Lithium ion secondary battery and electric device

Abstract

The invention provides a lithium ion secondary battery and an electric device. The lithium ion secondary battery comprises an electrolyte, wherein the electrolyte comprises alkali metal ions of which the ion radius is greater than that of lithium ions and a film-forming additive; based on the total mass of the electrolyte, the mass content A of the alkali metal ions and the mass content B of the additive meet the condition that B / A is greater than or equal to 0.10 and less than or equal to 6 * 10 < 4 >. The lithium ion secondary battery has relatively low direct current impedance and excellent cycle performance.

Description

Technical Field

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

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal, wind and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields, and the requirements for the electrical performance of secondary batteries are constantly increasing.

[0003] The performance of the electrolyte has a key impact on the performance of the secondary battery. Therefore, it is necessary to develop electrolytes to improve the performance of secondary batteries to meet the application needs of the new generation of electrochemical systems. Summary of the invention

[0004] The purpose of the present application is to provide a lithium-ion secondary battery, aiming to reduce the DC impedance of the lithium-ion secondary battery and improve the power performance and cycle performance of the lithium-ion secondary battery.

[0005] In order to achieve the above-mentioned object, the first aspect of the present application provides a lithium ion secondary battery, comprising an electrolyte, wherein the electrolyte comprises an alkali metal ion having an ion radius greater than that of a lithium ion and a film-forming additive;

[0006] Based on the total mass of the electrolyte, the mass content A of the alkali metal ion and the mass content B of the additive satisfy: 0.10≤B / A≤6×10 4 .

[0007] The electrolyte including alkali metal ions and film-forming additives is conducive to reducing the DC impedance of lithium-ion secondary batteries, improving the metal dendrite phenomenon of lithium-ion secondary batteries, and thus improving the power performance and cycle performance of lithium-ion secondary batteries. On the one hand, the introduction of alkali metal ions whose metal ion radius is larger than that of lithium ions into the electrolyte facilitates the formation of a good channel for lithium ion transmission during the charging and discharging process of the lithium-ion secondary battery, thereby reducing the DC impedance of the lithium-ion secondary battery; on the other hand, the introduction of film-forming additives into the electrolyte is conducive to the formation of a uniform and dense inorganic SEI film at the interface between the negative electrode plate and the electrolyte, which can effectively inhibit metal dendrites and improve the safety of lithium-ion secondary batteries. In addition, the inorganic SEI film can also further hinder the interface side reactions between the electrolyte and the negative electrode plate, and improve the cycle performance of the lithium-ion secondary battery. In addition, the relationship between the mass content A of the alkali metal ions and the mass content B of the film-forming additives is controlled to satisfy 0.10≤B / A≤6×10 4 It can not only reduce the DC impedance of lithium-ion secondary batteries, but also further improve the power performance and cycle performance of batteries.

[0008] In any embodiment, the lithium ion secondary battery includes a negative electrode plate, the negative electrode plate includes a current collector and a negative electrode active material layer located on at least one side of the current collector and containing at least a negative electrode active material, and the porosity C of the negative electrode active material layer and the mass content A of the alkali metal ions in the total mass of the electrolyte satisfy: 10 -6 ≤A / C≤0.035, optional 5×10 -5 ≤A / C≤0.025.

[0009] Controlling the appropriate relationship between the porosity of the negative electrode active material layer and the mass content of alkali metal ions facilitates the electrolyte to better and faster infiltrate the negative electrode plate, so that lithium ions can be better transmitted, the concentration polarization of lithium ions during the transmission process can be improved, the electrical properties of lithium-ion secondary batteries can be enhanced, and the phenomenon of metal dendrites can be improved, taking into account the kinetics and cycle performance of lithium-ion secondary batteries.

[0010] In any embodiment, based on the total mass of the electrolyte, the mass content A of the alkali metal ions and the mass content B of the film-forming additive satisfy: 0.14≤B / A≤2000.

[0011] By controlling the relationship between the mass content A of the alkali metal ions and the mass content B of the film-forming additive to satisfy the above relationship, the DC impedance of the lithium-ion secondary battery can be further reduced, and the cycle performance of the battery can be improved.

[0012] In any embodiment, the alkali metal ion comprises Na + , K + , Cs + One or more of .

[0013] The above-mentioned alkali metal ions are all beneficial to the transmission of lithium ions and improve the power performance of the battery.

[0014] In any embodiment, based on the total mass of the electrolyte, the mass content A of the alkali metal ions satisfies: 1 ppm≤A≤7000 ppm, and can be optionally 100 ppm≤A≤7000 ppm.

[0015] Controlling the alkali metal ions within a suitable range can improve the power performance of the battery.

[0016] In any embodiment, the electrolyte further includes anions, wherein the anions include PO 2 F 2 - 、FSO 3 - DFOB - , BF 4 - DFOP- 、BOB - ,PO 3 F 2- One or more of .

[0017] In some embodiments, based on the total mass of the electrolyte, the mass content of the anions is greater than 0 and less than or equal to 5%. Optionally, based on the total mass of the electrolyte, the mass content of the anions is greater than 0 and less than or equal to 4%.

[0018] The above anions help improve the cycle performance and cycle life of secondary batteries. For example, for positive electrode sheets including lithium transition metal oxide positive electrode active materials, the lone pair electrons contained in the above anions can combine with lithium ions on the surface of the positive electrode sheets, change the Li / Ni mixing, stabilize the structure of the positive electrode sheets, change the charge transfer resistance (Rct) on the surface of the positive electrode sheets, and improve the cycle performance and cycle life of lithium-ion secondary batteries; for positive electrode sheets including lithium phosphate positive electrode active materials, the above anions can form a dense SEI film on the surface of the negative electrode sheets, improving the life of the battery.

[0019] Controlling the mass content of the introducing anions within an appropriate range can not only improve the cycle performance of lithium-ion secondary batteries, but also help reduce the formation of metal dendrites.

[0020] In any embodiment, the film-forming additive includes one or more of fluorocarbonate compounds, sulfate compounds, and sulfonate compounds.

[0021] The addition of film-forming additives is conducive to the formation of a uniform and dense inorganic SEI film. For example, fluorinated carbonate compounds can form a LiF-rich, LiCO-rich SEI film on the surface of the negative electrode. 3 The inorganic SEI film, sulfate compounds can form a Li-rich 2 SO 4 The inorganic SEI film, sulfonate compounds can form a Li-rich 2 SO 3 Inorganic SEI film. The inorganic SEI film can not only inhibit the phenomenon of metal dendrites, but also hinder the reaction between the electrolyte and the positive / negative electrode sheets, improve the stability of lithium-ion secondary batteries, and enhance their cycle performance.

[0022] In any embodiment, the fluorinated carbonate compound includes one or more of fluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate or trifluoromethylethylene carbonate, and optionally includes fluoroethylene carbonate;

[0023] The sulfate ester compound includes one or more of 4,4'-vinyl sulfate, vinyl sulfate, diethyl sulfate, dimethyl sulfate and 4,4-bis(1,3,2-dioxathiolane)-2,2,2,2-tetraoxide, and optionally includes one or more of 4,4'-vinyl sulfate and vinyl sulfate; and / or,

[0024] The sulfonate compound includes one or more of 1,3-propane sultone, propene sultone, and 3-fluoro-1,3-propane sultone, and optionally includes 1,3-propane sultone.

[0025] The above-mentioned fluorinated carbonate compounds, sulfate compounds, and sulfonate compounds can all form a uniform and dense inorganic SEI film.

[0026] In any embodiment, based on the total mass of the electrolyte, the mass content B of the film-forming additive satisfies: 0.1%≤B≤7%, optionally 0.1%≤B≤6%.

[0027] By controlling the mass content of the film-forming additive within a suitable range, a sufficiently dense inorganic SEI film can be formed, the formation of metal dendrites can be inhibited, the interface side reactions can be hindered, and the side reactions of lithium-ion secondary batteries can be reduced.

[0028] In any embodiment, the porosity C of the negative electrode active material layer is 20% to 60%, and can be optionally 20% to 40%.

[0029] Controlling the porosity of the negative electrode active material layer within an appropriate range can not only improve the wettability of the electrolyte to the negative electrode plate, thereby facilitating better transmission of lithium ions, improve the concentration polarization of lithium ions during transmission, enhance the electrical properties of lithium-ion secondary batteries, and inhibit the phenomenon of dendrites; it can also reduce the risk of increased contact area between the electrolyte and the negative electrode active material due to excessive porosity, and reduce the degree of side reactions.

[0030] In any embodiment, based on the total mass of the electrolyte, the mass content of the lithium salt is 8% to 20%, and optionally 8% to 15%.

[0031] Controlling the mass content of lithium salt within an appropriate range is beneficial to promoting the migration of lithium ions and reducing the DC impedance of lithium-ion secondary batteries.

[0032] In any embodiment, the lithium salt includes a first lithium salt and / or a second lithium salt, wherein the first lithium salt and the second lithium salt each independently include LiFSI, LiPF 6 , LiBF 4 、LiTFSI、LiClO 4 、LiAsF 6 In some embodiments, the first lithium salt is selected from LiFSI, and the second lithium salt is selected from LiPF 6 .

[0033] LiFSI has a larger anion, which can effectively promote the migration of lithium ions, so that the lithium-ion secondary battery has an excellent lithium-ion migration number, reduces its DC impedance and the precipitation of metal dendrites, and LiFSI itself is insensitive to water and has good thermal stability, which can further improve the safety of lithium-ion secondary batteries. 6 The thermal stability of LiFSI is better than that of LiPF. 6 The combination can take into account both the electrical performance and thermal stability of the lithium-ion secondary battery.

[0034] In some embodiments, LiFSI and LiPF 6 The mass ratio of LiFSI and LiPF is not less than 0.1 and not more than 5; Optionally, LiFSI and LiPF 6 The mass ratio is not less than 3 and not more than 5.

[0035] The mass ratio of the first lithium salt to the second lithium salt is controlled within a suitable range so that the lithium ion secondary battery has excellent electrical properties.

[0036] In any embodiment, the electrolyte further comprises a solvent, and the solvent comprises a cyclic ester solvent and / or a linear ester solvent;

[0037] The cyclic ester solvent includes one or more of ethylene carbonate and propylene carbonate;

[0038] The linear ester solvent includes one or more of dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl methyl carbonate, methyl formate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, isopropyl acetate, and isoamyl acetate.

[0039] The above solvents can be used in combination with alkali metal salts and film-forming additives to enable lithium-ion secondary batteries to have lower DC impedance and excellent cycle performance.

[0040] In some embodiments, based on the total mass of the solvent, the mass content of the cyclic ester solvent is A, and the mass content of the linear ester solvent is (100%-A). In some embodiments, A is 0-40%, 2%-40% or 5%-35%.

[0041] In any embodiment, based on the total mass of the solvent, the mass content of the cyclic ester solvent is 2% to 40%, optionally 5% to 35%; the mass content of the linear ester solvent is 50% to 100%, optionally 60% to 95%.

[0042] The mass contents of the cyclic ester solvent and the linear ester solvent are respectively controlled within a suitable range so that the lithium ion secondary battery has excellent electrical properties and safety.

[0043] In any embodiment, the negative electrode active material layer includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-carbon composite, lithium titanate, and silicon-oxygen composite.

[0044] The negative electrode active material layer including the above negative electrode active material has a suitable porosity.

[0045] In any embodiment, the lithium-ion secondary battery includes a positive electrode plate, and the positive electrode plate includes one or more of a lithium transition metal oxide positive electrode active material and a lithium phosphate positive electrode active material.

[0046] The second aspect of the present application also includes an electrical device, including the lithium-ion secondary battery described in the first aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a schematic diagram of a lithium-ion secondary battery according to one embodiment of the present application;

[0048] Figure 2 yes Figure 1 An exploded view of a lithium-ion secondary battery according to an embodiment of the present application is shown;

[0049] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0050] Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0051] Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown;

[0052] Figure 6 Schematic diagram of an electrical device using a lithium-ion secondary battery according to an embodiment of the present application as a power source.

[0053] Description of reference numerals:

[0054] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 lithium-ion secondary battery; 51 shell; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0055] Hereinafter, the embodiments of the lithium-ion secondary battery and 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 structures 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.

[0056] "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.

[0057] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0058] 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.

[0059] 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.

[0060] If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent 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.

[0061] 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).

[0062] The metal ion transfer rate seriously affects the battery performance. For example, for lithium batteries, a low lithium ion transfer rate can lead to undesirable phenomena such as increased DC impedance of lithium batteries and reduced cycle performance. Introducing other metal ions with larger ion radius into the electrolyte can form a good channel for lithium ion transfer during the charge and discharge process, thereby improving power performance. However, the other introduced metal ions have a larger electrode potential than lithium ions, which makes it easier to deposit and form more active metals during the deposition process, and even worse, form dendrites, which seriously affects the safety of the battery. Therefore, it is necessary to design a new battery that can take into account both power performance and cycle performance.

[0063] [Lithium-ion secondary battery]

[0064] Based on this, the present application proposes a lithium ion secondary battery, which includes an electrolyte, the electrolyte includes alkali metal ions whose ion radius is larger than that of lithium ions and a film-forming additive; based on the total mass of the electrolyte, the mass content A of the alkali metal ions and the mass content B of the additive satisfy: 0.10≤B / A≤6×10 4 .

[0065] As used herein, the term "alkali metal ion" refers to ions of alkali metals, including but not limited to Na + , K +or Cs + Alkali Metal Ions Alkali metal ions can be introduced into the secondary battery by adding an alkali metal salt to the electrolyte.

[0066] Herein, the term “film-forming additive” refers to an additive that reacts with metallic lithium to form an inorganic SEI film, including but not limited to fluorocarbonate compounds, sulfate compounds or sulfonate compounds.

[0067] The introduction of alkali metal ions whose metal ion radius is larger than that of lithium ions into the electrolyte facilitates the formation of a good channel for lithium ion transmission during the charge and discharge process of the lithium ion secondary battery, thereby reducing the DC impedance of the lithium ion secondary battery. However, the addition of alkali metal ions is prone to deposit and form metal dendrites during the charge and discharge process of the secondary battery. The introduction of film-forming additives into the electrolyte is conducive to the formation of a uniform and dense inorganic SEI film at the interface between the negative electrode and the electrolyte, which can effectively inhibit metal dendrites, help avoid or reduce the risks and hidden dangers brought by alkali metal ions, and improve the safety of lithium ion secondary batteries; the inorganic SEI film can also further hinder the interface side reactions between the electrolyte and the negative electrode. The introduction of alkali metal ions and film-forming additives helps to improve the power performance and cycle performance of lithium ion secondary batteries at the same time.

[0068] In some embodiments, based on the total mass of the electrolyte, the mass content A of the alkali metal ion and the mass content B of the film-forming additive satisfy B / A and can be 0.14, 0.2, 0.4, 0.5, 0.8, 1, 5, 10, 50, 100, 500, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 1×10 4 , 1.5×10 4 , 2×10 4 , 2.5×10 4 , 3×10 4 , 3.5×10 4 , 4×10 4 , 4.5×10 4 , 5×10 4 , 5.5×10 4 , 6×10 4 , or a value in the range formed by any two of the above points.

[0069] The mass content of metal ions can be determined by a detection method known to those skilled in the art, such as inductively coupled plasma technology, according to industry detection standards.

[0070] In some embodiments, based on the total mass of the electrolyte, the mass content A of the alkali metal ion and the mass content B of the film-forming additive satisfy: 0.2≤B / A≤5×104 In some embodiments, based on the total mass of the electrolyte, the alkali metal ion content A and the mass content B of the film-forming additive satisfy: 0.14≤B / A≤2000. The electrolyte comprising alkali metal ions and film-forming additives is beneficial to reduce the DC impedance of lithium-ion secondary batteries, improve the metal dendrite phenomenon of lithium-ion secondary batteries, and thus improve the power performance and cycle performance of lithium-ion secondary batteries.

[0071] It is understandable that since the reduced state of alkali metal ions is used as an electrode, its standard electrode potential is greater than the standard electrode potential of lithium. During the discharge process of lithium-ion secondary batteries, alkali metal ions are more likely to precipitate corresponding metals on the negative electrode side, and even worse, form metal dendrites, which seriously affect the cycle performance and safety of lithium-ion secondary batteries. Therefore, adding film-forming additives to the electrolyte helps to form a dense inorganic SEI film, inhibit the formation of metal dendrites, and improve the safety and cycle performance of secondary batteries. In addition, the relationship between the mass content A of alkali metal ions and the mass content B of film-forming additives is controlled to satisfy 0.10≤B / A≤6×10 4 It can not only reduce the DC impedance of lithium secondary batteries, but also further improve the battery's cycle performance.

[0072] In some embodiments, the lithium ion secondary battery includes a negative electrode plate, the negative electrode plate includes a current collector and a negative electrode active material layer located on at least one side of the current collector and containing at least a negative electrode active material, and the porosity C of the negative electrode active material layer and the mass content A of the alkali metal ions in the total mass of the electrolyte satisfy the following relationship: 10 -6 ≤A / C≤0.035, optional 5×10 -5 ≤A / C≤0.035or5×10 -5 ≤A / C≤0.025.

[0073] In some embodiments, the ratio A / C of the porosity C of the negative electrode active material layer to the mass content A of the alkali metal ions in the total mass of the electrolyte may be 10 -6 , 2×10 -6 , 5×10 -6 ,7×10 -6 , 10 -5 , 2×10 -5 , 5×10 -5 , 8×10 -5 , 10 -4 , 2×10 -4 , 5×10 -4 ,7×10 -4, 0.001, 0.002, 0.005, 0.008, 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, or a value in the range consisting of any two of the above points.

[0074] The porosity of the negative electrode active material layer can be adjusted by the compaction density of the negative electrode film layer. Generally speaking, increasing the compaction density can reduce the porosity of the material layer.

[0075] The porosity of the negative electrode active material layer can be measured by any known means, including but not limited to BET. As an example, for example, using an inert gas with a small molecular diameter such as helium or nitrogen, the real volume of the sample to be tested is accurately measured by the displacement method, and the porosity of the sample to be tested is obtained by combining Bohr's law (PV=nRT). Porosity P=(V11-V12) / V11×100%, where V11 represents the apparent volume of the negative electrode active material layer, and V12 represents the real volume of the negative electrode active material layer.

[0076] When the relationship between the porosity of the negative electrode active material layer and the mass content of alkali metal ions is controlled to meet an appropriate range, the electrolyte can better and faster infiltrate the negative electrode plate, so that lithium ions can be better transmitted, the concentration polarization of lithium ions during the transmission process can be improved, the electrical properties of lithium-ion secondary batteries can be enhanced, and the phenomenon of metal dendrites can be improved, taking into account the kinetics and cycle performance of lithium-ion secondary batteries.

[0077] In some embodiments, the alkali metal ion comprises Na + , K + , Cs + In some embodiments, the alkali metal ion comprises Na + In some embodiments, the alkali metal ion comprises K + In some embodiments, the alkali metal ion comprises Cs + In some embodiments, the alkali metal ion comprises Na + and Cs + .

[0078] The above-mentioned alkali metal ions are all beneficial to the transmission of lithium ions and improve the power performance of the battery.

[0079] In some embodiments, based on the total mass of the electrolyte, the mass content A of the alkali metal ions satisfies: 1ppm≤A≤7000ppm, and can be 100ppm≤A≤7000ppm. In some embodiments, based on the total mass of the electrolyte, the mass content A of the alkali metal ions can be 1ppm, 5ppm, 10ppm, 50ppm, 100ppm, 500ppm, 1000ppm, 2000ppm, 3000ppm, 4000ppm, 5000ppm, 6000ppm, 7000ppm, or a value in the range consisting of any two of the above points.

[0080] It can be understood that the alkali metal ions in the electrolyte can participate in the formation of the SEI film and consume part of the alkali metal ions, resulting in a decrease in the mass content of the alkali metal ions in the electrolyte. For example, the mass content of the alkali metal ions in the electrolyte can be 1 ppm. Therefore, based on the total mass of the electrolyte, the mass content of the alkali metal ions is 1 ppm to 7000 ppm, which is the range protected in the embodiments of the present application.

[0081] Controlling the alkali metal ions within a suitable range can improve the power performance of the battery.

[0082] In some embodiments, the electrolyte further includes anions, the anions including PO 2 F 2 - 、FSO 3 - DFOB - , BF 4 - DFOP - 、BOB - ,PO 3 F 2- In some embodiments, the anions included in the electrolyte may be introduced together with the alkali metal ions, or introduced into the electrolyte via an electrolyte additive, such as a lithium salt additive including one of the anions mentioned above.

[0083] In some embodiments, based on the total mass of the electrolyte, the mass content of the anions is greater than 0 and less than or equal to 5%. Alternatively, based on the total mass of the electrolyte, the mass content of the anions is greater than 0 and less than or equal to 4%. In some embodiments, based on the total mass of the electrolyte, the mass content of the anions can be 0.01%, 0.02%, 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a value in the range consisting of any two of the above points.

[0084] The mass content of anions in the electrolyte or the electrolyte of the secondary battery can be detected by detection equipment and methods commonly used in the art, for example, by testing the mass content of anions by nuclear magnetic resonance spectroscopy.

[0085] In some embodiments, the mass content of the anions can be tested using the Oxford Instruments X-Pulse desktop nuclear magnetic resonance spectrometer, for example, according to a commonly used detection method in the art.

[0086] The above anions help improve the cycle performance and cycle life of secondary batteries. For example, for positive electrode sheets including lithium transition metal oxide positive electrode active materials, the lone pair electrons contained in the above anions can combine with lithium ions on the surface of the positive electrode sheets, change the Li / Ni mixing, stabilize the structure of the positive electrode sheets, change the charge transfer resistance (Rct) on the surface of the positive electrode sheets, and improve the cycle performance and cycle life of lithium-ion secondary batteries; for positive electrode sheets including lithium phosphate positive electrode active materials, the above anions can form a dense SEI film on the surface of the negative electrode sheets, improving the life of the battery.

[0087] Controlling the mass content of the introducing anions within an appropriate range can not only improve the cycle performance of lithium-ion secondary batteries, but also help reduce the formation of metal dendrites.

[0088] In some embodiments, the film-forming additive includes one or more of fluorinated carbonate compounds, sulfate compounds, and sulfonate compounds.

[0089] In some embodiments, the film-forming additive comprises a fluorocarbonate compound. In some embodiments, the film-forming additive comprises a sulfate compound. In some embodiments, the film-forming additive comprises a sulfonate compound. In some embodiments, the film-forming additive comprises a fluorocarbonate compound and a sulfate compound. In some embodiments, the film-forming additive comprises a fluorocarbonate compound and a sulfonate compound.

[0090] The addition of film-forming additives is conducive to the formation of a uniform and dense inorganic SEI film. For example, fluorinated carbonate compounds can form a LiF-rich, LiCO-rich SEI film on the surface of the negative electrode. 3 The inorganic SEI film, sulfate compounds can form a Li-rich 2 SO 4 The inorganic SEI film, sulfonate compounds can form a Li-rich 2 SO 3 Inorganic SEI film. The inorganic SEI film can not only inhibit the phenomenon of metal dendrites, but also hinder the reaction between the electrolyte and the positive / negative electrode sheets, improve the stability of lithium-ion secondary batteries, and enhance their cycle performance.

[0091] In some embodiments, the fluorinated carbonate compound includes one or more of fluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate or trifluoromethylethylene carbonate, and optionally includes fluoroethylene carbonate;

[0092] The sulfate ester compound includes one or more of 4,4'-vinyl sulfate, vinyl sulfate, diethyl sulfate, dimethyl sulfate and 4,4-bis(1,3,2-dioxathiolane)-2,2,2,2-tetraoxide, and optionally includes one or more of 4,4'-vinyl sulfate and vinyl sulfate; and / or,

[0093] The sulfonate compound includes one or more of 1,3-propane sultone, propene sultone, and 3-fluoro-1,3-propane sultone, and optionally includes 1,3-propane sultone.

[0094] The above-mentioned fluorinated carbonate compounds, sulfate compounds, and sulfonate compounds can all form a uniform and dense inorganic SEI film.

[0095] In some embodiments, based on the total mass of the electrolyte, the mass content B of the film-forming additive satisfies: 0.1%≤B≤7%, optionally 0.1%≤B≤6%.

[0096] In some embodiments, based on the total mass of the electrolyte, the mass content B of the film-forming additive may be selected to be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, or a value in the range formed by any two of the above points.

[0097] By controlling the mass content of the film-forming additive within a suitable range, a sufficiently uniform and dense inorganic SEI film can be formed, dendrites can be inhibited, interface side reactions can be hindered, and side reactions of lithium-ion secondary batteries can be reduced.

[0098] In some embodiments, the porosity C of the negative electrode active material layer is 20% to 60%, and optionally 20% to 40%.

[0099] In some embodiments, the porosity C of the negative electrode active material layer may be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or a value in a range consisting of any two of the above points.

[0100] Controlling the porosity of the negative electrode active material layer within an appropriate range can not only improve the wettability of the electrolyte to the negative electrode plate, thereby facilitating better transmission of lithium ions, improving the concentration polarization of lithium ions during transmission, enhancing the electrical properties of lithium-ion secondary batteries, and inhibiting the phenomenon of dendrites, but also reduce the risk of increased contact area between the electrolyte and the negative electrode active material due to excessive porosity, thereby reducing the degree of side reactions.

[0101] In some embodiments, based on the total mass of the electrolyte, the mass content of the lithium salt is 8% to 20%, optionally 9% to 18%, or 8% to 15%.

[0102] In some embodiments, based on the total mass of the electrolyte, the mass content of the lithium salt is 8%, 9%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, or a value in the range formed by any two of the above points.

[0103] Controlling the mass content of lithium salt within an appropriate range is beneficial to promoting the migration of lithium ions and reducing the DC impedance of lithium-ion secondary batteries.

[0104] In some embodiments, the lithium salt includes a first lithium salt and / or a second lithium salt, and the first lithium salt and the second lithium salt are each independently selected from LiFSI, LiPF 6 , LiBF 4 、LiTFSI、LiClO 4 、LiAsF 6 , LiBOB, LiDFOB, LiDFOP.

[0105] In some embodiments, the lithium salt comprises a first lithium salt. In some embodiments, the lithium salt comprises a second lithium salt. In some embodiments, the lithium salt comprises a first lithium salt and a second lithium salt. In some embodiments, the first lithium salt is selected from LiFSI. In some embodiments, the second lithium salt is selected from LiPF 6 .

[0106] LiFSI has a larger anion, which can effectively promote the migration of lithium ions, so that the lithium-ion secondary battery has an excellent lithium-ion migration number, reduces its DC impedance and the precipitation of metal dendrites, and LiFSI itself is insensitive to water and has good thermal stability, which can further improve the safety of lithium-ion secondary batteries. 6 The thermal stability of LiFSI is better than that of LiPF. 6 The combination can take into account both the electrical performance and thermal stability of the lithium-ion secondary battery.

[0107] In some embodiments, the first lithium salt LiFSI and the second lithium salt LiPF 6The mass ratio of the first lithium salt LiFSI and the second lithium salt LiPF 6 The mass ratio is not less than 3 and not more than 5.

[0108] In some embodiments, the mass ratio of the first lithium salt to the second lithium salt may be 0.1, 0.2, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or a value in a range consisting of any two of the above points.

[0109] By controlling the mass ratio of the first lithium salt to the second lithium salt to meet an appropriate range, the lithium-ion secondary battery can have excellent electrical properties.

[0110] In some embodiments, the electrolyte further comprises a solvent, and the solvent comprises a cyclic ester solvent and / or a linear ester solvent;

[0111] The cyclic ester solvent includes one or more of ethylene carbonate and propylene carbonate;

[0112] The linear ester solvent includes one or more of dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl methyl carbonate, methyl formate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, isopropyl acetate, and isoamyl acetate.

[0113] The above solvents can be used in combination with alkali metal salts and film-forming additives to enable lithium-ion secondary batteries to have lower DC impedance and excellent cycle performance.

[0114] In some embodiments, based on the total mass of the solvent, the mass content of the cyclic ester solvent is A, and the mass content of the linear ester solvent is (100%-A); wherein the mass content A of the cyclic ester solvent is 0% to 40%, 2% to 40%, or 5% to 35%.

[0115] In some embodiments, based on the total mass of the solvent, the mass content of the cyclic ester solvent is 2% to 40%, optionally 5% to 35%; the mass content of the linear ester solvent is 50% to 100%, optionally 60% to 95%.

[0116] In some embodiments, based on the total mass of the solvent, the mass content of the cyclic ester solvent can be 0, 0.01%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, or a value in the range consisting of any two of the above points. Based on the total mass of the solvent, the mass content of the linear ester solvent is 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, or a value in the range consisting of any two of the above points.

[0117] The mass contents of the cyclic ester solvent and the linear ester solvent are respectively controlled within a suitable range so that the lithium ion secondary battery has excellent electrical properties and safety.

[0118] [Positive electrode]

[0119] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0120] 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.

[0121] 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.).

[0122] In some embodiments, the positive electrode active material may be 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: an olivine-structured lithium-containing phosphate, 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.

[0123] In some embodiments, the active material of the positive electrode includes one or more of a lithium transition metal oxide positive electrode active material and a lithium phosphate positive electrode active material.

[0124] In some embodiments, the lithium transition metal oxide has the structural formula shown below:

[0125] LiNi x Co y N z M 1-x-y-z O 2 ,

[0126] Wherein N is selected from Mn and Al, M is selected from any one of Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V and Ti, 0<x<1, 0≤y≤1, 0≤z≤1, x+y+z≤1.

[0127] In some embodiments, the lithium transition metal oxide includes lithium cobalt oxide (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 NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O 2 ) and at least one of its modified compounds.

[0128] In some embodiments, the lithium-containing phosphate includes lithium iron phosphate (e.g., 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] [Negative electrode]

[0133] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector and containing at least a negative electrode active material.

[0134] 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.

[0135] 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.).

[0136] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery known in the art. The negative electrode active material may be used alone or in combination of two or more.

[0137] In some embodiments, the negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-carbon composite, lithium titanate, and silicon-oxygen composite.

[0138] In some embodiments, the negative electrode active material 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).

[0139] In some embodiments, the negative electrode active material 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.

[0140] In some embodiments, the negative electrode active material layer may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0141] 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.

[0142] [Isolation film]

[0143] In some embodiments, the lithium-ion secondary battery further includes a separator, which can be any known porous separator with good chemical stability and mechanical stability.

[0144] 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. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different.

[0145] 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.

[0146] In some embodiments, the lithium-ion secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0147] In some embodiments, the outer packaging of the lithium ion secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the lithium ion 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 can be listed.

[0148] The shape of the lithium-ion secondary battery in this application can be cylindrical, square or any other shape. For example, Figure 1 The lithium ion secondary battery 5 is a square structure as an example.

[0149] In some embodiments, reference Figure 2 , 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 lithium-ion secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0150] In some embodiments, lithium-ion secondary batteries can be assembled into a battery module. The number of lithium-ion 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.

[0151] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of lithium-ion secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of lithium-ion secondary batteries 5 may be fixed by fasteners.

[0152] Optionally, the battery module 4 may further include a housing having a housing space, and the plurality of lithium-ion secondary batteries 5 are housed in the housing space.

[0153] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0154] Figure 4 and Figure 5 1 is a battery pack 1 as an example. Figure 4 and Figure 5 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and 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.

[0155] In addition, the present application also provides an electrical device, which includes at least one of the lithium-ion secondary battery, battery module, or battery pack provided in the present application. The lithium-ion 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 to these.

[0156] As the electrical device, a lithium-ion secondary battery, a battery module or a battery pack may be selected according to its usage requirements.

[0157] Figure 6 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, etc. In order to meet the power consumption device's requirements for high power and high energy density of lithium-ion secondary batteries, a battery pack or a battery module can be used.

[0158] 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 lithium-ion secondary battery may be used as a power source.

[0159] Example

[0160] 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.

[0161] 1. Preparation method

[0162] Example 1

[0163] 1) Electrolyte

[0164] In an argon atmosphere glove box (H 2 O<0.1ppm, O 2 <0.1ppm), cyclic ester solvent ethylene carbonate and linear ester solvent dimethyl carbonate were mixed in a mass ratio of 25:75 to obtain a mixed solvent. Then lithium salt lithium hexafluorophosphate and lithium bis(trifluoromethanesulfonyl imide) (LiFSI and LiPF 6 The mass ratio is 3:1) dissolved in the above mixed solvent to make the mass content of lithium salt 15%, stirred evenly, and then added alkali metal salt NaPO 2 F2 and a film-forming additive 4,4'-dithioethylene sulfate, and mixed evenly to obtain an electrolyte; wherein, based on the total mass of the electrolyte, the alkali metal ion Na + The mass content of isocyanate is 30 ppm, and the mass content of 4,4'-dithiovinyl sulfate is 2%.

[0165] 2) Preparation of positive electrode

[0166] 1 wt% polyvinylidene fluoride binder was fully dissolved in N-methylpyrrolidone, and then 1 wt% carbon black conductive agent and 98 wt% lithium transition metal oxide positive electrode active material LiNi were added. 0.5 Co 0.2 Mn 0.3 O 2 The mixture is stirred and mixed to obtain a positive electrode slurry. The slurry is evenly coated on the surface of the current collector aluminum foil to prepare a positive electrode film layer, and then transferred to a vacuum drying oven for complete drying. The dried electrode sheet is rolled and punched to obtain a positive electrode sheet.

[0167] 3) Preparation of negative electrode sheet

[0168] The negative electrode active material artificial graphite, conductive agent carbon black, thickener carboxymethyl cellulose (CMC), and adhesive styrene butadiene rubber (SBR) are mixed in a weight ratio of 96:2:1:1 and dissolved in deionized water to form a negative electrode slurry, and the negative electrode slurry is obtained under the action of a vacuum mixer, and then the slurry is coated on the surface of the copper foil. Finally, it is transferred to a vacuum drying oven for complete drying, and then cut and die-cut, and the compaction density of the electrode film layer is adjusted so that the porosity of the negative electrode active material is 40%, and the negative electrode sheet is obtained.

[0169] 4) Isolation film

[0170] Polypropylene film is used as the isolation film.

[0171] 5) Preparation of batteries

[0172] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, the separator is placed between the positive and negative electrode sheets to play an isolating role, the bare cell is welded with the pole ear, and the bare cell is placed in an aluminum shell, and baked at 80°C to remove water, and then the above-mentioned electrolyte is injected and sealed to obtain an uncharged battery. The uncharged battery is then subjected to the processes of static, hot and cold pressing, formation, shaping, and capacity testing in sequence to obtain the lithium-ion secondary battery product of Example 1.

[0173] Embodiments 2 to 30

[0174] The battery preparation methods in Examples 2 to 30 are basically similar to those in Example 1, but the preparation parameters of the electrolyte, the positive electrode active material, and the negative electrode active material are adjusted. The specific parameters are shown in Table 1.

[0175] Comparative Example 1

[0176] The battery preparation method in Comparative Example 1 is basically similar to that in Example 1, but there is no film-forming additive in the electrolyte. The specific parameters are shown in Table 1.

[0177] Comparative Example 2

[0178] The battery preparation method in Comparative Example 2 is basically similar to that in Example 1, but no alkali metal salt is added to the electrolyte. The specific parameters are shown in Table 1.

[0179] Comparative Example 3

[0180] The battery preparation method in Comparative Example 3 is basically similar to that in Example 1, but no alkali metal salt and film-forming additive are added to the electrolyte. The specific parameters are shown in Table 1.

[0181] Comparative Examples 4-5

[0182] The battery preparation methods in Comparative Examples 4 to 5 are basically similar to those in Example 1, but the range of B / A is adjusted. The specific parameters are shown in Table 1.

[0183] Comparative Examples 6-7

[0184] The battery preparation methods in Comparative Examples 6 to 7 are basically similar to those in Example 28, but the range of B / A is adjusted. The specific parameters are shown in Table 1.

[0185] 2. Performance Test

[0186] 1. Negative electrode performance test

[0187] 1) Porosity test of negative electrode active material layer

[0188] The real volume of the sample to be tested is accurately measured by displacement method using inert gas helium or nitrogen, and the porosity of the sample to be tested is obtained by combining Bohr's law (pV=nRT, p is pressure, V is gas volume, T is temperature, n is the amount of gas, and R is the molar gas constant). Porosity P=(V11-V12) / V11×100%, where V11 represents the apparent volume of the negative electrode active material layer, and V12 represents the real volume of the negative electrode active material layer.

[0189] 2. Battery performance test

[0190] 1) DC resistance (DCR) test

[0191] At -25℃, adjust the single battery state of charge to 50% SOC, let it stand for 30 minutes, record the battery voltage at this time as U1 (V), use 0.36C discharge for 10 seconds, record the battery voltage at this time as U2 (V), and the corresponding battery discharge current I (mA) is 0.36 × battery design capacity (mAh). DC resistance DCR (mΩ) = (U1-U2) / I.

[0192] 2) Cycle performance test

[0193] The cycle performance test process is as follows: at 25°C, the prepared battery is charged to 4.25V at a constant current of 2C, then charged at a constant voltage of 4.25V until the current drops to 0.05C, and after standing for 5 minutes, discharged to 2.5V at a constant current of 1C. This is the first charge / discharge cycle of the battery, and the discharge capacity of this time is recorded as the discharge capacity of the first cycle of the battery (C1); repeat the above steps for the same battery, and the process capacity of the battery after the nth cycle (Cn), the capacity retention rate after n cycles = Cn / C1×100%. Record the number of cycles at which the cycle capacity retention rate is 80%. The test process of the comparative example and other embodiments is the same as above.

[0194] 3) Metal dendrite test

[0195] The battery after n cycles was placed in an argon atmosphere glove box (H 2 O<0.1ppm, O 2 <0.1ppm) and visually observe the surface morphology of the negative electrode to determine whether metal dendrites are generated. The negative electrode sheet without white spots is judged as no metal dendrites, the negative electrode sheet with sporadic white spots is judged as slight metal dendrites, and the negative electrode sheet with dense white spots is judged as severe metal dendrites. The test process of the comparative example and other embodiments is the same as above.

[0196] 3. Determination of mass content of alkali metal ions

[0197] Test of alkali metal ions in electrolyte: Take 10 ml of the electrolyte prepared above and test it using the inductively coupled plasma atomic emission spectrometry of Thermo Fisher Scientific model ICAP-7400. When preparing a secondary battery, take 10 ml of free electrolyte from the injection port of the secondary battery and test it using the above method.

[0198] III. Analysis of test results of various embodiments and comparative examples

[0199] 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 Tables 1 and 2 below.

[0200] Table 1

[0201]

[0202]

[0203] Table 2

[0204]

[0205]

[0206] According to the above results, the lithium ion secondary batteries in Examples 1 to 30 all include an electrolyte, and the electrolyte includes an alkali metal ion having an ion radius greater than that of a lithium ion and a film-forming additive. Wherein, based on the total mass of the electrolyte, the mass content A of the alkali metal ion and the mass content B of the additive satisfy: 0.14≤B / A≤2000.

[0207] From the comparison between Examples 1 to 27 and Comparative Example 1, it can be seen that the electrolyte in the present application includes a film-forming additive 4,4'-disulfated vinyl ester, which is beneficial to increase the number of cycles at which the battery cycle capacity retention rate is 80%. From the comparison between Examples 1 to 27 and Comparative Example 2, it can be seen that the electrolyte in the present application includes an alkali metal ion Na with an ion radius larger than that of a lithium ion. + or K + , which is beneficial to reducing the DC impedance of the battery. From the comparison between Examples 1 to 27 and Comparative Example 3, it can be seen that the electrolyte in the embodiments of the present application includes both alkali metal ions having an ion radius greater than that of lithium ions and film-forming additives, which is beneficial to reducing the DC impedance of the battery and increasing the number of cycles at which the battery cycle capacity retention rate is 80%.

[0208] From the comparison of Examples 1 to 16, Examples 22 to 27 and Comparative Examples 4 to 5, and Examples 28 to 29 and Comparative Examples 6 to 7, it can be seen that, based on the total mass of the electrolyte, controlling the mass content A of the alkali metal ions and the mass content B of the additive to satisfy: 0.14≤B / A≤2000 is beneficial to increasing the number of cycles at which the battery cycle capacity retention rate is 80%.

[0209] It can be seen from Examples 1 to 8 and Examples 23 to 25 that, based on the total mass of the electrolyte, controlling the mass content A of the alkali metal ions and the mass content B of the additive to satisfy: 0.2≤B / A≤2000 can reduce the DC impedance of the battery, increase the number of battery cycles with a cycle capacity retention rate of 80%, and take into account both the power performance and cycle performance of the battery.

[0210] It can be seen from Examples 3, 15-16 and 26-27 that the porosity C of the negative electrode active material layer and the mass content A of the alkali metal ions in the total mass of the electrolyte are controlled to satisfy: 5×10 -5≤A / C≤0.035, the DC impedance of the battery and the number of cycles at which the cycle capacity retention rate is 80% are improved. From the comparison between Examples 3, 15 to 16, 26 and Example 27, it can be seen that the porosity C of the negative electrode active material layer and the mass content A of the alkali metal ions in the total mass of the electrolyte are controlled to meet the following conditions: 5×10 -5 ≤A / C≤0.025, which is further beneficial to increasing the number of cycles at which the battery cycle capacity retention rate is 80%.

[0211] From the comparison between Examples 2 to 4 and Example 1, it can be seen that, based on the total mass of the electrolyte, the mass content A of the alkali metal ions is controlled to satisfy 100ppm≤A≤7000ppm, which further reduces the DC impedance of the battery, increases the number of cycles with a battery cycle capacity retention rate of 80%, and improves the metal dendrites of the battery.

[0212] As can be seen from Examples 5 to 8, based on the total mass of the electrolyte, the mass content B of the film-forming additive is controlled to meet: 0.1% ≤ B ≤ 7%, which is helpful to reduce the DC impedance of the battery and increase the number of battery cycles with a cycle capacity retention rate of 80%. As can be seen from the comparison between Examples 5 to 7 and Example 8, based on the total mass of the electrolyte, the mass content B of the film-forming additive is further controlled to meet: 0.1% ≤ B ≤ 6%, which is beneficial to further reduce the DC impedance of the battery and improve the power performance of the battery.

[0213] As can be seen from Examples 3 and 9, the alkali metal ions in the electrolyte include Na + or K + , which are beneficial to reducing the DC impedance of the battery, increasing the number of cycles where the battery cycle capacity retention rate is 80%, and improving the metal dendrite condition of the battery.

[0214] It can be seen from Example 3 and Examples 12 to 14 that the film-forming additives in the electrolyte include one or more of 4,4'-ethylene disulfate, fluoroethylene carbonate, and 1,3-propane sultone, which can enable the battery to have a low DC impedance, increase the number of battery cycles, and improve the metal dendrites of the battery.

[0215] It can be seen from Examples 3 and 15 to 16 that controlling the porosity C of the negative electrode active material layer to 20% to 60% can reduce the DC impedance of the battery and improve the number of cycles at which the battery cycle capacity retention rate is 80%.

[0216] As can be seen from Examples 3 and 17 to 18, controlling the mass content of lithium salt to 8% to 20% based on the total mass of the electrolyte helps to improve the DC impedance of the battery and the number of cycles at which the battery cycle capacity retention rate is 80%. As can be seen from Examples 3 and 19 to 20, the lithium salt LiFSI and the lithium salt LiPF 6When the mass ratio is not less than 0.1 and not more than 5, it also helps to improve the metal dendrites of the battery.

[0217] As can be seen from Examples 3 and 21, artificial graphite or silicon-carbon composite can be used as the negative electrode active material layer, and as can be seen from Examples 3 and 28, LiNi 0.5 Co 0.2 Mn 0.3 O 2 Positive electrode active material or LiFePO 4 The preparation of positive electrode sheets using positive electrode active materials helps to obtain batteries with low DC impedance, high cycle numbers and improved metal dendrite conditions.

[0218] It can be seen from Examples 28 to 29 that, based on the total mass of the solvent, controlling the mass content of the cyclic ester solvent to 5% to 35% and the mass content of the linear ester solvent to 65% to 95% helps to improve the DC impedance and cycle number of the battery.

[0219] 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, characterized in that: The electrolyte includes an alkali metal ion having an ion radius greater than that of a lithium ion and a film-forming additive; Based on the total mass of the electrolyte, the mass content A of the alkali metal ion and the mass content B of the film-forming additive satisfy: 0.10≤B / A≤6×10 4 .

2. The lithium ion secondary battery according to claim 1, characterized in that: The lithium-ion secondary battery comprises a negative electrode plate, wherein the negative electrode plate comprises a current collector and a negative electrode active material layer located on at least one side of the current collector and comprising at least a negative electrode active material, wherein the porosity C of the negative electrode active material layer and the mass content A of the alkali metal ions in the total mass of the electrolyte satisfy the following relationship: 10 -6 ≤A / C≤0.035, optional 5×10 -5 ≤A / C≤0.

025.

3. The lithium ion secondary battery according to claim 1 or 2, characterized in that: Based on the total mass of the electrolyte, the mass content A of the alkali metal ions and the mass content B of the film-forming additive satisfy: 0.14≤B / A≤2000.

4. The lithium ion secondary battery according to any one of claims 1 to 3, characterized in that: The alkali metal ions include Na + , K + , Cs + One or more of .

5. The lithium ion secondary battery according to any one of claims 1 to 4, characterized in that: Based on the total mass of the electrolyte, the mass content A of the alkali metal ions satisfies: 1ppm≤A≤7000ppm, and can be optionally 100ppm≤A≤7000ppm.

6. The lithium ion secondary battery according to any one of claims 1 to 5, characterized in that: The electrolyte also includes anions, the anions include PO2F2 - 、FSO3 - DFOB - 、BF4 - DFOP - 、BOB - PO3F 2- One or more of .

7. The lithium ion secondary battery according to any one of claims 1 to 6, characterized in that: The film-forming additive includes one or more of fluorocarbonate compounds, sulfate compounds, and sulfonate compounds.

8. The lithium ion secondary battery according to claim 7, characterized in that: The fluorinated carbonate compound includes one or more of fluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate or trifluoromethylethylene carbonate, and optionally includes fluoroethylene carbonate; The sulfate ester compound includes one or more of 4,4'-vinyl sulfate, vinyl sulfate, diethyl sulfate, dimethyl sulfate and 4,4-bis(1,3,2-dioxathiolane)-2,2,2,2-tetraoxide, and optionally includes one or more of 4,4'-vinyl sulfate and vinyl sulfate; and / or, The sulfonate compound includes one or more of 1,3-propane sultone, propene sultone, and 3-fluoro-1,3-propane sultone, and optionally includes 1,3-propane sultone.

9. The lithium ion secondary battery according to any one of claims 1 to 8, characterized in that: Based on the total mass of the electrolyte, the mass content B of the film-forming additive satisfies: 0.1%≤B≤7%, and can be optionally 0.1%≤B≤6%.

10. The lithium ion secondary battery according to any one of claims 2 to 9, characterized in that: The porosity C of the negative electrode active material layer is 20% to 60%, and can be optionally 20% to 40%.

11. The lithium ion secondary battery according to any one of claims 1 to 10, characterized in that: Based on the total mass of the electrolyte, the mass content of the lithium salt is 8% to 20%, and can be optionally 8% to 15%.

12. The lithium ion secondary battery according to any one of claims 1 to 11, characterized in that: The lithium salt includes a first lithium salt, a second lithium salt or a combination of the first lithium salt and the second lithium salt, and the first lithium salt and the second lithium salt are each independently selected from one of LiFSI, LiPF6, LiBF4, LiTFSI, LiClO4, LiAsF6, LiBOB, LiDFOB, and LiDFOP.

13. The lithium ion secondary battery according to claim 12, characterized in that: The first lithium salt is selected from LiFSI, and the second lithium salt is selected from LiPF6; The mass ratio of the first lithium salt to the second lithium salt is not less than 0.1 and not more than 5; optionally, the mass ratio of the first lithium salt to the second lithium salt is not less than 3 and not more than 5.

14. The lithium ion secondary battery according to any one of claims 1 to 13, characterized in that: The electrolyte further comprises a solvent, wherein the solvent comprises a cyclic ester solvent and / or a linear ester solvent; The cyclic ester solvent includes one or more of ethylene carbonate and propylene carbonate; The linear ester solvent includes one or more of dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl methyl carbonate, methyl formate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, isopropyl acetate, and isoamyl acetate.

15. The lithium ion secondary battery according to claim 14, characterized in that: Based on the total mass of the solvent, the mass content of the cyclic ester solvent is A, and the mass content of the linear ester solvent is (100%-A); Wherein, the mass content A of the cyclic ester solvent is 2% to 40%, and can be optionally 5% to 35%.

16. The lithium ion secondary battery according to any one of claims 2 to 15, characterized in that: The negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-carbon composite, lithium titanate, and silicon-oxygen composite.

17. The lithium ion secondary battery according to any one of claims 1 to 16, characterized in that: The lithium-ion secondary battery comprises a positive electrode plate, and the positive electrode plate comprises one or more of a lithium transition metal oxide positive electrode active material and a lithium-containing phosphate positive electrode active material.

18. An electrical device, characterized in that: A lithium ion secondary battery comprising the lithium ion secondary battery according to any one of claims 1 to 17.

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