A negative electrode sheet, a secondary battery, and an electronic device

Abstract

The application provides a negative electrode sheet, a secondary battery and an electronic device. The negative electrode sheet comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material, a binder and inorganic particles, the negative electrode active material comprises graphite and a silicon-based material, in a pore distribution test of the negative electrode active material layer, a pore size range corresponding to a maximum pore volume is 0.6-1.2 mu m, and a proportion x of a total volume of pores with a pore size less than or equal to 0.5 mu m in all pores is 30-40%. The negative electrode sheet with the above characteristics can improve the adhesion between the negative electrode active material layer and the negative electrode current collector and between the negative electrode active material particles, thereby improving the problems such as negative electrode active material layer peeling during the cycle process, and further improving the expansion performance and cycle performance of the secondary battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemistry, and particularly relates to a negative electrode sheet, a secondary battery and an electronic device. BACKGROUND

[0002] Secondary batteries, such as lithium ion batteries, have many advantages, such as high working voltage, high energy density, long cycle life and wide working temperature range, and are widely used in the field of consumer electronics. With the rapid development of electric vehicles and mobile electronic devices, people have higher and higher requirements for the kinetic performance of secondary batteries.

[0003] For a secondary battery containing silicon-based material in the negative electrode active material layer, the silicon-based material expands greatly during the cycle process of deintercalating lithium ions and intercalates lithium slowly, which affects the charge rate of the secondary battery. In order to improve the charge rate of the secondary battery, the amount of binder and dispersant is usually reduced to reduce the impedance of the negative electrode sheet and improve the kinetic performance of the negative electrode sheet, so as to improve the charge rate of the secondary battery. However, reducing the amount of binder and dispersant will reduce the adhesion between the negative electrode active material layer and the negative electrode current collector, and the negative electrode active material layer is prone to delamination during the cycle process, thereby affecting the expansion performance of the secondary battery. SUMMARY

[0004] The purpose of the present application is to provide a negative electrode sheet, a secondary battery and an electronic device to improve the adhesion between the negative electrode active material layer and the negative electrode current collector. The specific technical solutions are as follows:

[0005] The first aspect of the present application provides a negative electrode sheet, which comprises a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material, a binder and inorganic particles, the negative electrode active material comprising graphite and a silicon-based material. In a pore distribution test of the negative electrode active material layer, the pore size range corresponding to the maximum pore volume is 0.6 μm to 1.2 μm, and the proportion x of the sum of the volumes of the pores with a pore size less than or equal to 0.5 μm to the total volume of all the pores is 30% to 40%. In the present application, in the pore distribution test of the negative electrode active material layer, a pore size distribution curve is obtained with the pore size as the abscissa and the pore volume as the ordinate, and the pore size corresponding to the maximum pore volume refers to the pore size value corresponding to the highest peak value of the pore volume in the pore size distribution curve. The negative electrode sheet comprises inorganic particles, which can be filled in the pores between the negative electrode active material particles, can increase the contact area between the negative electrode active material layer and the negative electrode current collector and between the negative electrode active material particles, and is beneficial to improve the adhesion between the negative electrode active material layer and the negative electrode current collector and between the negative electrode active material particles, thereby improving the structural stability of the negative electrode sheet without increasing the amount of the binder, and improving the problems such as delamination of the negative electrode active material layer during the cycle process. By adjusting the pore size range corresponding to the maximum pore volume of the negative electrode active material layer to 0.6 μm to 1.2 μm, most of the pores are concentrated and distributed around the maximum volume pore size, which can make the negative electrode active material particles in the negative electrode active material layer and the negative electrode active material particles and the inorganic particles adhere closely, and the proportion x of the sum of the volumes of the pores with a pore size less than or equal to 0.5 μm to the total volume of all the pores is in the range of 30% to 40%, which can reserve sufficient space for the diffusion of the electrolyte, so that the adhesion between the particles in the negative electrode active material layer and the diffusion performance of the electrolyte can be considered at the same time. The application of the negative electrode sheet to a secondary battery can improve the diffusion capacity of the electrolyte in the negative electrode sheet and improve the expansion performance and cycle performance of the secondary battery.

[0006] In some embodiments of the present application, the silicon-based material comprises at least one of silicon, silicon-oxygen and silicon-carbon. The selection of the silicon-based material in the above range can make the negative electrode sheet have a higher capacity, so that the application of the negative electrode sheet to a secondary battery can make the secondary battery have a higher energy density and good cycle performance.

[0007] In some embodiments of the present application, the Dv50 of the inorganic particles is a μm, 1≤a≤3, the Dv50 of the graphite particles is b μm, 10≤b≤22, and the Dv50 of the silicon-based material is c μm, 5≤c≤12. By adjusting the values of a, b, and c within the above ranges, the pore distribution of the negative electrode sheet is adjusted so that the pore size range corresponding to the maximum pore volume is 0.6 μm to 1.2 μm, and the sum of the volumes of the pores having a pore size less than or equal to 0.5 μm accounts for 30% to 40% of the total volume of all pores, thereby improving the structural stability of the negative electrode sheet and allowing the diffusion performance of the electrolyte in the negative electrode sheet to be taken into account. The application of the negative electrode sheet to a secondary battery is more conducive to improving the expansion performance and cycle performance of the secondary battery.

[0008] In some embodiments of the present application, by adjusting the values of a, b, and c within the above ranges, the pore distribution of the negative electrode sheet is adjusted so that the pore size range corresponding to the maximum pore volume is 0.7 μm to 0.9 μm, which can further improve the diffusion performance of the electrolyte in the negative electrode sheet, thereby further improving the cycle performance of the secondary battery.

[0009] In some embodiments of the present application, a / b satisfies 0.08≤a / b≤0.25, and a / c satisfies 0.1≤a / c≤0.35. By adjusting the relationship between the Dv50 of the inorganic particles, the graphite, and the silicon-based material, i.e., adjusting the values of a / b and a / c within the above ranges, the inorganic particles are more likely to fill the pores between the negative electrode active material particles, the pore distribution of the negative electrode sheet is optimized, the contact area between the negative electrode active material particles is increased, the adhesion between the negative electrode active material layer and the negative electrode current collector and between the negative electrode active material particles is further improved, and problems such as the peeling of the negative electrode active material layer during the cycle are solved, thereby improving the structural stability of the negative electrode sheet. The application of the negative electrode sheet to a secondary battery can improve the diffusion performance of the electrolyte in the negative electrode sheet and improve the expansion performance and cycle performance of the secondary battery.

[0010] In some embodiments of the present application, a / b satisfies 0.08≤a / b≤0.11, and a / c satisfies 0.1≤a / c≤0.16. By adjusting the values of a / b and a / c within the above ranges, the inorganic particles are more likely to fill the pores between the negative electrode active material particles, the pore distribution of the negative electrode sheet is further optimized, thereby further improving the structural stability of the negative electrode sheet and allowing the diffusion performance of the electrolyte in the negative electrode sheet to be taken into account. The application of the negative electrode sheet to a secondary battery is more conducive to improving the expansion performance and cycle performance of the secondary battery.

[0011] In some embodiments of the present application, the mass percentage of the silicon-based material is 1% to 20% based on the total mass of the graphite and the silicon-based material. By regulating the mass percentage of the silicon-based material within the above range, the negative electrode sheet can have a higher capacity, and thus when the negative electrode sheet is applied to a secondary battery, the secondary battery can have a higher energy density and good cycle performance.

[0012] In some embodiments of the present application, the mass percentage of the silicon-based material is 1% to 10% based on the total mass of the graphite and the silicon-based material. By regulating the mass percentage of the silicon-based material within the above range, the negative electrode sheet can have a higher capacity, and thus when the negative electrode sheet is applied to a secondary battery, the secondary battery can have a higher energy density while having good cycle performance and expansion performance.

[0013] In some embodiments of the present application, the inorganic particles include at least one of alumina or boehmite; the mass percentage of the inorganic particles is 0.1% to 0.5% based on the mass of the negative electrode active material layer. The above inorganic particles are selected, and the mass percentage of the inorganic particles is regulated within the above range, which is conducive to the inorganic particles filling in the pores between the negative electrode active material particles, better playing the binding role of the inorganic particles, further improving the adhesion between the negative electrode active material layer and the negative electrode current collector and between the negative electrode active material particles, and improving the problems such as delamination of the negative electrode active material layer during the cycle. When the negative electrode sheet is applied to a secondary battery, the expansion performance and cycle performance of the secondary battery can be improved.

[0014] In some embodiments of the present application, the specific surface area of the inorganic particles is 5 m 2 / g to 15 m 2 / g. A larger specific surface area is more conducive to contact and binding with the negative electrode active material particles, and regulating the specific surface area of the inorganic particles within the above range is conducive to better playing the binding role of the inorganic particles, improving the structural stability of the negative electrode sheet, and can also take into account the diffusion performance of the electrolyte in the negative electrode sheet. When the negative electrode sheet is applied to a secondary battery, the expansion performance and cycle performance of the secondary battery can be improved.

[0015] In some embodiments of the present application, the binder includes at least one of a butadiene-styrene copolymer, polyacrylic acid, or carboxymethyl cellulose; the mass percentage of the binder is 1.9% to 3% based on the mass of the negative electrode active material layer. Regulating the mass percentage of the binder within the above range makes the negative electrode sheet have a lower binder content, and in combination with the binding role of the inorganic particles, improves the structural stability of the negative electrode sheet. When the negative electrode sheet is applied to a secondary battery, the secondary battery can have a higher energy density while the expansion performance and cycle performance of the secondary battery are improved.

[0016] The second aspect of the present application provides a secondary battery comprising the negative electrode sheet provided by the first aspect of the present application. The negative electrode sheet provided by the first aspect of the present application has good structural stability, thereby improving the expansion performance and cycle performance of the secondary battery.

[0017] The third aspect of the present application provides an electronic device comprising the secondary battery provided by the second aspect of the present application. The secondary battery provided by the second aspect of the present application has good expansion performance and cycle performance, thereby the electronic device provided by the third aspect of the present application has a longer service life.

[0018] Advantages of the present application:

[0019] The present application provides a negative electrode sheet, a secondary battery and an electronic device. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, the negative electrode active material layer comprises a negative electrode active material, a binder and inorganic particles, the negative electrode active material comprises graphite and a silicon-based material, in a pore distribution test of the negative electrode active material layer, the pore diameter range corresponding to the maximum pore volume is 0.6-1.2 μm, and the sum of the volumes of the pores with a pore diameter less than or equal to 0.5 μm accounts for 30-40% of the total volume of all the pores. The negative electrode sheet comprises inorganic particles, which can be filled in the pores between the negative electrode active material particles, can increase the contact area between the negative electrode active material layer and the negative electrode current collector and between the negative electrode active material particles, and is conducive to improving the adhesion between the negative electrode active material layer and the negative electrode current collector and between the negative electrode active material particles, thereby improving the structural stability of the negative electrode sheet, improving the problems such as delamination of the negative electrode active material layer during the cycle process, and improving the expansion performance and cycle performance of the secondary battery. By adjusting the pore diameter corresponding to the maximum pore volume of the negative electrode active material layer within the range of the present application, the pore diameters of most of the pores are concentrated around the maximum pore diameter, which can make the negative electrode active material particles in the negative electrode active material layer and the inorganic particles adhere closely, and by adjusting the proportion x of the sum of the volumes of the pores with a pore diameter less than or equal to 0.5 μm to the total volume of all the pores within the range of the present application, sufficient space can be reserved for the diffusion of the electrolyte, which can take into account the adhesion between the particles in the negative electrode active material layer and the diffusion performance of the electrolyte at the same time. The application of the negative electrode sheet to the secondary battery can improve the diffusion capacity of the electrolyte in the negative electrode sheet, and improve the expansion performance and cycle performance of the secondary battery.

[0020] Of course, the implementation of any product or method of the present application does not necessarily require the simultaneous achievement of all the advantages described above. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art based on these drawings.

[0022] Figure 1 A scanning electron microscope photograph of the cross section of the negative electrode tab of Example 1-1 along the thickness direction thereof;

[0023] Figure 2 A scanning electron microscope photograph of the pores on the cross section of the negative electrode tab of Example 1-1 along the thickness direction thereof;

[0024] Figure 3 A scanning electron microscope photograph of the surface of the negative electrode active material layer of Example 1-1;

[0025] Figure 4 A pore distribution diagram of the negative electrode active material layer of Example 1-1 and Comparative Example 2. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. All other embodiments obtained by those skilled in the art based on the present application are within the scope of protection of the present application.

[0027] It should be noted that in the specific embodiments of the present application, the present application is explained by taking lithium ion batteries as examples of secondary batteries, but the secondary batteries of the present application are not limited to lithium ion batteries.

[0028] The first aspect of the present application provides a negative electrode sheet, which comprises a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material, a binder and inorganic particles, the negative electrode active material comprising graphite and a silicon-based material, in a pore distribution test of the negative electrode active material layer, the pore size range corresponding to the maximum pore volume is 0.6-1.2 μm, preferably 0.7-0.9 μm; the proportion x of the sum of the volumes of the pores with a pore size less than or equal to 0.5 μm to the total volume of all the pores is 30-40%. For example, the pore size range corresponding to the maximum pore volume can be 0.6 μm, 0.65 μm, 0.7 μm, 0.8 μm, 0.9 μm, 0.95 μm, 1.0 μm, 1.1 μm, 1.2 μm or a range formed by any two of them, and the value of x can be 30%, 31%, 33%, 35%, 36%, 38%, 40% or a range formed by any two of them. The pore size of the pores with a pore size less than or equal to 0.5 μm can be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm or a range formed by any two of them. The negative electrode sheet comprises inorganic particles, and the pore size corresponding to the maximum pore volume and the value of x are regulated within the above ranges, the inorganic particles can be filled in the pores between the negative electrode active material particles, can increase the contact area between the negative electrode active material layer and the negative electrode current collector and the contact area between the negative electrode active material particles, and is beneficial to improve the adhesion between the negative electrode active material layer and the negative electrode current collector and between the negative electrode active material particles, thereby improving the problems such as delamination of the negative electrode active material layer during the cycle without increasing the amount of binder, and improving the structural stability of the negative electrode sheet. When the negative electrode sheet is applied to a secondary battery, the diffusion capacity of the electrolyte in the negative electrode sheet can be improved, and the expansion performance and cycle performance of the secondary battery can be improved.

[0029] The inventors find that the negative electrode sheet comprising inorganic particles can improve the structural stability of the negative electrode sheet by regulating the pore size corresponding to the maximum pore volume in the negative electrode active material layer and the proportion of the sum of the volumes of the pores with pore sizes less than or equal to 0.5 μm to the total volume of all pores, so that the inorganic particles are filled in the pores between the negative electrode active material particles, play a bonding role, reduce the amount of binder in the negative electrode sheet, and still improve the adhesion between the negative electrode active material layer and the negative electrode current collector and between the negative electrode active material particles. The application of the negative electrode sheet to the secondary battery improves the diffusion ability of the electrolyte in the negative electrode sheet and the structural stability of the negative electrode sheet, is conducive to the ion transmission in the negative electrode sheet, and thus improves the expansion performance and cycle performance of the secondary battery. When the pore size corresponding to the maximum pore volume is too large, for example, greater than 1.2 μm, less inorganic particles are filled between the negative electrode active material particles, the negative electrode active material particles are loosely accumulated, the adhesion is not tight enough, the energy density of the secondary battery is greatly lost, and the risk of delamination of the negative electrode active material layer during the cycle process is increased, which affects the cycle performance and expansion performance of the secondary battery. When the pore size corresponding to the maximum pore volume is too small, for example, less than 0.6 μm, too many inorganic particles are accumulated in the pores between the negative electrode active material particles, which leads to too low porosity of the negative electrode sheet, is not conducive to the infiltration of the electrolyte into the negative electrode sheet and the diffusion of the electrolyte, and affects the lithium ion transmission in the negative electrode sheet, thereby affecting the cycle performance and expansion performance of the secondary battery. When the value of x is too large, for example, greater than 40%, too many inorganic particles are accumulated in the pores between the negative electrode active material particles, and the porosity of the negative electrode sheet is too low, which is not conducive to the infiltration of the electrolyte into the negative electrode sheet and the diffusion of the electrolyte, and affects the lithium ion transmission in the negative electrode sheet, thereby affecting the cycle performance and expansion performance of the secondary battery. When the value of x is too small, for example, less than 30%, less inorganic particles are filled between the negative electrode active material particles, which cannot play the bonding role of the inorganic particles, is not conducive to improving the adhesion between the negative electrode active material layer and the negative electrode current collector, and increases the risk of delamination of the negative electrode active material layer during the cycle process, thereby affecting the cycle performance and expansion performance of the secondary battery. The negative electrode sheet comprising inorganic particles and regulating the pore size corresponding to the maximum pore volume and the value of x in the above range can improve the problems such as delamination of the negative electrode active material layer during the cycle process without increasing the amount of binder, improve the structural stability of the negative electrode sheet, and be conducive to the ion transmission and diffusion of the electrolyte, thereby improving the expansion performance and cycle performance of the secondary battery.

[0030] In the present application, the pore distribution of the negative electrode active material layer is tested by taking the pore size as the abscissa and the pore volume as the ordinate to obtain a pore size distribution curve, and the pore size corresponding to the maximum pore volume refers to the pore size value corresponding to the highest peak value of the pore volume in the pore size distribution curve.

[0031] In the present application, the graphite includes at least one of natural graphite or artificial graphite, and the present application does not have a particular limitation thereon as long as the purpose of the present application can be achieved.

[0032] In some embodiments of the present application, the silicon-based material includes at least one of silicon, silicon oxygen (SiO k , 0 < k < 2), silicon carbon (SiC). The silicon-based material is selected from the above-mentioned range, which can make the negative electrode sheet have a higher capacity, so that the negative electrode sheet is applied to the secondary battery, which can make the secondary battery have a higher energy density and good cycle performance.

[0033] In some embodiments of the present application, the Dv50 of the inorganic particles is a μm, 1 < a < 3. The Dv50 of the graphite particles is b μm, 10 < b < 22, and the Dv50 of the silicon-based material is c μm, 5 < c < 12. For example, the value of a can be 1, 1.5, 2, 2.5, 3, or a range formed by any two of the above values, the value of b can be 10, 12, 14, 15, 16, 18, 20, 22, or a range formed by any two of the above values, and the value of c can be 5, 6, 7, 8, 9, 10, 11, 12, or a range formed by any two of the above values. By adjusting the values of a, b, and c within the above-mentioned ranges, the inorganic particles are filled in the pores between the negative electrode active material particles, which reduces the risk of delamination of the negative electrode active material layer during the cycle process, thereby further improving the structural stability of the negative electrode sheet, and the diffusion performance of the electrolyte in the negative electrode sheet can also be considered. The negative electrode sheet is applied to the secondary battery, which is more conducive to improving the expansion performance and cycle performance of the secondary battery. In the present application, Dv50 refers to the particle size distribution on the volume basis of the material, from the small particle size, to the particle size of 50% of the volume accumulation.

[0034] Further, by adjusting the values of a, b, and c within the above-mentioned ranges, the pore distribution of the negative electrode sheet is adjusted, and the pore size range corresponding to the maximum pore volume is 0.7 μm to 0.9 μm, which can further improve the diffusion performance of the electrolyte in the negative electrode sheet, thereby improving the capacity retention rate, i.e., improving the cycle performance of the secondary battery.

[0035] In some embodiments of the present application, a / b satisfies 0.08≤a / b≤0.25, and a / c satisfies 0.1≤a / c≤0.35. Preferably, a / b satisfies 0.08≤a / b≤0.11, and a / c satisfies 0.1≤a / c≤0.16. For example, the value of a / b can be 0.08, 0.09, 0.1, 0.11, 0.13, 0.15, 0.18, 0.2, 0.22, 0.25, or a range between any two of them. The value of a / c can be 0.1, 0.12, 0.13, 0.15, 0.16, 0.18, 0.2, 0.25, 0.3, 0.35, or a range between any two of them. By regulating the relationship between the Dv50 of the inorganic particles, graphite, and silicon-based material, i.e., regulating the value of a / b and a / c within the above range, it is more conducive for the inorganic particles to fill in the pores between the negative active material particles, increase the contact area between the negative active material particles, further improve the adhesion between the negative active material layer and the negative current collector, and the adhesion between the negative active material particles, and improve the problems such as the delamination of the negative active material layer during the cycle process, thereby improving the structural stability of the negative electrode sheet, and being conducive to the ion transmission and electrolyte diffusion in the negative electrode sheet. When the negative electrode sheet is applied to a secondary battery, the expansion performance and cycle performance of the secondary battery can be improved.

[0036] In some embodiments of the present application, the mass percentage of the silicon-based material is 1% to 20%, preferably 1% to 10%, based on the total mass of the graphite and the silicon-based material, for example, the mass percentage of the silicon-based material can be 1%, 2%, 3%, 5%, 6%, 8%, 10%, 12%, 15%, 18%, 20%, or a range between any two of them. By regulating the mass percentage of the silicon-based material within the above range, the negative electrode sheet can have a higher capacity, and when the negative electrode sheet is applied to a secondary battery, the secondary battery can have a higher energy density and good cycle performance.

[0037] In some embodiments of the present application, the inorganic particles include at least one of alumina (Al2O3) or boehmite (AlOOH); the mass percentage of the inorganic particles is 0.1% to 0.5% based on the mass of the negative electrode active material layer, for example, the mass percentage of the inorganic particles can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5% or a range between any two of the above values. By selecting the above inorganic particles and adjusting the mass percentage of the inorganic particles in the above range, the above inorganic particles fill the pores between the negative electrode active material particles, which can increase the contact area between the negative electrode active material particles, better play the binding role of the inorganic particles, further improve the adhesion between the negative electrode active material layer and the negative electrode current collector and between the negative electrode active material particles, and improve the problems such as delamination of the negative electrode active material layer during the cycle process, thereby improving the structural stability of the negative electrode sheet. When the negative electrode sheet is applied to a secondary battery, the expansion performance and cycle performance of the secondary battery can be improved.

[0038] In some embodiments of the present application, the specific surface area of the inorganic particles is 5m 2 / g to 15m 2 / g, for example, the specific surface area of the inorganic particles can be 5m 2 / g, 6m 2 / g, 7m 2 / g, 8m 2 / g, 9m 2 / g, 10m 2 / g, 11m 2 / g, 12m 2 / g, 13m 2 / g, 14m 2 / g, 15m 2 / g or a range between any two of the above values. By adjusting the specific surface area of the inorganic particles in the above range, the binding role of the inorganic particles can be better played, the problems such as delamination of the negative electrode active material layer during the cycle process can be improved, thereby improving the structural stability of the negative electrode sheet, and the diffusion performance of the electrolyte in the negative electrode sheet can be considered. When the negative electrode sheet is applied to a secondary battery, the expansion performance and cycle performance of the secondary battery can be improved.

[0039] In some embodiments of the present application, the binder comprises at least one of butadiene-styrene copolymer, polyacrylic acid or carboxymethyl cellulose, and the mass percentage of the binder is 1.9% to 3% based on the mass of the negative active material layer, for example, the mass percentage of the binder can be 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.5%, 2.6%, 2.8%, 3% or a range between any two of them. The mass percentage of the binder is regulated within the above range, so that the negative electrode sheet has a lower binder content, in combination with the binding effect of the inorganic particles, to improve the problems such as delamination of the negative active material layer during the cycle process, thereby improving the structural stability of the negative electrode sheet. When the negative electrode sheet is applied to a secondary battery, the secondary battery can have a higher energy density while improving the expansion performance and cycle performance of the secondary battery.

[0040] Generally, the specific surface area of the inorganic particles and the values of a, b and c can be changed by mechanical crushing, sieving and the like, which are not particularly limited in the present application and can be selected as needed as long as the purpose of the present application is achieved. The value of the maximum pore volume corresponding pore diameter and the proportion x of the sum of the volumes of the pores with a pore diameter less than or equal to 0.5 μm to the total volume of all pores can be changed by changing the values of a, b, c, a / b and a / c. In the case where the Dv50 of the graphite and the silicon-based material remains unchanged, by changing the particle size of the inorganic particles or adjusting the particle size of the graphite or the silicon-based material while keeping the particle size of the inorganic particles unchanged, the values of a / b and a / c are within a suitable range, thereby controlling the pore distribution of the negative electrode sheet, for example, increasing a, increasing the maximum pore volume corresponding pore diameter and decreasing x, and decreasing a, decreasing the maximum pore volume corresponding pore diameter and increasing x. The value of the maximum pore volume corresponding pore diameter and the value of x can also be changed by changing the cold-pressing pressure of the negative electrode sheet, increasing the cold-pressing pressure of the negative electrode sheet, increasing the compaction density, decreasing the maximum pore volume corresponding pore diameter and increasing x, and decreasing the cold-pressing pressure of the negative electrode sheet, decreasing the compaction density, increasing the maximum pore volume corresponding pore diameter and increasing x.

[0041] The second aspect of the present application provides a secondary battery comprising the negative electrode sheet provided by the first aspect of the present application. The negative electrode sheet provided by the first aspect of the present application has good structural stability, thereby improving the expansion performance and cycle performance of the secondary battery.

[0042] The negative current collector is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the negative current collector can include a copper foil, an aluminum foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, or a polymer substrate coated with a conductive metal, etc. Among them, the conductive metal includes, but is not limited to, copper, nickel, or titanium, and the material of the polymer substrate includes, but is not limited to, at least one of polyethylene, polypropylene, ethylene propylene copolymer, polyethylene terephthalate, polyethylene naphthalate, or poly-p-phenylene terephthalamide. In the present application, the thickness of the negative current collector and the negative active material layer is not particularly limited, as long as the object of the present application can be achieved. For example, the thickness of the negative current collector is 4 μm to 12 μm, and the thickness of the single-sided negative active material layer is 30 μm to 160 μm. In the present application, the negative active material layer can be provided on one surface in the thickness direction of the negative current collector, or on both surfaces in the thickness direction of the negative current collector. It should be noted that the "surface" here can be the entire area of the negative current collector, or a partial area of the negative current collector, which is not particularly limited in the present application, as long as the object of the present application can be achieved. The negative active material layer in the present application can further include a negative conductive agent and a negative dispersing agent. The types of the negative conductive agent and the negative dispersing agent are not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the negative conductive agent can be at least one of conductive carbon black, carbon nanotubes, carbon fibers, carbon dots, or graphene, and the negative dispersing agent can include, but is not limited to, carboxymethyl cellulose or sodium carboxymethyl cellulose.

[0043] The positive electrode tab is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the positive electrode tab includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The positive electrode current collector is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the positive electrode current collector can include a metal foil or a composite current collector, etc. The metal foil can be, for example, an aluminum foil. The composite current collector can include a polymer material base layer and a metal material layer disposed on at least one surface of the polymer material base layer. The metal material layer can include at least one of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, or a silver alloy. The polymer material base layer can include at least one of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, or polyethylene. The positive electrode active material layer of the present application includes a positive electrode active material. The type of the positive electrode active material is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the positive electrode active material includes at least one of lithium cobaltate, lithium nickel cobalt manganese oxide (NCM811, NCM622, NCM523, NCM111), lithium nickel manganese aluminate, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel lithium manganate, spinel lithium nickel manganate, or lithium titanate. The thickness of the positive electrode current collector and the positive electrode active material layer is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm. The thickness of the single-sided positive electrode active material layer is 30 μm to 150 μm. In the present application, the positive electrode active material layer can be disposed on one surface in the thickness direction of the positive electrode current collector, or can be disposed on both surfaces in the thickness direction of the positive electrode current collector. It should be noted that the "surface" herein can be the entire area of the positive electrode current collector, or can be a partial area of the positive electrode current collector, which is not particularly limited in the present application, as long as the object of the present application can be achieved. The positive electrode active material layer of the present application can further include a positive electrode binder. The type of the positive electrode binder is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the positive electrode binder can include, but is not limited to, at least one of polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, butadiene-styrene copolymer, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose, or potassium hydroxymethyl cellulose, etc. The positive electrode active material layer of the present application can further include a positive electrode conductive agent, which is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the positive electrode conductive agent can be the same as the negative electrode conductive agent described above.

[0044] The electrolyte of the present application can include a lithium salt and an organic solvent. The kind of the lithium salt according to the present application is not particularly limited as long as the object of the present application can be achieved, for example, the lithium salt can include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalato)borate (LiBOB), or lithium difluoro(oxalato)borate (LiDFOB). The kind of the above-mentioned organic solvent according to the present application is not particularly limited as long as the object of the present application can be achieved, for example, can 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 can include, but is not limited to, at least one of a chain carbonate compound or a cyclic carbonate compound. The above-mentioned chain carbonate compound can include, but is not limited to, at least one of dimethyl carbonate, diethyl carbonate (DEC), dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, or methyl ethyl carbonate. The above-mentioned cyclic carbonate compound can include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, or vinyl ethylene carbonate. The above-mentioned carboxylate compound can include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate (EP), propyl propionate, γ-butyrolactone, decanolactone, valerolactone, or hexanolactone. The above-mentioned ether compound can include, but is not limited to, at least one of dimethyl ether of ethylene glycol, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The above-mentioned other organic solvents can include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0045] The secondary battery of the present application further includes a separator to separate the positive electrode tab and the negative electrode tab, prevent internal short circuit of the secondary battery, allow electrolyte ions to pass freely, and not affect the electrochemical charging and discharging process. The separator of the present application is not particularly limited as long as the purpose of the present application can be achieved, for example, the material of the separator can include, but is not limited to, at least one of polyethylene, polypropylene, polytetrafluoroethylene-based polyolefin-based separator, polyester film (e.g., polyethylene terephthalate (PET) film), cellulose film, polyimide film, polyamide film, spandex or aramid film, etc. The type of the separator can include, but is not limited to, at least one of woven film, non-woven film (non-woven fabric), microporous film, composite film, calendered film, or spunlaced film, etc. The separator of the present application can have a porous structure, a porous layer is provided on at least one surface of the separator, the porous layer includes inorganic particles and a binder, the inorganic particles can include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder can include at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polymethyl acrylate, polyethyl acrylate, polybutyl acrylate, polyacrylic acid, polyacrylate, carboxymethyl cellulose sodium, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The size of the pore diameter of the porous structure of the present application is not particularly limited as long as the purpose of the present application can be achieved, for example, the size of the pore diameter can be 0.01 μm to 1 μm. In the present application, the thickness of the separator is not particularly limited as long as the purpose of the present application can be achieved, for example, the thickness can be 3 μm to 30 μm.

[0046] The secondary battery of the present application further includes a packaging bag for containing the positive electrode tab, the separator, the negative electrode tab, and the electrolyte, and other components in the secondary battery known in the art, the other components are not particularly limited in the present application. The packaging bag of the present application is not particularly limited, and can be a packaging bag known in the art as long as the purpose of the present application can be achieved. For example, an aluminum plastic film packaging bag can be used.

[0047] The secondary battery of the present application is not particularly limited, and can include any device that undergoes electrochemical reaction. In an embodiment of the present application, the secondary battery can include, but is not limited to, a lithium ion battery, a sodium ion battery, a lithium metal battery, a sodium metal battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery, etc.

[0048] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and the present application is not particularly limited, for example, can include but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding, etc. as needed to obtain an electrode assembly with a winding structure, placing the electrode assembly into a packaging bag, injecting electrolyte into the packaging bag and sealing to obtain a secondary battery; or stacking the positive electrode sheet, the separator and the negative electrode sheet in order, then fixing the four corners of the entire stack structure with tape to obtain an electrode assembly with a stack structure, placing the electrode assembly into a packaging bag, injecting electrolyte into the packaging bag and sealing to obtain a secondary battery. In addition, a current protection element, a guide plate, etc. can also be placed in the packaging bag as needed to prevent the pressure inside the secondary battery from rising and overcharging and discharging.

[0049] The third aspect of the present application provides an electronic device comprising the secondary battery provided by the second aspect of the present application. The secondary battery provided by the second aspect of the present application has good expansion performance and cycle performance, so that the electronic device provided by the third aspect of the present application has a longer service life. The electronic device of the present application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device can include, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, a power tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor, etc.

[0050] Embodiment

[0051] Hereinafter, embodiments and comparative examples are given to more specifically explain the embodiments of the present application. Various tests and evaluations were carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are on a mass basis.

[0052] Test methods and equipment:

[0053] Sampling method of negative electrode sheet:

[0054] The lithium ion battery discharged at 0.5C to 3.0V was disassembled, and the negative electrode sheet was removed. After soaking in dimethyl carbonate (DMC) for 20 minutes, the negative electrode sheet was rinsed with DMC and acetone in turn. Then the negative electrode sheet was placed in an oven and baked at 80°C for 12 hours to obtain the negative electrode sheet.

[0055] Pore size distribution test:

[0056] The negative electrode sheet obtained according to the above sampling method was used as a sample, and the pore size and pore size distribution of the negative electrode active material layer were tested by mercury porosimetry using a mercury porosimeter (Model PoreMaster 60, provided by Quantachrome Instruments, USA). A conical probe made of glass (volume 0.5 cm 3 , height 3.8 cm) was used as a sample container, and the negative electrode sheet was cut into a small piece of 10 mm x 10 mm and placed in the sample container. The pressure was set to 60,000 pounds per square inch (PSI), and then the pore size and pore size distribution of the negative electrode active material layer were measured using the mercury porosimeter. The negative electrode active material layer was scraped off from the negative electrode current collector, and the negative electrode current collector was cleaned, dried, and weighed to obtain the weight of the negative electrode current collector. The pore distribution of the negative electrode active material layer was calculated by subtracting the weight of the negative electrode current collector.

[0057] Particle size test:

[0058] The particle size distribution of the inorganic particles, graphite particles, and silicon-based materials was tested using a Malvern particle size tester (instrument model Master Sizer 2000). The sample preparation method was as follows: 0.02 g of a powder sample of the material to be tested was added to a 50 mL clean beaker, about 20 mL of deionized water was added, and the powder was uniformly dispersed in the water by ultrasonic cleaning in a 120 W ultrasonic cleaner for 5 minutes to obtain a particle size test sample of the material. In the volume-based particle size distribution of the material, the particle size reaching 50% of the volume accumulation was Dv50 from the small particle size.

[0059] Content test of inorganic particles and silicon-based materials:

[0060] The negative electrode sheet sample obtained according to the above sampling method was cut into a size of 1 cm x 1 cm and divided into two groups. One group was used as a scanning electron microscope test sample for observing the surface of the negative electrode sheet perpendicular to the thickness direction, and the other group was polished using an ion polisher (IB-09010CP) to polish the cross section along the thickness direction of the negative electrode sheet. The process parameters for polishing were a voltage of 6 kV, a time of 2 hours (h), an ion beam diameter of 500 μm, a polishing speed of 100 μm / h, and a vacuum degree of 10 -4 Pa, to obtain a polished cross section of the negative electrode sheet, thereby preparing a scanning electron microscope test sample for observing the cross section of the negative electrode sheet. The surface and cross section of the negative electrode sheet were observed by scanning electron microscopy, and scanning electron microscope photographs were taken.

[0061] Elemental analysis was performed by an energy dispersive spectrometer (EDS) associated with a scanning electron microscope to test the content of elements such as Figures 1 to 3The content of elements in the white particles and the dark gray particle regions was shown, then the negative active material layer on the surface of the negative electrode sheet was scraped off, and the scraped powder was heat-treated at 500°C for 4 hours in a tube furnace under nitrogen protection to obtain a powder sample for X-ray photoelectron spectroscopy (XPS) test. The elemental composition of the above-mentioned powder sample was measured by XPS, then the corresponding substance categories were confirmed in combination with the EDS analysis results, and the mass percentage content of inorganic particles and the mass percentage content of silicon-based materials were obtained by calculation.

[0062] Specific surface area test:

[0063] The specific surface area of the inorganic particles of each example and the comparative example was tested by a specific surface area analyzer (Tristar II 3020M) by nitrogen adsorption method. Among them, the specific test was carried out according to the national standard GB / T 19587-2017 “Gas adsorption BET method for determination of specific surface area of solid substances”.

[0064] Adhesion test:

[0065] The negative electrode sheet was taken out according to the above sampling method, and was dried at 60°C for 15h to obtain a negative electrode sheet sample, which was cut into a 15mm×110mm test strip for 180° peeling test. A double-sided tape (NITTO.NO5000NS) with a width of 15mm and a length of 60mm was attached to a steel plate with a size of 30mm×150mm, and then the test strip was attached to the double-sided tape through the double-sided tape, and the test surface faced downward. A paper tape with the same width as the test strip and a length of 60mm was connected to one end of the test strip through the double-sided tape, and a small stick with a mass of 2kg was rolled on the test strip for 8 times by hand, to obtain a test sample. A tensile testing machine was used for testing. The test sample was fixed on the test table, the paper tape was folded upward by 180°, and was fixed by a clamp, and then the tensile testing machine started to pull the paper tape at a speed of 50mm / min, until the test was ended after the negative active material layer on the surface of the double-sided tape was separated from the negative current collector, and the test data was saved. The adhesion F between the negative active material layer and the negative current collector was calculated according to the tensile force and the displacement of the stretching when the negative active material layer was separated from the negative current collector, and the unit was N / m.

[0066] Cycle performance test:

[0067] The lithium ion battery was placed in a constant temperature oven at 25°C ± 1°C for 30 minutes, charged at a constant current of 0.5C to 4.45V, then charged at a constant voltage of 4.45V to 0.025C, rested for 5 minutes, and then discharged at 0.5C to 3.0V. This was one cycle of charging and discharging, and the first cycle discharge capacity C0of the lithium ion battery was recorded. Then, the above cycle process was repeated for 500 cycles. The cycle discharge capacity at the 500th cycle C1was recorded. The 500-cycle cycle capacity retention rate = C1 / C0x 100%.

[0068] After 500 cycles according to the above cycle performance test process, the lithium ion battery was disassembled, and the surface of the negative electrode sheet was observed for delamination. If there was no delamination, the result was recorded as no; if there was delamination, the result was recorded as yes according to the observation.

[0069] Swelling performance test:

[0070] The initial thickness of the lithium ion battery before cycling was tested using a helical micrometer H0. When the lithium ion battery was cycled for 500 times according to the above cycle performance test process, the thickness of the lithium ion battery was tested again using a helical micrometer H1. The 500-cycle swelling rate = (H1-H0) / H0x 100%.

[0071] Example 1-1

[0072] Preparation of negative electrode sheet

[0073] A natural graphite and silicon-based material were used as the negative electrode active material. The natural graphite, silicon-based material silicon-carbon, inorganic particles alumina, binder butadiene-styrene copolymer (SBR), negative electrode conductive agent conductive carbon black (Super P), and negative electrode dispersing agent carboxymethyl cellulose (CMC) were mixed in a mass ratio of 93.8:3:0.1:2:0.1:1, then deionized water was added as a solvent to prepare a negative electrode slurry with a solid content of 50wt%, and the mixture was stirred uniformly. The negative electrode slurry was uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 10μm, and then dried at 110°C to obtain a negative electrode sheet with a single-sided coated negative electrode active material layer with a coating thickness of 150μm. Then the above steps were repeated on the other surface of the negative electrode sheet to obtain a double-sided coated negative electrode active material layer. After coating, the negative electrode sheet was cold-pressed and cut into a sheet with a size of 76.6mm x 875mm for use. The tap density of the negative electrode sheet was 1.7g / cm 3 .

[0074] Preparation of positive electrode sheet

[0075] The positive active material lithium cobaltate (LiCoO2), the positive electrode binder polyvinylidene fluoride (PVDF), and the positive electrode conductive agent Super P were mixed in a mass ratio of 97:1.6:1.4, N-methyl pyrrolidone (NMP) was added as a solvent, a slurry with a solid content of 75 wt% was prepared, and the slurry was stirred uniformly. The positive electrode slurry was uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10 μm, and the positive electrode active material layer was dried at 110°C. A single-sided coated positive electrode active material positive electrode sheet with a positive electrode active material layer thickness of 110 μm was obtained. Then, the above steps were repeated on the other surface of the positive electrode sheet, and a double-sided coated positive electrode active material positive electrode sheet was obtained. After the coating was completed, the positive electrode sheet was cold-pressed and cut into a sheet with a size of 74 mm x 867 mm for use. The tap density of the positive electrode sheet was 4.15 g / cm3. 3 .

[0076] <Preparation of electrolyte>

[0077] In a dry argon atmosphere glove box, the organic solvents ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and ethyl propionate (EP) were mixed in a mass ratio of EC:PC:DEC:EP=3:1:3:3, and then lithium salt lithium hexafluorophosphate (LiPF6) was added to the organic solvent to dissolve and mix uniformly, to obtain an electrolyte with a lithium salt concentration of 1 mol / L.

[0078] <Separator>

[0079] A polyethylene film with a thickness of 15 μm (provided by Celgard) was used.

[0080] <Preparation of lithium ion battery>

[0081] The positive electrode sheet, the separator, and the negative electrode sheet prepared above were stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and then wound to obtain an electrode assembly. After the tab was welded, the electrode assembly was placed in an aluminum-plastic film packaging shell, dried in a vacuum oven at 85°C for 12 hours to remove water, and then injected with the electrolyte prepared above. The lithium ion battery was obtained after vacuum packaging, standing, formation (0.02C constant current charging to 3.5V, and then 0.1C constant current charging to 3.9V), shaping, capacity testing, and other processes.

[0082] Examples 1-2 to 1-9

[0083] Except for adjusting the parameters according to Table 1, the rest was the same as Example 1-1.

[0084] Example 2-1

[0085] Except for adjusting the types of inorganic particles according to Table 2, the rest was the same as Example 1-1.

[0086] Example 2-2 to Example 2-5

[0087] The same as Example 1-1 except that the mass percentage content of the inorganic particles was regulated according to Table 2, and the mass percentage content of the graphite changed accordingly, and the mass percentage contents of the silicon-based material, the binder, the negative electrode conductive agent, and the negative electrode dispersing agent remained unchanged.

[0088] Example 2-6 to Example 2-7

[0089] The same as Example 1-1 except that the mass percentage content of the binder was regulated according to Table 2, and the mass percentage content of the graphite changed accordingly, and the mass percentage contents of the silicon-based material, the inorganic particles, the negative electrode conductive agent, and the negative electrode dispersing agent remained unchanged.

[0090] Example 2-8 to Example 2-10

[0091] The same as Example 1-1 except that the mass percentage content of the silicon-based material was regulated according to Table 2, and the mass percentage content of the graphite changed accordingly, and the mass percentage contents of the inorganic particles, the binder, the negative electrode conductive agent, and the negative electrode dispersing agent remained unchanged.

[0092] Comparative Example 1

[0093] The same as Example 1-1 except that no inorganic particles were added in the preparation of the negative electrode tab, and the mass percentage content of the graphite changed accordingly, and the mass percentage contents of the silicon-based material, the binder, the negative electrode conductive agent, and the negative electrode dispersing agent remained unchanged.

[0094] Comparative Example 2 to Comparative Example 5

[0095] The same as Example 1-1 except that the parameters were adjusted according to Table 1.

[0096] The relevant parameters and performance tests of each example and each comparative example are shown in Table 1 and Table 2. In Table 1 and Table 2, the adhesion between the negative electrode active material layer and the negative electrode current collector is F.

[0097] Table 1

[0098]

[0099] Note: " / " in Table 1 indicates that the substance does not exist or there is no relevant parameter.

[0100] As can be seen from Example 1-1 to Example 1-9, Comparative Example 1 to Comparative Example 5, the negative electrode sheet comprises inorganic particles, by changing the particle size of the inorganic particles or adjusting the particle size of the graphite or silicon-based material while keeping the Dv50 of the graphite and the silicon-based material unchanged, so that a / b and a / c are within a suitable range, thereby controlling the pore distribution of the negative electrode sheet, adjusting the pore size corresponding to the maximum pore volume and the value of x within the range of the present application, which can make the adhesion between the negative electrode active material layer and the negative electrode current collector larger, improve the debonding problem of the negative electrode active material layer, and the lithium ion battery has higher capacity retention rate and lower expansion rate, indicating that the lithium ion battery has better cycle performance and expansion performance.

[0101] In addition, the specific surface area of the inorganic particles is related to the particle size of the inorganic particles. Generally, the smaller the particle size of the inorganic particles, the larger the specific surface area, and vice versa. Therefore, when the particle size of the inorganic particles is small, the specific surface area is larger, and the contact with the negative electrode active material particles or the negative electrode current collector is more sufficient. As can be seen from Example 1-1 to Example 1-5, by adjusting the specific surface area of the inorganic particles within the range of the present application, the adhesion between the negative electrode active material layer and the negative electrode current collector can be made larger.

[0102] Figure 1 The scanning electron microscope photograph of the cross section of the negative electrode sheet of Example 1-1 along the thickness direction of itself is shown in FIG. 1-1. Figure 1 As can be seen from FIG. 1-1, the pore distribution on the surface of the negative electrode sheet is relatively uniform, Figure 1 The white spots in FIG. 1-1 are inorganic particles, which fill the pores between the negative electrode active material particles.

[0103] Figure 2 The scanning electron microscope photograph of the cross section of the negative electrode sheet of Example 1-1 along the thickness direction of itself is shown in FIG. 1-1. Figure 2 The white particles in FIG. 1-1 are inorganic particles, and the dark gray particles are negative electrode active material particles. As can be seen from FIG. 1-1, Figure 2 As can be seen from FIG. 1-1, the inorganic particles fill the pores between the negative electrode active material particles and adhere to the negative electrode active material particles on both sides of the pores. In addition, Figure 2 In FIG. 1-1, Pa 1 represents the starting point of the size shown on the inorganic particle diagram tested, Pa R1 represents the end point of the size on the inorganic particle diagram tested, and Pa 1=1.295 μm represents the distance between Pa 1 and Pa R1, i.e. the maximum size of the inorganic particles (i.e. the diameter of the circumscribed circle of the inorganic particles) is 1.295 μm.

[0104] Figure 3 The scanning electron microscope photograph of the surface of the negative electrode active material layer of Example 1-1 is shown in FIG. 1-1. Figure 3The white particles in the figure are inorganic particles, and the dark gray particles are negative active material particles. Figure 3 It can be seen that some inorganic particles are distributed in the pores between the negative active material particles, and some inorganic particles are distributed on the surface of the negative active material particles. Figure 3 In the figure, Pa 2 and Pa 3 represent the starting points of the size shown in the figure of the tested inorganic particles, Pa R2 and Pa R3 represent the ending points of the size shown in the figure of the tested inorganic particles, Pa 2 = 820.6 nm represents that the diameter of the circumscribed circle of the inorganic particles distributed on the surface of the negative active material particles is 820.6 nm. Pa 3 = 1.285 μm represents that the diameter of the circumscribed circle of the inorganic particles distributed in the pores between the negative active material particles is 1.285 μm.

[0105] Figure 4 The pore distribution diagram of the negative active material layer of Example 1-1 and Comparative Example 2. It can be seen that the pore diameter corresponding to the maximum pore volume in the negative electrode sheet of Example 1-1 is 0.7 μm, and the pore diameter corresponding to the maximum pore volume in the negative electrode sheet of Comparative Example 2 is 1.3 μm.

[0106] Table 2

[0107]

[0108] Note: In Table 2, the "mass percentage content of inorganic particles" is the value of the mass percentage content of inorganic particles based on the mass of the negative active material layer; the "mass percentage content of silicon-based material" is the value of the mass percentage content of silicon-based material based on the mass of the silicon-based material and graphite.

[0109] The type of inorganic particles usually affects the cycle performance and swelling performance of lithium ion batteries. It can be seen from Example 1-1 and Example 2-1 that, as long as the pore diameter corresponding to the maximum pore volume and the value of x are within the scope of the present application, selecting different inorganic particles has little effect on delamination, capacity retention rate and swelling rate.

[0110] It can be seen from Example 1-1, Example 2-2 to Example 2-5 that, under the condition that the mass percentage of the binder is the same, appropriately increasing the mass percentage of the inorganic particles can further improve the adhesion between the negative active material particles, further improve the swelling performance, and also improve the adhesion between the negative active material layer and the negative current collector, further improving the delamination. If the mass percentage of the inorganic particles is further increased on this basis, the improvement effect will not be significantly improved.

[0111] It can be seen from Example 1-1, Example 2-6 to Example 2-7 that, under the condition that the mass percentage content of the inorganic particles is certain, appropriately increasing the mass percentage content of the binder can improve the cycle performance and swelling performance of the lithium ion battery.

[0112] As can be seen from Example 1-1, Example 2-8 to Example 2-10, the mass percentage of the silicon-based material generally affects the cycle performance and swelling performance of the lithium ion battery. By adjusting the mass percentage of the silicon-based material within the scope of the present application, the swelling performance can be controlled within a suitable range to meet product requirements.

[0113] It should be noted that in this document, the terms "comprising", "including", or any other variant thereof are intended to cover non-exclusive inclusions, such that processes, methods, articles or devices that comprise a series of elements not only include those elements, but also include other elements not explicitly listed, or inherent to such processes, methods, articles or devices.

[0114] Each of the embodiments in the specification is described in a relevant manner, and the same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the difference from other embodiments.

[0115] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. A negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material, a binder, and inorganic particles, the negative electrode active material comprising graphite and a silicon-based material, in a pore distribution test of the negative electrode active material layer, a pore diameter range corresponding to a maximum pore volume is 0.6 μm to 1.2 μm, and a proportion x of a sum of pore volumes of pores having a pore diameter of less than or equal to 0.5 μm with respect to a total volume of all pores is 30% to 40%.

2. The negative electrode sheet according to claim 1, wherein the pore diameter range corresponding to the maximum pore volume is 0.7 μm to 0.9 μm.

3. The negative electrode sheet according to claim 1, wherein the silicon-based material comprises at least one of silicon, silicon-oxygen, and silicon-carbon.

4. The negative electrode sheet according to claim 1, wherein Dv50 of the inorganic particles is a μm, 1 ≤ a ≤ 3, Dv50 of the graphite particles is b μm, 10 ≤ b ≤ 22, and Dv50 of the silicon-based material is c μm, 5 ≤ c ≤ 12.

5. The negative electrode sheet according to claim 4, wherein a / b satisfies 0.08 ≤ a / b ≤ 0.25, and a / c satisfies 0.1 ≤ a / c ≤ 0.

35.

6. The negative electrode sheet according to claim 4, wherein a / b satisfies 0.08 ≤ a / b ≤ 0.11, and a / c satisfies 0.1 ≤ a / c ≤ 0.

16.

7. The negative electrode sheet according to claim 1, wherein a mass percentage content of the silicon-based material is 1% to 20% based on a total mass of the graphite and the silicon-based material.

8. The negative electrode sheet according to claim 1, wherein a mass percentage content of the silicon-based material is 1% to 10% based on a total mass of the graphite and the silicon-based material.

9. The negative electrode sheet according to claim 1, wherein the inorganic particles comprise at least one of alumina or boehmite, and a mass percentage content of the inorganic particles is 0.1% to 0.5% based on a mass of the negative electrode active material layer.

10. The negative electrode sheet according to claim 1, wherein The specific surface area of the inorganic particles is 5 m 2 / g to 15 m 2 / g.

11. The negative electrode sheet according to claim 1, wherein the binder comprises at least one of a butadiene-styrene copolymer, polyacrylic acid, or carboxymethyl cellulose, and a mass percentage content of the binder is 1.9% to 3% based on a mass of the negative electrode active material layer. 12.A secondary battery comprising the negative electrode sheet according to any one of claims 1 to 11. 13.An electronic device comprising the secondary battery according to claim 12.

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