Secondary battery and electric device

Abstract

The invention provides a secondary battery and an electric device. The secondary battery comprises a battery shell with a containing cavity, a battery cell assembly located in the containing cavity and electrolyte, the electrolyte comprises a chain carboxylic ester compound, and based on the total mass of the electrolyte, the mass content W of the chain carboxylic ester compound satisfies 0.03 < = W / R < = 7. The secondary battery has excellent fast charging performance and long service life.

Description

Technical Field

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

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal, wind and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields, driving the development of secondary batteries towards higher energy density, power performance, cycle life and other directions.

[0003] The fast charging performance and life performance of secondary battery cells are one of the hot topics in the battery field. The performance of the electrolyte has a key impact on the performance of the secondary battery. Therefore, it is urgent to improve the fast charging and life performance of the secondary battery by improving the composition of the electrolyte. Summary of the invention

[0004] In view of the problems existing in the background technology, the present application provides a secondary battery, aiming to improve the fast charging performance and service life of the secondary battery.

[0005] In a first aspect of the present application, a secondary battery is provided, comprising a battery housing having a receiving cavity, a battery cell assembly and an electrolyte located in the receiving cavity;

[0006] The electrolyte includes a chain carboxylate compound, wherein, based on the total mass of the electrolyte, the mass content W of the chain carboxylate compound and the residual space R satisfy: 0.03≤W / R≤7, the residual space Among them, V1 represents the internal volume of the secondary battery housing cavity; V2 represents the volume of the battery cell assembly; V3 represents the volume of the electrolyte; and C represents the discharge capacity of the secondary battery.

[0007] In some embodiments, the mass content W of the linear carboxylate compound and the residual space R satisfy: 0.05≤W / R≤7, 0.1≤W / R≤7, 0.15≤W / R≤6 or 3≤W / R≤7.

[0008] In the secondary battery provided in the present application, the chain carboxylate compound has a lower viscosity, which can well improve the transmission rate of metal ions (such as lithium ions and sodium ions) of the active substance in the electrolyte, and improve the dynamics and fast charging performance of the secondary battery, but the chain carboxylate compound has the defect of worsening gas production. When the mass content of the chain carboxylate compound and the residual space R satisfy the above relationship, the larger residual space can provide more space to accommodate the gas generated by the side reaction of the battery cell assembly, reduce the internal pressure of the battery shell or maintain the basic stability of the internal pressure of the battery shell, thereby extending the service life of the secondary battery.

[0009] In any embodiment, the chain carboxylate compound comprises a structure shown in Formula I,

[0010]

[0011] Wherein, R1 and R2 each independently include C 1-6 of alkyl.

[0012] In any embodiment, the chain carboxylate compound includes one or more of ethyl acetate, methyl acetate, propyl acetate, and methyl butyrate.

[0013] The electrolyte including the above-mentioned chain carboxylate compound has a lower viscosity, which is beneficial to improving the transmission rate of metal ions in the active material, improving the dynamics of the secondary battery, and thus improving the fast charging performance of the secondary battery.

[0014] In any embodiment, based on the total mass of the electrolyte, the mass content W of the chain carboxylate compound is 5% to 70%, and can be optionally 10% to 60%.

[0015] Controlling the mass content of the chain carboxylate compound within an appropriate range can not only effectively reduce the viscosity of the electrolyte, increase the transmission rate of metal ions, improve the dynamics of the secondary battery, and improve the fast charging performance of the secondary battery; it can also reduce the deterioration of the gas production performance caused by the excessively high mass content of the chain carboxylate compound, thereby improving the service life of the secondary battery, so that the secondary battery has both improved fast charging performance and good service life.

[0016] In any embodiment, R is 0.05 mL / Ah to 2 mL / Ah, and can be optionally 0.1 mL / Ah to 2 mL / Ah.

[0017] Controlling R within a suitable range can not only provide sufficient space for the battery case to accommodate the gas generated by the battery cell assembly, reduce the internal pressure of the battery case or maintain the basic stability of the internal pressure of the battery case, and extend the service life of the secondary battery; it can also control the volume of the accommodating cavity within a suitable range, reduce the increase in production costs caused by an excessively large battery case, and take into account both the service life and production cost of the secondary battery.

[0018] In any embodiment, the electrolyte further includes a film-forming additive, and the film-forming additive includes one or more of a sulfate compound and a fluorocarbonate compound.

[0019] The film-forming additive can form a film on the positive electrode side to inhibit the reaction of the chain carboxylic acid ester on the positive electrode side. At the same time, the film-forming additive can also form a uniform and dense SEI film on the negative electrode side, which can further inhibit the side reaction of the electrolyte on the negative electrode side, improve the gas production performance of the electrolyte, and increase the service life of the secondary battery.

[0020] In any embodiment, the sulfate ester compound includes one or more of 4,4'-vinyl sulfate, vinyl sulfate, diethyl sulfate, dimethyl sulfate and 4,4-bis(1,3,2-dioxathiacyclopentane)-2,2,2,2-tetraoxide, and optionally includes one or more of 4,4'-vinyl sulfate and vinyl sulfate.

[0021] The above-mentioned sulfate ester compounds can generate a Li2SO4-rich SEI film on the negative electrode side. The SEI film can inhibit the side reaction of the electrolyte on the negative electrode side, improve the gas production performance of the electrolyte, and increase the service life of the secondary battery.

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

[0023] The above-mentioned fluorinated carbonate compounds can generate a LiF-rich SEI film on the negative electrode side, and the SEI film can inhibit the side reaction of the electrolyte on the negative electrode side, improve the gas production performance of the electrolyte, and increase the service life of the secondary battery.

[0024] In any embodiment, based on the total mass of the electrolyte, the mass content A of the sulfate compound and the mass content B of the fluorocarbonate compound satisfy: 0.03≤A / B≤20, and can be 0.05≤A / B≤10.

[0025] The combination of sulfate compounds and fluorocarbonate compounds is beneficial to further inhibit the side reactions of the electrolyte. At the same time, the mass ratio between the sulfate compounds and the fluorocarbonate compounds is controlled within an appropriate range so that the secondary battery has excellent fast charging performance and service life.

[0026] In any embodiment, based on the total mass of the electrolyte, the mass content A of the sulfuric acid compound is 0.1% to 2%, and can be 0.5% to 2%; the mass content B of the fluorocarbonate compound is 0.1% to 5%, and can be 0.1% to 4%.

[0027] By controlling the mass content of sulfate compounds and fluorocarbonate compounds within appropriate ranges, the film-forming additives in the secondary battery can be within appropriate ranges, and the interface side reactions of the positive and / or negative electrodes can be inhibited, thereby improving the power performance and service life of the secondary battery.

[0028] In any embodiment, based on the total mass of the electrolyte, the mass content W of the chain carboxylate compound, the mass content A of the sulfate compound and the mass content B of the fluorocarbonate compound satisfy: 0.7≤W / (A+B)≤30, which can be 1≤W / (A+B)≤27.3.

[0029] The mass content W of the chain carboxylate compound, the mass content A of the sulfate compound and the mass content B of the fluorocarbonate compound are controlled to satisfy the relationship of 0.7≤W / (A+B)≤30, so as to achieve the synergistic effect between the chain carboxylate compound and the film-forming additive, and improve the fast charging performance and service life of the secondary battery. Further controlling the relationship between W, A and B to satisfy 1≤W / (A+B)≤27.3 is conducive to further improving the fast charging performance and service life of the secondary battery.

[0030] In any embodiment, the electrolyte further includes a lithium salt, and the lithium salt includes one or more of LiFSI and LiPF6; or the electrolyte further includes a sodium salt, and the sodium salt includes one or more of NaFSI and NaPF6.

[0031] In any embodiment, based on the total mass of the electrolyte, the mass content of the lithium salt or sodium salt is 8% to 20%, and can be optionally 10% to 15%; or, based on the total mass of the electrolyte, the mass content of the sodium salt is 9% to 21%, and can be optionally 11% to 16%.

[0032] Controlling the lithium salt or sodium salt within a suitable range is beneficial to improving the concentration polarization inside the battery cell assembly, thereby improving the service life of the secondary battery.

[0033] In any embodiment, the lithium salt includes LiFSI and LiPF6. Based on the total mass of the electrolyte, the mass ratio of LiFSI to LiPF6 is not less than 0.4 and not more than 7. Optionally, the mass ratio of LiFSI to LiPF6 is not less than 0.5 and not more than 2.

[0034] For lithium secondary batteries, the combination of LiFSI and LiPF6 can make the electrolyte have excellent lithium ion migration number and thermal stability. Controlling the mass content ratio of LiFSI and LiPF6 within an appropriate range is beneficial to improving the fast charging performance and service life of the secondary battery.

[0035] In any embodiment, the sodium salt comprises NaFSI and NaPF6. Based on the total mass of the electrolyte, the mass ratio of NaFSI to NaPF6 is not less than 0.4 and not more than 7, and optionally, the mass ratio of NaFSI to NaPF6 is not less than 0.5 and not more than 2.

[0036] For nano-secondary batteries, the combination of NaFSI and NaPF6 can make the electrolyte have excellent nano-ion migration number and thermal stability. Controlling the mass content ratio of NaFSI and NaPF6 within an appropriate range is beneficial to improving the fast charging performance and service life of secondary batteries.

[0037] In any embodiment, the viscosity of the electrolyte measured by a rotor test method at an ambient temperature of 25° C. is 2 mPa.s to 5 mPa.s, and can be optionally 3 mPa.s to 4.6 mPa.s.

[0038] The viscosity of the electrolyte is within an appropriate range, which is beneficial to increasing the transmission rate of metal ions, improving the dynamics of the secondary battery, and enhancing the fast charging performance of the secondary battery.

[0039] In any embodiment, the CB value of the secondary battery is 1.05 to 1.5, and can be optionally 1.05 to 1.3.

[0040] Controlling the CB value of the secondary battery within an appropriate range is beneficial for the negative electrode to provide sufficient active sites for receiving metal ions, improve the precipitation of active metals (such as lithium or sodium) at the interface of the negative electrode, and enhance the fast charging performance of the secondary battery.

[0041] In any embodiment, the secondary battery includes one or more of a lithium battery, a sodium battery, and a potassium battery.

[0042] A second aspect of the present application provides an electrical device, comprising the secondary battery of the first aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0044] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of the present application is shown;

[0045] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0046] Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0047] Figure 5 yes Figure 4An exploded view of a battery pack according to an embodiment of the present application is shown;

[0048] Figure 6 FIG. 1 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present application as a power source.

[0049] Description of reference numerals:

[0050] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 battery cell assembly; 53 cover plate. DETAILED DESCRIPTION

[0051] Hereinafter, the embodiments of the electrolyte, secondary battery and electrical device of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following 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.

[0052] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0053] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0054] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0055] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0056] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0057] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0058] The viscosity of the electrolyte affects the metal ion transmission rate, thus affecting the battery's charging capacity. Researchers have found that carboxylic acid ester compounds have a lower viscosity, and introducing carboxylic acid ester compounds into the electrolyte can effectively improve the metal ion transmission rate. However, carboxylic acid ester compounds are not resistant to redox and have poor compatibility with the positive / negative electrode sheets, which can easily lead to increased gas production in the battery, causing an increase in the internal pressure of the battery, which is not conducive to the battery's service life.

[0059] [Secondary battery]

[0060] The present application proposes a secondary battery that can take into account both the fast charging performance and the service life of the secondary battery.

[0061] The secondary battery comprises a battery housing having a receiving cavity, a battery cell assembly and an electrolyte in the receiving cavity; the electrolyte comprises a chain carboxylate compound, wherein, based on the total mass of the electrolyte, the mass content W and the residual space R of the chain carboxylate compound satisfy: 0.03≤W / R≤7, Among them, V1 represents the internal volume of the secondary battery housing cavity (ml); V2 represents the volume of the battery cell assembly (ml); V3 represents the volume of the electrolyte (ml); and C represents the discharge capacity of the secondary battery (Ah).

[0062] The housing cavity of a secondary battery generally refers to the internal space of the battery housing. Figure 2 As shown, the shell 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates are combined to form a receiving cavity.

[0063] In this application, the capacity of the secondary battery represented by C is the discharge capacity of the secondary battery. Generally speaking, the capacity of the secondary battery needs to be preset during the preparation process to meet different usage scenarios of the battery. This preset battery capacity is the design capacity. After the secondary battery is prepared, the discharge capacity can be obtained by testing. The design capacity and discharge capacity of the secondary battery, in some cases, such as during the preparation of the battery, the design capacity is used instead of the discharge capacity for material calculation and preparation; in other cases, such as after the battery is freshly prepared, the slight difference between the two is acceptable in the art and the two can be used instead. It is understood that in the preparation process of the battery, the design capacity can be used as the discharge capacity to adjust the residual space in order to obtain the desired secondary battery. For a secondary battery that has been prepared, the discharge capacity is used to calculate and adjust the residual space of the secondary battery. The test method of the discharge capacity of the secondary battery, or the calculation method of the design capacity of the secondary battery, are both public and known to those skilled in the art.

[0064] In some embodiments, the test method of the discharge capacity of a single cell in a secondary battery may include: placing the secondary battery in a 25°C environment and letting it stand until the battery temperature is constant at 25°C; charging with a current of 1 / 3C1 to the charge termination voltage; letting it stand for 10 minutes; charging with a current of 0.05C1 to the charge termination voltage; letting it stand for 10 minutes; discharging with a current of 1 / 3C1 to the discharge termination voltage, and recording the discharge capacity of this step as the battery discharge capacity C at 25°C@0.33C1, where C1 adopts the fixed capacity marked on the cell. The fixed capacity marked on the cell is also called the marked capacity.

[0065] In the present application, the residual space R can be adjusted by adjusting one or more parameters including V1, V2, V3 and C to obtain the expected residual space R value. In some embodiments, the shell of the secondary battery does not change, and the residual space R can be adjusted by adjusting one or more parameters including V2, V3 and C to obtain the expected residual space R value. In some embodiments, the shell of the secondary battery and the capacity of the battery do not change, and the residual space R can be adjusted by adjusting one or more parameters including V2 and V3 to obtain the expected residual space R value. The value of the residual space R can be adjusted in the manner including but not limited to the above. Based on the common technical knowledge in the field mastered by those skilled in the art, the expected residual space R value can be obtained by adjusting one or more parameters including V1, V2, V3 and C.

[0066] In some embodiments, based on the total mass of the electrolyte, the ratio W / R of the mass content W of the chain carboxylate compound and the residual space R can be selected to be 0.03, 0.05, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, or a value in the range consisting of any two of the above points.

[0067] In some embodiments, the mass content W and residual space R of the chain carboxylate compound satisfy: 0.05≤W / R≤7, 0.1≤W / R≤7, 0.3≤W / R≤7, 0.6≤W / R≤7, 0.7≤W / R≤7, 0.2≤W / R≤7, 0.15≤W / R≤6 or 3≤W / R≤7.

[0068] In the secondary battery provided by the present application, the use of a chain carboxylate compound can make the electrolyte have a lower viscosity, increase the transmission rate of metal ions in the active material of the secondary battery, improve the dynamics of the secondary battery, and improve the fast charging performance of the secondary battery; by regulating the mass content of the chain carboxylate compound and the space in the containing cavity not occupied by the battery cell components and the electrolyte, sufficient space can be provided to accommodate the gas generated by the side reactions of the battery cell components, avoid or reduce the deterioration of gas production defects caused by the use of the chain carboxylate compound, reduce the internal pressure of the battery shell or maintain the internal pressure of the battery shell basically stable, extend the service life of the secondary battery, and enable the secondary battery to have both fast charging performance and service life.

[0069] In some embodiments, the linear carboxylate compound comprises a structure shown in Formula I,

[0070]

[0071] Wherein, R1 and R2 each independently include C 1-6 of alkyl.

[0072] In some embodiments, R1 and R2 each independently include C 1-4 In some embodiments, R1 and R2 each independently include C 1-3 In some embodiments, R1 and R2 each independently include C 1-2 An alkyl group such as a methyl group or an ethyl group.

[0073] In some embodiments, the linear carboxylate compound includes one or more of ethyl acetate, methyl acetate, ethyl propionate, propyl acetate, methyl propionate, and methyl butyrate.

[0074] The electrolyte using the above-mentioned chain carboxylate compound as a solvent has a lower viscosity, which is beneficial to improving the transmission rate of metal ions and improving the dynamics of the secondary battery, thereby improving the fast charging performance of the secondary battery.

[0075] In some embodiments, based on the total mass of the electrolyte, the mass content W of the chain carboxylate compound is 5% to 70%, optionally 10%-60%, 10%-70%, 5%-60%, 30%-70%.

[0076] In some embodiments, based on the total mass of the electrolyte, the mass content W of the chain carboxylate compound can be selected to be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or a value in the range consisting of any two of the above points.

[0077] Controlling the mass content of the chain carboxylate compound within an appropriate range can not only effectively reduce the viscosity of the electrolyte, increase the transmission rate of metal ions, improve the dynamics of the secondary battery, and enhance the fast charging performance of the secondary battery; it can also reduce or minimize the impact of the gas production performance defects of the chain carboxylate compound on the service life of the secondary battery, and can take into account both the fast charging performance and the service life of the secondary battery.

[0078] In some embodiments, R is 0.05 mL / Ah to 2 mL / Ah, optionally 0.1 mL / Ah to 1.5 mL / Ah or 0.1 mL / Ah to 2 mL / Ah.

[0079] In some embodiments, R may be selected as 0.05 mL / Ah, 0.1 mL / Ah, 0.2 mL / Ah, 0.4 mL / Ah, 0.5 mL / Ah, 0.6 mL / Ah, 0.8 mL / Ah, 1 mL / Ah, 1.2 mL / Ah, 1.4 mL / Ah, 1.5 mL / Ah, 1.6 mL / Ah, 1.8 mL / Ah, 2 mL / Ah, or a value in the range consisting of any two of the above points.

[0080] By controlling R within a suitable range, sufficient space can be provided to accommodate the gas generated by the side reactions of the battery cell components, thereby reducing the internal pressure of the battery casing or maintaining the internal pressure of the battery casing basically stable, thereby extending the service life of the secondary battery. The volume of the accommodating cavity can also be controlled within a suitable range to avoid or reduce the increase in production costs caused by an excessively large battery casing, thereby taking into account both the service life and production cost of the secondary battery.

[0081] In some embodiments, the electrolyte further includes a film-forming additive, and the film-forming additive includes one or more of a sulfate compound and a fluorocarbonate compound.

[0082] In some embodiments, the electrolyte includes a sulfate compound. In some embodiments, the electrolyte includes a fluorinated carbonate compound. In some embodiments, the electrolyte includes a sulfate compound and a fluorinated carbonate compound.

[0083] The film-forming additive can form a film on the positive electrode side to inhibit the reaction of the chain carboxylic acid ester on the positive electrode side. At the same time, the film-forming additive can also form a uniform and dense SEI film on the negative electrode side, which can further inhibit the side reaction of the electrolyte on the negative electrode side, improve the gas production performance of the electrolyte, and increase the service life of the secondary battery.

[0084] In some embodiments, the sulfate ester compound includes one or more of 4,4'-vinyl sulfate, vinyl sulfate, diethyl sulfate, dimethyl sulfate and 4,4-bis(1,3,2-dioxathiacyclopentane)-2,2,2,2-tetraoxide, and optionally includes one or more of 4,4'-vinyl sulfate and vinyl sulfate.

[0085] The above-mentioned sulfate ester compounds can generate a Li2SO4-rich SEI film on the negative electrode side. The SEI film can inhibit the side reaction of the electrolyte on the negative electrode side, improve the gas production performance of the electrolyte, and increase the service life of the secondary battery.

[0086] In some embodiments, the fluorinated carbonate compound includes one or more of fluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate or trifluoromethylethylene carbonate, and optionally includes fluoroethylene carbonate.

[0087] The above-mentioned fluorinated carbonate compounds can generate a LiF-rich SEI film on the negative electrode side, and the SEI film can inhibit the side reaction of the electrolyte on the negative electrode side, improve the gas production performance of the electrolyte, and increase the service life of the secondary battery.

[0088] In some embodiments, based on the total mass of the electrolyte, the mass content A of the sulfate compound and the mass content B of the fluorocarbonate compound satisfy the following relationship: 0.03≤A / B≤20, optionally 0.05≤A / B≤10, 0.1≤A / B≤10, 0.2≤A / B≤10, 0.3≤A / B≤10, 0.4≤A / B≤10, 0.5≤A / B≤10, 0.7≤A / B≤10 or 1≤A / B≤10.

[0089] In some embodiments, based on the total mass of the electrolyte, the mass content A of the sulfate compound and the mass content B of the fluorocarbonate compound satisfy A / B, which can be selected as 0.02, 0.05, 0.1, 0.5, 1, 2, 4, 5, 6, 8, 10, 12, 14, 15, 16, 18, 20, or a value in the range consisting of any two of the above points.

[0090] The combined use of sulfate compounds and fluorocarbonate compounds is beneficial to further inhibit the side reactions of the electrolyte. At the same time, the mass ratio between the sulfate compounds and the fluorocarbonate compounds is controlled within an appropriate range so that the secondary battery has excellent fast charging performance and service life.

[0091] In some embodiments, based on the total mass of the electrolyte, the mass content A of the sulfuric acid compound is 0.1% to 2%, optionally 0.1%-1.5%, 0.5%-2% or 0.5%-1.5%.

[0092] In some embodiments, based on the total mass of the electrolyte, the mass content A of the sulfuric acid compound can be selected to be 0.1%, 0.2%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, 2%, or a value in the range formed by any two of the above points.

[0093] In some embodiments, based on the total mass of the electrolyte, the mass content B of the fluorocarbonate compound is 0.1% to 5%, optionally 0.1% to 4%, 1% to 5% or 1% to 4%.

[0094] In some embodiments, based on the total mass of the electrolyte, the mass content B of the fluorinated carbonate compound is 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a value in the range consisting of any two of the above points.

[0095] By controlling the mass content of sulfate compounds and fluorocarbonate compounds within appropriate ranges, the film-forming additives in the secondary battery can be within appropriate ranges, and the interface side reactions of the positive and / or negative electrodes can be inhibited, thereby improving the power performance and service life of the secondary battery.

[0096] In some embodiments, based on the total mass of the electrolyte, the mass content W of the chain carboxylate compound, the mass content A of the sulfate compound and the mass content B of the fluorocarbonate compound satisfy the following relationship: 0.7≤W / (A+B)≤30, optionally 1≤W / (A+B)≤27.3, 1≤W / (A+B)≤20, 1≤W / (A+B)≤18, 1≤W / (A+B)≤15, or 1≤W / (A+B)≤10.

[0097] In some embodiments, based on the total mass of the electrolyte, the mass content W of the chain carboxylate compound, the mass content A of the sulfate compound and the mass content B of the fluorocarbonate compound satisfy W / (A+B) and can be 0.7, 1, 2, 5, 6, 10, 14, 15, 18, 20, 22, 25, 26, 30, or a value in the range consisting of any two of the above points.

[0098] The mass content W of the chain carboxylate compound, the mass content A of the sulfate compound and the mass content B of the fluorocarbonate compound are controlled to satisfy the relationship of 0.7≤W / (A+B)≤30, so as to achieve the synergistic effect between the chain carboxylate compound and the film-forming additive, and improve the fast charging performance and service life of the secondary battery. Further controlling the relationship between W, A and B to satisfy 1≤W / (A+B)≤27.3 is conducive to further improving the fast charging performance and service life of the secondary battery.

[0099] In some embodiments, the electrolyte further includes one or more of a cyclic ester solvent and a linear ester solvent.

[0100] In some embodiments, the cyclic ester solvent includes one or more of ethylene carbonate and propylene carbonate; the linear ester solvent includes one or more of dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl methyl carbonate, methyl formate, butyl acetate, methyl propionate, ethyl butyrate, propyl butyrate, butyl butyrate, isopropyl acetate, and isoamyl acetate.

[0101] In some embodiments, the electrolyte further includes a lithium salt, and the lithium salt includes one or more of LiFSI and LiPF6.

[0102] In some embodiments, the electrolyte further includes a sodium salt, and the sodium salt includes one or more of NaFSI and NaPF6.

[0103] In some embodiments, based on the total mass of the electrolyte, the mass content of the lithium salt is 8% to 20%, and optionally 10% to 15%.

[0104] In some embodiments, based on the total mass of the electrolyte, the mass content of the lithium salt may be 8%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, or a value in the range formed by any two of the above points.

[0105] In some embodiments, based on the total mass of the electrolyte, the mass content of the sodium salt is 9% to 21%, and optionally 11% to 16%.

[0106] In some embodiments, based on the total mass of the electrolyte, the mass content of the sodium salt is 9%, 10%, 11%, 12%, 14%, 15%, 16%, 18%, 21%, or a value in the range formed by any two of the above points.

[0107] In some embodiments, the electrolyte of the secondary battery uses a complex solvent containing a chain carboxylate compound, for example, the electrolyte contains different types of chain carboxylate compounds. In some embodiments, the electrolyte further contains a cyclic ester solvent.

[0108] In some embodiments, the solvent used in the electrolyte includes ethyl acetate, ethylene carbonate and dimethyl carbonate.

[0109] Controlling the lithium salt or sodium salt within a suitable range is beneficial to improving the concentration polarization inside the battery cell assembly, thereby improving the service life of the secondary battery.

[0110] In some embodiments, the lithium salt includes LiFSI and LiPF6. In some embodiments, based on the total mass of the electrolyte, the mass ratio of LiFSI to LiPF6 is not less than 0.4 and not more than 7, and optionally, the mass ratio of LiFSI to LiPF6 is not less than 0.5 and not more than 6. In some embodiments, the mass ratio of LiFSI to LiPF6 is not less than 0.5 and not more than 2.

[0111] In some embodiments, based on the total mass of the electrolyte, the mass ratio of LiFSI and LiPF6 can be selected as 0.4, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, or a value in a range consisting of any two of the above points.

[0112] For lithium secondary batteries, the combination of LiFSI and LiPF6 can make the electrolyte have excellent lithium ion migration number and thermal stability. Controlling the mass content ratio of LiFSI and LiPF6 within an appropriate range is beneficial to improving the fast charging performance and service life of the secondary battery.

[0113] In some embodiments, the sodium salt includes NaFSI and NaPF6. In some embodiments, based on the total mass of the electrolyte, the mass ratio of NaFSI to NaPF6 is not less than 0.4 and not more than 7, optionally, the mass ratio of NaFSI to NaPF6 is not less than 0.5 and not more than 6. In some embodiments, the mass ratio of NaFSI to NaPF6 is not less than 0.5 and not more than 2.

[0114] In some embodiments, based on the total mass of the electrolyte, the mass content M of NaFSI and the mass content N of NaPF6 satisfy M / N, which can be selected as 0.4, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, or a value in the range consisting of any two of the above points.

[0115] For nano-secondary batteries, the combination of NaFSI and NaPF6 can make the electrolyte have excellent nano-ion migration number and thermal stability. Controlling the mass content ratio of NaFSI and NaPF6 within an appropriate range is beneficial to improving the fast charging performance and service life of secondary batteries.

[0116] In some embodiments, the viscosity of the electrolyte is 2 mPa.s to 5 mPa.s, and can be optionally 3 mPa.s to 4.6 mPa.s.

[0117] In some embodiments, the viscosity of the electrolyte may be selected to be 2 mPa.s, 2.5 mPa.s, 3 mPa.s, 3.5 mPa.s, 4 mPa.s, 4.5 mPa.s, 5 mPa.s, or a value in a range consisting of any two of the above points.

[0118] The viscosity of the electrolyte can be measured using any method known to those skilled in the art. In some embodiments, the viscosity can be measured according to the method in the "viscosity test" in the examples of this application.

[0119] The viscosity of the electrolyte is within an appropriate range, which is beneficial to increasing the transmission rate of metal ions, improving the dynamics of the secondary battery, and enhancing the fast charging performance of the secondary battery.

[0120] [Positive electrode]

[0121] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0122] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0123] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0124] In some embodiments, the positive electrode active material of the lithium secondary battery may adopt the positive electrode active material for the battery known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates containing olivine structure, lithium transition metal oxides 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 can also be used. These positive electrode active materials can 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, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05O2) and its modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0125] In some embodiments, the positive electrode active material of the sodium secondary battery includes at least one of a transition metal layered oxide, a polyanion compound, and a Prussian blue compound, including NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2、Na(Cu 1 / 9 Ni 2 / 9 Fe 1 / 3Mn 1 / 3 )O2、Na 2 / 3 Ni 1 / 6 Mn 2 / 3 Cu 1 / 9 Mg 1 / 18 O2, Na4Fe3(PO4)2P2O7, NaFePO4, Na3V2(PO4)3, Na 1.9 In some embodiments, the transition metal in the transition metal layered oxide may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Optionally, the layered transition metal oxide is, for example, Na x MO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0<x≤1. In some embodiments, the polyanionic compound may be a compound having metal ions, transition metal ions and tetrahedral (YO4) n- A class of compounds with anionic units. The metal ion can be selected from sodium ion, lithium ion, potassium ion, zinc ion; the transition metal can be selected from at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y can be selected from at least one of P, S and Si; n represents (YO4) n- In some embodiments, the Prussian blue compound may be a compound having sodium ions, transition metal ions and cyanide ions (CN-). The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. The Prussian blue compound may be, for example, Na a Me b Me' c(CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0<a≤2, 0<b<1, 0<c<1.

[0126] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0127] In some embodiments, the positive electrode film layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0128] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0129] [Negative electrode]

[0130] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector.

[0131] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0132] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0133] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0134] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0135] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0136] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0137] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0138] [Isolation film]

[0139] In some embodiments, the secondary battery further includes a separator, which can be any known porous separator with good chemical stability and mechanical stability.

[0140] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different.

[0141] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into a battery cell assembly by a winding process or a lamination process.

[0142] In some embodiments, a secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte in some embodiments.

[0143] In some embodiments, the CB value of the secondary battery is 1.05 to 1.5, and can be optionally 1.05 to 1.3. The CB value is the ratio of the capacity of the negative electrode of the battery cell that can be embedded with lithium (or sodium) to the capacity of the positive electrode that can be removed with lithium (or sodium). The type of active material, the coating thickness and compaction density of the pole piece can affect the CB value of the secondary battery. In some embodiments, the CB value of the secondary battery is adjusted by adjusting the coating thickness and compaction density of the pole piece.

[0144] Controlling the CB value of the secondary battery within an appropriate range is beneficial for the negative electrode to provide sufficient active sites for receiving metal ions, improve the active lithium or active sodium precipitated at the interface of the negative electrode, and enhance the fast charging performance of the secondary battery.

[0145] In some embodiments, the secondary battery includes one or more of a lithium battery, a sodium battery, and a potassium battery.

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

[0147] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

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

[0149] In some embodiments, reference Figure 2 , the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation film can form a battery cell assembly 52 through a winding process or a lamination process. The battery cell assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the battery cell assembly 52. ​​The number of battery cell assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0150] In some embodiments, secondary batteries may be assembled into a battery module. The number of secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

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

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

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

[0154] Figure 4 and Figure 5 1 is a battery pack 1 as an example. Figure 4 and Figure 5 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0155] In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

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

[0157] Figure 6The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for the secondary battery, a battery pack or a battery module can be used.

[0158] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0159] Example

[0160] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0161] 1. Preparation method

[0162] Example 1

[0163] 1) Electrolyte

[0164] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), ethyl acetate (30% of the total mass of the electrolyte), ethylene carbonate and dimethyl carbonate were mixed evenly, and lithium salt LiFSI accounting for 15% of the total mass of the electrolyte was added, and the electrolyte was prepared after stirring evenly. Among them, based on the total mass of the electrolyte, the mass ratio of ethylene carbonate and dimethyl carbonate in the electrolyte is 2:3, and the sum of the mass contents is 55% (100% - the mass content of ethyl acetate in the electrolyte - the mass content of lithium salt in the electrolyte - the mass content of film-forming additives in the electrolyte).

[0165] 2) Preparation of positive electrode

[0166] 1 wt% polyvinylidene fluoride binder was fully dissolved in N-methylpyrrolidone, and then 1 wt% carbon black conductive agent and 98 wt% ternary positive electrode active material Li[Ni 0.5 Co 0.2 Mn 0.3 ]O2 was stirred and mixed evenly to obtain a positive electrode slurry. The slurry was evenly coated on the surface of the current collector aluminum foil to prepare a positive electrode film layer with a coating thickness of 15 mg / cm 2 Then transfer to a vacuum drying oven for complete drying. The dried electrode is rolled and punched, and the compacted density is 3.4g / cm 3 , and obtain the positive electrode.

[0167] 3) Preparation of negative electrode sheet

[0168] The negative electrode active material artificial graphite, conductive agent carbon black, thickener carboxymethyl cellulose (CMC), and adhesive styrene butadiene rubber (SBR) were mixed in a weight ratio of 96:2:1:1 and dissolved in deionized water to prepare a negative electrode slurry. The negative electrode slurry was obtained under the action of a vacuum mixer, and then the slurry was coated on the surface of the copper foil with a coating thickness of 8.4 mg / cm 2 Finally, it was transferred to a vacuum drying oven for complete drying, followed by slitting and die-cutting. The compacted density was 3.4g / cm 3 , prepare the negative electrode sheet.

[0169] 4) Isolation film

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

[0171] 5) Preparation of batteries

[0172] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, and the separator is placed between the positive and negative electrode sheets to play an isolating role. The bare cell is welded with the pole ear, and the bare cell is placed in an aluminum shell, and baked at 80°C to remove water, and then the above electrolyte is injected and sealed to obtain an uncharged battery. The uncharged battery then undergoes the processes of static, hot and cold pressing, formation, shaping, and capacity testing in sequence. Among them, the internal volume of the secondary battery housing cavity is 1011.3ml, the volume of the battery cell assembly is 665ml, the volume of the electrolyte is 225ml, and the capacity of the secondary battery is 121.4Ah, and a lithium secondary battery product with a residual space of 1mL / Ah is obtained.

[0173] Example 2

[0174] The battery preparation method in Example 2 is basically similar to that in Example 1, but a film-forming additive is introduced into the electrolyte. The preparation method of the electrolyte is specifically as follows:

[0175] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), ethyl acetate (30% of the total mass of the electrolyte), ethylene carbonate and dimethyl carbonate were mixed evenly, and 15% of the total mass of the electrolyte was added with lithium salt LiFSI, stirred evenly, and then 1% of the total mass of the electrolyte was added with 4,4'-disulfate, mixed evenly, and the electrolyte was prepared. Among them, based on the total mass of the electrolyte, the mass ratio of ethylene carbonate to dimethyl carbonate in the electrolyte is 2:3, and the sum of the mass content is 54%.

[0176] Example 3

[0177] The battery preparation method in Example 3 is basically similar to that in Example 1, but a film-forming additive is introduced into the electrolyte. The preparation method of the electrolyte is specifically as follows:

[0178] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), ethyl acetate (30% of the total mass of the electrolyte), ethylene carbonate and dimethyl carbonate were mixed evenly, 15% of lithium salt LiFSI was added, stirred evenly, and then 3% of the total mass of the electrolyte was added with fluoroethylene carbonate, mixed evenly, and an electrolyte was prepared. Among them, based on the total mass of the electrolyte, the mass ratio of ethylene carbonate to dimethyl carbonate in the electrolyte was 2:3, and the sum of the mass contents was 52%.

[0179] Example 4

[0180] The battery preparation method in Example 4 is basically similar to that in Example 1, but a film-forming additive is introduced into the electrolyte. The preparation method of the electrolyte is specifically as follows:

[0181] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), methyl acetate (30% of the total mass of the electrolyte), ethylene carbonate and dimethyl carbonate were mixed evenly, 15% of lithium salt LiFSI was added and stirred evenly, and then 1% of the total mass of the electrolyte 4,4'-ethylene sulfate and 3% of the total mass of the electrolyte were added and mixed to prepare an electrolyte. Among them, based on the total mass of the electrolyte, the mass ratio of ethylene carbonate to dimethyl carbonate in the electrolyte is 2:3, and the sum of the mass content is 51%.

[0182] The battery preparation methods in Examples 5 to 11, Examples 18 to 29 and Examples 33 to 35 are basically similar to that in Example 4, but the electrolyte preparation parameters are adjusted. The specific parameters are shown in Table 1.

[0183] The preparation method of the batteries in Examples 12 to 17 is similar to that in Example 4, keeping the internal volume of the secondary battery containing cavity and the volume of the injected electrolyte the same, adjusting the volume of the battery cell assembly to 613 ml, the capacity of the secondary battery to 108.2 Ah, and obtaining a secondary battery with a residual space of 1.6 mL / Ah; adjusting the volume of the battery cell assembly to 772 ml, the capacity of the secondary battery to 140.2 Ah, and obtaining a secondary battery with a residual space of 0.1 mL / Ah; adjusting the volume of the battery cell assembly to 779.2 ml, the capacity of the secondary battery to 141.1 Ah, and obtaining a secondary battery with a residual space of 0.05 mL / Ah; adjusting the volume of the battery cell assembly to 620 ml, the capacity of the secondary battery to 110.2 Ah, and obtaining a secondary battery with a residual space of 1.5 mL / Ah; adjusting the volume of the battery cell assembly to 586 ml, the capacity of the secondary battery to 99.9 Ah, and obtaining a secondary battery with a residual space of 2 mL / Ah.

[0184] The preparation methods of the batteries in Examples 30 to 32 are similar to those in Example 4, but the coating thickness of the negative electrode sheet is adjusted to 8.1 mg / cm 2、10mg / cm 2 、11.6mg / cm 2 , so that the CB values ​​are 1.05, 1.3, and 1.5 respectively. The specific parameters are shown in Table 1.

[0185] Embodiment 36

[0186] 1) Electrolyte

[0187] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), ethyl acetate (30% of the total mass of the electrolyte), ethylene carbonate and dimethyl carbonate were mixed evenly, and sodium hexafluorophosphate, which was 15% of the total mass of the electrolyte, was added and stirred evenly, and then 1% of 4,4'-ethylene disulfate and 3% of fluoroethylene carbonate were added and mixed to prepare an electrolyte. Among them, based on the total mass of the electrolyte, the mass ratio of ethylene carbonate to dimethyl carbonate in the electrolyte was 2:3, and the sum of the mass contents was 51%.

[0188] 2) Preparation of positive electrode

[0189] 1 wt% polyvinylidene fluoride binder was fully dissolved in N-methylpyrrolidone, and then 1 wt% carbon black conductive agent and 98 wt% Prussian white were added and stirred to obtain positive electrode slurry. The slurry was evenly coated on the surface of the current collector aluminum foil to prepare the positive electrode film layer, and the coating thickness was 15 mg / cm 2 Then transfer to a vacuum drying oven for complete drying. The dried electrode is rolled and punched, and the compacted density is 3.4g / cm 3 , and obtain the positive electrode.

[0190] 3) Preparation of negative electrode sheet

[0191] The negative electrode active material hard carbon, conductive agent carbon black, thickener carboxymethyl cellulose (CMC), and adhesive styrene butadiene rubber (SBR) were mixed in a weight ratio of 96:2:1:1 and dissolved in deionized water to prepare a negative electrode slurry. The negative electrode slurry was obtained under the action of a vacuum mixer, and then the slurry was coated on the surface of the copper foil with a coating thickness of 8.4 mg / cm 2 Finally, it was transferred to a vacuum drying oven for complete drying, followed by slitting and die-cutting. The compacted density was 3.4g / cm 3 , prepare a negative electrode sheet without a negative electrode structure.

[0192] 4) Isolation film

[0193] Polypropylene film is used as the isolation film.

[0194] 5) Preparation of batteries

[0195] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, the separator is placed between the positive and negative electrode sheets to play an isolating role, the bare cell is welded with the pole ear, and the bare cell is placed in an aluminum shell, and baked at 80°C to remove water, and then the above-mentioned electrolyte is injected and sealed to obtain an uncharged battery. The uncharged battery is then subjected to the processes of static, hot and cold pressing, formation, shaping, and capacity testing in sequence to obtain the sodium secondary battery product of Example 33.

[0196] The battery preparation methods in Examples 37 to 38 are basically similar to those in Example 36, but the electrolyte preparation parameters are adjusted. The specific parameters are shown in Table 1.

[0197] The battery preparation method in Comparative Example 1 is basically similar to that in Example 1, wherein the volume of the battery cell assembly is adjusted to 783.4 ml, the capacity of the secondary battery is 142.3 Ah, and a secondary battery with a residual space of 0.02 mL / Ah and a W / R value of 15 is obtained; the specific parameters are shown in Table 1.

[0198] The battery preparation method in Comparative Example 2 is basically similar to that in Comparative Example 1, but the W / R value is adjusted to 0.02. The specific parameters are shown in Table 1.

[0199] The battery preparation method in Comparative Example 3 is basically similar to that in Comparative Example 1, but there is no film-forming additive in the electrolyte. The specific parameters are shown in Table 1.

[0200] The battery preparation method in Comparative Example 4 is basically similar to that in Comparative Example 2, but there is no film-forming additive in the electrolyte. The specific parameters are shown in Table 1.

[0201] The battery preparation method in Comparative Example 5 is basically similar to that in Example 1, but there is no chain carboxylate compound and film-forming additive in the electrolyte. The specific parameters are shown in Table 1.

[0202] The battery preparation method in Comparative Example 6 is basically similar to that in Comparative Example 1, but the electrolyte salt is adjusted to sodium salt. The specific parameters are shown in Table 1.

[0203] 2. Performance Test

[0204] 1. Electrolyte testing

[0205] 1) Viscosity test.

[0206] At a specific temperature, the shear force on the rotor as it rotates continuously at a constant speed in the sample causes the spring to produce a torque that is proportional to the viscosity, thus giving the viscosity value.

[0207] Specifically, the viscosity of the electrolyte is measured using a rotational viscometer, and the testing instrument is a Brookfield (DV-2TLV). At an ambient temperature of 25°C and an ambient humidity of less than 80%, 30 mL of the electrolyte is placed in a beaker, which is placed in a water bath at 25°C for at least 30 minutes, the rotor is placed in a sample cup, the electrolyte sample is added to about 0.3 cm from the cup mouth, the viscometer connected to the rotor is started, a speed of 70 rpm is selected for testing, 10 data points are collected, and the average value is the viscosity.

[0208] 2. Battery performance test

[0209] 1) DC resistance (DCR) test

[0210] At -25℃, adjust the single battery state of charge to 50% SOC, let it stand for 30 minutes, record the battery voltage at this time as U1 (V), use 0.36C discharge for 10 seconds, record the battery voltage at this time as U2 (V), and the corresponding battery discharge current I (mA) is 0.36 × battery design capacity (mAh). DC resistance DCR (mΩ) = (U1-U2) / I.

[0211] 2) Fast charging capability test

[0212] The batteries of the above embodiments and comparative examples were charged and discharged for the first time at a current of 1C (i.e., the current value at which the theoretical capacity is completely discharged within 1 hour), specifically comprising: at 35°C, the battery was charged at a constant current rate of 1C to a voltage of 4.25V, then charged at a constant voltage to a current ≤0.05C, left to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to a voltage of 2.8V, and its actual capacity was recorded as C0. Then the battery is charged with constant current of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0, 3.5C0, 4C0, 4.5C0, 5C0 in sequence to the full battery charge cut-off voltage of 4.25V or 0V negative electrode cut-off potential (whichever is reached first). After each charge is completed, it is necessary to discharge with 1C0 to the full battery discharge cut-off voltage of 2.8V. Record the SOC (State of Charge) at different charge rates to 10%, 20%, 30%, ..., 80% Charge, state of charge, when "SOC = 0" means the battery is fully discharged, when "SOC = 100%" means the battery is fully charged) the corresponding negative electrode potential, draw the charging rate-negative electrode potential curve under different SOC states, and obtain the charging rate corresponding to the negative electrode potential of 0V under different SOC states after linear fitting. The charging rate is the charging window under the SOC state, which is recorded as C10% SOC, C20% SOC, C30% SOC, C40% SOC, C50% SOC, C60% SOC, C70% SOC, C80% SOC, according to the formula (60 / C20% SOC+60 / C30% SOC+60 / C40% SOC+60 / C50% SOC+60 / C60% SOC+60 / C70% SOC+60 / C80% SOC)×10%, the charging time T of the battery from 10% SOC to 80% SOC is calculated in min. The shorter the time, the better the fast charging performance of the battery.

[0213] 3) High temperature gas production test

[0214] The high-temperature gas production test process is as follows: the prepared battery is charged to 100% SOC at a rate of 0.1C, stored at 60°C, and the internal pressure of the battery is monitored online using a barometer. When the cut-off pressure is 0.35MPa, the number of days stored at 60°C is recorded.

[0215] 4) Cycle performance test

[0216] The cycle performance test process is as follows: at 45°C, charge the prepared battery to 4.25V at a constant current of 1C, then charge at a constant voltage of 4.25V until the current drops to 0.05C, let it stand for 5 minutes, and then discharge it to 2.5V at a constant current of 1C. This is the first charge / discharge cycle of the battery, and the discharge capacity at this time is recorded as the discharge capacity of the first cycle of the battery (C1); repeat the above steps for the same battery, and the process capacity of the battery after the nth cycle (Cn), the capacity retention rate after n cycles = Cn / C1×100%. Record the number of cycles at which the cycle capacity retention rate is 80%. The test process of the comparative example and other embodiments is the same as above.

[0217] 5) Secondary battery CB value test

[0218] 1. The positive electrode de-lithium (or sodium) capacity test method is as follows:

[0219] Take the positive electrode after cold pressing or disassemble the battery in the PRS340 / 11-119-11 Braun glove box to take the positive plate electrode, and assemble it into a CR2430 model semi-button battery with a positive lithium (or sodium) plate. The area of ​​the positive electrode plate is a mm 2 , using 1M LIPF6, the mass ratio of ethylene carbonate: ethyl methyl carbonate: diethyl carbonate is 3:5:2 to prepare the electrolyte. The assembled half button cell was left to stand for 3h and tested at 25℃. 0.1C was charged and de-lithium (or sodium) in the voltage range of 2.5V-eV, where e is the upper limit voltage of the battery design, and 0.05C was discharged to 2.5V, and the cycle was repeated twice. The charge and de-ion capacity of the second cycle was recorded as Y mAh. The actual battery design has a positive electrode membrane length of b mm and a width of c mm. The number of faces of the positive active material coated on the positive current collector is d, and the positive electrode de-lithium (or sodium) capacity is X=Y / a×b×c×d.

[0220] 2. The negative electrode lithium (or sodium) capacity test method is:

[0221] Take the fresh cold-pressed negative electrode sheet or disassemble the battery in the PRS340 / 11-119-11 Bujuen glove box to take the negative electrode sheet and assemble it into a CR2430 model semi-button battery. The negative electrode sheet area is f mm 2 , using 1M LIPF6, ethylene carbonate: ethyl methyl carbonate: diethyl carbonate mass ratio of 3:5:2 to prepare the electrolyte. The assembled half button cell was left to stand for 3 hours, and the test was carried out at 25°C. The discharge was carried out at a voltage range of 2V-0V with 0.1C to insert lithium (or sodium), and then charged at 0.05C to remove lithium (or sodium) to 2V, and the cycle was repeated twice. The discharge button capacity of the second cycle was recorded as Z mAh. The actual battery design negative electrode membrane length is h mm and width is j mm. The number of negative electrode active materials coated on the negative electrode current collector is d, and the negative electrode lithium removal capacity is W = Z / f×h×i×d.

[0222] III. Analysis of test results of various embodiments and comparative examples

[0223] The batteries of the embodiments and comparative examples were prepared according to the above method, and various performance parameters were measured. The results are shown in Tables 1 and 2 below.

[0224] Table 1

[0225]

[0226]

[0227] Table 2

[0228]

[0229] According to the above results, the secondary batteries in Examples 1 to 38 all include a battery case having a receiving cavity, a battery cell assembly located in the receiving cavity, and an electrolyte; the electrolyte includes a chain carboxylate compound. Compared with Comparative Examples 3 and 4, based on the total mass of the electrolyte, the ratio of the mass content W of the chain carboxylate compound to the residual space R is not less than 0.03 and not more than 7, and the secondary batteries prepared have both good fast charging performance and service life.

[0230] In Example 2 and Example 3, film-forming additives 4,4'-ethylene disulfate and fluoroethylene carbonate were added respectively, which helped to inhibit the side reaction of the electrode, improve the gas production performance of the electrolyte, and increase the service life of the secondary battery.

[0231] Examples 4 to 6 adjusted the specific type of the linear carboxylate solvent, and the results showed that using methyl acetate, ethyl propionate or methyl propionate as the solvent was helpful in obtaining a secondary battery with both good fast charging performance and service life.

[0232] In Examples 7 to 11, the amount of ethyl acetate is adjusted, and compared with Comparative Example 2, within the range of 5% to 70% of the total mass of the electrolyte, it helps to improve the storage performance and cycle performance of the secondary battery, and at the same time, it also has suitable fast charging performance.

[0233] In Examples 7 to 13, when the ratio of the mass content W of the chain carboxylate compound to the residual space R varies in the range of 0.03 to 7, the secondary battery has good fast charging performance. When the ratio of the mass content W of the chain carboxylate compound to the residual space R is 0.3 to 0.7, the secondary battery has excellent fast charging performance, cycle performance and life cycle.

[0234] In Examples 12 to 17, the value of the residual space R was adjusted. Compared with Comparative Example 1, when R was in the range of 0.05 mL / Ah to 2 mL / Ah, the prepared secondary batteries had good cycle performance and service life; when R was in the range of 1.5 mL / Ah to 2 mL / Ah, the prepared secondary batteries had excellent fast charging performance, cycle performance and life cycle.

[0235] Examples 18 to 21 adjusted the amount of 4,4'-vinyl sulfate, Examples 22 to 25 adjusted the amount of fluoroethylene carbonate, and Example 26 adjusted the amounts of 4,4'-vinyl sulfate and fluoroethylene carbonate. The usage ratio of 4,4'-vinyl sulfate to fluoroethylene carbonate in the range of 0.03 to 10 helps to increase the high-temperature storage days and cycle number of the secondary battery, that is, to improve the life cycle and cycle performance of the secondary battery.

[0236] In Examples 27 to 29, the amount of lithium salt is adjusted to 8% to 20% of the total mass of the electrolyte. When it is within the above range, it helps to improve the cycle performance of the secondary battery.

[0237] Examples 33 to 35 adjust the type of lithium salt, and Examples 36 to 38 adjust the type of sodium salt. By using film-forming additives in conjunction with the solvent, secondary batteries prepared with different lithium salts or lithium salt combinations, sodium salts or sodium salt combinations can all have improved DC impedance.

[0238] Embodiments 30 to 32 adjust the CB value within the range of 1.05 to 3, which helps to improve the fast charging performance of the secondary battery.

[0239] Comparison of Comparative Example 4 with Comparative Example 5 shows that ethyl acetate helps to reduce DC impedance and improve fast charging performance.

[0240] Comparative Example 6 adjusts the size of the residual space R. Compared with Example 37, a suitable residual space value helps to improve the cycle performance of the secondary battery.

[0241] 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 secondary battery, characterized in that: It comprises a battery casing having a receiving cavity, a battery core assembly and an electrolyte located in the receiving cavity; The electrolyte includes a chain carboxylate compound, wherein the mass content W of the chain carboxylate compound satisfies, based on the total mass of the electrolyte: 0.03≤W / R≤7, R is the residual space, and Among them, V1 represents the internal volume of the secondary battery housing cavity; V2 represents the volume of the battery cell assembly; V3 represents the volume of the electrolyte; and C represents the discharge capacity of the secondary battery.

2. The secondary battery according to claim 1, characterized in that: The chain carboxylate compound includes a structure shown in Formula I, Wherein, R1 and R2 each independently include C 1-6 of alkyl.

3. The secondary battery according to claim 1 or 2, characterized in that: The chain carboxylate compound includes one or more of ethyl acetate, methyl acetate, ethyl propionate, propyl acetate, methyl propionate, and methyl butyrate.

4. The secondary battery according to any one of claims 1 to 3, characterized in that: Based on the total mass of the electrolyte, the mass content W of the chain carboxylate compound is 5% to 70%, and can be optionally 10% to 60%.

5. The secondary battery according to any one of claims 1 to 4, characterized in that: R is 0.05mL / Ah to 2mL / Ah, and can be optionally 0.1mL / Ah to 2mL / Ah.

6. The secondary battery according to any one of claims 1 to 5, characterized in that: The mass content W and the residual space R of the chain carboxylic acid ester compound satisfy: 0.05≤W / R≤7, 0.1≤W / R≤7, 0.15≤W / R≤6 or 3≤W / R≤7.

7. The secondary battery according to any one of claims 1 to 6, characterized in that: The electrolyte further includes a film-forming additive, and the film-forming additive includes one or more of a sulfate compound and a fluorocarbonate compound.

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

9. The secondary battery according to any one of claims 7 to 8, characterized in that: Based on the total mass of the electrolyte, the mass content A of the sulfate compound and the mass content B of the fluorocarbonate compound satisfy: 0.03≤A / B≤20, and can be 0.05≤A / B≤10.

10. The secondary battery according to any one of claims 7 to 9, characterized in that: Based on the total mass of the electrolyte, the mass content A of the sulfuric acid compound is 0.1% to 2%, and can be optionally 0.5% to 2%; The mass content B of the fluorocarbonate compound is 0.1% to 5%, and can be optionally 0.1% to 4%.

11. The secondary battery according to any one of claims 7 to 10, characterized in that: Based on the total mass of the electrolyte, the mass content W of the chain carboxylate compound, the mass content A of the sulfate compound and the mass content B of the fluorocarbonate compound satisfy: 0.7≤W / (A+B)≤30, which can be 1≤W / (A+B)≤27.

3.

12. The secondary battery according to any one of claims 1 to 11, characterized in that: The electrolyte further includes a lithium salt, and the lithium salt includes one or more of LiFSI and LiPF6; or, The electrolyte also includes a sodium salt, and the sodium salt includes one or more of NaFSI and NaPF6.

13. The secondary battery according to claim 12, characterized in that: Based on the total mass of the electrolyte, the mass content of the lithium salt is 8% to 20%, and can be optionally 10% to 15%; or Based on the total mass of the electrolyte, the mass content of the sodium salt is 9% to 21%, and can be optionally 11% to 16%.

14. The secondary battery according to claim 12 or 13, characterized in that: The lithium salt includes LiFSI and LiPF6; Based on the total mass of the electrolyte, the mass ratio of LiFSI to LiPF6 is not less than 0.4 and not more than 7. Optionally, the mass ratio of LiFSI to LiPF6 is not less than 0.5 and not more than 2.

15. The secondary battery according to any one of claims 12 to 14, characterized in that: The sodium salts include NaFSI and NaPF6; Based on the total mass of the electrolyte, the mass ratio of NaFSI to NaPF6 is not less than 0.4 and not more than 7. Optionally, the mass ratio of NaFSI to NaPF6 is not less than 0.5 and not more than 2.

16. The secondary battery according to any one of claims 1 to 15, characterized in that: The viscosity of the electrolyte measured by a rotor test method at an ambient temperature of 25° C. is 2 mPa.s to 5 mPa.s, and can be optionally 3 mPa.s to 4.6 mPa.s.

17. The secondary battery according to any one of claims 1 to 16, characterized in that: The CB value of the secondary battery is 1.05 to 1.5, and can be optionally 1.05 to 1.

3.

18. The secondary battery according to any one of claims 1 to 17, characterized in that: The secondary battery includes one or more of a lithium battery, a sodium battery, and a potassium battery.

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

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