Secondary battery, method for manufacturing secondary battery, battery module, battery pack, and power consumption device

Abstract

This application provides a secondary battery, a method for manufacturing the secondary battery, a battery module, a battery pack, and an electric power consuming device. The secondary battery includes an electrolytic solution and a positive electrode plate. Here, the positive electrode plate includes a layered material having a molecular formula of Li a Ni b Co c M1 d M2 e O f A g where 0.8 ≦ a ≦ 1.2, 0 < b < 0.98, 0 ≦ c < 0.1, 0 < d < 0.5, 0 ≦ e ≦ 0.5, 0 ≦ f ≦ 2, 0 ≦ g ≦ 2, b + c + d + e = 1, f + g = 2. The electrolytic solution includes lithium tetrafluoroborate. Based on the total mass of the electrolytic solution, the mass percentage of lithium tetrafluoroborate in the electrolytic solution is x%, and the secondary battery satisfies x > 0 and 0.05 ≦ c + x / 10 ≦ 0.15. This application can stabilize the crystal structure of the low-cobalt or cobalt-free positive electrode active material and improve the diffusion rate of lithium ions therein.

Description

[Technical Field]

[0001] The present application relates to the field of battery technology, and in particular to a secondary battery, a method for manufacturing a secondary battery, a battery module, a battery pack, and a power consuming device. [Background technology]

[0002] Secondary batteries are charged and discharged by repeated absorption and desorption of lithium ions between the positive and negative electrodes. These batteries offer excellent features, such as high energy density, long cycle life, pollution-free operation, and no memory effect. As a result, secondary batteries, as a clean energy source, are increasingly being used in a wide range of applications, from electronic products to energy storage systems for hydroelectric, thermal, wind, and solar power plants, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Cobalt is an important component of the positive electrode active material of secondary batteries. However, due to its low content in the earth's crust, difficulty in mining, and high cost, low-cobalt or cobalt-free positive electrode active materials are becoming an inevitable development trend. However, cobalt significantly contributes to the diffusion rate of lithium ions in positive electrode active materials. Therefore, low-cobalt or cobalt-free positive electrode active materials may reduce the diffusion rate of lithium ions in positive electrode active materials, potentially affecting the cycle life of secondary batteries. Summary of the Invention

[0003] The object of the present application is to provide a secondary battery, a method for manufacturing a secondary battery, a battery module, a battery pack, and a power consumption device, which stabilize the crystal structure of a low-cobalt or cobalt-free positive electrode active material and improve the diffusion rate of lithium ions therein.

[0004] According to a first aspect of the present application, there is provided a secondary battery including an electrolyte and a positive electrode plate, the positive electrode plate including a positive electrode current collector and a positive electrode film layer located on a surface of the positive electrode current collector, the positive electrode film layer having a molecular formula of Li a Ni b Co c M1 d M2 e O fA g [It] contains a layered material, M1 is selected from Mn, Al or a combination thereof, M2 is selected from one or more of Si, Ti, Mo, V, Ge, Se, Zr, Nb, Ru, Pd, Sb, Ce, Te and W, A is selected from one or more of F, N, P and S, 0.8 ≦ a ≦ 1.2, 0 < b < 0.98, 0 ≦ c < 0.1, 0 < d < 0.5, 0 ≦ e ≦ 0.5, 0 ≦ f ≦ 2, 0 ≦ g ≦ 2, b + c + d + e = 1, f + g = 2. The electrolyte contains lithium tetrafluoroborate. Based on the total mass of the electrolyte, the mass percentage of lithium tetrafluoroborate in the electrolyte is x%, and the secondary battery satisfies x > 0 and 0.05 ≦ c + x / 10 ≦ 0.15.

[0005] As a result of intensive research, the inventor of the present application has surprisingly found that by making the electrolyte contain lithium tetrafluoroborate and making the mass percentage x% of lithium tetrafluoroborate and the content c of cobalt element in the low-cobalt or cobalt-free cathode active material satisfy x > 0 and 0.05 ≦ c + x / 10 ≦ 0.15, the crystal structure of the low-cobalt or cobalt-free cathode active material can be stabilized, the diffusion rate of lithium ions inside it can be improved, and further, the secondary battery can be provided with significantly improved cycle performance. In addition, the secondary battery of the present application can further have good storage performance and kinetic performance.

[0006] In any embodiment of the present application, 0.05 ≦ c + x / 10 ≦ 0.12.

[0007] In any embodiment of the present application, 0 < x ≦ 1.0.

[0008] In any embodiment of the present application, the tap density of the positive electrode plate is P g / cm 3 [and] the secondary battery satisfies 25 ≦ P / (c + x / 10) ≦ 65, optionally 30 ≦ P / (c + x / 10) ≦ 50. Thereby, on the premise that the secondary battery has improved cycle performance and high energy density, it can have improved power performance. ​​

[0009] In any embodiment of the present application, the consolidation density P g / cm of the positive electrode plate 3 satisfies that P is 3.3 to 3.6. This contributes to the secondary battery having a high energy density.

[0010] In any embodiment of the present application, the electrolyte further contains one or more of fluoroethylene carbonate, lithium fluorosulfonyl imide salt, and lithium fluorosulfonic acid salt. The mass percentage of the fluoroethylene carbonate in the electrolyte is y1%, the mass percentage of the lithium fluorosulfonyl imide salt in the electrolyte is y2%, and the mass percentage of the lithium fluorosulfonic acid salt in the electrolyte is y3%. All are calculated based on the total mass of the electrolyte, and the electrolyte satisfies y1≧0, y2≧0, y3≧0, and 0<y1 + y2 + y3≦15. This contributes to forming a more stable interfacial film on the positive electrode and / or the negative electrode, thereby further improving the electrochemical performance of the secondary battery.

[0011] In any embodiment of the present application, the molecular formula of the lithium fluorosulfonyl imide salt is LiN(SO2R1)(SO2R2), and R1 and R2 are each independently F or C n F 2n+1 represents, n is an integer from 1 to 10, and optionally, the lithium fluorosulfonyl imide salt contains lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonyl imide, or a combination thereof.

[0012] In any embodiment of the present application, the molecular formula of the lithium fluorosulfonic acid salt is LiSO3R3, and R3 represents F, a partially fluorinated or fully fluorinated C1-C10 alkyl group. Optionally, the lithium fluorosulfonic acid salt contains lithium fluorosulfonic acid, lithium trifluoromethanesulfonic acid, or a combination thereof.

[0013] In any embodiment of the present application, the mass percentage y1% of fluoroethylene carbonate in the electrolyte satisfies 0 < y1 ≤ 2.5, optionally 0 < y1 ≤ 2.0. Thereby, the interfacial film of the negative electrode can be stabilized, and the cycle performance of the secondary battery can be effectively improved.

[0014] In any embodiment of the present application, the mass percentage y1% of fluoroethylene carbonate in the electrolyte satisfies 0.5 ≤ y1 / x ≤ 4.0, optionally 0.5 ≤ y1 / x ≤ 2.0. Thereby, the synergistic effect between lithium tetrafluoroborate and fluoroethylene carbonate can be fully exerted.

[0015] In any embodiment of the present application, the mass percentage y1% of fluoroethylene carbonate in the electrolyte satisfies 0 < y1 ≤ 2.5 and 0.5 ≤ y1 / x ≤ 4.0.

[0016] In any embodiment of the present application, the mass percentage y2% of lithium fluorosulfonyl imide salt in the electrolyte satisfies 0 < y2 ≤ 14. Thereby, the rate performance and low-temperature performance of the secondary battery can be significantly improved.

[0017] In any embodiment of the present application, the mass percentage y2% of lithium fluorosulfonyl imide salt in the electrolyte satisfies 1 ≤ y2 / x ≤ 28. Thereby, the synergistic effect between lithium tetrafluoroborate and lithium fluorosulfonyl imide salt can be fully exerted.

[0018] In any embodiment of the present application, the mass percentage y2% of lithium fluorosulfonyl imide salt in the electrolyte satisfies 0 < y2 ≤ 14 and 1 ≤ y2 / x ≤ 28.

[0019] In any embodiment of the present application, when 0 < b ≤ 0.7, the mass percentage y2% of the lithium fluorosulfonyl imide salt in the electrolyte satisfies 0 < y2 ≤ 5 and / or 1 ≤ y2 / x ≤ 10. Optionally, 0 < y2 ≤ 2.5, and optionally, 1 ≤ y2 / x ≤ 5.

[0020] In any embodiment of the present application, when 0.7 ≤ b < 0.98, the mass percentage y2% of the lithium fluorosulfonyl imide salt in the electrolyte satisfies 5 ≤ y2 ≤ 14 and / or 10 ≤ y2 / x ≤ 28. Optionally, 8 ≤ y2 ≤ 14, and optionally, 16 ≤ y2 / x ≤ 28.

[0021] In any embodiment of the present application, the mass percentage y3% of the lithium fluorosulfonic acid salt in the electrolyte satisfies 0 < y3 ≤ 1.0, and optionally 0 < y3 ≤ 0.5. Thereby, the high-temperature performance of the secondary battery can be greatly improved.

[0022] In any embodiment of the present application, the mass percentage y3% of the lithium fluorosulfonic acid salt in the electrolyte satisfies 0.001 ≤ y3 / x ≤ 2.0, and optionally 0.001 ≤ y3 / x ≤ 1.0. Thereby, the synergistic effect between lithium tetrafluoroborate and the lithium fluorosulfonic acid salt can be fully exerted.

[0023] In any embodiment of the present application, the mass percentage y3% of the lithium fluorosulfonic acid salt in the electrolyte satisfies 0 < y3 ≤ 1.0 and 0.001 ≤ y3 / x ≤ 2.0.

[0024] In any embodiment of the present application, the electrolyte further contains fluoroethylene carbonate, lithium fluorosulfonyl imide salt and lithium fluorosulfonic acid salt, and the electrolyte satisfies 0 < y1 ≤ 2.5, 0 < y2 ≤ 14, 0 < y3 ≤ 1.0, 0.5 ≤ y1 / x ≤ 4.0, 1 ≤ y2 / x ≤ 28, 0.001 ≤ y3 / x ≤ 2.0, 0.5 ≤ y2 / y1 ≤ 48. At this time, the overall performance of the secondary battery is further improved.

[0025] Optionally, when 0 < b ≤ 0.7, the electrolyte satisfies 0 < y1 ≤ 2.5, 0 < y2 ≤ 5, 0 < y3 ≤ 1.0, 0.5 ≤ y1 / x ≤ 4.0, 1 ≤ y2 / x ≤ 10, 0.001 ≤ y3 / x ≤ 2.0, 0.5 ≤ y2 / y1 ≤ 10.

[0026] Optionally, when 0.7 ≤ b < 0.98, the electrolyte satisfies 0 < y1 ≤ 2.5, 5 ≤ y2 ≤ 14, 0 < y3 ≤ 1.0, 0.5 ≤ y1 / x ≤ 4.0, 10 ≤ y2 / x ≤ 28, 0.001 ≤ y3 / x ≤ 2.0, 6 ≤ y2 / y1 ≤ 48.

[0027] In any embodiment of the present application, the electrolyte satisfies the following, that is, the electrolyte further contains fluoroethylene carbonate, lithium fluorosulfonyl imide salt and lithium fluorosulfonate salt, and the electrolyte satisfies 0 < y1 ≤ 2.5, 0 < y2 ≤ 14, 0 < y3 ≤ 1.0, 0.5 ≤ y1 / x ≤ 4.0, 1 ≤ y2 / x ≤ 28, 0.001 ≤ y3 / x ≤ 2.0, 0.5 ≤ y2 / y1 ≤ 48, 0.036 ≤ x / (y2 + y3) ≤ 1.0. Thereby, it contributes to forming an inorganic / organic composite interface film with excellent performance on the positive electrode and the negative electrode, and thereby the overall performance of the secondary battery can be further improved.

[0028] Optionally, when 0 < b ≤ 0.7, the electrolyte satisfies 0 < y1 ≤ 2.5, 0 < y2 ≤ 5, 0 < y3 ≤ 1.0, 0.5 ≤ y1 / x ≤ 4.0, 1 ≤ y2 / x ≤ 10, 0.001 ≤ y3 / x ≤ 2.0, 0.5 ≤ y2 / y1 ≤ 10, 0.1 ≤ x / (y2 + y3) ≤ 1.0.

[0029] Optionally, when 0.7 ≤ b < 0.98, the electrolyte satisfies 0 < y1 ≤ 2.5, 5 ≤ y2 ≤ 14, 0 < y3 ≤ 1.0, 0.5 ≤ y1 / x ≤ 4.0, 10 ≤ y2 / x ≤ 28, 0.001 ≤ y3 / x ≤ 2.0, 6 ≤ y2 / y1 ≤ 48, 0.036 ≤ x / (y2 + y3) ≤ 0.1.

[0030] In any embodiment of the present application, 0 < c < 0.1.

[0031] In any embodiment of the present application, c=0.

[0032] In any embodiment of the present application, based on the total mass of the positive electrode film layer, the molecular formula is Li a Ni b Co c M1 d M2 e O f A g The weight percentage of the layered material is between 80% and 99%, optionally between 85% and 99%.

[0033] In any embodiment of the present application, the secondary battery further satisfies the requirement that the mass of the electrolyte is 10% to 20% of the total mass of the secondary battery, which is advantageous for forming a dense interfacial film with low impedance on the surface of the positive electrode active material.

[0034] According to a second aspect of the present application, there is provided a method for manufacturing a secondary battery, the method including: a step 1 of assembling at least a positive electrode plate, a separator, a negative electrode plate, and an electrolyte into a secondary battery, the positive electrode plate including a positive electrode current collector and a positive electrode film layer located on a surface of the positive electrode current collector, the positive electrode film layer having a molecular formula of Li a Ni b Co c M1 d M2 e O f A gIt includes a layered material, where M1 is selected from Mn, Al or a combination thereof, M2 is selected from one or more of Si, Ti, Mo, V, Ge, Se, Zr, Nb, Ru, Pd, Sb, Ce, Te and W, A is selected from one or more of F, N, P and S, 0.8≦a≦1.2, 0<b<0.98, 0≦c<0.1, 0<d<0.5, 0≦e≦0.5, 0≦f≦2, 0≦g≦2, b + c + d + e = 1, f + g = 2, the electrolyte contains lithium tetrafluoroborate, optional fluoroethylene carbonate, optional lithium fluorosulfonylimide salt and optional lithium fluorosulfonate salt, the mass percentage of lithium tetrafluoroborate in the electrolyte is x%, the mass percentage of fluoroethylene carbonate in the electrolyte is y1%, the mass percentage of lithium fluorosulfonylimide salt in the electrolyte is y2%, the mass percentage of lithium fluorosulfonate salt in the electrolyte is y3%, all calculated based on the total mass of the electrolyte, x>0, y1≧0, y2≧0, y3≧0, step 1, and step 2 of selecting a secondary battery that satisfies 0.05≦c + x / 10≦0.15 from the secondary battery obtained in step 1.

[0035] The secondary batteries obtained by the manufacturing method of the present application can all have significantly improved cycle performance, good storage performance and kinetic performance.

[0036] In any embodiment of the present application, the method further includes the step of selecting a secondary battery that satisfies 0<x≦1.0 and 0.05≦c + x / 10≦0.15 from the secondary battery obtained in step 2. At this time, the manufactured secondary battery has further improved cycle performance.

[0037] In any embodiment of the present application, the method further includes the step of selecting a secondary battery that satisfies 25≦P / (c + x / 10)≦65 from the secondary battery obtained in step 2, P g / cm 3represents the consolidation density of the positive electrode plate. At this time, the manufactured secondary battery can have improved power performance on the premise of significantly improved cycle performance and high energy density.

[0038] In any embodiment of the present application, the method further includes a step of selecting a secondary battery that satisfies 0 < y1 + y2 + y3 ≤ 15, 0 < y1 ≤ 2.5, 0 < y2 ≤ 14, 0 < y3 ≤ 1.0, 0.5 ≤ y1 / x ≤ 4.0, 1 ≤ y2 / x ≤ 28, 0.001 ≤ y3 / x ≤ 2.0, 0.5 ≤ y2 / y1 ≤ 48 from the secondary batteries obtained in step 2. At this time, the comprehensive performance of the manufactured secondary battery is further improved.

[0039] Optionally, when 0 < b ≤ 0.7, the method further includes a step of selecting a secondary battery that satisfies 0 < y1 + y2 + y3 ≤ 15, 0 < y1 ≤ 2.5, 0 < y2 ≤ 5, 0 < y3 ≤ 1.0, 0.5 ≤ y1 / x ≤ 4.0, 1 ≤ y2 / x ≤ 10, 0.001 ≤ y3 / x ≤ 2.0, 0.5 ≤ y2 / y1 ≤ 10 from the secondary batteries obtained in step 2.

[0040] Optionally, when 0.7 ≤ b < 0.98, the method further includes a step of selecting a secondary battery that satisfies 0 < y1 + y2 + y3 ≤ 15, 0 < y1 ≤ 2.5, 5 ≤ y2 ≤ 14, 0 < y3 ≤ 1.0, 0.5 ≤ y1 / x ≤ 4.0, 10 ≤ y2 / x ≤ 28, 0.001 ≤ y3 / x ≤ 2.0, 6 ≤ y2 / y1 ≤ 48 from the secondary batteries obtained in step 2.

[0041] In any embodiment of the present application, the method further includes a step of selecting a secondary battery that satisfies 0 < y1 + y2 + y3 ≤ 15, 0 < y1 ≤ 2.5, 0 < y2 ≤ 14, 0 < y3 ≤ 1.0, 0.5 ≤ y1 / x ≤ 4.0, 1 ≤ y2 / x ≤ 28, 0.001 ≤ y3 / x ≤ 2.0, 0.5 ≤ y2 / y1 ≤ 48, 0.036 ≤ x / (y2 + y3) ≤ 1.0 from the secondary batteries obtained in step 2. At this time, the comprehensive performance of the manufactured secondary battery is further improved.

[0042] Optionally, when 0 < b ≤ 0.7, the method further includes the step of selecting a secondary battery that satisfies 0 < y1 + y2 + y3 ≤ 15, 0 < y1 ≤ 2.5, 0 < y2 ≤ 5, 0 < y3 ≤ 1.0, 0.5 ≤ y1 / x ≤ 4.0, 1 ≤ y2 / x ≤ 10, 0.001 ≤ y3 / x ≤ 2.0, 0.5 ≤ y2 / y1 ≤ 10, 0.1 ≤ x / (y2 + y3) ≤ 1.0 from the secondary battery obtained in step 2.

[0043] Optionally, when 0.7 ≤ b < 0.98, the method further includes the step of selecting a secondary battery that satisfies 0 < y1 + y2 + y3 ≤ 15, 0 < y1 ≤ 2.5, 5 ≤ y2 ≤ 14, 0 < y3 ≤ 1.0, 0.5 ≤ y1 / x ≤ 4.0, 10 ≤ y2 / x ≤ 28, 0.001 ≤ y3 / x ≤ 2.0, 6 ≤ y2 / y1 ≤ 48, 0.036 ≤ x / (y2 + y3) ≤ 0.1 from the secondary battery obtained in step 2.

[0044] According to a third aspect of the present application, a battery module including the secondary battery of the first aspect of the present application or the secondary battery manufactured by the method of the second aspect of the present application is provided.

[0045] According to a fourth aspect of the present application, a battery pack including one of the secondary battery of the first aspect of the present application, the secondary battery manufactured by the method of the second aspect of the present application, and the battery module of the third aspect of the present application is provided.

[0046] According to a fifth aspect of the present application, a power consumption device including at least one of the secondary battery of the first aspect of the present application, the secondary battery manufactured by the method of the second aspect of the present application, the battery module of the third aspect of the present application, and the battery pack of the fourth aspect of the present application is provided.

[0047] The secondary battery of the present application has significantly improved cycle performance, good storage performance, and kinetic performance. Since the battery module, battery pack, and power consumption device of the present application include the secondary battery according to the present application, they have at least the same advantages as the secondary battery.

Brief Description of the Drawings

[0048] In order to more clearly explain the technical solutions of the embodiments of the present application, the following briefly introduces the drawings that need to be used in the embodiments of the present application. It is obvious that the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings based on the drawings without any creative efforts.

[0049] [Figure 1] 1 is a schematic diagram of one embodiment of a secondary battery of the present application. [Figure 2] FIG. 2 is an exploded schematic view of an embodiment of the secondary battery of FIG. 1. [Figure 3] 1 is a schematic diagram of one embodiment of a battery module of the present application. [Figure 4] 1 is a schematic diagram of one embodiment of a battery pack of the present application. [Figure 5] FIG. 5 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 4. [Figure 6] 1 is a schematic diagram of an embodiment of a power consuming device in which the secondary battery of the present application is used as a power source; DETAILED DESCRIPTION OF THE INVENTION

[0050] Hereinafter, with appropriate reference to the drawings, embodiments specifically disclosing the secondary battery, method for manufacturing the secondary battery, battery module, battery pack, and power consumption device of the present application will be described in detail. However, unnecessary detailed description may be omitted. For example, detailed description of well-known matters and redundant description of actually identical structures may be omitted. This is to avoid unnecessarily lengthening the following description and to facilitate understanding by those skilled in the art. Note that the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and do not limit the subject matter described in the claims.

[0051] The "ranges" disclosed in this application are defined in the form of lower and upper limits, and a given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of the particular range. Such defined ranges may be inclusive or exclusive of the end values, and any combination is possible; i.e., any lower limit can be combined with any upper limit to form a single range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also possible. Furthermore, if 1 and 2 are listed as minimum range values ​​and 3, 4, and 5 are listed as maximum range values, the ranges 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5 are all possible. In this application, unless otherwise specified, a numerical range "a to b" is a shorthand notation for any combination of real numbers a to b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed herein, and "0-5" is merely a shorthand representation of combinations of these numbers. Also, expressing a parameter as an integer ≧2 is equivalent to disclosing that this parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0052] Unless otherwise stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present application.

[0053] Unless otherwise stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure content of the present application.

[0054] Unless otherwise specified, all steps in this application may be performed in order or randomly, and are preferably performed in order. For example, when the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed in order, or steps (b) and (a) performed in order. For example, when the method mentioned above may further include step (c), it means that step (c) may be added to the method in any order, and for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0055] Unless otherwise specified, the terms "comprise" and "include" used in this application may be open-ended or closed-ended. For example, the terms "comprise" and "include" may indicate that the compound may further include or include other components not listed, or may include or include only the listed components.

[0056] Unless otherwise stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied when A is true (or exists) and B is false (or does not exist), when A is false (or does not exist) but B is true (or exists), or when both A and B are true (or exist).

[0057] As used in this application, the terms "plurality" and "plurality" mean two or more than two.

[0058] A secondary battery, also known as a rechargeable battery or storage battery, refers to a battery that can continue to be used by activating the active material through charging after discharge. A secondary battery generally includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. During charging and discharging of a secondary battery, lithium ions are absorbed and desorbed by moving back and forth between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily serves to prevent short-circuiting between the positive and negative electrodes and allows lithium ions to pass through. The electrolyte serves to conduct lithium ions between the positive and negative electrodes.

[0059] During charging of a secondary battery, lithium ions preferentially desorb from the surface of the positive electrode active material, and then lithium ions in the bulk phase of the positive electrode active material are promptly replenished to the surface. The cobalt content of the positive electrode active material affects the ionic conductivity of the positive electrode active material in the following ways: (1) When the cobalt content of the positive electrode active material is high, lithium ions in the bulk phase can be promptly replenished to the surface of the positive electrode active material; (2) When the cobalt content of the positive electrode active material is low, lithium ions in the bulk phase cannot be promptly replenished to the surface of the positive electrode active material, while the surface lithium ions have already desorbed. This causes excessive lithium desorption from the surface of the positive electrode active material, which affects the crystalline structure of the positive electrode active material (e.g., irreversible distortion of the positive electrode active material and an increase in the number of lattice defects), thereby reducing the cycle performance of the secondary battery.

[0060] Cobalt can also stabilize the crystalline structure of the positive electrode active material. When the cobalt content in the positive electrode active material is reduced or absent, the dissolution rate of metal ions, especially manganese ions, from the positive electrode active material increases. The dissolved manganese ions migrate to the negative electrode and are reduced to metallic manganese. The resulting metallic manganese acts as a catalyst, catalyzing the decomposition of the solid electrolyte interphase (SEI) film on the negative electrode surface. Some of the resulting by-products are gaseous and prone to causing battery expansion, affecting the safety of the secondary battery. Others accumulate on the negative electrode surface, blocking the passage of lithium ions into and out of the negative electrode, increasing the impedance of the secondary battery and affecting its dynamic performance. To compensate for the loss of the SEI film, the electrolyte and active lithium ions in the battery are constantly consumed, irreversibly affecting the capacity retention rate of the secondary battery.

[0061] Therefore, stabilizing the crystalline structure of low-cobalt or cobalt-free positive electrode active materials and improving the diffusion rate of lithium ions therein are of practical importance. Researchers have been working to improve the diffusion rate of lithium ions in low-cobalt or cobalt-free positive electrode active materials, but no satisfactory solution has been found at present.

[0062] As a result of extensive research, the inventors of the present application have unexpectedly found that by including an appropriate amount of lithium tetrafluoroborate in the electrolyte and by ensuring that the content of lithium tetrafluoroborate and the content of cobalt element in the positive electrode active material satisfy a specific relationship, it is possible to stabilize the crystal structure of a low-cobalt or cobalt-free positive electrode active material and improve the diffusion rate of lithium ions therein.

[0063] secondary battery Specifically, an embodiment of the present application provides a secondary battery, which includes an electrolyte and a positive electrode plate. The positive electrode plate includes a positive electrode current collector and a positive electrode film layer located on the positive electrode current collector, the positive electrode film layer having a molecular formula of Lia Ni b Co c M1 d M2 e O f A g It contains a layered material that is g , where M1 is selected from Mn, Al, or a combination thereof, M2 is selected from one or more of Si, Ti, Mo, V, Ge, Se, Zr, Nb, Ru, Pd, Sb, Ce, Te, and W, A is selected from one or more of F, N, P, and S, 0.8 ≦ a ≦ 1.2, 0 < b < 0.98, 0 ≦ c < 0.1, 0 < d < 0.5, 0 ≦ e ≦ 0.5, 0 ≦ f ≦ 2, 0 ≦ g ≦ 2, b + c + d + e = 1, f + g = 2. The electrolyte contains lithium tetrafluoroborate (LiBF4). Based on the total mass of the electrolyte, the mass percentage of lithium tetrafluoroborate in the electrolyte is x%, and the secondary battery satisfies x > 0 and 0.05 ≦ c + x / 10 ≦ 0.15.

[0064] The electrolyte is one of the important factors affecting the performance of secondary batteries. Currently, the most widely commercially applied electrolyte system is a mixed carbonate solution of lithium hexafluorophosphate. However, lithium hexafluorophosphate has low thermal stability in a high-temperature environment and decomposes at high temperatures to produce PF5. PF5 has high Lewis acidity and acts on the lone pair of electrons on the oxygen atom in the organic solvent molecule to decompose the organic solvent. Moreover, PF5 also has high sensitivity to trace amounts of moisture in the electrolyte. When it comes into contact with water, HF is generated, thereby increasing the acidity of the electrolyte, further corroding the positive electrode active material and the positive electrode current collector, and easily causing the elution of transition metal ions in the positive electrode active material. As a result, lithium hexafluorophosphate not only cannot improve the diffusion rate of lithium ions in the low-cobalt or cobalt-free positive electrode active material but also corrodes the positive electrode active material and easily destroys its crystal structure. Therefore, it is necessary to improve the electrolyte.

[0065] As a result of extensive research, the inventors of the present application have unexpectedly discovered that by incorporating lithium tetrafluoroborate into the electrolyte, and by ensuring that the mass percentage x% of the lithium tetrafluoroborate and the cobalt content c of the low-cobalt or cobalt-free positive electrode active material satisfy x>0 and 0.05≦c+x / 10≦0.15, the crystalline structure of the low-cobalt or cobalt-free positive electrode active material can be stabilized, the diffusion rate of lithium ions therein can be improved, and the secondary battery can be provided with significantly improved cycle performance. Furthermore, the secondary battery of the present application can also have good storage performance and dynamic performance.

[0066] Although the mechanism is still unclear, the inventors speculate that the following points may be possible causes.

[0067] First, when the mass percentage (x%) of lithium tetrafluoroborate and the cobalt content (c) of the low-cobalt or cobalt-free positive electrode active material satisfy x > 0 and 0.05 ≦ c + x / 10 ≦ 0.15, the lithium tetrafluoroborate can form a dense, low-impedance interfacial film on the surface of the positive electrode active material, and the B atoms in the lithium tetrafluoroborate can sufficiently bond with the O atoms in the positive electrode active material, thereby reducing the charge transfer impedance of the positive electrode active material, reducing the diffusion resistance of lithium ions within the bulk phase of the positive electrode active material, preventing excessive lithium desorption from the surface of the positive electrode active material, and stabilizing the crystalline structure of the positive electrode active material. The more stable the crystalline structure of the positive electrode active material of the present application, the less likely it is that excessive lithium desorption from the surface will cause problems such as instability in the structural, chemical, or electrochemical properties of the positive electrode active material. Therefore, the secondary battery of the present application can have improved electrochemical performance, and in particular, can have significantly improved cycle performance.

[0068] Second, when the mass percentage (x%) of lithium tetrafluoroborate and the cobalt content (c) of the low-cobalt or cobalt-free positive electrode active material satisfy x > 0 and 0.05 ≦ c + x / 10 ≦ 0.15, the lithium tetrafluoroborate can form a dense, low-impedance interfacial film on the surface of the positive electrode active material, effectively reducing direct contact between the positive electrode active material and the electrolyte while also reducing the surface oxygen activity of the positive electrode active material. This reduces the oxidative decomposition of the electrolyte at the positive electrode and the amount of transition metal ion leaching, further improving the electrochemical performance of the secondary battery, such as reducing the irreversible loss of active lithium ions, reducing the volume expansion rate of the battery, and reducing the positive electrode interfacial impedance. Therefore, the secondary battery of the present application further exhibits good storage performance and dynamic performance.

[0069] Third, lithium tetrafluoroborate has high thermal stability and low sensitivity to moisture, which can improve the high-temperature stability of secondary batteries.

[0070] When c+x / 10<0.05, the content of lithium tetrafluoroborate in the electrolyte is insufficient to form a dense, low-impedance interfacial film on the surface of the low-cobalt or cobalt-free positive electrode active material, and lithium tetrafluoroborate cannot effectively reduce the charge transfer impedance of the low-cobalt or cobalt-free positive electrode active material, nor can it effectively reduce the diffusion resistance of lithium ions within the bulk phase of the low-cobalt or cobalt-free positive electrode active material to suppress excessive lithium desorption from the surface of the low-cobalt or cobalt-free positive electrode active material. As a result, the secondary battery is unlikely to have significantly improved cycle performance. When c+x / 10>0.15, the content of lithium tetrafluoroborate in the electrolyte is too high, and its solubility in the electrolyte is low, resulting in the presence of incompletely dissociated molecular lithium tetrafluoroborate in the electrolyte, which is prone to precipitation in the electrolyte, especially at low temperatures, and further increases safety risks such as separator penetration, thereby deteriorating both the safety performance and cycle performance of the secondary battery. Furthermore, the precipitated lithium tetrafluoroborate may further damage the electrode interface, thereby increasing self-discharge of the secondary battery. In some embodiments, optionally, 0.05≦c+x / 10≦0.14, 0.05≦c+x / 10≦0.13, 0.05≦c+x / 10≦0.12, 0.05≦c+x / 10≦0.11, or 0.05≦c+x / 10≦0.10.

[0071] In the present application, the mass percentage x% of lithium tetrafluoroborate satisfies x>0. When the content of lithium tetrafluoroborate is high, its solubility in the electrolyte is low, resulting in the presence of lithium tetrafluoroborate in a molecular state that is not completely dissociated. This lithium tetrafluoroborate is prone to precipitate in the electrolyte, particularly in low-temperature environments, and further increases safety risks such as separator penetration. Therefore, when the content of lithium tetrafluoroborate is high, the safety performance and cycle performance of the secondary battery may deteriorate. Furthermore, the precipitated lithium tetrafluoroborate further destroys the electrode interface, thereby causing an increase in self-discharge of the secondary battery. In some embodiments, optionally, 0 <x≦1.0である。

[0072] Further research by the inventors of the present application has revealed that the cobalt content in the positive electrode active material also affects the electronic conductivity of the positive electrode active material as follows: (1) When the cobalt content in the positive electrode active material is high, the positive electrode active material has good electronic conductivity; (2) When the cobalt content in the positive electrode active material is low, the electronic conductivity of the positive electrode active material deteriorates, and the power performance of the secondary battery also deteriorates. In addition, the higher the compaction density of the positive electrode plate, the worse the power performance of the secondary battery. Therefore, to ensure good power performance of the secondary battery, the conventional solution is to reduce the compaction density of the positive electrode plate, but this results in a loss of energy density of the secondary battery.

[0073] According to the unexpected discovery of the inventors of the present application, the compaction density P g / cm of the positive electrode plate 3When the mass percentage (x%) of lithium tetrafluoroborate and the cobalt content (c) of the low-cobalt or cobalt-free positive electrode active material satisfy the relationship 25≦P / (c+x / 10)≦65, the secondary battery can have improved power performance, including improved cycle performance and high energy density. For example, the initial power and power increase during cycling of the secondary battery are both significantly improved. While the mechanism is still unclear, the inventors speculate that the following possible reasons are possible: First, when the lithium tetrafluoroborate content is within an appropriate range, it can stabilize the crystalline structure of the low-cobalt or cobalt-free positive electrode active material, thereby providing good electronic conductivity. Second, an appropriate compaction density contributes to the formation of a good electronic conductive network in the positive electrode plate.

[0074] Therefore, when 25≦P / (c+x / 10)≦65, the secondary battery can have improved power performance with improved cycle performance and high energy density. This effectively avoids the following situation: When P / (c+x / 10)<25, the packing density of the positive plate may be low, which may result in a poor electronic conductive network in the positive plate, preventing the power performance of the secondary battery from being effectively improved and sacrificing the energy density of the secondary battery; or the lithium tetrafluoroborate content may be high, which may reduce the stability of the negative electrode interfacial film, further increasing the battery's internal resistance and degrading power performance. When P / (c+x / 10)>65, the lithium tetrafluoroborate content may be insufficient to compensate for the degradation of the secondary battery's power performance caused by the increased packing density of the positive plate, resulting in a deterioration of the secondary battery's power performance. Optionally, 25≦P / (c+x / 10)≦60, 25≦P / (c+x / 10)≦55, 25≦P / (c+x / 10)≦50, 25≦P / (c+x / 10)≦45, 25≦P / (c+x / 10)≦40, 30≦P / (c+x / 10)≦65, 30≦P / (c+x / 10)≦60, 30≦P / (c+x / 10)≦55, 30≦P / (c+x / 10)≦50, or 30≦P / (c+x / 10)≦45.

[0075] In some embodiments, optionally, the consolidation density P g / cm of the positive electrode plate 3 satisfies that P is 3.3 to 3.6, and further optionally 3.4 to 3.5. This contributes to the secondary battery having a high energy density.

[0076] [Electrolyte solution] In some embodiments, the electrolyte solution may further contain one or more of fluoroethylene carbonate (FEC), lithium fluorosulfonylimide salt, and lithium fluorosulfonate salt in addition to lithium tetrafluoroborate. The mass percentage of the fluoroethylene carbonate in the electrolyte solution is y1%, the mass percentage of the lithium fluorosulfonylimide salt in the electrolyte solution is y2%, and the mass percentage of the lithium fluorosulfonate salt in the electrolyte solution is y3%. All are calculated based on the total mass of the electrolyte solution, and the electrolyte solution satisfies y1≥0, y2≥0, y3≥0, and 0 < y1 + y2 + y3 ≤ 15. Lithium tetrafluoroborate can form a dense and low-impedance interfacial film on the surface of the positive electrode active material, but the long-term stability of the interfacial film formed on the negative electrode by lithium tetrafluoroborate is low. Therefore, when the electrolyte solution further contains the above compounds, it contributes to forming a more stable interfacial film on the positive electrode and / or the negative electrode, thereby further improving the electrochemical performance of the secondary battery.

[0077] In some embodiments, the electrolyte solution may further contain fluoroethylene carbonate. Optionally, the mass percentage y1% of the fluoroethylene carbonate satisfies 0 < y1 ≤ 2.5. For example, y1 may be in the range composed of 0.10, 0.20, 0.50, 0.75, 1.0, 1.25, 1.50, 1.75, 2.0, 2.5, or any numerical value above. Further optionally, 0 < y1 ≤ 2.0, 0 < y1 ≤ 1.75, 0 < y1 ≤ 1.5, 0 < y1 ≤ 1.25, 0 < y1 ≤ 1.0, 0 < y1 ≤ 0.75, or 0 < y1 ≤ 0.5.

[0078] In secondary batteries, fluoroethylene carbonate undergoes a reductive decomposition reaction at high potential, forming a ductile SEI film on the surface of the negative electrode active material. It also inhibits the reductive decomposition of organic solvents at low potentials and prevents the organic solvent from being absorbed into the negative electrode active material. Therefore, when fluoroethylene carbonate is added to the electrolyte, it can stabilize the negative electrode interfacial film, thereby effectively improving the cycle performance of the secondary battery. Furthermore, fluoroethylene carbonate is resistant to high-pressure oxidation, which is advantageous for compatibility with high-voltage positive electrode active materials, thereby improving the energy density of the secondary battery. However, when fluoroethylene carbonate decomposes at high temperatures, it forms HF, which increases the acidity of the electrolyte, destroys the structural stability of the positive electrode active material, and increases the amount of gas generated in the secondary battery, thereby degrading the high-temperature storage performance of the secondary battery. Therefore, the fluoroethylene carbonate content should not be too high.

[0079] In some embodiments, the mass percentage x% of lithium tetrafluoroborate and the mass percentage y1% of fluoroethylene carbonate may further satisfy 0.5≦y1 / x≦4.0. The present inventors unexpectedly discovered that when the relationship between the mass percentage x% of lithium tetrafluoroborate and the mass percentage y1% of fluoroethylene carbonate is rationally controlled to satisfy 0.5≦y1 / x≦4.0, the synergistic effect between lithium tetrafluoroborate and fluoroethylene carbonate can be fully exerted, thereby not only preventing a significant increase in gas generation in the secondary battery but also further improving the cycle performance of the secondary battery. A possible reason for this is that lithium tetrafluoroborate acts as a stabilizer for the positive electrode active material, with the B atoms in its structure interacting with the O atoms on the surface of the positive electrode active material, thereby preventing HF from damaging the structure of the positive electrode active material. Optionally, 0.5≦y1 / x≦3.5, 0.5≦y1 / x≦3.0, 0.5≦y1 / x≦2.5, 0.5≦y1 / x≦2.0, 0.5≦y1 / x≦1.5, 0.5≦y1 / x≦1.0.

[0080] In some embodiments, the electrolyte may further contain lithium fluorosulfonyl imide salt. The molecular formula of the lithium fluorosulfonyl imide salt may be LiN(SO2R1)(SO2R2), where R1 and R2 are each independently F or C n F 2n+1 is represented, and n is an integer from 1 to 10. Optionally, the lithium fluorosulfonyl imide salt includes lithium bis(fluorosulfonyl)imide (LiFSI), lithium trifluoromethanesulfonyl imide (LiTFSI), or a combination thereof.

[0081] Optionally, the mass percentage y2% of the lithium fluorosulfonyl imide salt satisfies 0 < y2 ≦ 14. For example, y2 may be a range composed of 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or any numerical value above.

[0082] The fluorosulfonyl imide anion is a weakly coordinating anion centered on N, with a conjugated group and highly electron-withdrawing -F or -C n F 2n+1The anion charge is highly delocalized, resulting in weak interaction between the anion and lithium ion. Therefore, fluorosulfonylimide lithium salt has low lattice energy and is easily dissociated, thereby increasing the ionic conductivity of the electrolyte, reducing the viscosity of the electrolyte, and improving the rate performance and low-temperature performance of the secondary battery. Furthermore, fluorosulfonylimide lithium salt has high thermal stability and is resistant to hydrolysis, thereby forming a thinner SEI film on the surface of the negative electrode active material, which has lower impedance and higher thermal stability, thereby reducing side reactions between the negative electrode active material and the electrolyte. Therefore, when fluorosulfonylimide lithium salt is further added to the electrolyte, the rate performance and low-temperature performance of the secondary battery can be significantly improved. However, fluorosulfonylimide lithium salt cannot withstand high pressures, can corrode the positive electrode current collector (e.g., aluminum foil) at high potentials, and can increase side reactions between the positive electrode active material and the electrolyte, which can easily affect the cycle performance of the secondary battery. Therefore, the content of fluorosulfonylimide lithium salt should not be too high.

[0083] In some embodiments, the mass percentage x% of lithium tetrafluoroborate and the mass percentage y2% of lithium fluorosulfonyl imide salt may further satisfy 1≤y2 / x≤28. According to the unexpected discovery of the inventor of the present application, when the relationship between the mass percentage x% of lithium tetrafluoroborate and the mass percentage y2% of lithium fluorosulfonyl imide salt is reasonably controlled to satisfy 1≤y2 / x≤28, the synergistic effect between lithium tetrafluoroborate and lithium fluorosulfonyl imide salt can be fully exerted, not only significantly deteriorating the cycle performance of the secondary battery, but also further improving the rate performance and low-temperature performance of the secondary battery. The following reasons may be considered as possible causes, that is, lithium tetrafluoroborate, as a stabilizer of the positive electrode active material, can form a dense and low-impedance interfacial film on the surface of the positive electrode active material, suppressing the side reaction between the positive electrode active material and the electrolyte, and lithium tetrafluoroborate has a passivation effect on the positive electrode current collector, which can be preferentially oxidized and decomposed on the surface of the positive electrode current collector to form a layer of passivation film, thereby effectively improving the corrosion of the positive electrode current collector by the lithium fluorosulfonyl imide salt.

[0084] According to further research by the inventor, the content b of nickel element in the positive electrode active material affects the improvement effect of the lithium fluorosulfonyl imide salt on the performance of the secondary battery. When the content of nickel element is high, the thermal stability of the positive electrode active material is low, and the high-temperature capacity decay is fast. Therefore, when a higher content of lithium fluorosulfonyl imide salt is adopted, the improvement effect on the high-temperature performance of the secondary battery is more significant. When the content of nickel element is low, the thermal stability of the positive electrode active material is high, and with the increase of the content of lithium fluorosulfonyl imide salt in the electrolyte, the improvement effect on the high-temperature performance of the secondary battery does not increase continuously.

[0085] In some embodiments, when 0 < b ≤ 0.7, the mass percentage y2% of the lithium fluorosulfonyl imide salt in the electrolyte satisfies 0 < y2 ≤ 5 and / or 1 ≤ y2 / x ≤ 10.

[0086] Optionally, 0 < y2 ≤ 4.5, 0 < y2 ≤ 4, 0 < y2 ≤ 3.5, 0 < y2 ≤ 3, 0 < y2 ≤ 2.5, 0 < y2 ≤ 2, 0 < y2 ≤ 1.5, or 0 < y2 ≤ 1.

[0087] Optionally, 1 ≤ y2 / x ≤ 9, 1 ≤ y2 / x ≤ 8, 1 ≤ y2 / x ≤ 7, 1 ≤ y2 / x ≤ 6, 1 ≤ y2 / x ≤ 5, 1 ≤ y2 / x ≤ 4, 1 ≤ y2 / x ≤ 3, or 1 ≤ y2 / x ≤ 2.

[0088] In some embodiments, when 0.7 ≤ b < 0.98, the mass percentage y2% of the lithium fluorosulfonylimide salt in the electrolyte satisfies 5 ≤ y2 ≤ 14 and / or 10 ≤ y2 / x ≤ 28.

[0089] Optionally, 5 ≤ y2 ≤ 13, 5 ≤ y2 ≤ 12, 5 ≤ y2 ≤ 11, 5 ≤ y2 ≤ 10, 6 ≤ y2 ≤ 14, 6 ≤ y2 ≤ 13, 6 ≤ y2 ≤ 12, 6 ≤ y2 ≤ 11, 6 ≤ y2 ≤ 10, 7 ≤ y2 ≤ 14, 7 ≤ y2 ≤ 13, 7 ≤ y2 ≤ 12, 7 ≤ y2 ≤ 11, 7 ≤ y2 ≤ 10, 8 ≤ y2 ≤ 14, 8 ≤ y2 ≤ 13, 8 ≤ y2 ≤ 12, 8 ≤ y2 ≤ 11, or 8 ≤ y2 ≤ 10.

[0090] Optionally, 12 ≤ y2 / x ≤ 28, 12 ≤ y2 / x ≤ 26, 12 ≤ y2 / x ≤ 24, 12 ≤ y2 / x ≤ 22, 12 ≤ y2 / x ≤ 20, 14 ≤ y2 / x ≤ 28, 14 ≤ y2 / x ≤ 26, 14 ≤ y2 / x ≤ 24, 14 ≤ y2 / x ≤ 22, 14 ≤ y2 / x ≤ 20, 16 ≤ y2 / x ≤ 28, 16 ≤ y2 / x ≤ 26, 16 ≤ y2 / x ≤ 24, 16 ≤ y2 / x ≤ 22, or 16 ≤ y2 / x ≤ 20.

[0091] In some embodiments, the electrolyte may further contain lithium fluorosulfonate salt. The molecular formula of the lithium fluorosulfonate salt may be LiSO3R3, where R3 represents F, a partially fluorinated or fully fluorinated C1-C10 alkyl group. Optionally, the lithium fluorosulfonate salt includes lithium fluorosulfonate, lithium trifluoromethanesulfonate, or a combination thereof.

[0092] Optionally, the mass percentage y3% of the lithium fluorosulfonate salt satisfies 0 < y3 ≤ 1.0. For example, y3 may be in the range composed of 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, 0.90, 1.0, or any numerical value above. Further optionally, 0 < y3 ≤ 0.9, 0 < y3 ≤ 0.8, 0 < y3 ≤ 0.7, 0 < y3 ≤ 0.6, 0 < y3 ≤ 0.5, 0 < y3 ≤ 0.4, 0 < y3 ≤ 0.3, or 0 < y3 ≤ 0.2.

[0093] The lithium fluorosulfonate salt can not only form an interfacial film on the surface of the negative electrode active material but also form an interfacial film on the surface of the positive electrode active material. At the same time, it has high thermal stability, which greatly improves the charge and discharge characteristics of the secondary battery at high temperatures, increases the high-temperature cycle capacity retention rate of the secondary battery, and can suppress the generation of gas. However, the ionic conductivity of the lithium fluorosulfonate salt is low and it is likely to affect the kinetic performance of the secondary battery. Therefore, the content of the lithium fluorosulfonate salt should not be too high.

[0094] In some embodiments, the mass percentage x% of lithium tetrafluoroborate and the mass percentage y3% of lithium fluorosulfonate may further satisfy 0.001 ≤ y3 / x ≤ 2.0. According to the unexpected discovery of the inventor of the present application, when reasonably controlling the relationship between the mass percentage x% of lithium tetrafluoroborate and the mass percentage y3% of lithium fluorosulfonate to satisfy 0.001 ≤ y3 / x ≤ 2.0, the synergistic effect between lithium tetrafluoroborate and lithium fluorosulfonate can be fully exerted, thereby contributing to the formation of a dense, stable and low-impedance interfacial film on the positive and negative electrodes, and further improving the high-temperature performance of the secondary battery. For example, it can improve the high-temperature cycle performance and high-temperature storage performance, and does not significantly deteriorate the kinetic performance of the secondary battery. Optionally, 0.001 ≤ y3 / x ≤ 1.5, 0.001 ≤ y3 / x ≤ 1.25, 0.001 ≤ y3 / x ≤ 1.0, 0.001 ≤ y3 / x ≤ 0.75, 0.001 ≤ y3 / x ≤ 0.5, or 0.001 ≤ y3 / x ≤ 0.25.

[0095] In some embodiments, the electrolyte may further contain any two of fluoroethylene carbonate, lithium fluorosulfonyl imide salt, and lithium fluorosulfonate.

[0096] For example, in some embodiments, the electrolyte may contain a combination of fluoroethylene carbonate and lithium fluorosulfonyl imide salt. Optionally, the mass percentage y1% of the fluoroethylene carbonate satisfies 0 < y1 ≤ 2.5, the mass percentage y2% of the lithium fluorosulfonyl imide salt satisfies 0 < y2 ≤ 14, and 0 < y1 + y2 ≤ 15.

[0097] Optionally, the mass percentage x% of lithium tetrafluoroborate, the mass percentage y1% of fluoroethylene carbonate, and the mass percentage y2% of the fluorosulfonylimide lithium salt further satisfy 0.5≦y1 / x≦4.0 and / or 1≦y2 / x≦28, thereby providing the secondary battery with significantly improved cycle performance, as well as improved rate performance and low-temperature performance.

[0098] Optionally, the mass percentage y1% of the fluoroethylene carbonate and the mass percentage y2% of the fluorosulfonylimide lithium salt may further satisfy 0.5≦y2 / y1≦48.

[0099] More optionally, the mass percentage of lithium tetrafluoroborate (x%), the mass percentage of fluoroethylene carbonate (y1%), and the mass percentage of fluorosulfonylimide lithium salt (y2%) simultaneously satisfy the following relationships: 0.5≦y1 / x≦4.0, 1≦y2 / x≦28, and 0.5≦y2 / y1≦48. Fluoroethylene carbonate can effectively improve the cycle performance of the secondary battery, the fluorosulfonylimide lithium salt can improve the rate performance and low-temperature performance of the secondary battery, and lithium tetrafluoroborate, as a stabilizer for the positive electrode active material, forms a dense, low-impedance interfacial film on the surface of the positive electrode active material, significantly improving the lithium ion diffusion rate of low-cobalt or cobalt-free positive electrode active material, suppressing side reactions between the positive electrode active material and the electrolyte, and suppressing damage to the structure of the positive electrode active material caused by HF. Therefore, by further rationally adjusting the content relationships among the three components so that 0.5≦y1 / x≦4.0, 1≦y2 / x≦28, and 0.5≦y2 / y1≦48 are simultaneously satisfied, the synergistic effects among the three components can be fully exerted, which is advantageous in fully suppressing the defects that occur when each component is used alone, and also enables the formation of positive and negative electrode interfacial films that are dense, stable, and have low impedance.

[0100] In particular, when 0 < b ≤ 0.7, the electrolyte may satisfy 0 < y1 ≤ 2.5 and 0 < y2 ≤ 5. Optionally, the electrolyte may further satisfy 0.5 ≤ y1 / x ≤ 4.0 and 1 ≤ y2 / x ≤ 10. Further optionally, the electrolyte may further satisfy 0.5 ≤ y2 / y1 ≤ 10.

[0101] In particular, when 0.7 ≤ b < 0.98, the electrolyte may satisfy 0 < y1 ≤ 2.5 and 5 ≤ y2 ≤ 14. Optionally, the electrolyte may further satisfy 0.5 ≤ y1 / x ≤ 4.0 and 10 ≤ y2 / x ≤ 28. Further optionally, the electrolyte may further satisfy 6 ≤ y2 / y1 ≤ 48.

[0102] For example, in some embodiments, the electrolyte may include a combination of fluoroethylene carbonate and lithium fluorosulfonate salt. Optionally, the mass percentage y1% of the fluoroethylene carbonate satisfies 0 < y1 ≤ 2.5, and the mass percentage y3% of the lithium fluorosulfonate salt satisfies 0 < y3 ≤ 1.0. Further optionally, the mass percentage x% of lithium tetrafluoroborate, the mass percentage y1% of fluoroethylene carbonate and the mass percentage y3% of lithium fluorosulfonate salt further satisfy 0.5 ≤ y1 / x ≤ 4.0 and / or 0.001 ≤ y3 / x ≤ 2.0. Thereby, the secondary battery has significantly improved cycle performance and at the same time improved high-temperature performance.

[0103] For example, in some embodiments, the electrolyte may include a combination of lithium fluorosulfonyl imide salt and lithium fluorosulfonate salt. Optionally, the mass percentage y2% of the lithium fluorosulfonyl imide salt satisfies 0 < y2 ≤ 14, the mass percentage y3% of the lithium fluorosulfonate salt satisfies 0 < y3 ≤ 1.0, and 0 < y2 + y3 ≤ 15.

[0104] Optionally, the mass percentage x% of lithium tetrafluoroborate, the mass percentage y2% of lithium fluorosulfonyl imide salt and the mass percentage y3% of lithium fluorosulfonate salt further satisfy 1 ≤ y2 / x ≤ 28 and / or 0.001 ≤ y3 / x ≤ 2.0. Thereby, the secondary battery has significantly improved cycle performance and at the same time has improved rate performance, low temperature performance and high temperature performance. Further optionally, the mass percentage x% of lithium tetrafluoroborate, the mass percentage y2% of lithium fluorosulfonyl imide salt and the mass percentage y3% of lithium fluorosulfonate salt simultaneously satisfy 1 ≤ y2 / x ≤ 28, 0.001 ≤ y3 / x ≤ 2.0, and 0.036 ≤ x / (y2 + y3) ≤ 1.0. Thereby, it contributes to forming an inorganic / organic composite interface film with excellent performance on the positive electrode and the negative electrode, and thereby the overall performance of the secondary battery can be further improved.

[0105] Particularly, when 0 < b ≤ 0.7, the electrolytic solution may satisfy 0 < y2 ≤ 5 and 0 < y3 ≤ 1.0. Optionally, the electrolytic solution may further satisfy 1 ≤ y2 / x ≤ 10 and 0.001 ≤ y3 / x ≤ 2.0. Further optionally, the electrolytic solution may further satisfy 0.1 ≤ x / (y2 + y3) ≤ 1.0.

[0106] Particularly, when 0.7 ≤ b < 0.98, the electrolytic solution may satisfy 5 ≤ y2 ≤ 14 and 0 < y3 ≤ 1.0. Optionally, the electrolytic solution may further satisfy 10 ≤ y2 / x ≤ 28 and 0.001 ≤ y3 / x ≤ 2.0. Further optionally, the electrolytic solution may further satisfy 0.036 ≤ x / (y2 + y3) ≤ 0.1.

[0107] In some embodiments, the electrolyte may simultaneously contain fluoroethylene carbonate, lithium fluorosulfonyl imide salt, and lithium fluorosulfonic acid salt. Optionally, the mass percentage y1% of the fluoroethylene carbonate satisfies 0 < y1 ≦ 2.5, the mass percentage y2% of the lithium fluorosulfonyl imide salt satisfies 0 < y2 ≦ 14, the mass percentage y3% of the lithium fluorosulfonic acid salt satisfies 0 < y3 ≦ 1.0, and 0 < y1 + y2 + y3 ≦ 15.

[0108] Optionally, the electrolyte further satisfies 0.5 ≦ y1 / x ≦ 4.0, 1 ≦ y2 / x ≦ 28, and 0.001 ≦ y3 / x ≦ 2.0. Thereby, the secondary battery has significantly improved cycle performance, and at the same time, improved rate performance, low-temperature performance, and high-temperature performance. Further optionally, the electrolyte simultaneously satisfies 0.5 ≦ y1 / x ≦ 4.0, 1 ≦ y2 / x ≦ 28, 0.001 ≦ y3 / x ≦ 2.0, and 0.5 ≦ y2 / y1 ≦ 48. At this time, the overall performance of the secondary battery is further improved. Further optionally, the electrolyte simultaneously satisfies 0.5 ≦ y1 / x ≦ 4.0, 1 ≦ y2 / x ≦ 28, 0.001 ≦ y3 / x ≦ 2.0, 0.5 ≦ y2 / y1 ≦ 48, and 0.036 ≦ x / (y2 + y3) ≦ 1.0. This contributes to forming an inorganic / organic composite interface film with excellent performance on the positive and negative electrodes, thereby further improving the overall performance of the secondary battery.

[0109] Particularly, when 0 < b ≦ 0.7, the electrolyte may satisfy 0 < y1 ≦ 2.5, 0 < y2 ≦ 5, and 0 < y3 ≦ 1.0. Optionally, the electrolyte may further satisfy 0.5 ≦ y1 / x ≦ 4.0, 1 ≦ y2 / x ≦ 10, and 0.001 ≦ y3 / x ≦ 2.0. Further optionally, the electrolyte may further satisfy 0.5 ≦ y2 / y1 ≦ 10 and / or 0.1 ≦ x / (y2 + y3) ≦ 1.0.

[0110] In particular, when 0.7 ≦ b < 0.98, the electrolyte may satisfy 0 < y1 ≦ 2.5, 5 ≦ y2 ≦ 14 and 0 < y3 ≦ 1.0. Optionally, the electrolyte may further satisfy 0.5 ≦ y1 / x ≦ 4.0, 10 ≦ y2 / x ≦ 28 and 0.001 ≦ y3 / x ≦ 2.0. Further optionally, the electrolyte may further satisfy 6 ≦ y2 / y1 ≦ 48 and / or 0.036 ≦ x / (y2 + y3) ≦ 0.1.

[0111] In some embodiments, the electrolyte further comprises a lithium salt and an organic solvent. In the present application, the types of the lithium salt and the organic solvent are not specifically limited and can be selected according to actual needs.

[0112] By way of example, the lithium salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluoro bis(oxalato)phosphate (LiDFOP) and lithium tetrafluoro(oxalato)phosphate (LiTFOP). Optionally, the lithium salt includes lithium hexafluorophosphate.

[0113] By way of example, the organic solvent may comprise one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0114] In the embodiments of the secondary battery of the present application, the electrolyte does not exclude other components other than the above components. In some examples, the electrolyte may optionally further include other additives, such as an additive for improving the overcharge performance of the battery, an additive for improving the high-temperature performance of the battery, or an additive for improving the low-temperature power performance of the battery.

[0115] In some embodiments, the mass of the electrolyte may be 10% to 20% of the total mass of the secondary battery. This is advantageous for forming a dense interfacial film with low impedance on the surface of the positive electrode active material. This effectively avoids the following situation: When the mass fraction of the electrolyte is less than 10%, the electrolyte's permeability to the positive and negative electrodes is low, the interfacial impedance is high, and the impedance increases rapidly after cycling, which may result in low capacity and poor cycling performance of the secondary battery. When the mass fraction of the electrolyte is more than 20%, interfacial side reactions between the electrolyte and the positive electrode and the electrolyte and the negative electrode increase, which may increase irreversible consumption of active lithium ions and cause severe battery volume expansion, which may result in poor cycling performance of the secondary battery.

[0116] The electrolyte solution may be prepared according to a method commonly used in the art. For example, an electrolyte solution can be obtained by uniformly mixing components such as an organic solvent, a lithium salt, lithium tetrafluoroborate, optional fluoroethylene carbonate, optional fluorosulfonylimide lithium salt, and optional fluorosulfonate lithium salt. The order of addition of each substance is not particularly limited. For example, components such as lithium salt, lithium tetrafluoroborate, optional fluoroethylene carbonate, optional fluorosulfonylimide lithium salt, and optional fluorosulfonate lithium salt may be added to an organic solvent and uniformly mixed to obtain an electrolyte solution. Alternatively, the lithium salt may be first added to an organic solvent, and then components such as lithium tetrafluoroborate, optional fluoroethylene carbonate, optional fluorosulfonylimide lithium salt, and optional fluorosulfonate lithium salt may be added to an organic solvent and uniformly mixed to obtain an electrolyte solution.

[0117] In the present application, each component and its content in the electrolyte may be measured according to a method known in the art, such as gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), etc.

[0118] It should be noted that when testing the electrolyte solution of the present application, the electrolyte solution may be obtained from a secondary battery. One exemplary method for obtaining the electrolyte solution from a secondary battery includes the following steps: discharge the secondary battery to the discharge cutoff voltage (for safety reasons, the battery is generally fully discharged), then perform a centrifugal process, and take an appropriate amount of the liquid obtained by the centrifugal process as the electrolyte solution. The electrolyte solution may also be obtained directly from the filling port of the secondary battery.

[0119] [Positive electrode] The positive electrode plate of the present application includes a positive electrode current collector and a positive electrode film layer located on the surface of the positive electrode current collector. For example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode film layer is located on one or both of the two facing surfaces of the positive electrode current collector.

[0120] The positive electrode current collector may be a metal foil sheet or a composite current collector. An example of the metal foil sheet is aluminum foil. The composite current collector may include a polymeric material base layer and a metal material layer formed on at least one surface of the polymeric material base layer. For example, the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. For example, the polymeric material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0121] The positive electrode membrane layer typically includes a positive electrode active material, an optional adhesive, and an optional conductive agent. The positive electrode membrane layer is typically formed by coating a positive electrode slurry on a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, the optional conductive agent, the optional adhesive, and any other components in a solvent and stirring the mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP). For example, the adhesive used in the positive electrode membrane layer may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin. For example, the conductive agent used in the positive electrode film layer may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0122] The positive electrode active material has the molecular formula Li a Ni b Co c M1 d M2 e O f A g The present invention includes a layered material in which

[0123] In some embodiments, the molecular formula is Li a Ni b Co c M1 d M2 e O f A g The layered material represented by formula (I) can be optionally doped with M2 cations, A anions, or both M2 cations and A anions, so that the crystalline structure of the resulting layered material after doping is more stable and the electrochemical performance of the secondary battery, such as cycle performance and rate performance, can be further improved.

[0124] In some embodiments, A is selected from F. After being doped with F, Li a Ni b Co c M1 d M2 e O f A g The structure is more stable, and the secondary battery can have better cycle performance and rate performance.

[0125] In some embodiments, M1 is selected from Mn.

[0126] In some embodiments, M1 is selected from Al.

[0127] In some embodiments, M1 is selected from a combination of Mn and Al. There is no particular limitation on the molar ratio of Mn and Al, and it can be selected according to actual needs.

[0128] In some embodiments, 0.50 ≦ b < 0.98. Optionally, 0.55 ≦ b < 0.98, 0.60 ≦ b < 0.98, 0.65 ≦ b < 0.98, 0.70 ≦ b < 0.98, 0.75 ≦ b < 0.98, or 0.80 ≦ b < 0.98.

[0129] In some embodiments, c = 0.

[0130] In some embodiments, 0 < c < 0.1. Optionally, 0 < c ≦ 0.09, 0 < c ≦ 0.08, 0 < c ≦ 0.07, 0 < c ≦ 0.06, 0 < c ≦ 0.05, 0 < c ≦ 0.04, 0 < c ≦ 0.03, 0 < c ≦ 0.02, or 0 < c ≦ 0.01.

[0131] In some embodiments, 0 < d ≦ 0.45. Optionally, 0 < d ≦ 0.40, 0 < d ≦ 0.35, 0 < d ≦ 0.30, 0 < d ≦ 0.25, 0 < d ≦ 0.20, 0 < d ≦ 0.15, or 0 < d ≦ 0.10.

[0132] In some embodiments, e = 0.

[0133] In some embodiments, 0 < e ≦ 0.5. Optionally, 0 < e ≦ 0.45, 0 < e ≦ 0.40, 0 < e ≦ 0.35, 0 < e ≦ 0.30, 0 < e ≦ 0.25, 0 < e ≦ 0.20, 0 < e ≦ 0.15, 0 < e ≦ 0.10, or 0 < e ≦ 0.05.

[0134] In some embodiments, f = 2, g = 0.

[0135] In some embodiments, f = 0, g = 2.

[0136] In some embodiments, 0 < f < 2, 0 < g < 2, and f + g = 2.

[0137] As an example, the molecular formula is Li a Ni b Co c M1 d M2 e O fA g The layered material is LiNi 0.7 Mn 0.3 O2, LiNi 0.69 Co 0.01 Mn 0.3 O2, LiNi 0.68 Co 0.02 Mn 0.3 O2, LiNi 0.65 Co 0.05 Mn 0.3 O2, LiNi 0.63 Co 0.07 Mn 0.3 O2, LiNi 0.61 Co 0.09 Mn 0.3 O2.

[0138] Li a Ni b Co c M1 d M2 e O f A gcan be manufactured according to a common method in the art. An exemplary manufacturing method is as follows: A lithium source, a nickel source, a cobalt source, an M1 element precursor, an optional M2 element precursor, and an optional A element precursor are mixed and then sintered to obtain the composite. The sintering atmosphere may be an oxygen-containing atmosphere, such as an air atmosphere or an oxygen atmosphere. The O2 concentration of the sintering atmosphere is, for example, 70% to 100%. The sintering temperature and sintering time may be adjusted according to actual conditions. For example, the lithium source may include, but is not limited to, one or more of lithium oxide (Li2O), lithium phosphate (Li3PO4), lithium dihydrogen phosphate (LiH2PO4), lithium acetate (CH3COOLi), lithium hydroxide (LiOH), lithium carbonate (Li2CO3), and lithium nitrate (LiNO3). For example, the nickel source may include, but is not limited to, one or more of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate. For example, the cobalt source may include, but is not limited to, one or more of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate. For example, the M1 element precursor may include, but is not limited to, one or more of an oxide, a nitrate compound, a carbonate compound, a hydroxide, and an acetate compound of the M1 element. For example, the M2 element precursor may include, but is not limited to, one or more of an oxide, a nitrate compound, a carbonate compound, a hydroxide, and an acetate compound of the M2 element. For example, the A element precursor may include, but is not limited to, one or more of ammonium fluoride, lithium fluoride, hydrogen fluoride, ammonium chloride, lithium chloride, hydrogen chloride, ammonium nitrate, ammonium nitrite, ammonium carbonate, ammonium bicarbonate, ammonium phosphate, phosphoric acid, ammonium sulfate, ammonium hydrogen sulfate, ammonium hydrogen sulfite, ammonium sulfite, ammonium hydrogen sulfide, hydrogen sulfide, lithium sulfide, ammonium sulfide, and elemental sulfur.

[0139] In some embodiments, Li a Ni b Co c M1 d M2 e O f Ag The surface of the positive electrode active material may further have a coating layer, such as a carbon coating layer. The carbon coating layer is advantageous in stabilizing the surface of the positive electrode active material, further reducing the charge transfer impedance of the positive electrode active material, and reducing the diffusion resistance of lithium ions within the bulk phase of the positive electrode active material. Optionally, the carbon coating layer includes amorphous carbon, such as soft carbon, hard carbon, or a combination thereof.

[0140] In some embodiments, the positive electrode active material is Li a Ni b Co c M1 d M2 e O f A g For example, the positive electrode active material may further include one or more of a lithium-containing phosphate and a modified compound thereof. For example, the lithium-containing phosphate may include one or more of a lithium iron phosphate, a composite material of lithium iron phosphate and carbon, a lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, a lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and a modified compound thereof.

[0141] In some embodiments, the molecular formula is Li a Ni b Co c M1 d M2 e O f A g The mass percentage of the layered material is 80% to 99%. For example, a Ni b Co c M1 d M2 e O f A g The weight percentage of the layered material, wherein the molecular formula is Li, is 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or any range of greater than or equal to ...a Ni b Co c M1 d M2 e O f A g The mass percentage of the layered material is 85% to 99%, 90% to 99%, 95% to 99%, 80% to 98%, 85% to 98%, 90% to 98%, 95% to 98%, 80% to 97%, 85% to 97%, 90% to 97%, or 95% to 97%.

[0142] [Negative electrode] The secondary battery according to the present application further includes a negative electrode plate. In some embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer located on a surface of the negative electrode current collector. For example, the negative electrode current collector has two surfaces facing each other in a thickness direction thereof, and the negative electrode film layer is located on one or both of the two facing surfaces of the negative electrode current collector.

[0143] The negative electrode current collector may be a metal foil sheet or a composite current collector. An example of the metal foil sheet is copper foil. The composite current collector may include a polymeric material base layer and a metal material layer formed on at least one surface of the polymeric material base layer. For example, the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. For example, the polymeric material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0144] The negative electrode film layer typically includes a negative electrode active material, an optional adhesive, an optional conductive agent, and other optional auxiliary agents. The negative electrode film layer is typically formed by coating a negative electrode slurry on a negative electrode current collector, drying, and cold-pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, the optional conductive agent, the optional adhesive, and other optional auxiliary agents in a solvent and stirring the mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water. For example, the adhesive used in the negative electrode film layer may include one or more of styrene butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid (PAA), polymethacrylic acid (PMAA), sodium polyacrylate (PAAS)), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). For example, the conductive agent used in the negative electrode film layer may include one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon spots, carbon nanotubes, graphene, and carbon nanofibers. Other optional additives may include thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)), PTC thermistor materials, etc.

[0145] The negative electrode active material may be a negative electrode active material for secondary batteries well known in the art. For example, the negative electrode active material may include one or more of natural graphite, artificial graphite, soft carbon, hard carbon, a silicone-based material, a tin-based material, and lithium titanate. The silicone-based material may include one or more of a silicone element, a silicone oxide, a silicone carbon composite, a silicone nitrogen composite, and a silicone alloy material. The tin-based material may include one or more of a tin element, a tin oxide, and a tin alloy material. The present application is not limited to these materials, and other conventionally known materials usable as negative electrode active materials for secondary batteries may also be used. These negative electrode active materials may be used alone or in combination.

[0146] [Separator] The secondary battery according to the present application may further include a separator. The separator is disposed between the positive electrode plate and the negative electrode plate to separate them. The present application does not particularly limit the type of the separator, and any known porous membrane having good chemical and mechanical stability may be selected.

[0147] In some embodiments, the separator may be made of one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0148] In some embodiments, the positive electrode plate, the separator, and the negative electrode plate can be fabricated into an electrode assembly by a winding process and / or a stacking process.

[0149] In some embodiments, the secondary battery may include an exterior body. The exterior body may be used to package the electrode assembly and the electrolyte. The exterior body of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, or a steel case. The exterior body of the secondary battery may be a pouch, such as a bag-shaped pouch. The pouch may be made of one or more plastic materials, such as polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0150] The present application does not particularly limit the shape of the secondary battery, which may be cylindrical, rectangular, or any other shape. Figure 1 shows a secondary battery 5 with a rectangular structure as an example.

[0151] In some embodiments, as shown in FIG. 2 , the exterior body may include a case 51 and a cover plate 53. The case 51 may include a bottom plate and side plates connected to the bottom plate, which together form a surrounding accommodating cavity. The case 51 has an opening communicating with the accommodating cavity, and the cover plate 53 is provided to cover the opening and close the accommodating cavity. The positive electrode plate, the negative electrode plate, and the separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is packaged in the accommodating cavity. An electrolyte is impregnated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more and can be adjusted as needed.

[0152] In some embodiments of the present application, the secondary battery according to the present application may be assembled into a battery module, and the number of secondary batteries included in the battery module may be multiple, and the specific number can be adjusted based on the application and capacity of the battery module.

[0153] Fig. 3 is a schematic diagram of an example battery module 4. As shown in Fig. 3, in the battery module 4, the plurality of secondary batteries 5 may be arranged in order along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 may be fastened with fasteners.

[0154] Optionally, the battery module 4 may further include a housing having an accommodating space, and the plurality of secondary batteries 5 are accommodated in the accommodating space.

[0155] In some embodiments, the battery modules may be further assembled into a battery pack, and the number of battery modules included in the battery pack may be adjusted based on the application and capacity of the battery pack.

[0156] 4 and 5 are schematic diagrams of an example battery pack 1. As shown in FIGS. 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 installed in the battery box. The battery box includes an upper housing 2 and a lower housing 3, and the upper housing 2 is provided to cover the lower housing 3 and is used to form an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0157] Manufacturing method An embodiment of the present application further provides a method for manufacturing a secondary battery, the method including at least step 1 and step 2.

[0158] Step 1: Assembling a positive electrode plate, a separator, a negative electrode plate, and an electrolyte into a secondary battery, wherein the positive electrode plate includes a positive electrode current collector and a positive electrode film layer located on the surface of the positive electrode current collector, and the positive electrode film layer has a molecular formula of Li a Ni b Co c M1 d M2 e O f A gIt contains a layered material, where M1 is selected from Mn, Al or a combination thereof, M2 is selected from one or more of Si, Ti, Mo, V, Ge, Se, Zr, Nb, Ru, Pd, Sb, Ce, Te and W, A is selected from one or more of F, N, P and S, 0.8≦a≦1.2, 0<b<0.98, 0≦c<0.1, 0<d<0.5, 0≦e≦0.5, 0≦f≦2, 0≦g≦2, b + c + d + e = 1, f + g = 2. The electrolyte contains lithium tetrafluoroborate, optional fluoroethylene carbonate, optional lithium fluorosulfonylimide salt and optional lithium fluorosulfonate salt. The mass percentage of lithium tetrafluoroborate in the electrolyte is x%, the mass percentage of fluoroethylene carbonate in the electrolyte is y1%, the mass percentage of lithium fluorosulfonylimide salt in the electrolyte is y2%, and the mass percentage of lithium fluorosulfonate salt in the electrolyte is y3%, all calculated based on the total mass of the electrolyte, where x>0, y1≧0, y2≧0, y3≧0.

[0159] Step 2, from the secondary battery obtained in Step 1, select a secondary battery that satisfies 0.05≦c + x / 10≦0.15.

[0160] When the secondary battery satisfies x>0 and 0.05≦c + x / 10≦0.15, it can stabilize the crystal structure of the low-cobalt or cobalt-free cathode active material and improve the diffusion rate of lithium ions inside it. Therefore, the secondary batteries obtained by the manufacturing method of this application can all have significantly improved cycle performance, good storage performance and kinetic performance.

[0161] In some embodiments, the method further includes the step of selecting a secondary battery that satisfies 0<x≦1.0 and 0.05≦c + x / 10≦0.15 from the secondary batteries obtained in Step 2. At this time, the manufactured secondary batteries have further improved cycle performance. Optionally, the secondary battery satisfies 0.05≦c + x / 10≦0.12.

[0162] In some embodiments, the method further includes a step of selecting a secondary battery satisfying 25 ≦ P / (c + x / 10) ≦ 65 from the secondary batteries obtained in step 2, where P g / cm 3 represents the consolidation density of the positive electrode plate. At this time, on the premise that the manufactured secondary battery has significantly improved cycle performance and high energy density, it can have improved power performance. Optionally, the secondary battery satisfies 30 ≦ P / (c + x / 10) ≦ 50.

[0163] In some embodiments, the method further includes a step of selecting a secondary battery that satisfies at least one of the following conditions (1) to (3) from the secondary batteries obtained in step 2.

[0164] (1) 0 < y1 ≦ 2.5, 0.5 ≦ y1 / x ≦ 4.0, optionally 0.5 ≦ y1 / x ≦ 2.0, (2) 0 < y2 ≦ 14, 1 ≦ y2 / x ≦ 28, (3) 0 < y3 ≦ 1.0, 0.001 ≦ y3 / x ≦ 2.0, optionally 0.001 ≦ y3 / x ≦ 1.0.

[0165] At this time, the manufactured secondary battery has at least one of further improved cycle performance, storage performance, rate performance, low-temperature performance and high-temperature performance.

[0166] In some embodiments, the method further includes a step of selecting a secondary battery that satisfies 0 < y1 + y2 + y3 ≦ 15, 0 < y1 ≦ 2.5, 0 < y2 ≦ 14, 0 < y3 ≦ 1.0, 0.5 ≦ y1 / x ≦ 4.0, 1 ≦ y2 / x ≦ 28, 0.001 ≦ y3 / x ≦ 2.0, 0.5 ≦ y2 / y1 ≦ 48 from the secondary batteries obtained in step 2. At this time, the comprehensive performance of the manufactured secondary battery is further improved.

[0167] Optionally, when 0 < b ≤ 0.7, the method further includes the step of selecting a secondary battery that satisfies 0 < y1 + y2 + y3 ≤ 15, 0 < y1 ≤ 2.5, 0 < y2 ≤ 5, 0 < y3 ≤ 1.0, 0.5 ≤ y1 / x ≤ 4.0, 1 ≤ y2 / x ≤ 10, 0.001 ≤ y3 / x ≤ 2.0, 0.5 ≤ y2 / y1 ≤ 10 from the secondary battery obtained in step 2.

[0168] Optionally, when 0.7 ≤ b < 0.98, the method further includes the step of selecting a secondary battery that satisfies 0 < y1 + y2 + y3 ≤ 15, 0 < y1 ≤ 2.5, 5 ≤ y2 ≤ 14, 0 < y3 ≤ 1.0, 0.5 ≤ y1 / x ≤ 4.0, 10 ≤ y2 / x ≤ 28, 0.001 ≤ y3 / x ≤ 2.0, 6 ≤ y2 / y1 ≤ 48 from the secondary battery obtained in step 2.

[0169] In some embodiments, the method further includes the step of selecting a secondary battery that satisfies 0 < y1 + y2 + y3 ≤ 15, 0 < y1 ≤ 2.5, 0 < y2 ≤ 14, 0 < y3 ≤ 1.0, 0.5 ≤ y1 / x ≤ 4.0, 1 ≤ y2 / x ≤ 28, 0.001 ≤ y3 / x ≤ 2.0, 0.5 ≤ y2 / y1 ≤ 48, 0.036 ≤ x / (y2 + y3) ≤ 1.0 from the secondary battery obtained in step 2. At this time, the comprehensive performance of the manufactured secondary battery is further improved.

[0170] Optionally, when 0 < b ≤ 0.7, the method further includes the step of selecting a secondary battery that satisfies 0 < y1 + y2 + y3 ≤ 15, 0 < y1 ≤ 2.5, 0 < y2 ≤ 5, 0 < y3 ≤ 1.0, 0.5 ≤ y1 / x ≤ 4.0, 1 ≤ y2 / x ≤ 10, 0.001 ≤ y3 / x ≤ 2.0, 0.5 ≤ y2 / y1 ≤ 10, 0.1 ≤ x / (y2 + y3) ≤ 1.0 from the secondary battery obtained in step 2.

[0171] Optionally, when 0.7 ≦ b < 0.98, the method further includes a step of selecting a secondary battery from the secondary batteries obtained in step 2 that satisfies 0 < y1 + y2 + y3 ≦ 15, 0 < y1 ≦ 2.5, 5 ≦ y2 ≦ 14, 0 < y3 ≦ 1.0, 0.5 ≦ y1 / x ≦ 4.0, 10 ≦ y2 / x ≦ 28, 0.001 ≦ y3 / x ≦ 2.0, 6 ≦ y2 / y1 ≦ 48, 0.036 ≦ x / (y2 + y3) ≦ 0.1.

[0172] Power consumption device Embodiments of the present application further provide a power consumption device, which includes at least one of the secondary battery, battery module or battery pack of the present application. The secondary battery, battery module or battery pack may be used as the power supply of the power consumption device or as the energy storage unit of the power consumption device. The power consumption device may be a mobile device (such as a mobile phone, laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, hybrid electric vehicle, plug-in hybrid electric vehicle, electric bicycle, electric scooter, electric golf cart, electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0173] As the power consumption device, a secondary battery, a battery module or a battery pack can be selected according to the requirements in its use.

[0174] Figure 6 is a schematic diagram of a power consumption device as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements for high power and high energy density of the power consumption device, a battery pack or a battery module can be adopted.

[0175] Another example of the power consumption device may be a mobile phone, a tablet computer, a laptop computer, etc. The power consumption device is generally required to be lightweight, and a secondary battery can be adopted as the power supply.

[0176] Examples The following examples are provided to more specifically describe the contents disclosed in this application, and these examples are provided for illustrative purposes only, and it will be apparent to those skilled in the art that various modifications and variations within the scope of the contents disclosed in this application will be apparent to those skilled in the art. Unless otherwise specified, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or can be synthesized by common methods and can be used directly without further treatment, and all equipment used in the examples is commercially available.

[0177] Example 1-1 Positive electrode plate manufacturing Positive electrode active material LiNi 0.65 Co 0.05 Mn 0.3 O2, the conductive agent carbon black, and the adhesive polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 97.5:1.4:1.1 in an appropriate amount of NMP solvent with sufficient stirring to form a homogeneous positive electrode slurry. The positive electrode slurry was then uniformly coated onto the surface of the aluminum foil positive electrode current collector, dried, and cold-pressed to obtain a positive electrode plate. The compaction density of the positive electrode plate was 3.5 g / cm. 3 is.

[0178] Negative electrode plate manufacturing The negative electrode active material graphite, the adhesive styrene butadiene rubber (SBR), the thickener carboxymethyl cellulose sodium (CMC-Na), and the conductive agent carbon black (Super P) were mixed in a mass ratio of 96.2:1.8:1.2:0.8 in an appropriate amount of deionized water as a solvent and stirred thoroughly to form a uniform negative electrode slurry. The negative electrode slurry was then uniformly coated on the surface of the copper foil of the negative electrode current collector, dried, and cold-pressed to obtain a negative electrode plate.

[0179] Separator A porous polyethylene (PE) membrane was employed as the separator.

[0180] Electrolyte production Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and LiPF6 and LiBF4 were uniformly dissolved in the organic solvent to obtain an electrolyte solution, in which the mass percentage of LiPF6 was 12.5% ​​and the mass percentage of LiBF4 was 0.1% based on the total mass of the electrolyte solution.

[0181] Secondary battery manufacturing A positive electrode plate, a separator, and a negative electrode plate were stacked in this order and wound up to obtain an electrode assembly. The electrode assembly was then placed in an outer casing, and the above-mentioned electrolyte solution was added. A secondary battery was obtained through processes such as packaging, standing, chemical formation, and aging. The mass of the electrolyte solution was 15% of the total mass of the secondary battery.

[0182] Examples 1-2 to 1-16 and Comparative Examples 1-1 to 1-7 The manufacturing method of the secondary battery is similar to that of Example 1, except that the type of positive electrode active material and manufacturing parameters of the electrolyte solution are adjusted, and the specific parameters are as shown in Table 1. " / " indicates that the corresponding component is not added to the electrolyte solution.

[0183] Test part (1) Room temperature cycle performance test of secondary batteries At 25°C, the secondary battery was charged at a constant current of 1C to 4.3V, and then continuously charged at a constant voltage until the current reached 0.05C. At this point, the secondary battery was fully charged. The charge capacity at this point was recorded and designated as the first charge capacity. The secondary battery was then allowed to stand for 5 minutes, after which it was discharged at a constant current of 1C to 2.8V. This constitutes one cycle of charge / discharge. The discharge capacity at this point was recorded and designated as the first discharge capacity. The secondary battery was subjected to a cycle charge / discharge test using the method described above, and the discharge capacity after each cycle was recorded. The capacity retention rate (%) of the secondary battery at 25°C after 600 cycles = discharge capacity after 600 cycles / first discharge capacity × 100%.

[0184] (2) High-temperature cycle performance test of secondary batteries At 45°C, the secondary battery was charged at a constant current of 1C to 4.3V, and then continuously charged at a constant voltage until the current reached 0.05C. At this point, the secondary battery was fully charged. The charge capacity at this point was recorded and designated as the first charge capacity. The secondary battery was then allowed to stand for 5 minutes, after which it was discharged at a constant current of 1C to 2.8V. This constitutes one cycle of charge / discharge. The discharge capacity at this point was recorded and designated as the first discharge capacity. The secondary battery was subjected to a cycle charge / discharge test using the method described above, and the discharge capacity after each cycle was recorded. The capacity retention rate (%) of the secondary battery at 45°C after 600 cycles = discharge capacity after 600 cycles / first discharge capacity × 100%.

[0185] (3) Initial DC internal resistance test for secondary batteries At 25°C, the secondary battery was charged to 4.3V at a constant current of 1C, and then continuously charged at a constant voltage until the current reached 0.05C, at which point the secondary battery was fully charged. The secondary battery was then discharged at a constant current of 0.5C to adjust the secondary battery to 50% SOC, with the voltage of the secondary battery recorded as U1. The secondary battery was then discharged at a constant current of 4C I1 for 30 seconds, with a measurement taken at 0.1 seconds, and the voltage at the end of discharge recorded as U2. The initial DC internal resistance of the secondary battery can be calculated using the discharge DC internal resistance at 50% SOC as follows: Initial DC internal resistance of the secondary battery (mΩ) = (U1 - U2) / I1.

[0186] (4) High-temperature storage performance test for secondary batteries At 60°C, the secondary battery was charged at a constant current of 1C up to 4.3V, and then continuously charged at a constant voltage until the current reached 0.05C. At this point, the volume of the secondary battery was measured using the drainage method and recorded as V0. The secondary battery was then placed in a thermostatic box at 60°C and stored for 30 days, after which it was removed and the volume of the secondary battery was measured using the drainage method and recorded as V1. The volume expansion rate (%) of the secondary battery after 30 days of storage at 60°C = [(V1 - V0) / V0] x 100%.

[0187] (5) Secondary battery self-discharge rate test The secondary battery was charged to 70% SOC at 25°C, and the open-circuit voltage of the secondary battery at this time was tested and recorded as OCV1. The secondary battery was then placed in a thermostatic box at 25°C and stored for three months, after which it was removed and the open-circuit voltage of the secondary battery was tested again and recorded as OCV2. The self-discharge rate of a secondary battery stored for three months at 25°C = [(OCV1-OCV2) / OCV1] x 100%. The lower the self-discharge rate of a secondary battery, the higher its capacity and safety performance.

[0188] (6) Low-temperature performance test of secondary batteries At -10°C, the secondary battery was charged at a constant current of 0.2C up to 4.3V, and then continuously charged at a constant voltage until the current reached 0.05C. At this point, the secondary battery was fully charged. The charge capacity at this point was recorded and designated as the first charge capacity. The secondary battery was then allowed to stand for 30 minutes, after which it was discharged at a constant current of 0.2C down to 2.8V. This constitutes one cycle of charge / discharge. The discharge capacity at this point was recorded and designated as the first discharge capacity. The secondary battery was subjected to a cycle charge / discharge test using the method described above, and the discharge capacity after each cycle was recorded. The capacity retention rate (%) of the secondary battery at -10°C after 200 cycles = discharge capacity after 200 cycles / first discharge capacity × 100%.

[0189] Table 1 shows the performance test results for Examples 1-1 to 1-16 and Comparative Examples 1-1 to 1-7.

[0190] As can be seen from the test results in Table 1, when the electrolyte contains lithium tetrafluoroborate, and the mass percentage of lithium tetrafluoroborate x% and the cobalt content c in the low-cobalt or cobalt-free positive electrode active material satisfy x>0 and 0.05≦c+x / 10≦0.15, the secondary battery has significantly improved cycle performance and good storage and dynamic performance. When the electrolyte does not contain lithium tetrafluoroborate, or the lithium tetrafluoroborate content is too high or too low and does not satisfy 0.05≦c+x / 10≦0.15, the cycle performance of the low-cobalt or cobalt-free secondary battery cannot be effectively improved, and the internal resistance of the secondary battery is high.

[0191] As can be seen from the test results in Table 1, the compaction density of the positive electrode plate, P g / cm 3 When the mass percentage x% of lithium tetrafluoroborate and the content c of cobalt element in the low-cobalt or cobalt-free positive electrode active material further satisfy 25≦P / (c+x / 10)≦65, the secondary battery can have a lower internal resistance.

[0192] The inventors further studied the influence of components other than lithium tetrafluoroborate in the electrolyte on the performance of the secondary battery.

[0193] The manufacturing methods of the secondary batteries of Examples 2-1 to 2-20 are similar to those of Examples 1-3, except that the manufacturing parameters of the electrolyte solution are adjusted, and the specific parameters are as shown in Table 2. " / " indicates that the corresponding component is not added to the electrolyte solution.

[0194] As can be seen from the test results in Table 2, when the electrolyte solutions of Examples 2-1 to 2-20 further contain one or more of fluoroethylene carbonate (FEC), lithium bis(fluorosulfonyl)imide (LiFSI) and lithium fluorosulfonate, it contributes to further improving the overall performance of the secondary battery.

[0195] As can be seen from the summary of the test results of Examples 2-9 and 1-3, 2-1 to 2-6, when the electrolyte solution of Examples 1-3 is used as a base and fluoroethylene carbonate, lithium bis(fluorosulfonyl)imide, and lithium fluorosulfonate are added at the same time, it contributes to obtaining a secondary battery with better overall performance.

[0196] As can be seen from the summary of the test results of Examples 2-7 to 2-20, adjusting the mass percentage y1% of fluoroethylene carbonate, the mass percentage y2% of lithium bis(fluorosulfonyl)imide, and the mass percentage y3% of lithium fluorosulfonate to simultaneously satisfy the following conditions contributes to obtaining a secondary battery with better overall performance. One possible reason for this is that an inorganic / organic composite interfacial film with excellent performance can be formed on both the positive and negative electrodes.

[0197] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any embodiment that has substantially the same configuration as the technical idea and achieves the same effects within the scope of the technical solution of the present application is included within the technical scope of the present application. Furthermore, various modifications that a person skilled in the art can make to the embodiments without departing from the spirit of the present application, and other forms constructed by combining some of the components of the embodiments, are also included within the scope of the present application.

[0198] JPEG0007801438000001.jpg213131 JPEG0007801438000002.jpg217107

[0199] JPEG0007801438000003.jpg226127JPEG0007801438000004.jpg22793 [Explanation of symbols]

[0200] In the drawings, the drawings are not necessarily drawn to scale. The reference numerals are as follows: 1 battery pack, 2 upper housing, 3 lower housing, 4 battery module, 5 secondary battery, 51 case, 52 electrode assembly, 53 cover plate.

Claims

1. A secondary battery including an electrolyte and a positive electrode plate, The positive electrode plate includes a positive electrode current collector and a positive electrode film layer located on the surface of the positive electrode current collector, and the positive electrode film layer has a molecular formula of Li ａ Ni ｂ Co ｃ M1 ｄ M2 ｅ O ｆ A ｇ wherein M1 is selected from Mn, Al or a combination thereof; M2 is selected from one or more of Si, Ti, Mo, V, Ge, Se, Zr, Nb, Ru, Pd, Sb, Ce, Te and W; A is selected from one or more of F, N, P and S; and 0.8≦a≦1.2, 0<b<0.98, 0≦c<0.1, 0<d<0.5, 0≦e≦0.5, 0≦f≦2, 0≦g≦2, b+c+d+e=1, f+g=2; the electrolyte solution contains lithium tetrafluoroborate, a mass percentage of the lithium tetrafluoroborate in the electrolyte solution is x % based on the total mass of the electrolyte solution, and the secondary battery satisfies x>0 and 0.05≦c+x / 10≦0.15; The compaction density of the positive electrode plate is P g / cm ３ and P is 3.3 to 3.6; A secondary battery, wherein the mass of the electrolyte is 10% to 20% of the total mass of the secondary battery.

2. 0.05≦c+x / 10≦0.12, and / or The secondary battery according to claim 1 , wherein 0<x≦1.

0.

3. The secondary battery according to claim 1 , wherein the secondary battery satisfies 25≦P / (c+x / 10)≦65.

4. 2. The secondary battery according to claim 1, wherein the electrolytic solution further comprises one or more of fluoroethylene carbonate, a lithium fluorosulfonylimide salt, and a lithium fluorosulfonate salt, wherein the mass percentage of the fluoroethylene carbonate in the electrolytic solution is y1%, the mass percentage of the lithium fluorosulfonylimide salt in the electrolytic solution is y2%, and the mass percentage of the lithium fluorosulfonate salt in the electrolytic solution is y3%, all of which are calculated based on the total mass of the electrolytic solution, and the electrolytic solution satisfies y1≧0, y2≧0, y3≧0, and 0<y1+y2+y3≦15.

5. The molecular formula of the fluorosulfonylimide lithium salt is LiN(SO ２ R １ ) (SO ２ R ２ ) wherein R 1 and R 2 each independently represent F or C n F 2n+1 , where n is an integer from 1 to 10; and / or The molecular formula of the lithium fluorosulfonate is LiSO ３ R ３ and R ３ 5. The secondary battery according to claim 4, wherein represents F, a partially fluorinated or fully fluorinated C1-C10 alkyl group.

6. The mass percentage y1% of the fluoroethylene carbonate in the electrolyte solution is 0<y1≦2.5, and / or The secondary battery according to claim 4 , wherein 0.5≦y1 / x≦4.0 is satisfied.

7. The mass percentage y2% of the fluorosulfonylimide lithium salt in the electrolyte solution is 0<y2≦14, and / or The secondary battery according to claim 4 , wherein 1≦y2 / x≦28 is satisfied.

8. when 0<b≦0.7, the mass percentage y2% of the fluorosulfonylimide lithium salt in the electrolyte solution satisfies 0<y2≦5 and / or 1≦y2 / x≦10; 8. The secondary battery according to claim 7, wherein when 0.7≦b<0.98, the mass percentage y2% of the fluorosulfonylimide lithium salt in the electrolyte solution satisfies 5≦y2≦14 and / or 10≦y2 / x≦28.

9. The mass percentage y3% of the lithium fluorosulfonate salt in the electrolyte solution is 0<y3≦1.0, and / or The secondary battery according to claim 4 , wherein 0.001≦y3 / x≦2.0 is satisfied.

10. 5. The secondary battery according to claim 4, wherein the electrolyte solution further contains fluoroethylene carbonate, a fluorosulfonylimide lithium salt, and a fluorosulfonate lithium salt, and the electrolyte solution satisfies the following conditions: 0<y1≦2.5, 0<y2≦14, 0<y3≦1.0, 0.5≦y1 / x≦4.0, 1≦y2 / x≦28, 0.001≦y3 / x≦2.0, and 0.5≦y2 / y1≦48.

11. 5. The secondary battery according to claim 4, wherein the electrolytic solution further contains fluoroethylene carbonate, a fluorosulfonylimide lithium salt, and a fluorosulfonate lithium salt, and the electrolytic solution satisfies the following conditions: 0<y1≦2.5, 0<y2≦14, 0<y3≦1.0, 0.5≦y1 / x≦4.0, 1≦y2 / x≦28, 0.001≦y3 / x≦2.0, 0.5≦y2 / y1≦48, and 0.036≦x / (y2+y3)≦1.

0.

12. The secondary battery according to claim 1 , wherein 0<c<0.

1.

13. The secondary battery according to claim 1 , wherein c=0.

14. Based on the total mass of the positive electrode film layer, the molecular formula is Li ａ Ni ｂ Co ｃ M1 ｄ M2 ｅ O ｆ A ｇ 2. The secondary battery according to claim 1, wherein the mass percentage of the layered material is 80% to 99%.

15. A method for manufacturing a secondary battery, comprising at least Step 1: Assembling a positive electrode plate, a separator, a negative electrode plate, and an electrolyte into a secondary battery, the mass of the electrolyte is 10% to 20% of the total mass of the secondary battery; The positive electrode plate includes a positive electrode current collector and a positive electrode film layer located on the surface of the positive electrode current collector, and the positive electrode film layer has a molecular formula of Li ａ Ni ｂ Co ｃ M1 ｄ M2 ｅ O ｆ A ｇ wherein M1 is selected from Mn, Al or combinations thereof; M2 is selected from one or more of Si, Ti, Mo, V, Ge, Se, Zr, Nb, Ru, Pd, Sb, Ce, Te and W; A is selected from one or more of F, N, P and S; and 0.8≦a≦1.2, 0<b<0.98, 0≦c<0.1, 0<d<0.5, 0≦e≦0.5, 0≦f≦2, 0≦g≦2, b+c+d+e=1, f+g=2; Step 1, wherein the electrolyte solution comprises lithium tetrafluoroborate, fluoroethylene carbonate, a fluorosulfonylimide lithium salt, and a fluorosulfonate lithium salt, wherein the mass percentage of the lithium tetrafluoroborate in the electrolyte solution is x%, the mass percentage of the fluoroethylene carbonate in the electrolyte solution is y1%, the mass percentage of the fluorosulfonylimide lithium salt in the electrolyte solution is y2%, and the mass percentage of the fluorosulfonate lithium salt in the electrolyte solution is y3%, all calculated based on the total mass of the electrolyte solution, and x>0, y1≧0, y2≧0, and y3≧0; From the secondary battery obtained in step 1, 0.05≦c+x / 10≦0.15 is satisfied and P g / cm is the compaction density of the positive electrode plate ３ and step 2 of selecting secondary batteries having a resistance of 3.3 to 3.

6.

16. The method according to claim 15, further comprising the step of selecting secondary batteries that satisfy the conditions 0<x≦1.0 and 0.05≦c+x / 10≦0.15 from the secondary batteries obtained in step 2.

17. The method according to claim 15, further comprising the step of selecting secondary batteries that satisfy 25≦P / (c+x / 10)≦65 from the secondary batteries obtained in step 2.

18. 16. The method of claim 15, further comprising the step of sorting secondary batteries that satisfy the following conditions from the secondary batteries obtained in step 2: 0<y1+y2+y3≦15, 0<y1≦2.5, 0<y2≦14, 0<y3≦1.0, 0.5≦y1 / x≦4.0, 1≦y2 / x≦28, 0.001≦y3 / x≦2.0, 0.5≦y2 / y1≦48.

19. 16. The method of claim 15, further comprising the step of sorting secondary batteries that satisfy the following conditions from the secondary batteries obtained in step 2: 0<y1+y2+y3≦15, 0<y1≦2.5, 0<y2≦14, 0<y3≦1.0, 0.5≦y1 / x≦4.0, 1≦y2 / x≦28, 0.001≦y3 / x≦2.0, 0.5≦y2 / y1≦48, 0.036≦x / (y2+y3)≦1.

0.

20. A battery module comprising the secondary battery according to claim 1 .

21. A battery pack comprising the secondary battery according to claim 1.

22. A power consuming device comprising at least one of the secondary battery according to claim 1, the battery module according to claim 20, and the battery pack according to claim 21.

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