Positive plate and preparation method thereof, battery and electric equipment

Abstract

The invention relates to the technical field of batteries, in particular to a positive plate and a preparation method thereof, a battery and electric equipment. The positive plate comprises a positive current collector and a positive active material layer arranged on one side of the positive current collector, the positive active material layer comprises a first active material layer and a second active material layer which are arranged in a stacked mode, the first active material layer is located between the second active material layer and the positive current collector, the first active material layer comprises LiMnx1Fey1PO4 and LiNia1Cob1Mc1O2, x1 + y1 = 1, a1 + b1 + c1 = 1, and the second active material layer is located between the first active material layer and the positive current collector. M comprises at least one of Mn, Al, Zr and Ti; the second active material layer comprises LiMnx2Fey2PO4 and LiNia2Cob2Mc2O2, x < 2 > + y < 2 > = 1, a < 2 > + b < 2 > + c < 2 > = 1, and M'comprises at least one of Mn, Al, Zr and Ti; the ratio of the mass content of Fe to the mass content of Co in the first active material layer is different from the ratio of the mass content of Fe to the mass content of Co in the second active material layer. According to the positive plate, micro-interface polarization can be improved, and the risk of local lithium precipitation caused by uneven charge distribution is reduced.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a positive electrode sheet and its preparation method, a battery and an electrical device. Background Technology

[0002] Cathode materials are the decisive factor in the electrochemical performance of lithium batteries, directly determining their energy density and safety. As market demands for lithium battery performance continue to rise, cathode materials are undergoing technological iteration and upgrades. Ternary lithium cathode materials possess high energy density, but they suffer from poor cycle performance, significant post-cycle gas generation, and poor safety performance. Lithium manganese iron phosphate materials offer high safety, but compared to ternary lithium, their lower energy density remains a disadvantage.

[0003] Improvements to existing cathode materials include: setting the active material layer as a double-layer structure, using different types of conductive agents in the double layers to enhance the adsorption of electrolyte by the active material layer, avoiding the decline in ion transport performance in the first active material layer close to the current collector and electron transport capability in the second active material layer farther from the current collector, thereby improving the kinetic performance of the battery during charging and discharging.

[0004] However, this method only improves the battery electrode structure and process, and cannot reconcile the inherent performance differences of different cathode materials. It may lead to potential differences at the micro-interface, uneven lithium insertion and extraction, and the risk of local lithium plating on the anode. Summary of the Invention

[0005] This application provides a positive electrode, a method for preparing the positive electrode, a battery, and an electrical device, which improves micro-interface polarization and reduces the risk of local lithium plating on the negative electrode.

[0006] A first aspect of this application provides a positive electrode sheet, comprising: a positive electrode current collector and a positive electrode active material layer disposed on one side of the positive electrode current collector, the positive electrode active material layer comprising a first active material layer and a second active material layer stacked thereon, the first active material layer being located between the second active material layer and the positive electrode current collector.

[0007] The first active material layer includes LiMn x1 Fe y1 PO4 and LiNi a1 Co b1 M c1 O2, where x1+y1=1, a1+b1+c1=1, and M includes at least one of Mn, Al, Zr, and Ti;

[0008] The second active material layer includes LiMn x2 Fe y2 PO4 and LiNi a2 Co b2 Mc2 O2, where x2+y2=1, a2+b2+c2=1, and M' includes at least one of Mn, Al, Zr, and Ti;

[0009] Furthermore, the ratio of the mass content of Fe to the mass content of Co in the first active material layer is different from the ratio of the mass content of Fe to the mass content of Co in the second active material layer.

[0010] In some embodiments, the ratio of the mass content of Fe to the mass content of Co in the first active material layer is greater than the ratio of the mass content of Fe to the mass content of Co in the second active material layer.

[0011] In some embodiments, the ratio of the mass content of Fe to the mass content of Co in the first active material layer, P1, and the ratio of the mass content of Fe to the mass content of Co in the second active material layer, P2, satisfy the relationship: 2≤P2<P1≤40.

[0012] In some embodiments, the value of y1 is in the range of 0.1-0.9; and / or, the value of y2 is in the range of 0.1-0.9.

[0013] In some embodiments, the value of y1 is in the range of 0.1-0.6, the value of y2 is in the range of 0.1-0.6, and y2 < y1.

[0014] In some embodiments, the value of y1 ranges from 0.3 to 0.6, the value of y2 ranges from 0.1 to 0.5, and the LiMn in the first active material layer... x1 Fe y1 The mass content of PO4 is not less than that of LiMn in the second active material layer. x2 Fe y2 The mass content of PO4, wherein y1 and y2 satisfy: y2 < y1.

[0015] In some embodiments, the value of b1 is in the range of 0.05-0.4; and / or, the value of b2 is in the range of 0.05-0.4.

[0016] In some embodiments, the first active material layer further includes at least one of a conductive agent, a binder, and a dispersant; and / or, the second active material layer further includes at least one of a conductive agent, a binder, and a dispersant.

[0017] In some embodiments, the thickness H1 of the first active material layer and the thickness H2 of the second active material layer satisfy: 0.7 ≤ H2 / H1 ≤ 8.8.

[0018] A second aspect of this application provides a method for preparing a positive electrode sheet, comprising the following steps:

[0019] LiMn x1 Fe y1 PO4, LiNi a1 Co b1 M c1 O2, conductive agent, binder, dispersant, and solvent are mixed uniformly according to a certain stoichiometric ratio to prepare a slurry for the first active material layer, and LiMn is added... x2 Fe y2 PO4, LiNi a2 Co b2 M' c2 O2, conductive agent, binder, dispersant and solvent are mixed evenly according to a certain stoichiometric ratio to prepare a slurry for the second active material layer, wherein x1+y1=1, a1+b1+c1=1, M includes at least one of Mn, Al, Zr and Ti, x2+y2=1, a2+b2+c2=1, and M' includes at least one of Mn, Al, Zr and Ti;

[0020] The slurry of the first active material layer is coated onto the surface of the positive electrode current collector, and the slurry of the second active material layer is coated onto the slurry surface of the first active material layer.

[0021] The positive electrode sheet is obtained by baking and curing; wherein the ratio of the mass content of Fe to the mass content of Co in the first active material layer is different from the ratio of the mass content of Fe to the mass content of Co in the second active material layer.

[0022] A third aspect of this application provides a battery comprising the aforementioned positive electrode plate.

[0023] A fourth aspect of this application provides an electrical device including the battery described above.

[0024] The positive electrode sheet of this application has at least the following beneficial effects: the positive electrode active material layer is configured to include two layers, a first active material layer and a second active material layer, both of which contain lithium manganese iron phosphate material and ternary lithium material. Furthermore, the ratio of the mass content of Fe to the mass content of Co in the first active material layer and the second active material layer is different. This allows for flexible adjustment of the Fe and Co contents in the first and second active material layers as needed, ensuring that the lithium manganese iron phosphate in the first active material layer is rapidly deintercalated and intercalated, and then rapidly transported through the ternary lithium channels in the second active material layer, thus avoiding lithium plating. It also helps to optimize the micro-interface impedance between different positive electrode materials, reduce polarization during battery charging and discharging, and improve the battery's charging and discharging performance. Attached Figure Description

[0025] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0026] Figure 1 This is a schematic diagram of the structure of the positive electrode sheet in some embodiments of this application.

[0027] Explanation of reference numerals in the attached figures:

[0028] 100. Positive electrode plate;

[0029] 110. Positive current collector;

[0030] 120. Positive electrode active material layer; 121. First active material layer; 122. Second active material layer. Detailed Implementation

[0031] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0032] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0033] The terms "first," "second," "third," "fourth," etc. (if applicable) in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the application described herein can be implemented, for example, in orders other than those illustrated or described herein. In embodiments of this application, the words "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in this application should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the words "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0034] refer to Figure 1An embodiment of the first aspect of this application provides a positive electrode 100, including a positive current collector 110 and a positive active material layer 120 coated on the surface of the positive current collector 110.

[0035] The positive electrode current collector 110 can be an aluminum foil, and the positive electrode active material layer 120 includes a first active material layer 121 and a second active material layer 122 stacked together. The first active material layer 121 is located between the second active material layer 122 and the positive electrode current collector 110, that is, the first active material layer 121 is coated on the surface of the positive electrode current collector 110, and the second active material layer 122 is coated on the surface of the first active material layer 121. Thus, in the battery, the arrangement of each layer on the positive electrode sheet 100 with the electrolyte is, in sequence, the positive electrode current collector 110, the first active material layer 121, the second active material layer 122, and the electrolyte.

[0036] The first active material layer 121 includes LiMn x1 Fe y1 PO4 (i.e., lithium iron phosphate) and LiNi a1 Co b1 M c1 O2 (ternary lithium material), wherein x1+y1=1, a1+b1+c1=1, and M includes at least one of Mn, Al, Zr, and Ti. In other words, M can include one of Mn, Al, Zr, and Ti, or M can include two or three of the above four materials, or M can be a combination of the above four materials. The second active material layer 122 includes LiMn. x2 Fe y2 PO4 and LiNi a2 Co b2 M' c2 O2, where x² + y² = 1, a² + b² + c² = 1, and M' includes at least one of Mn, Al, Zr, and Ti. In other words, both the first active material layer 121 and the second active material layer 122 can contain lithium manganese iron phosphate salt material and ternary lithium material.

[0037] Specifically, the relative content of each element in the lithium manganese iron phosphate salt material and ternary lithium material in the first active material layer 121 and the first active material layer 122 can be adjusted by changing the values ​​of x1, y1, a1, b1, c1 and x2, y2, a2, b2, and c2. This makes the ratio of the mass content of Fe to the mass content of Co in the first active material layer 121 different from the ratio of the mass content of Fe to the mass content of Co in the second active material layer 122, thereby making the material distribution of the positive electrode active material layer of the positive electrode sheet more reasonable.

[0038] According to the inventors' research, layered ternary lithium materials have high energy density, but they suffer from poor cycle performance, severe post-cycle gas generation, and poor safety performance. Lithium manganese iron phosphate (MFP) materials have high safety, but their low energy density remains a disadvantage compared to ternary lithium materials. Currently, different proportions of ternary lithium materials and MFP materials are mixed to meet applicable operating conditions. However, the one-dimensional conduction of lithium ions in MFP materials results in low ionic conductivity, while in terms of electron transport, the conductivity of MFP materials (10⁻⁶) is significantly lower. -13 S / cm) is lower than that of ternary lithium materials (10 -3 S / cm~10 -6 The S / cm ratio leads to inconsistent electron and ion transport rates after mixing. In particular, ions and electrons near the electrode / electrolyte side are transported unevenly along the electrode thickness, resulting in uneven charge distribution and severely affecting the electrochemical reaction kinetics.

[0039] Therefore, based on the inventors' research, the arrangement of the positive electrode active material layer 120 of the positive electrode sheet 100 is set as a double-layer structure of a first active material layer 121 and a second active material layer 122. Both the first active material layer 121 and the second active material layer 122 include lithium manganese iron phosphate material and ternary lithium material. The ratio of the mass content of Fe to the mass content of Co in the first active material layer 121 and the second active material layer 122 are different. This allows for adjustments to the content of lithium manganese iron phosphate material and ternary lithium in each layer, improving the rationality of the Fe and Co distribution in each layer, thereby maximizing the driving force of the first active layer for lithium ion insertion / extraction and the lithium ion transport efficiency in the second active material layer. Furthermore, controlling the ratio of Fe mass content to Co mass content in the first active material layer 121 and the second active material layer 122 is beneficial for meeting the trade-off between energy density and safety. It can also solve the micro-interface polarization caused by the intrinsic physicochemical properties difference between ternary lithium materials and lithium manganese iron phosphate materials, improve micro-interface polarization and impedance, and reduce the risk of local lithium plating caused by uneven charge distribution.

[0040] Furthermore, in this embodiment, the coating dimensions of the first active material layer 121 and the second active material layer 122 can be designed, and the coating thickness of the first active material layer 121 and the second active material layer 122 can be changed according to different working conditions, thereby improving the energy density of the battery while meeting the electrode thickness requirements, so as to match market demand.

[0041] In the embodiments of this application, during battery use, electrons are conducted through the current collector via the external circuit. A large potential difference exists between the positive electrode current collector 110 and the active material near the positive electrode current collector 110, i.e., a large potential difference within the first active material layer 121. This preferentially drives the active material to deintercalate and intercalate lithium ions. The ratio of Fe mass content to Co mass content in the first active material layer 121 is greater than that in the second active material layer 122, resulting in a higher proportion of lithium manganese iron phosphate material in the first active material layer 121. Since both lithium manganese iron phosphate and ternary lithium materials can reduce the electron / ion transport impedance, a higher proportion of lithium manganese iron phosphate material allows the lithium manganese iron phosphate material, with its higher impedance, to have sufficient driving potential to drive the active material to deintercalate and intercalate lithium ions, and controls the impedance difference between the two materials, resulting in a uniform charge distribution.

[0042] In some embodiments, the ratio of the mass content of Fe to the mass content of Co in the first active material layer, P1, and the ratio of the mass content of Fe to the mass content of Co in the second active material layer, P2, satisfy the following relationship: 2≤P2<P1≤40.

[0043] This ensures that the lithium manganese iron phosphate material in the first active material layer 121 can be rapidly transported through the transport channels of the ternary lithium material in the second active material layer 122 after lithium insertion / extraction. Furthermore, it optimizes the micro-interface impedance between different cathode materials, resulting in a more uniform charge distribution and reducing polarization during battery charging and discharging. In the embodiments of this application, the value of y1 ranges from 0.1 to 0.9. For example, the value of y1 can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9, and correspondingly, the value of x1 can be 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or 0.1. Of course, the value of y1 can also be other values, which designers can choose according to their needs; this application does not impose any restrictions on this. By selecting different values ​​for y1, corresponding to different lithium manganese iron phosphate materials, a balance can be found between improving battery energy density, battery rate performance, thermal stability, and battery cycle life to meet the needs of different applications. Understandably, the value of y2 can range from 0.1 to 0.9. For example, the value of y2 can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9. Of course, the value of y2 can also be other values, and designers can choose according to their needs. This application does not impose any restrictions on this. In this way, it has the same effect as the value of y1 mentioned above, and will not be elaborated further.

[0044] Furthermore, the value range of y1 is 0.1-0.6, the value range of y2 is 0.1-0.6, and y2 < y1.

[0045] Furthermore, the value of y1 ranges from 0.3 to 0.6, and the value of y2 ranges from 0.1 to 0.5. Also, in the first active material layer, LiMn... x1 Fe y1 The mass content of PO4 is not less than that of LiMn in the second active material layer. x2 Fe y2 The mass content of PO4, y1 and y2, satisfy: y2 < y1.

[0046] In this way, the Fe content in the first active material layer 121 can be greater than the Fe content in the second active material layer, which is beneficial to further reduce the ion transport impedance of the first active material layer 121, ensuring that lithium ions have sufficient driving potential for insertion and extraction in the first active material layer 121, thereby improving the charging and discharging efficiency of the battery.

[0047] In the embodiments of this application, the value range of b1 can be set to 0.05-0.4. For example, the value of b1 can be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, or 0.4. Of course, the value of b1 can also be other values, and designers can choose according to their needs. This application does not impose any restrictions on this.

[0048] By selecting different values ​​for b1, corresponding to different ternary lithium materials, a balance can be found between improving battery energy density, rate performance, thermal stability, and cycle life to meet the needs of different applications. Understandably, the value of b2 ranges from 0.05 to 0.4. For example, the value of b2 can be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, or 0.4. Of course, other values ​​for b2 are also possible, and designers can choose according to their needs; this application does not impose any restrictions on this. Thus, the same effect as the aforementioned b1 value is achieved, and will not be elaborated further.

[0049] In embodiments of this application, the first active material layer 121 may further include at least one of a conductive agent, a binder, and a dispersant. For example, the first active material layer 121 may include one of a conductive agent, a binder, and a dispersant, or a combination of two or three of them. Understandably, during the preparation of the first active material layer 121, the slurry of the first active material layer 121 also includes a solvent, which evaporates during the drying process after the slurry is coated.

[0050] Similarly, the second active material layer 122 may also include at least one of a conductive agent, a binder, a dispersant, and a solvent. For example, the second active material layer 122 may include one of a conductive agent, a binder, and a dispersant, or a combination of two or three of them. Understandably, during the preparation of the second active material layer 122, the slurry of the second active material layer 122 also includes a solvent, which evaporates during the drying process after the slurry is coated.

[0051] Conductive agents enhance the electronic conductivity of electrode materials, ensuring uniform current distribution within the electrodes and thus improving overall battery performance. Furthermore, improved conductivity allows for more efficient charging and discharging at high rates, making it suitable for applications requiring rapid energy conversion. Binders help bind active material particles and conductive agents together, forming a stable electrode structure and preventing material detachment during charge-discharge cycles. Dispersants help uniformly disperse active materials and conductive agents, preventing particle agglomeration and improving electrode uniformity and performance consistency. Improved material dispersibility allows for better control of electrode thickness and density, thereby optimizing battery energy density and volumetric efficiency. Solvents are used to mix active materials, conductive agents, and binders into a slurry, facilitating coating and molding. Appropriate solvents can improve the rheological properties of the slurry, ensuring uniformity and consistency during the coating process.

[0052] In the embodiments of this application, the thickness H1 of the first active material layer 121 and the thickness H2 of the second active material layer 122 satisfy: 0.7 ≤ H2 / H1 ≤ 8.8. For example, H2 / H1 can be 0.7, 0.8, 0.9, 1, 1.2, 1.5, 1.8, 2, 2.3, 2.5, 2.7, 3, 3.1, 3.3, 3.5, 3.8, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, or 8.8. Of course, the value of H2 / H1 can also be other values, and this embodiment does not limit this.

[0053] By selecting an appropriate thickness ratio between the first active material layer 121 and the second active material layer 122, a balance can be achieved between improving energy density and ensuring ion transport efficiency.

[0054] The second aspect of this application also provides a method for preparing a positive electrode 100, which includes the following steps:

[0055] S1: LiMn x1 Fe y1 PO4, LiNi a1 Co b1 M c1O2, conductive agent, binder, dispersant, and solvent are mixed uniformly according to a certain stoichiometric ratio to prepare a slurry with the first active material layer 121, and LiMn... x2 Fe y2 PO4, LiNi a2 Co b2 M' c2 O2, conductive agent, binder, dispersant and solvent are mixed uniformly according to a certain stoichiometric ratio to prepare a slurry for the second active material layer 122, wherein x1+y1=1, a1+b1+c1=1, M includes at least one of Mn, Al, Zr and Ti, x2+y2=1, a2+b2+c2=1, M' includes at least one of Mn, Al, Zr and Ti, and the ratio of the mass content of Fe to the mass content of Co in the first active material layer is different from the ratio of the mass content of Fe to the mass content of Co in the second active material layer;

[0056] S2: The slurry of the first active material layer 121 is coated onto the surface of the positive electrode current collector 110, and the slurry of the second active material layer 122 is coated onto the slurry surface of the first active material layer 121.

[0057] S3: Baking and curing to obtain positive electrode 100, wherein the ratio of the mass content of Fe to the mass content of Co in the first active material layer is different from the ratio of the mass content of Fe to the mass content of Co in the second active material layer.

[0058] In step S1, the LiMn in the first active material layer 121 can be used as a basis. x1 Fe y1 The mass percentage of PO4 M1, and the LiMn in the first active material layer 121 x1 Fe y1 The molar ratio of Fe in PO4, y1, and the LiNi in the first active material layer 121 a1 Co b1 M c1 The molar ratio b1 of Co in the first active material layer 121 determines the LiMn content. x1 Fe y1 PO4 and LiNi a1 Co b1 M c1 The amount of material used. Based on the LiMn content in the second active material layer 122. x2 Fe y2 The mass percentage of PO4 (M2) and the LiMn in the second active material layer 122 x2 Fe y2 The molar ratio of Fe in PO4, y2, and LiNi in the second active material layer 122 a2 Co b2M c2 The molar ratio of Co in the second active material layer 122, b2, determines the LiMn content. x2 Fe y2 PO4 and LiNi a2 Co b2 M c2 The amount of materials used.

[0059] In step S2, the positive electrode active material layer 120 can be coated on one side of the positive electrode current collector 110 along the thickness direction. That is, after coating the first active material layer 121 on one side of the positive electrode current collector 110, the second active material layer 122 is then coated on the first active material layer 121. The positive electrode active material layer 120 can also be coated on both sides of the positive electrode current collector 110 along the thickness direction. That is, after coating the first active material layer 121 on both sides of the positive electrode current collector 110, the second active material layer 122 is then coated on the first active material layer 121.

[0060] In this embodiment, lithium manganese iron phosphate salt materials and ternary lithium materials with different component contents are mixed uniformly with conductive agents, binders, dispersants and solvents in different stoichiometric ratios to obtain slurries for the first active material layer 121 and the second active material layer 122. After coating the slurry of the first active material layer 121 onto the positive electrode current collector 110, the second active material layer 122 is coated on the first active material layer 121. After baking and curing, a positive electrode sheet 100 is obtained. By controlling the ratio of Fe content to Co content in the first active material layer 121 and the second active material layer 122 in the positive electrode sheet 100, it is beneficial to rationally arrange the material distribution of the positive active material layer 120, which is beneficial to improve the driving force of the first active layer for the insertion and extraction of lithium ions from the active material, and improve the transport efficiency of lithium ions (or electrons) in the second active material layer. This allows lithium ions (or electrons) near the positive electrode current collector 110 (or near the electrolyte) to diffuse rapidly, thereby improving the charge and discharge performance of the battery. Furthermore, controlling the ratio of Fe mass content to Co mass content in the first active material layer 121 and the second active material layer 122 is beneficial to meeting the trade-off between energy density and safety. It can also solve the micro-interface polarization caused by the intrinsic physicochemical properties difference between ternary lithium materials and lithium manganese iron phosphate materials, improve micro-interface polarization and impedance, and reduce the risk of local lithium plating caused by uneven charge distribution.

[0061] Thirdly, embodiments of this application also provide a battery including the above-mentioned positive electrode 100, which has advantages corresponding to the above-mentioned positive electrode 100, and will not be described in detail here.

[0062] Generally, a battery includes an electrolyte, a battery cell, and a casing for encapsulating the battery cell. The electrolyte is injected into the battery cell inside the casing. The battery cell includes a positive electrode 100, a negative electrode, and a separator located between the positive electrode 100 and the negative electrode. The battery cell can be a stacked battery cell, meaning it is composed of a positive electrode 100, a separator, and a negative electrode stacked together.

[0063] Specifically, the negative electrode sheet includes a negative current collector and a negative electrode coating located on at least one side surface of the negative current collector. Specifically, the negative electrode coating can be provided on one side surface of the negative current collector, or negative electrode coatings can be provided on both opposite sides of the negative current collector in the thickness direction.

[0064] The embodiments of this application may employ conventional negative electrode current collectors in the art, for example, negative electrode current collectors may include copper foil.

[0065] In this embodiment, the negative electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the components used to form the negative electrode coating, such as the negative electrode active material, conductive agent, and binder, can be dispersed in a second solvent, such as water, to prepare a negative electrode slurry. The slurry is then coated on the surface of the negative electrode current collector and, after drying, rolling and other processes, the negative electrode sheet is obtained.

[0066] Corresponding to this solution, the negative electrode active material layer of the negative electrode sheet can also be set as a double-layered third active material layer and a fourth active material layer, with different silicon contents in the third active material layer and the fourth active material layer, thereby further improving the energy density of the battery.

[0067] The electrolyte in this application embodiment can be a conventional electrolyte in the art. For example, the electrolyte is a non-aqueous electrolyte, which may specifically include organic solvents, additives and electrolyte salts. Organic solvents include one or more of ethylene carbonate (EC), diethyl carbonate (DEC) and propylene carbonate (PC). Additives include, for example, fluoroethylene carbonate (FEC). Electrolyte salts may include lithium salts, such as lithium hexafluorophosphate (LiPF6), but are not limited thereto.

[0068] In this embodiment, the diaphragm is used to separate the positive electrode 100 and the negative electrode to prevent the positive electrode 100 and the negative electrode from short-circuiting due to contact. Conventional diaphragms in the art can be used in this embodiment, and there are no special limitations.

[0069] In this embodiment, the battery cell can be packaged using conventional housing materials in the art, such as flexible packaging materials like aluminum-plastic film, but is not limited to these.

[0070] The embodiments of this application can assemble components such as the positive electrode 100, separator, and negative electrode into a battery using conventional methods in the art. For example, the positive electrode 100, separator, and negative electrode can be stacked to obtain a stacked cell; then the cell is placed in a casing (outer packaging), and after conventional processes such as electrolyte injection and encapsulation, a battery is obtained.

[0071] Fourthly, embodiments of this application also provide an electrical device including the battery described above.

[0072] The electrical equipment provided in this embodiment can be an energy storage cabinet, an energy storage container, a vehicle, a spacecraft, etc. This application embodiment does not impose any special limitations on the electrical equipment.

[0073] According to the embodiments of this application, by setting the battery of the above embodiment, the charging efficiency of the battery is higher and the service life is longer, which helps to extend the working time of the electrical equipment and thus improve the working efficiency of the electrical equipment.

[0074] The present application will be further described below through specific embodiments.

[0075] Example 1: (1) Positive electrode slurry formulation: Lithium manganese iron phosphate material (LiMn) was added to mixing tank 1 and mixing tank 2 respectively. 0.5 Fe 0.5 PO4) and ternary lithium materials (LiNi) 0.7 Co 0.1 Mn 0.2 The positive electrode material (O2), conductive agent, binder, dispersant, and solvent NMP are mixed to form a slurry. The mixture is stirred until it is homogeneous. The mass ratio of lithium manganese iron phosphate material to ternary lithium material in mixing tank 1 is 7:3, which is denoted as slurry 1. The mass ratio of lithium manganese iron phosphate material to ternary lithium material in mixing tank 2 is 4:6, which is denoted as slurry 2. During the uncoated period, the mixture is stirred at low speed to ensure that the slurry is in good condition.

[0076] (2) Apply the above slurry 1 and slurry 2 simultaneously to the positive current collector 110 using a dual-die head, adjust the slurry feed rate, apply slurry 1 to the aluminum foil (i.e. the positive current collector 110), apply slurry 2 to slurry 1, with a coating width of 100 mm, and then bake and cure.

[0077] (3) The above positive electrode 100 is assembled with a separator, graphite negative electrode and other components into a full cell for testing after undergoing battery preparation processes such as rolling.

[0078] Examples 2-15: The preparation methods of the positive electrode 100 and the battery in Examples 2-15 are the same as those in Example 1.

[0079] In Example 2, the difference from Example 1 is that the ratio of the mass content of Fe to the mass content of Co in the first active material layer 121 is set to 7, and the ratio of the mass content of Fe to the mass content of Co in the second active material layer 122 is set to 3.

[0080] In Example 3, the difference from Example 1 is that the ratio of the mass content of Fe to the mass content of Co in the first active material layer 121 is set to 2, and the ratio of the mass content of Fe to the mass content of Co in the second active material layer 122 is set to 3.

[0081] In Example 4, the difference from Example 1 is that the ratio of the mass content of Fe to the mass content of Co in the first active material layer 121 is set to 19, and the ratio of the mass content of Fe to the mass content of Co in the second active material layer 122 is set to 5.

[0082] In Example 5, the difference from Example 1 is that the ratio of the mass content of Fe to the mass content of Co in the second active material layer 122 is set to 5.

[0083] In Example 6, the difference from Example 1 is that the ratio of the mass content of Fe to the mass content of Co in the second active material layer 122 is set to 2.

[0084] In Example 7, the difference from Example 1 is that the LiMn in the first active material layer 121 is... x1 Fe y1 The mass percentage M1 of PO4 is set to 0.9, and the ratio of the mass content of Fe to the mass content of Co in the first active material layer 121 is set to 45.

[0085] In Example 8, the difference from Example 1 is that the LiMn in the second active material layer 122 is... x2 Fe y2 The mass percentage of PO4, M2, is set to 0.8, and the ratio of the mass content of Fe to the mass content of Co in the second active material layer 122 is set to 20.

[0086] In Example 9, the difference from Example 1 is that the ratio of the thickness H2 of the second active material layer 122 to the thickness H1 of the first active material layer is 0.63.

[0087] In Example 10, compared with Example 1, the ratio of the thickness H2 of the second active material layer 122 to the thickness H1 of the first active material layer is 8.03.

[0088] In Example 11, the difference from Example 1 is that the active material in the first active material layer 121 is lithium manganese iron phosphate (LiMn). 0.5 Fe 0.5 PO4) and ternary lithium materials (LiNi) 0.7 Co 0.1 Mn 0.2 The cathode materials include O2, and the mass ratio of lithium manganese iron phosphate material and ternary lithium material is 7:3; the active material in the second active material layer 122 is lithium manganese iron phosphate material (LiMn). 0.9 Fe 0.1 PO4) and ternary lithium materials (LiNi) 0.7 Co 0.1 Mn 0.2 The cathode materials (such as O2), lithium manganese iron phosphate, and ternary lithium materials are in a mass ratio of 7:3, and the ratio of Fe mass content to Co mass content in the second active material layer 122 is set to 2.

[0089] In Example 12, the difference from Example 1 is that the active material in the first active material layer 121 is lithium manganese iron phosphate (LiMn). 0.5 Fe 0.5 PO4) and ternary lithium materials (LiNi) 0.7 Co 0.1 Mn 0.2 The cathode materials include O2, and the mass ratio of lithium manganese iron phosphate material and ternary lithium material is 7:3; the active material in the second active material layer 122 is lithium manganese iron phosphate material (LiMn). 0.4 Fe 0.6 PO4) and ternary lithium materials (LiNi) 0.7 Co 0.1 Mn 0.2 The cathode materials (such as O2), lithium manganese iron phosphate, and ternary lithium materials are in a mass ratio of 7:3, and the ratio of Fe mass content to Co mass content in the second active material layer 122 is set to 14.

[0090] In Example 13, the difference from Example 1 is that the active material in the first active material layer 121 is lithium manganese iron phosphate (LiMn). 0.2 Fe 0.8 PO4) and ternary lithium materials (LiNi) 0.7 Co 0.1 Mn 0.2 The mass ratio of positive electrode materials such as O2, lithium manganese iron phosphate, and ternary lithium materials is 7:3; the mass content of Fe in the first active material layer 121 is set to the mass content of Co to 19.

[0091] In Example 14, the difference from Example 1 is that the active material in the first active material layer 121 is lithium manganese iron phosphate (LiMn). 0.8 Fe 0.2 PO4) and ternary lithium materials (LiNi) 0.7 Co 0.1 Mn 0.2 The cathode materials include O2, and the mass ratio of lithium manganese iron phosphate material and ternary lithium material is 7:3; the active material in the second active material layer 122 is lithium manganese iron phosphate material (LiMn). 0.5 Fe 0.5 PO4) and ternary lithium materials (LiNi) 0.7 Co 0.1 Mn 0.2 The cathode materials (such as O2), lithium manganese iron phosphate material and ternary lithium material are in a mass ratio of 4:6. The mass content ratio of Fe to Co in the first active material layer 121 is set to 5, and the mass content ratio of Fe to Co in the second active material layer 122 is set to 3.

[0092] In Example 15, compared with Example 1, the ratio of the thickness H2 of the second active material layer 122 to the thickness H1 of the first active material layer is 10.26.

[0093] Comparative Example 1

[0094] LiMn 0.5 Fe 0.5 PO4 and LiNi 0.7 Co 0.1 Mn 0.2 O2 is mixed with conductive agent, binder, dispersant and NMP in a mass ratio of 17:83 to form a slurry, which is then coated on the positive current collector to prepare a positive electrode sheet. The positive electrode sheet is then assembled with a separator, graphite negative electrode and other components to form a full cell for testing.

[0095] Table 1. Parameter table for Examples 1-15 and Comparative Example 1

[0096]

[0097] Discharge DCIR test, discharge average voltage test and rate test were performed on Examples 1-10 and Comparative Example 1, respectively. The specific test methods are as follows:

[0098] Discharge DCIR test conditions: Under 25℃ conditions, charge to 4.3V with 1 / 3C constant current and constant voltage, cut-off current 0.05C, discharge at 1 / 3C for 90min to 50% SOC, rest for 30min; discharge at 1.5C for 30s, record the rest termination voltage V0, discharge termination voltage V1 and termination current A1, discharge DCIR=(V0-V1) / A1.

[0099] Discharge average voltage test conditions: Under 25℃ conditions, charge to 4.3V with 1 / 3C constant current and constant voltage, cut off current 0.05C, discharge to 2.5V with 1 / 3C, record discharge charge Q and capacity C, discharge average voltage = Q / C.

[0100] Rate testing conditions: At 25℃, charge and discharge at 0.5C constant current and constant voltage to the cutoff voltage. The cutoff current is 0.05C. Record the discharge capacity as Q0. Charge at 3C to the upper limit voltage and record the capacity Q1 after 20 minutes of charging.

[0101] Table 2. Test results of Examples 1-15 and Comparative Example 1

[0102]

[0103] Comparing the test results of Examples 1-6 and Comparative Example 1 confirms that by controlling the different Fe / Co mass content ratios of lithium manganese iron phosphate material and ternary lithium material, the material distribution of the positive electrode active material layer is reasonable, which is conducive to electron and lithium-ion transport, avoids lithium plating, and improves the charge and discharge performance of the battery.

[0104] Further combining Examples 1, 4, and 5, the ratio of Fe mass content to Co mass content in the first active material layer is made greater than that in the second active material layer, and the difference in the Fe / Co mass content ratio between the two layers is within a suitable range. The lithium manganese iron phosphate material in the first active material layer near the current collector is effectively driven to perform lithium insertion / extraction due to the larger potential difference. The higher Fe / Co mass content ratio in the first active material layer indicates a greater amount of lithium manganese iron phosphate material, which helps alleviate the charge impedance difference between the lithium manganese iron phosphate material and the ternary lithium material. The lower Fe / Co ratio in the second active material layer means an increased proportion of ternary lithium material, satisfying the requirement for rapid transport through the ternary lithium material channels in the second active material layer after lithium insertion / extraction in the first active material layer. This reduces polarization caused by high tortuosity and significantly improves the battery rate performance while reducing the battery's internal resistance.

[0105] The results from Examples 1 and 2 show that reducing the Fe content in the positive electrode active material layer (decreasing y1 and y2) reduces the Fe / Co mass ratio, leading to an increased impedance difference between the lithium manganese iron phosphate material and the ternary lithium material. This results in uneven current mass transfer, thus affecting the battery's rate performance. Furthermore, in Example 3, increasing the Co content (increasing b1 and b2) further exacerbates the intrinsic impedance difference, resulting in insufficient lithium-ion mass transfer in the first active material layer under high current, and increasing the risk of lithium plating in the battery.

[0106] Compared to Example 1, in Example 4, increasing only the Fe content of the positive electrode active material layer (increasing y1 and y2) can reduce the impedance difference between lithium manganese iron phosphate and ternary lithium materials, but it also leads to a decrease in the average voltage of the battery, affecting the battery energy density. Furthermore, the battery is more likely to reach the cutoff potential at high rates, affecting fast charging performance. Similarly, in Example 5, increasing the Fe molar ratio of the second active material layer also leads to a slight decrease in the average voltage and rate performance of the battery.

[0107] Compared to Example 1, Example 6 increases the molar ratio of Co in the ternary lithium material of the second active material layer, resulting in the Fe / Co mass content ratio of the second active material layer being outside the optimized range. This exacerbates the impedance difference between the lithium manganese iron phosphate material and the ternary lithium material far from the current collector side. At this time, the internal resistance of the battery under DC conditions is large, resulting in poor fast charging performance.

[0108] In Example 5, the increased proportion of ternary lithium material in the first active material layer leads to a decrease in average driving force, resulting in a significant decrease in battery capacity at high rates. In Example 6, the increased proportion of lithium manganese iron phosphate material in the second active material layer hinders charge transport along the electrode thickness direction in the first layer, exacerbating polarization, thus resulting in poorer impedance and rate performance compared to Example 1.

[0109] Compared to Example 1, Example 8 increased the amount of LiMn in the second active material layer. x2 Fe y2 The mass percentage of PO4, M2, makes the Fe / Co mass content ratio of the second active material layer too high, even exceeding the Fe / Co mass content ratio of the first active material layer, which in turn leads to an increase in battery impedance.

[0110] In conjunction with Examples 1, 9, 10, and 15, when the ratio of the thickness of the second active material layer to the thickness of the first active material layer is less than 0.5, the increase in the high LMFP ratio layer leads to a decrease in the average discharge voltage, and the potential difference decreases with the current collector towards the electrode thickness direction, weakening the delithiation driving force and affecting rate performance. When the ratio of the thickness of the second active material layer to the thickness of the first active material layer increases, although it is beneficial to improve the average discharge voltage of the battery, the high Fe / Co layer decreases, the overall intermaterial impedance increases, and the rate performance is reduced.

[0111] Combining Examples 1 and 11, since the mass content of Fe in the first active material layer is greater than that in the second active material layer, the battery impedance can be reduced and the rate performance of the battery can be improved.

[0112] Combining Examples 11 and 12, in Example 11, the Fe content y2 in the lithium manganese iron phosphate material in the second active material layer is 0.1, and in Example 12, the Fe content y1 in the lithium manganese iron phosphate material in the second active material layer is 0.6. This results in insufficient driving force for lithium ions in the first active material layer in Example 12, a reduced delithiation rate, a relatively increased battery impedance, and a slight lithium plating phenomenon.

[0113] Combining Examples 10, 13, and 14, in Example 10, the Fe content y1 in the lithium manganese iron phosphate material in the first active material layer is 0.5; in Example 13, the Fe content y1 in the lithium manganese iron phosphate material in the first active material layer is 0.8; and in Example 14, the Fe content y1 in the lithium manganese iron phosphate material in the first active material layer is 0.2. This results in increased battery impedance and decreased rate performance in Examples 13 and 14. It is evident that both excessively high and insufficient Fe content in the first active material layer are detrimental to lithium-ion transport.

[0114] Combining Examples 2 and 14, in Example 2, the Fe content y1 in the lithium manganese iron phosphate material in the first active material layer is 0.3, and in Example 14, the Fe content y1 in the lithium manganese iron phosphate material in the first active material layer is 0.2. This results in insufficient driving force for lithium ions in the first active material layer in Example 14, a reduced delithiation rate, a relatively increased battery impedance, and a slight lithium plating phenomenon.

[0115] In summary, the embodiments of this application, by controlling the ratio of the mass content of Fe to the mass content of Co in the first and second active material layers, not only meet the trade-off requirements of energy density and safety, but also solve the problem of ternary lithium (LiNi) a Co b M c O2) materials and lithium manganese iron phosphate (LiMn) x Fe y The intrinsic physicochemical properties of the PO4 material lead to micro-interface polarization, which improves micro-interface polarization and impedance, reducing the risk of local lithium plating caused by uneven charge distribution. Furthermore, a reasonable arrangement of the positive electrode active material layer 120 allows for rapid diffusion of lithium ions (or electrons near the electrolyte) on the side near the positive electrode current collector, thereby improving the battery's charge and discharge performance.

[0116] The various embodiments or implementation methods described in this specification are presented in a progressive manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the embodiments can be referred to each other.

[0117] It should be noted that the embodiments referred to in the specification, such as "one embodiment," "embodiment," "exemplary embodiment," and "some embodiments," may include specific features, structures, or characteristics, but not every embodiment necessarily includes that specific feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same embodiment. Moreover, when a specific feature, structure, or characteristic is described in connection with an embodiment, implementing such a feature, structure, or characteristic in conjunction with other embodiments, whether explicitly described or not, is within the knowledge scope of those skilled in the art.

[0118] Generally speaking, terms should be understood at least in part by their use in context. For example, at least in part by context, the term "one or more" as used in the text can be used to describe any feature, structure, or characteristic of the singular meaning, or a combination of features, structures, or characteristics of the plural meaning. Similarly, at least in part by context, terms such as "a" or "the" can also be understood to convey either singular or plural usage.

[0119] It should be readily understood that the terms “on,” “above,” and “on top of” in this disclosure should be interpreted in the broadest possible sense, such that “on” means not only “directly on something” but also “on something” with an intermediate feature or layer therebetween, and that “above” or “on top of” means not only “on top of something” but also “on top of something” without an intermediate feature or layer therebetween (i.e., directly on something).

[0120] Furthermore, for ease of explanation, spatially relative terms such as "below," "below," "under," "above," and "above" may be used to describe the relationship of one element or feature relative to other elements or features as shown in the figures. Spatially relative terms are intended to encompass different orientations of the device in use or operation other than those shown in the figures. The device may have other orientations (rotated 90 degrees or in other orientations), and the spatially relative descriptive terms used herein may be interpreted accordingly.

[0121] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A positive electrode plate, characterized in that, include: The device includes a positive current collector and a positive active material layer disposed on one side of the positive current collector. The positive active material layer comprises a first active material layer and a second active material layer stacked together, with the first active material layer located between the second active material layer and the positive current collector. The first active material layer includes LiMn x1 Fe y1 PO4 and LiNi a1 Co b1 M c1 O2, where x1+y1=1, a1+b1+c1=1, and M includes at least one of Mn, Al, Zr, and Ti; The second active material layer includes LiMn x2 Fe y2 PO4 and LiNi a2 Co b2 M' c2 O2, where x2+y2=1, a2+b2+c2=1, and M' includes at least one of Mn, Al, Zr, and Ti; Furthermore, the ratio of the mass content of Fe to the mass content of Co in the first active material layer is different from the ratio of the mass content of Fe to the mass content of Co in the second active material layer.

2. The positive electrode sheet according to claim 1, characterized in that, The ratio of the mass content of Fe to the mass content of Co in the first active material layer is greater than the ratio of the mass content of Fe to the mass content of Co in the second active material layer.

3. The positive electrode sheet according to claim 2, characterized in that, The ratio P1 of the mass content of Fe to the mass content of Co in the first active material layer and the ratio P2 of the mass content of Fe to the mass content of Co in the second active material layer satisfy the following relationship: 2≤P2<P1≤40.

4. The positive electrode sheet according to claim 1, characterized in that, The value of y1 is in the range of 0.1-0.9; and / or the value of y2 is in the range of 0.1-0.

9.

5. The positive electrode sheet according to claim 4, characterized in that, The value of y1 is in the range of 0.1-0.6, the value of y2 is in the range of 0.1-0.6, and y2 < y1.

6. The positive electrode sheet according to claim 5, characterized in that, The value range of y1 is 0.3-0.6, and the value range of y2 is 0.1-0.

5. Furthermore, the LiMn in the first active material layer x1 Fe y1 The mass content of PO4 is not less than that of LiMn in the second active material layer. x2 Fe y2 The mass content of PO4, wherein y1 and y2 satisfy: y2 < y1.

7. The positive electrode sheet according to any one of claims 1-6, characterized in that, The value of b1 is in the range of 0.05-0.4; and / or the value of b2 is in the range of 0.05-0.

4.

8. The positive electrode sheet according to any one of claims 1-6, characterized in that, The first active material layer further includes at least one of a conductive agent, a binder, and a dispersant; And / or, the second active material layer further includes at least one of a conductive agent, a binder, and a dispersant.

9. The positive electrode sheet according to any one of claims 1-6, characterized in that, The thickness H1 of the first active material layer and the thickness H2 of the second active material layer satisfy: 0.7≤H2 / H1≤8.

8.

10. A method for preparing a positive electrode sheet, characterized in that, Includes the following steps: LiMn x1 Fe y1 PO4, LiNi a1 Co b1 M c1 O2, conductive agent, binder, dispersant, and solvent are mixed uniformly according to a certain stoichiometric ratio to prepare a slurry for the first active material layer, and LiMn is added... x2 Fe y2 PO4, LiNi a2 Co b2 M' c2 O2, conductive agent, binder, dispersant and solvent are mixed evenly according to a certain stoichiometric ratio to prepare a slurry for the second active material layer, wherein x1+y1=1, a1+b1+c1=1, M includes at least one of Mn, Al, Zr and Ti, x2+y2=1, a2+b2+c2=1, and M' includes at least one of Mn, Al, Zr and Ti; The slurry of the first active material layer is coated onto the surface of the positive electrode current collector, and the slurry of the second active material layer is coated onto the slurry surface of the first active material layer. The positive electrode sheet is obtained by baking and curing; wherein the ratio of the mass content of Fe to the mass content of Co in the first active material layer is different from the ratio of the mass content of Fe to the mass content of Co in the second active material layer.

11. A battery, characterized in that, include: The positive electrode sheet according to any one of claims 1-9.

12. An electrical appliance, characterized in that, Includes the battery as described in claim 11.

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