from Examples 1-1, 1-15, 1-19 to 1-24 that when the diameter d of the fibers of the base membrane is within the range of this application, the obtained lithium-ion battery has a lower voltage drop per unit time K and a higher cycle capacity retention rate, indicating that the safety performance of the lithium-ion battery of this application is improved and has good cycle performance.

[0223] The crystallinity V of the base film usually affects the safety performance of the electrochemical device. It can be seen from Examples 1-1, 1-15, 1-19 to 1-28 that when the crystallinity V of the base film is within the range of this application, the obtained lithium-ion battery has a lower voltage drop per unit time K and a higher cycle capacity retention rate, indicating that the safety performance of the lithium-ion battery of this application is improved and has good cycle performance.

[0224] The puncture strength P1 of the base film and the unit puncture strength P2 of the base film usually affect the safety performance of the electrochemical device. It can be seen from Examples 1-1, 1-13, 1-15 to 1-29 that when the values ​​of P1 and P2 are within the range of this application, the obtained lithium-ion battery has a lower unit time voltage drop K and a higher cycle capacity retention rate, indicating that the safety performance of the lithium-ion battery of this application is improved and has good cycle performance.

[0225] As can be seen from Examples 1-1, 2-1 to 2-11, and Comparative Examples 2-1 to 2-6, when the values ​​of A, A / H, and the preparation parameters of the electrochemical device are within the ranges of this application, the resulting lithium-ion battery has a low voltage drop per unit time, K, and a high cycle capacity retention rate, indicating that the safety and cycle performance of the lithium-ion battery of this application are improved. When the preparation parameters of the electrochemical device are outside the ranges of this application, the resulting lithium-ion battery has a high voltage drop per unit time, K, and / or a cycle capacity retention rate that is worse than that within the ranges of this application, and the safety and cycle performance of the lithium-ion battery are significantly deteriorated.

[0226] The type of silicon-based particles usually affects the cycle performance of the electrochemical device. It can be seen from Examples 1-1 and 2-1 that when the type of silicon-based particles is within the scope of this application, the obtained lithium-ion battery has a lower voltage drop per unit time K and a higher cycle capacity retention rate, indicating that the cycle performance of the lithium-ion battery of the present application is improved and has good safety performance.

[0227] The type of inorganic particles usually affects the safety performance and cycle performance of the electrochemical device. It can be seen from Examples 1-1, 2-2 to 2-4 that when the type of inorganic particles is within the scope of this application, the obtained lithium-ion battery has a lower voltage drop per unit time K and a higher cycle capacity retention rate, indicating that the cycle performance and safety performance of the lithium-ion battery of the present application are improved.

[0228] The peel strength F between the ceramic layer and the base film usually affects the safety performance of the electrochemical device. It can be seen from Example 1-1, Example 2-9 to Example 2-11 that when the value of F is within the range of this application, the obtained lithium-ion battery has a low voltage drop per unit time K and a high cycle capacity retention rate, indicating that the safety performance of the lithium-ion battery of the present application is improved and has good cycle performance.

[0229] 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.

[0230] 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.

[0231] 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. An electrochemical device comprising an electrode assembly, wherein the electrode assembly comprises a positive electrode sheet, a separator, and a negative electrode sheet arranged in sequence; The negative electrode plate includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode material layer includes silicon-based particles; in, The depth of the silicon-based particles embedded in the isolation film is A μm, the thickness of the isolation film is H μm, 0≤A≤5, 0%≤A / H≤50%.

2. The electrochemical device according to claim 1, wherein The electrochemical device has a voltage drop per unit time of KmV / h, where 0≤K≤0.

06.

3. The electrochemical device according to claim 1 or 2, which satisfies at least one of the following conditions: (1)0≤A≤2； (2) 0% ≤ A / H ≤ 20%; (3) The voltage drop per unit time of the electrochemical device is K mV / h, 0≤K≤0.

04.

4. The electrochemical device according to claim 1, wherein The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector. The positive electrode material layer includes a positive electrode active material. The depth of the positive electrode active material embedded in the isolation membrane is B μm, and 0%≤B / H≤50%.

5. The electrochemical device according to claim 4, wherein 0%≤(A+B) / H≤60%.

6. The electrochemical device according to claim 1, wherein The isolation film includes a base film, the base film includes an observation area, the size of the observation area is 25 μm×40 μm, the ratio of the damaged area of ​​the base film in the observation area to the area of ​​the observation area is C%, and 0≤C≤40.

7. The electrochemical device according to claim 1, wherein The silicon-based particles include at least one of silicon-carbon particles or silicon-oxygen particles.

8. The electrochemical device according to claim 7, wherein The silicon-based particles include silicon-carbon particles.

9. The electrochemical device according to claim 1, wherein Based on the mass of the negative electrode material layer, the mass percentage of the silicon-based particles is W Si %,1≤W Si ≤45.

10. The electrochemical device according to claim 1, wherein The Dv50 of the silicon-based particles is D1 μm, the Dv90 of the silicon-based particles is D2 μm, 3≤D1≤12, and 4≤D2≤14.

11. The electrochemical device according to claim 1, wherein The ratio of the shortest diameter to the longest diameter of a single silicon-based particle is L, and 0.6≤L≤1.

12. The electrochemical device according to claim 11, wherein The Dv90 of the positive electrode active material is D3μm, 4≤D3≤14, and D3≤2H.

13. The electrochemical device according to claim 1, wherein The isolation film includes a base film, a ceramic layer and a bonding layer. The ceramic layer is arranged between the base film and the bonding layer. The thickness of the base film is h μm, and 2≤h≤7.

14. The electrochemical device according to claim 13, wherein The puncture strength of the basement membrane is P1 gf, the unit puncture strength of the basement membrane is P2 gf / μm, 220≤P1≤900, 55≤P2≤160.

15. The electrochemical device according to claim 13, wherein The diameter of the fibers of the base membrane is d μm, 0.05≤d≤0.

3.

16. The electrochemical device according to claim 13, wherein The crystallinity of the base film is V%, 60≤V≤80.

17. The electrochemical device according to claim 13, wherein The ceramic layer includes inorganic particles, and the inorganic particles include at least one of aluminum oxide, boehmite, barium titanate, barium sulfate, titanium dioxide, melamine cyanurate, triphenyl phosphate, melamine polyphosphate, or ammonium polyphosphate.

18. The electrochemical device according to claim 17, wherein The inorganic particles include at least one of melamine cyanurate, triphenyl phosphate or melamine polyphosphate.

19. The electrochemical device according to claim 13, wherein The peel strength between the ceramic layer and the base film is FN / m, 6≤F≤100.

20. The electrochemical device according to claim 13, wherein 2≤h≤5。 21. The electrochemical device according to claim 14, wherein 260≤P1≤900。 22. A method for preparing the electrochemical device according to any one of claims 1 to 21, comprising the following steps: The positive electrode sheet, the negative electrode sheet and the separator are prepared, the negative electrode sheet, the separator and the positive electrode sheet are stacked in order to assemble the electrode assembly, the electrode assembly is placed in a packaging bag, and the electrochemical device is obtained after packaging and shaping; wherein, during the shaping process, the compressive pressure of the electrochemical device is P3 MPa, the compressive time of the electrochemical device is t min, 1.2≤P3≤2.2, 20≤t≤120.

23. An electronic device, comprising the electrochemical device according to any one of claims 1 to 21, or the electrochemical device prepared by the preparation method according to claim 22.

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