Lithium-ion secondary battery, electric device

Abstract

The application relates to a lithium ion secondary battery and a power utilization device. Along the width direction of the positive electrode current collector, the positive electrode film layer comprises a first region and a second region, the first region is arranged on both sides of the second region; the first region comprises a first positive electrode active material; the second region comprises the first positive electrode active material and a second positive electrode active material, the ratio of the mass content of the first positive electrode active material in the second region to the mass content of the second positive electrode active material in the second region is (89-96):(1-8); the first positive electrode active material comprises a lithium-containing transition metal oxide with a layered structure, and the second positive electrode active material comprises a lithium-containing transition metal phosphate with an olivine structure. The design reduces the total mass content of manganese in the middle region of the positive electrode sheet, can reduce the manganese dissolution of the corresponding negative electrode sheet center region during high-temperature high-voltage storage, reduces the migration of the dissolved Mn ions to the damage of the SEI film of the negative electrode sheet, and improves the lithium precipitation of the negative electrode sheet.

Description

TECHNICAL FIELD

[0001] The application relates to a lithium ion secondary battery and a power utilization device. BACKGROUND

[0002] As a new sustainable energy storage technology, the lithium ion battery has the characteristics of low cost and environmental friendliness, and therefore its application has been developing more and more in recent years.

[0003] Therefore, higher requirements are put forward for the high-temperature storage performance of the lithium ion battery. SUMMARY

[0004] The application aims to provide a lithium ion secondary battery and a power utilization device.

[0005] Embodiments of the application are implemented as follows:

[0006] In a first aspect, the embodiments of the application provide a lithium ion secondary battery, comprising:

[0007] A positive electrode sheet, a negative electrode sheet and a separator film;

[0008] The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector;

[0009] In the width direction of the positive electrode current collector, the positive electrode film layer comprises a first region and a second region, and the first region is arranged on both sides of the second region;

[0010] The first region comprises a first positive electrode active material;

[0011] The second region comprises the first positive electrode active material and a second positive electrode active material, and the ratio of the mass content of the first positive electrode active material in the second region to the mass content of the second positive electrode active material in the second region is (89-96):(1-8);

[0012] The first positive electrode active material comprises a lithium-containing transition metal oxide with a layered structure, and the second positive electrode active material comprises a lithium-containing transition metal phosphate with an olivine structure.

[0013] In the technical solution, the first region is arranged on both sides of the second region along the width direction of the positive current collector, which is equivalent to that the second region is located in the middle region of the positive electrode sheet, and the positive electrode film layer in the second region includes both layered structure transition metal oxide and olivine structure lithium-containing transition metal phosphate, and the content of the layered structure lithium-containing transition metal oxide in the middle region of the positive electrode sheet is effectively reduced in the mass ratio range, so that the dissolution of transition metals such as manganese in the layered transition metal oxide in the middle region of the entire positive electrode sheet is reduced, compared with the positive electrode film layer containing only the layered transition metal oxide, the technical solution of the application can reduce the dissolution amount of transition metals such as manganese in the middle region of the positive electrode sheet, thereby reducing the dissolution of transition metals such as manganese in the middle region of the positive electrode sheet, and the total amount of transition metals such as manganese migrated to the middle region of the corresponding negative electrode sheet is also reduced, thereby reducing the damage to the SEI film of the negative electrode sheet and improving the lithium precipitation of the negative electrode sheet. Further, it is beneficial to improve the high-temperature storage performance of the battery.

[0014] In some embodiments, the ratio of the mass content of the first positive active material in the second region to the mass content of the second positive active material in the second region is (89-91):(6-8).

[0015] In some embodiments, the second region is a rectangular region, and along the width direction, the width of the second region is 20%-70% of the width of the positive electrode film layer; optionally, the width of the second region is 50%-70% of the width of the positive electrode film layer.

[0016] In some embodiments, the first region is arranged on the opposite sides of the positive electrode film layer.

[0017] In some embodiments, the mass content of the second positive active material in the second region accounts for 1%-8% of the total mass of the second region; optionally, the mass content of the second positive active material in the second region accounts for 6%-8% of the total mass of the second region.

[0018] In some embodiments, the mass content of the first positive active material and the second positive active material in the second region accounts for 95%-97% of the total mass of the second region.

[0019] In some embodiments, the mass content of the first positive active material in the first region accounts for 95%-97% of the total mass of the first region.

[0020] In some embodiments, the Dv50 of the first positive active material is 3.3-3.8 μm.

[0021] In some embodiments, the Dv50 of the second positive active material is 1.4-1.8 μm.

[0022] In some embodiments, the lithium-containing transition metal oxide of the layered structure comprises a chemical formula of: Li a Ni b Co c Mn d M e O f R g , wherein 0.75≤a≤1.2, 0.3<b<1.0, 0<c<0.4, 0<d<1, 0≤e≤0.2, 1≤f≤2.5, 0≤g≤1, f+g≤3, M comprises one or more elements of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, and R comprises one or more elements of N, F, S, and Cl.

[0023] In some embodiments, the lithium-containing transition metal phosphate of the olivine structure comprises a chemical formula of: Li 1+x Fe 1- y A y P 1-z R z O i , wherein x is any number within a range of -0.100 to 0.100, y is any number within a range of 0.001 to 0.500, z is any number within a range of 0.001 to 0.100, i is any number within a range of 3.5 to 4, A comprises one or more elements of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and R comprises one or more elements of B, S, Si, and N.

[0024] In a third aspect, the embodiments of the present application provide a power consumption device, which comprises the lithium ion secondary battery provided by any of the preceding embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0026] Figure 1 is a schematic diagram of a positive electrode film layer (including a tab) of an embodiment of the present application;

[0027] Figure 2 is a schematic diagram of a battery cell of an embodiment of the present application;

[0028] Figure 3 is an exploded view of the battery cell of one embodiment of the present application shown in FIG. 1; Figure 1

[0029] Figure 4 is a schematic view of the battery module of one embodiment of the present application;

[0030] Figure 5 is a schematic view of the battery pack of one embodiment of the present application;

[0031] Figure 6 is an exploded view of the battery pack of one embodiment of the present application shown in FIG. 2; Figure 4

[0032] Figure 7 is a schematic view of the power consuming device using the battery as a power source of one embodiment of the present application;

[0033] Figure 8 is a schematic view of the disintegration voltage test;

[0034] Figure 9 is a schematic view of the positive electrode slurry filtration performance test.

[0035] Figure legend:

[0036] 110 first region; 120 second region; 130 tab; 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0037] The embodiments of the technical solutions of the present application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, and cannot limit the protection scope of the present application.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs; the terms used herein are only for the purpose of describing specific embodiments of the present application, and are not intended to limit the present application; the terms "include" and "have" and any variations thereof in the specification and claims of the present application and the above description of drawings are intended to cover non-exclusive inclusion.

[0039] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0040] ​​In the description of the embodiments of the present application, the positions or position relations indicated by the technical terms "inner", "outer" and the like are based on the positions or position relations shown in the drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as limiting the embodiments of the present application.

[0041] In the description of the embodiments of the present application, unless otherwise explicitly specified and limited, the technical terms "mount", "connect", "connect", "fix" and the like should be understood in a broad sense, for example, can be fixed connection, can also be detachable connection, or integrated; can be directly connected, or indirectly connected through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0042] In this paper, the "embodiment" means that the specific features, structures or characteristics described in conjunction with the embodiment can be included in at least one embodiment of the present application. The phrase appears at various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment independent of or alternative to other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0043] In the embodiments of the present application, the same reference signs represent the same parts, and for the sake of brevity, the detailed description of the same parts is omitted in different embodiments. It should be understood that the height, length, width and other dimensions of various components in the embodiments of the present application shown in the drawings, and the overall height, length, width and other dimensions of the integrated device are only exemplary and should not constitute any limitation on the present application.

[0044] At present, the performance of lithium ion battery often drops sharply during high-temperature storage process. After disassembling the interface, it is found that there is serious lithium precipitation in the middle of the negative electrode sheet. After a series of research and analysis, the reason is that the transition metal elements (especially manganese elements) in the lithium-containing transition metal oxide with layered structure in the positive electrode sheet enhance the John-Teller effect under high-temperature storage conditions, which aggravates the dissolution of transition metal ions. These dissolved transition metal ions migrate to the negative electrode sheet and damage the SEI film of the negative electrode sheet, resulting in serious lithium precipitation in the middle of the negative electrode sheet. Thus, the kinetics of the negative electrode sheet decreases, and the expansion force of the battery in the middle of the negative electrode sheet increases the most as the battery use cycle extends, further deteriorating the kinetics of the negative electrode sheet, thereby causing the performance of the battery to drop sharply during high-temperature storage process.

[0045] Based on this, with reference to Figure 1 , the first aspect of the embodiments of the present application provides a lithium ion secondary battery, comprising: a positive electrode sheet, a negative electrode sheet and a separator.

[0046] Along the width direction of the positive electrode current collector, the positive electrode film layer includes a first region 110 and a second region 120, with the first region 110 disposed on both sides of the second region 120;

[0047] The first region 110 includes: a first positive electrode active material;

[0048] The second region 120 includes: a first positive electrode active material and a second positive electrode active material, wherein the mass content of the first positive electrode active material in the second region is (89-96):(1-8);

[0049] The first positive electrode active material includes a layered lithium-containing transition metal oxide, and the second positive electrode active material includes a lithium-containing transition metal phosphate with an olivine structure.

[0050] In the above technical solution, along the width direction of the positive electrode current collector, the first region is disposed on both sides of the second region, which is equivalent to the second region being located in the middle region of the positive electrode sheet. The positive electrode film layer of the second region includes two positive electrode materials: layered transition metal oxide and olivine-structured lithium-containing transition metal phosphate. Within the above-mentioned mass ratio range, the content of layered lithium-containing transition metal oxide in the middle region of the positive electrode sheet is effectively reduced. Therefore, the dissolution of transition metals such as manganese in the layered transition metal oxide in the middle region of the entire positive electrode sheet is reduced. Compared with the positive electrode film layer containing only layered transition metal oxide, the technical solution of this application can reduce the amount of manganese and other transition metal elements dissolved in the middle region of the positive electrode sheet, thereby reducing the dissolution of manganese and other transition metal elements in the middle region of the positive electrode sheet. Consequently, the total amount of manganese and other transition metal elements that can migrate to the corresponding middle region of the negative electrode sheet is also reduced, thereby reducing the damage to the SEI film of the negative electrode sheet and improving the lithium plating of the negative electrode sheet; thus, it is beneficial to improve the high-temperature storage performance of the battery.

[0051] In some embodiments of this application, during the charging and discharging process of the aforementioned lithium-ion secondary battery, active ions repeatedly insert and extract between the positive and negative electrode plates. The electrolyte acts as a conductor between the positive and negative electrode plates. A separator is disposed between the positive and negative electrode plates, primarily to prevent short circuits between the positive and negative electrodes, while simultaneously allowing ions to pass through.

[0052] Reference Figure 1 In the illustrated embodiment, the aforementioned "width direction" ( Figure 1 The direction of the middle arrow (Y) represents the width direction of the positive electrode film. The direction perpendicular to the width direction represents the length direction of the positive electrode film. For example, when forming an electrode assembly, the electrode assembly is formed by winding along the length direction.

[0053] Further optionally, in some embodiments of the present application, the ratio of the mass content of the first positive electrode active material in the second region to the mass content of the second positive electrode active material in the second region is (89, 90, 91, 92, 93, 94, 95, 96, or a range between any two of the aforementioned values):(1, 2, 3, 4, 5, 6, 7, 8, or a range between any two of the aforementioned values).

[0054] Further optionally, in some embodiments of the present application, the ratio of the mass content of the first positive electrode active material in the second region to the mass content of the second positive electrode active material in the second region is (89-91):(6-8).

[0055] In the above technical solution, the ratio of the mass content of the first positive electrode active material in the second region to the mass content of the second positive electrode active material in the second region is (89-91):(6-8), which is further beneficial to improve lithium precipitation in the middle of the negative electrode sheet.

[0056] Further, with reference to Figure 1 , for example, in the illustrated embodiments, the second region is a rectangular region, and along the first aspect of the positive electrode film layer, the width of the second region 120 is 20%-70% of the width of the positive electrode film layer 100.

[0057] In the above technical solution, by setting the width of the second region to be 20%-70% of the width of the positive electrode film layer along the width direction of the positive electrode film layer, lithium precipitation in the middle of the negative electrode sheet is improved.

[0058] For example, in some embodiments of the present application, along the width direction of the positive electrode film layer 100, the width of the second region 120 is 20%, 22%, 25%, 28%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% of the width of the positive electrode film layer 100, or a range between any two of the aforementioned values.

[0059] Further optionally, in some embodiments of the present application, the first region 110 is arranged on opposite sides of the positive electrode film layer.

[0060] Further optionally, in some embodiments of the present application, the width of the second region is 50%-70% of the width of the positive electrode film layer.

[0061] In the above technical solution, the width of the second region is 50%-70% of the width of the positive electrode film layer, which is further beneficial to improve lithium precipitation in the middle of the negative electrode sheet.

[0062] Further, in some embodiments of the present application, the mass content of the second positive electrode active material in the second region is 1%-8% based on the total mass of the second region 120.

[0063] Exemplarily, in some embodiments of the present application, the second positive electrode active material accounts for 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8% or a range between any two of the foregoing values of the total mass of the first positive electrode active material and the second positive electrode active material in the second region 120.

[0064] In the above technical solution, the mass content of the second positive electrode active material in the second region is 1% to 8% based on the total mass of the second region 120; within this range, it is further beneficial to reduce the manganese elution amount in the central region of the negative electrode sheet, thereby being beneficial to the SEI film on the surface of the negative electrode sheet and the kinetics of the negative electrode sheet, and thus the lithium precipitation in the middle of the negative electrode sheet can be effectively improved.

[0065] In the above technical solution, by setting the mass content of the second positive electrode active material in the second region to be 1% to 8% based on the total mass of the second region 120, it is further beneficial to reduce the influence of the middle expansion and extrusion of the battery cell. According to further research, when the mass content of the second positive electrode active material in the second region is 1% to 8%, the full charge rebound rate of the corresponding negative electrode sheet can be reduced by about 1.0% to 4% on a comparable basis, and the expansion force during the use of the corresponding battery under the same number of cycles can be reduced by 0.05 MPa to 0.3 MPa (generally, the expansion force threshold of a ternary system battery is 1.1 to 1.3 MPa); and thus it is beneficial to improve the lithium precipitation problem in the middle of the anode during the use of the battery, thereby prolonging the service life of the battery.

[0066] Further optionally, in some embodiments of the present application, the mass content of the second positive electrode active material in the second region is 6% to 8%.

[0067] In the above technical solution, the mass content of the second positive electrode active material in the second region is 6% to 8%; it is further beneficial to improve the lithium precipitation in the middle of the negative electrode sheet.

[0068] Further, in some embodiments of the present application, the Dv50 of the first positive electrode active material is 3.3 μm to 3.8 μm.

[0069] Exemplarily, in some embodiments of the present application, the Dv50 of the first positive electrode active material described above is 3.3 μm, 3.35 μm, 3.4 μm, 3.45 μm, 3.5 μm, 3.55 μm, 3.6 μm, 3.65 μm, 3.7 μm, 3.75 μm, 3.8 μm or a range between any two of the foregoing values.

[0070] In the above technical solution, by setting the Dv50 of the first positive electrode active material to 3.3μm~3.8μm, it is beneficial to the particle size matching of the positive electrode active material in the central region of the negative electrode sheet, which is beneficial to battery dynamics.

[0071] Further optionally, in some embodiments of this application, the Dv50 of the second positive electrode active material is 1.4 μm to 1.8 μm.

[0072] For example, in some embodiments of this application, the Dv50 of the second positive electrode active material is 1.4 μm, 1.45 μm, 1.5 μm, 1.55 μm, 1.6 μm, 1.65 μm, 1.7 μm, 1.75 μm, 1.8 μm or any two of the aforementioned values.

[0073] In the above technical solution, by setting the Dv50 of the second positive electrode active material to 1.4μm to 1.8μm, it is beneficial to the particle size matching of the positive electrode active material in the central region of the negative electrode sheet, which is beneficial to battery dynamics.

[0074] The above "D" V "50" has a well-known meaning in the art, representing the particle size corresponding to a cumulative volume distribution percentage of 50% for the porous conductive agent, which can be determined using instruments and methods known in the art. For example, it can be determined using a laser particle size analyzer, referring to GB / T19077-2016. The testing instrument can be the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0075] Further optionally, in some embodiments of this application, the mass content of the first positive electrode active material and the second positive electrode active material in the second region is 95% to 97% based on the total mass of the second region.

[0076] For example, in some embodiments of this application, the mass content of the first positive electrode active material and the second positive electrode active material in the second region is 95%, 96%, 97%, or a range between any two of the aforementioned values.

[0077] Further optionally, in some embodiments of this application, the mass content of the first positive electrode active material in the first region is 95% to 97% based on the total mass of the first region.

[0078] For example, in some embodiments of this application, the mass content of the first positive electrode active material in the first region is 95%, 96%, 97%, or any two of the aforementioned values.

[0079] In some embodiments of the present application, the second positive active material includes a lithium-containing transition metal phosphate with an olivine structure, which has a relatively stable temperature, so that the battery use process is not prone to positive active material particle breakage problem, so that the rebound rate of the central film area (second area) of the positive electrode plate is also less than that of the two side areas (two first areas), and the battery middle expansion extrusion problem can be improved; and further, the lithium-containing transition metal phosphate with an olivine structure is arranged in the second area, so that the CB value is reduced, the rebound rate of the positive electrode plate is reduced, and the middle area electrolyte immersion difficulty problem caused by the expansion of the electrode plate during the cycle process can be effectively solved, so as to achieve the purpose of prolonging the service life of the battery. Therefore, the rebound rate of the middle area of the positive and negative electrode plates can be improved, so as to improve the electrolyte immersion difficulty problem of the center area of the lithium ion battery caused by the large expansion force, avoid the center lithium precipitation, and prolong the service life.

[0080] Further optionally, in some embodiments of the present application, the lithium-containing transition metal oxide with a layered structure includes a chemical formula of: Li a Ni b Co c Mn d M e O f R g , wherein 0.75≤a≤1.2, 0.3<b<1.0, 0<c<0.4, 0<d<1, 0≤e≤0.2, 1≤f≤2.5, 0≤g≤1, f+g≤3, M includes one or more elements of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, and R includes one or more elements of N, F, S, and Cl.

[0081] For example, the lithium-containing transition metal oxide with a layered structure can be LiNi 0.4 Co 0.2 Mn 0.4 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, and LiNi 0.7 Co 0.15 Mn 0.15 O2, etc. Li a Ni b Co c M1 d M2 e O f R ga can be any one or more values in the range of 0.75-1.2, b can be any one or more values in the range of 0.3-1.0, c can be any one or more values in the range of 0-0.4, d can be any one or more values in the range of 0-1, e can be any one or more values in the range of 0-0.2, f can be any value in the range of 1-2.5, and g can be any one or more values in the range of 0-1.

[0082] Optionally, in the technical scheme of some embodiments of the present application, the lithium-containing transition metal phosphate with an olivine structure comprises a chemical formula of Li 1+x Fe 1-y A y P 1-z R z O i , wherein x is any numerical value in the range of -0.100-0.100, y is any numerical value in the range of 0.001-0.500, z is any numerical value in the range of 0.001-0.100, i is any numerical value in the range of 3.5-4, A comprises one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R comprises one or more elements selected from B, S, Si and N.

[0083] In the technical scheme of some embodiments of the present application, the compound Li 1+x Fe 1-y A y P 1-z RzO i can be prepared by the following steps:

[0084] (1) Dissolving and stirring an iron source, an element A source doped with iron, and an acid in a solvent to generate a suspension of the iron salt doped with element A, filtering the suspension and drying the filter cake to obtain the iron salt doped with element A;

[0085] (2) Adding a lithium source, a phosphorus source, and an element R source, a solvent, and the iron salt doped with element A obtained in step (1) into a reaction container to grind and mix, to obtain a slurry;

[0086] (3) Transferring the slurry obtained in step (2) to a spray drying device for spray drying granulation to obtain granules;

[0087] (4) Sintering the granules obtained in step (3) to obtain a positive electrode active material.

[0088] In any embodiment, the iron source can be an iron-containing substance known in the art that can be used to prepare lithium iron phosphate, for example, the iron source can be selected from one or a combination of elemental iron, iron oxide, iron phosphate, ferrous oxalate, ferrous carbonate.

[0089] The acid is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, organic acids such as oxalic acid and the like, for example, can be oxalic acid. The source of element R is selected from at least one of a sulfate, a borate, a nitrate and a silicate of element R. The source of element A is selected from at least one of an elemental form, an oxide, a phosphate, an oxalate, a carbonate and a sulfate of A.

[0090] In the technical solution of some embodiments of the present application, the second positive electrode active material further has a carbon-containing coating layer.

[0091] In the technical solution of some embodiments of the present application, the mass fraction of the carbon-containing coating layer in the lithium-containing transition metal phosphate with olivine structure is 1% to 3%; illustratively, the mass fraction of the carbon-containing coating layer in the lithium-containing transition metal phosphate with olivine structure is 1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.8%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5% or a range between any two of the foregoing values.

[0092] It should be noted that in the enumeration of the positive electrode active material in the present application, the molar content of Li is in the initial state of the material, i.e., the state before feeding, and when the positive electrode active material is applied in a battery system, the molar content of Li will change after charging and discharging cycles.

[0093] In addition, the preparation process and conditions of the material are different, and the molar content of O element is usually not strictly the coefficient of O element in the chemical formula, and will fluctuate, for example, Li 1+x Fe 1-y A y P 1-z R z O4, the molar content of O element is not strictly 4.

[0094] Illustratively, the second positive electrode active material can be LiFePO4, LiMn 0.1 Fe 0.9 PO4, LiMn 0.2 Fe 0.8 PO4, LiMn 0.3 Fe 0.7 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.5 Fe 0.5 PO4, LiMn 0.6 Fe 0.4PO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.8 Fe 0.2 PO4, LiMn 0.9 Fe 0.1 PO4, LiMnPO4, LiMn 0.5 Al 0.5 P 0.5 B 0.5 PO4, LiMn 0.5 Mg 0.5 P 0.5 S 0.5 PO4, LiMn, etc.

[0095] Further optionally, in some embodiments of the present application, the positive electrode film layer further optionally comprises a binder. As an example, the binder can comprise at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene-fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene-fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0096] Further optionally, in some embodiments of the present application, the conductive agent in the positive electrode film layer can comprise a porous carbon material and a non-porous carbon material; as an example, the porous carbon material comprises activated carbon, etc.; and the non-porous carbon material comprises at least one of acetylene black, carbon black, carbon nanotube, graphene, or carbon nanofiber.

[0097] Further optionally, in some embodiments of the present application, the conductive agent described above is added in the positive electrode slurry in an amount of 1% to 5% by mass. As an example, the conductive agent described above is added in the positive electrode slurry in an amount of 1%, 1.1%, 1.2%, 1.5%, 1.8%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.1%, 3.2%, 3.5%, 3.8%, 4%, 4.1%, 4.5%, 4.8%, 5%, or a range between any two of the foregoing values.

[0098] In some embodiments of the present application, the positive electrode slurry prepared above is coated on at least one surface of the positive electrode current collector, and after processes such as drying and cold pressing, a positive electrode sheet is obtained.

[0099] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode film layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0100] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0101] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0102] [Negative electrode plate]

[0103] The negative electrode sheet includes a negative current collector and a negative electrode film layer formed on at least one surface of the negative current collector.

[0104] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0105] In some optional embodiments of this application, the aforementioned negative electrode active material may include at least one of the following: hard carbon, graphite, soft carbon, carbon fiber, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form alloys with lithium, optionally, hard carbon.

[0106] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0107] In some embodiments, the negative electrode film layer can further optionally include a binder. The binder can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), lithium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), lithium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0108] In some embodiments, the negative electrode film layer can further optionally include a conductive agent. The conductive agent can be selected from at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0109] In some embodiments, the negative electrode film layer can further optionally include other auxiliary agents, such as thickening agents (e.g., lithium carboxymethyl cellulose (CMC-Li)) and the like.

[0110] In other embodiments, the current collector of the negative electrode tab can generally include a current collector body and a primer layer, which can be provided on at least one side of the current collector body. The primer layer can be substantially free of negative active material and can include a small amount of carbon material, but the carbon material forms a coating with a thickness that is too thin to function as a negative active material. When the current collector of the negative electrode tab includes a primer layer, the film layer can be provided on the surface of the side of the primer layer that is distal to the current collector. The negative electrode tab in this embodiment can be a tab without a negative active material layer. For a negative electrode tab without a negative active material layer, when the current collector of the negative electrode tab is free of a primer layer, the film layer can be provided on the surface of at least one side of the current collector; when the current collector of the negative electrode tab includes a primer layer, the film layer can be provided on the surface of the side of the primer layer that is distal to the current collector.

[0111] In some embodiments, the film layer can further include a binder for fixing the additive to the negative electrode tab. The type of the binder is not particularly limited and can be selected as desired by those skilled in the art.

[0112] [Electrolyte]

[0113] The type of the electrolyte is not particularly limited and can be selected as desired. For example, the electrolyte can be selected from at least one of a solid-state electrolyte and a liquid electrolyte (i.e., electrolyte solution). Battery cells using electrolyte solution, as well as some battery cells using solid-state electrolyte, are available.

[0114] The electrolyte functions to conduct ions between the positive electrode tab and the negative electrode tab.

[0115] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro oxalato borate, lithium difluoro dioxalato borate, lithium difluoro dioxalato phosphate, and lithium tetrafluoro oxalato phosphate.

[0116] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl 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, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0117] In some embodiments, the electrolyte solution can further optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain performance of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0118] [Separator]

[0119] In some embodiments, the type of the separator is not particularly limited, and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0120] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0121] In some embodiments of the present application, the positive electrode tab, the negative electrode tab, and the separator can be wound or stacked to form an electrode assembly 52.

[0122] In some embodiments, the lithium ion secondary battery can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above.

[0123] In some embodiments, the outer package of the lithium ion secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the lithium ion secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, etc. can be listed.

[0124] The shape of the lithium ion secondary battery is not particularly limited, and can be cylindrical, square, or any other shape. For example, Figure 2 is a square structure as an example of a lithium ion secondary battery.

[0125] In some embodiments, referring to Figure 3 , the outer package can include a housing 51 and a cover plate 53. The housing 51 can include a bottom plate and a side plate connected to the bottom plate, which enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be provided on the opening to close the receiving cavity. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be selected by those skilled in the art according to the specific actual needs.

[0126] In the above technical solution, the term "lithium ion secondary battery" can be at least one of a battery cell, a battery module or a battery pack.

[0127] For example, in some embodiments, the lithium ion secondary battery can be assembled into a battery module, and the number of battery cells contained in the battery module 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 module.

[0128] Figure 4 is a battery module 4 as an example. Referring to Figure 4 , in the battery module 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, it can also be arranged in any other way. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0129] Optionally, the battery module 4 can also include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0130] In some embodiments, the above battery module can also be assembled into a battery pack, and the number of battery modules contained 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.

[0131] Figure 5 and Figure 6 is a battery pack 1 as an example. Referring to Figure 5 and Figure 6 , the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be provided on the lower box body 3 to form a closed space for receiving the battery module 4. The plurality of battery modules 4 can be arranged in the battery box in any way.

[0132] Some embodiments of the present application provide a power consuming device, which comprises the lithium ion secondary battery provided by any of the preceding embodiments.

[0133] The battery cell, the battery module, or the battery pack can be used as a power source of the power consuming device, or can be used as an energy storage unit of the power consuming device. The power consuming device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0134] As the power consuming device, the battery cell, the battery module, or the battery pack can be selected according to the use requirement thereof.

[0135] Figure 7 The power consuming device is taken as an example. The power consuming device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the battery for the power consuming device, the battery pack or the battery module can be used.

[0136] The device taken as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and the battery can be used as a power source.

[0137] Embodiments

[0138] Hereinafter, the embodiments of the present application are described. The embodiments described below are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application. If the specific technology or condition is not indicated in the embodiments, the technology or condition described in the literature in the art or according to the product instruction is used. If the reagent or instrument used is not indicated by the manufacturer, it is a conventional product that can be obtained by market purchase.

[0139] Embodiment 1

[0140] A battery cell is provided, which is prepared according to the following steps:

[0141]

Preparation of positive electrode sheet

[0142] 1. Preparation of first positive electrode slurry

[0143] The first positive electrode active material (LiNi 0.5 Co 0.2 Mn 0.3 O2), conductive carbon black (SP), and binder (polyvinylidene fluoride (PVDF)) are mixed in a mass ratio of 97:1:2 to obtain a first positive electrode material; the solvent N-methyl pyrrolidone (NMP) is added and stirred uniformly to prepare a first positive electrode slurry.

[0144] 2. Preparing a second cathode slurry

[0145] The first cathode active material (LiNi 0.5 Co 0.2 Mn 0.3 O2), conductive carbon black (SP), binder (polyvinylidene fluoride (PVDF)), and the second cathode active material (LiFePO4) are mixed in a mass ratio of 91:1:2:6 to obtain a second cathode material; the second cathode material is stirred uniformly in a solvent N-methyl pyrrolidone (NMP) to prepare a second cathode slurry.

[0146] 3. Coating

[0147] An aluminum foil is used as the current collector.

[0148] The cathode film layer includes a first region and a second region along the width direction of the cathode current collector, and the first region is arranged on both sides of the second region; the width of the second region accounts for 50% of the width of the cathode film layer. The first cathode slurry prepared above is uniformly coated on the first region of the aluminum foil; and the second cathode slurry prepared above is uniformly coated on the second region of the aluminum foil. The coating weights of the first region and the second region are the same; both are 331 mg / 1540.25 mm 2 After coating, slitting and die cutting are performed, and the cathode electrode sheet is prepared as shown in Figure 1 Table 1.

[0149]

Preparation of the negative electrode sheet

[0150] The negative electrode active material graphite, conductive carbon black (SP), and binder styrene-butadiene rubber (SBR) are mixed in a mass ratio of 97.5:1:1.5 in a proper amount of deionized water to form a uniform negative electrode slurry; the negative electrode slurry is coated on a negative electrode current collector copper foil, and slitting is performed to obtain a negative electrode sheet.

[0151]

Preparation of the electrolyte

[0152] In an argon-filled glove box, ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) are mixed in a mass ratio of EC:DEC:EMC = 4:2:4, and then 1.0 mol / L lithium hexafluorophosphate (LiPF6) is added.

[0153]

Separator

[0154] The separator is a polyethylene separator.

[0155]

Battery assembly

[0156] The positive electrode sheet, the separator, and the negative electrode sheet are sequentially stacked and wound to form a battery monomer, and the battery monomer is subjected to processes such as heat pressing, casing, welding, liquid injection, and formation to form a battery.

[0157] Examples 2-7

[0158] The difference from Example 1 is that the performance parameters are different, as shown in Table 1, and the other aspects are similar to Example 1.

[0159] Comparative Example 1

[0160] The difference from Example 1 is the preparation of the positive electrode sheet. The positive electrode sheet of the comparative example is prepared as follows:

[0161] The first positive electrode active material (LiNi 0.5 Co 0.2 Mn 0.3 O2), conductive carbon black (SP), and binder (polyvinylidene fluoride (PVDF)) are mixed in a mass ratio of 97:1:2 to obtain a positive electrode material; and the positive electrode material is stirred uniformly in a solvent N-methyl pyrrolidone (NMP) to prepare a positive electrode slurry.

[0162] An aluminum foil is used as a current collector.

[0163] The positive electrode slurry prepared above is uniformly coated on the aluminum foil, and the coating weight is 331 mg / 1540.25 mm 2 . After coating, slitting and die cutting are performed; and a positive electrode sheet is obtained. The specific parameters are shown in Table 1, and the other aspects are similar to Example 1.

[0164]

Performance Test

[0165] Performance test of each example and comparative example sample:

[0166] 1. The battery monomer prepared in each example or comparative example (a sensor is clamped on the battery by a clamp, which can test the expansion force) is discharged at a rate of 0.33C to 2.5V at an ambient temperature of 25°C, and then charged to 4.35V at a rate of 0.33C; this is 1 cycle, and the capacity is recorded as Cn1, and then discharged at a rate of 0.33Cn to 2.5V, and after 10 minutes of storage, charged to 4.35V (corresponding to the full charge state of the battery) at a rate of 0.33Cn. During the above cycle, the maximum expansion force F1 corresponding to the cycle is read by the sensor. Then store it in a 50°C constant temperature box, and perform the above cycle every 30 days for 810 days. Test the capacity of the battery monomer, and record it as Cn x . Record the maximum expansion force Fn of the battery each time the capacity is tested, and then plot the capacity retention rate or the maximum expansion force of the battery as the vertical coordinate and the storage time as the horizontal coordinate.

[0167] Exemplarily,Figure 8 and Figure 9 The capacity retention rate graph and the expansion force change graph of Example 1 and Comparative Example 1 are shown.

[0168] According to the graph, the capacity retention rate of the battery 810 days at 50°C in the full charge state and the expansion force change rate of 810 days at 50°C are calculated according to the following formula

[0169] Capacity retention rate of 810 days at 50°C = Cn 810 / Cn1.

[0170] Expansion force change rate of 810 days at 50°C = F 810 / F1.

[0171] 2. Mn dissolution amount test

[0172] Each battery cell after the foregoing test was disassembled and the Mn dissolution amount in the middle region of the negative electrode tab was tested:

[0173] According to the GB / T 17359-2012 "Microbeam Analysis Energy Dispersive Spectroscopy Quantitative Analysis" standard, a scanning electron microscope-energy spectrometer (SEM-EDS) was used for testing.

[0174] The negative electrode tab obtained by disassembly was cut into 3mm*3mm negative electrode tab samples in the first region and the second region (the first region and the second region of the negative electrode tab correspond one-to-one with the first region and the second region of the positive electrode tab); the samples were respectively pasted on the sample table of the SEM-EDS, so that the surface of the negative electrode film layer away from the negative electrode current collector was upward, and it was ensured that the to-be-tested area of the sample table contained the negative electrode active material layer; the sample table loaded with the negative electrode tab was placed in the sample chamber of the SEM-EDS, vacuumized to 5*10 -5 mbar, then the distance between the sample and the condenser lens was adjusted to 8.5mm, then the high voltage was turned on, the appropriate region was focused, and the appropriate contrast and brightness were adjusted for surface scanning, and the mass percentage content of Mn in the negative electrode film layer was obtained by using INCA software; that is, the Mn dissolution amount.

[0175] The performance test results of each example, comparative example are shown in Table 2.

[0176] Table 1 Various parameters of the positive electrode film layer

[0177]

[0178] Table 2 Performance of lithium ion battery

[0179]

[0180]

[0181] From the above table data, it can be seen that:

[0182] The second area manganese dissolution amount of each of the embodiments is lower than that of the comparative example 1. It can be seen that the second area manganese dissolution amount in each of the embodiments is effectively reduced; especially for the embodiment 1, the embodiments 3-7, the second area manganese dissolution amount can be reduced from 0.8% to 0.15%-0.2% relative to the comparative example 1, and the second area manganese dissolution amount is greatly reduced. This shows that the scheme of the embodiments of the present application can effectively reduce the manganese dissolution of the negative electrode sheet of the battery, thereby being beneficial to improving the lithium precipitation of the negative electrode sheet.

[0183] Further, it can be seen that the battery 810-day 50°C capacity retention rate in each of the embodiments is effectively improved relative to the comparative example 1, which shows that the scheme of the embodiments of the present application can effectively improve the capacity retention rate of the battery.

[0184] Further, it can be seen that the battery 810-day 50°C capacity retention rate in each of the embodiments is effectively improved relative to the comparative example 1, which shows that the scheme of the embodiments of the present application can effectively improve the capacity retention rate of the battery.

[0185] The above-described embodiments are part of the embodiments of the present application, rather than all the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the claimed application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

Claims

1. A lithium-ion secondary battery, characterized in that, Comprising: a positive electrode sheet, a negative electrode sheet, and a separator film; the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector; along the width direction of the positive electrode current collector, the positive electrode film layer comprises a first region and a second region, the first region is arranged on both sides of the second region; the active material of the first region is: a first positive electrode active material; the active material of the second region is: a first positive electrode active material and a second positive electrode active material, the ratio of the mass content of the first positive electrode active material in the second region to the mass content of the second positive electrode active material in the second region is (89-96):(1-8); the first positive electrode active material is a layered structure lithium-containing transition metal oxide, and the second positive electrode active material is an olivine structure lithium-containing transition metal phosphate.

2. The lithium ion secondary battery according to claim 1, wherein the ratio of the mass content of the first positive electrode active material in the second region to the mass content of the second positive electrode active material in the second region is (89-91):(6-8).

3. The lithium ion secondary battery according to claim 1 or 2, wherein the second region is a rectangular region, and the width of the second region along the width direction is 20%-70% of the width of the positive electrode film layer.

4. The lithium ion secondary battery according to claim 1 or 2, wherein the second region is a rectangular region, and the width of the second region along the width direction is 50%-70% of the width of the positive electrode film layer.

5. The lithium ion secondary battery according to any one of claims 1-2, wherein the first region is arranged on both sides of the positive electrode film layer.

6. The lithium ion secondary battery according to any one of claims 1-2, wherein the mass content of the second positive electrode active material in the second region is 1%-8% based on the total mass of the second region.

7. The lithium ion secondary battery according to any one of claims 1-2, wherein the mass content of the second positive electrode active material in the second region is 6%-8% based on the total mass of the second region.

8. The lithium ion secondary battery according to any one of claims 1-2, wherein the mass content of the first positive electrode active material and the second positive electrode active material in the second region is 95%-97% based on the total mass of the second region.

9. The lithium ion secondary battery according to any one of claims 1-2, wherein the mass content of the first positive electrode active material in the first region is 95%-97% based on the total mass of the first region.

10. The lithium ion secondary battery according to any one of claims 1-2, wherein the Dv50 of the first positive electrode active material is 3.3 μm-3.8 μm.

11. The lithium ion secondary battery according to any one of claims 1-2, wherein ​ ​ ​ ​ ​ ​ ​ ​ ​ The Dv50 of the second positive electrode active material is 1.4 μm ~ 1.8 μm.

12. The lithium-ion secondary battery according to any one of claims 1 to 2, wherein The lithium-containing transition metal oxide of the layered structure comprises: a chemical formula of Li a Ni b Co c Mn d M e O f R g , wherein 0.75≤a≤1.2, 0.3<b<1.0, 0<c<0.4, 0<d<1, 0≤e≤0.2, 1≤f≤2.5, 0≤g≤1, f+g≤3, M comprises one or more elements of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, and R comprises one or more elements of N, F, S, Cl.

13. The lithium-ion secondary battery according to any one of claims 1 to 2, wherein The lithium-containing transition metal phosphate of the olivine structure includes: a chemical formula of Li 1+x Fe 1-y A y P 1-z R z O i , wherein x is an arbitrary value in a range of -0.100~0.100, y is an arbitrary value in a range of 0.001~0.500, z is an arbitrary value in a range of 0.001~0.100, i is an arbitrary value in a range of 3.5~4, A includes one or more elements of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and R includes one or more elements of B, S, Si, and N.

14. An electrical device, comprising: The power consuming device includes the lithium-ion secondary battery according to any one of claims 1 to 13.

Images