Secondary battery and electrical apparatus

Abstract

The present application belongs to the technical field of batteries. Disclosed are a secondary battery and an electrical apparatus. The secondary battery of the present application is based on the selection of a specific electrolyte. When the concentration of LiFSI in the electrolyte, the number of donors and the compaction density of a negative electrode sheet are configured to satisfy a specific range, while ensuring dissociation of a lithium salt, the electrolyte of the secondary battery can reduce the desolvation energy of lithium ions to the utmost extent, forms a stable interface layer on a positive and a negative electrode so as to help to improve the efficiency of lithium deintercalation on the negative electrode, has excellent dynamic performance, and can realize a rapid charging / discharging property in a wide temperature range.

Description

Secondary battery and power-consuming device Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a secondary battery and an electrical device. Background Art

[0002] Secondary batteries, such as lithium-ion batteries, have always been a key performance feature that people are eager to improve, but this performance is affected by many factors. If the electrolyte, one of the main materials of secondary batteries, is improperly selected, not only will the positive and negative electrodes (especially the negative electrode) not achieve good wettability, but it will also fail to ensure that the lithium ion desolvation energy in the electrolyte is maintained within a small range. Ultimately, this will not only lead to reduced kinetic performance of the secondary battery, but may also cause lithium plating, poor direct current resistance (DCR) performance, and ultimately fail to achieve sustained fast charging performance.

[0003] Summary of the Invention

[0004] In order to overcome the shortcomings of the existing technology, the present application provides a secondary battery and an electrical device. The secondary battery of the present application is based on the selection of an electrolyte with specific properties, and simultaneously controls the compaction density of the negative electrode in the battery to a specific parameter correlation range, so that the product not only has good DCR performance, but also does not exhibit obvious lithium plating during the charge and discharge process, and can achieve fast charge and discharge performance in a wide temperature range.

[0005] To achieve the above objectives, in a first aspect of the present application, a secondary battery is provided, comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the electrolyte comprises a lithium salt and a solvent, wherein the lithium salt comprises LiFSI, and the secondary battery satisfies:

[0006] Wherein, C0M is the concentration of LiFSI in the electrolyte;

[0007] DN kcal / mol is the donor number of the electrolyte;

[0008] PD g / cm 3 is the compaction density of the negative electrode sheet.

[0009] In some embodiments, the C0M satisfies: 0M<C0M<2M.

[0010] In some embodiments, the DN kcal / mol satisfies: 0 kcal / mol<DN kcal / mol<15 kcal / mol.

[0011] In some embodiments, the PD g / cm3 Meets: 1g / cm 3 <PD g / cm 3 <2g / cm 3 .

[0012] In some embodiments, the C0M satisfies: 0.1M≤C0M≤1M;

[0013] In some embodiments, the DN kcal / mol satisfies: 5kcal / mol≤DN kcal / mol≤10kcal / mol;

[0014] In some embodiments, the PD g / cm 3 Meets: 1.1g / cm 3 ≤PD g / cm 3 ≤1.8g / cm 3 .

[0015] In some embodiments, the lithium salt further comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorobis(oxalatophosphate), and lithium bis(trifluoromethylsulfonyl)imide.

[0016] In some embodiments, the electrolyte further comprises an additive, wherein the additive comprises a silicon-containing additive and a sulfur-containing additive.

[0017] In some embodiments, the silicon-containing additive comprises at least one of tris(trimethylsilyl)phosphite, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, trimethylfluorosilane, or heptamethyldisilazane.

[0018] In some embodiments, the sulfur-containing additive comprises at least one of 1,3-propane sultone and vinyl sulfate.

[0019] In some embodiments, the additive further comprises at least one of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate.

[0020] In some embodiments, the sulfur-containing additive comprises 1,3-propane sultone and vinyl sulfate, and a mass ratio of the 1,3-propane sultone to the vinyl sulfate is 7:3 to 5:5.

[0021] In some embodiments, the additive comprises lithium difluorophosphate.

[0022] In some embodiments, the additive has a mass content of 0.5 to 10 wt % in the electrolyte.

[0023] In some embodiments, the solvent comprises at least one of ethylene carbonate, propylene carbonate, butylene carbonate, trifluoroethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methylpropyl carbonate, diphenyl carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, ethyl 2,2-difluoroacetate, methyl 2,2-difluoroacetate, methyl 2,3,3,3-tetrafluoropropionate, γ-butyrolactone, acetonitrile, and sulfolane.

[0024] In some embodiments, the active material in the negative electrode plate includes at least one of a graphite material, a silicon-based material, and lithium metal.

[0025] In some embodiments, the active material in the positive electrode sheet comprises LiCoO2, LiFePO4, Li a Ni x Co y Mn (1-x-y) At least one of O2, wherein 0.9≤a≤1.1, 0<x<1, 0<y<1, x+y<1.

[0026] In a second aspect of the present application, the present application provides an electrical device, comprising the secondary battery, wherein the secondary battery serves as a power supply for the electrical device.

[0027] The beneficial effects of this application are:

[0028] The present application provides a secondary battery and an electrical device. Based on the selection of a specific electrolyte, when the concentration of LiFSI in the electrolyte, the number of donors, and the compaction density of the negative electrode sheet meet a specific range, the electrolyte of the secondary battery can minimize the desolvation energy of lithium ions while ensuring the dissociation of lithium salts, and form a stable interface layer between the positive and negative electrodes, promoting the efficiency of lithium insertion and extraction at the negative electrode, and achieving excellent kinetic performance, thereby achieving rapid charge and discharge performance over a wide temperature range. DETAILED DESCRIPTION

[0029] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0030] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0031] In this application, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0032] In the present application, there is no particular limitation on the specific dispersion and stirring treatment methods.

[0033] The reagents and instruments used in this application without manufacturer indication are all conventional products that can be purchased commercially.

[0034] The present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the electrolyte comprises a lithium salt and a solvent, wherein the lithium salt comprises LiFSI, and the secondary battery satisfies the following requirements:

[0035] Wherein, C0M is the concentration of LiFSI in the electrolyte;

[0036] DN kcal / mol is the donor number of the electrolyte;

[0037] PD g / cm 3 is the compaction density of the negative electrode sheet.

[0038] The solvents used in most electrolytes with high salt dissolution ability will cause the overall electrolyte to have a large DN value, while LiFSI has a weak Li + Binding energy can effectively reduce impedance and improve the fast charging capability of the battery, and LiFSI has high thermal stability, which can improve the storage stability of the electrolyte; but too high a concentration of LiFSI will corrode the aluminum current collector and affect battery performance; at the same time, the use of the electrolyte also needs to be associated with the negative electrode, because during the rapid charging and discharging process, the distribution of active materials on the negative electrode and the electrolyte infiltration will directly affect the energy density and lithium deintercalation kinetics of the overall product. In the technical solution of the present application, by comprehensively designing the concentration of LiFSI in the electrolyte, the DN value and the compaction density of the negative electrode, it is possible to effectively avoid insufficient dissociation of lithium salts in the electrolyte, minimize the energy required for lithium ion desolvation, reduce the interfacial impedance of the overall electrolyte, form an ideal and stable interface layer on the surface of the positive and negative electrode sheets, and promote the rapid deintercalation of lithium ions on the negative electrode sheet, and ultimately achieve ideal fast charging and discharging performance.

[0039] In some embodiments, the C0M satisfies: 0M<C0M<2M. Further preferably, the C0M satisfies: 0.1M≤C0M≤1M.

[0040] Within the range, the electrolyte in the secondary battery can ensure sufficient lithium ion solvent binding energy and has excellent kinetic performance.

[0041] In some embodiments, C0 may be in the range of one or any two of 0.1, 0.2, 0.3, 0.5, 0.8, 1.

[0042] In some embodiments, the C0 can be measured by GC-MS. The testing method of the DN value is a nuclear magnetic resonance method. Usually, the numerical value of the donor number DN of the electrolyte is measured using nuclear magnetic resonance (NMR), and several known solvents (for example, commonly used solvents, including but not limited to acetic anhydride, acetonitrile, DME, DMSO, pyridine, 1-methylimidazole) are tested. 23Na NMR and a standard fitting curve is constructed, followed by testing 10mM NaTFSI / electrolyte 23Na NMR, and the DN value is confirmed by comparing the displacement value with the standard fitting curve. The test of the compacted density PD can be tested by PRCD1100.

[0043] In some embodiments, the 0 kcal / mol<DN kcal / mol<15 kcal / mol, and more preferably, the 5 kcal / mol≤DN kcal / mol≤10 kcal / mol.

[0044] When the DN value is within the range, the electrolyte in the secondary battery can ensure that the lithium salt does not dissociate sufficiently or even precipitate, and further optimize the overall electrochemical performance.

[0045] In some embodiments, DN kcal / mol can be a range value of one or any two of 5 kcal / mol, 6 kcal / mol, 7 kcal / mol, 8 kcal / mol, 9 kcal / mol, 10 kcal / mol.

[0046] In some embodiments, the 1g / cm 3 <PD g / cm 3 <2g / cm 3 , further preferably, the 1.1g / cm 3 ≤PD g / cm 3 ≤1.8g / cm 3 .

[0047] When the compaction density of the negative electrode sheet is too low, it may affect the energy density of the secondary battery. However, if the compaction density is too high, it may cause the electrolyte to be unable to fully infiltrate the active material, ultimately reducing the kinetic performance of the secondary battery. Therefore, within the preferred range, the comprehensive performance of the product is the best.

[0048] In some embodiments, PD g / cm 3 Can be 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 The range of values ​​for one or both of .

[0049] In some embodiments, the lithium salt further comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorobis(oxalatophosphate), and lithium bis(trifluoromethylsulfonyl)imide.

[0050] In some embodiments, the concentration of the lithium salt in the electrolyte is 0.9 to 1.5 M. It is understood that when the electrolyte contains several different lithium salts, the concentration of the lithium salt refers to the total concentration of lithium contributed by the lithium salts in the electrolyte, that is, the total concentration of lithium produced by LiFSI and other lithium salts (at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorobis(oxalatophosphate), and lithium bis(trifluoromethylsulfonyl)imide).

[0051] In some embodiments, the concentration of the lithium salt in the electrolyte may be in the range of one or any two of 0.9 M, 1 M, 1.1 M, 1.2 M, 1.3 M, 1.4 M, and 1.5 M.

[0052] If the content of lithium salt in the electrolyte is too high, the overall viscosity of the electrolyte will increase, which is not conducive to the wetting of the negative electrode. However, if the content is too little, the conductivity of the electrolyte will decrease. Therefore, when the lithium salt content in the above moderate range is selected to be introduced into the electrolyte, the product can achieve better performance.

[0053] In some embodiments, the electrolyte further includes an additive.

[0054] In some embodiments, the weight content of the additive in the electrolyte is 0.5-10 wt %. It is understood that when the electrolyte contains several different additives, the weight content of the additive in the electrolyte is the total weight content of all additives in the electrolyte.

[0055] In some embodiments, the additive comprises a silicon-containing additive and a sulfur-containing additive.

[0056] In some embodiments, the silicon-containing additive comprises at least one of tris(trimethylsilyl)phosphite, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, trimethylfluorosilane, and heptamethyldisilazane.

[0057] In some embodiments, the mass content of the silicon-containing additive in the electrolyte is 0.1 to 4 wt %.

[0058] In some embodiments, the mass content of the silicon-containing additive in the electrolyte is in the range of one or any two of 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%.

[0059] In some embodiments, the sulfur-containing additive comprises at least one of 1,3-propane sultone and vinyl sulfate.

[0060] In some embodiments, the mass content of the sulfur-containing additive in the electrolyte is 0.05 to 3 wt %.

[0061] In some embodiments, the mass content of the sulfur-containing additive in the electrolyte is in the range of one or any two of 0.05wt%, 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, and 3wt%.

[0062] In some embodiments, the sulfur-containing additive comprises 1,3-propane sultone and vinyl sulfate, and the mass ratio of 1,3-propane sultone to vinyl sulfate is 7:3 to 5:5.

[0063] After screening, it was found that when the sulfur-containing additive contains both components and maintains in this ratio range, the electrochemical performance of the secondary battery is better.

[0064] In some embodiments, the additive further comprises at least one of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate.

[0065] In some embodiments, the additive comprises lithium difluorophosphate.

[0066] In some embodiments, the solvent comprises at least one of ethylene carbonate, propylene carbonate, butylene carbonate, trifluoroethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methylpropyl carbonate, diphenyl carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, ethyl 2,2-difluoroacetate, methyl 2,2-difluoroacetate, methyl 2,3,3,3-tetrafluoropropionate, γ-butyrolactone, acetonitrile, and sulfolane.

[0067] In some embodiments, the active material in the negative electrode plate includes at least one of a graphite material, a silicon-based material, and lithium metal.

[0068] In some embodiments, the active material in the positive electrode sheet comprises LiCoO2, LiFePO4, Li a Ni x Co y Mn (1-x-y) At least one of O2, wherein 0.9≤a≤1.1, 0<x<1, 0<y<1, x+y<1.

[0069] The present application is further described below with specific examples:

[0070] Example 1

[0071] A secondary battery, the preparation method comprising the following steps:

[0072] Preparation of electrolyte: At room temperature, in an argon-filled glove box (H2O <1ppm, O2 <1ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 3:7. Molecular sieves are used to remove water to obtain a mixed solvent, and LiFSI and LiPF6 are successively added to the obtained mixed solvent, and the mixture is stirred and cooled to ensure that the temperature of the electrolyte does not rise by more than 2°C. The concentration of LiFSI in the electrolyte is controlled to be 0.5M and the concentration of LiPF6 is controlled to be 0.7M to obtain a transparent liquid; vinylene carbonate, vinyl sulfate, lithium difluorophosphate and tris(trimethylsilane) phosphate are added to obtain an electrolyte, wherein the mass content of vinylene carbonate is 1wt%, the mass content of vinyl sulfate is 1.5wt%, the mass content of lithium difluorophosphate is 0.5wt%, and the mass content of tris(trimethylsilane) phosphate is 1wt%;

[0073] S2. Preparation of positive electrode sheet: The positive electrode active material Li (Ni 0.8 Mn 0.1 Co 0.1) O2, conductive agent acetylene black and binder PVDF are mixed in a mass ratio of 94:3:3 and evenly dispersed in 1-methyl-2-pyrrolidone (NMP) to prepare a uniform black slurry. The mixed black slurry is coated on both sides of aluminum foil, and then baked, rolled and cut into pieces to obtain a positive electrode sheet;

[0074] S3. Preparation of negative electrode sheet: The negative electrode active material graphite, conductive agent acetylene black (Super P) and binder SBR were mixed in a mass ratio of 94:3:3 and evenly dispersed in deionized water to form a uniform black slurry. The mixed slurry was coated on both sides of the copper foil, baked, rolled and cut into pieces to obtain a compaction density of 1.55g / cm 3 negative electrode;

[0075] S4. Preparation of secondary batteries: stack the positive electrode sheet, polyethylene separator, and negative electrode sheet in order, with the separator placed between the positive and negative electrode sheets, and obtain a bare battery cell through winding, hot pressing and shaping, and tab welding. Place the bare battery cell in an outer packaging aluminum-plastic film and bake it in an oven at 85±10°C for 24 hours. Inject the above-prepared electrolyte into the dried battery, let it stand, form it, and separate the capacity to obtain the secondary battery.

[0076] Example 2

[0077] The method for preparing the product in this embodiment is the same as that in embodiment 1, except that the solvent used in preparing the electrolyte is different, resulting in a different number of donors in the electrolyte. The preparation method of the electrolyte is as follows: at room temperature, in a glove box filled with argon (H2O<1ppm, O2<1ppm), EC:DEC (diethyl carbonate):EMC are uniformly mixed in a mass ratio of 1:2:7, and the mixture is stirred for 1 minute. The molecular sieve is used to remove water to obtain a mixed solvent, and LiFSI and LiPF6 are successively added to the obtained mixed solvent, and the mixture is stirred and cooled to ensure that the temperature of the electrolyte does not rise by more than 2°C. The concentration of LiFSI in the electrolyte is controlled to be 0.5M, and the concentration of LiPF6 is controlled to be 0.7M to obtain a transparent liquid; vinylene carbonate, vinyl sulfate, lithium difluorophosphate and tris(trimethylsilane) phosphate are added to obtain an electrolyte, wherein the mass content of vinylene carbonate is 1wt%, the mass content of vinyl sulfate is 1.5wt%, the mass content of lithium difluorophosphate is 0.5wt%, and the mass content of tris(trimethylsilane) phosphate is 1wt%.

[0078] Example 3

[0079] The method for preparing the product in this embodiment is the same as that in embodiment 1, except that the solvent used in preparing the electrolyte is different, resulting in a different number of donors in the electrolyte. The preparation method of the electrolyte is as follows: at room temperature, in a glove box filled with argon (H2O<1ppm, O2<1ppm), EC:EA (ethyl acetate):DEC:EMC are uniformly mixed in a mass ratio of 4:1:2:3, and the mixture is stirred for 1 min. The molecular sieve is used to remove water to obtain a mixed solvent, and LiFSI and LiPF6 are successively added to the obtained mixed solvent, and the mixture is stirred and cooled to ensure that the temperature of the electrolyte does not rise by more than 2°C. The concentration of LiFSI in the electrolyte is controlled to be 0.5M, and the concentration of LiPF6 is controlled to be 0.7M to obtain a transparent liquid; vinylene carbonate, vinyl sulfate, lithium difluorophosphate and tris(trimethylsilane) phosphate are added to obtain an electrolyte, wherein the mass content of vinylene carbonate is 1wt%, the mass content of vinyl sulfate is 1.5wt%, the mass content of lithium difluorophosphate is 0.5wt%, and the mass content of tris(trimethylsilane) phosphate is 1wt%.

[0080] Example 4

[0081] The method for preparing the product in this embodiment is the same as that in embodiment 1, except that the lithium salt used in preparing the electrolyte is different. The preparation method of the electrolyte is as follows: at room temperature, in a glove box filled with argon (H2O<1ppm, O2<1ppm), EC:EMC are mixed in a mass ratio of 3:7, and the mixture is stirred for 1 minute. Molecular sieves are used to remove water to obtain a mixed solvent. LiFSI and LiPF6 are added sequentially to the resulting mixed solvent with continuous stirring and cooling to ensure that the electrolyte temperature does not rise more than 2°C. The concentration of LiFSI in the electrolyte is controlled to be 0.1M and the concentration of LiPF6 in the electrolyte is controlled to be 1.1M, resulting in a transparent liquid. Vinylene carbonate, vinyl sulfate, lithium difluorophosphate, and tris(trimethylsilyl)phosphate are then added to obtain an electrolyte containing 1% vinylene carbonate by weight, 1.5% vinyl sulfate by weight, 0.5% lithium difluorophosphate by weight, and 1% tris(trimethylsilyl)phosphate by weight.

[0082] Example 5

[0083] The method for preparing the product in this embodiment is the same as that in embodiment 1, except that the lithium salt used in preparing the electrolyte is different. The preparation method of the electrolyte is as follows: at room temperature, in a glove box filled with argon (H2O<1ppm, O2<1ppm), EC:EMC are mixed in a mass ratio of 3:7, and the mixture is stirred for 1 minute. The molecular sieve is used to remove water to obtain a mixed solvent, and LiFSI and LiPF6 are successively added to the obtained mixed solvent, and the mixture is stirred and cooled continuously to ensure that the temperature of the electrolyte does not rise by more than 2°C. The concentration of LiFSI in the electrolyte is controlled to be 1M, and the concentration of LiPF6 is controlled to be 0.2M to obtain a transparent liquid; vinylene carbonate, vinyl sulfate, lithium difluorophosphate and tris(trimethylsilane) phosphate are added to obtain an electrolyte, wherein the mass content of vinylene carbonate is 1wt%, the mass content of vinyl sulfate is 1.5wt%, the mass content of lithium difluorophosphate is 0.5wt%, and the mass content of tris(trimethylsilane) phosphate is 1wt%.

[0084] Example 6

[0085] The method for preparing the product in this embodiment is the same as that in Example 1, with the only difference being that the compaction density of the final product is different when preparing the negative electrode sheet.

[0086] Example 7

[0087] The method for preparing the product in this embodiment is the same as that in Example 1, with the only difference being that the compaction density of the final product is different when preparing the negative electrode sheet.

[0088] Example 8

[0089] The method for preparing the product in this embodiment is the same as that in embodiment 1, except that the solvent used in preparing the electrolyte is different, resulting in a different number of donors in the electrolyte. The preparation method of the electrolyte is as follows: at room temperature, in a glove box filled with argon (H2O<1ppm, O2<1ppm), EC:EA:DEC:EMC are uniformly mixed in a mass ratio of 4:1:2:3, and the mixture is stirred for 1 min. Molecular sieves are used to remove water to obtain a mixed solvent. LiFSI and LiPF6 are added sequentially to the resulting mixed solvent with continuous stirring and cooling to ensure that the electrolyte temperature does not rise more than 2°C. The concentration of LiFSI in the electrolyte is controlled to be 0.5M and the concentration of LiPF6 in the electrolyte is controlled to be 0.7M to obtain a transparent liquid. Vinylene carbonate, vinyl sulfate, lithium difluorophosphate, and tris(trimethylsilyl)phosphate are added to obtain an electrolyte in which the mass content of vinylene carbonate is 1wt%, the mass content of vinyl sulfate is 1.5wt%, the mass content of lithium difluorophosphate is 0.5wt%, and the mass content of tris(trimethylsilyl)phosphate is 1wt%. At the same time, the compaction density of the negative electrode sheet also varies.

[0090] Example 9

[0091] The method for preparing the product in this embodiment is the same as that in embodiment 1, except that the solvent used in preparing the electrolyte is different, resulting in a different number of donors in the electrolyte. The preparation method of the electrolyte is as follows: at room temperature, in a glove box filled with argon (H2O<1ppm, O2<1ppm), EC:DEC:EMC are uniformly mixed in a mass ratio of 1:2:7, and the mixture is stirred for 1 minute. The molecular sieve is used to remove water to obtain a mixed solvent, and LiFSI and LiPF6 are added successively to the obtained mixed solvent, and stirring is continued and the temperature is lowered to ensure that the temperature of the electrolyte does not rise by more than 2°C. The concentration of LiFSI in the electrolyte is controlled to be 0.5M, and the concentration of LiPF6 is controlled to be 0.7M to obtain a transparent liquid; vinylene carbonate, vinyl sulfate, lithium difluorophosphate and tris(trimethylsilane) phosphate are added to obtain an electrolyte, wherein the mass content of vinylene carbonate is 1wt%, the mass content of vinyl sulfate is 1.5wt%, the mass content of lithium difluorophosphate is 0.5wt%, and the mass content of tris(trimethylsilane) phosphate is 1wt%; at the same time, the compaction density of the negative electrode sheet is also different.

[0092] Example 10

[0093] The method for preparing the product in this embodiment is the same as that in embodiment 1, except that the lithium salt and solvent are different when preparing the electrolyte, so that the number of donors in the electrolyte is different. The preparation method of the electrolyte is as follows: at room temperature, in a glove box filled with argon (H2O<1ppm, O2<1ppm), EC:EA:DEC:EMC are uniformly mixed in a mass ratio of 4:1:2:3, and the mixture is stirred for 1 minute. The molecular sieve is used to remove water to obtain a mixed solvent, and LiFSI and LiPF6 are successively added to the obtained mixed solvent, and the mixture is stirred and cooled continuously to ensure that the temperature of the electrolyte does not rise by more than 2°C. The concentration of LiFSI in the electrolyte is controlled to be 0.1M, and the concentration of LiPF6 is controlled to be 1.1M to obtain a transparent liquid; vinylene carbonate, vinyl sulfate, lithium difluorophosphate and tris(trimethylsilane) phosphate are added to obtain an electrolyte, wherein the mass content of vinylene carbonate is 1wt%, the mass content of vinyl sulfate is 1.5wt%, the mass content of lithium difluorophosphate is 0.5wt%, and the mass content of tris(trimethylsilane) phosphate is 1wt%.

[0094] Example 11

[0095] The method for preparing the product in this embodiment is the same as that in embodiment 1, except that the lithium salt and solvent are different when preparing the electrolyte, so that the number of donors in the electrolyte is different. The preparation method of the electrolyte is as follows: at room temperature, in a glove box filled with argon (H2O<1ppm, O2<1ppm), EC:DEC:EMC are uniformly mixed in a mass ratio of 1:2:7, and the mixture is stirred for 1 minute. Molecular sieves are used to remove water to obtain a mixed solvent, and LiFSI and LiPF6 are successively added to the obtained mixed solvent, and stirring is continued and the temperature is lowered to ensure that the temperature of the electrolyte does not rise by more than 2°C. The concentration of LiFSI in the electrolyte is controlled to be 1M, and the concentration of LiPF6 is controlled to be 0.2M to obtain a transparent liquid; vinylene carbonate, vinyl sulfate, lithium difluorophosphate and tris(trimethylsilane) phosphate are added to obtain an electrolyte, wherein the mass content of vinylene carbonate is 1wt%, the mass content of vinyl sulfate is 1.5wt%, the mass content of lithium difluorophosphate is 0.5wt%, and the mass content of tris(trimethylsilane) phosphate is 1wt%.

[0096] Example 12

[0097] The method for preparing the product in this embodiment is the same as that in embodiment 1, except that the lithium salt used in preparing the electrolyte is different. The preparation method of the electrolyte is as follows: at room temperature, in a glove box filled with argon (H2O<1ppm, O2<1ppm), EC:EMC are mixed in a mass ratio of 3:7, and the mixture is stirred for 1 minute. The molecular sieve is used to remove water to obtain a mixed solvent, and LiFSI and LiPF6 are added successively to the obtained mixed solvent, and stirring is continued and the temperature is lowered to ensure that the electrolyte temperature does not rise by more than 2°C. The concentration of LiFSI in the electrolyte is controlled to be 0.1M, and the concentration of LiPF6 is controlled to be 1.1M to obtain a transparent liquid; vinylene carbonate, vinyl sulfate, lithium difluorophosphate and tris(trimethylsilane) phosphate are added to obtain an electrolyte, wherein the mass content of vinylene carbonate is 1wt%, the mass content of vinyl sulfate is 1.5wt%, the mass content of lithium difluorophosphate is 0.5wt%, and the mass content of tris(trimethylsilane) phosphate is 1wt%; at the same time, the compaction density of the negative electrode sheet is also different.

[0098] Example 13

[0099] The method for preparing the product in this embodiment is the same as that in embodiment 1, except that the lithium salt used in preparing the electrolyte is different. The electrolyte is prepared by mixing EC and EMC in a mass ratio of 3:7 in a glove box filled with argon (H2O<1ppm, O2<1ppm) at room temperature, and then stirring for 10 minutes. The molecular sieve is used to remove water to obtain a mixed solvent, and LiFSI and LiPF6 are added successively to the obtained mixed solvent, and stirring is continued and the temperature is lowered to ensure that the electrolyte temperature does not rise by more than 2°C. The concentration of LiFSI in the electrolyte is controlled to be 1M, and the concentration of LiPF6 is controlled to be 0.2M to obtain a transparent liquid; vinylene carbonate, vinyl sulfate, lithium difluorophosphate and tris(trimethylsilane) phosphate are added to obtain an electrolyte, wherein the mass content of vinylene carbonate is 1wt%, the mass content of vinyl sulfate is 1.5wt%, the mass content of lithium difluorophosphate is 0.5wt%, and the mass content of tris(trimethylsilane) phosphate is 1wt%; at the same time, the compaction density of the negative electrode sheet is also different.

[0100] Example 14

[0101] The method for preparing the product in this example is the same as that in Example 1, except that the vinyl sulfate is replaced by an equal amount of 1,3-propane sultone.

[0102] Example 15

[0103] The method for preparing the product in this embodiment is the same as that in Example 1, except that a portion of the vinyl sulfate is replaced by 1,3-propane sultone, and the mass ratio of the two is vinyl sulfate:1,3-propane sultone=7:3.

[0104] Example 16

[0105] The method for preparing the product in this embodiment is the same as that in Example 1, except that a portion of the vinyl sulfate is replaced by 1,3-propane sultone, and the mass ratio of the two is vinyl sulfate:1,3-propane sultone=6:4.

[0106] Example 17

[0107] The method for preparing the product in this embodiment is the same as that in Example 1, except that a portion of the vinyl sulfate is replaced by 1,3-propane sultone, and the mass ratio of the two is vinyl sulfate:1,3-propane sultone=5:5.

[0108] Example 18

[0109] The method for preparing the product in this embodiment is the same as that in Example 1, except that a portion of the vinyl sulfate is replaced by 1,3-propane sultone, and the mass ratio of the two is vinyl sulfate:1,3-propane sultone=2:8.

[0110] Example 19

[0111] The method for preparing the product in this embodiment is the same as that in Example 1, except that a portion of the vinyl sulfate is replaced by 1,3-propane sultone, and the mass ratio of the two is vinyl sulfate:1,3-propane sultone=8:2.

[0112] Comparative Example 1

[0113] The method for preparing the product of this comparative example is the same as that of Example 1, except that the lithium salt and solvent are different when preparing the electrolyte, so that the number of donors in the electrolyte is different. The preparation method of the electrolyte is as follows: at room temperature, in a glove box filled with argon (H2O<1ppm, O2<1ppm), EC:EA:DEC:EMC are uniformly mixed in a mass ratio of 4:1:2:3, and the mixture is stirred for 1 minute. The molecular sieve is used to remove water to obtain a mixed solvent, and LiFSI and LiPF6 are added successively to the obtained mixed solvent, and stirring is continued and the temperature is lowered to ensure that the electrolyte temperature does not rise by more than 2°C. The concentration of LiFSI in the electrolyte is controlled to be 0.1M, and the concentration of LiPF6 is controlled to be 1.1M to obtain a transparent liquid; vinylene carbonate, vinyl sulfate, lithium difluorophosphate and tris(trimethylsilane) phosphate are added to obtain an electrolyte, wherein the mass content of vinylene carbonate is 1wt%, the mass content of vinyl sulfate is 1.5wt%, the mass content of lithium difluorophosphate is 0.5wt%, and the mass content of tris(trimethylsilane) phosphate is 1wt%; at the same time, the compaction density of the negative electrode sheet is also different.

[0114] Comparative Example 2

[0115] The method for preparing the product of this comparative example is the same as that of Example 1, except that the lithium salt and solvent are different when preparing the electrolyte, so that the number of donors in the electrolyte is different. The preparation method of the electrolyte is as follows: at room temperature, in a glove box filled with argon (H2O<1ppm, O2<1ppm), EC:DEC:EMC are uniformly mixed in a mass ratio of 1:2:7, and the electrolyte is prepared with The molecular sieve is used to remove water to obtain a mixed solvent, and LiFSI and LiPF6 are added successively to the obtained mixed solvent, and stirring is continued and the temperature is lowered to ensure that the temperature of the electrolyte does not rise by more than 2°C. The concentration of LiFSI in the electrolyte is controlled to be 1M, and the concentration of LiPF6 is controlled to be 0.2M to obtain a transparent liquid; vinylene carbonate, lithium difluorophosphate and tris(trimethylsilane) phosphate are added to obtain an electrolyte, wherein the mass content of vinylene carbonate is 1wt%, the mass content of lithium difluorophosphate is 0.5wt%, and the mass content of tris(trimethylsilane) phosphate is 1wt%; at the same time, the compaction density of the negative electrode sheet is also different.

[0116] Comparative Example 3

[0117] The method for preparing the product of this comparative example is the same as that of Example 1, except that the solvent used in preparing the electrolyte is different, resulting in a different number of donors in the electrolyte. The preparation method of the electrolyte is as follows: EC:EA:DEC:EMC are mixed uniformly in a mass ratio of 5:1:1:3, and the electrolyte is prepared with The molecular sieve is used to remove water to obtain a mixed solvent, and LiFSI and LiPF6 are successively added to the obtained mixed solvent, and the mixture is stirred and cooled to ensure that the temperature of the electrolyte does not rise by more than 2°C. The concentration of LiFSI in the electrolyte is controlled to be 0.5M, and the concentration of LiPF6 is controlled to be 0.7M to obtain a transparent liquid; vinylene carbonate, vinyl sulfate, lithium difluorophosphate and tris(trimethylsilane) phosphate are added to obtain an electrolyte, wherein the mass content of vinylene carbonate is 1wt%, the mass content of vinyl sulfate is 1.5wt%, the mass content of lithium difluorophosphate is 0.5wt%, and the mass content of tris(trimethylsilane) phosphate is 1wt%.

[0118] Comparative Example 4

[0119] The method for preparing the product of this comparative example is the same as that of Example 1, except that the solvent used in preparing the electrolyte is different, resulting in a different number of donors in the electrolyte. The preparation method of the electrolyte is as follows: EC:DEC:EMC are mixed uniformly in a mass ratio of 1:3:6, and the electrolyte is prepared with The molecular sieve is used to remove water to obtain a mixed solvent, and LiFSI and LiPF6 are added successively to the obtained mixed solvent, and the mixture is stirred and cooled continuously to ensure that the temperature of the electrolyte does not rise by more than 2°C. The concentration of LiFSI in the electrolyte is controlled to be 0.5M, and the concentration of LiPF6 is controlled to be 0.7M to obtain a transparent liquid; vinylene carbonate, vinyl sulfate, lithium difluorophosphate, and tris(trimethylsilyl)phosphate are added to obtain an electrolyte, wherein the mass content of vinylene carbonate is 1wt%, the mass content of vinyl sulfate is 1.5wt%, the mass content of lithium difluorophosphate is 0.5wt%, and the mass content of tris(trimethylsilyl)phosphate is 1wt%.

[0120] Comparative Example 5

[0121] The method for preparing the product of this comparative example is the same as that of Example 1, except that the amount of lithium salt, additive and solvent added during the preparation of the electrolyte is different, resulting in a different number of donors in the electrolyte. The preparation method of the electrolyte is as follows: EC:DEC:EMC are uniformly mixed in a mass ratio of 4:2:4, and the electrolyte is prepared with The molecular sieve is used to remove water to obtain a mixed solvent, and LiFSI and LiPF6 are successively added to the obtained mixed solvent, and the mixture is stirred and cooled to ensure that the temperature of the electrolyte does not rise by more than 2°C. The concentration of LiFSI in the electrolyte is controlled to be 0.05M, and the concentration of LiPF6 is controlled to be 1.15M to obtain a transparent liquid; the mass content of vinylene carbonate, vinyl sulfate, lithium difluorophosphate, and tris(trimethylsilane) phosphate are added to obtain an electrolyte, wherein the mass content of vinylene carbonate is 0.3wt%, the mass content of vinyl sulfate is 0.7wt%, the mass content of lithium difluorophosphate is 0.2wt%, and the mass content of tris(trimethylsilane) phosphate is 1wt%.

[0122] The parameters of the secondary batteries of the embodiments and comparative examples are shown in Table 1, where the LiFSI concentration C0 is tested by GC-MS, PD by PRCD1100, and DN by NMR. Y in Table 1 refers to:

[0123] Table 1

[0124] The performance tests of the secondary batteries prepared in the above examples and comparative examples were carried out respectively, and the specific methods are as follows:

[0125] (1) Room temperature DCR test: At 25±2°C, the secondary batteries obtained from each embodiment and comparative example were charged to 4.4V at 1C, then discharged at 1C capacity for 30 minutes, adjusted to 50% state of charge (SOC), and then discharged at 10C constant current pulse for 10 seconds. After adjusting the SOC to 50% according to the above-mentioned SOC adjustment method, the battery was charged for another 10 seconds and DCR was calculated as (voltage before pulse discharge - voltage after pulse discharge) / discharge current. After 500 cycles, the DCR was tested again. The DCR change rate (%) = (DCR of 500 cycles - initial DCR) / initial DCR * 100%;

[0126] (2) Normal temperature cycle performance test: At 25±2°C, the secondary batteries obtained from each embodiment and comparative example were subjected to charge and discharge cycle tests at a charge and discharge rate of 1C / 1C in the range of 2.8 to 4.4V, and the battery's first-week discharge capacity and the discharge capacity after 500 cycles were recorded. 500-week capacity retention (%) = 500-week discharge capacity / first-week discharge capacity * 100%

[0127] (3) Lithium deposition at the interface: In an environment of 25±2°C, a secondary battery was taken from each embodiment and comparative example for full charge and disassembly. First, the battery was allowed to stand for 30 minutes, and then the two tabs of the battery were taped to avoid metal contact and short circuit. The insulating film of the battery was removed, and the two tabs of the battery were cut off with scissors to avoid short circuit during subsequent disassembly. The tape on the upper and lower sides was torn off, and then the electrodes were unfolded in turn, taking care not to let the positive and negative electrodes touch. Finally, the unfolded electrodes were separated, and the lithium deposition on the surface of the negative electrode was observed. Among them, the area of ​​lithium deposition on the negative electrode surface was less than 5%, which was considered to be mild lithium deposition, the area of ​​lithium deposition on the negative electrode surface was 5% to 40%, which was considered to be moderate lithium deposition, and the area of ​​lithium deposition on the negative electrode surface was greater than 40%, which was considered to be severe lithium deposition. The test results are shown in Table 2.

[0128] Table 2

[0129] As can be seen from Table 2, the secondary batteries prepared in each embodiment have ideal electrochemical performance. Under 1C fast charge and discharge conditions, the secondary battery can still maintain a capacity retention rate of more than 87% after 500 cycles, and the DCR change rate is no more than 26%. At the same time, there is no obvious lithium precipitation phenomenon at the negative electrode interface. In addition, according to the comparison between Example 1 and Examples 15 to 19, it can be seen that when the sulfur-containing additives in the electrolyte are selected from vinyl sulfate and 1,3-propane sultone and the mass ratio is maintained at 7:3 to 5:5, the electrochemical performance of the secondary battery is better when the DN value of the electrolyte does not change significantly. It can be seen from the comparison between Example 1 and Examples 4 to 5 that when the concentration of LiFSI in the electrolyte changes, the cycle performance, impedance performance and interface stability of the product will change at the same time. If the LIFSI concentration is too high, aluminum current collector corrosion may occur, which may cause the electrochemical performance of the product to decline. According to the various embodiments and comparative examples, it can be seen that in addition to the electrolyte, the negative electrode sheet in contact with it also needs to maintain a suitable compaction density, and the Y value must be controlled within the range of 2.0 to 12.9 to ensure that it has an ideal energy density and lithium deintercalation efficiency. If the Y value is too large, it means that the impedance of the secondary battery is large or the compaction density of the negative electrode sheet is too small, which can easily lead to poor electrochemical cycle stability or too low energy density, and may cause lithium precipitation. However, if the Y value is too small, it means that the solvation energy of the electrolyte is too large, the impedance of the secondary battery increases, or the compaction density is too large, and the degree of electrolyte infiltration is low, which can also cause the comprehensive performance of the secondary battery to decline. On the other hand, according to the embodiments and comparative examples, it can be known that when the DN value becomes larger or smaller, it does not mean that the performance of the product will deteriorate. At this time, if it is matched with a reasonable compaction density electrode, the expected effect can still be achieved. When the electrolyte composition of the product is completely consistent, if the compaction density of the electrode sheet causes the Y value to fail to reach the specified range, the performance of the product still cannot meet the standard.

Claims

1. A secondary battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the electrolyte comprises a lithium salt and a solvent, wherein the lithium salt comprises LiFSI, and the secondary battery satisfies: in, C0M is the concentration of LiFSI in the electrolyte; DN kcal / mol is the donor number of the electrolyte; PD g / cm 3 is the compaction density of the negative electrode plate.

2. The secondary battery according to claim 1, wherein: The secondary battery satisfies at least one of the following conditions: (1) The C0M satisfies: 0M<C0M<2M; (2) The DN kcal / mol satisfies: 0 kcal / mol<DN kcal / mol<15 kcal / mol; (3) PD g / cm 3 Meets: 1g / cm 3 <PD g / cm 3 <2g / cm 3 .

3. The secondary battery according to claim 1, wherein: The secondary battery satisfies at least one of the following conditions: (a) the C0M satisfies: 0.1M≤C0M≤1M; (b) the DN kcal / mol satisfies: 5 kcal / mol≤DN kcal / mol≤10 kcal / mol; (c) PD g / cm 3 Meets: 1.1g / cm 3 ≤PD g / cm 3 ≤1.8g / cm 3 .

4. The secondary battery according to any one of claims 1 to 3, wherein: The lithium salt further comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorobis(oxalatophosphate), and lithium bis(trifluoromethylsulfonyl)imide.

5. The secondary battery according to claim 1, wherein: The electrolyte further comprises an additive, wherein the additive comprises a silicon-containing additive and / or a sulfur-containing additive.

6. The secondary battery according to claim 5, wherein: The silicon-containing additive comprises at least one of tris(trimethylsilyl)phosphite, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, trimethylfluorosilane, and heptamethyldisilazane; And / or, the sulfur-containing additive comprises at least one of 1,3-propane sultone and vinyl sulfate; 7. The secondary battery according to claim 5, wherein: The additive further comprises at least one of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate.

8. The secondary battery according to claim 6, wherein: The sulfur-containing additive comprises 1,3-propane sultone and vinyl sulfate, and the mass ratio of the 1,3-propane sultone to the vinyl sulfate is 7:3 to 5:

5.

9. The secondary battery according to any one of claims 1 to 3, wherein: The solvent comprises at least one of ethylene carbonate, propylene carbonate, butylene carbonate, trifluoroethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, ethyl 2,2-difluoroacetate, methyl 2,2-difluoroacetate, methyl 2,3,3,3-tetrafluoropropionate, γ-butyrolactone, acetonitrile, and sulfolane.

10. The secondary battery according to any one of claims 5 to 8, wherein: The additive includes lithium difluorophosphate.

11. The secondary battery according to any one of claims 5 to 8, wherein: The mass content of the additive in the electrolyte is 0.5-10wt%.

12. The secondary battery according to any one of claims 1 to 3, wherein: The active material in the negative electrode plate includes at least one of graphite material, silicon-based material and lithium metal.

13. The secondary battery according to any one of claims 1 to 3, wherein: The active material in the positive electrode sheet includes LiCoO2, LiFePO4, Li a Ni x Co y Mn (1-x-y) At least one of O2, wherein 0.9≤a≤1.1, 0<x<1, 0<y<1, x+y<1.

14. An electric device, comprising the secondary battery according to any one of claims 1 to 13, wherein the secondary battery serves as a power supply for the electric device.

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