Lithium secondary battery and electric device

Abstract

The invention provides a lithium secondary battery and an electric device, the battery comprises an electrolyte, the electrolyte comprises a carboxylic ester compound, and based on the mass of the electrolyte, the mass percentage A of the carboxylic ester compound is not less than 30% and not more than 70%; the battery meets the following conditions: 0.7 < = A * (T + L) / H < = 7.7, and A is the mass percentage of the carboxylic ester compound on the basis of the mass of the electrolyte; t is the thickness of the battery shell in the direction perpendicular to the connecting line of the positive electrode and the negative electrode of the battery, and the unit is millimeter; l is the length of the battery shell in the direction parallel to the connecting line of the positive electrode and the negative electrode of the battery, and the unit is millimeter; h is the height of the battery shell in the direction parallel to the gravity direction when the battery is placed on the ground, and the unit is millimeter. The invention aims to reduce the gas production degree in the cycle process and the storage process of the lithium secondary battery and comprehensively improve the performance of the lithium secondary battery by improving the electrolyte.

Description

Technical Field

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

[0002] In recent years, as the application scope of lithium-ion batteries has become more and more extensive, lithium-ion batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. As lithium-ion batteries have made great progress, higher requirements have been put forward for their energy density, cycle performance and safety performance. Improving the power performance, cycle and storage life of batteries has always been the goal of the industry, but due to the side reactions of the electrolyte at the anode and cathode interface, the overall performance of the battery cell is poor. Summary of the invention

[0003] The present application is made in view of the above-mentioned problems, and its purpose is to provide a lithium secondary battery, which aims to improve the electrolyte and the electrolyte infiltration, thereby reducing the gas production during the circulation and storage process of the lithium secondary battery, and comprehensively improving the performance of the lithium secondary battery.

[0004] In order to achieve the above-mentioned object, the first aspect of the present application provides a lithium ion secondary battery, the battery comprising an electrolyte, the electrolyte comprising a carboxylate compound, and based on the mass of the electrolyte, the mass percentage A of the carboxylate compound is not less than 30% and not more than 70%;

[0005] The battery satisfies: 0.7≤A*(T+L) / H≤7.7,

[0006] Wherein, A is the mass percentage of the carboxylic acid ester compound based on the mass of the electrolyte; T is the thickness of the battery shell in a direction perpendicular to the positive and negative poles of the battery, in millimeters; L is the length of the battery shell in a direction parallel to the positive and negative poles of the battery, in millimeters; H is the height of the battery shell in a direction parallel to the direction of gravity when the battery is placed on the ground, in millimeters.

[0007] The carboxylic acid ester compounds contained in the electrolyte provided by the present application have a low viscosity, which is conducive to the rapid reabsorption of the electrolyte and can improve the electrolyte infiltration problem; however, the reduction stability of the carboxylic acid ester compounds is poor, and excessive carboxylic acid ester compounds are prone to reduction side reactions at the negative electrode, which worsens the battery storage gas production. Therefore, when the battery size and the content of the carboxylic acid ester compounds meet 0.7≤A*(T+L) / H≤7.7, the battery gas production and electrolyte infiltration can be taken into account, and the battery cycle performance can be comprehensively improved.

[0008] In any embodiment, the carboxylate compound includes a compound of the structure shown in Formula I,

[0009]

[0010] Among them, R 1 , R 2 Each independently includes at least one of a C1-C6 alkyl group and a C1-C6 halogenated alkyl group.

[0011] In any embodiment, the carboxylate compound includes at least one of ethyl acetate, methyl acetate, methyl formate, methyl propionate, ethyl propionate, and propyl propionate.

[0012] The above-mentioned carboxylic acid ester solvent has a lower viscosity, which can better improve the ionic conductivity of the electrolyte and better improve the wetting problem of the electrolyte.

[0013] In any embodiment, the electrolyte contains a high viscosity solvent with a viscosity greater than 0.6 cP at 25° C., and based on the mass of the electrolyte, the mass percentage of the high viscosity solvent is 10%-40%, preferably, the mass percentage of the high viscosity solvent is 20%-30%.

[0014] In any embodiment, the dielectric constant of the high viscosity solvent is ≥60. Preferably, the high viscosity solvent includes at least one of ethylene carbonate (EC) and propylene carbonate (PC).

[0015] By controlling the content of the high-viscosity solvent within the above range, the gas production and electrolyte infiltration of the battery can be better taken into account, thereby comprehensively improving the cycle performance of the battery.

[0016] In any embodiment, the battery comprises an anode membrane, wherein the thickness of the anode membrane is 50-100 μm, preferably, the thickness of the anode membrane is 70-80 μm.

[0017] In any embodiment, the battery comprises a cathode membrane, wherein the thickness of the cathode membrane is 70-130 μm, preferably, the thickness of the cathode membrane is 100-120 μm.

[0018] In any embodiment, the battery comprises a separator, wherein the thickness of the separator is 5-20 μm, preferably, the thickness of the separator is 5-12 μm.

[0019] In any embodiment, the relationship between the thickness C of the separator and the thickness D of the cathode membrane is 5%≤C / D≤20%.

[0020] Increasing the thickness of the diaphragm to a certain extent is conducive to the electrolyte infiltration of the pole piece, and when the electrolyte is squeezed out, it can also be quickly absorbed; but when the thickness of the pole piece increases, the lithium ion transmission resistance increases, which deteriorates the battery DCR to a certain extent. Therefore, when the thickness of the anode diaphragm, cathode diaphragm, and diaphragm of the battery meets the above relationship, the normal temperature cycle performance and DCR of the battery can be better improved.

[0021] In any embodiment, the electrolyte contains lithium salt, and the mass percentage of the lithium salt is 8%-20% based on the mass of the electrolyte.

[0022] In any embodiment, the lithium salt includes at least one of LiPF6, LiFSI, and LiTFSI.

[0023] When the lithium salt concentration is high, the electrolyte kinetics is better and the DCR is lower; however, excessive lithium salt content will lead to a higher viscosity of the electrolyte, which is not conducive to electrolyte reabsorption and poor battery room temperature cycle. Therefore, when the lithium salt content meets the above range, the battery's DCR and room temperature cycle performance can be better improved.

[0024] In any embodiment, the electrolyte further comprises at least one of an additive X and an additive Y, and based on the mass of the electrolyte, the mass percentage of the additive X is 0.1% to 1%, and the mass percentage of the additive Y is 2% to 6%, wherein the additive X comprises at least one of a cyclic sulfonate and a cyclic sulfate, and the cyclic sulfonate and the cyclic sulfate contain a sulfate group, a sulfite group, and / or a sulfonic acid group, and / or wherein the additive Y comprises at least one of a cyclic carbonate containing an unsaturated bond, and the cyclic carbonate containing an unsaturated bond contains a carbonic acid group.

[0025] In any embodiment, the additive X includes at least one of 1,3-propane sultone (PS), 1,3-propene sultone (PES), butyl sultone (BS), methylene dimethyl methoxide (MMDS), and diethyl thiosulfate (DTD).

[0026] When the electrolyte contains the above-mentioned type of additive X, the gas generation during battery storage can be better reduced.

[0027] In any embodiment, the additive Y is vinylene carbonate (VC).

[0028] The above-mentioned type of additive Y is a commonly used SEI film-forming additive, which has good film-forming stability, can effectively reduce interface side reactions, and better improve the cycle performance of the battery. At the same time, VC and the above-mentioned type of additive X have a synergistic effect, which can better improve the room temperature life of the battery.

[0029] A second aspect of the present application provides an electrical device, comprising the lithium secondary battery of the first aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0031] Figure 2 is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0032] Figure 3 is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0033] Figure 4 yes Figure 3 An exploded view of a secondary battery according to an embodiment of the present application is shown.

[0034] Figure 5 FIG. 1 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present application as a power source.

[0035] Description of reference numerals:

[0036] 5 secondary battery; 51 housing; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0037] Hereinafter, the lithium secondary battery, its formation method and the embodiment of the electric device of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0038] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0039] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0040] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0041] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0042] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0043] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0044] Lithium-ion batteries are increasingly used in modern society because of their low price, high safety, long life and other advantages, but their energy density is low. In order to improve the energy density of the battery, thick coating, high pressure density, and larger batteries are usually adopted, but these will make it more difficult to infiltrate the electrolyte. If the electrolyte is not fully infiltrated during the cycle, it may affect the transmission of lithium ions and thus affect the battery life. By using some new solvents to reduce the viscosity of the electrolyte, the infiltration can be improved, but these new solvents often have other side effects, and the higher the dosage, the more obvious the side effects. The present application achieves the purpose of having better dynamics and high temperature performance through electrolyte formulation design and battery design.

[0045] [Lithium secondary battery]

[0046] In order to achieve the purpose, the first aspect of the present application provides a lithium ion secondary battery, the battery comprising an electrolyte, the electrolyte comprising a carboxylate compound, and based on the mass of the electrolyte, the mass percentage A of the carboxylate compound is not less than 30% and not more than 70%;

[0047] The battery satisfies: 0.7≤A*(T+L) / H≤7.7,

[0048] Wherein, A is the mass percentage of the carboxylic acid ester compound based on the mass of the electrolyte; T is the thickness of the battery shell in a direction perpendicular to the positive and negative poles of the battery, in millimeters; L is the length of the battery shell in a direction parallel to the positive and negative poles of the battery, in millimeters; H is the height of the battery shell in a direction parallel to the direction of gravity when the battery is placed on the ground, in millimeters.

[0049] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 1 , Figure 2 The secondary battery of a square structure is used as an example, and its thickness T, length L, and height H are shown in the figure.

[0050] In some embodiments, when the positive and negative electrodes of the battery are at the same end of the battery housing, the exemplary structure of the square battery is as follows: Figure 1 As shown. Figure 1When the battery is placed on the ground in the manner shown in the figure, with the positive and negative poles facing upward, the direction parallel to the direction of gravity is the height H of the battery shell, the direction parallel to the line connecting the positive and negative poles of the battery is the length L of the battery shell, and the direction perpendicular to the line connecting the positive and negative poles of the battery is the thickness T of the battery shell.

[0051] In some embodiments, when the positive and negative electrodes of the battery are at opposite ends of the battery housing, the exemplary structure of the square battery is as follows: Figure 2 As shown. Figure 2 When the battery is placed on the ground in the manner shown in the figure, the positive and negative poles are facing the sides respectively, the direction parallel to the direction of gravity is the height H of the battery shell, the direction parallel to the line connecting the positive and negative poles of the battery is the length L of the battery shell, and the direction perpendicular to the line connecting the positive and negative poles of the battery is the thickness T of the battery shell.

[0052] Affected by gravity, the electrolyte in the battery tends to settle at the bottom of the battery. As time goes by, the electrolyte continues to spread upward and infiltrate the pole piece, filling the gaps between the cathode and anode and the pores of the pole piece, thus acting as a bridge for lithium ion transmission. During the battery cycle, as the charge and discharge proceed, the pole piece continues to expand and contract, and the electrolyte is constantly squeezed out and reabsorbed. If the viscosity of the electrolyte is high and it is squeezed out and cannot be reabsorbed in time, it may cause a lack of electrolyte between the cathode and anode, or in the pores of the pole piece, and it is impossible to form an effective lithium ion transmission path, resulting in rapid battery capacity decay.

[0053] The carboxylic acid ester compounds contained in the electrolyte provided by the present application have a low viscosity, which is conducive to the rapid reabsorption of the electrolyte and can improve the electrolyte infiltration problem; however, the reduction stability of the carboxylic acid ester compounds is poor, and excessive carboxylic acid ester compounds are prone to reduction side reactions at the negative electrode, which worsens the battery storage gas production. Therefore, when the battery size and the content of the carboxylic acid ester compounds meet 0.7≤A*(T+L) / H≤7.7, the battery gas production and electrolyte infiltration can be taken into account, and the battery cycle performance can be comprehensively improved.

[0054] In some embodiments, the carboxylate compound includes a compound having a structure shown in Formula I,

[0055]

[0056] Among them, R 1 , R 2 Each independently includes at least one of a C1-C6 alkyl group and a C1-C6 halogenated alkyl group.

[0057] In some embodiments, in Formula I, R 1 , R 2 Each independently includes at least one of a C1-C5 alkyl group and a C1-C5 halogenated alkyl group.

[0058] In some embodiments, in Formula I, R 1 , R 2 Each independently includes at least one of a C1-C4 alkyl group and a C1-C4 halogenated alkyl group.

[0059] In some embodiments, in Formula I, R 1 , R 2 Each independently includes at least one of a C1-C3 alkyl group and a C1-C3 halogenated alkyl group.

[0060] In some embodiments, in Formula I, R 1 , R 2 Each independently includes at least one of a C1-C2 alkyl group and a C1-C2 halogenated alkyl group.

[0061] In some embodiments, the carboxylate compound includes at least one of ethyl acetate, methyl acetate, methyl formate, methyl propionate, ethyl propionate, and propyl propionate.

[0062] The above-mentioned carboxylic acid ester solvent has a lower viscosity, which can better improve the ionic conductivity of the electrolyte and better improve the wetting problem of the electrolyte.

[0063] In some embodiments, the electrolyte contains a high-viscosity solvent with a viscosity greater than 0.6 cP at 25° C., and the mass percentage of the high-viscosity solvent is 10%-40% based on the mass of the electrolyte.

[0064] The "viscosity" mentioned in this application refers to the resistance of a fluid to flow (the test method can refer to GB / T2794).

[0065] In some preferred embodiments, the mass percentage of the high viscosity solvent is 20%-30%.

[0066] In some embodiments, the dielectric constant of the high viscosity solvent is ≥60.

[0067] The "dielectric constant" mentioned in this application is also called the permittivity or relative permittivity, which is an important data characterizing the electrical properties of dielectrics or insulating materials, and is usually represented by ε. It refers to the ratio of the capacitance when the same material is used as the dielectric and when it is in a vacuum in the same capacitor, indicating the relative ability of the dielectric to store electrostatic energy in an electric field (the test method can refer to ASTM D150).

[0068] In some preferred embodiments, the high viscosity solvent includes at least one of ethylene carbonate (EC) and propylene carbonate (PC).

[0069] By controlling the content of the high-viscosity solvent within the above range, the gas production and electrolyte infiltration of the battery can be better taken into account, thereby comprehensively improving the cycle performance of the battery.

[0070] In some embodiments, the electrolyte contains lithium salt, and the mass percentage of the lithium salt is 8%-20% based on the mass of the electrolyte.

[0071] In some embodiments, the lithium salt includes at least one of LiPF6, LiFSI, and LiTFSI.

[0072] When the lithium salt concentration is high, the electrolyte kinetics is better and the DCR is lower; however, excessive lithium salt content will lead to a higher viscosity of the electrolyte, which is not conducive to electrolyte reabsorption and poor battery room temperature cycle. Therefore, when the lithium salt content meets the above range, the battery's DCR and room temperature cycle performance can be better improved.

[0073] In some embodiments, the electrolyte further comprises at least one of an additive X and an additive Y, and based on the mass of the electrolyte, the mass percentage of the additive X is 0.1% to 1%, and the mass percentage of the additive Y is 2% to 6%, wherein the additive X comprises at least one of a cyclic sulfonate and a cyclic sulfate, and the cyclic sulfonate and the cyclic sulfate contain a sulfate group, a sulfite group, and / or a sulfonic acid group, and / or the additive Y comprises at least one of a cyclic carbonate containing an unsaturated bond, and the cyclic carbonate containing an unsaturated bond contains a carbonic acid group.

[0074] In some embodiments, the additive X includes at least one of 1,3-propane sultone (PS), 1,3-propene sultone (PES), butyl sultone (BS), methylene dimethyl methoxide (MMDS), and dithiodisulfate (DTD).

[0075] When the electrolyte contains the above-mentioned type of additive X, the gas generation during battery storage can be better reduced.

[0076] In some embodiments, the additive Y is vinylene carbonate (VC).

[0077] The above-mentioned type of additive Y is a commonly used SEI film-forming additive, which has good film-forming stability, can effectively reduce interface side reactions, and better improve the cycle performance of the battery. At the same time, VC and the above-mentioned type of additive X have a synergistic effect, which can better improve the room temperature life of the battery.

[0078] In some embodiments, the electrolyte further comprises ethyl methyl carbonate (EMC).

[0079] EMC can improve low temperature performance and prevent the electrolyte from solidifying at low temperatures.

[0080] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0081] In some embodiments, the battery comprises an anode membrane, wherein the thickness of the anode membrane is 50-100 μm.

[0082] In some preferred embodiments, the thickness of the anode membrane is 70-80 μm.

[0083] In some embodiments, the battery comprises a cathode membrane, wherein the cathode membrane has a thickness of 70-130 μm.

[0084] In some preferred embodiments, the cathode membrane has a thickness of 100-120 μm.

[0085] In some embodiments, the battery comprises a separator, wherein the separator has a thickness of 5-20 μm.

[0086] In some preferred embodiments, the thickness of the separator is 5-12 μm.

[0087] In some embodiments, the relationship between the thickness C of the separator and the thickness D of the cathode membrane is 5%≤C / D≤20%.

[0088] The electrolyte infiltrates from the bottom of the battery upwards, often first infiltrating the diaphragm, and then from the diaphragm to the pole piece. Increasing the thickness of the diaphragm to a certain extent is conducive to the electrolyte infiltration of the pole piece, and when the electrolyte is squeezed out, it can also be quickly absorbed; but when the thickness of the pole piece increases, the lithium ion transmission resistance increases, which deteriorates the battery DCR to a certain extent. Therefore, when the thickness of the anode diaphragm, cathode diaphragm, and diaphragm of the battery meets the above relationship, the normal temperature cycle performance and DCR of the battery can be better improved.

[0089] [Positive electrode]

[0090] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the positive electrode active material of the first aspect of the present application.

[0091] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0092] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may 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 substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0093] In some embodiments, the positive electrode active material may adopt a positive electrode active material for a battery known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO 2 ), lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 、LiMn 2 O 4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (Also referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O 2 (Also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O 2 (Also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O 2 (Also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O 2 (Also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi0.85 Co 0.15 Al 0.05 O 2 ) and its modified compounds, etc. Examples of lithium phosphates containing olivine structures may include, but are not limited to, lithium iron phosphate (such as LiFePO 4 (also referred to as LFP), composite materials of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), at least one of a composite material of lithium manganese phosphate and carbon, a composite material of lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0094] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0095] In some embodiments, the positive electrode film layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0096] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0097] [Negative electrode]

[0098] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0099] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0100] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0101] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0102] In some embodiments, the negative electrode film layer may further include a binder. The binder may 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).

[0103] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0104] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0105] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0106] [Isolation film]

[0107] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0108] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0109] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0110] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0111] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0112] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 3 The secondary battery 5 is a square structure as an example.

[0113] In some embodiments, reference Figure 4 , the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include 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 connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0114] [Electrical devices]

[0115] In addition, the present application also provides an electrical device, which includes a lithium secondary battery provided by the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0116] As the electrical device, a secondary battery, a battery module or a battery pack may be selected according to its usage requirements.

[0117] Figure 5 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for the secondary battery, a battery pack or a battery module can be used.

[0118] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0119] Example

[0120] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0121] 1. Preparation method

[0122] Example 1

[0123] 1.1 Preparation of positive electrode sheet:

[0124] The positive electrode material, polyvinylidene fluoride (PVDF), and carbon black (SP) are mixed with a solvent in a mass ratio of 97:2:1, and stirred to obtain a uniformly dispersed positive electrode slurry. The positive electrode slurry is evenly coated on both surfaces of an aluminum foil, and dried, cold pressed, and cut to obtain a positive electrode sheet having a thickness of 105 μm.

[0125] 1.2 Preparation of negative electrode sheet:

[0126] The negative electrode active material (artificial graphite): carbon black (SP): styrene-butadiene rubber (SBR): sodium hydroxymethyl cellulose (CMC) is mixed with a solvent at a ratio of 97:0.5:1.5:1, a pore-forming agent is added, and a uniformly dispersed negative electrode slurry is obtained by stirring. The negative electrode slurry is evenly coated on both surfaces of the copper foil, and a negative electrode sheet is obtained after drying, cold pressing, and cutting. The thickness of the negative electrode sheet is 73 μm.

[0127] 1.3 Isolation film:

[0128] A polyethylene film is used as the separator, and the thickness of the separator is 7 μm.

[0129] 1.4 Preparation of electrolyte:

[0130] In an argon atmosphere glove box, based on the total mass of the electrolyte, 25% ethylene carbonate (EC), 50% ethyl acetate (EA), 7.5% ethyl methyl carbonate (EMC), 13% lithium hexafluorophosphate (LiPF 6 ), 0.5% of 1,3-propane sultone and 4% of vinylene carbonate are mixed and dissolved to obtain an electrolyte.

[0131] 1.5 Preparation of lithium-ion secondary batteries:

[0132] The positive electrode sheet, the negative electrode sheet and the separator are made into an electrode assembly through a winding process or a lamination process, and placed in a shell made of an aluminum shell, an aluminum-plastic film, etc. After the above-mentioned electrolyte is injected, allowed to stand at high temperature, formed, and divided, the battery of Example 1 is obtained. The length L of the battery is 362 mm, the thickness T is 47 mm, and the height H is 89 mm.

[0133] Embodiments 2 to 7

[0134] The battery preparation methods in Examples 2 to 7 are basically similar to those in Example 1, but the type or mass percentage of the carboxylic acid ester compound in the electrolyte is changed. The specific parameters are shown in Table 1-3-3.

[0135] Embodiments 8 to 12

[0136] The battery preparation methods in Examples 8 to 12 are basically similar to those in Example 1, but the type or mass percentage of the high-viscosity solvent in the electrolyte is changed. The specific parameters are shown in Tables 1-3.

[0137] Embodiments 13 to 16

[0138] The battery preparation methods in Examples 13 to 16 are basically similar to those in Example 1, but the battery size and the value of A*(T+L) / H are changed. The specific parameters are shown in Tables 1-3.

[0139] Examples 17 to 22

[0140] The battery preparation methods in Examples 17 to 22 are basically similar to those in Example 1, but the type or mass percentage of the lithium salt in the electrolyte is changed. The specific parameters are shown in Tables 1-3.

[0141] Embodiments 23 to 34

[0142] The battery preparation methods in Examples 23 to 34 are basically similar to those in Example 1, but the types or mass percentages of additives in the electrolyte are changed. The specific parameters are shown in Tables 1-3.

[0143] Embodiments 35 to 38

[0144] The battery preparation methods in Examples 35 to 38 are basically similar to those in Example 1, but the thickness of the anode membrane is changed. The specific parameters are shown in Tables 1-3.

[0145] Examples 39 to 42

[0146] The battery preparation methods in Examples 39 to 42 are basically similar to those in Example 1, but the thickness of the cathode membrane is changed. The specific parameters are shown in Tables 1-3.

[0147] Embodiments 43 to 46

[0148] The battery preparation methods in Examples 43 to 46 are basically similar to those in Example 1, but the thickness of the separator is changed. The specific parameters are shown in Tables 1-3.

[0149] Comparative Examples 1 to 3

[0150] The battery preparation methods in Comparative Examples 1 to 3 are substantially similar to those in Example 1, but the type or mass percentage of the low-viscosity solvent in the electrolyte is changed. The specific parameters are shown in Tables 1-3.

[0151] Comparative Examples 4 to 6

[0152] The battery preparation methods in Examples 4 to 6 are basically similar to those in Example 1, but the type or mass percentage of the high-viscosity solvent in the electrolyte is changed. The specific parameters are shown in Tables 1-3.

[0153] Comparative Examples 7 to 8

[0154] The battery preparation methods in Comparative Examples 7 to 8 are basically similar to those in Example 1, but the battery size and the value of A*(T+L) / H are changed. The specific parameters are shown in Tables 1-3.

[0155] Comparative Examples 9 to 11

[0156] The battery preparation methods in Comparative Examples 9 to 11 are basically similar to those in Example 1, but the type or mass percentage of the lithium salt in the electrolyte is changed. The specific parameters are shown in Table 1-3.

[0157] Comparative Examples 12 to 17

[0158] The battery preparation methods in Comparative Examples 12 to 17 are basically similar to those in Example 1, but the types or mass percentages of additives in the electrolyte are changed. The specific parameters are shown in Tables 1-3.

[0159] Comparative Examples 18-19

[0160] The battery preparation methods in Comparative Examples 18 to 19 are basically similar to those in Example 1, but the thickness of the anode membrane is changed. The specific parameters are shown in Table 1-3.

[0161] Comparative Examples 20-21

[0162] The battery preparation methods in Comparative Examples 20-21 are basically similar to those in Example 1, but the thickness of the cathode membrane is changed. The specific parameters are shown in Tables 1-3.

[0163] Comparative Examples 22-23

[0164] The battery preparation methods in Comparative Examples 22 to 23 are basically similar to those in Example 1, but the thickness of the separator is changed. The specific parameters are shown in Table 1-3.

[0165] 2. Performance Test Method

[0166] (1) Determination of 25℃ Cyclic Performance

[0167] At 25°C, the batteries of the embodiments and comparative examples were charged at a constant current of 0.5C to an upper voltage limit of 3.8V, and then charged at a constant voltage to a current of 0.05C; the batteries were left to stand for 5 minutes, and discharged at a constant current of 1 / 3C to 2.0V. This was the first charge and discharge cycle of the battery, and the discharge capacity at this time was recorded as the discharge capacity D1 of the first cycle of the battery. The battery was subjected to a cyclic charge and discharge test according to the above method, and the capacity Dn at the nth cycle of the battery was recorded, and the capacity retention rate was Dn / D1. The number of cycles when the capacity retention rate was 80% was recorded.

[0168] (2) DCR test

[0169] At 25°C, charge the battery at 0.5C constant current to the upper voltage limit of 3.8V, and then charge at constant voltage to the current of 0.05C. Then discharge at 0.5C for 1h to adjust the battery to 50% SOC, and record the voltage at this time as U1. Then discharge at 4C for 30s, and record the voltage at this time as U2. DCR = (U1-U2) / 4C.

[0170] (3) Storage gas production test

[0171] At 25°C, charge the battery at a constant current of 0.5C to the upper voltage limit of 3.8V, and then charge it at a constant voltage to a current of 0.05C. Then test the battery volume V0 using the water displacement method. Then put the battery in a 60°C environment and store it for 30 days. Take the battery out and place it at 25°C for 2 hours. After returning to room temperature, test the volume V2 using the water displacement method. The volume growth rate is V2 / V1-1.

[0172] III. Analysis of test results of various embodiments and comparative examples

[0173] The batteries of the embodiments and comparative examples were prepared according to the above method, and various performance parameters were measured. The results are shown in Table 3 below.

[0174] Table 1 Preparation parameters

[0175]

[0176]

[0177] Table 2 Preparation parameters

[0178]

[0179]

[0180]

[0181] Table 3 Preparation parameters and performance test results

[0182]

[0183]

[0184]

[0185] The lithium secondary batteries prepared in Examples 1 to 46 all have good performance, including lower DCR, better cycle performance, lower storage gas generation, etc.

[0186] It can be seen from Examples 1 to 7 that when preparing the electrolyte of a lithium secondary battery, using a variety of different types of carboxylic acid ester compounds (such as ethyl acetate, methyl acetate, methyl formate), or using different contents of carboxylic acid ester compounds (such as 30%, 40%, 50%, 60%, 70%), can make the prepared lithium secondary battery have better performance, including lower DCR, better cycle performance, lower storage gas production, etc.

[0187] In Comparative Examples 1 to 2, when preparing the electrolyte of the lithium secondary battery, a carboxylic acid ester compound with a content exceeding the range (for example, 0%, 80%) is used, and the comprehensive performance of the lithium secondary battery prepared therefrom is poor, for example, a high DCR, poor cycle performance, or high storage gas generation.

[0188] It can be seen from Examples 1 and 8 to 12 that when preparing the electrolyte for a lithium secondary battery, using a variety of different types of high viscosity solvents (e.g., ethylene carbonate, propylene carbonate) or using different contents of high viscosity solvents (e.g., 10%, 20%, 25%, 30%, 40%) can make the prepared lithium secondary battery have better performance, including lower DCR, better cycle performance, lower storage gas production, etc.

[0189] In Comparative Examples 3 to 4, when preparing the electrolyte for the lithium secondary battery, a high viscosity solvent with a content exceeding the range (e.g., 0%, 50%) is used, and the lithium secondary batteries prepared therefrom have poor overall performance, such as high DCR, poor cycle performance, or high storage gas generation.

[0190] It can be seen from Examples 1 and 13 to 16 that when preparing lithium secondary batteries, using a variety of different battery sizes so that the range of A*(T+L) / H is within the range of 0.7 to 7.7 can make the prepared lithium secondary batteries have better performance, including lower DCR, better cycle performance, lower storage gas production, etc.

[0191] In Comparative Examples 5 to 6, when preparing lithium secondary batteries, when the range of A*(T+L) / H exceeds the range of 0.7 to 7.7 (for example, 0.5, 8), the comprehensive performance of the prepared lithium secondary batteries is poor, such as high DCR, poor cycle performance, or high storage gas production.

[0192] It can be seen from Examples 1, 17 to 22 that when preparing the electrolyte of a lithium secondary battery, a variety of different types of lithium salts (such as LiPF 6 , LiFSI, LiTFSI), or using different contents of lithium salt (for example, 8%, 10%, 13%, 15%, 20%), can make the prepared lithium secondary battery have better performance, including lower DCR, better cycle performance, lower storage gas production, etc.

[0193] In Comparative Examples 7 to 8, when preparing the electrolyte for the lithium secondary battery, a lithium salt with a content exceeding the range (e.g., 5%, 25%) is used, and the lithium secondary batteries prepared therefrom have poor overall performance, such as high DCR, poor cycle performance, or high storage gas generation.

[0194] It can be seen from Examples 1 and 23 to 30 that when preparing the electrolyte of a lithium secondary battery, using a variety of different types of additives X (e.g., 1,3-propane sultone, 1,3-propenyl lactone, butyl sultone, methane disulfonic acid methylene ester, vinyl sulfate), or using different contents of additive X (e.g., 0.1%, 0.3%, 0.5%, 0.6%, 1%), the prepared lithium secondary battery can have better performance, including lower DCR, better cycle performance, lower storage gas production, etc.

[0195] In Comparative Examples 9 to 10, when preparing the electrolyte of the lithium secondary battery, the additive X with a content exceeding the range (for example, 0%, 1.5%) is used, and the comprehensive performance of the prepared lithium secondary battery is poor, such as high DCR, poor cycle performance, or high storage gas generation.

[0196] It can be seen from Examples 1 and 31 to 34 that when preparing the electrolyte of a lithium secondary battery, the additive Y is vinylene carbonate, and using different contents of the additive Y (for example, 2%, 3%, 4%, 5%, 6%) can make the prepared lithium secondary battery have better performance, including lower DCR, better cycle performance, lower storage gas production, etc.

[0197] In Comparative Examples 11 to 12, when preparing the electrolyte of the lithium secondary battery, the additive Y with a content exceeding the range (for example, 1%, 8%) is used, and the comprehensive performance of the prepared lithium secondary battery is poor, such as high DCR, poor cycle performance, or high storage gas generation.

[0198] It can be seen from Examples 1 and 35 to 46 that when preparing lithium secondary batteries, using a variety of different thicknesses of anode membranes (e.g., 50 μm, 70 μm, 73 μm, 80 μm, 100 μm), cathode membranes (e.g., 70 μm, 100 μm, 105 μm, 120 μm, 130 μm), and separators (e.g., 5 μm, 6 μm, 7 μm, 12 μm, 20 μm) can make the prepared lithium secondary batteries have better performance, including lower DCR, better cycle performance, lower storage gas production, etc.

[0199] In Comparative Examples 13 to 18, when preparing lithium secondary batteries, anode membranes (e.g., 110 μm, 40 μm), cathode membranes (e.g., 140 μm, 60 μm), and separators (e.g., 22 μm, 3 μm) with thicknesses outside the range were used. The comprehensive performance of the lithium secondary batteries prepared therefrom was poor, such as high DCR, poor cycle performance, or high storage gas production.

[0200] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A lithium ion secondary battery, It is characterized in that The battery includes an electrolyte, the electrolyte includes a carboxylic acid ester compound, and based on the mass of the electrolyte, the mass percentage A of the carboxylic acid ester compound is not less than 30% and not more than 70%; The battery satisfies: 0.7≤A*(T+L) / H≤7.7, Wherein, A is the mass percentage of the carboxylic acid ester compound based on the mass of the electrolyte; T is the thickness of the battery casing in a direction perpendicular to the line connecting the positive and negative electrodes of the battery, in millimeters; L is the length of the battery casing in a direction parallel to the line connecting the positive and negative electrodes of the battery, in millimeters; H is the height of the battery casing in a direction parallel to the direction of gravity when the battery is placed on the ground, in millimeters.

2. The battery according to claim 1, wherein the carboxylate compound comprises a compound having a structure shown in Formula I, in, R 1 , R 2 Each independently includes at least one of a C1-C6 alkyl group and a C1-C6 halogenated alkyl group. 3 . The battery according to claim 2 , wherein the carboxylate compound comprises at least one of ethyl acetate, methyl acetate, methyl formate, methyl propionate, ethyl propionate, and propyl propionate.

4. The battery according to any one of claims 1 to 3, wherein the electrolyte contains a high-viscosity solvent with a viscosity greater than 0.6 cP at 25°C, and based on the mass of the electrolyte, the mass percentage of the high-viscosity solvent is 10%-40%, preferably, the mass percentage of the high-viscosity solvent is 20%-30%. 5 . The battery according to claim 4 , wherein the dielectric constant of the high-viscosity solvent is ≥60, and preferably, the high-viscosity solvent comprises at least one of ethylene carbonate (EC) and propylene carbonate (PC). 6 . The battery according to claim 1 , comprising an anode membrane, wherein the thickness of the anode membrane is 50-100 μm, preferably, the thickness of the anode membrane is 70-80 μm.

7. The battery according to any one of claims 1 to 5, comprising a cathode membrane, wherein the cathode membrane has a thickness of 70-130 μm, preferably, wherein the cathode membrane has a thickness of 100-120 μm.

8. The battery according to any one of claims 1 to 5, comprising a separator, wherein the separator has a thickness of 5 to 20 μm, preferably, wherein the separator has a thickness of 5 to 12 μm. 9 . The battery according to claim 7 , wherein the relationship between the thickness C of the separator and the thickness D of the cathode membrane is 5%≤C / D≤20%.

10. The battery according to any one of claims 1 to 9, wherein the electrolyte comprises a lithium salt, and the mass percentage of the lithium salt is 8% to 20% based on the mass of the electrolyte.

11. The battery according to claim 10, wherein the lithium salt comprises at least one of LiPF6, LiFSI, and LiTFSI.

12. The battery according to any one of claims 1 to 11, wherein the electrolyte further comprises at least one of an additive X and an additive Y, and based on the mass of the electrolyte, the mass percentage of the additive X is 0.1% to 1%, and the mass percentage of the additive Y is 2% to 6%, The additive X comprises at least one of a cyclic sulfonate and a cyclic sulfate, wherein the cyclic sulfonate and the cyclic sulfate contain a sulfate group, a sulfite group, and / or a sulfonic acid group, and / or The additive Y includes at least one of cyclic carbonates containing unsaturated bonds, and the cyclic carbonates containing unsaturated bonds contain carbonic acid groups.

13. The battery according to claim 12, wherein the additive X comprises at least one of 1,3-propane sultone (PS), 1,3-propene sultone (PES), butane sultone (BS), methylene dimethyl methoxide (MMDS), and dithiodisulfate (DTD). 14 . The battery according to claim 12 , wherein the additive Y is vinylene carbonate (VC).

15. An electrical device, It is characterized in that A lithium ion battery comprising the lithium ion battery according to any one of claims 1 to 14.

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