A battery

Abstract

The application belongs to the technical field of batteries, and particularly relates to a battery. Compared with the prior art, the battery provided by the application promotes the dissociation and migration of lithium ions by adding lithium fluorosulfonate into electrolyte, thereby reducing the interface impedance of the negative electrode, and reducing the side reaction of the negative plate and the electrolyte by controlling the content of secondary particles in the negative electrode active material and the viscosity of the electrolyte, thereby reducing the gas production of the battery and improving the kinetic performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and in particular relates to a battery. Background Technology

[0002] Since their commercialization, lithium-ion batteries have been widely used in the power battery field due to their advantages such as 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 higher demands on the performance of lithium-ion batteries, such as long cycle life and normal operation under high and low temperature conditions.

[0003] Research has revealed that the electrolyte in lithium-ion batteries has a significant impact on battery performance. Adding a small amount of electrolyte additives to the electrolyte to form a stable protective film on the electrode surface is the most economical and effective strategy to improve electrode stability and achieve high-stability, high-energy-density lithium-ion batteries. Currently, various additives have been reported, among which lithium fluorosulfonate, as an electrolyte additive for lithium-ion batteries, can form a dense, low-resistivity SEI film on the negative electrode surface during lithium-ion battery 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, batteries containing lithium fluorosulfonate electrolyte may expand during storage due to the decomposition of lithium fluorosulfonate, which produces hydrogen fluoride or other volatile gases. 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] This invention provides a battery, comprising a negative electrode 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 the aggregation of multiple primary particles; the proportion of secondary particles in the negative electrode active material is a;

[0008] The electrolyte includes additives; the additives include lithium fluorosulfonate; the mass content of lithium fluorosulfonate in the electrolyte is b; the viscosity of the electrolyte at 25±0.02℃ is c mPa·s;

[0009] The battery meets 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 percentage of 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, 'a' is 10% to 30%;

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

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

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

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

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

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

[0021] Preferably, the negative electrode active material is selected from natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, silicon, and SiO2. x Silicon-carbon and Li4Ti5O 12 One or more of the following; and / or,

[0022] The battery further 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 materials or lithium-rich manganese-based materials.

[0023] Preferably, the electrolyte further includes an organic solvent; the organic solvent includes a low-viscosity solvent; the low-viscosity solvent includes carbonate solvents and / or carboxylic acid ester solvents;

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

[0025] The carboxylic acid ester 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 carboxylic acid ester solvent is 10% to 30% of the mass of the electrolyte.

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

[0029] Preferably, the additive further includes 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 reactions between the negative electrode sheet and the electrolyte are reduced, the gas production of the battery is reduced, and the dynamic performance of the battery is improved. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] This 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 the aggregation of multiple primary particles; the proportion of secondary particles in the negative electrode active material is 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 condition: 0.1≤(a×b / c)×10000≤550.

[0033] In this invention, there are no special restrictions on the source of any raw materials; they can be commercially available.

[0034] Adding lithium fluorosulfonate to the electrolyte can reduce interfacial impedance, but it easily leads to increased gas production. Reducing the proportion of secondary particles in the negative electrode active material layer can reduce side reactions with the electrolyte and decrease gas production; however, the extended lithium-ion transport path increases the discharge coefficient (DCR). Controlling the electrolyte viscosity can further reduce DCR. Therefore, this invention addresses the gas expansion problem during battery storage by comprehensively adjusting the relationship between the proportion of secondary particles in the negative electrode, the lithium fluorosulfonate content in the electrolyte, and the electrolyte viscosity. The battery must meet the condition: 0.1 ≤ (a×b / c)×10000 ≤ 550. If this condition exceeds the upper limit, severe gas expansion occurs; exceeding the lower limit increases DCR, leading to a decrease in the battery's fast-charging capability. Only within a suitable range can impedance be reduced while preventing battery gas expansion. In a specific embodiment of 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 of the present invention, the battery specifically satisfies the condition (a×b / c)×10000 as 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 during battery operation, thereby significantly improving the rate performance and cycle performance of the battery. In a specific embodiment of this 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 aggregation of multiple primary particles and have numerous pores. Therefore, a higher proportion of secondary particles (i.e., the ratio of the number of secondary particles to the total number of primary and secondary particles) leads to higher porosity and a larger specific surface area in the negative electrode active material layer, resulting in 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, leading to increased gas production. However, an excessively low proportion of secondary particles can also cause a decrease in DC resistance (…). The DCR increases; therefore, in the present invention, the proportion of secondary particles a in the negative electrode active material is preferably 10% to 60%, more preferably 10% to 50%, even more preferably 10% to 40%, and most preferably 10% to 30%; in some embodiments provided by the present invention, the proportion of secondary particles a in the negative electrode active material is 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 during the preparation of negative electrode slurry, primary particles may also agglomerate to form secondary particles depending on the process. Therefore, the proportion of secondary particles here refers to the proportion 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 also affects the porosity of the negative electrode active material layer. Excessively large particle sizes lead to an increase in the battery's DC internal resistance (DCR), while excessively small particle sizes result in increased reactivity between the negative electrode active material layer and the electrolyte due to an excessively large specific surface area, leading to increased gas production. Therefore, in this invention, the particle size Dn50 of the primary particles is preferably 5–14 μm; optionally, the particle size Dn50 of the primary particles is 5 μm, 8 μm, 10 μm, 12 μm, 14 μm, or any two of the above values. The particle size Dn50 of the secondary particles is preferably 15–25 μm; optionally, the particle size Dn50 of the secondary particles is 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, or any two of the above values. Unless otherwise specified in this invention, 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 of 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 one specific embodiment of the present invention, the type of negative electrode active material can be any negative electrode active material well known to those skilled in the art, and there are no special limitations. In the present invention, natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, silicon, and SiO are preferred. x Silicon-carbon and Li4Ti5O 12 One or more of the following; graphite is the optimal negative electrode active material of this invention due to its high bulk capacity and low electrode potential.

[0039] In one specific embodiment of 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 any two of the above values.

[0040] In a specific embodiment of 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 any two of the above values; the negative electrode conductive agent can be any negative electrode conductive agent well known to those skilled in the art, and there are no special limitations. In the present invention, conductive agent SP and / or acetylene black are preferred.

[0041] In a specific embodiment of 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 any two of the above values; the negative electrode binder can be any negative electrode binder known to those skilled in the art, and there are no special limitations. In the present invention, polyacrylic acid (PAA) and sodium carboxymethyl cellulose are preferred. (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 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 any two of the above values.

[0042] In a specific embodiment of 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 any two of the above values; the dispersant can be any dispersant well known to those skilled in the art, and there are no special limitations. In the present invention, polyvinylidene fluoride (PVDF) is preferred.

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

[0044] As a key component of a battery, the electrolyte plays a significant role in conduction between the positive and negative electrodes, acting as an ionic conductor. The performance of the electrolyte and its contact with the positive and negative electrodes have a major impact on the overall performance of the battery.

[0045] In one specific embodiment of the present invention, the electrolyte includes an additive; the additive includes lithium fluorosulfonate; lithium fluorosulfonate in the electrolyte can promote the dissociation and migration of lithium ions, thereby reducing the interfacial impedance of the negative electrode. However, 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 level of side reactions. 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 any two of the above values.

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

[0047] Electrolyte viscosity is a crucial parameter in battery design and performance evaluation. Both excessively high and low viscosity can negatively impact battery performance. High viscosity increases the resistance to ion movement within the electrolyte, reducing the battery's charge / discharge rate; conversely, excessively low viscosity can lead to overly fluid electrolyte, increasing side reactions between the electrolyte and the negative electrode active material, and also resulting in increased gas production. Therefore, in this invention, the viscosity of the electrolyte at room temperature is c mPa·s; c is preferably 0.5–5; optionally, c is 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or any two of the above values.

[0048] In one specific embodiment of the present invention, c is preferably 2 to 4; in some embodiments of the present invention, 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 carbonate solvents and / or carboxylic acid ester solvents; the main function of the solvent is to dissolve lithium salts; the carbonate solvent is preferably dimethyl carbonate (DMC); the carboxylic acid ester solvent is preferably one or more of methyl acetate, ethyl propionate and ethyl acetate (EA).

[0050] In one specific embodiment of the present invention, the viscosity of the electrolyte can be adjusted by regulating the proportion of different types of solvents in the solvent. The electrolyte preferably includes carbonate solvents and carboxylic acid ester solvents. Excessive carbonate solvent content in the electrolyte will lead to intensified reaction at the negative electrode interface and increased gas production, while insufficient content will result in a decrease in the overall viscosity of the electrolyte, hindering Li+ migration and increasing DCR. Therefore, the mass of the carbonate solvent is preferably 20% to 50% of the electrolyte mass. Optionally, the mass of the carbonate solvent is preferably 20%, 25%, 30%, 35%, 40%, 45%, 50% of the electrolyte mass or a range between any two of the above values. In some embodiments of the present invention, the mass of the carbonate solvent is specifically 30%, 27%, or 25% of the electrolyte mass. Excessive carboxylic acid ester solvent content in the electrolyte will lead to increased decomposition and gas production at high temperatures, while insufficient content will result in a decrease in the overall viscosity of the electrolyte, hindering Li+ migration and increasing DCR. Therefore, the mass of the carboxylic acid ester solvent is preferably 10% to 30% of the electrolyte mass; optionally, the mass of the carboxylic acid ester solvent is 10%, 15%, 20%, 25%, 30% of the electrolyte mass, or a range between any two of the above values; in some embodiments provided by the present invention, the mass of the carboxylic acid ester solvent is specifically 15%, 18%, or 20% of the electrolyte mass; carboxylic acid ester EA has a lower viscosity than carbonate DMC, but has higher reactivity at the negative electrode interface, leading to increased lithium loss. This deteriorates cycle life; therefore, the preferred mass ratio of the carbonate solvent to the carboxylic acid ester solvent is 1 to 4:1. Optionally, the mass ratio of the carbonate solvent to the carboxylic acid ester solvent is 1:1, 1.3:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, or any two of the above ratios. In some embodiments provided by the present invention, the mass ratio of the carbonate solvent to the carboxylic acid ester solvent is specifically 2:1, 1.5:1, 1.3:1, or 2:1.

[0051] In one specific embodiment of the present invention, the organic solvent further includes 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 methyl ethyl carbonate (EMC).

[0052] In a specific embodiment of the present invention, the electrolyte preferably further includes a lithium salt, which plays a conductive role in the electrolyte. The lithium salt can be any lithium salt well-known to those skilled in the art and is not particularly limited. In this invention, it is preferred to include, but not limited to, one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium fluorosulfonyl (perfluorobutylsulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(oxalate-borate), lithium difluorooxalate-borate, lithium trifluoromethanesulfonate, and lithium tetrafluorooxalate phosphate. The concentration of the lithium salt in the electrolyte is preferably 0.5–2 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 any range between two of the above values.

[0053] In one specific embodiment of the present invention, the additive preferably further includes vinylene carbonate (VC). Vinylene carbonate can promote SEI film formation at the negative electrode, but it will deteriorate DCR. Furthermore, if its content in the electrolyte is too high, VC will decompose excessively 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 transport will be hindered. Therefore, in the present invention, the mass of vinylene carbonate is preferably 0.1% to 5% of the electrolyte mass. Optionally, the mass of vinylene carbonate is 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% of the electrolyte mass, or a range between any two of the above values.

[0054] In a specific embodiment of the present invention, the battery preferably further 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 can be any positive electrode active material well known to those skilled in the art, and there are no special limitations. In the present invention, lithium iron phosphate (LiFePO4) and lithium manganese iron phosphate (LiMn) are preferred. x Fe1 -x The cathode active material is preferably 90% to 98% of the mass of the cathode active material layer; optionally, the mass content of the cathode active material in the cathode active material layer is specifically 90%, 92%, 94%, 95%, 95.5%, 96%, 96.5%, 97%, 98% or any two of the above values.

[0055] In one specific embodiment of the present invention, the positive electrode active material layer further includes a positive electrode binder and a positive electrode conductive agent; the positive electrode binder includes, but is not limited to, one or more of the binders 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% of the mass of the positive electrode active material layer. The positive electrode conductive agent is 0.5%, 4.0%, 4.5%, 5.0%, or 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 any two of the above values.

[0056] In a specific embodiment of the present invention, the positive electrode active material layer preferably further 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 any two of the above values; the dispersant can be any dispersant well known to those skilled in the art, and there are no special limitations. In the present invention, polyvinylidene fluoride (PVDF) is preferred.

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

[0058] According to the present invention, the battery preferably further includes a separator; the separator can be any separator known to those skilled in the art and there are no special limitations. In the present invention, polypropylene (PP) and / or polyethylene (PE) are preferred.

[0059] The battery provided by this invention can be prepared according to methods well known to those skilled in the art, and there are no special limitations. 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 mixed evenly 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 double-sided coated positive electrode sheet; then it is rolled and cut to obtain positive electrode sheet.

[0061] 2) Preparation of negative electrode sheet: The negative electrode active material, negative electrode conductive agent, and negative electrode binder are mixed evenly according to the mass ratio. Deionized water is added as a solvent, and the mixture is stirred under vacuum until the system is homogeneous to obtain a negative electrode slurry. The negative electrode slurry is evenly coated on both surfaces of the negative electrode current collector, air-dried at room temperature, and then transferred to an oven for further drying. After cold pressing and slitting, the negative electrode sheet is obtained. The particle size of the primary and secondary particles of the negative electrode active material is controlled by the crushing and shaping process during preparation; the proportion of secondary particles is mixed in according to the design.

[0062] 3) Electrolyte preparation: Mix carbonate solvent and carboxylic acid ester solvent in a suitable ratio to obtain an organic solvent. Then, dissolve the fully dried lithium salt in the mixed organic solvent, and add VC and an appropriate amount of lithium fluorosulfonate and mix thoroughly.

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

[0064] 5) Preparation of lithium-ion batteries: The above-mentioned positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, so that the separator is placed between the positive and negative electrode sheets to play a role in isolation. Then, the bare cell is wound up to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, standing, formation, shaping and other processes, a lithium-ion battery is obtained.

[0065] To further illustrate the present invention, the following describes a battery provided by the present invention in detail with reference to embodiments; the molecular weight of PVDF used in the embodiments and comparative examples is about 70W.

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

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

[0068] 1) Preparation of the positive electrode:

[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. This slurry was then coated onto aluminum foil to obtain a double-sided coated positive electrode sheet. After rolling and cutting, the positive electrode sheet (area density 360 g / m²) was obtained. 2 Compacted density 2.5 g / cm³3 ).

[0070] 2) Preparation of negative electrode sheet

[0071] Graphite of different particle sizes, including primary and secondary particles, was obtained commercially. Primary particles (average particle size 5–14 micrometers) and secondary particles (average particle size 15–25 micrometers) were mixed according to the mass ratios in Table 1 to obtain the negative electrode active material graphite.

[0072] Graphite (negative electrode active material), acetylene black (conductive agent), and SBR (binder) were mixed at a mass ratio of 96.5:1.5:2. Deionized water was added as a solvent, and the mixture was stirred under vacuum until homogeneous to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto both surfaces of the copper foil used as a negative electrode current collector. After air-drying at room temperature, the foil was transferred to an oven for further drying. The resulting material was then cold-pressed and slit to obtain the negative electrode sheet (area density 173.4 g / m²). 2 Compacted density 1.52 g / cm³ 3 ).

[0073] 3) Electrolyte preparation

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

[0075] 4) Diaphragm preparation

[0076] PE was chosen as the separator.

[0077] 5) Preparation of lithium-ion batteries

[0078] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The cells are 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 sealing, settling, formation, and volume adjustment, a lithium-ion battery is obtained. The specific steps for settling, formation, and volume determination are as follows: The battery is placed at 45℃ for 12 hours, during which time it is placed in a glass clamp with a pressure of 0.4–0.6 MPa. Two charging processes are performed: 1) Settling for 10 minutes; 2) Charging at 0.05C for 120 minutes and stopping; 3) Settling for 10 minutes; 4) Charging at 0.33C for 120 minutes and stopping; 5) End. After settling at 45℃ for 12 hours and resealing, the volume determination process is performed: 1) The battery is placed for 10 minutes; 2) The battery is charged at a constant current (0.33C) to a voltage of 3.65V, and then charged at a constant voltage (3.65V) to a current of 0.05C; 3) The battery is placed for 10 minutes; 4) The battery is discharged at a constant current (0.33C) to a voltage of 2.5V; 5) Steps 2–4 are repeated three times; 6) The battery is charged at a constant current (0.33C) for 1 hour to complete the volume determination.

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

[0080] Test method for secondary particle ratio:

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

[0082] Test method for lithium fluorosulfonate content:

[0083] The battery was discharged using a battery charging and discharging device under the following conditions: current 0.3C, cutoff voltage 2.5V. The battery was disassembled and the electrolyte collected in a glove box (H2O ≤ 0.1ppm, O2 ≤ 0.1ppm). There are three methods for collecting the electrolyte: After removing the battery cover, ① if there is free electrolyte, collect it into a 5mL sample tube using a pipette and seal it with sealing tape to prevent leakage. ② if there is no free electrolyte, a hydraulic press (Beijing Heng'ao Technology Co., Ltd.'s FY-30 hydraulic press) can be used 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, place the battery in an aluminum-plastic bag and seal it with a heat sealer. Transfer it to an ultrasonic oscillator and oscillate for 12 hours to allow the electrolyte in the electrode to mix thoroughly with the dichloromethane. Then, use a pipette to draw the mixture of dichloromethane and electrolyte into a 5 mL sample tube and seal the sample tube with sealing adhesive. Dilute the collected electrolyte sample 100 times with ultrapure water and inject it into a Thermo Fisher DIONEX AQ-1100 ion chromatograph for testing to obtain an IC spectrum. Compare the IC spectrum of the electrolyte to be tested with the IC spectrum of the standard to determine whether the electrolyte to be tested contains lithium fluorosulfonate, and then determine the content based on its peak area.

[0084] Methods for testing electrolyte viscosity:

[0085] Measurement using a Vicolab 400 viscometer: ① Clean the probe and measuring chamber with ethanol, and dry with a clean sponge swab; fill the measuring chamber with the electrolyte to be tested, then remove some to rinse the chamber, and add another 2 ml of the electrolyte to the measuring chamber. Use a magnetic pen to draw the probe and place it into the measuring chamber, ensuring the probe is completely immersed in the sample; ② Press the "Enter" button to select "Operate", then press "Enter" again to select "Measure Uiscosity" to begin measurement. When the U value is within ±1% and the T value is within ±0.2℃, record the current U value, which is the viscosity. If the measuring chamber temperature is 25±0.2℃, the test data is valid; otherwise, continue the constant temperature circulating water bath in the measuring chamber until the temperature meets the requirements.

[0086] DCR testing methods:

[0087] 1) Place the battery at room temperature until it reaches thermal equilibrium;

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

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

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

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

[0092] Methods for testing gas production:

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

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

[0095] The specific method for testing battery volume using the water displacement method is as follows:

[0096] 1) Add an appropriate amount of pure water to the container and test its density ρ with a hydrometer and record it;

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

[0098] 3) Submerge the battery cell body along with the tabs in pure water, ensuring that the battery cell does not contact the container wall. After stabilization, take a reading and record the data. Before the battery is placed in the oven for storage, this data is recorded as T0. After the battery is placed in the oven for storage, this data is recorded as T0.

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

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

[0101] Table 1. Battery component raw material formulation and performance test results

[0102]

[0103]

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

[0105]

[0106]

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

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

[0109] Comparing Examples 4-5 with Examples 10-11 and Examples 14-15, it can be seen that when the battery satisfies 1≤a×b / c≤25, the battery has better fast charging performance and safety performance.

[0110] According to Comparative Examples 1 and 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 all within a suitable range, the fast charging performance and safety performance of the battery will be affected when the value of a×b / c exceeds the range of 0.1 to 550.

[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 modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A battery, characterized in that, Including the negative electrode and the 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 the aggregation of multiple primary particles; the proportion of secondary particles in the negative electrode active material is a; The electrolyte includes additives; the additives include lithium fluorosulfonate; the mass content of lithium fluorosulfonate in the electrolyte is b; the viscosity of the electrolyte at 25±0.02℃ is c mPa·s; The battery meets 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 value of 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 value of 'a' is 10% to 30%; And / or, b is 0.2% to 2%; And / or, c is 2 to 4.

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

6. The battery according to claim 5, characterized in that, The particle size Dn50 of the primary particles is 5-10 μm; And / or, the particle size Dn50 of the secondary particles is 15-20 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, and SiO2. x Silicon-carbon and Li4Ti5O 12 One or more of the following; and / or, The battery further 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 materials or lithium-rich manganese-based materials.

8. The battery according to any one of claims 7, characterized in that, The electrolyte further includes an organic solvent; the organic solvent includes a low-viscosity solvent; the low-viscosity solvent includes carbonate solvents and / or carboxylic acid ester solvents; The carbonate solvent is selected from dimethyl carbonate; The carboxylic acid ester 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 carboxylic acid ester 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 carboxylic acid ester solvent is 1 to 4:

1.

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

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