Battery

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a battery. Compared with the prior art, the lithium fluorosulfonate is added into the electrolyte to promote dissociation and migration of lithium ions, so that the interface impedance of the negative electrode is reduced, meanwhile, by controlling the content of secondary particles in the negative electrode active material and the viscosity of the electrolyte, the side reaction between the negative electrode plate and the electrolyte is reduced, the gas production of the battery is reduced, and the service life of the battery is prolonged. The dynamic performance of the battery is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to a battery. Background Art

[0002] Since their commercialization, lithium-ion batteries have been widely used in the power battery field due to their high energy density, high power density, long cycle life, and environmental friendliness. At the same time, due to the diverse application environments of end devices, consumers are placing increasingly high demands on lithium-ion batteries for performance, such as long cycle life and ability to operate under high and low temperature conditions.

[0003] Research has found that the electrolyte in lithium-ion batteries has a significant impact on the performance of lithium-ion batteries. Adding a small amount of electrolyte additives to the electrolyte to form a stable protective film on the electrode surface is the most cost-effective strategy to improve electrode stability and achieve highly stable, high-energy-density lithium-ion batteries. Currently, a variety of additives have been reported, among which lithium fluorosulfonate is an electrolyte additive for lithium-ion batteries. It can form a dense, low-impedance SEI film on the surface of the negative electrode of the lithium-ion battery during operation, thereby significantly improving the rate performance and cycle performance of the lithium-ion battery. Therefore, lithium fluorosulfonate has been widely used in lithium-ion battery electrolytes.

[0004] However, during storage, batteries containing lithium fluorosulfonate electrolytes may produce hydrogen fluoride or other volatile gases due to the decomposition of lithium fluorosulfonate, which may increase gas production and cause battery expansion. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a battery with low interface impedance and low gas production.

[0006] The present invention provides a battery comprising a negative electrode sheet and an electrolyte;

[0007] The negative electrode sheet includes a negative electrode active material layer; the negative electrode active material layer includes a negative electrode active material; the negative electrode active material includes primary particles and secondary particles; the secondary particles are formed by agglomeration of multiple primary particles; the proportion of secondary particles in the negative electrode active material is a;

[0008] The electrolyte includes an additive; the additive includes lithium fluorosulfonate; the mass content of lithium fluorosulfonate in the electrolyte is b; the viscosity of the electrolyte at 25±0.02° C. is c mPa·s;

[0009] The battery satisfies the condition: 0.1≤(a×b / c)×10000≤550.

[0010] Preferably, the battery satisfies the condition: 1≤(a×b / c)×10000≤25.

[0011] Preferably, the a is 10% to 60%;

[0012] and / or, b is 0.01% to 5%;

[0013] And / or, c is 0.5 to 5.

[0014] Preferably, the a is 10% to 30%;

[0015] and / or, b is 0.2% to 2%;

[0016] And / or, c is 2-4.

[0017] Preferably, the particle size Dn50 of the primary particles is 5 to 14 μm;

[0018] And / or, the particle size Dn50 of the secondary particles is 15 to 25 μm.

[0019] Preferably, the particle size Dn50 of the primary particles is 5 to 10 μm;

[0020] And / or, the particle size Dn50 of the secondary particles is 15 to 20 μm.

[0021] Preferably, the negative electrode active material is selected from natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, silicon, SiO x , silicon carbon and Li4Ti5O 12 One or more of; and / or,

[0022] The battery also includes a positive electrode sheet; the positive electrode sheet includes a positive electrode active material layer; the positive electrode active material layer includes a positive electrode active material; the positive electrode active material is selected from lithium iron phosphate, lithium manganese iron phosphate, lithium nickel manganese oxide, ternary material or lithium-rich manganese-based material.

[0023] Preferably, the electrolyte further comprises an organic solvent; the organic solvent comprises a low-viscosity solvent; the low-viscosity solvent comprises a carbonate solvent and / or a carboxylate solvent;

[0024] The carbonate solvent is selected from dimethyl carbonate;

[0025] The carboxylate solvent is selected from one or more of methyl acetate, ethyl propionate and ethyl acetate.

[0026] Preferably, the mass of the carbonate solvent is 20% to 50% of the mass of the electrolyte;

[0027] The mass of the carboxylate solvent is 10% to 30% of the mass of the electrolyte.

[0028] Preferably, the mass ratio of the carbonate solvent to the carboxylate solvent is 1 to 4:1.

[0029] Preferably, the additive further comprises vinylene carbonate; the mass of the vinylene carbonate is 0.1% to 5% of the mass of the electrolyte.

[0030] Compared with the prior art, the battery provided by the present invention promotes the dissociation and migration of lithium ions by adding lithium fluorosulfonate to the electrolyte, thereby reducing the interfacial impedance of the negative electrode. At the same time, by controlling the content of secondary particles in the negative electrode active material and the viscosity of the electrolyte, the side reaction between the negative electrode sheet and the electrolyte is reduced, the gas production of the battery is reduced, and the dynamic performance of the battery is improved. DETAILED DESCRIPTION

[0031] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0032] The present invention provides a battery, comprising a negative electrode sheet and an electrolyte; the negative electrode sheet comprises a negative electrode active material layer; the negative electrode active material layer comprises a negative electrode active material; the negative electrode active material comprises primary particles and secondary particles; the secondary particles are formed by agglomeration of multiple primary particles; the number of secondary particles in the negative electrode active material accounts for a; the electrolyte comprises an additive; the additive comprises lithium fluorosulfonate; the mass content of lithium fluorosulfonate in the electrolyte is b; the viscosity of the electrolyte at room temperature is c mPa·s; the battery satisfies the following conditions: 0.1≤(a×b / c)×10000≤550.

[0033] The present invention has no particular limitation on the sources of all raw materials, and any commercially available raw materials may be used.

[0034] Adding lithium fluorosulfonate to the electrolyte can reduce interfacial impedance, but it can easily cause increased gas production. By reducing the proportion of secondary particles in the negative electrode active material layer, the side reaction with the electrolyte can be reduced, reducing gas production. However, the extended lithium ion transmission path will cause an increase in DCR. The DCR can be reduced by controlling the viscosity of the electrolyte. Therefore, the present invention solves the problem of gas expansion during battery storage by comprehensively adjusting the relationship between the proportion of secondary particles in the negative electrode plate, the content of lithium fluorosulfonate in the electrolyte, and the viscosity of the electrolyte. The battery meets the condition: 0.1≤(a×b / c)×10000≤550; if this condition exceeds the upper limit, the battery will produce serious gas expansion, and if it exceeds the lower limit, the DCR will increase, resulting in a decrease in the battery's fast charging capability. Only within the appropriate range can the impedance be reduced while avoiding gas expansion of the battery. In a specific embodiment provided by the present invention, preferably, the battery satisfies the condition: 0.1≤(a×b / c)×10000≤200; more preferably, the battery satisfies the condition: 1≤(a×b / c)×10000≤100; even more preferably, the battery satisfies the condition: 1≤(a×b / c)×10000≤50; most preferably, the battery satisfies the condition: 1≤(a×b / c)×10000≤25; in some embodiments provided by the present invention, the battery specifically satisfies the condition that (a×b / c)×10000 is 7.6, 15.2, 5.6, 25.0, 1.0, 4.4, 1.7, 1.2, 17.4, 0.9, 27.1, 114, 549.8, 0.4, 0.8, 112.6 or 0.1.

[0035] Lithium fluorosulfonate can form a dense low-resistance SEI film on the surface of the negative electrode of the battery during battery operation, thereby greatly improving the rate performance and cycle performance of the battery. In a specific embodiment provided by the present invention, the negative electrode sheet includes a negative electrode active material layer; the negative electrode active material layer includes a negative electrode active material; the negative electrode active material includes primary particles and secondary particles; the secondary particles are formed by the agglomeration of multiple primary particles, and there are many pores inside. Therefore, the higher the proportion of secondary particles (that is, the ratio of the number of secondary particles to the total number of primary particles and secondary particles), the higher the porosity of the negative electrode active material layer and the larger the specific surface area, which will lead to more side reactions between the negative electrode active material layer and the electrolyte. Lithium fluorosulfonate may decompose to produce hydrogen fluoride (HF) and other volatile gases, resulting in increased gas production, but too low a proportion of secondary particles will also cause a DC resistance ( DCR) increases; therefore, in the present invention, the number of secondary particles in the negative electrode active material accounts for a preferably 10% to 60%, more preferably 10% to 50%, more preferably 10% to 40%, and most preferably 10% to 30%; in some embodiments provided by the present invention, the number of secondary particles in the negative electrode active material accounts for a specifically 10%, 15%, 20% or 25%; in order to control the proportion of secondary particles, it can be controlled by adding raw materials at the beginning of preparation, and in the preparation process of the negative electrode slurry, the primary particles may also agglomerate to form secondary particles according to different processes. Therefore, the number of secondary particles here refers to the number of secondary particles in the final negative electrode sheet.

[0036] The particle size of the primary and secondary particles of the negative electrode active material will also affect the porosity of the negative electrode active material layer. If the particle size is too large, the direct current internal resistance (DCR) of the battery will increase. If the particle size is too low, the reaction activity of the negative electrode active material layer and the electrolyte will increase due to the large specific surface area, and the gas production will increase. Therefore, in the present invention, the particle size Dn50 of the primary particles is preferably 5 to 14 μm; optionally, the particle size Dn50 of the primary particles is 5 μm, 8 μm, 10 μm, 12 μm, 14 μm, or a range between any two of the above values; the particle size Dn50 of the secondary particles is preferably 15 to 25 μm; optionally, the particle size Dn50 of the secondary particles is 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, or a range between any two of the above values. In the present invention, unless otherwise specified, Dn50 refers to the particle size at which the particle number distribution reaches 50%, that is, the number of particles smaller than this value accounts for 50% of the total number of particles.

[0037] In a specific embodiment provided by the present invention, the particle size Dn50 of the primary particles is preferably 5 to 10 μm; the particle size Dn50 of the secondary particles is preferably 15 to 20 μm.

[0038] In a specific embodiment provided by the present invention, the type of the negative electrode active material is any negative electrode active material known to those skilled in the art, and is not particularly limited. In the present invention, natural graphite, artificial graphite, mesophase carbon microbeads, hard carbon, soft carbon, silicon, SiO x , silicon carbon and Li4Ti5O 12 One or more of; graphite due to its high body capacity and low electrode potential, and therefore as the optimal negative electrode active material of the present invention.

[0039] In a specific embodiment provided by the present invention, the mass content of the negative electrode active material in the negative electrode active material layer is preferably 90% to 98%; optionally, the mass content of the negative electrode active material in the negative electrode active material layer is 90%, 92%, 94%, 96%, 96.4%, 97%, 98% or a range between any two of the above values.

[0040] In a specific embodiment provided by the present invention, the negative electrode active material layer further includes a negative electrode conductive agent; the mass content of the negative electrode conductive agent in the negative electrode active material layer is preferably 0.5% to 5%; optionally, the mass content of the negative electrode conductive agent in the negative electrode active material layer is 0.5%, 0.6%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range between any two of the above values; the negative electrode conductive agent can be a negative electrode conductive agent well known to those skilled in the art, without special restrictions. In the present invention, it is preferably a conductive agent SP and / or acetylene black.

[0041] In a specific embodiment provided by the present invention, the negative electrode active material layer preferably further includes a negative electrode binder; the mass content of the negative electrode binder in the negative electrode active material layer is preferably 1% to 5%; optionally, the mass content of the negative electrode binder in the negative electrode active material layer is 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range between any two of the above values; the negative electrode binder is a negative electrode binder well known to those skilled in the art, and there is no special limitation. In the present invention, polyacrylic acid (PAA), sodium carboxymethyl cellulose are preferably used. (CMC) and one or more of styrene-butadiene rubber (SBR); the molecular weight of the PAA is preferably 30-100W; optionally, the molecular weight of the PAA is 30W, 40W, 50W, 60W, 70W, 80W, 90W, 100W or a range between any two of the above values; the particle size of the SBR is preferably 120-180nm; optionally, the particle size of the SBR is 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm or a range between any two of the above values.

[0042] In a specific embodiment provided by the present invention, the negative electrode active material layer preferably further includes a dispersant; the mass content of the dispersant in the negative electrode active material layer is preferably 0.5% to 5%; optionally, the mass content of the dispersant in the negative electrode active material layer is 0.5%, 0.6%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range between any two of the above values; the dispersant is a dispersant well known to those skilled in the art and is not particularly limited. In the present invention, polyvinylidene fluoride (PVDF) is preferred.

[0043] In a specific embodiment provided by the present invention, the negative electrode sheet further includes a negative electrode current collector; the negative electrode active material layer is provided on at least one surface of the negative electrode current collector; the negative electrode current collector includes but is not limited to copper foil, etc.

[0044] As a key component of batteries, the electrolyte plays a significant role in conducting electricity between the positive and negative electrodes. It is an ionic conductor. The properties of the electrolyte and its contact with the positive and negative electrodes have a significant impact on the overall performance of the battery.

[0045] In a specific embodiment provided by the present invention, the electrolyte includes an additive; the additive includes lithium fluorosulfonate; the lithium fluorosulfonate in the electrolyte can promote the dissociation and migration of lithium ions, thereby reducing the interfacial impedance of the negative electrode, but also because the inorganic SEI formed by lithium fluorosulfonate on the surface of the negative electrode is more porous, the electrolyte and the negative electrode are in closer contact, resulting in a higher side reaction, and lithium fluorosulfonate may decompose to produce hydrogen fluoride (HF) and other volatile gases, thereby increasing gas production. Therefore, in the present invention, the mass content b of lithium fluorosulfonate in the electrolyte is preferably 0.01% to 5%; optionally, the mass content b of lithium fluorosulfonate in the electrolyte is 0.01%, 0.05%, 0.1%, 0.2%, 0.5%, 1%, 1.5%, 1.9%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range between any two of the above values.

[0046] In a specific embodiment provided by the present invention, the mass content b of lithium fluorosulfonate in the electrolyte is preferably 0.2% to 2%.

[0047] The viscosity of the electrolyte is an important parameter in battery design and performance evaluation. Both too high and too low viscosity will have an adverse effect on the performance of the battery. Too high viscosity will increase the resistance to the movement of ions in the electrolyte and reduce the charge and discharge rate of the battery; while too low viscosity may cause the electrolyte to be too fluid, increase the side reactions between the electrolyte and the negative electrode active material, and also lead to increased gas production. Therefore, in the present invention, the viscosity of the electrolyte at room temperature is cm Pa·s; the c is preferably 0.5 to 5; optionally, the c is 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or a range between any two of the above values.

[0048] In a specific embodiment provided by the present invention, the c is preferably 2 to 4; in some embodiments provided by the present invention, the c is specifically 2.5, 2.3, 2.1 or 2.5.

[0049] According to the present invention, the electrolyte further includes an organic solvent; the organic solvent preferably includes a low-viscosity solvent; the low-viscosity solvent preferably includes a carbonate solvent and / or a carboxylate solvent; the main function of the solvent is to dissolve lithium salts; the carbonate solvent is preferably dimethyl carbonate (DMC); the carboxylate solvent is preferably one or more of methyl acetate, ethyl propionate and ethyl acetate (EA).

[0050] In a specific embodiment provided by the present invention, the purpose of adjusting the viscosity of the electrolyte can be achieved by adjusting the ratio of different types of solvents in the solvent; in the present invention, the electrolyte preferably includes a carbonate solvent and a carboxylate solvent; if the content of the carbonate solvent in the electrolyte is too high, the interface reaction with the negative electrode will be aggravated and the gas production will increase, but if the content is too low, the overall viscosity of the electrolyte will decrease, Li+ migration will be hindered, and DCR will increase, so the mass of the carbonate solvent is preferably 20% to 50% of the mass of the electrolyte; optionally, the mass of the carbonate solvent is preferably 20%, 25%, 30%, 35%, 40%, 45%, 50% or a range between any two of the above values ​​of the mass of the electrolyte; in some embodiments provided by the present invention, the mass of the carbonate solvent is specifically 30%, 27% or 25% of the mass of the electrolyte; if the content of the carboxylate solvent in the electrolyte is too high, the decomposition gas production will increase at high temperature, but if the content is too low, the overall viscosity of the electrolyte will decrease, Li+ migration will be hindered, and DCR will increase. Increase, so the mass of the carboxylate solvent is preferably 10% to 30% of the mass of the electrolyte; optionally, the mass of the carboxylate solvent is 10%, 15%, 20%, 25%, 30% of the mass of the electrolyte or a range between any two of the above values; in some embodiments provided by the present invention, the mass of the carboxylate solvent is specifically 15%, 18% or 20% of the mass of the electrolyte; carboxylate EA has a lower viscosity than carbonate DMC, but has a higher reaction activity with the negative electrode interface, resulting in increased lithium loss , which worsens the cycle life, so the mass ratio of the carbonate solvent to the carboxylate solvent is preferably 1-4:1; optionally, the mass ratio of the carbonate solvent to the carboxylate solvent is 1:1, 1.3:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1 or a range between any two of the above ratios; in some embodiments provided by the present invention, the mass ratio of the carbonate solvent to the carboxylate solvent is specifically 2:1, 1.5:1, 1.3:1 or 2:1.

[0051] In a specific embodiment provided by the present invention, the organic solvent further comprises a non-low-viscosity carbonate solvent; the non-low-viscosity carbonate solvent is preferably one or more of ethylene carbonate (EC), propylene carbonate, diethyl carbonate and ethyl methyl carbonate (EMC).

[0052] In a specific embodiment provided by the present invention, the electrolyte preferably further includes a lithium salt, which plays a conductive role in the electrolyte. The lithium salt is a lithium salt well known to those skilled in the art, and there is no special limitation. The present invention preferably includes but is not limited to one or more of lithium hexafluorophosphate, lithium bisfluorosulfonyl imide, lithium fluorosulfonyl (perfluorobutylsulfonyl) imide, lithium bis (trifluoromethylsulfonyl) imide, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium trifluoromethylsulfonate and lithium tetrafluorooxalatophosphate; the concentration of the lithium salt in the electrolyte is preferably 0.5 to 2 mol / L; optionally, the concentration of the lithium salt in the electrolyte is 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 2 mol / L or a range between any two of the above values.

[0053] In a specific embodiment provided by the present invention, the additive preferably also includes vinylene carbonate (VC); vinylene carbonate can promote SEI film formation at the negative electrode, but will deteriorate DCR, and if its content in the electrolyte is too high, VC will excessively decompose under high pressure or high temperature (such as during fast charging), producing gases such as CO2 and C2H4, which will lead to increased gas production. If the content is too low, it will lead to the inability to effectively form an SEI film at the negative electrode, and lithium ion transmission will be hindered. Therefore, in the present invention, the mass of the vinylene carbonate is preferably 0.1% to 5% of the mass of the electrolyte; optionally, the mass of the vinylene carbonate is 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% of the mass of the electrolyte or a range between any two of the above values.

[0054] In a specific embodiment provided by the present invention, the battery preferably further comprises a positive electrode sheet; the positive electrode sheet comprises a positive electrode active material layer; the positive electrode active material layer comprises a positive electrode active material; the positive electrode active material is a positive electrode active material well known to those skilled in the art, and is not particularly limited. In the present invention, lithium iron phosphate (LiFePO4), lithium manganese iron phosphate (LiMn x Fe1 -x PO4), lithium nickel manganese oxide (LNMO), ternary materials or lithium-rich manganese-based materials; the mass of the positive electrode active material is preferably 90% to 98% of the mass of the positive electrode active material layer; optionally, the mass content of the positive electrode active material in the positive electrode active material layer is specifically 90%, 92%, 94%, 95%, 95.5%, 96%, 96.5%, 97%, 98% or the range between any two of the above values.

[0055] In a specific embodiment provided by the present invention, the positive electrode active material layer further includes a positive electrode binder and a positive electrode conductor; the positive electrode binder includes but is not limited to one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA) and polyacrylonitrile (PAN); the mass of the positive electrode binder is preferably 0.01% to 5% of the mass of the positive electrode active material layer; optionally, the mass of the positive electrode binder is 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 5.0%, 6.0%, 7.0%, 8.0%, 9.0%, 10.0%, 11.0%, 12.0%, 13.0%, 14.0%, 15.0%, 16.0%, 17.0%, 18.0%, 19.0%, 20.0%, 21.0%, 22.0%, 23.0%, 24.0%, 25.0%, 26.0%, 27.0%, 28.0%, 29.0%, 30.0%, 31.0%, 32.0%, 33.0%, 34.0%, 35.0%, 36.0%, 37.0%, 38.0%, 39.0%, 40.0%, 41.0%, 42.0%, 43.0%, 44.0%, 45.0%, 46.0%, 47.0%, 48.0%, 49.0%, 50.0%, 51.0%, 52.0%, 53.0%, 54.0%, 55.0%, 56.0%, 57.0%, 58.0%, 59.0%, 60. .5%, 4.0%, 4.5%, 5.0% or the range between any two of the above values; the positive electrode conductive agent includes but is not limited to one or more of conductive carbon black, acetylene black, carbon nanotubes, graphene and carbon fiber materials; the mass of the positive electrode conductive agent is preferably 0.01% to 5% of the mass of the positive electrode active material layer; optionally, the mass of the positive electrode conductive agent is 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0% or the range between any two of the above values.

[0056] In a specific embodiment provided by the present invention, the positive electrode active material layer preferably also includes a dispersant; the mass content of the dispersant in the positive electrode active material layer is preferably 0% to 5%; optionally, the mass content of the dispersant in the positive electrode active material layer is 0%, 0.5%, 0.6%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range between any two of the above values; the dispersant is a dispersant well known to those skilled in the art, without any special restrictions, and polyvinylidene fluoride (PVDF) is preferably used in the present invention.

[0057] In a specific embodiment provided by the present invention, the positive electrode sheet further includes a positive electrode current collector; the positive electrode active material layer is provided on at least one surface of the positive electrode current collector; the positive electrode current collector includes but is not limited to aluminum foil and the like.

[0058] According to the present invention, the battery preferably further comprises a diaphragm; the diaphragm can be any diaphragm well known to those skilled in the art without any particular limitation, and in the present invention, polypropylene (PP) and / or polyethylene (PE) are preferred.

[0059] The battery provided by the present invention can be prepared according to methods well known to those skilled in the art without any particular limitation. Specifically, it can be prepared according to the following steps:

[0060] 1) Preparation of positive electrode sheet: The positive electrode active material, positive electrode conductive agent and positive electrode binder are uniformly mixed according to the mass ratio and dispersed in N-methylpyrrolidone (NMP) to obtain positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector to obtain a double-sided coated positive electrode sheet; and then the positive electrode sheet is obtained by rolling and cutting.

[0061] 2) Preparation of the Negative Electrode Sheet: The negative electrode active material, negative electrode conductive agent, and negative electrode binder are uniformly mixed according to the mass ratio. Deionized water is added as a solvent and stirred in a vacuum mixer until the system is uniform to obtain the negative electrode slurry. The negative electrode slurry is evenly coated on both surfaces of the negative electrode current collector. After drying at room temperature, the slurry is transferred to an oven for further drying. The negative electrode sheets are then cold pressed and cut. The particle size of the primary and secondary particles of the negative electrode active material is controlled by the pulverization and shaping processes during the preparation process. The proportion of secondary particles is mixed according to the design.

[0062] 3) Preparation of electrolyte: carbonate solvent and carboxylate solvent are mixed in appropriate proportions to obtain an organic solvent, then fully dried lithium salt is dissolved in the mixed organic solvent, and then VC and an appropriate amount of lithium fluorosulfonate are added and mixed thoroughly.

[0063] 4) Diaphragm preparation: Polypropylene (PP) and / or polyethylene (PE) are selected as the diaphragm.

[0064] 5) Preparation of lithium-ion batteries: The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to act as an insulator, and then wound to obtain a bare cell; the bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum packaging, standing, forming, and shaping, a lithium-ion battery is obtained.

[0065] In order to further illustrate the present invention, a battery provided by the present invention is described in detail below in conjunction with examples; the molecular weight of the PVDF used in the examples and comparative examples is about 70W.

[0066] The reagents used in the following examples are all commercially available.

[0067] Examples 1 to 17 and Comparative Examples 1 to 2

[0068] 1) Preparation of positive electrode sheet:

[0069] Lithium iron phosphate (particle size 0.1-2 μm), conductive agent acetylene black (particle size 30-60 nm), and binder PVDF were mixed uniformly in a mass ratio of 96.5:1.5:2 and dispersed in NMP to obtain a positive electrode slurry; the positive electrode slurry was coated on aluminum foil to obtain a double-sided coated positive electrode sheet; and then rolled and cut to obtain a positive electrode sheet (surface density 360 g / m 2 , compacted density 2.5g / cm3 ).

[0070] 2) Preparation of negative electrode sheet

[0071] Graphite of different primary and secondary particle sizes was obtained from the market. Primary graphite particles (average particle size 5-14 μm) and secondary graphite particles (average particle size 15-25 μm) were mixed according to the mass ratio in Table 1 to obtain negative electrode active material graphite.

[0072] The negative electrode active material graphite, conductive agent acetylene black, and binder SBR were mixed in a mass ratio of 96.5:1.5:2, and deionized water was added as a solvent. The mixture was stirred under a vacuum mixer until the system was uniform to obtain a negative electrode slurry. The negative electrode slurry was evenly coated on both surfaces of the negative electrode current collector copper foil, dried at room temperature, and then transferred to an oven for further drying. The negative electrode sheets (surface density 173.4 g / m2) were obtained by cold pressing and slitting. 2 , compacted density 1.52g / cm 3 ).

[0073] 3) Electrolyte preparation

[0074] EC, EMC, DMC and ethyl acetate (EA) were mixed to obtain an organic solvent, wherein the contents of DMC and EA in the electrolyte were shown in Table 1, and the rest was supplemented by EC and EMC, with a mass ratio of EC to EMC of 3:4. The fully dried lithium salt LiPF6 was then dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L, and then 2.5% by mass of vinylene carbonate (VC) and an appropriate amount of lithium fluorosulfonate were added and mixed thoroughly.

[0075] 4) Diaphragm preparation

[0076] PE was selected as the separator.

[0077] 5) Preparation of lithium-ion batteries

[0078] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to serve as an isolation, and then wound to obtain a bare cell; the bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte, and after vacuum packaging, standing, formation, constant capacity and other processes, a lithium-ion battery is obtained. Among them, the specific steps of standing, forming and constant volume are: standing at a high temperature of 45°C for 12 hours and putting on a glass clamp during this process, with a clamp pressure of 0.4 to 0.6 MPa, and performing two charging processes: 1) standing for 10 minutes; 2) charging at a rate of 0.05C for 120 minutes and stopping; 3) standing for 10 minutes, 4) charging at a rate of 0.33C for 120 minutes and stopping; 5) ending; after standing at a high temperature of 45°C for 12 hours, after secondary sealing, the constant volume step is performed: 1) the battery is set aside for 10 minutes; 2) the battery is charged with a constant current (0.33C) to a voltage of 3.65V, and the battery is charged with a constant voltage (3.65V) to a current of 0.05C; 3) the battery is set aside for 10 minutes; 4) the battery is discharged with a constant current (0.33C) to a voltage of 2.5V; 5) steps 2 to 4 are repeated three times; 6) the battery is charged with a constant current (0.33C) for 1 hour to complete the constant volume.

[0079] The battery performance was measured and the results are shown in Table 2.

[0080] Testing method for secondary particle ratio:

[0081] First, the negative electrode sheet morphology was tested using a Zeiss Gemini 300. The specific operation was as follows: the secondary battery was disassembled, the negative electrode sheet was removed and dried after soaking. After scraping the powder, the sample was attached to the sample stage with conductive adhesive and then placed in the sample chamber. The sample surface was scanned with high-energy focused electrons, and an image reflecting the sample surface morphology was obtained using a 1000× magnification. The graphite particle size was then calibrated using a nanomeasurer. The specific operation was as follows: after importing the SEM image into the Nanomesure software, the scale was set and statistical samples were selected (the more samples, the more accurate the results). Primary particles with a particle size of 5-14μm were selected and counted. Secondary particles with a particle size of 15-25μm were selected and counted. The proportion of secondary particles was calculated based on the ratio of secondary particles to (primary particles + secondary particles).

[0082] Test method for lithium fluorosulfonate content:

[0083] Use battery charging and discharging equipment to discharge the battery. The discharge conditions are: current 0.3C, cut-off voltage 2.5V. Disassemble the battery in a glove box (H2O ≤ 0.1ppm, O2 ≤ 0.1ppm) to collect the electrolyte. There are three ways to collect the electrolyte: After removing the battery cover, ① If there is free electrolyte, use a pipette to collect the electrolyte into a 5mL sample tube and seal it with sealing glue to prevent electrolyte leakage. ② If there is no free electrolyte, use a hydraulic press (Beijing Hengaode Technology Co., Ltd. FY-30 hydraulic press) to continuously pressurize until free electrolyte appears, collect the electrolyte into a sample tube and seal it. Alternatively, add an appropriate amount of dichloromethane extractant to the battery and record the dichloromethane content. After adding dichloromethane, put the battery into an aluminum-plastic bag and seal it with a heat sealer. Transfer it to an ultrasonic oscillator and oscillate it for 12 hours to allow the electrolyte in the electrode to be fully mixed with the dichloromethane. Then, use a pipette to draw the mixture of dichloromethane and electrolyte into a 5mL sample tube, and seal the sample tube with sealing glue; the collected electrolyte sample is first diluted 100 times with ultrapure water, and injected into the Thermo Fisher DIONEX AQ-1100 ion chromatograph with a syringe for testing to obtain an IC spectrum; the IC spectrum of the electrolyte to be tested is compared with the IC spectrum of the standard to determine whether the electrolyte to be tested contains lithium fluorosulfonate, and then the content is determined based on its peak area.

[0084] Test method for electrolyte viscosity:

[0085] Measurements using a Vicolab 400 viscometer: ① Clean the probe and measuring chamber with ethanol and dry them with a dust-free sponge. Fill the measuring chamber with the electrolyte to be tested and aspirate to rinse the chamber. Then, draw 2ml of the electrolyte to be tested into the measuring chamber. Use a magnetic pen to draw the probe into the chamber, ensuring it is completely immersed in the sample. ② Press the "Enter" button to select "Operate." Then, press the "Enter" key to select "Measure Viscosity" to begin measurement. When the U value is within ±1% and the T value is within ±0.2°C, record the current U value, which is the viscosity. If the measuring chamber temperature is within 25±0.2°C, the test data is valid. Otherwise, continue to place the sample in a constant-temperature circulating water bath within the measuring chamber until the required temperature is met.

[0086] DCR test method:

[0087] 1) Place the battery at room temperature until thermal equilibrium is reached;

[0088] 2) Perform three standard cycles at 1 / 3C current and record the standard capacity C of the battery;

[0089] 3) Adjust to the test temperature according to the temperature sequence (25℃ / -10℃) until thermal equilibrium is reached;

[0090] 4) Charge the battery to 50% SOC at a 1 / 3C discharge rate;

[0091] 5) Discharge at a current rate of 1C for 18 seconds. Record the battery voltage U2 before discharge is terminated, the current I, and the battery voltage U1 after the battery voltage stabilizes. Calculate the DC internal resistance DCR using the formula DCR = (U2 - U1) / I.

[0092] Gas production test method:

[0093] Charge at a constant current of 0.33C to an upper limit voltage of 3.65V, and charge at a constant voltage until the current is less than or equal to 0.05C. After full charge, use the water displacement method to test the battery volume, which is recorded as V0. Then place the battery in a 60℃ oven for 56 days. After the battery temperature drops to room temperature of 25℃, use the water displacement method to test the battery volume again, which is recorded as V1. Calculate the gas production at 60℃ using the following formula:

[0094] Gas production at 60°C = (V1-V0) / battery capacity.

[0095] The specific method of testing the volume of the battery by the drainage method is as follows:

[0096] 1) Add an appropriate amount of pure water to the container and use a density meter to measure its density ρ and record it;

[0097] 2) Place the aforementioned container on a balance and tare the balance (tare the balance before testing each cell);

[0098] 3) Immerse the battery cell body and the tabs together in pure water, ensuring that the battery cell does not touch the container wall. After stabilization, read and record the data. The data before the battery is placed in the oven for storage is recorded as T0, and the data after the battery is placed in the oven for storage is recorded as T0;

[0099] 4) Turn off the balance and seal the container to prevent the reagent from evaporating.

[0100] Calculate V1-V0 according to the following formula: V1-V0=T1 / ρ-T0 / ρ.

[0101] Table 1 Battery raw material formula and performance test results

[0102]

[0103]

[0104] Table 2 Battery raw material formula and performance test results

[0105]

[0106]

[0107] As can be seen from Table 2, the battery prepared in the embodiment of the present application has a discharge DCR of ≤58.5mΩ at room temperature and a storage gas production of ≤3.5mL / Ah at 60°C. It can be seen that the battery of the present application has both excellent fast charging performance and safety performance.

[0108] It can be seen from the comparison between Example 3 and Example 6, the comparison between Example 5 and Examples 7 to 8, and the comparison between Example 10 and Example 15 that when the proportion of secondary particles (a), the content of lithium fluorosulfonate in the electrolyte (b), and the viscosity of the electrolyte (c) are respectively controlled within the preferred range, the balance between the fast charging performance and the safety performance of the battery is better.

[0109] From the comparison between Examples 4 to 5 and Examples 10 to 11, and Examples 14 to 15, it can be seen that when the battery satisfies 1≤a×b / c≤25, the fast charging performance and safety performance of the battery are better.

[0110] According to Comparative Examples 1 to 2, even if the proportion of secondary particles (a), the content of lithium fluorosulfonate in the electrolyte (b), and the viscosity of the electrolyte (c) are respectively in the appropriate range, when the value of a×b / c exceeds the range of 0.1 to 550, the fast charging performance and safety performance of the battery will be affected.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A battery, characterized in that: Including negative electrode sheet and electrolyte; The negative electrode sheet includes a negative electrode active material layer; the negative electrode active material layer includes a negative electrode active material; the negative electrode active material includes primary particles and secondary particles; the secondary particles are formed by agglomeration of multiple primary particles; the proportion of secondary particles in the negative electrode active material is a; The electrolyte includes an additive; the additive includes lithium fluorosulfonate; the mass content of lithium fluorosulfonate in the electrolyte is b; the viscosity of the electrolyte at 25±0.02° C. is c mPa·s; The battery satisfies the condition: 0.1≤(a×b / c)×10000≤550.

2. The battery according to claim 1, characterized in that The battery satisfies the condition: 1≤(a×b / c)×10000≤25.

3. The battery according to claim 1 or 2, characterized in that The a is 10% to 60%; and / or, b is 0.01% to 5%; And / or, c is 0.5 to 5.

4. The battery according to claim 3, characterized in that The a is 10% to 30%; and / or, b is 0.2% to 2%; And / or, c is 2-4.

5. The battery according to any one of claims 4, characterized in that The particle size Dn50 of the primary particles is 5 to 14 μm; And / or, the particle size Dn50 of the secondary particles is 15 to 25 μm.

6. The battery according to claim 5, characterized in that The particle size Dn50 of the primary particles is 5 to 10 μm; And / or, the particle size Dn50 of the secondary particles is 15 to 20 μm.

7. The battery according to any one of claims 6, characterized in that The negative electrode active material is selected from natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, silicon, SiO x , silicon carbon and Li4Ti5O 12 One or more of; and / or, The battery also includes a positive electrode sheet; the positive electrode sheet includes a positive electrode active material layer; the positive electrode active material layer includes a positive electrode active material; the positive electrode active material is selected from lithium iron phosphate, lithium manganese iron phosphate, lithium nickel manganese oxide, ternary material or lithium-rich manganese-based material.

8. The battery according to any one of claims 7, characterized in that The electrolyte further comprises an organic solvent; the organic solvent comprises a low-viscosity solvent; the low-viscosity solvent comprises a carbonate solvent and / or a carboxylate solvent; The carbonate solvent is selected from dimethyl carbonate; The carboxylate solvent is selected from one or more of methyl acetate, ethyl propionate and ethyl acetate.

9. The battery according to claim 8, characterized in that The mass of the carbonate solvent is 20% to 50% of the mass of the electrolyte; The mass of the carboxylate solvent is 10% to 30% of the mass of the electrolyte.

10. The battery according to claim 8, characterized in that The mass ratio of the carbonate solvent to the carboxylate solvent is 1 to 4:

1.

11. The battery according to claim 10, characterized in that The additive further comprises vinylene carbonate; the mass of the vinylene carbonate is 0.1% to 5% of the mass of the electrolyte.

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