Battery cell, secondary battery, and electric device

Abstract

The invention relates to a battery monomer, a secondary battery and an electric device. The battery monomer comprises a positive pole piece and an electrolyte, the positive pole piece comprises a positive active material layer, and the thickness of the positive active material layer is T mm; the electrolyte comprises an isocyanate substance, and the mass ratio of the isocyanate substance in the electrolyte is A%; the ratio of the total mass of the electrolyte of the battery monomer to the capacity of the battery monomer is C g / Ah; a, C and T satisfy 0.1 < = A * C / T < = 20; the isocyanate substance can be subjected to nucleophilic reaction with moisture in the positive pole piece, so that side reaction caused by moisture in the positive pole piece is reduced; meanwhile, a reaction product of a nucleophilic reaction between the isocyanate substance and water can participate in generation of an SEI film, so that the stability of the SEI film is improved, and the high-temperature cycle performance of the battery monomer is further improved; furthermore, when A * C / T is more than or equal to 0.2 and less than or equal to 20, the high-temperature cycle performance and the dynamic performance can be considered.

Description

Technical Field

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

[0002] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0003] 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. With the development of lithium-ion batteries, higher requirements have been put forward for their energy density. Lithium iron phosphate materials are polyanion materials. Due to their advantages of high capacity, low price, abundant raw material sources, environmental friendliness, thermal stability and excellent cycle charge and discharge performance, they are used as positive electrode active materials of lithium-ion batteries.

[0004] However, when lithium iron phosphate materials are used as positive electrode active materials, the battery cycle performance is poor. Summary of the invention

[0005] The present application provides a battery cell, a secondary battery and an electrical device to improve the cycle performance of the battery cell, especially to significantly improve the cycle performance of the battery cell using lithium iron phosphate materials as positive electrode materials.

[0006] In order to achieve the above-mentioned object, the first aspect of the present application provides a battery cell, comprising:

[0007] A positive electrode sheet, the positive electrode sheet comprising a positive electrode active material layer, the thickness of the positive electrode active material layer is Tmm; and

[0008] An electrolyte, wherein the electrolyte contains an isocyanate substance, and the mass proportion of the isocyanate substance in the electrolyte is A%;

[0009] The ratio of the total mass of the electrolyte of the secondary battery to the capacity of the battery cell is C g / Ah;

[0010] A, C and T satisfy: 0.2≤A*C / T≤20.

[0011] Therefore, the present application adds isocyanate substances to the electrolyte, and the isocyanate substances can undergo nucleophilic reaction with the moisture in the positive electrode plate, thereby reducing the side reactions caused by the presence of moisture in the positive electrode plate; at the same time, the reaction products of the nucleophilic reaction between the isocyanate substances and moisture can participate in the formation of the SEI film, thereby improving the stability of the SEI film, and thereby improving the high-temperature cycle performance of the battery cell; further, when the mass proportion of the isocyanate substances in the electrolyte, the thickness of the positive electrode plate, and the ratio of the total mass of the electrolyte of the battery cell to the capacity of the battery cell satisfy 0.1≤A*C / T≤20, the isocyanate substances can effectively inhibit the influence of moisture in the positive electrode plate, taking into account the high-temperature cycle performance and kinetic performance of the battery cell.

[0012] In some embodiments, 0.01≤A≤0.5.

[0013] In some embodiments, 0.08≤T≤0.12.

[0014] In some embodiments, 2.5≤C≤4.5.

[0015] In some embodiments, the isocyanate substance has a structure shown in the following formula (I):

[0016]

[0017] Wherein, R1 includes any one of -CH3, -C2H5 and -OCH3; R2, R3, R4, R5 and R6 each independently include any one of hydrogen, isocyanate group and sulfonyl isocyanate group, and at least one of R2, R3, R4, R5 and R6 is an isocyanate group or a sulfonyl isocyanate group.

[0018] In some embodiments, the isocyanate substance includes one or more of toluene diisocyanate, p-toluenesulfonyl isocyanate, m-toluene isocyanate, 4-ethylphenyl isocyanate, 3,4-dimethylphenyl isocyanate and 3,5-dimethylphenyl isocyanate.

[0019] In some embodiments, the electrolyte further comprises fluoroethylene carbonate.

[0020] In some embodiments, the fluoroethylene carbonate has at least one of the following characteristics:

[0021] (1) The mass proportion of the fluoroethylene carbonate in the electrolyte is B%, and A and B satisfy the following: 1%≤A / B≤100%;

[0022] (2) The mass proportion of the fluoroethylene carbonate in the electrolyte is B%, and 0.1≤B≤1.

[0023] In some embodiments, the electrolyte further comprises a first lithium salt and a second lithium salt, wherein the first lithium salt comprises lithium hexafluorophosphate, and the second lithium salt comprises at least one of lithium bis(fluorosulfonyl)imide salt and lithium bis(trifluoromethanesulfonyl)imide.

[0024] In some embodiments, the first lithium salt and the second lithium salt have at least one of the following characteristics:

[0025] (1) The mass of the second lithium salt accounts for 10% to 80% of the mass of the first lithium salt;

[0026] (2) The sum of the mass proportions of the first lithium salt and the second lithium salt in the electrolyte is 8%-20%.

[0027] In some embodiments, the sum of the mass proportions of the first lithium salt and the second lithium salt in the electrolyte is 8%-20%.

[0028] In some embodiments, the positive electrode active material layer comprises a positive electrode active material, and the positive electrode active material has at least one of the following characteristics:

[0029] (1) The specific surface area of ​​the positive electrode active material is 8 m 2 / g-18m 2 / g;

[0030] (2) The positive electrode active material includes a lithium iron phosphate material.

[0031] A second aspect of the present application provides a secondary battery, comprising the battery cell of the first aspect of the present application.

[0032] The secondary battery of the present application has excellent high-temperature cycle performance and dynamic performance.

[0033] A third aspect of the present application provides an electrical device, comprising at least one of the battery cell of the first aspect of the present application and the secondary battery of the second aspect of the present application.

[0034] The electric device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery.

[0035] Details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the specification, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to better describe and illustrate the embodiments or examples provided by the present application, reference may be made to one or more drawings. The additional details or examples used to describe the drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes of these applications currently understood. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0037] Figure 1 It is a schematic diagram of a battery cell according to an embodiment of the present application.

[0038] Figure 2 for Figure 1 An exploded view of a battery cell according to an embodiment of the present application is shown.

[0039] Figure 3 It is a schematic diagram of a battery module according to one embodiment of the present application.

[0040] Figure 4 A schematic diagram of a battery pack according to an embodiment of the present application.

[0041] Figure 5 for Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0042] Figure 6 FIG. 1 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0043] Description of reference numerals:

[0044] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 cover plate; 6 electrical device. DETAILED DESCRIPTION

[0045] Below, some embodiments of the battery cells, secondary batteries and electrical devices of the present application are described in detail with appropriate reference to the 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 descriptions 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.

[0046] "Scope" disclosed in the present application can be 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 excluding end values, and any end value can be included or not included independently, and can be combined arbitrarily, 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 listed, and if the maximum range values ​​3,4 and 5 are also listed, the following scope can all be 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 for these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to listing the parameter as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9 and 10.

[0047] In the present application, "plurality", "multiple" and the like, unless otherwise specified, refer to a number greater than or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0048] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0049] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. The "implementation methods" mentioned herein have a similar understanding.

[0050] Those skilled in the art will appreciate that, in the methods of each embodiment or example, the order in which each step is written does not mean a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible internal logic. 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), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) can be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0051] In the present application, in the open technical features or technical solutions described by the words "contain", "include", "comprise", etc., unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions including additional members in addition to the listed members. For example, A includes a1, a2 and a3. Unless otherwise specified, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "A consists of a1, a2 and a3" and the feature or solution of "A not only includes a1, a2 and a3, but also includes other members". In the present application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0052] In this application, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

[0053] Lithium iron phosphate materials are polyanionic materials. They are used as positive active materials for lithium-ion batteries because of their high capacity, low price, abundant raw material sources, environmental friendliness, thermal stability, and excellent cycle charge and discharge performance. However, since lithium iron phosphate materials are usually nanomaterials with small particle sizes and are coated with polar functional groups on the surface, they have strong water absorption properties. After using them to make positive electrode sheets, although they will try their best to perform high-temperature baking processes before entering the shell, the residual moisture in the positive electrode sheets cannot be completely removed. And the thicker the positive electrode sheet, the lower the baking efficiency, and the more difficult it is to bake out the moisture in the positive electrode sheet. The residual moisture in the positive electrode sheet will decompose with the lithium salt in the electrolyte to produce HF; this side reaction will not only consume the lithium ions in the electrolyte and cause capacity loss, but the reaction products will also be enriched on the surface of the negative electrode sheet, resulting in the thickening of the SEI film and increasing the battery impedance, thereby causing irreversible loss of the battery's cycle stability. The reaction between lithium hexafluorophosphate and moisture is:

[0054] LiPF6+H2O→HF+PF5+LiF

[0055] In the related art, in order to remove moisture from the positive electrode plate, some water-removing and acid-removing additives can be used in the electrolyte to reduce the negative impact of moisture, but these additives often participate in film formation, resulting in increased battery impedance. In this regard, the following two measures can usually be used to improve: (1) Add additives with high reduction potential and low impedance to the electrolyte to form a SEI film before the water-removing additive reacts to form a film, so as to avoid the water-removing additive participating in film formation and deteriorating DCR; (2) Use DCR additives. However, the SEI film formed by the above two additives is a porous structure. Although the ion conductivity is high, it cannot effectively passivate the negative electrode. When the dosage is high, it will affect the high-temperature cycle performance of the battery.

[0056] In addition, the use of water-resistant lithium salts in the electrolyte can also slow down the decomposition of the electrolyte and improve battery performance. However, the film-forming stability of water-resistant lithium salt anions is not as good as that of hexafluorophosphate ions, and their excessive participation in film formation is not conducive to the high-temperature cycle life of the battery.

[0057] Based on the above problems, the present invention provides a battery cell, in which isocyanate substances are added to the electrolyte of the battery to reduce the influence of moisture in the positive electrode plate, and the isocyanate substances react with moisture to generate reaction products that can participate in the formation of SEI film, thereby improving the stability of the SEI film and improving the high-temperature cycle performance; at the same time, the amount of isocyanate substances in the electrolyte is adjusted based on the thickness of the positive electrode plate, which can take into account the high-temperature cycle performance and dynamic performance of the battery cell.

[0058] The first aspect of the present application provides a battery cell, comprising a positive electrode plate and an electrolyte; the positive electrode plate comprises a positive electrode active material layer, the thickness of the positive electrode active material layer is T mm; the electrolyte contains an isocyanate substance, and the mass proportion of the isocyanate substance in the electrolyte is A%; the ratio of the total mass of the electrolyte of the battery cell to the capacity of the battery cell is C g / Ah; A, C and T satisfy: 0.2≤A*C / T≤20.

[0059] It should be noted that A% refers to the mass proportion of isocyanate substances in the electrolyte in the battery cell obtained after formation or in the battery cell after continued charge and discharge cycles. T refers to the thickness of the positive electrode active material layer on one side of the positive electrode collector in the positive electrode plate of the battery cell obtained after formation. The ratio of the total mass of the electrolyte of the battery cell to the capacity of the battery cell refers to the ratio of the total mass of the electrolyte of the battery cell obtained after formation or in the battery cell after continued charge and discharge cycles to the capacity of the battery cell. "Battery cell obtained after formation" refers to a fresh battery cell obtained after formation, which has not been subjected to further charge and discharge cycles.

[0060] The physical meaning represented by A*C / T refers to the ratio between the weight (in g) of isocyanate substances required to be added for a battery cell capacity of 1Ah and the thickness (in mm) of the positive electrode plate. For example, A*C / T can be 0.2, 0.3, 0.5, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or a range between any two of the above values. When 0.2≤A*C / T≤20, the battery cell has excellent high-temperature cycle performance and kinetic performance; when A*C / T is lower than 0.1, the water removal effect of isocyanate substances is poor, which may result in the inability to effectively improve the high-temperature cycle performance of the battery cell; when A*C / T is higher than 20, the DC impedance of the battery cell may deteriorate.

[0061] It should be noted that in this application, unless otherwise specified, "battery cell" refers to a basic unit that can realize the mutual conversion of chemical energy and electrical energy, and further, generally speaking, at least includes a positive electrode sheet, a negative electrode sheet and an electrolyte. 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 active ions between the positive electrode sheet and the negative electrode sheet.

[0062] The liquid battery cell also includes a separator, which is arranged between the positive electrode and the negative electrode, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through. The electrolyte exists in the electrolyte.

[0063] As an example, whether the electrolyte mentioned above contains isocyanate substances can refer to GB / T9722-2006 "General Rules for Gas Chromatography of Chemical Reagents", and gas chromatography is used for qualitative and quantitative determination.

[0064] Understandably, the present application adds isocyanate substances to the electrolyte, and the isocyanate substances can undergo nucleophilic reaction with the moisture in the positive electrode plate, thereby reducing the side reactions caused by the presence of moisture in the positive electrode plate; at the same time, the reaction products of the nucleophilic reaction between the isocyanate substances and moisture can participate in the formation of the SEI film, thereby improving the stability of the SEI film, and thereby improving the high-temperature cycle performance of the battery cell; further, when the mass proportion of the isocyanate substances in the electrolyte, the thickness of the positive electrode active material layer, and the ratio of the total mass of the electrolyte of the battery cell to the capacity of the battery cell satisfy 0.2≤A*C / T≤20, the isocyanate substances can effectively inhibit the influence of moisture in the positive electrode plate, taking into account the high-temperature cycle performance and kinetic performance of the battery cell.

[0065] The nucleophilic reaction process between isocyanates and water is:

[0066] 2RNCO+H2O→RNHCONHR+CO2↑

[0067] In some embodiments, 0.01≤A≤0.5; for example, it can be, but not limited to, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.13, 0.15, 0.17, 0.2, 0.23, 0.25, 0.27, 0.3, 0.33, 0.35, 0.38, 0.4, 0.43, 0.45, 0.48, 0.5 or a range between any two of the above values. When the mass proportion of isocyanate substances in the electrolyte is higher than A%, the DC internal resistance of the battery may be deteriorated.

[0068] As an example, the mass proportion of the above-mentioned isocyanate substances in the electrolyte can be determined by referring to GB / T 9722-2006 "General Rules for Gas Chromatography of Chemical Reagents" using gas chromatography.

[0069] In some embodiments, 0.08≤T≤0.12; for example, it can be 0.08, 0.085, 0.09, 0.095, 0.1, 0.105, 0.11, 0.115, 0.12 or a range between any two of the above values. When the thickness of the positive electrode active material layer is greater than 0.12 mm, the more water contained in the positive electrode plate, the more isocyanate substances need to be added, which may affect the DC internal resistance of the battery cell.

[0070] As an example, the thickness of the positive electrode active material layer mentioned above can be measured by the following method: first, use a spiral micrometer to measure the thickness T1 of the middle of the positive electrode plate, and measure the thickness T2 of the positive electrode collector; if the positive electrode plate is coated on one side, the thickness of the positive electrode active material layer is T1-T2; if the positive electrode plate is coated on both sides, the thickness of the positive electrode active material layer is (T1-T2) / 2.

[0071] As a possible implementation, 2.5≤C≤4.5; for example, it can be but not limited to 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, 4.5 or a range between any two of the above values. When the ratio of the total mass of the electrolyte of the battery cell to the capacity of the battery cell is within the above range, the secondary battery has a longer cycle life and lower gas production.

[0072] As an example, the ratio of the total mass of the electrolyte of the battery cell mentioned above to the battery cell capacity can be measured by the following method: take a secondary battery, charge it to 3.8V at 0.3C and charge it at a constant voltage until the current is ≤0.05C, then discharge the battery to 2.0V at 0.1C, at which time the battery capacity is D and the battery weight is W1. The battery is then disassembled and all parts are immersed in DMC, with fresh DMC replaced every 12 hours. After 48 hours, take out all parts and dry them at 60°C and -80kPa. At this time, the mass is W2, and the ratio of the total mass of the electrolyte to the battery cell capacity is (W1-W2) / D.

[0073] In some embodiments, the isocyanate material has a structure shown in the following formula (I):

[0074]

[0075] Wherein, R1 includes any one of -CH3, -C2H5 and -OCH3; R2, R3, R4, R5, R6 each independently include any one of hydrogen, isocyanate group and sulfonyl isocyanate group, and at least one of R2, R3, R4, R5 and R6 is an isocyanate group or a sulfonyl isocyanate group.

[0076] When aromatic isocyanates are added to the electrolyte, on the one hand, aromatic isocyanates have good thermal stability and are electron-rich compounds, which can delocalize nitrogen nuclei and act as weak bases to inhibit the reaction of PF5, hindering the decomposition of LiPF6 to produce HF and LiF; on the other hand, the thickness of the SEI film formed by solvents is usually uneven and easily destroyed to form active sites, further inducing decomposition reactions of the electrolyte during the charge and discharge cycle; and aromatic isocyanates have a higher reduction potential than carbonate solvents, and can form a stable and uniform SEI film in advance before the solvent decomposes, avoiding the continuous reduction of the solvent and the structural degradation of the graphite electrode surface, and protecting the graphite electrode from HF corrosion, thereby improving the electrochemical properties of the graphite electrode.

[0077] In some embodiments, the isocyanate material includes one or more of toluene diisocyanate (TDI), p-toluenesulfonyl isocyanate (PTSI), m-toluene isocyanate, 4-ethylphenyl isocyanate, 3,4-dimethylphenyl isocyanate, and 3,5-dimethylphenyl isocyanate.

[0078] It should be noted that the isocyanate group plays a major role in isocyanate substances, so all isocyanate substances containing isocyanate groups are applicable. As examples, toluene diisocyanate (TDI), p-toluenesulfonyl isocyanate (PTSI), m-toluene isocyanate, 4-ethylphenyl isocyanate, 3,4-dimethylphenyl isocyanate and 3,5-dimethylphenyl isocyanate are provided. Other substances with the same or similar properties are also applicable to this application.

[0079] In some embodiments, the electrolyte further comprises fluoroethylene carbonate. The LUMO energy level of fluoroethylene carbonate is lower than that of isocyanate substances and solvents, and fluoroethylene carbonate forms an SEI film earlier in the electrolyte; at the same time, the SEI film generated by fluoroethylene carbonate contains more LiF components and has higher mechanical strength, so it can improve the cycle stability of the battery monomer to a certain extent.

[0080] In some possible embodiments, the mass proportion of fluoroethylene carbonate in the electrolyte is B%, and A and B satisfy: 1%≤A / B≤100%; for example, A / B can be but is not limited to 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100% or a range between any two of the above values.

[0081] Since fluoroethylene carbonate interacts with the strong Lewis acid PF5 produced by the decomposition of LiPF6 at high temperature, a de-F reaction will occur to generate acid products such as HF, which will increase the acidity of the electrolyte, cause the solvation of the transition metal elements of the positive electrode, and precipitate on the surface of the negative electrode, thereby causing the negative electrode electrons to leak, causing the electrolyte to continue to decompose on the surface of the negative electrode, and then consume the active Li of the negative electrode, causing the battery capacity to decay. When isocyanate substances are added to the electrolyte at the same time, on the one hand, the moisture in the positive electrode plate can be reduced or even removed, and on the other hand, the HF produced by the decomposition of fluoroethylene carbonate can be reduced or even removed, thereby improving the high temperature stability of the SEI film and improving the high temperature cycle. However, since the film formation impedance of isocyanate substances is large, adding too much isocyanate substances can deteriorate the DC impedance of the battery monomer, so it is necessary to regulate the amount of isocyanate substances and fluoroethylene carbonate. When the value of A / B is within the above range, fluoroethylene carbonate forms an SEI film earlier than isocyanate substances, reducing or even avoiding the participation of isocyanate substances in film formation, and reducing the deterioration of the DC internal resistance of the battery cell; at the same time, isocyanate substances can reduce or even remove HF produced by the decomposition of fluoroethylene carbonate, and improve high-temperature cycles; therefore, by controlling the value of A / B within the above range, the DC impedance of the battery cell can be reduced, and the high-temperature cycle life of the battery cell can be improved.

[0082] In some optional embodiments, the mass percentage of fluoroethylene carbonate in the electrolyte is B%, 0.1≤B≤1; for example, it can be but not limited to 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or a range between any two of the above values. When the mass percentage of fluoroethylene carbonate in the electrolyte is within the above range, the secondary battery has good kinetics and cycle performance.

[0083] It should be noted that the B% mentioned above refers to the mass proportion of fluoroethylene carbonate in the electrolyte in the battery monomer obtained after formation or in the battery monomer after further charge and discharge cycles. "Battery monomer obtained after formation" refers to fresh battery monomers obtained after formation and not further charged and discharged.

[0084] As an example, the mass proportion of the above-mentioned fluoroethylene carbonate in the electrolyte can be determined by referring to GB / T 9722-2006 and using gas chromatography.

[0085] In some embodiments, the electrolyte further comprises a first lithium salt and a second lithium salt, wherein the first lithium salt comprises lithium hexafluorophosphate, and the second lithium salt comprises at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide. LiPF6 has excellent comprehensive performance and low cost, but its own stability is poor, and it is easy to decompose under the action of water and high temperature. Its decomposition products HF and PF5 will further deteriorate the stability of the battery cell interface, thereby affecting the high temperature cycle performance of the battery cell; the second lithium salt is a lithium salt with good stability, high tolerance to water and temperature, and low degree of decomposition, thereby improving the high temperature cycle stability of the battery cell; the second lithium salt has high conductivity, which can improve the DCR of the battery cell, so adding LiPF6 and the second lithium salt to the electrolyte at the same time can improve the high temperature cycle performance of the battery cell to a certain extent.

[0086] In some possible embodiments, the mass of the second lithium salt accounts for 10%-80% of the mass of the first lithium salt. As an example, the mass of the second lithium salt accounts for a mass of the first lithium salt, but is not limited to 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or a range between any two of the above values. Since the decomposition products of the second lithium salt are more likely to produce gas, excessive gas production by the battery monomer is likely to occur when the content is too high; therefore, the amount of the first lithium salt and the second lithium salt needs to be regulated to significantly improve the high temperature cycle performance and kinetic performance of the battery monomer while reducing the gas production of the battery monomer. When the percentage of the mass of the second lithium salt to the mass of the first lithium salt is within the above range, the battery monomer has better high-temperature cycle performance and kinetic performance and lower gas production; when the percentage of the mass of the second lithium salt to the mass of the first lithium salt is higher than the above range, it is easy to cause the battery monomer to produce more gas; when the percentage of the mass of the second lithium salt to the mass of the first lithium salt is lower than the above range, it is easy to cause the battery to have poor high-temperature cycle performance and kinetic performance.

[0087] In some embodiments, the sum of the mass proportions of the first lithium salt and the second lithium salt in the electrolyte is 8%-20%; for example, it can be but is not limited to 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% or a range between any two of the above values.

[0088] As an example, the percentage of the mass of the first lithium salt to the mass of the second lithium salt mentioned above and the sum of the mass proportions of the first lithium salt and the second lithium salt in the electrolyte can be determined with reference to GB / T36240-2018.

[0089] It should be noted that the percentage of the mass of the first lithium salt to the mass of the second lithium salt mentioned above refers to the percentage of the mass of the first lithium salt to the mass of the second lithium salt in the battery cell obtained after formation. The sum of the mass proportions of the first lithium salt and the second lithium salt in the electrolyte refers to the sum of the mass proportions of the first lithium salt and the second lithium salt in the electrolyte in the battery cell obtained after formation.

[0090] In some embodiments, the positive electrode sheet comprises a positive electrode active material, and the specific surface area of ​​the positive electrode active material is 8 m 2 / g-18m 2 / g; for example, it can be but not limited to 8m 2 / g, 9m 2 / g, 10m 2 / g, 11m 2 / g, 12m 2 / g, 13m 2 / g, 14m 2 / g, 15m 2 / g, 16m 2 / g, 17m 2 / g, 18m 2 / g or the range between any two of the above values. Although the larger the specific surface area of ​​the positive electrode active material, the better its kinetic performance, as the specific surface area of ​​the positive electrode active material increases, it is easier to absorb water, affecting the interface stability of the negative electrode sheet, thereby causing the battery monomer to decay too quickly during high-temperature cycling.

[0091] As an example, the specific surface area of ​​the positive electrode active material mentioned above can be measured by referring to the gas adsorption BET method in GB / T 19587-2017.

[0092] In some embodiments, the positive electrode active material includes a lithium iron phosphate-based material.

[0093] In addition, the battery cell, the secondary battery, and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0094] The electrolyte contains electrolytes, which have the function of transferring ions between the positive electrode and the negative electrode. The present application has no particular restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0095] In addition to the first lithium salt and the second lithium salt, the electrolyte of the electrolyte of the present application may also include one or more of lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP) in some embodiments.

[0096] In some of the embodiments, the electrolyte further includes a solvent.

[0097] In some embodiments, the solvent may include ethylene carbonate (EC, ), propylene carbonate (PC, ), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethylene carbonate One or more of fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0098] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0099] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), and the like.

[0100] Positive electrode

[0101] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector.

[0102] In some embodiments, the positive electrode active material may also include one or more of a ternary material and a lithium iron manganese phosphate material; wherein the ternary material includes Li x (Ni a Co b Mn c )1-dM d O2-yA y (x is 0.2-1.2) and / or Li x Aa (Ni a Co b Mn c )1-dM d O2-yA y (x+a is 0.2-1.2); lithium manganese iron phosphate materials include Li a Mn1-yB y P1 z O4-D n (a is 0-1.1) and / or Li a A x Mn1-yB y P1 z O4-D n (a+x is 0-1.1).

[0103] It should be noted that the above definition of x includes the molar content of Li under different charge and discharge states of the battery (usually the battery voltage is between 2-5V).

[0104] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during the charging and discharging process, and the content of Li in the positive electrode plate is different when the battery is discharged to different states. In the list of positive electrode materials in this application, unless otherwise specified, the content of Li is the initial state of the material. The positive electrode material is applied to the positive electrode plate in the battery system, and after the charge and discharge cycle, the content of Li in the positive electrode material contained in the plate usually changes. Among them, the content of Li can be measured by molar content, but is not limited to this. Regarding "the content of Li is the initial state of the material", the initial state of the material refers to the state before the material is added to the positive electrode slurry. It is understandable that the new material obtained by appropriate modification on the basis of the listed positive electrode materials is also within the scope of the positive electrode material. The aforementioned appropriate modification refers to the acceptable modification method for the positive electrode material, and non-limiting examples include coating modification.

[0105] In the list of positive electrode materials in this application, the content of oxygen (O) is only a theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual content of O will fluctuate. Among them, the content of O can be measured by molar content, but is not limited to this.

[0106] As a non-limiting example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on any one or both of the two facing surfaces of the positive electrode current collector.

[0107] In some of the 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 layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0108] In some of the embodiments, the positive electrode active material may also use a positive electrode active material for a battery known in the art. As a non-limiting example, the positive electrode active material may also include one or more 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. Among them, examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide (such as LiCoO2), lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Non-limiting examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, one or more of a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.85 Co 0.15 Al 0.05 O2.

[0109] In some of these embodiments, the positive electrode active material layer may also optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0110] In some embodiments, the positive electrode active material layer may further include a conductive agent. As non-limiting examples, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0111] In some of the embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive active material, the conductive agent, the binder and any other components, are dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is coated on at least one side of the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained. The type of solvent can be selected from but not limited to any one of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode collector. The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode collector. The solid content of the positive electrode slurry can be 40wt%-80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000-25000mPa·s. When applying the positive electrode slurry, the coating unit area density based on dry weight (excluding solvent) can be 15-35 mg / cm 2 The compaction density of the positive electrode can be 2.5-3.0g / cm 3 , optional: 3.3-3.5g / cm 3 .

[0112] Negative electrode

[0113] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0114] As a non-limiting example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active material layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0115] In some of the embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. 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 obtained by forming a metal material on a polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0116] In some of the embodiments, the negative electrode active material may adopt the negative electrode active material for batteries known in the art. As a non-limiting example, the negative electrode active material may include one or more 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 include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include one or more 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.

[0117] In some embodiments, the negative electrode active material layer may further include a binder. The binder may include one or more 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).

[0118] In some embodiments, the negative electrode active material layer may further include a conductive agent, which may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0119] In some of the embodiments, the negative electrode active material layer may further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0120] In some of the 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 (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the surface of the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode collector coated with the negative electrode slurry can be on a single surface of the negative electrode collector or on both surfaces of the negative electrode collector. The solid content of the negative electrode slurry can be 40wt%-60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000-10000mPa·s. When coating the negative electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 75-220g / m 2 The compaction density of the negative electrode sheet can be 1.5g / cm 3 -2 g / cm 3 .

[0121] Isolation film

[0122] The present application has no particular limitation on the type of isolation membrane, and any known porous isolation membrane with good chemical stability and mechanical stability can be selected.

[0123] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane may 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 may be the same or different, without particular limitation.

[0124] In some embodiments, the isolation film has a thickness of 6-40 μm, and optionally 12-20 μm.

[0125] In some of the embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly by a winding process or a lamination process.

[0126] In some embodiments, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0127] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0128] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 1 The battery cell 5 is a square structure as an example.

[0129] In some of these 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 battery cell 5 can be one or more, and those skilled in the art can select according to actual needs.

[0130] Secondary battery

[0131] The second aspect of the present application provides a secondary battery, comprising the battery cell of the first aspect of the present application; and having excellent high temperature cycle performance and dynamic performance.

[0132] The secondary battery includes at least one battery cell. The secondary battery may include one or more battery cells.

[0133] The secondary battery may be a battery module or a battery pack.

[0134] The battery module includes at least one battery cell. The number of battery cells contained in the battery module can be one or more, and those skilled in the art can select a suitable number according to the application and capacity of the battery module.

[0135] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of battery cells 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 battery cells 5 may be fixed by fasteners.

[0136] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0137] In some of the embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select a suitable number according to the application and capacity of the battery pack.

[0138] 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.

[0139] In addition, the present application also provides an electrical device, which includes at least one of the battery cell and the secondary battery provided in the present application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto. Among them, the mobile device may be, for example, a mobile phone, a laptop computer, etc.; the electric vehicle may be, for example, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but are not limited thereto.

[0140] As an electrical device, a battery cell or a secondary battery can be selected according to its usage requirements.

[0141] Figure 6 The power consumption device 6 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 secondary batteries, a battery pack or a battery module can be used.

[0142] 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.

[0143] Example

[0144] 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 the techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0145] 1. Preparation of battery cells

[0146] Example 1

[0147] 1). Preparation of positive electrode

[0148] The positive electrode material LiFePO4, polyvinylidene fluoride (PVDF), carbon black (SP) were mixed with the solvent dimethyl sulfoxide in a mass ratio of 97:2:1, and a uniformly dispersed positive electrode slurry was obtained by stirring. The positive electrode slurry was evenly coated on the two surfaces of the aluminum foil, and the positive electrode sheet was obtained after drying, cold pressing and cutting. The thickness of the positive electrode active material layer was 0.09 mm, and the specific surface area of ​​the positive electrode material was 10 m 2 / g.

[0149] 2). Preparation of negative electrode sheet

[0150] Artificial graphite: carbon black (SP): styrene-butadiene rubber (SBR): sodium hydroxymethyl cellulose (CMC) are mixed in a mass ratio of 97:0.5:1.5:1, deionized water 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 the negative electrode sheet is obtained after drying, cold pressing, and cutting.

[0151] 3). Isolation film

[0152] A polyethylene film is used as the isolation film.

[0153] 4). Preparation of electrolyte

[0154] In an argon atmosphere glove box, ethylene carbonate (EC, as a solvent), dimethyl carbonate (DMC, as a solvent), ethyl methyl carbonate (EMC, as a solvent), diethyl carbonate (DEC, as a solvent), vinylene carbonate (VC, as an additive), fluoroethylene carbonate (FEC, as an additive), toluene diisocyanate (TDI, as an isocyanate substance), lithium hexafluorophosphate (LiPF6, as a first lithium salt), and lithium bistrifluoromethanesulfonyl imide (as a second lithium salt) are mixed in percentage by mass to obtain an electrolyte.

[0155] 5). Preparation of battery cells

[0156] 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, left to stand at high temperature, formed, and divided into volumes, a battery cell is obtained.

[0157] The ratio of the total mass of the electrolyte of the battery cell to the capacity of the battery cell is 3g / Ah.

[0158] Example 2-22

[0159] The difference between the preparation method of the battery monomer in Examples 2-22 and the preparation method of the battery monomer in Example 1 mainly lies in: at least one of the mass percentage of the solvent in the electrolyte, the mass percentage of isocyanate substances, the mass percentage of fluorocarbonate, the mass percentage of the first lithium salt, the type and / or mass percentage of the second lithium salt, the thickness of the positive electrode plate, the specific surface area of ​​the positive electrode active material, and the ratio of the total mass of the electrolyte of the battery monomer to the battery monomer capacity is different, as shown in Table 1.

[0160] Comparative Example 1

[0161] In Comparative Example 1, fluorocarbonate and isocyanate substances are added, and the second lithium salt is not added, and only the first lithium salt is used. See Table 1 for details.

[0162] Comparative Examples 2-3

[0163] The difference between the preparation method of the battery monomer in Comparative Examples 2-3 and the preparation method of the battery monomer in Example 1 is mainly that: at least one of the mass percentage of the solvent in the electrolyte, the mass percentage of the isocyanate substance, the mass percentage of the fluorocarbonate, the mass percentage of the first lithium salt, the type and / or mass percentage of the second lithium salt, the thickness of the positive electrode active material layer, the specific surface area of ​​the positive electrode active material, and the ratio of the total mass of the electrolyte of the battery monomer to the battery monomer capacity is different, as shown in Table 1.

[0164] The battery cells prepared in the above embodiments and comparative examples were tested for the following parameters:

[0165] The mass percentages of EC, DMC, EMC, DEC, isocyanate substances, FEC, the first lithium salt and the second lithium salt in the electrolyte, the mass percentage of the second lithium salt to the mass percentage of the first lithium salt, A*C / T and A / B are shown in Table 1 for details.

[0166] The parameter settings of the above embodiments and comparative examples are shown in Table 1.

[0167] Table 1

[0168]

[0169]

[0170] Among them, in Table 1, n represents the percentage of the mass of the second lithium salt to the mass of the first lithium salt, T represents the thickness of the positive electrode active material layer on one side of the positive electrode current collector, A% represents the mass proportion of isocyanate substances in the electrolyte, B% represents the mass proportion of fluoroethylene carbonate in the electrolyte, C represents the ratio of the total mass of the electrolyte of the battery cell to the capacity of the battery cell, BET represents the specific surface area of ​​the positive electrode active material, LiFSI represents bis(fluorosulfonyl)imide lithium salt, LiTFSI represents bis(trifluoromethanesulfonyl)imide lithium, and FEC represents fluoroethylene carbonate.

[0171] The percentage of the mass of the first lithium salt to the mass of the second lithium salt mentioned above and the sum of the mass proportions of the first lithium salt and the second lithium salt in the electrolyte are determined with reference to GB / T36240-2018.

[0172] The mass proportion of the above-mentioned fluoroethylene carbonate in the electrolyte can be referred to GB / T 9722-2006 and measured by gas chromatography.

[0173] The mass proportion of the above-mentioned isocyanate substances in the electrolyte can be referred to GB / T 9722-2006 and measured by gas chromatography.

[0174] 2. Battery Cell Performance Test

[0175] 1.60℃ high temperature cycle performance determination

[0176] At 60°C, charge the battery cells of each embodiment and comparative example at a constant current of 0.5C to an upper voltage limit of 3.8V, and then charge at a constant voltage to a current of 0.05C; let the battery stand for 5 minutes, and discharge at a constant current of 1 / 3C to 2.0V. This is the first charge and discharge cycle of the battery, and the discharge capacity at this time is recorded as the discharge capacity D1 of the first cycle of the battery; perform a cyclic charge and discharge test on the battery according to the above method, and record the capacity Dn at the nth cycle of the battery, and the capacity retention rate is Dn / D1. Record the number of cycles when the capacity retention rate is 80%.

[0177] 2.60℃ volume expansion test

[0178] At 60°C, charge the battery cell 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. At this time, the volume of the battery is tested by the water discharge method and recorded as V0; put the battery into a constant temperature box at 60°C, and take it out after storage for 30 days. At this time, the volume of the battery is tested by the water discharge method and recorded as V1. The volume expansion rate of the battery after storage at 60°C for 30 days = [(V1-V0) / V0]×100%.

[0179] 3.DCR test

[0180] At 25°C, charge the battery cell 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 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.

[0181] The performance test results of the above embodiments and comparative examples are shown in Table 2.

[0182] Table 2

[0183] Group 60℃ Cycles (cyls) DCR(mOhm) Volume expansion rate Example 1 1218 32.7 18.1％ Example 2 1270 31.1 18.2％ Example 3 1007 35.9 15.5％ Example 4 1154 33.7 16.1％ Example 5 1328 30.5 19.7％ Example 6 1253 32.8 17.4％ Example 7 1329 29.7 19.5％ Example 8 1173 28.5 19.3％ Example 9 1416 36.9 17.0％ Example 10 1251 31.2 18.3％ Embodiment 11 1355 30.7 17.7％ Example 12 1185 36.5 18.9％ Example 13 1325 32.6 17.9％ Embodiment 14 1057 28.4 18.8％ Embodiment 15 1132 30.4 18.0％ Example 16 1367 33.7 18.6％ Embodiment 17 1173 30.1 19.9％ Embodiment 18 1366 35.2 17.9％ Embodiment 19 1169 27.2 19.7％ Embodiment 20 953 37.8 15.0％ Embodiment 21 972 36.2 17.1％ Embodiment 22 885 39.3 14.9％ Comparative Example 1 557 26.7 28.3％ Comparative Example 2 621 21.1 29.4％ Comparative Example 3 475 57.3 47.3％

[0184] From the comparison of the results of Examples 1-22 and Comparative Examples 1-3, it can be seen that the battery monomer provided in the present application has little effect on the gas production of the battery monomer by adding isocyanate substances to the electrolyte and making A*C / T within the range of 0.2-20, and can significantly improve the high-temperature cycle performance of the battery monomer while taking into account the dynamic performance of the battery monomer.

[0185] The main difference between Example 2 and Example 20 is that two lithium salts are used in Example 2; the main difference between Example 21 and Example 22 is that two lithium salts are used in Example 21; from the comparison of the results of Example 2 and Example 20, and the comparison of the results of Example 22 and Example 21, it can be seen that when LiPF6 and the second lithium salt are used in the electrolyte at the same time, LiPF6 has better comprehensive performance, but its own stability is poor, and the decomposition products HF and PF5 will further deteriorate the interface stability of the battery monomer, thereby affecting the high-temperature cycle performance of the battery monomer; the second lithium salt is a lithium salt with good stability and a low degree of decomposition, thereby improving the high-temperature cycle stability of the battery monomer; and because the second lithium salt has a higher conductivity, it can improve the DCR of the monomer, so adding two lithium salts at the same time can improve the high-temperature cycle performance of the battery monomer to a certain extent, and the kinetic performance of the battery monomer is also improved to a certain extent.

[0186] The main difference between Examples 2-5 is that the percentage of the mass of the second lithium salt to the mass of the first lithium salt is different, and the percentage of the mass of the second lithium salt to the mass of the first lithium salt in Example 3 is the smallest; because the decomposition products of the second lithium salt are more likely to produce gas, based on the results of Examples 2-5, it can be seen that when the mass of the second lithium salt accounts for approximately 10%-80% of the mass of the first lithium salt, the gas production caused by the decomposition products of the second lithium salt is less, and the high temperature cycle performance and dynamic performance of the battery cell can be improved.

[0187] The main difference between Example 20 and Example 22 is that fluoroethylene carbonate is added to Example 20; from the comparison of the results of Example 20 and Example 22, it can be seen that the addition of fluoroethylene carbonate in the electrolyte has little effect on the gas production of the battery monomer, and fluoroethylene carbonate forms an SEI film containing more LiF components earlier in the electrolyte. The SEI film has high mechanical strength and can improve the cycle stability of the battery monomer to a certain extent, and improve the high-temperature cycle performance of the battery monomer. The main difference between Example 2 and Example 21 is that fluoroethylene carbonate is added to Example 2; from the comparison of the results of Example 2 and Example 21, it can be seen that by adding fluoroethylene carbonate to the electrolyte, fluoroethylene carbonate can cooperate with isocyanate substances to improve the dynamic performance of the battery monomer.

[0188] The main difference between Example 2 and Examples 6-7 is that the mass proportion of fluoroethylene carbonate in the electrolyte is different; from the results of Examples 2 and Examples 6-7, it can be seen that when the mass proportion of fluoroethylene carbonate in the electrolyte is 0.1%-1%, the battery cell has both good dynamic performance and high-temperature cycle performance.

[0189] The main difference between Example 2 and Examples 8-9 is that the mass proportion of isocyanate substances in the electrolyte is different; from the results of Example 2 and Examples 8-9, it can be seen that isocyanate substances can significantly improve the high-temperature cycle performance of battery monomers, but will deteriorate the DCR of battery monomers to a certain extent. When the mass proportion of isocyanate substances in the electrolyte is 0.01%-0.2%, the high-temperature cycle performance and dynamic performance of the battery monomer can be taken into account.

[0190] The main difference between Example 2 and Examples 11-12 is that the thickness of the positive electrode active material layer is different; since the thicker the positive electrode active material layer, the more water it contains, the more isocyanate substances need to be added, and the greater the impact on the DC internal resistance of the battery cell may be; based on the results of Examples 2 and Examples 11-12, it can be seen that when the thickness of the positive electrode active material layer is 0.08-0.12mm, the battery cell can take into account both high temperature cycle performance and dynamic performance.

[0191] The main difference between Example 2 and Examples 13-14 is that the specific surface area of ​​the positive electrode active material is different; since the larger the specific surface area of ​​the positive electrode active material, the better its kinetic performance, but as the specific surface area of ​​the positive electrode active material increases, it is easier to absorb water, affecting the interface stability of the negative electrode plate, thereby causing the battery monomer to decay too quickly during high-temperature cycling; Based on the results of Examples 2 and 13-14, it can be seen that the specific surface area of ​​the positive electrode active material is 8m 2 / g-18m 2 / g, the battery monomer has good dynamic performance and also good high temperature cycle performance.

[0192] The main difference between Example 2 and Examples 15-16 is that the ratio of the total mass of the electrolyte of the battery cell to the capacity of the battery cell is different; from the results of Examples 2 and 15-16, it can be seen that when the ratio of the total mass of the electrolyte of the battery cell to the capacity of the battery cell is 2.5g / Ah-4.5g / Ah, the battery cell has lower gas production and has better kinetic performance and high temperature cycle performance.

[0193] The above description of various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced to each other, and for the sake of brevity, they will not be repeated herein.

[0194] 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 battery cell, characterized in that: include: A positive electrode sheet, the positive electrode sheet comprising a positive electrode active material layer, the thickness of the positive electrode active material layer is T mm; as well as An electrolyte, wherein the electrolyte contains an isocyanate substance; the mass proportion of the isocyanate substance in the electrolyte is A%; The ratio of the total mass of the electrolyte of the battery cell to the capacity of the battery cell is C g / Ah; A, C and T satisfy: 0.2≤A*C / T≤20.

2. The battery cell according to claim 1, characterized in that: 0.01≤A≤0.5。 3. The battery cell according to any one of claims 1 to 2, characterized in that: 0.08≤T≤0.12。 4. The battery cell according to any one of claims 1 to 3, characterized in that: 2.5≤C≤4.5。 5. The battery cell according to any one of claims 1 to 4, characterized in that: The isocyanate substance has a structure shown in the following formula (I): Wherein, R1 includes any one of -CH3, -C2H5 and -OCH3; R2, R3, R4, R5 and R6 each independently include any one of hydrogen, isocyanate group and sulfonyl isocyanate group, and at least one of R2, R3, R4, R5 and R6 is an isocyanate group or a sulfonyl isocyanate group.

6. The battery cell according to any one of claims 1 to 5, characterized in that: The isocyanate substances include one or more of toluene diisocyanate, p-toluenesulfonyl isocyanate, m-toluene isocyanate, 4-ethylphenyl isocyanate, 3,4-dimethylphenyl isocyanate and 3,5-dimethylphenyl isocyanate.

7. The battery cell according to any one of claims 1 to 6, characterized in that: The electrolyte further comprises fluoroethylene carbonate.

8. The battery cell according to claim 7, characterized in that: The fluoroethylene carbonate has at least one of the following characteristics: (1) The mass proportion of the fluoroethylene carbonate in the electrolyte is B%, and A and B satisfy the following: 1%≤A / B≤100%; (2) The mass proportion of the fluoroethylene carbonate in the electrolyte is B%, and 0.1≤B≤1.

9. The battery cell according to any one of claims 1 to 8, characterized in that: The electrolyte further comprises a first lithium salt and a second lithium salt, wherein the first lithium salt comprises lithium hexafluorophosphate, and the second lithium salt comprises at least one of lithium bis(fluorosulfonyl)imide salt and lithium bis(trifluoromethanesulfonyl)imide.

10. The battery cell according to claim 9, characterized in that: The first lithium salt and the second lithium salt have at least one of the following characteristics: (1) The mass of the second lithium salt accounts for 10% to 80% of the mass of the first lithium salt; (2) The sum of the mass proportions of the first lithium salt and the second lithium salt in the electrolyte is 8%-20%.

11. The battery cell according to any one of claims 1 to 10, characterized in that: The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material has at least one of the following characteristics: (1) The specific surface area of ​​the positive electrode active material is 8 m 2 / g-18m 2 / g; (2) The positive electrode active material includes a lithium iron phosphate material.

12. A secondary battery, characterized in that: The invention comprises a battery cell as claimed in any one of claims 1 to 11.

13. An electrical device, characterized in that: The invention comprises at least one of the battery cell according to any one of claims 1 to 11 and the secondary battery according to claim 11.

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