Secondary battery, method for manufacturing the same, battery module, battery pack, and electric device

Abstract

The application provides a secondary battery and a preparation method thereof. The secondary battery comprises a positive electrode sheet and an electrolyte. The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector. The porosity of the positive electrode film layer is P. The electrolyte comprises a water removal additive. The mass percentage of the water removal additive in the electrolyte is a based on the total mass of the electrolyte. The secondary battery satisfies 0.2≤(a*100) / P≤3.5. The secondary battery of the application has improved initial direct current resistance (DCR) and high-temperature cycle performance while improving the porosity to balance high energy density and good kinetics. The application also provides a battery module, a battery pack and a power utilization device comprising the secondary battery of the application.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries, in particular to a secondary battery and a preparation method thereof, and a battery module, a battery pack and a power utilization device comprising the secondary battery. BACKGROUND

[0002] In recent years, with the increasingly wide application of lithium ion batteries, lithium ion batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. Since lithium ion batteries have achieved great development, higher requirements have been put forward for their energy density, cycle performance and safety performance, etc.

[0003] In the design of high-performance secondary batteries, the energy density of the battery can be improved by taking a thicker coating amount and a higher compaction density. With the increase of coating thickness or compaction density, the porosity gradually decreases from the current collector to the surface of the active material, which causes problems such as low impregnation and absorption efficiency of electrolyte, slow migration rate of lithium ions, and large internal resistance of the battery, and ultimately leads to increased initial direct current resistance (DCR) and poor cycle performance of the battery. By adding a pore-forming agent in the preparation of the positive electrode slurry, the porosity of the electrode sheet can be adjusted, effectively improving the impregnation of the electrolyte in the electrode sheet and increasing the migration speed of lithium ions. However, the positive electrode sheet with high porosity is prone to water absorption, so it is inevitable to introduce unwanted water during battery preparation. In addition, under high temperature conditions, the electrolyte of the lithium ion battery also self-catalyzes to produce water. These unwanted water in the secondary battery will cause a series of side reactions to rapidly deteriorate the performance of the battery.

[0004] Therefore, while improving the porosity to balance high energy density and good kinetics, certain strategies need to be taken to reduce the unwanted water in the battery, thereby improving the influence of water on the initial direct current resistance (DCR) and high-temperature cycle performance of the lithium ion battery. SUMMARY

[0005] The present application is made in view of the above-mentioned problems, and aims to provide a secondary battery to solve the problem of reducing the adverse effects of water in the battery on the performance of the battery while improving the porosity to balance high energy density and good kinetics, so that the secondary battery has improved initial direct current resistance (DCR) and high-temperature cycle performance, and to provide a preparation method of the secondary battery, and to provide a battery module, a battery pack and a power utilization device comprising the secondary battery.

[0006] To achieve the above-mentioned purpose, the first aspect of the present application provides a secondary battery comprising a positive electrode sheet and an electrolyte, wherein

[0007] The positive electrode tab comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, the positive electrode film layer has a porosity P, the electrolyte comprises a water removal additive, and the mass percentage of the water removal additive in the electrolyte is a based on the total mass of the electrolyte,

[0008] And the secondary battery satisfies:

[0009] 0.2≤(a*100) / P≤3.5.

[0010] Therefore, compared with the prior art, the secondary battery of the present application has improved initial direct current resistance (DCR) and high-temperature cycle performance while improving the porosity to balance high energy density and good kinetics.

[0011] In any embodiment, the secondary battery satisfies: 0.4≤(a*100) / P≤3.3; optionally, the secondary battery satisfies: 1.0≤(a*100) / P≤1.7.

[0012] By satisfying the above conditions, the initial direct current resistance (DCR) and / or high-temperature cycle performance of the secondary battery can be further improved while ensuring that the secondary battery improves the porosity to balance high energy density and good kinetics.

[0013] In any embodiment, the water removal additive is selected from at least one of a compound of structural formula I, a compound of structural formula II, and an isocyanate compound,

[0014]

[0015]

[0016] wherein,

[0017] R1, R2, R3, R4, R5, and R6 are independently of each other a silyl group having an alkyl group substituted with halogen or an unsubstituted alkyl group, and at least one of R1, R2, and R3 is a silyl group having an alkyl group substituted with halogen or an unsubstituted alkyl group, at least one of R4, R5, and R6 is a silyl group having an alkyl group substituted with halogen or an unsubstituted alkyl group,

[0018] Optionally, R1, R2, R3, R4, R5, and R6 are independently of each other a silyl group having an unsubstituted C1-C6 alkyl group or an unsubstituted C1-C6 alkyl group, and at least one of R1, R2, and R3 is a silyl group having an unsubstituted alkyl group, at least one of R4, R5, and R6 is a silyl group having an unsubstituted alkyl group,

[0019] Further optionally, R1, R2, R3, R4, R5, and R6 are independently of each other a silyl group having a methyl, ethyl, propyl, or butyl group, or a methyl, ethyl, propyl, or butyl group, and at least one of R1, R2, and R3 is a silyl group having a methyl, ethyl, propyl, or butyl group, and at least one of R4, R5, and R6 is a silyl group having a methyl, ethyl, propyl, or butyl group,

[0020] and

[0021] X is phosphorus or boron.

[0022] The adverse effects of water on the performance of the battery can be effectively reduced by the water removal additive selected from at least one of the compound of structural formula I, the compound of structural formula II, and the isocyanate compound, thereby enabling the secondary battery to have improved initial direct current resistance (DCR) and high-temperature cycle performance.

[0023] In any embodiment, the mass percentage a of the water removal additive in the electrolyte is 0.1% to 1% based on the total mass of the electrolyte, and optionally, the mass percentage a of the water removal additive in the electrolyte is 0.3% to 0.7%. When the mass percentage of the water removal additive in the electrolyte satisfies the above range, the adverse effects of water on the performance of the battery can be effectively reduced, thereby enabling the secondary battery to have improved initial direct current resistance (DCR) and high-temperature cycle performance.

[0024] In any embodiment, the water removal additive is selected from at least one of tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, diethyltrimethylsilyl phosphite, tris(trimethylsilyl) borate, hexamethylene diisocyanate, trimethylsilyl isocyanate, toluene diisocyanate, dicyclohexylmethane diisocyanate, and isophorone diisocyanate. By selecting the above water removal additive, the initial direct current resistance (DCR) and high-temperature cycle performance of the secondary battery can be further improved.

[0025] In any embodiment, the porosity P of the positive electrode film layer is 20% to 70%, and optionally, the porosity P of the positive electrode film layer is 30% to 50%. When the porosity of the positive electrode film layer satisfies the above range, it is advantageous to promote the immersion of the electrolyte, promote the transmission of lithium ions inside the positive electrode sheet, and enable the secondary battery to have a lower initial direct current resistance (DCR).

[0026] In any embodiment, the electrolyte comprises a film-forming additive, and the mass percentage of the film-forming additive in the electrolyte is b based on the total mass of the electrolyte, and the secondary battery satisfies: 0.03≤a / b≤0.7. By adding the film-forming additive to the electrolyte, the high-temperature cycle performance of the secondary battery can be improved; and by satisfying the above condition for the amount of the water additive and the film-forming additive in the electrolyte, the initial direct current resistance (DCR) and the high-temperature cycle performance of the secondary battery can be improved.

[0027] In any embodiment, the secondary battery satisfies: 0.05≤a / b≤0.5; optionally, the secondary battery satisfies: 0.15≤a / b≤0.35. By satisfying the above condition, the adverse effects of water on the performance of the battery can be further reduced, thereby further improving the initial direct current resistance (DCR) and the high-temperature cycle performance of the secondary battery.

[0028] In any embodiment, the film-forming additive is at least one of adiponitrile, lithium difluoro(oxalato)borate, ethylene carbonate, lithium difluorophosphate, lithium tetrafluoroborate, vinylene carbonate, 1,3-propane sultone, and lithium trifluoromethanesulfonate. By selecting the above film-forming additive, a protective film (SEI film) can be formed on the surface of the positive and negative electrode sheets, the deterioration of the battery performance caused by heating can be reduced, and the initial direct current resistance (DCR) and the high-temperature cycle performance of the secondary battery can be further improved.

[0029] In any embodiment, the electrolyte comprises a lithium salt, the lithium salt is at least one of lithium hexafluorophosphate, lithium difluoro(oxalato)borate, and lithium bisfluorosulfonylimide, and the mass percentage of the lithium salt in the electrolyte is 5%-18% based on the total mass of the electrolyte. By selecting the above lithium salt and by selecting the content of the lithium salt in the electrolyte, the initial direct current resistance (DCR) and the high-temperature cycle performance of the secondary battery can be improved.

[0030] The second aspect of the present application provides a preparation method of the secondary battery of the first aspect of the present application, comprising preparation of a positive electrode sheet, wherein

[0031] The preparation of the positive electrode sheet comprises forming a positive electrode film layer on at least one surface of a positive electrode current collector, the positive electrode film layer being formed by coating a positive electrode slurry on one surface of the positive electrode current collector, the positive electrode slurry comprising a positive electrode active material and a pore-forming agent.

[0032] Thus, in the case of ensuring a high coating amount, by adding the pore-forming agent in the preparation of the positive electrode sheet, the porosity of the positive electrode film layer is improved, which is conducive to promoting the immersion of the electrolyte and promoting the transmission of lithium ions inside the positive electrode sheet, so that the secondary battery has a lower initial direct current resistance (DCR); at the same time, by adding the water removal additive in the electrolyte, the adverse effects caused by the unwanted water (water brought by the increase of the porosity of the positive electrode sheet due to the use of the pore-forming agent and water generated at high temperature of the lithium ion battery) are effectively reduced, thereby improving the initial direct current resistance (DCR) and high-temperature cycle performance of the lithium ion battery.

[0033] In any embodiment, the pore-forming agent is selected from at least one of oxalic acid, ammonium bicarbonate, ammonium carbonate, urea, ammonium chloride and ammonium fluoride, and the mass ratio of the pore-forming agent to the positive electrode active material is 1:100-8:100. By selecting the above pore-forming agent, well-distributed pores can be formed in the positive electrode sheet, and the amount of the pore-forming agent and the positive electrode active material satisfies the above ratio, which ensures the effective infiltration and absorption of the electrolyte, effectively improves the lithium ion migration speed, and makes the secondary battery have a good initial direct current resistance (DCR).

[0034] The third aspect of the present application provides a battery module comprising the secondary battery of the first aspect of the present application or the secondary battery prepared according to the method of the second aspect of the present application.

[0035] The fourth aspect of the present application provides a battery pack comprising the battery module of the third aspect of the present application.

[0036] The fifth aspect of the present application provides an electric device comprising at least one selected from the secondary battery of the first aspect of the present application or the secondary battery prepared according to the method of the second aspect of the present application, the battery module of the third aspect of the present application or the battery pack of the fourth aspect of the present application.

[0037] The battery module, the battery pack and the electric device of the present application comprise the secondary battery of the first aspect of the present application or the secondary battery prepared according to the method of the second aspect of the present application, and thus at least have the same advantages as the secondary battery. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 is a schematic diagram of the secondary battery of an embodiment of the present application.

[0039] Figure 2 is a schematic diagram of the secondary battery of an embodiment of the present application. Figure 1 is an exploded view of the secondary battery of an embodiment of the present application.

[0040] Figure 3 is a schematic diagram of the battery module of an embodiment of the present application.

[0041] Figure 4is a schematic view of a battery pack according to an embodiment of the present application.

[0042] Figure 5 is Figure 4 is an exploded view of a battery pack according to an embodiment of the present application.

[0043] Figure 6 is a schematic view of an electrical device using a secondary battery as a power source according to an embodiment of the present application.

[0044] BRIEF DESCRIPTION OF DRAWINGS

[0045] 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 case; 52 electrode assembly; 53 top cap assembly DETAILED DESCRIPTION

[0046] Hereinafter, embodiments of the secondary battery and the method of manufacturing the same, the battery module, the battery pack, and the electrical device according to the present application are specifically disclosed with appropriate reference to the accompanying drawings. However, there can be cases where unnecessary detailed descriptions are omitted. For example, there can be cases where detailed descriptions of matters well known in the art, repetitive descriptions of substantially identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0047] The "ranges" disclosed in the present application are defined in the form of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this manner can include or exclude the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. In addition, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, a numerical range "a-b" represents a shorthand manner of describing each and every numerical value that is contained in the range between "a" and "b," wherein "a" and "b" are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0" and "5" have been listed herein, and "0-5" is merely a shorthand manner of describing each and every numerical value that is contained in the range between "0" and "5." In addition, when it is stated that a parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0048] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, if not particularly stated.

[0049] All technical features and optional technical features of the present application can be combined with each other to form new technical solutions, if not particularly stated.

[0050] All steps of the present application can be performed in sequence or randomly, preferably in sequence, if not particularly stated. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, the method can further comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0051] If not particularly stated, "including" and "comprising" mentioned in the present application are open-ended and can also be closed. For example, "including" and "comprising" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0052] If not particularly stated, in the present application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any one of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or A and B are both true (or exist).

[0053] In designing high-performance secondary batteries, the energy density of the battery can be increased by taking a thicker coating amount, a higher compaction density. With the increase of the coating thickness or the compaction density, the porosity gradually decreases from the current collector to the surface of the active material, which causes problems such as low impregnation and absorption efficiency of the electrolyte, slow lithium ion migration rate, and large internal resistance of the battery, and ultimately leads to poor rate performance and cycle performance of the battery. By adding a pore-forming agent in the preparation of the positive electrode slurry, the porosity of the electrode sheet can be adjusted, the impregnation of the electrolyte in the electrode sheet can be effectively improved, and the migration speed of lithium ions can be increased, thereby greatly improving the problems such as poor rate performance and poor cycle performance caused by the increase of the compaction density or the thickness of the positive electrode sheet. However, the positive electrode sheet with high porosity is easy to absorb water, so it is inevitable to introduce unwanted water during battery preparation. In addition, under high temperature conditions, the electrolyte of the secondary battery also self-catalyzes to produce water. These unwanted water in the secondary battery will cause a series of side reactions to rapidly deteriorate the performance of the battery. Therefore, while improving the porosity to balance the high energy density and good kinetics, certain strategies need to be taken to reduce the unwanted water in the battery (water caused by the increase of the porosity of the positive electrode sheet due to the use of the pore-forming agent and water produced by the secondary battery under high temperature) to improve the initial direct current resistance (DCR) and high-temperature cycle performance of the secondary battery.

[0054] To solve the above problems, the present application provides a secondary battery, which comprises a positive electrode sheet and an electrolyte, wherein

[0055] The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, the porosity of the positive electrode film layer is P, the electrolyte comprises a water removal additive, and the mass percentage of the water removal additive in the electrolyte based on the total mass of the electrolyte is a, and the secondary battery satisfies:

[0056] 0.2≤(a*100) / P≤3.5.

[0057] The present applicant has unexpectedly found that when a thicker coating amount and a higher compaction density are taken to increase the energy density of the battery, by adjusting the porosity of the positive electrode film layer, the impregnation of the electrolyte in the electrode sheet can be effectively improved, and the migration speed of lithium ions can be increased, so that the secondary battery has a lower initial direct current resistance (DCR); at the same time, by adding a water removal additive in the electrolyte, the adverse effects of the unwanted water in the battery can be effectively reduced, and when the porosity of the positive electrode film layer in the secondary battery and the amount of the water removal additive in the electrolyte satisfy the above relationship, a secondary battery with high energy density and improved initial direct current resistance (DCR) and high-temperature cycle performance is obtained.

[0058] In some embodiments, the secondary battery satisfies: 0.4≤(a*100) / P≤3.3; optionally, the secondary battery satisfies: 1.0≤(a*100) / P≤1.7. If the amount of water removal additive is too small and the porosity of the electrode sheet is too large, too much water is easily introduced into the battery, the water removal effect of the electrolyte is not obvious, leading to poor high-temperature cycle performance of the secondary battery; if the amount of water removal additive is too large and the porosity of the electrode sheet is too small, the film-forming resistance of the water removal additive is large, leading to deterioration of the initial direct current resistance (DCR) of the secondary battery. By satisfying the above conditions, the initial direct current resistance (DCR) and / or high-temperature cycle performance of the secondary battery can be further improved while ensuring that the secondary battery has high energy density.

[0059] In some embodiments, the water removal additive is selected from at least one of a compound of structural formula I, a compound of structural formula II, and an isocyanate compound,

[0060]

[0061]

[0062] wherein,

[0063] R1, R2, R3, R4, R5, and R6 are each independently a silyl group having a halogen-substituted or unsubstituted alkyl group or a halogen-substituted or unsubstituted alkyl group, and at least one of R1, R2, and R3 is a silyl group having a halogen-substituted or unsubstituted alkyl group, and at least one of R4, R5, and R6 is a silyl group having a halogen-substituted or unsubstituted alkyl group,

[0064] Optionally, R1, R2, R3, R4, R5, and R6 are each independently a silyl group having an unsubstituted C1-C6 alkyl group or an unsubstituted C1-C6 alkyl group, and at least one of R1, R2, and R3 is a silyl group having an unsubstituted alkyl group, and at least one of R4, R5, and R6 is a silyl group having an unsubstituted alkyl group,

[0065] Further optionally, R1, R2, R3, R4, R5, and R6 are each independently a silyl group having a methyl group, an ethyl group, a propyl group, or a butyl group, or a methyl group, an ethyl group, a propyl group, or a butyl group, and at least one of R1, R2, and R3 is a silyl group having a methyl group, an ethyl group, a propyl group, or a butyl group, and at least one of R4, R5, and R6 is a silyl group having a methyl group, an ethyl group, a propyl group, or a butyl group,

[0066] and

[0067] X is phosphorus or boron. The adverse effects of water on the performance of the secondary battery can be effectively reduced by the water removal additive selected from at least one of the compound of Structural Formula I, the compound of Structural Formula II, and the isocyanate compound, thereby improving the initial direct current resistance (DCR) and high-temperature cycle performance of the secondary battery.

[0068] In some embodiments, the mass percentage a of the water removal additive in the electrolyte is 0.1% to 1% based on the total mass of the electrolyte, and optionally, the mass percentage a of the water removal additive in the electrolyte is 0.3% to 0.7%. When the mass percentage of the water removal additive in the electrolyte satisfies the above range, the adverse effects of water on the performance of the secondary battery can be effectively reduced, thereby improving the initial direct current resistance (DCR) and high-temperature cycle performance of the secondary battery.

[0069] In some embodiments, the water removal additive is selected from at least one of tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, diethyl trimethylsilyl phosphite, tris(trimethylsilyl) borate, hexamethylene diisocyanate, trimethylsilyl isocyanate, toluene diisocyanate, dicyclohexylmethane diisocyanate, and isophorone diisocyanate. The water removal additive can combine with water in the secondary battery to prevent the destruction of the electrode interface by water, improve the stability of the electrolyte, and thereby improve the performance of the secondary battery. By selecting the above water removal additive, the initial direct current resistance (DCR) and high-temperature cycle performance of the secondary battery can be further improved.

[0070] In some embodiments, the porosity P of the positive electrode film layer is 20% to 70%, and optionally, the porosity P of the positive electrode film layer is 30% to 50%. When the porosity of the positive electrode film layer satisfies the above range, the immersion of the electrolyte is facilitated, and the lithium ion transmission inside the positive electrode sheet is facilitated, so that the secondary battery has a lower initial direct current resistance (DCR). In the present application, the porosity P of the positive electrode film layer can be measured according to GB / T 24586-2009, and the porosity in the present application is measured in %.

[0071] In some embodiments, the electrolyte comprises a film-forming additive, and the mass percentage of the film-forming additive in the electrolyte is b based on the total mass of the electrolyte, and the secondary battery satisfies: 0.03≤a / b≤0.7. The film-forming additive in the electrolyte has good film-forming effect, can form a solid electrolyte interface film (SEI film) on the surface of the negative electrode through electrochemical reaction during the initial charge-discharge of the lithium battery, effectively inhibits the intercalation of solvent molecules, and improves the high-temperature cycle performance of the secondary battery. When the amounts of the water removal additive and the film-forming additive in the electrolyte satisfy the above conditions, the initial direct current resistance (DCR) and the high-temperature cycle performance of the secondary battery can be improved. In the present application, the ratio of the mass percentage a of the water removal additive to the mass percentage b of the film-forming additive in the electrolyte (i.e., a / b) is the ratio of the added water removal additive to the added film-forming additive when the electrolyte is prepared. In the present application, the mass percentage a of the water removal additive and the mass percentage b of the film-forming additive in the electrolyte are both in %.

[0072] In some embodiments, the secondary battery satisfies: 0.05≤a / b≤0.5; optionally, the secondary battery satisfies: 0.15≤a / b≤0.35. By satisfying the above conditions, the adverse effects of water on the performance of the battery can be further reduced, thereby further improving the initial direct current resistance (DCR) and the high-temperature cycle performance of the secondary battery.

[0073] In some embodiments, the film-forming additive is at least one of hexanedinitrile, lithium difluoro(oxalato)borate, ethylene carbonate, lithium difluorophosphate, lithium tetrafluoroborate, vinylene carbonate, 1,3-propane sultone, and lithium trifluoromethanesulfonate. By selecting the above film-forming additive, a protective film (SEI film) can be formed on the surface of the positive and negative electrode sheets, reducing the deterioration of battery performance caused by heating, thereby further improving the initial direct current resistance (DCR) and the high-temperature cycle performance of the secondary battery.

[0074] In some embodiments, the electrolyte comprises a lithium salt selected from at least one of lithium hexafluorophosphate, lithium difluoro(oxalato)borate and lithium bis(fluorosulfonyl)imide, and the mass percentage of the lithium salt in the electrolyte is 5%-18% based on the total mass of the electrolyte. The decomposition of the lithium salt, such as lithium hexafluorophosphate (LiPF6), is conducive to the formation of a solid electrolyte interface film (SEI film), which can effectively improve the passivation layer of the electrode, prevent the erosion of moisture, reduce side reactions and prolong the service life of the battery. If the content of the lithium salt is too high, on the one hand, the electrolyte has too large viscosity and is difficult to infiltrate the pores, which is not conducive to the transmission of lithium ions; on the other hand, the content of the substances (such as fluorophosphate and lithium fluoride) generated by the decomposition of the lithium salt is too high, which can deteriorate the initial direct current resistance (DCR) of the secondary battery. If the content of the lithium salt is too low, the components (such as fluorophosphate and lithium fluoride) for forming the SEI film are affected, which affects the high-temperature cycle performance of the secondary battery. By selecting the above-mentioned lithium salt and by selecting the content of the lithium salt in the electrolyte, the initial direct current resistance (DCR) and the high-temperature cycle performance of the secondary battery can be improved.

[0075] In some embodiments, the electrolyte comprises an organic solvent, and the organic solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, fluoroethylene carbonate and sulfolane. The organic solvent in the electrolyte is conducive to the dissociation of the lithium salt, improves the conductivity of the electrolyte, and some organic solvent components, such as ethylene carbonate and sulfolane, also participate in the formation of the SEI film to avoid the destruction of the SEI film by water, thereby improving the interface stability.

[0076] The second aspect of the present application provides a preparation method of the secondary battery of the first aspect of the present application, comprising the preparation of the positive electrode sheet, wherein

[0077] The preparation of the positive electrode sheet comprises forming a positive electrode film layer on at least one surface of the positive electrode current collector, and the positive electrode film layer is formed by coating a positive electrode slurry on one surface of the positive electrode current collector, and the positive electrode slurry comprises a positive electrode active material and a pore-forming agent.

[0078] By adding the pore-forming agent in the preparation of the positive electrode sheet to improve the porosity of the positive electrode film layer under the condition of ensuring a high coating amount, the electrolyte is promoted to be infiltrated, and the transmission of lithium ions inside the positive electrode sheet is promoted, so that the secondary battery has a lower initial direct current resistance (DCR); at the same time, by adding the water-removing additive in the electrolyte, the adverse effects of the unwanted water (water brought by the increase of the porosity of the positive electrode sheet due to the use of the pore-forming agent and water generated at high temperature of the lithium ion battery) are effectively reduced, thereby improving the initial direct current resistance (DCR) and the high-temperature cycle performance of the lithium ion battery.

[0079] In addition, the secondary battery, the battery module, the battery pack and the power utilization device of the present application are described below with appropriate reference to the accompanying drawings.

[0080] In one embodiment of the present application, a secondary battery is provided.

[0081] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During charging and discharging of the battery, active ions are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, and functions to prevent short circuiting between the positive and negative electrodes, while allowing ions to pass through. In the present application, the battery group margin is 88-98%.

[0082] [Positive electrode sheet]

[0083] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including the positive electrode active material of the first aspect of the present application.

[0084] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode film layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0085] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0086] In some embodiments, the positive electrode active material can use a positive electrode active material for a battery known in the art. As an example, the positive electrode active material can include at least one of a lithium-containing phosphate having an olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive electrode active material for a battery can also be used. These positive electrode active materials can be used alone or in combination of two or more. Among them, examples of the lithium transition metal oxide can include, but are not limited to, lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which can also be referred to as NCM 333), LiNi 0.5 Co 0.2 Mn 0.3 O2(also can be referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2(also can be referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2(also can be referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2(also can be referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2), and modified compounds thereof. Examples of lithium-containing phosphates of olivine structure can include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4(also can be referred to as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite of lithium manganese iron phosphate and carbon.

[0087] In some embodiments, the pore-forming agent is selected from at least one of oxalic acid, ammonium bicarbonate, ammonium carbonate, urea, ammonium chloride, and ammonium fluoride, and the mass ratio of the pore-forming agent to the positive active material is 1:100-8:100. The pore-forming agent is added to the positive electrode slurry, is stable at room temperature, and is completely decomposed into gas to escape after the positive electrode sheet is dried, thereby forming pores in the positive electrode film layer and without other harmful substances remaining. By selecting the pore-forming agent described above, pores that are well-distributed in the positive electrode sheet can be formed, and the amount of the pore-forming agent to the positive active material satisfies the above ratio, ensuring effective infiltration and absorption of the electrolyte, effectively improving the lithium ion migration speed, and enabling the secondary battery to have a good initial direct current resistance (DCR).

[0088] In some embodiments, the positive electrode film layer can also optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0089] In some embodiments, the positive electrode film layer can also optionally include a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0090] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, the pore-forming agent, the conductive agent, the binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector; and subjecting the positive electrode slurry to drying, cold pressing, and the like to obtain the positive electrode sheet.

[0091] [Positive electrode sheet]

[0092] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0093] As an example, the negative electrode current collector has two surfaces opposite in the thickness direction thereof, and the negative electrode film layer is disposed on either one or both of the two surfaces of the negative electrode current collector.

[0094] In some embodiments, the negative electrode current collector can employ a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer (e.g., a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0095] In some embodiments, the negative electrode active material can employ a negative electrode active material known in the art for use in a battery. As an example, the negative electrode active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, lithium titanate, and the like. The silicon-based material can be selected from at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The tin-based material can be selected from at least one of elemental tin, a tin oxide compound, and a tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative electrode active material for a battery can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0096] In some embodiments, the negative electrode film layer can also optionally include a binder. The binder can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0097] In some embodiments, the negative electrode film layer further optionally comprises a conductive agent. The conductive agent can be selected from at least one of super-P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0098] In some embodiments, the negative electrode film layer further optionally comprises other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0099] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, and after processes such as drying, cold pressing, and the like, a negative electrode sheet is obtained.

[0100] [Electrolyte]

[0101] The electrolyte plays a role of conducting ions between the positive electrode sheet and the negative electrode sheet. The type of the electrolyte is not specifically limited in the present application and can be selected as needed. For example, the electrolyte can be in a liquid state, a gel state, or a full solid state.

[0102] In some embodiments, the electrolyte is an electrolyte solution.

[0103] In some embodiments, the electrolyte solution comprises a water removal additive selected from at least one of a compound of structural formula I, a compound of structural formula II, and an isocyanate compound,

[0104]

[0105]

[0106] wherein,

[0107] R1, R2, R3, R4, R5, and R6 are independently of each other a silyl group having a halogen-substituted or unsubstituted alkyl group or a halogen-substituted or unsubstituted alkyl group, and at least one of R1, R2, and R3 is a silyl group having a halogen-substituted or unsubstituted alkyl group, and at least one of R4, R5, and R6 is a silyl group having a halogen-substituted or unsubstituted alkyl group,

[0108] Optionally, the R1, R2, R3, R4, R5, and R6 are independently of each other a silyl group having a halogen-substituted or unsubstituted C1-C6 alkyl group or a halogen-substituted or unsubstituted C1-C6 alkyl group, and further optionally, the R1, R2, R3, R4, R5, and R6 are independently of each other a silyl group having a methyl group, an ethyl group, a propyl group, or a butyl group, or a methyl group, an ethyl group, a propyl group, or a butyl group.

[0109] and

[0110] X is phosphorus or boron.

[0111] In some embodiments, the water removal additive is selected from at least one of tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, diethyl trimethylsilyl phosphite, tris(trimethylsilyl) borate, hexamethylene diisocyanate, trimethylsilyl isocyanate, toluene diisocyanate, dicyclohexylmethane diisocyanate, and isophorone diisocyanate.

[0112] In some embodiments, the mass percentage a of the water removal additive in the electrolyte is 0.1% to 1%, based on the total mass of the electrolyte, and optionally, the mass percentage a of the water removal additive in the electrolyte is 0.3% to 0.7%. The water removal additive in the electrolyte can effectively reduce the adverse effects of water on the performance of the battery, thereby improving the initial direct current resistance (DCR) and high-temperature cycle performance of the secondary battery.

[0113] In some embodiments, the electrolyte includes a film-forming additive selected from at least one of hexanedinitrile, lithium difluoro(oxalato)borate, vinyl ethylene carbonate, lithium difluorophosphate, lithium tetrafluoroborate, vinylene carbonate, 1,3-propane sultone, and lithium trifluoromethanesulfonate, and the mass percentage of the film-forming additive in the electrolyte is b, based on the total mass of the electrolyte, and 0.03≤a / b≤0.7, optionally, 0.05≤a / b≤0.5, and further optionally, 0.15≤a / b≤0.35. By adding the above film-forming additive to the electrolyte, a protective film (SEI film) can be formed on the surface of the positive and negative electrode sheets, reducing the deterioration of the battery performance caused by heating, and the amount of the water removal additive and the film-forming additive in the electrolyte satisfying the above conditions can further reduce the adverse effects of water on the performance of the battery, thereby improving the initial direct current resistance (DCR) and high-temperature cycle performance of the secondary battery.

[0114] In some embodiments, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium difluoro(oxalato)borate, and lithium bisfluorosulfonylimide, and the mass percentage of the lithium salt in the electrolyte is 5% to 18%, based on the total mass of the electrolyte. By selecting the above lithium salt and by selecting the content of the lithium salt in the electrolyte, the initial direct current resistance (DCR) and high-temperature cycle performance of the secondary battery can be improved.

[0115] In some embodiments, the electrolyte includes an organic solvent selected from at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, fluoroethylene carbonate, and sulfolane. By selecting the above organic solvent, the initial direct current resistance (DCR) and / or high-temperature cycle performance of the secondary battery can be improved.

[0116] In some embodiments, the electrolyte solution can further optionally include an additive. For example, the additive can include an additive capable of improving certain performance of the battery, such as an additive capable of improving overcharge performance of the battery, an additive capable of improving high-temperature or low-temperature performance of the battery, etc.

[0117] [Separator]

[0118] In some embodiments, a separator is further included in the secondary battery. The type of the separator is not particularly limited in the present application, and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0119] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0120] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a stacking process.

[0121] In some embodiments, the secondary battery can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above.

[0122] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, etc. can be listed.

[0123] The shape of the secondary battery is not particularly limited in the present application, and it can be cylindrical, square, or any other shape. For example, Figure 1 is a square structure secondary battery 5 as an example.

[0124] In some embodiments, with reference to Figure 2 , the outer package can include a shell 51 and a cover plate 53. The shell 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be provided on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte solution is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and a person skilled in the art can select according to the specific actual needs.

[0125] In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0126] Figure 3 The battery module 4 is an example. Referring to FIG. 1, the battery module 4 includes a plurality of secondary batteries 5 and a housing 6 having a receiving space for receiving the plurality of secondary batteries 5. Figure 3 In the battery module 4, the plurality of secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements can also be used. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

[0127] Optionally, the battery module 4 can further include a housing having a receiving space for receiving the plurality of secondary batteries 5.

[0128] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0129] Figure 4 And Figure 5 The battery pack 1 is an example. Referring to FIG. 2, the battery pack 1 includes a plurality of battery modules 4 and a battery box 7 for receiving the plurality of battery modules 4. Figure 4 And Figure 5 In the battery pack 1, the battery box and the plurality of battery modules 4 arranged in the battery box can be included. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be arranged on the lower box body 3 to form a closed space for receiving the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0130] In addition, the application also provides a power utilization device, which includes at least one of the secondary battery, the battery module, or the battery pack provided by the application. The secondary battery, the battery module, or the battery pack can be used as a power supply of the power utilization device, or can be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0131] As the power utilization device, the secondary battery, the battery module, or the battery pack can be selected according to the use requirements thereof.

[0132] Figure 6is an example of an electric device. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the demand of the electric device for high power and high energy density of the secondary battery, a battery pack or a battery module can be used.

[0133] The device as another example can be a mobile phone, a tablet, a notebook, etc. The device generally requires thinning, and a secondary battery can be used as a power source.

[0134] Embodiments

[0135] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are for the purpose of explanation of the present application and should not be understood as a limitation of the present application. In the embodiments, unless a specific technique or condition is mentioned, the technique or condition described in the literature in the art or according to the product manual is used. The reagents or instruments used, unless the manufacturer is mentioned, are all conventional products that can be obtained on the market.

[0136] I. Raw materials

[0137] Tris(trimethylsilyl)phosphate (TMSP, purchased from Sigma-Aldrich)

[0138] Tris(trimethylsilyl)phosphite (TMSPi, purchased from Sigma-Aldrich)

[0139] Diethyltrimethylsilylphosphite (C7H 19 O3PSi, purchased from Shanghai Aladdin Bio-Chem Technology Co., Ltd.)

[0140] Tris(trimethylsilyl)borate (TMSB, purchased from Shanghai Aladdin Bio-Chem Technology Co., Ltd.)

[0141] Hexamethylene diisocyanate (HDI, purchased from Shanghai Aladdin Bio-Chem Technology Co., Ltd.)

[0142] Trimethylsilylisocyanate (C4H9NOSi, purchased from Shanghai Aladdin Bio-Chem Technology Co., Ltd.)

[0143] Ethylene carbonate (EC, purchased from Shanghai Aladdin Bio-Chem Technology Co., Ltd.)

[0144] Propylene carbonate (PC, purchased from Shanghai Aladdin Bio-Chem Technology Co., Ltd.)

[0145] Sulfolane (SL, purchased from Shanghai Aladdin Bio-Chem Technology Co., Ltd.)

[0146] Dimethyl carbonate (DMC, purchased from Shanghai Aladdin Bio-Chem Technology Co., Ltd.)

[0147] Ethyl methyl carbonate (EMC, purchased from Shanghai Aladdin Biochem Technology Co., Ltd.)

[0148] Diethyl carbonate (DEC, purchased from Shanghai McLean Biotech Co., Ltd.)

[0149] Vinylene carbonate (VC, purchased from Shanghai McLean Biotech Co., Ltd.)

[0150] Lithium hexafluorophosphate (LiPF6, purchased from Guangzhou Tianci High-tech Materials Co., Ltd.)

[0151] Preparation of primary and secondary batteries

[0152] Example 1

[0153]

Negative electrode sheet

[0154] The negative active material artificial graphite, the conductive agent carbon black, the binder styrene-butadiene rubber (SBR), and the thickening agent sodium carboxymethyl cellulose (CMC) were mixed in deionized water in a weight ratio of 97:0.5:1.5:1, and then uniformly coated on both sides of a copper foil, dried, and cold-pressed to obtain a negative electrode sheet. The coating amount was 0.2 g / cm 2 , and the compacted density was 1.6 g / cm 3 .

[0155]

Positive electrode sheet

[0156] The positive active material lithium iron phosphate (LFP), the conductive agent carbon black, and the binder polyvinylidene fluoride (PVDF) were fully stirred and mixed in a proper amount of N-methyl pyrrolidone (NMP) in a weight ratio of 97:0.5:2.5, and then a pore-forming agent ammonium carbonate powder was added and fully stirred and mixed to disperse uniformly, forming a uniform positive electrode slurry. The mass ratio of the pore-forming agent to the positive active material was 3:100. The positive electrode slurry was coated on the surface of a positive current collector aluminum foil, vacuum dried at 110°C for 10 min, and then roll-pressed to obtain a positive electrode sheet. The coating amount was 26 mg / cm 2 , and the compacted density was 2.5 g / cm 3 . The single-sided coating amount was adjusted to keep the capacity ratio of the negative electrode to the positive electrode at 1.1.

[0157]

Electrolyte

[0158] The electrolyte was prepared in a BRAUN glove box, which was filled with nitrogen with a purity of 99.999%, and the moisture in the glove box was controlled to be ≤5 ppm, and the temperature was room temperature. Ethylene carbonate (EC), dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), water removal additive tris (trimethylsilyl) borate (TMSB), lithium hexafluorophosphate (LiPF6) were mixed in a mass ratio of 25:30:20:14.7:0.3:10 to obtain the electrolyte, wherein the concentration of LiPF6 was 1 mol / L.

[0159]

Separator

[0160] The porous polyethylene polymer film was used as the separator.

[0161]

Preparation of the battery

[0162] The positive electrode sheet, the separator, and the negative electrode sheet were stacked in order, with the separator between the positive and negative electrode sheets to play a separating role, and then wound to obtain a bare battery cell; the bare battery cell with a capacity of 100 Ah was placed in an outer packaging foil, and 300 g of the prepared electrolyte was injected into the dried battery, and after vacuum packaging, standing, formation, shaping and other processes, the secondary battery of Example 1 was obtained. The outer packaging selected a hard shell shell with a length × width × height = 108 mm × 35.5 mm × 110.5 mm, and the shell material was aluminum, the shell thickness was 0.8 mm, and the group margin of the battery was 95%.

[0163] Examples 2-7

[0164] The preparation of the secondary battery was the same as that of Example 1, except that the mass ratio of the pore-forming agent to the positive active material, the composition of the electrolyte and the corresponding proportion were different, as shown in Table 1.

[0165] Examples 8-12

[0166] The preparation of the secondary battery was the same as that of Example 1, except that the water removal additives were tris (trimethylsilyl) phosphate (TMSP), hexamethylene diisocyanate (HDI), di (trimethylsilyl) phosphite (TMSPi) diethyl trimethylsilyl phosphate, trimethylsilyl isocyanate (C4H9NOSi), respectively, as shown in Table 1.

[0167] Examples 13-25

[0168] The preparation of the secondary battery was the same as that of Example 1, except that the mass ratio of the pore-forming agent to the positive active material, the composition of the electrolyte and the corresponding proportion were different, as shown in Table 1.

[0169] Comparative Example 1

[0170] The preparation of the secondary battery was the same as that of Example 1, except that no water removal additive and no film-forming additive vinylene carbonate (VC) were added to the electrolyte, and the composition and the corresponding proportion of the electrolyte were different, as shown in Table 1.

[0171] II. Test of Related Parameters

[0172] Test of Porosity of Positive Electrode Film Layer

[0173] The porosity of the positive electrode film layer in the positive electrode sheet in the above examples and comparative examples was determined according to GB / T 24586-2009 Determination of apparent density, true density and porosity of iron ores (routine method).

[0174] A certain mass of sample was placed in a true density instrument AccuPyc II1340, a closed test system, and helium or nitrogen was introduced according to the program. The true volume was calculated according to the Boyle's law (PV = nRT) by detecting the pressure of the gas in the sample chamber and the expansion chamber, and the porosity of the positive electrode film layer was obtained. The results are shown in Table 2.

[0175] III. Test of Performance of Secondary Battery

[0176] (1) Measurement of Initial Direct Current Resistance (DCR)

[0177] At 25°C, the batteries of the above examples and comparative examples were charged at 0.5C to 3.65V, and then charged at constant voltage to a current of 0.05C. The batteries were discharged at 0.5C for 30 minutes to adjust the batteries to 50% SOC, and the voltage of the batteries at this time was recorded as U1. The batteries were discharged at 4C for 30 seconds, with a sampling point of 0.1 second, and the voltage at the end of discharge was recorded as U2. The discharge DCR of the batteries at 50% SOC was used to represent the initial DCR of the batteries, and the initial DCR of the batteries = (U1-U2) / 4C. The measurement data are shown in Table 2.

[0178] (2) Test of Energy Density

[0179] At 25°C, the secondary batteries in the above examples and comparative examples were charged at 1 / 3C to 3.65V, and then charged at constant voltage at 3.65V to a current of 0.05C, and then discharged at 1 / 3C to 2.5V, and the discharge energy of the batteries at this time was recorded. The discharge energy of the batteries divided by the weight of the batteries was the weight energy density of the batteries, with the unit of Wh / kg. The measurement data are shown in Table 2.

[0180] (3) Test of 60°C Cycle Performance

[0181] The secondary batteries of the above examples and comparative examples were charged at 0.5C constant current to 3.65V, then charged at constant voltage to a current of 0.05C at 60℃, and then rested for 5 minutes, and discharged at 1 / 3C constant current to 2.5V, which was the first charge-discharge cycle process of the batteries. The discharge capacity of the first cycle of the batteries was recorded. The batteries were subjected to 1000 cycles of charge-discharge process according to the above method, and the discharge capacity of the batteries after 1000 cycles was recorded. The capacity retention rate (%) of the batteries after 1000 cycles at 60℃ = (discharge capacity of the batteries after 1000 cycles / discharge capacity of the first cycle of the batteries) x 100%.

[0182]

[0183]

[0184] As can be seen from the above, compared with Comparative Example 1, the secondary batteries of Examples 1-25 of the present application, when taking thicker coating amount and higher compaction density to improve the energy density of the batteries, by adjusting the porosity of the positive electrode film layer, the wettability of the electrolyte in the electrode sheet can be effectively improved, the migration speed of lithium ions is increased, so that the secondary battery has a lower initial direct current resistance (DCR); at the same time, by adding water removal additives in the electrolyte, the adverse effects of unwanted water in the battery can be effectively reduced, thereby obtaining a secondary battery with high energy density and improved initial direct current resistance (DCR) and high temperature cycle performance.

[0185] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are only examples, and embodiments having substantially the same configuration and playing the same role and effect as the technical idea within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art, other ways constructed by combining part of the elements of the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery characterized by comprising: The secondary battery includes a positive electrode tab, a negative electrode tab, and an electrolyte, wherein The positive electrode tab includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, The negative electrode tab includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material, the negative electrode active material including at least one of artificial graphite, natural graphite, soft carbon, hard carbon, a silicon-based material, and a tin-based material, The positive electrode film layer has a porosity P, and the electrolyte includes a water removal additive and a film forming additive, The water removal additive is selected from at least one of a compound of Formula I, a compound of Formula II, and an isocyanate compound, wherein, R1, R2, R3, R4, R5, and R6 are each independently a silyl group having an unsubstituted C1-C6 alkyl group or an unsubstituted C1-C6 alkyl group, and at least one of R1, R2, and R3 is a silyl group having an unsubstituted alkyl group, and at least one of R4, R5, and R6 is a silyl group having an unsubstituted alkyl group. The film forming additive is selected from at least one of adiponitrile, lithium difluoro(oxalato)borate, vinylene carbonate, lithium difluorophosphate, lithium tetrafluoroborate, vinylene carbonate, 1,3-propane sultone, and lithium trifluoromethanesulfonate. The mass percentage a of the water removal additive in the electrolyte is 0.1% to 1% based on the total mass of the electrolyte. The mass percentage a of the water removal additive in the electrolyte is 0.3% to 0.7%. The secondary battery satisfies:

2. The secondary battery according to claim 1, characterized by The porosity P of the positive electrode film layer is 30% to 70%, 0.2 ≤ (a*100) / P ≤ 3.5, and 0.03 ≤ a / b ≤ 0.

7.

3. The secondary battery according to claim 2, characterized by The secondary battery satisfies: 0.4 ≤ (a*100) / P ≤ 3.

3.

4. The secondary battery according to claim 1, characterized by The secondary battery satisfies: 1.0 ≤ (a*100) / P ≤ 1.

7.

5. The secondary battery according to claim 4, characterized by R1, R2, R3, R4, R5, and R6 are each independently a silyl group having an unsubstituted C1-C6 alkyl group or an unsubstituted C1-C6 alkyl group, and at least one of R1, R2, and R3 is a silyl group having an unsubstituted alkyl group, and at least one of R4, R5, and R6 is a silyl group having an unsubstituted alkyl group.

6. The secondary battery according to claim 1, characterized by R1, R2, R3, R4, R5, and R6 are each independently a silyl group having an unsubstituted C1-C6 alkyl group or an unsubstituted C1-C6 alkyl group, and at least one of R1, R2, and R3 is a silyl group having an unsubstituted alkyl group, and at least one of R4, R5, and R6 is a silyl group having an unsubstituted alkyl group.

7. The secondary battery according to claim 6, characterized by The mass percentage a of the water removal additive in the electrolyte is 0.1% to 1% based on the total mass of the electrolyte. The mass percentage a of the water removal additive in the electrolyte is 0.3% to 0.7%.

8. The secondary battery according to claim 1, characterized by The water removal additive is selected from at least one of tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, diethyl trimethylsilyl phosphite, tris(trimethylsilyl) borate, hexamethylene diisocyanate, trimethylsilyl isocyanate, toluene diisocyanate, dicyclohexylmethane diisocyanate, and isophorone diisocyanate.

9. The secondary battery according to claim 1, characterized by The porosity P of the positive electrode film layer is 30% to 50%.

10. The secondary battery according to claim 1, characterized by The secondary battery satisfies 0.05 ≤ a / b ≤ 0.

5.

11. The secondary battery according to claim 10, characterized by The secondary battery satisfies 0.15 ≤ a / b ≤ 0.

35.

12. The secondary battery according to claim 1, characterized by The electrolyte includes a lithium salt selected from at least one of lithium hexafluorophosphate, lithium difluoro(oxalato)borate, and lithium bis(fluorosulfonyl)imide, and the mass percentage of the lithium salt in the electrolyte is 5% to 18% based on the total mass of the electrolyte.

13. A method of producing the secondary battery according to any one of claims 1 to 12, characterized by, The preparation of the positive electrode tab includes forming a positive electrode film layer on at least one surface of a positive electrode current collector, the positive electrode film layer being formed by coating a positive electrode slurry on one surface of the positive electrode current collector, the positive electrode slurry including a positive electrode active material and a pore-forming agent. The pore-forming agent is selected from at least one of oxalic acid, ammonium bicarbonate, ammonium carbonate, urea, ammonium chloride, and ammonium fluoride, and the mass ratio of the pore-forming agent to the positive electrode active material is 1:100 to 8:

100.

14. The method of claim 13, wherein the method further comprises: The secondary battery of any one of claims 1 to 12.

15. A battery module, characterized by The battery module of claim 15.

16. A battery pack, characterized by At least one selected from the secondary battery of any one of claims 1 to 12, the battery module of claim 15, and the battery pack of claim 16.

17. An electrical device, comprising: ​

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