Negative electrode active material, secondary battery and electronic device

Abstract

A negative electrode active material, a secondary battery and an electronic device. The powder of the negative electrode active material has a pressurized compaction density of a g / cm3, a pressure relief compaction density of b g / cm3, and a pressure relief rebound rate of c, wherein c=(a-b) / a×100%, 1.5%≤c≤20%, and a and c meet the relational expression: c=k×(a-1), wherein 0.08≤k≤0.20. By regulating the value of k to be within the range and enabling a and c to meet the relational expression, the negative electrode active material can still have relatively high porosity under high compaction density; the electrolyte infiltration into a negative electrode sheet is facilitated, the diffusion rate of active ions is increased, and the dynamic performance of the secondary battery is improved; additionally, the heat dissipation performance of the negative electrode sheet can be improved, the temperature rise of the secondary battery is reduced, and the cycle performance of the secondary battery is improved.

Description

Negative electrode active material, secondary battery and electronic device

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on August 4, 2023, with application number 202310980458.7 and invention name “A negative electrode active material, negative electrode plate, secondary battery and electronic device”, the entire contents of which are incorporated by reference into this application. Technical Field

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

[0003] Secondary batteries have outstanding advantages such as high energy density, low self-discharge rate, long cycle life and stable discharge performance. They are widely used in industrial production and people's daily life.

[0004] Artificial graphite is commonly used as the negative electrode active material for secondary batteries. Because natural graphite is relatively soft and intolerant to pressure, negative electrode plates made of natural graphite have low porosity at high compaction densities, making heat dissipation difficult and resulting in high overall battery temperatures. Furthermore, as the charge and discharge cycles progress, the negative electrode plates, constrained by the packaging, are continuously squeezed by the internal expansion stress, further compacting the negative electrode plates and reducing their porosity. This makes electrolyte infiltration difficult, increases temperature rise, and accelerates cycle performance degradation. Therefore, there is a need to improve the performance of secondary batteries using natural graphite.

[0005] Summary of the Invention

[0006] The purpose of this application is to provide a negative electrode active material, a secondary battery, and an electronic device to reduce the temperature rise of the secondary battery and improve the cycle performance of the secondary battery. The specific technical solution is as follows:

[0007] The first aspect of the present application provides a negative electrode active material, the powder of which has a pressurized compaction density of ag / cm 3 , the pressure relief compaction density is bg / cm 3And the pressure relief rebound rate is c, c = (ab) / a × 100%, 1.5% ≤ c ≤ 20%; a and c satisfy: c = k × (a-1), 0.08 ≤ k ≤ 0.20, and the test tonnage of the pressurized compaction density is 5 tons. By making the value of k within the above range and making a and c satisfy the above relationship, the negative electrode active material can have a higher porosity at a high compaction density. The application of the negative electrode active material of the present application to secondary batteries is conducive to the electrolyte infiltration of the negative electrode plate, improving the diffusion rate of active ions (such as lithium ions), and improving the kinetic performance of the secondary battery, such as rate performance. At the same time, the higher porosity can increase the heat dissipation rate during the delithiation process of the negative electrode plate, improve the heat dissipation performance of the negative electrode plate, reduce the temperature rise of the secondary battery, thereby reducing the increase in the impedance of the secondary battery during the cycle and the decomposition of the solid electrolyte interface film (SEI film) on the surface of the negative electrode plate, and improving the cycle performance of the secondary battery.

[0008] In some embodiments of the present application, 5% ≤ c ≤ 15%, 0.15 ≤ k ≤ 0.20. By regulating the values ​​of c and k within the above range, the negative electrode active material can have a higher porosity at a high compaction density. Applying the negative electrode active material to a secondary battery can further increase the diffusion rate of ions and improve the kinetic performance of the secondary battery. At the same time, it is beneficial to further improve the heat dissipation performance of the negative electrode plate, reduce the temperature rise of the secondary battery, thereby reducing the increase in the impedance of the secondary battery during the cycle and the decomposition of the SEI film on the surface of the negative electrode plate, thereby improving the cycle performance of the secondary battery.

[0009] In some embodiments of the present application, 1.2 ≤ a ≤ 2.0. By regulating the value of a within the above range, the negative electrode active material can have a suitable pressure relief rebound rate. Application of the negative electrode active material in a secondary battery can improve the porosity of the negative electrode sheet and facilitate electrolyte infiltration of the negative electrode sheet, thereby reducing the temperature rise of the secondary battery and improving the kinetic and cycling performance of the secondary battery.

[0010] In some embodiments of the present application, 1.2 ≤ b ≤ 1.9. By regulating the value of b within the above range, the negative electrode active material can have a suitable pressure relief rebound rate. Application of the negative electrode active material in a secondary battery facilitates electrolyte infiltration of the negative electrode sheet, alleviating the accumulation of internal stress in the negative electrode sheet, thereby reducing the temperature rise of the secondary battery and improving its dynamic performance and cycle performance.

[0011] In some embodiments of the present application, the negative electrode active material includes graphite having hard carbon on its surface. The negative electrode active material having the above characteristics has good compressive resistance. The graphite particles have high crystallinity and can provide lithium storage sites. The hard carbon located on the surface of the graphite has low crystallinity, which can improve the electronic conductivity of the negative electrode active material and increase the pores for electrolyte infiltration. Applying the negative electrode active material having the above characteristics to a secondary battery can not only make the secondary battery have a higher energy density, but also reduce the temperature rise of the secondary battery and improve the dynamic performance and cycle performance of the secondary battery.

[0012] In some embodiments of the present application, the negative electrode active material satisfies 0.3≤I d / I g ≤0.7, I d is the peak intensity of the d peak in the Raman spectrum of the negative electrode active material, I g is the peak intensity of the g peak in the Raman spectrum of the negative electrode active material. d / I g The negative electrode active material with a value within the above range has an appropriate degree of surface defects, which is conducive to making the negative electrode active material have a suitable pressure release rebound rate, so that the negative electrode active material still has a good pore structure after cold pressing and has a higher porosity, thereby further improving the diffusion rate of active ions, improving the heat dissipation performance of the negative electrode plate, reducing the temperature rise of the secondary battery, and thereby reducing the increase in the impedance of the secondary battery during the cycle and the decomposition of the SEI film on the surface of the negative electrode plate, thereby better improving the kinetic performance and cycle performance of the secondary battery.

[0013] In some embodiments of the present application, the powdered negative electrode active material has an OI value of 2 to 5. By regulating the OI value of the powdered negative electrode active material within this range, the isotropic properties of the negative electrode active material can be enhanced, facilitating the diffusion of active ions. Application of negative electrode active materials with these characteristics in secondary batteries can balance the kinetic and cycling performance of the secondary battery.

[0014] In some embodiments of the present application, the degree of graphitization G of the negative electrode active material is 90.5% to 98%. By regulating the degree of graphitization of the negative electrode active material within the above range, it is indicated that the surface graphitization degree and crystallinity of the negative electrode active material are low, which can improve the electronic conductivity of the negative electrode active material and increase the pores for electrolyte infiltration, thereby improving the kinetic performance and cycle performance of the secondary battery.

[0015] The second aspect of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer comprises the negative electrode active material provided by the first aspect of the present application. The negative electrode active material of the present application is applied to the negative electrode sheet, resulting in the negative electrode sheet having a high porosity and good heat dissipation performance, thereby reducing the temperature rise of the secondary battery and improving the dynamic performance and cycle performance of the secondary battery.

[0016] In some embodiments of the present application, the compaction density of the negative electrode sheet is qg / cm 3 The porosity of the negative electrode sheet is p, where q and p satisfy p = -0.37 × q + h, 0.8 ≤ h ≤ 1.0; 1.2 ≤ q ≤ 1.9, and 10% ≤ p ≤ 60%. This negative electrode sheet possesses a high compaction density and high porosity, resulting in excellent heat dissipation. Its application in secondary batteries can reduce temperature rise and improve their dynamic and cycling performance.

[0017] In some embodiments of the present application, the OI value of the negative electrode plate ranges from 8 to 30. Negative electrode plates with an OI value within this range have good ion diffusion properties. Application of such negative electrode plates in secondary batteries can help reduce the temperature rise of the secondary battery and improve its kinetic and cycling performance.

[0018] In some embodiments of the present application, the negative electrode sheet satisfies 0.3≤I d ' / I g '≤0.8, I d ' is the peak intensity of the middle d peak of the Raman spectrum of the negative electrode in the 100μm×100μm area, I g ' is the peak intensity of the middle g peak of the Raman spectrum of the negative electrode in the 100μm×100μm area. d ' / I g The negative electrode sheet with a value of ' within the above range has good electronic conductivity. When applied to secondary batteries, it can improve the kinetic performance and cycle performance of the secondary batteries.

[0019] The third aspect of the present application provides an electronic device, which includes the secondary battery provided by the second aspect of the present application. The secondary battery of the present application has good cycle performance and dynamic performance, so that the electronic device of the present application has a long service life.

[0020] Beneficial effects of this application:

[0021] The present application provides a negative electrode active material, a secondary battery and an electronic device. The pressed density of the negative electrode active material powder is ag / cm 3, the pressure relief compaction density is bg / cm 3 And the pressure relief rebound rate is c, c = (ab) / a × 100%, 1.5% ≤ c ≤ 20%; a and c satisfy: c = k × (a-1), 0.08 ≤ k ≤ 0.20. By regulating the value of k within the above range and making a and c satisfy the above relationship, the negative electrode active material can have a higher porosity under high compaction density. The application of the negative electrode active material of the present application to secondary batteries is conducive to the infiltration of the electrolyte into the negative electrode plate, improving the diffusion rate of active ions (such as lithium ions), and improving the kinetic performance of the secondary battery, such as rate performance. At the same time, a higher porosity can increase the heat dissipation rate during the delithiation process of the negative electrode plate, improve the heat dissipation performance of the negative electrode plate, reduce the temperature rise of the secondary battery, thereby reducing the increase in the impedance of the secondary battery during the cycle and the decomposition of the SEI film on the surface of the negative electrode plate, and improving the cycle performance of the secondary battery.

[0022] 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

[0023] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0024] FIG1 is a scanning electron microscope (SEM) photograph of the particle morphology of the negative electrode active material prepared in Example 1-1;

[0025] FIG2 is a comparison of the 800-cycle performance of the lithium-ion batteries of Example 1-1 and Comparative Example 1-1;

[0026] FIG3 is a Raman spectrum of the negative electrode active materials prepared in Example 1-1 and Comparative Example 1-1;

[0027] FIG4 is a Raman spectrum of the negative electrode sheets of Example 1-1 and Comparative Example 1-5;

[0028] FIG5 is an X-ray diffraction spectrum of the negative electrode active material prepared in Example 1-1;

[0029] FIG6 is an X-ray diffraction spectrum of the negative electrode sheet of Example 1-1. DETAILED DESCRIPTION

[0030] The following will be combined with the accompanying drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the 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.

[0031] It should be noted that, in the specific embodiments of the present application, lithium-ion batteries are used as an example of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries.

[0032] To increase energy density, negative electrode sheets are typically required to have a high compaction density. However, a high compaction density results in a low porosity in negative electrode sheets, including natural graphite, making heat dissipation difficult, affecting the temperature rise and rate performance of secondary batteries. Furthermore, as cycles progress, the compaction density further increases due to expansion internal stress, making electrolyte infiltration difficult, increasing temperature rise, and accelerating cycle performance degradation.

[0033] In view of this, the first aspect of the present application provides a negative electrode active material, the pressurized compaction density of which powder is ag / cm 3 , the pressure relief compaction density is bg / cm 3 The pressure relief rebound rate is c, c = (ab) / a × 100%, 1.5% ≤ c ≤ 20%, preferably 5% ≤ c ≤ 15%; a and c satisfy: c = k × (a-1), 0.08 ≤ k ≤ 0.20, preferably 0.15 ≤ k ≤ 0.20, and the test tonnage of the pressurized compaction density is 5 tons. For example, the value of c can be 1.5%, 3%, 5%, 8%, 10%, 12%, 14%, 15%, 18%, 20%, or a range consisting of any two values ​​therein, and the value of k can be 0.08, 0.10, 0.12, 0.14, 0.15, 0.16, 0.18, 0.20, or a range consisting of any two values ​​therein. By regulating the value of k within the above range and ensuring that a and c satisfy the above relationship, the negative electrode active material can have a higher porosity at a high compaction density. The application of the negative electrode active material of the present application in a secondary battery facilitates electrolyte infiltration of the negative electrode plate, increases the diffusion rate of ions (such as lithium ions), and improves the kinetic performance of the secondary battery, such as rate performance. At the same time, the higher porosity can increase the heat dissipation rate of the negative electrode plate during lithium removal, improve the heat dissipation performance of the negative electrode plate, and reduce the temperature rise of the secondary battery, thereby reducing the increase in the impedance of the secondary battery during the cycle and the decomposition of the SEI film on the surface of the negative electrode plate, thereby improving the cycle performance of the secondary battery.

[0034] In some embodiments of the present application, 1.2≤a≤2.0, for example, the value of a can be 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, or a range consisting of any two of these values. By regulating the value of a within the above range, the negative electrode active material can have a suitable pressure relief rebound rate. Applying the negative electrode active material to a secondary battery is beneficial to increasing the porosity of the negative electrode sheet and facilitating the electrolyte infiltration of the negative electrode sheet, thereby reducing the temperature rise of the secondary battery and improving the kinetic performance and cycle performance of the secondary battery.

[0035] In some embodiments of the present application, 1.2≤b≤1.9. For example, the value of b can be 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or a range consisting of any two of these values. By regulating the value of b within the above range, the negative electrode active material can have a suitable pressure relief rebound rate. Applying the negative electrode active material to a secondary battery is beneficial to the electrolyte infiltration of the negative electrode sheet, alleviating the accumulation of internal stress in the negative electrode sheet, thereby reducing the temperature rise of the secondary battery and improving its dynamic performance and cycle performance.

[0036] In some embodiments of the present application, the negative electrode active material includes graphite having hard carbon on its surface. It should be noted that the "surface" here can be the entire area of ​​the surface of the graphite particles or a partial area of ​​the surface of the graphite particles. This application has no particular limitation on this, as long as the purpose of this application can be achieved. The negative electrode active material with the above characteristics has good compressive properties. The graphite particles have high crystallinity and can provide lithium storage sites. The hard carbon located on the surface of the graphite has a low degree of crystallinity, which can improve the electronic conductivity of the negative electrode active material and increase the pores for electrolyte infiltration. Applying the negative electrode active material with the above characteristics to a secondary battery can not only make the secondary battery have a higher energy density, but also reduce the temperature rise of the secondary battery and improve the dynamic performance and cycle performance of the secondary battery.

[0037] In some embodiments of the present application, the negative electrode active material satisfies 0.3≤I d / I g ≤0.7, I d is the peak intensity of the d peak in the Raman spectrum of the negative electrode active material, I g is the peak intensity of the g peak in the Raman spectrum of the negative electrode active material. d / I g The value of can be 0.3, 0.4, 0.5, 0.6, 0.7 or a range consisting of any two of these values. d / I gThe negative electrode active material with a value within the above range has an appropriate degree of surface defects, which is conducive to making the negative electrode active material have a suitable pressure release rebound rate, so that the negative electrode active material still has a good pore structure after cold pressing and has a higher porosity, thereby further improving the diffusion rate of lithium ions, improving the heat dissipation performance of the negative electrode plate, reducing the temperature rise of the secondary battery, reducing the increase in the impedance of the secondary battery during the cycle and the decomposition of the SEI film on the surface of the negative electrode plate, and better improving the kinetic performance and cycle performance of the secondary battery.

[0038] In some embodiments of the present application, the powder OI value of the negative electrode active material is 2 to 5. For example, the OI value of the powder of the negative electrode active material can be 2, 2.5, 3, 3.5, 4, 4.5, 5, or a range consisting of any two of these values. By regulating the OI value of the powder of the negative electrode active material within the above range, the isotropy of the negative electrode active material can be improved, which is conducive to the diffusion of lithium ions. The negative electrode active material with the above characteristics is applied to secondary batteries, which can take into account both the kinetic performance and cycle performance of the secondary battery.

[0039] In some embodiments of the present application, the degree of graphitization G of the negative electrode active material is between 90.5% and 98%. For example, the value of G can be 90.5%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or a range consisting of any two of these values. By regulating the degree of graphitization of the negative electrode active material within the above range, it is indicated that the surface graphitization degree and crystallinity of the negative electrode active material are low, which can improve the electronic conductivity of the negative electrode active material and increase the pores for electrolyte infiltration, thereby improving the kinetic performance and cycle performance of the secondary battery.

[0040] The preparation method of the negative electrode active material provided in the present application includes but is not limited to the following steps: mixing graphite and a precursor evenly, adding them to a reactor, introducing oxygen, first melting the precursor, and then causing a cross-linking reaction. The reacted sample is then cooled to room temperature, placed in a crucible, and carbonized under a nitrogen atmosphere. The carbonized product is sieved and demagnetized to obtain a negative electrode active material, wherein the negative electrode active material includes graphite with hard carbon on the surface. For example, the material of the precursor may include but is not limited to at least one of phenolic resin, epoxy resin, furan resin, acrylonitrile-butadiene-styrene copolymer (ABS resin), coal-based asphalt, polyacrylonitrile, polypropylene, citric acid or sucrose.

[0041] The present application has no particular restrictions on graphite, as long as the purpose of the present application can be achieved. For example, the graphite can be natural graphite. The present application has no particular restrictions on the particle size Dv50 of the above-mentioned graphite, as long as the purpose of the present application can be achieved. For example, the particle size Dv50 of the graphite can be 6μm to 23μm. Dv50 refers to the particle size at which 50% of the volume is accumulated, measured from the small particle size, in the volume-based particle size distribution of the material. The present application has special restrictions on the purity of the graphite, as long as the purpose of the present application can be achieved. For example, the purity of the graphite can be 90% to 99.99%. The present application has no special restrictions on the coking value of the precursor, as long as the purpose of the present application can be achieved. For example, the coking value of the precursor can be 20% to 80%. The present application has no special restrictions on the mass ratio of graphite to precursor, as long as the purpose of the present application can be achieved. For example, the mass ratio m:n of graphite to precursor can be 90:10 to 98:2. The present application does not particularly limit the conditions for the melting and cross-linking reactions, as long as the purpose of the present application can be achieved. For example, the temperatures of the melting and cross-linking reactions are each independently 200°C to 800°C, and the reaction time is each independently 2 hours to 8 hours. The present application does not particularly limit the gas flow rate of oxygen, as long as the purpose of the present application can be achieved. For example, the gas flow rate of oxygen is 2L / min to 10L / min. The present application does not particularly limit the conditions for the carbonization treatment, as long as the purpose of the present application can be achieved. For example, the temperature of the carbonization treatment is 800°C to 1300°C, and the reaction time is 12 hours to 20 hours. The present application does not particularly limit the methods of screening and demagnetization, which can be selected according to actual needs, as long as the purpose of the present application can be achieved. For example, it can be screened through a double-layer screen of a vibrating screen and demagnetized by an automatic powder electric demagnetizer. The present application does not particularly limit the mesh size of the screen, which can be selected according to actual needs. For example, a screen of 300 to 400 mesh can be selected.

[0042] Generally, the pressure relief rebound rates c and k can be adjusted by controlling the graphite particle size Dv50, the mass ratio of graphite to precursor m:n, the coking value of the precursor, the temperature and time of the cross-linking reaction, and the temperature and time of the carbonization treatment. Increasing the graphite particle size Dv50 decreases c and k; decreasing the graphite particle size Dv50 increases c and k. Increasing the m:n ratio decreases c and k; decreasing the m:n ratio increases c and k. Increasing the coking value of the precursor increases c and k; decreasing the coking value of the precursor decreases c and k. Increasing the cross-linking reaction temperature increases c and k; decreasing the cross-linking reaction temperature decreases c and k. Prolonging the cross-linking reaction time increases c and k. Shortening the cross-linking reaction time decreases c and k. Increasing the carbonization temperature increases c and k; decreasing the carbonization temperature decreases c and k. Prolonging the carbonization time decreases c and k. The shorter the carbonization treatment time, the greater the c and k.

[0043] The second aspect of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer comprises the negative electrode active material provided by the first aspect of the present application. The negative electrode active material of the present application is applied to the negative electrode sheet, resulting in the negative electrode sheet having a high porosity and good heat dissipation performance, thereby reducing the temperature rise of the secondary battery and improving the dynamic performance and cycle performance of the secondary battery.

[0044] In some embodiments of the present application, the compaction density of the negative electrode sheet is qg / cm 3 , the porosity of the negative electrode sheet is p, q and p satisfy p = -0.37×q+h, 0.8≤h≤1.0; 1.2≤q≤1.9, 10%≤p≤60%, for example, the value of h can be 0.8, 0.83, 0.85, 0.88, 0.9, 0.92, 0.95, 0.98, 1.0 or a range consisting of any two values ​​therein, the value of q can be 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or a range consisting of any two values ​​therein, and the value of p can be 10%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 60% or a range consisting of any two values ​​therein. The negative electrode sheet with the above characteristics has a high compaction density and a high porosity, and has good heat dissipation performance. Applying it to a secondary battery can reduce the temperature rise of the secondary battery and improve the dynamic performance and cycle performance of the secondary battery.

[0045] The present application does not particularly limit the method for regulating the compaction density of the negative electrode sheet, as long as the objectives of the present application can be achieved. For example, the compaction density of the negative electrode sheet can be regulated by adjusting the cold pressing pressure. Generally, increasing the cold pressing pressure increases the compaction density of the negative electrode sheet, while decreasing the cold pressing pressure decreases the compaction density of the negative electrode sheet.

[0046] In some embodiments of the present application, the OI value of the negative electrode plate is in the range of 8 to 30. For example, the OI value of the negative electrode plate can be 8, 9, 10, 13, 15, 18, 20, 22, 25, 28, 30, or a range consisting of any two of these values. Negative electrode plates with OI values ​​within the above ranges have good ion diffusion properties. Their application in secondary batteries is beneficial in reducing the temperature rise of the secondary battery and improving the kinetic and cycling performance of the secondary battery.

[0047] In some embodiments of the present application, the negative electrode sheet satisfies 0.3≤I d ' / I g '≤0.8, I d ' is the peak intensity of the middle d peak of the Raman spectrum of the negative electrode in the 100μm×100μm area, I g ' is the peak intensity of the middle g peak of the Raman spectrum of the negative electrode in the 100μm×100μm area. d ' / I g The value of ' can be 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.75, 0.8 or a range consisting of any two of these values. d ' / I g The negative electrode sheet with a value of ' within the above range has good electronic conductivity. Applying it to a secondary battery can improve the kinetic performance and cycle performance of the secondary battery.

[0048] 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, the negative electrode current collector may include copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, 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, there is no particular restriction on the thickness of the negative electrode current collector and the negative electrode active 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 4μm to 12μm, and the thickness of the single-sided negative electrode active material layer is 30μm to 160μm. In the present application, the negative electrode active material layer can be arranged on one surface in the thickness direction of the negative electrode current collector, or on both surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" herein can refer to the entire area of ​​the negative electrode current collector or a portion of the negative electrode current collector. This application is not particularly limited, as long as the purpose of this application can be achieved. Optionally, the negative electrode active material includes a thickener, which may include but is not limited to sodium carboxymethyl cellulose. The negative electrode active material layer of this application may also include a conductive agent and a binder.

[0049] The negative electrode active material layer in the present application may also include a binder or a thickener. The present application does not particularly limit the types of binders and thickeners, as long as the purpose of the present application can be achieved. For example, the binder may include but is not limited to polypropylene alcohol, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl pyrrolidone, polyethylene, polypropylene, epoxy resin, nylon, styrene-butadiene rubber, polyvinyl alcohol, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl butyral, water-based acrylic resin, carboxymethyl cellulose or sodium carboxymethyl cellulose, etc. At least one of the thickener may include but is not limited to carboxymethyl cellulose or sodium carboxymethyl cellulose. In some embodiments, the negative electrode sheet of the present application does not contain a conductive agent, such as acetylene black, Ketjen black, carbon nanotubes (CNTs), carbon fiber, carbon dots or graphene.

[0050] The present application has no special restrictions on the positive electrode sheet, as long as the purpose of the present application can be achieved. For example, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector. The present application has no special restrictions on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the positive electrode current collector may include a metal foil or a composite current collector, etc. For example, the metal foil may be an aluminum foil. The composite current collector may include a polymer material base layer and a metal material layer located on at least one surface of the polymer material base layer. The material of the metal material layer may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver or silver alloy. The polymer material base layer may 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 present application has no special restrictions on the type of positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material includes lithium cobalt oxide, lithium nickel cobalt manganese oxide (LiNi 0.90 Co 0.05 Mn 0.05 O2 (NCM955), NCM811, NCM622, NCM523, NCM111), at least one of lithium nickel manganese aluminum oxide, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium iron manganese phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel lithium manganese oxide, spinel lithium nickel manganese oxide or lithium titanate.

[0051] The present application has no particular restrictions on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5μm to 20μm. The thickness of the single-sided positive electrode active material layer is 30μm to 150μm. In the present application, the positive electrode active material layer can be arranged on one surface in the thickness direction of the positive electrode current collector, or on two surfaces in the thickness direction of the positive electrode current collector. It should be noted that the "surface" here can be the entire area of ​​the positive electrode current collector or a partial area of ​​the positive electrode current collector. The present application has no particular restrictions, as long as the purpose of the present application can be achieved. The positive electrode active material layer of the present application may also contain the above-mentioned binder. The positive electrode active material layer of the present application may also contain a conductive agent. The present application has no particular restrictions on the conductive agent, as long as the purpose of the present application can be achieved. For example, the conductive agent can be at least one of acetylene black, Ketjen black, carbon nanotubes, carbon fibers, carbon dots or graphene.

[0052] In the present application, the electrolyte includes a lithium salt and an organic solvent. The lithium salt may 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(oxalatoborate) (LiBOB) or lithium difluorooxalatoborate (LiDFOB). The present application has no particular restrictions on the concentration of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the above-mentioned organic solvent, as long as the purpose of the present application can be achieved, for example, it may include but is not limited to at least one of a carbonate compound, a carboxylate compound, an ether compound or other organic solvent. The above-mentioned carbonate compound may 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 may include but is not limited to at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate or methyl ethyl carbonate. The above-mentioned cyclic carbonate compound may include but is not limited to at least one of ethylene carbonate, propylene carbonate, butylene carbonate or vinyl ethylene carbonate. The above-mentioned carboxylate compound may include but is not limited to at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid, valerolactone or caprolactone. The above-mentioned ether compound may include but is not limited to at least one of ethylene glycol dimethyl ether, 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 other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. The electrolyte may further include additives, which may include, but are not limited to, at least one of fluoroethylene carbonate, 1,3-propane sultone, or adiponitrile.

[0053] The secondary battery of the present application also includes a diaphragm to separate the positive electrode sheet and the negative electrode sheet, prevent the internal short circuit of the secondary battery, allow the electrolyte ions to pass freely, and do not affect the electrochemical charge and discharge process. The present application has no particular restrictions on the diaphragm, as long as the purpose of the present application can be achieved. For example, the material of the diaphragm may include but is not limited to polyethylene, polypropylene, polytetrafluoroethylene-based polyolefin diaphragms, polyester films (such as polyethylene terephthalate (PET) films), cellulose films, polyimide films, polyamide films, spandex or aramid films, etc. At least one of the types of diaphragms may include but is not limited to woven films, non-woven films (non-woven fabrics), microporous films, composite films, rolled films or spun films, etc. The diaphragm of the present application may have a porous structure, and the porous layer is provided on at least one surface of the diaphragm, and the porous layer includes inorganic particles and a binder. The inorganic particles may include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The binder may include at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The present application does not particularly limit the size of the pore size of the porous structure, as long as the purpose of the present application can be achieved, for example, the size of the pore size can be 0.01 μm to 1 μm. In the present application, the thickness of the diaphragm 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.

[0054] The secondary battery of this application also includes a packaging bag for containing the positive electrode sheet, separator, negative electrode sheet, and electrolyte, as well as other components of the secondary battery known in the art. This application does not limit these other components. This application does not specifically limit the packaging bag and can be any packaging bag known in the art, as long as it can achieve the purpose of this application. For example, an aluminum-plastic film packaging bag can be used.

[0055] The secondary battery of the present application is not particularly limited and may include any device that generates an electrochemical reaction. In one embodiment of the present application, the secondary battery may include but is not limited to: a lithium ion battery, a sodium ion battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0056] The preparation process of the secondary battery of the present application is well known to those skilled in the art and is not particularly limited in the present application. For example, it may 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 and other operations as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly with a stacked structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, as needed, overcurrent protection elements, guide plates, etc. may be placed in the packaging bag to prevent pressure rise and overcharge and discharge inside the secondary battery.

[0057] The third aspect of the present application provides an electronic device, which includes the secondary battery provided by the second aspect of the present application. The secondary battery of the present application has good cycle performance and dynamic performance, so that the electronic device of the present application has a long service life.

[0058] 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.

[0059] Example

[0060] 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.

[0061] Test methods and equipment:

[0062] Sampling method for negative electrode sheets and negative electrode active materials:

[0063] The lithium-ion battery was discharged at a constant current of 1C to a voltage of 3.0V and then disassembled. The negative electrode was removed and soaked in dimethyl carbonate (DMC) for 20 minutes, followed by rinsing with DMC and acetone. The negative electrode was then placed in an oven and baked at 80°C for 12 hours to obtain the treated negative electrode sample. The negative electrode samples in the following Raman test, X-ray diffraction (XRD) test, and porosity test were all sampled using the above method.

[0064] The negative electrode active material layer on the negative electrode sheet was scraped off with a scraper. The scraped powder was then heat-treated in a tube furnace at 400°C for 4 hours under argon to remove the binder adhering to the surface of the negative electrode active material, thereby obtaining a negative electrode active material powder sample. The negative electrode active material samples used in the following powder compaction density, Raman scattering, XRD, and scanning electron microscopy measurements were all sampled using this method.

[0065] Powder compaction density test

[0066] The test of the compaction density of the powder is carried out in accordance with the national standard GB / T 24533-2009 "Graphite Negative Electrode Materials for Lithium-ion Batteries". The specific test steps are: weigh 1.0000g±0.0500g of the negative electrode active material powder sample and place it in a test mold (Carver 3619 13mm mold), and then place the sample in a powder compaction density meter (model: Sansi Zongheng UTM7305), with a test tonnage of 5 tons. The pressurized compaction density of the powder is a, the decompression compaction density is b, the mass of the negative electrode active material is m, the force area of ​​the negative electrode active material is S, and the thickness of the powder sample when pressurized is H a , the thickness of the powder sample when the pressure is released is H b , the calculation formulas of a and b are as follows: a=m / (S×H a ), b=m / (S×H b ).

[0067] Raman testing

[0068] The Raman spectrum of the negative electrode active material was tested using a laser microconfocal Raman spectrometer (HR Evolution, manufactured by HORIBA, France). The laser wavelength of the Raman spectrometer can be in the range of 532nm to 633nm. The negative electrode active material powder was tested. During the test, a 100μm×100μm range was scanned. The particles within this area were scanned and 100 points were tested at equal intervals. The test range of each point was 0.02cm. -1 to 0.05cm -1 Between. Recorded at 1300cm -1 to 1400cm -1 The peak between is the d peak, at 1500cm -1to 1600cm -1 The peak between the peaks is the g peak. The data was processed using Lab Spec software to obtain the peak intensities of the d peak and g peak of the particles, which were recorded as I d and I g , count the I of each point d / I g The intensity ratio of the 100 points is then calculated as the average value of the final I d / I g strength ratio.

[0069] Using the above method, take the negative electrode sample for testing and obtain I d ' / I g 'Intensity ratio.

[0070] X-ray diffraction (XRD) test (graphitization degree test)

[0071] According to the international standard JJS K 0131-1996 "General Rules for X-ray Diffraction Analysis", an X-ray diffractometer (Bruker D8 ADVANCE) was used, Cu Kα radiation, voltage 40KV, current 40mA, test angle 52° to 58°, and each step time 0.3s. The XRD pattern of the negative electrode active material powder was processed to obtain the interplanar spacing d of the 002 peak position of the negative electrode active material powder. 002 , a silicon standard with C:Si=5:1 (mass ratio) was used as a reference sample for scanning test, and the graphitization degree G of the negative electrode active material was calculated by the following formula:

[0072] G=(3.44-d 002 ) / (3.440-3.354)×100%.

[0073] X-ray diffraction (XRD) test (OI value test)

[0074] According to the international standard JJS K 0131-1996 "General Rules for X-ray Diffraction Analysis", an X-ray diffractometer (instrument model: Bruker D8 ADVANCE), Cu Kα rays, voltage 40KV, current 40mA, test angle 20° to 80°, each step time 0.3s, was used to scan the negative electrode active material powder and the negative electrode sheet to obtain XRD patterns, and the peak area C(004) of the (004) crystal plane diffraction peak and the peak area C(110) of the (110) crystal plane diffraction peak were analyzed and respectively obtained. The ratio of C(004) / C(110) was calculated to obtain the OI value of the negative electrode active material and the OI value of the negative electrode sheet.

[0075] Scanning electron microscope (SEM) testing

[0076] The JEOL JSM-6360LV scanning electron microscope and its supporting X-ray spectrometer were used to analyze the morphology and structure of the negative electrode active material samples, observe the morphological characteristics of the samples and take scanning electron microscope photos.

[0077] Pole piece porosity test

[0078] The negative electrode samples obtained using the above sampling method were prepared into 10 mm diameter discs. Thirty samples were tested for each example or comparative example. The porosity of the negative electrode active material layer was measured using an AccuPyc II 1340 true density meter in accordance with the national standard GB / T 24586-2009, "Determination of Apparent Density, True Density, and Porosity of Iron Ore," using helium as the test gas.

[0079] Temperature rise test

[0080] Wrap the lithium-ion battery with thermal insulation cotton, attach a temperature-sensing wire to the center, and use a multi-channel thermometer to collect points every 1 second to continuously monitor the surface discharge temperature rise of the lithium-ion battery. Place the lithium-ion battery in a 25℃ constant temperature box and let it stand for 30 minutes. At a test temperature of 25℃, charge it with a constant current of 2C to 4.25V, then discharge it with a current of 10C to 3V. Repeat the above charge / discharge process for 3 cycles. Read the maximum temperature rise at the end of 10C discharge on the multi-channel thermometer as T max ℃, 10C discharge temperature rise is T℃, then T=T max -25.

[0081] Rate performance test

[0082] At 25°C, the lithium-ion battery is charged to 4.25V at a constant current of 0.2C, then charged to 0.05C at a constant voltage of 4.25V, left to stand for 5 minutes, and then discharged to 3V at a rate of 0.2C to obtain the 0.2C discharge capacity. Then, it is charged to 4.25V at a constant current of 0.2C, charged to 0.05C at a constant voltage of 4.25V, left to stand for 30 minutes, and then discharged to 3V at a rate of 10C to obtain the 10C discharge capacity. The 10C / 0.2C rate performance of the lithium-ion battery = 10C discharge capacity / 0.2C discharge capacity × 100%.

[0083] Cyclic performance test

[0084] The lithium-ion battery was placed in a constant temperature box at 25℃±1℃ for 30 minutes. The cycle process was as follows: charging to 4.25V at a constant current of 2C, then charging to 0.05C at a constant voltage of 4.25V, standing for 15 minutes, and then discharging to 3V at a rate of 10C, and standing for 30 minutes. This was a charge and discharge cycle process, and the first cycle discharge capacity C0 of the lithium-ion battery was recorded. After that, the above cycle process was cycled 800 times, and a small rate capacity recovery was performed every 100 times at the 50th, 100th, and 101-800th cycles. The small rate capacity recovery charge and discharge process is as follows: the lithium-ion battery was placed in a constant temperature box at 25℃±1℃ for 30 minutes. The cycle process was as follows: charging to 4.25V at a constant current of 2C, then charging to 0.05C at a constant voltage of 4.25V, standing for 15 minutes, and then discharging to 3V at a rate of 0.2C, and standing for 30 minutes. Record the 800th cycle discharge capacity C1, 800 cycle capacity retention rate = C1 / C0×100%.

[0085] Example 1-1

[0086] <Preparation of negative electrode active material>

[0087] Natural graphite (particle size of 10 μm, purity of 99.9%) and precursor phenolic resin (coking value of 48%) were mixed uniformly in a mass ratio of m:n = 93:7, then placed in a vertical reactor, oxygen was introduced at a flow rate of 5 L / min, and high-temperature treatment was performed at T1 = 550°C for 4 hours. The heat-treated sample was cooled to room temperature, placed in a crucible, and then carbonized in a roller kiln at T2 = 1150°C for 15 hours under a nitrogen atmosphere. After cooling to room temperature, the sample was sieved through a double-layer 350-mesh vibrating screen and demagnetized by an automatic powder demagnetizer to obtain the negative electrode active material.

[0088] <Preparation of negative electrode sheet>

[0089] The prepared negative electrode active material, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) were mixed in a mass ratio of 97.4:1.2:1.4. Deionized water was then added as a solvent and stirred thoroughly to form a negative electrode slurry with a solid content of 40 wt%. The negative electrode slurry was evenly coated on one surface of a 6 μm thick negative electrode current collector copper foil and dried at 85°C for 4 hours to obtain a negative electrode sheet with a single-sided negative electrode active material coating of 80 μm. After cold pressing (cold pressing pressure tonnage of 15 tons), cutting, and slitting, the sheet was dried under vacuum conditions at 120°C for 12 hours to obtain a negative electrode sheet with a size of 76.6 mm x 875 mm.

[0090] <Preparation of positive electrode sheet>

[0091] The positive electrode active material, lithium nickel cobalt manganese oxide (NCM811), the conductive agent, acetylene black, and the binder, polyvinylidene fluoride (PVDF), were mixed in a mass ratio of 96.3:2.2:1.5. N-methylpyrrolidone (NMP) was added as a solvent and stirred thoroughly to prepare a positive electrode slurry with a solid content of 72 wt%. The positive electrode slurry was evenly coated on one surface of a 13 μm thick positive electrode current collector aluminum foil and dried at 85°C to obtain a single-sided positive electrode sheet with a 130 μm thick positive electrode active material layer. After cold pressing, cutting, and slitting, the sheet was dried under vacuum at 85°C for 4 hours to obtain a positive electrode sheet measuring 74 mm x 867 mm.

[0092] <Preparation of Electrolyte>

[0093] In a dry argon atmosphere glove box, the base solvents ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:PC:EMC:DEC = 1:3:3:3. Fluorinated ethylene carbonate and 1,3-propane sultone were then added, dissolved, and stirred uniformly. The lithium salt LiPF6 was then added and mixed uniformly to obtain an electrolyte. Based on the mass of the electrolyte, the mass percentage of the lithium salt was 12.5%, the mass percentage of fluoroethylene carbonate was 2%, the mass percentage of 1,3-propane sultone was 2%, and the balance was the base solvent.

[0094] <Diaphragm>

[0095] A polyethylene film with a thickness of 7 μm (supplied by Celgard) was used as a separator.

[0096] <Preparation of lithium-ion batteries>

[0097] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order, with the separator placed between the positive and negative electrode sheets to act as an insulator, and then wound to form an electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag, placed in an 80°C vacuum oven to dry for 12 hours to remove moisture, and then injected with the prepared electrolyte. After vacuum packaging, standing, formation (temperature 45°C, 0.1C constant current charging, cut-off time 1800s, then 0.5C constant current charging to 4.25V), degassing, and trimming, a lithium-ion battery is obtained.

[0098] Example 1-2 to Example 1-9

[0099] Except for adjusting the parameters according to Table 1, the rest is the same as Example 1-1.

[0100] Example 2-1 to Example 2-8

[0101] Except for adjusting the parameters according to Table 2, the rest is the same as Example 1-1.

[0102] Comparative Example 1-1 to Comparative Example 1-4

[0103] Except for adjusting the parameters according to Table 1, the rest is the same as Example 1-1.

[0104] Comparative Examples 1-5

[0105] Except that natural graphite (with a particle size of 10 μm and a purity of 99.9%) was used as the negative electrode active material and the parameters were adjusted according to Table 1, the rest was the same as Example 1-1.

[0106] The relevant parameters and performance tests of each embodiment and each comparative example are shown in Tables 1 and 2.

[0107] Table 1

[0108] Note: " / " in Table 1 indicates no relevant parameters. The brand of coal-based asphalt is high-temperature asphalt 250, with a coking value of 70%. The weight-average molecular weight of polyacrylonitrile is 15,000, and the coking value is 30%.

[0109] Referring to Table 1, it can be seen from Examples 1-1 to 1-9 and Comparative Examples 1-1 to 1-5 that when the pressure relief rebound rate c of the negative electrode active material satisfies c=k×(a-1), and the value of k is within the range of this application, the lithium-ion battery can have a lower temperature rise, a higher 10C / 0.2C rate performance, and an 800-cycle capacity retention rate, indicating that the lithium-ion battery has a lower temperature rise and better rate performance and cycle performance. When the value of k is not within the range of this application, the lithium-ion battery has a large temperature rise, a low 10C / 0.2C rate performance, and a low 800-cycle capacity retention rate. In particular, the lithium-ion battery of Comparative Example 1-4 has an excessively large temperature rise and cannot be discharged at a high rate of 10C. The 10C / 0.2C rate performance is only 5.2%, and the cycle drops sharply to 11.2% after 530 cycles.

[0110] The value of a, the value of b, I d / I g , the OI value of the powder of the negative electrode active material and the degree of graphitization G usually affect the temperature rise, rate performance and cycle performance of the lithium-ion battery. It can be seen from Examples 1-1 to 1-9 that when the above parameters are within the scope of this application, the lithium-ion battery can have a lower temperature rise, higher 10C / 0.2C rate performance and 800-cycle capacity retention rate, indicating that the lithium-ion battery has a lower temperature rise and good rate performance and cycle performance.

[0111] Table 2

[0112] The value of q, the value of p, the value of h, the OI value of the negative electrode and the I d ' / I g 'It usually affects the temperature rise, rate performance and cycle performance of lithium-ion batteries. From Examples 1-1, 2-1 to 2-8 and Comparative Examples 1-5, it can be seen that when the negative electrode active material of the present application is applied to lithium-ion batteries and the above parameters are controlled within the range of the present application, the lithium-ion batteries can have a lower temperature rise, higher 10C / 0.2C rate performance and 800-cycle capacity retention rate, indicating that the lithium-ion batteries have a low temperature rise and good rate performance and cycle performance.

[0113] Figure 1 shows a SEM image of the particle morphology of the negative electrode active material prepared in Example 1-1. As can be seen from Figure 1, the negative electrode active material particles exhibit a secondary particle structure, composed of primary particles. The secondary particles are relatively uniform in size and have a rounded appearance. The inventors speculate that particles of negative electrode active material with this morphology can enhance the isotropy of the negative electrode active material, facilitating the transport of active ions.

[0114] Figure 2 shows a comparison of the 800-cycle performance of the lithium-ion batteries of Example 1-1 and Comparative Example 1-1. As can be seen from Figure 2 , the lithium-ion battery of Example 1-1 exhibits slower capacity decay over cycling, with a capacity retention rate of 90.5% after 800 cycles. In contrast, the lithium-ion battery of Comparative Example 1-1 exhibits faster capacity decay over cycling, with a capacity retention rate of less than 80% after 750 cycles. This demonstrates that the lithium-ion battery of Example 1-1 of the present application exhibits superior cycling performance.

[0115] FIG3 is a Raman spectrum of the negative electrode active material prepared in Example 1-1 and Comparative Example 1-1. As can be seen from FIG3 , the negative electrode active material of Example 1-1 has a Raman spectrum of d The value is 206.1, I g The value is 466.8, then I d / I g =0.44. I of the negative electrode active material of Comparative Example 1-1 d The value is 108.6, I g The value is 602.2, then I d / I g =0.18.

[0116] FIG4 is a Raman spectrum of the negative electrode sheet of Example 1-1 and Comparative Example 1-5. As can be seen from FIG4, the I d 'The value is 124.8, I g 'The value is 390.7, then I d ' / I g '=0.32. I of the negative electrode active materials of Comparative Examples 1-5 d'The value is 70.9, I g 'The value is 548.7, then I d ' / I g '=0.13. I of the negative electrode d ' / I g The larger the value of ', the higher the electron conduction rate of the negative electrode plate, which indicates that the lithium-ion battery of Example 1-1 of the present application has better electron conduction performance.

[0117] Figure 5 shows the X-ray diffraction spectrum of the negative electrode active material prepared in Example 1-1. As can be seen from Figure 5, the negative electrode active material prepared in Example 1-1 exhibits a C(004) crystal plane diffraction peak at 2θ = 54.56° with a peak area of ​​2724.8, and a C(110) crystal plane diffraction peak at 2θ = 77.40° with a peak area of ​​681.20. The OI value of the negative electrode active material powder is C(004) / C(110) = 4.0.

[0118] Figure 6 shows the X-ray diffraction spectrum of the negative electrode of Example 1-1. As can be seen from Figure 6, the negative electrode of Example 1-1 exhibits a C(004) crystal plane diffraction peak at 54.64° with a peak area of ​​5089.3, and a C(110) crystal plane diffraction peak at 77.50° with a peak area of ​​171.3. The OI value of the negative electrode is C(004) / C(110) = 29.7.

[0119] It should be noted that, in this article, the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements that are inherent to such process, method, article or apparatus.

[0120] 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.

Claims

1. A negative electrode active material, the powder of which has a compacted density of ag / cm 3 , the pressure relief compaction density is bg / cm 3 The pressure relief rebound rate is c, c=(ab) / a×100%, 1.5%≤c≤20%; a and c satisfy: c=k×(a-1), 0.08≤k≤0.20, and the test tonnage of the pressurized compaction density is 5 tons.

2. The negative electrode active material according to claim 1, wherein 5%≤c≤15%, 0.15≤k≤0.

20.

3. The negative electrode active material according to claim 1 or 2, wherein 1.2≤a≤2.0。 4. The negative electrode active material according to any one of claims 1 to 3, wherein 1.2≤b≤1.9。 5. The negative electrode active material according to any one of claims 1 to 4, wherein The negative electrode active material includes graphite having hard carbon on the surface.

6. The negative electrode active material according to any one of claims 1 to 5, wherein The negative electrode active material satisfies 0.3≤I d / I g ≤0.7, I d is the peak intensity of the d peak in the Raman spectrum of the negative electrode active material, I g is the peak intensity of the g peak in the Raman spectrum of the negative electrode active material.

7. The negative electrode active material according to any one of claims 1 to 6, wherein The powder OI value of the negative electrode active material is 2 to 5.

8. The negative electrode active material according to any one of claims 1 to 7, wherein The graphitization degree G of the negative electrode active material is 90.5% to 98%.

9. A secondary battery comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the negative electrode sheet comprises a negative electrode collector and a negative electrode active material layer disposed on at least one surface of the negative electrode collector, wherein the negative electrode active material layer comprises the negative electrode active material according to any one of claims 1 to 8.

10. The secondary battery according to claim 9, wherein The compaction density of the negative electrode plate is qg / cm 3 The porosity of the negative electrode plate is p, q and p satisfy p=-0.37×q+h, 0.8≤h≤1.0; 1.2≤q≤1.9, 10%≤p≤60%.

11. The secondary battery according to claim 9 or 10, wherein: The OI value of the negative electrode plate ranges from 8 to 30.

12. The secondary battery according to any one of claims 9 to 11, wherein The negative electrode plate satisfies 0.3≤I d ' / I g '≤0.8,I d ' is the peak intensity of the middle d peak of the Raman spectrum of the negative electrode in the 100 μm×100 μm area, I g ' is the peak intensity of the middle g peak in the Raman spectrum of the negative electrode sheet in the 100 μm×100 μm area. 13 . An electronic device comprising the secondary battery according to claim 9 .

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