Secondary battery and electric device

Abstract

The invention provides a secondary battery and a power utilization device, in the secondary battery, the CB value of the secondary battery is A, electrolyte contains lithium fluorosulfonate and / or lithium tetrafluoroborate as an additive, the weight of the lithium fluorosulfonate and / or lithium tetrafluoroborate accounts for B% of the total weight of the electrolyte, and the secondary battery meets the following relational expression: A is less than 1.05; and 0.008 < = B / A < = 0.5. The secondary battery provided by the invention has a low CB value, high energy density and excellent high-rate cycle performance.

Description

Technical Field

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

[0002] In recent years, as the application scope of secondary batteries has become more and more extensive, secondary batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. As secondary batteries have made great progress, higher requirements have been put forward for their performance.

[0003] At present, in the design of secondary batteries, the CB value (cell balance) is the ratio of the negative electrode capacity per unit area to the positive electrode capacity per unit area. The CB value of secondary batteries is usually designed to be above 1.07 to ensure the battery's cycle performance, but a higher CB value leads to a significant decrease in the battery's energy density. Therefore, it is expected to reduce the CB value of lithium-ion batteries to increase the battery's energy density while still ensuring that the battery has good cycle performance. Summary of the invention

[0004] The present application has been made in view of the above-mentioned problems, and an object of the present application is to provide a secondary battery having a low CB value and excellent high-rate cycle performance.

[0005] In order to achieve the above-mentioned object, the first aspect of the present application provides a secondary battery, wherein the CB value of the secondary battery is A, the electrolyte contains B weight % of lithium fluorosulfonate and / or lithium tetrafluoroborate as additives relative to the total weight of the electrolyte, and the secondary battery satisfies the following relationship: A<1.05; and 0.008≤B / A≤0.5. The secondary battery of the present invention can obtain excellent high-rate cycle performance at a low CB value by adding a specific amount of lithium fluorosulfonate and / or lithium tetrafluoroborate as additives to the electrolyte.

[0006] In any embodiment, 0.9≤A<1.05, optionally, 0.98≤A≤1.04. Thus, the secondary battery can obtain high energy density and excellent cycle performance in a better balance.

[0007] In any embodiment, 0.04≤B / A≤0.37. This can further improve the energy density and cycle performance of the secondary battery.

[0008] In any embodiment, the conductivity of the electrolyte is 9.0 to 11.0 mS / cm at 25° C. By setting the conductivity of the electrolyte to be within the above range, the high-rate cycle performance of the secondary battery can be improved.

[0009] In any embodiment, the electrolyte contains lithium hexafluorophosphate and bis(fluorosulfonyl)imide as electrolyte salts, the content of the bis(fluorosulfonyl)imide lithium salt is C weight % relative to the total weight of the electrolyte, and the secondary battery satisfies the following relationship: 7.4≤C / A≤18.3, optionally, 9.0≤C / A≤14.3. By making the C / A value within the above range, the conductivity of the electrolyte can be improved.

[0010] In any embodiment, the content of the bisfluorosulfonyl imide lithium salt is 10% to 18% relative to the total weight of the electrolyte. By setting the content of the bisfluorosulfonyl imide lithium salt within the above range, the conductivity of the electrolyte can be improved.

[0011] In any embodiment, the electrolyte includes cyclic ester and chain ester as solvents, and the chain ester has a viscosity of 0.4 to 0.8 cp at 25° C. By making the viscosity of the chain ester within the above range, it is beneficial to improve the conductivity of the electrolyte, thereby improving the high-rate cycle performance of the battery.

[0012] In any embodiment, the content of the chain ester is D weight % relative to the total weight of the solvent, and the secondary battery satisfies the following relationship: 5.6≤D / 10A≤9.4, optionally, 6.2≤D / 10A≤7.9. By making the D / 10A value within the above range, it is beneficial to improve the high-rate cycle performance of the battery.

[0013] In any embodiment, the content of the chain ester is 60 wt % to 95 wt % relative to the total weight of the solvent, which is beneficial for controlling the viscosity of the electrolyte and thus improving the high-rate cycle performance of the battery.

[0014] In any embodiment, the chain ester includes carboxylic acid ester and / or carbonate ester. This is beneficial for controlling the viscosity of the electrolyte, thereby improving the high-rate cycle performance of the battery.

[0015] In any embodiment, the carboxylate includes at least one selected from ethyl acetate, ethyl propionate, propyl propionate, methyl acetate, methyl propionate, methyl butyrate, and ethyl butyrate, and the carbonate includes at least one selected from ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, and methyl propyl carbonate. This is beneficial to improving the high-rate cycle performance of the battery.

[0016] In any embodiment, the cyclic ester includes at least one selected from ethylene carbonate, propylene carbonate, and γ-butyrolactone, and the content of the cyclic ester is 5 wt % to 30 wt % relative to the total weight of the solvent. This is beneficial for controlling the viscosity of the electrolyte, thereby improving the high-rate cycle performance of the battery.

[0017] In any embodiment, the solvent includes ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and ethyl acetate. By making the solvent include ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and ethyl acetate, it is more conducive to improving the high-rate cycle performance of the battery.

[0018] The second aspect of the present application further provides an electrical device, which includes the secondary battery of the first aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of a battery cell according to an embodiment of the present application.

[0020] Figure 2 yes Figure 1 An exploded view of a battery cell according to an embodiment of the present application is shown.

[0021] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0022] Figure 4 It is a schematic diagram of a battery pack according to one embodiment of the present application.

[0023] Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0024] 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.

[0025] Description of reference numerals:

[0026] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0027] The following describes in detail the implementation of the secondary battery and the electrical device of the present application. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0028] "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.

[0029] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0030] 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.

[0031] The term “secondary battery” mentioned in the present application includes a battery cell, a battery module, and a battery pack.

[0032] In existing secondary batteries, the CB value of the battery is relatively high, usually above 1.07, and some even exceed 1.1. By making the CB value higher, the negative electrode capacity exceeds the positive electrode capacity more, and sufficient space can be provided for lithium during the charge and discharge process to avoid deposition and formation of dendrites on the negative electrode surface, so that the battery has better cycle performance. But on the other hand, a high CB value also means waste of the negative electrode, resulting in low energy density of the battery. However, in order to obtain high energy density, when the CB value is reduced, lithium precipitation occurs, and the high-rate cycle performance of the battery is seriously deteriorated. Therefore, it is expected to reduce the CB value of the battery to increase the energy density of the battery while still ensuring that the secondary battery has excellent high-rate cycle performance.

[0033] The present application adds a specific amount of lithium fluorosulfonate and / or lithium tetrafluoroborate as additives to the electrolyte of the secondary battery, thereby having a lower CB value than existing secondary batteries and excellent high-rate cycle performance.

[0034] In one embodiment of the present application, the CB of the secondary battery is A, the electrolyte contains B weight % of lithium fluorosulfonate and / or lithium tetrafluoroborate as additives relative to the total weight of the electrolyte, and the secondary battery satisfies the following relationship:

[0035] A < 1.05; and

[0036] 0.008≤B / A≤0.5.

[0037] The inventors of the present application have found through extensive research that by adding a specific amount of lithium fluorosulfonate and / or lithium tetrafluoroborate to the electrolyte, a low-impedance interface film can be formed in the electrolyte, effectively improving lithium precipitation, thereby achieving excellent high-rate cycle performance even at low CB values. From the perspective of effectively forming a low-impedance interface film, lithium fluorosulfonate is preferred.

[0038] The CB value of a battery can be determined by the following method: after fully discharging a secondary battery (for example, in the case of a lithium-ion battery, discharging to 2.5V means fully discharging), the battery is disassembled to obtain the positive and negative electrode sheets respectively, and metal lithium is used as a counter electrode for each of the positive and negative electrode sheets, and each is assembled into a button cell, and the capacity is discharged at 0.1 mA to test the corresponding capacity. For the detailed CB value test process, please refer to the test method section of the embodiment of this application.

[0039] In some embodiments, 0.9≤A<1.05, optionally, 0.98≤A≤1.04. Thus, the secondary battery can obtain high energy density and excellent cycle performance in a better balance.

[0040] In some embodiments, 0.04≤B / A≤0.37, optionally, B / A may be 0.05, 0.06, 0.08, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.5, 3.0, 3.5, etc. Thus, the energy density and cycle performance of the secondary battery can be further improved.

[0041] In some embodiments, the conductivity of the electrolyte is 9.0-11.0 mS / cm at 25° C. By increasing the conductivity of the electrolyte to be within the above range, lithium ion transport is accelerated, and the high-rate cycle performance of the secondary battery can be improved.

[0042] In some embodiments, the electrolyte contains lithium hexafluorophosphate and bis(fluorosulfonyl)imide as electrolyte salts, and the content of bis(fluorosulfonyl)imide is C wt % relative to the total weight of the electrolyte, and the secondary battery satisfies the following relationship: 7.4≤C / A≤18.3, optionally, 9.0≤C / A≤14.3. By making the C / A value within the above range, the conductivity of the electrolyte can be improved.

[0043] In some embodiments, the content of the bis(fluorosulfonyl)imide lithium salt (LiFSI) is 10% to 18% relative to the total weight of the electrolyte. By setting the content of the bis(fluorosulfonyl)imide lithium salt within the above range, the conductivity of the electrolyte can be improved.

[0044] In some embodiments, the electrolyte includes cyclic esters and chain esters as solvents, and the chain ester has a viscosity of 0.4 to 0.8 cp at 25°C. When the solvent includes multiple chain esters, the viscosity here refers to the viscosity of the mixed chain esters. By making the viscosity of the chain ester within the above range, it is beneficial to improve the conductivity of the electrolyte, and thus to improve the high-rate cycle performance of the battery.

[0045] In some embodiments, the content of the chain ester is D weight % relative to the total weight of the solvent, and the secondary battery satisfies the following relationship: 5.6≤D / 10A≤9.4, optionally, 6.2≤D / 10A≤7.9. By making the D / 10A value within the above range, it is beneficial to improve the high-rate cycle performance of the battery.

[0046] In some embodiments, the content of the chain ester is 60 wt % to 95 wt % relative to the total weight of the solvent, which is beneficial for controlling the viscosity of the electrolyte and thus improving the high-rate cycle performance of the battery.

[0047] In some embodiments, the chain ester includes carboxylic acid ester and / or carbonate ester, which is helpful to control the viscosity of the electrolyte, thereby improving the high-rate cycle performance of the battery.

[0048] In some embodiments, the carboxylate includes at least one selected from ethyl acetate, ethyl propionate, propyl propionate, methyl acetate, methyl propionate, methyl butyrate, and ethyl butyrate, and the carbonate includes at least one selected from ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, and methyl propyl carbonate. This is beneficial to improving the high-rate cycle performance of the battery.

[0049] In some embodiments, the cyclic ester includes at least one selected from ethylene carbonate, propylene carbonate, and γ-butyrolactone, and the content of the cyclic ester is 5 wt % to 30 wt % relative to the total weight of the solvent, thereby helping to control the viscosity of the electrolyte and thus improve the high-rate cycle performance of the battery.

[0050] In some embodiments, the solvent includes ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and ethyl acetate. By making the solvent include ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and ethyl acetate, it is more conducive to improving the high-rate cycle performance of the battery.

[0051] In addition, the secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0052] In general, in addition to the above-mentioned electrolyte, secondary batteries also include positive electrode sheets, negative electrode sheets and separators. During the battery charging and discharging process, active ions are embedded and removed back and forth between the positive electrode sheets and the negative electrode sheets. The electrolyte plays the role of conducting ions between the positive electrode sheets and the negative electrode sheets. The separator is set between the positive electrode sheets and the negative electrode sheets, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0053] [Positive electrode]

[0054] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the positive electrode active material of the first aspect of the present application.

[0055] 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.

[0056] 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.).

[0057] In some embodiments, when the secondary battery is a lithium ion battery, the positive electrode active material may be a positive electrode active material for lithium ion batteries known in the art.

[0058] The battery will be accompanied by Li deintercalation and consumption during the charge and discharge process, and the molar content of Li is different when the battery is discharged to different states. In the list of positive electrode materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode material is used in the battery system, and the molar content of Li will change after charge and discharge cycles.

[0059] In the list of positive electrode materials in this application, the molar content of O is only a theoretical state value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an 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 NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] [Negative electrode]

[0064] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0065] 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.

[0066] 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.).

[0067] 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.

[0068] 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).

[0069] 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.

[0070] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0071] 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.

[0072] [Electrolytes]

[0073] The electrolyte plays a role in conducting ions between the positive electrode and the negative electrode. In the present application, the electrolyte is in liquid state.

[0074] In some embodiments, the electrolyte salt may include at least one selected from the group consisting of lithium perchlorate, lithium hexafluoroarsenate, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate in addition to the above-mentioned lithium hexafluorophosphate and lithium bisfluorosulfonyl imide salts.

[0075] In some embodiments, the solvent may include conventional solvents in the art in addition to the above-mentioned solvents of the present application.

[0076] In some embodiments, the electrolyte may also optionally include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0077] [Isolation film]

[0078] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0079] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0080] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0081] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0082] 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.

[0083] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 1 The battery cell 5 is a square structure as an example.

[0084] In some embodiments, reference Figure 2 , the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0085] 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.

[0086] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0087] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0088] 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.

[0089] 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.

[0090] In addition, the present application also provides an electric device, which includes at least one of the battery cells, battery modules, or battery packs provided in the present application. The battery cells, battery modules, or battery packs can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric 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.

[0091] As the electrical device, a secondary battery, a battery module or a battery pack may be selected according to its usage requirements.

[0092] Figure 6 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. 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.

[0093] 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 light and thin, and a secondary battery may be used as a power source.

[0094] Example

[0095] Hereinafter, the present application will be specifically described by way of examples. The examples described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. Where specific techniques or conditions are not indicated in the examples, the techniques or conditions described in the literature in this area or the product specifications are used. Where the manufacturers of reagents or instruments are not indicated, they are all conventional products that can be obtained commercially.

[0096] Example 1

[0097] [Preparation of electrolyte]

[0098] In an argon atmosphere glove box with a water content of <10 ppm, ethylene carbonate as a cyclic ester and ethyl methyl carbonate, dimethyl carbonate and ethyl acetate as chain esters were mixed in a weight ratio of 30:20:30:20 to obtain solvent 1-1, wherein the content of the chain ester was 70 wt % relative to the total weight of solvent 1-1. Electrolyte salts of lithium hexafluorophosphate and lithium bisfluorosulfonyl imide (LiFSI) and additives of lithium fluorosulfonate were added to the solvent 1-1, and the electrolyte was obtained after being fully stirred and dissolved, so that the electrolyte contained 0.204 wt % of lithium fluorosulfonate, 5 wt % of lithium hexafluorophosphate, and 14 wt % of LiFSI relative to the total weight of the electrolyte.

[0099] [Preparation of positive electrode sheet]

[0100] The positive electrode active material nickel cobalt manganese ternary material (LiNi 0.8 Co 0.1 Mn 0.1 O2, capacity of 180mAh / g), binder polyvinylidene fluoride, conductive agent acetylene black are mixed in a mass ratio of 8:1:1, and solvent NMP (N-methylpyrrolidone) is added to obtain positive electrode slurry under the action of a vacuum mixer. The positive electrode slurry is 0.2826g (dry weight) / 1540.25mm 2 The amount of the coating was evenly coated on the positive electrode current collector aluminum foil with a thickness of 13 μm; the aluminum foil was dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then cold pressed and cut to obtain the positive electrode sheet.

[0101] [Preparation of negative electrode sheet]

[0102] Artificial graphite (capacity of 350mAh / g), conductive carbon black, and binder acrylate were mixed in a mass ratio of 92:2:6, and deionized water was added to obtain negative electrode slurry under the action of a vacuum mixer. 2 The amount of the negative electrode current collector is evenly coated on the negative electrode current collector copper foil with a thickness of 8 μm; the copper foil is dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then cold pressed to achieve a negative electrode film layer thickness of 100 microns, and then cut to obtain negative electrode sheets.

[0103] [Isolation film]

[0104] The isolation membrane was purchased from Cellgard Company, model number is cellgard2400.

[0105] [Preparation of Secondary Battery]

[0106] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrode sheets to play an isolating role, and then wound to obtain a bare cell. The bare cell is placed in an outer packaging foil, and the 8.6g prepared electrolyte is injected into the dried battery. After vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery is obtained.

[0107] Embodiment 2-6

[0108] A secondary battery was produced in the same manner as in Example 1 except that the content and type of the electrolyte additive were adjusted as shown in Table 1.

[0109] Example 7

[0110] The negative electrode slurry was 0.1315g (dry weight) / 1540.25mm 2 A secondary battery was prepared in the same manner as in Example 1 except that an amount of 200 μm was uniformly coated on a negative electrode current collector copper foil having a thickness of 8 μm. .

[0111] Example 8

[0112] The negative electrode slurry was 0.1239g (dry weight) / 1540.25mm 2 A secondary battery was prepared in the same manner as in Example 1 except that an amount of was uniformly coated on a negative electrode current collector copper foil having a thickness of 8 μm.

[0113] Example 9

[0114] The negative electrode slurry was 0.115g (dry weight) / 1540.25mm 2 A secondary battery was prepared in the same manner as in Example 1 except that an amount of was uniformly coated on a negative electrode current collector copper foil having a thickness of 8 μm.

[0115] Examples 10-16

[0116] A secondary battery was produced in the same manner as in Example 1 except that the type and content of the electrolyte salt in the electrolyte were adjusted as shown in Table 1.

[0117] Examples 17-22

[0118] The content of the chain ester in the electrolyte solvent 1-1 was adjusted to obtain the following solvents 1-2, 1-3, 1-4, 1-5, 1-6, and 1-7, respectively. Otherwise, secondary batteries were prepared in the same manner as in Example 1. Solvent 1-2: prepared by mixing ethylene carbonate as a cyclic ester and methyl ethyl carbonate, dimethyl carbonate, and ethyl acetate as chain esters in a weight ratio of 43.9:10:30:16.1;

[0119] Solvent 1-3: obtained by mixing ethylene carbonate as a cyclic ester and ethyl methyl carbonate, dimethyl carbonate and ethyl acetate as chain esters in a weight ratio of 42.9:10:30:17.1;

[0120] Solvent 1-4: obtained by mixing ethylene carbonate as a cyclic ester and ethyl methyl carbonate, dimethyl carbonate and ethyl acetate as chain esters in a weight ratio of 36.8:15:25:23.2;

[0121] Solvent 1-5: obtained by mixing ethylene carbonate as a cyclic ester and ethyl methyl carbonate, dimethyl carbonate and ethyl acetate as chain esters in a weight ratio of 19.4:15:25:40.6;

[0122] Solvent 1-6: obtained by mixing ethylene carbonate as a cyclic ester and ethyl methyl carbonate, dimethyl carbonate and ethyl acetate as chain esters in a weight ratio of 4.1:20:20:55.9;

[0123] Solvent 1-7: Ethylene carbonate as a cyclic ester and ethyl methyl carbonate, dimethyl carbonate and ethyl acetate as chain esters were mixed at a weight ratio of 3.1:20:20:56.9.

[0124] Embodiment 23

[0125] The type of electrolyte solvent in Example 1 was adjusted so that the electrolyte solvent did not contain carboxylic acid esters. The cyclic ester ethylene carbonate and the chain esters ethyl methyl carbonate and dimethyl carbonate were mixed in a weight ratio of 30:30:40 to obtain solvent 2. Except for this, a secondary battery was made in the same manner as Example 1.

[0126] Comparative Example 1

[0127] A secondary battery was produced in the same manner as in Example 1 except that lithium fluorosulfonate was not added.

[0128] Comparative Example 2

[0129] A secondary battery was produced in the same manner as in Example 1 except that the B / A value was set to be less than 0.008.

[0130] Comparative Example 3

[0131] A secondary battery was produced in the same manner as in Example 1 except that the B / A value was set to be greater than 0.5.

[0132] Comparative Example 4

[0133] A secondary battery was produced in the same manner as in Example 1 except that the battery CB value (A value) was changed to 1.05.

[0134] The secondary batteries obtained in the above examples and comparative examples were tested as follows.

[0135] 1. CB value (A value) measurement

[0136] After discharging the battery to 2.5V, the battery is disassembled to obtain the negative electrode. Metal lithium is used as the counter electrode for the negative electrode to assemble into a button battery. The button battery uses a standard 2046 button battery metal shell, the electrode is cut into a small disc with a diameter of 14mm, the metal lithium sheet uses a small disc with a diameter of 16mm, and the middle isolation membrane uses a PP isolation membrane with a diameter of 18mm. For the above button battery, it is discharged to 0.05V with 36mA, and its discharge capacity is recorded as N1.

[0137] After the battery is fully charged to 4.4V, the battery is disassembled to obtain the positive electrode. Metal lithium is used as the counter electrode for the positive electrode to assemble into a button cell. The button cell uses a standard 2046 button cell metal shell, the electrode is cut into a small disc with a diameter of 14mm, the metal lithium sheet uses a small disc with a diameter of 16mm, and the middle separator uses a PP separator with a diameter of 18mm. For the above button cell, discharge with 18mA to 3.0V, and its discharge capacity is recorded as N2.

[0138] Thus, the CB value of the battery is obtained as N1 / N2.

[0139] 2. Viscosity

[0140] The test is conducted based on the national standard GB / T10247-2008 Appendix D Rotational Viscometer. For details, please refer to the following test steps: Take a certain mass of electrolyte sample and place it in a sample container, and use the Brookfield DV2TLV rotational viscometer to test it. At a certain temperature, when the rotor rotates continuously at a constant speed in the sample, the shear force it receives causes the spring to generate torque, which is proportional to the viscosity, and the viscosity value is obtained.

[0141] The test equipment meets the following test environmental conditions: 1. Equipment external environment: temperature: 25°C, humidity: RH<80%; 2. Equipment internal environment: 2 / 3 of the sample container is immersed in a water bath, the medium is water, and water is used to maintain a constant temperature for the sample.

[0142] 3. Conductivity

[0143] Refer to the density meter method on page 5 of the industry standard HG / T4067-2015 "Lithium Hexafluorophosphate Electrolyte".

[0144] Specific test steps: Use a dry, clean, corrosion-resistant sample bottle to take about 100 mL of sample, seal it in a constant temperature water bath at 25℃±0.5℃, shake it from time to time, and when the sample temperature is constant, replace the sample bottle cap with a rubber stopper with an electrode. When the temperature is within the range of 25℃±0.5℃, read the data in the conductivity meter, which is the conductivity of the sample being tested.

[0145] 4. Energy density

[0146] At 25°C, charge the lithium-ion battery at a constant current of 1A to 4.3V, then charge at a constant voltage until the current is less than 0.5A. Then discharge the battery at a constant current of 1A to 2.5V, then at a constant current of 0.5A to 2.5V, and finally at 0.1A to 2.5V, record the discharge capacity C (Ah) of the battery, and record the voltage value U (V) of the battery when the discharge reaches half of the capacity.

[0147] At this time, weigh the battery and record the mass m (kg).

[0148] Battery energy W = C × U, battery energy density = W / m.

[0149] 5. High rate cycle performance test

[0150] At 25°C, the lithium-ion battery was charged to 4.3V at a 2C constant current, and then discharged to 2.5V at a 2C constant current for 100 cycles.

[0151] Capacity retention rate (%) of the secondary battery 2C after 100 cycles = discharge capacity after 100 cycles / first cycle discharge capacity × 100%.

[0152] The performance test results of each embodiment and comparative example are shown in the following Table 1.

[0153]

[0154] Based on the results in Table 1, it can be seen that compared with the comparative example, in the embodiment of the present application, by adding a specific amount of lithium fluorosulfonate and / or lithium tetrafluoroborate as an additive in the electrolyte of the secondary battery, it can have a lower CB value than the existing secondary battery, and can have both high energy density and excellent high-rate cycle performance. In addition, by comparing Examples 1 to 9 with Examples 10 to 16 and Examples 17 to 23, it is shown that the present application can further improve the high-rate cycle performance and obtain a more excellent technical effect by including a specific amount of LiFSI as an electrolyte salt or / and a specific amount of chain ester as a solvent in the electrolyte.

[0155] In addition, in Comparative Examples 1 to 3, lithium fluorosulfonate was not added to the electrolyte or its content was not within the scope of the present application, so the high-rate cycle performance was poor and the technical effect of the present application could not be obtained. In Comparative Example 4, the CB value was high and the energy density was low, and the technical effect of the present application could not be obtained.

[0156] 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, wherein: The CB value of the secondary battery is A, the electrolyte contains B weight % of lithium fluorosulfonate and / or lithium tetrafluoroborate as additives relative to the total weight of the electrolyte, and the secondary battery satisfies the following relationship: A < 1.05; and 0.008≤B / A≤0.

5.

2. The secondary battery according to claim 1, characterized in that: 0.9≤A<1.05, optionally, 0.98≤A≤1.

04.

3. The secondary battery according to claim 1 or 2, characterized in that: 0.04≤B / A≤0.

37.

4. The secondary battery according to any one of claims 1 to 3, characterized in that The conductivity of the electrolyte at 25° C. is 9.0 to 11.0 mS / cm.

5. The secondary battery according to claim 4, characterized in that: The electrolyte solution includes lithium hexafluorophosphate and bis(fluorosulfonyl)imide lithium salt as electrolyte salts, and the content of the bis(fluorosulfonyl)imide lithium salt is C wt % relative to the total weight of the electrolyte solution. The secondary battery satisfies the following relationship: 7.4≤C / A≤18.3, optionally, 9.0≤C / A≤14.

3.

6. The secondary battery according to claim 5, characterized in that: The content of the bisfluorosulfonyl imide lithium salt is 10% to 18% relative to the total weight of the electrolyte.

7. The secondary battery according to any one of claims 4 to 6, characterized in that: The electrolyte solution includes cyclic ester and chain ester as solvents, and the chain ester has a viscosity of 0.4-0.8 cp at 25°C.

8. The secondary battery according to claim 7, characterized in that: The content of the chain ester is D wt % relative to the total weight of the solvent, and the secondary battery satisfies the following relationship: 5.6≤D / 10A≤9.4, optionally, 6.2≤D / 10A≤7.

9.

9. The secondary battery according to claim 7 or 8, characterized in that: The content of the chain ester is 60 wt % to 95 wt % relative to the total weight of the solvent.

10. The secondary battery according to any one of claims 7 to 9, characterized in that The chain esters include carboxylic acid esters and / or carbonate esters.

11. The secondary battery according to any one of claims 7 to 10, characterized in that: The carboxylic acid ester includes at least one selected from ethyl acetate, ethyl propionate, propyl propionate, methyl acetate, methyl propionate, methyl butyrate, and ethyl butyrate, The carbonate includes at least one selected from ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, and methyl propyl carbonate.

12. The secondary battery according to any one of claims 7 to 11, characterized in that: The cyclic ester includes at least one selected from ethylene carbonate, propylene carbonate, and γ-butyrolactone, and the content of the cyclic ester is 5 wt % to 30 wt % relative to the total weight of the solvent.

13. The secondary battery according to any one of claims 7 to 12, characterized in that: The solvent includes ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and ethyl acetate.

14. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 13.

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