Secondary battery and electrical device

Abstract

A secondary battery and an electrical device. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The conductivity of the electrolyte is 14 mS / cm to 22 mS / cm; the electrolyte comprises a first additive; the first additive comprises at least one of compounds represented by formula I and formula II; in formula I, R1 is selected from H, a fluorine atom, fluoro-substituted or unsubstituted C1-C12 alkyl, and fluoro-substituted or unsubstituted C2-C10 alkenyl; in formula II, R2, R3, R4, and R5 are each independently selected from a hydrogen atom, a fluorine atom, fluoro-substituted or unsubstituted C1-C6 alkyl, fluoro-substituted or unsubstituted C1-C6 alkoxy, C2-C6 alkenyl or C2-C6 alkynyl, and R2, R3, R4, and R5 are not all hydrogen atoms.

Description

Secondary battery and power consuming device

[0001] Cross Reference to Related Applications

[0002] The present disclosure is based on and claims priority to Chinese Patent Application No. 202411364702.8, filed on September 27, 2024, entitled “Secondary battery and power consuming device”, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of secondary batteries, and in particular to a secondary battery and a power consuming device. BACKGROUND

[0004] In recent years, with the application range of secondary batteries becoming more and more extensive, secondary batteries are widely used in energy storage power supply systems such as hydropower, thermal power, wind power and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, etc. Due to the great development of secondary batteries, higher requirements are put forward for their energy density and cycle performance, etc. SUMMARY

[0005] The present disclosure is made in view of the above-mentioned problems, and aims to provide a secondary battery and a power consuming device, which can improve the cycle performance while taking into account high energy density.

[0006] A first aspect of the present disclosure provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, the electrolyte having an electrical conductivity of 14 mS / cm-22 mS / cm, the electrolyte comprising a first additive, the first additive comprising at least one of a compound represented by Formula I and Formula II,

[0007] In Formula I, R1 is selected from H, a fluorine atom, a fluorine-substituted or unsubstituted C1-C12 alkyl group, a fluorine-substituted or unsubstituted C2-C10 alkenyl group;

[0008] In Formula II, R2, R3, R4 and R5 are each independently selected from a hydrogen atom, a fluorine atom, a fluorine-substituted or unsubstituted C1-C6 alkyl group, a fluorine-substituted or unsubstituted C1-C6 alkoxy group, a C2-C6 alkenyl group or a C2-C6 alkynyl group, and R2, R3, R4 and R5 are not simultaneously a hydrogen atom. Thus, the secondary battery of the present disclosure can take into account high energy density and good cycle performance.

[0009] In some embodiments, the electrolyte has an electrical conductivity of 14 mS / cm to 19 mS / cm. In this way, the transport rate of active ions can be improved, and the concentration polarization in the secondary battery can be reduced, lithium precipitation at the negative electrode interface can be inhibited, and the cycle performance of the secondary battery can be improved.

[0010] In some embodiments, in formula I, R1 is selected from a hydrogen atom, a fluorine atom, a fluorine-substituted or unsubstituted C1-C6 alkyl group, a fluorine-substituted or unsubstituted C2-C6 alkenyl group; and / or in formula II, R2, R3, R4 and R5 are each independently selected from a hydrogen atom, a fluorine atom, a fluorine-substituted or unsubstituted C1-C4 alkyl group, a fluorine-substituted or unsubstituted C1-C4 alkoxy group, a C2-C4 alkenyl group or a C2-C4 alkynyl group, and R2, R3, R4 and R5 are not simultaneously a hydrogen atom. In this way, the cycle performance of the secondary battery can be improved.

[0011] In some embodiments, the first additive includes at least one of fluoroethylene carbonate and vinylene carbonate. In this way, the cycle performance of the secondary battery can be more improved.

[0012] In some embodiments, the electrolyte includes a first solvent, and the first solvent includes a compound represented by formula III,

[0013] In formula III, R 11 is selected from a hydrogen atom, a fluorine-substituted or unsubstituted C1-C4 alkyl group, and R 12 is selected from a fluorine-substituted or unsubstituted C1-C4 alkyl group. By using the carboxylic acid ester solvent represented by formula III, the electrical conductivity of the electrolyte can be significantly improved, and the viscosity of the electrolyte can be reduced, and the cycle performance of the secondary battery can be improved.

[0014] In some embodiments, the first solvent is selected from one or more of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. In some embodiments, the first solvent is selected from one or more of ethyl formate, methyl acetate, and ethyl acetate. In this way, the cycle performance of the secondary battery can be more improved.

[0015] In some embodiments, the electrolyte further includes a second additive, and the second additive includes at least one of a compound of formula IV and formula V,

[0016] In formula IV, R a , R b each independently represents H, or R a and R b are connected to form a structure, R grepresents a fluorine atom, a fluorine-substituted or unsubstituted C1-C6 alkyl group, a C1-C6 alkoxy group, or

[0017] R in formula V c R in formula V d R in formula V e R in formula V f each independently represents H or a fluorine atom.

[0018] In some embodiments, the second additive includes one or more of vinyl sulfate, bis vinyl sulfate, and .

[0019] In the present disclosure, by adding the above-mentioned second additive in the electrolyte, a dense SEI film can be formed at the negative electrode interface, having good passivation effect, improving the stability of the negative electrode interface, thereby inhibiting the reduction of carboxylic acid ester solvents on the negative electrode, further improving the cycle performance of the secondary battery.

[0020] In some embodiments, the mass content of the first additive in the electrolyte is 0.01%-5%. Thus, it is beneficial to alleviate the volume expansion and shrinkage of high-capacity graphite during charging and discharging, and reduce the destruction of SEI caused by the expansion and shrinkage, and is beneficial to improve the cycle performance.

[0021] In some embodiments, the mass content of the first solvent in the electrolyte is 20%-80%. Thus, it is more beneficial to improve the cycle performance of the secondary battery.

[0022] In some embodiments, the mass ratio of the first solvent to the second additive in the electrolyte is 2200:1 to 10:1. Thus, it is beneficial to improve the electrical conductivity of the electrolyte, while the second additive can form a dense protective film at the negative electrode interface, inhibit the side reaction of the first solvent passing through the interface, and maintain the good stability of the negative electrode interface.

[0023] In some embodiments, the mass content of the second additive in the electrolyte is 0.01%-2%. The second additive can form a dense SEI film on the surface of the negative electrode during formation, which can inhibit the side reaction of the first solvent passing through the interface film on the negative electrode, and improve the cycle performance of the battery.

[0024] In some embodiments, the electrolyte further comprises a second solvent, and the second solvent comprises at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate. The above-mentioned cyclic esters such as ethylene carbonate, propylene carbonate, and butylene carbonate have high dielectric constants and can dissociate lithium ions in the electrolyte, thereby facilitating the secondary battery to have more movable lithium ions, so as to achieve high ionic conductivity; the above-mentioned linear esters such as dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate can adjust the viscosity of the electrolyte on the one hand and the low-temperature freezing point of the electrolyte on the other hand, so that the electrolyte has balanced performance.

[0025] In some embodiments, in the electrolyte, the mass ratio of the first solvent to the second solvent is 1:3 to 9:1. Thereby, the electrolyte has high conductivity, suitable viscosity, and low-temperature freezing point.

[0026] In some embodiments, the negative electrode tab comprises a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, the area density of the negative electrode film layer is greater than or equal to 10.5 mg / cm 2 ; and / or the negative electrode film layer comprises a graphite material, the gram capacity of the graphite material is greater than or equal to 355 mAh / g. Thereby, the energy density of the secondary battery is improved.

[0027] In some embodiments, the area density of the negative electrode film layer is 12.0 mg / cm 2 -18.5 mg / cm 2 ; and / or the gram capacity of the graphite material is 362 mAh / g-370 mAh / g. Thereby, the energy density of the secondary battery is improved.

[0028] In some embodiments, the thickness of the negative electrode film layer located on one side of the negative electrode current collector is 70 μm-125 μm. Thereby, the negative electrode tab has high capacity, so that the battery has high energy density.

[0029] In some embodiments, the compaction density of the negative electrode tab is 1.45 g / cm 3 -1.78 g / cm 3 . Thereby, the energy density of the secondary battery is improved.

[0030] In some embodiments, the powder compaction density of the graphite material under a pressure of 50,000 N is greater than or equal to 1.83 g / cc. Thereby, the energy density of the secondary battery is improved.

[0031] In some embodiments, the powder compaction density of the graphite material under a pressure of 50,000 N is 1.93 g / cc-2.05 g / cc. Thereby, the energy density of the secondary battery is improved.

[0032] In some embodiments, the specific surface area of the graphite material is 0.6 m 2 / g-1.4 m 2 / g. Thereby, the cycle performance of the secondary battery is improved

[0033] In some embodiments, the volume distribution particle size Dv50 of the graphite material is 12 μm-22 μm. Thereby, the negative electrode film layer has a high compaction density, and the secondary battery has a high energy density.

[0034] In some embodiments, the positive electrode tab includes a positive electrode current collector and a positive electrode film layer on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a lithium-containing phosphite.

[0035] In some embodiments, the chemical formula of the lithium-containing phosphite includes: Li m A a Fe x D d P y E e O z G g , A includes at least one element of Al, Na, K or Mg; D includes at least one element of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti or V; E includes at least one element of B, S, Si or N; G includes at least one element of S, F, Cl or Br; 0.5≤m≤1.15; 0≤a≤0.1; 0.5≤x≤1; 0≤d≤0.5; 0.5≤y≤1; 0≤e≤0.5; 3.5≤z≤4; 0≤g≤0.5.

[0036] A second aspect of the present disclosure provides a power utilization device including the secondary battery of the first aspect of the present disclosure. Thereby, the power utilization device has at least the advantages of the secondary battery of the present disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0037] FIG. 1 is a schematic view of a secondary battery according to an embodiment of the present disclosure.

[0038] FIG. 2 is an exploded view of the secondary battery according to an embodiment of the present disclosure shown in FIG. 1.

[0039] FIG. 3 is a schematic view of a battery module according to an embodiment of the present disclosure.

[0040] FIG. 4 is a schematic view of a battery pack according to an embodiment of the present disclosure.

[0041] FIG. 5 is an exploded view of the battery pack according to an embodiment of the present disclosure shown in FIG. 4.

[0042] FIG. 6 is a schematic view of a power-using device using a secondary battery as a power source according to an embodiment of the present disclosure.

[0043] BRIEF DESCRIPTION OF DRAWINGS 1: battery pack; 2: upper case; 3: lower case; 4: battery module; 5: secondary battery; 51: case; 52: electrode assembly; 53: top cap assembly DETAILED DESCRIPTION

[0044] Hereinafter, embodiments of the secondary battery and the power-using device according to the present disclosure are specifically disclosed while appropriately referring to the accompanying drawings. However, there are cases where unnecessary detailed explanations are omitted. For example, there are cases where detailed explanations of matters that are already well known, repeated explanations of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following explanations are provided so that those skilled in the art can fully understand the present disclosure, and are not intended to limit the subject matter recited in the claims.

[0045] The "range" disclosed in the present disclosure is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting one lower limit and one upper limit, and the selected lower limit and upper limit define the boundaries of a specific range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also contemplated. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present disclosure, unless otherwise specified, a numerical range "a-b" represents a shorthand manner of describing each and every numerical value that is within the range constituted by "a" and "b", both of which are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, and "0-5" is merely a shorthand manner of describing these numerical combinations. In addition, when it is stated that a certain parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and the like.

[0046] All embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions, if not specifically stated otherwise.

[0047] All technical features and optional technical features of the present disclosure can be combined with each other to form new technical solutions, if not specifically stated otherwise.

[0048] With the rapid development of electric vehicles, people's requirements for the endurance mileage of electric vehicles are increasing, and therefore batteries with higher energy density are needed. However, with the further improvement of the energy density of secondary batteries, the secondary batteries tend to have a large volume change during the charge and discharge cycle process, causing the destruction of the electrode structure, the pulverization of the particles, the increase of the internal resistance, and the like. In the cycle process, an unstable SEI film or CEI film is formed on the surface of the electrode, and the continuous growth and rupture of these interface films consume the electrolyte and the electrode material, leading to further increase of the internal resistance of the battery, and all the above will affect the cycle performance of the secondary battery. At present, the secondary battery usually adopts a graphite material with high gram capacity and / or increases the area density of the negative electrode film layer to realize high energy density. However, the negative active material with high gram capacity is prone to swelling during the cycle process, which destroys the SEI film and consumes active ions, thereby leading to rapid capacity decay and cycle performance deterioration of the secondary battery. On the other hand, when a high area density negative electrode sheet is used, the thickness of the negative electrode sheet increases, which makes the transmission path of lithium ions in the sheet long, and will lead to the deterioration of the sheet kinetics, and further adversely affect the cycle performance of the battery. Therefore, how to improve the cycle performance of the battery while having high energy density has gradually become a research hotspot in the field of batteries.

[0049] Based on this, the present disclosure provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the conductivity of the electrolyte is 14 mS / cm-22 mS / cm, and the electrolyte comprises a first additive, the first additive comprises at least one of the compounds represented by formula I and formula II,

[0050] In the formula, R1 is selected from H, a fluorine atom, a fluorine-substituted or unsubstituted C1-C12 alkyl group, a fluorine-substituted or unsubstituted C2-C10 alkenyl group;

[0051] In the formula, R2, R3, R4 and R5 are each independently selected from a hydrogen atom, a fluorine atom, a fluorine-substituted or unsubstituted C1-C6 alkyl group, a fluorine-substituted or unsubstituted C1-C6 alkoxy group, a C2-C6 alkenyl group or a C2-C6 alkynyl group, and R2, R3, R4 and R5 are not hydrogen atoms at the same time.

[0052] With the increase of the areal density of the negative electrode sheet, the mass of the negative electrode film layer under the same unit area increases, resulting in the increase of the thickness of the negative electrode sheet, making the transmission path of lithium ions in the electrode sheet long, leading to the deterioration of the electrode kinetics, and further adversely affecting the cycle performance of the battery. By making the conductivity of the electrolyte 14-22 mS / cm, the transmission rate of active ions can be improved by increasing the conductivity of the electrolyte, reducing the influence of the increase of the areal density of the negative electrode sheet on the transmission of active ions, and also helping to reduce the concentration polarization in the secondary battery, inhibit the lithium precipitation at the negative electrode interface, and thus improve the cycle performance of the secondary battery. Exemplarily, the conductivity of the electrolyte can be 14 mS / cm, 16 mS / cm, 18 mS / cm, 20 mS / cm, 22 mS / cm, or a value between any two of them. In some alternative embodiments, the conductivity of the electrolyte is 14-19 mS / cm.

[0053] On the other hand, with the use of high-capacity graphite materials, high-capacity graphite materials are more prone to swelling, making the secondary battery more prone to swelling during the cycle process, leading to the destruction of the SEI film, the consumption of active ions, and thus the rapid decay of the capacity of the secondary battery and the deterioration of the cycle performance. In the present disclosure, by adding the above-mentioned first additive to the electrolyte, a reticular cross-linked (with a certain flexibility) interface film (SEI film) can be formed at the negative electrode interface, which can inhibit the swelling of the graphite material and reduce the cycle decay caused thereby, thereby improving the cycle performance of the secondary battery.

[0054] Although the mechanism is not clear, the inventors have found that for secondary batteries with high energy density, the use of electrolyte with conductivity in the range of 14-22 mS / cm, while introducing the first additive of the present disclosure, can improve the transmission rate of active ions in the electrolyte, while inhibiting the swelling of the negative active material, and through the synergistic effect of high-conductivity electrolyte and the first additive, the cycle stability of the secondary battery is significantly improved; thus, the secondary battery can balance high energy density and good cycle performance.

[0055] In the present disclosure, the term "C1-C12 alkyl" refers to a group formed by removing one hydrogen atom from a straight-chain or branched-chain alkane molecule with 1-12 carbon atoms, for example including but not limited to methyl, ethyl, propyl, n-butyl, isobutyl, sec-butyl and tert-butyl, n-pentyl, isopentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, etc. "C1-C6 alkyl" refers to a group formed by removing one hydrogen atom from a straight-chain or branched-chain alkane molecule with 1-6 carbon atoms, for example including but not limited to methyl, ethyl, propyl, n-butyl, isobutyl, sec-butyl and tert-butyl, n-pentyl, isopentyl, neopentyl, hexyl, etc.

[0056] In the present disclosure, the term "fluorine-substituted C1-C12 alkyl" refers to a group formed by substituting part or all of the hydrogen atoms in the above-described C1-C12 alkyl with the above-described fluorine atom, and includes, for example, but is not limited to, fluoromethyl, fluoroethyl, fluoropropyl, fluorobutyl, fluoropentyl, fluorohexyl, fluoropropyl, fluoropentyl, fluorohexyl, fluoropropyl, fluoropentyl, fluorohexyl, fluoropropyl, fluoropentyl, fluorohexyl, fluoropropyl, fluoropentyl, fluorohexyl, and the like.

[0057] In the present disclosure, the term "C2-C10 alkenyl" refers to a group formed by removing one hydrogen atom from a straight-chain or branched-chain alkene having 2 to 10 carbon atoms and having at least one carbon-carbon double bond, and includes, for example, but is not limited to, ethenyl, propenyl, butenyl, pentenyl, 1,3-pentadienyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, and the like. "C2-C6 alkenyl" refers to a group formed by removing one hydrogen atom from a straight-chain or branched-chain alkene having 2 to 6 carbon atoms and having at least one carbon-carbon double bond, and includes, for example, ethenyl, propenyl, butenyl, pentenyl, 1,3-pentadienyl, hexenyl.

[0058] In the present disclosure, the term "fluorine-substituted C2-C10 alkenyl" refers to a group formed by substituting part or all of the hydrogen atoms in the above-described C2-C10 alkenyl with the above-described fluorine atom, and includes, for example, but is not limited to, fluorinated ethenyl, fluorinated propenyl, fluorinated butenyl, fluorinated pentenyl, fluorinated pentadienyl, fluorinated hexenyl, fluorinated heptenyl, fluorinated octenyl, fluorinated nonenyl, fluorinated decenyl, and the like.

[0059] In the present disclosure, the term "C1-C6 alkoxy" refers to a group formed by an alkyl group having 1 to 6 carbon atoms and one oxygen atom, and includes, for example, but is not limited to, methoxy, ethoxy, propoxy, pentoxy, hexyloxy, heptyloxy, and the like.

[0060] In the present disclosure, the term "C2-C6 alkynyl" refers to a group formed by removing one hydrogen atom from an alkyne having 2 to 6 carbon atoms and having at least one carbon-carbon triple bond, and includes, for example, but is not limited to, ethynyl, propynyl, butynyl, pentynyl, hexynyl, and the like.

[0061] In some embodiments, in Formula I, R1 is selected from the group consisting of a hydrogen atom, a fluorine atom, a fluorine-substituted or unsubstituted C1-C6 alkyl group, a fluorine-substituted or unsubstituted C2-C6 alkenyl group; and / or, in Formula II, R2, R3, R4, and R5 are each independently selected from the group consisting of a hydrogen atom, a fluorine atom, a fluorine-substituted or unsubstituted C1-C4 alkyl group, a fluorine-substituted or unsubstituted C1-C4 alkoxy group, a C2-C4 alkenyl group, or a C2-C4 alkynyl group, and R2, R3, R4, and R5 are not simultaneously a hydrogen atom.

[0062] In some embodiments, the first additive includes at least one of fluoroethylene carbonate, vinylene carbonate.

[0063] In some embodiments, the first additive has a mass content of 0.01% to 5% in the electrolyte. By having the mass content of the first additive in the above range, it is beneficial to form an SEI rich in organic components on the surface of the negative electrode, which can alleviate the volume expansion and shrinkage of high-capacity graphite during charge and discharge, and reduce the destruction of the SEI caused by the expansion and shrinkage. Illustratively, the mass content of the first additive is 0.01%, 0.05%, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 4.0%, 5.0%, or a value between any two of them. In some alternatives, the mass content of the first additive in the electrolyte is 0.5% to 5%.

[0064] In some embodiments, the electrolyte includes a first solvent, and the first solvent includes a compound represented by Formula III,

[0065] In Formula III, R 11 selected from a hydrogen atom, a fluorine-substituted or unsubstituted C1-C4 alkyl group, R 12 selected from a fluorine-substituted or unsubstituted C1-C4 alkyl group. In the present disclosure, by using a carboxylic acid ester solvent represented by Formula III, the conductivity of the electrolyte can be significantly improved, and the viscosity of the electrolyte can be reduced. Thus, it is beneficial to improve the active ion diffusion capacity, reduce the concentration polarization in the secondary battery, improve the cycle performance of the secondary battery, and in addition, it is possible to improve the transport efficiency of the active ion in the electrode sheet, thereby further improving the cycle performance of the secondary battery.

[0066] Here, C1-C4 alkyl refers to a group formed by removing one hydrogen atom from a straight-chain or branched alkane molecule having 1-4 carbon atoms, for example, including but not limited to methyl, ethyl, propyl, n-butyl, isobutyl, sec-butyl, and t-butyl, etc.

[0067] Fluorine-substituted C1-C4 alkyl refers to a group formed by substituting at least one hydrogen atom in the above C1-C4 alkyl group with a fluorine atom, for example, including but not limited to fluoromethyl, fluoroethyl, fluoropropyl, fluorobutyl.

[0068] In some embodiments, the first solvent is selected from one or more of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate. Alternatively, the first solvent includes ethyl formate, methyl acetate, ethyl acetate, ethyl propionate.

[0069] In some embodiments, the mass content of the first solvent in the electrolyte is 20-80%. Thereby, it is beneficial to make the electrolyte have a higher electrical conductivity and a lower viscosity. Illustratively, the mass content of the first solvent is 20%, 30%, 40%, 50%, 60%, 70%, 80% or a value between any two of them. In some alternative embodiments, the mass content of the first solvent in the electrolyte is 30-70%.

[0070] In some embodiments, the electrolyte of the present disclosure further comprises a second additive, the second additive comprising at least one of compounds of Formula IV and Formula V,

[0071] In Formula IV, R a , R b each independently represents H, or R a and R b form a structure of , R g represents a fluorine atom, a fluorine-substituted or unsubstituted C1-C6 alkyl group, a C1-C6 alkoxy group or

[0072] In Formula V, R c , R d , R e , R f each independently represents H or a fluorine atom.

[0073] In the present disclosure, by adding the above-mentioned second additive in the electrolyte, a dense SEI film can be formed at the negative electrode interface, having a good passivation effect, improving the stability of the negative electrode interface, thereby inhibiting the reduction of carboxylic acid ester solvents on the negative electrode, further improving the cycle performance of the secondary battery.

[0074] In some alternative embodiments, the second additive comprises one or more of vinyl sulfate (DTD), bis vinyl sulfate (bis-DTD), (D-mannitol trithionate, tri-DTD), .

[0075] Here, C1-C6 alkyl group, C1-C6 alkoxy group have the same definition as described above.

[0076] For the compound of Formula IV, for example, but not limited to, the following compounds are included:

[0077] (bis-DTD), (3DTD), etc.

[0078] For compounds of formula V, for example, they include: wait.

[0079] In some embodiments, the mass ratio of the first solvent to the second additive in the electrolyte is between 2200:1 and 10:1. By keeping the mass ratio of the first solvent to the second additive within this range, the electrolyte can have high conductivity, meeting the requirements of high compaction density and thick electrodes for high liquid-phase lithium-ion transport capacity. Simultaneously, the second additive can form a dense protective film at the negative electrode interface, suppressing side reactions caused by the first solvent crossing the interface and maintaining good stability at the negative electrode interface. For example, the mass ratio of the first solvent to the second additive in the electrolyte can be 2200:1, 1000:1, 500:1, 200:1, 50:1, 10:1, or a value within a range consisting of any two of these values.

[0080] In some embodiments, the mass content of the second additive in the electrolyte is 0.01%-2%. By keeping the mass content of the second additive within the above range, the second additive can form a dense SEI film on the negative electrode surface during formation, which has a very good passivation effect, can suppress the first solvent from crossing the interfacial film and causing side reactions at the negative electrode, and improve the cycle performance of the battery. Exemplarily, the mass content of the second additive in the electrolyte can be 0.01%, 0.05%, 0.1%, 0.3%, 0.5%, 0.7%, 1.0%, 1.5%, 2.0%, or a value within a range of any two of these values. In some optional embodiments, the mass content of the second additive can be 0.1%-2%.

[0081] In some embodiments, the electrolyte further comprises a second solvent, the second solvent comprising at least one selected from ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate. In some embodiments, the mass ratio of the first solvent to the second solvent in the electrolyte is 1:3-9:1. The above-mentioned cyclic esters such as ethylene carbonate, propylene carbonate, butylene carbonate, etc. have high dielectric constant, which can dissociate lithium ions in the electrolyte, thereby facilitating the secondary battery to have more movable lithium ions, so as to realize high ionic conductivity; the above-mentioned linear esters such as dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, etc. can adjust the viscosity of the electrolyte on the one hand, and can adjust the low-temperature freezing point of the electrolyte on the other hand, thereby facilitating the electrolyte to have balanced performance. Exemplarily, the mass ratio of the first solvent to the second solvent can be 1:3, 2:3; 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or a value between any two of them.

[0082] In some embodiments, the negative electrode tab comprises a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, the negative electrode film layer has an area density greater than or equal to 10.5 mg / cm 2 , and / or the negative electrode film layer comprises a graphite material, the graphite material has a gram capacity greater than or equal to 355 mAh / g. In the present disclosure, the term "area density" refers to the mass of the negative electrode film layer per unit area. By making the area density of the negative electrode film layer greater than or equal to 10.5 mg / cm 2 , and making the gram capacity of the graphite material greater than or equal to 355 mAh / g, by increasing the area density of the negative electrode film layer, the mass of the negative electrode film layer is increased, while the gram capacity of the graphite material is improved, the combined effect of the two is conducive to improving the energy density of the secondary battery. Exemplarily, the area density of the negative electrode film layer can be 10.5 mg / cm 2 , 11 mg / cm 2 , 11.5 mg / cm 2 , 12 mg / cm 2 , 12.5 mg / cm 2 , 13 mg / cm 2 , 13.5 mg / cm 2 , 14 mg / cm 2 , 14.5 mg / cm 2 , 15 mg / cm 2 , 15.5 mg / cm 2 , 16 mg / cm 2 , 16.5 mg / cm 2 , 17 mg / cm 2 , 17.5 mg / cm 2 , 18 mg / cm 2, 18.5 mg / cm 2 or a range between any two of these values. In some alternative embodiments, the face density of the negative electrode film layer is 12.0-18.5 mg / cm 2 . Illustratively, the graphite material can have a gravimetric capacity of 355 mAh / g, 357 mAh / g, 359 mAh / g, 360 mAh / g, 361 mAh / g, 362 mAh / g, 363 mAh / g, 365 mAh / g, 370 mAh / g, or a range between any two of these values. In some alternative embodiments, the graphite material has a gravimetric capacity of 362 mAh / g-370 mAh / g.

[0083] In some embodiments, the negative electrode film layer can be disposed on one side surface or both side surfaces of the negative electrode current collector. The thickness of the negative electrode film layer on one side of the negative electrode current collector is 70 μm-125 μm. By having the thickness in the above range, the negative electrode sheet has a high capacity, and thus the secondary battery has a high energy density.

[0084] In some embodiments, the negative electrode sheet has a compacted density of 1.45 g / cm 3 - 1.78 g / cm 3 . Illustratively, the negative electrode sheet has a compacted density of 1.45 g / cm 3 , 1.5 g / cm 3 , 1.55 g / cm 3 , 1.60 g / cm 3 , 1.65 g / cm 3 , 1.70 g / cm 3 , 1.75 g / cm 3 , 1.78 g / cm 3 , or a range between any two of these values. By having the compacted density in the above range, the energy density of the battery is improved.

[0085] In some embodiments, the graphite material has a powder compaction density under 50000N pressure of greater than or equal to 1.83 g / cc. By having the powder compaction density of the graphite material in the above range, it is beneficial to increase the gravimetric capacity of the negative electrode sheet, and thus to increase the energy density of the secondary battery. Illustratively, the graphite material has a powder compaction density under 50000N pressure of 1.83 g / cc, 1.85 g / cc, 1.87 g / cc, 1.90 g / cc, 1.93 g / cc, 1.95 g / cc, 1.97 g / cc, 1.99 g / cc, 2.01 g / cc, 2.03 g / cc, 2.05 g / cc, or a value between any two of them. In some alternative embodiments, the graphite material has a powder compaction density under 50000N pressure of 1.93 g / cc-2.05 g / cc.

[0086] In some embodiments, the graphite material has a specific surface area of 0.6 m 2 / g-1.4 m 2 / g. By having the specific surface area of the graphite material in the above range, it is beneficial to reduce the occurrence of surface side reactions, and thus to reduce the consumption of active ions, further improving the cycle performance of the secondary battery. Illustratively, the graphite material has a specific surface area of 0.6 m 2 / g, 0.8 m 2 / g, 1.0 m 2 / g, 1.2 m 2 / g, 1.4 m 2 / g, or a value between any two of them.

[0087] In some embodiments, the graphite material has a volume distribution particle size Dv50 of 12 μm-22 μm. By having the volume distribution particle size Dv50 of the graphite material in the above range, it is beneficial for the negative electrode film layer to have a high compaction density, and thus for the secondary battery to have a high energy density. Illustratively, the graphite material has a volume distribution particle size Dv50 of 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 22 μm, or a value between any two of them.

[0088] In the present disclosure, the graphite material can be prepared by the following method.

[0089] Step 1: crush and shape the needle coke raw material (carbon content greater than 93.0%, volatile content less than 6.5%, sulfur element content less than 1.0%) to obtain a shaped material with a Dv50 of 9-13 μm;

[0090] Step 2: granulate the above shaped material together using a granulator to obtain a granulated material.

[0091] Step 3: Pre-carbonize the granulating agent at 1000-1500°C under nitrogen atmosphere to obtain an intermediate.

[0092] Step 4: Graphitize the intermediate at 3000-3200°C to obtain artificial graphite.

[0093] In some embodiments, the softening point of the granulating agent is 180-270°C. The softening point of the granulating agent refers to the temperature at which the granulating agent changes from solid state to softening state with certain fluidity. In the present disclosure, the softening point can be tested by using instruments and methods known in the art, for example, it can be determined according to GB / T 4507-2014. When the softening point of the granulating agent is within the above range, the molecular weight of the condensed polycyclic aromatic hydrocarbon in the granulating agent is large and the content is high, which is conducive to improving the cohesiveness of the granulating agent, reducing the amount of the granulating agent used in the granulating step, reducing the residual carbon content of the granulating agent, and thus improving the gram capacity and the compaction density of the artificial graphite. Illustratively, the softening point of the granulating agent can be 180°C, 200°C, 220°C, 240°C, 260°C, 270°C, or a value between any two of the above values.

[0094] In some embodiments, the coking value of the granulating agent is 50%-70%. The coking value of the granulating agent refers to the percentage of the mass of the coke residue formed after the granulating agent is heated, burned or otherwise treated under specific experimental conditions to the mass of the original sample. In the present disclosure, the coking value can be tested by using methods known in the art. Illustratively, it can be determined according to GB / T 8727-2008. When the coking value of the granulating agent is within the above range, it is conducive to improving the gram capacity and the compaction density of the artificial graphite, and thus improving the energy density of the secondary battery.

[0095] In some embodiments, the mass ratio of the shaping agent to the granulating agent is 100:(6-12). When the ratio of the shaping agent to the granulating agent is within the above range, it is conducive to reducing the amount of residual carbon brought by the granulating agent, improving the gram capacity and the compaction density of the artificial graphite, and thus improving the energy density of the secondary battery.

[0096] In some embodiments, the negative current collector can be a metal foil or a composite current collector. For example, as a metal foil, a copper foil can be used. The composite current collector can include a high molecular material base layer and a metal layer formed on at least one surface of the high molecular material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a high molecular material base layer (such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0097] In some embodiments, the negative electrode film layer further optionally comprises a binder. The binder can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0098] In some embodiments, the negative electrode film layer further optionally comprises a conductive agent. The conductive agent can be selected from at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0099] In some embodiments, the negative electrode film layer further optionally comprises other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0100] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, and after processes such as drying, cold pressing, and the like, the negative electrode sheet can be obtained.

[0101] In some embodiments, the electrolyte further comprises an electrolyte salt.

[0102] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bistrifluoromethylsulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoroboric oxalate, lithium difluorophosphoric oxalate, and lithium tetrafluorophosphoric oxalate.

[0103] In the present disclosure, the area density of the negative electrode film layer can be determined by the following method: after disassembling the secondary battery to obtain the negative electrode sheet, 15 pieces of the negative electrode sheet and current collector (of the same production batch number as the negative electrode sheet) of a certain area S (unit cm 2 ) are punched, the mass is weighed, and the average value is calculated. The average value of the mass of the negative electrode sheet is M1 (unit mg), and the average value of the mass of the current collector is M2 (unit mg); when the active material layer is arranged on one side of the current collector, the area density is (M1-M2) / S, and when the active material layer is arranged on both sides of the current collector, the area density is (M1-M2) / 2S.

[0104] In the present disclosure, the thickness of the negative electrode film layer is in the meaning known in the art and can be tested by methods known in the art. For example, after disassembling the secondary battery, the negative electrode tab is obtained, and the thickness of the negative electrode film layer is measured by using a micrometer (for example, Mitutoyo 293-100, accuracy of 0.1 μm). The thickness range given in the present disclosure is the thickness range of the negative electrode film layer on one side of the negative electrode current collector.

[0105] In the present disclosure, the compaction density of the negative electrode film layer is in the meaning known in the art and can be tested by methods known in the art. For example, after disassembling the battery according to the method as above, the area density and thickness of the negative electrode film layer are obtained, and the compaction density of the negative electrode film layer is calculated according to the following formula: compaction density of the negative electrode film layer = area density of the negative electrode film layer / thickness of the negative electrode film layer.

[0106] In the present disclosure, the electrical conductivity of the material is in the meaning known in the art and can be tested by methods known in the art. An exemplary testing method is as follows: using a Mettler S700-K conductivity meter, testing is performed based on the testing standard specified in HG / T 4067-2015.

[0107] In the present disclosure, the gram capacity of the material is in the meaning known in the art and can be tested by methods known in the art. An exemplary testing method is as follows: sample powder, conductive agent, binder and optional other additives are mixed with a solvent in a certain mass ratio to obtain a slurry; the prepared slurry is coated on the surface of a negative electrode current collector copper foil, dried in an oven and reserved; an electrolyte is prepared by dissolving an electrolytic salt in an organic solvent to a certain concentration; then a CR2430 type button cell is assembled in an argon glove box with a lithium metal sheet as a counter electrode and a polyethylene (PE) film as a separator film. At 25°C, the button cell prepared as above is first discharged at a current of 0.15 mA to 0.005 V, left for 5 minutes, then discharged at a current of 10 μA to 0.005 V, and the first circle discharge capacity of the button cell is recorded; then the button cell is charged at a current of 0.3 mA to 2.0 V, and the first circle charge capacity is recorded, and the ratio of the charge capacity to the mass of the sample is the gram capacity of the material.

[0108] In the present disclosure, the powder compaction density of the material is in the meaning known in the art and can be determined by instruments and methods known in the art. For example, it can be determined by referring to GB / T 24533-2009 through an electronic pressure testing machine (for example, UTM7305 type electronic pressure testing machine). An exemplary testing method is as follows: 1 g of sample powder is weighed and added into a mold with a bottom area of 1.327 cm 2 , and pressed to 50000 N, kept for 30 s, then unloaded, kept for 10 s, and then the powder compaction density of the material under a pressure of 50000 N is recorded and calculated.

[0109] In the present disclosure, the volume distribution particle size Dv50 of a material is the meaning well known in the art, which represents the particle size corresponding to the cumulative volume distribution percentage reaching 50%, and can be measured by instruments and methods known in the art. For example, GB / T 19077-2016 can be referred to, and a laser particle size analyzer can be used for measurement. The testing instrument can be a Mastersizer 3000 laser particle size analyzer of Malvern Instruments Ltd., UK.

[0110] In the present disclosure, the specific surface area of a material is the meaning well known in the art, and can be measured by instruments and methods known in the art. For example, GB / T 19587-2017 can be referred to, and a nitrogen adsorption specific surface area analysis test method can be used for measurement, and the BET (Brunauer Emmett Teller) method can be used for calculation. The testing instrument can be a Tri-Star 3020 specific surface area and pore size analysis tester of Micromeritics, USA.

[0111] Positive electrode tab

[0112] In some embodiments, the positive electrode tab includes a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material. There is no particular limitation on the positive electrode active material, and a positive electrode active material known in the art for a secondary battery can be used. As an example, the positive electrode active material can include at least one of a lithium-containing phosphate of olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present disclosure is not limited to these materials, and other conventional materials that can be used as a battery positive electrode active material can also be used. These positive electrode active materials can be used alone only one or two or more can be used in combination.

[0113] In some embodiments, the positive electrode active material includes a lithium-containing phosphate.

[0114] In some embodiments, the chemical formula of the lithium-containing phosphate includes Li m A a Fe x D d P y E e O z G gA includes at least one element of Al, Na, K, or Mg; D includes at least one element of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti, or V; E includes at least one element of B, S, Si, or N; G includes at least one element of S, F, Cl, or Br; 0.5

[0115] In some embodiments, the positive active material includes lithium iron phosphate. When the positive electrode film layer includes lithium iron phosphate as the positive active material, since the charge cut-off voltage of the lithium iron phosphate positive material is low, less than or equal to 3.8 V, the electrochemical oxidation potential of the first additive is higher than 3.8 V, and thus it is stable on the surface of the lithium iron phosphate positive electrode and no side reaction occurs, which is conducive to reducing the capacity decay caused by the positive electrode interface side reaction.

[0116] As an example, the positive current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode film layer is disposed on either one or both of the two opposite surfaces of the positive current collector.

[0117] In some embodiments, the positive current collector can adopt a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be adopted. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0118] In some embodiments, the positive electrode film layer can also optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0119] In some embodiments, the positive electrode film layer can also optionally include a conductive agent. As an example, the conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0120] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector, and then drying, cold-pressing and the like to obtain the positive electrode sheet.

[0121] Separating film

[0122] In some embodiments, the secondary battery further comprises a separating film. The type of the separating film is not particularly limited in the present disclosure, and any known porous structure separating film having good chemical stability and mechanical stability can be selected.

[0123] In some embodiments, the material of the separating film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separating film can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separating film is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

[0124] In some embodiments, the positive electrode sheet, the negative electrode sheet and the separating film can be formed into an electrode assembly by a winding process or a stacking process.

[0125] In some embodiments, the secondary battery can comprise an outer package. The outer package can be used to package the above-mentioned electrode assembly and electrolyte.

[0126] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate and polybutylene succinate, etc. can be listed.

[0127] The shape of the secondary battery is not particularly limited in the present disclosure, and it can be cylindrical, square or any other shape. For example, FIG. 1 is a secondary battery 5 of a square structure as an example.

[0128] In some embodiments, referring to FIG. 2, the outer package can comprise a shell 51 and a cover plate 53. The shell 51 can comprise a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be arranged on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separating film can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of the electrode assembly 52 contained in the secondary battery 5 can be one or more, which can be selected by those skilled in the art according to the specific actual needs.

[0129] In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0130] FIG. 3 is a battery module 4 as an example. Referring to FIG. 3, in the battery module 4, a plurality of secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements can also be made. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

[0131] Optionally, the battery module 4 can further include a housing having an accommodation space, and the plurality of secondary batteries 5 can be accommodated in the accommodation space.

[0132] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0133] FIGS. 4 and 5 are a battery pack 1 as an example. Referring to FIGS. 4 and 5, the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be arranged on the lower box body 3 to form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0134] In addition, the present disclosure also provides a power utilization device including at least one of the secondary battery, the battery module, or the battery pack provided by the present disclosure. The secondary battery, the battery module, or the battery pack can be used as a power source of the power utilization device, or can be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0135] As the power utilization device, the secondary battery, the battery module, or the battery pack can be selected according to the use requirements thereof.

[0136] FIG. 6 is a power utilization device as an example. The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the secondary battery for the power utilization device, a battery pack or a battery module can be used.

[0137] As another example of the device, it can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and a secondary battery can be used as a power source.

[0138] Examples

[0139] Hereinafter, the embodiments of the present disclosure will be described. The embodiments described below are exemplary and are for the purpose of explaining the present disclosure only and are not to be understood as limiting the present disclosure. In the embodiments, the specific techniques or conditions not mentioned are performed in accordance with the techniques or conditions described in the literature in the field or in accordance with the product manual. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be obtained commercially.

[0140] Preparation of electrolyte

[0141] Electrolyte 1-1

[0142] In an argon atmosphere glove box with a water content < 10 ppm, first, the second solvent ethylene carbonate (EC) and the first solvent ethyl acetate (EA) were mixed in the amounts shown in Table 1 to prepare an organic solvent mixture, then the fully dried lithium salt LiPF6 was dissolved in the above organic solvent mixture, and then the first additive vinylene carbonate and the second additive divinyl sulfite (bis-DTD) were added and mixed uniformly to obtain the electrolyte shown in Table 1. Among them, the concentration of lithium salt was 1 mol / L.

[0143] The electrolyte prepared above was tested for conductivity, and the measured conductivity was ~ 15.0 mS / cm.

[0144] Conductivity test

[0145] The conductivity of the electrolyte was tested using a Mettler S700-K conductivity meter based on the test standard specified in the HG / T4067-2015 standard, and the test error was ± 0.4 mS / cm.

[0146] Electrolytes 1-2 to 1-23

[0147] The preparation method of electrolytes 1-2 to 1-23 was similar to that of electrolyte 1-1, except that the types and amounts of the first additive, the second additive, the first solvent, and the second solvent were adjusted as shown in Table 1.

[0148] Electrolyte 1-1’

[0149] The preparation method of electrolyte 1-1’ was similar to that of electrolyte 1-1, except that the conductivity of the electrolyte was less than 14 mS / cm by adjusting the solvent.

[0150] Electrolyte 1-2’

[0151] The preparation method of electrolyte 1-2’ was similar to that of electrolyte 1-1, except that no first additive was added, and the amounts of the second additive, the first solvent, and the second solvent were adjusted.

[0152] Table 1: Electrolyte formulation

[0153] Preparation of negative electrode sheet

[0154] Negative electrode sheet 2-1

[0155] (1) Preparation of graphite

[0156] Step 1: The calcined needle coke raw material (carbon content of 98.5%, volatile content of 1.0%, sulfur element content of 0.5%) was mechanically ground and shaped to obtain shaped material with Dv50 of 11 μm.

[0157] Step 2: The above shaped material was granulated together with granulating pitch (softening point of 200°C; coking value of 60%) as a granulating agent in a granulating kettle, to obtain granulated material, wherein the mass ratio of the shaped material and the granulating agent was 100:8.

[0158] Step 3: The above granulated material was pre-carbonized at 1150°C for 2h under a nitrogen atmosphere to obtain an intermediate.

[0159] Step 4: The above intermediate was graphitized at a high temperature of 3200°C, and the graphitized granules were screened and demagnetized to obtain artificial graphite.

[0160] (2) Preparation of negative electrode sheet

[0161] The above artificial graphite, conductive agent Super P, thickening agent sodium carboxymethyl cellulose, and binder styrene-butadiene rubber were mixed in a weight ratio of 96.6:0.80:1.0:1.6 in an appropriate amount of solvent deionized water to form a negative electrode slurry. The negative electrode slurry was coated on both sides of the negative electrode current collector copper foil by extrusion coating, and after drying and cold pressing, a negative electrode film layer was formed on both sides of the negative electrode current collector, with a thickness of 90 μm for a single negative electrode film layer, thereby obtaining a negative electrode sheet.

[0162] Negative electrode sheets 2-2 to 2-4

[0163] The conditions in the preparation steps of the graphite were adjusted according to the values in Table 2 below, and other conditions were the same as above, to obtain negative electrode sheets 2-2 to 2-4.

[0164] Test of specific capacity of graphite:

[0165] The prepared material, conductive agent carbon black (Super P) and binder polyvinylidene fluoride (PVDF) were mixed uniformly in a mass ratio of 91.6:1.8:6.6 with a solvent N-methyl pyrrolidone (NMP) to prepare a slurry; the prepared slurry was coated on the surface of a negative electrode current collector copper foil, dried in an oven and reserved; ethylene carbonate (EC), methyl ethyl carbonate (EMC) and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent, then LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L; then a metal lithium sheet was used as a counter electrode, a polyethylene (PE) film was used as a separator film, and the above electrolyte was assembled into a CR2430 type button cell in an argon glove box; the obtained button cell was left for 12 h.

[0166] At 25°C, the prepared button cell was first discharged at a current of 0.15 mA to 0.005 V, left for 5 min, then discharged at a current of 10 μA to 0.005 V, and the first circle discharge capacity of the button cell was recorded; then the button cell was charged at a current of 0.3 mA to 2.0 V, and the first circle charge capacity of the button cell was recorded, and the ratio of the charge capacity to the sample mass was the gram capacity of the material.

[0167] Test of powder compaction density

[0168] According to GB / T 24533-2009, the test was performed by an electronic pressure testing machine (UTM7305 type electronic pressure testing machine). Specifically, 1 g of sample powder was weighed and added to a mold with a bottom area of 1.327 cm 2 , pressurized to 50,000 N, kept for 30 s, then released, kept for 10 s, then recorded and calculated to obtain the powder compaction density of the material under a pressure of 50,000 N.

[0169] Test of surface density and thickness of the prepared negative electrode film layer

[0170] The prepared negative electrode sheet after cold pressing was tested by the following method: 15 pieces of negative electrode sheet and current collector (with the same production batch number as the negative electrode sheet) with a certain area S (unit: cm 2 ) were punched out, weighed, and the average value was calculated. The average value of the mass of the negative electrode sheet was M1 (unit: mg), and the average value of the mass of the current collector was M2 (unit: mg); when the active material layer was arranged on both sides of the current collector, the surface density was (M1-M2) / 2S.

[0171] The thickness H1 of the negative electrode sheet was measured using a Mitutoyo 293-100 micrometer (precision: 0.1 μm) after the negative electrode active material on one side of the negative electrode sheet prepared after cold pressing was wiped off, and then the thickness H2 of the negative electrode current collector was measured after all the negative electrode active material was wiped off. The thickness of the single layer of the negative electrode film layer was (H1-H2).

[0172] Table 2:

[0173] Example 1

[0174] 1. Preparation of the positive electrode sheet

[0175] Lithium iron phosphate, conductive agent carbon black (Super P), and binder polyvinylidene fluoride were mixed in a weight ratio of 96:2:2, and an appropriate amount of solvent NMP was added, and the mixture was stirred uniformly to obtain a positive electrode slurry. The positive electrode slurry was coated on both surfaces of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained.

[0176] 2. Isolation film

[0177] A polyethylene film was used as the isolation film, which was treated with a 1.5 mg adhesive layer (PVDF as the adhesive) on both sides and a 1 μm heat-resistant layer (a commonly used heat-resistant layer formula in the art, with aluminum oxide as the heat-resistant particles) on one side.

[0178] 3. Preparation of the battery

[0179] The positive electrode sheet and the negative electrode sheet prepared above were placed in order with the isolation film in the middle of the positive electrode sheet and the negative electrode sheet to play a role of isolation, and then wound to obtain an electrode assembly; the electrode assembly was placed in an outer package, dried, and then electrolyte was injected, and after processes such as vacuum packaging, standing, formation, and shaping, a secondary battery was obtained.

[0180] The secondary battery prepared above was tested for performance according to the following method. The test results are shown in Table 3 below.

[0181] (1) Energy density test of the secondary battery

[0182] At 25°C, the secondary battery was charged at a current of 1 / 3 C to 3.65 V, and then charged at a constant voltage of 3.65 V until the current was 0.05 C, and then discharged at a current of 1 / 3 C to 2.5 V, and the discharge energy of the battery at this time was recorded. The weight energy density of the battery was obtained by dividing the battery discharge energy by the weight of the battery, and the unit was Wh / kg.

[0183] (2) Cycle performance test of the secondary battery

[0184] The secondary battery was charged at a current of 1 / 3 C to a voltage of 3.65 V at 45°C, and then charged at a voltage of 3.65 V to a current of 0.05 C, and after standing for 5 min, the battery was discharged at a current of 1 / 3 C to a voltage of 2.0 V, which was one charge-discharge cycle process, and the discharge capacity of this time was the discharge capacity C1 of the first cycle. After the cycle charge-discharge test was carried out according to the above method, until the discharge capacity decayed to 80% of the initial value C1, the cycle was ended, and the cycle number when the capacity decayed to 80% was recorded as the "80% SOH cycle number".

[0185] The greater the 80% SOH cycle number, the better the cycle performance of the battery cell and the longer the cycle life.

[0186] (3) Test method for thickness and surface density of negative electrode film layer in secondary battery:

[0187] After the above tested secondary battery was completely discharged, the negative electrode sheet was obtained, and the surface density and thickness of the negative electrode film layer were tested according to the following method. The test results are shown in Table 3.

[0188] The thickness H1 of the negative electrode sheet was measured by using a Mitutoyo 293-100 micrometer with an accuracy of 0.1 μm after the secondary battery was disassembled. The thickness H2 of the negative electrode current collector was measured by using a micrometer after the negative electrode film layer on the negative electrode sheet was removed. The single-layer thickness of the negative electrode film layer was (H1-H2).

[0189] The negative electrode sheet was obtained after the secondary battery was disassembled, and 15 pieces of negative electrode sheet and current collector (with the same production batch number as the negative electrode sheet) with a certain area S (unit cm 2 ) were punched out, and the mass was weighed to obtain the average value. The average mass of the negative electrode sheet was M1 (unit mg), and the average mass of the current collector was M2 (unit mg). When the active material layer was arranged on one side of the current collector, the surface density was (M1-M2) / S, and when the active material layer was arranged on both sides of the current collector, the surface density was (M1-M2) / 2S.

[0190] Example 2-26

[0191] The preparation method of Example 2-26 was similar to that of Example 1, except that the type of electrolyte was adjusted according to the parameters in Table 3.

[0192] Comparative Example 1

[0193] The preparation method of Comparative Example 1 was similar to that of Example 1, except that the negative electrode sheet 2-2 and the electrolyte 1-1' were used.

[0194] Comparative Example 2

[0195] The preparation method of Comparative Example 2 was similar to that of Example 1, except that the negative electrode sheet 2-2 and the electrolyte 1-2' were used.

[0196] Table 3

[0197] From the above results, it was found that in Examples 1 to 26, by making the electrolyte have a conductivity of 14 mS / cm to 22 mS / cm and including the first additive, excellent cycle performance could be obtained while taking into account high energy density. In contrast, in Comparative Examples 1 and 2, the cycle performance was severely deteriorated, and it was not possible to simultaneously take into account high energy density and high cycle performance effects.

[0198] Note that the present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration as the technical idea and exerting the same effects within the scope of the technical solution of the present disclosure are all included in the technical scope of the present disclosure. Furthermore, within the scope of the gist of the present disclosure, other modes obtained by applying various modifications that can be thought of by those skilled in the art to the embodiments, or by combining part of the constituent elements of the embodiments, are also included in the scope of the present disclosure.

Claims

1. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte solution, the electrolyte solution has an electrical conductivity of 14 mS / cm to 22 mS / cm, The electrolyte includes a first additive, the first additive including at least one of a compound represented by Formula I and Formula II, In formula I, R1is selected from the group consisting of H, a fluorine atom, a fluorine-substituted or unsubstituted C1-C12alkyl group, a fluorine-substituted or unsubstituted C2-C10alkenyl group; in formula II, R2, R3, R4, and R5 are each independently selected from a hydrogen atom, a fluorine atom, a fluorine-substituted or unsubstituted C1-C6 alkyl group, a fluorine-substituted or unsubstituted C1-C6 alkoxy group, a C2-C6 alkenyl group, or a C2-C6 alkynyl group, and R2, R3, R4, and R5 are not simultaneously a hydrogen atom.

2. The secondary battery according to claim 1, wherein the electrolyte solution has an electrical conductivity of 14 mS / cm to 19 mS / cm.

3. The secondary battery according to claim 1 or 2, wherein in formula I, R1 is selected from a hydrogen atom, a fluorine atom, a fluorine-substituted or unsubstituted C1-C6 alkyl group, or a fluorine-substituted or unsubstituted C2-C6 alkenyl group; and / or in formula II, R2, R3, R4, and R5 are each independently selected from a hydrogen atom, a fluorine atom, a fluorine-substituted or unsubstituted C1-C4 alkyl group, a fluorine-substituted or unsubstituted C1-C4 alkoxy group, a C2-C4 alkenyl group, or a C2-C4 alkynyl group, and R2, R3, R4, and R5 are not simultaneously a hydrogen atom.

4. The secondary battery according to any one of claims 1 to 3, wherein the first additive includes at least one of fluoroethylene carbonate and vinylene carbonate.

5. The secondary battery according to any one of claims 1-4, wherein, The electrolyte includes a first solvent, the first solvent including a compound represented by Formula III, In formula III, R 11 is selected from the group consisting of a hydrogen atom, a fluorine-substituted or unsubstituted C1-C4 alkyl group, R 12 is selected from the group consisting of a fluorine-substituted or unsubstituted C1-C4 alkyl group.

6. The secondary battery according to claim 5, wherein the first solvent is selected from one or more of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

7. The secondary battery according to claim 6, wherein the first solvent is selected from one or more of ethyl formate, methyl acetate, and ethyl acetate.

8. The secondary battery according to any one of claims 5-7, wherein, The electrolyte further comprises a second additive, the second additive comprising at least one of the compounds of Formula IV and Formula V, In formula IV, R a , R b each independently represents H, or R a with R b to form Structure, R g represents a fluorine atom, a fluorine-substituted or unsubstituted C1-C6 alkyl group, a C1-C6 alkoxy group, or In the formula V, R c , R d , R e , R f each independently represents H or a fluorine atom.

9. The secondary battery according to claim 8, wherein The second additive includes one or more of vinyl sulfates, bis vinyl sulfates, and ​ 10. The secondary battery according to any one of claims 1-9, wherein, in the electrolyte solution, the first additive has a mass content of 0.01% to 5%.

11. The secondary battery according to any one of claims 5-10, wherein in the electrolyte solution, the first solvent has a mass content of 20% to 80%.

12. The secondary battery according to any one of claims 8-11, wherein, in the electrolyte solution, the second additive has a mass content of 0.01% to 2%.

13. The secondary battery according to any one of claims 8-12, wherein, in the electrolyte solution, the mass ratio of the first solvent to the second additive is 2200:1 to 10:

1.

14. The secondary battery according to any one of claims 5-13, wherein, the electrolyte solution further includes a second solvent, the second solvent including at least one selected from ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate.

15. The secondary battery according to claim 14, wherein in the electrolyte solution, the mass ratio of the first solvent to the second solvent is 1:3 to 9:

1.

16. The secondary battery according to any one of claims 1-15, wherein, The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, the negative electrode film layer having an area density of 10.5 mg / cm2or more 2 ; and / or the negative electrode film layer includes a graphite material, the graphite material having a gravimetric capacity of 355 mAh / g or more.

17. The secondary battery according to any one of claims 1-16, wherein, The face density of the negative electrode film layer is 12.0 mg / cm 2 - 18.5 mg / cm 2 , and / or, the graphite material has a gravimetric capacity of 362 mAh / g to 370 mAh / g.

18. The secondary battery according to any one of claims 1-17, wherein, the negative electrode film layer located on one side of the negative electrode current collector has a thickness of 70 μm to 125 μm.

19. The secondary battery according to any one of claims 1-18, wherein, The compacted density of the negative electrode sheet is 1.45 g / cm 3 -1.78 g / cm 3 .

20. The secondary battery according to any one of claims 1-19, wherein, the graphite material has a powder compaction density under a pressure of 50,000 N of 1.83 g / cc or more.

21. The secondary battery according to any one of claims 1-20, wherein, the graphite material has a powder compaction density under a pressure of 50,000 N of 1.93 g / cc to 2.05 g / cc.

22. The secondary battery according to any one of claims 1-21, wherein, The specific surface area of the graphite material is 0.6 m 2 / g-1.4 m 2 / g.

23. The secondary battery according to any one of claims 1-22, wherein, the graphite material has a volume distribution particle size Dv50 of 12 μm to 22 μm.

24. The secondary battery according to any one of claims 1-23, wherein, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector, the positive electrode film layer including a lithium-containing phosphate.

25. The secondary battery according to claim 24, wherein The chemical formula of the lithium-containing phosphate includes: Li m A a Fe x D d P y E e O z G g , the A includes at least one element among Al, Na, K or Mg;The D includes at least one element among Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti or V;The E includes at least one element among B, S, Si or N;The G includes at least one element among S, F, Cl or Br;0.5≤m≤1.15;0≤a≤0.1;0.5≤x≤1;0≤d≤0.5;0.5≤y≤1;0≤e≤0.5;3.5≤z≤4;0≤g≤0.5。 26.An electric device comprising the secondary battery according to any one of claims 1 to 25.

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