CN116759585A - Battery cell - Google Patents
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- Publication number
- CN116759585A CN116759585A CN202310769890.1A CN202310769890A CN116759585A CN 116759585 A CN116759585 A CN 116759585A CN 202310769890 A CN202310769890 A CN 202310769890A CN 116759585 A CN116759585 A CN 116759585A
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- Prior art keywords
- coating
- coating layer
- pole piece
- battery
- equal
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- 238000000576 coating method Methods 0.000 claims abstract description 163
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- 239000011148 porous material Substances 0.000 claims abstract description 94
- 239000003792 electrolyte Substances 0.000 claims abstract description 24
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 abstract description 39
- 229910001416 lithium ion Inorganic materials 0.000 abstract description 39
- 229910052744 lithium Inorganic materials 0.000 abstract description 37
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 abstract description 33
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- VDVLPSWVDYJFRW-UHFFFAOYSA-N lithium;bis(fluorosulfonyl)azanide Chemical compound [Li+].FS(=O)(=O)[N-]S(F)(=O)=O VDVLPSWVDYJFRW-UHFFFAOYSA-N 0.000 description 4
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- SBLRHMKNNHXPHG-UHFFFAOYSA-N 4-fluoro-1,3-dioxolan-2-one Chemical compound FC1COC(=O)O1 SBLRHMKNNHXPHG-UHFFFAOYSA-N 0.000 description 2
- 229910015900 BF3 Inorganic materials 0.000 description 2
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- 239000002033 PVDF binder Substances 0.000 description 2
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- PFYQFCKUASLJLL-UHFFFAOYSA-N [Co].[Ni].[Li] Chemical compound [Co].[Ni].[Li] PFYQFCKUASLJLL-UHFFFAOYSA-N 0.000 description 1
- IDSMHEZTLOUMLM-UHFFFAOYSA-N [Li].[O].[Co] Chemical class [Li].[O].[Co] IDSMHEZTLOUMLM-UHFFFAOYSA-N 0.000 description 1
- KFDQGLPGKXUTMZ-UHFFFAOYSA-N [Mn].[Co].[Ni] Chemical compound [Mn].[Co].[Ni] KFDQGLPGKXUTMZ-UHFFFAOYSA-N 0.000 description 1
- RLJDSHNOFWICBY-UHFFFAOYSA-N [P]=O.[Fe].[Li] Chemical class [P]=O.[Fe].[Li] RLJDSHNOFWICBY-UHFFFAOYSA-N 0.000 description 1
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- NDPGDHBNXZOBJS-UHFFFAOYSA-N aluminum lithium cobalt(2+) nickel(2+) oxygen(2-) Chemical class [Li+].[O--].[O--].[O--].[O--].[Al+3].[Co++].[Ni++] NDPGDHBNXZOBJS-UHFFFAOYSA-N 0.000 description 1
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- 230000001351 cycling effect Effects 0.000 description 1
- QHGJSLXSVXVKHZ-UHFFFAOYSA-N dilithium;dioxido(dioxo)manganese Chemical compound [Li+].[Li+].[O-][Mn]([O-])(=O)=O QHGJSLXSVXVKHZ-UHFFFAOYSA-N 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
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- 239000004615 ingredient Substances 0.000 description 1
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- 150000002500 ions Chemical class 0.000 description 1
- 229910000625 lithium cobalt oxide Inorganic materials 0.000 description 1
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 1
- 229910002102 lithium manganese oxide Inorganic materials 0.000 description 1
- FRMOHNDAXZZWQI-UHFFFAOYSA-N lithium manganese(2+) nickel(2+) oxygen(2-) Chemical class [O-2].[Mn+2].[Ni+2].[Li+] FRMOHNDAXZZWQI-UHFFFAOYSA-N 0.000 description 1
- QEXMICRJPVUPSN-UHFFFAOYSA-N lithium manganese(2+) oxygen(2-) Chemical class [O-2].[Mn+2].[Li+] QEXMICRJPVUPSN-UHFFFAOYSA-N 0.000 description 1
- 229910001496 lithium tetrafluoroborate Inorganic materials 0.000 description 1
- 229910021437 lithium-transition metal oxide Inorganic materials 0.000 description 1
- IGILRSKEFZLPKG-UHFFFAOYSA-M lithium;difluorophosphinate Chemical compound [Li+].[O-]P(F)(F)=O IGILRSKEFZLPKG-UHFFFAOYSA-M 0.000 description 1
- 238000011068 loading method Methods 0.000 description 1
- FPYJFEHAWHCUMM-UHFFFAOYSA-N maleic anhydride Chemical compound O=C1OC(=O)C=C1 FPYJFEHAWHCUMM-UHFFFAOYSA-N 0.000 description 1
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- 229920002239 polyacrylonitrile Polymers 0.000 description 1
- 229920000573 polyethylene Polymers 0.000 description 1
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- 239000004810 polytetrafluoroethylene Substances 0.000 description 1
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 1
- 238000003672 processing method Methods 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- QQONPFPTGQHPMA-UHFFFAOYSA-N propylene Natural products CC=C QQONPFPTGQHPMA-UHFFFAOYSA-N 0.000 description 1
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- LIVNPJMFVYWSIS-UHFFFAOYSA-N silicon monoxide Chemical class [Si-]#[O+] LIVNPJMFVYWSIS-UHFFFAOYSA-N 0.000 description 1
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- 235000010413 sodium alginate Nutrition 0.000 description 1
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/64—Carriers or collectors
- H01M4/66—Selection of materials
- H01M4/665—Composites
- H01M4/667—Composites in the form of layers, e.g. coatings
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/362—Composites
- H01M4/366—Composites as layered products
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/021—Physical characteristics, e.g. porosity, surface area
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Composite Materials (AREA)
- Materials Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
The invention provides a battery, which comprises an electrode assembly, a shell and electrolyte, wherein the electrode assembly comprises a first pole piece, a second pole piece and a diaphragm, and the second pole piece comprises a second current collector and a coating; the coating comprises a first coating and a second coating, wherein the second coating is arranged at the edges of the two ends of the first coating in the first direction of the second pole piece, and/or the second coating is arranged at the edges of the two ends of the first coating in the second direction of the second pole piece, and the first direction and the second direction are mutually perpendicular; the pore tortuosity coefficient of the second coating is greater than the pore tortuosity coefficient of the first coating. According to the invention, the pore tortuosity coefficient of the coating layer positioned at the edge area of the second pole piece is larger than that of the coating layer positioned at the middle area of the second pole piece, so that the solid-phase diffusion of lithium ions at the edge area of the second pole piece is reduced, and the lithium precipitation phenomenon of the edge area caused by the fact that the lithium ions are inserted into the edge area of the second pole piece in the charging process can be limited.
Description
Technical Field
The invention relates to the technical field of batteries, in particular to a battery.
Background
The lithium ion battery has wide application in the fields of new energy automobiles and mobile terminals due to the advantages of high energy density, quick charge, long service life and the like. With the increasing requirements for various electronic products, consumers have higher requirements for the safety of lithium ion batteries.
The lithium ion is separated out on the surface of the negative plate in a metal form, which is a big safety problem of the current lithium ion battery, and the lithium ion battery is found to have more serious lithium separation condition in the edge area of the negative plate of the lithium ion battery than in the body area of the negative plate by disassembling the battery core. Edge lithium extraction is one of the most common lithium extraction conditions, and the occurrence of edge lithium extraction in lithium ion batteries reduces the capacity retention during cycling and increases the safety risk of internal short circuits.
Disclosure of Invention
The invention aims to solve the problems that the lithium precipitation in the edge area of the negative electrode plate of the traditional lithium ion battery affects the capacity retention rate of the lithium ion battery and affects the safety risk of the lithium ion battery.
In order to solve the above problems, the present invention provides a battery including an electrode assembly, a case, and an electrolyte, the electrode assembly being located in the case, the electrolyte being injected into the case where the electrode assembly is mounted, the electrode assembly including a first electrode sheet, a second electrode sheet, and a separator;
the second pole piece comprises a second current collector and a coating, and the coating is arranged on at least one side surface of the second current collector;
the coating comprises a first coating and a second coating, wherein the second coating is arranged at the edges of the two ends of the first coating in the first direction of the second pole piece, and/or the second coating is arranged at the edges of the two ends of the first coating in the second direction of the second pole piece, and the first direction and the second direction are mutually perpendicular;
the pore tortuosity coefficient of the second coating is larger than that of the first coating, and is calculated by the following formula:
wherein tau is the pore tortuosity coefficient of the coating, R s The S is the area of the pole piece, epsilon is the porosity of the coating, rho is the resistivity of the electrolyte, and L is the thickness of the coating.
Further, the pore tortuosity coefficient of the first coating layer is represented by a, the pore tortuosity coefficient of the second coating layer is represented by B, and the relationship between a and B is satisfied: B-A is more than or equal to 0.5 and less than or equal to 3.0.
Further, the first coating has a pore tortuosity value A in the range of 1 < A < 4.5 and the second coating has a pore tortuosity value B in the range of 1 < B < 5.
Further, the second coating has an OI value greater than the OI value of the first coating.
Further, with OI 1 Representing the OI value of the first coating to OI 2 Indicating the OI value of the second coating, OI 1 And OI 2 The relation is satisfied: OI is less than or equal to 1.05 2 /OI 1 ≤2.05。
Further, at both ends of the width direction of the second pole piece, the width of the second coating is 0.5mm to 3mm; and/or, at both ends of the length direction of the second pole piece, the length of the second coating is 0.5mm to 3mm.
Further, the second coating has a porosity greater than the first coating.
Further, the first coating layer has a porosity of 20% to 40%, and the second coating layer has a porosity of 25% to 45%.
Further, the thickness of the second coating layer is smaller than the thickness of the first coating layer, and h is expressed as a ratio of the thickness of the first coating layer to the thickness of the second coating layer, and h satisfies the relation: h is more than 1.05 and less than 2.50.
Further, the second pole piece is a negative pole piece, the first pole piece is a positive pole piece, the first pole piece comprises a first current collector and a third coating, the third coating is arranged on at least one side surface of the first current collector, and the pore tortuosity coefficient of the middle area of the third coating is equal to that of the edge of the third coating.
According to the battery disclosed by the invention, the pore tortuosity coefficient of the second coating is larger than that of the first coating, so that the pore tortuosity coefficient of the coating positioned in the edge area of the second coating is larger than that of the coating positioned in the middle area of the second coating, the second coating with the large pore tortuosity coefficient can provide more pore structures, lithium ions in the second coating can be fully contacted with electrolyte in the battery cycle process, the liquid phase transmission of the lithium ions is promoted, the lithium intercalation capacity of the second coating is improved, the solid phase diffusion of the lithium ions in the edge area of the second coating is reduced, and the lithium precipitation phenomenon of the edge area caused by the lithium ion intercalation in the edge area of the second coating in the charging process can be limited; in addition, the pore tortuosity coefficient of the second coating is larger, so that the pore structure of the edge area of the second pole piece is more than that of the middle area of the second pole piece, the pore structure can provide a heat dissipation channel, the heat dissipation of the edge area of the second pole piece is faster than that of the middle area, when the heat is generated in the battery, the heat can be conducted into the pore structure of the edge area of the second pole piece through the pore structure of the middle area of the second pole piece, and therefore the heat generated in the battery can be conducted out to the outside of the battery rapidly, the heat dissipation is facilitated, the safety risk of the battery on fire combustion caused by heat accumulation is reduced, and the safety of the battery is improved.
Drawings
Fig. 1 is a schematic structural view of a negative plate according to an embodiment of the present invention;
reference numerals illustrate:
10-current collector; 20-coating; 21-a first coating; 22-a second coating.
Detailed Description
In order that the above objects, features and advantages of the invention will be readily understood, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings.
It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other.
In addition, the terms "comprising," "including," "containing," "having" and their derivatives are not limiting, as other steps and other ingredients not affecting the result may be added. Materials, equipment, reagents are commercially available unless otherwise specified.
The embodiment provides a battery including an electrode assembly, a case, and an electrolyte in the case, the electrolyte being injected into the case where the electrode assembly is mounted, the electrode assembly including a positive electrode sheet (i.e., a first electrode sheet), a negative electrode sheet (i.e., a second electrode sheet), and a separator disposed between the positive electrode sheet and the negative electrode sheet.
As shown in fig. 1, the negative electrode sheet provided in the present embodiment includes a second current collector 10 and a coating layer 20, the coating layer 20 being provided on at least one side surface of the second current collector 10 in the thickness direction;
the coating layer 20 includes a first coating layer 21 and a second coating layer 22, the second coating layer 22 being provided at both end edges of the first coating layer 21 in the width direction (first direction, i.e., y-axis direction in fig. 1) of the negative electrode sheet, and/or the second coating layer 22 being provided at both end edges of the first coating layer 21 in the length direction (second direction, i.e., x-axis direction in fig. 1) of the negative electrode sheet; wherein the pore tortuosity coefficient of the second coating layer 22 is greater than the pore tortuosity coefficient of the first coating layer 21.
In this embodiment, the pore tortuosity coefficient of the coating can be calculated by the following formula:
wherein tau is the pore tortuosity coefficient of the coating, R s The S is the area of the pole piece, epsilon is the porosity of the coating, rho is the resistivity of the electrolyte, and L is the thickness of the coating.
In this embodiment, the pore tortuosity coefficient of the second coating 22 located in the edge area of the negative electrode sheet is greater than that of the first coating 21 located in the middle area of the negative electrode sheet, and under the condition of the same surface density and compaction density, the second coating 22 with a large pore tortuosity coefficient can provide more pore structures, which is favorable for fully contacting lithium ions in the second coating 22 with electrolyte in the battery cycle process, promoting the liquid phase transmission of the lithium ions, improving the lithium intercalation capacity of the second coating 22, and being favorable for reducing the solid phase diffusion of the lithium ions in the edge area of the negative electrode sheet, thereby being capable of limiting the lithium precipitation phenomenon in the edge area caused by the lithium ion intercalation in the edge area of the negative electrode sheet in the charging process. The first coating layer 21 with small pore tortuosity coefficient has a compact structure, enhances the conductivity of lithium ions, is beneficial to improving the capacity and energy density of the battery, and ensures that the battery has higher capacity retention rate in the circulating process. In addition, the pore tortuosity coefficient of the second coating 22 is larger, so that the pore structure of the edge area of the negative electrode plate is more than that of the middle area of the negative electrode plate, the pore structure can provide a heat dissipation channel, the heat dissipation of the edge area of the negative electrode plate is faster than that of the middle area, when the interior of the battery generates heat, the heat can be conducted to the pore structure of the edge area of the negative electrode plate by the pore structure of the middle area of the negative electrode plate, and therefore the heat generated in the battery can be conducted out to the outer side of the battery rapidly, the heat dissipation is facilitated, the safety risk of battery ignition combustion caused by heat accumulation is reduced, and the safety of the battery is improved.
In this embodiment, the second coating layer 22 may be disposed at both end edges of the first coating layer 21 in the longitudinal direction of the negative electrode sheet, the second coating layer 22 may be disposed at both end edges of the first coating layer 21 in the width direction of the negative electrode sheet, and the second coating layer 22 may be disposed at both end edges of the first coating layer 21 in the longitudinal direction of the negative electrode sheet and at both end edges of the first coating layer 21 in the width direction of the negative electrode sheet. On the basis of the above-described embodiment, the first coating layer 21 is provided with the second coating layer 22 at both end edges in the length direction of the anode sheet, and the first coating layer 21 is provided with the second coating layer 22 at both end edges in the width direction of the anode sheet, that is, the first coating layer 21 is circumferentially provided with the second coating layer 22. Therefore, more pore structures can be provided in the edge areas of the negative electrode plate in the length direction and the width direction, so that solid-phase diffusion of lithium ions in the edge area of the negative electrode plate is reduced, the lithium precipitation phenomenon in the edge area caused by the fact that the lithium ions are embedded into the edge area of the negative electrode plate in the charging process is limited, the heat dissipation efficiency of the negative electrode plate can be improved, and the safety of a battery is further improved.
In this embodiment, the width of the second coating layer 22 is 0.5mm to 3mm at both end edges in the width direction of the negative electrode sheet; the second coating layer 22 has a length of 0.5mm to 3mm at both end edges in the length direction of the anode sheet, that is, 0.5 mm.ltoreq.L in FIG. 1 1 ≤3mm，0.5mm≤L 2 Is less than or equal to 3mm. The size of the second coating 22 is set within the range, so that the size of the second coating 22 is prevented from being smaller, the solid-phase diffusion of lithium ions in the edge area of the negative electrode sheet is limited, the lithium precipitation phenomenon of the edge area of the negative electrode sheet can be further limited, the size of the second coating 22 is also prevented from being larger, the pore structure of the edge area is increased, the active substances in the second coating 22 are reduced, and the energy density of the battery is reduced.
On the basis of the above embodiment, the pore tortuosity coefficient of the first coating layer 21 is represented by a, and the pore tortuosity coefficient of the second coating layer 22 is represented by B, and then a and B satisfy the relation: B-A is more than or equal to 0.5 and less than or equal to 3.0. Specifically, the relationships satisfied by A and B include, but are not limited to: B-A is more than or equal to 0.5 and less than or equal to 1, B-A is more than or equal to 1 and less than or equal to 1.5, B-A is more than or equal to 1.5 and less than or equal to 1, B-A is more than or equal to 2 and less than or equal to 2.5, and B-A is more than or equal to 2.5 and less than or equal to 3.0. The pore tortuosity coefficient of the second coating 22 and the pore tortuosity coefficient of the first coating 21 are set in the range, so that the situation that the pore tortuosity coefficient difference of the two coatings is large to cause too large lithium intercalation difference of the two coatings is avoided, the consistency of pole pieces is maintained, the capacity retention rate of a battery is higher when the battery circulates under a high multiplying power, the circulating stability is better, the phenomenon that lithium is separated from the edge area of a negative pole piece is easily caused due to small pore tortuosity difference of the two coatings can be avoided, and the heat dissipation efficiency of the negative pole piece is influenced, so that the safety of the battery is influenced.
In this embodiment, the range of the pore tortuosity coefficient A of the first coating layer 21 is 1 < A < 4.5, and the range of the pore tortuosity coefficient B of the second coating layer 22 is 1 < B < 5. Specifically, the range of pore tortuosity coefficient a of the first coating layer 21 includes, but is not limited to: a is more than 1 and less than 1.5, A is more than or equal to 1.5 and less than 2, A is more than or equal to 2 and less than or equal to 2.5, A is more than or equal to 2.5 and less than or equal to 3, A is more than or equal to 3 and less than or equal to 3.5, A is more than or equal to 3.5 and less than or equal to 4, and A is more than or equal to 4 and less than or equal to 4.5; the range of pore tortuosity coefficients B of the second coating 22 includes, but is not limited to: b is more than or equal to 1 and less than 2, B is more than or equal to 2 and less than or equal to 2.7, B is more than or equal to 2.7 and less than or equal to 3.2, B is more than or equal to 3.2 and less than or equal to 3.8, B is more than or equal to 3.8 and less than or equal to 4.3, and B is more than or equal to 4.3 and less than or equal to 5. The pore tortuosity coefficient of the first coating layer 21 and the pore tortuosity coefficient of the second coating layer 22 should keep that the pore tortuosity coefficient of the second coating layer 22 is always larger than the pore tortuosity coefficient of the first coating layer 21 when the pore tortuosity coefficients are specifically set. In this embodiment, the pore tortuosity coefficient of the first coating layer 21 and the pore tortuosity coefficient of the second coating layer 22 are respectively set in the above ranges, so that lithium ions are convenient to transmit, and the lithium precipitation phenomenon at the edge area of the negative electrode sheet is avoided, and meanwhile, the first coating layer 21 and the second coating layer 22 have good ion conductivity and electrical conductivity.
In this embodiment, the porosity of the second coating layer 22 is greater than the porosity of the first coating layer 21. In general, the greater the porosity of the coating, the greater the pore tortuosity coefficient of the coating. In this embodiment, by setting the porosity of the second coating layer 22 to be greater than that of the first coating layer 21, the edge region of the negative electrode sheet provides more space for accommodating lithium ions, so that the lithium capacity of the second coating layer 22 can be increased, thereby being beneficial to further reducing the solid-phase diffusion of lithium ions in the edge region of the negative electrode sheet.
As an alternative embodiment, the porosity of the first coating 21 is 20% to 40% and the porosity of the second coating 22 is 25% to 45%, specifically, the porosity range of the first coating 21 includes, but is not limited to: 20%, 25%, 30%, 35%, 40%; the porosity range of the second coating 22 includes, but is not limited to 25%, 28%, 32%, 38%, 45%. The porosity of the first coating layer 21 and the porosity of the second coating layer 22 should be kept such that the porosity of the second coating layer 22 is always greater than the porosity of the first coating layer 21 when specifically set. In this embodiment, the porosities of the first coating layer 21 and the second coating layer 22 are set within the above range, so that the porosity of the first coating layer 21 and the second coating layer 22 can be avoided from being too large while the lithium capacity of the second coating layer 22 can be increased, the energy density of the battery is reduced, the capacity of the battery is affected, the porosity of the first coating layer 21 and the second coating layer 22 can be avoided from being too small, and the liquid-phase diffusion of lithium ions is limited.
In this embodiment, the porosities of the first coating layer 21 and the second coating layer 22 may be determined by an image processing method, an inert gas adsorption method, or the like.
In this embodiment, the thickness of the second coating layer 22 is smaller than the thickness of the first coating layer 21. In this embodiment, by setting the thickness of the second coating layer 22 to be smaller than that of the first coating layer 21, the thickness of the active material layer in the edge region of the negative electrode sheet is thinned, the amount of active material in the edge region of the negative electrode sheet is reduced, the diffusion path of lithium ions in the edge region is also facilitated to be shortened, the accumulation amount of lithium ions is reduced, and further the lithium precipitation risk in the edge region of the negative electrode sheet is facilitated to be reduced.
On the basis of the above embodiment, the ratio of the thickness of the first coating layer 21 to the thickness of the second coating layer 22 is h, which satisfies the relation: h is more than 1.05 and less than 2.50. Specifically, the relationship satisfied by h includes, but is not limited to: h is more than or equal to 1.05 and less than or equal to 1.20, h is more than or equal to 1.20 and less than or equal to 1.35, h is more than or equal to 1.35 and less than or equal to 1.50, h is more than or equal to 1.50 and less than or equal to 1.75, h is more than or equal to 1.75 and less than or equal to 2.0, h is more than or equal to 2.0 and less than or equal to 2.15, h is more than or equal to 2.15 and less than or equal to 2.30, and h is more than or equal to 2.30 and less than or equal to 2.50. In this embodiment, the ratio of the thickness of the first coating layer 21 to the thickness of the second coating layer 22 is set within the above range, so that the risk of lithium precipitation in the edge region of the negative electrode sheet is reduced, and meanwhile, the poor flatness of the surface of the negative electrode sheet can be avoided, and the quality of the battery is also prevented from being affected.
As an alternative embodiment, the thickness of the first coating layer 21 ranges from 17 μm to 35 μm and the thickness of the second coating layer 22 ranges from 15 μm to 33 μm.
In other embodiments of the application, the pore tortuosity coefficients of the first and second coatings 21, 22 may also be varied by adjusting the particle size, compaction density, stacking means of the active materials in the coatings, increasing pore formers, adjusting the ratio of the individual components in the coatings, and the like. For example: the particle size of the active material in the coating increases, resulting in porosity of the coating and coatingAnd thereby increase the pore tortuosity coefficient of the coating. The increased compacted density of the coating increases the ohmic resistance of the coating, thereby increasing the pore tortuosity coefficient of the coating. The increased proportion of binder in the coating formulation increases the ohmic resistance of the coating, thereby increasing the pore tortuosity coefficient of the coating. As an alternative embodiment, if a pore-forming agent is added to the coating, the pore-forming agent may be Polyacrylonitrile (PAA), polyvinyl alcohol (PVA), boron trifluoride (BF) 3 ) One or more of the following.
On the basis of the above embodiment, the OI value of the second coating layer 22 is larger than the OI value of the first coating layer 21. The OI value refers to the ratio of 004 peak intensities to 110 peak intensities in the x-ray diffraction test data, i.e., I (004)/I (110). The OI values of the first coating 21 and the second coating 22 are related to the physical and chemical characteristics of the particle size of the active material, the compaction density of the coating, and the like, and are also related to factors such as the proportion of the conductive agent, and by adjusting the OI values of the first coating 21 and the second coating 22 and ensuring that the OI value of the second coating 21 is greater than the OI value of the first coating 21, the diffusion of lithium ions from the middle region of the anode sheet to the edge region of the anode sheet can be reduced, thereby alleviating the problem of lithium precipitation at the edge region of the anode sheet and being beneficial to prolonging the cycle times of the battery.
Based on the above embodiment, the following steps are taken as OI 1 Indicating the value of OI of the first coating 21, expressed as OI 2 Indicating the value of OI of the second coating 22, OI 1 And OI 2 The relation is satisfied: OI is less than or equal to 1.05 2 /OI 1 Less than or equal to 2.05. Specifically, OI 1 And OI 2 Satisfied relationships include, but are not limited to: OI is less than or equal to 1.05 2 /OI 1 ＜1.2、1.2≤OI 2 /OI 1 ＜1.4、1.4≤OI 2 /OI 1 ＜1.6、1.6≤OI 2 /OI 1 ＜1.8、1.8≤OI 2 /OI 1 < 2.05. The OI value ratio of the two coatings is set in the range, so that the lithium precipitation phenomenon of the edge area of the negative electrode sheet is relieved, and meanwhile, the power performance, the charging multiplying power capability and the circulation capability of the battery can be ensured.
In this embodiment, the first coating layer 21 includes an active material, a conductive agent, and a binder, and the second coating layer 22 includes an active material, a conductive agent, and a binder. The contents of the active material, the conductive agent and the binder in this embodiment are not further limited, and may be set by those skilled in the art according to actual circumstances. As an alternative embodiment, the mass ratio of the active material in the first coating layer 21 is 90% to 98%, i.e., the mass of the active material accounts for 90% to 98% of the mass of the first coating layer 21. The mass ratio of the active material in the second coating layer 22 is 90% to 98%, i.e., the mass of the active material accounts for 90% to 98% of the mass of the second coating layer 22. Thus, the loading amount of the active material in the first and second coating layers 21 and 22 can be increased, which is advantageous for increasing the energy density of the battery.
In this embodiment, the active materials in the first coating layer 21 and the second coating layer 22 are independently selected from one or more of graphite, hard carbon, soft carbon, lithium titanate, and silicon-based materials. That is, the active materials in the first coating layer 21 and the second coating layer 22 may be the same or different. Among them, silicon-based materials include, but are not limited to, elemental silicon, silicon alloys, silicon oxides, silicon-carbon composites, and the like. As an alternative embodiment, the first coating 21 has a compacted density in the range of 1.5g/cm 3 To 2.0g/cm 3 The second coating 22 has a compacted density in the range of 1.5g/cm 3 To 2.5g/cm 3 。
In this embodiment, the specific kinds of the conductive agent and the binder are not further limited, and may be selected by those skilled in the art according to practical situations. Illustratively, the conductive agent may be one or more of conductive carbon black, carbon nanotubes, graphite, graphene, carbon fibers, carbon microspheres, and the like. The binder can be one or more of styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyimide, carboxymethyl cellulose, sodium alginate and the like.
In this example, the ohmic resistance Rs of the coating can be obtained by measuring the corresponding coating by a resistor meter, HPPC (Hybrid PulsePower Characteristic, hybrid pulse capability feature), EIS (Electrochemical Impedance Spectroscopy ). The ohmic resistance Rs of the coating is related to factors such as the particle size of the active material, the formulation ratio (e.g., type of conductive agent, content of conductive agent, binder content, etc.), the compaction density, etc.
In this embodiment, the area of the negative electrode sheet may be calculated by measuring the length and width of the negative electrode sheet.
In this example, the resistivity of the electrolyte may be measured, and as an alternative embodiment, the resistivity of the electrolyte may be from 60 Ω cm to 200 Ω cm.
The electrolyte comprises electrolyte salt, an organic solvent and an additive, wherein the mass of the electrolyte salt accounts for 10-15 wt% of the total mass of the electrolyte, and the mass of the additive accounts for 0.1-15 wt% of the total mass of the electrolyte.
Specifically, the electrolyte salt includes a lithium salt selected from lithium hexafluorophosphate (LiPF) 6 ) Lithium difluorophosphate (LiPF) 2 O 2 ) Difluoro lithium bis (oxalato) phosphate (LiPF) 2 (C2O 4 ) 2 ) Lithium tetrafluorooxalate phosphate (LiPF) 4 C 2 O 4 ) Lithium oxalate phosphate (LiPO) 2 C 2 O 4 ) One or more of lithium bis (oxalato) borate (LiBOB), lithium difluoro (lipofb), lithium tetrafluoroborate (LiBF 4), lithium bis (fluorosulfonyl) imide (LiTFSI), and lithium bis (fluorosulfonyl) imide (LiFSI). The organic solvent is selected from one or more of Ethylene Carbonate (EC), propylene Carbonate (PC), diethyl carbonate (DEC), ethyl Propionate (EP), propyl Propionate (PP), ethyl Acetate (EA), ethyl n-butyrate (EB) and gamma-butyrolactone (GBL), and 1, 2-tetrafluoroethyl-2, 3-tetrafluoropropyl ether (TTE). The additive is selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (VC), 1, 3-Propane Sultone (PS), ethylene sulfate (DTD), methylene Methane Disulfonate (MMDS), propylene Sultone (PST), maleic anhydride, diethanol anhydride, succinic anhydride, succinonitrile (SN), hexadinitrile (ADN), ethylene glycol bis (propionitrile) ether (EGBE) and hexane dinitrile (HTCN).
As an alternative embodiment, the electrolyte in this example includes ethylene carbonate, propylene carbonate, and diethyl carbonate, and the lithium salt is lithium hexafluorophosphate (LiPF 6 ) Wherein the mass ratio of the ethylene carbonate to the propylene carbonate to the diethyl carbonate is EC: PC: dec=1:1:3.
As an optional practiceIn an embodiment, the electrolyte in this embodiment may be prepared by the following method: in a glove box filled with inert gas (H 2 O<10ppm，O 2 <5 ppm), ethylene carbonate, propylene carbonate and diethyl carbonate were mixed in a mass ratio EC: PC: dec=1:1:3, and then lithium hexafluorophosphate (LiPF) accounting for 13wt% of the total mass of the electrolyte was slowly added to the mixed solution 6 ) And (5) obtaining the electrolyte after the water and the free acid are detected to be qualified.
The current collector 10 of the present embodiment is further provided with an empty current collector region, i.e., a region of the surface of the current collector 10 where the coating 20 is not provided. The empty collector region may be welded to the tab. As an alternative embodiment, the empty collector regions are provided at both ends of the negative electrode sheet in the width direction, so that the negative electrode sheet is wound into an electrode assembly.
In the present embodiment, the materials of the second current collector 10 include, but are not limited to, metal foil, alloy foil, composite foil of metal and polymer, and the like. The second current collector 10 may be copper, nickel, stainless steel, or the like, for example.
The negative electrode sheet provided in this embodiment may be prepared by a method known in the art. Illustratively, the method for preparing the negative electrode sheet may include: the first active paste is coated on the middle area of the second current collector 10, then the second active paste is coated on the periphery of the first active paste, and after drying and pressing, a first coating 21 and a second coating 22 are respectively formed on the second current collector 10, wherein the first active paste and the second active paste can comprise active materials, conductive agents, binders and solvents. Wherein the coating means includes, but is not limited to, one or more of dripping, brushing, spraying, knife coating, and the like. In this embodiment, the process parameters such as the coating time and temperature are not further limited, and may be set by those skilled in the art according to practical situations.
The positive electrode sheet in this embodiment may be a positive electrode sheet commonly used in the art, including but not limited to a lithium cobaltate positive electrode sheet, a lithium iron phosphate positive electrode sheet, a nickel cobalt manganese ternary positive electrode sheet, a nickel cobalt aluminum ternary positive electrode sheet, a nickel cobalt lithium positive electrode sheet, and a lithium manganate positive electrode sheet.
The positive plate comprises a first current collector and a third coating, the third coating is arranged on at least one side surface of the first current collector, and the pore tortuosity coefficient of the middle area of the third coating is equal to that of the edge area of the third coating, namely, the pore tortuosity coefficients of all areas of the third coating are the same. In the battery of this embodiment, the pore tortuosity coefficient of each region in the coating of the positive electrode sheet is the same, and the pore tortuosity coefficient of the coating of the edge region of the negative electrode sheet is greater than the pore tortuosity coefficient of the coating of the middle region of the negative electrode sheet, which is favorable for further reducing the solid-phase diffusion of lithium ions in the edge region of the negative electrode sheet, and can further limit the lithium precipitation phenomenon in the edge region caused by the insertion of lithium ions into the edge region of the negative electrode sheet in the charging process, and also is favorable for uniform distribution of positive electrode potential, reducing the loss of positive electrode active materials, and being favorable for maintaining the battery to have higher energy density.
The material of the first current collector includes, but is not limited to, metal foil, alloy foil, composite foil of metal and polymer, etc. The first current collector may be, for example, aluminum, nickel, titanium, or the like.
The third coating layer includes an active material, and the active material in the third coating layer includes, but is not limited to, lithium transition metal composite oxides and the like, and specifically, the lithium transition metal composite oxides may include, but are not limited to, lithium cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt aluminum oxides, lithium iron phosphorus oxides, lithium manganese oxides, or a combination of one or more of these lithium transition metal oxides added with other transition metals or non-transition metals, and the like.
The separator of the present embodiment may employ a separator commonly used in the art, including, but not limited to, one or more combinations of polyethylene, polypropylene, non-woven fabrics, and poly-fiber materials.
The housing in this embodiment may be a housing commonly used in the art, including but not limited to an aluminum plastic film housing, an aluminum shell, or a steel shell.
In order to further explain the present invention in detail, the present invention will be further described with reference to specific examples. The experimental methods used in the examples of the present invention are all conventional methods unless otherwise specified; other materials, reagents, etc. used in the examples of the present invention were purchased commercially unless otherwise specified.
Example 1
The present embodiment provides a battery including an electrode assembly formed by winding a positive electrode sheet and a negative electrode sheet, the total thickness of the electrode assembly being 6mm, wherein:
the positive plate comprises a positive current collector and a positive active material layer arranged on the surface of the positive current collector, and aluminum foil is selected as the positive current collector; the positive electrode active material layer comprised 97.9wt% of positive electrode active material lithium cobaltate (170 mAh/g), 0.6wt% of conductive carbon black, 0.4wt% of carbon nanotubes and 1.1wt% of polyvinylidene fluoride, and had a width of 80mm, and an areal density of 34mg/cm 2 。
The negative plate comprises a negative current collector and a negative active material layer arranged on the surface of the negative current collector, and copper foil is selected as the negative current collector; the width of the anode active material layer is 82mm, the anode active material layer comprises a first coating layer 21 and a second coating layer 22, the first coating layer 21 is arranged in the middle area of the anode sheet, the two second coating layers 22 are respectively arranged at the edge areas of the two ends of the first coating layer 21 in the width direction of the anode sheet, wherein the first coating layer 21 comprises 97wt% of graphite (the gram capacity is 350mAh/g, the particle size is 7-15 mu m), 1wt% of conductive carbon black, 1.4% of styrene-butadiene rubber and 0.6% of carboxymethyl cellulose; the second coating 22 comprises 97wt% graphite (g capacity 350mAh/g, particle size 15 μm to 20 μm), 1wt% conductive carbon black, 1.4% styrene-butadiene rubber, and 0.6% carboxymethylcellulose.
The width of the first coating layer 21 was 78mm, the pore tortuosity coefficient was 2.5, the width L1 of the second coating layer 22 was 2mm, the pore tortuosity coefficient was 3.5, and the areal densities of the first coating layer 21 and the second coating layer 22 were 17.5mg/cm 2 A compaction density of 1.74g/cm 3 The difference in pore tortuosity coefficient between the second coating layer 22 and the first coating layer 21 was 1.0. In addition, the second coating layer 22 has an OI value greater than that of the first coating layer 21, OI 2 /OI 1 1.5.
Example 2
This example provides a battery identical to that of example 1, except that:
the first coating layer 21 in the anode active material layer includes 97wt% of graphite (g capacity of 350mAh/g, particle diameter of 7 μm to 15 μm), 1wt% of conductive carbon black, 1.4% of styrene-butadiene rubber, and 0.6% of carboxymethyl cellulose; the second coating 22 comprises 97wt% graphite (g capacity 350mAh/g, particle size 18 μm to 22 μm), 1wt% conductive carbon black, 1.4% styrene-butadiene rubber, and 0.6% carboxymethylcellulose.
The pore tortuosity coefficient of the first coating layer 21 is 2.5, the pore tortuosity coefficient of the second coating layer 22 is 3.8, and the pore tortuosity coefficient difference between the second coating layer 22 and the first coating layer 21 is 1.3. In addition, the second coating layer 22 has an OI value greater than that of the first coating layer 21, OI 2 /OI 1 1.8.
Example 3
This example provides a battery identical to that of example 1, except that:
the first coating layer 21 in the anode active material layer includes 97wt% of graphite (gram capacity of 350mAh/g, particle diameter of 7 μm to 15 μm), 1wt% of carbon nanotubes, 1.4% of styrene-butadiene rubber, and 0.6% of carboxymethyl cellulose; the second coating 22 comprises 97wt% graphite (g capacity 350mAh/g, particle size 7 μm to 15 μm), 1wt% conductive carbon black, 1.4% styrene-butadiene rubber, and 0.6% carboxymethylcellulose.
The pore tortuosity coefficient of the first coating layer 21 is 1.8, the pore tortuosity coefficient of the second coating layer 22 is 2.5, and the pore tortuosity coefficient difference between the second coating layer 22 and the first coating layer 21 is 0.7. In addition, the second coating layer 22 has an OI value greater than that of the first coating layer 21, OI 2 /OI 1 1.0.
Example 4
This example provides a battery identical to that of example 1, except that:
the first coating layer 21 in the anode active material layer includes 97wt% of graphite (g capacity of 350mAh/g, particle diameter of 7 μm to 15 μm), 1wt% of conductive carbon black, 1.4% of styrene-butadiene rubber, and 0.6% of carboxymethyl cellulose; the second coating 22 comprises 98wt% graphite (g capacity 350mAh/g, particle size 7 μm to 15 μm), 1.4% styrene-butadiene rubber, and 0.6% carboxymethylcellulose.
The pore tortuosity coefficient of the first coating layer 21 is 2.5, the pore tortuosity coefficient of the second coating layer 22 is 3.3, and the pore tortuosity coefficient difference between the second coating layer 22 and the first coating layer 21 is 0.8. In addition, the second coating layer 22 has an OI value greater than that of the first coating layer 21, OI 2 /OI 1 1.0.
Example 5
This example provides a battery identical to that of example 1, except that:
the first coating layer 21 in the anode active material layer includes 97wt% of graphite (g capacity of 350mAh/g, particle diameter of 7 μm to 15 μm), 1wt% of conductive carbon black, 1.4% of styrene-butadiene rubber, and 0.6% of carboxymethyl cellulose; the second coating 22 comprises 96wt% graphite (g capacity 350mAh/g, particle size 7 μm to 15 μm), 1wt% conductive carbon black, 2.4% styrene-butadiene rubber, and 0.6% carboxymethylcellulose.
The pore tortuosity coefficient of the first coating layer 21 is 2.5, the pore tortuosity coefficient of the second coating layer 22 is 3.9, and the pore tortuosity coefficient difference between the second coating layer 22 and the first coating layer 21 is 1.4. In addition, the second coating layer 22 has an OI value greater than that of the first coating layer 21, OI 2 /OI 1 1.0.
Example 6
This example provides a battery identical to that of example 1, except that:
the compacted density of the first coating 21 was 1.74g/cm 3 The compacted density of the second coating 22 was 1.92g/cm 3 。
The pore tortuosity coefficient of the first coating layer 21 is 2.5, the pore tortuosity coefficient of the second coating layer 22 is 4.2, and the pore tortuosity coefficient difference between the second coating layer 22 and the first coating layer 21 is 1.7. In addition, the second coating layer 22 has an OI value greater than that of the first coating layer 21, OI 2 /OI 1 1.3.
Comparative example
This example provides a battery identical to that of example 1, except that:
the slurry of the middle region and the edge region of the anode active material layer was the same, and the anode active material layer included 97wt% of graphite (g capacity of 350mAh/g, particle size of 7 μm to 15 μm), 1wt% of conductive carbon black, 1.4% of styrene-butadiene rubber, and 0.6% of carboxymethyl cellulose.
The width of the anode active material layer was 82mm, the pore tortuosity coefficient was 2.5, and the areal density of the anode active material layer was 17.5mg/cm 2 A compaction density of 1.74g/cm 3 In addition, the second coating layer 22 has an OI value equal to that of the first coating layer 21, OI 2 /OI 1 1.0.
The parameters of the negative electrode sheets in examples 1 to 6 and comparative examples are shown in table 1.
TABLE 1
The lithium ion batteries provided in examples 1 to 6 and comparative examples were subjected to cycle performance test, and the cycle test method was as follows:
charging at 25deg.C to 4.2V, constant voltage charging at 4.2V to cut-off current of 1.5C, charging at 1.5C to 4.4V, constant voltage charging at 4.4V to cut-off current of 0.05C, standing for 15min, discharging at 0.7C to 3V, and standing for 15min. After 300 circles of circulation, the capacity retention rate is tested, and after the lithium ion batteries in each group are disassembled, whether lithium is separated out from the edge of the negative plate is observed, and the test results are shown in table 2:
TABLE 2
As can be seen from table 2, the capacity retention rate of the lithium ion batteries provided in examples 1 to 6 after 300 cycles was improved compared to the comparative examples, and the lithium precipitation problem was not found in the negative electrode sheet edge regions of the lithium ion batteries in examples 1 to 6, indicating that the improvement of the cycle performance of the lithium ion batteries and the improvement of the lithium precipitation phenomenon in the negative electrode sheet edge regions were facilitated by increasing the difference in pore tortuosity coefficients of the second coating layer and the first coating layer in the present example. As is clear from the combination of examples 1 to 6, the pore tortuosity coefficient of the edge region of the negative electrode sheet can be increased by increasing the particle size of the negative electrode active material, adjusting the proportion of each component in the negative electrode active material layer, and increasing the compaction density of the second coating layer, so that the lithium precipitation phenomenon of the edge region of the negative electrode sheet can be reduced and the safety of the battery can be improved on the basis of increasing the capacity retention rate. In addition, the difference in pore tortuosity coefficients of the second coating layer 22 and the first coating layer 21 in examples 1 to 6 satisfies 0.5.ltoreq.B-A.ltoreq.3.0, and it is demonstrated that setting the difference in pore tortuosity coefficients of the second coating layer 22 and the first coating layer 21 in this range can also avoid the phenomenon of lithium precipitation in the edge region of the negative electrode sheet while improving the capacity retention rate.
Further, as is clear from examples 1,2 and comparative example, the second coating layer OI value can be increased by increasing the particle diameter of the anode active material in the second coating layer, leading to OI 2 /OI 1 The dynamic performance of the edge area of the negative electrode plate can be reduced, the lithium precipitation risk of the edge area of the negative electrode plate is reduced, and the capacity retention rate is improved. From example 6 and comparative example, it is known that the OI value of the second coating can be increased by increasing the compacted density of the second coating, resulting in OI 2 /OI 1 The dynamic performance of the edge area of the negative electrode plate can be reduced, the lithium precipitation risk of the edge area of the negative electrode plate is reduced, and the capacity retention rate is improved.
As can also be seen from table 2, the lithium ion batteries produced from the negative electrode sheets of example 1, example 2, example 5 and example 6 have higher capacity retention, and examples 3 and 4 times, illustrate that the difference in pore tortuosity coefficients of the second coating layer 22 and the first coating layer 21 is increased, and the OI is increased 2 /OI 1 Is beneficial to improving the capacity retention rate.
Although the present disclosure is described above, the scope of protection of the present disclosure is not limited thereto. Various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the disclosure, and these changes and modifications will fall within the scope of the invention.
Claims (10)
1. A battery comprising an electrode assembly, a housing, and an electrolyte, the electrode assembly being located within the housing, the electrolyte being injected into the housing where the electrode assembly is mounted, the electrode assembly comprising a first electrode sheet, a second electrode sheet, and a separator;
the second pole piece comprises a second current collector and a coating, and the coating is arranged on at least one side surface of the second current collector;
the coating comprises a first coating and a second coating, wherein the second coating is arranged at the edges of the two ends of the first coating in the first direction of the second pole piece, and/or the second coating is arranged at the edges of the two ends of the first coating in the second direction of the second pole piece, and the first direction and the second direction are mutually perpendicular;
the pore tortuosity coefficient of the second coating is larger than that of the first coating, and is calculated by the following formula:
wherein tau is the pore tortuosity coefficient of the coating, R s The S is the area of the pole piece, epsilon is the porosity of the coating, rho is the resistivity of the electrolyte, and L is the thickness of the coating.
2. The battery of claim 1, wherein the pore tortuosity factor of the first coating is denoted by a and the pore tortuosity factor of the second coating is denoted by B, a and B satisfying the relationship: B-A is more than or equal to 0.5 and less than or equal to 3.0.
3. The battery of claim 2, wherein the first coating has a pore tortuosity value a in the range of 1 < a < 4.5 and the second coating has a pore tortuosity value B in the range of 1 < B < 5.
4. The battery of claim 1, wherein the second coating has an OI value that is greater than the OI value of the first coating.
5. The battery of claim 4, wherein the battery is characterized by the following OI 1 Representing the OI value of the first coating to OI 2 Indicating the OI value of the second coating, OI 1 And OI 2 The relation is satisfied: OI is less than or equal to 1.05 2 /OI 1 ≤2.05。
6. The battery according to claim 1, wherein the width of the second coating layer is 0.5mm to 3mm at both ends in the width direction of the second electrode sheet; and/or, at both ends of the length direction of the second pole piece, the length of the second coating is 0.5mm to 3mm.
7. The battery of claim 1, wherein the porosity of the second coating is greater than the porosity of the first coating.
8. The battery of claim 7, wherein the first coating has a porosity of 20% to 40% and the second coating has a porosity of 25% to 45%.
9. The battery of claim 1, wherein the thickness of the second coating is less than the thickness of the first coating, and wherein h is expressed as the ratio of the thickness of the first coating to the thickness of the second coating, and h satisfies the relationship: h is more than 1.05 and less than 2.50.
10. The battery of claim 1, wherein the second pole piece is a negative pole piece, the first pole piece is a positive pole piece, the first pole piece comprises a first current collector and a third coating, the third coating is disposed on at least one side surface of the first current collector, and a pore tortuosity coefficient of a middle region of the third coating is equal to a pore tortuosity coefficient at an edge of the third coating.
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