Secondary battery and electronic device

Abstract

The invention discloses a secondary battery and an electronic device, the secondary battery comprises a negative electrode plate, a positive electrode plate and an electrolyte, the negative electrode plate comprises a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector, the negative electrode material layer comprises a first-class negative electrode material and a second-class negative electrode material, when the lithium discharge voltage of the negative electrode material is 0.5-3.0 V, the corresponding discharge capacity of the negative electrode material is less than or equal to 30% of the total capacity of the negative electrode material; when the lithium discharge voltage of the second-class negative electrode material is 0.5-3.0 V, the corresponding discharge capacity of the second-class negative electrode material is greater than or equal to 50% of the total capacity of the second-class negative electrode material; the total capacity refers to the total discharge capacity of the first-class or second-class negative electrode material when the lithium discharge voltage is 0.01-3.0 V. According to the present invention, by using the specific combination of the first-class negative electrode material and the second-class negative electrode material, the purpose of inhibiting the over-discharge expansion of the secondary battery is achieved.

Description

Technical Field

[0001] The present application relates to the field of energy storage technology, and more specifically, to a secondary battery and an electronic device. Background Art

[0002] Batteries play an extremely important role in modern society. They are not only the energy source for many devices and systems, but also play a key role in promoting technological progress, promoting sustainable development, and ensuring social operation.

[0003] The normal use of batteries is crucial to extending their life, ensuring equipment performance and ensuring safety. Therefore, over-discharge should be avoided as much as possible in daily use of batteries. Battery over-discharge specifically refers to the state in which the battery is discharged below its minimum safe voltage during use. During the battery over-discharge process, the negative electrode potential continues to rise. After reaching the decomposition potential of the SEI film, the SEI film will decompose, producing gases such as CO, CO, CH and heat, causing the battery to swell. Battery expansion caused by over-discharge is called over-discharge expansion. Over-discharge expansion will cause the battery to perform poorly, including capacity attenuation, increased internal resistance, etc., which will have a negative impact on the battery life.

[0004] Therefore, it is of great significance to develop a secondary battery that can suppress over-discharge expansion. Summary of the invention

[0005] In view of the above problems existing in the prior art, an object of the present application is to provide a secondary battery and an electronic device, which can suppress over-discharge expansion.

[0006] The first aspect of the present application provides a secondary battery, which includes a negative electrode sheet, a positive electrode sheet and an electrolyte, the negative electrode sheet includes a negative electrode collector and a negative electrode material layer arranged on at least one surface of the negative electrode collector, the negative electrode material layer includes a first type of negative electrode material and a second type of negative electrode material, when the first type of negative electrode material has a discharge voltage to lithium of 0.5V to 3.0V, its corresponding discharge capacity is less than or equal to 30% of its total capacity; when the second type of negative electrode material has a discharge voltage to lithium of 0.5V to 3.0V, its corresponding discharge capacity is greater than or equal to 50% of its total capacity; the total capacity refers to the total discharge capacity of the first or second type of negative electrode material when the discharge voltage to lithium is 0.01V to 3.0V.

[0007] The present application uses a combination of a specific Class I negative electrode material and a Class II negative electrode material. At a low potential in an over-discharge state of the battery, the Class II negative electrode material has a lithium storage capacity greater than that of the Class I negative electrode material. The Class II negative electrode material can de-lithium at a low potential of the battery, so that lithium can still be de-lithiated from the secondary battery at a low potential in an over-discharge state, thereby improving the battery voltage drop caused by leakage current and hindering the increase in negative electrode potential, inhibiting the decomposition of the SEI film, and improving over-discharge expansion and storage performance after over-discharge.

[0008] In some embodiments, a type of anode material includes at least one of graphite, hard carbon, soft carbon, silicon oxide, and silicon carbon. By selecting the above type of anode material, over-discharge expansion and storage performance after over-discharge can be improved.

[0009] In some embodiments, a second type of anode material includes at least one of lithium vanadate materials, titanium-based materials, and niobium-based oxides. By selecting the above second type of anode material, over-discharge expansion and storage performance after over-discharge can be improved.

[0010] In some embodiments, the lithium vanadate materials include at least one of Li3VO4, Li3V2O5, Li4V2O5, LiVO3, and LiV3O8. By selecting the above lithium vanadate materials, over-discharge expansion and storage performance after over-discharge can be improved.

[0011] In some embodiments, the titanium-based materials include TiO2, Li4Ti5O 12 and the like. By selecting the above titanium-based materials, over-discharge expansion and storage performance after over-discharge can be improved.

[0012] In some embodiments, the niobium-based oxides include Nb 16 W5O 55 , Nb 18 W 16 O 93 , TiNb2O7, Nb 16 W5O 93 , Cr 0.5 Nb 24.5 O 62 , Ti2Nb 14 O 39 , TiNb 24 O 62 , TiNb6O 17 , Ni2Nb 34 O 87 , Cu2Nb 34 O 87 , V3Nb 17 O 50 , Zn2Nb 34 O 87 , Al 0.5 Nb 24.5 O62, MoNb 12 O 33 , ZrNb 24 O 62 , AlNb 11 O 29 , Mg2Nb 34 O 87 , GaNb 11 O29 , Mo3Nb 14 O 44 , CrNb 11 O 29 , HfNb 24 O 62 , FeNb 11 O 28 , GaNb 49 O 124 , NaNb 13 O 33 , Ni2Nb 34 O 87 , TiNb6O 17 , WNb 12 O 33 , LiNbO3, Li3NbO4, TiCr 0.5 Nb 10.5 , O2, VNb9O 25 , KNb5O 13 , K6Nb 10.8 O30, PNb9O 25 , Nb 18 W8O 69 , Ti2Nb 10 O 29 , Cr 0.2 Fe 0.8 Nb 11 O 29 , Fe 0.8 Mn 0.2 Nb 11 O 29 , Fe 0.8 V 0.2 Nb 11 O 29 , Cu 0.02 Ti 0.94 Nb 2.04 at least one of those in O7. By selecting the above niobium-based oxides, over-discharge expansion and storage performance after over-discharge can be improved.

[0013] In some embodiments, the average particle size of a first type of anode material is 10 μm to 15 μm. When the average particle size of the first type of anode material is within the above range, the expansion stress is more dispersed, the SEI film is less likely to rupture repeatedly, the consumption of active lithium is reduced, the secondary battery is less likely to experience over-discharge, and moreover, the specific surface area of the first type of anode material is smaller, the side reaction between it and the electrolyte is better inhibited, and gas generation expansion is less likely to be triggered, thus being more conducive to further suppressing over-discharge expansion and storage performance after over-discharge of the secondary battery.

[0014] In some embodiments, the average particle size of a second type of anode material is 1 μm to 8 μm。 When the average particle size of the second type of negative electrode material is within the above range, there are many contact points between it and the first type of negative electrode material, binder, conductive agent, etc., which can better construct a conductive network, reduce the defects in the negative electrode material layer, thereby better inhibiting the decomposition of the SEI film, and further more conducive to further inhibiting the over-discharge swelling and storage performance after over-discharge of the secondary battery.

[0015] In some embodiments, a carbon material layer is provided on the surface of the second type of negative electrode material. The average thickness of the carbon material layer is H μm, and the average particle size of the second type of negative electrode material is D μm. H and D satisfy the following relationship: 0.01 ≤ H / D ≤ 0.2. When H / D is within the above range, it can not only better disperse the internal stress of the second type of negative electrode material, but also better prevent the side reaction between the second type of negative electrode material and the electrolyte, thereby better maintaining the stability of the SEI film, and further more conducive to further inhibiting the over-discharge swelling and storage performance after over-discharge of the secondary battery.

[0016] In some embodiments, the second type of negative electrode material includes an M element, and the M element is selected from at least one of V, Ti, and Nb; based on the mass of the negative electrode material layer, the mass percentage content of the M element is L%, and L is 0.3 to 25. Controlling the mass percentage content L% of the M element to be 0.3% to 25% is more conducive to further inhibiting the over-discharge swelling and storage performance after over-discharge of the secondary battery.

[0017] In some embodiments, the electrolyte includes a high reduction potential compound, and the high reduction potential compound is selected from at least one of LiBF4, NaBF4, KBF4, CsBF4, LiDFOB, NaDFOB, KDFOB, CsDFOB, LiBOB, NaBOB, KBOB, and CsBOB. Based on the mass of the electrolyte, the mass proportion of the high reduction potential compound is P%, and P is 0.01 to 5. Controlling the mass proportion P% of the high reduction potential compound to be 0.01% to 5% is more conducive to further inhibiting the over-discharge swelling and storage performance after over-discharge of the secondary battery.

[0018] In some embodiments, the secondary anode material includes element M, and element M is selected from at least one of V, Ti, and Nb; based on the mass of the anode material layer, the mass percentage of element M is L%; the electrolyte includes a high reduction potential compound, and the high reduction potential compound is selected from at least one of LiBF4, NaBF4, KBF4, CsBF4, LiDFOB, NaDFOB, KDFOB, CsDFOB, LiBOB, NaBOB, KBOB, and CsBOB; based on the mass of the electrolyte, the mass ratio of the high reduction potential compound is P%; L and P satisfy the following relationship: 1.5 ≤ L / P ≤ 30. When L / P is within the above range, it can not only better maintain the integrity of the SEI film, but also better inhibit the decomposition of the electrolyte, thereby better inhibiting the occurrence of gas generation, and further more conducive to further inhibiting the over-discharge swelling of the secondary battery.

[0019] The second aspect of the present application provides an electronic device, including the secondary battery as in the first aspect.

[0020] Compared with the prior art, the beneficial effects of the present application are as follows:

[0021] By using a combination of specific primary anode materials and secondary anode materials, in the low potential state of over-discharge of the battery, the secondary anode material has a lithium storage capacity greater than that of the primary anode material. The secondary anode material can de-lithiate at the low potential of the battery, so that lithium can still be released at the low potential of the over-discharge state of the secondary battery, improving the battery voltage drop caused by leakage current and hindering the increase of the anode potential, inhibiting the decomposition of the SEI film, and improving the over-discharge swelling and storage performance after over-discharge.

[0022] Additional aspects and advantages of the embodiments of the present application will be described, shown, or elucidated in part in the subsequent description, or through the implementation of the embodiments of the present application. Detailed Embodiments

[0023] For the sake of brevity, the present application specifically discloses only some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly recorded; and any lower limit can be combined with other lower limits to form a range not explicitly recorded. Similarly, any upper limit can be combined with any other upper limit to form a range not explicitly recorded. In addition, each individually disclosed point or single numerical value itself can be used as a lower limit or an upper limit and combined with any other point or single numerical value or combined with other lower limits or upper limits to form a range not explicitly recorded.

[0024] Unless otherwise specified, the terms used in the present application have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values of the various parameters mentioned in the present application can be measured by various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the embodiments of the present application).

[0025] A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0026] The terms "class one" and "class two" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, features defined as "class one" and "class two" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0027] Primary and secondary batteries

[0028] The first aspect of the present application provides a secondary battery, which includes a negative electrode sheet, a positive electrode sheet and an electrolyte, the negative electrode sheet includes a negative electrode collector and a negative electrode material layer arranged on at least one surface of the negative electrode collector, the negative electrode material layer includes a first type of negative electrode material and a second type of negative electrode material, when the first type of negative electrode material has a discharge voltage to lithium of 0.5V to 3.0V, its corresponding discharge capacity is less than or equal to 30% of its total capacity; when the second type of negative electrode material has a discharge voltage to lithium of 0.5V to 3.0V, its corresponding discharge capacity is greater than or equal to 50% of its total capacity; the total capacity refers to the total discharge capacity of the first or second type of negative electrode material when the discharge voltage to lithium is 0.01V to 3.0V.

[0029] The present application uses a combination of a specific Class I negative electrode material and a Class II negative electrode material. At a low potential in an over-discharge state of the battery, the Class II negative electrode material has a lithium storage capacity greater than that of the Class I negative electrode material. The Class II negative electrode material can de-lithium at a low potential of the battery, so that lithium can still be de-lithiated from the secondary battery at a low potential in an over-discharge state, thereby improving the battery voltage drop caused by leakage current and hindering the increase in negative electrode potential, inhibiting the decomposition of the SEI film, and improving over-discharge expansion and storage performance after over-discharge.

[0030] In some embodiments, when the lithium discharge voltage of a type of negative electrode material is between 0.5V and 3.0V, its corresponding discharge capacity is less than or equal to 30%, 29.5%, 29%, 28.5%, 28%, 27.5%, 27%, 26.98%, 26.95%, 26.9%, 26.7%, 26.5%, 26%, 25.5%, 25%, 24.5%, 24%, 23.5%, 23%, 22.5%, 22%, 21.5%, 21%, 20%, 19%, 18.9%, 18.7%, 18.68%, 18.6%, 18.5%, 18.3%, 18%, 17%, 16%, 15.2%, 15.1%, 15.07%, 15.05%, 15%, 14%, 13%, 12%, 11.9%, 11.7%, 11.5%, 11.47%, 11.45%, 11.4%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, 0.1%, 0% of its total capacity, or the range formed by any two of these values.

[0031] In some embodiments, when the lithium discharge voltage of a type of negative electrode material is between 0.5V and 3.0V, its corresponding discharge capacity is greater than or equal to 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 62%, 65%, 67%, 70%, 71%, 72%, 73%, 74%, 74.1%, 74.14%, 74.15%, 74.17%, 74.19%, 74.2%, 74.25%, 74.29%, 74.3%, 74.4%, 74.5%, 75%, 76%, 77%, 77.1%, 77.2%, 77.23%, 77.25%, 77.3%, 77.5%, 77.7%, 77.9%, 78%, 79%, 80%, 82%, 85%, 87%, 90%, 91%, 91.01%, 91.05%, 91.07%, 91.1%, 91.2%, 91.5%, 91.7%, 91.9%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100% of its total capacity, or the range formed by any two of these values.

[0032] In some embodiments, the type of negative electrode material includes at least one of graphite, hard carbon, soft carbon, silicon oxide, and silicon carbon. By selecting the above type of negative electrode material, over-discharge swelling and storage performance after over-discharge can be improved.

[0033] In some embodiments, the silicon oxide includes at least one of SiOx (0.5 ≤ x ≤ 1.5) and carbon-coated SiOx (0.5 ≤ x ≤ 1.5).

[0034] In some embodiments, in the silicon carbon, the mass percentage of carbon is 3% to 60%, and the mass percentage of silicon is 40% to 97%.

[0035] In some embodiments, the secondary anode materials include at least one of lithium vanadate materials, titanium-based materials, and niobium-based oxides. By selecting the above secondary anode materials, over-discharge expansion and storage performance after over-discharge can be improved.

[0036] In some embodiments, the lithium vanadate materials include at least one of Li3VO4, Li3V2O5, Li4V2O5, LiVO3, and LiV3O8. By selecting the above lithium vanadate materials, over-discharge expansion and storage performance after over-discharge can be improved.

[0037] In some embodiments, the titanium-based materials include TiO2, Li4Ti5O 12 and at least one of the following. By selecting the above titanium-based materials, over-discharge expansion and storage performance after over-discharge can be improved.

[0038] In some embodiments, the niobium-based oxides include Nb 16 W5O 55 、Nb 18 W 16 O 93 、TiNb2O7、Nb 16 W5O 93 、Cr 0.5 Nb 24.5 O 62 、Ti2Nb 14 O 39 、TiNb 24 O 62 、TiNb6O 17 、Ni2Nb 34 O 87 、Cu2Nb 34 O 87 、V3Nb 17 O 50 、Zn2Nb 34 O 87 、Al 0.5 Nb 24.5 O62、MoNb 12 O 33 、ZrNb 24 O 62 、AlNb 11 O 29 、Mg2Nb34 O 87 , GaNb 11 O 29 , Mo3Nb 14 O 44 , CrNb 11 O 29 , HfNb 24 O 62 , FeNb 11 O 28 , GaNb 49 O 124 , NaNb 13 O 33 , Ni2Nb 34 O 87 , TiNb6O 17 , WNb 12 O 33 , LiNbO3, Li3NbO4, TiCr 0.5 Nb 10.5 O2, VNb9O 25 , KNb5O 13 , K6Nb 10.8 O30, PNb9O 25 , Nb 18 W8O 69 , Ti2Nb 10 O 29 , Cr 0.2 Fe 0.8 Nb 11 O 29 , Fe 0.8 Mn 0.2 Nb 11 O 29 , Fe 0.8 V 0.2 Nb 11 O 29 , Cu 0.02 Ti 0.94 Nb 2.04 O7. By selecting the above niobium-based oxides, over-discharge expansion and storage performance after over-discharge can be improved.

[0039] In some embodiments, the average particle size of a first type of negative electrode material is 10 μm, 10.2 μm, 10.5 μm, 10.8 μm, 11 μm, 11.2 μm, 11.5 μm, 11.8 μm, 12 μm, 12.2 μm, 12.5 μm, 12.8 μm, 13 μm, 13.2 μm, 13.5 μm, 13.8 μm, 14 μm, 14.2 μm, 14.5 μm, 14.8 μm, 15 μm, or a range formed by any two of these values. In some embodiments, the average particle size of the first type of negative electrode material is from 10 μm to 15 μm. When the average particle size of the first type of negative electrode material is within the above range, the expansion stress is more dispersed, the SEI film is less likely to rupture repeatedly, the consumption of active lithium is reduced, over-discharge of the secondary battery is less likely to occur, and moreover, the specific surface area of the first type of negative electrode material is smaller, the side reaction between it and the electrolyte is better inhibited, and gas generation and expansion are less likely to be triggered, thus being more conducive to further inhibiting over-discharge expansion of the secondary battery.

[0040] In some embodiments, the average particle size of a second type of negative electrode material is 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5 μm, 5.2 μm, 5.5 μm, 5.8 μm, 6 μm, 6.2 μm, 6.5 μm, 6.8 μm, 7 μm, 7.2 μm, 7.5 μm, 7.8 μm, 8 μm, or a range formed by any two of these values. In some embodiments, the average particle size of the second type of negative electrode material is from 1 μm to 8 μm 。 When the average particle size of the second type of negative electrode material is within the above range, there are many contact points between it and the first type of negative electrode material, binder, conductive agent, etc., and a conductive network can be better constructed, defects in the negative electrode material layer can be reduced, thereby better inhibiting the decomposition of the SEI film, and further being more conducive to further inhibiting over-discharge expansion of the secondary battery.

[0041] In some embodiments, a carbon material layer is provided on the surface of the secondary anode material. The average thickness of the carbon material layer is H μm, and the average particle size of the secondary anode material is D μm. H and D satisfy the following relationship: H / D is 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.115, 0.12, 0.125, 0.13, 0.135, 0.14, 0.145, 0.15, 0.155, 0.16, 0.165, 0.17, 0.175, 0.18, 0.185, 0.19, 0.195, 0.2 or a range composed of any two of these values. In some embodiments, 0.01 ≤ H / D ≤ 0.2. When H / D is within the above range, it can not only better disperse the internal stress of the secondary anode material, but also better prevent the side reaction between the secondary anode material and the electrolyte, thereby better maintaining the stability of the SEI film, and further more conducive to further suppressing the over-discharge swelling of the secondary battery.

[0042] In some embodiments, the form of carbon in the carbon material layer includes but is not limited to at least one of graphene, carbon nanotubes, SuperP, acetylene black, amorphous carbon, graphite, and porous carbon.

[0043] In this application, the secondary anode material with a carbon material layer on its surface can be prepared by any known means in the art. For example, the secondary anode material with a carbon material layer on its surface can be obtained by the following preparation method: using chemical vapor deposition (CVD), decomposing the gaseous carbon source and depositing it on the surface of the secondary anode material layer to form a carbon material layer, thereby obtaining the secondary anode material with a carbon material layer on its surface. Among them, the gaseous carbon source includes but is not limited to at least one of methane, acetylene, propylene, ethylene, natural gas, and cyclohexane.

[0044] In some embodiments, the secondary negative electrode material includes an M element, and the M element is selected from at least one of V, Ti, and Nb; based on the mass of the negative electrode material layer, the mass percentage content of the M element is L%, and L is 0.3, 0.35, 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, 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, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 20.5, 21, 21.5, 22, 22.5, 23, 23.5, 24, 24.5, 25 or a range composed of any two of these values. In some embodiments, L is from 0.3 to 25. Controlling the mass percentage content L% of the M element to be from 0.3% to 25% is more beneficial to further suppressing the over-discharge swelling and storage performance after over-discharge of the secondary battery.

[0045] In some embodiments, the electrolyte includes a high reduction potential compound, and the high reduction potential compound is selected from at least one of LiBF4, NaBF4, KBF4, CsBF4, LiDFOB, NaDFOB, KDFOB, CsDFOB, LiBOB, NaBOB, KBOB, CsBOB; based on the mass of the electrolyte, the mass proportion of the high reduction potential compound is P%, and P is 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, 0.095, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5 or a range composed of any two of these values. In some embodiments, P is from 0.01 to 5. Controlling the mass proportion P% of the high reduction potential compound to be from 0.01% to 5% is more beneficial to further suppressing the over-discharge swelling and storage performance after over-discharge of the secondary battery.

[0046] In some embodiments, the secondary negative electrode material includes an M element, and the M element is selected from at least one of V, Ti, and Nb; based on the mass of the negative electrode material layer, the mass percentage of the M element is L%; the electrolyte includes a high reduction potential compound, and the high reduction potential compound is selected from at least one of LiBF4, NaBF4, KBF4, CsBF4, LiDFOB, NaDFOB, KDFOB, CsDFOB, LiBOB, NaBOB, KBOB, CsBOB; based on the mass of the electrolyte, the mass proportion of the high reduction potential compound is P%; L and P satisfy the following relationship: L / P is 1.5, 1.6, 1.7, 1.8, 1.9, 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, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 20.5, 21, 21.5, 22, 22.5, 23, 23.5, 24, 24.5, 25, 25.5, 26, 26.5, 27, 27.5, 28, 28.5, 29, 29.5, 30 or a range composed of any two of these values. In some embodiments, 1.5 ≤ L / P ≤ 30. When L / P is within the above range, it can not only better maintain the integrity of the SEI film, but also better inhibit the decomposition of the electrolyte, thereby better inhibiting the generation of gas, and further more conducive to further inhibiting the over-discharge swelling of the secondary battery.

[0047] <Negative electrode sheet>

[0048] This application has no particular limitation on the negative electrode current collector, as long as the purpose of this application can be achieved. For example, it may include but is not limited to at least one of copper foil, aluminum foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, and composite current collector. In some embodiments, the composite current collector may include but is not limited to at least one of carbon-copper composite current collector, nickel-copper composite current collector, and titanium-copper composite current collector.

[0049] In some embodiments, in the negative electrode sheet, the negative electrode material layer further includes at least one of a conductive agent, a binder, and a thickener; the present application places no particular restrictions on the conductive agent and the binder, as long as the objectives of the present application can be achieved. For example, the conductive agent may include, but is not limited to, at least one of metal-based materials and conductive polymers. In some embodiments, the metal-based materials may include, but are not limited to, at least one of metal powders and metal fibers, and the metal may include, but is not limited to, at least one of copper, nickel, aluminum, and silver. In some embodiments, the conductive polymers may include, but are not limited to, at least one of polyphenylene derivatives, polythiophene, polypyrrole, polyaniline, polyacetylene, poly(phenylene), and polyfluorene. Again, for example, the binder may include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polyesters, polyvinyl alcohols, polyacrylic acid, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon. Still, for example, the thickener may include, but is not limited to, at least one of carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and their salts.

[0050] In some embodiments, the structure of the negative electrode sheet is a negative electrode sheet structure known to those skilled in the art and can be used in secondary batteries.

[0051] In some embodiments, the preparation method of the negative electrode sheet is a preparation method of the negative electrode sheet known to those skilled in the art and can be used in secondary batteries. For example, the negative electrode sheet can be obtained by the following preparation method: mixing the components in the negative electrode material layer (including a first type of negative electrode material, a second type of negative electrode material, and optionally a conductive agent, a binder, and a thickener, etc.) in a solvent, and heating the thickener before use as needed to prepare a negative electrode slurry, and coating and / or spraying the negative electrode slurry on the negative electrode current collector. In some embodiments, the solvent may include, but is not limited to, at least one of water, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, trimethyl phosphate, acetone, and dipropylene glycol dimethyl ether.

[0052] <Positive electrode sheet>

[0053] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector.

[0054] The present application places no particular limitation on the positive current collector, as long as the object of the present application can be achieved. For example, it may include, but is not limited to, at least one of aluminum foil, aluminum alloy foil, composite current collector, carbon cloth, and carbon paper. In some embodiments, the composite current collector may include, but is not limited to, an aluminum-carbon composite current collector.

[0055] In some embodiments, the positive electrode material layer includes a positive electrode active material. The present application places no particular limitation on the positive electrode active material, as long as the object of the present application can be achieved. For example, it may include, but is not limited to, at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, lithium titanate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, and lithium manganese silicate. The chemical formula of the lithium-rich manganese-based material is γLi2MnO3·(1-γ)LiGO2, where 0 < γ < 1 and G is a transition metal such as nickel, cobalt, or iron. In some embodiments, the lithium nickel cobalt manganese oxide includes at least one of NCM811, NCM622, NCM523, and NCM111. In the present application, a substance different from its composition may be attached to the surface of the positive electrode active material. Exemplarily, the substances attached to the surface may include, but are not limited to, at least one of aluminum oxide, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide, lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, aluminum sulfate, lithium carbonate, calcium carbonate, magnesium carbonate, and carbon. By attaching the above substances to the surface of the positive electrode active material, the oxidation reaction of the electrolyte on the surface of the positive electrode active material can be inhibited, and the service life of the electrochemical device can be improved.

[0056] In some embodiments, the positive electrode material layer further includes at least one of a conductive agent, a binder, and a thickener; the present application does not particularly limit the conductive agent and the binder, as long as the object of the present application can be achieved. For example, the conductive agent may include, but is not limited to, at least one of carbon-based materials, metal-based materials, and conductive polymers. In some embodiments, the carbon-based materials may include, but are not limited to, at least one of graphite, carbon black, acetylene black, Super-P, Ketjen black, carbon fiber, carbon nanotube, graphene, and amorphous carbon. In some embodiments, the metal-based materials may include, but are not limited to, at least one of metal powder and metal fiber, and the metal may include, but is not limited to, at least one of copper, nickel, aluminum, and silver. In some embodiments, the conductive polymers may include, but are not limited to, at least one of polyphenylene derivatives, polythiophene, polypyrrole, polyaniline, polyacetylene, poly(phenylene), and polyfluorene. Again, for example, the binder may include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polyacrylate, polyvinyl alcohol, polyacrylic acid, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon. Still, for example, the thickener may include, but is not limited to, at least one of carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and their salts.

[0057] In some embodiments, the structure of the positive electrode sheet is a positive electrode sheet structure known in the art and can be used for secondary batteries.

[0058] In some embodiments, the preparation method of the positive electrode sheet is a preparation method of the positive electrode sheet known in the art and can be used for secondary batteries. For example, the positive electrode sheet can be obtained by the following preparation method: mixing the components in the positive electrode material layer [including the positive electrode active material, and optionally a conductive agent, a binder, a thickener, etc.] in a solvent, and heating the thickener before use as needed to prepare a positive electrode slurry, and coating and / or spraying the positive electrode slurry on the positive electrode current collector. In some embodiments, the solvent may include, but is not limited to, at least one of water, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, trimethyl phosphate, acetone, and dipropylene glycol dimethyl ether.

[0059] <Electrolyte>

[0060] In some embodiments, the electrolyte includes an organic solvent and an electrolyte.

[0061] In some embodiments, there are no particular limitations on the organic solvent in the present application, as long as the object of the present application can be achieved. The organic solvent used in the present application can be an organic solvent known in the prior art. For example, the organic solvent can include, but is not limited to, at least one of carbonate compounds, carboxylate compounds, ether compounds, and other organic solvents. Among them, the carbonate compounds can include, but are not limited to, at least one of linear carbonate compounds, cyclic carbonate compounds, and fluorinated carbonate compounds. The linear carbonate compounds can 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), and ethyl methyl carbonate (EMC). The cyclic carbonates can include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinylene ethylene carbonate (VEC). The fluorinated carbonate compounds can include, but are not limited to, at least one of fluorinated ethylene 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, and trifluoromethyl ethylene carbonate. The carboxylate compounds can 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, and caprolactone. The ether compounds can 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, and tetrahydrofuran. The other organic solvents can 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, and trioctyl phosphate.

[0062] In some embodiments, the electrolyte may include, but is not limited to, at least one of inorganic lithium salts, fluorinated organic lithium salts, and lithium salts containing dicarboxylic acid complexes. Among them, the inorganic lithium salts may include, but are not limited to, at least one of LiClO4, LiBF4, LiAsF6, LiPF6, LiSbF6, LiSO3F, LiPO2F2, LiN(FSO2)2. The fluorinated organic lithium salts may include, but are not limited to, at least one of LiCF3SO3, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic lithium 1,3 - hexafluoropropane disulfonimide, cyclic lithium 1,2 - tetrafluoroethane disulfonimide, LiPF4(CF3)2, LiN(CF3SO2)(C4F9SO2), LiC(CF3SO2), LiPF4(CF3SO2)2, LiPF4(C2F5)2, LiPF4(C2F5SO2)2, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, LiBF2(C2F5SO2)2. The lithium salts containing dicarboxylic acid complexes may include, but are not limited to, at least one of lithium tris(oxalato)phosphate, lithium difluoro bis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

[0063] In some embodiments, the concentration of the electrolyte is 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 0.7 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.7 mol / L, 2 mol / L, 2.2 mol / L, 2.5 mol / L, 2.7 mol / L, 3 mol / L, 3.2 mol / L, 3.5 mol / L, 3.7 mol / L, 4 mol / L, 4.2 mol / L, 4.5 mol / L, 4.7 mol / L, 5 mol / L or a range composed of any two of these values. In some embodiments, the concentration of the electrolyte is from 0.5 mol / L to 3 mol / L.

[0064] In some embodiments, the electrolyte solution further includes an additive.

[0065] In some embodiments, there are no particular restrictions on the additives in this application, as long as the objectives of this application can be achieved. The additives used in this application can be additives known in the prior art. For example, the additives can include, but are not limited to, at least one of polynitrile compounds, sulfur-containing additives, fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), and 1,4-butane sultone. Among them, the polynitrile compound includes at least one of dinitrile compounds and trinitrile compounds. The dinitrile compound is a compound containing 2 cyano groups (-CN), and can include, but are not limited to, malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile, sebaconitrile, methylmalononitrile, ethylmalononitrile, isopropylmalononitrile, tert-butylmalononitrile, methylsuccinonitrile, 2-methylenepentanedinitrile, 1,4-dicyano-3-butene, 2,2-dimethylsuccinonitrile, 2,3-dimethylsuccinonitrile, 2,3,3-trimethylsuccinonitrile, 2,2,3,3-tetramethylsuccinonitrile, 2,3-diethyl-2,3-dimethylsuccinonitrile, 2,2-diethyl-3,3-dimethylsuccinonitrile, dicyclohexyl-1,1-dicarbonitrile, dicyclohexyl-2,2-dicarbonitrile, dicyclohexyl-3,3-dicarbonitrile, 2,5-dimethyl-2,5-hexanedicarbonitrile, 2,3-diisobutyl-2,3-dimethylsuccinonitrile, 2,2-diisobutyl-3,3-dimethylsuccinonitrile, 2-methylglutaronitrile, 2,3-dimethylglutaronitrile, 2,4-dimethylglutaronitrile, 2,2,3,3-tetramethylglutaronitrile, 2,2,4,4-tetramethylglutaronitrile, 2,2,3,4-tetramethylglutaronitrile, 2,3,3,4-tetramethylglutaronitrile, 1,4-dicyanopentane, 2,6-dicyanoheptane, 2,7-dicyanooctane, 2,8-dicyanononane, 1,6-dicyanodecane, 1,2-dicyanobenzene, 1,3-dicyanobenzene, 1,4-dicyanobenzene, 3,3'-(ethylenedioxy)dipropionitrile, 3,3'-(ethylenedithio)dipropionitrile, 1,4-dicyano-2-butene, fumarodinitrile, and the like. The trinitrile compound is a compound containing 3 cyano groups (-CN).

[0066] In some embodiments, the preparation method of the electrolyte is a method well-known in the art and can be used for the preparation of the electrolyte of secondary batteries. For example, the electrolyte can be obtained by the following preparation method: mixing each component in the electrolyte (including high reduction potential compounds, organic solvents, electrolytes, and optional additives, etc.).

[0067] <Separator>

[0068] The separator is disposed between the positive electrode plate and the negative electrode plate to prevent internal short circuit of the secondary battery, allow electrolyte ions to pass through freely, and not affect the progress of the electrochemical charge and discharge process. There is no particular limitation on the separator in this application, as long as the object of this application can be achieved. The separator used in this application can be a separator known in the prior art. For example, the types of the separator can include but are not limited to at least one of a woven film, a non-woven film, a microporous film, a composite film, a rolled film, and a spun film. The materials of the separator can include but are not limited to at least one of polyolefins (PO) mainly composed of polyethylene (PE) and polypropylene (PP), polyester, cellulose, polyimide (PI), polyamide (PA), spandex, and aramid. The polyester can include but is not limited to a polyethylene terephthalate (PET) film.

[0069] In some embodiments, the separator includes a base layer. The base layer can include but is not limited to at least one of a non-woven fabric, a film, and a composite film having a porous structure. The materials of the base layer can include but are not limited to at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. In some embodiments, the base layer can include but is not limited to at least one of a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, and a polypropylene-polyethylene-polypropylene porous composite film.

[0070] In some embodiments, the separator further includes a surface treatment layer disposed on at least one surface of the base layer. The surface treatment layer can include but is not limited to at least one of a polymer layer, an inorganic layer, and a layer formed by mixing a polymer and an inorganic substance. The polymer layer includes a polymer. There is no particular limitation on the polymer in this application, as long as the object of this application can be achieved. For example, the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene ether, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene). The inorganic layer includes inorganic particles and a binder. There is no particular limitation on the inorganic particles and the binder in this application, as long as the object of this application can be achieved. For example, the inorganic particles can include but are not limited to at least one of alumina, silica, magnesia, 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, and barium sulfate. Another example is that the binder can include but is not limited to at least one of the binders used in the above positive electrode material layer or negative electrode material layer.

[0071] In some embodiments, there is no particular limitation on the thickness of the separator in this application, as long as the object of this application can be achieved. For example, the thickness of the separator is 1 μm to 500 μm.

[0072] <Packaging bag>

[0073] In some embodiments, the secondary battery further includes a packaging bag for accommodating the positive electrode sheet, negative electrode sheet, separator, and electrolyte, as well as other components known in the art in the secondary battery. There are no particular limitations on other components in this application. There are no particular limitations on the packaging bag in this application, as long as the object of this application can be achieved. The packaging bag used in this application can be a packaging bag known in the prior art. For example, the packaging bag can include, but is not limited to, an aluminum-plastic film packaging bag.

[0074] <Preparation method of secondary battery>

[0075] The preparation method of the secondary battery is well-known to those skilled in the art. There are no particular limitations on the preparation method of the secondary battery in this application, as long as the object of this application can be achieved. For example, the preparation method of the secondary battery can include, but is not limited to, the following steps: stacking the positive electrode sheet, separator, and negative electrode sheet in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly. Then, placing the electrode assembly into the packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain the secondary battery; or stacking the positive electrode sheet, separator, and 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 packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain the secondary battery. In addition, an overcurrent protection element, a guide plate, etc. can be placed in the packaging bag as needed to prevent the pressure inside the secondary battery from rising and overcharging / discharging.

[0076] II. Electronic device

[0077] The second aspect of this application provides an electronic device including the secondary battery as in the first aspect.

[0078] There are no particular limitations on the electronic device in this application, as long as the object of this application can be achieved. The electronic device used in this application can be an electronic device known in the prior art. For example, the electronic device can include, but is not limited to, at least one of 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 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 moped, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flash, a camera, a large household secondary battery, and a lithium-ion capacitor.

[0079] III. Examples

[0080] The present application will be further clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by those skilled in the art based on the present application fall within the scope of protection of the present application.

[0081] It should be noted that in the specific embodiments of the present application, a lithium-ion secondary 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 secondary battery.

[0082] In the following examples and comparative examples, the reagents, materials, and instruments used can be obtained commercially without special instructions. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0083] Testing methods and equipment:

[0084] (1) Discharge capacity test of type I or type II anode materials:

[0085] At 25 °C, a type I or type II anode material, a conductive agent Super-P, and a binder PVDF are mixed in a mass ratio of 80:10:10, and N-methylpyrrolidone (NMP, the solid-liquid ratio of the type I or type II anode material to NMP is 1 g:2 mL) is added, and stirred thoroughly to form a uniform anode slurry; the above anode slurry is coated on a copper foil with a thickness of 10 μm (anode current collector), and then dried and cold-pressed to obtain a copper foil with a thickness of 80 μm; then it is punched into small round pieces with a diameter of 14 mm to be used as anode electrodes; and a lithium sheet is used as the anode electrode, a 12-μm-thick polypropylene film is used as the separator, and a 1 mol / L LiPF6 solution (the solvent is ethylene carbonate and propylene carbonate with a volume ratio of 1:1) is used as the electrolyte to assemble a coin-type half-cell.

[0086] On a Blue Electric battery test system (LAND CT2001A), the above coin-type half-cell is subjected to charge and discharge tests at a working voltage range of 0.5 V to 3.0 V and a current density of 10 mA / g, and its first discharge specific capacity is recorded. This first discharge specific capacity is the discharge capacity corresponding to the lithium discharge voltage of the type I or type II anode material at 0.5 V to 3.0 V.

[0087] (2) Total capacity test of type I or type II anode materials:

[0088] Assemble the coin-type half-cell according to the method in (1) above. Then, on a Blue Electric Battery Test System (LAND CT2001A), perform charge-discharge tests on the above coin-type half-cell in the working voltage range of 0.01 V to 3.0 V and at a current density of 10 mA / g, and record its initial discharge specific capacity. This initial discharge specific capacity is the total discharge capacity when the lithium discharge voltage of the first or second type of anode material is between 0.01 V and 3.0 V.

[0089] (3) Testing the average particle size of the first or second type of anode material:

[0090] Use a Malvern particle size analyzer (instrument model: MasterSizer2000) to test the particle size distribution of the first or second type of anode material. The sample preparation method is as follows: Add about 0.02 g of the powder sample of the first or second type of anode material to a 50 mL clean beaker, add 20 mL of deionized water, and ultrasonicate in a 120 W ultrasonic cleaner for 5 min to obtain a sample dispersion. In the volume-based particle size distribution of the first or second type of anode material, start measuring from the small particle size. The particle size at which the volume cumulative reaches 50% is Dv50, and the particle size at which the volume cumulative reaches 10% is Dv10. Moreover, use the size of Dv50 as the average particle size of the first or second type of anode material.

[0091] (4) Testing the mass percentage of carbon and silicon in silicon carbide:

[0092] First, test the mass percentage of silicon in silicon carbide. The value obtained by subtracting the tested value from 100% is the mass percentage of carbon. Among them, the test for the mass percentage of silicon in silicon carbide is as follows:

[0093] Weigh 0.1 g of silicon carbide and add it to a polytetrafluoroethylene (PTFE) beaker. Drop in 10 mL of nitric acid and heat to digest it; then drop in another 10 mL of nitric acid and heat to repeat the digestion once. After cooling to room temperature, filter the digestion solution to remove the filter residue and transfer it to a volumetric flask and make up the volume to 100 mL. Add the prepared solution to the nebulizer and use inductively coupled plasma optical emission spectrometry for testing to obtain the mass percentage of silicon in silicon carbide.

[0094] (5) Testing the average thickness of the carbon material layer in the second type of anode material with a carbon material layer on its surface:

[0095] Use a focused ion beam (FIB) to slice the second type of anode material with a carbon material layer on its surface, and then observe it through a high-resolution transmission electron microscope (HRTEM, model: TalosF200X). Randomly select five regions to record the thickness of the carbon material layer in the second type of anode material with a carbon material layer on its surface, and calculate the arithmetic mean to obtain the average thickness of the carbon material layer in the second type of anode material with a carbon material layer on its surface.

[0096] (6) Test of the mass percentage content L% of the M element of the second type of negative electrode material in the negative electrode material layer:

[0097] The secondary battery is disassembled, the negative electrode material layer is removed from the negative electrode sheet, and after drying, 0.4 g of the negative electrode material layer is taken, 10 mL of aqua regia (concentrated nitric acid and concentrated hydrochloric acid are mixed in a volume ratio of 1:1) and 2 mL of HF are added to dissolve, and the solution is transferred into a 100 mL volumetric flask and fixed to volume. The content of the M element in the solution is measured by an ICP inductively coupled spectrometer (ICP analyzer), and the mass percentage content of the M element in the negative electrode material layer is calculated by L%; the M element is selected from at least one of V, Ti, and Nb.

[0098] (7) Test of the content of each component in the electrolyte:

[0099] The secondary battery was discharged at a constant current of 0.5C to 3.0V and then disassembled, the electrolyte was collected, and the removed positive electrode sheet, negative electrode sheet, and separator were centrifuged. The liquid obtained after centrifugation and the above electrolyte were evenly mixed, and then tested using a gas chromatography-mass spectrometer (instrument model: Agilent 8890) and an ion chromatography (instrument model: AQUION ion chromatography) to obtain each component in the electrolyte and test its content.

[0100] (8) Over-discharge expansion test of secondary batteries:

[0101] At 25°C, the thickness of the secondary battery of each embodiment or comparative example was measured with a flat thickness gauge, which was recorded as T0; then the secondary battery was discharged at 0.1C to 2.0V for over-discharge, and stored at 25°C for 7 days, and then the thickness of the secondary battery was measured again with a flat thickness gauge, which was recorded as T1; the thickness expansion rate T (%) was calculated according to the following formula:

[0102] T = (T1-T0) / T0×100%;

[0103] The thickness expansion rate T (%) is used to characterize the over-discharge expansion degree of the secondary battery. The smaller the T value is, the smaller the over-discharge expansion degree of the secondary battery is, that is, the better the effect of suppressing the over-discharge expansion of the secondary battery is.

[0104] (9) K value test of secondary battery:

[0105] At 25°C, the voltage of the secondary battery of each embodiment or comparative example was measured with a voltmeter, which was recorded as K0; then the secondary battery was discharged at 0.1C to 2.0V for overdischarge, and stored at 25°C for 7 days, and then the voltage of the secondary battery was measured again with a voltmeter, which was recorded as K1; the K value (mV / h) was calculated according to the following formula:

[0106] K = (K0-K1) / (7×24h);

[0107] The storage performance of the secondary battery after over-discharge is characterized by the K value (mV / h). The smaller the K value, the better the storage performance of the secondary battery after over-discharge.

[0108] Example 1

[0109] 1. Preparation of the second type of negative electrode material with a carbon material layer on the surface

[0110] Lithium vanadate material Li3VO4 was laid flat on a quartz boat and placed in the constant temperature zone of a CVD furnace. Argon (flow rate 200 sccm) was introduced to exclude air, and the oxygen content was maintained at <1 ppm. The temperature was raised to 600 °C at a rate of 10 °C / min and held stable for 30 min. Then, gaseous carbon source acetylene (flow rate 50 sccm) and hydrogen (flow rate 150 sccm) were introduced, and the pressure was maintained at 30 Pa for 30 min to decompose the gaseous carbon source and deposit it on the surface of the second type of negative electrode material layer to form a carbon material layer. Finally, the carbon source was turned off, and it was naturally cooled to room temperature under argon protection to obtain the second type of negative electrode material with a carbon material layer on the surface;

[0111] Among them, a carbon material layer is provided on the surface of the second type of negative electrode material. The form of carbon in the carbon material layer is amorphous carbon. The average thickness of the carbon material layer is H μm, H = 0.1. The average particle size of the second type of negative electrode material (with a carbon material layer) is D μm, D = 5, and H / D = 0.02. The second type of negative electrode material includes element M, and element M is V;

[0112] 2. Preparation of the negative electrode sheet

[0113] A first type of negative electrode material (graphite), a second type of negative electrode material with a carbon material layer on the surface, binder styrene-butadiene rubber, and thickener carboxymethyl cellulose were mixed in N-methylpyrrolidone (NMP) in a mass ratio of 47:48:3:2 to prepare a negative electrode slurry. The negative electrode slurry was coated on one surface of a negative electrode current collector copper foil and dried to obtain a negative electrode sheet with a negative electrode material layer coated on one side. The above steps were repeated on the other surface of the negative electrode current collector copper foil to obtain a negative electrode sheet with a negative electrode material layer coated on both sides. After cold pressing, slicing, and slitting, it was dried to obtain a negative electrode sheet with a specification of 78 mm × 875 mm;

[0114] Among them, when the lithium discharge voltage of the first type of negative electrode material is between 0.5 V and 3.0 V, its corresponding discharge capacity (55 mA·h) is equal to 15.07% of its total capacity (365 mA·h); when the lithium discharge voltage of the second type of negative electrode material is between 0.5 V and 3.0 V, its corresponding discharge capacity (260 mA·h) is equal to 74.29% of its total capacity (350 mA·h). The second type of negative electrode material includes element M, and element M is V, Ti, and Nb. Based on the mass of the negative electrode material layer, the mass percentage content of element M is L%, L = 18. The average particle size of the first type of negative electrode material is 12 μm. The thickness of the negative electrode material layer is 120 μm;

[0115] 3. Preparation of the positive electrode sheet

[0116] Mix the cathode active material lithium cobaltate, conductive agent graphite, and binder polyvinylidene fluoride (PVDF) with a mass ratio of 80:10:10 in the solvent N-methylpyrrolidone to prepare a positive electrode slurry. Coat the positive electrode slurry on one surface of the positive electrode current collector aluminum foil and dry it to obtain a positive electrode sheet with a single-sided coated positive electrode material layer; repeat the above steps on the other surface of the positive electrode current collector aluminum foil to obtain a positive electrode sheet with a double-sided coated positive electrode material layer; after cold pressing, slicing, and slitting, dry it to obtain a positive electrode sheet with a specification of 74 mm × 867 mm;

[0117] Among them, the thickness of the positive electrode material layer is 80 μm;

[0118] 4. Preparation of the electrolyte

[0119] In a dry argon atmosphere glove box, mix the organic solvents ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a mass ratio of EC:PC:EMC:DEC = 10:30:30:30 and mix them evenly. Then add fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), and a high reduction potential compound CsBF4, dissolve and stir well, and then add the inorganic lithium salt LiPF6. After mixing evenly, obtain the electrolyte;

[0120] Among them, based on the mass of the electrolyte, the mass ratio of the high reduction potential compound is P%, P = 1, L / P = 18, the mass ratio of fluoroethylene carbonate (FEC) is 2%, the mass ratio of 1,3-propane sultone (1,3-PS) is 2%; the mass ratio of LiPF6 (electrolyte) is 12.5%;

[0121] 5. Separator

[0122] Use a polyethylene porous membrane with a thickness of 15 μm (provided by Celgard) as the separator;

[0123] 6. Preparation of the secondary battery

[0124] Connect the positive electrode sheet and the negative electrode sheet made above to the electrode tabs respectively. Stack the positive electrode sheet, separator, and negative electrode sheet in sequence, and perform operations such as winding and folding according to needs to obtain a wound electrode assembly. Put the electrode assembly into an aluminum-plastic film packaging bag, inject the electrolyte into the packaging bag and seal it, and let it stand, form (constant current charge at 0.2C for 120 s, then constant current charge at 1C for 180 s, and finally constant current charge at 1.5C to 4.5V), degas, and trim the edges to obtain the secondary battery.

[0125] Examples 2 to 9 and Comparative Examples 1 to 5

[0126] Except for adjusting the first type of negative electrode material and the second type of negative electrode material according to Table 1, the rest are the same as in Example 1. In Table 1, when the lithium discharge voltage of the first type of negative electrode material is from 0.5V to 3.0V, the discharge capacity is A mA·h, and when the lithium discharge voltage of the first type of negative electrode material is from 0.01V to 3.0V, the total discharge capacity is B mA·h; when the lithium discharge voltage of the second type of negative electrode material is from 0.5V to 3.0V, the discharge capacity is E mA·h, and when the lithium discharge voltage of the second type of negative electrode material is from 0.01V to 3.0V, the total discharge capacity is F mA·h. By adjusting the specific type and mass ratio of the first type of negative electrode material, A and B of the first type of negative electrode material can be as shown in Table 1. By adjusting the specific type and mass ratio of the second type of negative electrode material, E and F of the second type of negative electrode material can be as shown in Table 1. In addition, the mass percentage content of element M in the negative electrode material layer is L%; by adjusting the mass ratio of the first type of negative electrode material and the second type of negative electrode material (that is, keeping the ratio of the total mass of the first type of negative electrode material and the second type of negative electrode material, the mass of the binder, and the mass of the thickener unchanged at 95:3:2, and only changing the mass ratio of the first type of negative electrode material and the second type of negative electrode material), the L value is stably maintained at 18.

[0127] Table 1 Condition parameters and test results of Examples 1 to 9 and Comparative Examples 1 to 5

[0128]

[0129] Note: In the above table, "silicon carbide: graphite = 1:1" in Example 3 and Comparative Example 3 means that the first type of negative electrode material is silicon carbide and graphite with a mass ratio of 1:1; in the above silicon carbide, the mass percentage content of carbon is 58% and the mass percentage content of silicon is 42%; "none" in Comparative Examples 1 to 5 means that Comparative Examples 1 to 5 do not use the second type of negative electrode material.

[0130] As can be seen from Table 1, when the first type of negative electrode material and the second type of negative electrode material are within the scope of the present application, the over-discharge expansion and storage performance after over-discharge of the secondary battery can be improved. Specifically, by comparing the examples using the same type of first type of negative electrode material with the comparative examples, it can be known that the solution provided by the present application can improve the over-discharge expansion and storage performance after over-discharge. For example, compare Example 1 with Comparative Example 1, Example 2 with Comparative Example 2, Example 3 with Comparative Example 3, Example 4 with Comparative Example 4, and Example 5 with Comparative Example 5.

[0131] Examples 10 to 14

[0132] Except for adjusting the mass percentage L% of element M in the negative electrode material layer and the mass ratio P% of the high reduction potential compound (CsBF4) in the electrolyte according to Table 2, the rest are the same as in Example 3. By adjusting the mass ratio of the first type of negative electrode material to the second type of negative electrode material (that is, keeping the ratio of the total mass of the first type of negative electrode material and the second type of negative electrode material, the mass of the binder, and the mass of the thickener unchanged at 95:3:2, and only changing the mass ratio of the first type of negative electrode material to the second type of negative electrode material), L is as shown in Table 2. By keeping the concentration of LiPF6 and the mass ratios of FEC and PS in the electrolyte unchanged and changing the mass ratio of CsBF4 to the organic solvent, P is as shown in Table 2.

[0133] Table 2 Condition parameters and test results of Examples 3, 10 to 14

[0134] L P L / P Thickness swelling rate T (%) K value (mV / h) Example 3 18 1 18 8 0.07 Example 10 25 1 25 10 0.09 Example 11 0.3 1 0.3 12 0.10 Example 12 0.75 0.025 30 14 0.15 Example 13 0.75 5 0.15 13 0.16 Example 14 0.75 0.01 75 15 0.17

[0135] As can be seen from Table 2, when the values of L and P are within the scope of this application, the over-discharge swelling and storage performance after over-discharge of the secondary battery can be improved. In particular, when further regulating 0.025 ≤ P ≤ 5, the over-discharge swelling and storage performance after over-discharge can be further improved. In addition, when further regulating 1.5 ≤ L / P ≤ 30, the over-discharge swelling and storage performance after over-discharge can be further improved.

[0136] Examples 15 to 19

[0137] Except for adjusting the average particle sizes of the first type of negative electrode material and the second type of negative electrode material according to Table 3, the rest are the same as in Example 3. By crushing and classifying the first type of negative electrode material, the average particle size W μm of the first type of negative electrode material is as shown in Table 3. By crushing and classifying the lithium vanadate material in the second type of negative electrode material and adjusting the deposition time in the preparation method of the second type of negative electrode material with a carbon material layer on its surface, D and H are as shown in Table 3. The second type of negative electrode material has a carbon material layer on its surface, the average thickness of the carbon material layer is H μm, and the average particle size of the second type of negative electrode material (with a carbon material layer) is D μm. Changes in the values of D and / or H will cause changes in the values of E, F, and L. In addition, by adjusting the mass ratio of the first type of negative electrode material to the second type of negative electrode material (that is, keeping the ratio of the total mass of the first type of negative electrode material and the second type of negative electrode material, the mass of the binder, and the mass of the thickener unchanged at 95:3:2, and only changing the mass ratio of the first type of negative electrode material to the second type of negative electrode material), the value of L is stably maintained at 18.

[0138] Table 3 Condition parameters and test results of Examples 4, 15 to 19

[0139]

[0140] Note: In the above table, "H = 0" in Example 17 means that there is no carbon material layer on the surface of the secondary negative electrode material in Example 17, and "D = 5" in Example 17 means that the average particle size of the secondary negative electrode material (lithium vanadate material Li3VO4) is 5 μm.

[0141] As can be seen from Table 3, when 0.01 ≤ H / D ≤ 0.2, the over-discharge expansion and storage performance after over-discharge of the secondary battery are improved.

[0142] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application rather than to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A secondary battery comprising a negative electrode sheet, a positive electrode sheet and an electrolyte, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, characterized in that: The negative electrode material layer includes a type of negative electrode material and a type of negative electrode material. When the lithium discharge voltage of the type of negative electrode material is 0.5V to 3.0V, the corresponding discharge capacity is less than or equal to 30% of its total capacity; when the lithium discharge voltage of the type of negative electrode material is 0.5V to 3.0V, the corresponding discharge capacity is greater than or equal to 50% of its total capacity; the total capacity refers to the total discharge capacity of the type one or type two negative electrode materials when the lithium discharge voltage is 0.01V to 3.0V.

2. The secondary battery according to claim 1, characterized in that: The negative electrode material includes at least one of graphite, hard carbon, soft carbon, silicon oxygen, and silicon carbon.

3. The secondary battery according to claim 1, characterized in that: The second type of negative electrode material includes at least one of lithium vanadate material, titanium-based material, and niobium-based oxide.

4. The secondary battery according to claim 3, characterized in that: The second type of negative electrode material satisfies at least one of the following: (1) The lithium vanadate material includes at least one of Li3VO4, Li3V2O5, Li4V2O5, LiVO3, and LiV3O8; (2) The titanium-based material includes TiO2, Li4Ti5O 12 At least one of; (3)Nb containing the mentioned iron-based compounds 16 W5O 55 , Nb 18 W 16 O 93 , TiNb2O7, Nb 16 W5O 93 , Cr 0.5 Nb 24.5 O 62 , Ti2Nb 14 O 39 , TiNb 24 O 62 , TiNbO 17 , Ni2Nb 34 O 87 , Cu2Nb 34 O 87 , V3Nb 17 O 50 , Zn2Nb 34 O 87 , Al 0.5 Nb 24.5 O62, MoNb 12 O 33 , ZrNb 24 O 62 , AlNb 11 O 29 , Mg2Nb 34 O 87 , GaN 11 O 29 , Mo3Nb 14 O 44 , CrNb 11 O 29 , HfNb 24 O 62 , FeNb 11 O 28 , GaN 49 O 124 , NaNb 13 O 33 , Ni2Nb 34 O 87 , TiNbO 17 , WNb 12 O 33 , LiNbO3, Li3NbO4, TiCr 0.5 Nb 10.5 O2, VNb9O 25 , KNbO 13 , K6Nb 10.8 O30, PNb9O 25 , Nb 18 W8O 69 、Ti2Nb 10 O 29 Cr 0.2 Fe 0.8 Nb 11 O 29 , Fe 0.8 Mn 0.2 Nb 11 O 29 , Fe 0.8 V 0.2 Nb 11 O 29 , Cu 0.02 Ti 0.94 Nb 2.04 At least one of O7.

5. The secondary battery according to claim 1, characterized in that: The secondary battery satisfies at least one of the following: (1) The average particle size of the negative electrode material is 10 μm to 15 μm; (2) The average particle size of the second type of negative electrode material is 1 μm to 8 μm.

6. The secondary battery according to claim 1, characterized in that: A carbon material layer is provided on the surface of the second type of negative electrode material, the average thickness of the carbon material layer is H μm, the average particle size of the second type of negative electrode material is D μm, and H and D satisfy the following relationship: 0.01≤H / D≤0.

2.

7. The secondary battery according to claim 1, characterized in that: The second type of negative electrode material includes an M element, and the M element is selected from at least one of V, Ti, and Nb; based on the mass of the negative electrode material layer, the mass percentage of the M element is L%, and L is 0.3 to 25.

8. The secondary battery according to claim 1, characterized in that: The electrolyte includes a high reduction potential compound, which is selected from at least one of LiBF4, NaBF4, KBF4, CsBF4, LiDFOB, NaDFOB, KDFOB, CsDFOB, LiBOB, NaBOB, KBOB, and CsBOB. Based on the mass of the electrolyte, the mass proportion of the high reduction potential compound is P%, and P is 0.01 to 5.

9. The secondary battery as claimed in claim 8, wherein the second type of negative electrode material comprises an M element, and the M element is selected from at least one of V, Ti, and Nb; based on the mass of the negative electrode material layer, the mass percentage of the M element is L%, and L is 0.3 to 25; L and P satisfy the following relationship: 1.5≤L / P≤30.

10. An electronic device, characterized in that: The invention comprises a secondary battery as claimed in any one of claims 1 to 9.

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