Rapidly rechargeable long-life secondary battery, battery module, battery pack, and electrical device

Abstract

The present application provides a fast-chargeable, long-life secondary battery, a battery module, a battery pack, and an electric device. In particular, the secondary battery according to the present application includes an electrode assembly and an electrolyte, the electrode assembly including a positive electrode plate, a negative electrode plate, and a separator, the positive electrode plate including a positive electrode tab, and the negative electrode plate including a negative electrode tab, and the temperature rise coefficient of the positive electrode tab is expressed by the following formula: where S1 is the total cross-sectional area of ​​the positive electrode tab, and its unit is mm 2 where C is the capacity of the electrode assembly in Ah, and the electrolyte contains a thermally stable salt and an additive that inhibits decomposition of the lithium salt. [Equation 4] JPEG2023541212000042.jpg1223

Description

[Technical field]

[0001] The present application belongs to the technical field of batteries, and in particular to a fast-chargeable long-life secondary battery, a battery module, a battery pack, and an electric device. [Background technology]

[0002] Lithium-ion batteries have the advantages of high energy density, long service life, energy saving, environmental friendliness, etc., and are widely used in various fields such as new energy vehicles and energy storage power stations. With the acceleration of the pace of life and the development of electronic products, consumers are strongly required to shorten the charging time of lithium-ion batteries and increase the discharge power, that is, to increase the charge and discharge rate of the battery. However, when increasing the charge and discharge rate of the battery, the temperature rise coefficient of the tab inside the battery cell will increase significantly, the temperature rise of the tab will be large, the decomposition of the electrolyte around the tab will be accelerated, and it will be decomposed into highly active substances such as HF and PF5, not only will the content of lithium salt decrease, but also the SEI will be destroyed and the consumption of the electrolyte will be accelerated. This will result in insufficient content of electrolyte after the battery cell has been cycled for a certain period of time, resulting in insufficient dynamic performance of the battery cell, and the corresponding impedance of the SEI will increase sharply, finally resulting in a decrease in the power performance of the battery cell after cycling, and a sharp increase in the internal resistance of the battery cell. In addition, in response to the consumer's demand for high energy density battery cells, when charging and discharging at the same rate, the current in the tab of the battery cell will be even larger, and the temperature rise coefficient of the tab will be even larger. Summary of the Invention

[0003] The present application has been made in view of the above problems, and has an object to provide a long-life secondary battery that can be rapidly charged and maintains high power performance even in the middle and later stages of the cycle.

[0004] To achieve the above object, the present application provides a secondary battery, a battery module including the secondary battery, a battery pack including the battery module, and an electric device including the secondary battery, battery module, or battery pack.

[0005] A first aspect of the present application provides a secondary battery, the secondary battery including an electrode assembly and an electrolyte, the electrode assembly including a positive electrode plate, a negative electrode plate, and a separator, the positive electrode plate including a positive electrode tab, the negative electrode plate including a negative electrode tab, and a temperature rise coefficient α Ah / mm of the positive electrode tab is expressed by the following formula:

number

[0006] In some embodiments, α is 2 to 9.5. When α is within the above numerical range, the following can be avoided. If α is too large, the positive electrode tab cannot withstand the current value when discharging at a high rate, and the tab is likely to melt. If α is too small, the volume of the tab in the battery cell becomes large, and the volume energy density of the battery cell is too small.

[0007] In some embodiments, the mass fraction m1% of the additive RSO3F for suppressing the decomposition of the lithium salt is 0.1% to 10%, and optionally 0.2% to 5%. When m1 is within the above numerical range, the following can be avoided. If m1 is too low, the decomposition of the lithium salt cannot be suppressed, and the thermal stability of the electrolyte is poor. If m1 is too high, the conductivity of the electrolyte deteriorates significantly, the kinetic performance of the electrolyte is insufficient, the polarization is large during charge and discharge at a high rate, the discharge power deteriorates, and in severe cases, it also affects the lithium precipitation in the battery cell, resulting in deterioration of the cycle performance.

[0008] In some embodiments, the concentration w% of the stable lithium salt is 8% to 30%, and optionally 10% to 23%. By keeping the w% within the above range, it is possible to avoid the following: if the concentration of the stable lithium salt is too low, the thermal stability of the electrolyte cannot be improved, and if the concentration is too high, the concentration of the electrolyte is too high, which deteriorates the dynamic performance of the electrolyte, and deteriorates the charge and discharge power of the battery cell.

[0009] In some embodiments, the heat stable salt has a temperature above 200° C. that corresponds to a 5% weight loss rate.

[0010] In some embodiments, in the molecular formula of the heat stable salt, x=1 and y=1, or x=1 and y=2, or x=2 and y=1.

[0011] In some embodiments, in the molecular formula of the heat stable salt, R1 and R2 are each independently selected from a fluorine atom and a trifluoromethyl group, and optionally, R1 and R2 are both fluorine atoms or both trifluoromethyl groups.

[0012] In some embodiments, the thermally stable salt is one or more selected from lithium bis(fluorosulfonyl)imide, potassium bis(fluorosulfonyl)imide, cesium bis(fluorosulfonyl)imide, barium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, LiF(SON)SOF, and LiCFSONSOF.

[0013] In some embodiments, the additive that inhibits decomposition of the lithium salt is one or more selected from LiSO3F, NaSO3F, or KSO3F.

[0014] In some embodiments, the electrolyte further comprises a fluorine-based solvent, the fluorine-based solvent being one or more selected from fluorinated carbonate, fluorobenzene, and fluoroether. The fluorine-based solvent is used to reduce the electron cloud density of the stable lithium salt and increase the electrochemical stability of the solvated stable lithium salt, thus reducing the decomposition and consumption of the electrolyte. The content of the fluorine-based solvent in the electrolyte is m2%, and the ratio of m2 to α, m2 / α, is 1-8.

[0015] In some embodiments, the fluorinated carbonate has one of the following formulas: [ka] and / or the fluorobenzene is represented by the following chemical formula: [ka] and / or the fluoroether is R 1’ -OR 2’ R3, R4, R5, R6, R 1’ , R 2’ Each independently -C x’ F y’ H z’ where 1≦x'≦6, y'>0, z'>0 are satisfied, and 0≦y'≦2x', 0≦z'≦2x' are satisfied. R7, R8, R9, R 10 , R 11 , R 12 are each independently one of F or H.

[0016] In some embodiments, R 1’ , R 2’ are each independently selected from -C2F4H, -CF3, -C3F6H, -C2F3H2, and -C3F4H3; and optionally, R 1’ , R 2’are each independently selected from -CF2-CF2H, -CF3, -CF2-CFH-CF3, -CH2-CF3, -CH2-CF2-CHF2, and optionally, the fluoroether is selected from those represented by the following chemical formula: [ka]

[0017] In some embodiments, R5 and R6 are each independently selected from -C2F3H, -CFH, and -CH2; optionally, R5 and R6 are each independently selected from -CH-CF3, -CHF, and -CH2; and optionally, the fluorinated carbonate is selected from those represented by the following chemical formula: [ka]

[0018] In some embodiments, R5 and R6 are each independently selected from -CH3, -C2F3H2, -CFH2, and -C2FH4; and optionally, R5 and R6 are each independently selected from -CH3, -CH2-CF3, -CH2-F, and -CH2-CH2-F; and optionally, the fluorinated carbonate is selected from those represented by the following chemical formula: [ka]

[0019] In some embodiments, the electrolyte further contains an additive that is easily oxidized by losing electrons, and the additive that is easily oxidized by losing electrons is one or more selected from a phosphite ester, a borate ester, and a phosphate ester. The additive that is easily oxidized by losing electrons can be oxidized to form a film before the stable lithium salt, and decomposition of the stable lithium salt can be suppressed. The content of the additive that is easily oxidized by losing electrons in the electrolyte is m3%, and the ratio of m3 to α, m3 / α, is 0.1 to 0.9.

[0020] In some embodiments, the phosphite has the formula: [ka] and / or the phosphate ester is represented by the following chemical formula: [ka] and / or the boric acid ester is represented by the following chemical formula: [ka] R 13 , R 14 , R 15 , R 16 , R 17 , R 18 , R 19 , R 20 , R 21 are each independently selected from an alkyl group, a fluoroalkyl group, a silane group, an alkenyl group, and a phenyl group.

[0021] In some embodiments, R 13 , R 14 , R 15 are each independently 1-6 Alkyl groups (e.g., methyl and ethyl groups), C 1-6 fluoroalkyl groups (e.g., fluoromethyl groups, fluoroethyl groups, e.g., -CH2-CF3); Optionally, the phosphite is selected from those represented by the following formula: [ka]

[0022] In some embodiments, R 16 , R 17 , R 18 are each independently 1-6Fluoroalkyl groups (e.g., fluoromethyl groups, fluoroethyl groups, e.g., -CH2-CF3), C 1-6 an alkenyl group (e.g., an allyl group); and optionally the phosphate ester is selected from those represented by the following chemical formula: [ka]

[0023] In some embodiments, R 19 , R 20 , R 21 are each independently 1-6 Alkyl groups (e.g., methyl and ethyl groups), C 1-6 Fluoroalkyl groups (e.g., fluoromethyl groups, fluoroethyl groups, e.g., -CH2-CF3), and optionally the borate ester is selected from those represented by the following chemical formula: [ka]

[0024] In a second aspect of the present application, there is provided a battery module including the secondary battery according to the first aspect of the present application.

[0025] In a third aspect of the present application, there is provided a battery pack including a battery module according to the second aspect of the present application.

[0026] In a fourth aspect of the present application, there is provided an electric device including the secondary battery according to the first aspect of the present application, the battery module according to the second aspect of the present application, or the battery pack according to the third aspect of the present application.

[0027] The secondary battery according to the present application can suppress decomposition of the electrolyte near the tab, significantly improve the thermal stability of the electrolyte, suppress decomposition of the electrolyte at high temperatures, extend the life of the battery cell, and solve the problem of shortened life of the battery cell caused by heat generation of the tab during rapid charging of the battery cell. [Brief description of the drawings]

[0028] [Figure 1] FIG. 1 is a schematic diagram of a secondary battery according to an embodiment of the present application. [Diagram 2] FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 1. [Diagram 3] FIG. 1 is a schematic diagram of a battery module according to an embodiment of the present application. [Figure 4] FIG. 1 is a schematic diagram of a battery pack according to an embodiment of the present application. [Diagram 5] FIG. 5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 4. [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. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Hereinafter, the embodiments of the present application will be described in detail using examples. The detailed description of the following examples is for illustrative purposes only and does not limit the scope of the present application, i.e., the present application is not limited to the described examples.

[0030] Hereinafter, embodiments of a secondary battery and a manufacturing method thereof, a battery module, a battery pack, and an electric device according to the present application will be specifically disclosed in detail, but unnecessary detailed description may be omitted. For example, detailed description of well-known matters and duplicated description of actually similar configurations may be omitted. This is to avoid the following description becoming unnecessarily long and to allow a person skilled in the art to easily understand.

[0031] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit. The selected lower limit and upper limit define the limits of a particular range. The ranges defined in this way may or may not include the limit values ​​and may be arbitrarily combined, i.e., it is possible to define a range by combining any lower limit and any upper limit. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it should be understood that the ranges 60-110 and 80-120 are also predictable. In addition, if the lower limit values ​​are 1 and 2 and the upper limit values ​​are 3, 4, and 5, any of the ranges 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 are also predictable. In this application, unless otherwise stated, the numerical range "a-b" is shorthand for any combination of real numbers between the real numbers a and b. For example, the numerical range "0 to 5" includes all real numbers between "0 and 5" as described in the specification, and "0 to 5" is merely an abbreviation for combinations of these numerical values. In addition, when a parameter is expressed as an integer of 2 or more, for example, integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 are disclosed.

[0032] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined to form a new technical solution.

[0033] Unless otherwise stated, all technical features and optional technical features of the present application can be combined to form a new technical solution.

[0034] Unless otherwise stated, all steps in this application may be performed in sequence or randomly. It is preferable to perform them in sequence. For example, if the method includes step (a) and step (b), the method may include step (a) and step (b) performed in sequence, or may include step (b) and step (a) performed in sequence. For example, if the method further includes step (c), step (c) can be incorporated into the method in any order, for example, the method may include the order of step (a), step (b) and step (c), the order of step (a), step (c) and step (b), the order of step (c), step (a) and step (b), etc.

[0035] Unless otherwise specified, the terms "comprising" and "including" used in this application may be open-ended or closed-ended. For example, the terms "comprising" and "including" may include or include unlisted elements, or may include or include only the listed elements.

[0036] Unless otherwise specified, in this application, the term "or" is a broad expression. For example, the phrase "A or B" means "A, B, or A and B." More specifically, when A exists (or exists) and B does not exist (or does not exist), when A does not exist (or does not exist) and B exists (or exists), or when both A and B exist (or exist), the condition of "A or B" is satisfied.

[0037] secondary battery

[0038] As described in the background art, the secondary battery may be, for example, a lithium-ion battery. In a typical lithium-ion battery, during a fast charging process, the tab generates excessive heat, and the electrolyte near the tab decomposes to generate highly acidic active substances such as HF and PF5, which significantly deteriorates the cycle life of the battery cell. In addition, as the volumetric energy density of the battery cell increases, the temperature rise coefficient of the battery tab becomes larger, which further accelerates the decomposition of the electrolyte near the tab, thereby shortening the life of the battery cell.

[0039] Generally, during the charging and discharging process, the decomposition of the electrolyte is proportional to the temperature rise of the tab, and the higher the temperature rise of the tab, the more the decomposition of the electrolyte progresses. At a certain charging and discharging rate, the temperature rise of the tab of the battery cell is mainly proportional to the resistivity of the tab and the capacity of the battery cell, and since the positive electrode tab is generally made of aluminum and its resistivity is much higher than that of the negative electrode tab (which is generally made of copper), the temperature rise of the positive electrode tab is generally higher during the charging and discharging process. According to an embodiment of the present application, there is provided a secondary battery comprising an electrode assembly and an electrolyte, the electrode assembly comprising a positive electrode plate, a negative electrode plate, and a separator, the positive electrode plate comprising a positive electrode tab, the negative electrode plate comprising a negative electrode tab, and a temperature rise coefficient α Ah / mm of the positive electrode tab is expressed by the following formula:

number

[0040] In some embodiments, α is 2 to 9.5 (e.g., 2 to 2.5, 2.5 to 3, 3 to 3.5, 3.5 to 4, 4 to 4.5, 4.5 to 5, 5 to 5.5, 5.5 to 6, 6 to 6.5, 6.5 to 7, 7 to 7.5, 7.5 to 8, 8 to 8.5, 8.5 to 9, or 9 to 9.5). By setting α within the above numerical range, the following can be avoided: if α is too large, the positive electrode tab cannot withstand the current value when discharging at a high rate, and the tab is likely to melt, and if α is too small, the volume of the tab in the battery cell becomes large, and the volumetric energy density of the battery cell becomes too small.

[0041] The secondary battery according to the present application contains a thermally stable salt and an additive that suppresses the decomposition of the lithium salt in the electrolyte. The thermally stable salt significantly increases the thermal stability of the electrolyte and can suppress the decomposition of the electrolyte at high temperatures. However, the thermally stable salt is weak against oxidation and easily decomposed and consumed, so the concentration of the lithium salt in the electrolyte and the total amount of the electrolyte continue to decrease. The inventors of the present application have found that by using RSO3F as an additive that suppresses the decomposition of the lithium salt, the decomposition of the highly thermally stable lithium salt can be significantly suppressed.

[0042] The molecular formula of the heat stable salt used in this application is (M y+ ) x / y R1(SO2N) x SO2R2, M y+ But Li + , Na + , K + , Rb + , Cs + , Mg 2+ , Ca 2+ , B.A. 2+ , Al 3+ , Fe 2+ , Fe 3+ , Ni 2+ , Ni 3+ and optionally, M y+ But Li + , K + , Cs + , B.A. 2+wherein y is the valence of M; wherein R1 and R2 are each independently selected from a fluorine atom, a fluoroalkyl group having 1 to 20 carbon atoms (e.g., 1 to 6), a fluoroalkoxy group having 1 to 20 carbon atoms (e.g., 1 to 6), and an alkyl group having 1 to 20 carbon atoms (e.g., 1 to 6), x is an integer selected from 1, 2, and 3.

[0043] In terms of weight percent, the thermally stable salt is present in the electrolyte at w%. In some embodiments, w% is between 8% and 30%, and optionally between 10% and 23% (e.g., between 8% and 9%, between 9% and 10%, between 10% and 11%, between 11% and 12%, between 12% and 13%, between 13% and 14%, between 14% and 15%, between 15% and 16%, between 16% and 17%, between 17% and 18%, between 18% and 19%, between 19% and 20%, between 20% and 21%, between 21% and 22%, between 22% and 23%, between 23% and 24%, between 24% and 25%, between 25% and 26%, between 26% and 27%, between 27% and 28%, between 28% and 29%, or between 29% and 30%). When the w% is within the above range, the following can be avoided: if the concentration of the thermally stable lithium salt is too low, the thermal stability of the electrolyte cannot be improved; if the concentration is too high, the concentration of the electrolyte will be too high, which will deteriorate the dynamic performance of the electrolyte and deteriorate the charge / discharge power of the battery cell.

[0044] The additive for suppressing the decomposition of the lithium salt used in this application is one or more of RSO3F, where R is Li + , Na + , K + , Rb + , Cs + One or more selected from the above.

[0045] In terms of mass percentage, the content of the additive that suppresses the decomposition of the lithium salt in the electrolyte is m1%. In some embodiments, the mass fraction m1% of the additive RSO3F that suppresses the decomposition of the lithium salt is from 0.1% to 10%, optionally from 0.2% to 5% (for example, 0.1% to 0.2%, 0.2% to 0.4%, 0.4% to 0.6%, 0.6% to 0.8%, 0.8% to 1%, 1% to 1.5%, 1.5% to 2%, 2% to 2.5%, 2.5% to 3%, 3% to 3.5%, 3.5% to 4%, 4% to 4.5%, 4.5% to 5%, 5% to 6%, 6% to 7%, 7% to 8%, 8% to 9% or 9% to 10%). When m1 is within the above range, the following can be avoided. If m1 is too low, the decomposition of the lithium salt cannot be suppressed, the thermal stability of the electrolyte is poor. If m1 is too high, the conductivity of the electrolyte deteriorates significantly, the kinetic performance of the electrolyte is insufficient, the polarization is large during high-rate charge and discharge, the discharge power deteriorates, and in severe cases, it also affects the lithium precipitation of the battery cell, resulting in deteriorated cycle performance.

[0046] Furthermore, the inventor of the present application has found through a large number of experiments that when w, m1 and α satisfy 0.5 < m1w / α < 20, the problem of the decomposition of the electrolyte due to the heat generation of the tab during the process of high-rate charge and discharge of the battery cell can be better solved, the total consumption of the electrolyte decreases, and the power performance of the battery cell in the middle of the cycle can be improved. In some embodiments, w, m1 and α satisfy 1 < m1w / α < 14. In some embodiments, m1w / α is 0.5 to 0.6, 0.6 to 0.7, 0.7 to 0.8, 0.8 to 0.9, 0.9 to 1, 1 to 2, 2 to 3, 3 to 4, 4 to 5, 5 to 6, 6 to 7, 7 to 8, 8 to 9, 9 to 10, 10 to 11, 11 to 12, 12 to 13, 13 to 14, 14 to 15, 15 to 16, 16 to 17, 17 to 18, 18 to 19 or 19 to 20.

[0047] In some embodiments, for the thermal stability salt, the temperature corresponding to a 5% weight loss rate is above 200 °C. The relationship between the weight and temperature of the thermal stability salt can be measured by thermogravimetric analysis, and the temperature when 5% of the weight decreases can be obtained.

[0048] In some embodiments, in the molecular formula of the heat stable salt, x=1 and y=1, or x=1 and y=2, or x=2 and y=1.

[0049] In some embodiments, in the molecular formula of the heat stable salt, R1 and R2 are each independently selected from a fluorine atom and a trifluoromethyl group. In some embodiments, R1 and R2 are both fluorine atoms or both trifluoromethyl groups.

[0050] In some embodiments, the thermally stable salt is one or more selected from lithium bis(fluorosulfonyl)imide (LiFSI), potassium bis(fluorosulfonyl)imide (KFSI), cesium bis(fluorosulfonyl)imide (CsFSI), barium bis(fluorosulfonyl)imide (Ba(FSI)2), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), Li2F(SON)2SO2F, and LiCF3SONSO2F.

[0051] In some embodiments, the additive that inhibits decomposition of the lithium salt is one or more selected from LiSO3F, NaSO3F, or KSO3F.

[0052] In the secondary battery according to the present application, the electrolyte may further include a fluorine-based solvent, which reduces the electron cloud density of the stable lithium salt, enhances the electrochemical stability of the solvated stable lithium salt, and thus reduces the decomposition and consumption of the electrolyte. The fluorine-based solvent is one or more selected from fluorinated carbonate, fluorobenzene, and fluoroether. The content of the fluorine-based solvent is m2%, and the ratio m2 / α of m2 to α is 1 to 8, for example, 1 to 1.5, 1.5 to 2, 2 to 2.5, 2.5 to 3, 3 to 3.5, 3.5 to 4, 4 to 4.5, 4.5 to 5, 5 to 6, 6 to 7, or 7 to 8.

[0053] In some embodiments, the fluorinated carbonate has one of the following formulas: [ka] In some embodiments, the fluorobenzene has the formula: [ka] In some embodiments, the fluoroether is R 1’ -OR 2’ R3, R4, R5, R6, R 1’ , R 2’ Each independently -C x’ F y’ H z’ where 1≦x'≦6, y'>0, z'>0 are satisfied, and 0≦y'≦2x', 0≦z'≦2x' are satisfied. R7, R8, R9, R 10 , R 11 , R 12 are each independently one of F or H.

[0054] In some embodiments, R 1’ , R 2’ are each independently selected from -C2F4H, -CF3, -C3F6H, -C2F3H2, and -C3F4H3.

[0055] In some embodiments, R 1’ , R 2’ are each independently selected from -CF2-CF2H, -CF3, -CF2-CFH-CF3, -CH2-CF3, and -CH2-CF2-CHF2.

[0056] In some embodiments, the fluoroether is selected from those represented by the following formula: [ka]

[0057] In some embodiments, R5, R6 are each independently selected from -C2F3H, -CFH, and -CH2.

[0058] In some embodiments, R5, R6 are each independently selected from -CH-CF3, -CHF, and -CH2.

[0059] In some embodiments, the fluorinated carbonate is selected from those represented by the following formula: [ka]

[0060] In some embodiments, R5, R6 are each independently selected from -CH3, -C2F3H2, -CFH2, and -C2FH4.

[0061] In some embodiments, R5, R6 are each independently selected from -CH3, -CH2-CF3, -CH2-F, and -CH2-CH2-F.

[0062] In some embodiments, the fluorinated carbonate is selected from those represented by the following formula: [ka]

[0063] In some embodiments, the fluorinated solvent is fluorobenzene (ie, 1-fluorobenzene).

[0064] In the secondary battery of the present application, the electrolyte may further include an additive that is easy to lose electrons, which can be oxidized to form a film first, thereby suppressing the decomposition of stable lithium salt and reducing the total consumption of electrolyte, so that the electrolyte in the battery cell during the middle of the cycle is sufficient, the kinetic performance of lithium ion migration is relatively good, the interface impedance is relatively small, and the power performance of the battery cell during the middle of the cycle is relatively good.

[0065] In some embodiments, the additive susceptible to losing electrons is one or more selected from phosphites, borates, and phosphates.

[0066] In some embodiments, the content of the additive that easily loses electrons in the electrolyte is m3%, and the ratio of m3 to α, m3 / α, is 0.1 to 0.9, for example, 0.1 to 0.2, 0.2 to 0.3, 0.3 to 0.4, 0.4 to 0.5, 0.5 to 0.6, 0.6 to 0.7, 0.7 to 0.8, or 0.8 to 0.9.

[0067] In some embodiments, the phosphite has the formula: [ka] In some embodiments, the phosphate ester has the following formula: [ka] In some embodiments, the borate ester has the formula: [ka] R 13 , R 14 , R 15 , R 16 , R 17 , R 18 , R19 , R 20 , R 21 are each independently selected from an alkyl group, a fluoroalkyl group, a silane group, an alkenyl group, and a phenyl group.

[0068] In some embodiments, R 13 , R 14 , R 15 are each independently 1-6 Alkyl groups (e.g., methyl and ethyl groups), C 1-6 It is selected from fluoroalkyl groups (eg, fluoromethyl groups, fluoroethyl groups, eg, -CH2-CF3).

[0069] In some embodiments, the phosphite is selected from Additive 1 or Additive 2, which are represented by the following formula: [ka]

[0070] In some embodiments, R 16 , R 17 , R 18 are each independently 1-6 Fluoroalkyl groups (e.g., fluoromethyl groups, fluoroethyl groups, e.g., -CH2-CF3), C 1-6 alkenyl groups (eg allyl groups).

[0071] In some embodiments, the phosphate ester is selected from Additive 3 or Additive 4, which are represented by the following chemical formula: [ka]

[0072] In some embodiments, R 19 , R 20 , R 21 are each independently 1-6 Alkyl groups (e.g., methyl and ethyl groups), C 1-6It is selected from fluoroalkyl groups (e.g., fluoromethyl group, fluoroethyl group, e.g., -CH2-CF3).

[0073] In some embodiments, the borate ester is selected from additive 5 or additive 6 represented by the following chemical formulae.

Chemical formula

[0074] In some embodiments, in the electrolyte of the secondary battery according to the present application, the additives that suppress the decomposition of the thermally stable salt and the lithium salt are LiFSI and LiSO3F, respectively. In some preferred embodiments, w, m1, and α satisfy 1 < m1w / α < 14. In some more preferred embodiments, α is 2 to 9.5.

[0075] In some embodiments, in the secondary battery according to the present application, the electrolyte contains the thermally stable salt LiFSI and the additive LiSO3F that suppresses the decomposition of the lithium salt, and further contains a fluorine-based solvent. The fluorine-based solvent is selected from methyl 2,2,2-trifluoroethyl carbonate, fluorobenzene, trans-4,5-difluoro-1,3-dioxolan-2-one, Formula 1 of the above fluorinated ether, and a mixed solvent of methyl 2,2,2-trifluoroethyl carbonate / trans-4,5-difluoro-1,3-dioxolan-2-one / fluorobenzene (e.g., a mixed solvent with a mass ratio of 3 / 1 / 1). In some preferred embodiments, the content of the fluorine-based solvent is m2%, and the ratio m2 / α of m2 to α is 1 to 8.

[0076] In some embodiments, in the secondary battery according to the present application, the electrolyte contains a thermally stable salt LiFSI and an additive LiSO3F that suppresses decomposition of a lithium salt, and further contains an additive that easily loses electrons, the additive that easily loses electrons being selected from the above-mentioned Additive 1, Additive 2, Additive 3, Additive 4, and Additive 5. In some preferred embodiments, the content of the additive that easily loses electrons in the electrolyte is m3%, and the ratio of m3 to α, m3 / α, is 0.1 to 0.9.

[0077] In the secondary battery according to the present application, the electrolyte further includes an organic solvent, and the type of the organic solvent is not particularly limited and can be selected according to actual requirements. In some embodiments, the organic solvent includes one or more of a chain carbonate ester, a cyclic carbonate ester, and a carboxylate ester. The chain carbonate ester, the cyclic carbonate ester, and the carboxylate ester are not particularly limited and can be selected according to actual requirements. Optionally, the organic solvent includes one or more of diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, ethylene carbonate (EC), propylene carbonate, butylene carbonate, γ-butyrolactone, methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, methyl propionate, and tetrahydrofuran.

[0078] In the secondary battery according to the present application, the electrolyte may contain an additive for improving gas generation, storage or power performance of the battery. In some embodiments, the additive is one or more selected from a cyclic carbonate compound containing an unsaturated bond, a halogen-substituted cyclic carbonate compound, a sulfate compound, a sulfite compound, a sultone compound, a disulfonic acid compound, a nitrile compound, an aromatic compound, an isocyanate compound, a phosphazene compound, a cyclic acid anhydride compound, a phosphite compound and a carboxylate compound, and the cyclic carbonate compound containing an unsaturated bond and the halogen-substituted cyclic carbonate compound are different from the above-mentioned cyclic carbonates.

[0079] In addition, the secondary battery, the battery module, the battery pack, and the electric device according to the present application will be described below with reference to the drawings.

[0080] In one embodiment of the present application, a secondary battery is provided.

[0081] Generally, a secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During the charging and discharging process of the battery, active ions are repeatedly inserted and removed between the positive electrode plate and the negative electrode plate. The electrolyte is for conducting ions between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, and mainly prevents short-circuiting between the positive electrode and the negative electrode while allowing ions to pass through.

[0082] [Positive plate]

[0083] In the secondary battery according to the present application, the positive electrode plate includes a positive electrode current collector and a positive electrode material layer provided on the positive electrode current collector and including a positive electrode active material, and the positive electrode material layer may be provided on one surface of the positive electrode current collector or on two surfaces of the positive electrode current collector.

[0084] In some embodiments, a metal foil or a composite current collector is used as the positive electrode current collector. For example, an aluminum foil can be used as the metal foil. The composite current collector can include a polymeric material base layer and a metal layer formed on at least one surface of the polymeric material base layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymeric material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0085] In some embodiments, the positive electrode active material may be a positive electrode active material for batteries known in the art. For example, the positive electrode active material may include at least one of lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and modified compounds thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may 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 include lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (simply NCM 333 (sometimes referred to as "LiNi") 0.5 Co 0.2 Mn 0.3 O2 (simply NCM 523 (sometimes referred to as "LiNi") 0.5 Co 0.25 Mn 0.25 O2 (simply NCM 211 (sometimes referred to as "LiNi") 0.6 Co 0.2 Mn 0.2O2 (simply NCM 622 (sometimes referred to as "LiNi") 0.8 Co 0.1 Mn 0.1 O2 (simply NCM 811 Lithium nickel cobalt aluminum oxide (e.g. LiNi 0.85 Co 0.15 Al 0.05 Examples of lithium-containing phosphates having an olivine structure include, but are not limited to, at least one of lithium iron phosphate (e.g., LiFePO4 (sometimes simply referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

[0086] In some embodiments, the positive electrode material layer optionally further comprises an adhesive. The type and content of the adhesive are not specifically limited and can be selected according to actual requirements. For example, the adhesive comprises at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropene copolymer and fluorine-containing acrylic resin.

[0087] In some embodiments, the positive electrode material layer optionally further includes a conductive agent, for example, at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0088] In some embodiments, the positive plate can be prepared as follows: The components for preparing the positive plate, such as the positive active material, conductive agent, adhesive, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to obtain a positive paste, which is then applied to a positive current collector, and the positive plate is obtained through steps such as drying and cold pressing.

[0089] In some embodiments, the positive electrode material layer includes a large single crystal lithium nickel cobalt manganese oxide (NCM523) positive electrode active material, acetylene black as a conductive agent, and polyvinylidene fluoride (PVDF) as an adhesive.

[0090] [Negative plate]

[0091] In the secondary battery according to the present application, the negative electrode plate includes a negative electrode current collector and a negative electrode material layer provided on the negative electrode current collector and including a negative electrode active material, and the negative electrode material layer may be provided on one surface of the negative electrode current collector or on two surfaces of the negative electrode current collector.

[0092] In some embodiments, a metal foil or a composite current collector is used as the negative electrode current collector. For example, a copper foil can be used as the metal foil. The composite current collector can include a polymeric base layer and a metal layer formed on at least one surface of the polymeric substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymeric substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0093] In some embodiments, the negative electrode active material may be a negative electrode active material for batteries known in the art. For example, the negative electrode active material may include at least one of graphite (e.g., artificial graphite, natural graphite), soft carbon, hard carbon, mesocarbon microbeads, carbon fiber, carbon nanotube, silicon-based material, tin-based material, and lithium titanate. The silicon-based material is at least one selected from elemental silicon, silicon oxide, silicon carbon composite, silicon nitrogen composite, and silicon alloy. The tin-based material is at least one selected from elemental tin, tin oxide, and tin alloy. The present application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may be used. These negative electrode active materials may be used alone or in combination of two or more.

[0094] In some embodiments, the negative electrode membrane layer optionally further comprises an adhesive, which is at least one selected from 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).

[0095] In some embodiments, the negative electrode film layer optionally further includes a conductive agent, which is at least one selected from superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0096] In some embodiments, the negative electrode material layer includes artificial graphite as a negative electrode active material, acetylene black as a conductive agent, and styrene butadiene rubber (SBR) as an adhesive.

[0097] In some embodiments, the negative electrode material layer may optionally include other auxiliary agents, such as, for example, a thickening agent (eg, sodium carboxymethylcellulose (CMC-Na)).

[0098] In some embodiments, the negative plate can be prepared as follows: The above-mentioned components for preparing the negative plate, such as the negative active material, the conductive agent, the adhesive, and any other components, are dispersed in a solvent (e.g., deionized water) to obtain a negative paste, which is then applied to a negative current collector, and the negative plate is obtained through steps such as drying and cold pressing.

[0099] [Separator]

[0100] In the secondary battery according to the present application, the separator is disposed between the positive electrode plate and the negative electrode plate, and separates the positive electrode plate and the negative electrode plate. The type of the separator is not specifically limited, and any known separator having a porous structure with good chemical stability and mechanical stability can be used. In some embodiments, the material of the separator is at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single layer film or a multilayer composite film, and is not particularly limited here. When the separator is a multilayer composite film, the material of each layer may be the same or different, and is not particularly limited here.

[0101] The secondary battery according to the present application may be a lithium ion battery.

[0102] The secondary battery according to the present application can be fabricated by a conventional method. In some embodiments, the positive electrode plate, the negative electrode plate and the separator are fabricated into an electrode assembly by a winding process or a stacking process. Illustratively, the fabrication method includes the following steps: Step 1: A positive electrode plate, a separator, and a negative electrode plate are stacked in order, with the separator located between the positive electrode plate and the negative electrode plate, and then wound to obtain an electrode assembly. Step 2: The electrode assembly is placed in the housing of the secondary battery, dried, and then the electrolyte is injected. After the formation and leaving processes, the secondary battery is obtained.

[0103] In some embodiments, the secondary battery according to the present application includes a package, which is used to enclose the electrode assembly and the electrolyte.

[0104] In some embodiments, the package of the secondary battery may be a hard case such as a hard plastic case, an aluminum case, a steel case, etc., or a soft pack such as a bag-shaped soft pack. The material of the soft pack may be a plastic such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0105] In the present application, the shape of the secondary battery is not particularly limited, and may be cylindrical, rectangular, or any other shape. For example, FIG. 5 shows a secondary battery 5 having a rectangular structure as an example.

[0106] In some embodiments, as shown in FIG. 6, the package includes a housing 51 and a cover plate 53. The housing 51 includes a bottom plate and a side plate connected to the bottom plate, and is configured to enclose a chamber with the bottom plate and the side plate. The housing 51 has an opening communicating with the chamber, and the cover plate 53 is provided to close the opening and seal the chamber. The positive electrode plate, the negative electrode plate and the separator are formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is sealed in the chamber. An electrolyte is infiltrated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and can be selected by those skilled in the art according to actual requirements.

[0107] In some embodiments, the secondary batteries can be assembled into a battery module, and the number of secondary batteries included in the battery module can be one or more, with the specific number being selectable by those skilled in the art according to the application and capacity of the battery module.

[0108] Fig. 3 shows an example of a battery module 4. As shown in Fig. 3, in the battery module 4, a plurality of secondary batteries 5 are arranged in order in the length direction of the battery module 4. Of course, any other arrangement may be used. Furthermore, the plurality of secondary batteries 5 are fixed by a fixing member.

[0109] Optionally, the battery module 4 may have a housing having an accommodation space for accommodating a plurality of secondary batteries 5 .

[0110] In some embodiments, the above battery modules can be assembled into a battery pack, and the number of battery modules included in the battery pack can be one or more, and the specific number can be selected by one skilled in the art according to the application and capacity of the battery pack.

[0111] 4 and 5 show a battery pack 1 as an example. As shown in Fig. 4 and 5, the battery pack 1 includes a battery case and a plurality of battery modules 4 arranged in the battery case. The battery case includes an upper case 2 and a lower case 3, and the upper case 2 is provided to cover the lower case 3, thereby forming an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery case in any manner.

[0112] The present application further provides an electric device including the secondary battery, battery module, or battery pack according to the present application. The secondary battery, battery module, or battery pack may be used as a power source for the electric device, or may be used as an energy storage unit for the electric device. The electric device may include, but is not limited to, mobile equipment (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., fully electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), trains, ships, satellites, energy storage systems, etc. A secondary battery, battery module, or battery pack may be selected for the electric device according to its usage requirements.

[0113] 6 shows an example of an electric device. The electric device can be a full electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high rate and high energy density requirements for the secondary battery of the electric device, a battery pack or a battery module can be used.

[0114] As another example, the device may be a mobile phone, a tablet, a laptop, etc. Such devices are generally required to be light and thin, and therefore may use secondary batteries as a power source.

[0115] Working Example The following examples of the present application are described. The examples described below are illustrative and are merely used to explain the present application, and are not intended to limit the present application. For specific techniques or conditions not specified in the examples, techniques or conditions described in the literature in the field are used, or are performed according to the product instructions. Reagents or equipment used without a manufacturer's name are all conventional products available on the market.

[0116] The lithium ion batteries according to the examples and comparative examples were all prepared by the following method.

[0117] (1) Preparation of positive electrode plate The positive electrode active material NCM523, the conductive agent acetylene black, and the adhesive polyvinylidene fluoride (PVDF) were dissolved in the solvent N-methylpyrrolidone (NMP) in a weight ratio of 96.5:1.5:2, and thoroughly mixed to obtain a positive electrode paste. The positive electrode paste was then uniformly applied to the positive electrode current collector until the weight of the applied paste was 18.18 mg / cm. 2 Then, the positive electrode plate was obtained through drying, cold pressing, and cutting. (2) Preparation of negative electrode plate The active material, artificial graphite, conductive agent, acetylene black, adhesive, styrene butadiene rubber (SBR), and thickener, sodium carboxymethyl cellulose (CMC-Na), were dissolved in deionized water as a solvent in a weight ratio of 95:2:2:1, and mixed uniformly with the deionized water to obtain a negative electrode paste. The negative electrode paste was then uniformly applied to the copper foil of the negative electrode current collector, with the application weight being 10.58 mg / cm. 2 After drying, a negative electrode sheet was obtained, which was then cold pressed and cut to obtain a negative electrode plate. (3) Preparation of electrolyte In a glove box under an argon gas atmosphere (H2O<0.1ppm, O2<0.1ppm), the organic solvents EC / EMC were mixed uniformly in a mass ratio of 3 / 7, and the salts and additives shown in Tables 1-4 were added and stirred uniformly to obtain the corresponding electrolyte solution. (4) Preparation of separator: A polypropylene membrane was used as the separator. (5) Method for measuring cross-sectional area S of tab Disassemble the battery cell, use a micrometer to measure the thickness h (μm) of the positive tabs, and use an ordinary ruler to measure the average width L (mm) of the tabs. If the total number of positive tabs in one battery cell is n, the average cross-sectional area of ​​the positive tabs in the corresponding battery cell is S = n × L × h / 1000 (mm 2 ). (6) Preparation of Lithium-ion Batteries The positive plate, separator, and negative plate are stacked in order so that the separator is located between the positive plate and the negative plate to separate them, and then wound to obtain an electrode assembly. The electrode assembly is placed in a battery housing, dried, and then electrolyte is injected, and a lithium-ion battery is obtained through the formation and standing processes. The mass of the electrolyte, n4 (g), is n4 = 2.8g / Ah × C, where 2.8g / Ah is the electrolyte injection coefficient and C is the capacity of the battery cell (unit: Ah).

[0118] The lithium-ion battery testing process is as follows: 1. Battery cell capacity test At 25°C, the lithium ion battery was charged at a constant current of 1C up to 4.35V, then charged at a constant voltage of 4.35V until the current became less than 0.05C, and then discharged at 0.33C down to 2.8V to obtain the discharge capacity C (unit: Ah). 2. Cycle performance test of lithium-ion batteries at 45℃ At 45°C, the lithium-ion battery was charged to 4.35V at a constant current of 1.5C, then charged at a constant voltage of 4.35V until the current was less than 0.05C, and then discharged to 2.8V at a constant current of 1.5C, which was one charge-discharge process. The charge and discharge were repeated 500 cycles. 3. Internal resistance of battery cells The power of the battery cell after 500 cycles was adjusted to 50% SOC, and the internal resistance of the battery was measured with an AC resistance meter, with a perturbation voltage of 5 mV and a frequency of 1000 Hz. 4. Electrolyte test The weight of the battery cell after 500 cycles was measured using a balance and recorded as n1 (g), and the battery cell after 500 cycles was discharged to 2.8 V at a constant current of 0.1 C and centrifuged (5000 rpm x 30 min), and the electrolyte was taken and analyzed by ion chromatography to obtain the corresponding lithium salt content w2. In the ion chromatography analysis process, a sample was weighed and diluted to a constant volume with deionized water, and the anion content of the treated sample was measured using a DIONEX ICS-900 system. The plates and separators of the battery cells are immersed in DMC three times to thoroughly remove the residual electrolyte inside the plates and separators, and then the battery cell packages, plates and separators are vacuum dried under 60℃ for 24h, weighed and recorded as n2(g), therefore, the mass of the residual electrolyte in the corresponding battery cells is n3(g)=n1-n2, and the mass fraction of the corresponding residual electrolyte is n3 / n4. The mass of the lithium salt in the residual electrolyte is w2×n3, and the mass of the lithium salt in the electrolyte initially injected into the battery cell is w2×n4. The mass fraction of the lithium salt in the residual electrolyte is the mass of the lithium salt in the residual electrolyte / the mass of the lithium salt in the electrolyte initially injected into the battery cell×100%, i.e. (w2×n3) / (w2×n4).

[0119] The test results are shown in Tables 1-4.

[0120] [Table 1]

[0121] As can be seen from Table 1, the electrolyte of Comparative Example 1 did not contain the thermally stable salt LiFSI and the additive LiSO3F for suppressing decomposition of lithium salts, Comparative Example 2 did not contain LiSO3F, and Comparative Example 3 did not contain LiFSI, and after 500 cycles, the electrolyte decomposed significantly, the content of lithium salt remaining in the electrolyte was relatively low, and the internal resistance of the battery cell was relatively high. In Comparative Example 4, m1w / α was smaller than 0.5, and in Comparative Example 5, m1w / α was larger than 20. Compared to Examples 1-4, in Comparative Examples 4 and 5, the electrolyte decomposed significantly, the content of lithium salt remaining in the electrolyte was relatively low, and the internal resistance of the battery cell was relatively high after 500 cycles.

[0122] [Table 2]

[0123] As can be seen from Table 2, in Comparative Example 7, m1w / α was smaller than 0.5, and in Comparative Example 6, the temperature rise coefficient was smaller than 2. Compared to Examples 5 and 6, in Comparative Examples 6 and 7, the electrolyte was decomposed to a large extent after 500 cycles, the content of lithium salt remaining in the electrolyte was relatively low, and the internal resistance of the battery cell was relatively high.

[0124] [Table 3]

[0125] As can be seen from Table 3, in Comparative Example 9, m2 / α was smaller than 1, in Comparative Example 10, m2 / α was larger than 10, and in Examples 7 and 8, m2 / α was 1% to 8% (after rounding). Compared to Examples 7 and 8, in Comparative Examples 9 and 10, the internal resistance of the battery cells was relatively high after 500 cycles.

[0126] [Table 4]

[0127] As can be seen from Table 4, no additives that easily lose electrons were added to the electrolyte of Comparative Example 11, and in Comparative Example 11, the electrolyte was decomposed more after 500 cycles, the content of lithium salt remaining in the electrolyte was relatively low, and the internal resistance of the battery cell was higher than in Comparative Example 12 and Examples 13 to 19. In Comparative Example 12, m3 / α was smaller than 0.1%, and in Comparative Example 12, the internal resistance of the battery cell was higher after 500 cycles than in Example 13.

[0128] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely illustrative, and within the scope of the technical proposal of the present application, embodiments that have substantially the same configuration as the technical idea and can achieve the same effect also fall within the technical scope of the present application. In addition, various modifications made to the embodiments that a person skilled in the art can conceive within the scope of the gist of the present application, and other methods made by combining some of the components of the embodiments also fall within the scope of the present application. [Explanation of symbols]

[0129] 1 Battery pack 2 Upper case 3 Lower case 4 Battery Module 5 Secondary battery 51 Housing 52 Electrode Assembly 53 Cover plate

Claims

1. The battery includes an electrode assembly and an electrolyte, the electrode assembly including a positive electrode plate, a negative electrode plate, and a separator, the positive electrode plate including a positive electrode tab, the negative electrode plate including a negative electrode tab, and a temperature rise coefficient α Ah / mm of the positive electrode tab is expressed by the following formula: [0030] S1 is the total cross-sectional area of ​​the positive electrode tab, and its unit is mm ２ C is the capacity of the electrode assembly, in Ah; The electrolyte contains a thermally stable salt and an additive that inhibits decomposition of the lithium salt, The thermally stable salt has the molecular formula: (M ｙ＋ ) ｘ／ｙ R １ (SO ２ N) ｘ SO ２ R ２ and M ｙ＋ But Li ＋ , Na ＋ , K ＋ , Rb ＋ , Cs ＋ , Mg ２＋ , Ca ２＋ , Ba ２＋ , Al ３＋ , Fe ２＋ , Fe ３＋ , Ni ２＋ , Ni ３＋ and optionally, one or more selected from My ＋ But Li ＋ , K ＋ , Cs ＋ , Ba ２＋ wherein y is the valence of M; The R １ , R ２ are each independently selected from a fluorine atom, a fluoroalkyl group having 1 to 20 carbon atoms, a fluoroalkoxy group having 1 to 20 carbon atoms, and an alkyl group having 1 to 20 carbon atoms; x is an integer selected from 1, 2, and 3; The content of the thermally stable salt in the electrolyte is w% in mass percent; The additive that suppresses the decomposition of lithium salts is RSO ３ F, and R is Li ＋ , Na ＋ , K ＋ , Rb ＋ , Cs ＋ One or more selected from The content of the additive in the electrolyte that inhibits the decomposition of the lithium salt is m, in mass percent. １ %, Said w, m １ and α is 0.5<m １ w / α<20 is satisfied, α is 2 to 9.5, m １ % is 0.2% to 5% and w% is 10% to 23%.

2. The heat-stable salt has a temperature corresponding to a weight loss rate of 5% greater than 200°C. The secondary battery according to claim 1 .

3. In the molecular formula of the heat stable salt, x=1 and y=1, or x=1 and y=2, or x=2 and y=1; The secondary battery according to claim 1 .

4. In the molecular formula of the heat stable salt, R １ , R ２ are each independently selected from a fluorine atom and a trifluoromethyl group, and optionally, R １ , R ２ are both fluorine atoms or both trifluoromethyl groups; The secondary battery according to any one of claims 1 to 3.

5. The heat stable salts include lithium bis(fluorosulfonyl)imide, potassium bis(fluorosulfonyl)imide, cesium bis(fluorosulfonyl)imide, barium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, Li ２ F (SO ２ N) ２ SO ２ F, LiCF ３ SO ２ NSO ２ F, The secondary battery according to any one of claims 1 to 4.

6. The additive that inhibits the decomposition of lithium salts is LiSO ３ F, NaSO ３ F or KSO ３ F, The secondary battery according to any one of claims 1 to 5.

7. The electrolyte further contains a fluorine-based solvent, and the fluorine-based solvent is one or more selected from the group consisting of fluorinated carbonate, fluorobenzene, and fluoroether. The secondary battery according to any one of claims 1 to 6.

8. The fluorine-based solvent is contained in the electrolyte solution in an amount of m ２ %, m ２ The ratio m to α ２ / α is 1 to 8; The secondary battery according to claim 7.

9. The fluorinated carbonate is any of those represented by the following chemical formula: 【Chemistry 23】 and / or The fluorobenzene is represented by the following chemical formula: 【Chemistry 24】 and / or The fluoroether is R １’ -O-R ２’ and R ３ , R ４ , R ５ , R ６ , R １’ , R ２’ Each independently -C ｘ’ F ｙ’ H ｚ’ where 1≦x′≦6, y′>0, z′>0 are satisfied, and 0≦y′≦2x′, 0≦z′≦2x′ are satisfied; R ７ , R ８ , R ９ , R １０ , R １１ , R １２ are each independently one of F or H; The secondary battery according to claim 7 or 8.

10. R １’ , R ２’ Each independently represents -C ２ F ４ H, -CF ３ , -C ３ F ６ H, -C ２ F ３ H ２ , -C ３ F ４ H ３ is selected from Optionally, R １’ , R ２’ Each independently represents -CF ２ -CF ２ H, -CF ３ , -CF ２ -CFH-CF ３ , -CH ２ -CF ３ , -CH ２ -CF ２ -CHF ２ is selected from Optionally, the fluoroether is selected from those represented by the following formula: 【Chemistry 25】 The secondary battery according to claim 9.

11. R ５ , R ６ Each independently represents -C ２ F ３ H, -CFH, -CH ２ is selected from Optionally, R ５ , R ６ are each independently -CH-CF ３ , -CHF, -CH ２ is selected from Optionally, the fluorinated carbonate is selected from those represented by the following formula: 【Chemistry 26】 The secondary battery according to claim 9 or 10.

12. R ５ , R ６ Each independently represents -CH ３ , -C ２ F ３ H ２ , -CFH ２ , -C ２ FH ４ is selected from Optionally, R ５ , R ６ Each independently represents -CH ３ , -CH ２ -CF ３ , -CH ２ -F, -CH ２ -CH ２ -F, Optionally, the fluorinated carbonate is selected from those represented by the following formula: 【Chemical 27】 The secondary battery according to claim 9 or 10.

13. The electrolyte further includes an additive that easily loses electrons, and the additive that easily loses electrons is one or more selected from a phosphite ester, a borate ester, and a phosphate ester. The secondary battery according to any one of claims 1 to 12.

14. The additive that easily loses electrons is contained in the electrolyte at a content of m ３ %, m ３ The ratio m to α ３ / α is 0.1 to 0.9; The secondary battery according to claim 13.

15. The phosphite ester is represented by the following chemical formula: 【Chemistry 28】 and / or The phosphate ester is represented by the following chemical formula: 【Chemical 29】 and / or The boric acid ester is represented by the following chemical formula: 【Chemistry 30】 R １３ , R １４ , R １５ , R １６ , R １７ , R １８ , R １９ , R ２０ , R ２１ are each independently selected from an alkyl group, a fluoroalkyl group, a silane group, an alkenyl group, and a phenyl group; The secondary battery according to claim 13 or 14.

16. R １３ , R １４ , R １５ are each independently １－６ Alkyl groups (e.g., methyl and ethyl groups), C １－６ Fluoroalkyl groups (e.g., fluoromethyl groups, fluoroethyl groups, e.g., —CH ２ -CF ３ ) are selected from Optionally, the phosphite is selected from those represented by the following formula: 【Chemistry 31】 The secondary battery according to claim 15.

17. R １６ , R １７ , R １８ are each independently １－６ Fluoroalkyl groups (e.g., fluoromethyl groups, fluoroethyl groups, e.g., —CH ２ -CF ３ ), C １－６ alkenyl groups (e.g., allyl groups); Optionally, the phosphate ester is selected from those represented by the following formula: 【Chemistry 32】 The secondary battery according to claim 15.

18. R １９ , R ２０ , R ２１ are each independently １－６ Alkyl groups (e.g., methyl and ethyl groups), C １－６ Fluoroalkyl groups (e.g., fluoromethyl groups, fluoroethyl groups, e.g., —CH ２ -CF ３ ) are selected from Optionally, the borate ester is selected from those represented by the following formula: 【Chemical 33】 The secondary battery according to claim 15.

19. A battery module comprising the secondary battery according to any one of claims 1 to 18.

20. A battery pack comprising the battery module according to claim 19.

21. An electric device comprising the secondary battery according to any one of claims 1 to 18, the battery module according to claim 19, or the battery pack according to claim 20.

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