Battery cell, battery device, and electric device

Abstract

The application provides a battery monomer, a battery device and a power utilization device. The battery monomer comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, and the positive electrode film layer comprises a compound shown in formula I. The compound can chelate transition metal ions dissolved from a positive electrode active material surface, reduce the amount of transition metal ions dissolved on a negative electrode surface, and improve the cycle performance of the battery monomer.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a battery cell, a battery device, and an electrical device. Background Technology

[0002] In recent years, battery devices have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. With the increasing application of battery devices, higher requirements are being placed on their cycle performance and other aspects.

[0003] Battery devices typically consist of multiple individual cells. The positive electrode active material is crucial to the cycle performance of these cells. However, during battery cell operation, the positive electrode active material is prone to the dissolution of transition metal ions (such as nickel, cobalt, and manganese ions) due to the Jahn-Teller effect. These dissolved transition metal ions not only react with the electrolyte but also migrate to the negative electrode surface during charging, reverting to elemental metals. Under the catalytic action of these transition metals, the solid electrolyte interphase (SEI) film on the negative electrode surface decomposes rapidly, increasing cell polarization and exacerbating capacity decay, severely impacting the cell's cycle performance. Furthermore, the continuous deposition of transition metals on the negative electrode surface can form dendrites, which, in severe cases, can puncture the separator, causing an internal short circuit and posing safety risks. Therefore, a battery cell method that can mitigate the dissolution of transition metals in the positive electrode active material is urgently needed. Summary of the Invention

[0004] To address the aforementioned issues, this application provides a battery cell whose positive electrode film includes a compound with chelating groups. This compound can chelate transition metal ions dissolved from the surface of the positive electrode active material, forming a stable chelate that inhibits the migration of transition metal ions to the negative electrode, reduces the amount of transition metal ions dissolved on the negative electrode surface, thereby reducing the damage of the SEI film on the negative electrode surface caused by the transition metal element, reducing the polarization of the battery cell, and improving the cycle performance of the battery cell.

[0005] In a first aspect, this application provides a battery cell including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a compound of formula I.

[0006]

[0007] Wherein, R1 includes one of substituted or unsubstituted C1-C5 alkyl, substituted or unsubstituted C5-C9 unsaturated cycloalkanes, or substituted or unsubstituted C1-C5 alkoxy groups; R2 includes one of substituted or unsubstituted C1-C5 alkyl, or substituted or unsubstituted C5-C9 unsaturated cycloalkanes.

[0008] Adding a compound of formula I containing a β-diketone group to the positive electrode film layer can act as a bidentate ligand to chelate transition metal ions dissolved from the positive electrode active material due to the Jahn-Teller effect, forming a stable chelate. This inhibits the migration of transition metal ions to the negative electrode, reduces the amount of transition metal ions dissolved on the negative electrode surface, thereby reducing the damage of the SEI film on the negative electrode surface caused by elemental transition metals, reducing cell polarization, and improving the cycle performance of the cell. Furthermore, the compound of formula I is a lithium salt, which can improve the ion conduction performance of the positive electrode active material and weaken the impact of the compound's addition on the electrode's ion conduction performance.

[0009] In any embodiment, R1 comprises one of substituted or unsubstituted C1-C3 alkyl, substituted or unsubstituted C5-C6 unsaturated cycloalkanes, and substituted or unsubstituted C1-C3 alkoxy groups; and R2 comprises one of substituted or unsubstituted C1-C3 alkyl, and substituted or unsubstituted C5-C6 unsaturated cycloalkanes.

[0010] In any embodiment, R1 includes one of methyl, phenyl, methoxy, ethoxy, propoxy, and trifluoromethyl; R2 includes one of methyl, phenyl, and trifluoromethyl.

[0011] The R1 and R2 groups, including the chemically stable groups mentioned above, can enhance the structural stability and solubility of the compound shown in Formula I, which helps the compound shown in Formula I to be well distributed in the positive electrode system. At the same time, they can also increase the electron cloud density of the compound shown in Formula I, improve the coordination ability of the compound shown in Formula I with transition metal ions, reduce the amount of transition metal ions dissolved on the negative electrode surface, and improve the cycle performance of the battery cell.

[0012] In any embodiment, the compound represented by Formula I includes at least one of the following compounds:

[0013]

[0014]

[0015] The above-mentioned compounds have good ion coordination ability and antioxidant properties. When added to the positive electrode film, they can form stable chelates with the transition metal ions dissolved from the positive electrode active material, reduce the amount of transition metal ions dissolved in the negative electrode, and improve the cycle performance of the battery cell.

[0016] In any embodiment, based on the mass of the positive electrode film, the mass content of the compound represented by Formula I is 0.05%-1%.

[0017] The mass content of the compound shown in Formula I in the positive electrode film layer is within the above-mentioned range, which is conducive to the stable distribution of the compound shown in Formula I in the positive electrode film layer, fully chelating the transition metal ions dissolved from the surface of the positive electrode active material, reducing the amount of transition metal ions dissolved on the surface of the negative electrode, improving the stability of the negative electrode SEI film, improving the cycle performance of the battery cell, and also taking into account the impact of excessively high mass content of the compound shown in Formula I on the DC internal resistance (DCR) of the battery cell.

[0018] In any embodiment, based on the mass of the positive electrode film, the mass content of the compound shown in Formula I is 0.1%-0.45%, which can further chelate the transition metal ions dissolved from the surface of the positive electrode active material, reduce the amount of transition metal ions dissolved on the negative electrode surface, improve the stability of the negative electrode SEI film, and improve the cycle performance of the battery cell.

[0019] In any embodiment, the positive electrode film layer comprises a positive electrode active material, which includes at least one of manganese, cobalt, and nickel. Manganese, cobalt, or nickel helps improve the structural stability or capacity of the positive electrode active material; however, the ionic states of manganese, cobalt, and nickel contain unpaired d or f electrons, making the positive electrode active material susceptible to the Jahn-Teller effect, resulting in the dissolution of transition metal ions.

[0020] In any embodiment, the positive electrode active material includes manganese, and the manganese element has at least one of the valence states of +2, +3, and +4.

[0021] In positive electrode active materials, Mn 3+ d-electron systems with unpaired electrons are susceptible to the Jahn-Teller effect, leading to manganese leaching. Mn 2+ It can be converted into Mn during battery charging. 3+ This leads to manganese leaching. Mn 4+ Having d 0 Configuration, although Mn 4+ While it lacks unpaired electrons, hydrofluoric acid (HF) in the electrolyte can disrupt the crystal structure of the positive electrode active material, potentially promoting the growth of Mn. 4+ Reduced to Mn 3+ This leads to manganese leaching. Furthermore, moisture in the battery cell can exacerbate manganese leaching. Therefore, adding the compound shown in Formula I to the positive electrode active material with the aforementioned manganese valence state can reduce the amount of manganese ions leached from the positive electrode active material, decrease the amount of manganese ions leached on the negative electrode surface, and improve the cycle performance of the battery cell.

[0022] In any embodiment, the positive electrode active material includes at least one of lithium manganese iron phosphate, lithium manganese oxide, lithium nickel manganese oxide, lithium manganese cobalt oxide, lithium-rich manganese-based materials, and lithium nickel cobalt manganese oxide. These positive electrode active materials have advantages such as high safety, low cost, and good electrochemical performance; however, they all contain transition metal ions, and the dissolution of these transition metal ions during charge and discharge may affect the cycle performance of the battery cells.

[0023] In any embodiment, the volume average particle size Dv50 of the positive electrode active material is 0.1 μm-10 μm.

[0024] During charging and discharging, the insertion and extraction of active ions within the cathode active material induces lattice changes. A larger average particle size (Dv50) in the cathode active material results in a longer diffusion path for active ions, increasing local stress and potentially leading to cracks in the material, reducing its stability, and increasing the dissolution of transition metal ions. Controlling Dv50 within the aforementioned range can improve the stability of the cathode active material, thereby reducing the dissolution of transition metal ions and further minimizing the impact of transition metal precipitation on the cycle performance of the battery cell.

[0025] In any embodiment, the specific surface area of ​​the positive electrode active material is 0.3 m². 2 / g-25m 2 / g. Within a certain range, the larger the specific surface area of ​​the positive electrode active material, the more surface active sites it has, and the more easily it reacts with the electrolyte, leading to the dissolution of transition metal ions. Controlling the specific surface area of ​​the positive electrode active material within the above range can reduce the dissolution of transition metal ions, allowing the compound shown in Formula I to more effectively chelate ions and reduce the impact of transition metal ion dissolution on the cycle performance of the battery cell; at the same time, it has sufficient surface active sites to achieve the kinetic performance of the material.

[0026] In any embodiment, the positive electrode active material comprises lithium manganese iron phosphate, wherein the lithium manganese iron phosphate satisfies at least one of the following conditions:

[0027] (1) The general formula is Li(Mn) 1-x-c Fe x M c )PO4 / C, wherein 0.1≤x≤0.45, 0≤c≤0.1, and the dopant element M is a divalent metal, including at least one of Mg, Co, Ca, Sc, Ni and Zn;

[0028] (2) The lithium manganese iron phosphate includes secondary particles formed by primary particles and / or agglomeration of primary particles, wherein the volume average particle size Dv50 of the primary particles is 100nm-200nm and the volume average particle size Dv50 of the secondary particles is 2μm-5μm.

[0029] (3) The specific surface area of ​​the lithium manganese iron phosphate is 10 m². 2 / g-25m 2 / g.

[0030] The volume average particle size Dv50 of primary and secondary lithium manganese iron phosphate particles and the specific surface area of ​​active material particles within the above range help to reduce the degree of side reactions between lithium manganese iron phosphate and electrolyte. While reducing the precipitation of transition metal ions, it also has good kinetic performance, further improving the cycle performance of battery cells.

[0031] In any embodiment, the positive electrode active material comprises lithium manganese oxide, and the lithium manganese oxide satisfies at least one of the following conditions:

[0032] (1) The general formula is LiMn 2-y M 1y O4, wherein M1 includes at least one of Ni, V, Cr, Cu, Co, Fe, Mg, Ca, and Sc, 0 <y<2;

[0033] (2) The volume average particle size Dv50 of the lithium manganese oxide is 2μm-5μm;

[0034] (3) The specific surface area of ​​the lithium manganese oxide is 0.5 m². 2 / g-5m 2 / g.

[0035] The volume average particle size Dv50 and specific surface area of ​​lithium manganese oxide are within the above range. While reducing the precipitation of transition metal ions, it also takes into account the kinetic performance of the battery cell, and further improves the cycle performance of the battery cell.

[0036] In any embodiment, the positive electrode active material comprises a lithium-rich manganese-based material, and the lithium-rich manganese-based material satisfies at least one of the following conditions:

[0037] (1) The general formula is zLi2MnO3(1-z)LiM2O2, wherein M2 includes at least one of Mn, Ni, and Co, and 0 <z<1;

[0038] (2) The volume average particle size Dv50 of the lithium-rich manganese-based material is 3μm-10μm;

[0039] (3) The specific surface area of ​​the lithium-rich manganese-based material is 0.5 m². 2 / g-3m2 / g.

[0040] When the volume average particle size Dv50 and specific surface area of the lithium manganese oxide are within the above ranges, it is beneficial to reduce the dissolution amount of transition metal ions in the lithium manganese oxide, improve the cycle performance of the battery monomer, and balance the kinetic performance.

[0041] In any embodiment, the positive electrode active material includes lithium nickel cobalt manganese oxide, and the lithium nickel cobalt manganese oxide satisfies at least one of the following conditions:

[0042] (1) The lithium nickel cobalt manganese oxide is LiNi a Co b Mn 1-a-b O2, where 0 < a < 1 and 0 < b < 1; and / or

[0043] (2) The volume average particle size Dv50 of the lithium nickel cobalt manganese oxide is 1 μm - 5 μm; and / or

[0044] (3) The specific surface area of the lithium nickel cobalt manganese oxide is 0.3 m 2 / g - 5 m 2 / g.

[0045] When the volume average particle size Dv50 and specific surface area of the lithium nickel cobalt manganese oxide are within the above ranges, it is beneficial to reduce the dissolution amount of transition metal ions in the lithium nickel cobalt manganese oxide, improve the cycle performance of the battery monomer, and balance the kinetic performance.

[0046] In any embodiment, the positive electrode film layer includes the lithium iron phosphate manganese and the compound shown in Formula I. Based on the mass of the positive electrode film layer, the mass content of the compound shown in Formula I is 0.1% - 0.45%; or

[0047] The positive electrode film layer includes the lithium manganese oxide and the compound shown in Formula I. Based on the mass of the positive electrode film layer, the mass content of the compound shown in Formula I is 0.3% - 0.8%; or

[0048] The positive electrode film layer includes the lithium-rich manganese-based material and the compound shown in Formula I. Based on the mass of the positive electrode film layer, the mass content of the compound shown in Formula I is 0.3% - 0.8%; or

[0049] The positive electrode film layer includes the lithium nickel cobalt manganese oxide and the compound shown in Formula I. Based on the mass of the positive electrode film layer, the mass content of the compound shown in Formula I is 0.05% - 0.3%.

[0050] In the above-mentioned battery cells using lithium manganese iron phosphate, lithium manganese oxide, lithium-rich manganese-based materials, and lithium nickel cobalt manganese oxide as positive electrode active materials, controlling the content of the compound shown in Formula I in the positive electrode film layer within the above-mentioned range is beneficial to the compound shown in Formula I fully chelating the transition metal ions dissolved from the surface of the positive electrode active material and forming stable chelates, reducing the amount of transition metal ions dissolved on the negative electrode surface, improving the stability of the negative electrode SEI film, reducing the polarization of the battery cell, and improving the cycle performance of the battery cell.

[0051] A second aspect of this application provides a battery device including the battery cell described in the first aspect of this application.

[0052] A third aspect of this application provides an electrical device, including a single battery cell as described in the first aspect of this application or a battery device as described in the second aspect of this application. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application;

[0054] Figure 2 yes Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0055] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application;

[0056] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0057] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown;

[0058] Figure 6 This is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to one embodiment of this application;

[0059] Figure 7 The cycle capacity decay curves of individual battery cells in Examples 1-2, Example 10, and Comparative Example 1 of this application are shown.

[0060] Figure 8 The bar chart shows the manganese leaching content of the negative electrode sheet of the battery cell after 1000 cycles of the battery cells of Examples 1-2, Example 10 and Comparative Example 1 of this application;

[0061] Figure 9 The battery cell cycle capacity decay curves of Embodiments 9, 12, and 4 of this application are shown.

[0062] Figure 10The bar chart shows the manganese leaching content of the negative electrode sheet after 1000 cycles of the battery cells of Examples 9, 12, and Comparative Example 4 of this application.

[0063] Figure label:

[0064] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0065] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery cell, battery device, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0066] The "range" disclosed in this application is defined by 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 a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, 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 a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" 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 "0-5" have been listed in this application; "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 disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0067] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0068] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0069] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may 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.

[0070] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0071] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0072] During the use of a battery cell, the stability of the positive electrode active material decreases due to the Jahn-Teller effect, making it prone to transition metal ion dissolution. These dissolved transition metal ions not only react with the electrolyte to generate more stable products, exacerbating the irreversible departure tendency of transition metal ions, but also migrate through the electrolyte to the negative electrode surface, depositing and being reduced to elemental metals. Under the catalytic effect of these transition metals, the decomposition of the SEI film on the negative electrode surface is accelerated, increasing the polarization of the battery cell, accelerating the capacity decay of the battery cell, and severely affecting its cycle performance.

[0073] Based on this, a first aspect of this application provides a battery cell including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a compound represented by Formula I.

[0074]

[0075] R1 includes one of substituted or unsubstituted C1-C5 alkyl, substituted or unsubstituted C5-C9 unsaturated cycloalkanes, and substituted or unsubstituted C1-C5 alkoxy groups;

[0076] R2 includes one of substituted or unsubstituted C1-C5 alkyl groups or substituted or unsubstituted C5-C9 unsaturated cycloalkanes.

[0077] In this application, the term "substituted" means that at least one hydrogen atom of the compound or chemical moiety is replaced by another substituent (group or chemical moiety), wherein each substituent independently includes one of hydroxyl, mercapto, amino, cyano, nitro, aldehyde, halogen atom, alkenyl, alkynyl, aryl, heteroaryl, C1-6 alkyl, and C1-6 alkoxy.

[0078] In this application, the term "C1-C5 alkyl" refers to a branched or straight-chain saturated aliphatic monovalent hydrocarbon group comprising 1 to 5 carbon atoms, wherein the group is not unsaturated, has one to five carbon atoms, and is attached to the remainder of the molecule by a single bond. For example, C1-C5 alkyl includes one of methyl, ethyl, propyl, butyl, and pentyl.

[0079] In this application, the term "C5-C9 unsaturated cyclic group" refers to an unsaturated cyclic group with 5 to 9 ring atoms. These groups typically contain at least one double bond (and sometimes a triple bond) and form a cyclic structure. The ring atoms include carbon atoms and heteroatoms; exemplarily, heteroatoms include at least one of sulfur and nitrogen atoms.

[0080] In this application, the term "C1-C5 alkoxy" refers to a group formed by an alkyl group having 1 to 5 carbon atoms bonded to an oxygen atom. For example, C1-C5 alkoxy groups include one of methoxy, ethoxy, propoxy, butoxy, and pentoxy.

[0081] The reason for not adhering to any theoretical constraints is likely due to the fact that during the charging and discharging process of a single battery cell, when the positive electrode active material undergoes transition metal ion dissolution due to the Jahn-Teller effect, the compound shown in Formula I, containing a β-diketone group, has a bidentate ligand structure. This structure can chelate the transition metal ions dissolved from the surface of the positive electrode active material, forming a stable chelate that inhibits the migration of transition metal ions to the negative electrode, reduces the amount of transition metal ions dissolved on the negative electrode surface, thereby reducing the damage of elemental transition metals to the SEI film on the negative electrode surface, lowering battery polarization, and improving the cycle performance of the battery cell. Furthermore, the compound shown in Formula I is a lithium salt. When dissolved in an organic solvent, it dissociates into Li+ ions, which move freely in the electrolyte, becoming a charge transport carrier, improving the ion-conducting performance of the positive electrode active material, and weakening the impact of its addition on the ion-conducting performance of the electrode sheet.

[0082] In this application, the Jahn-Teller effect refers to the process by which a nonlinear molecular system eliminates degenerate states to form a new system with low symmetry and low energy; that is, the phenomenon that ions or molecules with degenerate electronic states lower their energy levels due to geometric distortion. This effect typically occurs in systems with unpaired d or f electrons.

[0083] In some embodiments, R1 comprises one of substituted or unsubstituted C1-C3 alkyl, substituted or unsubstituted C5-C6 unsaturated cycloalkanes, and substituted or unsubstituted C1-C3 alkoxy groups; and R2 comprises one of substituted or unsubstituted C1-C3 alkyl, and substituted or unsubstituted C5-C6 unsaturated cycloalkanes.

[0084] In this application, the term "C1-C3 alkyl" refers to a branched or straight-chain saturated aliphatic monovalent hydrocarbon group comprising 1 to 3 carbon atoms, wherein the group is not unsaturated, has one to three carbon atoms, and is attached to the remainder of the molecule by a single bond. For example, C1-C3 alkyl includes one of methyl, ethyl, and propyl.

[0085] In this application, the term "C5-C6 unsaturated cyclic group" refers to an unsaturated cyclic group with 5 to 6 ring atoms. These groups typically contain at least one double bond (and sometimes a triple bond) and form a cyclic structure. The ring atoms include carbon atoms and heteroatoms; for example, heteroatoms include at least one of sulfur and nitrogen atoms.

[0086] In this application, the term "C1-C3 alkoxy" refers to a group formed by an alkyl group consisting of 1 to 3 carbon atoms bonded to an oxygen atom. For example, C1-C3 alkoxy groups include one of methoxy, ethoxy, and propoxy groups.

[0087] In some embodiments, R1 includes one of methyl, phenyl, methoxy, ethoxy, propoxy, and trifluoromethyl; R2 includes one of methyl, phenyl, and trifluoromethyl.

[0088] In some embodiments, both R1 and R2 comprise methyl groups. In some embodiments, R1 comprises methyl groups and R2 comprises methyl groups. In some embodiments, both R1 and R2 comprise phenyl groups.

[0089] In the compound shown in Formula I, the R1 and R2 groups include the above-mentioned substituents. On the one hand, this can enhance the structural stability and solubility of the compound shown in Formula I, so that the compound shown in Formula I is stably distributed in the positive electrode film. On the other hand, it can increase the electron cloud density of the compound shown in Formula I, enhance its coordination ability with transition metal ions, and facilitate the formation of stable chelates, thereby reducing the amount of transition metal ions deposited on the negative electrode and improving the cycle performance of the battery cell.

[0090] In some embodiments, the compound represented by Formula I includes at least one of the following compounds:

[0091]

[0092]

[0093] The above compounds have good metal ion coordination ability and antioxidant properties. When added to the positive electrode film, they can form stable chelates with the transition metal ions dissolved from the positive electrode active material, reduce the dissolution of transition metal ions and the amount of deposition on the negative electrode, and improve the cycle performance of the battery cell.

[0094] In some embodiments, based on the mass of the positive electrode film, the mass content of the compound represented by Formula I is 0.05%-1%.

[0095] In this application, the mass content of the compound represented by Formula I refers to the mass of the compound represented by Formula I in the positive electrode film layer divided by the total mass of the positive electrode film layer. The mass content of the compound represented by Formula I can be determined by quantitative nuclear magnetic resonance spectroscopy (NMR) according to standard 20242561-T-306. For example, the battery cell is disassembled, the positive electrode is removed, and the active material on the positive electrode is scraped off with a scraper. The mass content of the compound represented by Formula I is determined by quantitative nuclear magnetic resonance spectroscopy (NMR) according to standard 20242561-T-306.

[0096] In some embodiments, based on the mass of the positive electrode film, the mass content of the compound represented by Formula I is 0.05%-0.8%, 0.05%-0.6%, 0.05%-0.4%, 0.1%-1%, 0.1%-0.8%, or 0.1%-0.6%. In some embodiments, based on the mass of the positive electrode film, the mass content of the compound represented by Formula I is 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, or 1%, and may also be any value within the range of 0.05%-0.8%.

[0097] During the charging and discharging process of a battery cell, the positive electrode active material undergoes transition metal ion dissolution due to the Jahn-Teller effect. If the content of the compound shown in Formula I in the positive electrode film is too low, it cannot completely chelate the dissolved transition metal ions, leading to their precipitation at the negative electrode and affecting the cycle performance of the battery cell. If the content of the compound shown in Formula I in the positive electrode film is too high, it may form a passivation film on the positive electrode surface, hindering the insertion and extraction of Li+ ions, increasing the polarization of the battery cell, increasing the cell's DCR, and causing a decline in battery performance. When the content of the compound shown in Formula I in the positive electrode film is within the aforementioned range, it is beneficial for the compound shown in Formula I to fully chelate the transition metal ions dissolved from the surface of the positive electrode active material in the positive electrode film, improving the cycle performance of the battery cell and reducing the impact of the compound shown in Formula I on the cell's DCR.

[0098] In some embodiments, based on the mass of the positive electrode film, the mass content of the compound represented by Formula I is 0.1%-0.45%.

[0099] The content of the compound shown in Formula I in the positive electrode film layer is within the above range, which is beneficial for the compound to further chelate the transition metal ions dissolved from the surface of the positive electrode active material, reduce the amount of transition metal ions dissolved on the negative electrode surface, improve the stability of the negative electrode SEI film, and improve the cycle performance of the battery cell.

[0100] In some embodiments, the positive electrode film layer includes a positive electrode active material, which includes at least one of manganese, cobalt, and nickel, thereby helping to improve the structural stability or capacity of the positive electrode active material.

[0101] The initial valence state of nickel in positive electrode active materials is Ni. 2+ When a single battery cell begins to charge, the Ni in the positive electrode... 2+ When nickel loses electrons, it is oxidized. The oxidation state of nickel varies from Ni... 2+ Gradually becoming Ni 3+ And Ni 3+ Having d 8 The electronic configuration of Ni, in an octahedral coordination environment, is in an active Jahn-Teller state, making it prone to lattice distortion. 3+ Ni dissolves from the lattice of the positive electrode active material; 3+ Ni is generated through a disproportionation reaction. 2+ and Ni 4+ , where Ni 2+ It is deposited on the negative electrode surface through the electrolyte.

[0102] The initial valence state of cobalt in positive electrode active materials is Co. 3+ When a single battery cell begins to charge, the Co in the positive electrode...3+ When cobalt loses electrons, it is oxidized. The valence state of cobalt changes from Co... 3+ Gradually becoming Co 4+ And Co 3+ Having d 6 The electronic configuration of Co is in an active Jahn-Teller effect state in an octahedral coordination environment, making it prone to lattice distortion. 3+ Co dissolves from the crystal lattice of the positive electrode active material. 3+ A disproportionation reaction occurs to produce Co. 2+ and Co 4+ , of which Co 2+ It is deposited on the negative electrode surface through the electrolyte.

[0103] The initial valence state of manganese in positive electrode active materials is generally Mn. 2+ Mn 3+ Mn 4+ Mn 3+ Having d 4 The electronic configuration of Mn, in an octahedral coordination environment, is in an active Jahn-Teller state, making it prone to lattice distortion, which leads to Mn 3+ Mn dissolved from the lattice of the positive electrode active material 3+ A disproportionation reaction occurs to generate Mn. 2+ and Mn 4+ , among which, Mn 2+ It is deposited on the negative electrode surface through the electrolyte.

[0104] During the use of battery cells, positive electrode active materials containing manganese, cobalt, and nickel may exhibit transition metal ion dissolution due to the Jahn-Teller effect. Adding the compound shown in Formula I to the positive electrode film can chelate the dissolved transition metal ions to form a stable chelate, inhibiting the migration of transition metal ions to the negative electrode, reducing the amount of transition metal ions dissolved on the negative electrode surface, thereby reducing the damage of the SEI film on the negative electrode surface by the transition metal elements, reducing the polarization of the battery cell, and improving the cycle performance of the battery cell.

[0105] In some embodiments, the positive electrode active material includes manganese, wherein the manganese has a valence state of at least one of +2, +3, and +4.

[0106] The manganese element in the positive electrode active material is Mn. 2+ When a battery cell begins to charge, manganese ions move from Mn... 2+ Transform into Mn 3+ , because Mn 3+ In an octahedral coordination environment, the Jahn-Teller effect is active, which easily leads to lattice distortion and structural defects in the positive electrode active material, making Mn...3+ It dissolves from the lattice of the positive electrode active material.

[0107] The manganese element in the positive electrode active material is Mn. 3+ When a battery cell begins to charge, manganese ions move from Mn... 3+ Transform into Mn 4+ The structural stability of the positive electrode active material may be affected, but this does not necessarily lead to severe manganese dissolution, because Mn 4+ Having d 0 The electronic configuration of the cathode material does not exhibit the Jahn-Teller effect in an octahedral coordination environment. However, if water is present in the battery cell, the hydrofluoric acid produced in the electrolyte can disrupt the lattice of the cathode active material, causing the Mn content in the cathode active material to decrease. 3+ Dissolution.

[0108] The manganese element in the positive electrode active material is Mn. 4+ When a single battery cell begins to charge, Mn 4+ In a fully oxidized state, its electronic configuration is d. 0 It has virtually no electrochemical activity and is unlikely to undergo significant structural changes. However, if water is present in the battery cell, leading to the presence of a large amount of hydrofluoric acid in the electrolyte, it can disrupt the crystal lattice of the positive electrode active material, potentially promoting the growth of Mn. 4+ Reduced to Mn 3+ This may cause the Mn in the positive electrode active material to be affected. 3+ Dissolution.

[0109] Adding the compound shown in Formula I to the positive electrode film can chelate the Mn dissolved from the positive electrode active material. 3+ One compound molecule of Formula I can provide two shared electron pairs, and three compound molecules of Formula I can share one Mn. 3+ Forming d 10 In chelates with a full-shell structure, the outer electrons of Mn are completely occupied, placing it in its lowest spin state and resulting in high stability. This inhibits Mn... 3+ Mn generated by the disproportionation reaction 2+ Mn migrates towards the negative electrode, reducing the amount of Mn dissolved on the negative electrode surface, thereby reducing the damage of Mn to the SEI film on the negative electrode surface, reducing cell polarization, and improving the cycle performance of the cell.

[0110] In some embodiments, the positive electrode active material includes at least one of lithium manganese iron phosphate, lithium manganese oxide, lithium nickel manganese oxide, lithium manganese cobalt oxide, lithium-rich manganese-based materials, and nickel cobalt lithium manganese oxide.

[0111] The aforementioned positive electrode active materials are commonly used positive electrode active materials for lithium battery cells, and nickel, cobalt, and manganese ions will dissolve during the use of the battery cells. The compounds shown in Formula I added to the positive electrode film layer of this application can chelate the nickel, cobalt, and manganese ions dissolved on their surface, forming stable chelates. This inhibits the migration of nickel, cobalt, and manganese ions to the negative electrode, reduces the precipitation of nickel, cobalt, and manganese ions on the negative electrode surface, thereby reducing the damage of elemental nickel, cobalt, and manganese to the SEI film on the negative electrode surface, reducing battery cell polarization, and improving the cycle performance of the battery cell.

[0112] In some embodiments, the volume average particle size Dv50 of the positive electrode active material is 0.1 μm-10 μm.

[0113] In this application, the term "volume average particle size Dv50" refers to the particle size that, in the volumetric particle size distribution, represents the percentage of particles that accumulate to 50% from the smallest particle size side. It can be detected using equipment and methods known in the art, such as using positive electrode active material as a sample and testing the particle Dv50 using a Mastersizer2000E laser particle size analyzer according to the testing standard GB / T19077-2016.

[0114] In some embodiments, the volume average particle size Dv50 of the positive electrode active material is 0.1 μm-8 μm, 0.1 μm-6 μm, 0.1 μm-4 μm, or 0.1 μm-2 μm. In some embodiments, the volume average particle size Dv50 of the positive electrode active material is 0.1 μm, 0.5 μm, 1 μm, 2 μm, 4 μm, 6 μm, 8 μm, or 10 μm, and can also be any value within the range of 0.1 μm-10 μm.

[0115] During the charging and discharging process of a battery cell, the insertion and extraction of active ions within the positive electrode active material cause lattice changes. A larger volume average particle size (Dv50) of the positive electrode active material requires active ions to travel a longer diffusion path to reach its surface. This longer diffusion path can lead to increased local stress, resulting in crack formation in the positive electrode active material, reducing its stability, and increasing the dissolution of transition metal ions. Controlling the volume average particle size (Dv50) of the positive electrode active material within the aforementioned range helps reduce the dissolution of transition metal ions, allowing the compound shown in Formula I in the positive electrode film to more effectively chelate the dissolved transition metal ions, further reducing the deposition of elemental transition metals on the negative electrode and improving the cycle performance of the battery cell.

[0116] In some embodiments, the specific surface area of ​​the positive electrode active material is 0.3 m². 2 / g-25m 2 / g.

[0117] In this application, the term "specific surface area" refers to the total area per unit mass of material. It can be tested using equipment and methods known in the art, such as the nitrogen adsorption specific surface area analysis method according to GB / T19587-2017, and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis can be performed using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc.

[0118] In some embodiments, the specific surface area of ​​the positive electrode active material is 0.3 m². 2 / g-20m 2 / g, 0.3m 2 / g-15m 2 / g, 0.3m 2 / g-10m 2 / g, 0.3m 2 / g-5m 2 / g, 0.3m 2 / g-1m 2 / g, 0.3m 2 / g-0.5m 2 / g. In some embodiments, the specific surface area of ​​the positive electrode active material is 0.3m². 2 / g, 0.5m 2 / g, 1m 2 / g、2m 2 / g、4m 2 / g、6m 2 / g、8m 2 / g, 10m 2 / g、12m 2 / g、14m 2 / g, 16m 2 / g、18m 2 / g、20m 2 / g、22m 2 / g、24m 2 / g or 25m 2 / g, which can also be 0.3m 2 / g-25m 2 Any value within the range / g.

[0119] Within a certain range, the larger the specific surface area of ​​the positive electrode active material, the more active sites it contains. These active sites readily react with electrolytes or other substances (e.g., hydrofluoric acid), leading to the dissolution of transition metal ions. Controlling the specific surface area of ​​the positive electrode active material within the aforementioned range helps reduce the amount of transition metal ions dissolved from the material. This allows the compound shown in Formula I in the positive electrode film to more effectively chelate the dissolved transition metal ions, reducing their dissolution at the negative electrode and minimizing their impact on the cycle performance of the battery cell. Simultaneously, it also provides surface active sites to improve the kinetic performance of the positive electrode active material.

[0120] In some embodiments, the positive electrode active material includes lithium manganese iron phosphate, wherein the general formula of lithium manganese iron phosphate is Li(Mn) 1-x-c Fe x M c )PO4 / C, wherein 0.1≤x≤0.45, 0≤c≤0.1, and M includes at least one of Mg, Co, Ca, Sc, Ni and Zn.

[0121] Lithium manganese iron phosphate (LFP) cathode active materials possess advantages such as high safety, low cost, good electrochemical performance, and low-temperature performance. In battery cells using LFP as the cathode active material, manganese is expressed as Mn. 2+ It exists in form. During the charging process, Mn 2+ Transform into Mn 3+ Or a higher valence state. As mentioned above, due to the Jahn-Teller effect, Mn will... 3+ Mn leaching from the lattice of lithium manganese iron phosphate cathode active material affects the cycle performance of individual battery cells. The cathode film layer includes a compound of formula I, which can chelate Mn dissolved from the surface of the lithium manganese iron phosphate cathode active material. 3+ This reduces the manganese leaching content of the negative electrode and improves the cycle performance of the battery cell.

[0122] In some embodiments, lithium manganese iron phosphate comprises primary particles and / or secondary particles formed by agglomeration of primary particles.

[0123] In this application, a primary particle refers to the smallest unit of a particle within a certain identification range. A primary particle may contain defects of any form, but it is impossible to further define smaller particles within it. Primary particles can be in an unagglomerated or agglomerated state; the aggregate of agglomerated primary particles is called a secondary particle. Secondary particles have a defined surface and boundaries, but after cutting a cross-section of a secondary particle, it can be seen that it is formed by the agglomeration of numerous primary particles. Unagglomerated primary particles refer to those primary particles that have not undergone significant interparticle agglomeration to form secondary particles. The state of the positive electrode active material in the positive electrode active material layer can be determined by observing the particle morphology of a cross-section along the thickness direction of the positive electrode sheet.

[0124] The lithium manganese iron phosphate cathode active material comprises primary particles, which helps improve the conductivity of the cathode active material and provides more active sites to promote rapid transport of active ions. Furthermore, it can reduce the volume change of the cathode active material during charge and discharge, thereby reducing structural stress and improving cycle stability.

[0125] The lithium manganese iron phosphate cathode active material comprises secondary particles formed by the agglomeration of primary particles. This reduces interparticle porosity to some extent, decreasing the amount of electrolyte required while maintaining a good conductive network. Furthermore, it reduces side reactions, improves the structural stability of the material, and thus extends the cycle life of the battery cell.

[0126] In some embodiments, lithium manganese iron phosphate comprises secondary particles formed by the agglomeration of primary particles, wherein the volume average particle size Dv50 of the primary particles is 100nm-200nm, and the volume average particle size Dv50 of the secondary particles is 2μm-5μm.

[0127] In some embodiments, lithium manganese iron phosphate includes secondary particles formed by the agglomeration of primary particles, wherein the volume average particle size Dv50 of the primary particles is 100nm-180nm, 100nm-160nm, 100nm-140nm, or 100nm-120nm, and the volume average particle size Dv50 of the secondary particles is 2μm-4.5μm, 2μm-4μm, 2μm-3.5μm, or 2μm-3μm. In some embodiments, lithium manganese iron phosphate includes secondary particles formed by the agglomeration of primary particles, wherein the volume average particle size Dv50 of the primary particles is 100nm, 110nm, 120nm, 140nm, 160nm, or 180nm, or any value within the range of 100nm-200nm, and the volume average particle size Dv50 of the secondary particles is 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, or 5μm, or any value within the range of 2μm-5μm.

[0128] In this application, the volume average particle size (Dv50) of the primary particles in the secondary particles can be tested using any method known in the art. As an example, a cross-section along the thickness direction of the positive electrode sheet is obtained, and particles from any 10 regions of identical size and shape are observed in the same scanning electron microscope (SEM) image at 10kV and 30k magnification. Each of these 10 regions is then subdivided into five positions: the four corners and the center. The average particle size of any primary particle at each position is selected at this magnification, and the average of the average particle sizes at the four corners and the center is taken to obtain the average particle size of the primary particles in that region. Then, the average of the particle sizes obtained from the 10 regions is taken again as the volume average particle size (Dv50) of the primary particles. Specifically, the average of the major and minor axes of each particle is taken as the average particle size.

[0129] In a battery cell using lithium manganese iron phosphate as the positive electrode active material, the volume average particle size Dv50 of the primary and secondary particles of the positive electrode active material is within the above range. This is beneficial to reduce the amount of transition metal ions dissolved in the positive electrode active material, so that the compound shown in Formula I in the positive electrode film can more effectively chelate the dissolved transition metal ions, further reduce the amount of transition metal elemental deposition on the negative electrode sheet, and improve the cycle performance of the battery cell.

[0130] In some embodiments, the specific surface area of ​​lithium manganese iron phosphate is 10 m². 2 / g-25m 2 / g.

[0131] In some embodiments, the specific surface area of ​​lithium manganese iron phosphate is 10 m². 2 / g-20m 2 / g, 10m 2 / g-15m 2 / g. In some embodiments, the specific surface area of ​​lithium manganese iron phosphate is 10m². 2 / g、12m 2 / g、14m 2 / g, 16m 2 / g、18m 2 / g、20m 2 / g、22m 2 / g、24m 2 / g or 25m 2 / g, which can also be 10m 2 / g-25m 2 Any value within the range / g.

[0132] In battery cells using lithium manganese iron phosphate as the positive electrode active material, a specific surface area within the aforementioned range is beneficial for reducing the dissolution of transition metal ions from the positive electrode active material. This allows the compound shown in Formula I in the positive electrode film to more effectively chelate the dissolved transition metal ions, thereby reducing their impact on the cycle performance of the battery cell. Simultaneously, it can also provide surface active sites to improve the kinetic performance of the positive electrode active material.

[0133] In some embodiments, lithium manganese iron phosphate includes LiMn 0.6 Fe 0.4 PO4.

[0134] In some embodiments, the positive electrode film layer comprises the lithium manganese iron phosphate and the compound shown in Formula I, wherein the mass content of the compound shown in Formula I is 0.1%-0.45% based on the mass of the positive electrode film layer.

[0135] In some embodiments, the positive electrode film layer comprises the lithium manganese iron phosphate and the compound shown in Formula I, wherein the mass content of the compound shown in Formula I is 0.1%-0.4%, 0.1%-0.35%, 0.1%-0.3%, 0.1%-0.25%, 0.1%-0.2%, or 0.1%-0.15% based on the mass of the positive electrode film layer. In some embodiments, the positive electrode film layer comprises the lithium manganese iron phosphate and the compound shown in Formula I, wherein the mass content of the compound shown in Formula I is 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, or 0.45% based on the mass of the positive electrode film layer, and may also be any value within the range of 0.1%-0.45%.

[0136] Lithium manganese iron phosphate cathode active material is formed by the agglomeration of primary particles into secondary particles. The grain boundaries between these primary particles may contain more structural defects, specifically Mn... 3+ The dissolution provides an additional channel. Therefore, based on the mass of the positive electrode film, the mass content of the compound shown in Formula I within the above-mentioned range is beneficial for the compound shown in Formula I to fully chelate the Mn dissolved from the surface of the positive electrode active material. 3+ It forms a stable chelate and inhibits Mn 3+ Mn generated by the disproportionation reaction 2 + Migration towards the negative electrode reduces Mn 2+ The amount of leaching on the negative electrode surface is reduced, thereby reducing the damage of Mn to the SEI film on the negative electrode surface, reducing cell polarization, and improving the cycle performance of the cell.

[0137] In some embodiments, the positive electrode active material includes lithium manganese oxide, wherein the lithium manganese oxide has the general formula LiMn 2-y M1y O4, wherein M1 includes at least one of Ni, V, Cr, Cu, Co, Fe, Mg, Ca, and Sc, 0 <y<2。

[0138] Lithium manganese oxide cathode active materials possess advantages such as high energy density, low cost, high temperature resistance, and high safety. In lithium manganese oxide cathode active materials, manganese is primarily composed of Mn. 3+ and Mn 4+ As mentioned above, due to the Jahn-Teller effect, Mn exists in a certain form. 3+ Mn leaching from the lattice of lithium manganese oxide cathode active material affects the cycle performance of individual battery cells. The compound of formula I added to the cathode film can chelate Mn leached from the surface of the lithium manganese oxide cathode active material. 3+ This reduces the manganese leaching content of the negative electrode and improves the cycle performance of the battery cell.

[0139] In some embodiments, the volume average particle size Dv50 of the lithium manganese oxide is 2 μm-5 μm.

[0140] In some embodiments, the volume average particle size Dv50 of the lithium manganese oxide is 2μm-4.5μm, 2μm-4μm, 2μm-3.5μm, 2μm-3μm, or 2μm-2.5μm. In some embodiments, the volume average particle size Dv50 of the lithium manganese oxide is 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, or 5μm, and can also be any value within the range of 2μm-5μm.

[0141] In a battery cell using lithium manganese oxide as the positive electrode active material, if the volume average particle size Dv50 of the positive electrode active material is within the above range, it is beneficial to reduce the amount of transition metal ions dissolved in the positive electrode active material, so that the compound shown in Formula I in the positive electrode film can more effectively chelate the dissolved transition metal ions, further reduce the amount of transition metal elemental deposition on the negative electrode sheet, and improve the cycle performance of the battery cell.

[0142] In some embodiments, the specific surface area of ​​the lithium manganese oxide is 0.5 m². 2 / g-5m 2 / g.

[0143] In some embodiments, the specific surface area of ​​the lithium manganese oxide is 0.5 m². 2 / g-4.5m 2 / g, 0.5m 2 / g-4m 2 / g, 0.5m 2 / g-3.5m 2 / g, 0.5m 2 / g-3m2 / g, 0.5m 2 / g-2.5m 2 / g, 0.5m 2 / g-2m 2 / g, 0.5m 2 / g-1.5m 2 / g or 0.5m 2 / g-1.0m 2 / g. In some embodiments, the specific surface area of ​​the lithium manganese oxide is 0.5m². 2 / g, 1.0m 2 / g, 1.5m 2 / g、2m 2 / g, 2.5m 2 / g、3m 2 / g, 3.5m 2 / g、4m 2 / g, 4.5m 2 / g or 5m 2 / g, which can also be 0.5m 2 / g-5m 2 Any value within the range / g.

[0144] In battery cells using lithium manganese oxide as the positive electrode active material, a specific surface area within the aforementioned range is beneficial for reducing the dissolution of transition metal ions from the positive electrode active material. This allows the compound shown in Formula I in the positive electrode film to more effectively chelate the dissolved transition metal ions, thereby reducing their impact on the cycle performance of the battery cell. Simultaneously, it can also provide surface active sites to improve the kinetic performance of the positive electrode active material.

[0145] In some embodiments, the lithium manganese oxide includes LiMn2O4.

[0146] In some embodiments, the positive electrode film layer comprises the lithium manganese oxide and the compound shown in Formula I, wherein the mass content of the compound shown in Formula I is 0.3%-0.8% based on the mass of the positive electrode film layer.

[0147] In some embodiments, the positive electrode film layer comprises the lithium manganese oxide and the compound shown in Formula I, wherein the mass content of the compound shown in Formula I is 0.3%-0.6% or 0.3%-0.4% based on the mass of the positive electrode film layer. In some embodiments, the positive electrode film layer comprises the lithium manganese oxide and the compound shown in Formula I, wherein the mass content of the compound shown in Formula I is 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, or 0.8% based on the mass of the positive electrode film layer, and may also be any value within the range of 0.3%-0.8%.

[0148] The high reaction potential and sensitivity to hydrofluoric acid of lithium manganese oxide further exacerbate the reaction of Mn. 3+ It dissolves from the lattice of the positive electrode active material. Therefore, the mass content of the compound shown in Formula I within the above-mentioned range is beneficial for the compound shown in Formula I to fully chelate the Mn dissolved from the surface of the positive electrode active material. 3+ It forms a stable chelate and inhibits Mn 3+ Mn generated by the disproportionation reaction 2+ Migration towards the negative electrode reduces Mn 2+ The amount of leaching on the negative electrode surface is reduced, thereby reducing the damage of Mn to the SEI film on the negative electrode surface, reducing cell polarization, and improving the cycle performance of the cell.

[0149] In some embodiments, the positive electrode active material comprises a lithium-rich manganese-based material, the general formula of which is zLi₂MnO₃(1-z)LiM₂O₂, wherein M includes at least one of Mn, Ni, and Co, and O <z<1。

[0150] Lithium-rich manganese-based materials possess advantages such as high energy density, wide operating temperature range, low cost, and high safety. In lithium-rich manganese-based materials, manganese is primarily composed of Mn. 2+ Mn 3+ and Mn 4+ In its existing form, during the charging process, Mn 2+ Transform into Mn 3+ Or a higher valence state. As mentioned above, due to the Jahn-Teller effect, Mn 3+ Leaching from the lattice of lithium-rich manganese-based materials affects the cycle performance of individual battery cells. The positive electrode film includes a compound of formula I, which can chelate Mn dissolved from the surface of the lithium-rich manganese-based material. 3+ This reduces the manganese leaching content of the negative electrode and improves the cycle performance of the battery cell.

[0151] In some embodiments, the volume average particle size Dv50 of the lithium-rich manganese-based material is 3 μm-10 μm.

[0152] In some embodiments, the volume average particle size Dv50 of the lithium-rich manganese-based material is 3μm-8μm, 3μm-6μm, or 3μm-4μm. In some embodiments, the volume average particle size Dv50 of the lithium-rich manganese-based material is 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, or 10μm, and can also be any value within the range of 3μm-10μm.

[0153] In a battery cell using lithium-rich manganese-based materials as the positive electrode active material, if the volume average particle size Dv50 of the positive electrode active material is within the above range, it is beneficial to reduce the amount of transition metal ions dissolved in the positive electrode active material. This allows the compound shown in Formula I in the positive electrode film to more effectively chelate the dissolved transition metal ions, further reducing the amount of transition metal elements deposited on the negative electrode sheet and improving the cycle performance of the battery cell.

[0154] In some embodiments, the specific surface area of ​​the lithium-rich manganese-based material is 0.5 m². 2 / g-3m 2 / g.

[0155] In some embodiments, the specific surface area of ​​the lithium-rich manganese-based material is 0.5 m². 2 / g-2.5m 2 / g, 0.5m 2 / g-2m 2 / g, 0.5m 2 / g-1.5m 2 / g or 0.5m 2 / g-1m 2 / g, which can also be 0.5m 2 / g-3m 2 Any value within the range / g.

[0156] In battery cells using lithium-rich manganese-based materials as positive electrode active materials, a specific surface area within the aforementioned range is beneficial for reducing the dissolution of transition metal ions in the positive electrode active material. This allows the compound shown in Formula I in the positive electrode film to more effectively chelate the dissolved transition metal ions, thereby reducing their impact on the cycle performance of the battery cell. Simultaneously, it can also provide surface active sites to improve the kinetic performance of the positive electrode active material.

[0157] In some embodiments, the lithium-rich manganese-based material includes Li2MnO3·LiMnO2.

[0158] In some embodiments, the positive electrode film layer comprises the lithium-rich manganese-based material and the compound shown in Formula I, wherein the mass content of the compound shown in Formula I is 0.3%-0.8% based on the mass of the positive electrode film layer.

[0159] In some embodiments, the positive electrode film layer comprises the lithium-rich manganese-based material and the compound shown in Formula I, wherein the mass content of the compound shown in Formula I is 0.3%-0.6% or 0.3%-0.4% based on the mass of the positive electrode film layer. In some embodiments, the positive electrode film layer comprises the lithium-rich manganese-based material and the compound shown in Formula I, wherein the mass content of the compound shown in Formula I is 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, or 0.8% based on the mass of the positive electrode film layer, and may also be any value within the range of 0.3%-0.8%.

[0160] Based on the mass of the positive electrode film, the mass content of the compound shown in Formula I is within the above-mentioned range, which is beneficial for the compound shown in Formula I to fully chelate the Mn dissolved from the surface of the positive electrode active material. 3+ It forms a stable chelate and inhibits Mn 3+ Mn generated by the disproportionation reaction 2+ Migration towards the negative electrode reduces Mn 2+ The amount of leaching on the negative electrode surface is reduced, thereby reducing the damage of Mn to the SEI film on the negative electrode surface, reducing cell polarization, and improving the cycle performance of the cell.

[0161] In some embodiments, the positive electrode active material includes lithium nickel cobalt manganese oxide, wherein the general formula of lithium nickel cobalt manganese oxide is LiNi. a Co b Mn 1-a-b O2, where 0 <a<1,0<b<1。

[0162] Lithium nickel cobalt manganese oxide (NiCoMnO) cathode active materials possess advantages such as high energy density, high power density, low cost, and high safety. In NiCoMnO, nickel is the primary element in these materials. 2+ Cobalt exists, and it is represented by the element Co. 3+ The existing manganese element is Mn 3+ Yes, during the charging process, Ni 2+ Transformation into Ni 3+ As mentioned above, due to the Jahn-Teller effect, Ni... 3+ Co 3+ Mn 3+ Ni dissolves from the lattice of lithium nickel cobalt manganese oxide (LCO) cathode active material, affecting the cycle performance of the battery cell. The cathode film layer includes a compound of formula I, which can chelate Ni dissolved from the surface of the LCO cathode active material. 3+ Co 3+ Mn 3+ This reduces the leaching content of Ni, Co, and Mn in the negative electrode sheet, thereby improving the cycle performance of the battery cell.

[0163] In some embodiments, the volume average particle size Dv50 of the lithium nickel cobalt manganese oxide is 1 μm-5 μm.

[0164] In some embodiments, the volume average particle size Dv50 of the lithium nickel cobalt manganese oxide is 1μm-4.5μm, 1μm-4μm, 1μm-3.5μm, 1μm-3μm, 1μm-2.5μm, 1μm-2μm, or 1μm-1.5μm. In some embodiments, the volume average particle size Dv50 of the lithium nickel cobalt manganese oxide is 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, or 5μm, and can also be any value within the range of 1μm-5μm.

[0165] In a battery cell using lithium nickel cobalt manganese oxide as the positive electrode active material, if the volume average particle size Dv50 of the positive electrode active material is within the above range, it is beneficial to reduce the amount of transition metal ions dissolved in the positive electrode active material, so that the compound shown in Formula I in the positive electrode film can more effectively chelate the dissolved transition metal ions, further reduce the amount of transition metal elemental deposition on the negative electrode sheet, and improve the cycle performance of the battery cell.

[0166] In some embodiments, the specific surface area of ​​the lithium nickel cobalt manganese oxide is 0.3 m². 2 / g-5m 2 / g.

[0167] In some embodiments, the specific surface area of ​​the lithium nickel cobalt manganese oxide is 0.3 m². 2 / g-4.5m 2 / g, 0.3m 2 / g-4m 2 / g, 0.3m 2 / g-3.5m 2 / g, 0.3m 2 / g-3m 2 / g, 0.3m 2 / g-2.5m 2 / g, 0.3m 2 / g-2m 2 / g, 0.3m 2 / g-1.5m 2 / g, 0.3m 2 / g-1m 2 / g or 0.3m 2 / g-0.5m 2 / g. In some embodiments, the specific surface area of ​​the lithium nickel cobalt manganese oxide is 0.3m². 2 / g, 0.5m 2 / g, 1m 2 / g, 1.5m 2 / g、2m2 / g, 2.5m 2 / g、3m 2 / g, 3.5m 2 / g、4m 2 / g, 4.5m 2 / g or 5m 2 / g, which can also be 0.3m 2 / g-5m 2 Any value within the range / g.

[0168] In battery cells using lithium nickel cobalt manganese oxide as the positive electrode active material, a specific surface area within the aforementioned range is beneficial for reducing the dissolution of transition metal ions from the positive electrode active material. This allows the compound shown in Formula I in the positive electrode film to more effectively chelate the dissolved transition metal ions, thereby reducing their impact on the cycle performance of the battery cell. Simultaneously, it can also provide surface active sites to improve the kinetic performance of the positive electrode active material.

[0169] In some embodiments, lithium nickel cobalt manganese oxide includes LiNi 0.6 Co 0.2 Mn 0.2 O2.

[0170] In some embodiments, the positive electrode film layer comprises the lithium nickel cobalt manganese oxide and the compound shown in Formula I, wherein the mass content of the compound shown in Formula I is 0.05%-0.3% based on the mass of the positive electrode film layer.

[0171] In some embodiments, the positive electrode film layer comprises the lithium nickel cobalt manganese oxide and the compound shown in Formula I, wherein the mass content of the compound shown in Formula I is 0.05%-0.25%, 0.05%-0.2%, 0.05%-0.15%, or 0.05%-0.1% based on the mass of the positive electrode film layer. In some embodiments, the positive electrode film layer comprises the lithium nickel cobalt manganese oxide and the compound shown in Formula I, wherein the mass content of the compound shown in Formula I is 0.05%, 0.1%, 0.15%, 0.2%, or 0.25% based on the mass of the positive electrode film layer, and may also be any value within the range of 0.05%-0.3%.

[0172] Based on the mass of the positive electrode film, the mass content of the compound shown in Formula I is within the above-mentioned range, which is beneficial for the compound shown in Formula I to fully chelate the Ni dissolved from the surface of the positive electrode active material. 3+ Co 3+ Mn 3+ To form a stable chelate and inhibit Ni 3+ Co 3+ Mn 3+ Ni generated by the disproportionation reaction 2+ Co2+ Mn 2+ Migration towards the negative electrode reduces the leaching content of Ni, Co, and Mn on the negative electrode sheet, thereby reducing the damage of elemental Ni, Co, and Mn to the SEI film on the negative electrode surface, reducing cell polarization, and improving the cycle performance of the cell.

[0173] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0174] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include, but is not limited to, one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0175] In some embodiments, the positive electrode film layer may optionally include a positive electrode conductive agent. As an example, the positive electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0176] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resins, styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0177] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder, compound shown in Formula I and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry onto a positive current collector to form a positive electrode film layer; and obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0178] In some embodiments, the solvent may be any known and suitable solvent in the prior art, including but not limited to solvent oil, dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, acetone, dimethyl carbonate, ethyl cellulose, and polycarbonate.

[0179] In some embodiments, the solvent may be N-methylpyrrolidone (NMP).

[0180] [Negative electrode plate]

[0181] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0182] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0183] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0184] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in battery cells. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for battery cells may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0185] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0186] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0187] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)), plasticizers, etc.

[0188] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0189] [Electrolytes]

[0190] In some embodiments, the battery cell includes an electrolyte. The electrolyte acts as a conductor of ions between the positive and negative electrodes.

[0191] This application does not impose specific restrictions on the type of electrolyte, which can be selected according to requirements. For example, the electrolyte may include one or more of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0192] In some embodiments, the electrolyte comprises an electrolyte salt and a solvent. As an example, the electrolyte salt may include, but is not limited to, one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0193] In some embodiments, the solvent includes, but is not limited to, one or more of ester solvents, sulfone solvents, and ether solvents. For example, the solvent may include, but is not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0194] In some embodiments, the electrolyte may optionally include other additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery cell, such as additives that improve the overcharge performance of the battery cell, additives that improve the high-temperature or low-temperature performance of the battery cell, etc.

[0195] In this application, due to the large amount of Li in the electrolyte + It strongly inhibits the dissociation of the compound shown in Formula I, which may not have visible solubility in the electrolyte.

[0196] In some embodiments, when the battery cell contains moisture, the side reaction can cause the electrolyte to produce hydrofluoric acid, which disrupts the crystal lattice of the positive electrode active material and may further lead to the dissolution of transition metal ions from the positive electrode active material. In this case, the compound shown in Formula I can also chelate the transition metal ions dissolved from the positive electrode active material.

[0197] [Isolation membrane]

[0198] In some embodiments, the battery cell also includes a separator. The separator is disposed between the positive electrode and the negative electrode, and its main function is to prevent internal short circuits.

[0199] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0200] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0201] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0202] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0203] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0204] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 The example shown is a square-structured battery cell 5.

[0205] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0206] In some implementations, the battery cell can be a rechargeable battery cell that can be reactivated by charging after discharge to continue its use.

[0207] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0208] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0209] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0210] In some implementations, the battery device may include one or more battery modules for providing voltage and capacity. A battery module may include multiple individual battery cells connected in series, parallel, or a combination of these cells via a busbar.

[0211] In some embodiments, the battery device can be a battery pack, and the number of battery modules contained in the battery pack can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0212] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 5 and Figure 6 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0213] In addition, this application also provides an electrical device, which includes at least one of the battery cell, battery module, or battery pack provided in this application. The battery cell, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0214] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0215] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of individual battery cells, a battery pack or battery module can be used.

[0216] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0217] Example

[0218] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0219] I. Preparation of Compounds

[0220] Preparation Example 1

[0221] Preparation of lithium benzoylacetone: At room temperature (25℃-30℃), 0.151 mol of anhydrous lithium hydroxide was dissolved in 50 mL of water to obtain solution 1, and 0.154 mol of benzoylacetone (CAS: 93-91-4, Aladdin, purity 98%) was dissolved in 100 mL of anhydrous ethanol to obtain solution 2. Solution 1 was added dropwise to solution 2 with stirring to carry out the reaction. After reacting for 1 h, the reaction mixture was concentrated to a residual liquid volume of about 20 mL using a rotary evaporator, filtered, and washed three times with 20 mL of pure water to obtain a pale yellow crystalline crude product. The crude product was dissolved in 100 mL of 75% (volume fraction) ethanol, concentrated again to a residual liquid volume of about 20 mL, filtered, and washed three times with 20 mL of pure water. After vacuum drying at room temperature for 48 h, 18 g of colorless needle-like crystals, i.e., lithium benzoylacetone, were obtained.

[0222] Preparation Example 2

[0223] Preparation of lithium methyl acetoacetate: At room temperature, 0.151 mol of anhydrous lithium hydroxide was dissolved in 50 mL of water to obtain solution 1, and 0.25 mol of methyl acetoacetate (CAS: 108-85-2) was dissolved in 100 mL of anhydrous ethanol to obtain solution 2. Solution 1 was added dropwise to solution 2 with stirring to initiate the reaction. After reacting for 1 h, the reaction mixture was concentrated to a residual liquid volume of approximately 20 mL using a rotary evaporator, filtered, and washed three times with 20 mL of pure water to obtain a crude crystalline product. The crude product was dissolved in 100 mL of 75% (v / v) ethanol, concentrated again to a residual liquid volume of approximately 20 mL, filtered, and washed three times with 20 mL of pure water. After vacuum drying at room temperature for 48 h, 12.5 g of colorless needle-like crystals, i.e., lithium methyl acetoacetate, were obtained.

[0224] Preparation Example 3

[0225] Preparation of lithium methyl benzoate: At room temperature, 0.151 mol of anhydrous lithium hydroxide was dissolved in 50 mL of water to obtain solution 1, and 0.205 mol of methyl benzoate (CAS: 613-35-1) was dissolved in 100 mL of anhydrous ethanol to obtain solution 2. Solution 1 was added dropwise to solution 2 with stirring to carry out the reaction. After reacting for 1 h, the reaction mixture was concentrated to a residual liquid volume of about 20 mL using a rotary evaporator, filtered, and washed three times with 20 mL of pure water to obtain a crude crystalline product. The crude product was dissolved in 100 mL of 75% (v / v) ethanol, concentrated again to a residual liquid volume of about 20 mL, filtered, and washed three times with 20 mL of pure water. After vacuum drying at room temperature for 48 h, 20.3 g of colorless needle-like crystals, namely lithium methyl benzoate, were obtained.

[0226] II. Preparation of battery cells

[0227] Example 1

[0228] 1) Preparation of the positive electrode sheet:

[0229] The positive electrode active material is lithium manganese iron phosphate (LiMn). 0.6 Fe 0.4 PO4, conductive carbon black, binder polyvinylidene fluoride, and lithium acetylacetone (CAS: 18115-70-3) were mixed in a mass ratio of 97.8:1.4:0.5:0.3. N-methylpyrrolidone was added as solvent, and the mixture was stirred until homogeneous to obtain a positive electrode slurry with a solid content of 63%. The positive electrode slurry was uniformly coated on both sides of the positive electrode current collector aluminum foil, then dried at 85℃, cold-pressed, slit, and cut into sheets to obtain the positive electrode sheet. The coating amount on one side of the current collector was 0.32 g / 1540.25 mm. 2 .

[0230] 2) Preparation of negative electrode sheet

[0231] Artificial graphite (negative electrode active material), carbon black (conductive agent), styrene-butadiene rubber (binder), sodium carboxymethyl cellulose (thickener), and ethylene ethylene carbonate (plasticizer) were dissolved in deionized water at a weight ratio of 97:0.4:1.3:0.7:0.6 and mixed thoroughly to prepare a negative electrode slurry with a solid content of 53%. The negative electrode slurry was uniformly coated on both sides of the negative electrode current collector copper foil, and after drying, cold pressing, and slitting, negative electrode sheets were obtained. The coating amount on one side of the current collector was 0.145 g / 1540.25 mm. 2 .

[0232] 3) Separating membrane

[0233] Polypropylene film is used as the separator.

[0234] 4) Electrolyte

[0235] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the organic solvents ethylene carbonate and dimethyl carbonate are mixed evenly at a volume ratio of 4 / 6. Lithium salt LiPF6 with a mass content of 12.5% ​​is added and dissolved in the organic solvent. The mixture is stirred evenly, and additives are added to obtain the electrolyte.

[0236] 5) Battery cells

[0237] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. Then, they are wound to obtain a bare cell. The bare cell is placed in an outer aluminum casing and dried at 85°C for 6 hours. Electrolyte is then injected at an injection rate of 3.5 g / Ah. After vacuum sealing, settling, formation, and shaping, a battery cell is obtained. The formation process involves charging the battery cell to 100% SOC (State of Charge) with a constant current of 0.33C.

[0238] 100% SOC refers to the state of charge of a battery cell reaching its maximum capacity, i.e., the battery cell is fully charged. In this state, the battery cell stores the maximum amount of electricity allowed by its design and can no longer accept any more electrical energy input.

[0239] Example 2-12

[0240] The preparation methods of Examples 2-3 are similar to those of Example 1, except that the content of lithium acetylacetone compound in the positive electrode film is adjusted.

[0241] The preparation methods for Examples 4-6 are similar to those for Example 1, except that the types of compounds in the positive electrode film are adjusted, and the mass content of the compounds in the positive electrode film is adjusted accordingly. When the compound content in the positive electrode film changes, the proportion of positive electrode active material in the positive electrode film is adaptively adjusted so that the total mass of the positive electrode active material and the compounds accounts for 98.1% of the total mass of the positive electrode film.

[0242] The preparation methods of Examples 7-9 are similar to those of Example 1, except that the type of positive electrode active material in the positive electrode film is adjusted. Specifically, the positive electrode active material in Example 7 is adjusted to lithium manganese oxide (LiMn2O4); the positive electrode active material in Example 8 is adjusted to lithium-rich manganese-based material (Li2MnO3·LiMnO2); and the positive electrode active material in Example 9 is adjusted to lithium nickel cobalt manganese oxide (LiNi). 0.6 Co 0.2 Mn 0.2 O2.

[0243] The preparation methods of Examples 10-11 are similar to those of Example 1, except that the content of lithium acetylacetone compound in the positive electrode film is adjusted.

[0244] The preparation method of Example 12 is similar to that of Example 9, except that the content of lithium acetylacetone compound in the positive electrode film is adjusted.

[0245] Comparative Examples 1-4

[0246] The preparation method of Comparative Example 1 is similar to that of Example 1, except that lithium acetylacetone was not added to the positive electrode film.

[0247] The preparation methods of Comparative Examples 2-4 are similar to those of Examples 7-9, except that lithium acetylacetone was not added to the positive electrode film.

[0248] The specific parameters of the battery cells in each embodiment and comparative example are shown in Table 1.

[0249] Table 1. Preparation parameters of battery cells

[0250]

[0251] The following test methods were used to determine the powder parameters of the positive electrode active material:

[0252] 1) Test method for volume average particle size Dv50 of positive electrode active material

[0253] The battery cell is disassembled, and the positive electrode sheet is removed. The positive electrode sheet is then heat-treated to thermally decompose the components of the non-positive electrode active material in the positive electrode film layer, allowing the current collector in the positive electrode sheet to separate from the positive electrode film layer and the positive electrode active material in the film layer to be recovered. Following GB / T19077-2016 particle size distribution laser diffraction method, the particle size distribution of the positive electrode active material is tested using a Malvern particle size analyzer (Master Sizer 2000). In the volumetric particle size distribution of the material, starting from the smallest particle size, the particle size reaching 50% of the volumetric accumulation is defined as Dv50.

[0254] 2) Test method for specific surface area of ​​positive electrode active material

[0255] Referring to GB / T 19587-2017, the specific surface area of ​​the positive electrode active materials in the examples and comparative examples was measured by nitrogen adsorption / desorption using a specific surface area analyzer (TristarII 3020M) from Micromeritics, USA.

[0256] The battery cells prepared in each embodiment and comparative example were subjected to performance testing, and the testing methods are as follows:

[0257] 1) Test method for battery cell cycle capacity decay rate and curve

[0258] For a single battery cell with lithium manganese iron phosphate as the positive electrode active material: at 25°C and normal pressure (0.1MPa), the battery is charged at a constant current of 1C to a voltage of 4.1V, then discharged at a constant voltage of 4.1V to a current of 0.05C, and then discharged at a constant current of 1C to a voltage of 2.5V. The discharge capacity of the first cycle is recorded as C0. This is one charge-discharge cycle.

[0259] For a single battery cell with lithium manganese oxide as the positive electrode active material: at 25°C and normal pressure, the battery is charged at a constant current of 1C to a voltage of 4.3V, then discharged at a constant voltage of 4.3V to a current of 0.05C, and then discharged at a constant current of 1C to a voltage of 2.5V. The discharge capacity of the first cycle is recorded as C0. This is one charge-discharge cycle.

[0260] For a single battery cell with lithium-rich manganese-based positive electrode active material: at 25°C and normal pressure, the battery is charged at a constant current of 1C to a voltage of 4.8V, then discharged at a constant voltage of 4.8V to a current of 0.05C, and then discharged at a constant current of 1C to a voltage of 2.0V. The discharge capacity of the first cycle is recorded as C0. This is one charge-discharge cycle.

[0261] For a single battery cell with lithium nickel cobalt manganese oxide as the positive electrode active material: at 25°C and normal pressure, the battery is charged at a constant current of 1C to a voltage of 4.35V, then discharged at a constant voltage of 4.35V to a current of 0.05C, and then discharged at a constant current of 1C to a voltage of 2.8V. The discharge capacity of the first cycle is recorded as C0. This is one charge-discharge cycle.

[0262] Using the initial discharge capacity of each battery cell as 100%, repeated charge-discharge cycles were performed, and the discharge capacity of each cycle was recorded and plotted. After 1000 cycles for each battery cell, the discharge capacity C of the 1000th cycle was recorded. 1000 The capacity retention rate (%) after 1000 cycles is: C 1000 / C0×100%.

[0263] 2) Test method for manganese leaching content of negative electrode sheet:

[0264] After the battery cells have undergone cycle performance testing, they are disassembled, and the negative electrode is removed. The active material on the negative electrode is scraped off with a scraper, dissolved in a 1:1 volume ratio of nitric acid and hydrochloric acid (aqua regia), and the volume is adjusted to 100 mL. The manganese content (g / mL) in the solution is tested using an ICP analyzer. The manganese leaching content (ppm) of the negative electrode is calculated as: (Manganese content in solution ÷ Mass of negative electrode used) × 10. -4 .

[0265] The measurement results of the battery cells in each embodiment and comparative example are shown in Table 2 below.

[0266] Table 2. Test results of individual battery cells in each embodiment and comparative example.

[0267]

[0268] Based on the above results, it can be seen that the compounds of Formula I added to the positive electrode film layer in Examples 1-9 and Example 12 can chelate Mn dissolved from the surface of the positive electrode active material. 3+ This forms a stable chelate, reducing the amount of manganese dissolved on the negative electrode surface and improving the cycle capacity retention rate of the battery cell.

[0269] As can be seen from the comparison between Examples 1-3 and Comparative Example 1, in battery cells with lithium manganese iron phosphate as the positive electrode active material, adding lithium acetylacetone to the positive electrode film can reduce the amount of manganese dissolved on the negative electrode surface and improve the cycle capacity retention rate of the battery cell.

[0270] As can be seen from the comparison between Examples 4-6 and Comparative Example 1, in battery cells with lithium manganese iron phosphate as the positive electrode active material, the addition of lithium benzoyl acetone, lithium methyl acetoacetate, or lithium methyl benzoyl acetate to the positive electrode film layer can reduce the amount of manganese dissolved on the negative electrode surface and improve the cycle capacity retention rate of the battery cell.

[0271] As can be seen from the comparison between Example 7 and Comparative Example 2, in a battery cell with lithium manganese oxide as the positive electrode active material, adding lithium acetylacetone to the positive electrode film can reduce the amount of manganese dissolved on the negative electrode surface and improve the cycle capacity retention rate of the battery cell.

[0272] As can be seen from the comparison between Example 8 and Comparative Example 3, in battery cells where the positive electrode active material is a lithium-rich manganese-based material, adding lithium acetylacetone to the positive electrode film can reduce the amount of manganese dissolved on the negative electrode surface and improve the cycle capacity retention rate of the battery cell.

[0273] A comparison of Examples 9 and 12 with Comparative Example 4 shows that in battery cells with lithium nickel cobalt manganese oxide as the positive electrode active material, a lithium acetylacetone content of 0.15%-0.25% in the positive electrode film can reduce the leaching of manganese on the negative electrode surface and improve the cycle capacity retention rate of the battery cell. Based on this trend, it is speculated that in battery cells with lithium nickel cobalt manganese oxide as the positive electrode active material, an addition of 0.05%-0.3% lithium acetylacetone in the positive electrode film layer is beneficial for reducing the leaching of manganese on the negative electrode surface and improving the cycle capacity retention rate of the battery cell.

[0274] The measurement results of batteries in Examples 10-11 are shown in Table 3 below.

[0275] Table 3 Test results of Examples 10-11

[0276]

[0277] A comparison of Examples 1-3 and Examples 10-11 shows that in battery cells with lithium manganese iron phosphate as the positive electrode active material, a lithium acetylacetone content in the positive electrode film layer within the range of 0.1%-0.45% can reduce the leaching of manganese on the negative electrode surface and improve the cycle capacity retention rate of the battery cell. However, when the lithium acetylacetone content exceeds 0.45%, the leaching of manganese on the negative electrode surface increases, and the cycle performance of the battery cell decreases.

[0278] Figure 7 In the cycle capacity decay curves shown, among battery cells with lithium manganese iron phosphate as the positive electrode active material, the cell with 0.3% lithium acetylacetone added to the positive electrode film exhibited the least capacity decay after 1000 cycles, followed by the cell with 0.1% lithium acetylacetone. The cell with 0.5% lithium acetylacetone added to the positive electrode film experienced severe capacity decay after 1000 cycles, which was lower than the capacity retention rate of the cell without lithium acetylacetone added to the positive electrode film after 1000 cycles. This indicates that, in battery cells with lithium manganese iron phosphate as the positive electrode active material, increasing the amount of lithium acetylacetone added to the positive electrode film within the range of 0.1%-0.3% by mass helps to further improve cycle performance.

[0279] Figure 8 The bar chart showing the manganese leaching content of the negative electrode sheet after cycle performance testing of individual battery cells reveals that in battery cells with lithium manganese iron phosphate as the positive electrode active material, the lowest manganese leaching content is observed when the lithium acetylacetone content in the positive electrode film is 0.3%, followed by a lithium acetylacetone content of 0.1%. However, when the lithium acetylacetone content in the positive electrode film is 0.5%, the highest manganese leaching content is observed, exceeding that of negative electrode cells without added lithium acetylacetone in the positive electrode film. This indicates that in battery cells with lithium manganese iron phosphate as the positive electrode active material, increasing the amount of lithium acetylacetone added to the positive electrode film within the range of 0.1%-0.3% by mass helps to further reduce manganese leaching, improve the stability of the positive electrode active material, and enhance the cycle performance of the battery cell. This is also consistent with... Figure 7 The cycle capacity decay curve of the battery cell corresponds to that of the battery cell.

[0280] Figure 9In the cycle capacity decay curves of the battery cells shown, among the battery cells with lithium nickel cobalt manganese oxide as the positive electrode active material, the battery cells with a lithium acetylacetone content of 0.15% in the positive electrode film layer showed a lower degree of capacity decay after 1000 cycles than the battery cells with a lithium acetylacetone content of 0.25%. The battery cells without added lithium acetylacetone in the positive electrode film layer showed the most severe cycle capacity decay. This indicates that in battery cells with lithium nickel cobalt manganese oxide as the positive electrode active material, adding lithium acetylacetone with a mass content of 0.15%-0.25% in the positive electrode film layer can improve the cycle capacity retention rate of the battery cells.

[0281] Figure 10 The bar chart showing the manganese leaching content of the negative electrode sheet after cycle performance testing of individual battery cells reveals that, in battery cells with lithium nickel cobalt manganese oxide as the positive electrode active material, the manganese leaching content of the negative electrode sheet is lower in cells with 0.15% lithium acetylacetone in the positive electrode film compared to cells with 0.25% lithium acetylacetone. Conversely, battery cells without added lithium acetylacetone in the positive electrode film exhibit a higher manganese leaching content. This indicates that, in battery cells with lithium nickel cobalt manganese oxide as the positive electrode active material, a lithium acetylacetone content of 0.15%-0.25% in the positive electrode film can reduce the manganese leaching content of the negative electrode sheet, improve the stability of the positive electrode active material, and enhance the cycle performance of the battery cell. This is also consistent with... Figure 9 The cycle capacity decay curve of the battery cell corresponds to that of the battery cell.

[0282] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, characterized in that, The positive electrode includes a positive current collector and a positive electrode film disposed on at least one surface of the positive current collector, the positive electrode film comprising a compound of formula I. R1 includes one of substituted or unsubstituted C1-C5 alkyl, substituted or unsubstituted C5-C9 unsaturated cycloalkanes, and substituted or unsubstituted C1-C5 alkoxy groups; R2 includes one of substituted or unsubstituted C1-C5 alkyl groups or substituted or unsubstituted C5-C9 unsaturated cycloalkanes.

2. The battery cell according to claim 1, characterized in that, The R1 includes one of substituted or unsubstituted C1-C3 alkyl, substituted or unsubstituted C5-C6 unsaturated cycloalkanes, and substituted or unsubstituted C1-C3 alkoxy groups; The R2 includes one of substituted or unsubstituted C1-C3 alkyl groups and substituted or unsubstituted C5-C6 unsaturated cyclogroups.

3. The battery cell according to claim 1 or 2, characterized in that, R1 includes one of methyl, phenyl, methoxy, ethoxy, propoxy, and trifluoromethyl, and R2 includes one of methyl, phenyl, and trifluoromethyl.

4. The battery cell according to any one of claims 1 to 3, characterized in that, The compound represented by Formula I includes at least one of the following compounds:

5. The battery cell according to any one of claims 1 to 4, characterized in that, Based on the mass of the positive electrode film, the mass content of the compound shown in Formula I is 0.05%-1%.

6. The battery cell according to any one of claims 1 to 5, characterized in that, Based on the mass of the positive electrode film, the mass content of the compound shown in Formula I is 0.1%-0.45%.

7. The battery cell according to any one of claims 1 to 6, characterized in that, The positive electrode film layer includes a positive electrode active material, which includes at least one of manganese, cobalt and nickel.

8. The battery cell according to claim 7, characterized in that, The positive electrode active material includes manganese, and the manganese has at least one of the following valence states: +2, +3, and +4.

9. The battery cell according to claim 7 or 8, characterized in that, The positive electrode active material includes at least one of lithium manganese iron phosphate, lithium manganese oxide, lithium nickel manganese oxide, lithium manganese cobalt oxide, lithium-rich manganese-based materials, and lithium nickel cobalt manganese oxide; and / or The volume average particle size Dv50 of the positive electrode active material is 0.1 μm-10 μm; and / or The specific surface area of ​​the positive electrode active material is 0.3 m². 2 / g-25m 2 / g.

10. The battery cell according to claim 9, characterized in that, The positive electrode active material includes lithium iron manganese phosphate, and the lithium iron manganese phosphate satisfies at least one of the following conditions: (1) The general formula is Li(Mn) 1-x-c Fe x M c )PO4 / C, wherein 0.1≤x≤0.45, 0≤c≤0.1, and the dopant element M is a divalent metal, including at least one of Mg, Co, Ca, Sc, Ni and Zn; (2) The lithium manganese iron phosphate includes primary particles and / or secondary particles formed by the agglomeration of primary particles, wherein the volume average particle size Dv50 of the primary particles is 100nm-200nm and the volume average particle size Dv50 of the secondary particles is 2μm-5μm. (3) The specific surface area of ​​the lithium manganese iron phosphate is 10 m². 2 / g-25m 2 / g.

11. The battery cell according to claim 9, characterized in that, The positive electrode active material includes lithium manganese oxide, and the lithium manganese oxide satisfies at least one of the following conditions: (1) The general formula is LiMn 2-y M 1y O4, wherein M1 includes at least one of Ni, V, Cr, Cu, Co, Fe, Mg, Ca, and Sc, 0 <y<2; (2) The volume average particle size Dv50 of the lithium manganese oxide is 2μm-5μm; (3) The specific surface area of ​​the lithium manganese oxide is 0.5 m². 2 / g-5m 2 / g.

12. The battery cell according to claim 9, characterized in that, The positive electrode active material includes a lithium-rich manganese-based material, and the lithium-rich manganese-based material satisfies at least one of the following conditions: (1) The general formula is zLi2MnO3(1-z)LiM2O2, wherein M2 includes at least one of Mn, Ni, and Co, and 0 <z<1; (2) The volume average particle size Dv50 of the lithium-rich manganese-based material is 3μm-10μm; (3) The specific surface area of ​​the lithium-rich manganese-based material is 0.5 m². 2 / g-3m 2 / g.

13. The battery cell according to claim 9, characterized in that, The positive electrode active material includes lithium nickel cobalt manganese oxide, and the lithium nickel cobalt manganese oxide satisfies at least one of the following conditions: (1) The general formula is LiNi a Co b Mn 1-a-b O2, where 0 <a<1,0<b<1; (2) The volume average particle size Dv50 of the lithium nickel cobalt manganese oxide is 1μm-5μm; (3) The specific surface area of ​​the lithium nickel cobalt manganese oxide is 0.3 m². 2 / g-5m 2 / g.

14. The battery cell according to claim 9, characterized in that, The positive electrode film layer comprises the lithium manganese iron phosphate and the compound shown in Formula I, wherein the mass content of the compound shown in Formula I is 0.1%-0.45% based on the mass of the positive electrode film layer; or The positive electrode film layer includes the lithium manganese oxide and the compound shown in Formula I, and the mass content of the compound shown in Formula I is 0.3%-0.8% based on the mass of the positive electrode film layer; or The positive electrode film layer includes the lithium-rich manganese-based material and the compound shown in Formula I. Based on the mass of the positive electrode film layer, the mass content of the compound shown in Formula I is 0.3%-0.8%. or The positive electrode film layer comprises the lithium nickel cobalt manganese oxide and the compound shown in Formula I, and the mass content of the compound shown in Formula I is 0.05%-0.3% based on the mass of the positive electrode film layer.

15. A battery device, characterized in that, Includes the battery cell according to any one of claims 1 to 14.

16. An electrical appliance, characterized in that, Includes the battery cell according to any one of claims 1 to 14 or the battery device according to claim 15.

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