Secondary battery, battery module, battery pack, and power consumption device

Abstract

The present invention provides a secondary battery (5), a battery module (4), a battery pack (1), and a power consuming device. The secondary battery (5) includes an electrode assembly (52) and an electrolyte for infiltrating the electrode assembly (52), the electrode assembly (52) includes a negative electrode plate, a separator, and a positive electrode plate, the negative electrode plate includes a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector, and the bending degree of the negative electrode plate is τ, where τ is a bending degree of the negative electrode plate, and τ=0.5(ε) -α Formula I where ε is the porosity of the negative electrode material layer, α is the Bruggeman index of the negative electrode material, and τ and the conductivity of the electrolyte σ are (2τ) 0.5 +6≦σ≦(2τ) 0.5 +10 Formula II Meet the following. In this way, the secondary battery (5) has excellent rapid charging performance.

Description

Technical Field

[0001] The present application relates to the field of batteries, and particularly to secondary batteries, battery modules, battery packs, and power-consuming devices.

Background Art

[0002] Secondary batteries are widely applied because they have advantages such as reliable operating performance, no pollution, and no memory effect. For example, as environmental protection issues are being increasingly emphasized, new energy vehicles are becoming more and more popular, and the demand for power-type secondary batteries will increase explosively. However, as the application range of secondary batteries is becoming wider and wider, the performance of secondary batteries is also facing severe challenges.

[0003] As the pace of life speeds up, people strongly require the cycle life of secondary batteries, and rapid charging performance has also become an issue that people must consider.

Summary of the Invention

Problems to be Solved by the Invention

[0004] In view of the above problems, the present application is made, and an object thereof is to provide a secondary battery, a battery module, a battery pack, and a power-consuming device having excellent rapid charging performance.

Means for Solving the Problems

[0005] To achieve the above object, a first aspect of the present application is a secondary battery including an electrode assembly and an electrolytic solution for infiltrating the electrode assembly, wherein the electrode assembly includes a negative electrode plate, a separator, and a positive electrode plate, the negative electrode plate includes a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector, and if the degree of bending of the negative electrode plate is τ, then τ is τ = 0.5(ε) -α Formula I satisfies, ε is the porosity of the negative electrode material layer, α is the Bruggeman index of the negative electrode material, the τ and the conductivity σ of the electrolytic solution are (2τ) 0.5 +6≦σ≦(2τ) 0.5 +10 Formula II To provide a secondary battery that satisfies the following.

[0006] When the degree of bending τ of the negative electrode plate and the conductivity σ of the electrolytic solution satisfy the above relationship, the secondary battery can obtain excellent rapid charging characteristics and suppress lithium precipitation on the negative electrode.

[0007] In some embodiments, τ satisfies 2.3≦τ≦7. By setting the degree of bending τ within the above range, the kinetic performance of the negative electrode material can be enhanced, and furthermore, the rapid charging characteristics of the secondary battery can be enhanced.

[0008] In some embodiments, the range of σ is 8 mS / cm to 14 mS / cm. By setting the conductivity σ of the electrolytic solution within the above range, the kinetic performance of the electrolytic solution can be enhanced, and furthermore, the rapid charging characteristics of the secondary battery can be enhanced.

[0009] In some embodiments, the porosity ε of the negative electrode material layer is 25% to 45%. By setting the porosity of the negative electrode material layer within this range, the kinetic performance of the negative electrode material can be enhanced, and furthermore, the rapid charging characteristics of the secondary battery can be enhanced.

[0010] In some embodiments, the negative electrode material is graphite and α is 1.5 to 2.2. Thereby, the degree of bending of the negative electrode plate can be calculated more accurately.

[0011] In some embodiments, the electrolytic solution contains at least one of cyclic ester, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, methyl acetate, methyl formate, ethyl formate, methyl propionate, propyl formate, ethyl propionate, and propyl acetate, and the cyclic ester contains at least one of ethylene carbonate and propylene carbonate. Thereby, the conductivity of the electrolytic solution can be easily adjusted.

[0012] In some embodiments, the lithium salt of the electrolytic solution includes at least one of lithium hexafluorophosphate (LiPF6) and fluorine-containing lithium sulfonyl imide, and the concentration of the lithium salt is 0.5 to 1.5 mol / L. Thereby, the conductivity of the electrolytic solution can be further increased, and lithium precipitation on the negative electrode can be suppressed.

[0013] In some embodiments, the fluorine-containing lithium sulfonyl imide includes at least one of lithium bis(fluorosulfonyl)imide, lithium fluoro(trifluoromethylsulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, and lithium fluoro(perfluorobutylsulfonyl)imide, and preferably lithium bis(fluorosulfonyl)imide. Thereby, the conductivity of the electrolytic solution can be further increased, and lithium precipitation on the negative electrode can be suppressed.

[0014] In some embodiments, in the negative electrode plate, the thickness of the negative electrode material layer is 30 μm to 400 μm. Thereby, the coating amount of the negative electrode active material can be increased, and the energy density of the secondary battery can be further increased.

[0015] The second aspect of the present application provides a battery module including the secondary battery described in the first aspect of the present application.

[0016] The third aspect of the present application provides a battery pack including the battery module described in the second aspect of the present application.

[0017] The fourth aspect of the present application provides a power consumption device including at least one of the secondary battery described in the first aspect of the present application, the battery module described in the second aspect of the present application, and the battery pack described in the third aspect of the present application.

Advantages of the Invention

[0018] According to the present application, the rapid charging ability of the secondary battery can be enhanced, and lithium precipitation on the negative electrode can be suppressed.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments specifically disclosing the positive electrode active material of the present application, its manufacturing method, the positive electrode plate, the secondary battery, the battery module, the battery pack, and the electric device will be described in detail with appropriate reference to the drawings. Unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and duplicate descriptions of substantially the same structure may be omitted. This is to avoid making the following description unnecessarily redundant and to enable those skilled in the art to easily understand. Also, 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 gist described in the claims.

[0021] The "range" disclosed in this application is limited in the form of a lower limit and an upper limit. A predetermined range is limited by selecting one lower limit and one upper limit, and the boundary of the predetermined range is limited by the selected lower limit and upper limit. The range limited in this way may or may not include both end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form one range. For example, when ranges of 60-120 and 80-110 are listed for a certain parameter, ranges of 60-110 and 80-120 are also understood to be expected. Also, when the minimum range values are listed as 1 and 2, and the maximum range values are listed as 3, 4, and 5, ranges of 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 are all predictable. In this application, unless otherwise explained, the numerical range "a~b" represents an abbreviated expression of any combination of real numbers between a and b, and both 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 specification, and "0~5" is simply an abbreviated expression of the combination of these numerical values. Note that when it is described that a certain parameter is an integer ≧2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0022] Unless otherwise specified, all embodiments and alternative embodiments of this application can be combined with each other to form new technical solutions.

[0023] Unless otherwise specified, all technical features and alternative technical features of this application can be combined with each other to form new technical solutions.

[0024] Unless otherwise specified, the "including" and "comprising" mentioned in this application represent an open-ended form and may also be in a closed-ended form. For example, the above "including" and "comprising" can represent that other components not listed may be further included or comprised, or only the listed components may be included or comprised.

[0025] Unless otherwise specified, the term "or" in this application is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any one of the conditions that A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), or both A and B are true (or exist) satisfies the condition "A or B".

[0026] In one embodiment of this application, this application is a secondary battery including an electrode assembly and an electrolytic solution for infiltrating the electrode assembly. The electrode assembly includes a negative electrode plate, a separator, and a positive electrode plate. The negative electrode plate includes a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector. If the degree of bending of the negative electrode plate is τ, then τ is τ = 0.5(ε) -α Formula I satisfies, where ε is the porosity of the negative electrode material layer and α is the Bruggeman exponent of the negative electrode material, the τ and the conductivity σ of the electrolytic solution are (2τ) 0.5 + 6 ≤ σ ≤ (2τ) 0.5 + 10 Formula II and proposes a secondary battery that satisfies this condition.

[0027] Although the mechanism is not yet clear, the inventors of this application have processed a large amount of experimental data and unexpectedly found that when the degree of bending τ of the negative electrode plate and the conductivity σ of the electrolytic solution satisfy the above relationship, the secondary battery can obtain excellent rapid charging characteristics.

[0028] The inventor of the present application presumes that there are two factors that limit the rapid charging ability of secondary batteries: 1) the kinetic performance of lithium ions in the negative electrode, and 2) the liquid-phase diffusion ability of lithium ions in the electrolyte. When the performance of both does not match, for example, when the liquid-phase transfer of lithium ions is fast but the kinetic performance of the negative electrode material is poor, the lithium ions that have moved to the negative electrode surface cannot diffuse into the negative electrode in a timely manner, and the lithium ions are directly reduced to metallic lithium on the anode surface, that is, "lithium precipitation on the anode" occurs, bringing safety risks. When the kinetic performance of the negative electrode material is good, but the liquid-phase diffusion ability of lithium ions in the electrolyte is weak, the lithium ions detached from the positive electrode cannot reach the negative electrode in a timely manner, resulting in a decrease in the charging capacity of the secondary battery. Therefore, good rapid charging performance can be obtained only when the kinetic performances of the negative electrode material and the electrolyte match.

[0029] Here, as shown in FIG. 1, the degree of bending τ of the electrode plate represents the ratio of the migration path ΔL of lithium ions in the electrode plate to the thickness Δx of the electrode plate. The degree of bending τ and the porosity ε of the electrode plate are closely related. For different negative electrode materials, 0.5(ε) -α can be adopted to estimate the degree of bending τ.

[0030] The Bruggeman index α can be obtained by performing calculations on the SEM photographs of the negative electrode material layer using Wolfram Mathmatica software. Hereinafter, the calculation method of the Bruggeman index α will be described with reference to FIGS. 2 and 3.

[0031] First, SEM photographs of the upper surface and cross-section of the negative electrode material layer of the manufactured negative electrode plate are obtained. FIG. 2 is an example of the upper surface SEM photograph of the negative electrode material layer. FIG. 3 is an example of the cross-section SEM photograph of the negative electrode material layer.

[0032] Next, using Wolfram Mathmatica software, in the SEM photographs of the upper surface and cross-section of the negative electrode material layer, the major axes and minor axes of 50 to 90 active particles are manually marked, and the outer contour of each active particle is fitted.

[0033] Finally, using Wolfram Mathmatica software, based on the top view and cross-sectional SEM images of the negative electrode material layer with the outer contour of the active particles obtained above marked, the Bruggeman exponent α in the planar direction of the negative electrode material layer x , α y and the Bruggeman exponent α in the normal direction (cross-sectional direction) z are calculated. The α in the above formula (ε) -α is the Bruggeman exponent α in the normal direction (cross-sectional direction) here z .

[0034] Also, a porosity test is performed on the electrode plate manufactured above, and the test method for the porosity of the electrode plate is carried out with reference to GB / T 24586-2009.

[0035] In some embodiments, the bendability τ of the negative electrode plate and the conductivity σ of the electrolyte further satisfy (2τ) 0.5 +6≦σ≦(2τ) 0.5 +8. Thereby, the kinetic performance of the negative electrode material and the electrolyte can be further matched, and better rapid charging performance can be obtained.

[0036] In some embodiments, the τ satisfies 2.3≦τ≦7. By setting the bendability τ within the above range, the kinetic performance of the negative electrode material is enhanced, and the rapid charging characteristics of the secondary battery are further enhanced.

[0037] In some embodiments, the range of the σ is 8 mS / cm~14 mS / cm. By setting the conductivity σ of the electrolyte within the above range, the kinetic performance of the electrolyte can be enhanced, and the rapid charging characteristics of the secondary battery can be further enhanced.

[0038] In some embodiments, the porosity ε of the negative electrode material layer is 25%~45%. By setting the porosity of the negative electrode material layer within this range, the kinetic performance of the negative electrode material can be enhanced, and the rapid charging characteristics of the secondary battery can be further enhanced.

[0039] In some embodiments, the negative electrode material of the negative electrode plate is graphite, and α is 1.5 to 2.2. Thereby, the degree of bending of the negative electrode plate can be more accurately estimated. It should be noted that the negative electrode material is not limited to graphite and may be other commonly used negative electrode materials. The Bruggeman index α is similarly applicable to negative electrode materials other than graphite.

[0040] In some embodiments, the electrolytic solution includes at least one of cyclic esters, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, methyl acetate, methyl formate, ethyl formate, methyl propionate, propyl formate, ethyl propionate, and propyl acetate, and the cyclic ester includes at least one of ethylene carbonate and propylene carbonate. Thereby, the conductivity of the electrolytic solution can be easily adjusted.

[0041] In some embodiments, the lithium salt of the electrolytic solution includes at least one of lithium hexafluorophosphate (LiPF6) and fluorine-containing lithium sulfonyl imide, and the concentration of the lithium salt is 0.5 to 1.5 mol / L. Thereby, the conductivity of the electrolytic solution can be further increased, and lithium precipitation on the negative electrode can be suppressed.

[0042] In some embodiments, the fluorine-containing lithium sulfonyl imide includes at least one of lithium bis(fluorosulfonyl)imide, lithium fluoro(trifluoromethylsulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, and lithium fluoro(perfluorobutylsulfonyl)imide, and preferably lithium bis(fluorosulfonyl)imide. Thereby, the conductivity of the electrolytic solution can be further increased, and lithium precipitation on the negative electrode can be suppressed.

[0043] In some embodiments, in the negative electrode plate, the coating thickness of the negative electrode material layer is 30 μm to 400 μm. Thereby, the coating amount of the negative electrode active material can be increased, and further the energy density of the secondary battery can be increased.

[0044] Next, the secondary battery, battery module, battery pack, and power consumption device of the present application will be described with appropriate reference to the drawings.

[0045] [Secondary battery] In one embodiment of the present application, a secondary battery is provided.

[0046] Normally, a secondary battery includes a negative electrode plate, a positive electrode plate, an electrolyte, and a separator. During the charge and discharge process of the battery, active ions are repeatedly inserted and desorbed between the positive electrode plate and the negative electrode plate. The electrolyte serves to conduct ions between the positive electrode plate and the negative electrode plate. The separator is provided between the positive electrode plate and the negative electrode plate, mainly serving to prevent short circuit between the positive and negative electrodes, and at the same time allowing ions to pass through.

[0047] [Positive electrode plate] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material according to the first aspect of the present application.

[0048] As an example, the positive electrode current collector has two surfaces facing each other in its own thickness direction, and the positive electrode film layer is provided on either one or both of the two facing surfaces of the positive electrode current collector.

[0049] In some embodiments, as the positive electrode current collector, a metal foil or a composite current collector can be employed. For example, as the metal foil, an aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer material base (such as a base of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0050] In some embodiments, as the positive electrode active material, a positive electrode active material for a battery known in the art can be employed. For example, the positive electrode active material can include at least one of materials such as lithium-containing phosphates having an olivine structure, lithium transition metal oxides, and modified compounds thereof. However, the present application is not limited to these materials, and other conventional materials used as the positive electrode active material of the battery may be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which may be abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which may be abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which may be abbreviated as NCM 211 ), LiNi 0.6 Co 0.2 Mn0.2 O2 (which may be abbreviated as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which may be abbreviated as NCM 811 ), lithium nickel cobalt aluminum oxide (for example, LiNi 0.85 Co 0.15 Al 0.05 O2) and at least one of its modified compounds, etc., but not limited thereto. Examples of olivine-structured lithium-containing phosphates include lithium iron phosphate (for example, LiFePO4 (which may be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (for example, LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and at least one of a composite material of lithium manganese iron phosphate and carbon, but not limited thereto.

[0051] In some embodiments, the positive electrode film layer optionally further includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of vinylidene fluoride, tetrafluoroethylene, and propylene, a terpolymer of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene, a copolymer of tetrafluoroethylene and hexafluoropropylene, and a fluorine-containing acrylate resin.

[0052] In some embodiments, the positive electrode film layer optionally further includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0053] In some embodiments, the positive electrode plate can be manufactured by the following method. Components for manufacturing the above-described positive electrode plate, such as a positive electrode active material, a conductive agent, a binder, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry. After the positive electrode slurry is applied to the positive electrode current collector and subjected to processes such as baking and cold pressing, a positive electrode plate can be obtained.

[0054] [Negative electrode plate] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, and the negative electrode film layer contains a negative electrode active material.

[0055] As an example, the negative electrode current collector has two surfaces facing each other in its own thickness direction, and the negative electrode film layer is provided on either one or both of the two facing surfaces of the negative electrode current collector.

[0056] In some embodiments, as the negative electrode current collector, a metal foil or a composite current collector can be employed. For example, as the metal foil, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer material base (such as a base of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0057] In some embodiments, as the negative electrode active material, a negative electrode active material for batteries known in the art can be adopted. By way of example, the negative electrode active material can include at least one of materials such as artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material can be selected from at least one of silicon alone, silicon oxygen compounds, silicon carbon composites, silicon nitrogen composites, and silicon alloys. The tin-based material can be selected from at least one of tin alone, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials used as the negative electrode active material of the battery may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0058] In some embodiments, the negative electrode film layer optionally further includes a binder. The binder can 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).

[0059] In some embodiments, the negative electrode film layer optionally further includes a conductive agent. The conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0060] In some embodiments, the negative electrode film layer optionally further includes other auxiliaries such as a thickening agent (for example, sodium carboxymethyl cellulose (CMC-Na)).

[0061] In some embodiments, the negative electrode plate can be manufactured by the following method. Components for manufacturing the above-described negative electrode plate, such as a negative electrode active material, a conductive agent, a binder, and any other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry. After applying the negative electrode slurry to a negative electrode current collector and undergoing processes such as baking and cold pressing, a negative electrode plate can be obtained.

[0062] [Separator] Regarding the above separator, there is no particular limitation in the present application, and any known separator having a porous structure with electrochemical stability and mechanical stability can be selected according to actual needs. For example, it may be a single-layer or multi-layer thin film containing one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride.

[0063] [Electrolyte] The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. In the present application, the type of the electrolyte is not specifically limited and can be selected according to needs. For example, the electrolyte may be in a liquid, gel state, or all-solid state.

[0064] In some embodiments, an electrolytic solution is employed as the electrolyte. The electrolytic solution contains an electrolyte salt, a solvent, and an additive.

[0065] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bisoxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0066] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4 - butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0067] In some embodiments, the electrolyte contains additives. The additives include fluoroethylene carbonate and / or vinylene carbonate, and may further include other additives such as negative electrode film - forming additives and positive electrode film - forming additives, and may also include additives that can improve specific battery performance such as additives for improving the over - charge performance of the battery, additives for improving the high - temperature performance or low - temperature performance of the battery.

[0068] In some embodiments, the positive electrode plate, negative electrode plate and separator can be manufactured as an electrode assembly by a winding process or a lamination process.

[0069] In some embodiments, the secondary battery can include an outer package. The outer package can be used to package the above - mentioned electrode assembly and electrolyte.

[0070] In some embodiments, the outer package of the secondary battery may be a hard case such as a hard plastic case, an aluminum case, a steel case, etc. The outer package of the secondary battery may also be a soft pack such as a pouch - type soft pack. The material of the soft pack may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate and polybutylene succinate.

[0071] In the present application, the shape of the secondary battery is not particularly limited and may be cylindrical, rectangular, or any other arbitrary shape. For example, FIG. 4 shows a secondary battery 5 having a rectangular structure as an example.

[0072] In some embodiments, referring to FIG. 5, the exterior body may include a case 51 and a cover plate 53. Among them, the case 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates are connected so as to form an accommodation chamber. The case 51 has an opening communicating with the accommodation chamber, and the cover plate 53 can cover the opening so as to seal the accommodation chamber. The positive electrode plate, the negative electrode plate, and the separator can form an electrode assembly 52 by a winding process or a lamination process. The electrode assembly 52 is packaged in the accommodation chamber. The electrolytic solution infiltrates the electrode assembly 52. The number of electrode assemblies 52 included in the lithium-ion battery 5 may be one or more, and those skilled in the art can select according to specific actual needs.

[0073] Battery module In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries included in the battery module may be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0074] FIG. 6 shows a battery module 4 as an example. Referring to FIG. 6, in the battery module 4, a plurality of secondary batteries 5 may be arranged in sequence along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other form. Further, the plurality of secondary batteries 5 may be fixed by fastening members.

[0075] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of secondary batteries 5 are accommodated in the accommodation space.

[0076] Battery pack In some embodiments, the battery module can be further assembled into a battery pack. The number of battery modules included in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0077] FIGS. 7 and 8 show a battery pack 1 as an example. Referring to FIGS. 7 and 8, the battery pack 1 can include a battery box and a plurality of battery modules 4 provided in the battery box. The battery box includes an upper box 2 and a lower box 3. The upper box 2 covers the lower box 3 and can form a sealed space for accommodating the battery module 4. The plurality of battery modules 4 can be arranged in the battery box according to any method.

[0078] Power consumption device In addition, the present application further provides a power consumption device including at least one of the secondary battery, battery module, or battery pack provided by the present application. The secondary battery, battery module, or battery pack may be used as a power source of the power consumption device or as an energy storage unit of the power consumption device. The power consumption device can include, but is not limited to, mobile devices (such as mobile phones, notebook computers, etc.), electric vehicles (such as secondary battery electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric cars, ships, and satellites, energy storage systems, etc.

[0079] As the power consumption device, a secondary battery, battery module, or battery pack can be selected according to the usage needs thereof.

[0080] FIG. 9 shows a power consumption device as an example. The power consumption device is, for example, a secondary battery electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the requirements for high output and high energy density for the secondary battery of the power consumption device, a battery pack or a battery module can be adopted.

[0081] Another example of the device may be a mobile phone, a tablet, a notebook computer, etc. The device usually requires weight reduction and thinning, and a secondary battery can be adopted as a power source.

[0082] Example Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are merely for interpreting the present application and should not be understood as limiting the present application. When specific technologies or conditions are not specified in the embodiments, they are carried out according to the technologies or conditions described in the literature in the relevant field or according to the product specifications. When the manufacturer of the reagents or equipment used is not specified, they are all conventional products that are commercially available.

[0083] <Example 1> 〔1〕Manufacturing method (1) Preparation of the electrolyte In a glove box filled with argon (water content <10 ppm, oxygen content <1 ppm), with the total mass being 100 parts, the non-aqueous organic solvent contains 25.5 parts of ethylene carbonate and 59.5 parts of ethyl methyl carbonate. After mixing uniformly, 15 parts of lithium hexafluorophosphate (LiPF6) was gradually added to the non-aqueous organic solvent. After the lithium salt was completely dissolved, the target electrolyte was obtained. The conductivity of the target electrolyte at room temperature was tested.

[0084] The conductivity test of the electrolyte at room temperature is carried out with reference to HG-T 4067-2015.

[0085] (2) Preparation of the positive electrode plate: The LiNi of the positive electrode active material 0.5 Co0.2 Mn 0.3 O₂, Super P as the conductive agent, and polyvinylidene fluoride (PVDF) as the binder were prepared as a positive electrode slurry in N-methylpyrrolidone (NMP). The solid content in the positive electrode slurry was 50 wt%, and in the solid components, LiNi 0.5 Co 0.2 Mn 0.3 O₂, Super P, and PVDF had a mass ratio of 95:2:3. The positive electrode slurry was coated on an aluminum foil current collector, baked at 85 °C, then cold pressed, followed by edge cutting, cut into sheet form, divided into strip form, and finally baked under vacuum conditions at 85 °C for 4 h to produce a positive electrode plate.

[0086] (3) Preparation of negative electrode material - graphite A: Graphite with an average particle size Dv50 of 15 μm was prepared as the negative electrode material. The Bruggeman index α of the graphite was 1.9. Those skilled in the art can realize the adjustment of the Bruggeman index α of the graphite by adjusting the parameter of the average particle size of the graphite.

[0087] It should be noted that graphite B and graphite C can similarly be obtained by those skilled in the art by adjusting the particle size of the graphite.

[0088] (4) Preparation of negative electrode plate: The above-mentioned graphite as the negative electrode active material, Super P as the conductive agent, CMC as the thickening agent, and styrene-butadiene rubber (SBR) as the binder were uniformly mixed with deionized water to produce a negative electrode slurry. The solid content in the negative electrode slurry was 30 wt%, and the mass ratio of graphite, Super P, CMC, and the binder styrene-butadiene rubber (SBR) in the solid components was 94:3:3. The negative electrode slurry was coated on a copper foil current collector, baked at 85 °C, then cold pressed, followed by edge cutting, cut into sheet form, divided into strip form, and finally baked under vacuum conditions at 120 °C for 12 h to produce a negative electrode plate. Here, the pressure of the cold roll during cold pressing was 38 T, and a plate with a compression density of 1.24 g / cm 3 and a porosity of 45% was obtained.

[0089] It should be noted that the porosity of different negative electrode material (graphite) layers can be adjusted by controlling the compression density of the electrode plate by controlling the pressure of the cold roll.

[0090] (5) Manufacture of lithium-ion battery: A 16-μm polyethylene thin film (PE) was used as the separator. The manufactured positive electrode plate, separator, and negative electrode plate were laminated in sequence, with the separator between the positive and negative electrode plates, playing a role in isolating the positive and negative electrodes. After winding, a bare cell was obtained, tabs were welded, the bare cell was placed in an outer package, and the electrolyte manufactured above was injected into the dried cell. Then, packaging, static placement, formation, shaping, capacity testing, etc. were carried out, and the manufacture of the lithium-ion battery (soft pack lithium-ion battery with a thickness of 4.0 mm, width of 60 mm, and length of 140 mm) was completed.

[0091] 〔2〕Performance evaluation (i) Conductivity of the electrolyte at room temperature A conductivity test was carried out on the electrolyte manufactured in (1) above. The conductivity test of the electrolyte at room temperature was carried out with reference to HG-T 4067-2015.

[0092] (ii) Porosity test of the electrode plate A porosity test was carried out on the electrode plate manufactured in (3) above. The test method for the porosity of the electrode plate was carried out with reference to GB / T 24586-2009.

[0093] (iii) Rapid charging performance test For the battery manufactured in (4) above, at 25 °C, the lithium-ion battery was charged at a constant current of 1C to 4.25V, then charged at a constant voltage of 4.25V until the current reached 0.05C, and then discharged at a constant current of 1C to 2.8V. The discharge capacity D0 of the battery was recorded. Then, it was charged at a constant current of 4C to 4.25V, then charged at a constant voltage of 4.25V until the current reached 0.05C, and then discharged at a constant current of 1C to 2.8V. The discharge capacity D1 was recorded. The discharge capacity retention rate is D1 / D0.

[0094] (iv) Lithium precipitation status of the negative electrode After formation, the battery was charged at a constant current of 2C to 4.25V at 25°C, then charged at a constant voltage of 4.25V until the current was less than 0.05C, and then discharged at 1C to 2.8V for 10 cycle repetitions. After that, it was charged at a constant current of 2C to 4.25V, and then charged at a constant voltage of 4.25V until the current was less than 0.05C to obtain a fully charged battery.

[0095] After 10 cycle repetitions, the battery was disassembled and the lithium precipitation status of the negative electrode was observed.

[0096] The evaluation criteria after observation are as follows.

[0097] No lithium precipitation: The surface of the fully charged negative electrode in the inner region is golden, and when wiped with a lint-free paper, there is no gray metallic lithium powder on the paper.

[0098] A small amount of lithium precipitated: The surface of the fully charged negative electrode in the inner region is dark yellow, and when wiped with a lint-free paper, there is gray metallic lithium powder on the paper.

[0099] Gray spots: The surface of the fully charged negative electrode in the inner region is locally gray, and no golden color can be seen.

[0100] A large amount of lithium precipitated: The entire surface of the fully charged negative electrode in the inner region is gray, and no golden color can be seen.

[0101] In this application, the preferred order of lithium precipitation on the negative electrode is "no lithium precipitation" > "gray spots" > "a small amount of lithium precipitated" > "a large amount of lithium precipitated".

[0102] <Example 2> to <Example 8>, <Comparative Example 1> to <Comparative Example 2> In Examples 2 to 8 and Comparative Examples 1 to 2, except that the types and contents of each raw material of the electrolyte were changed as shown in Table 1 and the parameters such as the particle size of the negative electrode material and the compression density of the negative electrode plate were changed as shown in Table 2, the same manufacturing method as in Example 1 was adopted to obtain each secondary battery.

[0103]

Table 1

[0104]

Table 2

[0105] As can be seen from the test results in Table 2, corresponding to different anode materials, Examples 1 to 8 satisfying (2τ) 0.5 +6 ≤ σ ≤ (2τ) 0.5 +10 had significantly improved rapid charging performance and significantly improved lithium precipitation conditions at the anode compared to Comparative Examples 1 and 2. It can be seen from this that when the anode conforms to the kinetic performance of the electrolyte, good rapid charging performance can be obtained and lithium precipitation at the anode can be avoided. In Comparative Example 1, the conductivity of the electrolyte was low, the movement of lithium ions in the liquid phase was too slow, the lithium ions desorbed from the cathode accumulated at the cathode, and could not be inserted into the anode in a timely manner, so the potential of the cathode electrode rapidly increased and reached the cut-off potential, resulting in a low discharge capacity retention rate. In addition, electrons in the external circuit transferred to the anode, the potential of the anode decreased, and when lithium ions moved to the anode, it was possible that the lithium precipitation potential had already been reached, so lithium precipitation occurred. In Comparative Example 2, the conductivity of the electrolyte was too high. During charging, the lithium ions desorbed from the cathode reached the anode quickly, but due to the poor kinetic performance of the anode, the lithium ions accumulating at the interface of the anode could not be inserted into the anode quickly. As the potential of the anode decreased, the lithium ions at the interface were reduced to metallic lithium and became "dead lithium", so the rapid charging performance was also poor.

[0106] Also, as can be seen from the comparison between Examples 1 to 5 and Example 6, Examples 1 to 5 satisfying (2τ) 0.5 +6 ≤ σ ≤ (2τ) 0.5 +8 can obtain better rapid charging performance and can further suppress lithium precipitation at the anode.

[0107] It should be noted that this application is not limited to the above embodiments. The above embodiments are merely examples, and embodiments that have substantially the same configuration as the technical idea within the scope of the technical solution of this application and exhibit the same functions and effects are all included within the technical scope of this application. In addition, within the scope not departing from the gist of this application, various modifications that those skilled in the art can conceive can be added to the embodiments, and other forms constituted by combining some components in the embodiments are also included within the scope of this application.

Explanation of Reference Numerals

[0108] 1 Battery pack 2 Upper box 3 Lower box 4 Battery module 5 Secondary battery 51 Case 52 Electrode assembly 53 Top cover assembly

Claims

1. A secondary battery including an electrode assembly and an electrolytic solution for infiltrating the electrode assembly, wherein the electrode assembly includes a negative electrode plate, a separator, and a positive electrode plate, and the negative electrode plate includes a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector, if the degree of bending of the negative electrode plate is τ, then τ satisfies τ = 0.5(ε) －α Equation I , where ε is the porosity of the negative electrode material layer and α is the Bruggeman index of the negative electrode material, the τ and the conductivity σ of the electrolytic solution satisfy (2τ) ０．５ +6 ≤ σ ≤ (2τ) ０．５ +10 Formula II , the unit of the conductivity is mS / cm, the range of the conductivity σ of the electrolytic solution is 8.5 mS / cm to 12 mS / cm, and the range of the porosity ε of the negative electrode material layer is 25% to 45%. A secondary battery.

2. The secondary battery according to Claim 1, wherein τ satisfies 2.3 ≤ τ ≤ 7.

3. The secondary battery according to Claim 1 or 2, wherein the negative electrode material is graphite and α is 1.5 to 2.

2.

4. The secondary battery according to Claim 1 or 2, wherein the electrolytic solution includes at least one cyclic ester of ethylene carbonate and propylene carbonate, and at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, methyl acetate, methyl formate, ethyl formate, methyl propionate, propyl formate, ethyl propionate, and propyl acetate.

5. The secondary battery according to Claim 1 or 2, wherein the lithium salt of the electrolytic solution includes at least one of lithium hexafluorophosphate and fluorine-containing lithium sulfonylimide, and the concentration of the lithium salt is 0.5 to 1.5 mol / L.

6. The secondary battery according to Claim 5, wherein the fluorine-containing lithium sulfonylimide includes at least one of lithium bis(fluorosulfonyl)imide, lithium fluoro(trifluoromethylsulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, and lithium fluoro(perfluorobutylsulfonyl)imide.

7. The secondary battery according to Claim 1 or 2, wherein in the negative electrode plate, the thickness of the negative electrode material layer is 30 μm to 400 μm.

8. A battery module including the secondary battery according to Claim 1.

9. A battery pack including the secondary battery according to Claim 1.

10. A power consumption device including at least one selected from the secondary battery according to claim 1, the battery module according to claim 8, or the battery pack according to claim 9.

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