CN118336079A

CN118336079A - Secondary battery, battery pack and electric device

Info

Publication number: CN118336079A
Application number: CN202410471376.4A
Authority: CN
Inventors: 王其超; 吕腾啸; 陶李林; 康振洪
Original assignee: Xiamen Hithium Energy Storage Technology Co Ltd
Current assignee: Xiamen Hithium Energy Storage Technology Co Ltd
Priority date: 2024-04-18
Filing date: 2024-04-18
Publication date: 2024-07-12

Abstract

The application provides a secondary battery, a battery pack and electric equipment, wherein the secondary battery comprises an anode plate, a cathode plate and electrolyte, the electrolyte comprises 3-sulfolane and lithium difluorooxalate borate, the mass percentage of the 3-sulfolane is a, the mass percentage of the lithium difluorooxalate borate is b, the a is more than or equal to 0.1% and less than or equal to 2%, and the b is more than or equal to 0.1% and less than or equal to 2% based on the mass of the electrolyte; the positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode active material layer is arranged on the positive electrode current collector, a functional layer is arranged between the positive electrode current collector and the positive electrode active material layer, and the functional layer contains carbon black.

Description

Secondary battery, battery pack and electric device

Technical Field

The application relates to the technical field of electrochemistry, in particular to a secondary battery, a battery pack and electric equipment.

Background

Secondary batteries (e.g., lithium ion batteries) have advantages of high energy density, small self-discharge, light weight, and the like, and thus are widely used in the fields of energy storage devices and the like.

With the improvement of the performance requirements of the secondary battery, for example, the performance requirements of the secondary battery in the wind power generation energy storage scene or the solar power generation energy storage scene, the secondary battery is required to have higher energy density and stable cycle performance, so that the long-term stable operation requirement of the energy storage device in the energy storage application scene is met.

Disclosure of Invention

In order to solve the technical problems, the application discloses a secondary battery, a battery pack and electric equipment so as to improve the cycle performance of the secondary battery.

In a first aspect, the application provides a secondary battery, which comprises a positive electrode plate, a negative electrode plate and an electrolyte, wherein the electrolyte comprises 3-sulfolane and lithium difluorooxalate borate, the mass percentage of the 3-sulfolane is a, the mass percentage of the lithium difluorooxalate borate is b, the mass percentage of the lithium difluorooxalate borate is more than or equal to 0.1% and less than or equal to 2%, and the mass percentage of the b is more than or equal to 0.1% and less than or equal to 2%; the positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode active material layer is arranged on the positive electrode current collector, a functional layer is arranged between the positive electrode current collector and the positive electrode active material layer, and the functional layer contains carbon black.

In some embodiments of the application, 0.5% or less a 1.5% or less, 0.5% or less b 1.5% or less.

In some embodiments of the application, the following are satisfied between a and b: b/a is more than or equal to 0.5 and less than or equal to 2.

In some embodiments of the application, the electrolyte further comprises 1,3, 5-trifluorobenzene, the content of 1,3, 5-trifluorobenzene being c,0.1% c.ltoreq.2% based on the mass of the electrolyte.

In some embodiments of the application, 0.5% c 1.5%.

In some embodiments of the application, the electrolyte further comprises lithium hexafluorophosphate, the mass ratio of the lithium difluorooxalato borate to the lithium hexafluorophosphate being 0.04-0.16:1.

In some embodiments of the application, the Dv50 of the carbon black is from 0.2 μm to 2.0 μm.

In some embodiments of the application, the functional layer has a thickness of 0.8 μm to 1.2 μm.

In a second aspect, the present application provides a battery pack comprising a case and at least one secondary battery according to the first aspect, the secondary battery being accommodated in the case.

In a third aspect, the present application provides a powered device, including the secondary battery according to the first aspect or the battery pack according to the second aspect.

Compared with the prior art, the application has at least the following beneficial effects:

The application provides a secondary battery, a battery pack and electric equipment, wherein the electrolyte comprises 3-sulfolane and lithium difluorooxalate borate, the mass percentage of the 3-sulfolane is a, the mass percentage of the lithium difluorooxalate borate is b, the a is more than or equal to 0.1% and less than or equal to 2%, and the b is more than or equal to 0.1% and less than or equal to 2% based on the mass of the electrolyte; wherein a functional layer is arranged between the positive electrode current collector and the positive electrode active material layer, and the functional layer contains carbon black. The lithium difluorooxalate borate has higher reduction potential, so that an SEI (Solid Electrolyte Interphase, solid electrolyte interface) film can be formed earlier, and fluorine element and boron element in the lithium difluorooxalate borate are beneficial to forming a firm SEI film inner layer; 3-sulfolane can form lithium alkyl sulfonate with higher thermal stability on the outer layer of the SEI film; the functional layer in the positive electrode plate can improve the liquid retention capacity of the electrolyte. Through the combined action of the functional layer, the 3-sulfolane and the lithium difluorooxalate borate, the SEI film has the characteristics of high stability and low impedance, and simultaneously improves the liquid retaining capacity of electrolyte, thereby reducing the direct current impedance (DCR) of the secondary battery and improving the cycle performance of the secondary battery.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a schematic view of the structure of a positive electrode sheet according to an embodiment of the present application;

FIG. 2 is a schematic diagram of a household energy storage system according to one embodiment of the present application;

Fig. 3 is a schematic structural diagram of an energy storage system according to an embodiment of the present application.

Reference numerals illustrate: 1-energy storage device, 2-electric energy conversion device, 3-first user load, 4-second user load, 10-positive current collector, 20-functional layer, 30-positive active material layer, 400-energy storage system, 410-high voltage cable, 420-first electric energy conversion device, 430-second electric energy conversion device.

Detailed Description

The following description of the embodiments of the present application will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present application, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.

In the present application, the terms "upper", "lower", "left", "right", "front", "rear", "top", "bottom", "inner", "outer", "vertical", "horizontal", "lateral", "longitudinal" and the like indicate an azimuth or a positional relationship based on that shown in the drawings. These terms are only used to better describe the present application and its embodiments and are not intended to limit the scope of the indicated devices, elements or components to the particular orientations or to configure and operate in the particular orientations.

Also, some of the terms described above may be used to indicate other meanings in addition to orientation or positional relationships, for example, the term "upper" may also be used to indicate some sort of attachment or connection in some cases. The specific meaning of these terms in the present application will be understood by those of ordinary skill in the art according to the specific circumstances.

Furthermore, the terms "mounted," "configured," "provided," "connected," and "connected" are to be construed broadly. For example, it may be a fixed connection, a removable connection, or a unitary construction; may be a mechanical connection, or an electrical connection; may be directly connected, or indirectly connected through intervening media, or may be in internal communication between two devices, elements, or components. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art according to the specific circumstances.

Furthermore, the terms "first," "second," and the like, are used primarily to distinguish between different devices, elements, or components (the particular species and configurations may be the same or different), and are not used to indicate or imply the relative importance and number of devices, elements, or components indicated. Unless otherwise indicated, the meaning of "a plurality" is two or more.

In the present application, a lithium ion battery is used as an example of a secondary battery, but the secondary battery of the present application is not limited to a lithium ion battery.

The application provides a secondary battery, which comprises a positive electrode plate, a negative electrode plate and an electrolyte, wherein the electrolyte comprises 3-sulfolane and lithium difluorooxalate borate (LiODFB), the mass percentage of the 3-sulfolane is a, the mass percentage of the lithium difluorooxalate borate is b, the a is more than or equal to 0.1% and less than or equal to 2%, and the b is more than or equal to 0.1% and less than or equal to 2%; in other embodiments, 0.5% or less a or less than 1.5%,0.5% or less b or less than 1.5%. For example, a is 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.7% or 2%; b is 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.7% or 2%; the positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer, a functional layer is arranged between the positive electrode current collector and the positive electrode active material layer, and the functional layer contains carbon black.

Wherein, the structural formula of the 3-sulfolane is as follows:

The inventor researches and discovers that the reduction potential of the lithium difluoroborate is higher, the SEI film can be formed earlier, and fluorine element and boron element in the lithium difluoroborate are beneficial to forming a firm SEI film inner layer structure; the 3-sulfolane can form lithium alkyl sulfonate on the outer layer of the SEI film, and compared with lithium alkyl carbonate, the lithium alkyl sulfonate has higher stability, particularly higher thermal stability, so that the SEI film stability is improved. However, when the content of 3-sulfolane is too low (e.g., less than 0.1%), lithium alkylsulfonate cannot be formed sufficiently, and it is difficult to improve the stability of the SEI film; when the content of 3-sulfolane is too high (for example, higher than 2%), the resistance of the SEI film may be greatly increased; when the content of lithium difluorooxalato borate is too low (for example, lower than 0.1%), it is difficult to form a firm SEI film inner layer structure containing fluorine and boron elements, affecting the film formation stability of the SEI film; when the content of lithium difluorooxalato borate is too high (for example, higher than 2%), since the reduction potential of lithium difluorooxalato borate is very high, it is very easy to form a film, and also the resistance of the SEI film is greatly increased.

Based on the research, the electrolyte provided by the application contains 3-sulfolane and lithium difluorooxalate borate, and the SEI film can still have low impedance characteristics while improving the stability of the SEI film under the combined action of two additives by regulating and controlling the content of the 3-sulfolane and the lithium difluorooxalate borate within the range of the application;

The inventors have also found that the compacted density of the electrode sheet has a great influence on the wettability of the electrolyte. For lithium ion batteries used in energy storage devices, the compacted density of the negative electrode sheet is typically about 1.4g/cm ³, while the compacted density of the positive electrode sheet is as high as 2.4g/cm ³. The higher compaction density results in the porosity of the positive electrode plate to be reduced, if the wettability of the electrolyte is poor, the ion transmission path becomes far, the shuttling of lithium ions between the positive electrode and the negative electrode is blocked, and the electrode plate which is not contacted with the electrolyte cannot release the capacity. Illustratively, as shown in fig. 1, the positive electrode current collector 10 and the positive electrode active material layer 30 of the present application have a functional layer 20 therebetween, the functional layer containing carbon black. The carbon black has relatively small particle size, so that the specific surface area is large, and the adsorption capacity of the carbon black is improved, so that the functional layer can improve the liquid retention capacity of the electrolyte, and is beneficial to the reduction of DRC (discontinuous control) of a lithium ion battery and the improvement of the cycle performance.

In summary, the functional layer containing carbon black is arranged on the surface of the positive electrode current collector, and the electrolyte contains 3-sulfolane and lithium difluorooxalate borate, so that the SEI film has high stability and low impedance characteristics and simultaneously improves the liquid retaining capacity of the electrolyte by the combined action of the functional layer, the 3-sulfolane and the lithium difluorooxalate borate, thereby reducing DCR of the lithium ion battery, improving the cycle performance of the lithium ion battery, being more suitable for the energy storage device with high requirement on the long-term cycle performance of the lithium ion battery, and further reducing the operation cost of the energy storage device.

In some embodiments of the application, the following are satisfied between a and b: b/a is more than or equal to 0.5 and less than or equal to 2. For example, b/a=0.5, b/a=0.7, b/a=1, b/a=1.2, b/a=1.5, or b/a=2. The cycling performance of the lithium ion battery is improved by regulating and controlling the b/a within the range.

In some embodiments of the application, the electrolyte further comprises 1,3, 5-trifluorobenzene, the content of 1,3, 5-trifluorobenzene being 0.1% c.ltoreq.2% based on the mass of the electrolyte; in other embodiments, 0.5% c is 1.5%. For example, c is 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.7%, or 2%. By regulating the content of 1,3, 5-trifluoro benzene within the range, fluorine atoms in the lithium difluoro oxalate have strong electrophilicity and hydrophobicity, ODFB ^- in the lithium difluoro oxalate borate is easy to induce to form a film on a negative electrode, carbon black in a functional layer can attract 1,3, 5-trifluoro benzene to diffuse into the positive electrode plate due to electronegativity difference of fluorine atoms and carbon atom bonds, and the 1,3, 5-trifluoro benzene shows low surface tension characteristic, so that the wettability of electrolyte can be improved, the wettability of the positive electrode plate is obviously improved, and the cycle performance of the lithium ion battery is further improved. The inventors have also found that the content of 1,3, 5-trifluorobenzene is not too low or too high, and that when the content is too low (for example, less than 0.1%), it is difficult to achieve an effect of improving wettability of the positive electrode sheet; when the content is too high (for example, higher than 2%), the electronegativity of fluorine atoms is strong, which results in an increase in the instability of the electrolyte, which is liable to cause side reactions of the electrolyte, and which affects the cycle performance of the lithium ion battery. Based on the above, the functional layer containing carbon black is arranged on the surface of the positive electrode current collector, the content of 1,3, 5-trifluoro benzene is regulated and controlled within the range, and the synergistic effect of the 1,3, 5-trifluoro benzene and the carbon black in the functional layer improves the infiltration effect of the electrolyte on the positive electrode plate, and meanwhile, the electrolyte can keep good stability, so that the lithium ion battery has excellent cycle performance and simultaneously keeps low impedance characteristic.

In some embodiments of the application, the electrolyte further comprises lithium hexafluorophosphate (LiPF ₆), the mass ratio of lithium difluorooxalato borate to lithium hexafluorophosphate being 0.04-0.16:1.

The inventors have found that LiPF ₆ is easily decomposed into LiF and PF ₅, and that trace amounts of water are inevitably present in the electrolyte, and that PF ₅ reacts with water to easily form hydrofluoric acid which damages the SEI film. PF ₅ is a strong Lewis acid with electrophilic properties. The electrolyte contains 3-sulfolane and lithium difluorooxalate borate, ODFB ^- formed after the lithium difluorooxalate borate is dissolved has electron donating property, and ODFB ^- can be complexed with PF ₅ by regulating the mass ratio of the lithium difluorooxalate borate to the lithium hexafluorophosphate within the range, so that the reaction between the lithium difluorooxalate borate and water is prevented, and the generation of hydrofluoric acid is inhibited; in addition, 3-sulfolane can change the solvation structure of the lithium difluorooxalate borate, so that the lithium difluorooxalate borate is more uniformly distributed in the electrolyte, the contact opportunity of ODFB ^- and PF ₅ is increased, and therefore PF ₅ is more easily captured by ODFB ^-. Therefore, under the combined action of 3-sulfolane and lithium difluorooxalate borate, the effects of inhibiting the generation of hydrofluoric acid and improving the stability of the SEI film are achieved, so that the cycle performance of the lithium ion battery is improved.

In some embodiments of the application, the Dv50 of the carbon black is from 0.2 μm to 2.0 μm, for example, the Dv50 of the carbon black is 0.2 μm, 0.4 μm, 0.5 μm, 0.7 μm, 0.9 μm, 1.1 μm, 0.3 μm, 1.5 μm, 1.8 μm, or 2.0 μm. The Dv50 of the carbon black is regulated within the range, so that the carbon black with high specific surface area is obtained, and the liquid retention capacity of the functional layer to the electrolyte is improved.

In the present application, dv50 means that the particles reach a particle size of 50% by volume accumulation from the small particle size side in the particle size distribution on a volume basis.

In some embodiments of the application, the functional layer has a thickness of 0.8 μm to 1.2 μm, for example, the functional layer has a thickness of 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, or 1.2 μm. Through regulating and controlling the thickness of the functional layer within the range, the adhesive property between the positive current collector and the positive active material layer can be improved while the infiltration effect of the electrolyte on the positive electrode plate is improved.

In some embodiments of the present application, at least one of Ethylene Carbonate (EC), propylene Carbonate (PC), diethyl carbonate (DEC), ethyl Propionate (EP), propyl Propionate (PP), ethyl Methyl Carbonate (EMC), and dimethyl carbonate (DMC) may be further included in the electrolyte of the present application.

The preparation process of the electrolyte is not particularly limited, and for example, at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, methyl ethyl carbonate and dimethyl carbonate may be mixed according to a certain mass ratio or volume ratio to obtain a nonaqueous organic solvent, then an additive is added, and then lithium salt is added for dissolution and uniform mixing.

The concentration of LiPF ₆ in the electrolyte is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the concentration of LiPF ₆ in the electrolyte is 7.5wt% to 25wt%, in other embodiments, the concentration of LiPF ₆ in the electrolyte is 10wt% to 15wt%, e.g., the concentration of LiPF ₆ is 7.5wt%, 10wt%, 12wt%, 12.5wt%, 13wt%, 15wt%, 20wt%, or 25wt%.

The positive electrode active material layer of the present application may be single-layer coated or double-layer coated, that is, one surface of the positive electrode current collector has the positive electrode active material layer, or both surfaces of the positive electrode current collector have the positive electrode active material layer. The present application is not particularly limited as long as the object of the present application can be achieved, and may include, for example, but not limited to, aluminum foil, aluminum alloy foil, composite current collector, or the like. In the present application, the thickness of the positive electrode current collector is not particularly limited as long as the object of the present application can be achieved, for example, the thickness is 8 μm to 13 μm. The positive electrode active material layer of the present application may have a single-sided thickness of 100 μm to 200 μm.

In the present application, the positive electrode active material layer includes a positive electrode active material, and the present application is not particularly limited as long as the object of the present application can be achieved, and may include, for example, at least one of lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide, lithium manganate, and lithium manganese iron phosphate.

In the present application, the positive electrode active material layer may further include a positive electrode binder, which is not particularly limited as long as the object of the present application can be achieved, and may include, for example, at least one of a fluorine-containing resin, a polypropylene resin, a fibrous binder, a rubber-type binder, or a polyimide-type binder.

The negative electrode tab is not particularly limited as long as the object of the present application can be achieved, for example, the negative electrode tab generally includes a negative electrode current collector and a negative electrode active material layer. The anode active material layer may be provided on one surface or both surfaces in the thickness direction of the anode current collector. In the application, the anode active material layer is arranged on the surface of the anode current collector, namely, the anode active material layer can be arranged in a partial area of one surface of the anode current collector or can be arranged in all areas of one surface of the anode current collector. The negative electrode current collector is not particularly limited as long as the object of the present application can be achieved, and may include, for example, but not limited to, copper foil, copper alloy foil, nickel foil, composite current collector, or the like. In the present application, the thickness of the negative electrode current collector is not particularly limited as long as the object of the present application can be achieved, for example, the thickness is 4 μm to 12 μm. The negative electrode active material layer of the present application may have a thickness of 70 μm to 200 μm on one side.

In the present application, the anode active material layer includes an anode active material, wherein the anode active material is not particularly limited as long as the object of the present application can be achieved, and for example, may include at least one of artificial graphite, natural graphite, mesophase carbon microspheres, silicon, and silicon carbon.

In the present application, the anode active material layer may further include an anode binder therein. The negative electrode binder of the present application is not particularly limited as long as the object of the present application can be achieved, and may include at least one of acrylic acid ester, polyamide, polyimide, polyamideimide, polyvinylidene fluoride (PVDF), styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, and sodium carboxymethyl cellulose, for example.

The secondary battery also comprises a diaphragm, and the diaphragm is positioned between the positive pole piece and the negative pole piece to play a role in isolation.

The separator is not particularly limited in the present application, and those skilled in the art can select according to actual needs as long as the object of the present application can be achieved. For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer is at least one selected from polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric or a polypropylene-polyethylene-polypropylene porous composite membrane can be selected.

The secondary battery of the present application further includes a case, and the present application is not particularly limited to the case, and may be selected according to actual needs by those skilled in the art as long as the object of the present application can be achieved. For example, the housing may comprise an aluminium plastic film.

The method of manufacturing the secondary battery according to the present application is not particularly limited, and a manufacturing method known in the art may be selected as long as the object of the present application can be achieved. For example, the method of manufacturing the secondary battery includes, but is not limited to, the steps of: and stacking the positive electrode plate, the diaphragm and the negative electrode plate in sequence, winding and folding the positive electrode plate, the diaphragm and the negative electrode plate according to the need to obtain a bare cell with a winding structure, placing the bare cell into a packaging bag, injecting electrolyte into the packaging bag, and sealing to obtain the secondary battery.

The application also provides a battery pack comprising a case and at least one secondary battery in any of the above embodiments, the secondary battery being housed in the case. The battery pack with the two batteries has excellent performance and is beneficial to the use of the battery pack. The battery is accommodated in the box body, so that the fixing and protecting effects on the battery can be improved, and the service life of the battery pack is prolonged. It is understood that the battery pack may have one or more secondary batteries therein, and when the battery pack includes a plurality of secondary batteries, the plurality of secondary batteries may be connected in at least one of parallel and series.

The application also provides electric equipment, which comprises the secondary battery or the battery pack in any embodiment, and is beneficial to improving the product competitiveness and the service performance of the electric equipment. In an alternative embodiment, the powered device includes a powered device body, and the secondary battery or battery pack is used to power the powered device body. In an alternative embodiment, the powered device body includes a device anode and a device cathode, the positive electrode piece of the secondary battery or the battery pack is used for electrically connecting the device anode of the powered device body, and the negative electrode piece of the secondary battery or the battery pack is used for electrically connecting the device cathode of the powered device body to supply power to the powered device.

The powered device of the present application may include, but is not limited to: containers, household energy storage systems, battery cars, electric cars, ships, spacecraft, electric toys, electric tools, and the like, wherein spacecraft is, for example, an airplane, rocket, space shuttle, space spacecraft, and the like, electric toys include, for example, fixed or mobile electric toys, specifically, for example, electric car toys, electric ship toys, and electric airplane toys, and the like, and electric tools include, for example, metal cutting electric tools, grinding electric tools, assembling electric tools, and railway electric tools, specifically, for example, electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact electric drills, concrete vibrators, and electric planers.

Referring to fig. 2, fig. 2 is a schematic structural diagram of a household energy storage system according to an embodiment of the present application, and the embodiment of fig. 2 of the present application is illustrated by taking a household energy storage scenario in a user side energy storage as an example, and the energy storage device of the present application is not limited to the household energy storage scenario.

The application provides a household energy storage system, which comprises an electric energy conversion device 2 (photovoltaic panel), a first user load 3 (street lamp), a second user load 4 (such as household appliances like an air conditioner) and the like, and an energy storage device 1, wherein the energy storage device 1 is a small energy storage box and can be installed on an outdoor wall in a wall-hanging mode. In particular, the photovoltaic panel may convert solar energy into electrical energy during low electricity prices, and the energy storage device 1 is used to store the electrical energy and supply the electrical energy to street lamps and household appliances for use during peak electricity prices, or to supply power during power outage/outage of the power grid.

Referring to fig. 3, fig. 3 is a schematic structural diagram of an energy storage system 400 according to an embodiment of the present application, and the embodiment of fig. 3 of the present application is illustrated by taking a power generation/distribution side shared energy storage scenario as an example, and the energy storage device 1 of the present application is not limited to the power generation/distribution side energy storage scenario.

The present application provides an energy storage system 400, the energy storage system 400 comprising: the high-voltage cable 410, the first electric energy conversion device 420, the second electric energy conversion device 430 and the energy storage device 1 provided by the application, under the power generation condition, the first electric energy conversion device 420 and the second electric energy conversion device 430 are used for converting other forms of energy into electric energy, are connected with the high-voltage cable 410 and are supplied to the power distribution network power utilization side for use, and when the power load is lower, the first electric energy conversion device 420 and the second electric energy conversion device 430 store multiple generated electric energy into the energy storage device 1 when the power generation is excessive, so that the wind abandon and the light abandon rate are reduced, and the problem of new energy power generation and consumption is improved; when the power consumption load is high, the power grid gives an instruction, the electric quantity stored by the energy storage device 1 is cooperated with the high-voltage cable 410 to transmit electric energy to the power consumption side for use in a grid-connected mode, so that various services such as peak regulation, frequency modulation and standby are provided for the operation of the power grid, the peak regulation effect of the power grid is fully exerted, peak clipping and valley filling of the power grid are promoted, and the power supply pressure of the power grid is relieved.

Alternatively, the first and second power conversion devices 420 and 430 may convert at least one of solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy, mechanical energy, and the like into electric energy.

The number of the energy storage devices 1 may be plural, and the plurality of energy storage devices 1 may be connected in series or in parallel, and the plurality of energy storage devices 1 may be supported and electrically connected by using a separator (not shown). In the present embodiment, "a plurality of" means two or more. The energy storage device 1 may be further provided with an energy storage box for accommodating the energy storage device 1.

Alternatively, the energy storage device 1 may include, but is not limited to, a battery cell, a battery module, a battery pack, a battery system, and the like. The practical application form of the energy storage device 1 provided in the embodiment of the present application may be, but not limited to, the listed products, and may also be other application forms, and the embodiment of the present application does not strictly limit the application form of the energy storage device 1. The embodiment of the present application will be described by taking the energy storage device 1 as a multi-core battery as an example. When the energy storage device 1 is a single battery, the energy storage device 1 may be at least one of a cylindrical battery, a prismatic battery, and the like.

Examples

Hereinafter, embodiments of the present application will be described in more detail with reference to preparation examples, examples and comparative examples. The various tests and evaluations were carried out according to the following methods.

Example 1-1

< Preparation of Positive electrode sheet >

< Preparation of functional layer >

Mixing carbon black (Dv 50 is 1.0 μm) and polyacrylate according to a mass ratio of 1:3; adding deionized water as a solvent, preparing into a functional layer slurry with the solid content of 40wt%, uniformly stirring, uniformly coating the functional layer slurry on one surface of an anode current collector aluminum foil with the thickness of 10 mu m, and drying to obtain a functional layer with the thickness of 1.0 mu m;

< preparation of positive electrode active Material layer >

Mixing positive active materials of lithium iron phosphate (LiFePO ₄), conductive carbon black (Super-P) and a binder PVDF according to the mass ratio of 94:3:3; then adding N-methyl pyrrolidone (NMP) as a solvent, preparing positive electrode slurry with the solid content of 60wt%, uniformly stirring, uniformly coating the positive electrode slurry on the surface of the prepared functional layer, and drying, cold pressing, stripping and cutting to obtain the positive electrode plate. The positive electrode active material layer had a single-sided thickness of 100. Mu.m, and a compact density of 2.4g/cm ³.

< Preparation of negative electrode sheet >

Mixing negative electrode active material artificial graphite, thickener sodium carboxymethylcellulose (CMC), conductive carbon black (Super-P) and binder Styrene Butadiene Rubber (SBR) according to a mass ratio of 96:2:1:1, adding deionized water, preparing into negative electrode slurry with a solid content of 50wt%, and uniformly stirring. And uniformly coating the negative electrode slurry on one surface of a negative electrode current collector copper foil with the thickness of 6 mu m, and drying, cold pressing, slitting and cutting to obtain a negative electrode plate. The negative electrode active material layer had a thickness of 70 μm on one side and a compacted density of 1.4g/cm ³.

< Preparation of electrolyte >

In an argon atmosphere glove box with the moisture content less than or equal to 1ppm, mixing Ethylene Carbonate (EC), dimethyl carbonate (DMC) and methyl ethyl carbonate (EMC) according to the mass ratio of 1:1:1, then adding lithium salt LiPF ₆, dissolving in the solvent, adding 3-sulfolane and lithium difluorooxalato borate, and uniformly mixing to obtain the electrolyte. Wherein the addition amounts of 3-sulfolane and lithium difluorooxalato borate are shown in Table 1, and the concentration of LiPF ₆ in the electrolyte was 12.5wt%.

< Preparation of separator >

A polypropylene (PP) porous polymer film having a thickness of 16 μm was used as a separator.

< Preparation of lithium ion Battery >

And sequentially stacking the prepared positive electrode plate, the diaphragm and the negative electrode plate, so that the diaphragm is positioned between the positive electrode and the negative electrode to play a role in isolation, and winding to obtain the bare cell. And placing the bare cell in an aluminum plastic film packaging bag, vacuum drying, injecting electrolyte, and performing vacuum packaging, standing, formation and other procedures to obtain the lithium ion battery.

Examples 1 to 2 to 1 to 7

The procedure of example 1-1 was repeated except that the amounts of 3-sulfolane and lithium difluorooxalato borate added were adjusted in accordance with Table 1 in the < preparation of electrolyte >.

Example 2-1

The procedure of examples 1-3 was repeated except that 1,3, 5-trifluorobenzene was further added to the electrolyte. The specific preparation process of the electrolyte is as follows:

< preparation of electrolyte >

In an argon atmosphere glove box with the moisture content less than or equal to 1ppm, mixing Ethylene Carbonate (EC), dimethyl carbonate (DMC) and methyl ethyl carbonate (EMC) according to the mass ratio of 1:1:1, then adding lithium salt LiPF ₆, dissolving in the solvent, adding 3-sulfolane, lithium difluoro oxalato borate and 1,3, 5-trifluoro benzene, and uniformly mixing to obtain the electrolyte. Wherein the addition amounts of 3-sulfolane, lithium difluorooxalato borate and 1,3, 5-trifluorobenzene are shown in Table 2, and the concentration of LiPF ₆ in the electrolyte was 12.5wt%.

Examples 2 to 7

The procedure of example 2-1 was repeated except that the amount of 1,3, 5-trifluorobenzene to be added was adjusted in accordance with Table 2 in < preparation of electrolyte >.

Examples 3-1 to 3-4

The procedure of examples 2 to 3 was repeated except that the Dv50 of the carbon black and the thickness of the functional layer were controlled in accordance with table 3 in < preparation of positive electrode sheet >.

Comparative example 1

The procedure of examples 1 to 3 was repeated except that the functional layer was not formed in the positive electrode sheet. The preparation process of the positive electrode plate comprises the following steps:

< preparation of Positive electrode sheet >

Mixing anode active material LiFePO ₄, conductive carbon black (Super-P) and binder PVDF according to the mass ratio of 94:3:3; then adding N-methyl pyrrolidone (NMP) as a solvent, preparing positive electrode slurry with the solid content of 60wt%, uniformly stirring, uniformly coating the positive electrode slurry on one surface of a positive electrode current collector aluminum foil with the thickness of 10 mu m, and then drying, cold pressing, slitting and cutting to obtain a positive electrode plate. The thickness of one side of the positive electrode active material layer was 100. Mu.m.

Comparative examples 2 to 5

Comparative example 6

The procedure of example 2-1 was repeated except that the functional layer was not formed in the positive electrode sheet.

The preparation process of the positive electrode plate comprises the following steps:

< preparation of Positive electrode sheet >

TABLE 1 preparation parameters of examples 1-1 to 1-7 and comparative examples 1 to 5

TABLE 2 preparation parameters of examples 1-3, examples 2-1 to examples 2-7, comparative example 6

In table 2, "/" indicates that no relevant preparation parameters are present.

TABLE 3 preparation parameters for examples 3-1 to 3-4

	Carbon black Dv50 (μm)	Functional layer thickness (mum)
			Examples 2 to 3	1.0	1.0
Example 3-1	0.2	1.0
			Example 3-2	0.8	1.0
Examples 3 to 3	1.4	0.8
			Examples 3 to 4	2.0	1.2

Test method and apparatus:

Particle size testing:

The average particle diameter Dv50 of the carbon black material was measured using a laser particle size analyzer.

And (3) testing the cycle performance:

the lithium ion batteries prepared in each example and comparative example were charged to 3.65V at a constant current of 0.5 rate (C) at a test temperature of 25 ℃, charged to 0.05C at a constant voltage, and discharged to 2.5V at 0.5C after standing for 10 minutes (min). With the capacity obtained in this step as the initial discharge capacity C ₀, a cycle test of 0.5C charge/0.5C discharge was performed 1000 times (cycles), and the discharge capacity at the 1000 th cycle was recorded. Cycle capacity retention= (discharge capacity of 1000 th cycle/initial discharge capacity C ₀) ×100%.

Direct current impedance (DCR) test:

The lithium ion batteries prepared in each example and comparative example were placed in an environment of 25 ℃ and discharged to a voltage of 2.5V at a constant current of 0.5C, left for 5min, then charged to a voltage of 3.65V at a constant current of 0.5C, and charged to a current of 0.025C at a constant voltage. Standing for 5min, discharging to 2.5V at 0.1C constant current, charging to 3.65V at 0.5C constant current, and charging to 0.025C constant voltage, wherein the state of charge (SOC) of the lithium ion battery is 100%; after standing for 5min, the lithium ion battery was discharged for 5 hours (h) with a constant current of 0.1C, and the voltage V ₁ at this time was recorded, and the SOC of the lithium ion battery was 50%. Then, the current was discharged for 1 second(s) with a constant current of 1C, and the voltage V ₂ at this time was recorded. The 50% soc DCR of the lithium ion battery is: (V ₁-V₂)/I, i=1c.

Table 4 Performance parameters of examples 1-1 to 1-7 and comparative examples 1 to 5

	DCR(mΩ)	Capacity retention after 500 cycles
			Example 1-1	31.1	95.1％
Examples 1 to 2	28.8	95.6％
			Examples 1 to 3	27.2	96.2％
Examples 1 to 4	27.7	95.9％
			Examples 1 to 5	29.5	95.7％
Examples 1 to 6	29	95.4％
			Examples 1 to 7	29.3	95.1％
Comparative example 1	32.3	94.8％
			Comparative example 2	32.7	94.3％
Comparative example 3	32.5	94.2％
			Comparative example 4	31.6	93.9％
Comparative example 5	32.3	93.6％

As can be seen from examples 1-1 to 1-7 and comparative example 1 in combination with table 4, DCR of comparative example 1 is higher and capacity retention rate is lower, which is probably because the positive electrode sheet of comparative example 1 does not contain a functional layer, and thus it is difficult to improve the liquid retention capacity of the electrolyte; the DCR of the lithium ion battery is obviously reduced, and the capacity retention rate is obviously improved, which is probably because the DCR of the lithium ion battery is reduced and the cycle performance of the lithium ion battery is improved by arranging the functional layer containing carbon black on the surface of the positive electrode current collector and making the SEI film have high stability and low impedance characteristics under the combined action of 3-cyclobutene sulfone and lithium difluorooxalate borate.

As can be seen from examples 1-1 to 1-7 and comparative examples 2 to 5, when the 3-cyclobutene sulfone content is too high (e.g., comparative example 2), the DCR of the lithium ion battery is high and the capacity retention rate is low, which may be due to the fact that the 3-cyclobutene sulfone content is too high, the impedance of the SEI film is greatly increased and the cycle performance of the lithium ion battery is also affected; when the content of LiODFB is too high (e.g., comparative example 3), DCR of the lithium ion battery is high and the capacity retention rate is low, which may be due to the fact that the content of LiODFB is too high to form a film in a large amount and rapidly, resulting in a large increase in the resistance of the SEI film; when the 3-sulfolane content is too low (e.g., comparative example 4), the cycle performance of the lithium ion battery is low, probably because the 3-sulfolane content is too low to form enough lithium alkylsulfonate, and it is difficult to improve the stability of the SEI film; when the content of LiODFB is too low (e.g., comparative example 5), the cycle performance of the lithium ion battery is also low, which may be because the too low content of LiODFB is insufficient to form a stable SEI inner film containing fluorine and boron elements, and insufficient to complex PF ₅ generated in the electrolyte, and thus the film forming stability and resistance to attack by hydrofluoric acid of the SEI film are reduced. According to the application, the contents of 3-sulfolane and LiODFB are regulated and controlled within the range of the application, under the combined action of the two, the stability of the SEI film is improved, and the wettability of electrolyte to the positive electrode plate is also improved, so that the lithium ion battery has low impedance characteristics and excellent cycle performance, and is more suitable for an energy storage device with high requirement on the long-term cycle performance of the lithium ion battery, and the operation cost of the energy storage device is reduced.

It can also be seen from examples 1 and comparative examples 4 to 5 that when b/a is too small or too large, improvement of capacity retention rate of the lithium ion battery is not favored, which may be because, when b/a is too large (e.g., comparative example 4), it is difficult for less 3-cyclobutene sulfone to sufficiently promote complexation of LiODFB to PF ₅, to exert synergistic effect of both, and at the same time, lithium alkylsulfonate at the outer layer of the SEI film is less, which is not favored for improvement of stability of the SEI film; when b/a is too small (e.g., comparative example 5), although 3-sulfolane can promote the contact of LiODFB with PF ₅ to some extent, less LiODFB results in lower SEI inner layer film stability; the application can exert the synergistic effect of LiODFB and 3-cyclobutene sulfone by regulating and controlling b/a in the range of the application, thereby improving the cycle performance of the lithium ion battery.

It can also be seen from examples 1-1 and 1-2 to 1-7 that by controlling the mass ratio of lithium difluorooxalato borate to lithium hexafluorophosphate within the scope of the present application, a lithium ion battery having low impedance characteristics and further improved cycle performance can be advantageously obtained.

TABLE 5 Performance parameters for examples 1-3, examples 2-1 through examples 2-7, comparative example 6

As can be seen from examples 2-1 to 2-7 and examples 1-3 in combination with table 5, the cycle performance of the lithium ion battery was further improved and DCR overall tended to decrease by further adding 1,3, 5-trifluorobenzene to the electrolyte.

It can be seen from examples 2-1 to 2-5 and examples 2-6 to 2-7 that in the case that 1,3, 5-trifluorobenzene is contained in the electrolyte, DCR of the lithium ion battery is further reduced and the capacity retention rate is further improved by further controlling the content of 1,3, 5-trifluorobenzene within the range of the present application, so that the lithium ion battery of the present application has low impedance characteristics and excellent cycle performance, and is thus more suitable for use in energy storage devices requiring high long-term cycle performance of the lithium ion battery, thereby reducing the running cost of the energy storage device.

As can be seen from examples 2-1 and comparative example 6, in the case of containing 1,3, 5-trifluorobenzene in the electrolyte, when the carbon black-containing functional layer is present in the positive electrode sheet, the cycle performance of the lithium ion battery is significantly improved and the DCR is also somewhat reduced.

TABLE 6 Performance parameters for examples 3-1 to 3-4

	DCR(mΩ)	Capacity retention after 500 cycles
			Examples 2 to 3	24.5	98.3％
Example 3-1	23.7	97.9％
			Example 3-2	24.3	98.1％
Examples 3 to 3	24.9	98.0％
			Examples 3 to 4	25.3	97.7％

The Dv50 of the carbon black, the thickness of the functional layer, also generally have an effect on the performance of the lithium ion battery. It can be seen from examples 2-3 and 3-1 to 3-4 that the control of Dv50 of carbon black and the thickness of the functional layer within the range of the present application is advantageous for obtaining lithium ion batteries having low impedance characteristics and high cycle performance.

The secondary battery, the battery pack and the electric equipment disclosed by the application are described in detail, and specific examples are applied to explain the principle and the implementation mode of the application, and the description of the above examples is only used for helping to understand the technical scheme and the core application point of the embodiment of the application: meanwhile, as those skilled in the art will vary in the specific embodiments and application scope according to the idea of the present application, the present disclosure should not be construed as limiting the present application in summary.

Claims

1. A secondary battery is characterized by comprising a positive electrode plate, a negative electrode plate and electrolyte, wherein,

The electrolyte comprises 3-sulfolane and lithium difluoro-oxalato-borate, wherein the mass percentage of the 3-sulfolane is a, the mass percentage of the lithium difluoro-oxalato-borate is b, the mass percentage of the lithium difluoro-oxalato-borate is more than or equal to 0.1% and less than or equal to 2%, and the mass percentage of the lithium difluoro-oxalato-borate is more than or equal to 0.1% and less than or equal to 2%;

the positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode active material layer is arranged on the positive electrode current collector, a functional layer is arranged between the positive electrode current collector and the positive electrode active material layer, and the functional layer contains carbon black.

2. The secondary battery according to claim 1, wherein 0.5% or less a or less than 1.5% and 0.5% or less b or less than 1.5%.

3. The secondary battery according to claim 1, wherein the conditions between a and b are: b/a is more than or equal to 0.5 and less than or equal to 2.

4. The secondary battery according to claim 1, wherein the electrolyte further comprises 1,3, 5-trifluorobenzene, and the content of 1,3, 5-trifluorobenzene is c,0.1% c.ltoreq.2% based on the mass of the electrolyte.

5. The secondary battery according to claim 4, wherein 0.5% or less c or less 1.5% or less.

6. The secondary battery according to any one of claims 1 to 5, wherein the electrolyte further comprises lithium hexafluorophosphate, and a mass ratio of the lithium difluorooxalato borate to the lithium hexafluorophosphate is 0.04 to 0.16:1.

7. The secondary battery according to any one of claims 1 to 5, wherein the Dv50 of the carbon black is 0.2 μm to 2.0 μm.

8. The secondary battery according to any one of claims 1 to 5, wherein the functional layer has a thickness of 0.8 μm to 1.2 μm.

9. A battery pack comprising a case and at least one secondary battery according to any one of claims 1 to 8, the secondary battery being housed in the case.

10. A powered device comprising the secondary battery according to any one of claims 1 to 8, or comprising the battery pack according to claim 9.