Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device. The secondary battery comprises a negative pole piece and an electrolyte, the electrolyte comprises a compound shown in a formula I, based on the mass of the electrolyte, the mass ratio of the compound shown in the formula I is W1%, and W1 is larger than or equal to 2 and smaller than or equal to 50; the negative electrode piece 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 contains a silicon element, and based on the mass of the negative electrode material layer, the mass ratio of the silicon element is x%, and x is smaller than or equal to 25; the thickness of the negative electrode material layer is D [mu] m, the surface of the negative electrode material layer is provided with a plurality of concave parts, the depth of each concave part is d [mu] m, P = d / D, and P is greater than or equal to 0.1; and 0.4 < = W1 / (x * P) < = 62.5. The secondary battery provided by the invention has good low-temperature charging capability and high-temperature storage 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] Secondary batteries, such as lithium-ion batteries, have significant advantages such as high energy density, miniaturization, and light weight, and are widely used in mobile phones, laptops, tablets, drones, electric vehicles, power tools, power storage systems, etc. Generally, a lithium-ion battery consists of a positive electrode sheet, a negative electrode sheet, and an electrolyte. The electrolyte is responsible for maintaining ion transport between the positive electrode sheet and the negative electrode sheet, and is also responsible for maintaining a stable interface to enable the lithium-ion battery to work stably. At present, users also put forward higher and higher requirements for the performance of secondary batteries, such as low-temperature charging ability and high-temperature storage performance. Therefore, there is an urgent need to provide a secondary battery with good low-temperature charging ability and high-temperature storage performance to meet the increasing usage needs of people. Summary of the Invention

[0003] The purpose of the present application is to provide a secondary battery and an electronic device to improve the low-temperature charging ability and high-temperature storage performance of the secondary battery. The specific technical solutions are as follows:

[0004] It should be noted that in the summary of the invention of the present application, a lithium-ion battery is taken as an example of the secondary battery to explain the present application, but the secondary battery of the present application is not limited to lithium-ion batteries.

[0005] In the first aspect of the present application, a secondary battery is provided, which includes a negative electrode sheet and an electrolyte. The electrolyte includes a compound represented by Formula I:

[0006]

[0007] Wherein, R1 is selected from a fluorine atom, a C1-C5 alkyl group that is fully or partially substituted by fluorine, R2 and R3 are each independently selected from a C1-C5 alkyl group, R2 and R3 can be connected by a single bond to form a ring, based on the mass of the electrolyte, the mass percentage of the compound shown in formula I is W1%, 2 ≤ W1 ≤ 50; the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector, the negative electrode material layer contains silicon element, based on the mass of the negative electrode material layer, the mass percentage of silicon element is x%, x ≤ 25; the thickness of the negative electrode material layer is D μm, the surface of the negative electrode material layer is provided with a plurality of recesses, the depth of the recess is d μm, the depth of the recess relative to the negative electrode material layer is P, P = d / D, P ≥ 0.1; 0.4 ≤ W1 / (x×P) ≤ 62.5. By synergistically controlling the mass percentage of the compound shown in formula I in the electrolyte and the mass percentage of silicon element in the negative electrode material layer, the toughness and stability of the solid electrolyte interface film can be improved, thereby improving the high-temperature stability of the secondary battery; by synergistically controlling the mass percentage of the compound shown in formula I in the electrolyte and the depth of the recess relative to the negative electrode material layer, the channels for the electrolyte to flow in the negative electrode sheet can be enriched, the flow of the electrolyte can be accelerated, the wettability of the electrolyte to the negative electrode sheet can be improved, and at the same time, the stability of the electrolyte system can be improved, the exothermic oxidation decomposition of other organic solvents in the electrolyte can be reduced, and the self-heat generation of the secondary battery can be reduced, thereby improving the low-temperature charging ability and high-temperature storage performance of the secondary battery; by synergistically controlling the mass percentage of silicon element in the negative electrode material layer and the depth of the recess relative to the negative electrode material layer, the mechanical strength of the negative electrode sheet can be improved, thereby improving the high-temperature stability of the secondary battery. By regulating the values of W1, x, P, and W1 / (x×P) within the scope of this application, the low-temperature charging ability and high-temperature storage performance of the secondary battery can be improved, and at the same time, the energy density is relatively high.

[0008] In some embodiments of the present application, 5 ≤ W1 ≤ 30, preferably, 10 ≤ W1 ≤ 20. By regulating the value of W1 within the above range, it is beneficial to further improve the low-temperature charging ability and high-temperature storage performance of the secondary battery.

[0009] In some embodiments of the present application, the compound shown in formula I includes at least one of the following compounds:

[0010]

[0011]

[0012] The compound shown in Formula I above has good high-temperature stability and synergistically acts with the negative electrode sheet, which is beneficial to further improve the low-temperature charging ability and high-temperature storage performance of the secondary battery; on the other hand, when the electrolyte contains the compound shown in Formula I, a more stable electrolyte system can be provided, reducing the exothermic oxidation decomposition of other organic solvents in the electrolyte, reducing the self-heat generation of the secondary battery, and increasing the thermal runaway temperature threshold, thereby being beneficial to further improve the safety performance of the secondary battery.

[0013] In some embodiments of the present application, the minimum distance between two adjacent recesses is L μm, where 50 ≤ L ≤ 300. By adjusting the value of L within the scope of the present application, the recesses can have an appropriate distribution density, which is beneficial to the processing and preparation of the secondary battery. At the same time, the role of the recesses can be better exerted, thus being beneficial to improving the low-temperature charging ability of the secondary battery, while having good high-temperature storage performance and safety performance.

[0014] In some embodiments of the present application, 0.05 ≤ W1 / L ≤ 0.25. By adjusting the value of W1 / L within the scope of the present application, the electrolyte including the compound shown in Formula I and the negative electrode sheet synergistically act, which is beneficial to improving the low-temperature charging ability, high-temperature storage performance and safety performance of the secondary battery.

[0015] In some embodiments of the present application, 100 ≤ D ≤ 400. By adjusting the value of D within the scope of the present application, it is beneficial to improve the volume energy density of the secondary battery, and it is also beneficial to improve the low-temperature charging ability of the secondary battery, while having good high-temperature storage performance and safety performance.

[0016] In some embodiments of the present application, 0.1 ≤ P ≤ 0.5. By adjusting the value of P within the scope of the present application, it is beneficial to improve the volume energy density of the secondary battery, and it is also beneficial to improve the low-temperature charging ability and high-temperature storage performance of the secondary battery.

[0017] In some embodiments of the present application, 4 ≤ x ≤ 25. By adjusting the value of x within the scope of the present application, it is beneficial to improve the volume energy density of the secondary battery, and it is also beneficial to improve the low-temperature charging ability and high-temperature storage performance of the secondary battery.

[0018] In some embodiments of the present application, when observed along the thickness direction of the negative electrode sheet, the recess is quadrilateral, and the length of the shortest side of the quadrilateral is D1 mm, where 0.02 ≤ D1 ≤ 0.5. By adjusting the value of D1 within the scope of the present application, the processing and preparation of the negative electrode sheet are good, and it synergistically acts with the electrolyte including the compound shown in Formula I, which is beneficial to improving the low-temperature charging ability of the secondary battery, while having good high-temperature storage performance and safety performance.

[0019] In some embodiments of the present application, when observed in the thickness direction of the negative electrode tab, the concave portion is quadrilateral, and the sum of the areas of the quadrilaterals is S1 mm 2 , and the area of the negative electrode material layer is S2 mm 2 , 0.1 ≤ S1 / S2 ≤ 0.8. By regulating the value of S1 / S2 within the scope of the present application, the area ratio of the concave portion can be within a suitable range, which is beneficial to exert the role of the concave portion, thereby being beneficial to improving the low-temperature charging ability of the secondary battery, and having good high-temperature storage performance and safety performance at the same time.

[0020] In some embodiments of the present application, the electrolyte further includes a first component, and the first component includes at least one of fluorinated ethylene carbonate, difluorinated ethylene carbonate, vinylene carbonate or ethylene ethyl carbonate; based on the mass of the electrolyte, the mass ratio of the first component is W2%, 0.5 ≤ W2 ≤ 15, preferably, 1 ≤ W2 ≤ 8. Selecting an electrolyte including the first component of the above types and regulating the mass ratio W2% of the first component within the above range is beneficial to improving the low-temperature charging ability, high-temperature storage performance and safety performance of the secondary battery.

[0021] The second aspect of the present application provides an electronic device, which includes the secondary battery in any of the above embodiments. The electronic device of the present application has good use performance.

[0022] Advantages of the present application:

[0023] The present application provides a secondary battery and an electronic device. The secondary battery includes a negative electrode plate and an electrolyte. The electrolyte includes a compound represented by Formula I. Based on the mass of the electrolyte, the mass percentage of the compound represented by Formula I is W1%, where 2 ≤ W1 ≤ 50. The negative electrode plate includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The negative electrode material layer contains silicon element. Based on the mass of the negative electrode material layer, the mass percentage of the silicon element is x%, where x ≤ 25. The thickness of the negative electrode material layer is D μm. A plurality of recesses are provided on the surface of the negative electrode material layer, and the depth of the recesses is d μm. The depth of the recesses relative to the negative electrode material layer is P, and P = d / D, where P ≥ 0.1. 0.4 ≤ W1 / (x × P) ≤ 62.5. By synergistically controlling the mass percentage of the compound represented by Formula I in the electrolyte and the mass percentage of the silicon element in the negative electrode material layer, the toughness and stability of the solid electrolyte interface film can be improved, thereby improving the high-temperature stability of the secondary battery. By synergistically controlling the mass percentage of the compound represented by Formula I in the electrolyte and the depth of the recesses relative to the negative electrode material layer, the channels for the electrolyte to flow in the negative electrode plate can be enriched, the flow of the electrolyte can be accelerated, the wettability of the electrolyte to the negative electrode plate can be improved, and at the same time, the stability of the electrolyte system can be improved, the exothermic oxidation decomposition of other organic solvents in the electrolyte can be reduced, and the self-heat generation of the secondary battery can be reduced, thereby improving the low-temperature charging ability and high-temperature storage performance of the secondary battery. By synergistically controlling the mass percentage of the silicon element in the negative electrode material layer and the depth of the recesses relative to the negative electrode material layer, the mechanical strength of the negative electrode plate can be improved, thereby improving the high-temperature stability of the secondary battery. By adjusting the values of W1, x, P, and W1 / (x × P) within the scope of the present application, the low-temperature charging ability and high-temperature storage performance of the secondary battery can be improved, and at the same time, the energy density is relatively high.

[0024] Of course, it is not necessary for any product or method implementing the present application to achieve all the above-mentioned advantages simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and those of ordinary skill in the art can also obtain other embodiments according to these drawings.

[0026] Figure 1 It is a schematic structural diagram of a negative electrode plate along its thickness direction according to an embodiment of the present application;

[0027] Figure 2 It is a schematic structural diagram of a single-sided negative electrode material layer according to an embodiment of the present application;

[0028] Figure 3 It is a schematic structural diagram of a single-sided negative electrode material layer according to another embodiment of the present application.

[0029] Reference numerals: negative electrode plate 100, negative current collector 110, negative electrode material layer 120, recess 121. Detailed implementation manners

[0030] Next, the technical solutions in the present application will be clearly and completely described in conjunction with the embodiments of the present application and the drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0031] It should be noted that in the specific implementation manners 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. The specific technical solutions are as follows:

[0032] In a first aspect of the present application, a secondary battery is provided, which includes a negative electrode plate and an electrolyte. The electrolyte includes a compound represented by Formula I:

[0033]

[0034] Among them, R1 is selected from a fluorine atom, a C1-C5 alkyl group that is fully or partially substituted by fluorine, R2 and R3 are each independently selected from a C1-C5 alkyl group, R2 and R3 can be connected by a single bond to form a ring. Based on the mass of the electrolyte, the mass ratio of the compound shown in Formula I is W1%, 2 ≤ W1 ≤ 50, preferably, 5 ≤ W1 ≤ 30, more preferably, 10 ≤ W1 ≤ 20. For example, the value of W1 can be 2, 5, 8, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 22, 25, 28, 30, 32, 35, 38, 40, 42, 45, 48, 50 or a range composed of any two of these values. The negative electrode plate includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The negative electrode material layer contains silicon element. Based on the mass of the negative electrode material layer, the mass ratio of the silicon element is x%, x ≤ 25, preferably, 4 ≤ x ≤ 25. For example, the value of x can be 4, 6, 8, 10, 12, 14, 15, 17, 18, 19, 20, 22, 25 or a range composed of any two of these values. The thickness of the negative electrode material layer is D μm, and a plurality of recesses are provided on the surface of the negative electrode material layer. The depth of the recess is d μm, P = d / D, P ≥ 0.1, preferably, 0.1 ≤ P ≤ 0.5. For example, the value of P can be 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50 or a range composed of any two of these values. 0.4 ≤ W1 / (x × P) ≤ 62.5. For example, the value of W1 / (x × P) can be 0.4, 2, 5, 8, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 62.5 or a range composed of any two of these values.

[0035] The negative electrode material layer of the present application contains silicon element, and the mass percentage x% of silicon element in the negative electrode material layer is regulated within the scope of the present application. The silicon element can be derived from silicon-based particles, and the silicon-based particles have a high specific capacity, which can improve the energy density of the secondary battery. The compound shown in Formula I contained in the electrolyte has a relatively low highest occupied molecular orbital (HOMO orbital energy level), so it has good antioxidant ability, can reduce the gas generation during the storage of the secondary battery at high temperature, improve the high-temperature stability of the electrolyte. At the same time, the compound shown in Formula I has good interfacial compatibility with the silicon-based material, and also has appropriate lithium-ion solvation ability, good solubility in lithium salts, and is more likely to desolvate during the process of lithium-ion insertion and extraction at the interface, so as to improve the high-temperature storage performance of the secondary battery. However, the viscosity of the compound shown in Formula I is usually relatively large. When the electrolyte contains the compound shown in Formula I, it will affect its fluidity and the wettability of the positive electrode plate and the negative electrode plate, thus affecting the low-temperature charging ability of the secondary battery. In the present application, by providing a plurality of recesses on the surface of the negative electrode material layer and regulating the value of P within the scope of the present application, a flow channel for the electrolyte can be provided, the flow of the electrolyte can be accelerated, and the wettability of the electrolyte on the negative electrode plate can be improved, thereby improving the low-temperature charging ability of the secondary battery. On the other hand, when the electrolyte contains the compound shown in Formula I, a more stable electrolyte system can be provided, the exothermic oxidation decomposition of other organic solvents in the electrolyte can be reduced, and it can cooperate with the negative electrode plate of the present application to reduce the self-heat generation of the secondary battery, improve the thermal runaway temperature threshold, and thus improve the safety performance of the secondary battery. By synergistically controlling the mass percentage of the compound shown in Formula I in the electrolyte and the mass percentage of silicon element in the negative electrode material layer, the toughness and stability of the solid electrolyte interface film can be improved, thereby improving the high-temperature stability of the secondary battery; by synergistically controlling the mass percentage of the compound shown in Formula I in the electrolyte and the depth of the recess relative to the negative electrode material layer, the flow channels of the electrolyte in the negative electrode plate can be enriched, the flow of the electrolyte can be accelerated, the wettability of the electrolyte on the negative electrode plate can be improved, and at the same time, the stability of the electrolyte system can be improved, the exothermic oxidation decomposition of other organic solvents in the electrolyte can be reduced, and the self-heat generation of the secondary battery can be reduced, thereby improving the low-temperature charging ability and high-temperature storage performance of the secondary battery; by synergistically controlling the mass percentage of silicon element in the negative electrode material layer and the depth of the recess relative to the negative electrode material layer, the mechanical strength of the negative electrode plate can be improved, thereby improving the high-temperature stability of the secondary battery. In the present application, by regulating the values of W1, x, P, and W1 / (x×P) within the scope of the present application, the low-temperature charging ability and high-temperature storage performance of the secondary battery can be improved, and at the same time, the energy density is relatively high. In the present application, low temperature means the temperature is less than or equal to 0 °C, and high temperature means the temperature is greater than or equal to 45 °C.

[0036] When the value of W1 is too small, for example, less than 2, the content of the compound shown in Formula I is too small, the gas generation of the secondary battery during storage at high temperature is relatively large, the oxidation and heat release of other organic solvents in the electrolyte are relatively high, and the wettability of the electrolyte to the positive electrode sheet and the negative electrode sheet is poor, resulting in a poor effect on improving the high-temperature storage performance, low-temperature charging ability, and safety performance of the secondary battery; when the value of W1 is too large, for example, greater than 50, the content of the compound shown in Formula I is too large, the viscosity of the electrolyte is too large, and the wettability to the positive electrode sheet and the negative electrode sheet is poor, affecting the low-temperature charging ability and high-temperature storage performance of the secondary battery. When the value of x is too large, for example, greater than 25, the expansion of the negative electrode material layer after lithium intercalation is relatively large, affecting the high-temperature storage performance, low-temperature charging ability, and safety performance of the secondary battery. When the value of P is too small, for example, less than 0.1, the effect of improving the fluidity of the electrolyte and the wettability to the negative electrode sheet is poor, affecting the low-temperature charging ability and high-temperature storage performance of the secondary battery. When the value of W1 / (x×P) is too small, for example, less than 0.4, it is difficult to exert the synergistic effect between the electrolyte and the negative electrode sheet, and the compound shown in Formula I is difficult to act on the concave portions on the surface of the negative electrode material layer, resulting in a small improvement in the low-temperature charging ability, high-temperature storage performance, and safety performance of the secondary battery; when the value of W1 / (x×P) is too large, for example, greater than 62.5, the compound shown in Formula I easily undergoes excessive reaction in the concave portions on the surface of the negative electrode material layer, the wettability of the electrolyte to the positive electrode sheet and the negative electrode sheet is poor, and the energy density of the secondary battery is too low, affecting the low-temperature charging ability, high-temperature storage performance, and safety performance of the secondary battery.

[0037] Exemplarily, as Figure 1 shown, define the longitudinal direction of the negative electrode sheet itself as X and the thickness direction as Y. The negative electrode sheet usually has a long side and a short side, and the above longitudinal direction is the extension direction of the long side of the negative electrode sheet. It should be understood that the above definition of the direction is for the purpose of conveniently describing the present application. The negative electrode sheet 100 includes a negative electrode current collector 110 and negative electrode material layers 120 provided on two surfaces of the negative electrode current collector 110. The thickness of the negative electrode material layer 120 is D μm, and a plurality of concave portions 121 are provided on the surface of the negative electrode material layer 120, and the depth of the concave portions 121 is d μm.

[0038] In some embodiments, R1 is selected from a fluorine atom, difluoromethyl, trifluoromethyl, tetrafluoroethyl, pentafluoroethyl, heptafluoropropyl, or nonafluorobutyl; R2 is selected from methyl, ethyl, propyl, or butyl; R3 is selected from methyl, ethyl, propyl, or butyl. The electrolyte includes the compound shown in Formula I containing the groups within the above ranges, which is beneficial to improving the low-temperature charging ability, high-temperature storage performance, and safety performance of the secondary battery.

[0039] In some embodiments of the present application, the compound shown in Formula I includes at least one of the following compounds:

[0040]

[0041]

[0042] The compound shown in the above formula I has good high-temperature stability, good interfacial compatibility with silicon-based materials, and suitable lithium-ion solvation ability. While having good solubility in lithium salts, it is easier to desolvate during the process of lithium-ion insertion and extraction at the interface, which is conducive to further improving the high-temperature storage performance of secondary batteries. On the other hand, when the electrolyte contains the compound shown in the above formula I, a more stable electrolyte system can be provided, thereby reducing the exothermic oxidation decomposition of other organic solvents in the electrolyte, reducing the self-heat generation of secondary batteries, and increasing the thermal runaway temperature threshold, which is conducive to further improving the safety performance of secondary batteries.

[0043] In some embodiments of the present application, the minimum distance between two adjacent recesses is L μm, and 50 ≤ L ≤ 300. For example, the value of L can be 50, 80, 100, 120, 150, 180, 200, 220, 250, 280, 300 or a range composed of any two of these numerical values. By adjusting the value of L within the scope of the present application, the recesses can have a suitable distribution density, which is conducive to the processing and preparation of secondary batteries. At the same time, the role of the recesses can be better exerted, and they can cooperate with the electrolyte including the compound shown in formula I, which is conducive to improving the low-temperature charging ability of secondary batteries, while having good high-temperature storage performance and safety performance. In the present application, the minimum distances between two adjacent recesses can be the same or different, as long as the purpose of the present application can be achieved.

[0044] In some embodiments of the present application, 0.05 ≤ W1 / L ≤ 0.25. For example, the value of W1 / L can be 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25 or a range composed of any two of these numerical values. By adjusting the value of W1 / L within the scope of the present application, the electrolyte including the compound shown in formula I and the negative electrode sheet cooperate with each other, which is conducive to accelerating the flow of the electrolyte, improving the wettability of the electrolyte to the positive electrode sheet and the negative electrode sheet. At the same time, the electrolyte has good high-temperature stability, can also reduce the exothermic oxidation decomposition of other organic solvents in the electrolyte, reduce the self-heat generation of secondary batteries, and increase the thermal runaway temperature threshold, which is conducive to improving the low-temperature charging ability, high-temperature storage performance and safety performance of secondary batteries.

[0045] In some embodiments of the present application, 100 ≤ D ≤ 400. For example, the value of D can be 100, 120, 150, 180, 200, 220, 250, 270, 300, 320, 350, 380, 400, or a range composed of any two of these numerical values. By adjusting the value of D within the scope of the present application, it is beneficial to improve the volumetric energy density of the secondary battery, and at the same time, the kinetic performance of the secondary battery is good, which is conducive to improving the low-temperature charging ability of the secondary battery, and at the same time, the high-temperature storage performance and safety performance are good.

[0046] In some embodiments, 10 ≤ d ≤ 200. For example, the value of d can be 10, 20, 30, 40, 50, 60, 80, 100, 120, 140, 160, 180, 200, or a range composed of any two of these numerical values.

[0047] In some embodiments of the present application, when observed along the thickness direction of the negative electrode sheet, the concave portion is quadrilateral, and the length of the shortest side of the quadrilateral is D1 mm, 0.02 ≤ D1 ≤ 0.5. For example, the value of D1 can be 0.02, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, or a range composed of any two of these numerical values. By adjusting the value of D1 within the scope of the present application, the processing and preparation of the negative electrode sheet are good, which is also beneficial to accelerating the flow of the electrolyte, improving the wettability of the electrolyte to the positive electrode sheet and the negative electrode sheet, and can cooperate with the electrolyte including the compound shown in Formula I, so as to be beneficial to improving the low-temperature charging ability of the secondary battery, and at the same time, the high-temperature storage performance and safety performance are good.

[0048] In the present application, multiple concave portions can be distributed in a striped shape, multiple concave portions can be arranged along the width direction of the negative electrode sheet, or multiple concave portions can be arranged along the length direction of the negative electrode sheet, or multiple concave portions can be arranged along both the width direction and the length direction of the negative electrode sheet at the same time. In the present application, when multiple concave portions are distributed in a striped shape, the widths of the strips of the orthographic projections of two adjacent concave portions can be the same or different, and the length D1 of the shortest side of the quadrilateral is the maximum value of the above orthographic projection width, and the lengths of the strips can be the same or different, as long as the object of the present application can be achieved. The present application does not particularly limit the length of the strip, which can be designed according to the size of the negative electrode sheet, as long as the object of the present application can be achieved.

[0049] Specifically, in some embodiments, such as Figure 2As shown, a plurality of recesses 121 are provided on the surface of the negative electrode material layer 120. The plurality of recesses 121 are distributed in a striped pattern. Moreover, one side of the orthographic projection of a single recess 121 is parallel to one side of the negative electrode tab 100. The shape of the orthographic projection of a single recess 121 is a narrow and long rectangle, the width of the rectangle is D1, and the minimum distance between adjacent rectangles is L. In some other embodiments, as Figure 3 shown, the plurality of recesses 121 are distributed in a striped pattern. Moreover, there is an included angle between one side of the orthographic projection of a single recess 121 and one side of the negative electrode tab 100. The shape of the orthographic projection of a single recess 121 is a narrow and long rectangle, the width of the rectangle is D1, the minimum distance between adjacent rectangles is L, and the lengths of adjacent rectangles are different. The present application does not particularly limit the size of the above-mentioned included angle, as long as the purpose of the present application can be achieved. Exemplarily, the included angle is 25° to 65°. Figure 2 and Figure 3 The size, the number and the shape of the recesses in

[0050] are only examples and do not limit the protection scope of the present application. 2 In some embodiments of the present application, when observed in the thickness direction of the negative electrode tab, the recesses are quadrilateral, and the sum of the areas of the quadrilaterals is S1 mm 2 , and the area of the negative electrode material layer is S2 mm

[0051] The present application does not particularly limit the preparation method of the negative electrode tab, as long as the purpose of the present application can be achieved. For example, the preparation of the negative electrode tab may include, but is not limited to, the following steps: providing a negative electrode material layer on one surface of the negative electrode current collector, then repeatedly providing a negative electrode material layer on the other surface of the negative electrode current collector, and then etching recesses on the surface of the double-sided negative electrode material layer by a laser process to obtain the negative electrode tab. The present application does not particularly limit the method of regulating d, L, D1, and S1, as long as the purpose of the present application can be achieved. For example, the sizes of d, L, D1, and S1 can be regulated by regulating the parameters of the laser process.

[0052] In some embodiments of the present application, the electrolyte further includes a first component, and the first component includes at least one of vinylene carbonate, difluoro vinylene carbonate, fluoroethylene carbonate or ethylene ethyl carbonate. Selecting an electrolyte including the first component of the above types is conducive to forming a relatively dense SEI film on the surface of the negative electrode, reducing the side reaction between the negative electrode active material and the electrolyte, enabling the secondary battery to have a longer cycle life, improving the cycle stability of the secondary battery, and being able to cooperate with the negative electrode plate, thereby facilitating the improvement of the low-temperature charging ability, high-temperature storage performance and safety performance of the secondary battery.

[0053] In some embodiments of the present application, based on the mass of the electrolyte, the mass ratio of the first component is W2%, and 0.5 ≤ W2 ≤ 15. Preferably, 1 ≤ W2 ≤ 8. For example, the value of W2 can be 0.5, 0.7, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or a range composed of any two of these numerical values. By adjusting the mass ratio W2% of the first component within the above range, it is conducive to forming a relatively dense SEI film on the surface of the negative electrode, reducing the side reaction between the negative electrode active material and the electrolyte, enabling the secondary battery to have a longer cycle life, improving the cycle stability of the secondary battery, and being able to cooperate with the negative electrode plate, thereby facilitating the improvement of the low-temperature charging ability, high-temperature storage performance and safety performance of the secondary battery.

[0054] In the present application, the electrolyte further includes a lithium salt and other non-aqueous solvents. The present application places no particular limitation on the lithium salt, as long as the object of the present application can be achieved. For example, the lithium salt may include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB) or lithium difluoroborate. The present application places no particular limitation on the content of the lithium salt in the electrolyte, as long as the object of the present application can be achieved. For example, based on the mass of the electrolyte, the mass ratio of the lithium salt is 8% to 30%.

[0055] 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.

[0056] 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 carbonate compounds may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), or butylene carbonate (BC). The fluorinated carbonate compounds may include, but are not limited to, at least one of 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, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. The present application does not particularly limit the content of other non-aqueous solvents in the electrolyte, as long as the object of the present application can be achieved. For example, based on the mass of the electrolyte, the mass ratio of other non-aqueous solvents is 5% to 89.5%.

[0057] In some embodiments, the electrolyte may include the compound shown in Formula I, a lithium salt, and other non-aqueous solvents. The mass ratios of the compound shown in Formula I and the lithium salt are as described above, and the mass ratio of other non-aqueous solvents is 20% to 89.5%. The secondary battery including the above electrolyte has good low-temperature charging ability, high-temperature storage performance, and safety performance.

[0058] In some embodiments, the electrolyte may include the compound shown in Formula I, a first component, a lithium salt, and other non-aqueous solvents. The mass ratios of the compound shown in Formula I, the first component, the lithium salt, and other non-aqueous solvents are as described above. The secondary battery including the above electrolyte has good low-temperature charging ability, high-temperature storage performance, and safety performance.

[0059] In the present application, the negative electrode plate includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The statement that "the negative electrode plate includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or can be disposed on both surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the negative electrode current collector, or a partial area of the surface of the negative electrode current collector. There is no special limitation in the present application, as long as the purpose of the present application can be achieved.

[0060] In the present application, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes silicon-based particles. The silicon-based particles include at least one of pure silicon, silicon alloy, silicon-carbon composite material, or silicon-oxygen composite material (SiOx(0 < x ≤ 2)). Among them, the silicon alloy can include at least one of lithium-silicon alloy, silicon-germanium alloy, silicon-tin alloy, or silicon-aluminum alloy.

[0061] In the present application, the mass percentage x% of silicon element in the negative electrode material layer can be adjusted by controlling the mass percentage of silicon-based particles in the negative electrode material layer and the mass percentage of silicon element in the silicon-based particles. For example, when other conditions remain unchanged, the larger the mass percentage of silicon-based particles in the negative electrode material layer, the larger x%; the smaller the mass percentage of silicon-based particles in the negative electrode material layer, the smaller x%. When other conditions remain unchanged, the larger the mass percentage of silicon element in the silicon-based particles, the larger x%; the smaller the mass percentage of silicon element in the silicon-based particles, the smaller x%.

[0062] The negative electrode material layer further includes a negative electrode active material other than the silicon-based particles. There is no special limitation on the type of the negative electrode active material other than the silicon-based particles in the present application, as long as the purpose of the present application can be achieved. For example, the negative electrode active material other than the silicon-based particles can include at least one of natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12 , Li-Al alloy, or metallic lithium.

[0063] The negative electrode material layer of the present application further includes a negative electrode conductive agent and a negative electrode binder. The present application places no particular limitation on the negative electrode conductive agent and the negative electrode binder in the negative electrode material layer, as long as the object of the present application can be achieved. For example, the negative electrode conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials, or conductive polymers. The conductive carbon black may include, but is not limited to, at least one of acetylene black or Ketjen black. The above carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above carbon fibers may include, but is not limited to, vapor-grown carbon fibers (VGCF) and / or nanofibers. The above metal materials may include, but are not limited to, metal powders and / or metal fibers. Specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above conductive polymers may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. For example, the negative electrode binder may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamideimide, styrene-butadiene rubber, or polyvinylidene fluoride. The present application places no particular limitation on the mass ratio of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder in the negative electrode material layer. Those skilled in the art may select according to actual needs as long as the object of the present application can be achieved.

[0064] The present application places 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 a 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, or a titanium-copper composite current collector, etc. The present application places 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.

[0065] In the present application, the secondary battery further includes a positive electrode plate. The positive electrode plate includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector. The above "positive electrode material layer provided on at least one surface of the positive electrode current collector" means that the positive electrode material layer may be provided on one surface of the positive electrode current collector along its own thickness direction, or may be provided on both surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here may be the entire area of the positive electrode current collector or a partial area of the positive electrode current collector. The present application places no particular limitation as long as the object of the present application can be achieved.

[0066] The present application places no particular limitation on the positive electrode current collector, as long as the object 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.

[0067] The positive electrode material layer of the present application includes a positive electrode active material, and the positive electrode active material includes a substance capable of reversibly inserting and extracting active ions such as lithium ions. The positive electrode material layer can be one layer or multiple layers, and each layer in the multiple positive electrode material layers can contain the same or different positive electrode active materials. There is no particular limitation on the positive electrode active material in the present application as long as the purpose of the present application can be achieved. For example, the positive electrode active material can 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, or lithium titanate. The above lithium nickel cobalt manganese oxide can include LiNi 0.95 Co 0.03 Mn 0.02 O2 (Ni95), LiNi 0.91 Co 0.03 Mn 0.06 O2 (Ni91), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523) or LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM111) or at least one of them. In the present application, the positive electrode active material can also contain non-metallic elements. For example, the non-metallic elements include at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur.

[0068] The positive electrode material layer of the present application further includes a positive electrode conductive agent and a positive electrode binder. There is no particular limitation on the positive electrode conductive agent and the positive electrode binder in the positive electrode material layer of the present application as long as the purpose of the present application can be achieved. For example, the positive electrode conductive agent can be at least one of the above negative electrode conductive agents, and the positive electrode binder can be at least one of the above negative electrode binders. There is no particular limitation on the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in the positive electrode material layer of the present application, and those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0069] In the present application, there is 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 5 μm to 20 μm, preferably 6 μm to 18 μm; the thickness of the single-sided positive electrode material layer is 30 μm to 120 μm.

[0070] 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 it can achieve the purpose of the present application. 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.

[0071] In some embodiments, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric 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.

[0072] 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.

[0073] In some embodiments, the inorganic layer includes inorganic particles and an inorganic layer 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 inorganic layer binder in the present application. For example, it may be at least one of the above-mentioned negative electrode binders. In some embodiments, 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).

[0074] In the present application, there is no particular limitation on the thickness of the separator, as long as it can achieve the purpose of the present application. For example, the thickness of the separator may be 3 μm to 30 μm.

[0075] 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-mentioned 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 the purpose of the present application can be achieved. 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 the purpose of the present application can be achieved. The flexible housing can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0076] The secondary battery of the present application is not particularly limited, and it can include any device that undergoes an electrochemical reaction. In some embodiments, the secondary battery can include, but is not limited to: lithium-ion secondary batteries (lithium-ion batteries), lithium polymer secondary batteries, or lithium-ion polymer secondary batteries, etc.

[0077] The preparation process of the secondary battery of the present application is well-known to those skilled in the art, and 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 winding, folding, etc. according to needs to obtain a wound structure electrode assembly, placing the electrode assembly into the housing, injecting the electrolyte into the housing and sealing it to obtain the 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 structure electrode assembly, placing the electrode assembly into the housing, injecting the electrolyte into the housing and sealing it to obtain the secondary battery. In addition, an overcurrent protection element, a guide plate, etc. can also be placed in the housing as needed to prevent the pressure inside the secondary battery from rising and overcharging / discharging.

[0078] The second aspect of the present application provides an electronic device, which includes the secondary battery in any of the above embodiments. The electronic device of the present application has good performance in use.

[0079] 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, the electronic device can include, but is not limited to: laptop computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, portable cleaners, portable CD players, mini discs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, motorized bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0080] Examples

[0081] Hereinafter, examples and comparative examples are given to illustrate the embodiments of the present application more specifically. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0082] Testing methods and equipment:

[0083] Testing the mass percentage x% of silicon element based on the mass of the negative electrode material layer

[0084] Use a scanning electron microscope (SEM) to observe the surface of the negative electrode plate perpendicular to the thickness direction in the backscattering mode, and use an energy dispersive X-ray spectrometer (EDS) to scan the above surface of the negative electrode plate to obtain the mass percentage x% of silicon element based on the mass of the negative electrode material layer.

[0085] Testing d, L, D, D1, S1 / S2

[0086] The cross-section of the negative electrode plate along the thickness direction is ion-polished to obtain the cross-section of the negative electrode plate, and it is observed and measured under a scanning electron microscope to obtain the depth d of the concave part and the thickness D of the negative electrode material layer. After measuring 10 values respectively and taking the average, d and D are obtained.

[0087] Under a VHX5000 microscope, the magnification is set to 50 to 200 times, and the surface of the negative electrode material layer is observed along the thickness direction of the negative electrode plate and photographed. The area of the negative electrode material layer in the photo is recorded as S2, and the sum of the areas of the quadrilaterals (when observing along the thickness direction of the negative electrode plate, the concave part is quadrilateral) in the photo is recorded as S1. The length of the shortest side of the quadrilateral in the photo is recorded as D1, and the minimum distance between two adjacent quadrilaterals is recorded as L.

[0088] Low-temperature charging capacity test

[0089] Transfer the lithium-ion battery into a 0°C constant temperature oven. After placing it for 120 min, charge it at a constant current of 1C to 4.5V, then charge it at a constant voltage of 4.5V to 0.025C, let it rest for 5 minutes, and then discharge it at a constant current of 0.5C to 3V and let it rest for 60 minutes. After performing 10 cycles like this, charge the lithium-ion battery at a constant current of 1C to 4.5V, disassemble the lithium-ion battery to obtain the negative electrode plate, and observe the lithium deposition situation on the surface of the negative electrode plate.

[0090] Determination of lithium deposition degree: The degree of lithium deposition is determined according to the state of the negative electrode plate under full charge and disassembled. The non-lithium-deposited area on the surface of the negative electrode plate is golden yellow, and the lithium-deposited area is gray. Based on the total area of the single-sided negative electrode material layer, when the overall negative electrode plate shows golden yellow and the area showing gray is <1%, it is determined that there is no lithium deposition; when most of the negative electrode plate is golden yellow, but there are some areas showing gray, and the gray area is ≥1% and <10%, it is determined that there is slight lithium deposition; when some parts of the negative electrode plate have significant gray, but some areas can still be observed as golden yellow, and the area showing gray is ≥10% and <50%, it is determined that there is moderate lithium deposition; when most of the negative electrode plate shows gray, and the gray area is ≥50%, it is determined that there is severe lithium deposition.

[0091] High-temperature storage performance test

[0092] Place the lithium-ion battery in a constant-temperature environment of 25°C and let it stand for 30 minutes to make the lithium-ion battery reach a constant temperature. Then charge the lithium-ion battery at a constant current of 0.7C to 4.5V, and then charge it at a constant voltage of 4.5V until the current is 0.025C, and record the thickness of the lithium-ion battery, which is recorded as the initial thickness. Transfer the lithium-ion battery to a constant-temperature oven at 60°C for storage for 30 days. During this period, test and record the thickness of the lithium-ion battery every 6 days. Record the test thickness after 30 days as the storage thickness. Calculate the thickness expansion rate of the lithium-ion battery and use it as an index to evaluate the gas generation amount of the lithium-ion battery during high-temperature storage. High-temperature storage thickness expansion rate (%) = (storage thickness - initial thickness) / initial thickness × 100%.

[0093] Example 1-1

[0094] <Preparation of electrolyte>

[0095] In an argon atmosphere glove box with a water content of less than 10 ppm, diethyl carbonate and ethylene carbonate are mixed in a mass ratio of 1:1 to obtain a basic solvent. Then, the compound shown in formula I (formula I-1) and lithium salt lithium hexafluorophosphate (LiPF6) are added to the basic solvent and mixed evenly to obtain an electrolyte. Among them, based on the mass of the electrolyte, the mass ratio of the lithium salt LiPF6 is 12.5%, and the mass ratio W1% of the compound shown in formula I is shown in Table 1, and the balance is the basic solvent.

[0096] <Preparation of negative electrode plate>

[0097] Mix the silicon-carbon composite as the negative active material, artificial graphite as the negative active material, acetylene black as the negative conductive agent, and styrene-butadiene rubber as the negative binder according to a mass ratio of 37.5∶59.9∶1.4∶1.2. Add deionized water as the solvent and formulate it into a slurry with a solid content of 45 wt%. After stirring evenly with a vacuum mixer, the negative electrode slurry is obtained. The negative electrode slurry is 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 plate with a single-sided coated negative electrode material layer. Then repeat the above steps on the other surface of the copper foil to obtain a negative electrode plate with a double-sided coated negative electrode material layer. After drying at 120 °C, it is cold-pressed, and then concave portions are etched on the surface of the double-sided negative electrode material layer through laser processing technology. After that, it is cut into pieces and the tabs are welded to obtain a negative electrode plate with a specification of 78 mm × 875 mm for use. Among them, the tap density of the negative electrode material layer is 1.7 g / cm 3 , the thickness D of the negative electrode material layer, the depth d of the concave portion, the minimum distance L between two adjacent concave portions, D1, S1 / S2, and x% are shown in Table 1.

[0098] <Preparation of the positive electrode plate>

[0099] Mix the lithium cobalt oxide as the positive active material, conductive carbon black (Super P) as the positive conductive agent, and polyvinylidene fluoride (PVDF) as the positive binder according to a mass ratio of 97∶1.4∶1.6. Add N-methylpyrrolidone (NMP) as the solvent and formulate it into a slurry with a solid content of 75 wt%. After stirring evenly with a vacuum mixer, the positive electrode slurry is obtained. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10 μm and dried at 85 °C to obtain a positive electrode plate with a single-sided coated positive electrode material layer. After that, repeat the above steps on the other surface of the positive electrode plate to obtain a positive electrode plate with a double-sided coated positive electrode material layer. After coating, the positive electrode plate is cold-pressed, and then cut into pieces and the tabs are welded to obtain a positive electrode plate with a specification of 74 mm × 867 mm for use. Among them, the coating weight of the single-sided positive electrode material layer is 411 mg / 1540 mm 2 , and the thickness of the single-sided positive electrode material layer is 72.4 μm.

[0100] <Separator>

[0101] Use a polyethylene (PE) film with a thickness of 7 μm.

[0102] <Preparation of the lithium-ion battery>

[0103] Stack the prepared positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator placed in the middle of the positive electrode sheet and the negative electrode sheet to play an isolation role, and then wind them to obtain an electrode assembly. Place the electrode assembly in an aluminum-plastic film packaging shell, dry it in a vacuum oven at 85 °C for 12 h to remove moisture, inject the prepared electrolyte, and obtain a lithium-ion battery through processes such as vacuum packaging, standing, formation (constant current charging at 0.02C to 3.5V, and then constant current charging at 0.1C to 3.9V), shaping, and capacity testing.

[0104] Examples 1-2 to Examples 1-24

[0105] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as in Example 1-1. Among them, when the mass ratio W1% of the compound shown in Formula I changes, the mass ratio of the base solvent changes accordingly, the proportions of the components in the base solvent remain unchanged, and the mass ratio of the lithium salt LiPF6 remains unchanged; the mass ratio x% of silicon in the negative electrode material layer is regulated by regulating the mass ratio of silicon in the silicon-based particles; d, L, D1, and S1 / S2 are regulated by regulating the process conditions of laser processing.

[0106] Example 2-1

[0107] Except that <Preparation of electrolyte> adopts the following preparation method, the rest are the same as in Example 1-1.

[0108] <Preparation of electrolyte>

[0109] In an argon atmosphere glove box with a water content of less than 10 ppm, mix diethyl carbonate and ethylene carbonate in a mass ratio of 1:1 to obtain a base solvent, and then add the compound shown in Formula I (Formula I-1), the first component fluoroethylene carbonate, and the lithium salt lithium hexafluorophosphate (LiPF6) to the base solvent and mix evenly to obtain an electrolyte. Among them, based on the mass of the electrolyte, the mass ratio W1% of the compound shown in Formula I is 15%, the mass ratio W2% of the first component fluoroethylene carbonate is 0.5%, the mass ratio of the lithium salt LiPF6 is 12.5%, and the balance is the base solvent.

[0110] Examples 2-2 to Examples 2-8

[0111] Except for adjusting the relevant preparation parameters according to Table 2, the rest are the same as in Example 2-1. Among them, when the mass ratio W2% of the first component changes, the mass ratio of the base solvent changes accordingly, the proportions of the components in the base solvent remain unchanged, and the mass ratios of the compound shown in Formula I and the lithium salt LiPF6 remain unchanged.

[0112] Comparative Examples 1 to Comparative Examples 6

[0113] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1. Among them, when the mass ratio W1% of the compound shown in Formula I changes, the mass ratio of the base solvent changes accordingly, the ratio of each component in the base solvent remains unchanged, and the mass ratio of the lithium salt LiPF6 remains unchanged; the mass ratio x% of silicon element in the negative electrode material layer is regulated by regulating the mass ratio of silicon element in the silicon-based particles; d is regulated by regulating the process conditions of laser processing.

[0114] Comparative Example 7

[0115] Except that <Preparation of electrolyte> adopts the following preparation method, the rest is the same as in Example 1-1.

[0116] <Preparation of electrolyte>

[0117] In an argon atmosphere glove box with a water content of less than 10 ppm, diethyl carbonate and ethylene carbonate are mixed in a mass ratio of 1:1 to obtain a base solvent, and then a compound shown in Formula II and lithium hexafluorophosphate (LiPF6) are added to the base solvent and mixed evenly to obtain an electrolyte. Among them, based on the mass of the electrolyte, the mass ratio of the lithium salt LiPF6 is 12.5%, the mass ratio of the compound shown in Formula II is 15%, and the balance is the base solvent.

[0118]

[0119] Comparative Example 8

[0120] Except that in <Preparation of negative electrode sheet>, laser processing is not carried out to obtain a negative electrode sheet without concave portions on the surface of the negative electrode material layer, the rest is the same as in Example 1-1.

[0121] The preparation parameters and performance parameters of each example and comparative example are shown in Table 1 and Table 2.

[0122]

[0123]

[0124] As can be seen from Examples 1-1 to 1-24 and Comparative Examples 1 to 8, by adjusting the values of W1, x, P, and W1 / (x×P) within the scope of the present application, the electrolyte and the negative electrode sheet act synergistically, and the degree of lithium deposition during low-temperature charging of the lithium-ion battery is smaller, and the thickness expansion rate during high-temperature storage is smaller, indicating that the lithium-ion battery has good low-temperature charging ability and high-temperature storage performance. For the lithium-ion batteries of Comparative Examples 1 to 6, any one of W1, x, P, and W1 / (x×P) is not within the scope of the present application. The electrolyte of Comparative Example 7 does not include the compound shown in Formula I, and there is no recess on the surface of the negative electrode material layer of Comparative Example 8. The degree of lithium deposition during low-temperature charging of the lithium-ion batteries of Comparative Examples 1 to 8 is larger, and / or the thickness expansion rate during high-temperature storage is larger, indicating that the lithium-ion battery cannot simultaneously achieve good low-temperature charging ability and high-temperature storage performance.

[0125] The mass percentage W1% of the compound shown in Formula I affects the low-temperature charging ability and high-temperature storage performance of the lithium-ion battery. As can be seen from Examples 1-1 to 1-7 and Comparative Examples 1 to 2, when the value of W1 is too small, such as in Comparative Example 1, the degree of lithium deposition during low-temperature charging of the lithium-ion battery is larger, and the thickness expansion rate during high-temperature storage is larger; when the value of W1 is too large, such as in Comparative Example 2, the degree of lithium deposition during low-temperature charging of the lithium-ion battery is larger, and the thickness expansion rate during high-temperature storage is larger, indicating that the lithium-ion battery cannot simultaneously achieve good low-temperature charging ability and high-temperature storage performance. When the value of W1 is within the scope of the present application, the degree of lithium deposition during low-temperature charging of the lithium-ion battery is smaller, and the thickness expansion rate during high-temperature storage is smaller, indicating that the lithium-ion battery has good low-temperature charging ability and high-temperature storage performance.

[0126] The mass percentage x% of silicon element in the negative electrode material layer affects the low-temperature charging ability and high-temperature storage performance of the lithium-ion battery. As can be seen from Example 1-1, Examples 1-8 to 1-9, and Comparative Example 3, when the value of x is too large, such as in Comparative Example 3, the degree of lithium deposition during low-temperature charging of the lithium-ion battery is larger, and the thickness expansion rate during high-temperature storage is larger, indicating that the lithium-ion battery cannot simultaneously achieve good low-temperature charging ability and high-temperature storage performance. When the value of x is within the scope of the present application, the degree of lithium deposition during low-temperature charging of the lithium-ion battery is smaller, and the thickness expansion rate during high-temperature storage is smaller, indicating that the lithium-ion battery has good low-temperature charging ability and high-temperature storage performance.

[0127] The P value affects the low-temperature charging ability and high-temperature storage performance of lithium-ion batteries. It can be seen from Example 1-1, Examples 1-10 to 1-11, and Comparative Example 4 that when the value of P is too small, such as in Comparative Example 4, the degree of lithium deposition during low-temperature charging of the lithium-ion battery is greater, and the thickness expansion rate during high-temperature storage is greater, indicating that the lithium-ion battery cannot balance the low-temperature charging ability and high-temperature storage performance simultaneously. When the value of P is within the scope of this application, the degree of lithium deposition during low-temperature charging of the lithium-ion battery is smaller, and the thickness expansion rate during high-temperature storage is smaller, indicating that the lithium-ion battery has good low-temperature charging ability and high-temperature storage performance.

[0128] W1 / (x×P) affects the low-temperature charging ability and high-temperature storage performance of lithium-ion batteries. It can be seen from Examples 1-1 to 1-13, and Comparative Examples 5 to 6 that when the value of W1 / (x×P) is too small, such as in Comparative Example 5, the degree of lithium deposition during low-temperature charging of the lithium-ion battery is greater, and the thickness expansion rate during high-temperature storage is greater; when the value of W1 / (x×P) is too large, such as in Comparative Example 6, the degree of lithium deposition during low-temperature charging of the lithium-ion battery is greater, and the thickness expansion rate during high-temperature storage is greater, indicating that the lithium-ion battery cannot balance the low-temperature charging ability and high-temperature storage performance simultaneously. When the value of W1 / (x×P) is within the scope of this application, the degree of lithium deposition during low-temperature charging of the lithium-ion battery is smaller, and the thickness expansion rate during high-temperature storage is smaller, indicating that the lithium-ion battery has good low-temperature charging ability and high-temperature storage performance.

[0129] The type of the compound shown in Formula I affects the low-temperature charging ability and high-temperature storage performance of lithium-ion batteries. It can be seen from Example 1-1, Examples 1-14 to 1-16 that when the compound shown in Formula I within the scope of this application is selected, the degree of lithium deposition during low-temperature charging of the lithium-ion battery is smaller, and the thickness expansion rate during high-temperature storage is smaller, indicating that the lithium-ion battery has good low-temperature charging ability and high-temperature storage performance.

[0130] The values of L, W1 / L, D, D1, and S1 / S2 affect the low-temperature charging ability and high-temperature storage performance of lithium-ion batteries. It can be seen from Example 1-1, Examples 1-17 to 1-24 that when the values of L, W1 / L, D, D1, and S1 / S2 are within the scope of this application, the degree of lithium deposition during low-temperature charging of the lithium-ion battery is smaller, and the thickness expansion rate during high-temperature storage is smaller, indicating that the lithium-ion battery has good low-temperature charging ability and high-temperature storage performance.

[0131] Table 2

[0132]

[0133] Note: (1) " / " in Table 2 indicates no relevant preparation parameters; (2) In Examples 2-4, "the first component" is "fluoroethylene carbonate + vinylene carbonate", and "W2(%)" is "3 + 2", indicating that the first component is fluoroethylene carbonate and vinylene carbonate. Based on the total mass of the electrolyte, the mass percentage of fluoroethylene carbonate is 3%, and the mass percentage of vinylene carbonate is 2%.

[0134] The mass percentage W2% of the first component will affect the low-temperature charging ability and high-temperature storage performance of the lithium-ion battery. It can be seen from Examples 1-1, 2-1 to 2-7 that when the value of W2 is within the scope of this application, the degree of lithium deposition during low-temperature charging of the lithium-ion battery is small, and the thickness expansion rate during high-temperature storage is small, indicating that the lithium-ion battery has good low-temperature charging ability and high-temperature storage performance.

[0135] The type of the first component will affect the low-temperature charging ability and high-temperature storage performance of the lithium-ion battery. It can be seen from Examples 2-1 and 2-8 that when the first component within the scope of this application is selected, the degree of lithium deposition during low-temperature charging of the lithium-ion battery is small, and the thickness expansion rate during high-temperature storage is small, indicating that the lithium-ion battery has good low-temperature charging ability and high-temperature storage performance.

[0136] 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 term "comprising", "including" or any other variant thereof is 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.

[0137] Each embodiment in this specification is described in a related manner. The same or similar parts between each embodiment can be referred to each other, and the differences between each embodiment and other embodiments are emphasized in each embodiment.

[0138] The above are only the preferred embodiments of this application, and are not intended to limit this application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of this application shall be included within the scope of protection of this application.

Claims

1. A secondary battery, which includes a negative electrode sheet and an electrolyte, and the electrolyte includes a compound represented by Formula I, Among them, R1 is selected from a fluorine atom, a C1-C5 alkyl group that is fully or partially substituted by fluorine, R2 and R3 are each independently selected from C1-C5 alkyl groups, and R2 and R3 can be connected by a single bond to form a ring, Based on the mass of the electrolyte, the mass percentage of the compound represented by Formula I is W1%, 2 ≤ W1 ≤ 50; The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector, The negative electrode material layer contains silicon element, and based on the mass of the negative electrode material layer, the mass percentage of the silicon element is x%, x ≤ 25; The thickness of the negative electrode material layer is D μm, the surface of the negative electrode material layer is provided with a plurality of recesses, the depth of the recesses is d μm, and P = d / D, P ≥ 0.1; 0.4 ≤ W1 / (x×P) ≤ 62.

5.

2. The secondary battery according to claim 1, wherein, 5 ≤ W1 ≤ 30, preferably, 10 ≤ W1 ≤ 20.

3. The secondary battery according to claim 1, wherein, The compound represented by Formula I includes at least one of the following compounds:

4. The secondary battery according to claim 1, wherein, The minimum distance between two adjacent recesses is L μm, 50 ≤ L ≤ 300.

5. The secondary battery according to claim 4, wherein, 0.05 ≤ W1 / L ≤ 0.

25.

6. The secondary battery according to any one of claims 1 to 5, wherein, The secondary battery satisfies at least one of the following: (1)100≤D≤400； (2)0.1≤P≤0.5； (3)4≤x≤25。 7. The secondary battery according to any one of claims 1 to 5, wherein, Viewed along the thickness direction of the negative electrode sheet, the recess is quadrilateral, and the length of the shortest side of the quadrilateral is D1 mm, 0.02 ≤ D1 ≤ 0.

5.

8. The secondary battery according to any one of claims 1 to 5, wherein, When observed along the thickness direction of the negative electrode plate, the recess is quadrilateral, and the sum of the areas of the quadrilaterals is S1 mm 2 , and the area of the negative electrode material layer is S2 mm 2 , 0.1 ≤ S1 / S2 ≤ 0.

8.

9. The secondary battery according to any one of claims 1 to 5, wherein, The electrolyte further includes a first component, and the first component includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, vinylene carbonate or ethylene vinylene carbonate; Based on the mass of the electrolyte, the mass percentage of the first component is W2%, 0.5 ≤ W2 ≤ 15, preferably, 1 ≤ W2 ≤ 8.

10. An electronic device, which includes the secondary battery according to any one of claims 1 to 9.

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