Lithium supplement positive plate, preparation method thereof and lithium ion battery

Abstract

The invention relates to a lithium supplement positive plate, a preparation method thereof and a lithium ion battery. The lithium supplementing positive plate comprises a first positive electrode layer and a second positive electrode layer which are sequentially stacked on the surface of at least one side of the current collector; along the laying direction, the second positive electrode layer comprises a first area arranged in the middle area and a second area arranged around the first area; the material of the first positive electrode layer comprises a first positive electrode active material; in the second positive electrode layer, the materials of the first region and the second region respectively and independently comprise a second positive electrode active material; and the material of the first region further comprises a lithium supplement agent. Based on a strategy of cooperation of high nickel and lithium supplement, the high nickel material with the nickel content higher than 90% is used for providing energy density, the medium-high nickel material with the nickel content of 80%-90% is used for improving the cycle stability, and the lithium supplement agent is added in the specific area of the second positive electrode layer, so that synchronous improvement of the energy density, the cycle performance and the safety performance of the lithium ion battery is realized.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to positive electrode sheets, and more particularly to a lithium-added positive electrode sheet, its preparation method, and a lithium-ion battery. Background Technology

[0002] During the initial charge-discharge cycles of lithium-ion batteries, some active lithium is irreversibly consumed due to the formation of a solid electrolyte interphase (SEI) film on the negative electrode surface, leading to a decrease in coulombic efficiency and effective capacity loss in the first cycle. To improve the long-term cycle stability and capacity retention of batteries, replenishing the lost lithium through external means has become one of the key technologies in the industry. Currently, lithium replenishment technologies mainly include positive electrode lithium replenishment, negative electrode lithium replenishment, separator lithium replenishment, and electrolyte lithium replenishment. Among them, positive electrode lithium replenishment technology has developed particularly rapidly. By introducing specific lithium replenishment additives into the positive electrode slurry, additional lithium ions are released during the initial charging process of battery formation to compensate for the irreversible loss caused by SEI formation and subsequent growth, thereby effectively improving the initial coulombic efficiency and overall cycle performance of the entire battery.

[0003] CN118263545A discloses a positive electrode lithium replenishing agent, comprising a positive electrode lithium replenishing material and a modified material cross-linked and wound from the inside out on the surface of the positive electrode lithium replenishing material; wherein, the modified material comprises a conductive agent and a catalyst, and there is a bond between the functional groups of the conductive agent and the free hydroxyl groups on the surface of the catalyst; wherein, the conductive agent is a one-dimensional conductive agent having a linear or tubular shape. The positive electrode lithium replenishing agent provided by this invention effectively reduces the decomposition potential of the positive electrode lithium replenishing material, giving full play to the lithium replenishing function of the positive electrode lithium replenishing material; at the same time, the positive electrode lithium replenishing agent also improves conductivity, avoiding the problem of poor contact inside the electrode.

[0004] CN116885184A discloses a composite lithium supplementation material, a lithium supplementation cathode, and a lithium-ion battery comprising the composite lithium supplementation material. The composite lithium supplementation material includes at least a lithium oxalate lithium supplement agent L1, and further includes L2 and / or L3; L3 mainly consists of Mo-containing... x A 4.3V decomposition potential lithium oxalate supplement is prepared by spray drying of an aqueous solution of C / NC and lithium oxalate; L2 is a 4.1V decomposition potential lithium oxalate supplement prepared by freeze drying of an aqueous solution of Mo2CMXene and lithium oxalate etched by HF; L1 is a 4.1V decomposition potential lithium oxalate supplement prepared by freeze drying of an aqueous solution of Mo2CMXene and lithium oxalate etched by HF. x A lithium oxalate lithium replenisher with a decomposition potential of 3.8V is prepared by electrospinning and carbonization of an organic solution of Mo2CMXene, lithium oxalate, and PAN after C / NC or HF etching. Lithium-ion batteries and cathodes prepared using this composite lithium replenisher material can achieve lithium replenishment throughout their entire life cycle, exhibiting high cycle capacity and significant retention advantages.

[0005] CN117134003A discloses a method for lithium replenishment of the positive electrode, comprising: forming a lithium-containing layer with a thickness in the range of 1-15 μm on the positive electrode material layer of the lithium battery positive electrode, wherein the lithium-containing layer is composed of metallic lithium or a lithium alloy, and the thickness tolerance of the lithium-containing layer is within ±1 μm. Using this positive electrode lithium replenishment method, the initial efficiency of the lithium battery can be improved by about 10%, the specific capacity can be improved by about 10%, and the lithium replenishment effect is more significant; furthermore, there is no heat generation problem after lithium replenishment of the positive electrode, allowing for safe storage and use.

[0006] Existing technologies focus primarily on the lithium replenishing agent itself, aiming to uniformly replenish lithium to the positive electrode. However, there is limited research on the degree to which the negative electrode in different regions can accept lithium replenishment from the positive electrode in lithium-ion batteries. If the negative electrode cannot adequately accept lithium replenishment from the positive electrode, it will lead to the formation of lithium dendrites, affecting the battery's safety performance.

[0007] Therefore, it is of great significance to provide a lithium-ion cathode that simultaneously improves energy density and safety performance. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a lithium-added cathode sheet, its preparation method, and a lithium-ion battery. Based on a strategy of synergistic cooperation between high nickel content and lithium supplementation, the present invention provides a high-energy-density lithium-added cathode. The first cathode layer, using a high-nickel material with a nickel content exceeding 90% as the active material, serves as the energy density center. A second cathode layer, using a medium-to-high nickel material with a nickel content of 80%–90%, serves as the active material. The structure of the second cathode layer is designed such that lithium supplementation agent is added only in the central first region, while no lithium supplementation agent is added in the peripheral second region. This achieves a simultaneous improvement in the energy density, cycle performance, and safety performance of the lithium-ion battery.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a lithium-supplemented positive electrode sheet, the lithium-supplemented positive electrode sheet comprising a first positive electrode layer and a second positive electrode layer sequentially stacked on at least one side surface of a current collector; along the laying direction, the second positive electrode layer includes a first region disposed in an intermediate region and a second region disposed around the first region; the material of the first positive electrode layer comprises a first positive electrode active material, the first positive electrode active material having the chemical formula Ni. x1 Co y1 Mn z1 O2, 0.99≥x1≥0.9, 0.1≥y1≥0, 0.10≥z1≥0; In the second positive electrode layer, the materials of the first region and the second region each independently include the second positive electrode active material; The chemical formula of the second positive electrode active material is Ni. x2 Co y2 Mnz2 O2, 0.90≥x2≥0.8, 0.2≥y2≥0, 0.2≥z2≥0; the material of the first region also includes a lithium replenishing agent.

[0011] This invention provides a high-energy-density lithium-added cathode based on a strategy of synergistic cooperation between high nickel content and lithium replenishment. The first cathode layer, with a high-nickel material containing more than 90% nickel as the active material, serves as the energy density center. A second cathode layer, with a medium-to-high nickel material containing 80% to 90% nickel, is then deposited on its surface, exhibiting better stability. Based on the matching between the lithium provided by the positive electrode and the lithium accepted by the negative electrode in a lithium-ion battery, the structure of the second cathode layer is designed such that lithium replenishment is added only in the central first region to further improve energy density and cycle performance. No lithium replenishment is added to the edge second region to avoid lithium plating at the edge of the negative electrode due to insufficient kinetics and poor lithium acceptance, thus improving the safety performance of the lithium-ion battery.

[0012] Preferably, in the second positive electrode layer, the area ratio of the first region to the second region is (90~95):(5~10).

[0013] Preferably, the mass ratio of the first positive electrode active material in the first positive electrode layer, the total mass of the second positive electrode active material in the second positive electrode layer, to the mass ratio of the lithium supplement in the second positive electrode layer is (70~85):(14~25):(1~5).

[0014] Preferably, in the second positive electrode layer, the mass ratio of the second positive electrode active material to the lithium replenishing agent in the first region is (13.25~22):(1~5).

[0015] Preferably, in the second positive electrode layer, the mass ratio of the second positive electrode active material in the first region to the second region is (13.25~22):(0.75~3).

[0016] Preferably, the areal density of the first positive electrode layer is 300 g / m³. 2 ~450g / m 2 .

[0017] Preferably, the areal density of the second positive electrode layer is 55 g / m³. 2 ~180g / m 2 .

[0018] Preferably, the lithium supplement includes any one or a combination of at least two of Li2NiO2, Li2CO3, Li2O, Li2O2, Li6CoO4, Li5FeO4, aryl lithium compounds, or lithium naphthalene.

[0019] Preferably, the first positive electrode layer and the second positive electrode layer each independently include a conductive agent and a binder.

[0020] Preferably, in the first positive electrode layer, the mass ratio of the first positive electrode active material, the conductive agent, and the binder is (93~99):(0.5~6.5):(0.5~6.5).

[0021] Preferably, in the second positive electrode layer, the mass ratio of the total mass of the second positive electrode active material and the lithium replenishing agent to the mass ratio of the conductive agent and the binder in the first region is (85~93):(5~10):(2~5).

[0022] Preferably, in the second positive electrode layer, the mass ratio of the second positive electrode active material to the conductive agent and binder in the second region is (85~93):(5~10):(2~5).

[0023] Secondly, the present invention provides a method for preparing the lithium-supplemented positive electrode sheet described in the first aspect, the method comprising:

[0024] A first positive electrode layer slurry including a first positive electrode active material is provided; a first region slurry including a second positive electrode active material and a lithium supplement agent is provided; a second region slurry including the second positive electrode active material is provided; the first positive electrode layer slurry is coated on at least one side surface of a current collector and dried to obtain a first positive electrode layer; the surface of the first positive electrode layer is divided into a first region and a second region surrounding the first region along the laying direction; the first region slurry and the second region slurry are coated on the first region and the second region respectively and dried to obtain a second positive electrode layer.

[0025] Preferably, the solid content of the first positive electrode layer slurry, the first region slurry, and the second region slurry is each independently 40% to 70%.

[0026] Preferably, the drying temperature is 70℃~120℃.

[0027] Thirdly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising the lithium-replenishing positive electrode sheet described in the first aspect; the lithium-ion battery further comprising a negative electrode sheet.

[0028] Preferably, the negative electrode sheet includes a negative electrode active material, which includes graphite and / or silicon.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] This invention provides a high-energy-density lithium-added cathode based on a strategy of synergistic cooperation between high nickel and lithium replenishment. The first cathode layer, with a high nickel content of more than 90% as the cathode active material, serves as the energy density center. The second cathode layer, with a medium-high nickel content of 80% to 90% as the active material, is designed with lithium replenishment agent added only in the first region of the middle area and not in the second region of the edge. This achieves a simultaneous improvement in the energy density, cycle performance, and safety performance of lithium-ion batteries. Attached Figure Description

[0031] Figure 1 This is a cross-sectional schematic diagram of the lithium-filled positive electrode sheet provided in Example 1.

[0032] Figure 2 This is a schematic diagram of the structure of the second positive electrode layer of the lithium-added positive electrode sheet provided in Example 1.

[0033] Wherein, 1-first positive electrode layer; 2-second positive electrode layer; 21-first region; 22-second region; 3-current collector. Detailed Implementation

[0034] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0035] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0036] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0037] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0038] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0039] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0040] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0041] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0042] In this invention, the terms "first aspect," "second aspect," "third aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0043] In this invention, "optional" means that something is optional, that is, it refers to any one of the two parallel solutions of "having" or "not having". If there are multiple "optional" options in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, then each "optional" option is independent.

[0044] In this invention, "room temperature" generally refers to 4℃~35℃, and can refer to 20℃±5℃. In some embodiments of this invention, room temperature refers to 20℃~30℃.

[0045] In one specific embodiment, the present invention provides a lithium-supplemented positive electrode sheet, the lithium-supplemented positive electrode sheet comprising a first positive electrode layer and a second positive electrode layer sequentially stacked on at least one side surface of a current collector; along the laying direction, the second positive electrode layer includes a first region disposed in an intermediate region and a second region disposed around the first region; the material of the first positive electrode layer comprises a first positive electrode active material, the first positive electrode active material having the chemical formula Ni. x1 Co y1 Mn z1 O2, 0.99≥x1≥0.9, for example, can be 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98 or 0.99; 0.1≥y1≥0, for example, can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1; 0.10≥z1≥0, for example, can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1; in the second positive electrode layer, the materials of the first region and the second region each independently include the second positive electrode active material; the chemical formula of the second positive electrode active material is Ni. x2 Co y2 Mn z2 O2, 0.90≥x2≥0.8, for example, can be 0.8, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89 or 0.90, 0.2≥y2≥0, for example, can be 0, 0.05, 0.1, 0.15 or 0.2, 0.2≥z2≥0, for example, can be 0, 0.05, 0.1, 0.15 or 0.2; the material of the first region also includes a lithium replenishing agent.

[0046] This invention provides a high-energy-density lithium-added cathode based on a strategy of synergistic cooperation between high nickel content and lithium replenishment. The first cathode layer, with a high-nickel material containing more than 90% nickel as the active material, serves as the energy density center. A second cathode layer, with a medium-to-high nickel material containing 80% to 90% nickel, is then deposited on its surface, exhibiting better stability. Based on the matching between the lithium provided by the positive electrode and the lithium accepted by the negative electrode in a lithium-ion battery, the structure of the second cathode layer is designed such that lithium replenishment is added only in the central first region to further improve energy density and cycle performance. No lithium replenishment is added to the edge second region to avoid lithium plating at the edge of the negative electrode due to insufficient kinetics and poor lithium acceptance, thus improving the safety performance of the lithium-ion battery.

[0047] In some embodiments, the area ratio of the first region to the second region in the second positive electrode layer is (90~95):(5~10), for example, it can be 90:10, 91:9, 92:8, 93:7, 94:6 or 95:5.

[0048] In this invention, the shape of the first region is not particularly limited, but it is preferably the same as the shape of the positive electrode sheet and located at the geometric center of the positive electrode sheet.

[0049] In some embodiments, the mass ratio of the first positive electrode active material in the first positive electrode layer, the total mass of the second positive electrode active material in the second positive electrode layer, and the mass ratio of the lithium supplement in the second positive electrode layer is (70~85):(14~25):(1~5), for example, it can be 70:25:5, 72.5:23.5:4, 75:22:3, 77.5:20:2.5, 80:18:2, 82.5:16:1.5, or 85:14:1.

[0050] In some embodiments, in the second positive electrode layer, the mass ratio of the second positive electrode active material to the lithium supplement in the first region is (13.25~22):(1~5), for example, it can be 13.25:1, 13.5:2, 14:2.5, 16:3, 18:3.5, 20:4 or 22:5.

[0051] In some embodiments, the mass ratio of the second positive electrode active material in the first region to the second region in the second positive electrode layer is (13.25~22):(0.75~3), for example, it can be 13.25:0.75, 15:1, 17:1.5, 19:2, 20:2.5, 21:2.8 or 22:3.

[0052] In some embodiments, the areal density of the first positive electrode layer is 300 g / m³. 2 ~450g / m 2 For example, it could be 300g / m 2325g / m 2 350g / m 2 375g / m 2 400g / m 2 425g / m 2 Or 450g / m 2 .

[0053] In some embodiments, the areal density of the second positive electrode layer is 55 g / m³. 2 ~180g / m 2 For example, it could be 55g / m 2 60g / m 2 80g / m 2 100g / m 2 120g / m 2 140g / m 2 160g / m 2 Or 180g / m 2 .

[0054] In some embodiments, the lithium supplement includes any one or a combination of at least two of Li2NiO2, Li2CO3, Li2O, Li2O2, Li6CoO4, Li5FeO4, aryl lithium compounds, or lithium naphthalene. Typical but non-limiting combinations include combinations of Li2NiO2 and Li2CO3, combinations of Li2O and Li2O2, combinations of Li6CoO4 and Li5FeO4, or combinations of aryl lithium compounds and lithium naphthalene.

[0055] In some embodiments, the first positive electrode layer and the second positive electrode layer each independently include a conductive agent and a binder.

[0056] In some embodiments, the mass ratio of the first positive electrode active material, the conductive agent and the binder in the first positive electrode layer is (93~99):(0.5~6.5):(0.5~6.5), for example, it can be 93:6.5:0.5, 94:1:5, 95:3:2, 96:1:3, 97:2:1, 98:1:1 or 99:0.5:0.5.

[0057] In some embodiments, in the second positive electrode layer, the mass ratio of the total mass of the second positive electrode active material and the lithium replenishing agent to the mass ratio of the conductive agent and the binder in the first region is (85~93):(5~10):(2~5), for example, it can be 85:10:5, 86:9.5:4.5, 87:9:4, 88:8.2:3.8, 89:7.5:3.5, 90:7:3, 91:6.2:2.8, 92:5.5:2.5 or 93:5:2.

[0058] In some embodiments, in the second positive electrode layer, the mass ratio of the second positive electrode active material to the conductive agent and binder in the second region is (85~93):(5~10):(2~5), for example, it can be 85:10:5, 86:9.5:4.5, 87:9:4, 88:8.2:3.8, 89:7.5:3.5, 90:7:3, 91:6.2:2.8, 92:5.5:2.5 or 93:5:2.

[0059] In another specific embodiment, the present invention provides a method for preparing the lithium-added positive electrode sheet described in one of the foregoing specific embodiments, the preparation method comprising:

[0060] A first positive electrode layer slurry including a first positive electrode active material is provided; a first region slurry including a second positive electrode active material and a lithium supplement agent is provided; a second region slurry including the second positive electrode active material is provided; the first positive electrode layer slurry is coated on at least one side surface of a current collector and dried to obtain a first positive electrode layer; the surface of the first positive electrode layer is divided into a first region and a second region surrounding the first region along the laying direction; the first region slurry and the second region slurry are coated on the first region and the second region respectively and dried to obtain a second positive electrode layer.

[0061] In some embodiments, the solid content of the first positive electrode layer slurry, the first region slurry, and the second region slurry is each independently 40% to 70%, for example, it can be 40%, 45%, 50%, 55%, 60%, 65%, or 70%.

[0062] In some embodiments, the drying temperature is 70°C to 120°C, for example, it can be 70°C, 80°C, 90°C, 100°C, 110°C or 120°C.

[0063] In yet another embodiment, the present invention provides a lithium-ion battery, the lithium-ion battery including the lithium-replenishing positive electrode sheet as described in the preceding embodiment; the lithium-ion battery also includes a negative electrode sheet.

[0064] In some embodiments, the negative electrode includes a negative electrode active material, which includes graphite and / or silicon.

[0065] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0066] Example 1

[0067] This embodiment provides a lithium-added positive electrode sheet, such as... Figure 1As shown, the lithium-ion cathode includes a first cathode layer 1 and a second cathode layer 2 sequentially stacked on both sides of the current collector 3; along the laying direction, as... Figure 2 As shown, the second positive electrode layer 2 includes a first region 21 disposed at the geometric center of the positive electrode sheet and having the same shape as the positive electrode sheet, and a second region 22 disposed around the first region; the area ratio of the first region 21 to the second region 22 is 92:8.

[0068] The first positive electrode layer 1 is made of Ni in a mass ratio of 94:3:6. 0.93 Co 0.03 Mn 0.04 O2, SP, and PDVF; the areal density of the first positive electrode layer 1 is 350 g / m³. 2 ;

[0069] In Region 21, Ni 0.83 Co 0.07 Mn 0.1 The mass ratio of O2 to Li2NiO2 is 15.4:3, Ni 0.83 Co 0.07 Mn 0.1 The total mass ratio of O2 and Li2NiO2 to the mass ratio of SP and PDVF is 90:5:5. Ni in region 22... 0.83 Co 0.07 Mn 0.1 The mass ratio of O2, SP, and PDVF is 90:5:5; the areal density of the second positive electrode layer 2 is 87.5 g / m³. 2 ;

[0070] Ni in the first positive electrode layer 1 0.93 Co 0.03 Mn 0.04 The mass of O2, and the Ni in the second positive electrode layer 2 0.83 Co 0.07 Mn 0.1 The total mass of O2 and the mass ratio of Li2NiO2 are 80:17:3;

[0071] The method for preparing the lithium-added positive electrode includes:

[0072] Provides Ni with a solid content of 60% 0.93 Co 0.03 Mn 0.04 The first positive electrode layer slurry consists of O2, SP, and PDVF; Ni with a solid content of 50%. 0.83 Co 0.07 Mn 0.1 The first zone slurry consists of O2, Li2NiO2, SP, and PDVF; Ni with a solid content of 65%. 0.83 Co 0.07 Mn0.1 Second zone slurry containing O2, SP, and PDVF;

[0073] The first positive electrode layer slurry is coated on both sides of the current collector 3 and dried at 105°C to obtain the first positive electrode layer 1;

[0074] Along the laying direction, the surface of the first positive electrode layer 1 is divided into a first region 21 and a second region 22 surrounding the first region; the first region slurry and the second region slurry are coated on the first region 21 and the second region 22 respectively, and dried at 95°C to obtain the second positive electrode layer 2.

[0075] Example 2

[0076] This embodiment provides a lithium-filled positive electrode sheet, which includes a first positive electrode layer and a second positive electrode layer sequentially stacked on both sides of a current collector; along the laying direction, the second positive electrode layer includes a first region disposed at the geometric center of the positive electrode sheet, having the same shape as the positive electrode sheet, and a second region disposed around the first region; the area ratio of the first region to the second region is 90:10;

[0077] The first positive electrode layer is made of Ni in a mass ratio of 96:2:2. 0.96 Co 0.02 Mn 0.02 O2, SP, and PDVF; the areal density of the first positive electrode layer is 300 g / m³. 2 ;

[0078] In the first region, Ni 0.8 Co 0.1 Mn 0.1 The mass ratio of O2 to lithium naphthalene is 22:5, Ni 0.8 Co 0.1 Mn 0.1 The total mass ratio of O2 and lithium naphthalene to the mass ratio of SP and PDVF is 85:8:7, and Ni is present in the second region. 0.8 Co 0.1 Mn 0.1 The mass ratio of O2, SP, and PDVF is 88:6:6; the areal density of the second positive electrode layer is 128.5 g / m³. 2 ;

[0079] Ni in the first positive electrode layer 0.96 Co 0.02 Mn 0.02 The mass of O2, and the Ni in the second cathode layer 0.8 Co 0.1 Mn 0.1 The total mass of O2 and the mass ratio of lithium naphthalene are 70:25:5;

[0080] The method for preparing the lithium-added positive electrode includes:

[0081] Provides Ni with a solid content of 63% 0.96 Co 0.02 Mn 0.02 The first positive electrode layer slurry consists of O2, SP, and PDVF; Ni with a solid content of 53%. 0.8 Co 0.1 Mn 0.1 First-zone slurry containing O2, lithium naphthalene, SP, and PDVF; Ni with a solid content of 60%. 0.8 Co 0.1 Mn 0.1 Second zone slurry containing O2, SP, and PDVF;

[0082] A first positive electrode layer slurry is coated on both sides of the current collector and dried at 120°C to obtain the first positive electrode layer.

[0083] Along the laying direction, the surface of the first positive electrode layer is divided into a first region and a second region surrounding the first region; a first region slurry and a second region slurry are coated on the first region and the second region respectively, and dried at 70°C to obtain the second positive electrode layer.

[0084] Example 3

[0085] This embodiment provides a lithium-filled positive electrode sheet, which includes a first positive electrode layer and a second positive electrode layer sequentially stacked on both sides of a current collector; along the laying direction, the second positive electrode layer includes a first region disposed at the geometric center of the positive electrode sheet, having the same shape as the positive electrode sheet, and a second region disposed around the first region; the area ratio of the first region to the second region is 95:5;

[0086] The first positive electrode layer is made of Ni in a mass ratio of 92:5:3. 0.95 Co 0.02 Mn 0.03 O2, SP, and PDVF; the areal density of the first positive electrode layer is 400 g / m³. 2 ;

[0087] In the first region, Ni 0.83 Co 0.07 Mn 0.1 The mass ratio of O2 to Li5FeO4 is 13.25:1, Ni 0.83 Co 0.07 Mn 0.1 The total mass ratio of O2 and Li5FeO4 to SP and PDVF is 93:4:3, and Ni in the second region... 0.83 Co 0.07 Mn 0.1The mass ratio of O2, SP, and PDVF is 93:4:3; the areal density of the second positive electrode layer is 70.6 g / m³. 2 ;

[0088] Ni in the first positive electrode layer 0.95 Co 0.02 Mn 0.03 The mass of O2, and the Ni in the second cathode layer 0.83 Co 0.07 Mn 0.1 The total mass of O2 and the mass ratio of Li5FeO4 are 85:14:1;

[0089] The method for preparing the lithium-added positive electrode includes:

[0090] Provides Ni with a solid content of 63% 0.95 Co 0.02 Mn 0.03 The first positive electrode layer slurry consists of O2, SP, and PDVF; Ni with a solid content of 53%. 0.83 Co 0.07 Mn 0.1 The first zone slurry contains O2, Li5FeO4, SP, and PDVF; Ni with a solid content of 60%. 0.83 Co 0.07 Mn 0.1 Second zone slurry containing O2, SP, and PDVF;

[0091] A first positive electrode layer slurry is coated on both sides of the current collector and dried at 110°C to obtain the first positive electrode layer.

[0092] Along the laying direction, the surface of the first positive electrode layer is divided into a first region and a second region surrounding the first region; a first region slurry and a second region slurry are coated on the first region and the second region respectively, and dried at 85°C to obtain the second positive electrode layer.

[0093] Example 4

[0094] This embodiment provides a lithium-supplemented cathode sheet, wherein the area ratio of the first region 21 to the second region 22 is 88:12, and the Ni content in the first region is adaptively adjusted. 0.83 Co 0.07 Mn 0.1 Except for the mass ratio of O2 to Li5FeO4 being 14.6:3, everything else was the same as in Example 1.

[0095] Example 5

[0096] This embodiment provides a lithium-supplemented cathode sheet, wherein the area ratio of the first region 21 to the second region 22 is 97:3, and the Ni content in the first region is adaptively adjusted. 0.83 Co 0.07Mn 0.1 Except for the mass ratio of O2 to Li5FeO4 being 16.4:3, everything else was the same as in Example 1.

[0097] Example 6

[0098] This embodiment provides a lithium-added cathode sheet, which, except for the Ni in the first cathode layer... 0.93 Co 0.03 Mn 0.04 The mass of O2, and the Ni in the second cathode layer 0.83 Co 0.07 Mn 0.1 The total mass of O2 and the mass ratio of Li5FeO4 are 90:7:3. In the first region, Ni is adaptively adjusted. 0.83 Co 0.07 Mn 0.1 Except for the mass ratio of O2 to Li5FeO4 being 6.2:3, everything else was the same as in Example 1.

[0099] Example 7

[0100] This embodiment provides a lithium-added cathode sheet, which, except for the Ni in the first cathode layer... 0.93 Co 0.03 Mn 0.04 The mass of O2, and the Ni in the second cathode layer 0.83 Co 0.07 Mn 0.1 The total mass of O2 and the mass ratio of Li5FeO4 are 65:32:3. In the first region, Ni is adaptively adjusted. 0.83 Co 0.07 Mn 0.1 Except for the mass ratio of O2 to Li5FeO4 being 29.2:3, everything else was the same as in Example 1.

[0101] Example 8

[0102] This embodiment provides a lithium-added cathode sheet, which, except for the Ni in the first cathode layer... 0.93 Co 0.03 Mn 0.04 The mass of O2, and the Ni in the second cathode layer 0.83 Co 0.07 Mn 0.1 The total mass of O2 and the mass ratio of Li5FeO4 are 80:19.5:0.5, and the Ni content in the first region is adaptively adjusted. 0.83 Co 0.07 Mn 0.1 Except for the mass ratio of O2 to Li5FeO4 being 17.9:0.5, everything else was the same as in Example 1.

[0103] Example 9

[0104] This embodiment provides a lithium-added cathode sheet, which, except for the Ni in the first cathode layer... 0.93 Co 0.03 Mn 0.04 The mass of O2, and the Ni in the second cathode layer 0.83 Co 0.07 Mn 0.1 The total mass of O2 and the mass ratio of Li5FeO4 are 80:14:6, and the Ni content in the first region is adaptively adjusted. 0.83 Co 0.07 Mn 0.1 Except for the mass ratio of O2 to Li5FeO4 being 12.4:6, everything else was the same as in Example 1.

[0105] Comparative Example 1

[0106] This comparative example provides a lithium-added cathode sheet, except that the second cathode layer is not partitioned, and it is based on Ni... 0.83 Co 0.07 Mn 0.1 The mass ratio of O2 to Li5FeO4 is 17:3, Ni 0.83 Co 0.07 Mn 0.1 The second cathode layer slurry was prepared by coating the surface of the first cathode layer with a total mass ratio of O2 and Li5FeO4, and a mass ratio of SP and PDVF of 90:5:5. All other aspects were the same as in Example 1.

[0107] Performance testing:

[0108] A negative electrode sheet was prepared by mixing graphite with CMC and SBR in a mass ratio of 94:3:3, and the areal density of the negative electrode sheet was set according to N / P=1.1.

[0109] The prepared negative electrode sheet was matched with the lithium-supplemented positive electrode sheets provided in all the above examples and comparative examples. A 1 mol / L lithium hexafluorophosphate EC / DEC (volume ratio 1:1) solution was used as the electrolyte, and a polyethylene membrane was selected to prepare a lithium-ion battery. The electrical performance was then tested.

[0110] At 25℃ and within a voltage range of 2.5V to 4.3V, a 0.1C charge-discharge test was conducted to measure the initial efficiency and initial discharge specific capacity. Then, 100 charge-discharge cycles at 1C were performed to test the cycle capacity retention rate. The test results are shown in Table 1.

[0111] Lithium battery nail penetration test:

[0112] After fully charging the battery, place it on a test bench. Use a 5mm diameter high-temperature resistant steel needle to pierce the geometric center of the battery from top to bottom, perpendicular to the direction of the battery electrodes, at a speed of 25mm / s. Stop advancing the needle after penetration and observe for 1 hour. The results of the needle penetration test of lithium batteries in each embodiment and comparative example are shown in Table 2.

[0113] Table 1

[0114]

[0115] Table 2

[0116]

[0117] In summary, this invention achieves a simultaneous improvement in the energy density, cycle performance, and safety performance of lithium-ion batteries by using a first positive electrode layer with a high nickel content (greater than 90%) as the positive electrode active material and a second positive electrode layer with a medium-to-high nickel content (80% to 90%) as the active material, and by designing the structure of the second positive electrode layer to add lithium replenishing agent only in the middle first region and not in the edge second region.

[0118] Based on the test results of Example 1 and Comparative Example 1, compared with uniform lithium replenishment in the second positive electrode layer, Example 1 showed better first-cycle charge-discharge efficiency, discharge capacity and cycle retention rate, and only emitted smoke in the nail penetration test, indicating a significant improvement in safety performance.

[0119] Based on the test results of Examples 1, 4, and 5, the area ratio of the second region without lithium replenishment in the second positive electrode layer affects the electrochemical performance and safety performance of the assembled lithium-ion battery. If the area ratio is too large, it will lead to a decrease in the first efficiency and discharge capacity of the lithium-ion battery, and the lithium replenishment effect will be unsatisfactory. If the area ratio is too small, the lithium plating phenomenon cannot be effectively avoided, and smoke and fire will occur in the nail penetration test, bringing potential safety accident risks.

[0120] Based on the test results of Examples 1, 6, and 7, the mass ratio of the first positive electrode active material in the first positive electrode layer to the second positive electrode active material in the second positive electrode layer affects the electrochemical performance of the lithium-ion battery. If the mass of the first positive electrode active material is too high, it will exhibit a higher capacity in the first cycle, but the capacity decay will be more severe in long-term charge-discharge cycles, resulting in a worse cycle life. If the mass of the first positive electrode active material is too low, it will lead to a decrease in the energy density of the lithium-ion battery and a reduction in the discharge capacity.

[0121] According to the test results of Examples 1, 8 and 9, if the amount of lithium replenishing agent added is too small, it cannot effectively compensate for the irreversible lithium loss consumed in the negative electrode. If the amount of lithium replenishing agent added is too large, it will lead to an increase in the preparation cost of the positive electrode sheet. In addition, too much lithium will also cause the SEI film to thicken, reducing the capacity retention rate after long-term charge and discharge cycles.

[0122] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A lithium-added positive electrode sheet, characterized in that, The lithium-filled positive electrode includes a first positive electrode layer and a second positive electrode layer sequentially stacked on at least one side surface of the current collector; Along the laying direction, the second positive electrode layer includes a first region disposed in the middle region and a second region disposed around the first region; The first positive electrode layer is made of a first positive electrode active material, the chemical formula of which is Ni. x1 Co y1 Mn z1 O2, 0.99≥x1≥0.9, 0.1≥y1≥0, 0.10≥z1≥0; In the second positive electrode layer, the materials of the first region and the second region each independently include a second positive electrode active material; the chemical formula of the second positive electrode active material is Ni. x2 Co y2 Mn z2 O2, 0.90≥x2≥0.8, 0.2≥y2≥0, 0.2≥z2≥0; The material in the first region also includes lithium replenishing agent.

2. The lithium-filled positive electrode sheet as described in claim 1, characterized in that, In the second positive electrode layer, the area ratio of the first region to the second region is (90~95):(5~10).

3. The lithium-filled positive electrode sheet as described in claim 1 or 2, characterized in that, The mass ratio of the first positive electrode active material in the first positive electrode layer, the total mass of the second positive electrode active material in the second positive electrode layer, to the mass ratio of the lithium supplement in the second positive electrode layer is (70~85):(14~25):(1~5); And / or, the areal density of the first positive electrode layer is 300 g / m³. 2 ~450g / m 2 ; And / or, the areal density of the second positive electrode layer is 55 g / m³. 2 ~180g / m 2 .

4. The lithium-filled positive electrode sheet according to any one of claims 1 to 3, characterized in that, The lithium supplement includes any one or a combination of at least two of Li2NiO2, Li2CO3, Li2O, Li2O2, Li6CoO4, Li5FeO4, aryl lithium compounds, or lithium naphthalene.

5. The lithium-filled positive electrode sheet according to any one of claims 1 to 4, characterized in that, The first positive electrode layer and the second positive electrode layer each independently include a conductive agent and a binder.

6. The lithium-filled positive electrode sheet as described in claim 5, characterized in that, In the first positive electrode layer, the mass ratio of the first positive electrode active material, the conductive agent, and the binder is (93~99):(0.5~6.5):(0.5~6.5); And / or, in the second positive electrode layer, the mass ratio of the total mass of the second positive electrode active material and the lithium replenishing agent to the mass ratio of the conductive agent and the binder in the first region is (85~93):(5~10):(2~5); And / or, in the second positive electrode layer, the mass ratio of the second positive electrode active material to the conductive agent and binder in the second region is (85~93):(5~10):(2~5).

7. A method for preparing a lithium-added positive electrode sheet as described in any one of claims 1 to 6, characterized in that, The preparation method includes: Provides a first positive electrode layer slurry including a first positive electrode active material; a first region slurry including a second positive electrode active material and a lithium supplementing agent; and a second region slurry including the second positive electrode active material. A first positive electrode layer slurry is coated on at least one side of the current collector and dried to obtain the first positive electrode layer; Along the laying direction, the surface of the first positive electrode layer is divided into a first region and a second region surrounding the first region; The first region slurry and the second region slurry are coated on the first region and the second region respectively, and then dried to obtain the second positive electrode layer.

8. The preparation method according to claim 7, characterized in that, The solid content of the first positive electrode layer slurry, the first region slurry, and the second region slurry is independently 40%~70%; And / or, the drying temperature is 70℃~120℃.

9. A lithium-ion battery, characterized in that, The lithium-ion battery includes the lithium-filled positive electrode sheet as described in any one of claims 1 to 6; The lithium-ion battery also includes a negative electrode.

10. The lithium-ion battery as described in claim 9, characterized in that, The negative electrode sheet includes a negative electrode active material, which includes graphite and / or silicon.

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