Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device, the secondary battery comprises a positive pole piece, a negative pole piece and an electrolyte, the positive pole piece comprises a positive pole material layer, the positive pole material layer comprises a positive pole active material and a first carbon material, based on the mass of the positive pole material layer, the mass percentage content of the first carbon material is w%, and w is greater than or equal to 3 and less than or equal to 10; wherein the gram volume of the first carbon material is a mAh / g, and the gram volume of the positive electrode active material is b mAh / g; the electrolyte comprises a lithium salt, and the concentration of the lithium salt in the electrolyte is C mol / L; the secondary battery satisfies 1.0 + (99a + b) * w / 100b * 0.16 < = C < = 1.5 + (99a + b) * w / 100b * 0.16. The secondary battery provided by the invention has relatively high energy density and cycle performance, and also has good dynamic performance.

Description

Technical Field

[0001] The present application relates to the field of electrochemical technologies, and particularly to a secondary battery and an electronic device. Background Art

[0002] With the increasing demand for sustainable energy, secondary batteries have been widely used in application scenarios such as portable electronic devices and electric vehicles due to their advantages of high energy density, long life, and environmental friendliness. In order to meet the increasing demand for higher energy density in the above application scenarios, it is generally preferred to improve the energy density of the positive electrode material layer.

[0003] For example, conductive agents such as conductive carbon black and carbon nanotubes are usually added to the positive electrode material layer to improve the conductivity of the positive electrode plate, and thus improve the cycle performance of the secondary battery. However, the addition of the above conductive agents will reduce the proportion of the positive electrode active material in the positive electrode material layer, and thus reduce the specific capacity per gram of the positive electrode material layer, affecting the energy density of the secondary battery. Therefore, the energy density and cycle performance of the secondary battery cannot be taken into account at the same time. Summary of the Invention

[0004] The purpose of the present application is to provide a secondary battery and an electronic device to take into account the energy density and cycle performance of the secondary battery. The specific technical solutions are as follows:

[0005] In the first aspect of the present application, a secondary battery is provided, which includes a positive electrode plate, a negative electrode plate, and an electrolyte. The positive electrode plate includes a positive electrode material layer, and the positive electrode material layer includes a positive electrode active material and a first carbon material. Based on the mass of the positive electrode material layer, the mass percentage content of the first carbon material is w%, and 3 ≤ w ≤ 10; wherein, the specific capacity of the first carbon material is a mAh / g, and the specific capacity of the positive electrode active material is b mAh / g; the electrolyte includes a lithium salt, and the concentration of the lithium salt in the electrolyte is C mol / L; the secondary battery satisfies: 1.0 + (99a + b) × w / 100b × 0.16 ≤ C ≤ 1.5 + (99a + b) × w / 100b × 0.16. By adding the first carbon material within the content range of the present application, and the relationship between the specific capacity of the first carbon material, the specific capacity of the positive electrode active material, and the concentration C of the lithium salt in the electrolyte satisfies: 1.0 + (99a + b) × w / 100b × 0.16 ≤ C ≤ 1.5 + (99a + b) × w / 100b × 0.16, it is beneficial to improve the energy density and capacity retention rate of the lithium-ion battery and take into account good kinetic performance.

[0006] In this application, the first carbon material capable of exerting specific capacity can replace at least part of the existing conventional conductive agents such as conductive carbon black and carbon nanotubes. And controlling the mass percentage content of the first carbon material within the above range is beneficial to improving the conductivity of the positive electrode sheet while not reducing the proportion of the positive electrode active material with higher specific capacity in the positive electrode material layer, and improving the specific capacity of the positive electrode material layer, so as to achieve the purpose of improving the cycle performance of the secondary battery and taking into account the energy density. In this application, the concentrations of the lithium salts represented by 1.0+(99a+b)×w / 100b×0.16 and 1.5+(99a+b)×w / 100b×0.16 mainly include two parts. One part is the lithium salt concentration required for the specific capacity of the positive electrode active material to be exerted; the other part is the lithium salt concentration required for the specific capacity of the first carbon material to be exerted. Adding these two parts together is the lithium salt concentration required for the secondary battery in this application. It can be understood that the concentration of the lithium salt required in the secondary battery changes with the content of the first carbon material, the specific capacity of the positive electrode active material, and the specific capacity of the first carbon material. Exemplarily, the higher the mass percentage content w% of the first carbon material, the greater the concentration of the lithium salt required for the first carbon material to exert its own capacity, and vice versa; when the specific capacity of the first carbon material is higher, the greater the concentration of the lithium salt required for the first carbon material to exert its own capacity, and vice versa.

[0007] In some embodiments of this application, C is less than or equal to 2.2. In some embodiments of this application, C is less than or equal to 1.9. By controlling the value of C within the above range, it is beneficial to improve the kinetic performance and cycle performance of the secondary battery, and further improve the energy density of the secondary battery.

[0008] In some embodiments of this application, 60≤a≤140. By controlling the value of a within the above range, it is beneficial for the first carbon material to cooperate with the lithium salt in the electrolyte, and further improve the energy density of the secondary battery.

[0009] In some embodiments of this application, 160≤b≤240. By controlling the value of b within the above range, the positive electrode active material has a relatively high specific capacity, and the obtained secondary battery has a relatively high energy density.

[0010] In some embodiments of this application, the interlayer spacing of the first carbon material is D, and 0.34nm≤D≤0.42nm. By controlling the value of D within the above range, it is beneficial for the lithium salt anions to be embedded and removed between the layers of the first carbon material, so as to better exert the specific capacity of the first carbon material, improve the energy density of the secondary battery and take into account the kinetic performance.

[0011] In some embodiments of the present application, the average particle size d1 of the particles of the first carbon material is 1 μm to 10 μm. By controlling d1 within the above range, it is beneficial to form a more uniform conductive network in the positive electrode material layer, thereby improving the conductivity of the positive electrode sheet and the cycling performance of the secondary battery.

[0012] In some embodiments of the present application, the first carbon material includes at least one of hard carbon or graphite. By selecting the above first carbon material, it is beneficial to improve the energy density of the secondary battery and take into account the kinetic performance.

[0013] In some embodiments of the present application, the positive electrode active material includes at least one of lithium cobaltate or lithium nickel cobalt manganate. By selecting the above positive electrode active material, it is beneficial to take into account the specific capacity and conductivity of the positive electrode material layer, thereby taking into account the cycling performance and energy density of the secondary battery.

[0014] In some embodiments of the present application, the positive electrode active material includes at least one of lithium cobaltate or lithium nickel cobalt manganate containing a doping element, and the doping element includes at least one of Al, Mg, Ti, Nb, Zn, and W; based on the mass of the positive electrode active material, the mass percentage content M of the doping element is 0.4% to 1%. By doping the above doping element in the above content in lithium cobaltate or lithium nickel cobalt manganate, it is beneficial to strengthen the structural stability of the positive electrode active material and reduce the occurrence of side reactions, and further beneficial to further improve the cycling performance of the secondary battery.

[0015] In some embodiments of the present application, the average particle size d2 of the positive electrode active material is 5 μm to 20 μm. By controlling d2 within the above range, it is beneficial to reduce the consumption of the electrolyte during the cycling of the secondary battery, and at the same time reduce the internal resistance of the positive electrode sheet, thereby being beneficial to improving the cycling performance and kinetic performance of the secondary battery.

[0016] In some embodiments of the present application, the negative electrode sheet includes a negative electrode material layer, and the negative electrode material layer includes a second carbon material, and the graphitization degree of the second carbon material is 89% to 93%. By controlling the graphitization degree of the second carbon material within the above range, it is beneficial to improve the long-cycle performance of the secondary battery and at the same time beneficial to taking into account the energy density of the secondary battery.

[0017] In some embodiments of the present application, the electrolyte further includes ethylene carbonate and fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage content of ethylene carbonate is B1%, and the mass percentage content of fluoroethylene carbonate is B2%, 20 ≤ B1 ≤ 50, 0.5 ≤ B2 ≤ 10. By controlling the content of ethylene carbonate and fluoroethylene carbonate in the electrolyte within the above range, it is beneficial to improve the stability of the electrolyte in a high-voltage environment, thereby being beneficial to the effective utilization of the specific capacity of the first carbon material, and further improving the energy density of the secondary battery and taking into account the cycling performance.

[0018] In some embodiments of the present application, the lithium salt includes at least one of LiPF6, LiBF4, LiClO4, or LiDFOB. By selecting the above types of lithium salts, it is beneficial for them to be inserted into and removed from the first carbon material, exerting its capacity, thereby improving the energy density of the secondary battery and taking into account the kinetic performance and cycling performance.

[0019] The second aspect of the present application provides an electronic device, which includes the secondary battery in any of the foregoing embodiments.

[0020] Advantages of the present application:

[0021] The present application provides a secondary battery and an electronic device. The mass percentage content of the first carbon material in the secondary battery is w%, 3 ≤ w ≤ 10, the specific capacity of the first carbon material is a mAh / g, and the specific capacity of the positive electrode active material is b mAh / g; the electrolyte includes a lithium salt, and the concentration of the lithium salt in the electrolyte is C mol / L; the secondary battery satisfies: 1.0 + (99a + b) × w / 100b × 0.16 ≤ C ≤ 1.5 + (99a + b) × w / 100b × 0.16. Through the above settings, the first carbon material is matched with a suitable lithium salt concentration, which is not only beneficial for the effective exertion of the capacity of the first carbon material, but also beneficial for improving the conductivity of the positive electrode sheet, thereby improving the specific capacity and cycling performance of the secondary battery. At the same time, it is also beneficial to take into account the kinetic performance of the secondary battery.

[0022] Of course, it is not necessary for any product or method implementing the present application to achieve all the above-mentioned advantages simultaneously. Description of the Drawings

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other embodiments can also be obtained based on these drawings.

[0024] Figure 1 It is a transmission electron microscope photograph of the first carbon material in Example 1-1. Detailed Embodiments

[0025] The following will clearly and completely describe the technical solutions in the present application in conjunction with the embodiments of the present application and the drawings. Obviously, the described embodiments are only some embodiments of the present application, rather than all embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0026] It should be noted that in the specific embodiments of the present application, a lithium-ion battery is taken as an example of the secondary battery to explain the present application. However, the secondary battery of the present application is not limited to the lithium-ion battery.

[0027] In order to improve the conductivity of the positive electrode sheet and enhance the cycle performance of the secondary battery, a certain amount of conductive agent is usually added to the positive electrode material layer. However, the addition of the conductive agent will reduce the proportion of the positive electrode active material in the positive electrode material layer, thereby reducing the specific capacity per gram of the positive electrode material layer and affecting the energy density of the secondary battery. Based on the above problems, the present application provides a secondary battery and an electronic device, which can not only increase the specific capacity per gram of the positive electrode sheet but also improve the conductivity of the positive electrode sheet, thus taking into account the energy density, cycle performance, and kinetic performance of the secondary battery.

[0028] In a first aspect of the present application, a secondary battery is provided, which includes a positive electrode sheet, a negative electrode sheet, and an electrolyte. The positive electrode sheet includes a positive electrode material layer, and the positive electrode material layer includes a positive electrode active material and a first carbon material. Based on the mass of the positive electrode material layer, the mass percentage content of the first carbon material is w%, and 3 ≤ w ≤ 10; wherein, the specific capacity of the first carbon material is a mAh / g, and the specific capacity of the positive electrode active material is b mAh / g; the electrolyte includes a lithium salt, and the concentration of the lithium salt in the electrolyte is C mol / L; the secondary battery satisfies: 1.0 + (99a + b) × w / 100b × 0.16 ≤ C ≤ 1.5 + (99a + b) × w / 100b × 0.16.

[0029] The present application uses the first carbon material that can exert specific capacity to replace at least part of the existing conventional conductive agents such as conductive carbon black and carbon nanotubes, and the mass percentage content of the first carbon material is w%, and 3 ≤ w ≤ 10. For example, w can be 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10 or a range composed of any two of these values. When w < 3, the content of the first carbon material is too small, and the improvement of the conductivity of the positive electrode sheet is limited. The obtained secondary battery has a large impedance, affecting its rate performance and cycle performance. When w > 10, the content of the first carbon material in the positive electrode material layer is too high, which will reduce the intercalation kinetics performance of the lithium salt anions in the first carbon material, thereby affecting the full exertion of the capacity of the first carbon material, and will also reduce the proportion of the positive electrode active material with a higher specific capacity in the positive electrode material layer, thereby reducing the energy density of the secondary battery. Therefore, by adding the first carbon material within the content range of the present application, it is beneficial to improve the conductivity of the positive electrode sheet while increasing the specific capacity per gram of the positive electrode material layer, thereby achieving the purpose of improving the cycle performance of the secondary battery and taking into account the energy density.

[0030] The capacity of the first carbon material in the positive electrode tab needs the participation of the lithium salt in the electrolyte to react, that is, the capacity is generated by the insertion of the lithium salt anions in the electrolyte into the first carbon material. The inventors found that by regulating the concentration C of the lithium salt in the electrolyte, the specific capacity a mAh / g of the first carbon material and the specific capacity b mAh / g of the positive electrode active material satisfy the following relationship: 1.0 + (99a + b) × w / 100b × 0.16 ≤ C ≤ 1.5 + (99a + b) × w / 100b × 0.16. The concentrations of the lithium salt represented by 1.0 + (99a + b) × w / 100b × 0.16 and 1.5 + (99a + b) × w / 100b × 0.16 mainly include two parts. One part is the lithium salt concentration required for the specific capacity of the positive electrode active material to be exerted; the other part is the lithium salt concentration required for the specific capacity of the first carbon material to be exerted. The sum of these two parts is the lithium salt concentration required for the secondary battery of the present application. It can be understood that the concentration of the lithium salt required in the secondary battery changes with the content of the first carbon material, the specific capacity of the positive electrode active material, and the specific capacity of the first carbon material. Exemplarily, the higher the mass percentage content w% of the first carbon material, the greater the concentration of the lithium salt required for the first carbon material to exert its own capacity, and vice versa; when the specific capacity of the first carbon material is higher, the greater the concentration of the lithium salt required for the first carbon material to exert its own capacity, and vice versa. When C is too small, for example, C < 1.0 + (99a + b) × w / 100b × 0.16, the concentration of the lithium salt in the electrolyte is too low, which is not conducive to the exertion of the specific capacity of the first carbon material, and the energy density of the obtained lithium ion battery is on the low side. When C is too large, the concentration of the lithium salt in the electrolyte is too high, and the fluidity of the electrolyte becomes poor, affecting the kinetic performance of the secondary battery. Therefore, by regulating C within the scope of the present application, it is not only conducive to the insertion of lithium salt anions into the first carbon material to provide specific capacity, thereby improving the energy density of the secondary battery, but also conducive to taking into account the kinetic performance of the secondary battery.

[0031] It should be noted that the specific capacity of the material is usually divided into theoretical specific capacity and actual specific capacity. In the present application, the specific capacity a mAh / g of the first carbon material refers to the actual specific capacity exerted by the first carbon material in the secondary battery; the specific capacity b mAh / g of the positive electrode active material refers to the actual specific capacity exerted in the secondary battery. The test method for the specific capacity is detailed in the test method section. In addition, the first carbon material and the positive electrode active material with different specific capacities can be obtained by purchase.

[0032] Therefore, through the above settings, the first carbon material is matched with a suitable lithium salt concentration, which is not only conducive to the effective exertion of the capacity of the first carbon material, but also conducive to improving the conductivity of the positive electrode tab, thereby enhancing the specific capacity and cycle performance of the secondary battery. At the same time, it is also conducive to taking into account the kinetic performance of the secondary battery.

[0033] In some embodiments of the present application, C is less than or equal to 2.2. In some embodiments of the present application, C is less than or equal to 1.9. For example, C can be 1.12, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, 1.9, 1.95, 2, 2.05, 2.1, 2.15, 2.2 or a range composed of any two of these values. By adjusting the value of C within the above range, it is beneficial to promote the electrolyte to maintain appropriate fluidity, thereby promoting the transport of lithium salt anions, and is beneficial to improving the kinetic performance and cycling performance of the secondary battery. At the same time, the appropriate concentration is also beneficial to the full utilization of the specific capacity of the first carbon material and the positive electrode active material, further improving the energy density of the secondary battery.

[0034] In some embodiments of the present application, 60 ≤ a ≤ 140. For example, a can be 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140 or a range composed of any two of these values. By adjusting the value of a within the above range, it is beneficial for the first carbon material to synergistically interact with the lithium salt in the electrolyte, fully utilize the specific capacity of the first carbon material, and further improve the energy density of the secondary battery.

[0035] In some embodiments of the present application, 160 ≤ b ≤ 240. For example, b can be 160, 165, 170, 175, 180, 185, 190, 195, 200, 205, 210, 215, 220, 225, 230, 235, 240 or a range composed of any two of these values. By adjusting the value of b within the above range, the specific capacity of the positive electrode active material is relatively high, and the obtained secondary battery has a relatively high energy density.

[0036] In some embodiments of the present application, the interlayer spacing of the first carbon material is D, and 0.34 nm ≤ D ≤ 0.42 nm. For example, D can be 0.34 nm, 0.345 nm, 0.35 nm, 0.355 nm, 0.36 nm, 0.365 nm, 0.37 nm, 0.375 nm, 0.38 nm, 0.385 nm, 0.39 nm, 0.395 nm, 0.4 nm, 0.405 nm, 0.41 nm, 0.415 nm, 0.42 nm or a range composed of any two of these values. By adjusting the value of D within the above range, the structure of the first carbon material is more adapted to the size of the lithium salt anions in the electrolyte, which is beneficial to the intercalation and deintercalation of lithium salt anions between the layers of the first carbon material, thereby better exerting the specific capacity of the first carbon material, improving the energy density of the secondary battery and taking into account the kinetic performance.

[0037] In some embodiments of the present application, the average particle size d1 of the particles of the first carbon material is 1 μm to 10 μm. For example, d1 can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or a range composed of any two of these values. By controlling d1 within the above range, not only can the impedance of the first carbon material itself be reduced, but also it is beneficial to improve the dispersion degree of the first carbon material in the positive electrode material layer, form a more uniform conductive network, thereby improving the conductivity of the positive electrode sheet and the cycle performance of the secondary battery.

[0038] In some embodiments of the present application, the first carbon material includes at least one of hard carbon or graphite. The above first carbon material has a high specific capacity and is beneficial to the insertion and extraction of lithium salt anions in the electrolyte. Thus, by selecting the above first carbon material, it is beneficial to improve the energy density of the secondary battery and take into account the kinetic performance.

[0039] In some embodiments of the present application, the positive electrode active material includes at least one of lithium cobaltate or lithium nickel cobalt manganate. The above positive electrode active material has a high specific capacity but slightly poor conductivity. When combined with the first carbon material with a slightly lower capacity but good conductivity, it realizes complementary advantages, which is beneficial to taking into account the specific capacity and conductivity of the positive electrode material layer, and thus taking into account the cycle performance and energy density of the secondary battery.

[0040] In some embodiments of the present application, the positive electrode active material includes at least one of lithium cobaltate or lithium nickel cobalt manganate containing a doping element, and the doping element includes at least one of Al, Mg, Ti, Nb, Zn, W; based on the mass of the positive electrode active material, the mass percentage content M of the doping element is 0.4% to 1%. For example, M can be 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1%, or a range composed of any two of these values. By doping the above doping element in the above content in lithium cobaltate or lithium nickel cobalt manganate, it is beneficial to strengthen the structural stability of the positive electrode active material, reduce the structural damage and side reactions of the positive electrode active material when lithium ions are inserted into the first carbon material, and further improve the cycle performance of the secondary battery.

[0041] In some embodiments of the present application, the average particle size d2 of the positive electrode active material is from 5 μm to 20 μm. For example, d2 can be 5 μm, 6 μm, 7 μm, 9 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm or a range composed of any two of these values. By controlling d2 within the above range, it is beneficial to reduce the consumption of the electrolyte during the cycling of the secondary battery, and at the same time reduce the internal resistance of the positive electrode sheet, thereby being beneficial to improving the cycling performance and kinetic performance of the secondary battery.

[0042] In some embodiments of the present application, 0.1 ≤ d1 / d2 ≤ 1. By controlling d1 / d2 within the above range, the first carbon material can be uniformly filled into the positive electrode active material, which is beneficial to form a good conductive network, and further reduce the internal resistance of the positive electrode sheet, thereby being beneficial to improving the cycling performance and kinetic performance of the secondary battery.

[0043] The present application has no particular limitation on the content of the above positive electrode active material, as long as the purpose of the present application can be achieved. For example, based on the mass of the positive electrode material layer, the mass percentage content of the positive electrode active material can be from 87.5% to 96.5%.

[0044] The present application has no particular limitation on the content of the above conventional conductive agent, as long as the purpose of the present application can be achieved. For example, based on the mass of the positive electrode material layer, the mass percentage content of the conventional conductive agent can be from 0% to 0.5%.

[0045] The positive electrode material layer may further include a binder. The present application has no particular limitation on the type of the binder, as long as the purpose of the present application can be achieved. For example, the binder may include but is not limited to at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamideimide, styrene-butadiene rubber or polyvinylidene fluoride. The present application has no particular limitation on the content of the above binder, as long as the purpose of the present application can be achieved. For example, based on the mass of the positive electrode material layer, the mass percentage content of the binder can be from 0.5% to 2%.

[0046] The present application has no particular limitation on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector), etc.

[0047] The present application has no particular limitation on the thickness of the positive electrode current collector and the positive electrode 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 from 5 μm to 20 μm, and the thickness of the positive electrode material layer is from 30 μm to 120 μm.

[0048] In some embodiments of the present application, the negative electrode sheet includes a negative electrode material layer, and the negative electrode material layer includes a second carbon material, and the graphitization degree of the second carbon material is 89% to 93%. For example, the graphitization degree can be 89%, 89.2%, 89.5%, 89.7%, 90%, 90.2%, 90.5%, 90.8%, 91%, 91.2%, 91.5%, 91.8%, 92%, 92.3%, 92.5%, 92.8%, 93% or a range composed of any two of these values. By adjusting the graphitization degree of the second carbon material within the above range, it is beneficial to reduce the consumption of the electrolyte during the cycling of the secondary battery, thereby improving the long-cycle performance of the secondary battery, and at the same time, it is also beneficial to take into account the energy density of the secondary battery.

[0049] The present application does not particularly limit the type of the second carbon material, as long as the purpose of the present application can be achieved. For example, the second carbon material may include natural graphite, artificial graphite, mesophase microcarbon microspheres soft carbon, etc. The present application does not particularly limit the content of the second carbon material, as long as the purpose of the present application can be achieved. For example, based on the mass of the negative electrode material layer, the mass percentage content of the second carbon material is 80% to 98%.

[0050] In addition, in the present application, the negative electrode material layer may further include other negative electrode active materials. For example, the other negative electrode active materials may include, but are not limited to, hard carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, spinel-structured lithiated TiO2-Li4Ti 12 or at least one of Li-Al alloys. The present application does not particularly limit the content of the above other negative electrode active materials, as long as the purpose of the present application can be achieved. For example, based on the mass of the negative electrode material layer, the mass percentage content of the above other negative electrode active materials is 2% to 20%.

[0051] The negative electrode material layer further includes a negative electrode current collector, and the negative electrode material layer is disposed on at least one surface of the negative electrode current collector. The above "the negative electrode material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer may be disposed on one surface of the negative electrode current collector along its own thickness direction, or may be disposed on two surfaces of the negative electrode current collector along its own thickness direction. It should be noted that the "surface" here may be the entire area of the surface of the negative electrode current collector, or may be a partial area of the surface of the negative electrode current collector. The present application does not particularly limit it, as long as the purpose of the present application can be achieved.

[0052] The present application has no particular limitation on the negative electrode current collector, as long as the object of the present application can be achieved. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or composite current collector. Exemplarily, the composite current collector may be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.

[0053] In some embodiments of the present application, the negative electrode material layer may further include a binder. The present application has no particular limitation on the type of the binder, as long as the object of the present application can be achieved. For example, it may be at least one of the above-mentioned binders. The present application has no particular limitation on the mass ratio of the negative electrode active material, the conductive agent and the binder in the negative electrode material layer, and those skilled in the art can select according to actual needs as long as the object of the present application can be achieved.

[0054] The present application has no particular limitation on the thickness of the negative electrode material layer, as long as the object of the present application can be achieved. For example, the thickness of the negative electrode material layer is 20 μm to 100 μm.

[0055] The present application has no particular limitation on the thickness of the negative electrode current collector, as long as the object of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 20 μm.

[0056] In some embodiments of the present application, the electrolyte further includes ethylene carbonate and fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage content of ethylene carbonate is B1%, and the mass percentage content of fluoroethylene carbonate is B2%, where 20 ≤ B1 ≤ 50 and 0.5 ≤ B2 ≤ 10. For example, B1 may be 20, 22, 25, 28, 30, 32, 35, 37, 40, 43, 45, 47, 50 or a range composed of any two of these values. For example, B2 may be 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10 or a range composed of any two of these values. By regulating the contents of ethylene carbonate and fluoroethylene carbonate in the electrolyte within the above ranges, it is beneficial to improve the stability of the electrolyte in a high-voltage environment, thereby facilitating the effective utilization of the specific capacity of the first carbon material, further improving the energy density of the secondary battery and taking into account the cycle performance.

[0057] In some embodiments of the present application, the lithium salt includes at least one of LiPF6, LiBF4, LiClO4 or lithium difluoro(oxalato)borate (LiDFOB). The anions of the above lithium salts have a relatively small radius and have high chemical stability at high voltages, which is beneficial for their insertion and extraction in the first carbon material to exert capacity, thereby improving the energy density of the secondary battery and taking into account the kinetic performance and cycle performance.

[0058] In the present application, the electrolyte further includes other non-aqueous solvents. The present application places no particular limitation on the other non-aqueous solvents, as long as the object of the present application can be achieved. For example, the other non-aqueous solvents may include, but are not limited to, at least one of carbonate compounds, carboxylate compounds, ether compounds, or other organic solvents.

[0059] The above-mentioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The above-mentioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The above-mentioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinylene ethylene carbonate (VEC). The fluorinated carbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethyl ethylene carbonate. The above-mentioned carboxylate compounds may include, but are 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, decanolide, valerolactone, or caprolactone. The above-mentioned ether compounds may include, but are not limited to, at least one of 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 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. This application has no particular limitation on the content of the non-aqueous solvent in the electrolyte, as long as the purpose of this application can be achieved. This application has no particular limitation on the content of the above-mentioned other non-aqueous solvents in the electrolyte, as long as the purpose of this application can be achieved. In some embodiments of this application, the electrolyte includes a lithium salt, ethylene carbonate, fluoroethylene carbonate, and the above-mentioned other non-aqueous solvents. In the electrolyte, the concentration of the lithium salt and the mass percentage content of ethylene carbonate and fluoroethylene carbonate are as shown above, and the rest is other non-aqueous solvents. In some embodiments of this application, based on the mass of the electrolyte, the mass percentage content of the other non-aqueous solvents is 20% to 95%. For example, the mass percentage content of the other non-aqueous solvents may be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or a range composed of any two of these values.

[0060] In the present application, the secondary battery further includes a separator. There is no particular limitation on the separator in the present application, as long as the object of the present application can be achieved. For example, the material of the separator may include, but is not limited to, at least one of polyolefins (PO) mainly composed of polyethylene (PE) and polypropylene (PP), polyesters (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid. The type of the separator may include at least one of a woven film, a non-woven film, a microporous film, a composite film, a rolled film or a spun film.

[0061] In some embodiments of the present application, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, a film or a composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used.

[0062] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

[0063] In some embodiments of the present application, the inorganic layer includes inorganic particles and a binder. There is no particular limitation on the inorganic particles in the present application. For example, the inorganic particles may include at least one of alumina, silica, magnesia, titania, hafnium dioxide, tin dioxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. There is no particular limitation on the binder in the present application. For example, the binder may be at least one of the above binders. In some embodiments of the present application, the polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene ether, polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0064] In the present application, there is no particular limitation on the thickness of the separator, as long as the object of the present application can be achieved. For example, the thickness of the separator may be 3 μm to 30 μm.

[0065] The secondary battery further includes a housing for accommodating the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte, as well as other components known in the field of secondary batteries. The present application does not limit the above other components. The present application has no special limitation on the housing, and it can be a housing well-known in the art as long as it can achieve the purpose of the present application. For example, the housing can be a hard shell housing or a flexible housing. The material of the hard shell housing can be metal. The present application does not limit the type of metal, and a metal hard shell housing known in the art can be used as long as it can achieve the purpose of the present application. The flexible housing can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0066] The preparation process of the secondary battery of the present application is well-known to those skilled in the art. The present application has no special limitation. For example, the preparation process of the secondary battery can include but is not limited to the following steps: stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and performing operations such as winding and folding according to needs to obtain a wound electrode assembly, placing the electrode assembly into the housing, injecting the electrolyte into the housing and sealing it to obtain a secondary battery. Or, stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and then fixing the four corners of the entire laminated structure with tape to obtain a laminated electrode assembly, placing the electrode assembly into the housing, injecting the electrolyte into the housing and sealing it to obtain a secondary battery. In addition, an overcurrent protection element, a guide plate, etc. can be placed in the housing according to needs to prevent the pressure inside the secondary battery from rising and overcharging and discharging.

[0067] The second aspect of the present application provides an electronic device, which includes the secondary battery in any of the foregoing embodiments. Thus, the electronic device provided by the present application has good use performance.

[0068] The present application has no special limitation on the type of the electronic device, and it can be any electronic device known in the prior art. In some embodiments of the present application, the electronic device can include but is not limited to a notebook computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal TV, a portable cleaner, a portable CD player, a minidisc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flash, a camera, a large household battery, and a lithium-ion capacitor, etc.

[0069] Examples

[0070] Hereinafter, examples and comparative examples are given to more specifically illustrate the embodiments of the present application. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0071] Testing method and device:

[0072] Sampling of negative electrode plate and positive electrode plate:

[0073] At 25 °C, the lithium-ion battery is discharged at a constant current of 0.5C until the discharge cut-off voltage, and the fully discharged lithium-ion battery is obtained. The lithium-ion battery is disassembled under an argon atmosphere, and the negative electrode plate and the positive electrode plate are soaked in a dimethyl carbonate (DMC) solvent for 2 h and dried at 60 °C for 1 h to obtain a negative electrode plate sample and a positive electrode plate sample. Among them, the discharge cut-off voltage of the lithium-ion batteries in the examples and comparative examples of this application is 3.0V. It can be understood that when the voltage range marked on the outer package of the factory battery is 3.0V to 4.65V, the charge cut-off voltage is 4.65V and the discharge cut-off voltage is 3.0V.

[0074] It can be understood that the charge cut-off voltage of the lithium-ion battery as an example in this application is 4.65V and the discharge cut-off voltage is 3.0V.

[0075] Mass percentage content w of the first carbon material and mass percentage content w2 of the positive electrode active material:

[0076] Scrape the positive electrode material layer powder from the positive electrode plate, weigh the mass m1, and perform thermogravimetric testing in air. Heat at 100 °C for 2 h, and the remaining mass m2 is the mass of the first carbon material and the positive electrode active material; heat at 600 °C for 2 h, and the remaining mass m3 is the mass of the positive electrode active material. That is, the mass of the first carbon material = m3 - m2, the mass percentage content w of the first carbon material = (m3 - m2) / m1, and the mass percentage content w2 of the positive electrode active material = m3 / m1.

[0077] Specific capacity:

[0078] b: Scrape n g of positive electrode material layer powder from the positive electrode plate, calcine it in air at 600 °C for 2 h, and then prepare a positive electrode plate according to the method of Example 1-1, cut it, stack it with a separator, a lithium metal negative electrode, and drop an electrolyte to assemble a coin cell. Charge the coin cell to 4.45V, and then discharge it at a current density of 0.1C to 3.0V to obtain the capacity C1. C1 is provided by the de-lithiation of the positive electrode active material. According to the mass of the positive electrode material layer powder taken and the mass percentage content w2 of the positive electrode active material, the mass n1 of the positive electrode active material can be calculated as n1 = n × w2, and then the specific capacity b of the positive electrode active material can be obtained by calculation as b = C1 / n1.

[0079] a: Charge the above-mentioned coin cell to 4.65 V, then discharge it to 3.0 V at a current density of 0.1 C to obtain the capacity C0. The capacity that C0 is more than C1 is the capacity C2 provided by the first carbon material, that is, C2 = C0 - C1. According to the mass of the positive electrode material layer powder taken and the mass percentage w of the first carbon material, the mass n2 of the first carbon material can be calculated as n2 = n × w, and then the specific capacity of the first carbon material can be obtained by calculation: a = C2 / n2.

[0080] The above-mentioned separator and electrolyte are the same as those in Example 1-1.

[0081] Concentration C of the lithium salt:

[0082] First, discharge the lithium-ion battery at a constant current of 0.5 C to 3 V at 25 °C. Then remove the packaging bag, cut off the tabs, wind the remaining electrode assembly and put it into a centrifuge tube, and centrifuge the electrolyte in a centrifuge.

[0083] Test the lithium salt concentration in the electrolyte by using ion chromatography (IC): Select a cation exchange chromatography column suitable for lithium ion analysis, and calibrate the system with the prepared lithium ion standard solution. Draw a standard curve to correlate the peak area with the lithium ion concentration. Inject the centrifuged electrolyte into the IC system, record the chromatogram of the sample, identify the characteristic peak of lithium ion, and convert the peak area of lithium ion in the sample into concentration using the standard curve. Thus, the concentration of lithium ion in the sample can be calculated according to the standard curve.

[0084] Interlayer spacing of the first carbon material:

[0085] Scrape 10 g of the positive electrode material layer powder from the positive electrode sample, grind it into fine powder, and prepare a sample thin slice using ion beam thinning technology. Then use a transmission electron microscope (TEM) and select 10 sample particles containing carbon elements for interlayer spacing test using the element analysis function.

[0086] Average particle size:

[0087] Take the positive electrode material layer powder obtained in the above interlayer spacing test, make it into a scanning electron microscope (SEM) sample for testing. Using the element analysis function of the scanning electron microscope, select 10 particles containing Co element and O element respectively, measure their circumscribed circle diameters, and calculate the average value of the above ten sizes as d1; the test method of d2 is the same as that of d1, but when selecting samples, samples containing carbon elements need to be selected for size testing.

[0088] Mass percentage of the doped element in the positive electrode active material:

[0089] Scrape n3 g of the positive electrode material layer sample from the positive electrode plate. Place it in a testing instrument and calcine it in air to 600 °C for 2 h. Weigh the remaining positive electrode material layer sample and place it in a digestion tank. Then add 10 mL of the digestion reagent aqua regia (obtained by mixing concentrated hydrochloric acid and concentrated nitric acid in a volume ratio of 3:1), and shake the digestion tank for 30 min before digestion. After digestion, the sample is fixed in volume with a volumetric flask. Use inductively coupled plasma optical emission spectrometry (ICP-OES). Through plasma excitation, characteristic spectra are emitted, and the types and masses of the doping elements Al, Mg, Ti, Nb, Zn, and W are determined by detecting these spectra;

[0090] The mass percentage content of the doping element in the positive electrode active material = mass of the doping element / (n3 × w2) × 100%.

[0091] Graphitization degree of the second carbon material:

[0092] Perform high-resolution transmission electron microscope observation and testing on the second carbon material. Combine with image analysis software to measure the interlayer spacing d, and then calculate its graphitization degree g through the Mering-Maire formula: g = (0.3440 - d) / (3440 - 0.3354).

[0093] Testing of energy density:

[0094] Use a three-dimensional scanner to measure the length L, width W, and height H of the battery.

[0095] At an ambient temperature of 25 °C, in a charge-discharge tester, charge the lithium-ion battery at a constant current of 0.5C until the voltage reaches 4.65V, then charge it at a constant voltage of 4.65V until the cut-off current is 0.05C. Let it stand for 10 min, and then discharge it at a constant current of 0.2C until 3V. Record the discharge capacity C and the discharge platform V. Then the volume energy density VED of the lithium-ion battery = (C × V) / (L × W × H), and the unit of volume energy density is Wh / L.

[0096] Impedance testing:

[0097] Use electrochemical impedance spectroscopy (EIS) technology to test the internal resistance of the lithium-ion battery. Conduct impedance testing on an electrochemical impedance spectrometer. The test frequency ranges from 100 kHz to 10 MHz, and the amplitude ranges from 5 mV to 0 mV. Record the impedance data at different frequencies during the test, including the real part (Z') and the imaginary part (Z”). Use analysis software to draw a Nyquist plot with the abscissa as Z' and the ordinate as Z”. The diameter of the semi-circle in the fitting curve is the impedance of the lithium-ion battery.

[0098] Testing of cycle capacity retention rate:

[0099] At 25 °C, a lithium-ion battery was charged with a constant current of 1.0C to a voltage of 4.65V using a charge-discharge tester, then charged at a constant voltage of 4.65V to 0.05C, and left to stand for 10 min; then discharged at a constant current of 0.5C to a voltage of 3V, left to stand for 15 min, and the full discharge capacity C0 at this time was recorded. The above was one cycle, and according to the above cycle to 800 cycles, the discharge capacity of the lithium-ion battery in the 800th cycle was C1. The cycle capacity retention rate of the lithium-ion battery was calculated by the following formula: Cycle capacity retention rate (%) = C1 / C0 × 100%.

[0100] Example 1-1

[0101] <Preparation of the positive electrode sheet>

[0102] The positive electrode active material lithium cobaltate, the first carbon material hard carbon material, and the binder polyvinylidene fluoride (PVDF) were mixed according to a mass ratio of 93.7:5:1.3, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%. After vacuum stirring evenly, the positive electrode material layer slurry was obtained. The positive electrode material layer slurry was evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10 μm, and dried at 120 °C to obtain a positive electrode sheet with a single-sided coated positive electrode material layer. The coating mass of the positive electrode material layer was 267.8 mg / 1540 mm 2 . Then the above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coated positive electrode material layer. After drying at 120 °C, it was cold-pressed, and then cut into pieces and welded with electrode tabs to obtain a positive electrode sheet with a specification of 74 mm × 867 mm for use. Among them, the thickness of the single-sided positive electrode material layer was 42 μm.

[0103] <Preparation of the negative electrode sheet>

[0104] The negative electrode active material artificial graphite, the binder styrene-butadiene rubber, and the conductive agent acetylene black were mixed according to a mass ratio of 97.4:1.4:1.2, and deionized water was added as a solvent to prepare a slurry with a solid content of 45 wt%. After vacuum stirring evenly with a vacuum mixer, the negative electrode slurry was obtained. The negative electrode slurry was evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 6 μm, and dried at 120 °C to obtain a negative electrode sheet with a single-sided coated negative electrode material layer. The coating mass of the negative electrode material layer was 142 mg / 1540 mm 2 . Then the above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coated negative electrode material layer. After drying at 120 °C, it was cold-pressed, and then cut into pieces and welded with electrode tabs to obtain a negative electrode sheet with a specification of 78 mm × 875 mm for use. Among them, the thickness of the single-sided negative electrode material layer was 54.5 μm.

[0105] <Preparation of the electrolyte>

[0106] In an environment with a water content of less than 10 ppm, dimethyl carbonate (DMC) is used as a solvent, and then the electrolyte salts LiPF6, ethylene carbonate, and fluoroethylene carbonate are added to the solvent and mixed evenly to obtain an electrolyte solution. Among them, based on the mass of the electrolyte solution, the mass percentage content of the electrolyte salt is 1.65 mol / L, the mass percentage content B1% of ethylene carbonate is 35%, the mass percentage content B2% of fluoroethylene carbonate is 5%, and the rest is the solvent.

[0107] <Preparation of separator>

[0108] A porous polyethylene film with a thickness of 7 μm (provided by Celgard) is used.

[0109] <Preparation of lithium-ion battery>

[0110] The above-prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator placed between the positive electrode sheet and the negative electrode sheet to play a role in isolation. Then, the four corners of the entire stacked sheet structure are fixed with tape to obtain an electrode assembly of the stacked sheet structure; the electrode assembly is placed in an aluminum-plastic film outer packaging foil, and the moisture is removed at 80 °C, and the above-prepared electrolyte solution is injected. After processes such as vacuum packaging, standing, formation, shaping, and capacity testing, a soft-pack lithium-ion battery is obtained. Among them, the formation temperature is 80 °C, and the formation standing time is 2 h.

[0111] Examples 1-2 to 1-21

[0112] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1. In Examples 1-1 to 1-21, when the mass percentage content w of the first carbon material changes, the mass percentage content of the binder remains unchanged. Correspondingly, the mass percentage content of the positive electrode active material is adjusted to change with the change of w.

[0113] Examples 1-22 to 1-37

[0114] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as Example 1-1. Among them, in Example 1-37, the mass percentage content of the conventional conductive agent changes, the mass percentage content of the binder remains unchanged. Correspondingly, the mass percentage content of the positive electrode active material is adjusted to change with the change of the mass percentage content of the conventional conductive agent.

[0115] Examples 2-1 to 2-14

[0116] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Example 1-1. Among them, in Examples 2-1 to 2-3 and Examples 2-6 to 2-14, the mass ratio of the doping elements Al and Mg is 1:1; in Example 2-4, the mass ratio of the doping elements Ti, Nb, and Zn is 1:1:1.

[0117] Comparative Examples 1 to 10

[0118] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1. Among them, in Comparative Examples 1 to 10, when the mass percentage content w of the first carbon material changes, the mass percentage content of the binder remains unchanged. Correspondingly, the mass percentage content of the cathode active material is adjusted to change with the change of w.

[0119] Table 1

[0120]

[0121]

[0122] Note: " / " in Table 1 represents the non-existence of relevant parameters.

[0123] It can be seen from Examples 1-1 to 1-21 and Comparative Examples 1 to 10 that in the examples, the mass percentage content w of the first carbon material is within the scope of this application, and the relationship between the specific capacity of the first carbon material, the specific capacity of the cathode active material b, and the concentration C of the lithium salt in the electrolyte satisfies: 1.0 + (99a + b) × w / 100b × 0.16 ≤ C ≤ 1.5 + (99a + b) × w / 100b × 0.16. The obtained lithium-ion battery has a lower impedance, a higher capacity retention rate, and a higher energy density. In Comparative Example 1, the mass percentage content w of the first carbon material is too high, and the obtained lithium-ion battery has poor cycling performance; in Comparative Example 2, the mass percentage content w of the first carbon material is too low, and the obtained lithium-ion battery has a large impedance and poor cycling performance. In Comparative Examples 3, 5, and 7, the concentration C of the lithium salt is lower than the lower limit of the above formula range, and the obtained lithium-ion battery not only has a large impedance, poor cycling performance, but also a low energy density. In Comparative Examples 4, 6, 8, and 9, the concentration C of the lithium salt is higher than the upper limit of the above formula range, and the obtained lithium-ion battery has a large impedance and poor cycling performance. When the cathode material layer does not include the first carbon material and a conventional conductive agent is used, such as in Comparative Example 10, the obtained secondary battery has a relatively large impedance and poor cycling performance. Thus, it shows that the lithium-ion battery that meets this application has a high energy density, good cycling performance, and good kinetic performance.

[0124] The mass percentage content w of the first carbon material generally affects the kinetic performance, cycling performance, and energy density of the lithium-ion battery. It can be seen from Examples 1-1 to 1-5 that when the mass percentage content w of the first carbon material is within the scope of this application, the obtained lithium-ion battery has a high energy density, a small impedance, and a high cycling capacity retention rate. Thus, it shows that when the mass percentage content w of the first carbon material is within the scope of this application, the obtained lithium-ion battery has a high energy density and good cycling performance, and also takes into account good kinetic performance.

[0125] The specific capacity a of the first carbon material generally affects the kinetic performance, cycling performance, and energy density of the lithium-ion battery. It can be seen from Examples 1-1, 1-6 to 1-11 that when the specific capacity a of the first carbon material is within the scope of this application, the obtained lithium-ion battery has a high energy density and a high cycling capacity retention rate. In addition, in this application, there is a linkage relationship between the concentration C of the lithium salt and the specific capacity a of the first carbon material. The change of a will also cause the value of C to change, thereby affecting the impedance of the lithium-ion battery. It can also be seen from Examples 1-6 to 1-11 that when the specific capacity a of the first carbon material is within the scope of this application, the obtained lithium-ion battery has a small impedance. Thus, it shows that when the specific capacity a of the first carbon material is within the scope of this application, the obtained lithium-ion battery has a high energy density and good cycling performance, and also takes into account good kinetic performance.

[0126] The specific capacity b of the positive electrode active material generally affects the kinetic performance, cycling performance, and energy density of the lithium-ion battery. It can be seen from Examples 1-1, 1-11 to 1-17 that when the specific capacity b of the positive electrode active material is within the scope of this application, the obtained lithium-ion battery has a high energy density and a high cycling capacity retention rate. In addition, in this application, there is a linkage relationship between the concentration C of the lithium salt and the specific capacity b of the first carbon material. The change of a will also cause the value of C to change, thereby affecting the impedance of the lithium-ion battery. It can also be seen from Examples 1-11 to 1-17 that when the specific capacity b of the positive electrode active material is within the scope of this application, the obtained lithium-ion battery has a small impedance. Thus, it shows that when the specific capacity b of the positive electrode active material is within the scope of this application, the obtained lithium-ion battery has a high energy density and good cycling performance, and also takes into account good kinetic performance.

[0127] The concentration C of the lithium salt generally affects the kinetic performance, cycling performance, and energy density of the lithium-ion battery. As can be seen from Examples 1-1 to 1-21, when the concentration C of the lithium salt is within the scope of this application, the obtained lithium-ion battery has a high energy density, a low impedance, and a high cycling capacity retention rate. This shows that when the concentration C of the lithium salt is within the scope of this application, the obtained lithium-ion battery has a high energy density and cycling performance, and also takes into account good kinetic performance.

[0128] Table 2

[0129]

[0130]

[0131] The interlayer spacing D of the first carbon material generally affects the kinetic performance, cycling performance, and energy density of the lithium-ion battery. As can be seen from Examples 1-1, 1-22 to 1-27, when the interlayer spacing D of the first carbon material is within the scope of this application, the obtained lithium-ion battery has a high energy density, a low impedance, and a high cycling capacity retention rate. This shows that when the interlayer spacing D of the first carbon material is within the scope of this application, the obtained lithium-ion battery has a high energy density and good cycling performance, and also takes into account good kinetic performance. Specifically, as Figure 1 shown, the transmission electron microscope photograph of the first carbon material in Example 1-1 can clearly observe the lattice fringes of the first carbon material, and its lattice spacing is 0.38 nm, that is, the interlayer spacing of the first carbon material is within the scope of this application.

[0132] The average particle size d1 of the particles of the first carbon material and the average particle size d2 of the positive electrode active material generally affect the kinetic performance, cycling performance, and energy density of the lithium-ion battery. As can be seen from Examples 1-1, 1-28 to 1-32, when the average particle size d1 of the particles of the first carbon material and the average particle size d2 of the positive electrode active material are within the scope of this application, the obtained lithium-ion battery has a high energy density, a low impedance, and a high cycling capacity retention rate. This shows that when the average particle size d1 of the particles of the first carbon material and the average particle size d2 of the positive electrode active material are within the scope of this application, the obtained lithium-ion battery has a high energy density and good cycling performance, and also takes into account good kinetic performance.

[0133] The type of lithium salt usually affects the kinetic performance, cycling performance, and energy density of lithium-ion batteries. As can be seen from Examples 1-1 and 1-33, when the type of lithium salt is within the scope of this application, the obtained lithium-ion batteries have a high energy density, low impedance, and high cycling capacity retention rate. This shows that when the type of lithium salt is within the scope of this application, the obtained lithium-ion batteries have a high energy density and good cycling performance, and also take into account good kinetic performance.

[0134] The type of cathode active material usually affects the kinetic performance, cycling performance, and energy density of lithium-ion batteries. As can be seen from Examples 1-1 and 1-34, when the type of cathode active material is within the scope of this application, the obtained lithium-ion batteries have a high energy density, low impedance, and high cycling capacity retention rate. This shows that when the type of cathode active material is within the scope of this application, the obtained lithium-ion batteries have a high energy density and good cycling performance, and also take into account good kinetic performance.

[0135] The type of the first carbon material usually affects the kinetic performance, cycling performance, and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 1-35 to 1-36, when the type of the first carbon material is within the scope of this application, the obtained lithium-ion batteries have a high energy density, low impedance, and high cycling capacity retention rate. This shows that when the type of the first carbon material is within the scope of this application, the obtained lithium-ion batteries have a high energy density and good cycling performance, and also take into account good kinetic performance.

[0136] Table 3

[0137]

[0138] Note: " / " in Table 3 represents the absence of relevant parameters.

[0139] The content and type of doping elements in the cathode active material usually affect the kinetic performance, cycling performance, and energy density of lithium-ion batteries. As can be seen from Examples 2-1 to 2-5, when the content and type of doping elements are within the scope of this application, the obtained lithium-ion batteries have a high energy density, low impedance, and high cycling capacity retention rate. This shows that when the content and type of doping elements are within the scope of this application, the obtained lithium-ion batteries have a high energy density and good cycling performance, and also take into account good kinetic performance.

[0140] The graphitization degree of the second carbon material usually affects the kinetic performance, cycling performance and energy density of the lithium-ion battery. It can be seen from Example 2-1, Example 2-6 to Example 2-7 that when the graphitization degree of the second carbon material is within the scope of the present application, the obtained lithium-ion battery has a high energy density, a low impedance and a high cycling capacity retention rate. Thus, it shows that when the graphitization degree of the second carbon material is within the scope of the present application, the obtained lithium-ion battery has a high energy density and good cycling performance, and also takes into account good kinetic performance.

[0141] The mass percentage content B1% of ethylene carbonate usually affects the kinetic performance, cycling performance and energy density of the lithium-ion battery. It can be seen from Example 2-1, Example 2-8 to Example 2-11 that when the mass percentage content B1% of ethylene carbonate is within the scope of the present application, the obtained lithium-ion battery has a high energy density, a low impedance and a high cycling capacity retention rate. Thus, it shows that when the mass percentage content B1% of ethylene carbonate is within the scope of the present application, the obtained lithium-ion battery has a high energy density and good cycling performance, and also takes into account good kinetic performance.

[0142] The mass percentage content B2% of fluoroethylene carbonate usually affects the kinetic performance, cycling performance and energy density of the lithium-ion battery. It can be seen from Example 2-1, Example 2-12 to Example 2-14 that when the mass percentage content B2% of fluoroethylene carbonate is within the scope of the present application, the obtained lithium-ion battery has a high energy density, a low impedance and a high cycling capacity retention rate. Thus, it shows that when the mass percentage content B2% of fluoroethylene carbonate is within the scope of the present application, the obtained lithium-ion battery has a high energy density and good cycling performance, and also takes into account good kinetic performance.

[0143] The above are only the preferred embodiments of the present application, and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included within the scope of protection of the present application.

[0144] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variation thereof are intended to cover non-exclusive inclusion, so that a process, method or article including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method or article.

[0145] Each embodiment in this specification is described in a related manner. For the same or similar parts among the embodiments, reference can be made to each other. The key point of each embodiment is to illustrate the differences from other embodiments.

Claims

1. A secondary battery comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the positive electrode sheet comprises a positive electrode material layer, the positive electrode material layer comprises a positive electrode active material and a first carbon material, and based on the mass of the positive electrode material layer, the mass percentage of the first carbon material is w%, 3≤w≤10; wherein, The gram capacity of the first carbon material is a mAh / g, and the gram capacity of the positive electrode active material is b mAh / g; The electrolyte includes a lithium salt, and the concentration of the lithium salt in the electrolyte is C mol / L; The secondary battery satisfies: 1.0+(99a+b)×w / 100b×0.16≤C≤1.5+(99a+b)×w / 100b×0.

16.

2. The secondary battery according to claim 1, wherein C is less than or equal to 2.

2.

3. The secondary battery according to claim 1, wherein C is less than or equal to 1.

9.

4. The secondary battery according to claim 1, wherein 60≤a≤140, and / or, 160≤b≤240.

5. The secondary battery according to claim 1, wherein The interlayer distance of the first carbon material is D, 0.34nm≤D≤0.42nm.

6. The secondary battery according to claim 1, wherein The average particle size d1 of the first carbon material particles is 1 μm to 10 μm.

7. The secondary battery according to claim 1, wherein The first carbon material includes at least one of hard carbon or graphite.

8. The secondary battery according to any one of claims 1 to 7, which satisfies at least one of the following characteristics: (1) The positive electrode active material includes at least one of lithium cobalt oxide or lithium nickel cobalt manganese oxide; (2) The positive electrode active material includes at least one of lithium cobalt oxide or lithium nickel cobalt manganese oxide containing an impurity element, and the impurity element includes at least one of Al, Mg, Ti, Nb, Zn, and W; based on the mass of the positive electrode active material, the mass percentage M of the impurity element is 0.4% to 1%.

9. The secondary battery according to any one of claims 1 to 7, wherein The average particle size d2 of the positive electrode active material is 5 μm to 20 μm.

10. The secondary battery according to any one of claims 1 to 7, wherein The negative electrode plate includes a negative electrode material layer, the negative electrode material layer includes a second carbon material, and the graphitization degree of the second carbon material is 89% to 93%.

11. The secondary battery according to any one of claims 1 to 7, wherein The electrolyte also includes ethylene carbonate and fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage of ethylene carbonate is B1%, the mass percentage of fluoroethylene carbonate is B2%, 20≤B1≤50, 0.5≤B2≤10.

12. The secondary battery according to any one of claims 1 to 7, wherein The lithium salt includes at least one of LiPF6, LiBF4, LiClO4 or LiDFOB. 13 . An electronic device comprising the secondary battery according to claim 1 .

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