Secondary battery and electric device

Abstract

A secondary battery and an electric device. In the secondary battery, solvents with a high viscosity and a low viscosity are combined, specific types of electrolyte additives are compounded and build a parameter relationship together with the resistivity of a negative electrode film, and therefore the overall electrolyte injection amount is increased without affecting the electron conduction of a negative electrode, thereby improving the infiltration effect of an electrolyte; moreover, since unique electrolyte components are selected, the degree of interfacial side reactions of the electrolyte is low during operation of the secondary battery, the probability of gas production is low at a normal temperature or high temperature, and the ion conduction capability is high. The secondary battery has good dynamic performance, low risks of high-temperature gas production and a DCR increase, and ideal fast-charge application performance.

Description

Secondary battery and power-consuming device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese invention patent application CN202311598064.1 filed on November 27, 2023, the entire contents of which are incorporated into this application by reference. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a secondary battery and an electrical device. Background Art

[0004] Secondary batteries, particularly lithium-ion batteries, have long been a technological bottleneck for power battery applications due to insufficient rate performance. This is especially true when charging at high rates, where polarization effects of various materials significantly reduce the battery's actual capacity. Furthermore, the high overpotential of lithiated graphite during charging causes the electrode potential to drop below 0V, leading to lithium metal deposition at the negative electrode. This impacts the battery's lifespan and increases the risk of internal short circuits. Furthermore, the thermal stability of existing lithium-ion batteries needs to be improved, making them susceptible to thermal runaway in some fast-charging applications.

[0005] In order to improve the overall performance of lithium-ion secondary batteries, researchers will modify the electrolyte or negative electrode so that the electrolyte or negative electrode can effectively cope with fast charging scenarios. However, these modified products are developed under laboratory conditions and have not undergone integration and actual simulation. When applied to actual full batteries, these products cannot perform at the performance under laboratory conditions.

[0006] Summary of the Invention

[0007] The purpose of the present application is to overcome the shortcomings of the existing technology and provide a secondary battery and an electrical device. The secondary battery of the present application is based on the selection of an electrolyte with specific properties, and at the same time, combined with the parameter relationship of the membrane resistivity of the negative electrode plate in the actual scenario, it can effectively improve the wettability of the electrolyte in the negative electrode, while ensuring that the electronic conductivity of the negative electrode itself will not decrease; the electrolyte has a low degree of interfacial side reaction when the secondary battery is working, a small probability of gas production at room temperature or high temperature, and a strong ion conductivity; the secondary battery has excellent kinetic performance and good safety performance, and is very suitable for fast charging scenarios.

[0008] To achieve the above-mentioned object, in a first aspect of the present application, the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the electrolyte comprises a solvent and an additive; the additive comprises a first additive, a second additive, and a third additive; the solvent comprises a low-viscosity organic solvent and a high-viscosity organic solvent, wherein the viscosity of the low-viscosity organic solvent is ≤0.7 mPa.s, and the viscosity of the high-viscosity organic solvent is >0.7 mPa.s;

[0009] The secondary battery satisfies:

[0010] Wherein, the IC g / Ah is the injection coefficient of the electrolyte;

[0011] The EΩ·cm is the film resistivity of the negative electrode, d=6.70;

[0012] R is the mass ratio of the low-viscosity organic solvent to the total amount of solvent in the electrolyte;

[0013] The α is the mass percentage of the first additive in the electrolyte;

[0014] The β is the mass percentage of the second additive in the electrolyte;

[0015] The γ is the mass percentage of the third additive in the electrolyte;

[0016] The first additive includes a carbonate compound; the second additive includes a sulfur-based compound; and the third additive includes a phosphorus-based compound and / or a boron-based compound.

[0017] As an embodiment of the present application, the secondary battery satisfies at least one of the following conditions:

[0018] (1)2.30≤IC≤2.80;

[0019] (2)0.210≤E≤0.253;

[0020] (3)0.40≤R≤0.80;

[0021] (4) 0.1% ≤ α ≤ 1.0%;

[0022] (5) 0.1% ≤ β ≤ 3.0%;

[0023] (6)0.1%≤γ≤2%.

[0024] As an embodiment of the present application, the low-viscosity organic solvent includes at least one of dimethyl carbonate, ethyl methyl carbonate, methyl acetate, methyl propionate, methyl butyrate, methyl acetate, ethyl acetate, propyl acetate, ethyl butyrate, and propyl propionate.

[0025] As an embodiment of the present application, the secondary battery satisfies at least one of the following conditions:

[0026] (1) The carbonate compound includes at least one of vinylene carbonate and fluoroethylene carbonate;

[0027] (2) The sulfide compound includes at least one of vinyl sulfate, 1,3-propane sultone, propenyl-1,3-sultone, ethylene sulfite, methylene methanedisulfonate, and 1,4-butane sultone;

[0028] (3) The phosphorus-based compound includes at least one of tris(trimethylsilyl)phosphate and lithium difluorophosphate;

[0029] (4) The boron-based compound includes lithium difluorooxalatoborate.

[0030] As an embodiment of the present application, the high-viscosity organic solvent includes at least one of ethylene carbonate, propylene carbonate, butylene carbonate, diethyl carbonate, methylpropyl carbonate, diphenyl carbonate, and γ-butyrolactone.

[0031] As an embodiment of the present application, the high-viscosity organic solvent comprises at least one of ethylene carbonate, propylene carbonate, and diethyl carbonate, and the low-viscosity organic solvent comprises ethyl methyl carbonate and / or ethyl acetate.

[0032] As an implementation scheme of the present application, the α:β=0.25~0.5.

[0033] As an embodiment of the present application, the negative electrode sheet contains a negative electrode active material, and the negative electrode active material includes a graphite material.

[0034] In a second aspect of the present application, the present application provides an electrical device, comprising the secondary battery, wherein the secondary battery serves as a power supply for the electrical device.

[0035] The beneficial effects of this application are:

[0036] The present application provides a secondary battery and an electrical device. The secondary battery of the present application uses a combination of high-viscosity and low-viscosity solvents, and is compounded with specific types of electrolyte additives, and is connected in parallel with the membrane resistance of the negative electrode, so that the overall electrolyte injection volume is increased without affecting the electronic conduction of the negative electrode, thereby improving the electrolyte infiltration effect; on the other hand, the unique selection of electrolyte components can make the interface side reaction degree of the electrolyte low when the secondary battery is working, the gas production at high temperature is small, and the ion conductivity is strong; the secondary battery has excellent kinetic performance, low risk of high-temperature gas production and DCR growth, and has ideal fast charging application performance. DETAILED DESCRIPTION

[0037] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0038] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0039] In this application, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0040] In the present application, there is no particular limitation on the specific dispersion and stirring treatment methods.

[0041] The reagents and instruments used in this application without manufacturer indication are all conventional products that can be purchased commercially.

[0042] The present application is further described below with specific examples:

[0043] The present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the electrolyte comprises a solvent and an additive; the additive comprises a first additive, a second additive, and a third additive; the solvent comprises a low-viscosity organic solvent and a high-viscosity organic solvent, wherein the viscosity of the low-viscosity organic solvent is ≤0.7 mPa.s, and the viscosity of the high-viscosity organic solvent is greater than 0.7 mPa.s;

[0044] The secondary battery satisfies:

[0045] Wherein, the IC g / Ah is the injection coefficient of the electrolyte;

[0046] The EΩ·cm is the film resistivity of the negative electrode, d=6.70;

[0047] R is the mass ratio of the low-viscosity organic solvent to the total amount of solvent in the electrolyte;

[0048] The α is the mass percentage of the first additive in the electrolyte;

[0049] The β is the mass percentage of the second additive in the electrolyte;

[0050] The γ is the mass percentage of the third additive in the electrolyte;

[0051] The first additive includes a carbonate compound; the second additive includes a sulfur-based compound; and the third additive includes a phosphorus-based compound and / or a boron-based compound.

[0052] The composition of lithium-ion secondary battery systems is a key factor affecting lithium-ion secondary batteries. For example, the composition of the electrolyte and the negative electrode affects the balance between the electrochemical performance and safety performance of lithium-ion batteries. During the process of electrolyte injection and infiltration of the negative electrode sheet, there is a correlation between the interparticle gaps between the active material in the negative electrode sheet and the wetting effect of the electrolyte. When the gap is within an appropriate range, the electrolyte wetting effect is better, and the electrolyte has better lithium ion conductivity in the negative electrode; at the same time, it can ensure the electron conductivity between the particles. Therefore, coordinating the relationship between the two can effectively improve the electrochemical performance of the product. In addition, when the secondary battery is working, the electrolyte will experience loss and interfacial side reactions, so it is necessary to fully consider whether it is sufficient in the battery. However, if the electrolyte composition is not selected properly, as the amount of electrolyte added increases, the interfacial impedance and the consumption of active lithium will increase, which is detrimental to the battery's kinetic performance and cycle life. On the other hand, when the negative electrode sheet is rolled, more planes are parallel to the surface of the sheet, and the degree of contact between the active material particles and the degree of contact between the active material and the binder also change. At this time, the membrane resistivity of the negative electrode sheet changes the penetration efficiency of the current applied to the sheet during the test compared to the loose state. The membrane resistivity of the negative electrode sheet has a certain relationship with the permeation of the electrolyte and ion conduction, but the inventor found that the relationship between the membrane resistivity of the negative electrode sheet and physical properties such as the compaction density is not the same (with the increase of the compaction density, the membrane resistivity of the negative electrode sheet does not change linearly). Therefore, the secondary battery of the present application is based on the selection of electrolyte with specific properties, and at the same time, it is combined with the parameter relationship between the membrane resistivity of the negative electrode, which can effectively improve the wettability of the electrolyte in the negative electrode, while ensuring that the electronic conductivity of the negative electrode itself will not decrease. It can also reduce the degree of interfacial side reactions of the electrolyte when the secondary battery is working, so that the battery produces less gas at high temperature and has strong ion conductivity, so that the secondary battery has excellent kinetic performance and good safety performance, which is very suitable for fast charging scenarios.

[0053] In some embodiments, 2.30≤IC≤2.80; for example, the injection coefficient IC g / Ah of the electrolyte is a range value of one or any two of 2.30g / Ah, 2.35g / Ah, 2.40g / Ah, 2.45g / Ah, 2.50g / Ah, 2.55g / Ah, 2.60g / Ah, 2.65g / Ah, 2.70g / Ah, 2.75g / Ah, and 2.80g / Ah.

[0054] The filling coefficient of the electrolyte has a certain relationship with the performance of the secondary battery. When the filling coefficient is within the above range, the lithium ions in the charging and discharging process can be effectively conducted, ensuring the actual capacity of the secondary battery, and improving the service life of the secondary battery. It can also ensure that the secondary battery has a high energy density, which is beneficial to improving the overall performance of the secondary battery.

[0055] Specifically, the IC test method is as follows: Weigh the total mass of the battery to obtain m1. Then, drain the electrolyte from the battery and re-add dimethyl carbonate to fully soak the battery interior and wash out any residual lithium salts. Repeat this three times. Then, dry the battery at 80°C for 24 hours to ensure that all residual dimethyl carbonate solvent is removed. Weigh the post-baking mass of the battery to obtain the dry battery mass m2. The original mass of the electrolyte in the battery is m = m1 - m2. Let the battery design capacity be C, and the electrolyte filling coefficient IC = C / m.

[0056] In some embodiments, 0.210≤E≤0.253; the film resistivity EΩ·cm of the negative electrode plate is in the range of one or any two of 0.210Ω·cm, 0.215Ω·cm, 0.220Ω·cm, 0.225Ω·cm, 0.230Ω·cm, 0.240Ω·cm, 0.250Ω·cm, and 0.253Ω·cm.

[0057] As mentioned above, the intercalation and deintercalation efficiency of lithium ions in the negative electrode and the wettability of the electrolyte affect the membrane resistivity of the negative electrode. When the membrane resistivity of the negative electrode is set within the above range, it can effectively ensure that the secondary battery has a higher energy density and avoid ion transmission failure of the negative electrode.

[0058] The film resistivity of the negative electrode was directly measured using the four-probe method. Specifically, the measurements were made using an ST2258C multi-function digital four-probe tester, with three parallel measurements taken and the average value calculated.

[0059] In some embodiments, 0.40≤R≤0.80; for example, the mass ratio R of the low-viscosity organic solvent to the total amount of solvent in the electrolyte is in the range of one or any two of 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, and 0.80.

[0060] R is the proportion of low-viscosity organic solvents in the electrolyte. Within the above range, the viscosity of the overall electrolyte can be ensured to be within a reasonable range, so that the electrolyte has better wettability on the electrode, which is beneficial to the conduction of lithium ions and reduces high-temperature gas production.

[0061] Specifically, the R, α, β, and γ test methods are as follows: the content of each component in the electrolyte can be monitored by combining electrolyte quantification, organic matter qualitative analysis, and ion composition analysis. The reference standard for electrolyte quantification is GB / T 9722-2006, "General Rules for Gas Chromatography of Chemical Reagents." Specific testing conditions include: FID detector, detector temperature 300°C, inlet temperature 250°C, split ratio 100:1, injection volume 0.2 μL, chromatographic column: KB-200, 60 m x 0.32 mm x 0.50 μm. The reference standard for organic matter qualitative analysis is GB / T 9722-2006, "General Rules for Mass Spectrometry Methods," MS ion source temperature 230°C, inlet temperature 240°C, split ratio 150:1, injection volume 0.2 μL, chromatographic column: HP-5MS, 30 m x 0.32 mm x 0.25 μm. The ion composition analysis method refers to GB / T 19282-2014, "Analysis Method for Lithium Hexafluorophosphate Products," and GB / T 34672-2017, "General Rules for Ion Chromatography." For electrolyte sample pretreatment, dilute 1g of the sample 100-fold. The eluent concentrations are 4.1 mmol / L Na₂CO₃, 2.7 mmol / L NaHCO₃, 20% acetonitrile, and 0.05 mol / L methanesulfonic acid. The test duration is 65 minutes. R is calculated by summing the mass ratios of the low-viscosity solvents to the total electrolyte solvent. α, β, and γ can also be measured using the above method.

[0062] In some embodiments, 0.1%≤α≤1.0%; for example, α may be in the range of one or any two of 0.1%, 0.2%, 0.3%, 0.5%, 0.8%, 1%. More preferably, 0.2%≤α≤0.5%.

[0063] In some embodiments, 0.1%≤β≤3.0%; for example, β may be in the range of one or any two of 0.1%, 0.2%, 0.3%, 0.5%, 0.8%, 1%, 2%, 3%. More preferably, 1%≤β≤1.5%.

[0064] In some embodiments, 0.1%≤γ≤2%; for example, γ can be a range of one or any two of 0.1%, 0.2%, 0.3%, 0.5%, 0.8%, 1%, 2%, and 3%.

[0065] More preferably, 1%≤γ≤1.5%.

[0066] The α is the mass percentage of the first additive in the additives in the electrolyte, β is the mass percentage of the second additive in the additives in the electrolyte, and γ is the mass percentage of the third additive in the additives in the electrolyte. The three are used together and the content range is controlled, which can effectively improve the cycle performance of the secondary battery, reduce the risk of high-temperature gas production and DCR increase, and reduce the side reactions caused by the use of the additives alone. The three additives work together and check and balance each other. When within the range, the secondary battery can not only ensure cycle stability, but also have a low probability of high-temperature gas production and excellent kinetic performance, which is very suitable for fast charging conditions.

[0067] In some embodiments, the compaction density PD of the negative electrode sheet satisfies: 1.35 g / cm 3 ≤PD g / cm 3 ≤1.78g / cm 3 ; For example, it can be 1.35g / cm 3 , 1.40g / cm 3 , 1.45g / cm 3 , 1.50g / cm 3 , 1.55g / cm 3 , 1.60g / cm 3 , 1.65g / cm 3 , 1.70g / cm 3 , 1.78g / cm 3 The compaction density of the negative electrode sheet is related to the efficiency of lithium ion insertion and extraction in the negative electrode and the wettability of the electrolyte. When the compaction density of the negative electrode sheet is set in the above range, it can effectively reduce the risk of internal short circuit caused by particle shedding on the negative electrode sheet and ensure that the secondary battery has a high energy density. In some embodiments, the low-viscosity organic solvent includes at least one of dimethyl carbonate, ethyl methyl carbonate, methyl acetate, methyl propionate, methyl butyrate, methyl acetate, ethyl acetate, propyl acetate, ethyl butyrate and propyl propionate.

[0068] In some embodiments, the high-viscosity organic solvent includes at least one of ethylene carbonate, propylene carbonate, butylene carbonate, diethyl carbonate, methylpropyl carbonate, diphenyl carbonate, and γ-butyrolactone.

[0069] In some embodiments, the carbonate compound includes at least one of vinylene carbonate, vinyl ethylene carbonate, and fluoroethylene carbonate.

[0070] In some embodiments, the sulfur-based compound includes at least one of vinyl sulfate, 1,3-propane sultone, propenyl-1,3-sultone, ethylene sulfite, methylene methanedisulfonate, and 1,4-butane sultone.

[0071] In some embodiments, the phosphorus-based compound includes at least one of tris(trimethylsilyl)phosphate and lithium difluorophosphate.

[0072] In some embodiments, the boron-based compound includes lithium difluorooxalatoborate.

[0073] In the electrolyte, the combination of the three additives can not only effectively suppress the risk of high-temperature gas production caused by low-viscosity solvents, but also avoid the deterioration of the DCR performance of the secondary battery. In particular, the ratio under the parameter relationship described in this application can make the comprehensive electrochemical performance of the secondary battery better.

[0074] In some embodiments, the high-viscosity organic solvent comprises at least one of ethylene carbonate, propylene carbonate, and diethyl carbonate, and the low-viscosity organic solvent comprises ethyl methyl carbonate and / or ethyl acetate.

[0075] In some embodiments, the electrolyte includes an electrolyte salt, and the electrolyte salt includes at least one of lithium hexafluorophosphate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethylsulfonyl imide, lithium tetrafluoroborate, lithium perchlorate, lithium tetrafluorophosphate, lithium bisoxalatodifluorophosphate, and lithium bisoxalatoborate.

[0076] More preferably, the electrolyte salt is lithium hexafluorophosphate.

[0077] Lithium hexafluorophosphate has an ideal ion migration number and dissociation constant in the electrolyte system described in this application, and also has better environmental resistance and electrode adaptability.

[0078] More preferably, the mass content of the electrolyte salt in the electrolyte is 10 to 20 wt%.

[0079] In some embodiments, the α:β=0.25-0.5.

[0080] When the ratio of the first additive to the second additive is within the above range, the cycle life of the secondary battery can be further improved, and the safety performance of the secondary battery can be improved, and the degree of high-temperature gas generation can be lowered.

[0081] More preferably, the ratio of α to γ ​​is 0.12 to 0.5, and the ratio of β to γ ​​is 0.6 to 1.5. When this condition is met, the comprehensive electrochemical performance of the secondary battery can be further optimized.

[0082] In some embodiments, the negative electrode sheet contains a negative electrode active material, and the negative electrode active material includes a graphite material.

[0083] Further preferably, the particle size Dv of the graphite material is 50 The particle size Dv of the graphite material90 The ratio is 0.5 to 0.75. Dv 50 is the particle size corresponding to the cumulative volume distribution percentage of 50% of the graphite material, Dv 90 is the particle size corresponding to the cumulative volume distribution percentage of 90% of the graphite material.

[0084] Further preferably, the particle size Dv of the graphite material 50 ≤ 15 μm, and the particle size Dv of the graphite material 90 ≤ 25 μm.

[0085] The particle size Dv of the graphite material 50 and the Dv of the graphite material 90 can be obtained by testing with a laser particle size analyzer.

[0086] The inventors found through experiments that when in the electrolyte system described in this application, graphite materials with different particle size distributions also have different degrees of balance in their wettability to the electrolyte and their own conductivity. When the particle size distribution is within a reasonable range, it can avoid the shedding of some small particles during charge and discharge, which affects the conductivity and cycle performance of the secondary battery, and a reasonable particle size distribution can improve the impregnation performance of the negative electrode sheet to the electrolyte. When the graphite material within the above range is used as the negative electrode active material, the secondary battery can exhibit better performance.

[0087] In some embodiments, the positive electrode sheet includes a positive electrode active material layer, and the positive electrode active material layer contains a compound with the chemical formula Li a Ni x Co y M z O2, where M is selected from at least one of Mn, Al, Zr, Ti, V, Mg, Fe, B, Mo, 0.95 ≤ a ≤ 1.2, 0.33 ≤ x < 1, 0 < y ≤ 0.33, 0 < z ≤ 0.33, and x + y + z = 1.

[0088] This application also provides an electrical device that uses the above secondary battery as a power supply. Since the above secondary battery has better cycle performance and lower gas generation performance, the electrical device has a longer battery life and better safety performance.

[0089] The following further elaborates on this application with specific examples, and these examples should not be construed as limiting the scope claimed in this application:

[0090] Example 1

[0091] A secondary battery, and the preparation method includes the following steps:

[0092] (1) The positive electrode active material Li(Ni 0.8 Mn 0.1 Co 0.1 )O2 (NMC811), conductive agent acetylene black (Super P) and binder polyvinylidene fluoride (PVDF) were mixed uniformly in a mass ratio of NMC811:Super P:PVDF=94:3:3, and dispersed in 1-methyl-2-pyrrolidone (NMP) to prepare a uniform black slurry. The mixed slurry was coated on both sides of aluminum foil, baked, rolled and cut into pieces to obtain a positive electrode sheet. The compaction density of the positive electrode active material layer was 3.40g / cm 3 ;

[0093] (2) The negative electrode active material graphite (Gr, particle size Dv 50 12μm, particle size Dv 90 The conductive agent acetylene black (Super P), the thickener CMC and the binder SBR were mixed uniformly in a mass ratio of AG:Super P:CMC:SBR=96.2:1.2:1.2:1.4, and dispersed in deionized water to form a uniform black slurry. The mixed slurry was coated on both sides of the copper foil, and then baked, rolled and cut into pieces to obtain a negative electrode sheet. The compaction density of the negative electrode sheet was 1.5g / cm 3 The film resistivity of the negative electrode is E, in Ω·cm;

[0094] (3) Preparation of electrolyte:

[0095] (3.1) Ethylene carbonate (EC), a high-viscosity organic solvent, ethyl methyl carbonate (EMC), a low-viscosity organic solvent, and diethyl carbonate (DEC) were mixed in a mass ratio of 30:40:30 to form a mixed solvent. Molecular sieve to remove water and set aside;

[0096] (3.2) In an argon-filled glove box at room temperature, 12.5% ​​by weight of lithium hexafluorophosphate (LiPF6) was added to the mixed solvent obtained in step (3.1) with continuous stirring and cooling to obtain a colorless, transparent liquid.

[0097] (3.3) adding 0.2% by mass of vinylene carbonate, 0.5% by mass of vinyl sulfate, and 0.5% by mass of lithium difluorophosphate to the obtained colorless transparent liquid to obtain the electrolyte;

[0098] (4) The prepared positive electrode sheet, separator (PP separator with a thickness of 14 μm), and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets. After winding, hot pressing and shaping, and tab welding, a bare cell is obtained. The bare cell is placed in an outer packaging aluminum-plastic film and baked in an oven at 85±10°C for 24 hours. The prepared electrolyte is injected into the dried battery, allowed to stand, formed, and divided to complete the preparation of the lithium-ion soft pack battery. The electrolyte injection coefficient is IC, which is expressed in g / Ah.

[0099] Example 2

[0100] A secondary battery differs from the first embodiment only in the filling coefficient.

[0101] Example 3

[0102] A secondary battery differs from the first embodiment only in the filling coefficient.

[0103] Example 4

[0104] A secondary battery differs from Example 2 only in that the film resistivity of the negative electrode sheet is different (different film resistivities can be obtained by adjusting the rolling parameters during the preparation of the negative electrode sheet).

[0105] Example 5

[0106] A secondary battery, the difference from Example 2 is only that the film resistivity of the negative electrode sheet is different.

[0107] Example 6

[0108] A secondary battery, the difference from Example 2 is only that the film resistivity of the negative electrode sheet is different.

[0109] Example 7

[0110] A secondary battery differs from Example 2 only in that in step (3.1), the mixed solvent is ethylene carbonate, ethyl methyl carbonate, a low-viscosity organic solvent dimethyl carbonate (DMC), and diethyl carbonate prepared in a mass ratio of 30:20:45:5.

[0111] Example 8

[0112] A secondary battery is different from Example 2 only in that in step (3.1), the mixed solvent is ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate prepared in a mass ratio of 20:20:60.

[0113] Example 9

[0114] A secondary battery differs from Example 2 only in that in step (3.1), the mixed solvent is ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and low-viscosity organic solvent ethyl acetate (EA) prepared in a mass ratio of 20:20:40:20.

[0115] Example 10

[0116] A secondary battery, the only difference from Example 7 is that in step (3.3), the amount of vinylene carbonate added is 0.1%.

[0117] Example 11

[0118] A secondary battery, the difference from Example 7 is that in step (3.3), the amount of vinylene carbonate added is 0.5%.

[0119] Example 12

[0120] A secondary battery, the difference from Example 7 is only that in step (3.3), the amount of vinylene carbonate added is 1%.

[0121] Example 13

[0122] A secondary battery, the difference from Example 7 is that in step (3.3), vinylene carbonate is replaced by fluoroethylene carbonate, and the added amount is 0.2%.

[0123] Example 14

[0124] A secondary battery, the only difference from Example 7 is that in step (3.3), the amount of vinyl sulfate added is 1%.

[0125] Example 15

[0126] A secondary battery, the only difference from Example 7 is that in step (3.3), the amount of vinyl sulfate added is 1.5%.

[0127] Example 16

[0128] A secondary battery, the only difference from Example 7 is that in step (3.3), the amount of vinyl sulfate added is 3%.

[0129] Example 17

[0130] A secondary battery, the only difference from Example 7 is that in step (3.3), vinyl sulfate is replaced by 1,3-propane sultone, and the added amount is 1.5%.

[0131] Example 18

[0132] A secondary battery, the only difference from Example 7 is that in step (3.3), vinyl sulfate is replaced by propenyl-1,3-sultone, and the added amount is 1.5%.

[0133] Example 19

[0134] A secondary battery, the difference from Example 7 is that in step (3.3), vinyl sulfate is replaced by methylene methanedisulfonate, and the added amount is 1.5%.

[0135] Example 20

[0136] A secondary battery, the difference from Example 15 is that in step (3.3), the lithium difluorophosphate is replaced by tris(trimethylsilyl)phosphate, and the added amount is 1%.

[0137] Example 21

[0138] A secondary battery, the only difference from Example 15 is that in step (3.3), 1% of tris(trimethylsilyl)phosphate is further added.

[0139] Example 22

[0140] A secondary battery, the only difference from Example 15 is that in step (3.3), 1% of tris(trimethylsilyl)phosphate is further added, and the added amount of lithium difluorophosphate is 0.9%.

[0141] Example 23

[0142] A secondary battery, the only difference from Example 15 is that in step (3.3), lithium difluorophosphate is replaced by lithium difluorooxalatoborate, and 1% of tris(trimethylsilyl)phosphate is added.

[0143] Examples 24 to 29

[0144] A secondary battery, the difference from Example 7 is only that in the step (3.3), the added amounts of vinylene carbonate and vinyl sulfate are different.

[0145] Example 30

[0146] A secondary battery, the difference from Example 1 is only in the particle size D of the negative electrode active material graphite 50 13 μm, particle size D 90 It is 18μm.

[0147] Example 31

[0148] A secondary battery, the difference from Example 1 is only in the particle size D of the negative electrode active material graphite 50 12μm, particle size D 90 25μm.

[0149] Example 32

[0150] A secondary battery, the difference from Example 1 is only in the particle size D of the negative electrode active material graphite 50 14 μm, particle size D 90 It is 18μm.

[0151] Example 33

[0152] A secondary battery, the only difference from Example 1 is that the content of vinyl sulfate and lithium difluorophosphate is adjusted to 0.1%.

[0153] Comparative Example 1

[0154] A secondary battery differs from the first embodiment only in the filling coefficient.

[0155] Comparative Example 2

[0156] A secondary battery differs from Example 1 in that in step (3.1), the mixed solvent is ethylene carbonate and ethyl methyl carbonate prepared in a mass ratio of 30:70, and the electrolyte injection coefficient is different.

[0157] Comparative Example 3

[0158] A secondary battery differs from Example 1 only in that the film resistivity of the negative electrode sheet is different (different film resistivities can be obtained by adjusting the rolling parameters during the preparation of the negative electrode sheet).

[0159] Comparative Example 4

[0160] A secondary battery differs from Example 1 in that in step (3.1), the mixed solvent is ethylene carbonate and ethyl methyl carbonate prepared in a mass ratio of 30:70, and the electrolyte injection coefficient and the membrane resistivity of the negative electrode are different.

[0161] Comparative Example 5

[0162] A secondary battery is provided, which differs from Example 1 only in that in step (3.1), the mixed solvent is ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate prepared in a mass ratio of 30:10:60.

[0163] Comparative Example 6

[0164] A secondary battery, which differs from Example 1 in that in step (3.1), the mixed solvent is ethylene carbonate and ethyl methyl carbonate prepared in a mass ratio of 15:85, and the injection coefficient is 2.5 g / Ah.

[0165] Comparative Example 7

[0166] A secondary battery is different from Example 1 only in that ethylene carbonate is not added in step (3.3).

[0167] Comparative Example 8

[0168] A secondary battery, which is different from Example 1 only in that vinyl sulfate is not added in step (3.3).

[0169] Comparative Example 9

[0170] A secondary battery, which is different from Example 1 only in that lithium difluorophosphate is not added in step (3.3).

[0171] Comparative Example 10

[0172] A secondary battery differs from Example 1 in that the filling coefficient and the negative electrode film resistivity are different. In the step (3.1), the mixed solvent is prepared by mixing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a mass ratio of 20:20:60; in the step (3.3), fluoroethylene carbonate equivalent to 1% of the total mass of the electrolyte, 3% of vinyl sulfate, 1% of tris(trimethylsilyl)phosphate, and 0.9% of lithium difluorophosphate are added to the colorless transparent liquid to obtain the electrolyte.

[0173] The performance tests of the secondary batteries prepared in the above examples and comparative examples were carried out respectively, and the specific methods are as follows:

[0174] (1) -20°C Direct Current Resistance (DCR) test: At 25±2°C, the secondary batteries obtained from each embodiment and comparative example were charged at 1C to 4.25V, then discharged at 1C for 30 minutes to 50% SOC. After adjusting the temperature to -20°C, the batteries were discharged at 0.36C for 10 seconds. The discharge DCR at -20°C was calculated as follows: (voltage change before and after discharge) / discharge current*100%.

[0175] (2) Room Temperature Cycling Performance Test: The secondary batteries obtained from each embodiment and comparative example were subjected to charge and discharge cycling tests at a charge and discharge rate of 4C / 1C within the range of 2.5 to 4.25V at 25±2°C. The number of cycles at which the battery capacity retention reached 80% was recorded. Capacity retention (%) = discharge specific capacity corresponding to the final cycle / discharge specific capacity at the first cycle * 100%.

[0176] (3) Battery lithium deposition test method: adjust the temperature to -10°C, charge with a charging current of 0.13C to the upper voltage limit, discharge with a discharge current of 1C to the lower voltage limit, cycle 10 times, adjust the temperature to 25°C, charge with a charging current of 1C to the upper voltage limit, disassemble the battery, and observe whether lithium deposition occurs on the interface. If the area of ​​lithium deposition on the surface of the negative electrode is less than 2%, it is considered that there is no lithium deposition. If the area of ​​lithium deposition on the surface of the negative electrode is greater than or equal to 2% and less than 5%, it is considered that there is slight lithium deposition. If the area of ​​lithium deposition on the surface of the negative electrode is 5% to 50%, it is considered that there is moderate lithium deposition. If the area of ​​lithium deposition on the surface of the negative electrode is greater than 50%, it is considered that there is severe lithium deposition.

[0177] (4) High-temperature storage gas generation test: The soft-pack batteries obtained in the examples and comparative examples were charged at 25±2°C at a constant current rate of 1C to 4.25V, and then charged at a constant voltage of 4.25V until the current was less than 0.05C, so that they were in a fully charged state at 4.25V. The volume of the fully charged battery before storage was measured and recorded as V0. The fully charged battery was then placed in an oven at 60±2°C. After 150 days, the battery was removed and its volume after storage was immediately measured and recorded as V1. The volume expansion rate (%) was calculated as (V1-V0) / V0*100%.

[0178] The test results are shown in Tables 1 to 3, where the

[0179] Table 1

[0180] Table 2

[0181] Table 3

[0182] From Table 2 we can see that:

[0183] 1) When the secondary battery meets the range requirements of X, the secondary battery has ideal electrochemical performance, its DCR at low temperature can be maintained within the range of 400Ω, and its cycle life at room temperature reaches more than 900 times; on the other hand, the secondary battery has high stability and safety, the lithium deposition condition of the negative electrode surface is good, and the volume expansion rate at high temperature does not exceed 50%.

[0184] 2) According to the data of Examples 1 to 33 and Comparative Example 3, it can be seen that the negative electrode is closely related to the electrolyte. When the membrane resistivity of the negative electrode is in a suitable range, the interface impedance of the secondary battery is small, which can inhibit lithium plating at the negative electrode. When the membrane resistivity of the negative electrode is in a suitable range, the contact efficiency between the negative electrode active material particles in the negative electrode sheet and between the active particles and the binder is high, which has better conduction efficiency for ions and electrons, and is beneficial to improving the cycle life of the secondary battery.

[0185] 3) According to the performance of the secondary batteries prepared in Examples 1 to 33 and Comparative Examples 5 and 6, it can be seen that the viscosity of the solvent in the electrolyte has a great influence on the secondary battery. When the viscosity of the solvent is in an appropriate range, the wettability of the electrolyte can be improved, the lithium ion conduction efficiency can be improved, and the conductivity, cyclability and safety can be improved.

[0186] 4) According to the products of Examples 1 to 33 and Comparative Examples 7 to 9, it can be seen that when the three additives in the electrolyte described in the present application are present at the same time, both the fast charge cycle life and the safety performance of the secondary battery can be taken into account.

[0187] 5) It can be seen from Examples 1 to 33 and Comparative Example 10 that the secondary battery described in this application is constructed based on the overall component relationship. Even if the individual parameters of the individual components meet the range requirements, if the relationship between the components after combination is not considered, the performance of the prepared secondary battery may still not meet the standards.

[0188] 6) As the first additive to ensure fast charging performance and the second additive to ensure safety performance, if the two are maintained in a specific ratio, the overall performance of the product will be better. It can be seen from Examples 7, 10 to 12, and 14 to 16 that the amount of addition of the two directly affects the two performances of the product. Therefore, when the addition amounts of the two are 0.2 to 0.5% and 1 to 1.5% respectively, the product performance is better. According to the comparison between Examples 24 and 27 to 29, it can be seen that even if the total amount of the two additives is the same, if the ratio of the two is maintained within the range of 0.25 to 0.5, the performance of the product can still be maintained better.

[0189] 7) In the negative electrode of the secondary battery, when graphite material is selected as the active material, in addition to the film resistivity, if the particle size Dv is selected 50 and particle size Dv 90 When the ratio is 0.5 to 0.75, the graphite material can better maintain the balance between electrolyte wettability and electronic conductivity, as shown in Example 1 and Examples 30 to 32. The secondary battery performance of Example 1 and Example 30 that meet the preferred range is better.

Claims

1. A secondary battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the electrolyte comprises a solvent and an additive; the additive comprises a first additive, a second additive and a third additive; the solvent comprises a low-viscosity organic solvent and a high-viscosity organic solvent, wherein the viscosity of the low-viscosity organic solvent is ≤0.7 mPa.s, and the viscosity of the high-viscosity organic solvent is >0.7 mPa.s; The secondary battery meets the following requirements: in, The IC g / Ah is the injection coefficient of the electrolyte; The EΩ·cm is the film resistivity of the negative electrode, d=6.70; R is the mass ratio of the low-viscosity organic solvent to the total amount of solvent in the electrolyte; The α is the mass percentage of the first additive in the electrolyte; The β is the mass percentage of the second additive in the electrolyte; The γ is the mass percentage of the third additive in the electrolyte; The first additive includes a carbonate compound; the second additive includes a sulfur-based compound; and the third additive includes a phosphorus-based compound and / or a boron-based compound.

2. The secondary battery according to claim 1, wherein: The secondary battery satisfies at least one of the following conditions: (1) 2.30≤IC≤2.80; (2)0.210≤E≤0.253； (3)0.40≤R≤0.80； (4)0.1％≤α≤1.0％； (5)0.1％≤β≤3.0％； (6)0.1%≤γ≤2%.

3. The secondary battery according to claim 1, wherein: The low-viscosity organic solvent includes at least one of dimethyl carbonate, ethyl methyl carbonate, methyl acetate, methyl propionate, methyl butyrate, methyl acetate, ethyl acetate, propyl acetate, ethyl butyrate and propyl propionate.

4. The secondary battery according to claim 1, wherein: The high-viscosity organic solvent includes at least one of ethylene carbonate, propylene carbonate, butylene carbonate, diethyl carbonate, methylpropyl carbonate, diphenyl carbonate, and γ-butyrolactone.

5. The secondary battery according to any one of claims 1 to 4, wherein: The secondary battery meets the following condition: the carbonate compound includes at least one of vinylene carbonate, vinyl ethylene carbonate, and fluoroethylene carbonate.

6. The secondary battery according to any one of claims 1 to 4, wherein: The secondary battery satisfies the following condition: the sulfur-based compound includes at least one of vinyl sulfate, 1,3-propane sultone, propenyl-1,3-sultone, ethylene sulfite, methylene methanedisulfonate, and 1,4-butane sultone.

7. The secondary battery according to any one of claims 1 to 4, wherein: The secondary battery meets the following condition: the phosphorus-based compound includes at least one of tris(trimethylsilyl)phosphate and lithium difluorophosphate.

8. The secondary battery according to any one of claims 1 to 4, wherein: The secondary battery satisfies the following condition: the boron-based compound includes lithium difluorooxalatoborate.

9. The secondary battery according to any one of claims 1 to 4, wherein: The high-viscosity organic solvent includes at least one of ethylene carbonate, propylene carbonate, and diethyl carbonate, and the low-viscosity organic solvent includes ethyl methyl carbonate and / or ethyl acetate.

10. The secondary battery according to any one of claims 1 to 4, wherein: The α:β=0.25~0.

5.

11. The secondary battery according to any one of claims 1 to 4, wherein: The negative electrode sheet contains a negative electrode active material, and the negative electrode active material includes a graphite material, and the particle size Dv of the graphite material is 50 The particle size Dv of the graphite material 90 The ratio is 0.5 to 0.75; among them, Dv 50 Dv is the particle size corresponding to the volume cumulative distribution percentage of the graphite material reaching 50%, 90 It is the particle size corresponding to when the volume cumulative distribution percentage of the graphite material reaches 90%.

12. The secondary battery according to claim 11, wherein: The particle size Dv of the graphite material 50 ≤15μm, the particle size Dv of the graphite material 90 ≤25μm.

13. An electrical device, comprising the secondary battery according to any one of claims 1 to 12, wherein the secondary battery serves as a power supply for the electrical device.

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